JPH0764114A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device mounted with a photoelectric conversion device which is improved in S/N by lessening the loss of a signal charge quantity and is simultaneously improved in heat radiatability to prevent the influence of a temp. rise. CONSTITUTION:The photoelectric conversion elements constituted by forming a metallic layer 121 on a substrate 109, forming bipolar type transistors(Trs) thereon, constituting the base regions of the TRs of deep bases 118a and shallow bases 118b and subjecting the deep bases 118a and the metallic layer 121 to Schuttky joining are formed on the TFT substrate of a liquid crystal panel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device having a liquid crystal display section and a photoelectric conversion section on the same substrate.

[0002]

2. Description of the Related Art A liquid crystal element for sandwiching a liquid crystal substance between two electrode substrates and applying a voltage to change the optical properties of the liquid crystal to display an image is more compact and has higher definition than a CRT. It is widely used as a display device.

A device having more various functions has been proposed by integrating a photoelectric conversion device in a part of the liquid crystal display device. For example, by irradiating the eyeball of the observer with infrared light and detecting the infrared light, the line-of-sight direction of the observer can be detected.

In such a system, a liquid crystal display device and a detection device, which have been conventionally arranged separately, are integrated, which greatly contributes to downsizing of a camera or a video device.

7 and 8 show the structure of a liquid crystal display device equipped with a conventional photoelectric conversion device. In the figure, 101 is a photoelectric conversion unit, 102 is a liquid crystal display unit, 103 is a substrate, 104 is a thin film transistor (hereinafter referred to as "TFT"), 105 is a pixel electrode, 106 is a TFT channel region, 107 is a source diffusion layer, and 108 is a source diffusion layer. Is a drain diffusion layer, 109 is a substrate, 1
10 is a gate insulating layer, 111 is a gate electrode, 112, 1
14 to 116 are insulating layers, 113 is an electrode, 809 is a substrate,
813 is an electrode, 812, 814 to 816 are insulating layers, 81
7 is a collector, 818 is a base, and 819 is an emitter.

FIG. 7A is a schematic plan view of a liquid crystal display panel having a photoelectric conversion section. The liquid crystal display panel has a liquid crystal display unit 102 and a photoelectric conversion unit 101 on a single substrate 103 made of a transparent material such as semiconductor or glass. As shown in FIG. 7, a pair of photoelectric conversion units is arranged on the left and right, but if necessary, only one or two pairs including the upper and lower sides are arranged. Each photoelectric conversion unit can have a line sensor structure in which a large number of photoelectric conversion elements are arranged in a line, or an area sensor structure in which two photoelectric conversion elements are arranged in a two-dimensional array.

FIG. 7B is a sectional view of the liquid crystal display section.
A TFT 104 having a thin film single crystal semiconductor as a channel region 106 on a semiconductor substrate whose surface is insulated or a substrate 109 made of a transparent insulating material such as glass, and a pixel electrode made of a transparent conductive material such as ITO connected to a drain diffusion layer 108 of the TFT 104. 105, source diffusion layer 107 of TFT 104
Source electrode 113, which is connected to
It is composed of the gate electrode 111 of the TFT. Adjacent TFTs are separated by a thick insulating layer 116, and the surfaces of the TFTs are insulated by multiple insulating layers 112, 114, 115. A liquid crystal is sandwiched between the substrate shown in the figure and a substrate (not shown) having a counter electrode to form a liquid crystal display panel. Also,
In order to improve gradation and image quality, another electrode that is grounded may be provided below the pixel electrode 105 and a storage capacitor may be formed between the pixel electrode 105 and the pixel electrode 105.

In an actual liquid crystal display device, the pixel TFT 10
4 are arranged in a two-dimensional array, and the gate electrodes 111 and the source electrodes 113 are connected in the horizontal and vertical directions. The wiring to which the gate electrode is connected is called a scanning line, and turns on / off the channel of the TFT at a predetermined timing.
Further, the image signal is input to the signal line to which the source electrode is connected, and when the TFT is turned on, a predetermined image signal is written in the pixel electrode. The difference between the pixel potential at this time and the potential of the counter electrode on the other substrate is applied to the liquid crystal. The liquid crystal changes the light transmittance according to the applied voltage and displays image information.

FIG. 8 is a sectional view of the photoelectric conversion section.
A collector 817, a base 818, and an emitter 819 of a bipolar transistor are arranged on a semiconductor substrate whose surface is insulated or a substrate 809 made of an insulating transparent material such as glass. The emitter is extracted by an electrode 813 to give a signal output. A thick insulating layer 81 is provided between adjacent photoelectric conversion elements.
6 separated and the surface is a multi-layered insulating layer 812, 814, 8
It is insulated by 15. This type of photoelectric conversion element is B
ASIS (Base-Store Type Image)
The sensor is called a sensor type, in which holes generated by incident light are accumulated in the base 818 and an electron current proportional to the number of holes is output by the amplifying action of the bipolar transistor. For details of the operating principle of BASIS, see, for example, IEEE Transactions on Elec.
tron Devices Vol. 36, No.
1, January 1989 pp. 31-38
"A Novel Bipolar Imaging
Device with Self-Noise Re
reduction Capability ”N. Tan
aka, T .; Ohmi, Y. Nakamura
It is described in.

[0010]

In the liquid crystal display device equipped with the conventional photoelectric conversion device, the thickness of the thin film silicon cannot be made sufficiently thick, so that a part of the incident light passes through the thin film silicon and is lost in the signal charge amount. Occurs and the S / N decreases. In particular, when the wavelength of the light to be detected is long, such as the line-of-sight detection sensor, the loss is large. Since the photoelectric conversion device is formed on the insulating layer,
The heat dissipation is extremely poor, and the temperature rise due to the heat causes (1) the dark current of the photoelectric conversion device to increase and the S / N to deteriorate. (2) the on-resistance of the transistor changes and the output voltage fluctuates. there were.

[0011]

The present invention is a display device which solves the above-mentioned problems, and more specifically, it comprises a first substrate provided with a thin film transistor as a switching element for each pixel and a second substrate. What is claimed is: 1. An active matrix liquid crystal display device, comprising a liquid crystal sandwiched between the first substrate and a photoelectric conversion unit in the vicinity of the display unit, wherein the photoelectric conversion unit is provided between the first substrate and the photoelectric conversion unit. The liquid crystal display device is characterized in that a metal layer overlapping at least a part of the conversion portion is provided, and the semiconductor layer of the photoelectric conversion portion and the metal layer are Schottky-bonded.

In the present invention, the photoelectric conversion unit is a base storage type image sensor (Base-Sto).
re Type Image Sensor and charge coupled device (Change Coupled Device)
e) is preferably used. Further, when the above image sensor is used, it is preferable that the photoelectric conversion portion has first and second base regions having different depths, and the deeper base region is in contact with the metal layer.

[0013]

EXAMPLES AND OPERATION The present invention will be described in detail below with reference to examples.

(Embodiment 1) The liquid crystal display device of the present invention is the same as the conventional liquid crystal display device in the configuration of the liquid crystal display portion and the image operating method. Therefore, it has the liquid crystal display panel shown in FIG. FIG. 1 is a cross-sectional view of the photoelectric conversion part of this embodiment.
It shows in (a). In the figure, 109 is a substrate, 112, 114-1
16 is an insulating layer, 113 is an electrode, 117 is a collector, 11
Reference numerals 8a and 118b are bases, 119 is an emitter, and 121 is a metal layer. In this embodiment, the metal layer 121 forming a Schottky junction with silicon of the photoelectric conversion portion is present on the semiconductor substrate whose surface is insulated or the substrate 109 made of a transparent insulating material. In this embodiment, Pt or Pt
Si was used. The base region of the bipolar transistor includes a deep base 118a in contact with the metal layer 121 and a shallow base 118b in contact with the deep base 118a and not reaching the metal layer 121, and has an impurity concentration of 10 ¹⁶ to 10 ¹⁸ cm ^−3. . The n-type collector 117 surrounds the base and contacts the metal layer 121. Inside the shallow base 118b is an n ⁺ type emitter 119 located on the surface of the silicon layer, to which the emitter electrode 113 is connected. The adjacent pixels are insulated from each other by the insulating layer 116 of SiO _{2, and} the surface of the silicon layer is the interlayer insulating layer 112 of silicon oxide and SiN.
Are sequentially covered and protected by the interlayer insulating layers 114 and 115.

The photoelectric conversion principle of this embodiment is exactly the same as that of the conventional example described above. However, the metal layer 121 and the deep base 11
The presence of 8a has the following features.

Since the silicon layer is in contact with the metal layer,
Since the heat generated by the photoelectric conversion device is released to the external terminal through the metal layer, the temperature rise is suppressed.

Infrared light that has passed through a silicon layer thickness of several microns is reflected by the metal layer and has an opportunity to contribute again to the photoelectric conversion signal.

Due to the depletion layer extending to the silicon by the metal layer, the charges in the region close to the substrate are more efficiently collected in the base region.

The above will be described with reference to FIG. 2A shows the spread of the depletion layer when the potential of Pt is substantially equal to that of the base 118a, and FIG. 2B shows the spread of the depletion layer when the potential of Pt is substantially equal to the potential of the collector 117. Show. The spread of the depletion layer according to the present invention is shown in FIG.
In (b), by biasing Pt in the positive direction with respect to the base region, the region of the deep base 118a near the metal layer 121 is depleted. Due to the electric field in the depletion layer, holes generated in this region are easily collected in the base region. In the conventional structure, some of the carriers generated in this region diffuse to the adjacent element, which is a cause of S / N deterioration. In this example, the photoelectric conversion efficiency is improved because an opportunity to generate electron-hole pairs is obtained.

The stray light / external light incident from the substrate side is completely reflected by the metal layer 121 and does not cause noise.

Next, the manufacturing process of the liquid crystal display device of this embodiment will be described.

The manufacturing process of the first substrate having the metal layer is shown in FIG. First, a silicon substrate 302 whose surface is oxidized by 5000 to 10000Å is prepared (a). After removing the oxide film of the necessary part of the metal layer by about 3000 to 8000Å,
A metal that forms a Schottky junction with n-type silicon, such as Pt, Co, or Al, is deposited on the order of 1000 to 5000 Å by a sputtering method, a CVD method, or the like (b). Next, the metal layer 303 on the thick oxide film 301a is removed by polishing to make the surface flat (c). The oxide film serves as a stopper during polishing. Next, another silicon substrate 304 is prepared and bonded to the above-mentioned polished wafer (d). After bonding, heat treatment is performed at a temperature not exceeding the melting point of the metal layer 303 to improve bonding strength. Finally, the silicon layer is thinned to a desired thickness by polishing.

The subsequent steps will be described with reference to FIGS. 1 and 7. Since the display part and the photoelectric conversion part have different thicknesses of the silicon layer, once they are made thin, they are made to have a thickness of 3 to 5 μm necessary for the photoelectric conversion part by epitaxial growth. After that, only the display portion may be thinned to 3000 Å to 1 μm.

In this embodiment, the silicon layer is 1E13-15.
cm ⁻³ of n-type silicon was used. First, a deep base region 118a is formed in this silicon layer by ion implantation and thermal diffusion. Next, the p-type layer of the display section (channel region 106)
And the shallow base layer 118b were formed by ion implantation and thermal diffusion. In the present embodiment, the p-type layer and the deep base layer of the display section have a concentration of 1E16 cm ⁻³ and the shallow base layer concentration of 1E17 cm ⁻³ , but each has a concentration of 1E1 depending on the purpose.
Approximately 5 to 1E17 cm ^-3 and 1E16 to 1E18 cm ^-3 are possible.

Next, an insulating film 116 for separation is formed by the LOCOS method. The thickness was set to 10000Å. Next, the n ⁺ regions of the source diffusion layer 107 and the drain diffusion layer 108 of the MOSFET and the emitter 119 were formed by ion implantation and heat treatment. Implanted dopant is Ph ^+, injection volume was set to 5E15 cm ^-2, As ⁺ as the dopant,
The injection amount can be about 1E15 to 1E16 cm ⁻² .
In the cross-sectional view, the source and drain n ⁺ layers reach the substrate 109, but this is not always necessary.

A polysilicon electrode is formed on the previously formed gate oxide film of 200 to 1000 Å. Ion implantation of the source and drain is usually performed with the polysilicon gate being self-aligned. BPS by CVD method
After depositing a G film (insulating film 112) of about 7,000 Å, a contact hole is formed and an aluminum electrode 113 is deposited and patterned.

After that, the first interlayer insulating layer 114 is deposited and the transparent pixel electrode 105 is formed in the display portion. The pixel electrode 105 is in direct contact with the drain 108, and
It was formed using TO (Indium Tin Oxide). Finally, a silicon nitride film (insulating layer 115) to be a passivation film is formed.

As another method of manufacturing the first substrate (TFT substrate), ELTRAN (Epitaxial Layer) is used.
r Transfer on Porous Sili
con) method. In this method, a substrate (FIG. 4) having an epitaxial layer formed on a silicon wafer having a surface made porous by 5 to 50 μm is used instead of the second silicon wafer in FIG. 3D. This wafer has a silicon substrate 40 after the epitaxial layer 403 side is bonded.
1. The porous silicon 402 is subsequently removed by etching with a mixed solution of HF and H ₂ O ₂ to obtain an SOI substrate using an epitaxial layer having a uniform film thickness and good quality. TF
The manufacturing method of T and the photoelectric conversion part is exactly the same as that of the case of the first substrate.

Further, as the TFT structure, the one having polysilicon as a channel, the one having a single crystal by recrystallizing polysilicon, or the one having amorphous silicon as a channel has the same effect.

Furthermore, even if the conductivity type of the MOS transistor is the p-channel type and the conductivity type of the bipolar transistor is the pnp type, the effect of the present invention will not be impaired at all, since a simple voltage change is required. .

(Embodiment 2) FIG. 5 shows a cross section of a photoelectric conversion portion according to a second embodiment of the present invention. In this embodiment, the deep base formed in the first embodiment is omitted. In this embodiment, since the depletion layer does not spread to the base region due to the metal layer, the crosstalk is similar to the conventional one, but the heat dissipation effect, the infrared light reflection effect, and the effect of blocking visible light from the back surface are obtained in the first embodiment. Is obtained in the same manner as. Further, there is an advantage that the step of forming a deep base is not necessary and the transistor structure is the same as the conventional one.

(Embodiment 3) FIG. 6 is a sectional view of a photoelectric conversion portion according to a third embodiment of the present invention. In this embodiment, the photoelectric conversion unit is C
CD (Charge Coupled Device)
And The basic configuration and operation of the CCD are, for example,
M. IEEE Trans by Yamagishi et al.,
Electron Devices, Ed-38, p
p. 976 (1991). In this embodiment, a negative bias is applied to the p-well a in FIG. 6 so that the depletion layer does not extend. Even in the case of CCD, infrared light passing through silicon can be reflected by the metal film and photoelectrically converted again.

Further, it is possible to obtain an ideal light shielding film for visible light incident from the back surface. Further, although the heat generated by the CCD is 10 to 100 times larger than that of the BASIS photoelectric conversion device, this heat can be discharged to the outside through the metal film. In this embodiment, the S / N of the photoelectric conversion device was improved and the output voltage was stabilized.

[0034]

As described above, in the liquid crystal display device of the present invention, the heat generated in the photoelectric conversion portion is discharged, dark current increase due to temperature rise is prevented, infrared light is reflected, and the silicon layer is again formed. The efficiency of photoelectric conversion can be increased by making the light incident on the base layer, which promotes the convergence of carriers to the base region, prevents crosstalk, and makes the metal layer ideal for external light from the back side and visible light that becomes stray light. It can also serve as a light-shielding film.

Therefore, according to the present invention, the photoelectric conversion device is formed on the thin film, and is easily exposed to a relatively high temperature by a backlight or the like, and is high for light having a relatively long wavelength such as infrared light. Even a liquid crystal display device having a visual axis detection function that requires detection sensitivity can be stably used without lowering the visual axis detection function.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a photoelectric conversion unit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a depletion layer of a photoelectric conversion unit according to the present invention.

FIG. 3 is a manufacturing process diagram of a photoelectric conversion unit according to an embodiment of the present invention.

FIG. 4 is a diagram showing another manufacturing process of the photoelectric conversion section of the embodiment of the present invention.

FIG. 5 is a sectional view of a photoelectric conversion unit according to a second embodiment of the present invention.

FIG. 6 is a sectional view of a photoelectric conversion part according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a conventional liquid crystal display panel.

FIG. 8 is a cross-sectional view of a conventional photoelectric conversion unit.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 24, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

Such a liquid crystal display device and a detection device are integrated.
The downsized system is suitable for downsizing cameras and video devices.
It will contribute a lot.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

Of a liquid crystal display device equipped with a photoelectric conversion device.
Structural examples are shown in FIGS. 7 and 8. In the figure, 101 is a photoelectric conversion unit, 102 is a liquid crystal display unit, 103 is a substrate, 104 is a thin film transistor (hereinafter referred to as "TFT"), 105 is a pixel electrode, 106 is a TFT channel region, 107 is a source diffusion layer, and 108 is a source diffusion layer. Is a drain diffusion layer, 109 is a substrate, 11
0 is a gate insulating layer, 111 is a gate electrode, and 112 and 11
4 to 116 are insulating layers, 113 is an electrode, 809 is a substrate, 8
13 is an electrode, 812, 814 to 816 are insulating layers, 817
Is a collector, 818 is a base, and 819 is an emitter.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

In a liquid crystal display device equipped with a photoelectric conversion device
In this case, for example, since the thickness of the thin film silicon cannot be made sufficiently thick, a part of the incident light passes through the thin film silicon, resulting in a loss in the amount of signal charges and a decrease in S / N. In particular, when the wavelength of the light to be detected is long, such as the line-of-sight detection sensor, the loss is large. Since the photoelectric conversion device is formed on the insulating layer,
The heat dissipation is remarkably poor, and the temperature rise due to heat causes (1) the dark current of the photoelectric conversion device to increase and the S / N to deteriorate. (2) The on-resistance of the transistor changes and the output voltage changes. There were cases where problems such as

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 31/108 H04N 5/66 102 A H01L 31/10 C

Claims (4)

[Claims] 1. A liquid crystal is sandwiched between a first substrate provided with a thin film transistor as a switching element for each pixel and a second substrate, and a photoelectric conversion unit is provided in the vicinity of a display unit on the first substrate. In the active matrix liquid crystal display device having the above, a metal layer overlapping at least a part of the photoelectric conversion unit is provided between the first substrate and the photoelectric conversion unit, and the semiconductor layer of the photoelectric conversion unit and the semiconductor layer are provided. A liquid crystal display device characterized in that a metal layer is Schottky bonded. 2. The liquid crystal display device according to claim 1, wherein the photoelectric conversion unit is a base storage type image sensor. 3. The photoelectric conversion part has first and second base regions having different depths, and the deeper base region is in contact with the metal layer. Liquid crystal display device. 4. The liquid crystal display device according to claim 1, wherein the photoelectric conversion unit is a charge coupled device.