JPH0720474A - Liquid crystal oriented film for phase control element and formation of the same and phase control element - Google Patents

Abstract

PURPOSE:To improve phase control characteristics and more particularly the resolution of a display element, etc., to be wobbled by forming the liquid crystal oriented films to be formed on electrodes of the phase control element of polyimide. CONSTITUTION:The surfaces of transparent glass substrates 20, 21 are provided with transparent electrodes 13, 14 and are further formed with polyimide films 22, 23 as the liquid crystal oriented films thereon. These polyimide oriented films 22, 23 are subjected to prescribed rubbing treatments. The substrates 20, 21 with such oriented films are so assembled that the orientation treatment directions thereof are, for example, counterparalleled with each other on the opposite face. Glass beads 24 meeting the desired gap length are used as the spacers. The spacers are dispersed into a sealing material 25 for adhering the circumference in the case of the area smaller than the size of the transparent substrates, by which the gap between the substrates is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to liquid crystal, plasma, EL
For a phase control element suitable for wobbling (picture element shifting) such as a display with discrete pixels such as (electroluminescence) or a solid-state image sensor represented by a CCD (charge coupled device) with discrete imaging pixels. Liquid crystal alignment film,
The present invention relates to a forming method thereof and a phase control element.

[0002]

2. Description of the Related Art When a line-sequential scanning pixel display is carried out by the NTSC system or the like for a display device having a discrete pixel array such as a liquid crystal, plasma, EL or the like in a mosaic pattern, a dot pattern, etc. The luminance signal, which should be a signal, is roughly sampled and the position information in the horizontal direction is lost. If the vertical pixel resolution cannot be implemented by the number of scanning lines, the positional resolution of the luminance signal or the like (that is,
Display resolution) was reduced.

For example, a TFT (T
In the hin-Film-Transistor) -TN (Twisted Nematic) liquid crystal viewfinder, in the NTSC system, one frame (that is, one picture displayed by the viewfinder) is an even scan line and an odd scan line. The frame frequency is 30 Hz (that is, the field frequency is 60 Hz). Since the current TFT viewfinder cannot mount 525 scanning lines of the NTSC system, the method of writing the odd field and the even field in the same pixel is adopted. For this reason, the vertical resolution is currently lower than that of the NTSC principle.

Further, due to the large pixel size and the presence of joints of non-display pixel portions such as a black matrix, a mosaic-like screen having a discrete pixel array is conspicuous, and the texture of the screen is deteriorated.

The above phenomenon similarly occurs in the image pickup by the CCD. That is, since the image pickup pixels forming the CCD are discrete, the image information of the subject is sampled at the constituent pixel pitch, which lowers the horizontal and vertical spatial resolution.

Therefore, a method has been proposed in which the wobbling technique is adopted to introduce a pixel shifting element and spatially shift the images of the odd field and the even field to improve the vertical resolution. This is also applied in the horizontal direction, and the horizontal resolution can be improved.

It is known that a liquid crystal element is used as a phase control element in such a pixel shifting element. That is, this liquid crystal element is combined with a birefringent medium such as a quartz plate and placed in the optical path of a display element or the like to be wobbled, and by switching the applied voltage, the phase of the incident light to the liquid crystal element is modulated to change the polarization plane. The optical axis is selectively shifted in the predetermined direction (wobbling direction) by the birefringence effect of the birefringent medium depending on the presence or absence of this rotation.

In this case, in the liquid crystal device, the phase should ideally be shifted by 180 degrees in the entire visible light wavelength region throughout the device, but since the liquid crystal medium has birefringence wavelength dispersion, for example, It is difficult to obtain linearly polarized light in the entire region of 400 to 700 nm. Therefore, in consideration of human visual characteristics, it is preferable to design so that a phase difference of about 260 nm occurs when a He-Ne light source is used.

However, since the phase difference of the liquid crystal element depends on the birefringence index (and further the cell gap) of the liquid crystal medium (this will be described in detail later), variations in the phase difference within the element and over time occur. If so, the phase controllability deteriorates. The cause of this is that if the liquid crystal alignment film is unstable, the pretilt angle of the liquid crystal changes, the surface condition of the alignment film changes, and the liquid crystal alignment changes, which causes a large phase control characteristic. Change it.

[0010]

The present inventors have found that the present invention is very effective especially for the above-mentioned wobbling element, has good film stability and can be uniformly formed, and can significantly improve phase control characteristics. The inventors have found an alignment film and have devised the present invention.

[0011]

That is, according to the present invention, at least one of a ferroelectric liquid crystal, an antiferroelectric liquid crystal, and a smectic liquid crystal exhibiting an electroclinic effect is provided between opposing electrodes that are optically transparent. The present invention relates to a liquid crystal alignment film for a phase control element, which is formed on the electrode in a phase control element filled with one type of liquid crystal and is made of polyimide.

The liquid crystal alignment film according to the present invention is mainly composed of polyimide, and has at least one infrared absorption peak at 2830 cm ^-1 or more, which is attributed to CH stretching of the alignment film molecule, and has the above-mentioned alignment. it is desirable to have an infrared absorption peak attributable to the carbonyl group of membrane molecules from 1600 cm ^-1 in the range of 1800 cm ^-1.

Further, according to the present invention, a liquid crystal composed of at least one selected from a ferroelectric liquid crystal, an antiferroelectric liquid crystal, and a smectic liquid crystal exhibiting an electroclinic effect is provided between the counter electrodes which are optically transparent. A phase control element which is filled and in which a liquid crystal alignment film made of polyimide is formed on the electrode, and is in the optical path of an optical element to be wobbling or high resolution (especially between the display element and the observation position). , Or in the optical path between the subject and the image sensor) and is arranged in combination with a birefringent medium, and is used for wobbling an optical element such as the display element or the image sensor in one dimension or two dimensions. A phase control element is also provided.

The liquid crystal alignment film according to the present invention is a very stable film because it is made of polyimide (particularly, the average degree of polymerization of molecules is preferably 50 or more).
It does not easily change over time, maintains its surface state, and can be formed with a uniform film thickness, so it maintains the pretilt angle and orientation of the liquid crystal, and has phase control characteristics, especially for display elements such as wobbling. It is an alignment film that is extremely effective in improving resolution.

This liquid crystal alignment film is obtained by the method according to the present invention,
That is, it is formed by a method having at least a step of irradiating the electrode with infrared rays (particularly near infrared rays), a step of coating the light irradiation surface with a polyimide precursor, and a step of heat-treating the polyimide precursor to imidize it. It is desirable to do. By this method, the polyimide film can be formed to have a uniform film thickness.

As the liquid crystal alignment film, CH (hydrocarbon group) is used.
Although polyvinyl alcohol having ## STR3 ## is also conceivable, it has been found that polyvinyl alcohol has a poor stability, though the film forming process is easy. On the other hand, the polyimide alignment film according to the present invention characterized by having CH and a carbonyl group has good stability, a uniform film thickness can be obtained, and the surface property is further improved.

In the phase control element for the wobbling element,
Alignment film stability and pretilt angle spatial uniformity are required, and extremely strict standards must be met.

The liquid crystal alignment film according to the present invention can sufficiently satisfy such requirements, and in particular, the deviation of the pretilt angle of liquid crystal molecules with respect to the substrate in the liquid crystal element, the change with time,
And, the variation within −30 ° C. to 70 ° C. is within 50%, and the deviation of the film thickness within the element is also within 50%.

Further, in any liquid crystal such as a ferroelectric liquid crystal used in the present invention, the direction of the liquid crystal director easily changes in response to the action of an electric field, and the response speed is very fast (for example, both rise time and fall time). Since it is on the order of μsec, which is much faster than the fall time of twisted nematic liquid crystals), it can be driven at video rates.

In the present invention, an optical element such as a display element or an image pickup element which is to have a high resolution is a liquid crystal such as a twisted nematic liquid crystal, a ferroelectric liquid crystal or an antiferroelectric liquid crystal composed of discrete pixels. It may be a display element, a self-luminous display element such as a light emitting diode, or a CCD or the like.

[0021]

EXAMPLES Examples of the present invention will be described below.

First, referring to FIG. 1, a liquid crystal cell 3 as a phase control element for wobbling according to this embodiment will be described. That is, transparent electrodes (for example,
100 Ω / □ ITO) 13 and 14 are provided on the polyimide films 22 and 23 according to the present invention as a liquid crystal alignment film.
Are formed. This polyimide alignment film is formed by the method described below and is subjected to a predetermined rubbing treatment.

A substrate having such an alignment film is assembled so that the alignment treatment directions thereof are, for example, antiparallel on the opposing surfaces,
As the spacer, glass beads (true yarn ball: diameter 0.8 to 3.0 μm (Catalyst Kasei)) according to the target gap length 24
Is used. The spacer depends on the size of the transparent substrate.
If the area is small, the sealing material that adheres to the surrounding area (UV-curable adhesive material (eg Photorec: Sekisui Chemical Co., Ltd.)
The gap between the substrates is controlled by dispersing, for example, about 0.3 wt% in (M. If the substrate area is large, sprinkle the above-mentioned true thread balls on the substrate at an average density of 100 / mm ² and then make a gap to secure a liquid crystal injection hole around the cell and use the above sealing material to surround the cell. Are glued together.

After that, a ferroelectric liquid crystal (for example, CS-1014 manufactured by Chisso Corporation) is injected under reduced pressure in a state showing fluidity at an isotropic phase temperature or a chiral nematic phase temperature. After injecting the liquid crystal, the liquid crystal is gradually cooled to remove the liquid crystal on the glass substrate around the injection hole and then sealed with an epoxy adhesive to manufacture a ferroelectric liquid crystal element. The ferroelectric liquid crystal used may be Chisso Corp., Merck Ltd., BDH Corp., or any other known ferroelectric liquid crystal compound or non-chiral liquid crystal composition, but there is no limitation thereto. Moreover, it is not necessary to limit the phase sequence, and what is necessary is to take a chiral smectic liquid crystal phase in the operating temperature range.

The liquid crystal layer structure of the chiral smectic liquid crystal element used here has a bookshelf structure in antiparallel, a chevron structure in parallel, or a pseudo bookshelf structure depending on the combination of the alignment treatment directions.

The polyimide alignment films 22 and 23 described above are shown in FIG.
It is desirable to show an infrared spectrum as shown in.

That is, at least one infrared absorption peak attributed to CH stretching of the alignment film molecule is present at 2830 cm ^-1 or more,
And it has in the range of 1800 cm ^-1 The infrared absorption peak attributable to the carbonyl group of the alignment layer molecules from 1600 cm ^-1.

Here, the infrared spectrum of the polyimide obtained from polyamic acid RN-721 (manufactured by Nissan Chemical Industries, Ltd.) is shown. The infrared spectrum was measured by the following method. A polyimide film was formed on a glass substrate by a usual method, and this film was removed from the substrate using a cutter knife to give a powder. The polyimide powder and KBr (potassium bromide) powder were mixed, placed in a mold, and pressure was applied to produce tablets. Although the amount of polyimide is very small with respect to KBr, KBr is transparent in the infrared, and therefore infrared spectrum can be obtained even with a very small amount of polyimide by performing measurement with a sample of this tablet. As KBr, a special reagent for infrared absorption measurement manufactured by Nacalai Tesque, Inc. was used.

Such a polyimide liquid crystal alignment film is made of polyimide having an average degree of polymerization of 50 or more, is a very stable film, does not easily change over time, and maintains its surface state. Therefore, the pretilt angle and the orientation of the liquid crystal can be maintained, and the resolution of the phase control special feature, in particular, the display element to be wobbled which will be described later, can be significantly improved.

For the phase control element according to the present embodiment, a material containing CH such as polyvinyl alcohol may be used for the liquid crystal alignment film in addition to polyimide. However, the stability and uniformity peculiar to the phase control element may be used. It has been found that a polyimide containing a carbonyl group is suitable for satisfying the conditions.

FIG. 3 shows a manufacturing process of the liquid crystal cell 3 including film formation of this polyimide alignment film and rubbing treatment.

To form a polyimide film, a polyimide precursor, polyamic acid, is applied onto a substrate and imidized to facilitate film formation. However, when the wettability of the polyamic acid solution to the substrate is poor, by irradiating the substrate with infrared rays immediately before the application of the polyamic acid, the wettability becomes extremely good, and a uniform polyimide film is easily and inexpensively produced. can get. This is extremely advantageous in forming the polyimide film with a uniform film thickness.

That is, what should be noted in the step shown in FIG. 3 is that infrared rays (particularly near infrared rays) are irradiated before the polyamic acid (or polyamic acid) which is a precursor of polyimide is spin-coated on the transparent electrode. Is what you are doing.

The surface of the conductive film is activated by this light irradiation, and by this surface activation, the wettability or adsorptivity of the polyamic acid to the conductive film is further improved, and a coating film having a uniform film thickness without coating unevenness is obtained. It was found to be reliable and easy to obtain. However, polyimide film forming conditions (eg humidity)
It has been confirmed that a uniform film thickness can be obtained without irradiation of near-infrared rays.

In this infrared irradiation, in particular, if the component within the range of 0.5 to 6.0 μm (further, 0.5 to 3.0 μm) of the spectral distribution is 10 mW / cm ² or more (further, 50 mW / cm ² or more). It is desirable to perform light irradiation for at least 1 to 3 minutes so that the energy is reached.

Further, the application of the polyamic acid is preferably carried out by the spin coating method from the viewpoint of productivity. Then, it is desirable to perform spin coating immediately after the above infrared light irradiation. In this way, by performing the above-mentioned coating immediately after light irradiation, the coating is performed while the activated state of the coated surface is sufficiently maintained and good wettability is exhibited,
It is thought that better results will be obtained.

Contrary to this, when there is a spatial variation (non-uniform thickness) in the film thickness of the polyimide film, that is, when the surface roughness of the film surface is high, the alignment state of the liquid crystal varies spatially. The phase control characteristic is deteriorated, which is not preferable. However, the polyimide film according to the present invention, particularly when improving the wettability of the polyamic acid during the film formation, surely makes the film thickness uniform, and improves the orientation of the liquid crystal and the spatial uniformity of the pretilt angle. . By setting the thickness of this polyimide alignment film to 400 nm or less, it becomes possible to prevent light interference.

Thus, the above-mentioned polyimide liquid crystal alignment film according to the present invention can simultaneously realize the stability of the alignment film and the spatial uniformity of the pretilt angle, and satisfy the strict standards required for the phase control element. It will be possible.

Although a SiO oblique vapor deposition film is known as a liquid crystal alignment film, the above-mentioned alignment film according to the present invention is a rubbing film obtained by subjecting a polyimide film to a rubbing treatment, so that the manufacturing process is inexpensive. Also, it has high industrial utility value due to its excellent orientation characteristics.

Further, if the cell gap in the liquid crystal element is made uniform, the spatial deviation of the phase difference can be reduced, and the criteria for producing the specified phase difference in the entire area of the element can be satisfied. Desirable for improvement. In particular, an element using a ferroelectric liquid crystal is usually 10 μm or less,
A cell gap smaller than that of TN liquid crystal (twisted nematic liquid crystal) is required, but it is desirable to secure this cell gap.

The polyimide liquid crystal alignment film according to the present invention is obtained by imidization of polyamic acid. A general reaction scheme of this imidization is shown in the following formula. The polyamic acid 1 is dehydrated and ring-closed in the heat treatment step to become the polyimide 2 .

[0042]

[Chemical 1]

Here, since the structure of the portions represented by R ¹ and R ² in the above formula has a great influence on the characteristics of the polyimide to be formed, a structure suitable for the required characteristics of the liquid crystal element and the manufacturing process is used as the liquid crystal alignment film. It is necessary to choose. For example, a material having a structure shown in Table 1 below can be given.

[0044]

[Table 2]

The polyimide liquid crystal alignment film according to the present invention is suitable for a chiral smectic ferroelectric liquid crystal (FLC), but in addition to this, if the switching speed is high, for example, the following antiferroelectric liquid crystal is used. (AFLC)
It is also applicable to the smectic A phase exhibiting the electroclinic effect.

<Anti-ferroelectric liquid crystal> The anti-ferroelectric liquid crystal is C
It was discovered by handani et al. in 1988 and is characterized by the following three points. (1) Utilizes switching between an antiferroelectric state and two stable states of three stable states. (2) A clear threshold value characteristic is exhibited, and a high contrast when driven by multiplex can be obtained. (3) Use positive and negative hysteresis alternately,
Since the occurrence of internal polarization is suppressed, the image sticking phenomenon is unlikely to occur.

The characteristics of this antiferroelectric liquid crystal material are:
Unlike ferroelectric liquid crystals, chiral liquid crystals are the majority of the composition (spontaneous polarization is large, almost 10 times that of ferroelectric liquid crystals), and the substituent for the asymmetric carbon is CH.
₃ group, CF ₃ group, compounds having C ₂ H ₅ group is readily indicates the antiferroelectric, the core structure is expanded. For example, there is CS-4000 manufactured by Chisso Corporation.

<Smectic liquid crystal exhibiting electroclinic effect> The electroclinic effect is a phenomenon in which the tilt angle of the orientation vector is induced by the electric field in the smectic A phase composed of chiral molecules when the temperature is constant. . In the smectic A phase, the orientation vector points in the normal direction of the smectic layer and rotates freely around the major axis. However, application of an electric field along the layer inhibits the free rotation, and the polarization P in the electric field direction is Induced.

Assuming that the linear combination of the polarization P and the tilt angle θ is P = kθ, P = (ε⊥ ^* −ε⊥0) ε _O Ε Therefore, θ = (ε⊥ ^* −ε⊥0) ε _O Like Ε / k,
A tilt angle proportional to the applied electric field E is generated. Where ε⊥ ^*
And ε⊥0 are the permittivity of the racemate of the optically active substance, and ε _O is the permittivity of vacuum. From this, the larger the difference in the dielectric constants of the racemic chiral liquid crystals, the greater the electroclinic effect.

Next, the above-mentioned polyimide liquid crystal alignment film based on the present invention and the wobbling by the liquid crystal device using the same will be described with reference to specific examples.

Example 1 A polyimide liquid crystal alignment film according to the present invention and a polyvinyl alcohol liquid crystal alignment film for comparison were respectively formed on a test substrate as described below, and after rubbing treatment, a cell was prepared. The gap was adjusted to 1.6 μm and the corresponding antiparallel test cells were prepared. The thickness of each alignment film was about 50 nm. In this example, the film thicknesses of the polyimide film and the polyvinyl alcohol film were measured with an alpha-step 200 surface shape measuring device manufactured by Tencor Instruments, Inc., USA. The test cell substrate used is 40 mm x 25 mm x 2.5 mm.
The glass plate of No. 1 was coated with a transparent electrode ITO, which was not patterned, on one surface thereof.

As the material of the above-mentioned polyimide liquid crystal alignment film,
Nissan Chemical Industries, Ltd. polyamic acid: San Ever R
N-721 (0621) was used. This polyamic acid is mixed with 21 type thinner manufactured by the same company, and the final film thickness is 50 nm.
Was prepared. 0.5 ml of this polyamic acid mixed solution was dropped on the substrate, and spin coating was performed at 1000 rpm for 4 seconds, and subsequently, at 3500 rpm for 30 seconds.
Then, heat treatment was carried out at 80 ° C. for 15 minutes to remove the solvent, and at 240 ° C. for 60 minutes to imidize the polyamic acid. As a result, a polyimide film was obtained. This infrared spectrum is as shown in FIG. 2, and its measuring method has already been described.

On the other hand, the above polyvinyl alcohol is a Wako first-class reagent (n = 1500-180) manufactured by Wako Pure Chemical Industries, Ltd.
0) was used. Since polyvinyl alcohol is water-soluble,
It was dissolved in pure water and the concentration was adjusted so that the final film thickness was 50 nm. 0.5 ml of this polyvinyl alcohol / water mixed solution was dropped on the substrate, and spin coating was performed at 1000 rpm for 4 seconds, and subsequently, at 3500 rpm for 30 seconds.
Then, heat treatment was performed at 60 ° C. for 30 minutes and 180 ° C. for 30 minutes.

In the above, the wettability of the polyamic acid mixed solution with respect to the glass substrate is insufficient, the portion where the film thickness is thick or the film thickness is thin, and the portion where the transparent electrode of the substrate is exposed due to no wetting, It was revealed by visual inspection and surface shape measurement that such problems may occur. Therefore, according to the method described above, the glass substrate was irradiated with near infrared rays for 90 seconds immediately before spin coating. For this near infrared irradiation, an R100 / 110V 250WRH infrared lamp manufactured by Iwasaki Electric Co., Ltd. was used.

Immediately after this near-infrared irradiation, the above polyamic acid solution was similarly spin-coated, and as a result, the wettability of the polyamic acid was greatly improved. Then, from the surface shape measurement of the polyimide film obtained by imidization in the same manner as described above, the polyimide film on the substrate irradiated with near infrared rays has a substantially uniform film thickness, but the polyimide on the substrate not irradiated with near infrared rays The film was difficult to be uniform. The measurement results are summarized in Table 2 below (however, the humidity was 60% during the formation of the polyimide film).
% When held).

[0056]

Next, the polyimide film and the polyvinyl alcohol film formed as described above were subjected to a rubbing treatment in order to align the liquid crystal molecules in a fixed direction. That is,
Bemberg CF or rayon is wound around the roller as a buff material, and the vacuum chucked substrate is pushed in by 0.1 to 0.2 mm.
Rubbing was performed twice under the conditions of a stage speed of 150 mm / min and a roller rotation speed of 95 rpm.

Then, an ultraviolet curable adhesive (Photorec: manufactured by Sekisui Fine Chemical Co., Ltd.) containing 0.3 wt% of spacers (manufactured by Catalysis Kasei Co., Ltd.) was used.
Each of the two rubbing-treated glass substrates faced each other so that the rubbing directions of the alignment films were antiparallel to each other. In this case, a test cell was assembled so that the cell gap was 1.6 μm, and the adhesive was cured by irradiation with ultraviolet rays.

Ferroelectric liquid crystal CS-1014 manufactured by Chisso Corp. was vacuum-injected into this test cell, and the injection port was closed to complete the cell.

The FLC liquid crystal cell thus produced was used as a liquid crystal element for wobbling (picture element shifting) described later, and the resolution of the liquid crystal display element was measured. In addition, in order to compare the stability of various alignment films, we measured the resolution immediately after injecting liquid crystal and then placed it in a constant temperature bath kept at a temperature of 24 ° C and a humidity of 60%.
It was stored for 30 days, and the resolution was measured again. It should be noted that the resolution evaluation here is an NTSC resolution evaluation pattern (video signal pattern generator: MTS manufactured by Sony Corporation).
The signal from G-1000) was video-input and the resolution of black and white lines was determined by observation. The results are summarized in Table 3 below.

[0061]

From this result, the following is clear. First, since the resolution without a pixel shifting element is 240, the element with a polyvinyl alcohol alignment film is
Although it initially has the effect of increasing the resolution, it can be seen that the resolution deteriorates over time due to the instability of the alignment film.
On the other hand, it is clear that the polyimide film, in particular, the film whose uniformity of film thickness is improved by irradiation with near infrared rays, is stable over time and maintains high resolution. Also,
Even when the near-infrared irradiation is not performed, the polyimide film is stable over time, so that the resolution is rather better than that of the polyvinyl alcohol film over time.

Concrete Example 2 The film thickness data of the polyimide film shown in Table 2 above was obtained when the humidity at the time of applying the polyamic acid on the substrate to form the film was 60%. However, when this humidity was set to 20% and a film was formed in the same manner as in Example 1, it was found that, as shown in Table 4 below, a substantially uniform film can be formed regardless of the presence or absence of near infrared irradiation.

[0064]

Therefore, depending on the humidity during film formation, a substantially uniform film can be prepared without irradiating near infrared rays.
It is advantageous.

Next, wobbling (picture element shifting) using the liquid crystal element according to the present invention will be described. 4 and 5 schematically show an example of an optical device incorporating a wobbling element.

In this example, the present invention is applied to a liquid crystal optical display device 1, in which a liquid crystal display element (LCD) 2 sequentially arranged in the same optical path along the light traveling direction and a phase modulation optical device. A ferroelectric liquid crystal element (FLC) 3 as an element (phase control element) and a birefringent medium 4 made of a transparent substrate such as a quartz plate are combined. Here, for easy understanding, each constituent element is a liquid crystal display element L.
Each section corresponding to one constituent display pixel 5 of the CD is shown, and the polyimide liquid crystal alignment film and the like are omitted (the same applies hereinafter).

The pixels 5 of the LCD 2 are composed of a discrete pixel array such as a mosaic as a whole, and the liquid crystal used is TN (twisted nematic) or STN.
(Super twist nematic), SH (super homeotropic), FLC, etc. This LCD
Although not shown, reference numeral 2 has a polarizing plate on the panel itself as is well known, and the output light 6 has a linearly polarized light.

For the linearly polarized light 6, the above F
The wobbling element (picture element shifting element) 7 composed of the LC 3 and the birefringent medium 4 shifts the picture element in the parallel direction or the vertical direction.

To this end, one extraordinary optical axis 8 of the FLC element 3 is arranged so as to be parallel or perpendicular to the polarization plane 9 of the display pixel 5, and the equivalent uniaxial optical axis (uniaxial X of the extraordinary optical axis 10 of the transparent substrate 4 having various optical anisotropy)
The projection component on the −Y plane (incident side) is arranged in parallel (Y direction) or perpendicular (X direction) with respect to the polarization plane 9.

The liquid crystal used for the FLC element 3 is capable of high-speed switching at a video rate, and examples thereof include chiral smectic liquid crystal, and the birefringent medium 4 can be a crystal plate or the like. However, an antiferroelectric liquid crystal (AFLC) or a smectic liquid crystal exhibiting an electroclinic effect (for example, smectic A) is also effective instead of FLC, and
Of course, birefringent elements other than the quartz plate can be used.

Next, the wobbling operation of the display device 1 will be briefly described.

First, as shown in FIG. 4, the ferroelectric liquid crystal element 3
When the switch state of 1 is the state 1, since the polarization plane 9 of the light 6 emitted from the display element 2 side and the extraordinary optical axis 8 of the ferroelectric liquid crystal element 3 are parallel, the transmitted light 11 maintains the polarization plane. The crystal plate 4 having birefringence is irradiated. Since the crystal plate 4 includes the extraordinary optical axis 10 of the crystal in the plane of incident polarization, the light polarized in the Y-axis direction is refracted in the direction in which the extraordinary optical axis 10 of the crystal plate 4 is tilted, and the air layer is again formed. When it goes out to 12, it becomes parallel to the optical axis, and a deviation from the optical axis of the incident light occurs in the Y direction.

On the other hand, as shown in FIG. 5, the ferroelectric liquid crystal element 3
When the switch state of is the state 2, the polarization plane 9 and the extraordinary optical axis 8
Since the light has an angle of about 45 degrees, the transmitted light 11 rotates in the direction of the extraordinary optical axis and becomes linearly polarized light (Y-axis direction) → elliptically polarized light → circularly polarized light → elliptically polarized light → linearly polarized light (X-axis direction). The polarization plane is changed by 90 degrees from the initial state by changing the inside of the ferroelectric liquid crystal element 3, and the crystal plate 4 is irradiated with the polarized plane. In the crystal plate 4, since the extraordinary optical axis 10 of the crystal is not included in the plane of incident polarization, the light 11 is not refracted but maintains the optical axis as it is, and again exits to the air layer as outgoing light 12.

As described above, the optical axis is shifted depending on the presence or absence of refraction by the quartz plate 4 in the switch state of the FLC 3, that is, in the state 1 and the state 2, and the shift of the optical axis can be used as the operation principle of the pixel shift. it can.

Here, the cone angle of the liquid crystal that determines the switch state in the FLC 3 will be described. In the ferroelectric liquid crystal (the same applies to the anti-ferroelectric liquid crystal), the switching behavior of the liquid crystal director due to the application of the electric field is that liquid crystal molecules follow the South-Goldstone mode described in P150 of "Liquid Crystal Dictionary" (published by Baifukan). Move on a virtual cone. Furthermore, smectic A having an electroclinic effect
The liquid crystal (P145 of the same liquid crystal dictionary) has a cone angle unique to each liquid crystal composition similar to the cone angle even when the soft mode described in P119 of the same liquid crystal dictionary is used.

That is, consider the cone model of the liquid crystal 15 sandwiched between the transparent electrodes 13-14 made of ITO (Indium tin oxide in which indium is doped with tin) as shown in FIG. The opening angle of the cone is called the cone angle θr, and the projection of this cone angle on the glass substrate with the transparent electrode is called the apparent cone angle θ. Optically, the apparent cone angle θ may be considered.

In the normally white TN liquid crystal display device shown in FIG. 7, light from a light source is transmitted without applying an electric field to the TN liquid crystal. Here, a combination of the backlight 17-polarizing plate 18-TN liquid crystal 2-polarizing plate 19 or reflection plate-polarizing plate 18-TN liquid crystal 2-polarizing plate 19 is used.
Shows the same TN liquid crystal display element as the conventional one.
Needless to say, the TN liquid crystal element 2 and the ferroelectric liquid crystal element 3 are provided with transparent electrodes on both sides thereof.

In this case, as the electric field strength increases, T
The twist of the N liquid crystal 2 is released, and light is gradually leaked through the polarizing plate to realize gradation display, but any transmitted light is polarized by the polarizing plate 19 in front of the ferroelectric liquid crystal element 3 and has the same linear polarization. Therefore, the pixel shifting can be performed according to the above-described operation principle.

In the normally black TN liquid crystal display element shown in FIG. 8, light is transmitted in a state where an electric field is applied to the TN liquid crystal, and the twist of the TN liquid crystal 2 gradually increases as the electric field strength decreases. It returns, it gets darker gradually,
Although gradation display is realized, since any transmitted light becomes the same linearly polarized light by the polarizing plate 19 in front of the ferroelectric liquid crystal element 3, the pixel shifting can be performed according to the above-described operation principle.

As described above, it is clear that the present invention can be applied to any type of liquid crystal display element as long as the light emitted from the display element is substantially linearly polarized light.

Although the above-mentioned example relates to a display element having polarized light, the present invention can of course be applied to a non-polarized display element.

As shown in FIG. 9, when the polarization degree of the light from the display pixel 5 is small, a polarizing plate 19 may be inserted in the optical path connecting the display element 2 and the pixel shifting element 7 for polarization. good. The optical arrangement conditions are the same as in the case of the liquid crystal display element described above.

The non-polarizing display 2 that can be used here is a self-luminous display element such as a plasma display or an LED display.

As described above, based on the present invention, a phase modulation element such as a chiral smectic liquid crystal that can be driven at a video rate (ferroelectric liquid crystal, antiferroelectric liquid crystal, or smectic A liquid crystal having an electroclinic effect). ) 3 is used to arrange the wobbling element 7 in the optical path connecting the display such as liquid crystal, plasma, LED, etc., which is composed of discrete pixels, and the retina of the observer, and wobbling (pixel shifting).
The following [1] can be used as the phase modulation element 3 and the following [2] can be used as the birefringent medium.

[1] At least two states exist in the switch state of the ferroelectric liquid crystal, the antiferroelectric liquid crystal or the smectic A liquid crystal having the electroclinic effect, which can be driven at the video rate, and at least two of them exist. A chiral smectic liquid crystal device with an extraordinary optical axis forming an angle of 26 to 64 degrees, which is optically arranged so that the polarization plane can be rotated.

[2] A transparent substrate that shifts the optical axis depending on the polarization direction of the incident light, and specifically, (a) has an equivalent uniaxial extraordinary optical axis component in the wobbling direction. Arranged (b) A device in which the substrate facing surface through which light is transmitted is not parallel, and the apparent extraordinary optical axis is parallel or perpendicular to a plane perpendicular to both planes.

For the above wobbling operation, the phase may be shifted by 180 degrees in order to rotate the polarization plane of the liquid crystal by 90 degrees. Birefringence (n _e -n _o), the following relationship exists between a cell gap d and the phase difference [delta]. δ = 2πd (n _e −n _o ) / λ

Here, it is sufficient to set δ = π. For this purpose, the cell gap d should be set to d = λ / 2 (n _e −n _o ). However, in reality, since the angle α (pretilt angle) formed by the liquid crystal molecules with the substrate is not 0 degree, n _e becomes small and the gap length d must be made longer.

Here, the ordinary _{ray no} is independent of the incident angle and is equal to the refractive index n⊥ in the short axis direction of the liquid crystal molecule. In other words, n _o = n
It is ⊥.

Specifically, n _e is a function of the pretilt angle α,

[Equation 1]

D depends on the pretilt angle α as follows. d = λ / 2 [n _e (α) -n _o]

That is, α can be obtained from the type of alignment film, and the optimum gap d can be calculated based on the above relational expression. further,
When the pretilt angle α is 90 degrees, the gap length d is calculated by the above equation.
Is infinite, so a pretilt angle of 0 to 89 degrees is required. However, since it is difficult to control the pretilt angle beyond 45 degrees, a pretilt angle of 0 to 45 degrees is practically preferable.

In wobbling (picture element shifting), the response time of rising and falling is 1/3 of the field time.
It is preferable that the ratio of the rising time and the falling time does not exceed twice each other.

In this respect, when a nematic liquid crystal is used,
Even at a high speed, the rise time when an electric field is applied is relatively short, but the fall time when off is long, so switching in the field is not sufficient, and an effective pixel shifting effect cannot be obtained. The twisted nematic pixel shifting element has a minimum rise / fall time of about 15 msec (room temperature) when the transmittance change is 0 to 90%.
2: 1 line interlace scanning method (1/60 second (16.7 ms) per field) is quite difficult to realize, and if the 4: 1 line interlace scanning method is applied with the same number of frames,
It is 1/120 seconds (8.3 ms) per field, and it becomes impossible to follow at all.

On the other hand, the pixel shifting method using the ferroelectric liquid crystal element is effective because its switching time is shorter than that of the TN liquid crystal. By the way, the rise and fall times of the ferroelectric liquid crystal element are in the order of μsec, and even the slowest one is several ms or less.

Table 5 below shows the response times of various liquid crystals for comparison, and the response speed of the liquid crystals usable in the present invention is extremely fast.

The above-described high resolution technique (wobbling technique) can be used in any form such as a direct-view type, a reflection type and a projection type. Of these, FIGS. 10 to 11 show two examples of projection displays.

In the example of FIG. 10, the light from the halogen lamp 17 is led to the display element 2 as a backlight through the cold filter 43, and after the above wobbling process, the lens system is moved.
An image is projected from 44 to screen 45.

FIG. 11 shows a mirror type display, which is a light source.
The light from 17 is passed through the filter 46, separated into predetermined wavelength lights (R, G, B) by the respective dichroic mirrors 47, made incident on the respective wobbling elements from the condenser lens 48, wobbled there, and then again. The combined image is projected on the screen 45.

The above-mentioned high resolution technique is used in the visible light wavelength range for application as a display.

The present invention is not limited to the display element 2 described above,
It is also applied to the case where the above-mentioned wobbling element 7 is arranged in the optical path that connects the image pickup device such as CCD including discrete pixels and the object.

The imaging device 71 shown in FIGS. 12 and 13 according to the present invention.
Also in the case of applying to, the various conditions, principles, and explanations described in the above-mentioned display device are preferably adopted in the same manner. In the following, the contents similar to those of the above-described display device will not be particularly described repeatedly, but in comparison therewith, the description will be mainly given to those specific to the imaging device.

When an image sensor such as a CCD is used, the object-polarizer-F is placed in the optical path connecting the object and the image sensor 53.
The LC element, the birefringent substrate, and the image pickup element are arranged in this order.
In this case, the lens system, the iris, and the wavelength limiting filter may be arranged anywhere in the optical path connecting the subject and the image sensor.

As shown in FIGS. 12 and 13, when the switching state of the ferroelectric liquid crystal element 3 is the state 1, the irradiation light component a from the object 50 side passes through the lens 51 and the diaphragm 52, It is polarized by the polarizing plate 19 in the pixel shifting direction. Since the plane of polarization of light and the extraordinary optical axis 8 of the ferroelectric liquid crystal element 3 are parallel, the transmitted light is applied to the quartz plate 4 having birefringence while maintaining the plane of polarization. In the crystal plate 4, since the extraordinary optical axis of the crystal is included in the plane of incident polarization, the light polarized in the Y-axis direction is refracted in the direction in which the extraordinary optical axis of the crystal plate is inclined, and when it goes out to the air layer again. It becomes parallel to the optical axis, and there is a deviation from the optical axis of the incident light.
Each picture element of the D image sensor 53 is irradiated.

On the other hand, when the switch state of the ferroelectric liquid crystal element 3 is the state 2, the transmitted light is rotated in the direction of the extraordinary optical axis because the polarization plane and the extraordinary optical axis 8 form an angle of about 45 degrees. , Linearly polarized light (Y-axis direction) → elliptically polarized light → circularly polarized light → elliptically polarized light → linearly polarized light (X-axis direction), the polarization plane changes 90 degrees from the initial state, and the crystal plate 4 changes. Is irradiated.
Since the crystal plate 4 does not include the extraordinary optical axis of the crystal in the plane of incident polarization, the optical axis is maintained as it is without refraction, and it exits to the air layer again and is irradiated to each pixel of the CCD image pickup element 53. .
That is, the a'portion of the subject is imaged. It will be understood that the shift of the optical axis between the state 1 and the state 2 can be used as the operation principle of the pixel shifting.

In the case of an optical system such as a video camera or a still video camera, since incident light from the outside world is not substantially polarized, a polarizing plate is inserted between the outside world (subject) and the ferroelectric switching element. It does not matter the positional relationship with respect to the lens and the diaphragm. Other optical arrangements are subject-
The order is lens-diaphragm-polarizing plate-ferroelectric switching element-transparent substrate having uniaxial optical anisotropy-imaging element. The image pickup elements to be combined here are CCD, M
The type of the OS element or the like does not matter.

Since such an image pickup device is a light receiving device unlike a display device, it is possible to improve the spatial resolution (spatial separation ability) of a subject. Here, since it can be performed by the simultaneous method instead of the sequential method like the display element,
The switching part of the FLC element 3 may act on the entire surface of the CCD element at the same time and does not require spatial electrode division of the phase modulation element 3.

That is, for example, the pixels of the CCD image pickup element are discrete, and if there is no deviation of the optical axis, a is
Although there are only b and c position resolutions, the frame is divided, and the information of a, b, and c are first accumulated in the simultaneous method and then transferred.
In the next field, the position information of a ', b', and c'is accumulated by the pixel shift of the ferroelectric liquid crystal element 3 by the simultaneous method,
By transferring and recombining with the first field, the vertical resolution is doubled.

A specific mounting example of the above-mentioned video camera of the cell: Handycam TR-1 (manufactured by Sony Corporation) will be described. First, an infrared cut filter and a low pass filter which can be used therein will be described.

[1] Normal Imaging of Visible Light A semiconductor imaging device such as a CCD imaging device has a sensitivity range of
It extends to 380-1200nm. When a normal visible light image is captured, the near-infrared light region, which cannot be sensed by the human eye, is captured, which adversely affects the image. Therefore, it is necessary to insert the infrared cut filter 61 between the subject 50 and the CCD 53 as shown in FIG.

Here, an example in which an infrared cut filter (cuts a wavelength of 700 nm or more) 61 is combined with the pixel shifting element is shown. Further, since the quartz plate used for the wobbling element is insufficient in cutting high frequency components, an optical low pass filter is required. Therefore, a crystal low-pass filter (a plurality of crystal plates) for 7-point blur that is generally used in a high-quality CCD video camera
It consists of 64. ) Was incorporated (Fig. 14, Fig. 15).

In this low-pass filter, incident light is made into a two-point blur by utilizing its birefringence in one crystal plate, and a two-point image is formed by stacking another crystal plate rotated around the optical axis. It is possible to improve the low-pass filter characteristics by blurring the four-point image into a seven-point image on the third crystal plate.

That is, by blurring the incident light in this manner, it is possible to remove a component of image information having a high spatial frequency, and avoid problems such as moire fringes and color false signals. However, in the case of one crystal plate, the high frequency component can be cut or dispersed only in the y direction, but in the above, the high frequency component can be cut or dispersed in both the x and y directions, and the high frequency component of the high frequency component can be retained while maintaining the sensitivity of the low frequency component. It is possible to further eliminate the influence on the image (the generation of a moire fringe pattern or a color false signal in the image output of the formed image).

FIG. 16 shows an implementation example in which such a low pass filter is not used, and FIG. 17 shows an implementation example in which the low pass filter is used.
It was shown to. In each case, the picture element shifting element (wobbling element) 7 is provided in front of the CCD 53.

When the low-pass filter 64 is used, the first extraordinary optical axis of the low-pass filter is the polarization at the time of wobbling.
When the angle is 30 to 60 °, the effect of the low pass filter is obtained, but in other cases, the low pass filter characteristic changes in the field. At this time, by inserting a λ / 4 plate (not shown) between the picture element shifting element 7 and the optical low-pass filter, the difference in the low-pass filter characteristics between fields can be reduced and the low-pass filter characteristics can be sufficiently exhibited. Like

FIG. 18 shows a color separation camera system using three CCDs. However, CCD drive circuit,
The wobbling element drive circuit is omitted.

[2] In the case of imaging infrared light By utilizing the near infrared light region of a semiconductor image pickup device such as a CCD image pickup device, it is possible to image only the near infrared light region which cannot be sensed by the human eye. . In this case, it is not necessary to intentionally insert an infrared cut filter.

In this case, to image only infrared light, it is necessary to insert a visible light cut filter (cuts 760 nm or less) between the subject and the CCD. Accordingly, the temperature distribution of the subject can be imaged. Since the imaging wavelength at this time extends to 700 to 1200 nm, the phase difference of the pixel shift element needs to be 350 to 600 nm, which is half the wavelength.

As described above, by using the phase control element according to the present invention, a high-speed wobbling (picture element shifting) is applied to a display including discrete pixels, a solid-state image sensor including discrete light-receiving pixels, and the like. It is possible to achieve high resolution efficiently, and it is possible to improve a mosaic dot-drawing screen or the like into a seamless continuous screen.

Although the embodiments of the present invention have been described above, the above embodiments can be further modified based on the technical idea of the present invention.

For example, the structure, material and shape of each component, the forming method, the assembling method, and the like, including the above-mentioned liquid crystal element, may be variously changed. The substrate is not limited to the glass plate and may be any other optically transparent material. Various liquid crystals can be adopted. The alignment film, the SiO oblique vapor deposition film, and other alignment films are liquid crystal devices other than the liquid crystal device using the polyimide alignment film according to the present invention (for example, for the LCD described above).
You can use it for.

The object to which the present invention is applied includes, of course, the optical system such as the display device and the image pickup device described above and the wobbling element which can be incorporated in the system.

[0124]

As described above, the present invention provides at least one kind selected from the ferroelectric liquid crystal, the antiferroelectric liquid crystal, and the smectic liquid crystal exhibiting the electroclinic effect between the counter electrodes which are optically transparent. Since the liquid crystal alignment film formed on the electrode in the phase control element filled with the liquid crystal is made of polyimide, this liquid crystal alignment film is a very stable film and is hard to change over time. Since the surface state can be maintained and the film can be formed to have a uniform film thickness, the pretilt angle and orientation of the liquid crystal can be maintained, and the phase control characteristics, particularly the resolution of the display element or the like to be wobbled can be improved. .

In any of the above-mentioned liquid crystals such as the ferroelectric liquid crystal, the direction of the liquid crystal director is easily changed in response to the action of the electric field and the response speed is very fast, so that it can be sufficiently driven at the video rate. Become.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal cell as a phase control element according to an exemplary embodiment of the present invention.

FIG. 2 is an infrared spectrum diagram of a polyimide liquid crystal alignment film used in the liquid crystal cell.

FIG. 3 is a process flow diagram for manufacturing the same liquid crystal cell.

FIG. 4 is a schematic diagram in state 1 of a display device using the liquid crystal cell as a wobbling element.

FIG. 5 is a schematic view of the same display device in a second state.

FIG. 6 is an explanatory diagram of a cone angle of a ferroelectric liquid crystal (FLC) used in the display device.

FIG. 7 is a schematic diagram of a case where a normally white TN liquid crystal display element is used in the display device.

FIG. 8 is a schematic view of a case where a normally black TN liquid crystal display element is used in the display device.

FIG. 9 is a schematic view of a display device using a display element having a small degree of polarization.

FIG. 10 is a cross-sectional view of a display to which the display device is applied.

FIG. 11 is a cross-sectional view of another application example to a display.

FIG. 12 is a schematic diagram in state 1 of an imaging device using the liquid crystal cell as a wobbling element.

FIG. 13 is a schematic diagram of the imaging device in a second state.

FIG. 14 is a schematic diagram of a mounted state of a crystal optical low-pass filter.

FIG. 15 is a principle diagram illustrating blurring caused by three crystal filters of the same.

FIG. 16 is a cross-sectional view of a mounting example of the imaging device.

FIG. 17 is a cross-sectional view of another mounting example.

FIG. 18 is a cross-sectional view of still another mounting example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... (Liquid crystal optical) display device 2 ... (Liquid crystal) display element 3 ... Ferroelectric liquid crystal element 4 ... Birefringent medium 5 ... Display pixel 7 ... Wobbling element (picture element Shifting element) 8, 10 ... Extraordinary optical axis 9 ... Polarization direction 13, 14 ... Transparent electrode 15 ... Liquid crystal 17 ... Light source 18, 19 ... Polarizing plate 20, 21 ... Transparent substrates 22, 23 ... Alignment film 50 ... Subject 53 ... CCD element 61 ... Infrared cut filter 64 ... Optical low-pass filter 71 ... Imaging device

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Eriko Matsui Eriko Matsui 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Hidehiko Takanashi 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Nobue Kataoka 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Yang Eiho 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni -Inside the corporation

Claims (4)

[Claims] 1. A liquid crystal comprising at least one selected from a ferroelectric liquid crystal, an antiferroelectric liquid crystal and a smectic liquid crystal exhibiting an electroclinic effect is filled between optically transparent counter electrodes. A liquid crystal alignment film for a phase control element, which is formed on the electrode in the phase control element and is made of polyimide. Wherein at least one Tsumochi infrared absorption peak attributed to CH stretching of the alignment film molecules 2830Cm ^-1 or more, and an infrared absorption peak attributable to the carbonyl group of the alignment film molecules 1600 cm ^{- The} liquid crystal alignment film according to claim 1, having a range of ¹ to 1800 cm ^-1 . 3. A liquid crystal composed of at least one selected from a ferroelectric liquid crystal, an antiferroelectric liquid crystal, and a smectic liquid crystal exhibiting an electroclinic effect is filled between optically transparent counter electrodes. A phase control element in which a liquid crystal alignment film made of polyimide is formed on the electrode, the optical element being arranged in combination with a birefringent medium in the optical path of the optical element to be wobbled, and wobbling the optical element. Phase control element used for. 4. A method comprising: irradiating at least an electrode with infrared rays; coating the light-irradiated surface with a polyimide precursor; and heat-treating the polyimide precursor to imidize it. 4. The method for forming a liquid crystal alignment film according to any one of 3 above.