JP3049085B2 - Thin-film two-terminal element and liquid crystal display device using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improved thin-film two-terminal element and an active matrix type liquid crystal display device using the same, which is used for OA, TV, and high-capacity flat panel displays. Is done.

(Prior art)

The idea of using an oxide layer formed by anodic oxidation of a metal as the insulating layer of a MIM type thin film two-terminal device composed of a metal layer, an insulating layer, and a metal layer is introduced in Japanese Patent Application Laid-Open No. 57-196589. In Japanese Patent Laid-Open No. 62-63333, a Ta ₂ O ₅ layer obtained by anodic oxidation of Ta is used as an insulating layer, but the specific dielectric constant (εr) is as high as 25, and 300 ° C. for removing impurities. , 3
It requires a heat treatment of about 0 minutes (in air).

In Japanese Patent Application Laid-Open No. 61-260219, amorphous silicon containing hydrogen or silicon oxide film, silicon nitride film and silicon oxynitride film having a higher silicon content than the stoichiometric ratio is used as an insulating layer. However, in order to form these material layers, it is necessary to heat the substrate to about 300 ° C., and dust is easily generated, and defects such as pinholes are easily generated. In addition, the relative dielectric constant (εr) is about 5-7.

However, an anodic oxide film was used as the insulating film described above.
In the MIM element, (1) Since the insulating film is limited to the anodic oxide film of the lower metal, control of the physical property value and, consequently, MIM
It is impossible to control the element characteristics arbitrarily.
(2) Since a heat treatment of about 300 to 500 ° C. is required, the substrate material used is limited to those having high heat resistance. (3) When it is used as a switching element of a liquid crystal display device because of its high relative dielectric constant ( Due to the constraint of MIM capacitance / liquid crystal capacitance <1/10), it is necessary to reduce the element area, and high-level fine processing is required.

Further, as described later, the relative permittivity εr and the steepness β of the element include: There is a drawback in that, when εr is high, the steepness is reduced and the display is not suitable for high-density display.

In addition, as the insulating layer, SiNx synthesized in the gas phase was used.
In MIM, although the disadvantages of (1) and (3) are almost eliminated, the film formation temperature is as high as about 300 ° C.
There is a similar problem with. Further, (4) there is a problem that pinholes are easily generated due to dust and the like, and the yield is reduced.

〔Purpose〕

The present invention has been made in view of the above points, the insulating layer,
The above problems (1) to (4) are obtained by forming a thin film having a small relative dielectric constant and hard silicon and oxygen as main constituent elements by employing a means of plasma-polymerizing an organosilicon compound. The purpose is to solve.

〔Constitution〕

A first aspect of the present invention is a thin-film two-terminal element having an insulating layer between a first conductor and a second conductor, wherein the insulating layer is obtained by forming a film using an organosilicon compound as a main source gas. The present invention relates to a thin film two-terminal element characterized by being a "plasma polymerized film containing oxygen as a main constituent element and at least hydrogen as an auxiliary constituent element."

A second aspect of the present invention relates to an active matrix liquid crystal display device using the thin-film two-terminal element as a switching element for pixel selection.

The thin film composed of the plasma polymerized film contains at least one of amorphous and microcrystalline in terms of the structural form, and has a thickness of 200 to 1 μm, preferably 300 to 4000.

 The characteristics of the plasma polymerized film can be summarized as follows. The relative dielectric constant is relatively low, approximately 2 to 6.

Since it is a gas phase synthesis, various physical properties, in particular, a specific resistance value can be controlled in a wide range by film forming conditions.

Since the film is formed under a low pressure (10 ^-4 to 10 ^-1 torr), generation of dust is small.

Relatively high hardness. Although the hardness varies depending on the film forming conditions, the hardness is generally 500 HV or more.

From the characteristics of the above-mentioned thin film, the following advantages are obtained in the thin-film two-terminal element formed using the thin film.

(B) Ta ₂ O ₅ , Al which has been used for two-terminal devices
_Since the dielectric constant is smaller than that of ₂ O ₃ , SiNx, etc., when an element having the same electric capacity is manufactured, the element size can be large.
Therefore, fine processing is not so required, and the element yield is improved from this point as well. (From the driving conditions of the liquid crystal, the ratio between the LCD and the element capacitance needs to be about C _LCD : Cs = 10: 1.) In addition, the IV characteristics of the obtained device are in accordance with the equation (I). Steepness Therefore, if the relative permittivity εr is small, the steepness increases, and the ratio between the on current I _on and the OFF current I _OFF can be increased. Therefore, it is possible to drive the LCD at a lower duty ratio, and a high-density LCD can be realized.

(B) Since various physical properties, in particular, the specific resistance value ρ can be controlled in a wide range, the design and control of the device characteristics can be performed, and the range in which the specifications of the device meeting the purpose can be satisfied is wide. That is, it is easy to perform an optimal design. Therefore, even though the thin film of the present invention is an insulating layer, its resistance value covers a semi-insulating to insulating region, and in this sense, the two-terminal element of the present invention is described in JP-A-61-275819. As an MSI element (Metal-Semi-Insulator).

(C) There are few defects such as pinholes due to dust, and the device yield is improved.

(D) Since it is a hard film, it is resistant to mechanical damage and the element yield is improved.

In view of the above points, the use of a plasma-polymerized film makes it possible to realize a low-cost, gradation (color) and high-density LCD.

The thin film in the present invention will be described in detail. In order to form a plasma polymerized film, a gas containing silicon or oxygen is mainly used. The phase state of these raw materials does not necessarily need to be a gaseous phase at normal temperature and normal pressure, but may be used in a liquid phase or a solid phase as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or decompression. is there. Specifically, siloxane acid-based hexamethyldisiloxane Me
₃ Si-O-SiMe ₃ , Tetramethyldisiloxane HSiMe ₂ -O-SiHM
e _2, tetramethoxysilane Si (OMe) _4, divinyltetramethyldisiloxane _{CH 2 = CHSiMe 2 -O-SiMe} 2 CH = CH 2,
Bis-chloromethyltetramethyldisiloxane ClCH ₂ SiM
e ₂ -O-SiMe ₂ CH ₂ Cl｝, disilazane-based ｛hexamethyldisilazane Me ₃ Si-NH-SiMe ₃ , tetramethyldisilazane Me ₂ H
Si-NH-SiHMe ₂ ｝ and other organosilicon compounds (tetramethylsilane SiMe ₄ , vinyltrimethylsilane CH ₂ ＝ CHSi
Me ₃ ). When oxygen atoms are contained in the raw material gas composition (specifically), it is not particularly necessary to replenish and supply oxygen atoms with another gas (for the purpose of further increasing the film hardness and film adhesion). When the source gas does not contain oxygen atoms (specifically, an oxygen source gas is used in combination. O ₂ , CO, Using CO ₂ or the like, the mixing ratio of the raw material gas / oxygen source gas is generally 4/1 to 1/2 (molar ratio).

As a method for forming a plasma polymerized film from a raw material gas in the present invention, the film forming active species is DC, low frequency, high frequency,
Alternatively, a method formed through a plasma state generated by a plasma method using a microwave or the like is preferable. However, for the purpose of increasing the area, improving the uniformity, and forming a film at a low temperature, the deposition is performed under a low pressure. Is preferred.

Further, active species can be formed by thermal decomposition at a high temperature. In addition, it may be formed through an ion state generated by an ionization evaporation method, an ion beam evaporation method, or the like, or may be formed from neutral particles generated by a vacuum evaporation method, a sputtering method, or the like. Alternatively, it may be formed by a combination of these.

An example of the deposition conditions of the plasma polymerized film thus produced in the case of the magnetic field confinement type plasma CVD method (see FIG. 6) is as follows.

Magnetic field strength: 600 G or more RF output: 0.1 to 50 W / cm ² Negative-Self-bias: 200 V or more Pressure: 10 ^-4 to 10 ^-1 Deposition temperature: room temperature to 350 ° C. Due to this plasma state, the raw material gas becomes radicals and ions. By being decomposed and reacting, it is composed of silicon atoms and oxygen atoms on the substrate, contains at least hydrogen, and is amorphous and microcrystalline (crystal size is several tens of
数 μm) is deposited. Table 1 shows various characteristics of the thin film.

In the case of plasma CVD, which is suitable for mass production, the lower the pressure, the longer the life of the active species, so that the substrate temperature can be lowered, the uniformity over a large area can be achieved, and the specific resistance and hardness tend to increase. Furthermore, at low pressures, the plasma density decreases, and the method utilizing the magnetic field confinement effect is particularly effective for increasing the specific resistance.

Further, this method has a feature that a high-quality film can be similarly formed under a relatively low temperature condition of about room temperature to about 150 ° C., and thus is most suitable for lowering the temperature of the MIM element manufacturing process.

Therefore, there is a feature that the degree of freedom in selecting a substrate material to be used is widened, and a uniform film can be obtained over a large area in order to easily control the substrate temperature. Further, as shown in Table 1, the structure and physical properties of the plasma-polymerized film can be controlled in a wide range, so that there is an advantage that device characteristics can be freely designed. Furthermore, the dielectric constant of the film is 2-6, which is
Because it is smaller than Ta ₂ O ₅ , Al ₂ O ₃ , and SiNx used in the above, when making an element with the same electric capacity, the element size can be large, so it does not require much fine processing. The yield is improved.

The present invention will be further described with reference to FIGS. 1 and 2 show a sandwich type, and FIGS. 3 and 5 show a coplanar type. These variations include a first conductor 2 serving as a bus line and a second conductor 3 serving as a pixel electrode.
(A) and (b) because there are various aspects, and the other points are substantially the same in both materials and manufacturing methods. [FIG. 1 (a),
(B)].

First, an insulating substrate (a material is a glass plate, a plastic plate, a flexible plastic film, or the like) 1
Then, a second conductor 3 serving as a pixel electrode is formed. Specifically, as shown in FIG. 1B, the side 32 not in contact with the insulating layer 4 is formed first. The material is a transparent conductor such as ITO, In ₂ O ₃ , ZnO, SnO ₂ and is formed by a method such as vapor deposition sputtering. Further, a side 31 in contact with the insulating layer 4 is laminated thereon. The material is SnO ₂ or translucent metal. Metal types are Al and N
i, Cr, NiCr, Pt, Ag, Au, Cu, Mo, Ti, Ta, etc.
Same as 32. Next, the second conductor 3 was patterned by wet or dry etching into a predetermined pattern, and an insulating layer (here, a plasma polymerized film) 4 was coated thereon by a plasma CVD method, an ion beam method, or the like.
Specifically, in the plasma CVD apparatus of FIG. 6, a mixed gas of tetramethylsilane / O ₂ = 2/1 was used, and
Under the conditions of 05 Torr, RF output; 0.3 W / cm ² , substrate temperature; room temperature, magnetic field; OG, a plasma polymerized film of about 1000 mm was deposited. Thereafter, the insulating layer 4 was formed by patterning into a predetermined pattern by dry etching, wet etching or a lift-off method using a resist. Further, a first conductor 2 serving as a bus line is formed thereon. Specifically, the insulating layer 4
Is formed first. The material is SnO ₂ or translucent metal. Metal types are Al, Ni, Cr, NiCr, Pt, Ag, A
u, Cu, Mo, Ti, Ta, etc., and the formation method is vapor deposition, sputtering, or the like, similar to 32.

Further, the side 22 not in contact with the insulating layer 4 is laminated (the material is the above metal or a transparent conductor such as ITO, In ₂ O ₃ , ZnO, SnO ₂ ).
Then, patterning is performed to complete the device. It should be noted that FIGS. 1 (b), 2 (b), 3 (b), 4 and 5 are all laminated, but do not come into contact with the insulating layer unless there are two layers in particular. The material on the side may be a single layer [FIG. 1 (a), FIG. 2 (a), FIG. 3 (a)]. Here, the thickness of each of the lower electrode, the upper electrode, and the transparent electrode is usually in the range of several hundreds to several thousand square meters. The appropriate thickness of the film is 200 to 1 μm in consideration of the pressure resistance of the switching element for driving the liquid crystal, the film peeling due to the increase in the film thickness, and the driving voltage limit. That is, when the temperature is 200 ° or less, the element withstand voltage is reduced to 1.5 V or less, which is not suitable for LCD. Also one
Above μm, the film stress increases, peeling frequently occurs, and
Since the threshold voltage becomes 30 V or more, it becomes difficult to design a driver circuit.

FIG. 8 shows the IV characteristics of the two-terminal element of the present invention corresponding to FIGS. It can be seen that, with respect to the biases of + and-, the characteristics are excellent in symmetry and large in steepness. Using this device, an active matrix type LCD with a 100 × 100 bit, 0.37 mm pitch was fabricated, and a frame frequency of 6
As a result of driving with a pulse of 0 Hz, a good display quality was obtained with a contrast of 6: 1 and a viewing angle of ± 60 ° even at a 1/2000 duty.

In order to make the liquid crystal display device of the present invention using the substrate having the MIM element as described above, a second substrate on which this substrate and a stripe-shaped common electrode are formed is prepared, and a liquid crystal is formed between the two substrates by an ordinary method. A layer may be formed.

Since the thin film of claim 1 is used for the insulating layer of the thin-film two-terminal device, the thin-film two-terminal device of the present invention is manufactured by 1) a gas-phase synthesis method such as a plasma polymerization method.
The physical properties can be controlled over a wide range depending on the film forming conditions, and thus the degree of freedom in device design is large.

2) Since the dielectric constant is low, a high level of fine processing technology is not required, and the sharpness of the MIM can be increased, which is advantageous for increasing the area of the panel.

3) Since a high-quality film can be formed even at a low temperature near room temperature, there is no restriction on the material of the substrate and it is suitable for increasing the area.

4) The characteristics of the insulating layer are uniform and have excellent withstand voltage and threshold voltage.

5) Since it is hard and can be formed into a thick film, it is hard to receive mechanical damage, and a reduction in pinholes due to the thick film can be expected.

The liquid crystal display using the thin-film two-terminal element of the present invention has high density and high image quality (contrast, viewing angle).

[Brief description of the drawings]

1 to 5 show specific examples of the configuration of the thin-film two-terminal element of the present invention. (A) shows the case where the electrode has a single-layer structure, and (b) shows the case where the electrode has a laminated structure. FIG. 6 is a cross-sectional view showing an example of an apparatus for manufacturing a plasma-polymerized film by a magnetic field confining capacitively coupled plasma CVD method used in the present invention, and FIG. 7 is another type of manufacturing apparatus used in the present invention. 1 is an example of an inductively coupled plasma CVD apparatus. Fig. 8 a, b
Is the IV characteristic curve of the MIM element It is a graph which shows a characteristic curve. DESCRIPTION OF SYMBOLS 1 ... Insulating board 2 ... 1st conductor (it becomes a bus line) 3 ... 2nd conductor (it becomes a pixel electrode) 4 ... Insulating layer (plasma polymerization film) 21 ... 1st conductor is in contact with the insulating layer when it has a laminated structure Side layer 22: Layer not in contact with the insulating layer when the first conductor has a laminated structure 31 ... Layer on the side in contact with the insulated conductor when the second conductor has a laminated structure 32: When the second conductor has a laminated structure Layer on the side not in contact with the insulating layer of the above 101 ... earth electrode, 102 ... RF electrode 103 ... substrate, 104 ... RF power supply 105 ... bias power supply, 106 ... magnetic field coil 107 ... rotary pump 108 ... matching network 109 ... pirani gauge

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masayoshi Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Inventor Katsuyuki 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Kenji Kameyama 1-3-6 Nakamagome, Ota-ku, Tokyo, Japan Ricoh Co., Ltd. (56) References JP-A-61-174509 (JP, A) JP-A-61- 205917 (JP, A) JP-A-61-260219 (JP, A) JP-A-62-30225 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1362 G02F 1 / 1333 H01L 49/02

Claims (2)

(57) [Claims] 1. A thin-film two-terminal device having an insulating layer between a first conductor and a second conductor, wherein the insulating layer is obtained by forming a film using an organosilicon compound as a main source gas. A thin film two-terminal element, which is a "plasma polymerized film containing hydrogen as an auxiliary constituent element as a main constituent element". 2. An active matrix type liquid crystal display device using the thin-film two-terminal element according to claim 1 as a switching element for pixel selection.