JP2005181829A - Liquid crystal device, and projection display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently suppress a flicker when electrode materials of a couple of substrates between which liquid crystal is sandwiched are different from each other. <P>SOLUTION: The liquid crystal device 100 constituted by sandwiching a liquid crystal layer 50 between substrates 10 and 20 having electrodes 9 and 23 made of mutually different electrode materials has alignment films 31 and 21, differing in specific dielectric constat, formed on both the substrates. At this time, alignment films which are relatively large in specific dielectric constant are formed on a surface of an electrode which is relatively small in work function of a liquid crystal interface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal device and a projection display device.

Conventionally, a reflection type liquid crystal device in which one of the electrodes is a reflection electrode such as Al is known.
JP-A-10-206845

However, the reflection type liquid crystal device as described above has a problem that flicker is likely to occur and sufficient display characteristics cannot be obtained. As a method of eliminating the flicker, for example, a method of adjusting the driving to balance the potential between the upper and lower substrates is conceivable. However, since the size of the flicker depends on the temperature or the like, the adjustment is difficult. In addition, this method requires a separate compensation circuit, which increases costs.
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a liquid crystal device capable of sufficiently preventing the occurrence of flicker with a simple configuration, and a projection display device including the liquid crystal device. And

In order to solve the above problems, a liquid crystal device of the present invention is a liquid crystal device in which a liquid crystal layer is sandwiched between a pair of substrates provided with electrodes, and is provided on both substrates on the surface of at least one electrode. It is characterized in that a work function adjusting layer is provided so as to reduce the work function difference at the liquid crystal interface of the electrode.
The inventor paid attention to the difference in work function between the upper and lower electrodes in contact with the liquid crystal layer as a cause of the occurrence of the flicker described above. That is, in the conventional liquid crystal device described above, a transparent electrode such as ITO is formed on one substrate, and a reflective electrode such as Al is formed on the other substrate. Has occurred. Such a difference in work function causes a shift in the common potential of both electrodes and causes flicker. In the present invention, the work function adjustment layer can solve the work function imbalance at the liquid crystal interface between the two electrodes, thereby enabling display without flicker. In particular, in the present invention, since the electrical characteristics of the electrode surface (the work function of the liquid crystal interface) are directly improved, the common potential does not change even if the temperature changes as in the case where the drive is adjusted. Stable display characteristics can always be obtained. In the present invention, the work function adjusting layer is preferably made of an inorganic material. In general, since an inorganic material has a relative dielectric constant larger than that of an organic material, the use of the inorganic material for the work function adjustment layer widens the adjustment range of the work function and facilitates adjustment.

  By the way, as a specific form of the work function adjusting layer, the work function adjusting layer is composed of a pair of alignment films provided on the surfaces of the electrodes of both substrates. A material in which the relative dielectric constant of the first alignment film provided on the surface of the electrode having a small work function is larger than the relative dielectric constant of the other second alignment film can be used. In this embodiment, since the work function adjusting layer is also used as the alignment film, the device configuration is simplified.

  In the above embodiment, the first alignment film includes a first film made of an oblique deposition film and a second film having a relative dielectric constant larger than that of the first film. it can. As described above, by forming the first alignment film in a multilayer structure, an alignment film excellent in both the alignment control power of liquid crystal and the work function adjustment power can be obtained. Note that the stacking order of the first film and the second film can be arbitrarily determined, but when the second film is formed on the first film, the first film and the second film are generated by the uneven surface of the first film. It is desirable that an uneven shape reflecting the surface shape of the first film is formed on the surface of the second film so as not to impair the orientation control force. Also, SiOx is suitable for the first film, and TiOx, AlOx (Al oxide), etc. are suitable for the second film.

  Further, in the above embodiment, the pair of substrates are opposed to each other via a sealing material provided in a frame shape, and the first film is not covered with the sealing material in a region within the frame of the sealing material. The provided one can be used. By disposing the sealing material away from the first film in this manner, contamination of the first film due to impurities from the sealing material can be prevented, and the reliability of orientation can be improved.

In addition, the magnitude | size of the work function of an electrode surface is influenced by the material of the electrode, and the structure of the lower layer side of an electrode. For example, when one of the electrodes is configured as a reflective electrode (that is, one electrode is made of a conductive material having a relatively low work function such as Al or Ag, and the other electrode is a relatively work function such as ITO. In the case of a conductive material having a large thickness), the common potential shifts due to the work function difference between the two electrodes. In addition, even if the electrode material is the same for both substrates, when either substrate is composed of an element substrate having a switching element (that is, one substrate is composed of an element substrate having TFTs, circuit wiring, etc.) When the other substrate is made of a counter substrate in which a solid electrode is simply formed), there is a slight difference in the work function at the liquid crystal interface between both electrodes. For this reason, if this invention is applied with respect to such a structure, the effect of this invention can be exhibited more fully.
The present invention is not limited to a liquid crystal device using an insulating substrate such as a glass substrate, but can be applied to a liquid crystal device called LCOS (Liquid Crystal On Silicon) using a semiconductor substrate such as a silicon substrate as an element substrate. it can.

  The projection display device of the present invention includes the above-described liquid crystal device as light modulation means. Thereby, high quality and stable projection display can be realized.

[Liquid Crystal Device]
The liquid crystal device of the present invention will be described below with reference to the drawings.
In this embodiment, an example of an active matrix liquid crystal device (liquid crystal light valve) used for a light valve of a projection display device will be described.
1 is a plan view of the liquid crystal device according to the present embodiment as viewed from the side of the counter substrate together with each component, FIG. 2 is a cross-sectional view taken along the line HH ′ of FIG. 1, and FIG. FIG. In each drawing used in the following description, the scale is different for each layer and each member so that each layer and each member can be recognized on the drawing. In this specification, the surface on the liquid crystal layer side of each member constituting the liquid crystal device is referred to as an “inner surface”, and the surface on the opposite side is referred to as an “outer surface”.

  As shown in FIGS. 1 and 2, in the liquid crystal device 100 of this embodiment, the TFT array substrate 10 and the counter substrate 20 are bonded together by a sealing material 52 provided in a rectangular frame shape, and are partitioned by the sealing material 52. Liquid crystal 50 is sealed and held in the region. An injection port 55 for injecting liquid crystal is formed in the sealing material 52, and the liquid crystal injection port 55 is sealed with a sealing material 54. A counter electrode 23 is formed on the inner surface side of the counter substrate 20, and a pixel electrode 9 is formed on the inner surface side of the TFT array substrate 10.

  A peripheral parting 53 made of a light-shielding material is formed in a region inside the sealing material 52, while a data line driving circuit 201 and a mounting terminal 202 are provided on one side of the TFT array substrate 10 in a region outside the sealing material 52. The scanning line driving circuit 104 is formed along two sides adjacent to the one side. On the remaining side of the TFT array substrate 10, a plurality of wirings 105 are provided for connecting the scanning line driving circuits 104 provided on both sides of the image display area. In addition, an inter-substrate conductive material 106 for providing electrical continuity between the TFT array substrate 10 and the counter substrate 20 is disposed at at least one corner of the counter substrate 20.

  In the liquid crystal device 100, the type of liquid crystal 50 to be used, that is, an operation mode such as a TN (Twisted Nematic) mode, an STN (Super Twisted Nematic) mode, a VAN (Vertical Alignment Nematic) mode, or a normally white mode / no mode. Depending on the mari black mode, a retardation plate, a polarizing plate, and the like are arranged in a predetermined direction, but the illustration is omitted here. Further, in the case where the liquid crystal device 100 is configured for color display, for example, red (R), green (G), blue (B) in the region of the counter substrate 20 facing each pixel electrode 9 of the TFT array substrate 10. The color filter is formed together with the protective film.

Next, the configuration of the main part of the liquid crystal device 100 will be described. FIG. 3 is a schematic view showing an enlarged cross section of the non-pixel region (outer region of the sealing material 52) and the periphery of the formation region of the sealing material 52 of the liquid crystal device 100.
As shown in FIG. 3, the liquid crystal device 100 of the present embodiment has a configuration in which a liquid crystal layer 50 is sandwiched between a pair of substrates 10 and 20 that are opposed to each other via a sealing material 52 arranged in a rectangular frame shape. Yes.

  The TFT array substrate 10 is formed with TFTs as pixel switching elements and circuit portions such as the scanning line driving circuit 104 and the data line driving circuit 201 described above, and a plurality of pixel electrodes corresponding to each pixel. 9 are arranged in a matrix. Known materials can be used for the substrate 10 and the pixel electrode 9. For example, in a transmissive liquid crystal device, a light-transmitting substrate such as glass, quartz, or plastic can be used as the substrate 10, and a light-transmitting conductive material such as ITO can be used as the pixel electrode 9. On the other hand, in the case of a reflective liquid crystal device, a transparent substrate such as glass, quartz, or plastic as well as a semiconductor substrate such as a silicon substrate can be used as the substrate 10, and Al, Ag, or the like can be used as the pixel electrode 9. A highly reflective metal material can be used. In addition, when a reflective film is separately formed between the pixel electrode 9 and the substrate, a light-transmitting conductive material such as ITO can be used for the pixel electrode 9. When the pixel electrode 9 is made of a metal film such as Al, the pixel electrode 9 functions as a reflective electrode.

  On the other hand, a counter electrode (common electrode) 23 common to each pixel is formed on the entire surface of the counter substrate 20. Since the substrate 20 and the counter electrode 23 are required to have optical transparency, a transparent substrate such as glass, quartz, or plastic is used for the substrate 20, and the transparent electrode such as ITO is used for the counter electrode 23. Material is used.

  And the inorganic alignment films 31 and 21 which consist of inorganic materials, such as SiOx, TiOx, AlOx, are formed in the surface of the board | substrates 10 and 20 comprised in this way, respectively. These alignment films 31 and 21 function as the work function adjusting layer of the present invention. The material, film thickness, film structure, etc. of each alignment film are the same as the electrode material of both substrates, the structure on the lower layer side of the electrodes, etc. Designed optimally accordingly. For example, when the pixel electrode 9 is made of Al, Ag, or the like having a work function smaller than that of ITO or the like, a difference occurs in the common potential due to the difference in the work functions of the electrodes 9 and 23. For this reason, in this case, in order to equalize the work function at the liquid crystal interface between the electrodes 9 and 23 (or to reduce the work function difference), an alignment film (on the pixel electrode 9 side having a small work function) The first alignment film 31 is made of a material having a relative dielectric constant relatively larger than that of the alignment film (second alignment film) 21 on the counter electrode 23 side. Further, even if the electrode material of the pixel electrode 9 and the counter electrode 23 is the same, if one substrate is an element substrate provided with a switching element, depending on the difference in the structure on the lower layer side of both electrodes, There is a slight difference in the work function at the liquid crystal interface. For example, in the active matrix type liquid crystal device as in this example, the work function of the electrode 9 on the element substrate side is slightly smaller than that of the electrode 23 on the counter substrate side. Therefore, in this case as well, the alignment film 31 on the pixel electrode 9 side is made of a material having a relatively higher relative dielectric constant than the alignment film (second alignment film) 21 on the counter electrode 23 side. .

In this example, for example, the alignment film (second alignment film) 21 on the counter substrate side is an oblique deposition film such as SiO _2, and the alignment film (first alignment film) 31 on the TFT array substrate side is SiO ₂ or the like. A multilayer film including a first film made of the obliquely deposited film and a second film having a relative dielectric constant larger than that of the first film. In this way, while providing the alignment film 31 with a liquid crystal alignment function (that is, the shape of the column of the oblique vapor deposition film), the alignment film 31 has a higher relative dielectric constant than the alignment film 21 on the counter substrate side. can do. For example, in FIG. 3, the alignment film 31 has a two-layer structure of a first film 31a made of SiO ₂ arranged on the liquid crystal layer 50 side and a second film 31b made of TiO ₂ arranged on the substrate 10 side. Make. Note that the formation order of the first film and the second film can be arbitrarily determined, and the second film made of TiO ₂ or the like can be formed on the first film made of SiO ₂ or the like. is there. However, in this case, it is necessary to prevent the uneven shape (column shape) on the surface of the first film from being flattened by the second film. Specifically, the film thickness of the second film may be about several nm so that an uneven shape reflecting the surface shape of the first film is formed on the surface of the second film.

  The alignment films 31 and 21 are patterned in the central portion (that is, the image display area) of each substrate, and the alignment films 31 and 21 are sealed to prevent contamination by impurities from the sealing material. The sealant 52 is provided in a region within the frame of the material 52 so as not to be hung on the sealant 52.

  As described above, in the present embodiment, the relative dielectric constants of the alignment films 31 and 21 covering the electrodes 9 and 23 on both substrates are made different to make the work functions of the liquid crystal interfaces between the electrodes 9 and 23 equal in magnitude (or Since the work function difference is small, display without flicker is possible. In particular, in the present embodiment, since the work function of the electrode is directly adjusted, even if the temperature is changed as in the case where the drive is adjusted, the common potential does not fluctuate, and a stable display characteristic is always obtained. In this embodiment, the alignment film is made of an inorganic material having a high relative dielectric constant, and serves both as a work function adjustment and an alignment film.

  Further, in this embodiment, since the sealing material 52 is arranged outside the alignment films 31 and 21 by a certain distance, a liquid crystal device with high alignment reliability can be obtained. In this example, both the first film 31a and the second film 31b of the alignment film 31 are patterned. However, the second film 31b that does not directly contribute to the alignment or only assists the alignment is necessarily patterned. There is no need, and the entire surface of the substrate may be solid.

[Example 1]
Next, a first embodiment of the present invention will be described.
In this example, an LCOS type liquid crystal device according to the present invention was manufactured by the following procedure.
First, Al is sputtered on a silicon substrate, and an Al electrode (reflection electrode) is formed by patterning. Next, a 50 nm TiO2 film is formed on the surface of the substrate on which the Al electrode is formed by vapor deposition or sputtering, and then SiO2 is implanted onto the TiO2 film from an angle of elevation of 50 [deg.] (Oblique vapor deposition). . The thickness of this obliquely deposited film is 10 nm. On the other hand, apart from this silicon substrate, a glass substrate having an ITO electrode formed on the inner surface side is prepared, and SiO2 is obliquely deposited on the ITO electrode. This obliquely deposited film is 18 nm. Next, these substrates are bonded to each other with a sealing material to produce an empty cell, and a liquid crystal having negative dielectric anisotropy is injected into the empty cell. Thus, the reflective liquid crystal device according to the present invention is manufactured.
Further, a comparative liquid crystal device was manufactured by the same method. This comparative liquid crystal device has the same configuration as the liquid crystal device of the present invention, except that TiO 2 is not formed on the Al electrode.
Next, the central potential difference (shift in common potential) of these liquid crystal devices was measured. As a result, in the liquid crystal device for comparison, a shift of 500 mV occurs in the common potential between the Al electrode and the ITO electrode, whereas in the liquid crystal device of the present invention, this is reduced to 200 mV.

[Example 2]
Next, a second embodiment of the present invention will be described.
In this example, a reflective liquid crystal device according to the present invention was manufactured by the following procedure.
First, Al is sputtered on a silicon substrate, and an Al electrode (reflection electrode) is formed by patterning. Next, SiO2 is obliquely deposited by 10 nm on the surface of the substrate on which the Al electrode is formed, and then a TiO2 film is deposited on the obliquely deposited film by 5 nm by vapor deposition or sputtering. On the other hand, a glass substrate having an ITO electrode formed on the inner surface side is prepared separately from this silicon substrate, and TiO2 is obliquely deposited on the ITO electrode. This obliquely deposited film is 20 nm. Next, these substrates are bonded to each other with a sealing material to produce an empty cell, and a liquid crystal having negative dielectric anisotropy is injected into the empty cell. Thus, the reflective liquid crystal device according to the present invention is manufactured.
Next, the center potential difference (shift in common potential) of this liquid crystal device was measured. As a result, in the liquid crystal device of the present invention, the common potential shift was reduced to 100 mV.

[Example 3]
Next, a third embodiment of the present invention will be described.
In this example, a reflective liquid crystal device according to the present invention was manufactured by the following procedure.
First, Al is sputtered on a silicon substrate, and an Al electrode (reflection electrode) is formed by patterning. At this time, a slit for controlling liquid crystal alignment is formed in the Al electrode. Next, TiO2 is vapor-deposited or sputtered on the surface of the substrate on which the Al electrode is formed, and subsequently, an inorganic liquid containing silicon acid is formed on the TiO2 film by spin coating, and the SiO2 film is formed by baking. To do. On the other hand, apart from this silicon substrate, a glass substrate having an ITO electrode formed on the inner surface side is prepared, and SiO2 is obliquely deposited on the ITO electrode. Next, these substrates are bonded to each other with a sealing material to produce an empty cell, and a liquid crystal having negative dielectric anisotropy is injected into the empty cell. Thus, the reflective liquid crystal device according to the present invention is manufactured.
Next, the center potential difference (shift in common potential) of this liquid crystal device was measured. In this example, the common potential shift was reduced to 100 mV. In this example, the film on the silicon substrate side does not include the oblique vapor deposition film, but the orientation control is possible because the oblique vapor deposition film is formed on the glass substrate side.

[Example 4]
Next, a fourth embodiment of the present invention will be described.
In this example, a transmissive liquid crystal device according to the present invention was manufactured by the following procedure.
First, an ITO film is formed on a glass substrate (TFT array substrate) on which a p-Si TFT is formed, and an ITO electrode is formed by patterning. Next, SiO2 is obliquely vapor-deposited by 10 nm on the surface of the substrate on which the ITO electrode is formed, and then a TiO2 film is deposited by 1 nm on the oblique vapor-deposited film by vapor deposition or sputtering. On the other hand, a glass substrate (opposite substrate) having an ITO electrode formed on the inner surface side is prepared separately from the TFT array substrate, and SiO2 is obliquely deposited on the ITO electrode on the counter substrate side. This obliquely deposited film is 20 nm. Next, these substrates are bonded to each other with a sealing material to produce an empty cell, and a liquid crystal having negative dielectric anisotropy is injected into the empty cell. As described above, the transmissive liquid crystal device according to the present invention is manufactured.
Further, a comparative liquid crystal device was manufactured by the same method. This comparative liquid crystal device has the same configuration as that of the above-described liquid crystal device of the present invention except that TiO 2 is not formed on the ITO electrode on the TFT array substrate side.
Next, the center potential difference (shift in common potential) of this liquid crystal device was measured. As a result, in the liquid crystal device for comparison, there was a slight shift in the common potential between the ITO electrode on the TFT array substrate side and the ITO electrode on the counter substrate side. That is, even when the electrode materials of both the substrates are the same, it is considered that there is a slight imbalance in the work function of the liquid crystal interface between the two electrodes because the configurations on the lower layer side of the electrodes differ between the two substrates. On the other hand, in the liquid crystal device according to the present invention, there was no shift in common potential and no flicker occurred.

[Projection type display device]
Next, a projection-type liquid crystal display device (liquid crystal projector) will be described as an example of an electronic apparatus using the above-described liquid crystal device.
FIG. 4 is a diagram showing a schematic configuration of the liquid crystal projector. As shown in this figure, a lamp unit 1102 including a white light source such as a halogen lamp is provided inside the projector 1100. The projection light emitted from the lamp unit 1102 is separated into three primary colors of red (R), green (G), and blue (B) by three mirrors 1106 and two dichroic mirrors 1108 arranged inside. Are guided to the light valves 100R, 100G and 100B corresponding to the respective primary colors.

  Here, the configuration of the light valves 100R, 100G, and 100B is the same as that of the liquid crystal device according to the above-described embodiment, and R, G, and B primary colors supplied from a processing circuit (not shown) that inputs an image signal. Each is driven by a signal. In addition, B light has a long optical path compared to other R colors and G colors, and therefore, in order to prevent the loss, B light passes through a relay lens system 1121 including an incident lens 1122, a relay lens 1123, and an exit lens 1124. Led.

The lights modulated by the light valves 100R, 100G, and 100B are incident on the dichroic prism 1112 from three directions. In the dichroic prism 1112, R and B light is refracted by 90 degrees, while G light travels straight. In this manner, after the images of the respective colors are combined, a color image is projected onto the screen 1120 by the projection lens 1114.
The projection type display device of the present embodiment can realize high-quality and stable projection display by including the liquid crystal device of the above-described embodiment as a light modulation unit.

In addition, this invention is not limited to the above-mentioned embodiment, It can implement in various deformation | transformation in the range which does not deviate from the meaning of this invention.
For example, in the above-described embodiment, the projection display device of the present invention has been described as a transmissive projector. However, a reflective liquid crystal device can be used as a light valve so that the projector can be a reflective projector. In this case, a liquid crystal device serving as a light valve may be a liquid crystal device having a structure called LCOS using a silicon substrate as the substrate, in addition to a normal glass substrate.
Further, the shapes and combinations of the constituent members shown in the above-described examples are merely examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

FIG. 6 is a plan view illustrating an example of a liquid crystal device of the invention. Sectional drawing which follows the H-H 'line | wire of FIG. Sectional drawing which expands and shows the sealing material peripheral part of a liquid crystal device. The schematic diagram which shows an example of the projection type display apparatus of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 9 ... Pixel electrode, 10 ... TFT array substrate (element substrate), 20 ... Counter substrate, 21 ... Second alignment film, 23 ... Counter electrode, 31 ... First Alignment film, 31a ... first film, 31b ... second film, 50 ... liquid crystal layer, 52 ... sealing material, 100, 100R, 100G, 100B ... liquid crystal device, 1100. ..Projection display devices

Claims (12)

A liquid crystal device comprising a liquid crystal layer sandwiched between a pair of substrates provided with electrodes,
A liquid crystal device, wherein a work function adjusting layer is provided on at least one electrode surface to reduce a work function difference at a liquid crystal interface between electrodes provided on both substrates.   The liquid crystal device according to claim 1, wherein the work function adjusting layer is made of an inorganic material.   The work function adjusting layer is composed of a pair of alignment films provided on the surfaces of the electrodes of both substrates, and the first alignment provided on the surface of the electrode having a relatively small work function among the pair of alignment films. 3. The liquid crystal device according to claim 1, wherein the relative dielectric constant of the film is larger than that of the other second alignment film.   The said 1st orientation film contains the 1st film | membrane which consists of an oblique vapor deposition film | membrane, and the 2nd film | membrane with a larger dielectric constant than this 1st film | membrane, The 3rd aspect is characterized by the above-mentioned. Liquid crystal device.   5. The liquid crystal device according to claim 4, wherein the first film is made of SiOx.   6. The liquid crystal device according to claim 4, wherein the second film is made of TiOx.   6. The liquid crystal device according to claim 4, wherein the second film is made of an AL oxide.   The pair of substrates are opposed to each other via a seal material provided in a frame shape, and the first film is provided in a region within the frame of the seal material so as not to be caught by the seal material. The liquid crystal device according to any one of claims 4 to 7.   The liquid crystal device according to claim 1, wherein one of the two electrodes is configured as a reflective electrode.   The liquid crystal device according to claim 1, wherein one of the pair of substrates is an element substrate provided with a switching element.   The liquid crystal device according to claim 1, wherein one of the pair of substrates is made of a silicon substrate. A projection display device comprising the liquid crystal device according to claim 1 as light modulation means.

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