JP2545590B2 - Liquid crystal device - Google Patents

Description

The present invention relates to a liquid crystal device having a non-linear element having a conductor-insulator-conductor structure or a conductor-semiconductor-conductor structure.

[Conventional technology]

The structure of a conventional non-linear element is shown in FIGS.
FIG. 1 is a plan view of the non-linear element and the pixel when the non-linear element is used for driving a pixel of a liquid crystal display device, and FIG. 2 is a sectional view taken along the line bb 'in FIG. As a structure of a conventional non-linear element, as shown in FIG. 1 or 2, it is known that a first conductor [1], an insulator [3], and a second conductor [2] are laminated. ing. Here, the hatched portion in FIG. 1 is a non-linear element. The first conductor [1] is connected to the pixel electrode [5] via the insulator [3] and the second conductor [2]. In particular, the first conductor [1] is tantalum (Ta) and the insulator [3] is tantalum oxide (TaOx).
The pixel structure of a liquid crystal display device using a non-linear element in which the second conductor [2] is chromium (Cr) and the pixel electrode [5] is a transparent conductive film of ITO is well known. Each of these films is usually formed on a glass substrate. There are a pixel electrode and a non-linear element for allowing a specific charge to flow into the pixel electrode, a glass substrate on which a pattern for wiring between pixels is formed, and a glass substrate on which a pattern serving as a counter electrode is formed by sandwiching a liquid crystal. An outline of a liquid crystal display device is one in which the plates are laminated at an appropriate interval (several microns), and liquid crystal is enclosed and aligned between the two glass substrates. Since the liquid crystal display device has a function as a display body by transmitting light and controlling the amount of transmitted light, the two substrates are preferably colorless and transparent. The amount of transmitted light is adjusted as follows. Light from a fluorescent lamp or the like as a light source passes through a deflection plate and becomes linearly polarized light. This deflected light is made incident on the liquid crystal display device, and the deflection direction of the deflected light is changed by changing the inclination of the liquid crystal. By passing this light through another deflecting plate again, the amount of light passing through the second deflecting plate is changed and display can be performed. To change the tilt of the liquid crystal here,
An appropriate potential difference is applied to the liquid crystal in a region where the tilt of the liquid crystal is changed (the minimum unit of this region is a pixel). Since the tilt of the liquid crystal can be changed by the applied potential difference, the amount of transmitted light can be controlled by the applied potential difference to this pixel. An element is formed in each pixel in order to hold the potential difference once applied here until the next potential difference is applied. Therefore, as the characteristics of the element, it is ideal that the element resistance becomes zero when a potential difference is applied to the pixel and becomes infinite when the potential difference is held. When a non-linear element is used in a liquid crystal display device, it is generally necessary to make the area of the element sufficiently smaller than that of the transparent pixel electrode in order to bring the characteristics of the element close to ideal. If the transparent pixel electrode is 200 μm square, the size of the non-linear element is designed to be 4 μm square or less. Many parameters are included in the determination of the size of the non-linear element, and the most important parameter among them is the ratio of the capacitance and resistance of the transparent pixel electrode to the capacitance and resistance of the non-linear element. Also, the capability of the process of forming the non-linear element cannot be ignored. Generally, the ratio of the area of the non-linear element to the area of the transparent pixel electrode is set to about 1/1500 to 1/3000. Further, in the case of a liquid crystal display device, it can be visually confirmed if the potential difference applied to the pixels between adjacent pixels has a difference of several percent. Therefore, the same level of uniformity is required for the area of the non-linear element, and the area uniformity between the non-linear elements is required to be 1/10 μm ² level.

[Problems to be Solved by the Invention]

However, in the above-mentioned prior art, the non-linear element portion shown in FIG. 1 or 2 [the diagonally downward-sloping portion in FIG. 1]
Is extremely fine, it is difficult to make a large number (usually 100,000 pixels or more) of non-linear elements uniformly over a wide area due to variations in photo-etching, which is a means of forming non-linear elements. It has been difficult to increase the yield of liquid crystal display devices and the like in which nonlinear elements are integrated.

Further, when the second conductor [2] has poor adhesion to the substrate [6], the second conductor [2] has many defects that are peeled or cut off on the substrate [6], and the nonlinear element It has been difficult to increase the yield of liquid crystal display devices and the like in which In particular, the first conductor [1] is made of Ta, the second conductor [2] is made of Cr, and the substrate [6] is made of glass.
When the etching of Ta, which is the first conductor [1], is performed by dry etching, the adhesion between Cr, which is the second conductor [2], and the glass, which is the substrate [6], is poor and the second Defects such as peeling and breakage on the substrate [6] of the conductor [2] and in the vicinity of the stepped portion of the first conductor [1] were remarkable.

First, the first conductor must be patterned by dry etching. This is because when wet etching is used, the step portion of the pattern end face of the first conductor is raised, and the second conductor is cut without step coverage at the step portion. By using dry etching, the step portion of the pattern end face of the first conductor can be tapered and the step coverage of the second conductor can be improved. However, after the first conductor is etched by the plasma used for dry etching, the substrate is also exposed to the plasma and the surface of the substrate is roughened. In particular, this roughening is remarkable in the glass with many impurities, that is, in the glass having a low cost, and is hardly present in the case of crystal glass (quartz glass). In this case the second
A defect that the conductor is peeled or cut occurs. In addition, Ta, Si, etc., which have been etched once during dry etching, may be deposited again on the substrate.
At this time, the material deposited again takes the form of carbon polymer and cannot be removed by the plasma used for etching. The deposition of these carbon polymers is often deposited in a strip shape at a position of several μm from the step portion of the pattern end face of the first conductor, and the adhesion of the second conductor formed in this portion is poor. And defects such as breakage and peeling occur. Examples of these breaks and peelings are shown in FIGS. 6 and 7. The pattern failure of the second conductor due to breakage or peeling occurs from several percent to several tens percent,
The yield is remarkably deteriorated.

The prior art has the above problems. Therefore, the present invention solves such a problem, and an object of the present invention is to provide a liquid crystal display device in which a large number of non-linear elements are uniformly formed over a wide area with few defects and the non-linear elements are integrated. It is to improve the yield.

[Means for solving the problem]

In the liquid crystal device of the present invention, liquid crystal is sandwiched between a pair of substrates facing each other, and a signal electrode and a pixel electrode are formed on at least one of the substrates, and the signal electrode and the pixel electrode are 1 conductor-insulator-second conductor, or first
A conductor, a semiconductor, and a second conductor, which are electrically connected via a non-linear element formed by stacking them in this order.
A liquid crystal device, wherein the conductor is formed of the same material and in the same process as the signal electrode, and is electrically connected to the signal electrode, and the second conductor is electrically connected to the pixel electrode. The second conductor extends from the non-linear element portion, and an end portion of the second conductor overlaps the pixel electrode. The second conductor extends from the non-linear element portion to the end portion, and the first conductor is provided below the second conductor. A plurality of island-shaped protection portions are formed by the same material and the same process as the conductor.
The second conductor and the pixel electrode have an overlapping portion in a region sandwiched between two island-shaped protection portions.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 3 is a plan view of a non-linear element according to the present invention, and is a plan view of a part of the non-linear element and the pixel when the non-linear element is used for driving a pixel of a liquid crystal display device.

Examples will be described below based on an element structure (hereinafter referred to as a MIM element) that is particularly well known as a non-linear element. That is, the first and the conductor [1] are Ta, and the insulator [3]
Is an oxide of Ta (hereinafter, referred to as TaOx), and the second conductor [2] is Cr.

In FIG. 3, the slanted lines on the lower left form a non-linear element, and it is desirable that the area is small in terms of element characteristics. A nonlinear element is also a capacitor in its structure. From the aspect of application, a small element capacitance is required from the viewpoint of electrical efficiency. In addition, variations in the size of the element directly cause variations in the characteristics of the element, resulting in defects in display performance. As described above, the non-linear element is small and must be formed in large numbers uniformly. This is generally well known.

In FIG. 3, TaOx [3] is sandwiched between Ta [1] and Cr [2] to form a MIM element, but the pattern width of the first conductor [1] in the portion forming the MIM element is It is usually as small as several μm or less. Other portions formed in the same step as the first conductor [1] portion, for example, the signal electrode [1 ′] portion and the terminal portion,
It is usually several tens of μm to several hundreds of μm. Therefore, when the first conductor [1] and the signal electrode [1 '] of the MIM element have to be formed in the same photo-etching process, the pattern has considerable design variation. The etching rate is the highest in the portion where the MIM element is formed, which is the smallest variation, and the variation in etching also becomes large. Regarding this variation, there are variations due to the etching itself and the location where the portion forming the MIM element is present.
In the former case, for example, the etching rate of the peripheral portion of the substrate is fast, and conversely, the etching rate of the central portion of the substrate is fast. In the case of dry etching, the main cause of this variation is that the density of plasma involved in etching has an uneven distribution on the substrate. In the latter case, for example, some pattern exists around the portion forming the MIM element, or does not exist,
If it exists, the etching rate may change depending on its density and size.

Generally, etching is performed by attaching a resist on the pattern to be left, but if no pattern is left on the periphery at this time, the etching rate becomes faster, and conversely, if a solid pattern is left on the periphery, the etching rate becomes slower. . Therefore, in the case of a liquid crystal display device, even if there is no variation in etching during the process, the etching rate is fast in the portion near the center of the screen and slow in the portion near the periphery of the screen. In the case of a liquid crystal display device, there are basically only pixels near the center of the screen, and the pattern density (resist density) is low. On the other hand, there is a terminal part for connection with the outside near the periphery of the pixel,
The pattern density (resist density) is the highest. As a result MI
The variation of the M element becomes large, and the tendency becomes larger as the MIM element becomes finer.

Therefore, if the protective portion [4] is formed in the same material and in the same process as Ta [1] in the vicinity of the portion where the MIM element of Ta [1] is formed (the diagonally downward-sloping portion in FIG. 3), the TaIM No matter where the MIM element is located on the substrate in the vicinity of the part, the etching rate is uniformly reduced and the uniformity is improved because of the protection part [4]. As a matter of course, the etching rate changes depending on the position of the protective section [4] from the MIM element section, and the closer the protective section [4] is, the slower the etching rate. In particular, when Ta etching is performed by dry etching, the above tendency becomes large.

Therefore, to some extent, the T
It is possible to set the etching rate of a and Ta
It is possible to reduce variations in the etching rate due to the pattern design and the process.

In addition, when Cr [2] has poor adhesion to the substrate [6],
Defects such as Cr [2] peeling off or breaking from the substrate [6] occur, but the above-mentioned defects are reduced by the structure shown in FIG. This is effective when the adhesion between Cr and the substrate is poor, but the adhesion between Cr and Ta is good. This is particularly remarkable when the substrate is glass and Ta patterning is performed by dry etching. The above reason is shown below.

The Ta [1] etching is generally performed by dry etching. At this time, the glass substrate exposed to plasma (for example, COF radicals) as an etching gas has poor adhesion to metal. Therefore, Cr [2] has poor adhesion to the substrate [6]. Poor adhesion is remarkable when the glass substrate contains a large amount of impurities (when the cost is low). Also, from the viewpoint of miniaturization of the MIM element, Cr must be made extremely thin with a part of the MIM element to be several μm. Further, due to the problem of alignment accuracy with Ta, Cr in the portion forming the element needs to have a length corresponding to a margin in consideration of alignment accuracy as shown in FIG. Therefore, in the conventional liquid crystal display device, there are many defects in which a particularly thin portion is peeled off or cut in the Cr portion which must be formed on the substrate having poor adhesion. As shown in FIG. 3, if the protective portion [4] is formed of Ta, the area that must be formed in a location where Cr is thin and has a low density is narrow, and the Cr pattern is widened on the protective portion [4]. In areas where adhesion is poor, Cr can be formed in a pattern as wide as possible. As a result, the area where Cr is peeled or cut can be narrowed, and these defects are reduced.

In addition, almost no redeposition occurs in the part between Ta [1] and the protective part [4] forming the MIM element part, so that the Cr pattern defect due to the redeposition is reduced.

The embodiment shown in FIG. 3 considers the case where IT [5] cannot be step-covered at the stepped portion of the protective portion [4] and is disconnected in the structure as shown in FIG. is there. In this embodiment, Cr [2] and IT [5]
The contacting part [6] is the same as the condition between the part forming the MIM element and the protection part [4], and the adhesion of Cr is not lost, and Ta is stepped on IT [5]. Does not require partial step coverage.

In the example of FIG. 5, the substrate [6], Ta [1], and Cr [2] are used.
In order to improve the adhesion with the film, an insulating film is formed as a base on the substrate [6] before forming Ta [1]. For example, the insulator may be an oxide of Ta (TaOx). Usually, TaOx is also etched when forming a Ta pattern. If the etching is performed uniformly over the entire surface of the substrate, it is possible to etch only the Ta pattern and leave the underlying TaOx. This means increasing the adhesion of Cr. Generally, due to process variations
Due to the influence of Ta pattern, etching is not performed uniformly. Therefore, it is necessary to perform etching in accordance with the portion having the slowest etching rate. That is, normally, TaOx as a base does not remain in the portion where the adhesion of Cr is desired to be increased in the vicinity of the portion where the MIM element is formed. The underlying TaOx is merely used to enhance the adhesion between Ta and the substrate. Here, protector [4] is placed near the MIM element
If formed at the same time as the pattern of a, the protective part [4] and M
The etching rate becomes slower in the area between the IM elements
However, the underlying insulating film remains in the areas where it is thin and adhesion is to be improved. As a result, the adhesion between Cr and the substrate can be increased, and the peeling and breakage of Cr can be reduced.

Although TaOx has been described as an example of the insulator [3], a non-linear element in which the insulator [3] is a semiconductor film also has the same effect.

〔The invention's effect〕

As described above, in the liquid crystal device of the present invention, the liquid crystal is sandwiched between the pair of substrates facing each other, the signal electrode and the pixel electrode are formed on at least one of the substrates, and the signal electrode and the pixel electrode are formed. Is electrically connected via a non-linear element formed by stacking a first conductor-insulator-second conductor or a first conductor-semiconductor-second conductor in this order. 1. A liquid crystal device in which one conductor is formed of the same material and in the same process as the signal electrode and is electrically connected to the signal electrode, and the second conductor is electrically connected to the pixel electrode. The second conductor extends from the non-linear element portion, and an end portion of the second conductor overlaps with the pixel electrode. The second conductor extends from the non-linear element portion to the end portion at a lower portion of the second conductor. Same material and same work as 1 conductor A plurality of island-shaped protection portions are formed, and the second conductor and the pixel electrode have an overlapping portion in a region sandwiched by the two island-shaped protection portions. When a large number are formed over a wide area, variations in characteristics due to non-uniformity of the shape of the non-linear element and defects such as disconnection of the second conductor between the non-linear element part and the pixel electrode part are prevented. In addition, since it is possible to prevent the occurrence of defects due to disconnection of the pixel electrode in the stepped portion of the island-shaped protection portion, it is possible to improve the production yield.

In addition, since the island-shaped protection part can be formed of the same material and in the same step as the first conductor, the number of steps is not increased as compared with the conventional liquid crystal device, and the cost is not increased due to the structure change. The above essential elements are also satisfied.

[Brief description of drawings]

FIG. 1 is a plan view of a conventional non-linear element. FIG. 2 is a sectional view of a conventional non-linear element. FIG. 3 is a plan view of a non-linear element according to an embodiment of the present invention. FIG. 4 is a plan view of a non-linear element according to a comparative example of the present invention. FIG. 5 is a sectional view of a non-linear element according to an embodiment of the present invention. FIG. 6 is a plan view of a conventional non-linear element. FIG. 7 is a plan view of a conventional non-linear element. 1 ... 1st conductor (Ta) 2 ... 2nd conductor (Cr) 3 ... Insulator (TaOx) or semiconductor (shown by the diagonal line to the right in the figure) 4 ... Protective part 5 ... Pixel electrode (IT) 6 ... Substrate (glass) The non-linear element part is shown by a diagonal line descending to the left in the figure.

Claims (1)

(57) [Claims] 1. A liquid crystal is sandwiched between a pair of opposing substrates, a signal electrode and a pixel electrode are formed on at least one of the substrates, and the signal electrode and the pixel electrode are made of a first conductor. -Insulator-Second conductor or first conductor-Semiconductor-Second conductor is electrically connected via a non-linear element formed by stacking in this order, and the first conductor is the signal electrode. A liquid crystal device formed of the same material and by the same process as, and electrically connected to the signal electrode, the second conductor being electrically connected to the pixel electrode, wherein the second conductor is It extends from the non-linear element portion, and its end portion overlaps with the pixel electrode, and from the non-linear element portion to the end portion, the same material as that of the first conductor is formed under the second conductor. Multiple islands formed by the same process Protection portion is formed in a region sandwiched between the protective portion of two of the island, a liquid crystal device which comprises said pixel electrodes and the overlapped portion and the second conductor.