Liquid crystal device and projector

A liquid crystal device includes a pair of substrates facing each other, and a liquid crystal layer sandwiched between the pair of substrates. One of the pair of substrates includes data lines and scanning lines that intersect each other, pixels arranged in a matrix, at least one first electrode, and at least one second electrode that applies an electric field generated between the first electrode and the second electrode to the liquid crystal layer. Each of the first electrode and the second electrode includes a plurality of electrode portions, and a joint portion for connecting the plurality of electrodes. At least a portion of the joint portion of the first electrode and at least a portion of the joint portion of the second electrode are arranged so as to overlap at least the data lines or the scanning lines, and are aligned in a line extending along the at least the data lines or the scanning lines.

BACKGROUND

1. Technical Field

The present invention relates to relates to a liquid crystal device and a projector.

2. Related Art

In existing liquid crystal display apparatuses such as twisted nematic (TN) liquid crystal display apparatuses, electrodes disposed on a pair of substrates between which a liquid crystal is sealed apply an electric field in a direction substantially vertical to a surface of the substrates to control an alignment of liquid crystal molecules to modulate a light transmittance. Recently, a method in which electrodes disposed on one of the pair of substrates apply an electric field in a direction substantially parallel to a surface of the one substrate has been available. This liquid crystal display mode is referred to as a lateral electric field or in-plane switching (IPS) mode.

As with a vertical alignment (VA) mode, the lateral electric field mode is adopted in liquid crystal panels for direct-view large television screens, and provides in-plane switching of a director of the liquid crystal molecules, thus achieving the advantage of low viewing-angle dependence. Liquid crystal light valves of projectors as well as direct-vision display apparatuses, including lateral-electric-field liquid crystal panels, have been proposed. In the lateral electric field mode, in particular, thin film transistors (hereinafter abbreviated as TFTs) are used as pixel switching elements, thereby achieving the advantage of no need for common electrodes on a counter substrate.

FIG. 15is a plan view of a pixel, showing an example of a lateral-electric-field liquid crystal device of the related art. In the liquid crystal device of the related art, as shown inFIG. 15, a plurality of data lines101and a plurality of scanning lines102are orthogonal to each other. A TFT103is disposed near an intersection of each of the data lines101and each of the scanning lines102. A comb-shaped pixel electrode104and a comb-shaped common electrode105are disposed so as to be interdigitated with each other, and the pixel electrode104is connected to the TFT103through a contact hole106. The common electrode105is electrically connected to a common electrode line108through a contact hole107. With the above structure, a potential corresponding to an image signal is applied to the pixel electrode104from the data line101via the TFT103, and a potential common to pixels is applied to the common electrode105from the common electrode line108via the contact hole107. As used herein, electrode portions extending in parallel to each other in each comb-shaped electrode are referred to as “strip-shaped electrode portions”, and a portion for connecting the strip-shaped electrode portions is referred to as a “joint portion”. The electrodes104and105include joint portions104band105barranged along the data lines101, and strip-shaped electrode portions104aand105a, respectively. The strip-shaped electrode portions104aand the strip-shaped electrode portions105aare alternately disposed so as to face each other, and a lateral electric field is generated between the strip-shaped electrode portions104aand the strip-shaped electrode portions105a. A liquid crystal is driven by the lateral electric field (see, for example, JP-A-9-258242).

JP-A-9-258242 noted above describes that bus lines such as data lines and scanning lines and comb-shaped electrodes are defined on different layers so that the bus lines and the comb-shaped electrodes can overlap each other in plan view, thereby increasing the aperture ratio. However, the structure described in JP-A-9-258242 has a problem. While a uniform lateral electric field is generated in a liquid crystal layer at a position where the strip-shaped electrode portions of each of the electrodes face each other (e.g., a position surrounded by a circle A inFIG. 15) to provide normal display, it is difficult to generate a lateral electric field immediately above the joint portion of the electrode that partially overlaps the bus lines, resulting in a low light transmittance at the corresponding position during bright display. Further, a lateral electric field with various directions is generated in at a position where the strip-shaped electrode portions and the joint portion face each other (e.g., a position surrounded by a circle B inFIG. 15) to cause alignment disorder of the liquid crystal, resulting in a low light transmittance at the corresponding position during bright display. Therefore, the surface area can substantially contribute to the display is reduced and a sufficient aperture ratio of the pixels is not obtained, thus preventing bright display. The low-aperture-ratio problem becomes more serious in particular for liquid crystal devices with a smaller pixel pitch such as liquid crystal devices used for liquid crystal light valves.

SUMMARY

An advantage of some aspects of the invention is that it provides a liquid crystal device capable of ensuring a sufficient pixel aperture ratio and realizing bright display. Another advantage of some aspects of the invention is that it provides a projector with a high display quality including the liquid crystal device.

According to a first aspect of the invention, a liquid crystal device includes a pair of substrates facing each other, and a liquid crystal layer sandwiched between the pair of substrates. One of the pair of substrates includes data lines, scanning lines, the data lines and the scanning lines intersecting each other, pixels arranged in a matrix, at least one first electrode, and at least one second electrode that applies an electric field generated between the first electrode and the second electrode to the liquid crystal layer. Each of the first electrode and the second electrode includes a plurality of electrode portions, and a joint portion for connecting the plurality of electrodes portions. At least a portion of the joint portion of the first electrode and at least a portion of the joint portion of the second electrode are arranged so as to overlap one line of the data lines or the scanning lines, and are aligned in a line extending along the line.

The liquid crystal device according to the first aspect of the invention still has a difficulty with the related art. That is, a uniform lateral electric field is generated in the liquid crystal layer at a portion where the electrode portions of the first electrode and the electrode portions of the second electrode face each other, thereby providing a normal display. On the other hand, a uniform lateral electric field is not generated at a portion just above the joint portions of the first and second electrodes and a portion where the electrode portions face the joint portions, resulting in a low light transmission during bright display. According to the liquid crystal device of the first aspect of the invention, however, at least a portion of the joint portion of the first electrode and at least a portion of the joint portion of the second electrode are arranged so as to overlap at least the data lines or the scanning lines, and are aligned in a line extending along the at least the data lines or the scanning lines, thereby reducing the size of a region with a low transmittance over the related art. Therefore, the aperture ratio can be increased, and a liquid crystal device capable of achieving a bright display can be realized.

Specifically, if the electrode portions of the first and second electrodes are alternately arranged in a direction in which the data lines (or the scanning lines) extend, in order to connect the plurality of electrode portions without short-circuiting the first and second electrodes, it is necessary to arrange the first and second electrodes so that the joint portion of the first electrode and the joint portion of the second electrode are placed at positions opposite to each other with respect to the longitudinal direction of the electrode portions and the open ends of the electrode portions (opposite to the joint portion) of the first electrode can be oriented in a direction opposite to that of the second electrode. In general, as with the related art shown inFIG. 15, it is conceived that the joint portion of the first electrode (e.g., a common electrode) and the joint portion of the second electrode (e.g., a pixel electrode) are arranged side-by-side. This arrangement, however, increases the width of a region with a low transmittance and reduces the pixel aperture ratio. In the liquid crystal device of the first aspect of the invention, in contrast, instead of the side-by-side arrangement of the joint portion of the first electrode and the joint portion of the second electrode, the joint portion of the first electrode and the joint portion of the second electrode are arranged so as to overlap at least the data lines or the scanning lines and to be aligned in a line along the at least the data lines or the scanning lines, thereby significantly reducing the width of the region with a low transmittance over the related art. Therefore, the pixel aperture ratio can be improved.

According to a second aspect of the invention, a liquid crystal device includes a pair of substrates facing each other, and a liquid crystal layer sandwiched between the pair of substrates. One of the pair of substrates includes data lines, scanning lines, a first pixel group including a plurality of pixels arranged in columns, a second pixel group adjacent to the first pixel group and including a plurality of pixels arranged in columns, a plurality of first electrodes, and a plurality of second electrodes that apply an electric field generated between the first electrodes and the second electrodes to the liquid crystal layer. Each of the first electrodes includes a plurality of electrode portions, and a joint portion for connecting the plurality of electrode portions. Each of the second electrodes includes a plurality of electrode portions, and a joint portion for connecting the plurality of electrode portions. At least a portion of the joint portion of one of the second electrodes which is associated with the second pixel group is placed between the joint portions of two of the first electrodes which are associated with the first pixel group. The terms “first pixel group” and “second pixel group” mean pixel arrays each including a plurality of pixels arranged in columns. For example, a pixel array is formed of, a plurality of pixels associated with a single scanning line.

In the liquid crystal device of the second aspect of the invention, at least a portion of a joint portion of one of the second electrodes which are associated with the second pixel group is placed between joint portions of two of the first electrodes which are associated with the first pixel group, thereby reducing the size of a region with a low transmittance over the related art. Therefore, the aperture ratio car be increased, and a liquid crystal device capable of achieving a bright display can be realized.

In the liquid crystal apparatus of the second aspect of the invention, preferably, at least a portion of the joint portion of each of the first electrodes and at least a portion of the joint portion of each of the second electrodes are arranged so as to overlap a corresponding one of the data lines or the scanning lines.

In the liquid crystal device, a region where the data lines and the scanning lines are arranged is a non-opening region (light-shielded region) that does not basically contribute to the display. Therefore, at least a portion of the joint portions of the first and second electrodes is placed so as to overlap the data lines or the scanning lines, thereby minimizing the reduction of the aperture ratio.

Further, preferably, the electrode portions of the first electrode and the electrode portions of the second electrode cross obliquely to the data lines or the scanning lines.

The electrode portions of the first and second electrodes are arranged so as to cross obliquely to the data lines or the scanning lines, thereby alternately arranging the joint portions of the first electrodes and the joint portions of the second electrodes to relatively easily align at least a portion of the joint portions in a line. This is because it is necessary to place each of the electrode portions so as to correspond to a pixel and to place each of the joint portions between two adjacent pixels.

Further, the electrode portions of the first electrode may be arranged so as to extend across adjacent two of the pixels.

With the above arrangement, electrode portions of a first electrode arranged so as to extend across two adjacent pixels serve as an electrode (common electrode) common to these two pixels. Therefore, the number of electrode portions of first electrodes is not excessively increased, and a peripheral portion of the pixels can also be effectively utilized for the display, thereby further increasing the aperture ratio.

According to a third aspect of the invention, a liquid crystal device includes a pair of substrates facing each other, and a liquid crystal layer sandwiched between the pair of substrates. One of the pair of substrates includes data lines, scanning lines, the data lines and the scanning lines intersecting each other, pixels arranged in a matrix, first electrodes, second electrodes that apply an electric field generated between the first electrodes and the second electrodes to the liquid crystal layer, each of the first electrodes including a plurality of electrode portions, and a joint portion for connecting the plurality of electrode portions, each of the second electrodes including a plurality of electrode portions, and a joint portion for connecting the plurality of electrode portions, a first pixel group including a plurality of the pixels which are arranged in columns, and a second pixel group adjacent to the first pixel group and including a plurality of the pixels which are arranged in columns. The first pixel group and the second pixel group are arranged so as to be offset with respect to each other in a direction in which the pluralities of pixels of the first pixel group are arrayed. A plurality of the first electrodes and a plurality of the second electrodes which are associated with the first pixel group, and a plurality of the first electrodes and a plurality of the second electrodes which are associated with the second pixel group are arranged so as to be offset with respect to each other in the direction in which the pluralities of pixels of the first pixel group are arrayed. The joint portions of the first electrodes and the joint portions of the second electrodes, which are adjacent to each other in the direction in which the pluralities of pixels of the first pixel group are arrayed, are alternately arranged. The terms “first pixel group” and “second pixel group” mean pixel arrays each including a plurality of pixels arranged in columns. For example, a pixel array is formed of a plurality of pixels associated with a particular scanning line.

The liquid crystal device of the third aspect of the invention still has a difficulty with the related art. That is, a uniform lateral electric field is generated in the liquid crystal layer at a portion where the electrode portions of the first electrode and the electrode portions of the second electrode face each other, thereby providing a normal display. On the other hand, a uniform lateral electric field is not generated at a portion immediately above the joint portions of the first and second electrodes and a portion where the electrode portions face the joint portions, resulting in a low light transmission during bright display. According to the liquid crystal device of the third aspect of the invention, however, the first pixel group and the second pixel group are arranged so as to be offset with respect to each other in a direction in which the plurality of pixels are arrayed; a plurality of the first and second electrodes which are associated with the first pixel group, and a plurality of the first and second electrodes which are associated with the second pixel group are arranged so as to be offset with respect to each other in the direction in which the plurality of pixels are arrayed; and the joint portions of the first electrodes and the joint portions of the second electrode are alternately arranged, the first electrodes and the second electrode being adjacent to each other in the direction in which the plurality of pixels are arrayed, thereby the size of a region with a low transmittance over the related art. Therefore, the aperture ratio can be increased, and a liquid crystal device capable of achieving a bright display can be realized.

Specifically, if the electrode portions of the first and second electrodes are alternately arranged in a direction in which the data lines (or the scanning lines) extend, in order to connect the plurality of electrode portions without short-circuiting the first and second electrodes, it is necessary to arrange the first and second electrodes so that the joint portions of the first electrodes and the joint portions of the second electrodes are placed at positions opposite to each other with respect to the longitudinal direction of the electrode portions and the open ends of the electrode portions (opposite to the joint portions) of the first electrodes can be oriented in a direction opposite to that of the second electrodes. In general, as with the related art shown inFIG. 15, it is conceived that the joint portions of the first electrodes (e.g., common electrodes) and the joint portions of the second electrodes (e.g., pixel electrodes) are arranged side-by-side. This arrangement, however, increases the width of a region with a low transmittance and reduces the pixel aperture ratio. In the liquid crystal device of the third aspect of the invention, in contrast, instead of the side-by-side arrangement of the joint portions of the first electrodes and the joint portions of the second electrodes, the joint portions of the first electrodes and the joint portions of the second electrodes are alternately arranged, the first electrodes and the second electrodes being adjacent to each other in the direction in which the plurality of pixels are arrayed, thereby significantly reducing the width of the region with a low transmittance over the related art. Therefore, the pixel aperture ratio can be improved.

Further, preferably, at least a portion of the joint portions of the first electrodes and at least a portion of the joint portions of the second electrodes are arranged so as to overlap the data lines or the scanning lines.

In the liquid crystal device, a region where the data lines and the scanning lines are arranged is a non-opening region (light-shielded region) that does not basically contribute to the display. Therefore, at least a widthwise portion of the joint portions of the first and second electrodes is placed so as to overlap the data lines or the scanning lines, thereby minimizing the reduction of the aperture ratio.

Further, the liquid crystal device of the third aspect of the invention may further include a display area including the pixels arranged in a matrix, and the first pixel group and the second pixel group may be arranged so as to be inclined with respect to a horizontal direction of the display area.

With the arrangement of the liquid crystal device of the third aspect of the invention, the pixels are arranged so as to be offset with respect to each other. In this case, there is a drawback in that a straight line might be displayed obliquely when a straight line extending in the horizontal direction of the display area is displayed or when a straight line extending in the vertical direction of the display area is displayed. Accordingly, a plurality of pixels that are arranged in a direction in which scanning lines extend are arranged so as to be inclined with respect to the horizontal direction of the display area, thus preventing the straight line from being displayed obliquely.

In the liquid crystal devices of the first to third aspects of the invention, preferable structures will now be described.

Preferably, a portion of at least the joint portion of the first electrode or the joint portion of the second electrode is formed so as to narrow from the electrode portions thereof.

A portion of a joint portion of a first electrode (or a second electrode) is arranged so as to narrow from electrode portions thereof, thereby easily placing a joint portion of one of the first and second electrodes between joint portions of the other two adjacent electrodes to easily provide the design specific to the invention. Furthermore, the size of a region with a low transmittance can further be reduced, and the aperture ratio can further be increased.

Further, a plurality of the first electrodes which are adjacent in a direction in which the data lines or the scanning lines extend may be formed into a continuous electrode pattern.

With the above structure, a common potential can be stably supplied to a plurality of first electrodes.

Further, the one of the pair of substrates may further include a common potential line to which a common potential is supplied, and the first electrode and the common potential line may be electrically connected through a contact hole that is formed for each of the pixels.

With this structure, even if the first electrodes are independent for each pixel, a common potential can be supplied to the first electrodes via a common potential line without using a drawn wiring line. Since a line (such as a capacitor line) to which a common potential is supplied is effectively utilized, no other lines are required for supplying a common potential to the first electrodes. Therefore, an improvement in the aperture ratio can be achieved.

Furthermore, the structure described above in which a plurality of adjacent first electrodes is formed into a continuous electrode pattern, and the structure described above in which a first electrode and a common potential line are electrically connected through a contact hole are used in combination, thus ensuring an electrical connection using one of the connection structures if the other connection structure fails. Therefore, a high-reliability liquid crystal device with a redundant structure formed of those connection structures can be achieved.

Preferably, at least one of the first electrode and the second electrode is formed of a transparent electrically conductive material.

This structure allows a portion immediately above the first electrode and the second electrode to contribute to the display. Therefore, the aperture ratio can further be increased.

According to an aspect of the invention, a projector includes a light source, a light modulator that modulates light emitted from the light source, the light modulator including the liquid crystal device according to the invention, and a projection unit that projects the light modulated by the light modulator.

Since the liquid crystal device of the invention is used as a light modulator, a projector capable of achieving a bright image display can be realized.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

First Embodiment

A first embodiment of the invention will be described hereinafter with reference toFIGS. 1 to 6.

A liquid crystal device according to the first embodiment is an IPS transmissive-mode liquid crystal device used for a liquid crystal light valve of a projector, by way of example.

FIG. 1is a plan view of a liquid crystal device1according to the first embodiment and components thereof, as viewed from the side of a counter substrate.FIG. 2is a cross-sectional view of the liquid crystal device1, taken along a line II-II ofFIG. 1.FIG. 3is an equivalent circuit diagram of the liquid crystal device1.FIGS. 4 and 5are plan views of a plurality of adjacent pixels on a TFT array substrate of the liquid crystal device1. For easy illustration of components on the TFT array substrate,FIG. 4shows only components in layers lower than layers having pixel electrodes and common electrodes, andFIG. 5mainly shows a pattern of pixel electrodes and common electrodes.FIG. 6is a cross-sectional view of the pixels, taken along a line VI-VI ofFIG. 4when the components shown inFIGS. 4 and 5are laminated. In the figures used in conjunction with the following embodiments, layers and parts are illustrated in different scales so as to allow recognition of the layers and parts in the figures.

As shown inFIGS. 1 and 2, the liquid crystal device1of the first embodiment includes a TFT array substrate2and a counter substrate3bonded to each other by a sealant4, and a liquid crystal layer5sealed in a region defined by the sealant4. The liquid crystal layer5is composed of a liquid crystal material having a negative anisotropy of dielectric constant. A light-shielding film (or peripheral partition)6composed of a light-shielding material is disposed within the region where the sealant4is defined. In a peripheral circuit region outside the sealant4, a data-line driving circuit7and external-circuit mounting terminals8are disposed along a side of the TFT array substrate2, and scanning-line driving circuits9are disposed along two sides adjacent to the side. A plurality of wires10for connecting the scanning-line driving circuits9disposed on both sides of a display area R is disposed along the remaining side of the TFT array substrate2. The counter substrate3includes inter-substrate conducting members11at the corners thereof for establishing an electrical connection between the TFT array substrate2and the counter substrate3.

The horizontal and vertical directions of the display area R are represented by arrows H and V, respectively. The horizontal direction H extends along a given side of the rectangular display area R (a side extending in the lateral direction ofFIG. 1), and the vertical direction V extends along a side adjacent to the given side (a side extending in the longitudinal direction ofFIG. 1).

FIG. 3is an equivalent circuit diagram of the liquid crystal device1of the first embodiment. The display area R of the liquid crystal device1includes a plurality of pixels arranged in a matrix, and each of the pixels includes a pixel electrode13. A TFT14, which is a pixel switching element for controlling current supply to the pixel electrode13is disposed beside the pixel electrode13. A data line15is electrically connected to a source of the TFT element4. Image signals S1, S2, . . . , and Sn are supplied to the data lines15. The image signals S1, S2, . . . , and Sn may be supplied to the data lines15in a line sequential manner in that order, or may be supplied to a plurality of adjacent data lines15group by group.

A scanning line16is electrically connected to a gate of the TFT14. Scanning signals G1, G2, . . . , and Gm are supplied to the scanning lines16at a predetermined timing in a pulsed form. The scanning signals G1, G2, . . . , and Gm are applied to the scanning lines16in a line sequential manner in that order. The pixel electrode13is electrically connected to a drain of the TFT14. When the TFTs14serving as switching elements are turned on for a certain period by the scanning signals G1, G2, . . . , and Gm supplied from the scanning lines16, the image signals S1, S2, . . . , and Sn supplied from the data lines15are written into the liquid crystal of the respective pixels at a predetermined timing.

The image signals S1, S2, . . . , and Sn written at a predetermined level into the liquid crystal are held for a certain period in liquid crystal capacitors defined between the pixel electrodes13and common electrodes, which will be described below. In order to prevent the held image signals S1, S2, . . . , and Sn from leaking, storage capacitors18are defined between the pixel electrodes13and capacitor lines17, and are placed parallel to the liquid crystal capacitors. When a voltage signal is applied to the liquid crystal in the manner described above, the alignment of the liquid crystal molecules changes according to the level of the voltage applied. Thus, light incident on the liquid crystal is modulated, thereby providing gradation display.

As shown inFIGS. 4 and 5, the plurality of data lines15and the plurality of scanning lines16are arranged in a lattice pattern on the TFT array substrate2, and a plurality of pixels20corresponding to regions surrounded by the data lines15and the scanning lines16are placed in a matrix. The pixel electrodes13(second electrodes) and common electrodes21(first electrodes) are disposed in association with the pixels20. As described below, each of the data lines15has a layered structure including an aluminum film, and each of the scanning lines16is formed of, for example, an electrically conductive polysilicon film. The scanning line16is electrically connected to a gate electrode23in a semiconductor layer22, which faces a channel region22ashown as a shaded area inFIG. 4, through a contact hole24, and a pattern of the gate electrode23is included in a pattern of the scanning line16. At an intersection between the gate electrode23and the data line15is disposed the TFT14, which is a pixel switching element configured such that the gate electrode23faces the channel region22aon the channel region22a.

As shown inFIG. 6, the liquid crystal device1includes the TFT array substrate2and the counter substrate3. The TFT array substrate2includes a substrate26such as a quartz substrate, a glass substrate, or a silicon substrate, and the counter substrate3includes a substrate27such as a glass substrate or a quartz substrate. On the TFT array substrate2, the pixel electrodes13and the common electrodes21are disposed, and an alignment film28subjected to a predetermined alignment treatment such as a rubbing treatment is disposed above the pixel electrodes13and the common electrodes21. The pixel electrodes13are composed of a transparent electrically conductive material such as indium tin oxide (hereinafter abbreviated as ITO). On the counter substrate3, an alignment film29subject to a predetermined alignment treatment such as a rubbing treatment is disposed. A liquid crystal is filled in a space surrounded by the sealant4(seeFIGS. 1 and 2) between the TFT array substrate2and the counter substrate3to form the liquid crystal layer5. The liquid crystal layer5is configured to have an initial alignment state by the alignment films28and29under application of no electric field.

On the TFT array substrate2, further, various components including the pixel electrodes13, the common electrodes21, and the alignment film28are defined in a layered form. In the following description, layers shown inFIG. 6are referred to first to sixth layers from the bottom. The first layer includes the scanning lines16. The second layer includes the gate electrodes23, the TFTs14, etc. The third layer includes the storage capacitors18. The fourth layer includes the data lines15etc. The fifth layer includes the capacitor lines17etc. The sixth layer (top layer) includes the pixel electrodes13, the common electrodes21, the alignment layer28, etc. A base insulating film31is defined between the first and second layers. A first inter-layer insulating film32is defined between the second and third layers, and a second inter-layer insulating film33is defined between the third and fourth layers. A third inter-layer insulating film34is defined between the fourth and fifth layers, and a fourth inter-layer insulating film35is defined between the fifth and sixth layers. Thus, short-circuiting between the components described above is prevented. Each of the insulating films31,32,33,34, and35has a contact hole or the like for electrically connecting the upper and lower electrically conductive layers. Those component elements will be described in the order from the bottom. Of the layers described above, the first to fourth layers are shown as a lower layer portion inFIG. 4, and the fifth and sixth layers are shown as an upper layer portion inFIG. 5.

Layered Structure: Configuration of First Layer including Scanning Lines, etc.

The first layer includes the scanning lines16composed of an elemental metal, an alloy, a metal silicide, a polysilicide, a lamination thereof, an electrically conductive polysilicon, or the like, including at least one high melting point metal such as Ti, Cr, W, Ta, or Mo. The scanning lines16are patterned into a stripe extending in the horizontal direction ofFIG. 4, as viewed in plan view. More specifically, the stripe-patterned scanning lines16include main portions that extend in the horizontal direction as viewed inFIG. 4, and protruding portions that extend in the vertical direction as viewed inFIG. 4in which the data lines15extend. The protruding portions that extend from the main portions of the scanning lines16adjacent to each other are not connected to each other. The scanning lines16are therefore separated from one another.

Layered Structure: Configuration of Second Layer including TFTs etc.

The second layer includes the TFTs14including the gate electrodes23. Each of the TFTs14is formed of, for example, an n-channel TFT. The TFT14has a lightly doped drain (LDD) structure including, as shown inFIG. 6, the channel region22a, a lightly doped source region22b, a heavily doped source region22c, a lightly doped drain region22d, and a heavily doped drain region22e. The semiconductor layer22of the TFT14is formed of, for example, a polysilicon film. The TFT14preferably has the LDD structure shown inFIG. 6, but may have an offset structure in which no impurity ions are implanted into the lightly doped source region22band the lightly doped drain region22d. Alternatively, the TFT14may be a self-aligned TFT in which impurity ions are implanted at a high concentration using the gate electrode23as a mask to form a heavily doped source region and a heavily doped drain region in a self-aligned manner.

The second layer further includes first relay electrodes37that are composed of the same material as that of the gate electrodes23. As shown inFIG. 4, each of the first relay electrodes37is formed into an island-shaped pattern so as to be located at a substantially center position of a side of a corresponding one of the pixels20extending in the horizontal direction thereof, as viewed in plan view. The first relay electrodes37and the gate electrodes23are formed of, for example, electrically conductive polysilicon films. On the TFT array substrate2, a sheet layer38is formed below the semiconductor layer22of the TFT14and above the base insulating film31so as to overlie a contact hole39, which will be described below, as viewed in plan view.

Layered Structure: Configuration of Spacing between First and Second Layers, including Base Insulating Film

The base insulating film31which is composed of, for example, a silicon oxide film, is formed above the scanning lines16and below the TFTs14described above. The base insulating film31has a function for insulating the TFTs14from the scanning lines16. Since the base insulating film31is formed over an entire surface of the substrate26, the base insulating film31further has a function for preventing characteristic variation of the TFTs14due to the surface roughness after polishing of the substrate26or residual contamination after cleaning.

The base insulating film31includes the contact holes24on both sides of the semiconductor layers22shown inFIG. 4, as viewed in plan view. Each of the contact holes24is defined in a channel length direction of the semiconductor layer22that extends along the data line15, and a portion of the gate electrode23is defined so as to fill the contact hole24. That is, the gate electrode23has a sidewall portion23bformed integrally therewith so as to extend from the gate electrode23. Thereby, as shown inFIG. 4, the semiconductor layer22of the TFT14is covered from the lateral side as viewed in plan view to prevent light from entering from at least that side. The sidewall portion23bis defined so as to fill the contact hole24, and a lower end thereof is in contact with the scanning line16. Therefore, the scanning line16and the gate electrode23are electrically connected to each other. Since the scanning lines16are defined in a stripe pattern as described above, the gate electrodes23residing on one row are always at the same potential.

Layered Structure: Configuration of Third layer including Storage capacitors, etc.

The third layer includes the storage capacitors18. Each of the storage capacitors18includes a lower electrode41and a capacitor electrode42so as to face each other with a dielectric film43therebetween. The lower electrode41is electrically connected to the heavily doped drain region22eof the TFT14, and the capacitor electrode42is electrically connected to the pixel electrode13. The storage capacitor18serves to significantly increase the potential retaining characteristic of the pixel electrode13. As shown in the plan view ofFIG. 4, the storage capacitor18of the first embodiment is defined so as not to enter the display area R (in other words, the storage capacitor18is defined so as to reside within a light-shielded region between the pixels20) to ensure the display of bright images without reducing the pixel aperture ratio.

More specifically, the lower electrode41is formed of, for example, an electrically conductive polysilicon film and serves as a pixel-potential-side capacitor electrode. The lower electrode41may be composed of a single-layer film including a metal or an alloy, or a multi-layer film. In addition to the function as a pixel-potential-side capacitor electrode, the lower electrode41further has a function for relaying between the pixel electrode13and the heavily doped drain region22eof the TFT14. The relay connection is performed through the lower electrode41and the first relay electrode37described above.

The capacitor electrode42serves as a fixed-potential-side capacitor electrode of the storage capacitor18. In the first embodiment, the capacitor line17that is at a fixed potential and the capacitor electrode42are electrically connected to each other, thereby allowing the capacitor electrode42to be at a fixed potential. The capacitor electrode42is composed of an elemental metal, an alloy, a metal silicide, a polysilicide, a lamination thereof, or a tungsten silicide, including at least one high melting point metal such as Ti, Cr, W, Ta, or Mo. Since the capacitor electrode42is composed of such a metal material, the capacitor electrode42has a function for blocking light entering the TFT14from above.

The dielectric film43has a relatively thin thickness of, for example, approximately 5 to 200 nm, and is composed of a silicon oxide film, a silicon nitride film, or the like such as a high temperature oxide (HTO) film or a low temperature oxide (LTO). In the first embodiment, the dielectric film43has a two-layer structure including a silicon oxide film43aas a lower layer and a silicon nitride film43bas an upper layer. The silicon nitride film43bin the upper layer is patterned so as to have a larger size than that of the lower electrode41of the pixel-potential-side capacitor electrode, and is formed within a light-shielded region (non-opening region). While the dielectric film43has a two-layer structure in the first embodiment, the dielectric film43may have a three-layer structure including, for example, a silicon oxide film, a silicon nitride film, and a silicon oxide film, or a four-or-more-layer structure according to a situation. Alternatively, the dielectric film43may have a single-layer structure.

Layered Structure: Configuration of Spacing between Second and Third Layers, including First Inter-Layer Insulating Film

The first inter-layer insulating film32is formed above the TFTs14, the gate electrodes23, and the first relay electrodes37and below the storage capacitors18. The first inter-layer insulating film32is composed of a film of silicate glass such as non-doped silicate glass (NSG), phosphosilicate glass (PSG), borosilicate glass (BSG), or borophosphosilicate glass (BPSG), a silicon nitride film, or a silicon oxide film.

The first inter-layer insulating film32includes the contact holes39through which the heavily doped source regions22cof the TFTs14and the data lines15are electrically connected. The contact holes39is opened so as to pass through the second inter-layer insulating film33and the first inter-layer insulating film32from a surface of the second inter-layer insulating film33to a surface of the semiconductor layer22. The first inter-layer insulating film32further includes contact holes45through which the heavily doped drain regions22eof the TFTs14and the lower electrodes41of the storage capacitors18are electrically connected. The first inter-layer insulating film32further includes contact holes46through which the lower electrodes41of the storage capacitors13and the first relay electrodes37are electrically connected. The first inter-layer insulating film32further includes contact holes48through which the first relay electrodes37and second relay electrodes47, which will be described below, are electrically connected, the contact holes48passing through the second inter-layer insulating film33and the first inter-layer insulating film32.

Layered Structure: Configuration of Fourth Layer, including Data Lines, etc.

The fourth layer includes the data lines15. The data lines15are continuously formed on a surface of the second inter-layer insulating film33and a surface of the semiconductor layers22of the TFTs14that are exposed on a sidewall and bottom portion of the contact holes39. As shown inFIG. 6, each of the data lines15has a three-layer structure including, from the bottom, an aluminum layer15a, a titanium nitride layer15b, and a silicon nitride layer15c. The silicon nitride layer15cis patterned so as to have a somewhat larger size to cover the aluminum layer15aand titanium nitride layer15bformed therebelow. The fourth layer further includes capacitor-line relay layers49and the second relay electrodes47, which have a three-layer structure including the same materials as those of the data lines15.

Layered Structure: Configuration of Spacing between Third and Fourth Layers, including Second Inter-Layer Insulating Film

As described above, the second inter-layer insulating film33, which is composed of a film of silicate glass such as NSG, PSG, BSG, or BPSG, a silicon nitride film, or a silicon oxide film, or the like, is formed above the storage capacitors18and below the data lines15. The second inter-layer insulating film33has opened therein the contact holes39through which the heavily doped source regions22cof the TFTs14and the data lines15are electrically connected, and the contact holes50through which the capacitor-line relay layers49and the capacitor electrodes42of the storage capacitors18are electrically connected. The second inter-layer insulating film33further includes the contact holes48through which the second relay electrodes47and the first relay electrodes37are electrically connected.

Layered Structure: Configuration of Fifth Layer including Capacitor Lines, etc.

The fifth layer includes the capacitor lines17. The capacitor lines17extend from and around an image display area of the liquid crystal device1where the plurality of pixels are arranged. The capacitor lines17are electrically connected to a predetermined constant potential source, and are at a fixed potential. The fifth layer further includes third relay electrodes52that are composed of the same material as that of the capacitor lines17. The third relay electrodes52relay an electrical connection between the second relay electrodes47and the pixel electrodes13through contact holes53and54, which will be described below. The capacitor lines17and the third relay electrodes52have a two-layer structure including an aluminum layer as a lower layer and a titanium nitride layer as an upper layer.

Layered Structure: Configuration of Spacing between Fourth and Fifth Layers, including Third Inter-Layer Insulating Film

The third inter-layer insulating film34, which is composed of a film of silicate glass such as NSG, PSG, BSG, or BPSG, a silicon nitride film, a silicon oxide film, or the like, is formed above the data lines15and below the capacitor lines17. The third inter-layer insulating film34has opened therein the contact holes55through which the capacitor lines17and the capacitor-line relay layers49are electrically connected, and the contact holes53through which the third relay electrodes52and the second relay electrodes47are electrically connected.

Layered Structure: Configuration of Sixth Layer and Spacing between Fifth and Sixth Layers, including Pixel Electrodes, Common Electrodes, etc.

The sixth layer includes the pixel electrodes13, the common electrodes21, and the alignment film28overlying the pixel electrodes13and the common electrodes21. The fourth inter-layer insulating film35, which is composed of a film of silicate glass such as NSG, PSG, BSG, or BPSG, a silicon nitride film, a silicon oxide film, or the like underlies the pixel electrodes13and the common electrodes21. The fourth inter-layer insulating film35has opened therein the contact holes54through which the pixel electrodes13and the third relay electrodes52are electrically connected. That is, the contact holes54shown inFIG. 5are defined in a region where the pixel electrodes13and the third relay electrodes52overlap each other. The pixel electrodes13and the TFTs14are electrically connected through the contact holed54, the third relay electrodes52, the contact holes53, the second relay electrodes47, the contact holes48, the first relay electrodes37, the contact holes46, the lower electrodes41, and the contact holes45.

The fourth inter-layer insulating film35further has opened therein contact holes56through which the common electrodes21and the capacitor lines17(common potential lines) are electrically connected. That is, the contact holes56shown inFIG. 5, are defined in a region where the common electrodes21and the capacitor lines17overlap each other. Therefore, the common electrodes21and the capacitor lines17are electrically connected through the contact holes56, and a common potential (fixed potential) is applied to the common electrodes21via the capacitor lines17. In other words, since it is necessary to supply a fixed potential to the common electrodes21, in the structure of the first embodiment, the capacitor lines17through which a fixed potential is supplied underlie the common electrodes21, and a fixed potential is supplied to the common electrodes21using the capacitor lines17. While in the first embodiment, a fixed potential is supplied to the common electrodes21using the capacitor lines17, any line capable of supplying a fixed potential, other than the capacitor lines17, may be used.

On the counter substrate3, a black matrix58(light-shielding layer, seeFIG. 5) is defined on the substrate27so as to extend in a direction along the scanning lines16, and the alignment film29is defined so as to cover the black matrix58. The liquid crystal device1of the first embodiment is an IPS liquid crystal device, and includes no electrodes for driving the liquid crystal on the counter substrate3. While the black matrix58of the first embodiment is formed into a stripe so as to extend only in the direction along the scanning lines16, the data lines15or capacitor lines17composed of a metal are defined along the data lines15and serve as light-shielding layers. Therefore, the four sides of each of the pixels20are surrounded by light-shielding films although the black matrix58is formed into a stripe. The alignment film28of the TFT array substrate2and the alignment film29of the counter substrate3may be organic alignment films composed of polyimide or the like. For liquid crystal light valve applications of projectors, preferably, the alignment films28and29are inorganic alignment films such as high light-resistant silicon oxide films in view of irradiation of high-brightness light.

Structure of Pixel Electrodes and Common Electrodes

Next, the structure of the pixel electrodes13and the common electrodes21, which is the most significant feature of the first embodiment, will be described with reference toFIG. 5.

As shown inFIG. 5, each of the pixel electrodes13includes two strip-shaped electrode portions13a(electrode portions) and a joint portion13bfor connecting the two strip-shaped electrode portions13a, and is formed into a U shape. Although the pixel electrode13is segmented into portions referred to as a strip-shaped electrode portion and a joint portion, the pixel electrode13is actually an integrated electrode pattern composed of a transparent electrically conductive material such as ITO. The two strip-shaped electrode portions13aextend in a direction that obliquely crosses the data lines15(not shown inFIG. 5) and the scanning lines16, and are arranged parallel to each other. In the first embodiment, the angle defined between the direction in which the strip-shaped electrode portions13aextend and the direction in which the scanning lines16extend (hereinafter referred to as an “extending direction of the scanning lines16”) is set to 70°. The pixel electrode13is configured such that lower ends of the strip-shaped electrode portions13a, as viewed inFIG. 5, are connected to the joint portion13band upper ends of the strip-shaped electrode portions13aare open.

As with the pixel electrodes13, each of the common electrodes21includes two strip-shaped electrode portions21aand a joint portion21bfor connecting the two strip-shaped electrode portions21a, and is formed into a U shape. The common electrode21is also an integrated pattern composed of a transparent electrically conductive material such as ITO. The two strip-shaped electrode portions21aextend parallel to each other so that the angle with respect to the extending direction of the scanning lines16is set to 70°. As opposite to the pixel electrodes13, the common electrode21is configured such that upper ends of the strip-shaped electrode portions21a, as viewed inFIG. 5, are connected to the joint portion21band lower ends of the strip-shaped electrode portions21aare open. Since the pixel electrodes13and the common electrodes21are formed of a transparent electrically conductive material such as ITO, portions just above the strip-shaped electrode portions13aand21aof the electrodes13and21can contribute to the display to some extent. Thus, the aperture ratio is increased.

One of the strip-shaped electrode portions21aof the common electrode21is placed between the two strip-shaped electrode portions13aof the pixel electrode13, and one of the strip-shaped electrode portions13aof the pixel electrode13is placed between the two strip-shaped electrode portions21aof the common electrode21. That is, the U-shaped pixel electrode13and common electrode21are arranged so as to be interdigitated with each other. As viewed along the extending direction of the scanning lines16, the strip-shaped electrode portions13aof the pixel electrode13and the strip-shaped electrode portions21aof the common electrode21are alternately arranged. A large proportion of the two strip-shaped electrode portions13aof the pixel electrode13is located in a light-transmitted region of each of the pixels20where the black matrix58is opened. While a large proportion of one of the two strip-shaped electrode portions21a(the strip-shaped electrode portion21aat the left inFIG. 5) of the common electrode21is located in a light-transmitted region of each of the pixels20, the other strip-shaped electrode portion21a(the strip-shaped electrode portion21aat the right inFIG. 5) crosses the data line15(not shown inFIG. 5), the capacitor line17, etc., and extends across two of the pixels20which are adjacent in the extending direction of the scanning lines16.

In the first embodiment, the open ends of the two strip-shaped electrode portions13aof the pixel electrode13are oriented in a direction opposite to the open ends of the two strip-shaped electrode portions21aof the common electrode21. The arrangement of the joint portions13band21bof the pixel electrode13and the common electrode21will be focused on. The joint portion13bof the pixel electrode13and the joint portion21bof the common electrode21are not arranged side-by-side in the direction in which the data lines15extend (hereinafter referred to as an extending direction of the data lines15″) in parallel to each other (that is, the U-shaped pixel electrode13and common electrode21are not arranged back-to-back), but instead are alternately arranged in the extending direction of the scanning lines16so that a portion of the joint portion13band a portion of the joint portion21bare aligned in a line that extends along the scanning line16.

In a plurality of rows adjacent to each other in the extending direction of the data lines15, the pixel electrodes13in a given row (for example, the upper row of two rows of pixels show inFIG. 5) that are arranged in the extending direction of the scanning lines16, and the pixel electrodes13in a row adjacent to the given row (for example, the lower row shown inFIG. 5) that are arranged in the extending direction of the scanning lines16are offset with respect to each other by a half pitch of the pixel electrodes13in the extending direction of the scanning lines16. Likewise, the common electrodes21in a given row that are arranged in the extending direction of the scanning lines16and the common electrodes21in a row adjacent to the given row that are arranged in the extending direction of the scanning lines16are offset with respect to each other by a half pitch of the common electrodes21in the extending direction of the scanning lines16. In the first embodiment, for example, the pitch of the pixels20is 12 μm×12 μm, the width of the strip-shaped electrode portions13aand21ais 1 μm (the same width for the pixel electrodes13and the common electrodes21), and the pitch of the strip-shaped electrode portions13aand21ais 3 μm.

Now, connection portions at which the strip-shaped electrode portions13aand the joint portion13bof the pixel electrode13are connected and at which the strip-shaped electrode portions21aand the joint portion21bof the common electrode21are connected will be focused on. The strip-shaped electrode portions13aand21aand the joint portions13band21bare not linearly bent only once at an angle of 70°, but instead have oblique portions having an obtuse angle defined between the direction in which the strip-shaped electrode portions13aand21aextend and the direction in which the joint portions13band21bextend. In the first embodiment, by way of example, the strip-shaped electrode portions13aand21aand the joint portions13band21bare bent twice at an angle of substantially 125°. That is, the pixel electrode13and the common electrode21are contoured so as to narrow toward the connection portions from the open ends of the strip-shaped electrode portions13aand21a.

Not only the positional relationship between the pixel electrodes13and the common electrodes21but also the shape of the connection portions at which the strip-shaped electrode portions13aand21aand the joint portions13band21bare connected are appropriately determined so that the joint portion13bof one of the pixel electrodes13in a given row can be placed in a space between the joint portions21bof two of the common electrodes21in a row adjacent to the given row. Conversely, the joint portion21bof one of the common electrodes21in a given row can be placed in a space between the joint portions13bof two of the pixel electrodes13in a row adjacent to the given row. Therefore, as described above, the joint portions13bof the pixel electrodes13and the joint portions21bof the common electrodes21are alternately arranged in the extending direction of the scanning lines16, and a portion of each of the joint portions13band a portion of each of the joint portions21bare aligned in a line. In other words, if a plurality of pixels corresponding to one of the scanning lines16is referred to as a pixel group and two pixel groups adjacent in the extending direction of the data lines15are first and second pixel groups, respectively, at least a portion of the joint portion13bof one of the pixel electrodes13which is associated with the second pixel group is placed between the joint portions21bof two of the common electrodes21which are associated with the first pixel group. Further, at least a portion of the joint portion21bof one of the common electrodes21which is associated with the second pixel group is placed between the joint portions13bof two of the pixel electrodes13which are associated with the first pixel group.

In the liquid crystal device1of the first embodiment, a pair of polarizing plates (not shown) is disposed outside the TFT array substrate2and the counter substrate3. The pair of polarizing plates is arranged so that polarizing axes thereof are parallel to the extending (direction of the data lines15or the scanning lines16and are orthogonal to each other (cross-Nicol arrangement). Further, the alignment direction of the alignment films28and29of the TFT array substrate2and the counter substrate3coincides with the direction of the polarizing axis of one of the polarizing plates. Therefore, the alignment direction of the liquid crystal molecules under generation of no electric field in the liquid crystal layer5coincides with the polarizing axis direction of the polarizing plates, and a dark (black) display (normally black mode) is obtained. When a voltage (e.g., 5 V) corresponding to an image signal is applied to the pixel electrodes13, a lateral electric field substantially parallel to the substrate surface is applied to the liquid crystal layer5, and the alignment of the liquid crystal molecules is rotated by a predetermined angle within a plane substantially parallel to the substrate surface. Thereby, the light transmittance is modulated according to the angle, and a bright (white) display with a predetermined gradation level is obtained.

For example, assuming that the alignment direction of the liquid crystal molecules is parallel to the extending direction of the scanning lines16under application of no voltage, then, in the first embodiment, since the strip-shaped electrode portions13aand21aof the electrodes13and21are arranged so as to have an angle of 70° with respect to the scanning lines16, a lateral electric field generated in a direction vertical to the strip-shaped electrode portions13aand21awould be inclined by 20° with respect to the scanning lines16. In this case, the angle defined between the alignment direction of the liquid crystal molecules under application of no voltage and the direction of the lateral electric field is 20°, and the liquid crystal molecules in the liquid crystal layer5will be aligned in the direction parallel to the lateral electric field when the lateral electric field is applied. Therefore, no liquid crystal alignment disorder (called disclination) occurs. The structure of the first embodiment prevents display defects caused by alignment disorder, resulting in high-quality display of images even with the use of the arrangement of typical polarizing plates in which the polarizing axes of the polarizing plates are parallel to the extending direction of data lines or scanning lines.

In the liquid crystal device1of the first embodiment, the strip-shaped electrode portions13aand21aof the pixel electrodes13and the common electrodes21are arranged parallel to each other, and a uniform lateral electric field is generated in the liquid crystal layer5at a portion where the electrode portions13aand21aface each other. Thus, a normal bright display is obtained. On the other hand, a uniform lateral electric field is not generated at a portion just above the joint portions13band21bof the electrodes13and21and at a portion where the strip-shaped electrode portions13aand21aface the joint portions13band21b, resulting in a low light transmittance during bright display. According to the liquid crystal device1of the first embodiment, however, the joint portions13bof the pixel electrodes13and the joint portions21bof the common electrodes21are alternately arranged in the extending direction of the scanning lines16, and a widthwise portion of the joint portions13bof the pixel electrodes13and a widthwise portion of the joint portions21bof the common electrodes21are aligned in a line, thereby reducing the size of a region with a low transmittance over the related art. Therefore, the aperture ratio can be increased. A liquid crystal device capable of achieving a bright display can thus be realized.

In the first embodiment, the joint portions13band21bof the pixel electrodes13and the common electrodes21are placed so as to overlap the scanning lines16. Since a region where the scanning lines16are located is a region where light is blocked by the black matrix58, the reduction of the aperture ratio can be minimized. Further, the strip-shaped electrode portions13aand21aof the pixel electrodes13and the common electrodes21extend obliquely to the data lines15and the scanning lines16, and the corners of the connection portions at which the strip-shaped electrode portions13aand21aand the joint portions13band21bare connected are formed obliquely. Therefore, the joint portions of the pixel electrodes13or the common electrodes21can be relatively easily placed between the joint portions of the other electrodes. Further, since one of the strip-shaped electrode portions21aof each of the common electrodes21obliquely crosses the data line15and extends across two of the pixels20which are adjacent in the extending direction of the scanning lines16, the one strip-shaped electrode portion21acan serve as a common electrode shared between the two pixels20. Therefore, a peripheral portion of the pixels20can be effectively utilized for the display, and the aperture ratio can further be improved.

According to the first embodiment, the common electrodes13and the capacitor lines17are electrically connected through the contact holes56. Therefore, even if the common electrodes13are separated for each of the pixels20, a fixed potential can be supplied to the common electrodes13via the capacitor lines17. Since the capacitor lines17through which a fixed potential is supplied are effectively utilized, no other lines are required for supplying a common potential. Therefore, the aperture ratio can be improved.

Second Embodiment

A second embodiment of the invention will not be described with reference toFIG. 7.

The basic structure of a liquid crystal device according to the second embodiment is similar to that of the first embodiment, except for the structure of common electrodes. Only a portion different from that of the first embodiment will be described with reference to a plan view shown inFIG. 7, and a description of the other portions, which are common to those of the first embodiment, is omitted. InFIG. 7, components common to those shown inFIG. 1are represented by the same reference numerals.

In the second embodiment, as shown inFIG. 7, one of the two strip-shaped electrode portions21aof each of the common electrodes21extends from the open end thereof, and is connected to the joint portion21bof the common electrode21that is adjacent thereto in the extending direction of the data lines15. In the second embodiment, therefore, unlike the first embodiment, the common electrodes21are not independent for each pixel, and a plurality of the common electrodes21which are associated with a plurality of the pixels20which are arranged in the extending direction of the data lines15are formed into an integrated continuous electrode pattern. The electrode pattern is drawn on the TFT array substrate2to the outside of the image display area, and is fixed at a common potential. The remaining components, such as the pixel electrodes13, are the same as those of the first embodiment.

According to the structure of the second embodiment, the plurality of common electrodes21arranged in the extending direction of the data lines15are electrically connected, thereby stably supplying a common potential to the plurality of common electrodes21. In the second embodiment, in particular, the above-described structure and the structure described in the first embodiment in which the common electrodes21and the capacitor lines17are electrically connected through the contact holes56so that a common potential can be supplied via the capacitor lines17are used in combination. Therefore, even if one of the connection structures fails, the other connection structure can be used to establish an electrical connection, thereby realizing a high-reliability liquid crystal device with a redundant structure.

Third Embodiment

A third embodiment of the invention will be described with reference toFIGS. 10 and 11.

The basic structure of a liquid crystal device according to the third embodiment is similar to that of the first embodiment, except for the arrangement and shape of pixels.

FIGS. 10 and 11are plan views of a plurality of adjacent pixels on a TFT array substrate of the liquid crystal device of the third embodiment. For easy illustration of components on the TFT array substrate,FIG. 10shows only components in layers lower than layers having pixel electrodes and common electrodes, andFIG. 11mainly shows a pattern of pixel electrodes and common electrodes.

Only a portion different from that of the first embodiment will be described with reference to the plan views shown inFIGS. 10 and 11, and a description of the other portions, which are common to those of the first embodiment, is omitted. The cross-sectional structure of the liquid crystal device is similar to that of the first embodiment. InFIGS. 10 and 11, components common to those shown inFIGS. 4 and 5are represented by the same reference numerals.

As shown inFIGS. 10 and 11, a plurality of data lines15and a plurality of scanning lines16are arranged in a lattice pattern on a TFT array substrate2, and a plurality of pixels20corresponding to regions surrounded by the data lines15and the scanning lines16are arranged in a matrix. In the third embodiment, as shown inFIG. 10, in a plurality of rows adjacent to each other in the extending direction of the data lines15, the pixels20in a given row (for example, the upper row of two rows of pixels shown inFIG. 10) that are arranged in the extending direction of the scanning lines16, and the pixels20in a row adjacent to the given row (for example, the lower row shown inFIG. 10) that are arranged in the extending direction of the scanning lines16are arranged so as to be offset with respect to each other by a substantially quarter pitch of the pixels20in the extending direction of the scanning lines16. Pixel electrodes13(second electrodes) and common electrodes21(first electrodes) are disposed in each of the pixels20which are arranged so as to be offset with respect to each other by a quarter pitch for each row in the extending direction of the scanning lines16. If a plurality of pixels corresponding to one of the scanning lines16is referred to as a pixel group and two pixel groups adjacent in the extending direction of the data lines15are first and second pixel groups, the first and second pixel groups are arranged so as to be offset with respect to each other in the direction in which the plurality of pixels20are arrayed.

Each of the data lines15has a layered structure including an aluminum film, etc., and each of the scanning lines16is composed of, for example, an electrically conductive polysilicon film. The scanning line16is electrically connected to a gate electrode23in a semiconductor layer22, which faces a channel region22ashown as a shaded area inFIG. 10, through a contact hole24, and a pattern of the gate electrode23is included in a pattern of the scanning lines16. A TFT14, which is a pixel switching element configured such that the gate electrode23is placed on the channel region22aso as to face the channel region22a, is disposed at an intersection between the gate electrode23and the data line15.

Structure of Pixel Electrodes and Common Electrodes

Next, the structure of the pixel electrodes13and the common electrodes21, which is the most significant feature of the third embodiment, will be described with reference toFIG. 11.

As shown inFIG. 11, each of the pixel electrodes13includes two strip-shaped electrode portions13a(electrode portions) and a joint portion13bfor connecting the two strip-shaped electrode portions13a, and is formed into a U shape. Although the pixel electrode13is segmented into portions referred to as a strip-shaped electrode portion and a joint portion, the pixel electrode13is actually an integrated electrode pattern composed of a transparent electrically conductive material such as ITO. The two strip-shaped electrode portions13aextend parallel to the data line15(not shown inFIG. 11), and are arranged parallel to each other. The pixel electrode13is configured such that lower ends of the strip-shaped electrode portions13a, as viewed inFIG. 11, are connected to the joint portion13band upper ends of the strip-shaped electrode portions13aare open.

As with the pixel electrodes13, each of the common electrodes21includes two strip-shaped electrode portions21aand a joint portion21bfor connecting the two strip-shaped electrode portions21a, and is formed into a U shape. The common electrode21is also an integrated pattern composed of a transparent electrically conductive material such as ITO. The two strip-shaped electrode portions21aextend parallel to the extending direction of the data lines15, and extend parallel to each other. As opposite to the pixel electrodes13, the common electrode21is configured such that upper ends of the strip-shaped electrode portions21a, as viewed inFIG. 11, are connected to the joint portion21band lower ends of the strip-shaped electrode portions21aare open. Since the pixel electrodes13and the common electrodes21are formed of a transparent electrically conductive material such as ITO, portions immediately above the strip-shaped electrode portions13aand21aof the electrodes13and21can contribute to the display to some extent. Thus, the aperture ratio is increased.

One of the strip-shaped electrode portion21aof the common electrode21is placed between the two strip-shaped electrode portions13aof the pixel electrode13, and one of the strip-shaped electrode portions13aof the pixel electrode13is placed between the two strip-shaped electrode portions21aof the common electrode21. That is, the U-shaped pixel electrode13and the common electrode21are arranged so as to be interdigitated with each other. As viewed along the extending direction of the scanning lines16, the strip-shaped electrode portions13aof the pixel electrode13and the strip-shaped electrode portions21aof the common electrode21are alternately arranged. A large proportion of the two strip-shaped electrode portions13aof the pixel electrode13is located in a light-transmitted region of each of the pixels20where the black matrix58is opened. While a large proportion of one of the two strip-shaped electrode portions21a(the strip-shaped electrode portion21aat the left inFIG. 11) of the common electrode21is located in a light-transmitted region of each of the pixels20, the other strip-shaped electrode portion21a(the strip-shaped electrode portion21aat the right inFIG. 11) overlaps the data line15(not shown inFIG. 11), the capacitor line17, etc., in plan view, and is located outside the light-transmitted region.

In the third embodiment, the open ends of the two strip-shaped electrode portions13aof the pixel electrode13are oriented in a direction opposite to the open ends of the two strip-shaped electrode portions21aof the common electrode21in association with the pixel20. The arrangement of the joint portions13band21bof the pixel electrode13and the common electrode21will be focused on. The joint portion13bof the pixel electrode13and the joint portion21bof the common electrode21are not arranged side-by-side in the extending direction of the data lines15in parallel to each other (that is, the U-shaped pixel electrode13and common electrode21are not arranged back-to-back), but instead are alternately arranged in the extending direction of the scanning lines16(in a direction in which a plurality of pixels constituting a pixel group are arrayed) so that a widthwise portion of the joint portion13band a widthwise portion of the joint portion21bare aligned in a line. Two of the pixels20that are arranged side-by-side along the data lines15are arranged so as to be offset with respect to each other by a quarter pitch, thereby achieving the above arrangement.

In a plurality of rows adjacent to each other in the extending direction of the data lines15, the pixel electrodes13in a given row (for example, the upper row of two rows of pixels shown inFIG. 11) that are arranged in the extending direction of the scanning lines16, and the pixel electrodes13in a row adjacent to the given row (for example, the lower row shown inFIG. 11) that are arranged in the extending direction of the scanning lines16are offset with respect to each other by a quarter pitch of the pixel electrodes13in the extending direction of the scanning lines16(in a direction in which a plurality of pixels constituting a pixel group are arrayed). Likewise, the common electrodes21in a given row that are arranged in the extending direction of the scanning lines16and the common electrodes21in a row adjacent to the given row that are arranged in the extending direction of the scanning lines16are offset with respect to each other by a quarter pitch of the common electrodes21in the extending direction of the scanning lines16. In the third embodiment, for example, the pitch of the pixels20is 12 μm×12 μm, the width of the strip-shaped electrode portions13aand21ais 1 μm (the same width for the pixel electrodes13and the common electrodes21), and the pitch of the strip-shaped electrode portions13aand21ais 3 μm.

Now, connection portions at which the strip-shaped electrode portions13aand the joint portion13bof the pixel electrode13are connected and at which the strip-shaped electrode portions21aand the joint portion21bof the common electrode21are connected will be focused on. The strip-shaped electrode portions13aand21aand the joint portions13band21bare not bent only once at a right angle, but instead have oblique portions having an obtuse angle defined between the direction in which the strip-shaped electrode portions13aand21aextend and the direction in which the joint portions13band21bextend. In the third embodiment, by way of example, the strip-shaped electrode portions13aand21aand the joint portions13band21bare bent twice. That is, the pixel electrode13and the common electrode21are contoured so as to narrow toward the connection portions from the open ends of the strip-shaped electrode portions13aand21a.

Not only the positional relationship between the pixel electrodes13and the common electrodes21but also the shape of the connection portions at which the strip-shaped electrode portions13aand21aand the joint portions13band21bare connected are appropriately determined so that the joint portion13bof one of the pixel electrodes13in a given row can be placed in a space between the joint portions21bof two of the common electrodes21in a row adjacent to the given row. Conversely, the joint portion21bof one of the common electrodes21in a given row can be placed in a space between the joint portions13bof two of the pixel electrodes13in a row adjacent to the given row. Therefore, as described above, the joint portions13bof the pixel electrodes13and the joint portions21bof the common electrodes21are alternately arranged in the extending direction of the scanning lines16, and a widthwise portion of each of the joint portions13band a widthwise portion of each of the joint portions21bare aligned in a line.

In the liquid crystal device1of the third embodiment, a pair of polarizing plates (not shown) is disposed outside the TFT array substrate2and the counter substrate3. The pair of polarizing plates is arranged so that polarizing axes thereof cross the extending direction of the data lines15or the scanning lines16and are orthogonal to each other (cross-Nicol arrangement). Further, the alignment direction of the alignment films28and29of the TFT array substrate2and the counter substrate3coincides with the direction of the polarizing axis of one of the polarizing plates. Therefore, the alignment direction of the liquid crystal molecules under generation of no electric field in the liquid crystal layer5coincides with the polarizing axis direction of the polarizing plate, and a dark (black) display (normally black mode) is obtained. When a voltage (e.g., 5 V) corresponding to an image signal is applied to the pixel electrodes13, a lateral electric field substantially parallel to the substrate surface is generated in the liquid crystal layer5, and the alignment of the liquid crystal molecules is rotated by a predetermined angle within a plane substantially parallel to the substrate surface. Thereby, the light transmittance is modulated according to the angle, and a bright (white) display with a predetermined gradation level is obtained.

For example, assuming that the alignment direction of the liquid crystal molecules defines an acute angle with respect to the extending direction of the scanning lines16under application of no voltage, then, in the third embodiment, since the strip-shaped electrode portions13aand21aof the electrodes13and21are arranged vertical to the scanning lines16, a lateral electric field generated in a direction vertical to the strip-shaped electrode portions13aand21awould be parallel to the extending direction of the scanning lines16. In this case, the angle defined between the alignment direction of the liquid crystal molecules under application of no voltage and the direction of the lateral electric field is an acute angle, and the liquid crystal molecules in the liquid crystal layer5will be aligned in the direction parallel to the lateral electric field when the lateral electric field is applied. Therefore, no liquid crystal alignment disorder (called disclination) occurs.

In the liquid crystal device1of the third embodiment, the strip-shaped electrode portions13aand21aof the pixel electrodes13and the common electrodes21are arranged parallel to each other, and a uniform lateral electric field is generated in the liquid crystal layer5at a portion where the electrode portions13aand21aface each other. Thus, a normal bright display is obtained. On the other hand, a uniform lateral electric field is not generated at a portion just above the joint portions13band21bof the electrodes13and21and at a portion where the strip-shaped electrode portions13aand21aface the joint portions13band21b, resulting in a low light transmittance during bright display. According to the liquid crystal device1of the third embodiment, however, the joint portions13bof the pixel electrodes13and the joint portions21bof the common electrodes21are alternately arranged in the extending direction of the scanning lines16, and a widthwise portion of the joint portions13bof the pixel electrodes13and a widthwise portion of the joint portions21bof the common electrodes21are aligned in a line, thereby reducing the size of a region with a low transmittance over the related art. Therefore, the aperture ratio can be increased. A liquid crystal device capable of achieving a bright display can thus be realized.

In the third embodiment, the joint portions13band21bof the pixel electrodes13and the common electrodes21are placed so as to overlap the scanning lines16. Since a region where the scanning lines16are located is a region where light is blocked by the black matrix58, the reduction of the aperture ratio can be minimized. Further, the pixel electrodes13and the common electrodes21are arranged so as to be offset with respect to each other by a quarter pitch in the extending direction of the scanning lines16, and the corners of the connection portions at which the strip-shaped electrode portions13aand21aand the joint portions13band21bare connected are formed obliquely. Therefore, the joint portions of one of the pixel electrodes13or the common electrodes21can be relatively easily placed between the joint portions of the other electrodes.

According to the third embodiment, the common electrodes13and the capacitor lines17are electrically connected through the contact holes56. Therefore, even if the common electrodes13are separated for each of the pixels20, a fixed potential can be supplied to the common electrodes13via the capacitor lines17. Since the capacitor lines17through which a fixed potential is supplied are effectively utilized, no other lines are required for supplying a common potential. Therefore, the aperture ratio can be improved.

Fourth Embodiment

A fourth embodiment of the invention will now be described with reference toFIG. 12.

The basic structure of a liquid crystal device of the fourth embodiment is similar to that of the third embodiment, except for the structure of common electrodes. Only a portion different from that of the third embodiment will be described with reference to a plan view shown inFIG. 12, and a description of the other portions, which are common to those of the third embodiment, is omitted. InFIG. 12, components common to those shown inFIG. 11are represented by the same reference numerals.

In the fourth embodiment, as shown inFIG. 12, one of the two strip-shaped electrode portions21a(in the example shown inFIG. 12, the strip-shaped electrode portion21aat the right) of each of the common electrodes21extends from the open end thereof, and is connected to the joint portion21bof the common electrode21that is adjacent thereto in the extending direction of the data lines15. In the fourth embodiment, therefore, unlike the third embodiment, the common electrodes21are not independent for each pixel, and a plurality of the common electrodes21which are associated with a plurality of the pixels20which are arranged in the extending direction of the data lines15are formed into an integrated continuous electrode pattern. The electrode pattern is drawn on the TFT array substrate2to the outside of the image display area, and is fixed at a common potential. The remaining components, such as the pixel electrodes13, are the same as those of the third embodiment.

According to the structure of the fourth embodiment, the plurality of common electrodes21arranged in the extending direction of the data lines15are electrically connected, thereby stably supplying a common potential to the plurality of common electrodes21. In the fourth embodiment, in particular, the above-described structure and the structure described above in the first embodiment in which the common electrodes21and the capacitor lines17are electrically connected through the contact holes56so that a common potential can be supplied via the capacitor lines17are used in combination. Therefore, even if one of the connection structures fails, the other connection structure can be used to establish an electrical connection, thereby realizing a high-reliability liquid crystal device with a redundant structure.

Fifth Embodiment

A fifth embodiment of the invention will be described hereinafter with reference toFIG. 13.

The basic structure of a liquid crystal device of the fifth embodiment is similar to that of the third embodiment, except for the arrangement of pixels. Only a portion different from that of the third embodiment will be described with reference to a plan view shown inFIG. 13, and a description of the other portions, which are common to those of the third embodiment, is omitted. InFIG. 13, components common to those shown inFIG. 11are represented by the same reference numerals.

In the fifth embodiment, as shown inFIG. 13, the scanning lines16are inclined with respect to a horizontal direction (the horizontal direction H shown inFIG. 1) of a display area (the display area R shown inFIG. 1), and the data lines15are inclined with respect to a vertical direction (the vertical direction V shown inFIG. 1) of the display area. The data lines15are bent at intersections with the scanning lines16. Therefore, a plurality of the pixels20which are arranged in the extending direction of the scanning lines16are inclined with respect to the horizontal direction of the display area, and a plurality of the pixels20which are arranged in the extending direction of the data lines15are inclined with respect to the vertical direction of the display area.

In the structure of the third and fourth embodiments, since the plurality of pixels20are offset with respect to each other in the extending direction of the scanning lines16, there is a drawback in that a straight line might be displayed obliquely when a straight line extending in the horizontal direction of the screen (display area) is displayed or when a straight line extending in the vertical direction of the screen is displayed. According to the fifth embodiment, a plurality of the pixels20which are arranged in the extending direction of the scanning lines16are inclined with respect to the horizontal direction of the screen, and a plurality of the pixels which are arranged in the extending direction of the data lines15are inclined with respect to the vertical direction of the screen. Therefore, the straight line can be prevented from being displayed obliquely even though the straight line is displayed as a slightly zigzag line to ensure high representation of the straight line.

Projector

A projector including the liquid crystal device1of the embodiments described above as a light valve will now be described.FIG. 14is a plan view showing an example structure of a projector1100according to an embodiment of the invention. As shown inFIG. 14, the projector1100includes a lamp unit1102including a white light source such as a halogen lamp. Projection light emitted from the lamp unit1102is separated into light components R, G, and B of three primary colors, i.e., red (R), green (G), and blue (B), by four mirrors1106and two dichroic mirrors1108provided in a light guide1104. The light components R, G, and B are directed to liquid crystal panels1110R,1110B, and1110G serving as light valves, respectively.

The structure of the liquid crystal panels1110R,1110B, and1110G is equivalent to that of the liquid crystal device1described above, and the liquid crystal panels1110R,1110B, and1110G are driven by primary color signals R, G, and B supplied from an image signal processing circuit, respectively. The light components R, G, and B modulated by the liquid crystal panels1110R,1110B, and1110G enter a dichroic prism1112from three directions. In the dichroic prism1112, the light components R and B are refracted at 90 degrees while the light component G advances straight. After images of the respective colors are combined, a color image is projected onto a screen or the like through a projector lens1114.

According to the embodiment, the liquid crystal device1of the embodiments described above having a high pixel aperture ratio is used as a light valve, thereby achieving a projector capable of performing a bright display.

The technical scope of the invention is not limited to the embodiments described above, and a variety of modifications can be made without departing from the scope of the invention. In the embodiments described above, strip-shaped electrode portions of each electrode extend in a direction in which the data lines extend, and a joint portion of the electrode and a corresponding one of the scanning lines overlap each other. For example, this arrangement may be rotated by 90°, and the strip-shaped electrode portions may extend in a direction in which the scanning lines extend and the joint portion and the data line may overlap each other so that the joint portions of the respective electrodes may be aligned in a line along the data lines.

In the embodiments described above, a connection portion at which the strip-shaped electrode portions and the joint portion are connected is bent twice so as to define an obtuse angle to allow the joint portions of the pixel electrodes or the common electrodes to be easily placed between the joint portions of the other electrodes. Instead of the above structure, the corners of a connection portion at which the strip-shaped electrode portions and the joint portions are connected may be curved. Alternatively, in addition to the corners of a connection portion at which the strip-shaped electrode portions and the joint portions are connected, the joint portions may be entirely bent at the center thereof to the extent that the aperture ratio is not greatly reduced. Further, in the liquid crystal device of the embodiments described above, since the pixel pitch is as small as approximately 12 μm, only two strip-shaped electrode portions of each electrode are required. However, the number and size of strip-shaped electrode portions may be changed as necessary according to the pixel pitch. Other specific components, except for pixel electrodes and common electrodes, can be changed as necessary.

EXAMPLES

The inventors conducted a simulation to demonstrate an effect of the improved aperture ratio according to the invention. A result of the simulation will now be described.

In Example 1, a negative liquid crystal with an dielectric constant anisotropy Δ∈ of −5.5 and a refractive index anisotropy of Δn of 0.14 was used. As shown inFIG. 8A, an electrode arrangement including pixel electrodes61that are independent from each other, and common electrodes62that are patterned so as to be connected to each others which is similar to that of the second embodiment, was used. The pitch of pixels was 12 μm×12 μm, the width of strip-shaped electrode portions61aand62awas 1 μm, and the pitch of the strip-shaped electrode portions61aand62awas 3 μm.

In Comparative Example 1, conditions similar to those of Example 1, except for an electrode arrangement shown inFIG. 9A, were used. Referring toFIG. 9A, the electrode arrangement includes pixel electrodes63and common electrodes64.

Results of a simulation of transmittance distribution when a bright display was conducted by applying a voltage of 5 V between the pixel electrodes and the common electrodes are shown inFIGS. 8B and 9B.FIG. 8Bshows the result of the simulation in Example 1, andFIG. 9Bshows the result of the simulation in Comparative Example 1. It was assumed in this simulation that a portion corresponding to the data lines and a portion corresponding to the scanning lines were shielded from light using a black matrix BM with a width of 2 μm and a width of 4 μm, respectively.

In Comparative Example 1, as can be seen fromFIG. 9B, a dark (low-light-transmittance) region was greatly expanded toward the inside of a region to be brightly displayed within the black matrix BM. The dark region correspond to a region where the strip-shaped electrode portions63aand64aof the electrodes63and64face joint portions63band64bof the electrodes63and64shown inFIG. 9A. In Example 1, on the other hand, as can be seen fromFIG. 8B, the size of an observed dark region expanded toward the inside of a region to be brightly displayed was significantly smaller than that of Comparative Example 1. According to the invention, therefore, it was found that the effective pixel aperture ratio could be improved. Further, the inventors actually produced a model of a liquid crystal device of the invention, and measured the pixel aperture ratio. The measurement result matched the result of the simulation above.