JPH05281575A - Liquid crystal driving thin film transistor device - Google Patents

Abstract

PURPOSE:To prevent write delay and enable uniform high-contrast display by providing a thin film transistor and a black matrix formed of an inorganic insulating body with conductors of specific conduction electron density dispersed therein. CONSTITUTION:A gate line 12 is formed on a black matrix 11 formed on a transparent base 10 made of glass or the like, and a detached semiconductor layer 15 and a transparent picture element electrode 13 are further formed through an insulating layer 14. A source electrode 17 and a drain electrode 18 are connected to the semiconductor layer 15 through an n<+> layer 16. In this case, an inorganic insulating body with conductors of 6.9X10<21>cm<-3> or more in conduction electron density dispersed therein is used as the black matrix, and it is desirable that the respective dispersion bodies are mutually spaced to such an extent that the wave functions are not overlapped, or more. The black matrix 11 thereby functions electrically as an insulating body, so that the delay of the gate line and a signal line is hardly generated. In addition, capacity coupling to the gate line, signal line and picture elements is further reduced so as to eliminate contrast difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving black matrix thin film transistor device having a black matrix formed on a substrate.

[0002]

2. Description of the Related Art A normally white type projection type flat panel using a TN type liquid crystal has come to have a higher contrast in recent years. Along with this increase in contrast, the development of a so-called black matrix-on-array thin film transistor (hereinafter referred to as BMTFT) in which a black matrix is formed on a substrate on which a thin film transistor is formed is desired. As such a BMTFT, one using a black dye or a resin mixed with a raw material as a black matrix (see, for example, JP-A-62-153904 and JP-A-59-195682) and a metal. Two types are known as typical ones, one used (see, for example, JP-A-64-62617).

For the former black matrix using a black resin, a polyimide containing a black dye or pigment is often used. However, since dyes decompose at around a hundred and several tens of degrees Celsius and pigments at around 250 degrees Celsius
It is not suitable for a TFT process including a film forming process of an oxide film, a transparent electrode, a semiconductor thin film, etc., which needs to be formed or annealed before and after. Further, the black resin requires a film thickness of several μm or more in order to completely block light. This required film thickness is not so large that it cannot be ignored with respect to the gap of the liquid crystal cell, that is, the space (about 5 μm) of the space into which the liquid crystal is injected, and it disturbs the alignment of the injected liquid crystal, which is not preferable. ..

Since the latter black matrix using a metal is a metal, as described below, the probability of a short circuit between the gate line, the signal line, and the pixel is significantly increased, or the gate line and the signal line are shorted. It causes an increase in capacity and causes a delay in signal transmission. In addition, the capacitive coupling between the signal line and the pixel is increased to cause non-uniformity of contrast in the upper and lower portions of the screen.

FIGS. 10 to 12 show an example of a conventional BMTFT having a black matrix made of a metal thin film. 10 is a plan view and FIG. 11 is a line XI in FIG.
-A sectional view taken along line XI, and Fig. 12 shows a line XII- in Fig. 10.
It is sectional drawing along XII.

A metal thin film B shown in FIGS. 10 to 12.
The MTFT has a lower passivation film 31 on a glass substrate 30. SiO is formed on the passivation film 31.
_A gate line 32 made of Ta or the like, a transparent pixel electrode 33 made of ITO or the like, and a source electrode 37 also serving as a signal line made of Al or the like are formed through an insulating film 34 made of ₂ or Si ₃ N _4. There is. The TFT is composed of an island-shaped amorphous silicon layer 35, and is connected with a drain electrode 38 composed of Al or the like. A black matrix 40 made of a metal such as Cr is formed at a position corresponding to a gap between each wiring and each pixel. 41 in the figure is an upper passivation film.

In a TFT using such a metal black matrix, the metal black matrix line 40 overlaps the gate line 32, the signal line 37 or the pixel 33 as shown in FIGS. 11 and 12. That is, the semiconductor layers to be insulated overlap each other over a considerable area, and the probability of a short circuit between wirings increases significantly. As a result, even if it is not so, TF for liquid crystal has a low manufacturing yield
The yield of T is decisively low. Further, when the black matrix is not formed, an unnecessary insulating film between the black matrix and the gate must be provided because the black matrix is a metal. Since the process is added, the cost becomes high.

Further, in the metal BMTFT, there are a method of keeping the metal black matrix line at a fixed potential and a method of putting it in a floating state. In the method of maintaining a fixed potential, capacitive coupling occurs between the metal black matrix line, the gate line, and the signal line, and the write current is delayed. Further, in the floating system, the capacitance between the signal line and the pixel becomes large due to the presence of the metal black matrix, and the pixel potential fluctuation accompanying the change in the signal potential becomes large. The signal potential has an opposite polarity in the next frame in order to prevent deterioration of the liquid crystal, but at the top of the screen, it takes 1 frame time NT until the signal potential polarity is reversed.
In the SC method, it takes about 16 milliseconds, whereas in the lower part of the screen, the signal potential polarity is reversed in about 2 milliseconds. Therefore, the lower part of the screen has a poorer contrast than the upper part.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and suppresses the decrease in manufacturing yield,
Another object of the present invention is to provide a liquid crystal thin film transistor capable of uniform and high-contrast display without causing a writing delay.

[0010]

According to the present invention, there is provided a liquid crystal driving thin film transistor device having a black matrix and a thin film transistor comprising a semiconductor thin film, a gate, a source and a drain formed on a substrate. As a black matrix, 6.9 × 10
There is provided a thin film transistor device for a liquid crystal, which uses an inorganic insulator in which a conductor having a conduction electron density of ²¹ cm ⁻³ or more is dispersed.

Conductors of the present invention (including metals and semiconductors)
In the black matrix made of an insulating film in which is dispersed, it is preferable that the dispersed conductors are separated from each other by at least 10 angstroms or more so that the wave functions do not overlap each other. In this case, the particle size of the dispersed conductor is 2r
In Angstrom, the volume ratio of the dispersed conductor to the insulating pair is about r ³ / {6 (r + 10) ³ } or less.
The conduction electron density of each dispersed conductor is not so different from that of the bulk material (6.9 × 10 ²¹ cm ⁻³ or more).

[0012]

In the conductor-dispersed insulating film black matrix of the present invention, the dispersed conductors are dispersed so as not to overlap their wave functions, and thus electrically function as an insulator. On the other hand, since the conduction electron density in the dispersed conductor is not so different from that of the bulk material, the plasma vibration is almost the same as that of the bulk material, and almost all incident visible light is reflected.

That is, the condition that an electromagnetic wave having an angular frequency ω is reflected by a material having a plasma frequency ω _p is
ω <ω _p .

Here, ω _p is represented by the formula ω _p = (4πne ² / m _q ) ^1/2 (where n is the conduction electron density and m _q is the effective mass of conduction electrons). From this equation, n ≧ ω ² m / (4πe
^{If 2} ) is satisfied, the material will reflect electromagnetic waves. Now, ω = 4.7 × 10 ¹⁵ rad / sec (ultraviolet light), m _q = m ₀ = 9 × 10 ⁻²⁸ g (static mass of electron)
And the conduction electron density n is 6.9 × 10 ²¹ cm
^{At -3 and} above, the material reflects visible light. Note that the plasma frequency ω _p is
This is not only a function of the conduction electron density, but also a function of the effective mass m _q of conduction electrons. If the effective mass is significantly different from the rest mass of the electron, then the material will reflect electromagnetic waves if n> 7.6 × 10 ⁴⁸ m _q .

Although it is considered that the surface of the dispersed conductor is covered with an oxide film, the light incident on the oxide film is scattered or reflected by the conductor inside. The conductor is
When each thickness is 300 to 1000 angstroms (A) or more, visible light is almost totally reflected. Therefore, the conductor-dispersed insulating film black matrix of the present invention also has a cumulative thickness of the dispersed conductor of 300 to 1000.
When it is A, the incident visible light is almost blocked, and it functions well as a black matrix. Further, even if the cumulative thickness of the dispersed conductor does not reach such a thickness, in the projection type liquid crystal display device using the schlieren optical system, the incident visible light is scattered by the dispersed conductor. Can be removed by squeezing. Therefore, also in this case, the conductor-dispersed insulating film of the present invention functions as a black matrix.

Further, since the conductor-dispersed insulating film black matrix of the present invention is itself an electric insulator as described above, it has a great advantage that problems such as short circuit between wirings do not occur. .. In addition, if the conductor-dispersed insulating film is used as it is as the insulating film between the conductor layers, the black matrix can be formed without increasing the number of manufacturing steps.

Furthermore, since the black matrix of the present invention is an insulator, the conductors dispersed therein are in a floating state, and the write current is hardly delayed. Further, it has various advantages over the floating type conventional metal black matrix.

[0018]

Embodiments of the present invention will now be described in more detail with reference to the drawings.

1 to 4 show an example of a TFT using the black matrix of the present invention in the lowermost layer. Figure 1
2 is a plan view, FIG. 2 is a sectional view taken along line II-II in FIG. 1, FIG. 3 is a sectional view taken along line III-III in FIG. 1, and FIG. 4 is line IV in FIG. 4 is a sectional view taken along line IV. FIG.

The BMTFT of the present invention shown in FIGS. 1 to 4.
Is a transparent substrate 10 such as a glass substrate on which a black matrix 11 of the present invention made of a conductor-dispersed insulating film is formed. Since this black matrix also has the function of the lower passivation layer, it covers a wider area than the conventional metal black matrix. A gate line 12 is formed on the black matrix 11, and an island-shaped semiconductor (amorphous silicon) layer 15 and T are formed via an insulating layer 14 made of SiO ₂ , Si ₃ N ₄ or the like.
A gate line 12 made of a or the like and a transparent pixel electrode 13 made of ITO or the like are formed. A source electrode 17 (also serving as a signal line) and a drain electrode 18 made of Al or the like are connected to the semiconductor layer 15 via an n ⁺ layer 16. In the figure, 19 is an upper passivation layer.

Such a conductor dispersed insulating film BMT of the present invention
The FT can be manufactured, for example, as follows.

First, an insulating film (black matrix) 11 in which a conductor is dispersed is formed on a glass substrate 10 (this will be described in detail later). Next, the transparent pixel electrode 1 made of ITO or the like is formed by backside exposure self-alignment.
3 is formed. Subsequently, like the conventional TFT described above,
The gate line 12 is made of Ta or the like, the insulating layer 14 is made of TaO ₂ , SiO _2, or the like, the island-shaped semiconductor layer 15, the n ⁺ layer 16, and Al.
Source electrode 17 and drain electrode 18, Si
The black matrix TFT of the present invention is obtained by forming the upper passivation layer 19 of ₃ N ₄ or the like.

As shown in FIGS. 1 to 4, the black matrix 11 of the present invention is overwhelmingly larger than the TFT portion and completely blocks the light from the back surface of the substrate.
The light leakage current of can be almost completely eliminated. Moreover, since the transparent electrode 13 can be formed by self-alignment by back surface exposure using the black matrix line 11 as a mask, the aperture ratio can be maximized.

Now, the black matrix 11 of the present invention
As shown in FIG. 5, has a stripe structure in which conductors 112 are dispersed as a dispersed phase (discontinuous phase) in a continuous phase 111 made of an insulator. In this example, the conductors 111 are represented as particles dispersed in the insulator continuous phase 112.

FIG. 6 shows another embodiment of the conductor-dispersed insulating film black matrix of the present invention. The black matrix of this embodiment is composed of a multilayer film in which an island-shaped ultra-thin film 114 made of a conductor and a continuous insulator thin film 113 are laminated. The ultra-thin conductor film 114 is formed to be extremely thin so as not to be a continuous film, has an island-like structure composed of isolated islands 114, and electrically functions as an insulator. Each isolated island 114 corresponds to the conductor 112 in FIG.

Next, an example of the method for producing the black matrix of the dispersed conductive insulating film will be described by taking the multilayer structure of the conductor ultrathin film / insulator thin film of FIG. 6 as an example.

For example, by using a two-gun RF magnetron sputtering device, the substrate is alternately brought close to the vicinity of the target of the insulating film and the target of the conductor, and the insulator and the conductor are alternately deposited to form the multilayer film. be able to.
At this time, the thickness of one layer of the conductor ultrathin film can be controlled to several tens of A by appropriately controlling the time for which the substrate is located near the target of the conductor, and the conductor ultrathin film can be obtained as an island structure (that is, , When forming a conductor ultra-thin film, stop the deposition before the film becomes continuous). Then, a resist film is formed by photolithography, and the multilayer film is etched into an etchant for the insulating film, whereby the multilayer film can be processed into a stripe shape. At this time, the insulator,
Depending on the combination of the conductor and the etchant, the dispersed conductor may adhere to the substrate as a residue. For example, SiO ₂ or Si ₃ N ₄ as the insulating film and Mo or A as the conductor.
1, Mo-Ta alloy or Cu, when using a mixed etchant of hydrofluoric acid and nitric acid as an etchant, or SiO ₂ or Si ₃ N ₄ as an insulator, and A as a conductor
l, When an ammonium fluoride-based etchant is used as the etchant, the etchant dissolves both the conductor and the insulator, so that the multilayer black matrix line can be manufactured without producing a residue.

The black matrix line can be formed not only by the wet lithographic method but also by the ion beam milling method. In that case, as an insulator, Si
Ti, Ta, Cr, W, N having O ₂ or Si ₃ N ₄ and having a milling rate similar to that of an insulator as a conductor
b, Fe, Mo, Zr, Al or the like can be used.

Furthermore, the black matrix of the present invention can also be formed by forming a porous ceramic thin film by sputtering or the like and embedding a conductor in the hole.

As described above, since the conductor-dispersed insulating film black matrix of the present invention is itself an electric insulator, it has a great advantage that it does not cause a problem such as a short circuit between wirings. In addition, since the conductor-dispersed insulating film can be used as it is as an insulating film between the conductor layers, the black matrix of the present invention can be formed by an ordinary insulating film forming step, and the number of manufacturing steps is not increased.

Furthermore, since the black matrix of the present invention is an insulator, the conductors dispersed therein are in a floating state, and the write current is hardly delayed. Further, it has the following advantages with respect to the floating type metal black matrix.

The conductor-dispersed insulating film of the present invention shown in FIG. 5 has the model shown in FIG. 7, that is, the conductors 112 having the thickness t and separated from each other by the distance d and dispersed in the insulator continuous phase 111. It is considered to be electrically equivalent to the model. Therefore, the equivalent circuit has a width d, as shown in FIG.
It can be represented by a series connection of _n capacitances C ₁ to C _n of thickness t. The effective capacity C _BM per unit length in this case is represented by 1 / C _BM = Σ _i ⁿ 1 / C _i . Here, n is the total number of capacitances shown in FIG. 8, and C _i is the capacitance per unit length of one capacitance shown in FIG.

As an example, the particle size of the dispersed conductor 111 is now 2
r The 50A, average distance d of 50A between distributed conductors, total thickness of the dispersion conductors (effective thickness) t 500A, if the width of the black matrix line and ^{10μm, n = 10 × 10 4} /100 = 10 ³ C _i = εt / d = ε × 500 × 10 ⁻¹⁰ / 50 × 10 ⁻¹⁰ = 10ε (F / m), and thus 1 / C _BM = Σ _i ⁿ 1 / C _i = 10 ³ / 10ε C _BM = ε / 100 (F / m).

Next, the capacitive coupling between the signal line and the pixel will be considered in the case of the conventional floating type metal black matrix and the case of the conductor dispersed insulating film black matrix of the present invention.

First, in the case of the conventional floating type metal black matrix line, as shown in FIG. 11, the overlap L _OV of the signal line, the pixel and the metal black matrix is 4 μm, and the signal line, the pixel and the metal black matrix line are If the spacing d _{OV is set} to 0.5 μm and the capacitances C _sb and C _bg per unit length between them are simply considered as parallel plate conductors having an area L _OV × Lm and a spacing d _OV , then C _sb = C _bg = εL _OV / D _OV = ε4 × 10 ⁻⁶ × 1 / 0.5 × 10 ⁻⁶ = 8ε (F / m).

In the case of a pixel having a width of about 100 μm as shown in FIG. 13, the size of C _b-g0 shown in the same figure is ε (F / m).
Therefore, after all, the capacitance C between the signal line and the pixel per unit length in the conventional metal black matrix
_bg is by calculation from the equivalent circuit shown in the figure, a _{C bg = C sb × C bg} / (C sb + C bg) + C b-g0 = 5ε (F / m).

On the other hand, for comparison, the structure as shown in FIG. 9 similar to that of FIG. 13 is used, and the unit length per unit length when the conductor dispersed insulating film of the present invention is used as the black matrix 40 '. The signal line-pixel capacitance C _bg is represented by an equivalent circuit as shown in the figure, but C _sb , C _BM , C
The series capacitance of _bg is given by the following formula: C _bg = 1 / [1 / C _sb + 1 / C _BM + 1 / C _bg ] + C _{s-g 0} = 1 / [1 / 8ε + 1 / (ε / 100) + 1 / 8ε] + ε = ε / 100 + εε (F / m).

The actual pixel size is about 100 μm in width × 300 μm in length, and the signal line-pixel capacitance per pixel is (conventional) C _bg = 300 × 10 ⁻⁶ C _bg = 1 in each case. 0.5 × 10 ⁻³ ε (invention) C _bg = 300 × 10 ⁻⁶ C _bg = 0.3 × 10 ⁻³ ε.

By the way, the fluctuation of the pixel potential due to the fluctuation of the signal line potential is called crosstalk, and its amount ΔV.
_sg is expressed by the following equation.

ΔV _sg = (C _bg * Δ _sig + C _bg * Δ _sig ) / (C _LC + C _CB + 2 * C _bg ) where C _LC and C _CB are the pixel-counter electrode capacitance per pixel, Auxiliary capacitors, each of which is about 0.02εF. Further, Δ _sig is a signal potential range and has a value of about 10V.

Therefore, the crosstalk amount ΔV _{sg in} the case of using the conventional metallic black matrix line of the floating system is ΔV _sg = (2 × 1.5 × 10 ⁻³ ε × 10) / (0.02ε × 2 + 2) × 1.5 × 10 ⁻³ ε) = 0.7V.

On the other hand, when the black matrix of the conductor-dispersed insulating film of the present invention is used, ΔV _sg = (2 × 0.3 × 10 ⁻³ ε × 10) / (0.02ε × 2 + 2 × 0. 3 × 10 ⁻³ ε) = 0.15V, and the crosstalk amount is ¼ to 1 as compared with the case of the floating type metal black matrix line.
It can be / 5. This amount of crosstalk is almost comparable to that when the black matrix is not formed. As a result, it is possible to reduce flicker when performing frame inversion drive and non-uniformity of display brightness at the top and bottom of the screen. Further, it can also function as a light-shielding film as a countermeasure against the light leak current of the TFT, which brings a great advantage in terms of process.

[0043]

As described above, the conductor dispersed insulating film black matrix of the present invention reflects or scatters incident visible light because the conductor has a high plasma vibration. Further, since it electrically functions as an insulator due to the dispersion effect, the gate line and the signal line are hardly delayed.
Furthermore, it is possible to significantly reduce the capacitive coupling between the gate line, the signal line and the pixel, reduce flicker, and provide an image with no difference in contrast between the upper and lower portions of the screen. Also,
In the manufacturing process, problems such as short circuit between wirings do not occur, and it is not necessary to add the number of steps for forming the black matrix. Further, when forming the pixel electrode, if the black matrix is used as a mask for photolithography and self-aligned by backside exposure to form the transparent electrode, the aperture ratio can be maximized. Also,
Since the black matrix of the present invention hardly causes capacitive coupling, it can be formed large enough to shield the entire surface of the TFT portion from light, and the light leakage current of the TFT can be completely eliminated.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a black matrix TFT of the present invention.

2 is a cross-sectional view taken along the line I-I of FIG.

3 is a cross-sectional view taken along the line II-II in FIG.

4 is a cross-sectional view taken along the line III-III in FIG.

FIG. 5 is a schematic perspective view showing an example of a black matrix of the present invention.

FIG. 6 is a schematic perspective view showing another example of the black matrix of the present invention.

FIG. 7 is a model perspective view of a black matrix of the present invention.

8 is an electrical equivalent circuit diagram of the black matrix of FIG.

FIG. 9 is an equivalent circuit diagram between a signal line and a pixel when the black matrix of the present invention is used.

FIG. 10 is a schematic plan view of a conventional black matrix TFT.

11 is a cross-sectional view taken along the line XI-XI of FIG.

12 is a cross-sectional view taken along the line XII-XII in FIG.

FIG. 13 is an equivalent circuit diagram between a signal line and a pixel when a conventional floating type metal black matrix is used.

[Explanation of symbols]

10 ... Transparent substrate, 11 ... Conductor dispersed black matrix, 12 ... Gate line, 13 ... Pixel electrode, 15 ... Semiconductor layer, 17 ... Source electrode, 18 ... Drain electrode.

Claims (1)

[Claims] 1. A liquid crystal driving thin film transistor device comprising a thin film transistor having a semiconductor thin film, a gate, a source and a drain formed on a substrate and having a black matrix, wherein the black matrix is 6.9. A thin film transistor device for liquid crystal, comprising an inorganic insulator in which a conductor having a conduction electron density of × 10 ²¹ cm ^-3 or more is dispersed.