JP2798965B2 - Matrix display device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a matrix display device, and more particularly to an active matrix display device applicable to a liquid crystal display, other flat panel displays, and the like.

[Conventional technology]

Metals-insulators in active matrix display devices
As a typical example of a metal element (hereinafter sometimes referred to as “MIM element”), as shown in JP-A-62-62333, Ta is used as a lower electrode, and Ta ₂ O ₅ (anodized film) is used as an insulating film. The upper electrode is made of Cr or Cr / ITO, and is obtained by performing heat treatment at about 300 to 500 ° C. in order to obtain polarity symmetry. As another example, Japanese Patent Application Laid-Open No. 61-260219 proposes a device using ITO as a lower electrode, SiNx (film formation by a plasma CVD method) as an insulating film, and Cr as an upper electrode.

Further, a matrix display device using such a MIM element and connecting each pixel to two scanning lines via two MIM elements has been proposed in JP-A-63-187279. .

However, these conventional MIM elements have the following problems. Therefore, in a matrix display device using this MIM element, disconnection, short-circuit, and the like often occur, and display defects easily occur.

That is, in the case of using a anodic oxide film as the insulating film in the conventional MIM element, (1) since the insulating film is limited to the anodic oxide film of the lower metal, the control of the physical property value and, consequently, the control of the characteristics of the MIM element. (2) Since heat treatment at about 300 to 500 ° C. is required, the material of the substrate to be used is limited to those having high heat resistance, and (3) the relative permittivity. Therefore, when used as a switching element of a liquid crystal display device, (in general, the MIM capacitor /
It is necessary to reduce the element area (since it is said that there is a restriction that the liquid crystal capacity is less than 1/10), and there are drawbacks such as the need for advanced fine processing. In the case of a MIM device using SiNx as an insulating film, the above (1)
Although the drawbacks of (3) and (3) are eliminated, the deposition temperature is 300
Since the temperature is as high as about ° C., the same problem as the above (2) remains, and there is a problem that pinholes are easily generated by dust and the like, and the yield is reduced.

〔Purpose〕

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a matrix display device having a configuration in which display defects due to disconnection, short circuit, and the like are unlikely to occur.

〔Constitution〕

In the matrix display device of the present invention, each of a plurality of pixel electrodes provided on at least one substrate constituting the device is connected to two scanning electrodes adjacent to the pixel electrode via a MIM element, In addition, the MIM element is characterized in that a hard carbon film is interposed between the first conductor and the second conductor.

As described above, the first feature of the present invention resides in the material of the insulating film formed between the first conductor and the second conductor of the MIM element used in the present invention. It is composed of a hard carbon film (i-C film, diamond-like carbon film, amorphous diamond film, amorphous diamond film, etc.) containing at least one of amorphous and microcrystalline with carbon atoms and hydrogen atoms as main structure forming elements. ing. One of the features of the hard carbon film is that it is a vapor-grown film, so that its physical properties can be controlled over a wide range by controlling the film-forming conditions, as described later. Therefore, even if it is referred to as an insulating film, its resistance value covers the region from the semi-insulator to the insulator, and in this sense, the MIM element of the present invention is disclosed in, for example, JP-A-61-275811.
Of the MSI element (Metal-Semi-Insulato)
r) and SIS devices (semiconductor-insulator-semiconductor, where “semiconductor” is a highly doped impurity).

The hard carbon film according to the present invention will be described in detail.
In order to form a hard carbon film, a hydrocarbon gas is used as an organic compound gas or the like. The phase state of these raw materials does not necessarily need to be a gas phase at normal temperature and normal pressure, and any liquid or solid phase can be used as long as it can be vaporized through melting, vapor deposition, sublimation, etc. by heating or decompression. is there.

For hydrocarbon gas as a source gas, for example, CH
_{4, C 2 H 8, C} 4 paraffinic hydrocarbons H _10, etc., olefinic hydrocarbons such as C ₂ H _4, acetylenic carbon hydrogen, diolefinic hydrocarbons, more of all such aromatic hydrocarbons hydrocarbons Gases containing at least hydrogen can be used.

Further, other than hydrocarbons, compounds such as alcohols, ketones, ethers, esters and the like containing at least a carbon element can be used.

As a method for forming a hard carbon film from a raw material gas in the present invention, a method in which a film forming active species is formed through a plasma state generated by a plasma method using a direct current, a low frequency, a high frequency, a microwave, or the like. Although preferable, a method utilizing a magnetic field effect is more preferable for performing deposition under a low pressure for the purpose of increasing the area, improving the uniformity, and controlling the temperature at a low temperature. Active species can also be formed by thermal decomposition at high temperatures.

In addition, it may be formed through an ion state generated by an ionization evaporation method or an ion beam evaporation method, or may be formed from neutral particles generated by a vacuum evaporation method, a sputtering method, or the like, Further, it may be formed by a combination of these.

An example of the conditions for depositing the hard carbon film thus produced in the case of the plasma CVD method is generally as follows.

RF output: 0.1 to 50 W / cm ² Pressure: 10 ^{-3 to} 10 Torr Deposition temperature: room temperature to 950 ° C., preferably room temperature to 300 ° C.

The raw material gas is decomposed into radicals and ions by the plasma state and reacts with each other, so that amorphous (amorphous) and microcrystalline (crystal size of several tens of degrees) composed of carbon atoms C and hydrogen atoms H are formed on the substrate. (Several .mu.m). Table 1 shows the properties of the hard carbon film.

Note) Measuring method; Specific resistance (ρ): Determined from the IV characteristics of a coplanar cell.

Optical band gap (Egopt): The absorption coefficient (α) is determined from the spectral characteristics, and (αhν) ^1/2 = B (hν−Egopt)
Is determined from the relationship.

Hydrogen content in film (C _H ): 2900 cm ^-1 from infrared absorption spectrum
The peaks in the vicinity are integrated and multiplied by the absorption cross section A to obtain the peak.
That is, C _H = A · ∫α (w) /w.dw SP ³ / SP ² ratio: The infrared absorption spectrum is decomposed into Gaussian functions assigned to SP ³ and SP ² , respectively, and is obtained from the area ratio. .

Vickers hardness (H): According to a micro Vickers meter.

 Refractive index (n): Based on ellipsometer.

 Defect density: Depends on ESR.

As a result of analysis by IR absorption method and Raman spectroscopy, the hard carbon film thus formed shows that the carbon atom has a hybrid orbital of SP ^{3 and} a hybrid orbital of SP ² as shown in FIGS. 1 and 2, respectively. It is clear that the formed interatomic bonds are mixed. The ratio between SP ³ and SP ² bonds can be roughly estimated by separating peaks in the IR spectrum. In the IR spectrum, spectra of many modes are overlapped and measured at 2800 to 3150 cm ^-1. The assignment of peaks corresponding to each wave number is clear, and the Gaussian distribution as shown in FIG. By performing peak separation, the peak areas of the respective peaks are calculated, and if the ratio is determined, the SP ³ / SP ² ratio can be known.

According to X-ray and electron diffraction analyses, it can be seen that the film is in an amorphous state (a-C: H) and / or an amorphous state including fine crystal grains of several tens of degrees to several μm.

Generally, in the case of the plasma CVD method suitable for mass production, R
The smaller the F output, the higher the specific resistance and hardness of the film,
The lower the pressure, the longer the life of the active species is. Therefore, the substrate temperature is reduced, the uniformity over a large area is achieved, and the specific resistance and hardness tend to increase. Furthermore, since the plasma density decreases at low pressure, the method using the magnetic field confinement effect is as follows.
It is particularly effective for increasing the specific resistance.

In addition, this method is performed at room temperature to 300 ° C., and further at room temperature to 150 ° C.
Since it has the feature that a high-quality hard carbon film can be similarly formed even at a relatively low temperature condition of about ° C, it is most suitable for lowering the temperature of the MIM element manufacturing process. Therefore, there is a feature that a degree of freedom in selecting a substrate material to be used is widened and a uniform film can be obtained over a large area because the substrate temperature can be easily controlled. The structure and physical properties of the hard carbon film are as follows:
As shown in Table 1, since it can be controlled in a wide range,
There is also an advantage that device characteristics can be freely designed.

Furthermore, since the dielectric constant of the film is about 3-5, which is smaller than Ta ₂ O ₅ , Al ₂ O ₃ , SiNx, etc. used in conventional MIM elements, an element with the same electric capacity is made. In this case, since the element size is large, fine processing is not so required, and the yield is improved. Normally, the MIM element capacitance and the liquid crystal capacitance are connected in series in an equivalent circuit, so that it is necessary to set C _MIM : C _LCD = 1: 10 in order to apply a sufficient voltage to the MIM element. ing. Further, since the hardness of the film is high, damage due to the rubbing step at the time of enclosing the liquid crystal material is small, and the yield is also improved from this point.

As described above, the MIM element using the hard carbon film as the insulating layer eliminates the drawbacks of the conventional technology, but as the area of the liquid crystal display device increases or the capacity ratio increases, the disconnection of the scanning electrode and the element increase. It is very difficult to eliminate any defects such as short circuits.

A second feature of the present invention is that display defects are less likely to occur by connecting each pixel electrode to two scanning electrode lines via a MIM element. Specifically, a disconnection in the element portion and the scan electrode line does not cause a defect because charges can be injected into the liquid crystal layer through a normal scan electrode line. Regarding pixel defects caused by short circuit of the element part,
Two MIMs associated with the display electrode corresponding to the defective pixel
Pixel defects can be corrected by removing short-circuited elements from the elements by using a method such as laser irradiation and driving only normal elements.

FIG. 4 shows an example of an electrode configuration diagram provided on one substrate (not shown) constituting the liquid crystal display device of the present invention.
In FIG. 4, 1 is a scanning electrode, 2 is a MIM element, and 3 is a pixel electrode.

FIG. 5 shows an equivalent circuit of an arbitrary pixel when a liquid crystal display device using the substrate (not shown) of FIG. 4 is assembled, and (a) shows two circuits connected to this pixel. MI
This is a case where there is no defect such as short circuit or disconnection in both the M element and the two scanning electrodes connected through the M element. On the other hand, FIG. 2B shows a case where one MIM element is short-circuited and is removed by irradiating a laser beam. Fifth
4A and 4B, reference numeral 4 denotes the resistance of the liquid crystal, 5 denotes the capacitance of the liquid crystal, 6 and 8 denote the resistance of the MIM element, 7 and 9 denote the capacitance of the MIM element, and 10 denotes the drive circuit.

When the drive voltage Von is applied by the drive circuit, the voltage V applied to the MIM element is Is represented by

Here, C _LCD is the capacitance of the liquid crystal, and C _MIM is the combined capacitance of the MIM elements.

In the case of FIG. 5 (a), the area of the MIM element is twice as large as that of FIG. 5 (b), but the capacitance is doubled, so that the voltage V becomes smaller for the same drive voltage Von, and the current flowing through the MIM element Do not differ significantly.

Further, as described above, in order for a sufficient voltage to be applied to the MIM element, it is necessary that C _MIM必要 C _LCD , and as described above, it is usually designed that C _MIM : C _LCD = 1: 10. You. Since the capacitance is proportional to the area, when two pixels are provided in parallel in one pixel, the area must be reduced to half of that in the case where only one is provided in order to satisfy the above-mentioned constraint. As described above, the relative permittivity of the hard carbon film is relatively small, about 3 to 5, so that it is not necessary to reduce the element size so much, and this is also advantageous.

FIG. 6 is another example of the electrode configuration diagram of the present invention. 4th
The difference from the figure is that the aperture ratio is further increased in that the MIM element is provided in the concave portion of the pixel electrode. Note that the MIM elements do not need to be arranged symmetrically to the left and right of the pixel, and may be provided at any place.

FIG. 7 is an enlarged view of the MIM element portion of the present invention including a part of the scanning electrode and the pixel electrode. like this
To make a MIM element, for example, a transparent conductive thin film such as ITO, ZnO: Al, In ₂ O ₃ , SnO ₂ is sputtered as a pixel electrode 11 on a transparent substrate (not shown) such as glass, plastic plate, plastic film, etc. Hundreds to thousands depending on the method of vapor deposition, etc.
A film is formed to a thickness of about the same, and is etched into a predetermined pattern. Next, as the lower electrode 12, Al, Ta, Ti, Cr, Ni, Cu, Au, Ag,
A conductive thin film of W, Mo, Pt or the like is formed into a thickness of several hundreds to several thousand degrees by a method such as sputtering or vapor deposition, and is etched into a predetermined pattern. Next, a hard carbon film is formed as an insulator 13 by a plasma CVD method or an ion beam method.
After forming the film to a thickness of 00 to 8000 °, preferably 200 to 6000 °, more preferably 300 to 4000 °, the film is etched into a predetermined pattern. As an etching method, a dry etching method is preferably used. If the film pressure of the hard carbon film is smaller than this, there are problems such as a sharp increase in defects due to pinholes (the defect rate exceeds 1%), and it is not possible to ensure uniformity of the film thickness. If it is large, there are problems such as easy peeling due to stress and excessively high driving voltage.

In addition, the hard carbon film includes, in addition to carbon and hydrogen atoms, Group III, IV, and V elements of the periodic table, alkali metal elements, alkaline earth metal elements, nitrogen atoms, oxygen atoms, and chalcogen-based materials. An element or a halogen atom may be included as one of the constituent elements.

This impurity doping further increases the stability of the device and the degree of freedom in device design. The amount of these impurities is usually 5% for Group III
atomic% or less, and 35 atomic% for Group IV elements
Hereinafter, the same applies to Group V elements of 5 atomic% or less, alkali metal elements of 5 atomic% or less, alkaline earth metal elements of 5 atomic% or less, nitrogen atoms of 5 atomic% or less, oxygen atoms of 5 atomic% or less, and alcohols. It is 35 atomic% or less for system elements, and 35 atomic% or less for halogen atoms. The amounts of these elements or atoms can be measured by a conventional method of elemental analysis, for example, Auger analysis. Further, this amount can be adjusted by the amount of another compound contained in the source gas, the film forming conditions, and the like.

Finally, Pt, Al, Cr, Ti, Ni, Cu, Au, Ag,
A conductive thin film of W, Mo, Ta or the like is formed to a thickness of several hundreds to several thousand Å by a method such as sputtering or vapor deposition, and is etched into a predetermined pattern.

The configuration of the MIM element is not limited to this.After the MIM element is created, a transparent electrode is provided on the uppermost layer, a transparent electrode also serves as an upper or lower voltage, and a MIM element is provided on a side surface of the lower electrode. Various configurations are possible, such as those formed with.

 Next, examples will be described.

Example 1 On a Pyrex glass substrate as one transparent substrate, ITO was deposited to a thickness of about 1000 mm by a sputtering method and then patterned to form a pixel electrode. Next, MIM elements were made as active elements as follows. First, Al was deposited on a pixel electrode of a substrate to a thickness of about 1000 mm by a vapor deposition method, and then patterned to form a lower electrode. A hard carbon film as an insulating film was deposited thereon to a thickness of about 800 mm by a plasma CVD method, and then patterned by dry etching. The film forming conditions at this time are as follows.

Pressure: 0.035 Torr CH ₄ Flow rate: 20 SCCM RF power: 0.2 W / cm ² Further, Ni is deposited on each hard carbon insulating film by evaporation method to about 1000
After being deposited thick, it was patterned to form an upper electrode.

On a Pyrex substrate as the other transparent substrate (counter substrate), ITO was deposited to a thickness of about 1000 mm by a sputtering method, and then patterned in a stripe shape to form a common pixel electrode.

Next, a polyimide film was formed as an alignment film on both substrates, and a rubbing treatment was performed.

Subsequently, these substrates are opposed to each other with the pixel electrode side facing inward, bonded through a gap material having a diameter of about 5 μm, and a commercially available liquid crystal material is sealed in the cell thus formed. A liquid crystal display as shown in FIG.
8, 15 is a transparent substrate, 16 is a pixel electrode, 16 'is a common pixel electrode, 17 is a MIM element, 18 is a common electrode (scanning electrode) or common wiring, 19 is an alignment film, 20 is a gap material, 21 is a gap material, Is a liquid crystal material.

Example 2 An Al thin film having a thickness of about 1000 mm was formed on a glass plate by a vapor deposition method, and then patterned by etching to form a lower metal electrode. A hard carbon film having a thickness of about 600 mm was coated thereon, followed by dry etching. Patterned into an insulating film, and furthermore, about 10
An MIM device of the type shown in FIG. 9 was made by coating an ITO film having a thickness of 00 mm and patterning by etching to form an upper transparent pixel electrode. In FIG. 9, 15 is a transparent substrate, 22 is a metal electrode, 11 is a transparent electrode, and 13 is a hard carbon insulating film. The conditions for forming the hard carbon film 13 here are as follows.

Pressure: 0.05 Torr CH ₄ Flow rate: 10 SCCM RF power: 0.1 W / cm ² Next, on a plastic film as a counter substrate,
After depositing about 500mm thick ITO by sputtering method,
A common pixel electrode was formed by patterning in a stripe shape. Subsequently, a polyimide film was provided thereon in the same manner as in Example 1 and rubbed.

After bonding these two substrates through a gap material in the same manner as in Example 1, a commercially available liquid crystal material was sealed to produce a liquid crystal display device.

〔effect〕

As described above, the hard carbon film in the MIM element used in the present invention is 1) manufactured by a gas phase synthesis method such as a plasma CVD method, so that the physical properties can be controlled widely by the film formation conditions, and therefore,
Large degree of freedom in device design.

2) Since it is hard and can be formed into a thick film, it is hard to be damaged mechanically, and a reduction in pinholes due to the thick film can be expected.

3) Since a high-quality film can be formed even at a low temperature around room temperature, there is no restriction on the material of the substrate.

4) It is suitable for thin film devices because of its excellent uniformity of film thickness and film quality.

5) Low dielectric constant does not require advanced microfabrication technology, and is therefore advantageous for increasing the area of the device. For example, it is suitable as a highly reliable switching device for liquid crystal display. It is.

Further, in the matrix display device of the present invention, each pixel electrode is connected to two scan electrode lines via two MIM elements, so that a defect in the element portion due to disconnection and disconnection of the scan electrode basically occurs. Not to be. In addition, a defect caused by a short circuit in the element portion can be made a normal pixel by correction. This makes it possible to improve the production yield.

[Brief description of the drawings]

1 and 2 show an IR absorption spectrum and a Raman spectrum of a hard carbon film in a MIM device used in the present invention, respectively. FIG. 3 is a Gaussian distribution diagram in which the peaks of SP ³ binding and SP ² binding in FIGS. 1 and 2 are separated. FIG. 4 shows an example of an electrode configuration diagram when the present invention is applied to a liquid crystal display device. FIG. 5 is an equivalent circuit diagram of an arbitrary pixel of a liquid crystal display device formed using the substrate (not shown) of FIG. FIG. 6 shows another example of the electrode configuration diagram of the present invention. FIG. 7 is an enlarged view showing the MIM element section of the present invention including a part of the scanning electrode and the pixel electrode. FIG. 8 is a partially cutaway perspective view of a liquid crystal display device to which the matrix display device according to the present invention is applied. FIG. 9 is another sectional explanatory view of the MIM element used in the present invention. DESCRIPTION OF SYMBOLS 1 ... Scan electrode 2 ... MIM element 3 ... Pixel electrode, 12 ... Lower electrode 11, 16 ... Pixel electrode, 13 ... Insulating layer 14 ... Upper electrode, 15 ... Transparent substrate 17 ... MIM Element, 18 Common electrode 21 Liquid crystal material

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-187279 (JP, A) JP-A 64-40929 (JP, A) JP-A 64-7577 (JP, A) JP-A-1- 217326 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/136 G02F 1/1343 G09F 9/30 H01L 49/02

Claims (1)

(57) [Claims] In a matrix display device using a thin-film two-terminal element, each of a plurality of pixel electrodes provided on at least one substrate constituting the display device is connected to the pixel electrode via the thin-film two-terminal element. The thin-film two-terminal element is connected to two adjacent scanning electrodes, and the thin-film two-terminal element is connected to the first conductor and the second conductor.
Wherein a hard carbon film is interposed between said conductors.