Liquid crystal display in which at least one pixel includes both a transmissive region and a reflective region

A liquid crystal display device according to the present invention includes a first substrate, a second substrate, and a liquid crystal layer interposed between the first substrate and the second substrate. The first substrate includes: a plurality of gate lines; a plurality of source lines arranged to cross with the plurality of gate lines; a plurality of switching elements disposed in the vicinity of crossings of the plurality of gate lines and the plurality of source lines; and a plurality of pixel electrodes connected to the plurality of switching elements. The second substrate includes a counter electrode. A plurality of pixel regions are defined by the plurality of pixel electrodes, the counter electrode, and the liquid crystal layer interposed between the plurality of pixel electrodes and the counter electrode, and each of the plurality of pixel regions includes a reflection region and a transmission region.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a liquid crystal display device and a
 method for fabricating the liquid crystal display device. More
 particularly, the present invention relates to a liquid crystal display
 device having a transmission display region and a reflection display
 region in each pixel, and a method for fabricating such a liquid crystal
 display device.
 2. Description of the Related Art
 Due to the features of being thin and consuming low power, liquid crystal
 display devices have been used in a broad range of fields including office
 automation (OA) apparatuses such as wordprocessors and personal computers,
 portable information apparatuses such as portable electronic Schedulers,
 and a camera-incorporated VCR provided with a liquid crystal monitor.
 Such liquid crystal display devices include a liquid crystal display panel
 which does not emit light itself, unlike a CRT display and an
 electroluminescence (EL) display. Therefore, a so-called transmission type
 is often used as the liquid crystal display device, which includes an
 illuminator called a backlight disposed at the rear or one side thereof,
 so that the amount of the light from the backlight which passes through
 the liquid crystal panel is controlled by the liquid crystal panel in
 order to realize image display.
 In such a transmission type liquid crystal display device, however, the
 backlight consumes 50% or more of the total power consumed by the liquid
 crystal display device. Providing the backlight therefore increases the
 power consumption.
 In order to overcome the above problem, a reflection type liquid crystal
 display device has been used for portable information apparatuses which
 are often used outdoors or carried with the users. Such a reflection type
 liquid crystal display device is provided with a reflector formed on one
 of a pair of substrates in place of the backlight so that ambient light is
 reflected from the surface of the reflector.
 Such a reflection type liquid crystal display device is operated in a
 display mode using a polarizing plate, such as a twisted nematic (TN) mods
 and a super twisted nematic (STN) mode which have been broadly used in the
 transmission type liquid crystal display devices. In recent years, there
 has been vigorous development of a phase change type guest-host mode which
 does not use a polarizing plate and thus realizes a brighter display.
 The reflection type liquid crystal display device using the reflection of
 ambient light is disadvantageous in that the visibility of the display is
 extremely lower when the surrounding environment is dark. Conversely, the
 transmission type liquid crystal display device is disadvantageous when
 the environment is bright. That is, the color reproducibility is lower and
 the display is not sufficiently recognizable because the display light is
 less bright than the ambient light. In order to improve the display
 quality under a bright environment, the intensity of the light from the
 backlight needs to be increased. This increases the power consumption of
 the backlight and thus the resultant liquid crystal display device.
 Moreover, when the liquid crystal display device needs to be viewed at a
 position exposed to direct sunlight or direct illumination light, the
 display quality is inevitably lower due to the ambient light. For example,
 when a liquid crystal display screen fixed in a car or a display screen of
 a personal computer used at a fixed position receives direct sunlight or
 illumination light, surrounding images are mirrored, making it difficult
 to observe the display itself.
 In order to overcome the above problems, a construction which realizes both
 a transmission mode display and a reflection mode display in one liquid
 crystal display device has been disclosed in, for example, Japanese
 Laid-Open Publication No. 7-333598. Such a liquid crystal display device
 uses a semi-transmissive reflection film which transmits part of light and
 reflects part of light.
 FIG. 52 shows such a liquid crystal display device using a
 semi-transmissive reflection film. The liquid crystal display device
 includes polarizing plates 30a and 30b, a phase plate 31, a transparent
 substrate 32, black masks 33, a counter electrode 34, alignment films 35,
 a liquid crystal layer 36, metal-insulator-metal (MIM) elements 37, pixel
 electrodes 38, a light source 39, and a reflection film 40.
 The pixel electrodes 38, which are the semitransmissive reflection films,
 are extremely thin layers made of metal particles or layers having
 sporadical minute hole defects or concave defects therein formed over
 respective pixels. Pixel electrodes with this construction transmit light
 from the light source 39 and at the same time reflect light from outside
 such as natural light and indoor illumination light, so that both the
 transmission display function and the reflection display function are
 simultaneously realized.
 The conventional liquid crystal display device shown in FIG. 52 has
 following problems. First, when an extremely thin layer of deposited metal
 particles is used as the semi-transmissive reflection film of each pixel,
 since the metal particles have a large absorption coefficient, the
 internal absorption of incident light is large and some of the light is
 absorbed without being used for display, thereby lowering the light
 utilization efficiency.
 When a film having sporadical minute hole defects or concave defects
 therein is used as the pixel electrode 38 of each pixel, the structure of
 the film is too complicated to be easily controlled, requiring precise
 design conditions. Thus, it is difficult to fabricate the film having
 uniform characteristics. In other words, the reproducibility of the
 electrical or optical characteristics is so poor that control of the
 display quality in the above liquid crystal display device is extremely
 difficult.
 For example, if thin film transistors (TFTs), which in recent years have
 been generally used as the switching elements of liquid crystal display
 devices, are attempted to be used for the above liquid crystal display
 device shown in FIG. 52, an electrode for the formation of a storage
 capacitor in each pixel needs to be formed by an electrode/interconnect
 material other than that for the pixel electrode. In this case, the pixel
 electrode made of the semi-transmissive reflection film, as in this
 conventional device, is not suitable for the formation of a storage
 capacitor. Moreover, even when the semi-transmissive reflection film as
 the pixel electrode is formed over part of the interconnects and elements
 via an insulating layer, the pixel electrode which includes a transmissive
 component hardly contributes to an increase in the numerical aperture.
 Also, if light is incident on a semiconductor layer of the switching
 element such as a MIM and a TFT, an optically pumped current is generated.
 The formation of the semi-transmissive reflection film as the
 light-shading layer is insufficient for the protection of the switching
 element from light. To ensure light-shading, another light-shading film is
 required to be disposed on the counter substrate.
 SUMMARY OF THE INVENTION
 The liquid crystal display device of this invention includes a first
 substrate, a second substrate, and a liquid crystal layer interposed
 between the first substrate and the second substrate, a plurality of pixel
 regions being defined by respective pairs of electrodes for applying a
 voltage to the liquid crystal layer, wherein each of the plurality of
 pixel regions includes a reflection region and a transmission region.
 In one embodiment of the invention, the first substrate includes a
 reflection electrode region corresponding to the reflection region and a
 transmission electrode region corresponding to the transmission region.
 In another embodiment of the invention, the reflection electrode region is
 higher than the transmission electrode region, forming a step on a surface
 of the first substrate, and thus a thickness of the liquid crystal layer
 in the reflection region is smaller than a thickness of the liquid crystal
 layer in the transmission region.
 In still another embodiment of the invention, the occupation of an area of
 the reflection region in each of the pixel regions is in the range of
 about 10 to about 90%.
 Alternatively, the liquid crystal display device of this invention includes
 a first substrate, a second substrate, and a liquid crystal layer
 interposed between the first substrate and the second substrate, wherein
 the first substrate includes: a plurality of gate lines; a plurality of
 source lines arranged to cross with the plurality of gate lines; a
 plurality of switching elements disposed in the vicinity of crossings of
 the plurality of gate lines and the plurality of source lines; and a
 plurality of pixel electrodes connected to the plurality of switching
 elements, the second substrate includes a counter electrode, a plurality
 of pixel regions are defined by the plurality of pixel electrodes, the
 counter electrode, and the liquid crystal layer interposed between the
 plurality of pixel electrodes and the counter electrode, and each of the
 plurality of pixel regions includes a reflection region and a transmission
 region.
 In one embodiment of the invention, the first substrate includes a
 reflection electrode region corresponding to the reflection region and a
 transmission electrode region corresponding to the transmission region.
 In another embodiment of the invention, the reflection electrode region is
 higher than the transmission electrode region, forming a step on a surface
 of the first substrate, and thus a thickness of the liquid crystal layer
 in the reflection region is smaller than a thickness of the liquid crystal
 layer in the transmission region
 In still another embodiment of the invention, the thickness of the liquid
 crystal layer in the reflection region is about a half of the thickness of
 the liquid crystal layer in the transmission region.
 In still another embodiment of the invention, each of the pixel electrodes
 includes a reflection electrode in the reflection electrode region and a
 transmission electrode in the transmission electrode region.
 In still another embodiment of the invention, the reflection electrode and
 the transmission electrode are electrically connected to each other.
 In still another embodiment of the invention, each of the pixel electrodes
 includes a transmission electrode, and the reflection region includes the
 transmission electrode and a reflection layer isolated from the
 transmission electrode.
 In still another embodiment of the invention, the reflection electrode
 regions overlap at least a portion of the plurality of gate lines, the
 plurality of source lines, and the plurality of switching elements.
 In still another embodiment of the invention, at least either of the
 reflection electrode regions and the transmission electrode regions have a
 layer formed of the same material as a material for the plurality of gate
 lines or the plurality of source lines.
 In still another embodiment of the invention, the occupation of an area of
 the reflection region in each of the pixel regions is in the range of
 about 10 to about 90%.
 In still another embodiment of the invention, the first substrate further
 includes storage capacitor electrodes for forming storage capacitors with
 the pixel electrodes via an insulating film, wherein the reflection
 electrode regions overlap the storage capacitor electrodes.
 In still another embodiment of the invention, the liquid crystal display
 device further includes microlenses on a surface of the first substrate
 opposite to the surface facing the liquid crystal layer.
 In still another embodiment of the invention, each of the reflection
 electrode regions includes a metal layer and an interlayer insulating film
 formed under the metal layer.
 In still another embodiment of the invention, the metal layer has a
 continuous wave shape.
 In still another embodiment of the invention, a surface of the interlayer
 insulating layer is of a concave and convex shape.
 In still another embodiment of the invention, the interlayer insulating
 layer is formed of a photosensitive polymer resin film.
 In still another embodiment of the invention, the interlayer insulating
 layer covers at least a portion of either the switching element, the
 plurality of gate lines, or the plurality of source lines.
 In still another embodiment of the invention, the reflection electrodes are
 formed at the same level as the plurality of gate lines or the plurality
 of source lines.
 In still another embodiment of the invention, the reflection electrodes are
 formed at the same level as the plurality of gate lines, and the
 reflection electrodes are electrically connected to the gate lines for the
 pixel electrodes adjacent to the reflection electrodes.
 In still another embodiment of the invention, the same signals applied to
 the counter electrode are applied to the reflection electrodes.
 In still another embodiment of the invention, the reflection electrodes are
 formed at the same level as the plurality of gate lines, and the
 reflection electrodes form storage capacitors by overlapping drain
 electrodes of the switching elements or the transmission electrodes.
 In still another embodiment of the invention, the reflection electrode is
 formed of Al or an Al alloy.
 In still another embodiment of the invention, the transmission electrode is
 formed of ITO, and a metal layer interposes between the transmission
 electrode and the reflection electrode.
 According to another aspect of the invention, a method for fabricating a
 liquid crystal display device is provided. The liquid crystal display
 device includes a first substrate, a second substrate, and a liquid
 crystal layer interposed between the first substrate and the second
 substrate, the first substrate including: a plurality of gate lines; a
 plurality of source lines arranged to cross with the plurality of gate
 lines; a plurality of switching elements disposed in the vicinity of
 crossings of the plurality of gate lines and the plurality of source
 lines; and a plurality of pixel electrodes connected to the plurality of
 switching elements, the second substrate including a counter electrode, a
 plurality of pixel regions are defined by the plurality of pixel
 electrodes, the counter electrode, and the liquid crystal layer interposed
 between the plurality of pixel electrodes and the counter electrode, each
 of the plurality of pixel regions including a reflection region and a
 transmission region. The method includes the steps of: forming the
 transmission electrode regions using a material having a high light
 transmittance on the first substrate; forming photosensitive polymer resin
 layers; and forming reflection layers made of a material having a high
 reflectance on the polymer resin layers.
 In one embodiment of the invention, the photosensitive polymer resin layers
 have a plurality of concave and convex portions.
 Alternatively, a method for fabricating a liquid crystal display device of
 this invention is provided. The liquid crystal display device includes a
 first substrate, a second substrate, and a liquid crystal layer interposed
 between the first substrate and the second substrate, the first substrate
 including: a plurality of gate lines; a plurality of source lines arranged
 to cross with the plurality of gate lines; a plurality of switching
 elements disposed in the vicinity of crossings of the plurality of gate
 lines and the plurality of source lines; and a plurality of pixel
 electrodes connected to the plurality of switching elements, the second
 substrate including a counter electrode, a plurality of pixel regions are
 defined by the plurality of pixel electrodes, the counter electrode, and
 the liquid crystal layer interposed between the plurality of pixel
 electrodes and the counter electrode, each of the plurality of pixel
 regions including a reflection region and a transmission region. The
 method includes the steps of: forming the transmission electrode regions
 using a material having a high light transmittance on the first substrate;
 forming protection films on the transmission electrode regions; and
 forming layers having a high reflectance on portions of the protection
 films to form the reflection electrode regions.
 In one embodiment of the invention, the transmission electrode regions are
 formed at the same level as the plurality of source lines.
 Thus, the invention described herein makes possible the advantages of (1)
 providing a liquid crystal display device of a type realizing both a
 transmission mode display and a reflection mode display simultaneously
 where the light utilization efficiencies of ambient light and light from a
 backlight are improved compared with the conventional liquid crystal
 display device of the same type and an excellent display quality is
 obtained, and (2) providing a method for fabricating such a liquid crystal
 display device. In particular, in the liquid crystal display device
 according to the present invention, the display quality obtained when the
 environment is bright significantly improves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 EXAMPLE 1
 A liquid crystal display device of Example 1 according to the present
 invention includes an active matrix substrate and a transparent counter
 substrate (e.g., a glass substrate), which has a counter electrode facing
 pixel electrodes. A liquid crystal layer is interposed between the active
 matrix substrate and the counter substrate. A plurality of pixel regions
 are defined by respective pairs of the pixel electrodes and the counter
 electrode for applying a voltage to the liquid crystal layer. The pixel
 region includes a pair of electrodes and the liquid crystal layer between
 the pair of electrodes. This definition is also applicable to a simple
 matrix type liquid crystal display device, which has a plurality of
 scanning electrodes and a plurality of signal electrodes.
 The liquid crystal display device according to the present invention has at
 least one transmission electrode region and at least one reflection region
 in each pixel. The transmission and reflection regions include the liquid
 crystal layer and the pair of the electrodes interposing the liquid
 crystal layer. A region of an electrode which defines the transmission
 region is referred to as a transmission electrode region and a region of
 an electrode which defines the reflection region is referred to as a
 reflection electrode region.
 FIG. 1 is a plan view of one pixel portion of an active matrix substrate of
 the liquid crystal display device of Example 1. FIG. 2 is a sectional view
 taken along line a-b of FIG. 1.
 Referring to FIGS. 1 and 2, the active matrix substrate includes pixel
 electrodes 1 arranged in a matrix. Gate lines 2 for supplying scanning
 signals and source lines 3 for supplying display signals are disposed
 along the peripheries of the pixel electrodes 1 so as to cross each other
 at right angles.
 The gate lines 2 and the source lines 3 are overlapped by peripheral
 portions of the corresponding pixel electrodes 1 via an interlayer
 insulating film 19. The gate lines 2 and the source lines 3 are composed
 of metal films.
 Thin film transistors (TFTS) 4 are formed in the vicinity of the respective
 crossings of the gate lines 2 and the source lines 3. A gate electrode 12
 of each of the TFTs 4 is connected to the corresponding gate line 2, to
 drive the TFT 4 with a signal input into the gate electrode 12 via the
 gate line 2. A source electrode 15 of the TFT 4 is connected to the
 corresponding source line 3, to receive a data signal from the source line
 3. A drain electrode 16 of the TFT 4 is connected to a connecting
 electrode 5 which is in turn electrically connected to the corresponding
 pixel electrode 1 via a contact hole 6.
 The connecting electrode 5 forms a storage capacitor with a storage
 capacitor electrode 8 via a gate insulating film 7. The storage capacitor
 electrode 8 is composed of a metal film and connected to a counter
 electrode 10 formed on a counter substrate 9 via an interconnect (not
 shown). The storage capacitor electrodes 8 may be formed together with the
 gate lines 2 during the same step.
 Each of the pixel electrodes 1 includes a reflection electrode region 22
 including a metal film and at least one transmission electrode region 20
 composed of an ITO film. The reflection electrode region 22 is formed to
 overlie the gate line 2, the source line 3, the TFT 4, and the storage
 capacitor electrode 8, while the transmission electrode region 20 is
 surrounded by the reflection electrode region 22.
 The active matrix substrate of Example 1 with the above construction is
 fabricated in the following manner.
 First, the gate electrodes 12, the gate lines 2, the storage capacitor
 electrodes 8, the gate insulating film 7, semiconductor layers 13, channel
 protection layers 14, the source electrodes 15, and the drain electrodes
 16 are sequentially formed on a transparent insulating substrate 11 made
 of glass or the like.
 Then, a transparent conductive film 17 and a metal film 18 are sequentially
 deposited by sputtering and patterned into a predetermined shape to form
 the source lines 3 and the connecting electrodes 5.
 Thus, the source lines 3 have a double-layer structure composed of the
 transparent conductive film 17 made of ITO and the metal film 18. With
 this structure, even if a defect such as a disconnection is generated in
 the metal film 18, the electrical connection is maintained via the
 transparent conductive film 17. This reduces the generation of
 disconnections in the source lines 3.
 Thereafter, a photosensitive acrylic resin is applied to the resultant
 substrate by a spin application method to form the interlayer insulating
 film 19 with a thickness of 3 .mu.m. The acrylic resin is then exposed to
 light according to a desired pattern and developed with an alkaline
 solution. Only the light-exposed portions of the film are etched with the
 alkaline solution to form the contact holes 6 through the interlayer
 insulating film 19. By employing this alkaline development, well-tapered
 contact holes 6 are obtained.
 Using a photosensitive acrylic resin for the interlayer insulating film 19
 is advantageous in the aspect of productivity in view of the following
 points. Since the spin application method can be employed for the thin
 film formation, a film as thin as several micrometers can be easily
 formed. Also, no photoresist application step is required at the
 patterning of the interlayer insulating film 19.
 In this example, the acrylic resin is colored and can be made transparent
 by exposing the entire surface to light after patterning. The acrylic
 resin may also be made transparent by chemical processing.
 Thereafter, a transparent conductive film 21 is formed by sputtering and
 patterned, thereby forming transparent conductive films 21. The
 transparent conductive films 21 are made of ITO.
 Thus, the transparent conductive films 21 are electrically connected to the
 respective connecting electrodes 5 via the-contact holes 6.
 A metal film 23 is then formed on the transparent conductive films 21 and
 patterned so as to overlie the gate lines 2, the source lines 3, the TFTs
 4, and the storage capacitor electrodes 8, to be used as the reflection
 electrode regions 22 of the pixel electrodes 1. The portions of the
 transparent conductive films 21 which are not covered with the metal films
 23 constitute the transmission electrode regions 20. The transparent
 conductive films 21 and the metal films 23 are electrically connected with
 each other. Any adjacent pixel electrodes are separated by the portions
 located above the gate lines 2 and the source lines 3 so as not to be
 electrically connected with each other.
 The metal films 23 are made of Al. They may also be made of any conductive
 material having a high reflectance such as Ta.
 In this example, as shown in FIG. 2, a liquid crystal layer includes
 dichromatic pigment molecules 24 mixed in liquid crystal. The absorption
 coefficient of such a dichromatic pigment varies depending on the
 orientation direction of molecules thereof. The orientation direction of
 the dichromatic pigment molecules 24 changes when the orientation
 direction of the liquid crystal molecules 25 is changed by controlling the
 electric field between the counter electrode 10 and the pixel electrodes
 1. The resultant change in the absorption coefficient of the dichromatic
 pigment molecules 24 is used to generate an image display.
 By using the liquid crystal display panel of Example 1 with the above
 construction, the display can effectively use light which has been emitted
 from a backlight and passed through the transmission electrode regions 20
 when the ambient light is low and light reflected by the reflection
 electrode regions 22 when the ambient light is high. Also, both the
 transmission electrode regions 20 and the reflection electrode regions 22
 can be used to generate a display. Moreover, a liquid crystal display
 device providing a bright display can be realized.
 In this example, the metal films 23 of the reflection electrode regions 22
 of the pixel electrodes 1 overlie the TFTs 4, the gate lines 2, and the
 source lines 3. This eliminates the necessity of providing light-shading
 films for preventing light from entering the TFTs 4 and light-shading
 portions of the pixel a electrode located above the gate lines, the source
 lines, and the storage capacitor electrodes. In such portions, light
 leakage tends to be generated in the form of domains, declination lines,
 and the like in certain display regions. As a result, regions which are
 conventionally unusable as display regions because they are blocked by the
 light-shading films can be used as display regions. This allows for
 effective use of the display regions.
 When the gate lines and the source lines are made of metal, they serve as
 light-shading regions in a transmission type display device, and thus are
 unusable as display regions. In the liquid crystal display device of this
 example, however, such regions which are used as light-shading regions in
 the conventional transmission type display device are usable as reflection
 electrode regions of the pixel electrodes. Thus, a brighter display can be
 obtained.
 In this example, the metal film 23 is formed on the transparent conductive
 film 21. This allows the metal film 23 to have an uneven surface in
 compliance with an uneven surface of the transparent conductive film 21.
 The uneven surface of the metal film 23 is advantageous over a flat
 surface since an uneven surface receives ambient light at various incident
 angles. The resultant liquid crystal display device provides a brighter
 display.
 FIGS. 3 and 4 are plan views of alternative embodiment of the liquid
 crystal display devices of Example 1 according to the present invention.
 In these alternative examples, the ratio of the areas of the transmission
 electrode region 20 to the reflection electrode region 22 of each pixel
 electrode 1 is changed from that shown in FIG. 1. In this way, a liquid
 crystal display device having a desired reflectance and transmittance is
 obtained.
 In the alternative examples shown in FIGS. 3 and 4, the connecting
 electrode 5 is located in the reflection electrode region 22. This
 suppresses a decrease in the brightness of light which has passed through
 the transmission electrode region 20.
 In Example 1, the metal film 23 of the reflection electrode region 22 of
 the pixel electrode 1 in formed on the transparent conductive film 21.
 Alternatively, as shown in FIG. 6, the metal film 23 may be formed so as
 to overlap the transparent conductive film 21 only partially in order to
 be electrically connected with each other.
 EXAMPLE 2
 In Example 2, a method for forming the uneven surface of the metal film 23
 will be described.
 FIG. 5 is a plan view partially illustrating the metal film 23 formed on
 the interlayer insulating film 19 (not shown). FIG. 6 is a sectional view
 taken along line c-d of FIG. 5.
 The surface of the interlayer insulating film 19 is made uneven by etching
 or the like, and the metal film 23 is formed on the uneven surface.
 Thus, by forming the metal film 23 on the interlayer insulating film 19
 which may be first formed flat by the spin application method or the like,
 but then have the surface thereof made uneven as described above, the
 metal film 23 having an uneven surface is obtained.
 In a reflection type liquid crystal display device, the uneven surface of
 the metal film 23 is advantageous over a flat surface since an uneven
 surface receives ambient light at various incident angles. Thus, by
 forming the metal films 23 of the pixel electrodes 1 on the interlayer
 insulating film 19 so as to have an uneven surface obtained by etching or
 the like as shown in FIG. 6, the resultant reflective liquid crystal
 display device provides a brighter display.
 The uneven surface of the metal film 23 is not limited to the shape shown
 in FIG. 5, i.e., the surface having concave portions of a circular shape
 in plan. Alternatively, the surface of the metal film 23 and thus the
 surface of the underlying interlayer insulating film 19 may have concave
 portions of a polygonal or elliptic shape in plan. The section of the
 concave portions may be of a polygonal shape, in place of the
 semi-circular shape as shown in FIG. 6.
 EXAMPLE 3
 In Example 3, a liquid crystal display device which employs a guest-host
 display method will be described.
 FIG. 7 is a sectional view of a liquid crystal display device of this
 example according to the present invention. The same components as those
 of Example 1 are denoted by the same reference numerals as those in FIG.
 2.
 When the guest-host display method is employed using a mixture of a
 guest-host liquid crystal material, ZLI 2327 (manufactured by Merck & Co.,
 Inc.) containing black pigments therein and 0.5% of an optically active
 substance, S-811 (manufactured by Merck & Co., Inc.), the following
 problem arises. That is, if the optical path length dt of transmitted
 light from the blacklight in the transmission region using the backlight
 is significantly different from the optical path length 2dr of reflected
 light from ambient light in the reflection region, the brightness and the
 contrast of the resultant display are significantly different between the
 case where light from the backlight is used and the case where ambient
 light is used even when the same voltage is applied to the liquid crystal
 layer.
 Accordingly, the thickness dt of the portions of the liquid crystal layer
 located on the transparent conductive films 21 of the transmission regions
 and the thickness dr of the portions of the liquid crystal layer located
 on the metal films 23 of the reflection regions should be set to satisfy
 the relationship of dt=2dr. In this example, therefore, the thickness of
 the metal films 23 is changed to satisfy this relationship.
 Thus, by equalizing the optical path length dt of transmitted light from
 the backlight in the transmission regions and the optical path length 2dr
 of reflected light from ambient light in the reflection region, with each
 other, substantially the some brightness and contrast can be obtained
 irrespective of which type of light is used (light from backlight or light
 from ambient light) so long as the same voltage is applied to the liquid
 crystal layer. In this way, a liquid crystal display device having better
 display characteristics is obtained.
 The brightness and the contrast can be made uniform to some extent by
 approximating, not necessarily equalizing, the optical path length dt of
 transmitted light from the backlight in the transmission region and the
 optical path length 2dr of reflected light from ambient light in the
 reflection region.
 The contrast can also be made uniform irrespective of which type of light
 is used (light from backlight or light from ambient light) by changing the
 driving voltage applied to the liquid crystal layer, even when the optical
 path length dt of transmitted light in the transmission region is
 significantly different from the optical path length 2dr of reflected
 light in the reflection region.
 Thus, in the liquid crystal display devices in Examples 1 to 3 above, where
 the transmission mode display and the reflection mode display are realized
 using a single substrate, the regions which are conventionally blocked
 from light by the use of a black mask can be used as reflection electrode
 regions of the respective pixel electrodes. This allows for effective use
 of the display regions of the pixel electrodes of the liquid crystal
 panel, and thus increases the brightness of the liquid crystal display
 device.
 In Examples 1 to 3, the storage capacitor electrode is provided for forming
 a storage capacitor with each pixel electrode via the insulating film, and
 the reflection electrode region of the pixel electrode overlies the
 storage capacitor electrode. Accordingly, the region where the storage
 capacitor electrode is formed can be utilized for display as a reflection
 electrode region of the pixel electrode.
 The metal film of the reflection electrode region of each pixel electrode
 is formed on the transparent conductive film. By using a transparent
 conductive film having an uneven surface, the resultant reflection
 electrode region of the pixel electrode has an uneven surface, which makes
 it possible to utilize ambient light having various incident angles as
 display light.
 The metal film of the reflection region of each pixel electrode may be
 formed on an interlayer insulating film having an uneven surface. The
 resultant reflection electrode region of the pixel electrode has an uneven
 surface, which makes it possible to utilize ambient light having various
 incident angles as display light.
 The metal film of the reflection electrode region of each pixel electrode
 is made thicker than the transparent conductive film located in the
 transmission region of the pixel electrode. This make it possible to
 approximate the optical path length of ambient light which passes and
 returns through the portion of the liquid crystal layer located in the
 reflection electrode region of the pixel electrode and the optical path
 length of light from the backlight which passes through the portion of the
 liquid crystal layer located on the transmission electrode region of the
 pixel electrode and compare the path length to each other. By knowing the
 approximate optical path lengths, changes in the characteristics of light
 passing through the liquid crystal layer in the reflection region and the
 transmission region can be made uniform.
 The thickness of the portion of the liquid crystal layer located on the
 reflection electrode region of each pizel electrode is made one half of
 the thickness of the portion of the liquid crystal layer located on the
 transmission electrode region thereof. This makes it possible to
 approximate the optical path length of ambient light which passes and
 returns through the portion of the liquid crystal layer located on the
 reflection electrode region of the pixel electrode and the optical path
 length of light from the backlight which passes through the portion of the
 liquid crystal layer located on the transmission electrode region of the
 pixel electrode and compare the path length to each other. By knowing the
 approximate optical path lengths, changes in the characteristics of light
 passing through the liquid crystal layer in the reflection region and the
 transmission region can be made uniform.
 EXAMPLE 4
 FIG. 8A is a plan view of one pixel portion of an active matrix substrate
 of a liquid crystal display device of Example 4 according to the present
 invention. FIG. 8B is a sectional view taken along line A--A of FIG. 8A.
 The active matrix substrate of this example includes gate lines 41, data
 lines 42, driving elements 43, drain electrodes 44, storage capacitor
 electrodes 45, a gate insulating film 46, an insulating substrate 47,
 contact holes 48, an interlayer insulating film 49, reflection pixel
 electrodes 50, and transmission pixel electrodes 51.
 Each of the storage capacitor electrodes 45 is electrically connected to
 the corresponding drain electrode 44 and overlaps the corresponding gate
 line 41 via the gate insulating film 46. The contact holes 48 are formed
 through the interlayer insulating film 49 to connect the transmission
 pixel electrodes 51 and the storage capacitor electrodes 45.
 Each pixel of the active matrix substrate with the above construction
 includes a reflection pixel electrode 50 and a transmission pixel
 electrode 51. Thus, as shown in FIG. 8B, each pixel is composed of the
 reflection electrode region, including the reflection pixel electrode 50,
 which reflects light from outside, and the transmission electrode region,
 including the transmission pixel electrode 51, which transmits light from
 a backlight.
 FIG. 9 is a sectional view of a liquid crystal display device of this
 example including the active matrix substrate shown in FIGS. 8A and 8B.
 The liquid crystal display device also includes a color filter layer 53, a
 counter electrode 54, a liquid crystal layer 55, alignment films 56, a
 polarizing plate 57, and a backlight 58.
 The regions of the transmission pixel electrodes 51 (transmission electrode
 region) which transmit light from the backlight 58 do not contribute to
 the brightness of the panel when the backlight 58 is off. Conversely, the
 regions of the reflection pixel a electrode 50 (reflection electrode
 region) which reflect light from outside contribute to the brightness of
 the panel regardless of the ON/OFF state of the backlight 58. In each
 pixel, therefore, the area of the reflection electrode region is desirably
 larger than the area of the transmission electrode region.
 In this example, the reflection pixel electrode 50 is formed on the
 corresponding transmission pixel electrode 51 so as to be electrically
 connected to each other so that the same signals are input into the
 reflection pixel electrode 50 and the transmission pixel electrode 51.
 Alternatively, the reflection pixel electrode 50 and the transmission
 pixel electrode 51 may not be electrically connected to each other so as
 to receive different signals for different displays.
 In the liquid crystal display device shown in FIG. 9, part of the light
 from the backlight 58 incident on the reflection pixel electrode 50 is not
 usable as display light. In order to overcome this problem, a modified
 liquid crystal display device shown in FIG. 10 includes a microlens 59 and
 a microlens protection layer 60 for each pixel. With this construction,
 light from the backlight 58 is converged on the transmission electrode
 region on which the reflection pixel electrode 50 is not formed, via the
 microlens 59, to increase the amount of light which passes through
 transmission region and thus to improve the brightness of display.
 FIG. 11A is a plan view of one pixel portion of an alternative active
 matrix substrate of the liquid crystal display device of Example 4
 according to the present invention. FIG. 11B is a sectional view taken
 along line B--B of FIG. 11A.
 In the active matrix substrate shown in FIGS. 11A and 11B, the region of
 the transmission pixel electrode 51 and the region of the reflection pixel
 electrode 50 of each pixel are reversed from those of the active matrix
 substrate shown in FIGS. 8A and 8B. The ratio of the areas of the region
 of the reflection pixel electrode 50 and the region of the transmission
 pixel electrode 51 may be changed appropriately.
 When the active matrix substrate shown in FIGS. 8A and 8B and that shown in
 FIGS. 11A and 11B are compared, the active matrix substrate shown in FIGS.
 8A and 8B is advantageous in the points that light from outside is
 prevented from entering the driving element 43 since the reflection pixel
 electrode 50 is formed over the driving element 43 and that the formation
 of the microlens 59 for converging light is easier since the region of the
 transmission pixel electrode 51 is located in the center of each pixel.
 In this example, since the light reflection region and the light
 transmission region are formed in one pixel, the aperture ratio of the
 pixel is as large as possible. To satisfy this, a high aperture structure
 is adopted in this example where the interlayer insulating film 49,
 composed of an organic insulating film, is interposed between the pixel
 electrodes and the levels of the gate lines 41 and the source lines 43.
 Other structures may also be adopted.
 EXAMPLE 5
 FIG. 12A is a plan view of one pixel portion of an active matrix substrate
 of a liquid crystal display device of Example 5 according to the present
 invention. FIG. 12B is a sectional view taken along line C--C of FIG. 12A.
 In the active matrix liquid crystal display device of Example 5, reflection
 pixel electrodes 50 are formed on tilted or concave and convex portions of
 an interlayer insulating film 49. Light from outside is therefore
 reflected from the reflection pixel electrodes 50 in a wider range of
 directions, so that the angle of visibility becomes wider.
 The interlayer insulating film 49 in this example is formed so as to be
 thickest at portions located above gate lines 41 and source lines 42 and
 be completely etched away at portions located above drain electrodes 44,
 forming the tilted or concave and convex portions. This eliminates the
 necessity of forming contact holes for electrically connecting the drain
 electrodes 44 and the reflection pixel electrodes 50, and thus prevents a
 disturbance in the orientation of liquid crystal molecules from occurring
 due to sharp steps at contact holes. This contributes to an increase in
 the aperture ratio.
 In this example, the drain electrodes 44, which are transparent electrodes
 made of ITO, serve as the transmission pixel electrodes 51.
 The tilt angle of the tilted portions or the pitch of the concave and
 convex portions of the interlayer insulating film 49 should be
 sufficiently small so that an alignment film can be formed on the
 resultant substrate and rubbed. Thus, optimal conditions should be
 determined depending on the respective rubbing conditions and the types of
 liquid crystal molecules.
 In this example, as in Example 4, microlenses may be provided below the
 drain electrodes 44 as the transmission pizel electrodes 51, to improve
 the brightness of the display when the backlight is on.
 EXAMPLE 6
 FIG. 13A is a plan view of one pixel portion of an active matrix substrate
 of a liquid crystal display device of Example 6 according to the present
 invention.
 FIG. 13B is a sectional view taken along line D--D of FIG. 13A.
 In this example, reflection pixel electrodes 50 are formed at the same
 level as gate lines 41 at and during the same step. With this
 configuration, since a separate step for forming the reflection pixel
 electrodes 50 is not required, the number of steps and the production cost
 do not increase.
 In this example, the reflection pixel electrodes 50 are not connected to
 drain electrodes 44 constituting driving elements 43, but are used only
 for the reflection of light from outside. Only the transmission pixel
 electrodes 51 serve as the electrodes for driving the liquid crystal. In
 other words, the transmittance of light reflected by the reflection pixel
 electrodes 50 is controlled by controlling the liquid crystal layer with a
 voltage at the transmission pixel electrodes 51.
 If no signal is input into each of the reflection pixel electrodes 50, a
 floating capacitance is generated between the reflection pixel electrode
 50 and the corresponding drain electrode 44 or transmission pixel
 electrode 51. To avoid this problem, the reflection pixel electrodes 50
 should desirably be provided with such a signal that does not adversely
 affect the display. By connecting each of the reflection pixel electrodes
 50 with an adjacent gate line 41, the generation of a floating capacitance
 is prevented, and a storage capacitor can be formed between a reflection
 pixel electrode 50 and a corresponding drain electrode 44.
 In this example, as in Example 4, microlenses may be provided to converge
 light on the transmission pixel electrodes, to improve the brightness of
 display when the backlight is on.
 In this example, also, since the light reflection region and the light
 transmission region are formed in one pixel, the aperture ratio of the
 pixel is as large as possible. To satisfy this, a high aperture structure
 is adopted where an organic insulating film is used as the interlayer
 insulating film. Other structures may also be adopted.
 EXAMPLE 7
 FIG. 14A is a plan view of one pixel portion of an active matrix substrate
 of a liquid crystal display device of Example 7 according to the present
 invention. FIG. 14B is a sectional view taken along line E--E of FIG. 14A.
 In this example, reflection pixel electrodes 50 are formed at the same
 level as source lines 42. With this configuration, since the reflection
 pixel electrodes 50 can be formed at the formation of the source lines 42,
 the number of steps and the production cost do not increase.
 In this example, since a high aperture structure via an interlayer
 insulating film 49 is adopted, the reflection pixel electrodes 50 are used
 only for the reflection of light from outside. Only transmission pixel
 electrodes S serve as the electrodes for driving the liquid crystal.
 This example is different from Example 6 in that in this example the
 reflection pixel electrode 50 in each pixel is electrically connected to
 the corresponding drain electrode 44. In an alternative case where the
 interlayer insulating film 49 is not formed at the region above the drain
 electrode 44 and the drain electrode 44 is used as the transmission pixel
 electrode, the reflection pixel electrode 50 also contributes to the
 driving of the liquid crystal molecules.
 In this example, as in Example 4, microlenses may be provided to converge
 light on the transmission pixel electrodes 51, to improve the brightness
 of display when the backlight is on.
 In this example, also, since the light reflection region and the light
 transmission region are formed in one pixel, the aperture ratio of the
 pixel is as large as possible. To satisfy this, a high aperture structure
 is adopted where an organic insulating film is used as the interlayer
 insulating film. Other structures may also be adopted.
 Thus, in Examples 4 to 7 above according to the present invention, the
 active matrix liquid crystal display device capable of switching between
 the reflection type and the transmission type is realized.
 Such a liquid crystal display device can provide a sufficient brightness
 irrespective of the conditions of use, while realizing a reduced power
 consumption and a prolonged use duration, by the user's switching the mode
 between the transmission type and the reflection type depending on the use
 conditions.
 Also realized is a transmission/reflection switchable active matrix liquid
 crystal display device which can be used as a reflection type liquid
 crystal display device when the environment is bright and as a
 transmission type liquid crystal display device when the environment is
 dark.
 Since the reflection pixel electrodes and the transmission pixel electrodes
 are electrically connected with each other, no interconnect is required to
 supply the driving signals independently. This simplifies the construction
 of the active matrix substrate.
 When the reelection pixel electrodes are formed above the driving elements,
 light from outside is prevented from entering the driving elements.
 The transmission pixel electrodes do not contribute to the brightness of
 the panel when the backlight is off, while the reflection pixel electrodes
 contribute to the brightness of the panel regardless of the ON/OFF state
 of the backlight. Accordingly, by increasing the area of the reflection
 pixel electrodes, the brightness of display can be stabilized even when
 the backlight is off or emits less light.
 Light from the backlight which is blocked by the reflection pixel
 electrodes, the gate lines, and the like can be converged on the
 transmission pixel electrodes. This makes it possible to increase the
 brightness of the display device without increasing the brightness of the
 backlight itself.
 The reflection pixel electrodes can be made to reflect light from outside
 in a wide range of directions. This allows for a wider angle of
 visibility.
 The reflection pixel electrodes may be formed without an additional step
 for this formation. This prevents the number of steps and the production
 cost from increasing
 The reflection pixel electrodes may be electrically connected to the gate
 lines. This prevents the generation of a floating capacitance and allows
 for the formation of a storage capacitor with the drain electrodes.
 The reflection pixel electrodes may be provided with the same signals as
 those applied to the counter electrode. This prevents the generation of a
 floating capacitance. Also, the reflection pixel electrodes may be used
 for the formation of a storage capacitor for the voltage applied to the
 pixel electrodes.
 EXAMPLE 8
 In Example 8, a reflection/transmission type liquid crystal display device
 according to the present invention will be described.
 First, the principle of the generation of an interference color in the
 liquid crystal display device of Example 8 will be described.
 FIG. 23 is a conceptual view illustrating the generation of an interference
 color. Light is incident on a glass substrate and the incident light is
 reflected by a reflection film to be output from the glass substrate.
 In the above case, an interference color is considered to be generated when
 light incident at an incident angle .theta.i is reflected from a convex
 portion and a concave portion of the reflection film and output at an
 output angle .theta.o. The optical path difference .delta. between the two
 reflected light beams is represented by expression (1) below:
EQU .delta.=Lsin.theta.i+h(1cos.theta.i'+1/
 cos.theta.o').multidot.n-{Lsin.theta.o+h(tan.theta.i'+tan.theta.o')sin.the
 ta.o}=L(sin.theta.i-sin.theta.o)+h{(1/cos.theta.i'+1/
 cos.theta.o').multidot.n-(tan.theta.i'+tan.theta.o')sin.theta.o} (1)
 wherein .theta.i' is the incident angle at the concave portion of the
 reflection film, .theta.o' is the output angle at the concave portion of
 the reflection film, L is the distance between the incident points of the
 two light beams on the glass substrate, h is the height of the point on
 the convex portion of the reflection film from which one of the light
 beams is reflected, with respect to the point on the concave portion
 thereof from which the other light beam is reflected, and n is the
 refractive index of the glass substrate.
 Since the calculation of expression (1) is possible only when
 .theta.i=.theta.o and .theta.i'=.theta.o', the optical path difference 6
 is simplified into expression (2) below when .theta.i=.theta.o=.theta. and
 .theta.i'=.theta.o'.
EQU .delta.=h{2n/cos.theta.'-2tan.theta.'.multidot.sin.theta.} (2)
 When arbitrary wavelengths .lambda.1 and .lambda.2 are taken into
 consideration, the output light beams reflected from the convex portion
 and the concave portion are weakened by each other when
 .delta./.lambda.1=m.+-.1/2 (m is an integer) and intensified by each other
 when .delta./.lambda.2=m. Thus, expression (3) below is established.
EQU .delta.=(1/.lambda.1-1/.lambda.2)=1/2 (3)
 Expression (3) above is also represented by expression (4) below:
EQU .delta.=(.lambda.1.multidot..lambda.2)/2.multidot.(.lambda.2-.lambda.1)
 (4)
 Accordingly, from expressions (2) and (4) above, the height h can be
 represented by expression (5) below:
EQU h=1/2.multidot.{(.lambda.1.multidot..lambda.2)/
 (.lambda.2-.lambda.1)}.multidot.{cos.theta.'/
 (2n-2sin.theta.'.multidot.sin.theta.)} (5)
 From the above, it has been found that, in order to eliminate the
 generation of an interference color, the reflection surface of the
 reflection film should have a continuous wave shape.
 In this example, in order to form such a reflection film, at least two
 types of convex portions with different heights are formed on a base
 plate, a polymer resin film is formed on the base plate covering the
 convex portions, and a reflection thin film made of a material having a
 high light reflection efficiency is formed on the polymer resin film.
 The thus-fabricated reflection thin film can be used for the reflection
 portions of the reflection/transmission type liquid crystal display device
 Since such reflection portions have a reflection surface of a continuous
 wave shape, light reflected from the reflection portions is prevented from
 generating an interference. When the convex portions are optically formed
 by use of a photomask, they can be formed with good reproducibility by
 setting the same light irradiation conditions.
 In the reflection/transmission type liquid crystal display device of this
 example, the convex portions are preferably not formed in the transmission
 portions made of a material having a high light transmission efficiency in
 order to improve the transmission efficiency. However, the display by use
 of transmitted light is possible even if the convex portions are formed in
 the transmission portions.
 FIG. 15 is a sectional view of a reflection/transmission type liquid
 crystal display device of this example according to the present invention.
 Referring to FIG. 15, a gate insulating film 61a is formed an a glass
 substrate 61. High convex portions 64a and low convex portions 64b are
 formed randomly on the portions of the glass substrate 61 located below
 reflection electrodes 69 having a light reflection function. The high
 convex portions 64a and the low convex portions 64b are covered with a
 polymer resin film 65.
 Since the high convex portions 64a and the low convex portions 64b are
 formed on the glass substrate 61 via the gate insulating film 61a, the
 upper surfaces of the portions of the polymer resin film 65 formed on the
 high convex portions 64a and the low convex portions 64b are of a
 continuous wave shape. The polymer resin film 65 is formed almost all over
 the glass substrate 61, not only in the regions below the reflection
 electrodes 69.
 The reflection electrodes 69, which are made of a material having a light
 reflection function, are formed on the portions of the polymer resin film
 65 having the continuous wave shape which are formed on the high convex
 portions 64a and the low convex portions 64b.
 Transmission electrodes 68 are also formed on the glass substrate 61 via
 the gate insulting film 61a, separately from the reflection electrodes 69.
 The transmission electrodes 68 are made of a material having a light
 transmission function, such as indium tin oxide (ITO).
 A polarizing plate 90 is attached to the back surface of the
 thus-fabricated active matrix substrate when it is mounted as a module. A
 backlight 91 is then disposed on the polarizing plate 90.
 Part of light emitted form the backlight 91 and directed to the
 transmission electrodes 68 passes through the transmission electrodes 68
 and thus the active matrix substrate. However, part of light directed to
 the reflection electrodes 69 is reflected from the back surfaces of the
 reflection electrodes 69 to return to the is backlight 91. Since the back
 surfaces of the reflection electrodes 69 are of a continuous wave shape,
 light reflected from the reflection electrodes 69 is scattered as shown by
 the arrows in FIG. 15. Such scattered light is again reflected from the
 backlight 91 toward the active matrix substrate. Part of such light passes
 through the transmission electrodes 68 and thus the active matrix
 substrate.
 Thus, in the active matrix substrate including the reflection electrodes 69
 of the above-described shape, the light from the backlight reflected by
 the reflection electrodes 69 can be used for display. This allows for more
 effective use of light than that expected from an actual aperture ratio,
 unlike the conventional transmission type liquid crystal display device.
 Specifically, if the reflection electrodes are of a flat shape, regular
 reflection is mainly generated, which is difficult to be reflected again
 to pass through the transmission electrodes 68. In this example, however,
 the reflection electrodes 69 of a continuous wave shape serve to return
 the reflected light toward the portions of the backlight located below the
 transmission electrodes 68, allowing for further effective use of light.
 FIG. 16 is a graph showing the relationship of the aperture ratio to the
 transmittance and reflectance observed when the reflectances of the
 reflection electrodes 69 and the backlight 91 as compared with the
 standard white plate are about 90%, and the transmittance of the
 polarizing plate 90 is about 40%. Note that this relationship was
 calculated on the assumption that pixel electrodes cover the entire
 display surface, not considering the existence of bus lines and active
 elements.
 As is observed from FIG. 16, the reflectance of the reflection electrode 69
 for light incident from outside on the side of a counter substrate is
 obtained by multiplying the reflectance of the reflection electrode 69 by
 the ratio of the area of the reflection electrode 69 to the area of the
 entire pixel electrode. The transmittance of the transmission electrode 68
 for light from the backlight 91 is equal to, not just the aperture ratio a
 (i.e., the ratio of the area of the transparent electrode 68 to the area
 of the entire pixel electrode), but a value b, including a component of
 light from the backlight reflected by the reflection electrode 69, which
 can be utilized for display added to the aperture ratio a.
 Thus, since the light from the backlight 91 reflected by the reflection
 electrodes 69 is also utilized, more effective use of light than that
 expected from the actual aperture ratio is possible, unlike the
 conventional transmission type liquid crystal display device.
 FIG. 17 is a graph showing the relationship between the aperture ratio and
 the light transmission efficiency (transmittance/aperture ratio). As is
 observed from FIG. 17, it has been found from such a calculation that,
 when the aperture ratio is 40%, the light from the backlight 91 reflected
 by the reflection electrode 69 can be utilized up to about 50% of the
 intensity of the light which has directly passed through the transmission
 electrode 68 from the backlight 91. From the calculation results shown in
 FIG. 17, it has also been found that the greater the ratio of the area of
 the reflection electrode 69 to the area of the entire pixel electrode is,
 the higher the use efficiency of the light reflected by the reflection
 electrode 69 becomes.
 Hereinbelow, a specific example of the reflection/transmission type liquid
 crystal display device of Example 8 will be described.
 FIG. 18 is a plan view of the reflection/transmission type liquid crystal
 display device of Example 8 according to the present invention. FIGS. 19A
 to 19F are sectional views taken along line F--F of FIG. 18, illustrating
 the process of fabricating the liquid crystal display device of this
 example.
 Referring to FIGS. 18 and 19F, an active matrix substrate 70 of the
 reflection/transmission type liquid crystal display device includes a
 plurality of gate bus lines 72, as scanning lines, and a plurality of
 source bus lines 74, as signal lines, which are formed to cross with each
 other. In each of the rectangular regions surrounded by the adjacent gate
 bus lines 72 and the adjacent source bus lines 74, a transmission
 electrode 68 made of a material having a high light transmission
 efficiency and a reflection electrode 69 made of a material having a high
 reflection efficiency are disposed. The transmission electrode 68 and the
 reflection electrode 69 constitute one pixel electrode.
 A gate electrode 73 extends from the gate bus line 73 toward the pixel
 electrode at a corner portion of each of the region where the pixel
 electrode is formed. A thin film transistor (TFT) 71 is formed as a
 switching element at the end portion of the gate electrode 73. The gate
 electrode 73 itself constitutes part of the TFT 71.
 The TFT 71 is located above the gate electrode 73 formed on a glass
 substrate 61 as shown in FIG. 19F. The gate electrode 73 is covered with a
 gate insulating film 61a, and a semiconductor layer 77 is formed on the
 gate insulating film 61a so as to cover the gate electrode 73 via the gate
 insulating film 61a. A pair of contact layers 78 are formed on the side
 portions of the semiconductor layer 77.
 A source electrode 75 is formed on one of the contact layers 78 and
 electrically connected to the corresponding source bus line 74. The side
 portion of the source electrode 75 overlaps the gate electrode 73 in an
 insulating manner, constituting part of the TFT 71. A drain electrode 76,
 which also constitutes part of the TFT 71, is formed on the other contact
 layer 78 so as to be away from the source electrode 75 and overlaps the
 gate electrode 73 in an insulating manner. The drain electrode 76 is
 electrically connected to the pixel electrode via an underlying electrode
 81a.
 A storage capacitor is formed by forming the underlying electrode 81a so as
 to overlap the gate bus line 72 used for the adjacent pixel electrode in
 the next pixel row via the gate insulating film 61a. The underlying
 electrode 81a may be formed over substantially the entire region where
 convex portions are formed as will be described hereinafter, so as to
 unify the influence of the process of forming this layer.
 High convex portions 64a and low convex portions 64b and an overlying
 polymer resin film 65 are formed under each of the reflection electrodes
 69.
 The upper surface of the polymer resin film 65 is of a continuous wave
 shape reflecting the existence of the convex portions 64a and 64b. Such a
 polymer resin film 65 is formed over substantially the entire glass
 substrate 61, not only in the regions below the reflection electrodes 69.
 In this example, OFPR-800 manufactured by Tokyo Ohka Co., Ltd., for
 example, is used for the polymer resin film 65.
 The reflection electrode 69 is formed on the portion of the polymer resin
 film 65 having the continuous wave shape which is formed on the high
 convex portions 64a and the low convex portions 64b. The reflection
 electrode 69 is made of a material having a high reflection efficiency,
 such as Al. The reflection electrode 69 is electrically connected to the
 corresponding drain electrode 76 via a contact hole 79.
 In each pixel of the reflection/transmission type liquid crystal display
 device of this example, the transmission electrode 68 is formed separately
 from the reflection electrode 69. The transmission electrode 68 is made of
 a material having a high light transmission efficiency such as ITO.
 The method for forming the reflection electrodes 69 and the transmission
 electrodes 68 which are main portions of the reflection/transmission type
 active matrix substrate 70 will be described with reference to FIGS. 19A
 to 19F.
 First, as shown in FIG. 19A, the plurality of gate bus lines 72 (see FIG.
 18) made of Cr, Ta, or the like and the gate electrodes 73 extending from
 the gate bus lines 72 are formed on the glass substrate 61.
 The gate insulating film 61a made of SiN.sub.x, SiO.sub.x, or like is
 formed on the entire surface of the glass substrate 61 covering the gate
 bus lines 72 and the gate electrodes 73. The semiconductor layers 77 made
 of amorphous silicon (a-Si), polysilicon, CdSe, or the like are formed on
 the portions of the gate insulating film 61a located above the gate
 electrodes 73. The pair of contact layers 78 made of a-Si or the like are
 formed on both side portions of each of the semiconductor layers 77.
 The source electrode 75 made of Ti, Mo, Al, or the like is formed on one of
 the contact layers 78, while the drain electrode 76 made of Ti, Mo, Al, or
 the like is formed on the other contact layer 78.
 In this example, as the material of the glass substrate 61, product number
 7059 manufactured by Corning Inc. with a thickness of 1.1 mm was used.
 As shown in FIG. 19B, a metal layer 81 which constitutes part of the source
 bus lines 74 is formed by sputtering. The metal layer 81 is also used to
 form the underlying electrodes 81a.
 Subsequently, as shown in FIG. 19C, an ITO layer 80 which also constitutes
 part of the source bus lines 74 is formed by sputtering and patterned.
 Thus, in this example, the source bus lines 74 are of a double-layer
 structure consisting of the metal layer 81 and the ITO layer 80. This
 double-layer structure is advantageous in that even if the metal film 81
 constituting the source bus line 74 is partly defective, the electric
 connection of the source bus line 74 is maintained by the ITO layer 80.
 This reduces the occurrence of disconnections in the source bus line 74.
 The ITO layer 80 is also used to form the transmission electrodes 68. This
 makes it possible to form the transmission electrodes 68 simultaneously
 with the formation of the source bus lines 74, preventing an increase in
 the number of layers.
 Then, as shown in FIG. 19D, rounded convex portions 64a and 64b, having
 substantially circular cross-sections are formed of a resist film of a
 photosensitive resin over the regions on which the reflection electrodes
 69 are to be formed. Preferably, the convex portions 64a and 64b are not
 formed on the transmission electrodes 68 so that a voltage is efficiently
 applied to the liquid crystal layer. optically, however, not so large
 influence Is observed when the convex portions 64a and 64b are formed on
 the transmission electrodes 68.
 Hereinbelow, the process of forming the convex portions 64a and 64b in the
 reflection electrode regions will be briefly described with reference to
 FIGS. 20A to 20D.
 First, as shown in FIG. 20A, a resist film 62 made of a photosensitive
 resin is formed on the glass substrate 61 (actually, with the metal layer
 81 and the underlying electrode 81a formed thereon as shown in FIG. 19D)
 by a spin coat method. The resist film 62 is formed of the same
 photosensitive resin as that used for the polymer resin film 65 to be
 described hereinafter, i.e., OPR-800, by spin coating at a speed
 preferably in the range of about 500 to about 3000 rpm, in this example at
 1500 rpm, for 30 seconds, so as to obtain a thickness of 2.5 .mu.m.
 Then, the resultant glass substrate 61 with the resist film 62 formed
 thereon is prebaked at 90.degree. C. for 30 minutes, for example.
 Subsequently, as shown in FIG. 20B, a photomask 63 is disposed above the
 resist film 62. The photomask 63 has a shape as shown in FIG. 21, for
 example, which includes two types of circular pattern holes 63a and 63b
 formed through a plate 63c. The photomask 63 is then irradiated with light
 from above as shown by the arrows in FIG. 20B.
 The photomask 63 in this example has the circular pattern holes 63a with a
 diameter of 5 .mu.m and the circular pattern holes 63b with a diameter of
 3 .mu.m arranged at random. The space between any adjacent pattern holes
 should be at least about 2 .mu.m. If the space is too large, however, the
 polymer resin film 65 to be formed thereon at a later step will hardly
 succeed in obtaining a continuous wave shape.
 The resultant substrate is developed with a developer with a concentration
 of 2.38%, e.g., NMD-3 manufactured by Tokyo Ohka Co., Ltd. As a result, as
 shown in FIG. 20C, a number of minute convex portions 64a' and 64b' with
 different heights are formed on the reflection electrode regions of the
 glass substrate 61. The top edges of the convex portions 64a' and 64b' are
 squared. The convex portions 64a' with a height of 2.48 .mu.m and the
 convex portions 64b' with a height of 1.64 .mu.m are formed from the
 pattern holes 63a with a diameter of 5 .mu.m and the pattern holes 63b
 with a diameter of 3 .mu.m, respectively.
 The heights of the convex portions 64a' and 64b' can be changed by changing
 the sizes of the pattern holes 63a and 63b, the light exposure time, and
 the developing time. The size of the pattern holes 63a and 63b are not
 limited to those described above.
 Thereafter, a shown in FIG. 20D, the glass substrate 61 with the convex
 portions 64a' and 64b' formed thereon is heated at about 200.degree. C.
 for one hour. This softens the square top edges of the convex portions
 64a' and 64b', to form the rounded convex portions 64a and 64b having
 substantially circular cross sections.
 Then, as shown in FIG. 19E, a polymer resin is applied on the resultant
 glass substrate 61 by spin coating and patterned to form the polymer resin
 film 65. The material OFPR-800 mentioned above is used as the polymer
 resin and applied by spin coating at a speed preferably in the range of
 about 1000 to about 3000 rpm. In this example, the spin coating was
 conducted at a speed of 2000 rpm.
 In this way, the polymer resin film 65 having an upper surface of a
 continuous wave shape is obtained on the glass substrate 61, which is flat
 having no convex portions.
 As shown in FIG. 19F, the reflection electrodes 69 made of Al are formed on
 predetermined portions of the polymer resin film 65 by sputtering, for
 example. Materials suitable for the reflection electrodes 69 include,
 besides Al and an Al alloy, Ta, Ni, Cr, and Ag having a high light
 reflection efficiency. The thickness of the reflection electrodes 69 is
 preferably in the range of about 0.01 to about 1.0 .mu.m.
 A polarizing plate (not shown) is attached to the back surface of the
 thus-fabricated active matrix substrate of this example. A backlight is
 then disposed on the outer surface of the polarizing plate.
 Electric corrosion is generated if the Al film is formed after the portions
 of the polymer resin film 65 located on the transmission electrodes 68 are
 removed. Therefore, the portions of the polymer resin film 65 located on
 the transmission electrodes 68 should be removed after the formation of
 the reflection electrodes 69. This removal can be done by ashing, together
 with the removal of the portions of the polymer resin film 65 located
 above terminal electrodes for the connection of drivers form d on the
 peripheries of the active matrix substrate 70. This improves the process
 efficiency and allows for efficient voltage application to the liquid
 crystal layer.
 If the polymer resin film 65 is not used in the process of forming the
 convex portions, a layer of Mo or the like may be formed between the
 transmission electrodes 68 made of ITO and the ref lecithin electrodes 69
 made of Al, to prevent the generation of electric corrosion.
 The thus-formed reflection electrodes 69, made of a material having a high
 light reflection efficiency, have an upper surface in a continuous wave
 shape since the underlying polymer resin film 65 has the continuous wave
 shape as described above.
 In this example, the transmission electrodes 68 are formed simultaneously
 with the formation of the source bus lines 74. When the source bus lines
 74 are of a single-layer structure composed of the metal layer 81, not the
 double-layer structure composed of the metal layer 81 and the ITO layer 80
 as described above, the transmission electrodes 68 may be formed
 separately from the formation of the source bus lines 74.
 The wavelength dependence of light reflected from the reflection electrodes
 69 having a continuous wave shape and made of a material having a high
 light reflection efficiency was measured in a manner as shown in FIG. 22.
 An object structure for measurement was formed by simulating conditions
 for the reflection electrodes 69 equivalent to an actual liquid crystal
 display device during an actual use. Specifically, a dummy glass 66 having
 a refractive index of 1.5, which is substantially equal to the refractive
 index of the actual liquid crystal layer is attached to the active matrix
 substrate 70, with the reflection electrodes 69 and the transmission
 electrodes 68 formed thereon with an ultraviolet-setting adhesive 67
 having a refractive index of about 1.5.
 As the measurement system, a light source L1 is disposed so that an
 incident light beam L1' is incident at an incident angle .theta.i with
 respect to the normal ml of the dummy glass 66, and a photomultimeter L2
 is disposed so as to capture a fixed-angle light beam reflected at an
 output angle .theta.o with respect to the normal m2.
 With the above construction, the photomultimeter L2 captures the intensity
 of a scattered light beam L2' which is reflected at the output angle
 .theta.o among scattered light beams which are incident on the dummy glass
 66 at the incident angle .theta.i, as the incident light beam L1'.
 The above measurement was conducted under the conditions of
 .theta.i=30.degree. and .theta.o=20.degree. in order to avoid the
 photomultimeter L2 from capturing a regular-reflected light beam which is
 emitted from the light source L1 and reflected from the surface of the
 dummy glass 66.
 FIG. 24 is a graph showing the wavelength dependence of reflected light in
 this example.
 As shown in FIG. 24, the wavelength dependence of the reflectance is hardly
 recognized in this example, which proves that a good white color display
 is obtained.
 In this example, the shape of the pattern holes 63a and 63b of the
 photomask 63 is a circle. Other shapes such as a rectangle, an ellipse,
 and a strips may also be used.
 In this example, the convex portions 64a and 64b with two different heights
 are formed. Alternatively, convex portions with a single height or those
 with three or more different heights may also be formed to obtain
 reflection electrodes having good reflection characteristics.
 It has been found, however, that reflection electrodes with better
 wavelength dependence of the reflection characteristics are obtained when
 convex portions with two or more different heights are formed then when
 convex portions with a single height are formed.
 If it is ensured that the upper surface of a continuous wave shape can be
 obtained only by the convex portions 64a and 64b, the formation of the
 polymer resin film 65 is not required. Only the resist film 62 (See FIGS.
 20B and 20C) is formed to obtain the upper surface of a continuous wave
 shape and then the reflection electrodes 69 are formed thereon. In this
 case, the step of forming the polymer resin film 65 can be omitted.
 In this example, OFPR-800 manufactured by Tokyo Ohka Co., Ltd. is used as
 the photosensitive resin material. Any other photosensitive resin material
 of the negative or positive type which can be patterned by an exposure
 process may also be used. Examples of such photosensitive resin materials
 include: OMR-83, OMR-85, ONNR-20, OFPR-2, OFPR-830, and OFPR-500
 manufactured by Tokyo Ohka Co., Ltd.; TF-20, 1300-27, and 1400-27
 manufactured by Shipley Co.; Photoneath manufactured by Toray Industries,
 Inc.; RW-101 manufactured by Sekisui Fine Chemical Co., Ltd.; and R101 and
 R633 manufactured by Nippon Kayaku K.K.
 In this example, the TFTs 71 are used as the switching elements. The
 present invention is also applicable to active matrix substrates using
 other switching elements such as metal-insulator-metal (MIM) elements,
 diodes, and varistors.
 Thus, as described above, in the liquid crystal display device and the
 method for fabricating the liquid crystal display device of Example 8, the
 reflection electrodes made of a material having a high light reflection
 efficiency are formed so as to have a continuous wave shape. This. reduces
 the wavelength dependence of the reflection and thus permit realization of
 a good white color display by reflection without the generation of an
 interference colors
 Since the convex portions are formed on the substrate by an optical
 technique using a photomask, good reproducibility is ensured. The
 resultant wave-shaped upper surfaces of the reflection electrodes can also
 be obtained with good reproducibility.
 The transmission electrodes made of a material having a high light
 transmission efficiency are formed simultaneously with the formation of
 the source bus lines. This allows for the formation of the transmission
 electrodes of the reflection/transmission type liquid crystal display
 device without increasing the number of steps compared with the
 conventional liquid crystal display device.
 By forming a continuous wave shape for the reflection electrodes, more
 effective use of light than that expected from the actual aperture ratio
 is possible.
 According to the liquid crystal display device of this example, the
 reflection portion made of a material having a high light reflection
 efficiency and a transmission portion made of a material having a high
 light transmission efficiency are formed in one display pixel. With this
 construction, when the environment is pitchdark, the device serves as a
 transmission type liquid crystal display device which displays images
 utilizing light from the backlight passing through the transmission
 portion. When the environment is comparatively dark, the device serves as
 a reflection/transmission type liquid crystal display device which
 displays images utilizing both light from the backlight passing through
 the transmission portion and light reflected from the reflection portion
 composed of a film having a comparatively high reflectance. When the
 environment is bright, the device serves as a reflection type liquid
 crystal display device which displays images utilizing light reflected
 from the reflection portion composed of a film having a comparatively high
 reflectance.
 In other words, according to this example, the pixel electrode of each
 pixel is composed of the reflection portion made of a material having a
 high light reflection efficiency and the transmission portion made of a
 material having a high light transmission efficiency. Thus, a liquid
 crystal display device having a good light utilization efficiency in any
 of the above-described cases and an excellent productivity is realized.
 In this example, the upper surface of the reflection portion made of a
 material having a reflection function is of a continuous wave shape. This
 prevents the occurrence of a mirror phenomenon without providing a light
 scattering means, which is necessary when the reflection portion is flat,
 thus realizing a paper-white display.
 In this example, a photosensitive polymer resin film having a plurality of
 convex portions underlies the reflection portion made of a material having
 a reflection function. With this construction, even if a variation exists
 in the continuous smooth concave and convex shape, it does not influence
 the display. Thus, the liquid crystal display device can be fabricated
 with good productivity.
 The transmission portion made of a material having a high light
 transmission efficiency is formed simultaneously with the formation of the
 source bus lines. This greatly shortens the fabrication process of the
 liquid crystal display device.
 A protection film is formed between the transmission portion and the
 reflection portion. This prevents the generation of electric corrosion
 between the transmission portion and the reflection portion.
 The reflection material remaining on the transmission portions and terminal
 electrodes is simultaneously removed when the patterning of the reflection
 portions is conducted. This greatly shortens the fabrication process of
 the liquid crystal display device.
 In this examples light emitted from the backlight passes through the
 transmission portion to leave the substrate, while it is reflected from
 the back surface of the reflection portion to be returned to the backlight
 and reflected again toward the substrate. Part of the re-reflected light
 passes through the transmission portion to leave the substrate.
 It is conventionally difficult to direct the rereflected light to
 effectively pass through the transmission portion since regular reflection
 mainly occurs when the reflection portion is flat. In this example,
 however, since the reflection portion is of a continuous wave shape, the
 light emitted from the backlight is scattered, allowing the reflected
 light to effectively return toward the portion of the backlight located
 below the transmission portion. Thus, more effective use of light than
 that expected from the actual aperture ratio is possible, unlike the
 conventional transmission type liquid crystal display device.
 EXAMPLE 9
 FIG. 25 is a partial sectional view of a transmission/reflection type
 liquid crystal display device 100 of Example 9 according to the present
 invention.
 Referring to FIG. 25, the liquid crystal display device 100 includes an
 active matrix substrate 70 shown in FIG. 18 (corresponding to the F'--F'
 cross section), a counter substrate (color filter substrate) 160, and a
 liquid crystal layer 140 interposed therebetween. The
 transmission/reflection type active matrix substrate 70 includes a
 plurality of gate bus lines 72, as scanning lines, and a plurality of
 source bus lines 74, as signal lines, formed on an insulating glass
 substrate 61 so as to cross with each other. In each of the rectangular
 regions surrounded by the adjacent gate bus lines 72 and the adjacent
 source bus lines 74, a transmission electrode 68 made of a material having
 a high light transmission efficiency and a reflection electrode 69 made of
 a material having a high light reflection efficiency are disposed. The
 transmission electrode 68 and the reflection electrode 69 constitute one
 pixel electrode. The counter substrate (color filter substrate) 160
 includes a color filter layer 164 and a transparent electrode 166 made of
 ITO or the like formed in this order on an insulating glass substrate 162.
 Vertical alignment films (not shown) are formed on the surfaces of the
 substrates 70 and 160 facing the liquid crystal layer 140. In order to
 define the direction of liquid crystal molecules oriented by the electric
 field, the vertical alignment films are rubbed in a direction so as to
 provide a pretilt angle to the liquid crystal molecules. A nematic liquid
 crystal material having a negative dielectric anisotropy (e.g., MJ
 manufactured by Merck & Co., Inc.) is used for the liquid crystal layer
 140.
 Each pixel which is a minimum display unit of the liquid crystal display
 device 100 includes a reflection region 120R defined by the reflection
 electrode 69 and the transmission region 120T defined by the transmission
 electrode 68. The thickness of the liquid crystal layer 140 is dr in the
 reflection region 120T and dt (dt=2dr) in the transmission region 120T, so
 that the optical path lengths of light beams contributing to the display
 (reflected light beams in the reflection region and transmitted light
 beams in the transmission region) are substantially equal to each other.
 Although dt=2dr is preferable, dt and dr may be appropriately determined
 in the relationship with the display characteristics as far as dt&gt;dr.
 Typically, dt is about 4 to about 6 .mu.m and dr is about 2 to about 3
 .mu.m. In other words, a stop of, about 2 to about 3 .mu.m is formed in
 each pixel region of the active matrix substrate 70. when the reflection
 electrode 69 has a concave and convex shaped surface as shown in FIG. 25,
 the average value of thicknesses should be dr. In this way, the
 transmission/reflection type liquid crystal display device 100 includes
 two types of regions (the reflection regions and the transmission regions)
 where the thickness of the liquid crystal layer 140 is different
 therebetween. In this example, the active matrix substrate 70 includes the
 reflection regions 120R and the transmission regions 120T having different
 heights formed on the side facing the liquid crystal layer 140.
 A liquid crystal display device (diagonal: 8.4 inches) having the
 construction shown in FIG. 25 was actually fabricated and subjected to a
 64 gray-level display to evaluate the display characteristics
 (transmittance and reflectance) of the device. The evaluation results are
 shown in FIG. 26. The liquid crystal display device was fabricated under
 the following conditions. The ratio of the area of the transmission region
 120T to that of the reflection region 120R in one pixel was 4:6. The
 transmission electrodes 68 were made of ITO, while the reflection
 electrodes 69 were made of Al. The thickness dt of the liquid crystal
 layer 140 in the transmission regions 120T was set at about 5.5 .mu.m,
 while the thickness of the liquid crystal layer 140 in the reflection
 regions 120R were set at about 3 .mu.m.
 The transmittance of the liquid crystal display device in the transmission
 mode using light from a backlight was measured by MB-5 manufactured by
 Topcon Co., while the reflectance of the liquid crystal display device in
 the reflection mode using ambient light was measured by LCD-5000
 manufactured by Otsuka Electronics Co., Ltd. by use of an integrating
 sphere.
 As is apparent from FIG. 26, the variations in the reflectance and-the
 transmittance in the 64 gray-level display (the solid line and the dotted
 line in FIG. 26, respectively) substantially match with each other.
 Accordingly, a gray-level display with a sufficient display quality is
 realized even if the display in the transmission mode using light from the
 backlight and the display in the reflection mode using ambient light are
 conducted simultaneously. The contrast ratios in the transmission mode and
 the reflection mode were about 200 and about 25, respectively.
 Hereinbelow, the evaluation results of color reproducibility will be
 described. FIGS. 27 and 28 are chromaticity diagrams of a conventional
 transmission type liquid crystal display device and the
 transmission/reflection type liquid crystal display device of this
 example, respectively, under ambient light with different brightnesses.
 The same backlight was used for these liquid crystal display devices.
 As is apparent from FIG. 27, as the illuminance on the display screen by
 ambient light increases from 0 lx to 8,000 lx and then to 17,000 lx, the
 range of the color reproducibility (the area inside the triangle in FIG.
 27) of the conventional liquid crystal display device significantly
 decreases. This is recognized by the observer as color blurring. In the
 transmission/reflection type liquid crystal display device, however, as is
 observed from FIG. 28, the range of the color reproducibility when the
 illuminance is 8,000 lx is substantially the same as that when the
 illuminance is 0 lx. Moreover, only a minor decrease is observed in the
 color reproducibility when the illuminance is 17,000 lx. Color blurring is
 therefore hardly recognized.
 In the conventional transmission type liquid crystal display device, the
 contrast ratio is lower due to the reflection of ambient light from the
 surface of the display panel, as well as due to reflected light from a
 black mask for light shading, interconnect lines, and the like. On the
 contrary, in the transmission/reflection type liquid crystal display
 device of this example, which provides a reflection mode display using
 ambient light in addition to the transmission mode display, the lowering
 of the contrast ratio due to the reflection of ambient light in the
 transmission mode display can be suppressed by the reflection mode
 display. Thus, the contrast ratio obtained by the liquid crystal display
 device of this example will not become lower than the contrast ratio which
 may be obtained by only the reflection mode display irrespective of how
 bright ambient light becomes. As a result, in the transmission/reflection
 type liquid crystal display device of this example, the color
 reproducibility is hardly lowered even under bright ambient light and thus
 a display with high visibility can be obtained under any environment.
 FIG. 29 shows an alternative embodiment of the construction of this
 example, where a reflection electrode region 160R includes a reflection
 layer (reflection plate) 169 and a portion of a transmission electrode
 168. This is unlike the construction shown in FIG. 25, where the
 reflection electrode region 120R includes a reflection electrode 69 having
 a reflection characteristic. The height of the reflection electrode region
 160R of the active matrix substrate can be controlled by adjusting the
 thickness of the reflection layer 169 and/or an insulating layer 170
 formed on the reflection layer 169.
 EXAMPLE 10
 FIG. 30 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 10 according to the present invention.
 FIG. 31 is a sectional view taken along line G--G of FIG. 30.
 Referring to FIGS. 30 and 31, a plurality of gate lines 202 and a plurality
 of source lines 203 are formed on a transparent insulating substrate 201,
 made of glass or plastic, so as to cross with each other. Each region
 surrounded by the adjacent gate lines 202 and the adjacent source lines
 203 defines a pixel. A TFT 204 is disposed in the vicinity of each of the
 crossings of the gate lines 202 and the source lines 203. A drain
 electrode 205 of each TFT 204 is connected to a corresponding pixel
 electrode 206. The portion of each pixel where the pixel electrode 206 is
 formed is composed of two regions as is viewed from the top, i.e., a
 region T having a high transmission efficiency and a region R having a
 high reflection efficiency. In this example, an ITO layer 207 constitutes
 the top layer of the region T as a layer having a high transmission
 efficiency, while an Al layer 208 (or an Al alloy layer) constitutes the
 top layer of the region R as a layer having a high reflection efficiency.
 The layers 207 and 208 constitute the pixel electrode 206 of each pixel.
 The pixel electrode 206 overlaps a gate line 202a for the adjacent pixel
 in the next pixel row via a gate insulating film 209. During driving, a
 storage capacitor for the driving of liquid crystal is formed at this
 overlap portion.
 The TFT 204 includes a gate electrode 210 branched from the corresponding
 gate line 202 (in this case 202a), a gate insulating film 209, a
 semiconductor layer 212, a channel protection layer 213, and n.sup.- -Si
 layers 211 which are to be source/drain electrodes deposited in this
 order.
 Though not shown, the resultant active matrix substrate is provided with an
 alignment film, and then bonded with a counter substrate having a
 transparent electrode and an alignment film formed thereon. Liquid crystal
 is injected in a space between the two substrates in a sealing manner, and
 a backlight is disposed on the rear side of the resultant structure,
 thereby completing the liquid crystal display device of this example.
 A mixture of a guest-host liquid crystal material, ZLI2327 (manufactured by
 Merck & Co., Inc.) containing black pigments therein and 0.5% of an
 optically active substance, S-811 (manufactured by Merck & Co., Inc.) was
 used as the liquid crystal. An electrically controlled birefringence (ECB)
 mode may also be used as the liquid crystal mode by disposing polarizing
 plates on the top and bottom surfaces of the liquid crystal layer. When a
 color display is desired, a color filter (referred to as a CF layer)
 composed of red, green, and blue colored layers is disposed on top of the
 liquid crystal layer.
 Hereinbelow, a method for fabricating such an active matrix substrate of
 this example will be described.
 First, the gate lines 202 and the gate electrodes 210 made of Ta are formed
 on the insulating substrate 201, and the gate insulating film 209 is
 formed over the entire resultant substrate. Subsequently, the
 semiconductor layer 212 and the channel protection layer 213 are formed
 above each of the gate electrodes 210, followed by the formation of the
 n.sup.- -Si layers 211 as the source electrodes 211 and drain electrodes
 205 (or 211).
 An ITO layer 203a (a lower layer) and a metal layer 203b (an upper layer)
 are formed in this order by sputtering and patterned to form the source
 lines 203. In this example, Ti was used for the metal layer 203b.
 This double-layer structure of the source lines 203 is advantageous in that
 even if the metal layer 203b constituting each source line 203 is partly
 defective, the electric connection of the source line 203 is maintained by
 the ITO layer 203a, reducing the occurrence of disconnections in the
 source lines 203.
 The ITO layer 207 of the region T having a high transmission efficiency is
 formed of the same material at the same step as the ITO layer 203a of the
 source line 203. The region R having a high reflection efficiency is
 formed by forming an Mo layer 214 and the Al layer 208 by sputtering in
 this order and patterning. The Al layer 208 can provide a sufficiently
 stable reflection efficiency (about 90%) when the thickness thereof is
 about 150 nm or more. In this example, the thickness of the Al layer 208
 was 150 nm to obtain the reflection efficiency of 90% and thus to allow
 ambient light to be effectively reflected. Ag, Ta, W, and the like may
 also be used in place of Al or an Al alloy for the layer (Al layer 208)
 having a high reflection efficiency.
 In this example, the ITO layer 207 and the Al layer 208 are used as the
 pixel electrode 206 of each pixel. Alternatively, layers of Al or an Al
 alloy with different thicknesses may be formed to define a region having a
 high transmission efficiency and a region having a high reflection
 efficiency as the regions T and R, respectively. This makes the
 fabrication process simpler than in the case of using different materials.
 Also, the layer having a high reflection efficiency of the region R (the
 Al layer 208 in this example) may be made of the same material as that
 used for the metal layer 203b of the source line 203. This makes it
 possible to fabricate the liquid crystal display device of this example by
 the same process as that used in the fabrication of a conventional
 transmission type liquid crystal display device.
 As described above, each pixel electrode 206 is composed of the region T
 having a high transmission efficiency and the region R having a high
 reflection efficiency. This construction realizes a liquid crystal display
 device where a transmission mode display, a reflection mode display, and a
 transmission/reflection mode display are possible by utilizing ambient
 light and illumination light more efficiently, compared with the
 conventional liquid crystal display device using a semi-transmissive
 reflection film.
 The ITO layer 207 is formed, as the pixel electrode 206, over the entire
 region of each pixel and above the gate line 202a of the adjacent pixel,
 in the next pixel row, via the gate insulating film 209, interposed
 therebetween. The Al layer 208 is formed on the ITO layer 207 via the Mo
 layer 214, interposed therebetween, to constitute the region R in the
 center portion of the pixel like an island. In this way, since the ITO
 layer 207 and the Al layer 208 are electrically connected with each other,
 the regions T and R apply the same voltage received from the same TFT 204
 to the liquid crystal. Thus, a declination line which may occur when the
 orientation of the liquid crystal molecules varies within one pixel during
 the voltage application is prevented.
 The interposition of the Mo layer 214 between the ITO layer 207 and the Al
 layer 208 serves to prevent the generation of electric corrosion due to
 the contact between the ITO layer 207 and the Al layer 208 via an
 electrolytic solution in the fabrication process.
 In this example, good display characteristics are obtained by setting the
 ratio of the area of the region T to that of the region R at 60:40. The
 area ratio is not limited to this value, but may be appropriately changed
 depending on the transmission reflection efficiency of the regions T and R
 and the use of the device.
 In this example, the area of the region R is preferably about 10 to about
 90% of the effective pixel area (i.e., the total of the area of the region
 T and the area of the region R). If this percentage is below about 10%,
 i.e., the region having a high transmission efficiency occupies a too
 large a portion of the pixel, there arises a problem which arises in
 conventional transmission type liquid crystal display devices, i.e., the
 problem that the display is blurred when the environment becomes too
 bright. Conversely, if the percentage of the region R exceeds about 90%, a
 problem arises when the environment becomes too dark to observe the
 display only by ambient light. That is, even if the backlight is turned on
 during such an occasion, the occupation of the region T is so small that
 the resultant display is not recognizable.
 In particular, when the liquid crystal display device is applied to an
 apparatus which is mainly used outdoors, battery life is an important
 factor, and the device should be designed so as to utilize ambient light
 efficiently to realize a lower power consumption. Accordingly, the area of
 the region R, having a high reflection efficiency, is preferably about 40
 to about 90% of the effective pixel area. When the area occupation of the
 region R is about 40%, the environment where only the reflection mode
 display is sufficient for display becomes limited, and thus the amount of
 time requiring light from the backlight becomes too long. This reduces
 battery life.
 On the other hand, when the liquid crystal display device is applied to an
 apparatus which is mainly used indoors, the device should be designed so
 as to utilize light from the backlight efficiently. Accordingly, the area
 of the region R is preferably about 10 to about 60% of the effective pixel
 area. When the area occupation of the region R exceeds 60%, the region T
 for transmitting light from the backlight becomes too small. To compensate
 for this, the brightness of the backlight must be substantially increased
 when compared with, for example, a transmission type liquid crystal
 display device. This increases the power consumption and lowers the
 backlight utilization efficiency of such a device.
 The liquid crystal display device of this example was actually mounted in a
 battery-driven video camera. As a result, the display was kept bright and
 recognizable regardless of the brightness of ambient light by adjusting
 the brightness of, the backlight. In particular, when the device was used
 outdoors during a fine weather, it was not necessary to light the
 backlight, thus reducing the power consumption. Therefore, battery life is
 significantly increased when compared with a device with only a
 transmission type liquid crystal display device.
 EXAMPLE 11
 FIG. 32 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 11 according to the present invention.
 FIG. 33 is a sectional view taken along line H--H of FIG. 32.
 In this example, the portion of each pixel where the pixel electrode is
 formed is divided into two regions at the center thereof as is viewed from
 the top, i.e., a region T having a high transmission efficiency and a
 region R having a high reflection efficiency.
 The same components are denoted by the same reference numerals as those in
 FIGS. 30 and 31 in Example 10. The pixels, the structure of the TFTS, and
 the fabrication process of the device are substantially the same as those
 described in Example 10.
 Referring to FIGS. 32 and 33, an ITO layer 207 is formed over the region of
 each pixel ranging from the center portion to a vicinity of a
 corresponding gate line 202, and partly connected to a drain electrode 205
 of a TFT 204. An Al layer 208, having a high reflection efficiency,
 overlaps the ITO layer 207 via an Mo layer 214 at the center portion of
 the pixel. The Al layer 208 extends on the side of the pixel opposite to
 the region of the ITO layer 207, to overlap a gate line 202a for the
 adjacent pixel in the next pixel row via a gate insulating film 209.
 Since the ITO layer 207 and the Al layer 208 are electrically connected via
 the Mo layer 214, electric corrosion due to the contact between the ITO
 layer 207 and the Al layer 208 is suppressed. The overlap between the Al
 layer 208, i.e., the region R and the gate line 202a, and the adjacent
 pixel is accomplished via the insulating film 209. This overlap forms a
 storage capacitor during the driving of liquid crystal, and this overlap
 portion of the region R also contributes to the display. This
 significantly increases the effective area of the pixel compared with the
 conventional construction.
 In order to further increase the aperture ratio of the pixel, a film having
 a high reflection efficiency such as the Al layer 208 may be formed above
 the TFT 204 or the source line 203, via an insulating film, to serve as
 part of the pixel electrode 206 (which is electrically connected to the
 drain electrode 205). In such a case, however, the thickness, the
 material, and the pattern design of the insulating film should be
 appropriately determined so that the degradation of image quality due to a
 parasitic capacitance generated between the pixel electrode 206 and the
 TFT 204 or the source line 203 is minimized.
 EXAMPLE 12
 FIG. 34 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 12 according to the present invention.
 FIG. 35 is a sectional view taken along line I--I of FIG. 34.
 This example is different from Example 11 in that a common line 215 is
 formed under the region R having a high reflection efficiency, via a gate
 insulating film 209.
 The same components are denoted by the same reference numerals as those in
 FIGS. 30 to 33 in Examples 10 and 11. The pixels, the structure of the
 TFTs, and the fabrication process of the device are substantially the same
 as those described in Examples 10 and 11.
 Referring to FIGS. 34 and 35, an ITO layer 207 is formed over the region of
 each pixel ranging from the center portion to a vicinity of a
 corresponding gate line 202 and connected to a drain electrode 205 of a
 TFT 204. An Al layer 208 having a high reflection efficiency overlaps the
 ITO layer 207 via an Mo layer 214 at the center portion of the pixel. The
 Al layer 208 and extends on the side of the pixel opposite to the region
 of the ITO layer 207 in the vicinity of a gate line 202a for the adjacent
 pixel in the next pixel row, overlapping the common line 215 via a gate
 insulating film 209.
 Since the ITO layer 207 and the Al layer 208 are electrically connected via
 the Mo layer 214, electric corrosion due to the contact between the ITO
 layer 207 and the Al layer 208 is suppressed. The overlap between the Al
 layer 208, i.e., the region R and the common line 215 via the insulating
 film 209 forms a storage capacitor during the driving of liquid crystal,
 contributing to an improved display. This formation of the storage
 capacitor will not lower the aperture ratio.
 In order to further increase the aperture ratio of the pixel, a film having
 a high reflection efficiency such as the Al layer 208 may be formed above
 the TFT 204 or the source line 203, via an insulating film, to serve as
 part of the pixel electrode 206 (which is electrically connected to the
 drain electrode 205). In such a case, however, the thickness and the
 material of the insulating film should be appropriately determined so that
 no parasitic capacitance is generated between the pixel electrode 206 and
 the TFT 204 or the source line 203. For example, after the formation of
 the ITO layers 207, an organic insulating film having a dielectric
 constant of about 3.6 may be deposited over the entire resultant substrate
 to a thickness as large as about 3 .mu.m. Then, the Al layer 208 may be
 formed in each pixel, so as to overlap the TFT 204 or the source line 203
 and to be electrically connected to the drain electrode 205. This
 electrical connection can be realized via a contact hole by forming a
 contact hole on the drain electrode 205 or the ITO layer 207.
 In this example, the portion of each pixel where the pixel electrode 206 is
 formed is divided into two regions, i.e., a region having a high
 transmission efficiency (region T) and a region having a high reflection
 efficiency (region R). Alternatively, the portion may be divided into
 three or more regions. For example, as shown in FIG. 36, the pixel
 electrode 206 may be divided into three regions, i.e., the region T having
 a high transmission efficiency, the region R having a high reflection
 efficiency, and a region C having a different transmission or reflection
 efficiency from the other two regions.
 EXAMPLE 13
 FIG. 37 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 13 according to the present invention.
 FIGS. 38A to 38D are sectional views taken along line J--J of FIG. 37,
 illustrating the process of fabricating the liquid crystal display device
 of this example.
 In this example, regions R having a high reflection efficiency are made of
 the same material as that used for source lines. The same components are
 denoted by the same reference numerals as those in FIGS. 30 to 36 in
 Examples 10 to 12. The pixels, the structure of the TFTs, and the
 fabrication process of the device are substantially the same as those
 described in Examples 10 to 12 unless otherwise specified.
 In this example, each pixel includes a region T having a high transmission
 efficiency formed in the center portion thereof and a region R surrounding
 the region T. The outer profile of the region R is a square along two gate
 lines-and two source lines. The region R includes a layer, having a high
 reflection efficiency, made of the same material as that for the source
 line, realizing a high reflection efficiency.
 The process of fabricating such a liquid crystal display device will be
 described with reference to FIGS. 38A to 38D.
 Referring to FIG. 38A, gate lines 202 (see FIG. 37) and gate electrodes
 210, a gate insulating film 209, semiconductor layers 212, channel
 protection layers 213, and n.sup.+ -Si layers 211, which are to be source
 electrodes 211 and drain electrodes 205 (or 211) are sequentially
 deposited on an insulating substrate 201 by sputtering. Then, a conductive
 film 241 for source lines 203 (see FIG. 37) is deposited on the resultant
 substrate by sputtering.
 Referring to FIG. 38B, the conductive film 241 is patterned to form layers
 242 having a high reflection efficiency, drain-pixel electrode connecting
 layers 243, and the source lines 203. The regions of the layers 242 having
 a high reflection efficiency correspond to the regions R.
 Referring to FIG. 38C, an interlayer insulating film 244 is formed over the
 resultant substrate, and then contact holes 245 are formed through the
 interlayer insulating film 244.
 Referring to FIG. 38D, a layer 246 having a high transmission efficiency,
 made of ITO, is formed over the entire area of each pixel. The layer 246
 having a high transmission efficiency may be made of any other material
 having a high transmission efficiency. The layer 246 having a high
 transmission efficiency is connected to the connecting layer 243 via the
 contact hole 245 formed through the interlayer insulating film 244, thus
 being electrically connected to a corresponding drain electrode 205. The
 layer 246 having a high transmission efficiency also serves as the pixel
 electrode for applying a voltage to a liquid crystal layer, so that the
 voltage is applied to the portions of the liquid crystal layer
 corresponding to both the regions T and R via the layer 246 having a high
 transmission efficiency. Thus, in this example, each pixel electrode is
 composed of only the layer 246 having a high transmission efficiency, and
 are not composed of the region T having a high transmission efficiency and
 the region R having a high reflection efficiency. This construction is
 advantageous over the transmission type liquid crystal display device in
 that the region having a high reflection efficiency can be formed without
 increasing the number of process steps and that failure in the formation
 of pixel electrodes is minimized.
 EXAMPLE 14
 FIG. 39 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 14 according to the present invention.
 FIGS. 40A to 40D are sectional views taken along line K--K of FIG. 39,
 illustrating the process of fabricating the liquid crystal display device
 of this example.
 In this example, regions R (the hatched portion in FIG. 39) having a high
 reflection efficiency are made of the same material as is used for gate
 lines. The same components are denoted by the same reference numerals as
 those in FIGS. 30 to 38 in Examples 10 to 13. The pixels, the structure of
 the TFTs, and the fabrication process of the device are substantially the
 same as those described in Examples 10 to 13 unless otherwise specified.
 In this example, each pixel includes a rectangular region T having a high
 transmission efficiency formed in the center portion thereof and a region
 R substantially composed of two connected strips surrounding the region T
 as is viewed from the top. The outer profile of the region R is a square
 along two gate lines and two source lines. The region R includes a layer,
 having a high reflection efficiency, made of the same material as that for
 the gate line, realizing a high reflection efficiency.
 The process of fabricating such a liquid crystal display device will be
 described with reference to FIGS. 40A to 40D.
 Referring to FIG. 40A, a conductive film is formed on an insulating
 substrate 201. The conductive film is then patterned to form gate
 electrodes 210, gate lines 202 (see FIG. 39), and layers 242 having a high
 reflection efficiency. The layers 242 having a high reflection efficiency
 correspond to the regions R.
 Referring to FIG. 40B, a gate insulating film 209, semiconductor layers
 212, channel protection layers 213, and n.sup.- -Si layers 211 which are
 to be source electrodes 211 and drain electrodes 205 (or 211) are
 sequentially deposited on the resultant substrate by sputtering. Then,
 metal layers 203b, used as part of source layers 203, and drain-pixel
 electrode connecting layers 243 are formed during the same step. The
 connecting layers 243 partly overlap drain electrodes 205 of TFTs 204.
 Referring to FIG. 40C, IT0 is deposited on the resultant substrate by
 sputtering and patterned to form layers 246 having a high transmission
 efficiency and ITO layers 203a as part of the source lines 203. The layers
 246 having a high transmission efficiency are formed over the entire areas
 of respective pixels, and the ITO layers 203a are formed on the metal
 layers 203b to have the same pattern As the metal layers 203b. The layers
 246 having a high transmission efficiency partly overlap the connecting
 layers 243 to be electrically connected to the respective TFTs 204.
 Referring to FIG. 40D, a passivation film 247 is formed and patterned.
 Thus, each pixel of the liquid crystal display device of this example
 includes the region T having a high transmission efficiency in the center
 portion thereof, and the region R having a high reflection efficiency
 surrounding the region T in a shape of two connected strips along the
 adjacent source lines. In this case, since the ITO layers 203a of the
 source lines 203 and the layers 242, having a high reflection efficiency
 are located at different levels, the gap between the ITO layer 203a and
 the layer 242, having a high reflection efficiency, of each pixel, which
 is required to prevent a leakage therebetween, can be narrowed, and thus
 the aperture ratio of the pixel can be increased, compared with the case
 where the regions T and R are formed in reverse (i.e., the case where the
 layer having a high reflection efficiency is located in the center portion
 of the pixel).
 In this example, as in Example 13, each pixel electrode is composed of only
 one type of electrode (i.e., the layer 246 having a high transmission
 efficiency). This construction is advantageous over the construction where
 the pixel electrode is composed of two types of electrodes in that the
 occurrence of defects is reduced and efficient fabrication of the device
 is possible.
 In this example, each source line 203 is of a double layer structure
 composed of the metal layer 203b and the ITO layer 203a. Even if the metal
 layer 203b is partly defective, the electric connection of the source line
 203 is maintained by the ITO layer 203a. This reduces the occurrence of
 disconnections in the source line 203.
 EXAMPLE 15
 FIG. 41 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 15 according to the present invention.
 FIGS. 42A to 42C are sectional views taken along line L--L of FIG. 41,
 illustrating the process of fabricating the liquid crystal display device
 of this example.
 In this example, pixel electrodes extend over gate lines and/or source
 lines via an insulating film so as to increase the effective pixel area
 (the area substantially functioning as a pixel).
 The same components are denoted by the same reference numerals used in
 Examples 10 to 14. The pixels, the structure of the TFTs, and the
 fabrication process of the device are substantially the same as those
 described in Examples 10 to 14 unless otherwise specified.
 As shown in FIG. 41, in this example, each pixel includes a region T having
 a high transmission efficiency formed in the center portion thereof and a
 region R (a hatched portion in FIG. 41) a square formed from narrow
 strips, surrounding the region T as is viewed from the top. The pixel
 electrode including a layer having a high transmission efficiency overlaps
 adjacent gate lines 202 and source lines 203 via an interlayer insulating
 film, so that a voltage can be applied to the portions of a liquid crystal
 layer located above the gate lines 202 and the source lines 203. This
 ensures a larger effective pixel area than in Examples 10 to 14. In this
 example, the gate lines 202 and the source lines 203 serve as layers
 having a high reflection efficiency in the region R.
 The process of fabricating such a liquid crystal display device will be
 described with reference to FIGS. 42A to 42C.
 Referring to FIG. 42A, gate electrodes 210, gate lines 202 (see FIG. 41), a
 gate insulating film 209, semiconductor layers 212, channel protection
 layers 213, and n.sup.- -Si layers 211, which are to be source electrodes
 211 and drain electrodes 205 (or 211) are sequentially deposited on an
 insulating substrate 201 by sputtering. At least either of the gate lines
 202 and the source lines 203, which are to be overlapped by light
 transmission layers as the pixel electrodes at a later step, are
 preferably made of a material having a high reflection efficiency.
 Referring to FIG. 42B, an interlayer insulating film 244 is formed on the
 resultant substrate, and then contact holes 245 are formed through the
 interlayer insulating film 244.
 Referring to FIG. 42C, a material having a high transmission efficiency
 such as ITO is deposited on the resultant substrate by sputtering and
 patterned to form layers 246 having a high transmission efficiency. The
 layers 246, having a high transmission efficiency, are connected, via the
 contact holes 245, to connecting layers 243 which are in turn connected to
 drain electrodes 205 of TFTs 204. At this time, the layers 246 having a
 high transmission efficiency are patterned so as to overlap at least
 either of the gate lines 202 and the source lines 203. With this
 construction, the gate lines 202 and/or the source lines 203 which are
 overlapped by the layers 246 having a high transmission efficiency via the
 interlayer insulating film 244, can be used as the layers having a high
 reflection efficiency.
 The display device having the above construction should be designed so that
 a degradation of the image quality, due to a phenomenon such as crosstalk,
 does not occur due to a capacitance generated between the layer 246,
 having a high transmission efficiency, and the gate line 202 or the source
 line 203.
 Thus, in this example, each pixel includes the region T having a high
 transmission efficiency formed in the center portion thereof and the
 region R having a high reflection efficiency formed at positions
 corresponding to the adjacent gate lines and/or the source lines. This
 eliminates the necessity of forming an additional layer having a high
 reflection efficiency, and thus the process can be shortened.
 EXAMPLE 16
 FIG. 43 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 16 according to the present invention.
 FIGS. 44A to 44F are sectional views taken along line M--M of FIG. 43,
 illustrating the process of fabricating the liquid crystal display device
 of this example.
 As shown in FIG. 43, each pixel of the liquid crystal display device of
 this example includes a region T having a high transmission efficiency in
 the center portion thereof, and a region R (hatched portions in FIG. 43)
 having a high reflection efficiency composed of two strips along adjacent
 source lines 203 formed on the sides of the region T.
 As shown in FIG. 44F, the region R includes high convex portions 253a and
 low convex portions 253b formed randomly on an insulating substrate 201, a
 polymer resin layer 254 formed over these convex portions 253a and 253b,
 and a layer 242, having a high reflection efficiency, formed on the
 polymer resin layer 254. The resultant layer 242, which constitutes the
 surface layer of the region R, has a surface of a continuous wave shape,
 and is electrically connected to a drain electrode 205 via a contact hole
 245 and an underlying electrode (not shown).
 The method for fabricating such a liquid crystal display device will be
 described with reference to FIGS. 44A to 44F.
 Referring to FIG. 44A, a plurality of gate lines 202 (see FIG. 43) and gate
 electrodes 210 branched from the gate lines 202, made of Cr, Ta, or the
 like, are formed on the insulating substrate 201.
 Then, a gate insulating film 209, made of SiN.sub.x, SiO.sub.x, or the
 like, is formed over the insulating substrate 201 covering the gate lines
 202 and the gate electrodes 210. Semiconductor layers 212, made of
 amorphous silicon (a-Si), polysilicon, CdSe, or the like, are formed on
 the portions of the gate insulating film 209 located above the gate
 electrodes 210. A channel protection layer 213 is formed on each of the
 semiconductor layers 212. A pair of contact layers 248, made of a-Si or
 the like, are formed on both side portions of the channel protection layer
 extending to the side portions of the semiconductor layers 212.
 A source electrode 249, made of Ti, Mo, Al, or the like, is formed on one
 of the contact layers 248, while the drain electrode 205 made of Ti, Mo,
 Al, or the like, is formed on the other contact layer 248.
 In this example, as the material of the insulating substrate 201, a glass
 plate with a thickness of 1.1 mm, product number 7059 manufactured by
 Corning Inc. may be used.
 Referring to FIG. 44B, a conductive film is formed on the resultant
 substrate by sputtering and patterned, to form metal layers 203b used as
 part of the source lines 203 and the underlying electrodes 250
 simultaneously. Each of the underlying layers 250 may be formed to partly
 overlap the gate electrode 202 for the adjacent pixel in the next pixel
 row, via the gate insulating film 209, so as to form a storage capacitor
 therebetween.
 Each of the gate lines 202 used to form a storage capacitor may be
 overlapped by a layer having a high reflection efficiency, or the
 reflection efficiency of the gate line 202 itself may be made high to
 serve as part of the pixel region (the region R, to further increase the
 aperture ratio.
 Referring to FIG. 44C, ITO is deposited on the resultant substrate by
 sputtering and patterned to form ITO layers 203a which constitute the
 source lines 203 together with the metal layers 203b.
 In this example, each source line 203 is of a double-layer structure
 composed of the metal layer 203b and the ITO layer 203a. The double-layer
 structure is advantageous in that, even if the metal layer 203b is partly
 defective, the electric connection of the source line 203 is maintained by
 the ITO layer 203a. This reduces the occurrence of disconnections in the
 source line 203.
 Simultaneously with the formation of the ITO layers 203a, layer 246, having
 a high transmission efficiency and which constitute the pixel electrodes,
 are also obtained by the patterning. In this way, the layers 246 having a
 high transmission efficiency as the pixel electrodes can be formed
 simultaneously with the source lines 203.
 Referring to FIG. 44D, a resist film 252, made of a photosensitive resin,
 is formed and patterned, and then heat-treated in order to round it, so
 that the high convex portions 253a and the low convex portions 253b,
 having a substantially circular cross-section, are formed on the portions
 of the resultant substrate corresponding to the regions R. Such convex
 portions 253a and 253b are preferably not formed on the layers 246 having
 a high transmission efficiency so that a voltage can be efficiently
 applied to a liquid crystal layer. Even if the convex portions 253a and
 253b are formed on the layers 246, however, no significant optical
 influence will be observed so long as the convex portions are transparent.
 Referring to FIG. 44E, a polymer film 254 is formed over the convex
 portions 253a and 253b. With this film, the concave and convex shaped
 surface of the region R can be made more continuous by reducing the number
 of flat portions. This step may be omitted by changing the fabrication
 conditions.
 Referring to FIG. 44F, layers 242 having a high reflection efficiency made
 of Al as the pixel electrodes are formed on predetermined portions of the
 polymer films 254 by sputtering, for example. Materials suitable for the
 layers 242 having a high reflection efficiency include, besides Al and an
 Al alloy, Ta, Ni, Cr, and Ag having a high light reflection efficiency.
 The thickness of the layers 242 having a high reflection efficiency is
 preferably in the range of about 0.01 to about 1.0 .mu.m.
 Thus, each pixel of the liquid crystal display device of this example
 includes the region T having a high transmission efficiency formed in the
 center portion thereof, and the region R having a high reflection
 efficiency formed along the adjacent source lines. With this construction,
 since the ITO layers 203a of the source lines 203 and the layers 242
 having a high reflection efficiency are located at different levels, the
 gap between the ITO layer 203a and the layer 242 with a high reflection
 efficiency of each pixel, which is required to prevent a leakage
 therebetween, can be narrowed, and thus the aperture ratio of the pixel
 can be increased, compared with the case where the regions T and R are
 formed in reverse (i.e., the case when the layer having a high reflection
 efficiency is located in the center portion of the pixel).
 In this example, the layers 242 having a high reflection efficiency have a
 smooth concave and convex shaped surface to allow reflected light to be
 scattered in a wide range of directions. When a scattering sheet is
 jointly used, such convex portions need not be formed with the resist film
 252, instead the surface of the layers 242 having a high reflection
 efficiency can be made flat. In either case, the layers 242, having a high
 reflection efficiency, and the layers 246 having a high transmission
 efficiency, exist as individual layers with a third substance (e.g., a
 resin and a metal such as Mo) interposed therebetween. With this
 construction, in the specific case where the layers having a high
 transmission efficiency are made of ITO and the layers having a high
 reflection efficiency are made of Al or an Al alloy, Al patterning failure
 due to an electric corrosion which tends to be generated at the Al etching
 step can be reduced.
 EXAMPLE 17
 FIG. 45 is a partial plan view of an active matrix substrate of a liquid
 crystal display device of Example 17 according to the present invention.
 FIG. 46 is a sectional view taken along line N--N of FIG. 45.
 Referring to FIGS. 45 and 46, the active matrix substrate includes pixel
 electrodes 206 formed in a matrix and gate lines 202 for supplying
 scanning signals and source lines 203 for supplying display signals
 running along the peripheries of the pixel electrodes 206 so as to cross
 with each other.
 The pixel electrodes 206 overlap the gate lines 202 and the source lines
 203 at the peripheries via an interlayer insulating film 244. The gate
 lines 202 and the source lines 203 are composed of metal films.
 A TFT 204 is formed in the vicinity of each of the crossings of the gate
 lines 202 and the source lines 203 as the switching element for supplying
 display signals to the corresponding pixel electrode 206. A gate electrode
 210 of the TFT 204 is connected to the corresponding gate line 202 to
 drive the TFT 204 with signals input into the gate electrode 210. A source
 electrode 249 of the TFT 204 is connected to the corresponding source line
 203 to receive data signals. A drain electrode 205 of the TFT 204 is
 electrically connected to a connecting electrode 255 and then to the pixel
 electrode 206 via a contact hole 245.
 The connecting electrode 255 forms a storage capacitor with a common line
 215 via a gate insulating film 209.
 The common line 215 is composed of a metal film, and connected to a counter
 electrode formed on a counter substrate 256 via an interconnect (not
 shown). The common line 215 may be formed during the same step as the
 formation of the gate lines 202 to shorten the fabrication process.
 Each of the pixel electrodes 206 is composed of a layer 242 having a high
 reflection efficiency made of Al or an Al alloy and a layer 246 having a
 high transmission efficiency made of ITO. When viewed from the top, the
 pixel electrode 206 is divided into three regions, i.e., two regions T
 having a high transmission efficiency and a region R having a high
 reflection efficiency (corresponding to the hatched portion in FIG. 45).
 The layer 242 having a high reflection efficiency may also be composed of
 a conductive metal layer having a high reflection efficiency such as Ta as
 in the above examples.
 Each region R is designed to cover part of light-shading electrodes and
 interconnect lines, such as the gate lines 202, the source lines 203, the
 TFT 204, and the common line 215, which do not transmit light from a
 backlight. With this construction, the regions of each pixel portion which
 are not usable as the regions T can be used as the region R having a high
 reflection efficiency. This increases the aperture ratio of the pixel
 portion. The regions T of each pixel portion are surrounded by the region
 R.
 The method for fabricating the active matrix with the above construction
 will be described.
 First, the gate electrodes 210, the gate lines 202, the common lines 215,
 the gate insulating film 209, semiconductor layers 212, channel protection
 layers 213, the source electrodes 249, and the drain electrodes 205 are
 sequentially formed on a transparent insulating substrate 201 made of
 glass or the like.
 Then, a transparent conductive film and a metal film which are to
 constitute the source lines 203 and the connecting electrodes 255 are
 deposited on the resultant substrate by sputtering and patterned into a
 predetermined shape.
 Thus, each of the source lines 203 is of a double-layer structure composed
 the ITO layer 203a and the metal layer 203b. The double-layer structure is
 advantageous in that, even if the metal layer 203b is partly defective,
 the electric connection of the source lines 203 is maintained by the ITO
 layer 203a. This reduces the occurrence of disconnections in the source
 lines 203.
 Thereafter, e photosensitive acrylic resin is applied to the resultant
 substrate by a spin application method to form the interlayer insulating
 film 244 with a thickness of about 3 .mu.m. The acrylic resin is then
 exposed to light according to a desired pattern and then developed with an
 alkaline solution. Only the light-exposed portions of the film are etched
 away with the alkaline solution to form the contact holes 245 through the
 interlayer insulating film 244. By employing this alkaline development,
 well-tapered contact holes 245 are obtained.
 Using a photosensitive acrylic resin for the interlayer insulating film 244
 is advantageous in the aspect of productivity in view of the following
 points. Since the spin application method can be employed for the thin
 film formation, a film as thin as several micrometers can be easily formed
 Also, no photoresist application step is required at the patterning of the
 interlayer insulating film 244.
 In this example, the acrylic resin is originally colored and can be made
 transparent by exposing the entire surf ace to light after the patterning.
 The acrylic resin may also be made transparent by chemical processing.
 Thereafter, an ITO film is formed by sputtering and patterned, to be used
 as the layers 246 having a high transmission efficiency of the pixel
 electrodes 206. Thus, the layers 246 having a high transmission
 efficiency, which constitute the pixel electrodes 206, are electrically
 connected to the corresponding connecting electrodes 255 via the contact
 holes 245.
 The layers 242 having a high reflection efficiency, made of Al or an Al
 alloy, are then formed on the portions of the layers 246 having a high
 transmission efficiency, which correspond to the regions R, so as to
 overlie the gate lines 202, the source lines 203, the TFTs 204, and the
 common lines 215. The two layers 242 and 246 are electrically connected
 with each other, thereby forming pixel electrodes 206. Any adjacent pixel
 electrodes 206 are separated along the portions located above the gate
 lines 202 and the source lines 203 so as not to be electrically connected
 with each other.
 As shown in FIG. 46, the thus-fabricated active matrix substrate and the
 counter substrate 256 are bonded together, and liquid crystal is injected
 in a space between the substrates to complete the liquid crystal display
 device of this example.
 As described above, the liquid crystal display device of this example
 includes the layers 242, having a high reflection efficiency, formed above
 the TFTs 204, the gate lines 202, and the source lines 203 so as to
 constitute the regions R of the pixel electrodes 206. This eliminates the
 necessity of providing light-shading films for preventing light from
 entering the TOTs 204 and light-shading the portions of the pixel
 electrodes 206 located above the gate lines 202, the source lines 203, and
 the common lines 215. In such portions, a light leakage tends to be
 generated in the form of domains, declination lines, and the like in
 display regions. As a result, the regions which are conventionally
 unusable an display regions because they are blocked by the light-shading
 films can be made usable as display regions. This allows for effective use
 of the display regions.
 When the gate lines and the source lines are composed of metal films, they
 block light from a backlight in a conventional transmission type display
 device and thus are unusable as display regions. In this example, however,
 the region T having a high transmission efficiency is formed in the center
 portion of each pixel (as two separate portions in this example). The
 region R, having a high reflection efficiency, is formed in a shape of
 strips surrounding the region T That is, the region R having a high
 reflection efficiency overlies the gate lines, the source lines, the
 common line, and the switching element, and is used as the reflection
 electrode region of each pixel electrode. This construction increases the
 aperture ratio of the pixel electrode more than the case of the reverse
 pattern (i.e., the pattern where the region T surrounds the region R.
 Alternatively, the region R of each pixel may be formed as shown in FIG. 47
 (hatched portion) including the connecting electrode 255. This suppresses
 the decrease in the brightness of light passing through the region T.
 EXAMPLE 18
 In the above examples, the present invention was applied to the active
 matrix liquid crystal display device. The present-invention can also be
 applied to a simple matrix liquid crystal display device.
 Hereinbelow, a basic construction of a pair of a column electrode (a signal
 electrode) and a row electrode (a scanning electrode) which face each
 other will be described. In the simple matrix liquid crystal display
 device, the region where the pair of the column electrode and the row
 electrode cross with each other defines a pixel.
 FIGS. 48A to 48C show one example of such a pixel region. Referring to FIG.
 48A, a transmission electrode region is formed in the center portion of
 the column electrode in one pixel region, while a reflection electrode
 region is formed in the remaining peripheral portion thereof. The
 construction of the column electrode may be as shown in FIG. 48B or 48C.
 The height of the reflection electrode region can be adjusted by forming
 an interlayer insulating film between the reflection electrode and the
 transmission electrode as shown in FIG. 48C.
 Alternatively, as shown in FIG. 49A, a reflection electrode region may be
 formed in the center portion of the column electrode in one pixel region,
 while a transmission electrode region is formed in the remaining
 peripheral portion thereof. The construction of the column electrode may
 be as shown in FIG. 49B or 49C. The height of the reflection electrode
 region can be adjusted by forming an interlayer insulating film between
 the reflection plate and the transmission electrode as shown in FIG. 49C.
 Alternatively, as shown in FIGS. 50A, 50D and 50C and FIGS. 51A and 51B,
 the column electrode may have a strip-shaped reflection electrode region.
 Such a strip-shaped reflection electrode region may be formed along one
 side of the column electrode as shown in FIGS. 50A to 50C, or along the
 center thereof as shown in FIGS. 51A and 51B.
 Hereinbelow, the features of the liquid crystal display device according to
 the present invention distinguished from the conventional reflection type
 or transmission type liquid crystal display device will be described.
 In the conventional reflection type liquid crystal display device, the
 display is effected by use of ambient light to realize low power
 consumption. Accordingly, when ambient light is lower than a certain limit
 value, the display fails to be recognized even if the device is being used
 in an environment where sufficient power supply is possible. This is one
 of the biggest shortcomings of the reflection type liquid crystal display
 device.
 If the reflection characteristics of the reflects tion electrodes vary at
 the fabrication, the ambient light utilization efficiencies of the
 reflection electrodes also vary. This varies the critical value of the
 ambient light intensity at which the display becomes unrecognizable
 depending on the panels. At the fabrication, therefore, the variation in
 the reflection characteristics must be controlled more carefully than the
 variation in the aperture ratio of which control is required for the
 conventional transmission type liquid crystal display device. Otherwise, a
 liquid crystal display device having stable display characteristics is not
 obtained.
 On the contrary, in the liquid crystal display device according to the
 present invention, light from a backlight is utilized under the
 environment where sufficient power supply is possible as in the
 conventional transmission type liquid crystal display device. Accordingly,
 the display can be recognized regardless of the intensity of ambient
 light. Thus, the variation in the ambient light utilization efficiency due
 to the variation in the reflection characteristics is not required to be
 controlled as strictly as that in the reflection type liquid crystal
 display device.
 On the other hand, in the conventional transmission type liquid crystal
 display device, when ambient light becomes bright, the surface reflection
 components of the light increases, making it difficult to recognize the
 display. In the liquid crystal display device according to the present
 invention, when ambient light becomes bright, the reflection regions are
 used together with the transmission regions. This increases the panel
 brightness, and thus improves the visibility.
 Thus, the liquid crystal display device according to the present invention
 can overcome both the problems that visibility is lowered due to surface
 reflection under high (i.e., bright) ambient light in a conventional
 transmission type liquid crystal display device and that display
 recognition becomes difficult due to a decrease in the panel brightness
 under low (i.e., dark) ambient light in a conventional reflection type
 liquid crystal display device simultaneously. In addition to the above,
 both the features of these devices can be obtained.
 As described above, according to the present invention, each pixel includes
 a region having a higher transmission efficiency and a region having a
 higher reflection efficiency than in the case of using a semi-transmissive
 reflection film. In each region, a layer having a high transmission
 efficiency or a layer having a high reflection efficiency serves as the
 pixel electrode. With this construction, unlike the conventional liquid
 crystal display device using a semi-transmissive reflection film, the
 utilization efficiency of ambient light and illumination light is
 prevented from decreasing due to stray-light phenomenon, for example. Good
 images can be displayed regardless of the brightness of ambient light by
 using either a reflection mode display, a transmission mode display, or
 both a reflection mode display and a transmission mode display. Since both
 light from the backlight and the ambient light contribute to the display
 simultaneously and efficiently, power consumption significantly decreases
 compared with the transmission type liquid crystal display device which
 always uses light from the backlight.
 In other words, the shortcomings that visibility is significantly lower
 under low ambient light in a conventional reflection type liquid crystal
 display device and the display recognition becomes difficult under high
 ambient light in a conventional transmission type liquid crystal display
 device can be overcome simultaneously by increasing the light utilization
 efficiency according to the present invention.
 Since the regions having a high reflection efficiency partly cover the gate
 lines, the source lines, and/or the switching elements, light incident on
 these portions can also be used for the display. Therefore, the effective
 area of the pixel increases markedly. This not only overcomes the problems
 of the conventional device using the semi-transmissive reflection film,
 but also increases the aperture ratio of each pixel even if compared with
 a normal transmission type liquid crystal display device.
 In the case where only a layer having a high transmission efficiency
 constitutes a pixel electrode, the occurrence of a defect caused by the
 pixel electrode can be reduced, compared with the case where a layer
 having a high transmission efficiency and a layer having a high reflection
 efficiency are electrically connected with each other to form a pixel
 electrode of one pixel and the case where a layer having a high
 transmission efficiency and a layer having a high reflection efficiency
 partly overlap each other to form a pixel electrode of one pixel. As a
 result, the yield increases.
 The layer having a high transmission efficiency or the layer having a high
 reflection efficiency may be made of the same material as that for the
 source lines or the gate lines. This simplifies the fabrication process of
 the liquid crystal display device.
 The occupation of the area of the region having a high reflection
 efficiency in the effective pixel area is set at about 10 to about 90%.
 This setting overcomes both the problems that the display becomes less
 recognizable when ambient light is too high in a convention transmission
 type liquid crystal display device and that the display becomes completely
 unrecognizable when the intensity of ambient light is extremely low in a
 conventional reflection type liquid crystal display device. Thus, an
 optimal display can be realized as a reflection mode display, a
 transmission mode display, or both a reflection mode display and a
 transmission mode display, regardless of the amount of ambient light.
 The reflection/transmission type liquid crystal display device according to
 the present invention is especially effective when it is applied to an
 apparatus in which the display screen is not swingable or which cannot be
 moved to a better environment for the convenience of the operator.
 The liquid crystal display device according to the present invention was
 actually used as a view finder (monitor screen) in a battery-driven
 digital camera and a video camera. As a result, it has been found that the
 power consumption was kept at a low level while the brightness suitable
 for observation was maintained by adjusting the brightness of the
 backlight regardless of the brightness of the ambient light.
 When the conventional transmission type liquid crystal display device is
 used outdoors under bright sunlight, the display become less recognizable
 even if the brightness of the backlight is increased. Under such
 occasions, the liquid crystal display device of the present invention can
 be used as a reflection type device by turning off the backlight, or it
 can be used as the transmission/reflection type device by lowering the
 brightness of the backlight. As a result, good display quality and reduced
 power consumption can be realized.
 When the liquid crystal display device according to the present invention
 is used indoors with bright sunlight coming thereinto, the reflection mode
 display and the transmission mode display may be switched therebetween or
 both may be used depending on the directional position of the object, to
 obtain a more recognizable display. When the monitor screen receives
 direct sunlight, the manner described in the case of an outdoors use under
 bright sunlight may be adopted. When the object is to be imaged in a dark
 corner of a room, the backlight is turned on in order to use the device as
 a reflection/transmission mode display.
 When the liquid crystal display device according to the present invention
 is used as a monitor screen in a car apparatus such as a car navigator,
 also, an invariably recognizable display is realized regardless of the
 brightness of ambient light.
 In a car navigator using the conventional liquid crystal display device, a
 backlight having a higher brightness than that used in a personal computer
 and the like is used, so as to be usable during a fine weather and in an
 environment receiving direct sunlight. However, despite such a high
 brightness, the display is still less recognizable under the environment
 described above. On the other hand, a backlight with such a high
 brightness is so bright that the user is dazzled and adversely influenced.
 In a car navigator using the liquid crystal display device according to
 the present invention, a reflection mode display can always be used
 together with a transmission mode display. This allows for a good display
 under a bright environment without increasing the brightness of the
 backlight. Conversely, under a pitch-dark environment, a recognizable
 display is realized by obtaining only a low brightness (about 50 to 100
 cd/m.sup.2) of the backlight.
 Various other modifications will be apparent to and can be readily made by
 those skilled in the art without departing from the scope and spirit of
 this invention. Accordingly, it is not intended that the scope of the
 claims appended hereto be limited to the description as set forth herein,
 but rather that the claims be broadly construed.