JPH0317631A - Thin-film diode element - Google Patents

Abstract

PURPOSE:To suppress the change in photocurrent by incident light so as to diminish the change and to stabilize the image display of a liquid crystal display panel by disposing an a-Si film of thin-film diode (TFD) elements formed of a 3-sheet mask system in such a manner that the exposed end face thereof is positioned on the side inner than the side faces of lower light shielding metal and upper electrodes. CONSTITUTION:An ITO electrode 2 and the lower light shielding metal 17 are formed on a glass substrate 1 and after both are patterned, the a-Si film 4 and an upper electrode 9 are formed thereon. The exposed end face of the a-Si film 4 intrudes to the inner side of the upper electrode 9 and the lower light shielding metal 17 on the side faces thereof and the surface area of the a-Si film 4 decreases if an anisotropic etching is executed by using the resist and the upper electrode 9 as a mask. The a-Si film is so constituted that the exposed end face thereof introduces to the inner side than the side face of the lower light shielding metal and the upper electrode in such a manner and, therefore, the incident light is shielded by the lower light shielding metal and the upper electrode even if the incident light is scattered light. The image change by the photocurrent is thus minimized and the image display of the liquid crystal display panel is stabilized to an easily visible state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film diode element used as a nonlinear display element for driving a liquid crystal display panel or the like. [Conventional technology] The drive method for liquid crystal display panels that is currently widely used is as follows:
There are passive types that do not include a switching element and active types that have a switching element. Recently, active matrices using thin-film active elements have been viewed as promising for high-density display. These active elements include thin film transistors (TPTs) and thin film diodes (TFDs).
) etc. are used, especially amorphous silicon (a-Si)
For example, a magazine, Proc. IEE [! , Vol-5
9, p. 15661579. It is already known from Figure 4 shows an equivalent circuit of the diode ring of the nonlinear element described in the above literature. TF
Forward threshold of D {i voltage V is 0, depending on the material,
3-1. O V, and a higher voltage is preferable for liquid crystal display panels, so two rows of TFD groups connected in series in multiple stages are used, and in order to have bidirectionality, two rows of TFD groups are used. The contacts are connected in a reverse direction. Furthermore, it is well known that the photocurrent of a TFD element changes due to light, and as a countermeasure for this, a structure fabricated using a four-mask method is also known. FIG. 5 is a schematic cross-sectional view showing the structure. This structure consists of an a
-Si film process, and this a-St film process consists of n layer 5 and l layer.
It has a p-i-n junction consisting of a layer 6 and a p-layer 7, on which an insulating film 8 of SiNx and an upper electrode 9 located at the top are formed. In this structure, the upper and lower light-shielding films 3 made of a-St film block light in both the upper and lower directions, while the sides of the a-Si film 4 are sealed with insulating films 8, which improves the light-shielding properties. In addition, when used in a liquid crystal display panel, the a-St film does not come into direct contact with the liquid crystal material, so it is free from impurities in the liquid crystal material and impurities remaining in the glass substrate and TFD substrate. Or, it has a structure that eliminates the negative effects of foreign substances. The first mask is ITO wire 8i2, the second mask is light shielding film 3 and a-SiWi4 soil, and the third mask is insulating film 8.
The upper electrode 9 is formed in the fourth image. Next, the structure of a liquid crystal display panel using this four-mask type TFD element will be shown. Fig. 6 is a partially cutaway perspective view of the same, which will be described including the manufacturing process. In FIG. 6, there is a glass substrate l1 on which TFDIO is formed, a color filter 13 and an ITOtliil on the glass substrate l2.
Using a printing technique, several hundred to twenty polyimide resins for orienting the Rin crystal material are applied to each of the opposing surfaces on the opposing substrate consisting of these three parts formed in this order.
Approximately 00 fl [Print to form a film. After the boiled resin is heat-treated, the resin surface is rubbed with shallow lines using a rubbing machine in order to align the liquid crystal 15 in a desired direction. A gap adjusting agent made of, for example, glass iron or plastic balls, which adjusts the gap between the two substrates, is appropriately scattered as a spacer on the screen portion of the glass substrate II side, which is one of the upper and lower substrates obtained, and then the TFDIO side is After aligning the pixel electrode pattern on the substrate 11 and the electrode pattern on the opposing substrate side, the upper and lower substrates are adhered to the periphery of the screen, excluding the liquid crystal injection port, using a sealing adhesive. Next, both the upper and lower substrates are placed in a vacuum container, and the gap between the upper and lower substrates is depressurized and then released to atmospheric pressure, and liquid crystal is instantly injected to the full. After this, seal the injection port with ultraviolet resin. The liquid crystal display panel shown in FIG. 6 is obtained by cutting both the upper and lower substrates thus completed into a predetermined size, and pasting polarizing plates 16 of plastic film on the upper and lower sides of the display area. When this liquid crystal display panel is irradiated with the light shown by the arrow in Fig. 6, an image signal voltage is applied to each pixel, and an electric field is applied between the upper and lower substrates, the liquid crystal display panel changes according to the signal voltage level. Depending on the voltage and transmittance characteristics of , images are displayed by blocking or transmitting light. The color filter 13 is used to filter the three primary colors of red and blue. When displayed using green, a full-color display is possible by combining the displayed colors.

However, the above four-mask type diode element structure is
The large number of masks used increases manufacturing man-hours, resulting in higher product costs.As a countermeasure, a three-mask TFD element structure has been proposed, in which the number of masks is reduced by one. ing. Fig. 7 is a schematic cross-sectional view showing the structure, and parts common to Fig. 5 are indicated by the same symbols. In Figure 7,
The first layer on the glass substrate l is an ITO electrode 2, on which an a-Si film and an upper electrode 9 are formed in order. The side surfaces are processed by dry etching so that they are perpendicular to the thickness direction. T of this kind of three-mask method
The FD element structure is also used, for example, in the liquid crystal display panel shown in FIG. 6, but in the manufacturing process, a film for orienting the liquid crystal material is applied to the image display screen portion of the TFD side substrate, including the upper surface of the TFD element. At this time, since the a-Si film 4 has a vertical shape in the thickness direction, the alignment film is formed filling the image display screen portion without any gaps. [Problems to be Solved by the Invention] The above discussion has mainly focused on TFD elements used in liquid crystal display panels, but the three-mask type TFD element structure still has the following problems.

As mentioned earlier, a photocurrent is generated in a TFD due to light, so when it is incorporated into a liquid crystal display panel like the one shown in Figure 6 to display an image, the image does not change depending on the illuminance level of the viewing environment. is desired. However, for indoor viewing, the illuminance is generally 3000 lux (hereinafter referred to as L×
10.00 or less when outdoors.
It will be viewed in an environment of 0Lx or higher. Outdoor illuminance 10
．． At ooOLX or higher, the surface reflection of the glass surface of the liquid crystal display panel becomes strong, making it difficult to see the image, so approximately 1
A light shielding property is required for illuminance of about 0,OOOLκ.

Therefore, a TFD with three masks as shown in Figure 7 is used.
It has already been proposed to form a lower light-shielding metal on the ITO pole 2 of the element structure to shield light, and this is basically based on the same purpose as the four-mask structure shown in Figure 5. It is something. However, when doing this, as mentioned above, the side shape of a-SiIl9I4 is perpendicular to the thickness direction, and in this case, when the incident light to the TFD element is a parallel beam, the lower light shielding metal Even if the light is blocked by the light blocking performance of the a-Si film 4, when scattered light is incident on the side surface of the a-Si film 4, a change in the t current at a constant voltage of the IV characteristic of the TFD occurs depending on the amount of incident light. This change in t current depends on the amount of incident light, so in order to keep the display condition of the panel as low as possible, the change in current must be small, and as mentioned earlier, 3000 Lκ under indoor light. It is necessary to ensure that the image display does not change, or that the change is extremely small, under an environment where the outdoor light is around 10,000K. The present invention has been made in view of the above-mentioned points, and its purpose is to provide a TFD element capable of suppressing changes in light t2it caused by incident light to be small and stabilizing image display on a liquid crystal display panel. The purpose is to provide. [Means for Solving the Problems] In order to solve the above problems, the TFD element of the present invention has the following features:
The a-sill of the TFD element, which is implemented using a three-mask method, is arranged so that its exposed end face is inside the side surfaces of the lower light-shielding metal and the upper electrode. [Function] Since the TFD element of the present invention is constructed as described above,
Since the a-Si film is recessed from the lower light-shielding metal and the upper electrode, the incident light does not directly irradiate the a-Si, reducing changes in the light flow due to light. In other words, in the case of parallel light flux, the light is blocked by the lower light shielding metal and the upper electrode, and in the case of scattered light, the incident angle of the incident light is blocked to a certain extent, suppressing photocurrent changes and adversely affecting image display. It works to prevent it from coming out.

(Example) Hereinafter, the present invention will be explained based on examples.

Figure 1 (A). (B) shows a schematic cross-sectional view of the TFD element of the present invention, each of which is a cross-sectional view seen from a direction perpendicular to each other, and parts common to those in FIG. 7 are designated by the same reference numerals. The difference between Fig. 1 (A) and Fig. 7 is that the lower light-shielding metal l
7 was used, and the exposed end surface of the a-Si film of the pin junction was positioned Wb inward from the side surfaces of the upper electrode 9 and the lower smoked metal 17. When the TFD element is horizontally controlled in this way, when light enters from the direction of the arrow, the lower light-shielding metal l7 and the upper it-19
The light will be blocked by

Next, the method for manufacturing the TFD element of the present invention will be described.
The TFD element of the present invention can be manufactured by a three-mask method, and FIGS. 2(A) to (D) and (l!) to
(H) is a schematic cross-sectional view showing the main manufacturing process, and each corresponds to the other when viewed from a perpendicular direction. In addition, the same reference numerals are used here as well for parts common to those in Fig. 7. First, ITOqi2 was placed on a glass substrate l.
A film with a thickness of about 1,000 Ω and a sheet resistance of 20 Ω/hole is formed by sputtering or electron beam evaporation, and then a film with a thickness of about 100 Ω/hole is formed using these methods.
The membrane of 0 to 2000 people is used as the lower light-shielding metal 17. Thereafter, using the first mask pattern, the lower light-shielding metal 17 is etched to the pattern size by a photolithography process and then by an etching method. Next, the etching solution is changed and the ITO electrode 2 is etched to the same size as the lower light-shielding metal 17 [Figure 2 (A)]
, (E) ).

Next, in order to form an a-Sl film on this, the p layer 7 is formed by several hundred to 400 Al layers 6 by plasma CVD method.
1000 to 3000 people, n layer 5 to several lOO to 4o
Deposit in the order of o people. The p-layer is doped with boron, and the n-layer is doped with phosphorus. Next, after going through a photolithography process using the second mask pattern, it was transferred to a dry etching device, and an etching gas of 10% oxygen added to Cl24 was introduced, and a radio frequency (RF) i force of 50 was applied.
Apply 0W and reduce the gas pressure to 0. Dry enching under I Torr [Figure 2 (B). (F)). Thereafter, the upper electrode 9 is formed on top of this by sputtering or electron beam evaporation to a thickness of approximately 100 mm, and wet etching is performed using a third mask pattern through a photolithography process. [Figure 2 (C),
(G) ), further transferred to a dry etching device,
C.F. 10% III IR jr? RF power of 300 to 750 W and 0.1 to 0.0 W was introduced using a resist and upper electrode 9 (not shown) as masks.
Perform isotropic engineing under a gas pressure of 2 Torr. Thus, the exposed end face of the a-Si film soil is
9 and the side surface of the lower light-shielding metal 17, and the surface area of the a-Sill soil becomes smaller [Fig. 2 (D
), (l{) ) . In addition, Fig. 2 (D) and (H)
During the dry etching process of CCI. A gas mixed with several percent oxygen was introduced into the RF output of 300W. Gas pressure 0. I Torr
It is also possible to perform anisotropic etching. In this way, the exposed end face of the a-SiM4 has a shape perpendicular to the thickness direction. Then, by further over-etching and managing the time, it is possible to keep the vertical shape as it is.
+The exposed end surface of the membrane soil can be brought inside the upper electrode 9 and the lower light-shielding metal l7. A schematic cross-sectional view of the TFD element in this case is shown in Figure 3cA) and (B). [Effects of the Invention] Conventionally, liquid crystal display panels incorporating TFD elements generate photocurrent due to incident light, so depending on the illuminance level of the indoor and outdoor viewing environment, the image may change and become difficult to see. However, in the present invention, as described in the embodiment, the a-Sill of the TFD element is constructed so that its exposed end face is inside the side surface of the lower light-shielding metal and the upper t8i, so that the incident light is Whether it is parallel light flux or scattered light, it is blocked by the lower light-shielding metal and the upper electrode, and the visual Q.
! In the environmental illuminance range of 3,000 to 10,000 Lx, the image change due to photocurrent is extremely small, and the image display on the liquid crystal display panel can be stabilized in an easy-to-see state.

[Brief explanation of the drawing]

FIG. 1(A) is a schematic cross-sectional view showing the structure of the TFD element of the present invention, and FIG. 1(B) is a schematic cross-sectional view viewed from a direction perpendicular to FIG. 1(A). FIGS. 2(A) to (D) show T of the present invention.
The manufacturing process diagram of the FD element, Figure 2 ([!) to ()I), is
Fig. 2 (A) to (D) are schematic cross-sectional views seen from the right angle direction, Fig. 3 (A) is a schematic cross-sectional view showing a shape different from that in Fig. 1, and Fig. 3 (B) is a schematic cross-sectional view showing a shape different from that in Fig. 1. , also a schematic cross-sectional view seen from the right angle direction of FIG. 3(A), FIG. 4 is a diode ring equivalent circuit diagram of a TFD element, and FIG. A schematic cross-sectional view, FIG. 6 is a partially cutaway perspective view of a conventional TFD element, and FIG.
1 is a schematic cross-sectional view of a conventional TFD element manufactured using a single mask method. 1, 11, 12: Glass substrate, 2, 14: ITO [
Pole, lfi optical film, 4: a-Si film, 5: n layer, 6:
i@, 7: p layer, Ilifi green film, 9: upper electrode, 10:
TFD, 13: Color 7 I/L/Yuichi, 15: Liquid crystal, 16: Polarizing plate, 17 Lower light shielding metal. Figure 3 Figure 4 Figure 5 099999 combination Figure 6 Figure 7

Claims (1)

[Claims] 1) A thin film diode that is provided with a lower light-shielding metal, amorphous silicon having a pin junction, and an upper electrode on a substrate, and is used as a nonlinear display element in each pixel of a liquid crystal display panel to drive this liquid crystal display panel. 1. A thin film diode element, wherein an exposed end surface of the amorphous silicon is located inside a side surface of the lower light-shielding metal and the upper electrode.