JP2008165029A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display, having a drive circuit element on the same substrate in one body, the drive circuit being placed in stable operation, while suppressing deterioration in display contrast. <P>SOLUTION: An array substrate 10 has a transparent substrate 12 sectioned into a display region R1 and a drive circuit region R2; a first thin-film transistor 20 for driving pixel electrodes 44 formed in the display region R1 and disposed in matrix in the display region R1; a second thin-film transistor 50 which is formed in the drive circuit region R2 of the transparent substrate 12 and supplying a drive signal to the first thin-film transistor 20; a first conductive light-shielding film 14 provided on a lower-layer side of the first thin-film transistor 20; and a second conductive light-shielding film 44 provided on a lower-layer side of the second thin-film transistor 50, the array substrate 10 being such that the first light-shielding film 14 is grounded to be set to a ground potential and the second light-shielding film 44 is electrically connected to the gate electrode 56 of the second thin-film transistor 50. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device using a thin film transistor (TFT).

  The liquid crystal display device can have a thin display portion, and there is an increasing demand for use as a display device such as office equipment and a computer or a special display device.

  Among these, a liquid crystal display device in which a TFT using amorphous silicon (a-Si) or polysilicon (p-Si) is arranged on a matrix as a switching element has high display quality and low power consumption. Its development is actively underway.

  In particular, a TFT using p-Si (p-Si TFT) has a mobility about 10 to 100 times higher than that of a TFT using a-Si (a-Si TFT), and is used as a pixel switching element by taking advantage of the advantage. In addition, a driving circuit integrated liquid crystal display device in which a pixel TFT and a driving circuit TFT are integrally formed on the same substrate by using a p-Si TFT for a peripheral driving circuit is known.

  p-Si is classified into high-temperature polysilicon and low-temperature polysilicon depending on the difference in crystal growth process temperature. High-temperature polysilicon is formed by SPC (solid phase growth) at a high temperature, so that a uniform semiconductor layer can be easily obtained. For example, it is suitable for a projection type liquid crystal display device such as a projector that requires a high resolution of 300 ppi or more. Used for. However, it is necessary to form high-temperature polysilicon on an expensive substrate having excellent heat resistance such as a quartz substrate, and the production cost is higher than that of low-temperature polysilicon. Therefore, a projection type liquid crystal display device using low-temperature polysilicon. The practical application of this is desired.

  By the way, in TFT, when a semiconductor layer such as silicon is irradiated with light, a leak current flows. Therefore, in the liquid crystal display device, there is a problem that a leak current is generated in the pixel TFT due to light from the backlight and the contrast of the display is deteriorated. In the case of a projector that emits strong light, the above problem is likely to occur. Therefore, by providing a metal light-shielding film on the upper layer side and lower layer side of the pixel TFT, it is possible to prevent the semiconductor layer from being irradiated with light and to suppress the leakage current.

  In a liquid crystal display device having such a light-shielding film, a light-shielding film on the lower side of the pixel TFT is provided with a conductive material, electrically connected to the gate electrode of the pixel TFT, and the scanning line connected to the gate electrode. It is known that by reducing the electrical resistance, the occurrence of crosstalk or the like can be suppressed even during high-frequency driving, and stable operation can be performed (see, for example, Patent Document 1).

However, when the light shielding film on the lower layer side of the pixel TFT and the gate electrode are electrically connected, a leakage current is likely to occur, and there is a problem of degrading the display contrast and the like. In particular, since a TFT made of low-temperature polysilicon is more likely to generate a leakage current than a case of high-temperature polysilicon, in a liquid crystal display device using a TFT made of low-temperature polysilicon, when a light shielding film and a gate electrode are electrically connected, The contrast deterioration due to the leakage current becomes more remarkable.
JP 2005-202439 A

  The present invention has been made in view of the above problems, and provides a liquid crystal display device capable of suppressing display current deterioration by suppressing leakage current of pixel TFTs and capable of stable operation even when driving at a high frequency. The purpose is to do.

  The display device of the present invention is a liquid crystal display device configured by sandwiching a liquid crystal layer between an array substrate and a counter substrate, wherein the array substrate includes a transparent substrate partitioned into a display region and a drive circuit region, A first thin film transistor that drives pixel electrodes arranged in a matrix in the display region, and a second thin film transistor that is formed in the drive circuit region of the transparent substrate and supplies a drive signal to the first thin film transistor; A conductive first light-shielding film provided on a lower layer side of the first thin film transistor; and a conductive second light-shielding film provided on a lower layer side of the second thin film transistor, wherein the first light-shielding film is grounded The second light-shielding film is electrically connected to the gate electrode of the second thin film transistor.

  According to the present invention, it is possible to stabilize the operation during high-frequency driving while suppressing deterioration of display contrast.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing a liquid crystal display device 1 according to an embodiment of the present invention, and FIG. 2 is a plan view of a glass substrate 12 showing the arrangement of light shielding films 14 and 44.

  As shown in FIG. 1, the liquid crystal display device 1 includes an array substrate 10, a counter substrate 100 disposed to face the array substrate 10, and a liquid crystal layer 90 disposed between the array substrate 10 and the counter substrate 100. And. The array substrate 10 and the counter substrate 100 are bonded together by a seal member (not shown) that forms a predetermined gap for sandwiching the liquid crystal layer 90.

  The liquid crystal layer 90 is composed of a liquid crystal composition sealed between the array substrate 10 and the counter substrate 100. Further, polarizing plates 18 and 110 are respectively attached to both surfaces of the liquid crystal display device 1, and a light source (not shown) is disposed on the back thereof.

  The array substrate 10 is divided into a display region R1 for displaying an image and a drive circuit region R2 in which a drive circuit is formed on the outer periphery thereof, and the display region R1 includes a plurality of signal lines (see FIG. The driving circuit includes an n-type p-Si TFT (hereinafter referred to as a pixel TFT) 20 which is a switching element connected to the pixel electrode 44 at a crossing portion between a gate line (not shown) and a gate line (not shown). The region R2 includes an n-type p-Si TFT (hereinafter referred to as a drive circuit TFT) 50 that is a drive circuit element. The pixel TFT 20 is driven by a drive signal such as a video signal or a gate signal from the drive circuit TFT 50.

More specifically, each of the TFTs 20 and 50 has a transparent substrate 12 such as a glass substrate. The display region R1 on the upper surface of the transparent substrate 12 has a conductive material such as molybdenum-tungsten alloy. The semiconductor layer 22, the gate insulating layer 24, and the gate electrode 26 of the pixel TFT 20 are sequentially stacked via the first light-shielding film 14 made of the above metal material and the insulating layer 16 such as SiO ₂ , and the top gate type pixel TFT 20 is formed. Is formed.

  As shown in FIG. 2, the first light-shielding film 14 is provided in an island shape on the upper surface of the transparent substrate 12 corresponding to the semiconductor layer 22, and is drawn out to the outside of the transparent substrate 12 by a lead wire 14a and connected to the ground. And set to ground potential.

  The semiconductor layer 22 of the pixel TFT 20 includes a channel region 28, LDD (Lightly Doped Drain) regions 30 and 31 doped with phosphorus (P +) ions at a low concentration adjacent to the channel region 28, and LDD regions 30 and 31. It has a source region 32 and a drain region 34 which are adjacently doped with phosphorus (P +) ions at a high concentration, and is disposed in a region on the first light shielding film 14.

Further, the transparent substrate 12 upper surface of the driving circuit region R2, molybdenum - semiconductor layer of the second light-shielding film 44 and the SiO ₂ drive circuit via an insulating layer 16 such as TFT50 made of a conductive metal material such as tungsten alloy 52 The gate insulating layer 24 and the gate electrode 56 are sequentially stacked to form a top gate type driving circuit TFT50.

  Like the first light shielding film 14, the second light shielding film 44 is provided in an island shape on the upper surface of the transparent substrate 12 corresponding to the semiconductor layer 52, and the second light shielding film 44 is connected to each other. The line 44 a is electrically connected to the gate electrode 56 of the drive circuit TFT 50.

  The semiconductor layer 52 of the drive circuit TFT 50 includes a channel region 58, LDD regions 60 and 61 doped with phosphorus (P +) ions at a low concentration adjacent to the channel region 58, and phosphorus ( It has a source region 62 and a drain region 64 doped with P +) ions at a high concentration, and is disposed in a region on the second light shielding film 44.

An interlayer insulating layer 36 made of SiO ₂ or the like is provided on the gate insulating layer 24 and the gate electrodes 26 and 56, and a source electrode 38 and a drain connected to the semiconductor layer 22 in the display region R1 thereon. An electrode 40 is formed, and a source electrode 68 and a drain electrode 70 connected to the semiconductor layer 52 are formed in the drive circuit region R2.

  One end of the source electrode 38 and the drain electrode 40 is connected to the source region 32 and the drain region 34 of the pixel TFT 20 via contact holes provided in the interlayer insulating layer 36, and the other end of the drain electrode 40 is connected to the passivation. The pixel electrode 44 made of ITO disposed on the source electrode 38 and the drain electrode 40 is connected via the layer 42. The source electrode 38 extends across the LDD regions 30 and 31 so that the end on the drain electrode 40 side covers at least the LDD region 31 on the drain electrode 40 side, and faces the semiconductor layer 22 from above. The light is shielded. One end of each of the source electrode 68 and the drain electrode 70 is connected to the source region 62 and the drain region 64 of the drive circuit TFT 50 through a contact hole provided in the interlayer insulating layer 36. The end portion on the electrode 70 side extends over both LDD regions 60 and 61 so as to cover at least the LDD region 61 on the drain electrode 70 side, and shields light from above toward the semiconductor layer 22. Yes. Reference numeral 46 denotes an alignment film laminated on the passivation layer 42.

  In the counter substrate 100, a color filter layer 104, a common electrode 106, and an alignment film 108 are sequentially stacked on a transparent substrate 102 such as a glass substrate.

  As described above, in the liquid crystal display device according to this embodiment, the first light shielding film 14 formed on the lower layer side of the pixel TFT 20 is electrically connected to the ground and set to the ground potential, and the gate electrode of the driving TFT 50 56 is electrically connected to the second light shielding film 44 formed on the lower layer side of the driving TFT 50. For this reason, in the pixel TFT 20, by setting the first light-shielding film 14 to the ground potential, it is possible to suppress the occurrence of leakage current in the pixel TFT 20 and to reduce the deterioration of display contrast and to obtain a good display, and in the drive circuit TFT 50, The second light-shielding film 44 and the gate electrode 56 are electrically connected, the second light-shielding film 44 and the gate electrode 56 are disposed above and below the channel region 58 of the drive circuit TFT 50, and the second light-shielding film 44 is gated. By being electrically connected to the electrode 56, a channel is formed at both upper and lower interfaces of the channel region 58, whereby an on-current can be increased. Accordingly, since the drive circuit TFT 50 can be driven with a sufficient on-current, it is possible to improve the occurrence of malfunction due to variations in the characteristics of the drive circuit TFTs 50. Therefore, the on-current value of the drive circuit TFT 50 can be reduced. The drive circuit can be stably driven even during high frequency driving while suppressing the reduction, and the display quality can be improved. Further, even when the liquid crystal display device is a high-definition pixel of 300 ppi or more, or when the pixel TFT 20 is made of low-temperature polysilicon, the occurrence of leakage current of the pixel TFT 20 can be suppressed, and the projector has excellent display quality. It is possible to manufacture projection type liquid crystal display devices such as those using inexpensive low-temperature polysilicon.

It is sectional drawing which shows the structure of the liquid crystal display device in one Embodiment of this invention. It is a top view which shows arrangement | positioning of a light shielding film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 10 ... Array substrate 12 ... Transparent substrate 14 ... 1st light shielding film 44 ... 2nd light shielding film 20 ... Pixel TFT
22, 52... Semiconductor layers 26 and 56... Gate electrodes 28 and 58... Channel regions 32 and 62... Source regions 34 and 64. TFT

Claims (2)

In a liquid crystal display device configured by sandwiching a liquid crystal layer between an array substrate and a counter substrate,
The array substrate includes a transparent substrate partitioned into a display region and a drive circuit region, a first thin film transistor for driving pixel electrodes formed in the display region and arranged in a matrix in the display region, and the driving of the transparent substrate. A second thin film transistor formed in a circuit region for supplying a driving signal to the first thin film transistor; a conductive first light shielding film provided on a lower layer side of the first thin film transistor; and a lower layer side of the second thin film transistor. A conductive second light-shielding film,
The liquid crystal display device, wherein the first light-shielding film is grounded and set to a ground potential, and the second light-shielding film is electrically connected to a gate electrode of the second thin film transistor.   2. The liquid crystal display device according to claim 1, wherein each of the thin film transistors has an LDD region between a channel region and a source and drain region, and at least the LDD region is shielded by a source electrode connected to the source region. .

Images