JPH02213821A - Thin film transistor, active matrix circuit board and image display device using the transistor - Google Patents

Abstract

PURPOSE:To attain a high yield and to improve responsiveness as well as to eliminate the unequalness of a screen by equivalently increasing the (channel width)/(channel length) ratio of thin-film transistors (TFTRs) consisting of amorphous silicon films (a-Si) to provide a higher on current. CONSTITUTION:The width of the region in the transverse direction of the channels which attain electrical contact of drain electrodes 5 and source electrodes 6 of semiconductor film patterns is so disposed as to be on the inner side on gate electrodes 2 and the side walls of the semiconductor patterns existing on the lateral side of the channels are coated with the patterns of the drain electrodes 5 and the source electrodes 6. The side walls of the semiconductor patterns, therefore act as the drain electrodes 5 or the source electrodes 6 as well. Since the (channel width)/(channel length) ratio of the TFTRs is thereby equivalently increased, the on current of the TFTRs can be increased. The defective characteristics of the TFTRs which are provided in respective picture elements are decreased in the active matrix circuit board constituted of such TFTRs; in addition, the responsiveness is improved and the unequalness of the screen is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film transistor whose active layer is a semiconductor film mainly composed of silicon, an active matrix circuit board using the transistor, and an image display device.

[Conventional technology]

Conventionally, amorphous silicon film (amorphous 5il)
ioon.

A thin film transistor (amorphous 5ilicon Th1n
Film Tra-nsistor, hereinafter a-8
(abbreviated as i'l'FT) is attracting attention as a switching element for active matrix drive type display devices.

FIGS. 3(a) to 3(d) are cross-sectional views illustrating a conventional a-3i TFT. In Fig. 3 Ca) to (d), 1 is an insulating substrate, 2 is a gate electrode (first electrode), 5 is a gate insulating film (first insulating film), 4 is an a-Si film, 5 6 is a drain electrode (second electrode), and 6 is a source electrode (third electrode). a-8iT in Figure 3 (c) + (d)
FT is the second. The fifth electrodes 5 and 6 are connected to the first insulating film 3 and a
- Since it is inserted between the Si film 4, the first insulating film 3 and a
- The Si film 4 cannot be formed in a connected manner. Therefore, Figure 3 (
a) + (b) Especially a-8i of the structure of Fig. 3(b)
TFT is widely used. Note that, for example, Japanese Patent Application Laid-Open No. 59-113666 is related to this type of device.

[Problem to be solved by the invention]

The above-mentioned conventional technology is shown in Section 3 (b), and the a-
In the 8i TFT, since the current flows across the thickness direction of the a-8i film 4, the bulk resistance of the a-Si film 4 and the a-S
i film 4 and the second. It is affected by the state of the interface between the third electrodes 5°6.

Therefore, in order to prevent this, as shown in FIG. 7(a), the second. Third electrodes 5 and 6 and silicon-based film (a-8i film) 4
NFI silicon-based thin film doped with phosphorus P (a
-Si film) 51.61 can be inserted. According to this, the second. Although the contact resistance at 5.6 parts of the third electrode can be significantly reduced, the mobility of the a-8i TFT obtained from this is generally 0.6 to α5 d/Vs. Also second. Even if the contact between the third electrodes 4, 5 and the a-Si film 4 is improved, it often deteriorates due to disturbances in the manufacturing process, causing variations in the on-current and lowering the manufacturing yield. Therefore, improvements in the characteristics of a-8i TFTs, particularly increases in on-current, have been awaited.

In contrast, according to the present inventors, an a-8i TFT having a cross-sectional structure as shown in FIG. 7(b) can be considered. This is done by connecting the a-Si film 4 pattern to the gate electrode 2 in the length direction of the channel (in the direction of the source electrode 6 as seen from the drain electrode 5, or in the direction of the drain electrode 5 as seen from the source electrode 6).
The length of the second. This forms the third electrodes 5 and 6. This a-
It is conceivable that an effective mobility of V) 1 ad / V-s can be obtained with good reproducibility using a 3i TFT, but in this case, the drain current depends on the size of the four a-Si film patterns, especially the second. It largely depends on the length of the third electrodes 5 and 6. Therefore, in order to obtain a high on-current in this 'I'FT, it is necessary to make the four patterns of the a-8i film small so that the channel length is shortened.

When applied to switching elements of a matrix circuit board, there are limits to the photoetching process due to the large area of the board and the angle of 9, etc., and the a-S biofilm pattern cannot be made so small. Therefore, even if the mobility becomes high, there is a possibility that a high on-current cannot be expected. Note that an n+a-Si film can also be inserted into the electrode portion shown in FIG. 7(b).

The present invention provides a thin film transistor that can improve the characteristics of an a-3i TFT, particularly increase the on-state current, and provide an active matrix circuit board and an image display device using the transistor.

[Means for solving the problem] The above purpose is to provide a gate electrode (first electrode) on an insulating substrate.
and a gate insulating film (first insulating film) covering the gate electrode, and a region overlapping with and existing on the gate insulating film (first insulating film) with the gate electrode (first electrode). A silicon-based semiconductor film (A-Si film) pattern provided with a limited amount of silicon, and a drain electrode (second electrode) and a drain electrode (second electrode) disposed so as to partially cover the semiconductor film pattern.
In a thin film transistor comprising a summation electrode (third electrode), at least a region in the length direction of the channel that makes electrical contact with the drain electrode (first electrode) and the source electrode (third electrode) of the semiconductor film pattern. The region in the horizontal (width) direction perpendicular to
and a thin film transistor configured such that at least one of the regions in the width direction of the channel of the source electrode (third electrode) is arranged so as to protrude from the semiconductor pattern so as to cover the sidewall of the semiconductor pattern in the region, and the thin film transistor. This is achieved by an active matrix circuit board constructed using the above-mentioned active matrix circuit board, and an image display device constructed using the active matrix circuit board.

[Effect]

In the above thin film transistor, the region of the semiconductor film pattern existing on the gate electrode (first electrode) has a low resistance as the voltage is applied to the gate electrode (first electrode), and this semiconductor film has a low resistance region. The semiconductor film and the drain electrode (
By making electrical contact between the second electrode) and the source electrode (third electrode), the effects of the bulk resistance of the semiconductor film and the contact resistance between the semiconductor film and the metal film can be suppressed, resulting in a large drain current. Therefore, according to the present invention, the width of the region in the channel width direction that makes electrical contact with the drain electrode (second electrode) and the source electrode (third electrode) of the semiconductor film pattern is set to the gate electrode ( first electrode)
When the sidewalls of the semiconductor pattern located on the inside of the top and existing on the side of the channel are covered with the drain electrode (second electrode) and source electrode (third electrode) pattern, the semiconductor pattern As a result, the sidewalls also function as drain or source electrodes, and the (channel width)/(channel length) ratio of the channel of the thin film transistor becomes equivalently large, making it possible to increase the on-current of the thin film transistor. An active matrix circuit board made of thin film transistors can achieve a high yield by significantly reducing the number of thin film transistors with defective characteristics provided in each pixel. The characteristics of the active matrix circuit board constructed using the same make it possible to improve responsiveness and eliminate screen unevenness.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

FIGS. 1(a) to 1(d) are a partial plan view and a plan view of various parts showing a first embodiment of a thin film transistor and an active matrix circuit board using the transistor according to the present invention. 1(a) to 1(d) show a part of an active matrix circuit board using an amorphous silicon thin film transistor a-8i TFT as a switching element according to the present invention, and FIG. FIG. 1(b) is a cross-sectional view along A-A', FIG. 1(0) is a cross-sectional view along B-B', and FIG. 1(d) is a cross-sectional view along c-c'. be.

In FIGS. 1(a) to (d), 1 is an insulating substrate such as a glass plate, 2 is a first electrode (gate electrode) made of a metal film such as chromium Cr, and 3 is an insulating film such as a silicon nitride film. 4 is a semiconductor film mainly composed of silicon (a = Si film); 5 is a second electrode (drain electrode) made of a metal film such as aluminum At; 6 is the same (third electrode (source electrode, pole) made of a metal film such as At, 7 is ITO (Indium Tin 0)
8 is a gate line (gate bus line, scanning line), 9 is a drain line (drain bus line, signal line, data line). be. Figure 1(a)
The part surrounded by the circle is the TFT part, and the first section (d) is a cross-sectional view from the drain electrode 5 to the source electrode part. 11th J, (a) first electrode 2 and gate line 8,
The second electrode 5 and the drain line 9 are connected to each other. FIG. 1(b) shows how the a-Si film 4 is covered by the drain electrode 5 in the drain electrode part, and FIG. 1(Q) shows how the a=S1 film 4 is covered by the source electrode 6 in the source electrode part. shows.

A feature of the present invention is that the a-8i film 4 at the contact portion between the a-Si film 4, the drain electrode 5, and the source electrode 6 is aligned in the lateral (width) direction perpendicular to the length direction of the channel as shown in FIG.
b) As shown in t (Q), the side wall (end face) placed on the gate electrode 2 and existing in the lateral direction perpendicular to the length direction of the channel of the a-Si film 4 pattern is used as the drain electrode. 5 and the point covered with source electrode 6. Although both walls (side surfaces) of the a-Si film 4 are coated here, it is also possible to coat only one side, which equivalently increases the (channel width)/(channel length) ratio, so the on-current increases. Note that in this example, even in the a-8i TFT, 1 c
In order to obtain a mobility on the order of d/V-s, four patterns of a-Si films are connected to the gate electrode in the length direction of the channel as shown in FIG. 1(d) or FIG. 7(b). The drain electrode 5 and the source electrode 6 are made shorter than the length of the a-Si film 4 by at least the thickness of the a-Si film 4.

The second factor is the square root of the drain current of the a-3i TFT in FIG. This is a characteristic contingency that shows the relationship between and gate voltage (V). In FIG. 2, characteristic A is a-8 of this embodiment, which is the first factor.
The data and characteristic B1 obtained for iTFT are shown in Figure 7 (
The data obtained for the a-8i TFT in the conventional section 7 (a) of a), the characteristic B2 is n+a in the conventional Fig. 7 (a).
-8i membrane 51 a-8iTF when +61 is not inserted
Data obtained for T, characteristic B3 is No. 71m(b)
This is data obtained for a-3iTF'[' (no n+a-3i film is used in the electrode part).

Here, for the characteristic A of this embodiment shown in FIG.
was formed into an island pattern of 100 μm×100 μm, the width of the drain electrode 5 and the source electrode 6 was 120 μm, and the interval between the drain electrode 5 and the source electrode 6 was 10 μm.

For other characteristics B1 to B3, a-Si film 4f12
The island pattern is 0 sm (width) x 100 μm (length), and the width of the drain electrode 5 and source electrode 6 is 100 μm.
and the distance between the drain electrode 5 and source electrode 6 is 10 μm.
And so. Further, the thicknesses of the a-3i film 4 and the gate insulating film 3 were all the same. Therefore, apparently all a-8iTs have a channel width of 100 μm and a channel length of 10 μm.
It becomes FT.

However, in the a-8i TFT of FIG. 7(b) with characteristic B3, a
Since the entire -Si film 4 serves as a channel, the (channel width)/(channel length) ratio has a small value of 1. Also in the case of the a-8i'l'' FT according to the present invention shown in FIG. 1 with characteristic A, the a-S
It is the same as characteristic B3 except for the difference in the handling condition of the i-film 4. In characteristic B1, the n+a-8i film 51. of FIG. 7(a).
There is also a reduction in contact resistance at the electrode part due to 61, and cL3i
An effective mobility of /V·S was obtained. In characteristic B2, the drain current (2) was significantly reduced due to the large contact resistance of the electrode portion. On the other hand, in characteristic B3, 1 cy/l/V
-s effective mobility is obtained, but since the (channel width)/(channel length) ratio is small, the (channel width) of characteristic B1
/(channel length) ratio is 10 and the drain current I
p level decreases. Characteristics AO a-8iT according to the invention
In FT, the basic channel region is the y-factor (b
), but the drain current Ip is characteristic B.
3, and more than twice as large as characteristic B1. Assuming that the effective mobility is the same as that of characteristic B3, the (channel width)/(channel length) ratio is 5 times or more.

In this way, according to this embodiment, the a-S i
By arranging the side wall of the film 4 on the gate electrode 2 and providing the drain electrode 5 and source electrode 6 to cover this side wall, a large on-current can be obtained even with conventional processing accuracy, and a- By shortening the length of the 8i film 4 in the direction of the drain electrode 5 and source electrode 6, an even larger (channel width)/(channel length) ratio can be obtained, resulting in an even larger drain current (on current). can get.

FIGS. 3(a) and 3(b) are a partial plan view and a sectional view showing a second embodiment of a thin film transistor and an active matrix circuit board using the transistor according to the present invention. In the fifth factor Ca) and Cb), a part of the active matrix IJ circuit board used as the a-8iTFTk switching element according to the present invention is shown, and FIG.
-3i A plan view centered on the TFT section, and FIG. 3(b) is a sectional view taken along line A-A'. Figure 3 (a) l (b)
The same reference numerals as in FIGS. 1(a) to (d) indicate corresponding parts.

The a-3i TFT of this example is AA' in FIG. 3(a).
71k(a) in the cross-sectional structure of FIG. 3(b) showing the cross-section.
This is similar to FIG. 1(a) of the first embodiment in that the NFF1 silicon film 51.61 is inserted between the A-8I film 4, the drain electrode 5, and the source electrode 6. direction c
Figure 7 (
b). Also in this embodiment, the feature of the present invention is that the a-8i TFT section in FIG.
In the lateral (width) direction perpendicular to the length direction of the channel, the a-Si film at the contact portion between the 8i film 4, the drain electrode 5, and the source electrode 6 is gate-shaped in the same manner as in No. 11m(b), Ca). The point is that the drain electrode 5 and the source electrode 6 cover the side walls (end faces) disposed on the electrode 2 and existing in the lateral direction perpendicular to the length direction of the channel of the a-8i film 4 pattern.

According to this embodiment, since FIG. 7(a) is used for the cross-sectional structure in the length direction of the channel of the a-8i TFT, the (channel width)/(channel length) ratio is It can be determined by the patterning in Figure 7 (
It is larger than that using b). But a-S
The on-current is limited due to the bulk resistance of the i film 4 and the contact resistance between the n+a-8i film 51, 61 and the drain electrode 5 and source electrode 6, and CL5 ~ 0.5 d/V-s
In many cases, the mobility is , and element variations are likely to occur. However, by applying the present invention, [a-3i film 5
Current also flows from the side surfaces of the channel in the lateral (width) direction 9, increasing the on-state current. This effect is almost equivalent to that of the first embodiment.

FIGS. 4(a) and 4(b) are a partial plan view and a sectional view showing a third embodiment of a thin film transistor and an active matrix circuit board using the transistor according to the present invention. 4(a)+(b) shows a part of an active matrix circuit board using an a-8i TFT according to the present invention as a switching element, and FIG. 4(a) shows a-
A plan view centered on the 3i TFT section, and FIG. 4(b) is a sectional view taken along line A-A'.

In this embodiment, the drain line 9 and the display pixel electrode 7 are connected by a plurality of three a-8i TFTs in the first embodiment shown in FIGS. 1(a) to 1(d).

As in this embodiment, when increasing the on-current by increasing the (channel width)/(channel length) ratio, instead of using one TPT, multiple TPTs with small channel widths are arranged side by side. , the present invention is applied to the formation of the a-Si film 4, the drain electrode 5, and the source electrode 6, and the a-8i film 4 is placed on the gate electrode 2 in the lateral direction perpendicular to the length direction of the channel. , a - The side wall of the Si film 4 in the direction perpendicular to the length direction of the channel is connected to the drain electrode 5.
, it is more effective to cover it with the source electrode 6.

According to this embodiment, for example, a
-By changing the pattern dimensions of the Si film 4, drain electrode 5, and source electrode 6 (channel width)/(channel length)
Set the ratio to a value of 45. The a-8i film 4 is divided into three Ts with a small (channel width)/(channel length) ratio of 1.
As a PT, by applying the present invention to the drain electrode part and the source electrode part, (channel width)/(channel length)
The ratio can equivalently be made close to 15. This means that the (channel width)/(channel length) ratio is equivalently 5 for each TPT.
This is because it can be made to a value close to . This can be easily understood from the first embodiment. Further, by applying the present invention, a large on-current can be obtained even if the apparent channel length is increased, so there is an effect that the off-current of the TPT can be lowered.

FIGS. 5(a) and 5(b) are a plan view and a cross-sectional view of essential parts of an embodiment of an image display device using an active matrix circuit board using thin film transistors according to the present invention. 51J(a), (b), for example a-S 1T according to the invention of FIGS. 1(a) to (d)
An embodiment of an image display device consisting of a liquid crystal display device using an active matrix circuit board as an FTt-switching element is shown, FIG. 5(a) is a plan view of the main part, and FIG. 5(b) is a cross section thereof. It is a diagram. Figure 5 (a) + (b)
70 is, for example, a-8i shown in FIGS. 1(a) to (d).
Active matrix circuit board using TFT, 1~
7 indicates the same reference numerals and the same parts in FIGS. 1(a,) to (d). 20 is a polarizing plate, 1 is a glass plate, 21 is a color filter, 23 is a counter electrode of the display pixel electrode 7 made of a transparent conductive film, and 22.
26 is a protective film, 24 is an alignment film, and 25 is a liquid crystal filled in the void.

The image display device of this embodiment has the above-described configuration and is for color display. Further, this display device can be easily manufactured in the same manner as the manufacturing process of a well-known color liquid crystal display device. In addition to the configuration shown in FIG. 5, the actual display device is provided with various electric circuit control systems and illumination means from the back as a well-known image display device, but these are omitted.

〔Effect of the invention〕

According to the present invention, the on-current can be increased by increasing the (channel width)/(channel length) ratio of the a-Si thin film transistor isometrically. Therefore, in an active matrix circuit board constructed of such a-3i thin film transistors, the number of defective a-3i thin film transistors provided in each pixel is significantly reduced, and a high yield can be achieved. Furthermore, in an image display device using this active matrix IJ circuit board, since the A-3I thin film transistor and the active matrix circuit board constructed using it have the above-mentioned characteristics, it is possible to improve responsiveness and reduce screen unevenness. It has the effect of being able to eliminate this problem, and will greatly contribute to the development of this technical field.

[Brief explanation of the drawing]

11m (a) to (d) are partial plan views and cross-sectional views showing a first embodiment of a thin film transistor according to the present invention and an active matrix circuit board using the transistor; FIG. Drain current square root and G
(a) and (b) are a partial plan view and a sectional view showing a second embodiment of a thin film transistor and an active matrix circuit board using the transistor according to the present invention;
Figures (a) and (b) are partial plan views and cross-sectional views showing a third embodiment of a thin film transistor and an active matrix circuit board using the transistor according to the present invention, and Figures 5 (a) and (b) are A plan view and a cross-sectional view of main parts showing an embodiment of an image display device using an active matrix circuit board using thin film transistors according to the present invention, Part 3
FIGS. 7(a) to 7(d) are cross-sectional views illustrating conventional thin film transistors, and FIGS. 7(a) and 7(b) are cross-sectional views illustrating conventional thin film transistors. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... Gate electrode (first electrode), 5... Gate insulating film (first insulating film), 4...
Silicon-based semiconductor film (a-8'i film), 5... Drain electrode (second electrode), 6... Source electrode (third electrode), 7... Display pixel electrode, 8... ... Gate line (gate bus line), 9... Drain line (drain bus line), 51.61... N-type silicon thin film, 20.
...Polarizing plate, 21...Color filter, 22.26.
...Protective film, 23... Counter electrode, 24... Alignment film,
25...Liquid crystal, 70...Active matrix circuit board. η the same

Claims (1)

[Claims] 1. An insulating substrate, a first electrode provided on the insulating substrate serving as a gate electrode, and a first electrode provided on the first electrode pattern so as to cover the pattern. an insulating film formed on the first insulating film, a silicon-based semiconductor film pattern provided on the first insulating film so as to overlap with the first electrode and have a limited area; In a thin film transistor comprising a second electrode and a third electrode pattern which act as a drain electrode or a source electrode, respectively, and which are arranged so as to cover the semiconductor film pattern, the second electrode and the third electrode of the semiconductor film pattern are in electrical contact with each other. on the first electrode pattern, at least a lateral region perpendicular to the length direction of the channel,
and at least one of the sidewalls of the lateral region of the semiconductor film pattern is covered with the second and third electrode patterns so that the channel width is equivalently increased. Thin film transistor. 2. A plurality of thin film transistors according to claim 1 are provided in a matrix, and the first electrodes of the thin film transistors in the same row are connected to a first bus line, and the second electrodes of the thin film transistors in the same column are connected to a first bus line. An active matrix circuit board configured by connecting a second bus line to a second bus line. 3. A display pixel electrode is connected to the third electrode of each thin film transistor of the active matrix circuit board according to claim 2, and a counter electrode is provided opposite to the display pixel electrode, and the display pixel electrode and the counter electrode are provided. An image display device characterized in that a display cell is constructed by filling and sealing a liquid crystal in a gap between the two.