JPS6285471A - Thin film diode - Google Patents

Abstract

PURPOSE:To obtain a thin film diode which has a small current even under high illumination by using an amorphous semiconductor film having 1.85eV or higher of a band gap in an I-type amorphous semiconductor layer, thereby reducing a photosensitivity. CONSTITUTION:A P-type amorphous silicon (a-Si) layer 81 is formed approx. 500Angstrom thick through a Cr electrode 51 on a transparent conductive film 2 which forms a scanning electrode on a glass plate 1, an I-type amorphous silicon carbide (a-SiC:H) layer 9 is then formed 0.2-0.5mum thick, and an N-type a-Si layer 83 is further laminated approx. 500Angstrom thick. The I-type a-SiC:H is produced by glow discharge-decomposing the mixture of silane gas and methane gas. When the mixture ratio of the silane gas to the methane gas is increased, for example, 10% to 30%, the band gap of the a-SiC:H is raised from 1.85eV to 2.3eV. The N-type layer is covered with a Cr electrode 52, and the side is coated with an insulating film 6. A current value which flows in a region of 0.5V or lower becomes 10<-11>A or lower as designated by two-dotted chain line 23, and a leakage current can be suppressed to sufficiently low value.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a thin film diode having an i-layer made of an amorphous semiconductor and used, for example, in an active matrix of a liquid crystal display device.

[Prior art and its problems]

FIG. 3 is a conceptual diagram of an active matrix liquid crystal display panel using thin film diodes to prevent crosstalk. S,, S,, S,... are scanning lines, Dl. DI+D3... indicates a data line, and these two lines are each formed on a transparent glass plate, and the glass plates are separated by a predetermined interval of about 10- so that the scanning line and the data line are perpendicular to each other. They are overlapped and liquid crystal 13 is injected between them. Antiparallel diodes 11 and 12 are connected in series with the liquid crystal as nonlinear elements to prevent crosstalk caused by voltage being applied to portions of the liquid crystal other than the selected points. This kind of display panel was developed in Japanese Patent Application 1986-57.
It is publicly known from the No. 273 publication. Figure 4 is an enlarged view of the scanning line side panel (al is a plan view,
(b) is a cross-sectional view taken along the line A-A of (al).A linear scanning electrode pattern 2 and a planar pixel electrode pattern 3 are both formed of a transparent conductive film on a glass plate 1.Scanning There is an amorphous silicon (a-3t) diode 41°42 above the electrode 2 and pixel electrode 3.a-
The 3i diodes 41 and 42 have dimensions of 15μ square to 30μ square, and each has a p-layer of about 500 layers, one layer of 0.5p thick, and a layer of about 500 layers formed by plasma CVD.
It is composed of an n-layer of about 1,000 layers, and Cr electrodes 51 and 52 with a thickness of about 1,000 layers are in contact with both the upper and lower surfaces. This diode pattern has Cr electrodes on transparent electrodes 2 and 3,
pin junction a-3t layer. After sequentially stacking Cr electrodes, the electrodes are partially patterned using photolithography. Next, an insulating film pattern 6 is formed to insulate the end face of the diode pattern. This insulating film pattern was decomposed by glow discharge using silane gas and ammonia gas.
It is produced by forming a 5tJa film with a thickness of 0.00 to several microns and then patterning it by photolithography. Furthermore, a metal wiring pattern 7 is formed on it by photolithography, short-circuiting the n-layer side electrode 52 of the A-3T diode 41 on the scanning electrode 2 and the transparent conductive film of the pixel electrode 3. a-3L diode 42 n
The layer-side electrode 52 and the transparent conductive film of the scanning electrode 2 are connected. In this way, the antiparallel connected diode 11 shown in FIG.
°12 is completed. In the active matrix panel using the diodes 11 and 12, when data is applied to the liquid crystal, a current of about 1 to 10 μA is passed through the diode, and the data is stored in the capacitance formed by the liquid crystal 13. Liquid crystal display devices are used in various brightness locations, including indoors and outdoors. Therefore, in order to obtain a clear image, it is important that the leakage current of the diodes 11 and 12 does not increase even under bright outdoor conditions. The solid line 21 in FIG. 5 shows the current/voltage characteristics of such a thin film diode in the dark.When the voltage is below 0.5V, the current flowing through the diode is below 10-''A, and when the voltage across the diode is set to this potential level, If the voltage is maintained, the signal written in the capacitance of the liquid crystal 13 will be maintained.However, when this diode is irradiated with 10,0001x light, the output current will be 0.5V as shown by the broken line 22.
Increases at voltages below. This is thought to be due to the photovoltaic current of the diode, but as the leakage current increases in the low voltage region, the signal is no longer retained in the capacitance of the liquid crystal 13, resulting in a decline in its function as an active matrix. Become. This problem must be solved not only for thin film diodes used in liquid crystal display devices, but also for the practical use of thin film diodes in general.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a thin film diode that has a diode structure with a small photovoltaic effect and has a small leakage current in a low voltage region during light irradiation.

[Key points of the invention]

According to the present invention, at least a portion in the thickness direction of one layer of the thin film diode is made of an amorphous semiconductor having a band gap of 1 and 85 eV or more, thereby reducing photosensitivity and achieving the above object. An amorphous semiconductor having a voltage of 1.85 eV or more is produced by glow discharge decomposition of a mixture of silane gas and 10% or more methane gas. It is effective to use amorphous silicon carbide.

[Embodiments of the invention]

1 and 2 show an embodiment of the present invention, and parts common to those in FIG. 4 are given the same reference numerals. In FIG. 1, a transparent conductive film 2 forming a scanning electrode on a glass plate 1 is shown.
P-type amorphous silicon (a-3t) 1181 is formed on the Cr electrode 51 to a thickness of approximately 500 mm, and then i-type amorphous silicon carbide (a
-SiC:H)N9 is formed to a thickness of 0.2 to 0.5 cr, and an n-type a-3t layer 83 is further laminated to a thickness of about 500 cr. Type 1 a-3iC:H is produced by glow discharge decomposition of a mixture of silane gas and methane gas. When the mixing ratio of methane gas to silane gas is increased from 10% to 30%, for example, a-S
The bandgap of iC:H is from 1.85eV to 2.3
It increases to eV. A Cr electrode 52 is deposited on the n-layer,
The characteristics of the diode whose side surfaces are covered with the insulating film 6 are that, as shown by the two-dot chain line 23 in FIG. 5, the current value flowing in the region of 0.5 V or less is 10-" A or less, which is a sufficiently low value as a leakage current. However, when the ratio of methane gas is reduced to 10% or less, the bandgap of the i-layer is about 1.8 eV, which is about the same as that of a-3t, and the diode characteristics follow the line in Figure 5. Although it is slightly improved from 22,
There was no big difference. The i-layer has a band gap of 1 and a − of 85 eV or more.
When an l-type amorphous 5l-0:H film with a band gap of 1.85 eV obtained by glow discharge decomposition of a mixed gas of Si II a and 10% or more Ot was used instead of the SiC layer 9, similar results were obtained. It worked. In addition, using a mixed gas of silane gas and ammonia gas, the band gap is 1.
．． When an 85 eV amorphous SiN:H film was produced and a diode was formed in place of the single layer 9, a -
The same effect as 3iC:H was obtained. In the embodiment shown in FIG. 2, after forming the I-type A-3L layer 82 on the P-type A-31 layer 81 to a thickness of 50 to 300 layers,
Band gap 1.85e is obtained using the same method as in the case of Fig. 1.
The l type a-SiC layer 9 of V or more is formed to a thickness of about 0.2 to 0.5 -, and then the 1 type a-3l layer 82 is formed again to a thickness of about 50 mm.
Laminated to a thickness of ~300, and finally an n-type a-3l layer 8
3 was formed. In this case, two layers 81. Characteristics are improved by interposing 1li82 with a narrow bandgap without directly contacting the 1st layer 9 with a wide bandgap to the n-layer 83, and the output current under light irradiation of 10,0O01x is shown at one point in Fig. 5. 2×10−” as shown by the dashed line 24
The performance of the active matrix using this diode has been improved. FIGS. 6 and 7 show an embodiment of a thin film diode using a metal-semiconductor Schottky junction. 6th
In the embodiment shown in the figure, l is in contact with the Cr electrode 51.
Type a-3l layer 82. The bandgap current showed a slightly large value (100% increase). However, the non-defective product rate was lower than that in the example shown in FIG. In the embodiment shown in FIG. 7, in contact with the Cr electrode 51,
After forming the PT electrode 53 with a thickness of 100 mm, an i-type A-8L layer 82. i-type a-SiC layer 9
゜I type a-3l layer 82. An n-type a-3l layer 83 was formed, and the output current value was comparable to the characteristic shown by the line 23 in FIG. The embodiment shown in FIG. 8 has a pi junction structure, and an A7. The metal electrode 5 such as Ag is 100 to 100
After forming the layer to a thickness of 0, the i-type a-3l layer 82. The l type a-3iC layer 9+ is replaced with the type a-5t layer 82. p-type a-
Thirty-one layers 81 were laminated in sequence, and this case also exhibited output characteristics comparable to line 23 in FIG.

【Effect of the invention】

According to the present invention, photosensitivity is reduced by using an amorphous semiconductor film with a band gap larger than 1.85 eV for part or all of the l-type amorphous semiconductor layer constituting the pin junction, pl junction, or Schottky junction. As a result, we were able to obtain a thin film diode with low current even under high illumination. By incorporating this diode, it was possible to form a high-performance active matrix panel. It is clear that the present invention produces exactly the same effect even if the stacking order of the layers constituting the diode is reversed.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views showing two embodiments of the present invention in diodes having pin junctions, Figure 3 is an explanatory diagram of an active matrix display panel, and Figure 4 is a thin film which is the object of the present invention. A part of an active matrix panel using diodes is shown, (a) is a top view, (b)
is a sectional view taken along line A-A of ial, FIG. 5 is an output characteristic diagram of an embodiment of the present invention and a conventional thin film diode, and FIGS. 6, 7, and 8 have a Schottky junction and a pi junction. FIG. 3 is a cross-sectional view showing three embodiments of the invention in a diode. 1 glass plate, 5: metal electrode, 51.52: Cr electrode, 53: Pt electrode, 81: a-3 ip layer, 82:
a-3liii, 83: a-3ln layer, 9: a-3lC
i layer. Figure 5 Figure 6

Claims (1)

[Claims] 1) A thin film diode having an i-layer made of an amorphous semiconductor, wherein at least a part of the i-layer in the thickness direction is made of the amorphous semiconductor with a band gap of 1.85 eV or more. 2) In the diode according to claim 1,
A thin film diode characterized in that the amorphous semiconductor with a band gap of 1.85 eV or more is amorphous silicon carbide produced by glow discharge decomposition of a gas mixture of silane gas and 10% or more methane gas.