JP2006030836A - Reflection type liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display element with which a high-performance display panel having an aperture ratio of ≥90% when pixel intervals of the reflection type liquid crystal display element is set to ≤10 μm can be obtained. <P>SOLUTION: The reflection liquid crystal element is constituted by arranging an element substrate 18 comprising a plurality of switching transistors 19 formed on a substrate, an insulating layer 16 formed on the plurality of switching transistors 19, and a plurality of pixel electrodes connected to the switching transistors 19 via through holes formed in the insulating layer 16, and comprises a common electrode 14 disposed opposite the element substrate 18 and a liquid crystal layer 15 filled between the common electrode 14 and element substrate 18; and the plurality of pixel electrodes 12 are arranged at intervals smaller than a prescribed width and a reflecting film 17 is formed between the plurality of pixel electrodes 12 and insulating layer 16. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an active matrix reflective liquid crystal display element.

  Conventionally, as a device that uses liquid crystals that maintain a certain order like a solid, but have fluidity like a liquid and change the alignment with an electric field and appear as a change in optical properties. Liquid crystal display devices are known. The liquid crystal display element used in this liquid crystal display device encloses liquid crystal between a common electrode and an individually controllable pixel electrode arranged against the common electrode, and selectively applies an electric field controlled by a data signal to the pixel electrode. By doing so, the optical characteristic of the liquid crystal between corresponding pixel electrodes is changed.

This liquid crystal display element is roughly classified into a transmissive liquid crystal display element and a reflective liquid crystal display element.
A liquid crystal display device using a transmissive liquid crystal display element has an advantage that the configuration of the optical system becomes relatively simple, so that it is easy to reduce the cost. On the other hand, when the display panel is downsized, switch transistors and wiring for selecting pixel electrodes are used. There is a drawback that the area ratio increases, the aperture ratio decreases, and the brightness of the image decreases and becomes darker.

FIG. 1 of Non-Patent Document 1 describes a transmissive liquid crystal display element and a TFT array of a reflective liquid crystal display element. As shown in FIG. 1, the reflective liquid crystal display element includes a reflective pixel electrode. Since the switch transistor and the wiring are arranged below, the aperture ratio does not decrease even when the display panel is downsized, and a bright image can be obtained.
Therefore, a reflective liquid crystal display element using a small and high-density display panel is suitable for a liquid crystal display device of an enlarged projection method.

  The pixel interval of the reflective liquid crystal display element used in the reflective display device described in Non-Patent Document 1 is 30 μm × 36 μm, and the aperture ratio is 70%. This indicates that the transmissive liquid crystal display element has higher performance than the aperture ratio of 60%.

These liquid crystal pixel electrodes are formed by exposing a photomask to a resist and developing it in the photoresist method shown in FIG.
“High-density reflective TFT array for liquid crystal projection type high vision”, Yone Takubo et al., Television Society Vol. 44, No5, pp. 544-549 (1990)

  However, in order to form the pixel electrode of the reflection type liquid crystal display element of the reflection type display device described above, a high performance display using a photoresist method with a higher pixel spacing of 10 μm and an aperture ratio of 90% or more. When used in a panel, incident light that has passed through the inter-pixel gap is reflected by a reflective liquid crystal display element even though the aperture ratio is 92% theoretically at the inter-pixel gap of 0.4 μm, which is the limit of the photoresist method. The problem is that diffuse reflection is caused to decrease the aperture ratio, and that only an aperture ratio of about 82% is obtained in actual measurement.

  Accordingly, the present invention has been made to solve the above-described problems, and a high-performance display panel having an aperture ratio of 90% or more when the pixel interval of the reflective liquid crystal display element is 10 μm or less. An object of the present invention is to provide a reflective liquid crystal display element capable of obtaining the above.

  As a means for achieving the above object, a reflective liquid crystal display device according to a first invention includes a plurality of switching transistors formed on a substrate, an insulating layer formed on the plurality of switching transistors, and the insulating layer. An element substrate composed of a plurality of pixel electrodes connected to the switching transistor through a through hole generated in the layer is arranged, and a common electrode opposed to the element substrate, the common electrode and the element In a reflective liquid crystal display element comprising a liquid crystal layer filled with a substrate, a space between the plurality of pixel electrodes is set to a predetermined width or less, and a reflective film is provided between the plurality of pixel electrodes and the insulating layer. It is an object of the present invention to provide a reflective liquid crystal display element characterized by being formed.

  According to the present invention, the incident light that has passed through the inter-pixel gap does not cause irregular reflection in the reflective liquid crystal display element, and the inter-pixel gap is narrowed from 0.075 μm to 0.15 μm, thereby reflecting the liquid crystal display. A high performance display panel can be obtained in which the aperture ratio is 90% or more when the pixel spacing of the element is 10 μm or less.

Hereinafter, a liquid crystal display device and a reflective liquid crystal display element according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view of a reflective liquid crystal display element used in a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 shows a state in which incident light is input to an electrodeless portion of the reflective liquid crystal display element of FIG. FIG. 3 is a diagram showing an opening state due to a gap between pixels, FIG. 4 is a diagram showing a calculated value and an actual measurement value of an aperture ratio due to the gap between pixels, and FIG. 5 is a pixel according to a nanoprint method. It is a figure which shows an electrode production | generation procedure.

  First, as shown in FIG. 1, a reflective liquid crystal display device according to an embodiment of the present invention includes a plurality of switching transistors 19 formed on a substrate, an insulating layer 16 formed on the plurality of switching transistors 19, An element substrate 18 composed of a plurality of pixel electrodes connected to the switching transistor 19 through a through hole generated in the insulating layer 16 is arranged and shared with the common electrode 14 disposed opposite to the element substrate 18. In a reflective liquid crystal display device comprising a liquid crystal layer 15 filled between the electrode 14 and the element substrate 18, the space between the plurality of pixel electrodes 12 is set to a predetermined width or less, and the plurality of pixel electrodes 12 and the insulating layer 16 A reflective film 17 is formed between the two.

  1 will be described in more detail. A drain 2, a source 3, and an auxiliary capacitance element 4 are formed on the surface of the single crystal silicon substrate 1, and polycrystalline silicon is interposed between the drain 2 and the source 3 through a gate oxide film 5. A gate transistor 7 is provided to constitute a MOS transistor as a switch transistor.

  A silicon electrode 8 is provided on the auxiliary capacitance element 4 via an oxide film 6 to constitute an auxiliary capacitance. The drain 2 is connected to the signal electrode 10. The source 3 and the auxiliary capacitor silicon electrode 8 are connected via a metal electrode 11. An insulating film 9 is formed between them.

Next, an insulating layer 16 is formed on the signal electrode 10 and the metal electrode 11 for planarization, and an insulating reflective film 17 is further formed thereon.
In order to efficiently reflect incident light, the insulating reflective film 17 is formed of, for example, a multilayer film of TiO 2 and SiO 2, and the thickness is set within 1 μm in consideration of the reflection efficiency.

  A reflective pixel electrode 12 is formed on the insulating reflective film 17 and connected to the metal electrode 11. When connecting, the insulating reflective film 17 and the insulating layer 16 penetrate. One reflection pixel electrode 12 is provided for one pixel and is arranged on the matrix as a whole. As a material of the reflective pixel electrode 12, a metal having high reflectance such as aluminum or gold is used.

  Since the insulating reflective film 17 is provided on the entire substrate surface except for the penetrating portion of the reflective pixel electrode 12 connected to the metal electrode 11, it is possible to prevent incident light from leaking between the reflective pixel electrodes 12.

Next, a liquid crystal light distribution film 13 is formed over the reflective pixel electrode 12 and the exposed insulating reflective film 17, and a transparent common electrode 14 is prepared on the liquid crystal light distribution film 13 to contain the liquid crystal 15.
In this way, a reflective liquid crystal display element is formed.

Next, the operation will be described.
First, when a selection voltage is applied to the polycrystalline silicon gate 7, a channel is formed between the drain 2 and the source 3, and the drain 2 and the source 3 are electrically connected, and then the source 3 passes through the metal electrode 11. The electrically connected reflective pixel electrode 12 is charged to the potential of the signal electrode 10.

  When the voltage of the polycrystalline silicon gate 7 becomes a non-selection voltage, the channel is disconnected and the source 3 and the reflection pixel electrode 12 are in a floating state until the next gate selection voltage is applied. The potential of the electrode 12 is maintained at the signal potential. The liquid crystal 15 is subjected to an optical displacement only while a predetermined potential is applied between the reflective pixel electrode 12 and the common electrode 14.

Incident light entering from the transparent common electrode 14 is transmitted according to the pattern of the liquid crystal 15 subjected to optical displacement, and this transmitted light is transmitted through the alignment film 13 of the liquid crystal and then made of a thin reflective pixel electrode 12 made of metal. And return to the incident optical path.
The light transmitted through the portion other than the reflective pixel electrode 12 is reflected by the surface of the insulating reflective film 17 and returns to the incident optical path as shown in the non-electrode portion (1) of FIG.

  In this way, most of the incident light is reflected by the thin reflective pixel electrode 12, and the rest is reflected by the insulating reflective film 17 and returns to the incident optical path. Since the insulating reflective film 17 is disposed immediately below the reflective pixel electrode 12, it does not enter the transistor component portion, so that unnecessary fluctuation of the pixel voltage can be prevented.

  FIG. 3 shows reflection patterns with gaps between pixels of 0.4 μm, 0.2 μm, and 0.1 μm when the pixel interval of the reflective pixel electrode 12 is 10 μm × 10 μm. As described above, when the inter-pixel gap is large, white lines appear strongly in the vertical and horizontal directions and become smaller as the inter-pixel gap is smaller.

This is shown in FIG. The aperture ratio is measured by measuring the ratio of reflected light to incident light 100.
The aperture ratio calculation value in FIG. 4 is calculated from the area of the reflective pixel electrode 12 and the inter-pixel gap, and is a straight line with respect to the inter-pixel gap as indicated by S0, S1, S2, and S3.
The aperture ratio measured value B is the case where there is no reflective film 17, and as shown in the electrodeless part (2) of FIG. Let Accordingly, as shown by L0, L1, L2, and L3 in FIG. However, the gap between the pixels rapidly approaches the calculated aperture ratio from around 0.15 μm. This is because the wavelength of light to be used is 450 nm to 750 nm and is close to the inter-pixel gap, so that incident light is hardly scattered.
If the inter-pixel gap is less than or equal to the wavelength of light used, interference between incident light and reflected light tends to occur. Therefore, the inter-pixel gap needs to have a maximum light wavelength of 750 nm, that is, 0.075 μm or more. Therefore, it is effective to set the gap between pixels from 0.075 μm to 0.15 μm.

  The aperture ratio measured value A is obtained when the reflective film 17 is provided, and the aperture ratio is improved because there is no irregular reflection or leakage light inside the reflective liquid crystal display element compared to the case where the reflective film 17 is not provided. In this case, the aperture ratio becomes 90% or more from around 0.2 μm, but also approaches the calculated aperture ratio rapidly from around 0.15 μm.

  Therefore, from the measured values shown in FIG. 4, the reflective film 17 is effective in improving the aperture ratio, and if the gap between pixels is changed from 0.075 μm to 0.15 μm, a better aperture ratio can be obtained and the gap between pixels is difficult to see. An image with reflected light of image quality can be obtained.

Next, FIG. 5 shows a manufacturing method of the reflective pixel electrode 12 by a nanoprint method capable of realizing an accuracy of 10 nm in order to realize a gap between pixels of 0.075 μm to 0.15 μm.
First, the pattern of the reflective pixel electrode 12 is molded, an AL electrode is formed on the Si substrate, and a resist (PMMA) is applied thereon (1).
Next, the mold and the Si substrate are heated to raise the temperature until the resist is softened (2).
Then, the mold is pressed against the resist (3).
The resist is cured by cooling the mold and the resist while being pressurized (4).
Next, the mold is peeled off from the resist (5).
Etching is then performed (6).
Finally, the resist is removed (7).

  If the pattern of the reflective pixel electrode 12 is formed in this manner, a gap between pixels of 0.075 μm to 0.15 μm can be easily obtained.

  As described above, according to the embodiment of the present invention, if the reflective film 17 is set to have a width equal to or larger than the inter-pixel gap immediately below the inter-pixel gap of the reflective pixel electrode 12, the aperture ratio can be greatly improved. If the inter-pixel gap is changed from 0.075 μm to 0.15 μm, the wavelength of light to be used is close to the inter-pixel gap, so that incident light is hardly scattered and the aperture ratio can be further improved.

It is a figure which shows sectional drawing of the reflection type liquid crystal display element used for the liquid crystal display device in embodiment of this invention. It is a figure which shows the state which input incident light into the electrodeless part of the reflective liquid crystal display element of FIG. It is a figure which shows the opening state by the gap between pixels. It is a figure which shows the calculated value and measured value of the aperture ratio by the gap between pixels. It is a figure which shows the pixel electrode production | generation procedure by a nanoprint method. It is a figure which shows sectional drawing of the reflection type liquid crystal display element used for the conventional liquid crystal display device. It is a figure which shows the state which input incident light into the electrodeless part of the reflection type liquid crystal display element of FIG. It is a figure which shows the pixel electrode production | generation procedure by the conventional photomask.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Single crystal silicon substrate, 2 ... Drain, 3 ... Source, 4 ... Auxiliary capacitance element, 5 ... Gate oxide film, 6 ... Oxide film, 7 ... Polycrystal Silicon gate, 8 ... silicon electrode, 9 ... insulating film, 10 ... signal electrode, 11 ... metal electrode, 12 ... reflective pixel electrode, 13 ... liquid crystal alignment film, 14 ... -Common electrode, 15 ... Liquid crystal, 16 ... Insulating layer, 17 ... Reflective film, 18 ... Element substrate

Claims (1)

A plurality of switching transistors formed on the substrate, an insulating layer formed on the plurality of switching transistors, and a plurality of pixel electrodes connected to the switching transistor through a through hole formed in the insulating layer; In a reflective liquid crystal display element comprising: a common electrode arranged in an array; a common electrode disposed opposite to the element substrate; and a liquid crystal layer filled between the common electrode and the element substrate.
A reflective liquid crystal display element, wherein a space between the plurality of pixel electrodes is set to a predetermined width or less, and a reflective film is formed between the plurality of pixel electrodes and the insulating layer.

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