JPS62219665A - Superlattice thin-film transistor - Google Patents

Abstract

PURPOSE:To obtain the titled transistor, photoconductivity thereof is inhibited and which is difficult to be subject to the effect of stray light and displays stable performance characteristics, by using a superlattice constituted by alternately laminating a large number of a-Si:H layers and a-SiNx:H layers as a semiconductor layer. CONSTITUTION:A superlattice 3 organized by alternately laminating a large number of a-Si:H and a-SiNx:H is employed as a semiconductor layer in a thin-film transistor using an amorphous semiconductor layer. A gate electrode G is formed at a predetermined position on a substrate 1 consisting of glass, etc., a gate insulating film 2 composed of a-SiO2, etc. is laminated on the gate electrode and a-Si:H layers and a-SiNx:H layers having prescribed layer thickness (such as 10Angstrom -100Angstrom ) are laminated alternately in a large number, and the superlattice 3, the whole layer thickness thereof is brought to approximately 2,500Angstrom , is shaped in a stratified manner. A source electrode S and a drain electrode D are formed at predetermined positions on the superlattice 3, and carriers flowing in the superlattice 3 are controlled by applied voltage to the gate electrode G between the source electrode S and the drain electrode D.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a thin film transistor (
(hereinafter referred to as TPT), the semiconductor layer is a-S
By creating an amorphous superlattice structure consisting of i:H and a-SiNx:H, we are aiming to suppress the photoconductivity seen in conventional ASI TFTs and to realize TFTs that are less affected by stray light. It is something that

[Industrial application field]

The present invention relates to a TPT formed using an amorphous semiconductor.

Hitherto, a-3t type TPT in particular has been widely used as a switching element for driving, for example, a matrix type liquid crystal display device or a near image sensor, since it can be formed at low temperature and in a large area.

[Conventional technology]

Conventional TPTs include a single film of a-Si:H between a source electrode and a drain electrode, and carriers flowing within this single film are controlled by a gate electrode provided through a gate insulating film. It is known what has been done.

[Problem that the invention seeks to solve]

The a-3i:H single film used in the above conventional TPT is
Because of their high photoconductivity, when exposed to light, they tend to malfunction due to stray light, for example, the light causes them to turn on even though they have been turned off.

[Means for solving problems]

The present invention uses a superlattice formed by alternately laminating a large number of a-3i:H layers and a-SiNx:H layers as a semiconductor layer.

[For production]

Compared to the conventional a-3i:H single film, the superlattice with the above structure has a different current flowing when exposed to light (hereinafter referred to as photocurrent) and a current flowing when not exposed to light (hereinafter referred to as photocurrent). (referred to as dark current) is very small. Therefore, TPT using this superlattice as a semiconductor layer has suppressed photoconductivity, is less susceptible to stray light, and exhibits extremely stable operating characteristics.

〔Example〕

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

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention. In the figure, a gate electrode G is formed at a predetermined position on a substrate 1 made of glass or the like, and a gate insulating film 2 such as a SiO2 and a superlattice 3 to be described later are provided in a layered manner on top of the gate electrode G. A source electrode S and a drain electrode are formed at predetermined positions, and the carriers flowing in the superlattice 3 between the source electrode S and the drain electrode are controlled by the voltage applied to the gate electrode G. .

The superlattice 3 has a predetermined layer thickness (for example, 10 to 100 layers).
The structure has a structure in which a large number of a-3i:H layers and a-SiNx:H layers having a layer of 1000000000000000000 persons are laminated alternately, and the total layer thickness thereof is, for example, about 2,500000000000000000000000000000000000000000000000000000000000000000000 People. Such a superlattice 3 is manufactured by switching gas for each layer by plasma CVD, optical CVD, or the like. For example, a-3i
When producing the :H layer, SiH4 gas diluted with hydrogen is used, and when producing the a-SiNx:H layer, 5iHa gas and NH3 gas diluted with hydrogen are used.

Therefore, in the superlattice 3 having the above structure, the dark current and photocurrent in the in-plane direction, the a-3trH layer and the a-S
FIG. 4 shows the results of measuring the relationship between the iNx:H layer thickness (the thickness of the former layer is Ls and the thickness of the latter layer is LN). Note that here, Ls=L, and a-SiNxs
Flow rate ratio of 5iHa gas and NH3 gas when creating H layer (
NNH3/Ns, Hsr) was fixed at 1. A voltage of 100 V was applied in the in-plane direction of this superlattice 3, and white light of 25 L x was used as the irradiation light when measuring the photocurrent.

In Figure 4, in the case of the a-3i:H single film shown for reference, there is a very large difference of about 3 orders of magnitude between the dark current (indicated by the square mark) and the photocurrent (indicated by the △ mark). In other words, it can be seen that the current changes significantly just by shining light on it (high photoconductivity). On the other hand, in the case of the above-mentioned superlattice, the difference between the dark current (indicated by .) and the photocurrent (indicated by ○) is very small compared to the above-mentioned a-Si:H single film, and the photoconductivity is is suppressed. Therefore, the TPT of this example using such a superlattice is not affected by stray light,
It has very stable operating characteristics.

In addition, in the same figure, the layer thickness Ls (-L,) is 100 people.

As the number of participants decreases from 30 to 10, it can be seen that both the dark current and the photocurrent decrease, and the photoconductivity is further suppressed. Considering this point, the above layer thickness Ls,
It is desirable that L is 30 Å or less.

Next, FIG. 2 shows a schematic configuration of a second embodiment of the present invention. In the figure, a superlattice 13 is sandwiched between a source electrode S and a drain electrode from both ends. The superlattice 13 has the same structure as the superlattice 3 described above, and has the relationship shown in FIG. 4. Even with such a configuration, the photoconductivity can be suppressed to a very low level, making it less susceptible to stray light.

Next, FIG. 3 shows a schematic configuration of a third embodiment of the present invention. In this figure, the structure shown in FIG. 1 is obtained by removing the gate insulating film 2, that is, the superlattice 23 is directly formed on the glass substrate 1 and the gate electrode G. This superlattice 23 was also produced in the same manner as the superlattice 3.13 described above, and has the relationship shown in FIG. 4. The reason why the gate insulating film 2 can be removed here is as follows.

First, in a superlattice with a total film thickness of 2400 layers,
FIG. 3 shows the relationship between the voltage applied in the film thickness direction and the current flowing in the film thickness direction at that time.

Note that the electrode area at this time was 3 va x 3 vm.

In the same figure, in the case of L, = L, = 100 people (curve I), the voltage is 10"' regardless of the magnitude of the applied voltage.
It has a large resistivity of Ω·cm or more. L,=Ls=3
In the case of 0 people (curve ■) and the case of = Ls = 10 people (curve ■), the thickness of each layer becomes gradually thinner compared to the case of curve I, and leakage current due to the tunneling effect occurs accordingly. When the applied voltage is around 5 to IOV, it is 1013Ω・
It maintains a resistivity higher than the mark.

These resistivities in the film thickness direction are significantly larger than the resistivity in the in-plane direction, which is less than 10 Ω·cm. Therefore, due to this anisotropic property of resistivity, the film is substantially insulated in the thickness direction, and the gate electrode G
There is no need for a gate insulating film between the superlattice 23 and the superlattice 23.

If the gate insulating film is not required in this way, the structure becomes very simple, which is very advantageous in terms of reliability and cost reduction. Furthermore, as in the first and second embodiments, photoconductivity can also be suppressed, making it less susceptible to stray light.

〔Effect of the invention〕

According to the present invention, since photoconductivity can be suppressed to a small level by the superlattice structure, it is possible to realize a TPT with stable operating characteristics that are not affected by stray light. Furthermore, by utilizing the anisotropy of electrical resistance in the superlattice, a simple TPT without a gate insulating film can be realized.

[Brief explanation of drawings]

1, 2, and 3 are the first and second embodiments of the present invention, respectively.
, a schematic configuration diagram showing the third embodiment, and FIG. 4 shows in-plane dark current and photocurrent in the superlattice according to the present invention,
FIG. 5 is a diagram showing the relationship between each layer thickness (L, t, s). FIG. 5 is a diagram showing the relationship between applied voltage and current in the thickness direction of the superlattice. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Gate insulating film, 3.13.23...Superlattice, S...Source electrode, D...Drain electrode, G...Gate electrode,

Claims (1)

[Claims] 1) In a thin film transistor using an amorphous semiconductor layer, the semiconductor layer is a superlattice (3, 13 , 23). 2) The superlattice thin film transistor according to claim 1, wherein the a-Si:H layer has a thickness of 30 Å or less. 3) The a-Si:H layer and the a-SiN_x:H
2. The superlattice thin film transistor according to claim 1, wherein each of the layers has a thickness of 30 Å or less. 4) The superlattice according to any one of claims 1 to 3, characterized in that there is no gate insulating film (2) between the superlattice and the gate electrode (G). Thin film transistor.