JPS61174673A - thin film transistor - Google Patents

Abstract

PURPOSE:To increase the ON current, by allowing a limited thickness to each of the amorphous semiconductor film, the gate insulator film and the gate electrode. CONSTITUTION:The gate insulator film 3, so thin that thickness is less than 2,000Angstrom , can cover the border of the gate electrode 2 which is less than 700Angstrom thick. Light falling on the amorphous semiconductor film 4, after transmitting the gate electrode 2 or the insdulator film 5, is capable of transmtiting the film 4 that is less than 300Angstrom thick with hardly undergoing absorption to generate no light-induced leak current. The voltage applied to the gate electrode 2 is impressed to the amorphous semiconductor film 4 undergoing slight voltage drop across the insulator 3 to allow a large ON current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a thin film transistor used in an active matrix liquid crystal display device or the like.

[Summary of the invention]

This invention makes it possible to eliminate the need for light shielding of the thin film transistor and increase the on-current by reducing the thickness of the amorphous semiconductor film used as the semiconductor film in the thin film transistor used in active matrix display devices and the like. .

[Conventional technology]

Conventionally, as shown in FIG. 2, a gate electrode 2. with a thickness of 1500 angstroms or more is placed on a transparent insulating substrate 1 made of glass or the like. Gate insulation 111 with a thickness of 3000 angstroms or more!3. 4. Amorphous semiconductor film with a thickness of 2000 angstroms or more. A thin film transistor consisting of a two-layer film of an n0-type amorphous semiconductor film 6 and a metal electrode film 7 as a source or drain electrode, and an insulating film 5 has been known.

[Problem that the invention seeks to solve]

However, the conventional thin film transistor shown in FIG.

When light enters the amorphous semiconductor film 4 whose main component is silicon during operation of a transistor, a leakage current flows through the amorphous semiconductor film 4, which has high photoconductivity. For the purpose of using it in a bright place, a light shielding layer 1119 must be formed on the transistor, and the gate electrode 2 also has a light shielding layer 15
In order to cover the step caused by the gate electrode 2, which has a thickness of 1,500 angstroms or more, which must be formed to a thickness of 1,000 angstroms or more, the gate insulation needs to be 1 m! Since the thickness of the semiconductor layer 3 must be 3000 angstroms or more, the voltage applied to the gate electrode 2 is not sufficiently applied to the semiconductor layer 11!4, resulting in a disadvantage that a large on-current cannot be obtained.

Therefore, in order to solve these conventional drawbacks, the present invention aims to provide a thin film transistor that can obtain a large on-current without the need for light shielding even in a bright place.

[Means for solving problems]

In order to solve the above problems, the present invention eliminates light absorption by the semiconductor film by making the amorphous semiconductor film as thin as 300 angstroms or less.

We realized a thin film transistor that does not require light shielding, and achieved a large on-current by using a thin gate electrode and gate insulating film. Figure 3 shows a graph plotting the relationship between the thickness of the semiconductor film and the off-leakage current due to light in a thin film transistor using amorphous silicon as the semiconductor film that is not shielded from light, based on experimental results. As mentioned above, when the thickness of the amorphous silicon film is less than 300 angstroms, the off-leakage current due to light becomes about picoampere and can be ignored in practice.

[Effect]

The thin film transistor configured as described above.

Even if light is incident, the amorphous semiconductor film is thin (less than 300 angstroms), so there is almost no light absorption (electrons and holes generated by light absorption are immediately recombined on the surface of the amorphous semiconductor film, so there is no electrical conduction). The degree does not change either.

Since there is no need for light shielding, the thickness of the gate electrode may be 1,500 angstroms or less, ie, 700 angstroms or less. Therefore, even if the gate insulating film has a thickness of 2,000 angstroms or less, the step caused by the gate electrode can be covered. When the gate insulating film becomes thinner, the gate voltage is effectively applied to the semiconductor film, so that the on-current of the transistor can be increased from the conventional level of about 10E-5 amperes to about 10E-4 amperes.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In the cross-sectional view of the channel portion of the thin film transistor of the present invention shown in FIG.
- Gate electrode made of metal such as chromium or aluminum with a thickness of less than 700 angstroms2. 3. Gate insulating film made of silicon oxide or silicon nitride with a thickness of 2000 angstroms or less. 4. Amorphous semiconductor film mainly composed of silicon with a thickness of 300 angstroms or less. A two-layer film of a source or drain electrode, an amorphous semiconductor film 6 mainly made of n-type silicon, and a metal electrode film 7 made of chromium and aluminum, and silicon oxide.

Insulation made of silicon nitride! A thin film transistor consisting of 5 is formed. Since the gate electrode 2 is as thin as 700 angstroms or less for a thin film transistor, the gate insulating film 3 can cover the end of the gate electrode 2 even if it is as thin as 2000 angstroms or less. The light transmitted through the gate electrode 2 or the gate electrode 2 and incident on the amorphous semiconductor film 4 is
Since the gate insulating film 3 is thin (less than 2,000 angstroms), almost no light is absorbed (it does not pass through and generate a leakage current), and since the gate insulating film 3 is thin (less than 2,000 angstroms), the voltage applied to the gate electrode 2 is The voltage loss caused by the insulation 1113 can be applied to the crystalline semiconductor 111114 with reduced voltage loss, and the on-state current of the thin film transistor of the present invention can be increased.

[Effects of the Invention] As explained above, the present invention reduces the thickness of the amorphous semiconductor film, eliminates the need for a light shielding film, simplifies the structure, and reduces the thickness of the gate electrode and gate insulating film. In particular, iWI has a large on-current! ! I! This has the effect of realizing a transistor.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the channel portion of a thin film transistor according to the present invention, FIG. 2 is a cross-sectional view of the channel portion of a conventional thin film transistor, and FIG. It is a figure showing a relationship. 2-・-・---------Gate electrode 3----------Gate insulating film 4----------1 amorphous semiconductor film 2I2
1

Claims (1)

[Claims] (1) The amorphous semiconductor film is formed on an insulating substrate and includes a gate electrode, a gate insulating film, an amorphous semiconductor film mainly composed of silicon, a source electrode, and a drain electrode. 300 angstroms or less in thickness, the gate insulating film has a thickness of 2000 angstroms or less, and the gate electrode has a thickness of 700 angstroms or less.