Patent Description:
Patent Literature <NUM>-<NUM> and the like disclose a liquid crystal display and an organic light-emitting diode display integrating a fingerprint sensor using a photosensor.

Document <CIT> describes an object to detect reflected light from an object and to improve accuracy of capturing an image in a photosensor included in a display panel. In the display panel including a photosensor, when an image of an object is captured, light is emitted from a light source to the object and reflected light enters the photosensor. In the case where the incident light is too strong with respect to sensitivity of the photosensor, luminance of the light source is lowered. In the case where the incident light is too weak with respect to sensitivity of the photosensor, the luminance of the light source is increased.

Document <CIT> describes a liquid crystal device including a first substrate, a second substrate that is bonded to the first substrate with pillar-shaped spacers interposed therebetween, and a liquid crystal layer that is provided between the first substrate and the second substrate. The first substrate includes pixel electrodes each having a plurality of unit electrode portions and connecting portions that connect the unit electrode portions; switching elements that are connected to the pixel electrodes; and wiring lines that are arranged between adjacent pixel electrodes to be connected to the switching elements. In the liquid crystal device, each wiring line includes a light shielding portion having a size larger than that of the spacer between the connecting portion of one pixel electrode and another pixel electrode positioned in the vicinity of the connecting portion, and the spacer is arranged to overlap the light shielding portion.

Document <CIT> describes a liquid crystal display including an insulating substrate, a semiconductor, a gate insulating layer, a gate line, an interlayer insulating layer, a data line, a drain electrode, a passivation layer, and a pixel electrode. The semiconductor is formed on the insulating substrate and includes source, drain, and channel regions. The gate line is formed on the gate insulating layer over the semiconductor, and overlaps the channel region thereof. The data line is formed on the interlayer insulating layer and has a source electrode electrically connected to the source region and a drain electrode electrically connected to the drain region. The passivation layer is formed on the data line and drain electrode. The pixel electrode is formed on the passivation layer, and electrically connected to the drain electrode. The data line overlaps the drain region.

When the fingerprint sensor using the photosensor is provided in the screen of the liquid crystal display panel, it is necessary to provide a light shielding film, which blocks light from entering from the back side to the semiconductor film for fingerprint imaging of each photosensor, on the back side of each semiconductor film.

When providing the light shielding film as described above, diffraction of light occurs at the periphery of the light shielding film, causing loss of light output from the display screen. This loss of light can be a factor that lowers the brightness of the display screen. In addition, if such a fingerprint sensor is provided in a portion of the screen, the presence of the fingerprint sensor may become more noticeable in the display screen.

An object of the present invention is to provide a display device having a fingerprint sensor and the fingerprint sensor for a display device capable of suppressing loss of light due to diffraction of light.

According to the present invention, by rounding the outer contour shape of the light shielding film, the circumferential length of the light shielding film is shortened, and the amount of diffraction of light can be reduced in accordance with the reduction in the amount of shortening. As a result, it is possible to reduce loss of the light output to the display screen due to diffraction of the light caused by the fingerprint sensor provided in the screen of the display device.

<FIG> show examples of structures of display devices to which the present invention is applied. <FIG> show cut out portions of a display device <NUM>, and <FIG> is a cross-sectional view of the thickness directions B1 and B2 along the predetermined directions A1 and A2, and <FIG> is a cross-sectional view of the thickness directions B1 and B2 along the directions D1 and D2 perpendicular to the directions A1 and A2, and <FIG> is a plan view. Among the directions B1 and B2, B1 indicates the display surface side, and B2 indicates the non-display surface side opposite to the display surface side. In the plane view of <FIG>, transparent or translucent objects are omitted, and only the black matrix BM, the photosensor PS, and the switching element TR are shown. Of these, portions hidden behind the black matrix BM are indicated by dotted lines.

Display device <NUM> is a thin film transistor (TFT) type active matrix liquid crystal display. Since the configuration of the active matrix liquid crystal display is well known, the detailed description of the well-known configuration is omitted in the following description.

As shown in the figure, the glass substrates <NUM>, <NUM>, <NUM> as transparent substrates are provided in this order from the display surface side B1 toward the non-display surface side B2. In place of the glass substrates, plastic substrates such as polycarbonate substrates can be used.

The display surface side B1 of the glass substrate <NUM> is provided with a polarizing element PL, a transparent cover glass <NUM> is provided on the polarizing element PL. A fingerprint image can be captured by bringing a finger FG of the human body into contact with the surface of the cover glass <NUM>.

The non-display surface side B2 of the glass substrate <NUM> is provided with a color filter <NUM>.

Color filter <NUM> has a black matrix BM having a light shielding property formed in a lattice shape corresponding to each pixel of the screen on the non-display surface side B2 of the glass substrate <NUM>, and the coloring units 50R, <NUM>, and 50B for transmitting light. As the material of the black matrix BM, various materials can be used, but a metal chromium film can be used for the reasons of light shielding, ease of manufacturing, corrosion resistance, and the like. The coloring units 50R, <NUM>, and 50B are formed of a well-known resist material, and are, for example, an organic resin material containing a pigment.

On the display surface side B1 of the glass substrate <NUM>, switching elements TR each made of thin film transistor (TFT) are formed in a matrix shape corresponding to pixels, on the switching elements TR, with a protective insulating film <NUM> interposed, pixel electrodes EL2 are formed in a matrix shape. As the TFTs, well-known low-temperature poly-Si (LTPS) type or amorphous Si type is employed.

The non-display surface side B2 of the glass substrate <NUM>, a common electrode EL1 facing the pixel electrodes EL2 is formed. The common electrode EL1 and the pixel electrodes EL2 are formed of a transparent conductive film such as indium tin oxide (ITO).

Well-known liquid crystal materials LC are filled between the common electrode EL1 and the pixel electrodes EL2.

The non-display surface B2 side of the glass substrate <NUM> is provided with a polarizing element PL, the backlight <NUM> as a light source is provided on the non-display surface side B2 of the polarizing element PL. As the backlight <NUM>, a well-known backlight is employed.

On the display surface side B1 of the glass substrate <NUM>, an array of transparent photosensors PS arranged in a matrix is formed on a portion of the screen of the display device. The photosensors PS can also be provided throughout the screen. In the present embodiment, a single photosensor PS is provided for each pixel, but the construction is not limited thereto, and it is also possible to provide a plurality of photosensors PS for each pixel. The array of the photosensors PS is configure to receive light passing through the coloring units 50R, <NUM>, and 50B of the color filter <NUM> from the display surface side B1 toward the non-display surface B2 side, and detect the light intensity of each of R (red), G (green) and B (blue) colors.

As shown in <FIG>, light L from the backlight <NUM> is reflected by a finger FG placed on the cover glass <NUM>, and the reflected light passes through the coloring units 50R, <NUM>, 50B of the color filter <NUM> and is incident on the photosensor PS. In <FIG>, the finger FG is schematically shown as small, but in reality, a plurality of sets of RGB photosensors PS are arranged within the intervals of one stripe of the fingerprint, and the intensities of the respective RGB lights of the reflected lights from the corresponding fingerprint portions are detected. By mapping this, a color image of the fingerprint can be captured.

<FIG> and <FIG> show structural examples of a single photosensor PS according to an embodiment of the present invention.

Photosensor PS shown in <FIG> and <FIG> is a TFT (thin film transistor) of a well-known double-gate structure, <NUM> is a semiconductor film, <NUM> is a bottom gate electrode, <NUM> is a bottom gate electrode, <NUM> is a bottom gate insulating film, <NUM> is a channel protective film, <NUM> is an extrinsic semiconductor film, <NUM> is an extrinsic semiconductor film, <NUM> is a source electrode, <NUM> is a drain electrode, <NUM> is an interlayer insulating film, <NUM> is a top gate electrode, <NUM> is a source line, <NUM> is a drain line, and <NUM> is a top gate line.

In <FIG>, the semiconductor film <NUM>, the bottom gate electrode <NUM> and the bottom gate line <NUM> are drawn by solid lines, and other components are drawn by dotted lines.

The photosensor PS is a photoelectric conversion element, and includes a bottom gate electrode <NUM>, a semiconductor film <NUM> facing the bottom gate electrode <NUM> and sandwiching a bottom gate insulating film <NUM> between the bottom gate electrode <NUM>, a channel protective film <NUM> formed on a central portion of the semiconductor film <NUM>, extrinsic semiconductor films <NUM> and <NUM> formed on both end portions of the semiconductor film <NUM> so as to be separated from each other, a source electrode <NUM> formed on the extrinsic semiconductor film <NUM>, a drain electrode <NUM> formed on the extrinsic semiconductor film <NUM>, a semiconductor film <NUM>, and a top gate electrode <NUM> facing the semiconductor film <NUM> while sandwiching an interlayer insulating film <NUM> and a channel protective film <NUM>.

Bottom gate electrodes <NUM> are formed in a matrix form on the display surface side B1 of the glass substrate <NUM> described above so as to correspond to the photosensors PS. On the display surface side B1 of the glass substrate <NUM>, a bottom gate line <NUM> extending laterally is formed, and the bottom gate electrodes <NUM> of photosensors PS which are laterally arranged in the same row are formed integrally with the common bottom gate line <NUM>. Bottom gate electrode <NUM> has conductivity and light shielding property, and is formed of a material having conductivity and light shielding property such as Cr, Mo, Ta, W. Bottom gate line <NUM> is formed of a material having at least conductivity, may have a light-transmitting property at the same time. Examples of the conductive and light-transmitting material include indium oxide, zinc oxide, or tin oxide, or a mixture containing at least one of them (e.g., tin-doped indium oxide (ITO), zinc-doped indium oxide).

On the bottom gate electrode <NUM> and the bottom gate line <NUM>, the bottom gate insulating film <NUM> common to all photosensors PS is formed. The bottom gate insulating film <NUM> has an insulating property and a light transmitting property, and is made of, for example, silicon nitride or silicon oxide.

On the bottom gate insulating film <NUM>, a semiconductor film <NUM> is formed for each photosensor PS. The semiconductor film <NUM> is a layer formed of amorphous silicon or polysilicon. A channel protective film <NUM> is formed on the semiconductor film <NUM>. Channel protective film <NUM> has a function of protecting the interface of the semiconductor film <NUM> from the etchant used in patterning, has an insulating and light-transmitting property, and made of, for example, silicon nitride or silicon oxide. When light L is incident on the semiconductor film <NUM>, the semiconductor film is activated to cause electron-hole pairs in an amount corresponding to the amount of light be generated around the interface between the channel protective film <NUM> and the semiconductor film <NUM>.

An extrinsic semiconductor film <NUM> is formed on one end portion of the semiconductor film <NUM> so as to partially overlap with the channel protective film <NUM>, and an extrinsic semiconductor film <NUM> is formed on the other end portion of the semiconductor film <NUM> so as to partially overlap with the channel protective film <NUM>. The extrinsic semiconductor films <NUM> and <NUM> are made of polysilicon containing n-type impurity ions.

A patterned source electrode <NUM> is formed on the extrinsic semiconductor film <NUM>. A patterned drain electrode <NUM> is formed on the extrinsic semiconductor film <NUM>. Further, the source line <NUM> and the drain line <NUM> extending in the longitudinal direction on the <FIG> are formed on the bottom gate insulating film <NUM>, the source electrodes <NUM> of each photosensor PS of the same column arranged in the longitudinal direction are formed integrally with the common source line <NUM>, and the drain electrodes <NUM> of each of the photosensors PS of the same column arranged in the longitudinal direction are formed integrally with the common drain line <NUM>. Source electrode <NUM>, drain electrode <NUM>, source line <NUM> and drain line <NUM> are at least electrically conductive and any light-shielding or light-transmitting material is applicable. Examples of the light-shielding conductive material include Cr, Mo, Ta, and W. Examples of the light-transmitting conductive material include indium oxide, zinc oxide, or tin oxide, or a mixture containing at least one of these (e.g., tin-doped indium oxide (ITO), zinc-doped indium oxide).

In the example of <FIG>, although the light shielding source line <NUM> and the drain line <NUM> overlap corners of the bottom gate electrode <NUM>, if they are arranged not to overlap the corners, the effect of the present invention is further exhibited.

Further, when the source line <NUM> and the drain line <NUM> are composed of a conductive and light-transmitting material, it is possible to freely lay out each corner portion of the bottom gate electrode <NUM>, the source line <NUM> and the drain line <NUM> while maximizing the effect of the present invention.

A common interlayer insulating film <NUM> is formed on the channel protective film <NUM>, the source electrode <NUM>, the drain electrode <NUM>, the source line <NUM>, and the drain line <NUM> of the photosensor PS. The interlayer insulating film <NUM> has an insulating property and a light-transmitting property, and is made of, for example, silicon nitride or silicon oxide.

A patterned top gate electrode <NUM> is formed on the interlayer insulating film <NUM>. Further, on the interlayer insulating film <NUM>, there is formed a top gate line <NUM> extending laterally, and the top gate electrode <NUM> of each photosensor PS of the same row arranged laterally are formed integrally with the common top gate line <NUM>. The top gate electrode <NUM> and the top gate line <NUM> are conductive and light-transmitting metal oxides, and are formed of, for example, indium oxide, zinc oxide, or tin oxide, or a mixture containing at least one of them (e.g., tin-doped indium oxide (ITO), zinc-doped indium oxide).

On the top gate electrode <NUM> and the top gate line <NUM>, not shown, a common protective insulating film is formed. The protective insulating film has an insulating property and a light-transmitting property, and is made of, for example, silicon nitride or silicon oxide.

Photosensor PS configured as described above is a transparent photoelectric conversion element having a semiconductor film <NUM> as a light receiving portion.

The above-described layers are formed on the glass substrates <NUM>, <NUM>, and <NUM> by appropriately performing a film-forming process such as a well-known PVD method or a CVD method, a mask process such as a photolithography method, and a thin film patterning process such as an etching method. Thereafter, the glass substrate <NUM> and the glass substrate <NUM> are positioned so that the color filter <NUM> and the photosensor PS are opposed to each other, and the substrates are bonded to each other using an adhesive such as an ultraviolet curing resin. To such a bonded product, a process of attaching the glass substrate 40and injecting the liquid crystal material LC, and the like is applied to produce the display device <NUM>.

In the photosensor PS described above, the bottom gate electrode <NUM> of the present invention as a light shielding film prevents the light from the backlight <NUM> from entering the semiconductor film <NUM>. Diffraction phenomenon of light occurs in the outer peripheral edge portion of the bottom gate electrode <NUM>.

<FIG> shows the principle of the diffraction phenomenon of light.

The restriction ST shown in <FIG> has an aperture AP, and when irradiating the light L1 toward the aperture AP, the light L1 normally travels straight as in the light L2 in <FIG> when passing through the aperture AP, but a portion of the light passing near the inner peripheral edge of the aperture AP is bent to be diffracted light L3, which causes a loss due to the diffracted light. The amount of diffracted light L3 increases as the circumferential length of the peripheral portion of the aperture AP increases.

Therefore, in order to reduce the amount of diffracted light L3 of the aperture AP, it is considered to be effective to shorten the circumferential length of the peripheral portion of the aperture AP.

Table <NUM> below shows the circumferential length and circumferential length ratio in a case where the shape of the aperture AP is a circular having a radius R and a case where the aperture is square under the same area conditions.

As can be seen from Table <NUM>, it can be said that the amount of light loss due to diffraction of light increases by about <NUM>% when the shape of the aperture AP is square as compared with the case where it is circular even if the area is the same.

In the present embodiment, according to the principle of suppressing the loss of light due to diffraction of light described above, as shown in <FIG>, the outer contour shape in the top view of the bottom gate electrode <NUM> is rounded.

In <FIG>, the bottom gate electrode <NUM> has four corners C1 to C4, and the radius of curvature of each of the corner portions C1 to C4 is R1.

Rectangle shown by a one-dot chain line in <FIG> is a virtual electrode <NUM> having the same area as the bottom gate electrode <NUM>.

W1 in <FIG> is the width of the bottom gate line <NUM>, <NUM>×W1 is the width in the longitudinal direction of the virtual electrode <NUM>, W2 is the width in the lateral direction of the virtual electrode. In the present embodiment, W1 is <NUM>, and W2 is <NUM>.

The radius of curvature R1 can be variously set, but the lower limit value is preferably larger than <NUM>.

As shown in <FIG>, to a film formed in a film forming process such as a well-known PVD method and CVD method, an elongated mask pattern <NUM> having four corner portions CP at right angles is transferred by a mask process such as a photolithography method and a thin film patterning process such as an etching method, while the width Wd of the mask pattern <NUM> is variously changed, to form film patterns <NUM> of the same material as the bottom gate electrode <NUM>.

Even if the corner portions CP of the mask pattern <NUM> are at right angles, roundness CR is formed in the four corner portions of the film pattern <NUM> formed.

If the width Wd of the mask pattern <NUM> is up to about <NUM>, straight portions SL are formed at both ends in the longitudinal direction of the film pattern <NUM>.

It was found that when the width Wd of the mask pattern <NUM> was narrowed down to <NUM>, the straight portion SL disappeared.

In this way, roundness is formed in each corner portion C1 to C4 of the bottom gate electrode <NUM> due to the forming step of the bottom gate electrode <NUM>, but by increasing the radius of curvature R1 than the radius of curvature of the roundness formed, the effect of the present invention is exhibited. For this reason, the lower limit value of the radius of curvature R1 is made larger than <NUM>.

In <FIG>, the four corner portions C1B to C4B of the semiconductor film <NUM> are rounded corresponding to the bottom gate electrode <NUM>. The reason why the corner portions C1B to C4B of the semiconductor film <NUM> are rounded is to secure the distance between the outer peripheral edge portion of the bottom gate electrode <NUM> and the outer peripheral edge portion of the semiconductor film <NUM> to a certain value or more. If the distance between the corner portions C1 to C4 of the bottom gate electrode <NUM> and the corner portions C1B to C4B is too close, the light shielding function of the bottom gate electrode <NUM> may be partially lost, so the rounding is formed in order to avoid this. Further, even if the corner portions C1B to C4B of the semiconductor film <NUM> are rounded, the light-receiving sensitivity of the semiconductor film <NUM> is not lowered if the area of the semiconductor film <NUM> is maintained. The radius of curvature R2 of the corner portions C1B to C4B is not particularly limited, but is set within a range in which the distance between the outer peripheral edge portion of the bottom gate electrode <NUM> and the outer peripheral edge portion of the semiconductor film <NUM> can be secured to a certain value or more.

In the present embodiment, the four corner portions C1B to C4B of the semiconductor film <NUM> are rounded, but when the distance between the outer peripheral edge portion of the bottom gate electrode <NUM> and the outer peripheral edge portion of the semiconductor film <NUM> can be secured at a certain level or more, a configuration in which the semiconductor film <NUM> is not rounded may be employed.

As described above, according to the present embodiment, by applying a rounding process to the corner portions C1 to C4 of the bottom gate electrode <NUM> as a light shielding film, it is possible to shorten the circumferential length of the bottom gate electrode <NUM>, and as a result, it is possible to suppress the loss of light from the backlight <NUM>.

The following embodiment is not according to the invention and is present for illustration purposes only.

<FIG> shows the outer contour shape of the bottom gate electrode and the semiconductor film in a top view of the photosensor according to a second embodiment of the present invention. In the second embodiment, the configuration other than the shape of the semiconductor film 200A and the bottom gate electrode 300A is the same as the first embodiment.

Outer contour shape in top view of the bottom gate electrode 300A is circular except for the connecting portion to the bottom gate line <NUM> is substantially circular. Further, the outer contour shape in the top view of the bottom gate electrode 300A is formed in substantially all curves except the connecting portion to the bottom gate line <NUM>.

Thus, by making the outer contour shape of the bottom gate electrode 300A substantially a circular shape in top view, as described with reference to <FIG> and Table <NUM>, it is possible to minimize the loss due to diffracted light.

In addition, the outer contour shape of the semiconductor film 200A is a concentric circle having the same center as the center Ct of the bottom gate electrode 300A. By setting the outer contour shape of the semiconductor film 200A to be concentric with the bottom gate electrode 300A, it is possible to maintain the light receiving sensitivity of the semiconductor film 200A.

The outer contour shapes of the bottom gate electrode 300A and the semiconductor film 200A are not limited thereto, an they may be elliptical or other curved shapes.

Although a liquid crystal display panel is exemplified as the display device in the above embodiment, the present invention is not limited to this, and the present invention can be applied to other types of liquid crystal display panels, and can be applied to other display devices such as an organic light-emitting diode panel in addition to the liquid crystal display panel.

In the above embodiment, the case where the photosensor of the present invention is provided in the inner layer of the liquid crystal display panel is exemplified, but the present invention is not limited to this, and the photosensor can be provided on the surface of the display device.

Claim 1:
A fingerprint sensor for a display device (<NUM>), having a plurality of photosensors (PS) arranged in a matrix,
each of the photosensors (PS) comprising:
a semiconductor film (<NUM>) for converting incident light into an electrical signal; and
a light shielding film (<NUM>) disposed on a lower layer side than the semiconductor film (<NUM>) and for blocking incidence of light to the semiconductor film (<NUM>) from the lower layer side,
characterised in that
the light shielding film (<NUM>) has four corner portions (C1, C2, C3, C4) in outer contour shape in a top view, wherein each of the corner portions (C1, C2, C3, C4) is rounded to suppress loss of light due to diffraction of light from the lower layer side occurring in an outer peripheral edge portion of the light shielding film (<NUM>).