JP2525615B2 - Transistor - Google Patents

Description

The present invention relates to a transistor applied to an active matrix type liquid crystal display, an image sensor, a three-dimensional integrated circuit, or the like.

[Conventional technology]

Conventional thin film transistors are, for example, JAPAN DISPLAY′8
6 had the structure shown in 1986, P196-P199. This structure is generalized and its outline is shown in FIG. (A)
The drawing is a top view and the drawing (b) is a sectional view taken along line AA '. On an insulating substrate 201 such as glass, quartz, sapphire,
A source region 202 and a drain region 203, which are made of a polycrystalline silicon thin film and to which impurities serving as donors or acceptors are added, are formed. In contact with this, the source electrode 2
04 and a drain electrode 205 are provided, and a channel region 206 made of a polycrystalline silicon thin film is formed so as to contact with and connect the source region 202 and the drain region 203 on the upper side. The gate insulating film 207 is formed so as to cover them.
Is provided. Further, a gate electrode 208 is provided in contact with this.

[Problems to be solved by the invention]

However, the conventional thin film transistor has the following problems.

FIG. 3 shows a top view of the thin film transistor, and FIG. 4 shows its equivalent circuit.

The gate electrode 304 overlaps with the source electrode 301 via the gate insulating film to form a stray capacitance 401. Similarly, the gate electrode 304 is the drain electrode 302 through the gate insulating film.
To form a stray capacitance 402. Stray capacitance 401 and
402 is determined by the area where the source electrode 301, the drain electrode 302, and the gate electrode 304 overlap. When the pattern shift of the gate electrode 304 occurs in the direction of arrow 305 as shown in FIG. 3B, the stray capacitance 401 decreases and the stray capacitance 402 increases. On the contrary, when the pattern shift of the gate electrode 304 occurs in the direction of arrow 306 as shown in FIG.
Increases and stray capacitance 402 decreases. That is, the stray capacitance of the thin film transistor greatly varies due to the pattern shift of the gate electrode 304 with respect to the source electrode 301 and the drain electrode 302. The main cause of pattern displacement is the gate electrode 30
4 are misalignment, pitch misalignment between photomasks, etc. Therefore, the stray capacitance varies within the same substrate or between substrates, making it difficult to keep the circuit constant constant.
When applied to a liquid crystal display, the display quality varies and the image quality is degraded. Further, as the size of the liquid crystal display becomes larger, the pattern shift becomes larger and the display quality is remarkably deteriorated, which is a great obstacle to the size increase.

When applied to an image sensor or a three-dimensional integrated circuit, it becomes difficult to keep the circuit constant constant, which is a great obstacle to practical use.

The present invention solves such a problem, and an object of the present invention is to provide a transistor having no variation in stray capacitance.

[Means for solving problems]

The transistor of the present invention comprises a source wiring and a drain wiring made of a metal, a transparent conductive film or the like, and a silicon film containing impurities serving as a donor / acceptor, and one end thereof is extended to be connected to the source wiring and the drain wiring, respectively. A source electrode and a drain electrode that are arranged so as to be parallel to each other at least in part, a semiconductor layer that is in contact with the upper surface of the source electrode and the upper surface of the drain electrode, and connects the two, and A gate insulating film that covers the semiconductor layer, and a protruding portion that is parallel to the source electrode and the drain electrode, and is arranged so as to be orthogonal to the source electrode and the drain electrode, the semiconductor layer through the gate insulating film. It is characterized in that it is composed of a divided gate electrode.

Example 1 The present invention will be described in detail based on examples below. FIG. 1 shows an example of a transistor according to the present invention. (A)
Is a top view and (b) is a cross-sectional view at BB ′. On an insulating substrate 101 such as glass, quartz, sapphire,
A source electrode 102 and a drain electrode 103 made of a silicon thin film, such as polycrystalline silicon or amorphous silicon doped with impurities such as donors or acceptors, are formed. The film thickness is preferably 500-5000Å. A semiconductor layer 106 made of a silicon thin film such as polycrystalline silicon or amorphous silicon is formed in contact with the upper side of the source electrode and the upper side of the drain electrode so as to connect them. The film thickness is preferably 2000Å or less. A source wiring 104 made of metal, a transparent conductive film, or the like is in contact with the source electrode 102, and a drain wiring 105 is also in contact with the drain electrode 103. The whole is covered with a gate insulating film 107 such as SiO ₂ , SiN _x , and SiON. A gate electrode 108 made of a metal and a transparent conductive film is formed on the source electrode 102 and the drain electrode 10.
Source wiring without overlapping with 3 and gate insulating film 107
The semiconductor layer 106 is divided by the protrusion parallel to 104, and the source electrode 102 and the drain electrode 103 are formed in a cross shape so as to be divided via the gate insulating film 107. The gate insulating film 107 also serves as an interlayer insulating film that maintains insulation between wirings. The thin film transistor configured in this way is
Even if the gate electrode 504 is deviated in the direction of arrow 505 as shown in FIG.
The area where 02 and the gate electrode 504 overlap is constant and does not change. The same is true even if the gate electrode 504 has a pattern shift in the direction of arrow 506 as shown in FIG. Therefore, the stray capacitances 401 and 402 of the thin film transistor become constant without being affected by the pattern shift of the gate electrode. That is, it is possible to eliminate variations in stray capacitance within the same substrate or between substrates, and it is possible to keep the circuit constant constant. When applied to a liquid crystal display, there is no variation in display quality, and image quality can be significantly improved. Further, even if the liquid crystal display becomes large, the influence of the pattern shift is completely eliminated, and a large display with high image quality can be realized.

When it is applied to an image sensor or a three-dimensional integrated circuit, the circuit constant can be made constant and it can be put to practical use.

The thin film transistor of the present invention can be divided into transistors having two structures (a) and (b) as shown in FIG. The characteristics of the thin film transistor of FIG. 6 (a) are shown in FIG. 7, and the characteristics of the thin film transistor of FIG. 6 (b) are shown in FIG. The horizontal axis is the gate voltage V _GS , and the vertical axis is the logarithmic value of the drain current I _D. The drain-in voltage V _D is 4 (V), the channel length is 20 μm, and the channel width is 10 μm. Polysilicon is used for the silicon thin film in the channel region and its thickness is 20
It is 0Å. The thin film transistor having the structure shown in FIG. 6A is an offset gate, and has a smaller on-current than the conventional thin film transistor. In the thin film transistor having the structure of FIG. 6B, the off current is larger than that of the conventional thin film transistor due to the leak current of the semiconductor layer 603 in the portion which is not modulated by the gate electrode 604.
However, when the thin film transistors having these two structures are combined, the characteristics shown in FIG. 9 are obtained, and the characteristics identical to those of the conventional thin film transistor can be obtained.

A glass substrate is widely used as an insulating substrate for forming a thin film transistor. Generally, when a glass substrate is heat-treated and returned to room temperature, the dimension after the heat treatment becomes smaller than the dimension before the heat treatment. (Hereinafter called substrate shrinkage)
As an example, the shrinkage of # 7059 (made by Corning)
Shown in Figure 11. The horizontal axis shows the heat treatment temperature, and the vertical axis shows the amount of shrinkage of the substrate per 10 cm. As is clear from FIG. 11, a rapid shrinkage of the substrate occurs due to the heat treatment at 500 ° C. or higher.

The thin film transistor of the present invention, when the semiconductor layer 106 uses a semiconductor such as polycrystalline silicon formed at a high temperature of 500 ° C. or higher, shrinkage of the substrate is not a problem and is particularly effective. Can be created.

[Embodiment 2] FIG. 10 shows another embodiment of the present invention. As shown in FIG. 10 (a), a source electrode 1001 and a drain electrode 1002, which are formed of a silicon thin film such as polycrystalline silicon or amorphous silicon to which impurities serving as donors or acceptors are added, are formed in a horizontal plane. Source electrode 1001 and drain electrode
1002 may be a metal or a conductive thin film such as a transparent conductive film. A semiconductor layer 1003 made of a silicon thin film such as polycrystalline silicon or non-quality silicon is formed so as to connect both the source electrode 1001 and the drain electrode 1002. The whole is covered with a gate insulating film such as SiO ₂ , SIN _X , and SiON. A gate electrode 1004 made of a conductive material such as metal or a transparent conductive film is formed on this. This, the gate electrode
1004 divides the semiconductor layer 1003 by two protrusions parallel to the longitudinal direction of the source electrode 1001 and the drain electrode 1002. The gate electrode 1004 divides the source electrode 1001, the drain electrode 1002, and the semiconductor layer 1003 in the direction perpendicular to the source electrode 1001. In the thin film transistor thus configured, the area where the source electrode 1001 and the drain electrode 1002 and the gate electrode 1004 overlap with each other is constant even if the gate electrode 1004 shifts in the direction of the arrow 1005 as shown in FIG. 10B. Yes, there is no change in stray capacitance. Further, as shown in FIG. 10 (c), even if the gate electrode 1004 has a pattern shift in the direction of arrow 1006, it is completely the same.
Has the same effect as.

〔The invention's effect〕

 The present invention has the following excellent effects.

First, the stray capacitance of the transistor can be made constant regardless of the pattern shift. As a result, the circuit constant of the active matrix substrate using the transistors or the logic circuit using the transistors can be made constant.

Second, since the circuit constant can be made constant, the active matrix substrate or the logic circuit can be easily designed.

Thirdly, since the tolerance for pattern deviation can be designed to be large, strict process control as in the past is not necessary, and the yield is greatly improved.

Fourth, since the stray capacitance can be made constant regardless of the pattern deviation, it is possible to eliminate the variation within the substrate or the variation between the substrates, the quality can be greatly improved, and the uniform characteristics can be obtained on the large area substrate. It is possible to realize the formation of a transistor.

Fifth, the transistor characteristics are as small as those of the conventional ones. Both OFF current and large ON current can be compatible.

Sixth, there is no problem with the shrinkage of the substrate due to the heat treatment of the glass substrate for forming the transistor. This is particularly effective when using a thin film formed at a high temperature such as polycrystalline silicon.

As described above, the thin film transistor of the present invention has many excellent effects. Its application range is wide-ranging, such as active matrix substrates for displays, their peripheral circuits, image sensors, and three-dimensional integrated circuits.

[Brief description of drawings]

1 (a) and 1 (b) show the structure of the thin film transistor of the present invention, (a) is a top view, and (b) is a sectional view. 2A and 2B show the structure of a conventional thin film transistor, FIG. 2A being a top view and FIG. 2B being a sectional view. 3A, 3B and 3C are top views showing the structure of a conventional thin film transistor. FIG. 4 is an equivalent circuit diagram of the thin film transistor. 5, (a) (b) (c), FIG. 6, (a) (b),
10 (a), (b) and (c) are top views showing the structure of the thin film transistor of the present invention. FIG. 7 is a graph showing the characteristics of the thin film transistor of the present invention, and FIG. 8 and FIG. FIG. 11 is a graph showing the storage amount with respect to the temperature of the glass substrate. 101, 201 ... substrate 102, 202, 301, 501, 601, 1001 ... source electrode 103, 203, 302, 502, 602, 1002 ... drain electrode 104, 204 ... source wiring 105, 205 ... drain wiring 106, 206, 303, 503, 603, 1003 ... Semiconductor layer 107, 207 ... Gate insulating layer 108, 208, 304, 504, 604, 1004 ... Gate electrode 401, 402 ... Stray capacitance

Claims (1)

(57) [Claims] 1. A source wiring and a drain wiring made of a metal, a transparent conductive film or the like, and a silicon film containing an impurity to serve as a donor / acceptor, one end of which is extended to be connected to the source wiring and the drain wiring, respectively. A source electrode and a drain electrode arranged so as to be parallel to each other at least in part, a semiconductor layer which is in contact with the upper surface of the source electrode and the upper surface of the drain electrode, and is covered so as to connect the two. A gate insulating film that covers the semiconductor layer, and a protruding portion that is parallel to the source electrode and the drain electrode, and is arranged so as to be orthogonal to the source electrode and the drain electrode, the semiconductor layer through the gate insulating film. A transistor consisting of a split gate electrode.