JP2014157293A - Electrooptical device and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an electrooptical device using an electrooptical effect based on a nematic phase induction/dissipation phenomenon according to the presence/absence of an external electric field, in an isotropic phase temperature range of a nematic liquid crystal material having a negative dielectric anisotropy.SOLUTION: An electrooptical device 10 includes: a first transparent substrate 11 and a second transparent substrate 21 which are oppositely arranged while sandwiching a nematic liquid crystal material having a negative dielectric anisotropy; a pair of pixel electrodes 20 and a common electrode 23 which are formed on at least one nematic liquid crystal material side of the first transparent substrate 11 and the second transparent substrate 21; and a pair of polarizing plates of a first polarizing plate 24 and a second polarizing plate 25 which are arranged on a side opposite to the nematic liquid crystal material side of the first transparent substrate 11 and the second transparent substrate 21.

Description

  The present disclosure relates to an electro-optical device and an electronic apparatus that utilize the appearance and disappearance phenomenon of a nematic phase depending on the presence or absence of an external electric field in a liquid crystal material in an isotropic phase temperature region.

  A liquid crystal display device, which is one of electro-optical devices using liquid crystals, has been characterized by its light weight, thinness, and low power consumption compared to a CRT (cathode ray tube). Has been. 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. .

  In addition, a horizontal electric field type liquid crystal display device has a pair of electrodes provided on one inner surface side of a pair of substrates arranged with a liquid crystal layer sandwiched therebetween, so that an electric field in a substantially horizontal direction is generated by liquid crystal molecules. Is applied to. 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 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. On the other hand, in recent years, an apparatus for displaying an image using the manifestation and disappearance phenomenon of a nematic phase due to the presence or absence of an external electric field in the liquid (isotropic phase) temperature region of a nematic liquid crystal material having a positive dielectric anisotropy. Has been proposed (for example, Patent Document 1). A liquid crystal display device using the manifestation and disappearance phenomenon of a nematic phase depending on the presence or absence of an external electric field in a nematic liquid crystal material having a positive dielectric anisotropy in the isotropic phase region has conventionally been oriented by a director oriented in a predetermined direction. Compared with a liquid crystal display device that changes the amount of transmitted light by changing the electric field by an electric field, it has a faster response characteristic.

JP 2011-043733 A

  Patent Document 1 is directed to a liquid crystal material having a positive dielectric anisotropy. However, it is not clear whether an electro-optical device using a liquid crystal material having a negative dielectric anisotropy and utilizing an electro-optical effect based on induction and disappearance phenomena of a nematic phase can be realized.

  The present disclosure relates to an electro-optical device and an electronic apparatus using an electro-optical effect based on induction and disappearance of a nematic phase due to the presence or absence of an external electric field in an isotropic phase temperature region of a liquid crystal material in which dielectric anisotropy is negative. An object of the present invention is to provide a response characteristic according to the presence or absence of an external electric field and to have a high speed similar to that of a liquid crystal material having a positive dielectric anisotropy.

  The present disclosure relates to a first substrate and a second substrate that are disposed to face each other with a nematic liquid crystal material having a negative dielectric anisotropy interposed therebetween, and the nematic liquid crystal material of at least one of the first substrate and the second substrate. An isotropic phase of the nematic liquid crystal material, comprising: a pair of electrodes formed on a side; and a pair of polarizing plates respectively disposed on opposite sides of the first substrate and the second substrate from the nematic liquid crystal material In the temperature region, the electro-optical device uses a change in light transmittance based on a phase transition from an isotropic phase to a nematic phase according to a voltage applied between the pair of electrodes.

  The present disclosure is an electronic apparatus including the above-described electro-optical device as a display device.

  In general, a nematic liquid crystal material exhibits an intermediate phase state between a solid and a liquid (isotropic phase), that is, a liquid crystal phase state. At a temperature (phase transition temperature) determined by the nematic liquid crystal material, a phase transition from the isotropic phase to the isotropic phase, for example, a phase transition occurs between the isotropic phase and the nematic phase. The electro-optical device of the present disclosure includes a phase transition from an isotropic phase according to a voltage applied between a pair of electrodes in an isotropic phase temperature region of a nematic liquid crystal material having a negative dielectric anisotropy, for example, a nematic phase. The change in the light transmittance due to the induction and disappearance phenomenon of refractive index anisotropy, which is an electro-optic effect based on the induction and disappearance phenomenon, is utilized. That is, if no voltage is applied between the pair of electrodes, the nematic liquid crystal material remains in an isotropic phase, but if a predetermined voltage is applied between the pair of electrodes, the isotropic phase nematic liquid crystal 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.

  Along with the induction and disappearance phenomenon of the nematic phase from the isotropic phase due to the presence or absence of voltage in the nematic liquid crystal material, the liquid crystal layer exhibits the occurrence and disappearance phenomenon of the phase difference as the electro-optic effect. In the electro-optical device, the light transmittance changes. That is, when the nematic liquid crystal material is in an isotropic phase, the liquid crystal layer does not generate an optical phase difference change, so that the electro-optical device has a transmittance depending on conditions determined by the pair of polarizing plates. On the other hand, when the nematic liquid crystal material undergoes a phase transition from the isotropic phase to the nematic phase due to an external electric field (external electric field), refractive index anisotropy occurs due to the electro-optic effect. For this reason, a phase difference of light transmitted through the liquid crystal layer is changed, and the transmittance of the electro-optical device is changed.

  Further, even in a direct-view display device configuration with a so-called counter electrode configuration in which electrodes are disposed on a first substrate and a second substrate that are opposed to each other with a nematic liquid crystal material having a negative dielectric anisotropy, It was confirmed that the transmittance changes by using induction and disappearance of nematic phase from isotropic phase with and without voltage. Furthermore, it has been clarified that the disappearance rate of the nematic phase caused by the voltage application is significantly faster than the realignment rate of the director in the nematic phase temperature range of the conventional nematic liquid crystal material. As described above, the present disclosure relates to an electro-optic effect utilizing an electro-optic effect based on a phase transition from an isotropic phase, for example, an induction and disappearance phenomenon of a nematic phase due to the presence or absence of an external electric field in an isotropic phase temperature region of a nematic liquid crystal material. A device can be provided, and the response characteristic when the external electric field disappears, which is a response characteristic depending on the presence or absence of an external electric field, can be made equivalent to a liquid crystal material having a positive dielectric anisotropy.

  According to the present disclosure, an electro-optical device using an electro-optical effect based on induction and disappearance of a nematic phase due to the presence or absence of an external electric field in an isotropic phase temperature region of a nematic liquid crystal material having a negative dielectric anisotropy. It is possible to provide a response characteristic according to the presence or absence of an external electric field and to have the same high-speed property as a nematic liquid crystal material having a positive dielectric anisotropy.

FIG. 1 is a plan view illustrating an outline of a one-pixel array substrate provided in the vertical electric field type electro-optical device according to the present embodiment. 2 is a cross-sectional view taken along line IB-IB in FIG. 1A. FIG. 3 is a schematic diagram showing a state of a nematic liquid crystal material having a negative dielectric anisotropy in the isotropic phase temperature region of the electro-optical device according to the present embodiment. FIG. 4 is a schematic diagram illustrating an arrangement state of directors induced when an electric field is applied to a nematic liquid crystal material having a negative dielectric anisotropy of the electro-optical device according to the present embodiment. FIG. 5 is a diagram showing the relationship between the transmittance and the applied voltage. FIG. 6 is a schematic diagram showing the interface between the liquid crystal layer and the alignment film in the presence or absence of an electric field. FIG. 7 is a cross-sectional view of a liquid crystal display device corresponding to a direct-view display device in which a pair of electrodes are arranged to face the liquid crystal phase. FIG. 8 is a diagram showing changes in the director depending on the presence or absence of an electric field in a liquid crystal layer of a nematic liquid crystal material whose dielectric anisotropy is different from positive and negative. FIG. 9 is a diagram showing the relationship between the transmittance and the applied voltage. FIG. 10 is a cross-sectional view illustrating an example of an electro-optical device including a temperature sensor. FIG. 11 is a perspective view illustrating an appearance of a television apparatus to which the present disclosure is applied. FIG. 12 is a perspective view illustrating an appearance of a digital camera to which the present disclosure is applied. FIG. 13 is a perspective view illustrating an appearance of a digital camera to which the present disclosure is applied. FIG. 14 is a perspective view illustrating an appearance of a video camera to which the present disclosure is applied. FIG. 15 is a perspective view illustrating an appearance of a notebook personal computer to which the present disclosure is applied. FIG. 16 is a front view of an open state showing a mobile phone to which the present disclosure is applied. FIG. 17 is a side view illustrating a mobile phone to which the present disclosure is applied. FIG. 18 is a front view in a closed state illustrating a mobile phone to which the present disclosure is applied. FIG. 19 is a left side view illustrating a mobile phone to which the present disclosure is applied. FIG. 20 is a right side view illustrating a mobile phone to which the present disclosure is applied. FIG. 21 is a top view illustrating a mobile phone to which the present disclosure is applied. FIG. 22 is a bottom view illustrating a mobile phone to which the present disclosure is applied.

Hereinafter, a mode for carrying out the technique of the present disclosure (hereinafter, referred to as an embodiment) will be described in detail with reference to the drawings in the following procedure.
1. 1. Electro-optical device to which the present disclosure is applied 1-1. Outline 1-2. Optical characteristics and electric field response 1-3. Interfacial orientation treatment 1-4. Direct view type display device 1-5. Driving method of electro-optical device 1-6. Example of temperature control 1-7. 1. Electro-optical device in another configuration Electronic equipment Composition of this disclosure

<1. Electro-optical device to which the present disclosure is applied>
The “surface” of the array substrate and the color filter substrate described in the present embodiment indicates a surface on which various wirings are formed or a surface on the side facing the liquid crystal material. In addition, each drawing used for explanation in the present embodiment is displayed with a different scale for each layer and each member so that each layer and each member can be recognized on the drawing. It is not necessarily displayed in proportion to the actual dimensions.

  Since the electro-optical device and the liquid crystal display device of each embodiment described below are for confirming the operation principle of the present disclosure, only a transparent overcoat layer is formed as the color filter layer of the color filter substrate. Something is used. Further, among the materials having a negative dielectric anisotropy (ε), several nematic liquid crystal materials were used. However, in the electro-optical device according to the following embodiment, as a material having a negative dielectric anisotropy, The product name MJ052996 made by Merck was used. This liquid crystal material undergoes a phase transition between a nematic phase and an isotropic phase at about 60 ° C. The liquid crystal material applicable to the electro-optical device and the liquid crystal display device according to the present embodiment may be a nematic liquid crystal material having a negative dielectric anisotropy and is not limited to the above-described product name MJ052996. Absent.

  FIG. 1 is a plan view illustrating an outline of a one-pixel array substrate provided in the vertical electric field type electro-optical device according to the present embodiment. 2 is a cross-sectional view taken along line IB-IB in FIG. 1A. As shown in FIG. 2, the electro-optical device 10 encloses the liquid crystal material 1 between the array substrate AR and the color filter substrate CF that are arranged to face each other. As a specific method of the interface alignment treatment at the interface of the liquid crystal layer LC, a method of forming an alignment film is used in the present embodiment.

  In the following, the electro-optical device 10 uses a vertical electric field method as an example, but is not limited thereto. For example, the electro-optical device 10 may use a lateral electric field method such as an FFS mode or an IPS mode.

<1-1. Overview>
The array substrate AR of the electro-optical device 10 has a plurality of scanning lines 12 using a metal such as aluminum or molybdenum on the surface of a first transparent substrate 11 as a first substrate using transparent glass having insulating properties. Are formed in parallel at equal intervals. In the array substrate AR, auxiliary capacitance lines 13 are formed in parallel at substantially the center between adjacent scanning lines 12. The auxiliary capacitance line 13 at the position where each pixel is to be formed is formed wide and serves as an auxiliary capacitance electrode 13a. The scanning line 12 is formed such that a position where a gate electrode G of a thin film transistor (TFT) is to be formed is partially wide.

  A gate insulating film 14 using silicon nitride or silicon oxide is laminated so as to cover the scanning lines 12, the auxiliary capacitance lines 13, and the exposed portions of the transparent substrate 11. On the surface of the gate insulating film 14 at the position where the gate electrode G is to be formed, a semiconductor layer 15 using amorphous silicon or polycrystalline silicon is formed. A plurality of signal lines 16 using a metal such as aluminum or molybdenum are formed on the surface of the gate insulating film 14 so as to intersect the scanning lines 12. A TFT source electrode S extends from the signal line 16, and 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 a region of one pixel.

  A drain electrode D formed simultaneously with the same material as the signal line 16 and the source electrode S is provided on the surface of the gate insulating film 14. The drain electrode D is disposed close to the source electrode S and is in partial contact with the semiconductor layer 15. 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 partially covers the auxiliary capacitance electrode 13a. A storage capacitor of each pixel is formed by the overlapping portion of the drain electrode D and the storage capacitor electrode 13a in plan view. A TFT serving as a switching element is formed by the gate electrode G, the gate insulating film 14, the semiconductor layer 15, the source electrode S, and the drain electrode D, and this TFT is provided in each pixel.

  A passivation film 17 using, 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. The surface of the passivation film 17 is made of a transparent resin material such as a photoresist, and 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.

  For each pixel, a pixel electrode 20 using a transparent conductive material such as ITO (Indium Thin Oxide) or IZO (Indium Zinc Oxide) is formed so as to cover the inner surface of the contact hole 19 and the surface of the interlayer film 18. Yes. A first alignment film 31 is formed on the surface of the pixel electrode 20 on the array substrate AR of the electro-optical device 10. In the present embodiment, a rubbed vertical alignment film is used as the first alignment film 31.

  The color filter substrate CF is provided with a transparent overcoat layer 22 instead of the color filter layer on the surface of a second transparent substrate 21 as a second substrate using transparent glass having insulating properties. 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 alignment film 32 is formed on the surface of the common electrode 23 on the color filter substrate CF of the electro-optical device 10. In the present embodiment, a rubbed vertical alignment film is used as the second alignment film 32. In the present embodiment, the rubbing direction of the second alignment film 32 is opposite to the rubbing direction of the first alignment film 31 (anti-rubbing process).

  The array substrate AR and the color filter substrate CF thus formed are opposed to each other, a sealing material is provided around both substrates, the two substrates are bonded together, and the liquid crystal material 1 is sealed between the substrates. Let it be a liquid crystal layer LC. Thereafter, the first polarizing plate 24 is arranged on the back surface side of the array substrate AR (for example, the side on which the light source is arranged), and the second polarizing plate 25 is arranged on the back surface side of the color filter substrate CF so as to have a crossed Nicols arrangement. By arranging them as a pair of polarizing plates, a longitudinal electric field type electro-optical device 10 is obtained. Although the layer thickness of the liquid crystal layer can be arbitrarily changed, in the present embodiment, the layer thickness of the liquid crystal layer of the electro-optical device 10 is, for example, 3 μm. Next, the operation principle of the electro-optical device 10 will be described.

  FIG. 3 is a schematic diagram showing a state of a nematic liquid crystal material having a negative dielectric anisotropy in the isotropic phase temperature region of the electro-optical device according to the present embodiment. As shown in FIG. 3, in a state where no voltage is applied between the pixel electrode 20 and the common electrode 23 (voltage non-application state), a nematic liquid crystal material having a negative dielectric anisotropy is in an isotropic phase. In the isotropic phase, there is no director as seen in the liquid crystal state. For this reason, in the isotropic phase of the nematic liquid crystal material, no refractive index anisotropy occurs, so that no phase change occurs even if light (polarized light) passes through the liquid crystal layer. This is the same whether the nematic liquid crystal material has a negative or positive dielectric anisotropy. In FIG. 2 (including FIG. 3), the pair of polarizing plates (the first polarizing plate 24 and the second polarizing plate 25) provided in the electro-optical device 10 are arranged in a crossed Nicols arrangement. For this reason, in the case of the isotropic phase, the light converted into the linearly polarized light transmitted through one polarizing plate cannot pass through the other polarizing plate.

  FIG. 4 is a schematic diagram illustrating an arrangement state of directors induced when an electric field is applied to a nematic liquid crystal material having a negative dielectric anisotropy of the electro-optical device according to the present embodiment. The major axis Zl of the director in FIG. 4 represents the direction of refractive index anisotropy. As shown in FIG. 4, when a voltage is applied between a pair of electrodes (between the pixel electrode 20 and the common electrode 23 included in the electro-optical device 10), an electric field E is formed as indicated by an arrow. Since it is a nematic liquid crystal material having a negative dielectric anisotropy, the major axis Z1 of the director is aligned in a direction orthogonal to the direction of the electric field E (electric field direction). In general, in an isotropic medium such as an isotropic phase, a refractive index anisotropy caused by the Kerr effect in which the refractive index anisotropy known as an electro-optic effect is proportional to the square of the electric field strength occurs. Also in this embodiment, refractive index anisotropy due to the Kerr effect occurs under an electric field strength less than a certain electric field. On the other hand, at a certain voltage or higher, a nematic phase is formed due to the phase transition caused by the electric field strength E, and a refractive index anisotropy higher than the Kerr effect is generated, which is the same as the refractive index anisotropy indicated by the nematic phase temperature.

  A nematic liquid crystal material having a negative dielectric anisotropy is used, and a pair of polarizing plates (the first polarizing plate 24 and the second polarizing plate 25) provided in the electro-optical device 10 of FIG. As shown in FIG. 4, the refractive index anisotropy due to the Kerr effect and the phase transition phenomenon due to the electric field is almost the same as the refractive index anisotropy in the nematic phase temperature region, so that it passes through the liquid crystal layer. The same optical effect can be obtained when the phase difference is changed. As a result, the light transmitted through one polarizing plate (for example, the first polarizing plate 24) and converted into linearly polarized light changes in phase difference while passing through the nematic phase, so the other polarizing plate (for example, The second polarizing plate 25) can be transmitted. On the other hand, in the case of the isotropic phase as shown in FIG. 3, the phase difference of the light passing through the liquid crystal layer does not change, so that the light transmitted through the first polarizing plate 24 cannot pass through the second polarizing plate 25. As a result, a normally black electro-optical device is obtained. In the electro-optical device in this case, black display becomes isotropic in the liquid crystal layer, and white display shows the same transmittance as the conventional one. Therefore, the orientation direction of the director oriented in a predetermined direction is changed by an electric field, Compared with a liquid crystal display device that changes the amount of transmitted light, the contrast is high. The present disclosure relates to an electro-optical device 10 having good electric field response and optical characteristics using an electro-optic effect based on the induction and disappearance phenomenon of a nematic phase caused by the presence or absence of an external electric field of a nematic liquid crystal material having a negative dielectric anisotropy. Is to provide.

<1-2. Optical characteristics and electric field response>
The electro-optical device 10 illustrated in FIG. 2 includes a liquid crystal material having a negative dielectric anisotropy. In the present embodiment, the first alignment film 31 and the second alignment film 32 included in the electro-optical device 10 are subjected to a vertical alignment process in which the interface alignment is perpendicular to the substrate surface. The reason why the vertical alignment treatment is performed is that the optical characteristics and response characteristics of the normally black type as an electro-optical device can be evaluated in both the nematic phase temperature region and the isotropic phase temperature region. First, the transmittance-voltage dependency, which is an optical characteristic, will be described.

  FIG. 5 is a diagram showing the relationship between the transmittance and the applied voltage. As shown in FIG. 5, at the temperature at which the nematic liquid crystal material included in the electro-optical device 10 is in the isotropic phase, the nematic liquid crystal material is in the isotropic phase when no voltage is applied. The rate was 0%. In addition, when a voltage is applied between the pair of electrodes, the electro-optical device 10 is confirmed to have a voltage increase and a sharp increase in transmittance at a certain voltage or higher, and is close to a temperature at which the nematic liquid crystal material becomes a nematic phase. It was confirmed to show transmittance. This voltage that causes a steep increase in transmittance is the threshold voltage of the induction and disappearance phenomenon of the nematic phase caused by the presence or absence of an external electric field, indicating that the phase transition to the nematic phase is caused by the electric field.

  Regarding the electric field response, the time dependency of the transmittance after removing the voltage was evaluated under the conditions of the phase transition temperature TNI-0.2 ° C. and the phase transition temperature TNI + 0.2 ° C. As a result, the time change of the transmittance after removing the voltage at the nematic phase temperature (at the phase transition temperature TNI−0.2 ° C.) is 30 ms to 80 ms, whereas the isotropic phase temperature (phase transition temperature TNI + 0 .2 ° C.), the time change of the transmittance after removing the voltage was about 0.2 ms. Thus, the time change of the transmittance after removing the voltage at the isotropic phase temperature is about 1/100 or less of the time change of the transmittance at the nematic phase temperature. The potential of this response characteristic is expected to be about 2 ns. Note that a nematic liquid crystal material having a negative dielectric anisotropy exhibits a voltage dependency in which the temporal change in transmittance after voltage application becomes shorter as the voltage increases. Such voltage dependence is caused by an electric field that changes the alignment direction of a director of a nematic liquid crystal material aligned in a predetermined direction by an electric field in a conventional electro-optical device, that is, in a nematic phase temperature region. The same tendency as the optical device was shown.

  The electric field response characteristics of the electro-optical device 10 as shown in FIG. 2 are the rise time until the transmittance of the electro-optical device 10 increases to a constant value when a voltage is applied, and the transmittance decreases when the voltage is removed. Thus, it can be said that the smaller the sum of the fall time until reaching 0%, the faster the response characteristic. From the result of the time dependency of the transmittance after removing the voltage described above, the electro-optical device 10 including the nematic liquid crystal material having a negative dielectric anisotropy at the isotropic phase temperature has a very long fall time. short. For this reason, the electro-optical device 10 including the nematic liquid crystal material having negative dielectric anisotropy at the isotropic phase temperature changes the light transmission amount by changing the alignment direction of the director aligned in a predetermined direction by an electric field. Compared with the liquid crystal display device to be made, it has a high-speed response characteristic. As a result, the electro-optical device 10 including a nematic liquid crystal material having a negative dielectric anisotropy may have a response characteristic equivalent to that of a nematic liquid crystal material having a positive dielectric anisotropy when the external electric field disappears. did it.

<1-3. Interfacial orientation treatment>
It is known that in a nematic liquid crystal material having a positive dielectric anisotropy, even in a system in which liquid crystal molecules such as isotropic phase are isotropically dispersed, there is an influence of interface alignment. The influence of the interface alignment is considered to be caused by the fact that some director is formed in the interface by performing the interface alignment treatment. Next, an interface alignment process when a nematic liquid crystal material having a negative dielectric anisotropy is used will be described.

  Induction of a nematic phase due to the presence or absence of an external electric field accompanying a temperature rise, for example, by subjecting each or at least one of the first transparent substrate 11 and the second transparent substrate 21 shown in FIG. And the high voltage shift of the threshold voltage of the disappearance phenomenon is suppressed. When the drive voltage is limited, the operable temperature range is also expanded. For this reason, in the electro-optical device 10 that has undergone the interface alignment treatment, even if the temperature rises, the increase in applied voltage is suppressed and the drive voltage is restricted even when the interface alignment treatment is not performed. In some cases, the operable temperature range is widened.

  FIG. 6 is a schematic diagram showing the interface between the liquid crystal layer and the alignment film in the presence or absence of an electric field. “//” in FIG. 6 indicates that the substrate surface has been subjected to a horizontal alignment process, and “⊥” indicates that a vertical alignment process has been performed. A plurality of short straight lines in FIG. 6 indicate the major axis Zl of the director. As shown in FIG. 9, even in the isotropic phase, a director resulting from this process is formed in the vicinity of the interface between the liquid crystal layer and the substrate surface by the interface alignment process. Further, the director varies depending on the interface alignment treatment.

  When a voltage is applied, a director resulting from the electric field is formed in the isotropic phase region. In the case of a nematic liquid crystal material having a negative dielectric anisotropy, a director is formed in the normal direction with respect to the direction of the generated electric field. For this reason, in the vertical alignment treatment, elastic strain occurs between the director in the liquid crystal layer and the director at the interface. When this elastic strain occurs, the threshold voltage of the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field is higher than that when no elastic strain occurs even at the same temperature. That is, the threshold voltage can be lowered by performing the interface alignment process in a direction in which no elastic energy is generated.

  The threshold voltage due to the interface treatment of the induction and disappearance of the nematic phase with and without an external electric field increased in the order of horizontal alignment, vertical alignment, and non-alignment. From this result, it is preferable that the nematic liquid crystal material having a negative dielectric anisotropy is subjected to an interface alignment process in the normal direction to the electric field direction, that is, a horizontal alignment process. By doing so, the above-described elastic strain can be suppressed, so that the threshold voltage can be lowered and the electro-optical device 10 can be driven at a low voltage.

  The threshold voltage of the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field is affected by the interface alignment treatment even in a nematic liquid crystal material having a negative dielectric anisotropy, and can realize a driving voltage lower than that of the non-alignment treatment. For this reason, it is more preferable to perform the interface alignment treatment than not to perform the alignment treatment.

  The interface treatment can be realized by using an alignment film generally made of a polyimide material and performing a rubbing treatment with a rubbing cloth as necessary. If such a method is used, the interface alignment process can be realized relatively easily. In addition to this, for example, the interface alignment treatment may be realized using a film for vapor deposition or photo-alignment. Further, the interfacial alignment treatment may be realized by forming irregularities on the electrode surface without forming a film for controlling the interface, or by rubbing the electrode surface with a rubbing cloth.

<1-4. Direct-view display device>
FIG. 7 is a cross-sectional view of a liquid crystal display device corresponding to a direct-view display device in which a pair of electrodes are arranged to face the liquid crystal phase. A liquid crystal display device 10A shown in FIG. 7 has a backlight 4 as a light source arranged on the array substrate AR side of the electro-optical device 10 shown in FIGS. An electric field is generated between the pixel electrode 20 and the common electrode 23 which are opposed electrodes in the liquid crystal display device 10 </ b> A in a normal direction with respect to the electrode surface. The liquid crystal display device 10 </ b> A visually recognizes display light directly from the backlight 4. Thus, the liquid crystal display device 10A is a direct-view type display device.

  FIG. 8 is a diagram showing changes in the director depending on the presence or absence of an electric field in a liquid crystal layer of a nematic liquid crystal material whose dielectric anisotropy is different from positive and negative. As shown in FIG. 8, the nematic liquid crystal material having a negative dielectric anisotropy and the nematic liquid crystal material having a positive dielectric anisotropy are directors (reference numerals 2, 2) formed in the direction of the electric field E. The major axis is different. As a result, the polarized light incident from the backlight 4 of FIG. 7 and formed through the polarizing plate 24 passes through a liquid crystal layer formed of a nematic liquid crystal material having a positive dielectric anisotropy, depending on the presence or absence of voltage. Regardless of this, no change in phase difference occurs. As a result, the transmittance change of the liquid crystal display device 10A does not occur. On the other hand, when passing through a liquid crystal layer formed of a nematic liquid crystal material having a negative dielectric anisotropy, a change in phase difference occurs depending on the presence or absence of a voltage. Will do.

  In the example shown in FIG. 8, even in the case of a liquid crystal material having positive dielectric anisotropy, a director (corresponding to reference numeral 2 ′) is generated by the electric field E between the opposing pixel electrode 20 and the common electrode 23. . However, the effect of changing the phase difference of the liquid crystal layer by the director does not occur in the direction of light incident from the backlight 4. Therefore, the liquid crystal display device 10 </ b> A using the liquid crystal material 1 ′ having a positive dielectric anisotropy does not generate a dimming action necessary as a liquid crystal display device. When the liquid crystal material 1 having a negative dielectric anisotropy is used, a dimming action is generated due to the effect of the phase difference change of the liquid crystal layer by the director. For this reason, the liquid crystal display device 10A using the liquid crystal material 1 having a negative dielectric anisotropy functions as a direct-view display device. Thus, by using a liquid crystal material having a negative dielectric anisotropy, a liquid crystal display device having a liquid crystal layer LC between the pixel electrode 20 and the common electrode 23 can be used as a direct-view display device. .

  In this embodiment, in a so-called direct-view type liquid crystal display device 10A using a nematic liquid crystal material having a negative dielectric anisotropy, the induction and disappearance phenomenon of the nematic phase from the isotropic phase due to the presence or absence of voltage is used. The change in transmittance was confirmed. As a result, according to the present disclosure, in the isotropic phase temperature region of a nematic liquid crystal material mainly having a positive dielectric anisotropy, the electric optical effect based on the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field is used. A direct-view liquid crystal display device that is difficult to realize with an optical device can be easily realized.

  As described above, by using a liquid crystal material having a negative dielectric anisotropy, a liquid crystal is formed between the pixel electrode 20 and the common electrode 23 using the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field. A direct-view display device such as the liquid crystal display device 10A provided with the layer LC can be realized. This increases the versatility of not only a liquid crystal display device but also an electro-optical device. Due to the liquid crystal material having a negative dielectric anisotropy, for example, a liquid crystal barrier such as 3D that is difficult to realize when a nematic liquid crystal material having a positive dielectric anisotropy is used, an optical shutter, etc. Etc. can be easily realized.

  If a nematic liquid crystal material having a positive dielectric anisotropy is used to realize a so-called direct-view liquid crystal display device or the like, there is a method using a prism or the like for controlling the directivity of the light source. However, when such a method is used, there is a possibility that a liquid crystal display device or the like is difficult to manufacture and causes a significant increase in manufacturing cost. By using a liquid crystal material having a negative dielectric anisotropy, it is not necessary to use a prism or the like for controlling the directivity of the light source, so that a liquid crystal display device or the like can be easily manufactured and its manufacturing cost can be reduced.

  The nematic phase induction and disappearance phenomenon due to the presence or absence of an external electric field has a critical point CP for the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field in a nematic liquid crystal material having a positive dielectric anisotropy. It has been known. It is considered that the critical temperature TCP indicated by the critical point CP and the critical electric field ECP exist in the isotropic phase temperature region of the nematic liquid crystal material having a positive dielectric anisotropy. That is, it shows that hysteresis occurs in the transmittance-voltage dependency in the electro-optical device under an environment having a temperature lower than the critical temperature TCP and an electric field strength lower than the critical electric field ECP.

  In addition, the induction and disappearance phenomenon of the nematic phase due to the presence or absence of an external electric field cannot be strictly distinguished as a phase transition phenomenon. However, since the electric field effect of refractive index anisotropy, which is an optical characteristic, does not disappear, a phenomenon in an environment exceeding the critical point CP, that is, exceeding the critical temperature TCP and the critical electric field ECP is also caused by the presence of an external electric field. Considered part of the induction and disappearance phenomenon.

  Even in a nematic liquid crystal material having a negative dielectric anisotropy, hysteresis similar to the hysteresis described above may occur. For this reason, the relationship between the transmittance and the applied voltage was obtained at a temperature higher than that shown in FIG.

  FIG. 9 is a diagram showing the relationship between the transmittance and the applied voltage. FIG. 9 shows an electro-optical device 10 using a nematic liquid crystal material having a negative dielectric anisotropy and having a liquid crystal layer between a pair of counter electrodes (pixel electrode 20 and common electrode 23) (FIGS. 1 and 2). The change of the transmittance of the electro-optical device 10 when the applied voltage between the counter electrodes of the electro-optical device 10 is changed is shown. The solid line in FIG. 9 shows the change in transmittance when the applied voltage is increased, and the dotted line shows the change in transmittance when the applied voltage is lowered. In A, B, and C shown in FIG. 9, the temperature of the liquid crystal material 1 is increased in this order.

  As shown in FIG. 9, when the temperature is lower than the critical temperature TCP, the change in transmittance is different between the increase and decrease in the applied voltage, indicating that it has hysteresis characteristics. When the temperature is equal to or higher than the critical temperature TCP, the hysteresis characteristics described above are not provided. Further, when the temperature is lower than the critical temperature TCP and the magnitude of the electric field E is lower than the critical electric field ECP, the above-described hysteresis characteristics are obtained. Has no characteristics. Further, the relationship between the applied voltage and the transmittance as shown in FIGS. 5 and 9 can be a numerical simulation in which, for example, the temperature of the nematic liquid crystal material and the electric field in the electric field E are changed. In the present embodiment, the relationship between the applied voltage and the transmittance shown in FIGS. 5 and 9 was obtained by experiments.

<1-5. Driving method of electro-optical device>
An electro-optical device that uses the induction and disappearance phenomenon of a nematic phase due to the presence or absence of an external electric field using a nematic liquid crystal material changes the orientation direction of a director aligned in a predetermined direction with a conventional electric field, thereby changing the amount of transmitted light. The liquid crystal display device can be driven using a driving method for changing the liquid crystal display device. However, since the above-described hysteresis occurs when the temperature T of the nematic liquid crystal material is in the range of TNI <T <TCP, it is necessary to consider the method for applying the driving voltage of the electro-optical device 10. In this case, it is preferable to drive the electro-optical device 10 by controlling the voltage applied between the pair of counter electrodes by, for example, overdrive, frequency modulation (for example, binary frequency modulation) or area modulation. Overdrive is a driving method in which a voltage applied between a pair of opposing electrodes is set to a predetermined voltage described above after a voltage higher than the predetermined voltage for a short time. Further, the electro-optical device 10 may be designed to be used under the condition of the critical temperature TCP or higher and the critical electric field ECP or higher, or the temperature of the nematic liquid crystal material may be controlled.

<1-6. Example of temperature control>
FIG. 10 is a cross-sectional view illustrating an example of an electro-optical device including a temperature sensor. An electro-optical device 10B illustrated in FIG. 10 includes the temperature sensor 40 in addition to the electro-optical device 10 illustrated in FIGS. In the case of an electro-optical device using an electric field induced phase transition in a nematic liquid crystal material having a negative dielectric anisotropy in an isotropic phase temperature region, it cannot be used at a temperature lower than the phase transition temperature. For this reason, it is preferable that the electro-optical device 10B controls the temperature of the nematic liquid crystal material used for the liquid crystal layer so as not to be affected by the temperature of the use environment. Furthermore, the electro-optical device 10B is preferably used at a temperature higher than the temperature critical temperature TCP, which is easy to drive.

  Further, the electro-optical device 10 </ b> B illustrated in FIG. 10 includes a temperature sensor 40. Although the place where the temperature sensor 40 is attached is not particularly limited, in the present embodiment, the temperature sensor 40 is attached on the side opposite to the liquid crystal layer of the first transparent substrate 11. The control device 50 as a temperature adjusting unit adjusts the temperature of the nematic liquid crystal material based on the temperature Ts detected by the temperature sensor 40 (corresponding to the temperature of the nematic liquid crystal material used for the liquid crystal layer).

  For example, the control device 50 performs control so that the temperature Ts detected by the temperature sensor 40 does not become less than the isotropic phase temperature TNI. In this case, for example, when there is a possibility that Ts <phase transition temperature, the control device 50 raises the temperature of the electro-optical device 10B by the heater 41 and keeps the temperature of the nematic liquid crystal material at or above the isotropic phase temperature.

  The temperature of the nematic liquid crystal material may be controlled using cooling by a fan provided in the electro-optical device 10B, for example, a fan used in a liquid crystal projector. Further, the electro-optical device 10B may adjust the temperature of the nematic liquid crystal material using, for example, a sheet or a heat sink that emits a temperature used in a television or the like. Based on such a cooling structure, a temperature raising and cooling mechanism is provided in the electro-optical device 10B, and temperature control is performed by a temperature sensor, so that voltage transmission within a certain temperature range allows a desired transmittance to be varied depending on the voltage. It can be provided stably.

  The control device 50 may switch the driving method of the electro-optical device 10B based on the temperature Ts detected by the temperature sensor 40. In this case, for example, when Ts <TCP, the nematic liquid crystal material is in the isotropic phase temperature region, but hysteresis occurs. For this reason, the control device 50 uses a driving method such as overdrive, frequency modulation (for example, binary frequency modulation) or area modulation between the pair of pixel electrodes 20 and the common electrode 23, and a nematic liquid crystal material. A voltage that causes a change in light transmittance based on the induction and disappearance phenomenon of the nematic phase from is applied. When Ts ≧ TCP, the temperature of the nematic liquid crystal material is in a temperature region in which hysteresis does not occur. It can be the same as the driving method in which the orientation direction of the director oriented in a predetermined direction is changed by an electric field to change the light transmission amount. A voltage that causes a change in light transmittance based on a change in the arrangement of the directors of the liquid crystal material 1 is applied. As described above, by changing the driving method of the electro-optical device 10B depending on whether the temperature of the nematic liquid crystal material is equal to or higher than the critical temperature TCP, the electro-optical device 10B can be appropriately driven in consideration of the influence of hysteresis. it can.

<1-7. Electro-Optical Device in Other Configuration>
In the above description, in the electro-optical devices 10, 10B and the liquid crystal display device 10A, the color filter substrate CF is provided with an overcoat layer instead of the color filter layer. However, a normal electro-optical device and a liquid crystal display are provided. If the apparatus is provided with color filter layers of various colors as in the apparatus, an electro-optical device and a liquid crystal display device capable of performing various color displays while exhibiting the above-described effects can be obtained. Furthermore, in the electro-optical devices 10 and 10B and the liquid crystal display device 10A described above, an example in which a pair of polarizing plates is arranged in a crossed Nicol arrangement is shown, but a pair of polarizing plates may be arranged in a parallel Nicol arrangement. In this case, the electro-optical devices 10 and 10B and the liquid crystal display device 10A described above are normally white types. Further, the electro-optical devices 10 and 10B and the liquid crystal display device 10A described above include 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. Although an example of the electrode arrangement similar to that of the vertical electric field type electro-optical device and liquid crystal display device is shown, the same electrode arrangement as that of the horizontal electric field type electro-optical device and liquid crystal display device such as the FFS mode and the IPS mode is adopted. You can also

<2. Electronic equipment>
Next, electronic devices using the electro-optical devices 10 and 10B and the liquid crystal display device 10A according to the present disclosure as display units, that is, specific examples of the electronic devices according to the present disclosure will be described.

  10 to 22 are diagrams illustrating examples of electronic apparatuses including the electro-optical device according to the present embodiment. The electro-optical devices 10 and 10B and the liquid crystal display device 10A can be applied to electronic devices in various fields such as television devices, digital cameras, notebook personal computers, mobile terminal devices such as mobile phones, and video cameras. . In other words, the electro-optical devices 10 and 10B and the liquid crystal display device 10A can be applied to electronic devices in various fields that display a video signal input from the outside or a video signal generated inside as an image or a video. is there.

(Application example 1)
The electronic apparatus illustrated in FIGS. 10 and 11 is a television apparatus to which the electro-optical devices 10 and 10B and the liquid crystal display device 10A are applied. The television apparatus includes, for example, a video display screen unit 510 including a front panel 511 and a filter glass 512, and the electro-optical devices 10 and 10B and the liquid crystal display device 10A are applied to the video display screen unit 510. The

(Application example 2)
The electronic apparatus shown in FIGS. 12 and 13 is a digital camera to which the electro-optical devices 10 and 10B and the liquid crystal display device 10A are applied. The digital camera includes, for example, a flash light emitting unit 521, a display unit 522, a menu switch 523, and a shutter button 524. The display unit 522 includes electro-optical devices 10, 10B and a liquid crystal display device 10A. Has been applied.

(Application example 3)
14 represents the appearance of a video camera to which the electro-optical devices 10 and 10B and the liquid crystal display device 10A are applied. This video camera has, for example, a main body 531, a subject photographing lens 532 provided on the front side surface of the main body 531, a start / stop switch 533 during photographing, and a display 534. The display unit 534 includes the electro-optical devices 10 and 10B and the liquid crystal display device 10A.

(Application example 4)
The electronic apparatus illustrated in FIG. 15 is a notebook personal computer to which the electro-optical devices 10 and 10B and the liquid crystal display device 10A are applied. This notebook personal computer has, for example, a main body 541, a keyboard 542 for inputting characters and the like, and a display unit 543 for displaying an image. The display unit 543 uses the electro-optical devices 10 and 10B and the liquid crystal display device 10A.

(Application example 5)
16 to 22 is a mobile phone to which the electro-optical devices 10 and 10B and the liquid crystal display device 10A are applied. This mobile phone is, for example, one in which an upper housing 551 and a lower housing 552 are connected by a connecting portion (hinge portion) 553, and includes a display 554, a sub-display 555, a picture light 556, and a camera 557. Yes. The display 554 is attached with the electro-optical devices 10 and 10B and the liquid crystal display device 10A.

<3. Configuration of the present disclosure>
This indication can take the following composition.
(1) a first substrate and a second substrate which are disposed opposite to each other with a nematic liquid crystal material having a negative dielectric anisotropy interposed therebetween;
A pair of electrodes formed on the nematic liquid crystal material side of at least one of the first substrate and the second substrate;
A pair of polarizing plates respectively disposed on opposite sides of the first substrate and the second substrate from the nematic liquid crystal material;
In the isotropic phase temperature region of the nematic liquid crystal material, an electrical property utilizing a change in light transmittance based on a phase transition from an isotropic phase to a nematic phase according to a voltage applied between the pair of electrodes. Optical device.
(2) The electro-optical device according to (1), wherein the first substrate and the second substrate are each subjected to an interface alignment process on an interface of the nematic liquid crystal material.
(3) The electro-optical device according to (2), wherein the interface alignment process is performed in a direction perpendicular to the electric field direction.
(4) The electro-optical device according to any one of (1) to (3), which is used at a temperature equal to or higher than a critical temperature of the nematic liquid crystal material and equal to or higher than a critical electric field of the nematic liquid crystal material.
(5) The electro-optical device according to any one of (1) to (4), wherein a voltage applied between the pair of electrodes is controlled by overdrive or a frequency modulation method.
(6) The electro-optical device according to any one of (1) to (5), further including a temperature adjustment unit that adjusts a temperature of the nematic liquid crystal material based on a temperature of the nematic liquid crystal material.
(7) An electronic apparatus including the electro-optical device according to any one of (1) to (6) as a display device.

  As mentioned above, although this indication was demonstrated, this indication is not limited by the content mentioned above. In addition, the constituent elements of the present disclosure described above include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. Furthermore, the above-described components can be appropriately combined. In addition, various omissions, substitutions, and changes of the components can be made without departing from the scope of the present disclosure.

DESCRIPTION OF SYMBOLS 1, 1 'Nematic liquid crystal material 2 Liquid crystal molecule 4 Backlight 10, 10B Electro-optical device 10A Liquid crystal display device 11 1st transparent substrate 20 Pixel electrode 21 2nd transparent substrate 22 Overcoat layer 23 Common electrode 24 1st polarization | polarized-light Plate 25 Second polarizing plate 31 First alignment film 32 Second alignment film 40 Temperature sensor 41 Heater 50 Controller AR Array substrate CF Color filter substrate LC Liquid crystal layer TNI Isotropic phase temperature

Claims (7)

A first substrate and a second substrate disposed opposite to each other with a nematic liquid crystal material having a negative dielectric anisotropy interposed therebetween;
A pair of electrodes formed on the nematic liquid crystal material side of at least one of the first substrate and the second substrate;
A pair of polarizing plates respectively disposed on opposite sides of the first substrate and the second substrate from the nematic liquid crystal material;
In the isotropic phase temperature region of the nematic liquid crystal material, an electrical property utilizing a change in light transmittance based on a phase transition from an isotropic phase to a nematic phase according to a voltage applied between the pair of electrodes. Optical device.   2. The electro-optical device according to claim 1, wherein the first substrate and the second substrate are each subjected to an interface alignment process on an interface of the nematic liquid crystal material.   The electro-optical device according to claim 2, wherein the interface alignment process is performed in a direction perpendicular to an electric field direction.   4. The electro-optical device according to claim 1, wherein the electro-optical device is used at a temperature not lower than a critical temperature of the nematic liquid crystal material and not lower than a critical electric field of the nematic liquid crystal material.   5. The electro-optical device according to claim 1, wherein a voltage applied between the pair of electrodes is controlled by overdrive or a frequency modulation method. 6.   6. The electro-optical device according to claim 1, further comprising a temperature adjustment unit configured to adjust a temperature of the nematic liquid crystal material based on a temperature of the nematic liquid crystal material.   An electronic apparatus comprising the electro-optical device according to claim 1 as a display device.

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