JP5553299B2 - Electro-optic device - Google Patents

Description

  The present invention relates to an electro-optical device that utilizes the appearance and disappearance phenomenon of a nematic phase depending on the presence or absence of an external electric field in a liquid crystal forming material in an isotropic phase temperature region. More specifically, in the liquid crystal forming material of the isotropic phase temperature region, the present invention uses a nematic phase induction phenomenon when an electric field is applied and a nematic phase disappearance phenomenon when the electric field is removed, and the driving voltage is low. In addition, the present invention relates to an electro-optical device having a high response speed with a wide operating temperature range.

  Conventionally, liquid crystal display devices are characterized by their light weight, thinness, and low power consumption as compared with CRTs (cathode ray tubes), and are therefore used in many electronic devices for display purposes. Conventional liquid crystal display devices are classified into a vertical electric field type and a horizontal electric field type when classified by a method of applying an electric field to a liquid crystal layer. A vertical electric field type liquid crystal display device applies a substantially vertical electric field to liquid crystal molecules by a pair of electrodes arranged with a liquid crystal layer interposed therebetween. As this vertical electric field type liquid crystal display device, a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, an MVA (Multi-domain Vertical Alignment) mode, an ECB (Electrically Controlled Birefringence) mode, and the like are known. .

  Further, a horizontal electric field type liquid crystal display device has a pair of electrodes insulated from each other on one inner surface side of a pair of substrates arranged with a liquid crystal layer sandwiched therebetween, so that a substantially horizontal electric field is It is applied to molecules. As the lateral electric field type liquid crystal display device, there are known an IPS (In-Plane Switching) mode in which a pair of electrodes do not overlap in a plan view and an FFS (Fringe Field Switching) mode in which they overlap.

  These conventional liquid crystal display devices display an image by changing the alignment direction of a director of liquid crystal aligned in a predetermined direction by an electric field and changing the amount of transmitted light. The operation principle of such a conventional liquid crystal display device will be described with reference to FIG. FIG. 11A is a schematic cross-sectional view of a conventional vertical electric field type liquid crystal display device, which is a liquid crystal display device using a change in optical phase difference that occurs when an external electric field (voltage) is applied to a liquid crystal layer as an optical element. is there. FIG. 11B is a diagram showing a light transmission state in the liquid phase display device. 11C and 11D show the arrangement state of the directors in the liquid crystal layer in the nematic liquid crystal layer having a positive dielectric anisotropy, and show a voltage non-application state (FIG. 11C) and a voltage application state (FIG. 11D). Most of these conventional liquid crystal display devices were used as display devices by changing the director of the liquid crystal below the nematic phase-isotropic phase transition temperature, such as nematic liquid crystals. is there.

  As shown in FIG. 11A, in the conventional liquid crystal display device, a liquid crystal layer is sandwiched between the array substrate AR and the color filter substrate CF, and the array substrate AR and the color filter substrate CF are respectively transparent on the liquid crystal layer side. An electrode is formed. A polarizing plate is disposed on the outer surface (the side opposite to the liquid crystal layer) of each of the array substrate AR and the color filter substrate CF, and a backlight light source is disposed on the outer surface of the polarizing plate on the array substrate AR side. ing. As shown in FIG. 11B, the light incident on the polarizing plate on the array substrate AR side from the backlight light source is converted into linearly polarized light, and this linearly polarized light is given a phase difference while passing through the liquid crystal layer. Only light parallel to the transmission axis of the polarizing plate on the layer side is transmitted and visually recognized.

  The director in the liquid crystal layer is arranged in the horizontal direction, for example, by the action of the alignment film formed on the surface of the transparent electrode when no electric field is applied (see FIG. 11C). Then, they are arranged in the vertical direction (see FIG. 11D). Thus, since the alignment state of the director of the liquid crystal layer changes between the non-application state of the electric field and the application state of the electric field, the phase of the light transmitted through the liquid crystal layer changes. Therefore, in a conventional liquid crystal display device, a predetermined image can be displayed by controlling the amount of transmitted light by the interaction between the electric field formed by the pair of electrodes and the transmission axis of the polarizing plate. . Note that the horizontal electric field type liquid crystal display device has a pair of electrodes formed on the array substrate AR, but the amount of light transmitted is controlled by the interaction between the electric field formed by the pair of electrodes and the transmission axis of the polarizing plate. Thus, there is no difference from the above-described vertical electric field type liquid crystal display device in that a predetermined image is displayed.

  On the other hand, various compounds have been conventionally known as liquid crystalline materials. For example, 4-cyano-4′pentylbiphenyl (hereinafter referred to as “5CB”) represented by the following chemical structural formula is solid at 24 ° C. or lower and is 35 ° C. or higher. It becomes liquid and exists as a liquid crystal state between 24 ° C. and 35 ° C. That is, 5CB undergoes a phase transition between a liquid crystal phase and a liquid phase (isotropic phase) at about 35 ° C.

  5CB exists as a nematic phase in the liquid crystal phase. When this nematic phase is heated, it transitions discontinuously to an isotropic phase at a boundary of about 35 ° C., but during that time it is optically and macroscopically isotropic, but microscopically nematic. A state indicating the nature of the phase (hereinafter referred to as “quasi-isotropic phase”) appears.

The temperature range in which this pseudo-isotropic property appears is as narrow as about 1K.
(1) By placing a polymer molecular network in a nematic phase mixed with a chiral agent, the quasi-isotropic phase in the absence of an electric field can be viewed macroscopically over a wide temperature range by a polymer network with a random structure. Be isotropic, and
(2) When an electric field is applied, dielectric anisotropy appears in the quasi-isotropic phase due to the electro-optic Kerr effect, so that optical anisotropy occurs, and when the electric field is removed, the original state is quickly restored.
(3) The response time at the time of electric field application-removal is on the order of 10 μsec, and considering that the response speed when the orientation direction of the conventional nematic phase is changed is several msec or more, it is very fast.
It has been shown that excellent electro-optic effects such as

Similarly, in Non-Patent Document 1 below, when a polymer molecular network is stretched in a blue phase appearing in a narrow region between a chiral nematic phase and an isotropic phase,
(4) The induced temperature of the blue phase spreads over 100K,
(5) When an electric field is applied to the blue phase, a birefringence phenomenon appears due to the electro-optic Kerr effect, and when the electric field is removed, the birefringence phenomenon disappears.
(6) The response time at the time of electric field application-removal is about 10 to 100 μsec for both the rise time and the fall time, and is much faster than the response speed when the orientation direction of the conventional nematic phase changes.
It has been shown that excellent electro-optic effects such as

JP-A-11-183937 JP 2001-265298 A JP 2007-323046 A

“Liquid Crystal” Vol. 9, No. 2 (2006), pp. 83-95

  Japanese Patent Application Laid-Open No. H10-228561 describes the use of the Kerr effect in the isotropic liquid phase of nematic liquid crystal having excellent high-speed response. However, none of the electro-optical elements of Patent Document 1 change in characteristics depending on the intensity of an applied electric field, that is, a high-speed electro-engineering element on the assumption that only the on-off characteristics of the electro-optical element are used. It is. Therefore, an optical switch element that is required to operate at high speed or an electro-optical switch element such as a color shutter is disclosed.

  On the other hand, in order to develop a display device using the above-described phenomenon, the inventor in the isotropic phase region of the liquid crystal forming material, the transmitted light amount due to the halftone based on the onset and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field. Various studies have been made on electro-optical devices that can be taken out arbitrarily. As a result, it has been confirmed that an electro-optical device capable of halftone display and achieving a high response speed can be obtained.

However, it has been found that this electro-optical device has a narrow operable temperature range, a high driving voltage, and a slow response speed during halftone display. Therefore, it is preferable for the electro-optical device to expand the operable temperature range, to reduce the driving voltage, and to increase the response speed during halftone display. Furthermore, there is a problem of improving the response characteristics in the vicinity of the phase transition temperature between the nematic phase and the isotropic phase.
The inventors have found that the problem of the electro-optical device based on the induction and disappearance phenomenon of the nematic phase due to the presence or absence of the external electric field of the liquid crystal forming material as described above is to use an alignment film, for example, as in the conventional liquid crystal display device. As a result, the present invention has been completed. The electro-optical device based on the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field in the liquid crystal forming material controls the amount of transmitted light by changing the orientation direction of the director of the liquid crystal as in the conventional liquid crystal display device. Therefore, the alignment film was originally thought to be unnecessary.

  In the electro-optical device using the electro-optic effect based on the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field in the isotropic phase temperature region of the liquid crystal forming material, the operable temperature region can be widened and driven. The purpose of the present invention is to obtain an electro-optical device that can reduce the operating voltage and can achieve a high response speed at the time of halftone display and an improved response characteristic in the vicinity of the phase transition temperature between the nematic phase and the isotropic phase. To do.

In order to achieve the above object, the electro-optical device of the present invention is disposed opposite to a liquid crystal layer made of a liquid crystal forming material that undergoes a phase transition between a nematic phase and an isotropic phase at a phase transition temperature, with the liquid crystal layer interposed therebetween. A pair of electrodes formed on the liquid crystal layer side of each of the first substrate and the second substrate and the first substrate and the second substrate and generating an electric field perpendicular to the substrate surface when a predetermined voltage is applied. When a pair of polarizing plates disposed on each outer side of the first substrate and the second substrate includes a first substrate and a second substrate, respectively, the interface between the liquid crystal layer, is applied between the pair of electrodes that to be the same as the director orientation of the liquid crystal layer when a nematic phase is induced in the vertical direction of the electric field due to the voltage, interface alignment processing to align the orientation of the directors of the liquid crystal layer is subjected, the liquid crystal Isotropic phase temperature at which the layers form an isotropic phase In-band, performs display using a change in light transmission rate based on the induced and disappearance phenomenon of the nematic phase in the liquid crystal layer corresponding to the voltage applied between the pair of electrodes.

  The liquid crystal forming material becomes solid at low temperature, becomes liquid (isotropic phase) at high temperature, becomes liquid crystal (nematic phase) between the two, and isotropic and nematic phases at a temperature (phase transition temperature) determined by the liquid crystal forming material. A phase transition occurs between In the electro-optical device of the present invention, in the isotropic phase temperature region of the liquid crystal forming material, it is based on the induction and disappearance phenomenon of the nematic phase from the isotropic liquid crystal forming material according to the voltage applied between the pair of electrodes. Utilizes changes in light transmittance. That is, if no voltage is applied between the pair of electrodes, the liquid crystal forming material remains in an isotropic phase, but if a predetermined voltage is applied between the pair of electrodes, the isotropic liquid crystal forming material undergoes a phase transition to the nematic phase. The nematic phase disappears when the voltage applied between the pair of electrodes is removed, and returns to the original isotropic phase.

  When the liquid crystal forming material is in an isotropic phase, no optical phase change occurs, so that the transmittance depends on the conditions determined by the pair of polarizing plates. On the other hand, when the liquid crystal forming material undergoes a phase transition from the isotropic phase to the nematic phase due to an external electric field (external electric field), an electro-optic effect is generated, so that a phase change occurs in the light transmitted through the liquid crystal forming material and the transmittance is increased. Change. The induction and disappearance rate of the nematic phase in the isotropic phase temperature region of this liquid crystal forming material is significantly faster than the realignment rate of the director in the nematic phase temperature region of conventional liquid crystal forming materials. An optical device is obtained.

In the electro-optical device of the present invention, the first substrate and the second substrate are each subjected to liquid crystal in a state where the vertical alignment film that aligns the direction of the director of the liquid crystal layer in the direction parallel to the electric field is not rubbed as the interface alignment process. It may be arranged at the interface with the layer . If the alignment film is not formed, the threshold voltage for inducing a phase transition between the nematic phase and the isotropic phase increases with the temperature rise. However, if the alignment film is formed, the nematic phase-isotropic phase with the temperature rise. The high voltage shift of the threshold voltage that induces the phase transition is suppressed, and the operable temperature range is widened. Therefore, according to the electro-optical device of the present invention, even when the temperature rises, the increase in the applied voltage is suppressed and the operable temperature range becomes wider than when the alignment film is not formed.

According to the electro-optical device having a configuration as this, if not rubbed alignment layer improves induced speed of the nematic phase from the isotropic phase (rising response speed), it is rubbed alignment film In this case, the disappearance speed (falling response speed) of the nematic phase is improved.

In conventional liquid crystal display device, F FS mode, there is a liquid crystal display device of the horizontal electric field method of IPS mode or the like, the present invention is applicable as an electro-optical device having such a horizontal electric field method. According to the electro-optical device having such a configuration, when the alignment film is rubbed, both the rising response speed and the falling response speed are improved.

FIG. 1A is a plan view illustrating an outline of a one-pixel array substrate of an electro-optical device common to Embodiments 1 to 3, and FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. 1A. 2A is a schematic diagram illustrating a state of a liquid crystal forming material in an isotropic phase temperature region of a vertical electric field type electro-optical device, and FIG. 2B is a schematic diagram illustrating an arrangement state of directors induced when an electric field is applied. is there. 3A to 3D are graphs showing VT curves of the comparative example and the electro-optical devices of Examples 1 to 3, respectively. 4A to 4D are graphs showing rising response speed curves of the electro-optical devices of the comparative example and Examples 1 to 3, respectively. 5A to 5D are graphs showing falling response speed curves of the electro-optical devices of the comparative example and Examples 1 to 3, respectively. 6A is below the phase transition temperature of the nematic phase-isotropic phase, FIG. 6B is the phase transition temperature of the nematic phase-isotropic phase, and FIG. 6C is above the phase transition temperature of the nematic phase-isotropic phase. 6 is a graph showing an actual response speed curve of an electro-optical device of a comparative example. 7A is below the nematic phase-isotropic phase transition temperature, FIG. 7B is at the nematic phase-isotropic phase transition temperature, and FIG. 7C is above the nematic phase-isotropic phase transition temperature. 4 is a graph showing actual response speed curves of the electro-optical device of Example 1. FIG. FIG. 8A is a graph showing the actual response speed curve of the electro-optical device of Example 2 at the nematic phase-isotropic phase transition temperature, and FIG. 8B is the nematic phase-isotropic phase transition temperature or higher. is there. FIG. 9A is a graph showing the actual response speed curve of the electro-optical device of Example 3 at the nematic phase-isotropic phase transition temperature, and FIG. 9B is the nematic phase-isotropic phase transition temperature or higher. is there. FIG. 10 is a graph showing the relationship between the temperature and the threshold voltage obtained from the response speed results of Examples 1 to 3 and the comparative example, and FIG. 10B was obtained from VT curves of Examples 1 to 3 and the comparative example. It is a graph which shows the relationship between temperature and a threshold voltage. FIG. 11A is a schematic cross-sectional view of a conventional vertical electric field type liquid crystal display device, FIG. 11B is a diagram showing a light transmission state thereof, and FIG. 11C is a schematic diagram showing an arrangement state of directors without an electric field applied. FIG. 11D is a schematic diagram illustrating an arrangement state of directors in an electric field application state.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the present invention will be described with reference to the drawings by way of examples and comparative examples. However, the following examples are intended to limit the present invention to those described herein. Instead, the present invention can be equally applied to various changes made without departing from the technical idea shown in the claims. The “surface” of the array substrate and the color filter substrate described here indicates a surface on which various wirings are formed or a surface on the side facing the liquid crystal forming material. In addition, in each drawing used for the description in this specification, each layer and each member are displayed at different scales so that each layer and each member can be recognized on the drawing. However, it is not necessarily displayed in proportion to the actual dimensions.

In addition, since the electro-optical device of each embodiment described below is for confirming the operation principle of the present invention, only the transparent overcoat layer is formed as the color filter layer of the color filter substrate CF. Is used. In addition, the liquid crystal forming material used in the electro-optical devices of the following embodiments is 5CB represented by the following chemical formula. This 5CB is a material having a positive dielectric anisotropy and undergoes a phase transition between a liquid crystal (nematic phase) phase and a liquid phase (isotropic phase) at about 35 ° C.

[Comparative Example and Examples 1-3]
First, a vertical electric field type electro-optical device 10 common to Embodiments 1 to 3 will be described with reference to FIG. As a specific method of the interface alignment treatment at the interface of the liquid crystal layer, a method of forming an alignment film is used here. The vertical electric field type electro-optical device of the comparative example has the same configuration as the electro-optical devices of Examples 1 to 3 except that the first alignment film and the second alignment film are not formed. To do. In addition, in the electro-optical devices of Examples 1 to 3, the first and second alignment films each using a horizontal alignment film that was rubbed (Example 1), and a vertical alignment film that was not rubbed was used. One (Example 2) and one using a rubbed vertical alignment film (Example 3) correspond to this. FIG. 1A is a plan view showing an outline of a one-pixel array substrate of the vertical electric field type electro-optical device 10 common to the first to third embodiments, and FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. FIG. As shown in FIG. 1B, the electro-optical device 10 has a configuration in which a liquid crystal forming material LC is sealed between an array substrate AR and a color filter substrate CF that are arranged to face each other.

  In the array substrate AR of the electro-optical device 10, a plurality of scanning lines 12 made of a metal such as aluminum or molybdenum are parallel to each other at equal intervals on the surface of a first transparent substrate 11 made of transparent insulating glass or the like. In addition, the auxiliary capacitance line 13 is formed in parallel at the approximate center between the adjacent scanning lines 12, and the auxiliary capacitance line 13 at the position where each pixel is to be formed is formed to be wide and auxiliary. The capacitor electrode 13a is formed. The scanning line 12 is formed so that the position where the gate electrode G of a thin film transistor TFT (Thin Film Transistor) is to be formed is partially wide.

  A gate insulating film 14 made of silicon nitride, silicon oxide, or the like is laminated so as to cover the scanning line 12, the auxiliary capacitance line 13, and the exposed portion of the glass substrate 11. A semiconductor layer 15 made of amorphous silicon, polycrystalline silicon, or the like is formed on the gate insulating film 14 where the gate electrode G is to be formed. Further, a plurality of signal lines 16 made of a metal such as aluminum or molybdenum are formed on the gate insulating film 14 so as to intersect the scanning lines 12, and the source electrode S of the TFT extends from the signal line 16. The source electrode S is in partial contact with the surface of the semiconductor layer 15. A region surrounded by the scanning lines 12 and the signal lines 16 in plan view corresponds to one pixel region.

  Further, a drain electrode D formed simultaneously with the same material as the signal line 16 and the source electrode S is provided on the gate insulating film 14, and the drain electrode D is disposed in the vicinity of the source electrode S and the semiconductor layer 15. Partially touching. Further, the drain electrode D is extended so that both ends of the auxiliary capacitance electrode 13a on the signal line 16 side are exposed so that the surface of the gate insulating film 14 is partially covered with the auxiliary capacitance electrode 13a. . In this case, the auxiliary capacitance of each pixel is formed by the overlapping portion of the drain electrode D and the auxiliary capacitance electrode 13a in plan view. The gate electrode G, the gate insulating film 14, the semiconductor layer 15, the source electrode S, and the drain electrode D constitute a TFT serving as a switching element, and this TFT is formed in each pixel.

  Further, a passivation film 17 made of, for example, silicon nitride or silicon oxide is laminated so as to cover the exposed portions of the signal line 16, the TFT, and the gate insulating film 14, and the surface of the passivation film 17 is made of a transparent resin material such as a photoresist. An interlayer film 18 having a flat surface is laminated. A contact hole 19 is formed in the passivation film 17 and the interlayer film 18 at a position corresponding to the drain electrode D of the TFT.

  A pixel electrode 20 made of a transparent conductive material such as ITO (Indium Thin Oxide) or IZO (Indium Zinc Oxide) is formed for each pixel so as to cover the inner surface of the contact hole 19 and the surface of the interlayer film 18. ing. In addition, the first alignment film 31 is formed on the surface of the pixel electrode 20 in the array substrate AR of the electro-optical device 10 according to the first to third embodiments. As the first alignment film 31, a film using a rubbing-processed horizontal alignment film is used in Example 1, a film using a non-rubbed vertical alignment film is used in Example 2, and a rubbing-processed vertical alignment is used. Those using a film correspond to Example 3, respectively. Further, the first alignment film is not formed on the array substrate of the electro-optical device of the comparative example.

  Further, the color filter substrate CF is provided with a transparent overcoat layer 22 instead of the color filter layer on the surface of the second transparent substrate 21 made of transparent insulating glass or the like. A common electrode 23 is laminated on the surface of the overcoat layer 22 over the entire surface of the color filter substrate CF. A second vertical alignment film 32 is formed on the surface of the common electrode 23 in the color filter substrate CF of the electro-optical device 10 according to the first to third embodiments. As the second alignment film, a film using a rubbed horizontal alignment film is used in Example 1, a film using a non-rubbed vertical alignment film is used in Example 2, and a rubbed vertical alignment film is used. Each of these corresponds to Example 3. Further, the second alignment film is not formed on the color filter substrate CF of the electro-optical device of the comparative example. Furthermore, the rubbing direction of the second alignment film 32 in Example 1 and Example 3 is opposite to the rubbing direction of the first alignment film 31 (anti-rubbing treatment).

  The array substrate AR and the color filter substrate CF thus formed are opposed to each other, and both substrates are bonded together by providing a sealing material around the substrates, and the liquid crystal forming material LC is sealed between the substrates. . Thereafter, the first polarizing plate 24 is arranged on the back surface side of the array substrate AR, and the second polarizing plate 25 is arranged on the back surface side of the color filter substrate CF, respectively, so that the crossed Nicols arrangement is obtained. 3 is obtained. The cell gap of the electro-optical device 10 is 3 μm.

  Here, the operation principle of the electro-optical device 10 according to the first to third embodiments will be described with reference to FIG. Since the electro-optical device of the comparative example has the same configuration as that of the electro-optical device 10 of the vertical electric field method of Examples 1 to 3 except that no alignment film is formed, Examples 1 to 3 are provided. It operates on the same operating principle as the vertical electric field type electro-optical device 10. 2A is a schematic diagram illustrating a state of a liquid crystal forming material in an isotropic phase temperature region of the electro-optical devices of Examples 1 to 3, and FIG. 2B is a schematic diagram illustrating an arrangement state of directors induced when an electric field is applied. FIG.

  As shown in FIG. 2A, in the isotropic phase temperature region, since the liquid crystal forming material exists as an isotropic phase (liquid), the light transmitted through the liquid crystal forming material is not affected at all. Therefore, since a pair of polarizing plates are arranged in crossed Nicols, light converted to linearly polarized light that has been transmitted through one polarizing plate cannot be transmitted through the other polarizing plate. However, when a voltage is applied between the pair of electrodes to apply an electric field to the liquid crystal forming material, a nematic phase is induced as shown in FIG. 2B. Since the light passing through this nematic phase undergoes a phase change due to the electro-optic Kerr effect, the phase of light that has been transmitted through one polarizing plate and converted to linearly polarized light changes while passing through the nematic phase. Thus, the light can be transmitted through the other polarizing plate. In this case, when the phase of the incident light is not changed by the liquid crystal forming material LC, the light transmitted through the first polarizing plate 24 cannot be transmitted through the second polarizing plate 25. Therefore, the normally black electro-optical device Become.

[Measurement of VT curve]
In order to confirm the operational characteristics of the comparative example and the electro-optical devices of Examples 1 to 3 created as described above, the following measurements were performed. In this measurement apparatus, an LCD7000 manufactured by Otsuka Electronics Co., Ltd. was used as an optical measurement apparatus, and AP529E manufactured by Anritsu Keiki Co., Ltd. was used as a temperature monitoring apparatus. The light transmittance was measured in the direct emission direction under 45 ° oblique incident light with respect to the cell substrate surface normal under the crossed Nicols condition. First, the electro-optical devices of the comparative example and Examples 1 to 3 are changed in a constant temperature bath from 34.7 ° C. to 35.8 ° C. in increments of 0.1 ° C., and at each temperature, the pixel electrode and the common electrode The transmittance (T) when the voltage applied during the period was changed from 0 V to 50 V was measured, and a voltage-transmittance (VT) curve was obtained. As a measurement result of the comparative example, VT curves at temperatures of 34.7 ° C., 34.9 ° C., 35.0 ° C., 35.1 ° C., and 35.2 ° C. are shown in FIG. The VT curve from 35.0 ° C. to 35.5 ° C. is shown in FIG. 3B, the VT curve from 34.9 ° C. to 35.6 ° C. is shown in FIG. The VT curves at temperatures of 35.1 ° C. to 35.8 ° C. are shown in FIG. 3C, respectively.

  Since the liquid crystal forming material 5CB used here is less than a nematic phase-isotropic phase transition temperature (hereinafter referred to as “Ni phase transition temperature”) at 34.7 ° C. and does not solidify, It exists as a nematic phase. According to the result of the comparative example shown in FIG. 3A, the transmittance due to light leakage is caused by the influence of disclination that occurs because the alignment of the nematic phase is not regulated because no alignment film is provided when no voltage is applied. Observed. Therefore, in the range where the voltage applied between the pixel electrode and the common electrode is small, due to the effect of alignment of the director in the liquid crystal layer, the transmittance tends to decrease compared to when no voltage is applied, Other than that, it has the same electro-optic effect as a normal vertical electric field type nematic liquid crystal. That is, in the case of the comparative example, when no voltage is applied, since the state of transmittance = 0 is observed at a Ni phase transition temperature of 34.9 ° C. or higher, it is confirmed that it exists as an isotropic phase. . In the applied voltage range up to 50 V, the temperature range in which the saturation state of the transmittance was confirmed is an induction phenomenon from the isotropic phase to the nematic phase between 0.3 ° C. and 34.9 ° C. to 35.1 ° C. Has been observed.

  In addition, according to the measurement result of Example 1 using the horizontal alignment film subjected to the rubbing process shown in FIG. 3B, light leakage based on the presence of the nematic phase is observed in the Ni phase transition temperature range of 35.0 ° C. However, at 35.1 ° C. or higher, the state of transmittance = 0 is observed when no voltage is applied, so that it is confirmed that it exists as an isotropic phase. In the applied voltage range up to 50 V, the temperature range in which the saturation state of the transmittance was confirmed was induced from the isotropic phase to the nematic phase between 0.5 ° C. and 35.1 ° C. to 35.5 ° C. A phenomenon has been observed.

  Further, according to the measurement result of Example 2 using the vertical alignment film not subjected to the rubbing process shown in FIG. 3C, the Ni phase transition temperature range of 35.0 ° C. and 34.9 ° C. is based on the presence of the nematic phase. Although light leakage is observed, at 35.1 ° C. or higher, a state of transmittance = 0 is observed when no voltage is applied, and therefore, it is confirmed that it exists as an isotropic phase. And, in the applied voltage range up to 50V, the temperature range in which the saturation state of the transmittance is confirmed is an induction phenomenon from the isotropic phase to the nematic phase between 0.6 ° C. and 35.1 ° C. to 35.6 ° C. Has been observed.

  Furthermore, according to the measurement result of Example 3 using the rubbed vertical alignment film shown in FIG. 3D, light leakage based on the presence of the nematic phase is observed at 35.1 ° C. or lower. Above 2 ° C., the state of transmittance = 0 is observed when no voltage is applied, so it is confirmed that it exists as an isotropic phase. Then, in the applied voltage range up to 50V, the temperature range in which the saturation state of the transmittance was confirmed is as follows. Induction of the nematic phase from the isotropic phase between 0.7 ° C. and 35.2 ° C. to 35.8 ° C. A phenomenon has been observed.

  When the measurement results of FIGS. 3A to 3D described above are compared, in the same temperature range up to 50 V, the alignment film is formed rather than the case where the alignment film is not formed (Comparative Example) (Examples 1 to 3). 3) confirms that the temperature range in which the induction phenomenon of the nematic phase occurs from the isotropic phase at the time of voltage application is expanded. Further, the temperature dependence of the voltage (hereinafter referred to as “threshold voltage”) Vth induced by the nematic phase from the isotropic phase at the time of voltage application is more than in the case where the alignment film of the comparative example is not formed (see FIG. 3A). However, the case where the alignment films of Examples 1 to 3 are provided (see FIGS. 3B to 3C) is significantly smaller. Therefore, if the temperature is the same, the voltage can be lowered, and if the driving voltage is the same, an induction phenomenon occurs at a high temperature, so that the operating temperature range is widened. In particular, the vertical alignment film shown in FIG. 3C subjected to the interface alignment process parallel to the electric field direction or the rubbing-processed vertical alignment film shown in FIG. 3D is compared with the horizontal alignment film shown in FIG. 3A or 3B. The above effect is very high, and it is particularly preferable when used as an electro-optical device.

  Moreover, when the inclination of the VT curve until the transmittance | permeability is saturated from the state of the transmittance | permeability = 0, when the horizontal alignment film by which the rubbing process of Example 1 was used (refer FIG. 3B) and Example 3 is shown. It can be seen that the vertical alignment film subjected to the rubbing treatment (see FIG. 3D) is steeper than the case where the vertical alignment film not subjected to the rubbing treatment in Example 2 is used (see FIG. 3C). .

[Measurement of rise response time tr]
Conventionally, the response speed of the induction and disappearance phenomenon of the nematic phase of the liquid crystal forming material when no voltage is applied and when a voltage is applied in such an isotropic phase temperature range is a change in the orientation direction of the director below the Ni phase transition temperature. It was considered to be much faster than. Accordingly, in the electro-optical devices of the comparative example and Examples 1 to 3, the rise response time tr from when the threshold voltage Vth and a predetermined voltage in the vicinity thereof were applied until the transmittance reached a constant value was measured. This rise time tr indicates the induced speed of the nematic phase in the isotropic phase temperature region. Of the results, the results with a relatively large rise time tr were obtained. FIG. 4A (Comparative Example), FIG. 4B (Example 1), FIG. 4C (Example 2) and FIG. 4D (Example 3). It was shown to. The horizontal axis is shown as applied voltage / threshold voltage (V / Vth), the applied voltage V is an effective voltage, and the threshold voltage Vth is a voltage induced by the nematic phase from the isotropic phase at the time of voltage application, that is, The voltage when an increase in transmittance is observed is shown.

  According to the measurement result of the electro-optical device of the comparative example shown in FIG. 4A, the rise response time tr is long in a wide voltage range at 34.9 ° C. just above the Ni phase transition temperature, but the temperature rises near Vth. Along with this, the voltage range in which the rise response time tr becomes longer is narrower. However, in any temperature range, there is a voltage range in which the rising response time tr is close to 30 to 40 msec near Vth. Further, according to the measurement result of the electro-optical device of Example 1 shown in FIG. 4B, the rise response time tr is long in a wide voltage range at 35.1 ° C. immediately above the Ni phase transition temperature, but the temperature is near Vth. As the voltage rises, the voltage range in which the rise response time tr becomes longer is narrower. However, in any case, there is a voltage range in which the rise response time tr is close to 30 to 40 msec near Vth.

  Further, according to the measurement result of the electro-optical device of Example 2 shown in FIG. 4C, the rise response time tr becomes longer in a wide voltage range at Ni phase transition temperature ranges of 35.0 ° C. and 35.1 ° C. or less. However, in the vicinity of Vth, the voltage range in which the rise response time tr becomes longer as the temperature rises becomes narrower. Furthermore, in any case, the response characteristic of the rising response time tr is very good, with the rising response time tr being about 15 to 25 msec in the vicinity of Vth. Further, according to the measurement result of the electro-optical device of Example 3 shown in FIG. 4D, the voltage range in which the rise response time tr becomes long is narrow even at 35.2 ° C. near Vth, and the temperature rises. The voltage range in which the rise response time tr becomes longer is narrower. However, in any case, there is a voltage range in which the rise response time tr is close to 30 to 45 msec near Vth.

  From the results shown in FIGS. 4A to 4D above, in the electro-optical devices of the comparative example and Examples 1 to 3, the rise response time tr is generally delayed near the Vth regardless of the temperature, but the rubbing process is performed. The rise response time tr of the electro-optical device of Example 2 using the vertical alignment film that is not rubbed or the example 3 using the vertical alignment film that is rubbed is the first example using the horizontal alignment film that is rubbed. In particular, Example 2 is a good result. Further, it can be seen that in the Ni phase transition temperature range, the voltage range in which the rising response time tr is long tends to widen in any case.

[Measurement of fall response time tf]
Next, in the electro-optical devices of the comparative example and Examples 1 to 3, the transmittance when the threshold voltage Vth and a predetermined voltage in the vicinity thereof are applied is set to 100%, and transmission is performed from the time when the predetermined voltage is removed. The time until the rate reached 10% was measured as the falling response time tf. The falling response time tf indicates the disappearance rate of the nematic phase in the isotropic phase temperature region. Among the results, the results with relatively large fall time tf were obtained. FIG. 5A (Comparative Example), FIG. 5B (Example 1), FIG. 5C (Example 2), and FIG. 5D (Example 3). )Pointing out toungue. The horizontal axis is shown as applied voltage / threshold voltage (V / Vth), the applied voltage V is an effective voltage, and the threshold voltage Vth is a voltage induced by the nematic phase from the isotropic phase at the time of voltage application, that is, The voltage when an increase in transmittance is observed is shown.

  According to the measurement result of the electro-optical device of the comparative example which does not use the alignment film shown in FIG. 5A, the fall response time tf of about 12 to 20 msec is obtained in a wide voltage range at 34.7 ° C. which is a nematic phase forming region. Obtained. The fall response time tf at 34.7 ° C. is considered to correspond to the time that is relaxed when the orientation direction of the nematic phase director is in a voltage non-application state. Moreover, in the Ni phase transition temperature range of 34.9 ° C., the falling response time tf shows a very specific response, but a very short falling response time tf of 1 msec or less is obtained above the Ni phase transition temperature. It has been.

  Further, the measurement result of the electro-optical device of Example 1 using the rubbing-processed horizontal alignment film shown in FIG. 5B seems to be short due to the influence of the analysis method, but is actually about 100 msec (the reason will be described later). ). In Example 1, the fall response time tf shows a specific response that becomes longer when the applied voltage is higher in the Ni phase transition temperature range of 35.1 ° C., but the fall response time tf falls as the temperature increases. The response time tf is shortened, and a very short falling response time tf of 0.1 msec is observed. Further, according to the measurement result of the electro-optical device of Example 2 using the vertical alignment film not subjected to the rubbing process illustrated in FIG. 5C, the falling response time tf is 35.0 ° C. and 35 ° C. in the Ni phase transition temperature range. When the applied voltage increases, the constant value is approximately 100 msec at .1 ° C., and when the temperature is further increased, a very short falling response time tf of 1 msec or less is obtained. Further, the measurement result of the electro-optical device of Example 3 using the vertical alignment film subjected to the bing treatment shown in FIG. 5D shows a specific response in the Ni phase transition temperature range of 35.2 ° C. When the temperature is higher than the phase transition temperature, a very short falling response time tf of 1 msec or less and the shortest 0.1 msec or less is obtained.

  The falling response time tf shows a specific result in the Ni phase transition temperature range. From the measurement result of the comparative example in which the alignment film is not formed and the horizontal alignment subjected to the rubbing treatment, the Ni phase In the transition temperature range, it seems to be indicated by the sum of the response characteristic at a temperature exceeding the Ni phase transition temperature and the response characteristic at a temperature lower than the Ni phase transition temperature. Further, in the case of the electro-optical device of Example 2 using the vertical alignment film that has not been rubbed, the current measurement method has a condition in which the phase difference change due to voltage does not occur below the Ni phase transition temperature. Considering the measurement results of the comparative example in which the alignment film is not formed in the Ni phase transition temperature range and the electro-optical device of Example 1 using the rubbed horizontal alignment, the temperature is confirmed to be lower than the Ni phase transition temperature. It is considered that the response time of tf becomes longer due to the influence of the initial transmittance (9 to 12%).

  The electro-optical device of Example 3 using the rubbed vertical alignment film shows different response characteristics from those of the comparative example and the electro-optical devices of Examples 1 and 2, and V in the temperature range above the Ni phase transition temperature. Although -T is almost the same as that of the vertical alignment cell, a maximum response time of 6 msec and a falling response time tf of 1/10 or less are obtained in the Ni phase transition temperature range. This is considered that the orientation environment contributes to the metastable state of the nematic phase induced by applying a voltage from the isotropic phase.

[Measurement of actual response characteristics]
Here, in the electro-optical devices of the comparative example and Examples 1 to 3, a temperature range lower than the Ni phase transition temperature (hereinafter referred to as “temperature range <Ni point”), a Ni phase transition temperature range (hereinafter referred to as “temperature”). Range = Ni point ”) and the actual response characteristics in the temperature range exceeding the Ni phase transition temperature (hereinafter,“ temperature range> Ni point ”) are shown in FIGS. . 6A is a graph showing the actual response speed curve of the electro-optical device of the comparative example, which is below the Ni phase transition temperature, FIG. 6B is the Ni phase transition temperature, and FIG. 6C is the Ni phase transition temperature. is there. 7A is a graph showing an actual response speed curve of the electro-optical device of Example 1 below the Ni phase transition temperature, FIG. 7B is the Ni phase transition temperature, and FIG. 7C is the Ni phase transition temperature. . FIG. 8A is a graph showing the actual response speed curve of the electro-optical device of Example 2 at the Ni phase transition temperature and FIG. 8B at the Ni phase transition temperature or higher. FIG. 9A is a graph showing the actual response speed curve of the electro-optical device of Example 3 at the Ni phase transition temperature and FIG. 9B at the Ni phase transition temperature or higher. 6 to 9 show actual response characteristics when a predetermined voltage is applied for 100 msec.

  In the comparative electro-optical device in which the alignment film is not formed, as shown in FIG. 6A, the initial transmittance increases as the applied voltage becomes higher in the temperature range <Ni point (black floating). Therefore, the monitoring time after removing the applied voltage was confirmed by changing from 100 msec to 2500 msec, but black floating was not eliminated. Therefore, it can be seen that in the electro-optical device of the comparative example, the falling response time tf is longer than the value shown in FIG. 6A. In the temperature range = Ni point, as shown in FIG. 6B, compared to the case of the temperature range <Ni point, the result of improving both the black floating and the falling response time tf is shown. Further, in the temperature range> Ni point, as shown in FIG. 6C, a result is obtained in which the occurrence of the black floating and the falling response time tf is not confirmed.

  Further, in the electro-optical device of Example 1 using the horizontal alignment film subjected to the rubbing process, the alignment film is formed in the temperature range <Ni point and temperature range> Ni point as shown in FIGS. 7A and 7C. The same tendency as the result confirmed by the electro-optical device of the comparative example which is not performed is shown. However, the black floating at the temperature range <Ni point is eliminated in about 100 msec. Note that the measurement result of the falling response time tf at the temperature range = Ni point is confirmed to be about 100 msec from the response measurement result of FIG. 5B, but shows a result greatly different from the analysis result. . The difference is that the transmittance when a predetermined voltage is applied is 100%, and the time from when the predetermined voltage is removed until the transmittance reaches 10% is measured as the falling response time tf. Due to the fact that That is, as shown in FIGS. 7A and 7B, when the electro-optical device according to the first embodiment removes a predetermined voltage, the transmittance once rises after taking a minimum value, and then decreases again. Therefore, in practice, it is necessary to set the time until the transmittance after decreasing again reaches 10% of the transmittance when a predetermined voltage is applied as the falling response time tf.

  Further, in the electro-optical device of Example 2 using the vertical alignment film that has not been rubbed, as shown in FIG. 8A, the transmittance of the falling response time tf is not particularly lowered at the temperature range = Ni point. The result was confirmed. Since the measurement range upper limit of the current falling response time tf was set to 100 msec, the actual response time is considered to be longer than 100 msec. This result is considered to reflect the influence of the transmittance (9-12%) of the measurement result of the VT characteristic at the temperature range <Ni point considered earlier (see FIG. 3C). The actual response measurement results shown in FIGS. 8A and 8B are shown in FIGS. 6B, 6C, 7B, 7C, 9A, and 9B, which are measurement results of the comparative example, Example 1 and Example 3. As apparent from the comparison with the results, the electro-optical device of Example 2 has a shorter rise time tr of the voltage portion corresponding to the VT halftone than the electro-optical device of Comparative Example and Examples 1 and 3. (The rising speed is fast), indicating that all transmittance halftones have the same rising tendency.

  Further, in the electro-optical device of Example 3 using the rubbed vertical alignment film, the fall time tf at the temperature range = Ni point is shorter than that of the electro-optical device of Example 2. On the other hand, the rise time tr is very similar to the results of the comparative example in which no alignment film is formed and the electro-optical device of Example 1 in which a rubbing-processed horizontal alignment film is formed. From this result, it can be considered that the rubbing treatment is performed on the vertical alignment film to have both the characteristics of the vertical alignment film and the rubbing horizontal alignment film. Comparing the response characteristics based on this idea, the rise time tr of the VT halftone has a relatively low transmittance response characteristic in which the horizontal alignment is dominant, and the vertical alignment is dominant as the transmittance increases. It turns out that it shows the tendency to become.

  Considering that the fall time tf is confirmed in the temperature range = Ni point and that the effect of the rubbing treatment contributes to the horizontal alignment, the electro-optical device of Example 3 applies a voltage in the isotropic phase temperature region. Due to the influence of the metastable state of the nematic phase induced by the vertical alignment by the vertical alignment film and the horizontal alignment by the rubbing process, the fall time tf as in the electro-optical device of Example 2 can be shortened. It is thought that it was made. However, in the electro-optical device of Example 3, the response of the fall time tf was improved, but the rise time tr was inconveniently bad. However, from the results of FIGS. 8 and 9, there is a possibility that a favorable effect can be derived with respect to the rise time tr and the fall time tf by combining the alignment film material and the alignment treatment under the optimum conditions. It suggests that you are.

  Next, FIG. 10 shows an analysis result regarding a tendency that the shift of the threshold voltage becomes smaller as the temperature becomes higher. FIG. 10A is a graph showing the relationship between the temperature (difference from Ni phase transition temperature) obtained from the response speed results of Examples 1 to 3 and the comparative example and the threshold voltage, and FIG. It is a graph which shows the relationship between the temperature (difference with Ni phase transition temperature) calculated | required from the VT curve of the comparative example, and a threshold voltage. However, the threshold voltage of the response speed is the voltage immediately before the response measurement is possible. In addition, the threshold voltage in the VT curve is qualitatively compared here, so that the voltage reaching the transmittance of 5% or the voltage closest to the transmittance of 5% is used.

  From the results shown in FIGS. 10A and 10B, the electro-optical devices of Examples 1 to 3 having the alignment film have a lower threshold voltage than the electro-optical device of the comparative example having no alignment film, and the temperature It can be confirmed that the amount of change in the threshold voltage decreases with an increase in. From this result, the orientation of the director of the liquid crystal layer induced by the electric field and the orientation of the interface alignment treatment are the same in the orientation environment, that is, in this electro-optical device, the liquid crystal phase die is aligned in the direction parallel to the electric field (vertical direction). It was confirmed that the electro-optical devices of Examples 2 and 3 that performed the interface alignment process for aligning the reflectors particularly well reduced the threshold voltage and that the change amount of the threshold voltage became smaller as the temperature increased.

  In the electro-optical devices of Examples 1 to 3, the color filter substrate CF is provided with an overcoat layer instead of the color filter layer. However, various colors such as a normal liquid crystal display device are used. If the color filter layer is provided, an electro-optical device capable of displaying various colors while obtaining the above effects can be obtained. Further, in the above-described first to third electro-optical devices, an example in which a pair of polarizing plates is arranged in a crossed Nicols configuration is shown, but a pair of polarizing plates can be arranged in a parallel Nicols configuration. In this case, a normally white type electro-optical device is obtained. Further, in the electro-optical devices according to the first to third embodiments, an example in which the electrode arrangement is the same as that of the conventional VA mode liquid crystal display device has been shown. An electrode arrangement similar to that of the apparatus may be employed.

  In this embodiment, a liquid crystal forming material having a positive dielectric anisotropy is used, but a liquid crystal forming material having a negative dielectric anisotropy may be used. Also in this case, it is preferable that the direction of the director of the liquid crystal layer induced by the electric field and the direction of the interface alignment treatment are the same based on the verification result in the electric field. In the above embodiment, a method of forming an alignment film has been shown as a method of interfacial alignment treatment at the interface of the liquid crystal layer. Other methods include a method of forming irregularities on the electrode surface, Alternatively, a method may be used in which a high molecular polymer is formed and a photo-alignment is performed on the high molecular polymer, or a method in which a rubbing treatment is performed on the electrode surface with a rubbing cloth.

  DESCRIPTION OF SYMBOLS 10 ... Electro-optical apparatus 11 ... 1st transparent substrate 12 ... Scanning line 13 ... Auxiliary capacitance line 13a ... Auxiliary capacitance electrode 14 ... Gate insulating film 15 ... Semiconductor layer 16 ... Signal line 17 ... Passivation film 18 ... Interlayer film 19 ... Contact Hole 20 ... pixel electrode 21 ... second transparent substrate 22 ... overcoat layer 23 ... common electrode 24 ... first polarizing plate 25 ... second polarizing plate 31 ... first alignment film 32 ... second alignment film LC ... liquid crystal Forming material AR ... Array substrate CF ... Color filter substrate TFT ... Thin film transistor tr ... Rise time tf ... Fall time

Claims (5)

A liquid crystal layer made of a liquid crystal forming material that undergoes a phase transition between a nematic phase and an isotropic phase at a phase transition temperature;
A first substrate and a second substrate disposed opposite to each other with the liquid crystal layer interposed therebetween;
A pair of electrodes formed on the liquid crystal layer side of each of the first substrate and the second substrate and generating an electric field perpendicular to the substrate surface when a predetermined voltage is applied ;
A pair of polarizing plates disposed on the outer surface side of each of the first substrate and the second substrate;
With
Each of the first substrate before SL and the second substrate, the interface between the liquid crystal layer, the liquid crystal layer when the nematic phase is induced in the vertical direction of the electric field by the voltage applied between the pair of electrodes to be the same as the director orientation, and surface alignment treatment to align the orientation of the directors of the liquid crystal layer is applied,
In the isotropic phase temperature region where the liquid crystal layer forms the isotropic phase, a change in light transmittance based on induction and disappearance of the nematic phase in the liquid crystal layer according to a voltage applied between the pair of electrodes is performed. Perform the display used,
Electro-optic device. As the interface alignment treatment, a vertical alignment film that aligns the direction of the director of the liquid crystal layer in a direction parallel to the electric field is disposed at the interface with the liquid crystal layer in a state where the rubbing treatment is not performed .
The electro-optical device according to claim 1. As the interface alignment treatment, a rubbing treatment is performed on the interface .
The electro-optical device according to claim 1 . The interface alignment process is obtained by forming irregularities on the interface,
The electro-optical device according to claim 1. The liquid crystal forming material is a material having a positive dielectric anisotropy.
The electro-optical device according to claim 1.