JP3156400B2 - Reflective liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device. Currently, a liquid crystal display device (L
CD) is attracting attention, but active matrix type L
In a CD, amorphous silicon (a-S) is used as a switching element in each pixel to drive a liquid crystal.
i) Thin film transistor (TFT) or polysilicon TFT
Is mainly used.

[0002]

2. Description of the Related Art The above-mentioned TFT has a high on-resistance,
Since the operation speed is slow, there is a limit in using it for fine display with a large number of pixels, and it has been difficult to improve the display quality.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to improve display quality by improving the performance of a switching element for driving a liquid crystal.

[0004]

Means for Solving the Problems To solve the above problems, MOSFETs arranged in a matrix and the MOSFETs
A data bus made of a light-reflective metal, connected to the drain of T and covering the gate electrode of the MOSFET;
A silicon substrate having a display electrode made of a light-reflective metal connected to the source of the OSFET and covering the gate electrode of the MOSFET and the data bus, and a scan bus connected to the gate electrode of the MOSFET formed on the surface thereof; A transparent substrate provided on the silicon substrate at a predetermined distance from the silicon substrate via a liquid crystal layer, and having a transparent electrode adhered thereto.

[0005]

According to the present invention, the data bus made of a light-reflective metal covers the gate electrode, and the display electrode made of the light-reflective metal covers the data bus and the gate electrode. Even if light enters from the gate, the reflection is repeated between the data bus and the display electrode, and the possibility that the light reaches the gate electrode is low. Further, even if the entering light reaches the gate electrode, the reaching light is attenuated by multiple reflections between the data bus and the display electrode, so that it hardly affects the light leak and the like. .
Therefore, good display is enabled.

[0006]

FIG. 1 is a sectional view of a first embodiment of the present invention. MOSFETs are arranged in a matrix on a silicon substrate 1 and are separated by a field oxide film 2. A data write electrode (data bus) 4 made of a reflective metal is connected to the drain of the MOSFET so as to cover the gate electrode 3, and light reflection is performed to cover the gate electrode 3 and the data write electrode 4 to the source of the MOSFET. The display electrode 5 made of a conductive metal is connected. A scan bus (not shown) is formed on the gate electrode 3, and a transparent substrate (not shown) on which a transparent electrode is attached via a liquid crystal layer is provided at a predetermined interval from the silicon substrate 1. I have.

In this example, the data write electrode 4 and the display electrode 5 use an aluminum (Al) film having a thickness of 1 μm. As shown in FIG. 1, since the data write electrode 4 covers the gate electrode 3 and the display electrode 5 covers the data write electrode 4 and the gate electrode 3, light enters from between the adjacent display electrodes 5. Even so, there is a low possibility that light will repeatedly reach between the data writing electrode 4 and the display electrode 5 and reach the gate electrode 3. Further, even if the entering light reaches the gate electrode 3, the reaching light is attenuated by a plurality of reflections between the data writing electrode 4 and the display electrode 5, and thus affects light leakage and the like. There are few things.

In the above-described structure, if the gate electrode 3 is formed using only a polysilicon film, even a small amount of light passes therethrough. Therefore, by using a light-reflecting or opaque material, It is possible to completely shield the channel region from light, reduce the leakage current of the MOSFET, and improve the image quality. Examples of such a gate electrode material include metal, metal silicide, and a composite film of metal silicide and polysilicon.

Further, a portion of a scan bus (not shown) connected to the gate electrode 3 and wired vertically to the gate electrode 3 straddles the data write electrode 4, and has a thickness of 1200 mm.
If a composite film of a polysilicon film and a WSi film having a thickness of 1800.degree. Is used, it is sufficient to block light, thereby reducing wiring resistance and further improving display quality.

In the above configuration, since the display electrode 5 is formed so as to cover the MOSFET, the display electrode 5 has unevenness and the image quality is degraded. Therefore, the thickness of the display electrode 5 is 3 μm.
It is possible to further improve the image quality by forming the film with an Al film and polishing and flattening the surface.

For polishing, colloidal silica (pH 9 to 10) having a particle size of 50 nm is used as an abrasive, and 13 rpm at 90 rpm.
Do for a minute. In addition, if unevenness occurs between the display electrodes, the thickness of the liquid crystal layer changes only in that portion and the image quality is deteriorated. A silicon dioxide (SiO ₂ ) film is deposited to a thickness of 3 μm by growth (CVD) and has a particle size of 50 n.
The measurement was performed for 13 minutes at a load of 100 g / cm ² and 90 rpm using m m colloidal silica (pH 9 to 10). As a result, the surface of the silicon substrate was flattened and the image quality could be improved.

FIG. 2 is a sectional view of a second embodiment of the present invention.
The display electrode 5 and the data write electrode 4 are formed so as to overlap with each other to shield the MOSFET and its periphery from light, reduce leak electrodes due to light, and improve display quality.

Also in this example, the data write electrode 4
The display electrode 5 uses an Al film having a thickness of 1 μm. A portion of the data writing electrode 4 where a scan bus (not shown) connected to the gate electrode 3 and wired vertically to the gate electrode 3 has a thickness of 1200 mm. Polysilicon film and thickness 1
An 800 ° WSi composite film is used.

Further, as shown in FIG.
The source electrode 12 connected to the source region of T is formed of a polysilicon film having a thickness of 2000 °
A thermal oxide film of Å is formed, and a storage capacitor electrode 10 composed of a composite film of a polysilicon film having a thickness of 1,200 と and a WSi film having a thickness of 1,800 形成 is formed thereon to form a stacked capacitor. The display electrode 5 is connected to the source electrode 12 and formed on the outermost surface.

In any of the embodiments, the MOSFET for driving the display electrode may have a source / source voltage depending on the case.
Since a withstand voltage between drains of 10 V or more is required, ion implantation of source / drain regions is performed using phosphorus ions (P ⁺ ) [energy 120 KeV, dose amount 1 × 10 ¹⁴ / cm ² ].
And arsenic ion (As ⁺ ) [energy 70 KeV, dose 4 × 10 ¹⁵ / cm ² ] twice, it is possible to increase the breakdown voltage.

[0016]

According to the present invention, in a MOSFET of a driving element in a reflection type liquid crystal display device, light is prevented from entering a channel below a gate electrode, a leak current due to light is reduced, and a surface of the element is flattened. This improves the quality of the image.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Field oxide film 3 Gate electrode 4 Data writing electrode 5 Display electrode 6 Protective film 10 Storage capacitor electrode 12 Source electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1368 H01L 29/78

Claims (1)

(57) [Claims] 1. MOSFET arranged in a matrix
Connected to the drain of the MOSFET,
A light-reflective metal covering the gate electrode of the SFET
Data bus and the source of the MOSFET
The gate electrode of the MOSFET and the data bus.
A display electrode made of a light-reflective metal;
The scan bus connected to the gate electrode of T and the surface
A silicon substrate formed, and the silicon substrate on the silicon substrate via a liquid crystal layer.
Is provided at a fixed interval and a transparent electrode is attached
A reflective liquid crystal display device having a transparent substrate .