JPH03148627A - Reflection type liquid crystal electrooptic device - Google Patents

Abstract

PURPOSE:To realize the reflection type electrooptic device which eliminates the need for a light shield mask by installing an insulating reflection body on the liquid crystal side of a switching element array substrate provided with a switching element array between two substrates where liquid crystal is sandwiched. CONSTITUTION:A liquid crystal layer 104 is sandwiched between the two opposite substrates 102 and 103 and the insulating reflection body 101 is provided on the switching element array substrate 103 on the side of the liquid crystal layer 104. This liquid crystal layer 104 is a twisted nematic liquid crystal layer which converts linear polarized incident light into nearly elliptic polarized light by its reflecting surface and rotates the plane of polarization of the incident light after the reflection by 90 deg. into linear polarized light on its projection surface. When no electric field is applied, a nontransmission state (black) is entered, so the peripheral part of each picture element is shielded automatically from light and the switching element array is shielded from light almost completely, so the need for a light shield mask is eliminated and mask positioning is therefore unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reflective liquid crystal electro-optical device provided with a switching element array.

[Prior art] A reflective liquid crystal electro-optical device equipped with a conventional switching element array is disclosed in Nikkei Electronics 19B1, 2/16.
As described in No. P, 164, a transparent substrate was used as the counter electrode, and a substrate provided with reflective electrodes was used as the switching element array substrate.

[Problem II to be Solved by the Invention] However, in conventional reflective liquid crystal electro-optical devices, it is necessary to use the pixel portion of the substrate on which the switching element array is arranged as a reflector, which increases the number of manufacturing steps and the need for transparent electrodes. required changes to established processes.

Furthermore, there is a problem in that the light-shielding mask covering the periphery of the pixels on the counter substrate must be aligned with the switching element array. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a reflective electro-optical device in which a conventional switching element array can be used as is, and alignment with a light-shielding mask is not required.

[Means for Solving the Problems] A reflective liquid crystal electro-optical device of the present invention is a reflective liquid crystal electro-optical device in which a liquid crystal is sandwiched between two opposing substrates, and a switching element array is installed on one substrate. In particular, the liquid crystal layer is characterized by having an insulating reflector on the liquid crystal side of the switching element array substrate. A twisted nematic liquid crystal layer is characterized in that the plane of polarization is rotated by 90 degrees, resulting in linearly polarized light.The incident light is linearly polarized parallel to or perpendicular to the molecular axis of the incident surface of the twisted nematic liquid crystal. The switching element array is characterized by sandwiching a twisted nematic liquid crystal layer which becomes linearly polarized light with the plane of polarization rotated by 90 degrees from the incident light at the output surface after reflection. [Special Embodiment] Example 1 FIG. 1 is a sectional view of a reflective electro-optical device of the present invention.

An insulating reflector 1 is placed on the switching cable array substrate 103.
01 is installed, and a liquid crystal 104 is sandwiched between the counter substrate 102 and the basic structure. Here, twisted nematic liquid crystal (hereinafter referred to as TN) was used for the liquid crystal layer. 105 is a pixel electrode, 106 is a polarizing plate, and 107 is a switching element. The other electrode 108 for applying an electric field is formed of a transparent electrode. Additionally, anti-reflection coatings are applied to the input/output surfaces and transparent electrode surfaces to suppress unnecessary light reflections.

Next, the reflective liquid crystal display mode used in this example will be explained. Although it is possible to use a general field effect birefringence type display mode (hereinafter referred to as ECB), in this example, the ECB mode using twisted nematic liquid crystal was used.

In this example, the switching element substrate is made of TP shown in Table 1.
T active matrix method, the above-mentioned Tl is used in the liquid crystal layer.
i-ECB mode is used. Detailed driving method and configuration can be found in Nikkei Electronics No. 351 (1981)
p, 211. From S”83 DIGEST
p-156 (1983), SID″85D Engineering G.E.S.
T p, 278 (1985), Japan Dis
It is based on that described in play89 p. 192.

Table 1 Driving method TPT active matrix pixel number
480x 440 Display effective area 96x88 am Display mode T): CB (field effect birefringence) liquid crystal layer thickness 2.4 μm Δnd 0-2 Twist angle 63° Reflector SiSIOzM electric film multilayer mirror (on switching element substrate) 2nd The figure shows the video applied voltage and reflectance (55
0 nm). First, we will explain when the voltage is zero. When the linearly polarized light 302 is incident, the locus of the elliptically polarized light rotates as shown in FIG. Almost circularly polarized light 30 on the reflector surface
1, the phase is rotated by 180 degrees, and it is reflected. The light passes through the liquid crystal layer again, and at the exit surface becomes linearly polarized light 303 whose polarization plane has been rotated by approximately 90 degrees and is emitted. For this reason, the light is blocked by the polarizing element and the reflectance decreases (off state). Next, a case where a voltage is applied will be explained. The liquid crystal molecules rearrange in the direction of the electric field due to the anisotropy of the dielectric field. As a result, the anisotropy of birefringence with respect to the incident light disappears, and the incident linearly polarized light is maintained as it is, reflected, and emitted. Therefore, there is no decrease in reflectance (on state).

Such a change in polarization occurs under limited conditions, and as a result of intensive study of these conditions, we have arrived at the present invention. The optical properties required for the liquid crystal layer are that when linearly polarized light is incident, it becomes circularly polarized light after passing through it, and that the phase of the reflective layer is 180°.
There are two reasons: the polarization plane is rotated by 90 degrees when the light is transmitted through the liquid crystal layer in the opposite direction.

FIGS. 4(a) and 4(b) are graphs showing Δnd and reflectance in the off state. The twist angle of the liquid crystal layer was taken as a parameter, and the polarization plane of the incident light was matched to the director of the liquid crystal molecules on the incident surface. The reflectance when on is determined by the transmittance of the polarizing element and is approximately constant. According to this, it was found that the reflectance becomes almost zero when the twist angle is about 60 degrees and Δnd=OJ2. As a result of further detailed investigation, it was found that a twist angle of 63 degrees is optimal.

Looking at the trajectory of the elliptically polarized light at this time, as shown in FIG. 3, it becomes circularly polarized light on the reflecting surface, and linearly polarized light that is rotated by 90 degrees from the time of incidence on the exit surface. Comparing this with the case of a 174λ plate, it is difficult to detect birefringence because the polarized light is incident along the director of the liquid crystal, and a large Δnd is required to receive the same phase change, and the period with respect to Δnd. It is characterized by a lack of sexuality. This allows the thickness of the liquid crystal layer to be set relatively large, ensuring margins in manufacturing.

Furthermore, the effect of Δn works in exactly the same way when linearly polarized light is perpendicularly incident on the director of the liquid crystal.

This is because Δn has no sign or negative.

FIGS. 5(a) and 5(b) show the relationship between Δnd and reflectance, using the angle of arrangement of the polarizing element with respect to the director of the liquid crystal as a parameter. According to this, there is a condition in which the reflectance is zero even when the direction of the polarizing element is +30 degrees. Looking at the locus of the elliptically polarized light in this case, as in Figure 4, it becomes old damage light on the reflective surface.

Other conditions like this can be found by changing the parameters. However, in order to suppress reflectance fluctuations due to wavelength, it is necessary to set Δnd to the minimum value, and since an extremely small Δnd results in too small a liquid crystal thickness, it is necessary to select a value between these values. Optical length is 2
In the case of a reflective type device, which is twice as large as that of a transmissive type liquid crystal element, the permissible liquid crystal thickness becomes a manufacturing problem. Therefore, it is required that Δnd be as large as possible. This is to increase the margin for device manufacturing. Considering the condition of Δnd=0.2 mentioned above, Δn is a typical value for a small liquid crystal, Δn=o−0
8, d is 2.5 μm.

On the other hand, in the 45-degree twisted type described in the conventional example, the optimum liquid crystal thickness is less than 2 μm, which is a factor that reduces device uniformity and yield.

In addition, such a liquid crystal mode is in a non-transparent state (
Since the pixel electrode can be set to black), there is no need for a light-shielding mask for the area where there is no pixel electrode.

Example 2 Figure 6 shows a polarizing beam splitter (hereinafter referred to as P
1 is a configuration diagram of a reflective liquid crystal electro-optical device using a liquid crystal display (referred to as BS).

A PBS 601 linearly polarizes the light source light 603 and makes it enter the liquid crystal panel 602 . The configuration of the liquid crystal panel and the process up to emission are the same as in Example 1. In PBS, the means for analyzing the emitted light is shifted by 90 degrees from the time of incidence. Therefore, the reflected output light 604 becomes small in the absence of an electric field, and the characteristics of applied voltage and reflectance become symmetrical with respect to the vertical axis as in FIG. 3 of Example 1.

Embodiment 3 The present invention can also be applied to an active matrix in which diodes and the like are arranged in an array.

FIG. 7 is a sectional view of a MIX liquid crystal electro-optical device using a metal-insulator-metal element (hereinafter referred to as M) as a diode element. The basic structure is that a liquid crystal 70 is placed between a MIX substrate 702 on which an insulating reflector 701 is installed and a counter substrate 703.
4 is sandwiched between them. 7o5 is a transparent electrode on the counter substrate for applying an electric field to the liquid crystal layer, and is a stripe electrode corresponding to the pixel size. In this example, a mirror made of a dielectric multilayer film was used as the insulating reflector. A mirror made of this dielectric multilayer film can be placed above or below the MIX element. Line-shaped signal transmission wiring 707 on board 706, M made of thin insulator made in part of it
M element 708 and pixel electrode 7 electrically connected to it
It consists of 12. Note that the pixel electrode also serves as the other metal thin film constituting the MIX and the reflective film of the electro-optical element. 71O is an anti-reducing coating, and 711 is a polarizing element.

More specific configurations are shown in Table 2.

Table 2 Number of pixels 220x 320 pixel pitch
80X90μm M substrate MIM element Dinga-Ta20s-CrTaa
Os 500 person oxidation method Wet anodization signal transmission wiring Ta Pixel electrode Cr reflective film reflector Dielectric multilayer film display mode TN-ECB (field effect birefringence) liquid crystal layer thickness 2.4μm Δn d 0.2 Twist angle 63@ or more Although the embodiments have been described, the present invention can be applied not only to the above embodiments but also to a wide range of reflective light control devices.

[Effects of the Invention] As described above, according to the present invention, a reflective light valve can be easily constructed by simply installing a reflector on a switching element array substrate.

Furthermore, since it can be set to a non-transmissive state (black) when there is no electric field, the peripheral area of the pixel can be automatically shielded from light. It can be used as a so-called self-line type light-shielding mask.

Furthermore, since the switching element array is always almost completely shielded from light, there is no need for a light-shielding mask, and furthermore, there is no need for mask alignment. In particular, TFs where leakage current occurs due to incident light and an increase in resistance when turned off is a problem.
This is particularly effective for T-type switching elements.

Furthermore, since the insulating reflector is electrically connected in series with the liquid crystal layer, there is an effect that direct current components that are extremely harmful to the liquid crystal layer can be removed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a reflective electro-optical device of the present invention.
- Figure 2 Hiro 1st rI! Applied voltage and reflectance of the device of J (55
0 nm). FIG. 3 is a diagram showing the trajectory of the elliptically polarized light in FIG. 2. Figures 4(a) and (b) show the relationship between Δnd and reflectance.
This is a graph showing. The angle of arrangement of the polarizing element with respect to the liquid crystal director is taken as the fifth (1(a) and (b) parameters), and the relationship between Δnd and reflectance is shown in Figure 6. FIG. 7 is a configuration diagram of a reflective liquid crystal electro-optical device. FIG. 7 is a cross-sectional view of the reflective electro-optical device addressed by MIM diodes. 101...Insulating reflector 102--Counter substrate 103-- - Switching element array substrate 104...
Liquid crystal layer 301--Circularly polarized light 601 on reflective surface 601--PBS 701--Insulating reflector 702-MIM substrate 703--Counter substrate 704--Liquid crystal 705--Counter electrode 70 row・One board 70 hoo... Signal transmission wiring 708-M engineering M element or above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kisaburo Suzuki (1 other person) /-11, 100 < ,,
,, 51/su10%;", -1～~,i
I03 ##,. Figure 1 Reflectance j Figure 2 1 \\ j { 1 \''/ 1[XX'I
/I1 〼l 5 ふ (b) 6″2 ″6017 Figure 6 17M

Claims (1)

[Claims] 1) In a reflective liquid crystal electro-optical device in which a liquid crystal is sandwiched between two opposing substrates and a switching element array is installed on one substrate, an insulating reflective layer is provided on the liquid crystal side of the switching element array substrate. A reflective liquid crystal electro-optical device characterized by having a body. 2) The liquid crystal layer is a twisted nematic liquid crystal layer in which linearly polarized incident light becomes circularly polarized light on the reflecting surface, and after reflection becomes linearly polarized light with the plane of polarization rotated by 90 degrees from the incident light on the exit surface. 2. A reflective liquid crystal electro-optical device according to claim 1. 3) A twisted nematic liquid crystal that receives linearly polarized incident light parallel to or perpendicular to the molecular axis of the incident surface of the twisted nematic liquid crystal, and after reflection becomes linearly polarized light with the polarization plane rotated by 90 degrees from the incident light at the exit surface. 3. A reflective liquid crystal electro-optical device according to claim 2, characterized in that the layers are sandwiched. 4) The reflective liquid crystal electro-optical device according to claim 1, wherein the switching element array is a thin film transistor array arranged in each pixel.