JPH02168237A - Thin-film two-terminal element type active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve image quality by interposing a silicon nitride layer doped with boron or silicon carbide layer between a metal and an insulator. CONSTITUTION:Cr is formed as a metal electrode on a lower glass substrate 1 and is patterned to an island shape to form lead electrodes 3; in succession, the 1st silicon nitride layer 4 doped with the boron is formed on the glass substrate 1 and thereafter, the 2nd silicon nitride layer 6 doped with the boron is formed thereon, by which the 3-layered structure is formed. Cr is then formed as an upper electrode 7 and is patterned. The diode characteristic having good symmetry is obtainable as well with the 3-layered structure formed by interposing the silicon carbide layers contg. the boron to both sides of the silicon nitride layers 4, 6. The good image quality having no flicker is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix liquid crystal display device using a thin film two-terminal element composed of metal-insulator-metal.

[Conventional technology]

BACKGROUND ART In recent years, applications of liquid crystal display devices (LCDs), mainly twisted nematic type, have been developed and are being used in large quantities in the fields of wristwatches and calculators. In addition, in recent years, matrix type LCDs have begun to be used, which have pixels arranged in a matrix and are capable of displaying arbitrary characters and graphics. In order to expand the field of application of this matrix type LCD, it is necessary to increase the display capacity. However, since the rise of the voltage-transmittance change characteristic of conventional LCDs is not very steep, when the number of scans in multiplex drive is increased to increase the display capacity, the The effective voltage ratio decreases, and a Talostalk occurs in which the transmittance of selected pixels decreases and the transmittance of non-selected pixels increases. As a result, the display contrast is significantly reduced, and the viewing angle at which a somewhat satisfactory contrast can be obtained is also narrowed, and in conventional LCDs, the maximum number of scan lines is about 60 lines.

In order to significantly increase the display capacity of this matrix type LCD, an active matrix LCD has been devised in which switching elements are arranged in series in each pixel of the LCD. The switching elements of active matrix LCD prototypes announced so far include thin film transistor elements (T
PT) is often used. On the other hand, since the manufacturing and structure are relatively simple, the manufacturing process can be simplified.
Thin film two-terminal devices expected to have high yield and low cost (
Active matrix LC using TFD (hereinafter abbreviated as TFD)
D is also attracting attention.

Such a one-film, two-terminal element type active matrix LC
In D (hereinafter abbreviated as TFD-LCD), an LCD that is considered to be close to the one for use in fragrances is an LCD that uses a metal-insulator-metal structure element (hereinafter abbreviated as MIM element or MIM) in TFD. It is. TF like M I M
By connecting D in series with the liquid crystal of each pixel, TFD
Due to the highly non-linearity of the voltage-current characteristic of the TFD-liquid crystal element, the rise of the voltage-transmittance change characteristic becomes steep.
It becomes possible to significantly increase the number of scan lines of a liquid crystal display device.

A conventional example of an LCD using such an MIM is described in a paper by Day Arbalaf et al.
Off metal insulator metal nonlinear
Devices for Use in Multiplexed Liquid Crystal Displays), IE Transactions on Electron AB 491, Vol. 28, No. 6, pp. 1, 736-739゜1
(Published in 981) (D, R, Baraff, eta
l, , ”The Optimization o
f Metal-1nsulfator-Meta
1Non-1inear Devices for
r Use in Multipfexed Li
quid Crystal Displays”I
EEE Trans.

Electron Devices, vol E
D-28, pp736-739 (1981))
Representatively shown.

In MIM, the most important material is that of the insulator layer. The most well-known insulating material is tantalum oxide (for example, Nakaji Ryozumi et al.

Written by 250 x 240 pixel lateral, M I M -
L CD Television Society Technical Report (I PD83-8
) p39-44. Published December 1983). When applying such an MIM element to a large-capacity display, the characteristics required are that the nonlinear coefficient α is large when the current (I) flowing through the element and the applied voltage (V) are expressed as aV'; The current-voltage characteristics are positive and negative symmetrical regardless of the polarity of the applied voltage, and the capacitance of the MIM element is small. However, although the MIM element using tantalum oxide has good symmetry, it has a nonlinear coefficient of 5 to 6, which is not so large, and also has a large dielectric constant, so it has drawbacks such as a large element capacitance. Therefore, silicon nitride, which has a low dielectric constant, has been developed as an insulator material for MIM devices.
Off Stoichiometric 5INx Layer, Blossom Deindus Off the Varnish ID-Volume 28
Pages 101-104.

Published in 1987) (M, 5uzuki et a.
t”A New Active Diode Ma
trix LCD using Off-sto
ichiometric SiNx Layer P
roceedings of the SID, Vol.
, 28ρ101-104.1987)).

[Problem to be solved by the invention]

This MIM element using silicon nitride has a nonlinear coefficient of 7.
~9, which is larger than that of tantalum oxide, but as shown by the broken line in Figure 2, the voltage-current characteristics often become asymmetric depending on the polarity of the applied voltage, which is why this MIM element was used in liquid crystal display devices. In some cases, flicker occurs, resulting in a reduction in image quality.

The purpose of the present invention is to improve the asymmetry of the voltage-current characteristics of the MIM element characteristics that cause such deterioration of image quality,
An object of the present invention is to provide a high-quality, large-capacity liquid crystal display device.

[Means to solve the problem]

The present invention provides a thin film in which a liquid crystal is sandwiched between a substrate on which a transparent electrode is formed and a thin film two-terminal element having a metal-insulator-metal structure using a silicon nitride film as an insulator. A thin film two-terminal active matrix liquid crystal display device characterized in that a boron-doped silicon nitride layer or silicon carbide layer is sandwiched between the metal and the insulator. be.

In the present invention, by sandwiching a boron-containing silicon nitride layer or silicon carbide layer between the metal electrode and the silicon nitride layer, the barrier that inhibits the injection of holes from the electrode can be reduced, and the positive voltage Also, the asymmetry in the current value due to the difference in the barrier to hole injection from each electrode when applying a negative voltage is eliminated. As a result, a liquid crystal display device with good image quality and no flicker can be realized.

〔Example〕

Examples of the present invention are shown below.

A cross-sectional view of a typical example of the TFD element obtained in this example is shown in FIG. 1. First, a lower glass substrate 1 is coated with a glass protective layer 2 such as 5i02. This protective layer 2 is not indispensable and may be omitted.Next, a 1000A Cr film is formed as a metal electrode on this layer and patterned into an island shape by photolithography to form a lead electrode 3.

Next, a first boron-doped silicon nitride layer 4 of 50 OA was formed on the glass substrate by a glow discharge decomposition method using a mixed gas of SiH4 gas and N2 gas mixed with 1% B2H6 gas, and then SiH4 The silicon nitride layer 5 was heated at 120OA from a mixed gas of SiH4 and N2.
A three-layer structure is formed by forming a boron-doped second silicon nitride layer 6 of 20 OA using a mixed gas of 821 (0.5% of 6 gases). Gas mixture ratio S when forming a hissilicon layer
iH4/N2 is 0.08. Also, the first doped with boron
The gas mixture ratio SiH4/N2 when forming the second silicon nitride layer was 0.2. Thereafter, 100 OA of Cr is formed as the upper electrode 7 and patterned by photolithography to form an M I M element array. Thereafter, ITO is patterned and formed as a pixel electrode.

Protection on top glass substrate N9. The film formation and patterning of the upper transparent electrode 10 are almost the same as in a normal simple multiplex LCD. Lower glass substrate 1 and upper glass substrate 8
After being subjected to orientation treatment, they were pasted together with spacers such as glass fibers interposed therebetween, and sealed with a regular epoxy adhesive. The cell thickness was 5 microns. Thereafter, ZLI-1565 (manufactured by Merck & Co., Ltd.), which is a TN type liquid crystal 11, was injected between the substrates to complete a TFD-LCD.

When the voltage-current characteristics of the two-terminal device formed according to the present invention were measured, it was found to be symmetrical with respect to the voltage polarity, as shown by the solid line in FIG. It was found that the symmetry was improved compared to the voltage-current characteristics (broken line) of the two-terminal element. Furthermore, it was found that the nonlinear coefficient was as thick as 8, and that it could be applied to a TFD-LCD having a high scanning line of 1000 or more.

The gas mixture ratio SiH4/N2 when forming the silicon nitride layer of this two-terminal element is required to be 0.02 or more and 0.6 or less in order to produce a two-terminal element with large nonlinearity. In addition, when forming the first and second boron-doped silicon nitride layers, the gas mixture ratio SiH4/N2 is 0.01 or more, and the boron mixture ratio is 50ρrn or more. -It had an effect on the symmetry of current characteristics. In this example, the nitrided dinocon layer was formed using a mixed gas of SiH4 and N2, but good diode characteristics were also obtained using a mixed gas of SiH4 and NI-1. In addition, in this example, 3
Although a layered structure is formed, the present invention is also effective in other film forming methods such as sputtering and CVD.

In this example, a silicon nitride layer doped with boron is used, but a diode with good symmetry can also be obtained using a three-layer structure in which boron-containing silicon carbide layers are sandwiched on both sides of the silicon nitride layer. characteristics were obtained. At this time, a silicon carbide layer was formed using a glow discharge decomposition method using a gas having a gas mixture ratio of SiH4/CH4 of 0.1 or more.

In this embodiment, a chromium electrode is used as the electrode, but the present invention is also effective even if other metals such as AI, Ta, Mo, W, and silicide are used for the upper and lead electrodes. Further, the present invention is also effective even if the transparent electrode such as ITO used as the pixel electrode also serves as the upper and lower electrodes of the two-terminal element.

T of 640×400 element formed using this example
An image evaluation of the FD-LCD revealed that the contrast was 20:1 or higher and the flicker was -37 dB, compared to a conventional TFD-LCD with a single layer structure of silicon nitride.
It is clear that this is a significant improvement compared to B.

〔Effect of the invention〕

As described above, according to the present invention, thin film two-terminal device characteristics with good symmetry and high nonlinearity can be obtained, so that a liquid crystal display device with large capacity and less flicker can be provided.

FIG. 2, which is a cross-sectional view of an example, is a diagram showing voltage-current characteristics of a thin film two-terminal device according to the present invention and a thin film two-terminal device according to a conventional example.

1... Lower glass substrate, 2.9... Glass protective film,
3... Lead electrode, 4... First silicon nitride layer doped with boron, 5... Silicon nitride layer, 6...
- Second silicon nitride layer doped with boron, 7...
- Upper electrode, 8... Upper glass electrode, 10... Upper transparent electrode, 11... Liquid crystal.

Claims (1)

[Claims] A liquid crystal is sandwiched between a substrate on which a transparent electrode is formed and a substrate on which thin film two-terminal elements having a metal-insulator-metal structure using a silicon nitride film as an insulator are formed in a matrix. A thin film two-terminal active matrix liquid crystal display device comprising a thin film two-terminal active matrix liquid crystal display device, characterized in that a boron-doped silicon nitride layer or silicon carbide layer is sandwiched between the metal and the insulator. Device.