KR100406742B1 - A 1-Panel LCoS Engine for FSC display - Google Patents

Abstract

The present invention relates to a 1-panel LCoS engine for an FSC display, wherein a compensation film is disposed on the front side of the liquid crystal cell, and a polarizing beam splitter and a projection lens are sequentially disposed on the front side of the compensation film, and are attached to the substrate. In an LCoS engine employing an optically compensated birefringent (OCB) mode with a reflective mirror, the liquid crystal cell spacing of the OCB mode is 2 to 3 μm and the response speed is 0.5 ms or less for 1-panel LCoS for FSC displays. By providing the engine, the response speed characteristics of the liquid crystal panel can be reduced to 0.5 ms or less.

Description

A-Panel LCoS Engine for FSC display

[Industrial use]

The present invention relates to a 1-panel LCoS engine for an FSC display, and more particularly, to a 1-panel LCoS engine for an FSC display in which a response speed characteristic of a liquid crystal panel is faster in a liquid crystal panel employing an OCB mode.

[Prior art]

BACKGROUND OF THE INVENTION High speed optical gates are conventionally focused on twisted nematic liquid crystals in optical systems to reduce the turn-on, turn-off optical response times of the optical gates.

Such photogates are disclosed by Tobias (International Handbook of Liquid Crystal Displays, OVUM Ltd., London, England, 1975, paragraph 9.5.3 FIGS F9.19 and F9.20).

Among such optical gates, liquid crystal devices have been used in conventional monochromatic devices, and have recently been developed to realize color using color filters (Handbook of Liquid Crystal Device (1990), p492. Edited by 142th Commission Panel of the Science Council of Japan) , published by Nikkan Kogyo Shinbun-sha).

However, the method of using the color filter has a problem in that there is a lot of light loss due to the color filter, and in the resolution and the driving circuit, one image element is composed of three pixels, thereby causing three losses.

To solve this problem, a field sequentialcolor (FSC) method has been developed.

However, even in the FSC method, there are various problems in high response speed, half-tone image, productivity, and the like, and are not currently implemented.

For example, a twisted nematic type of liquid crystal cannot be applied to the FSC method with a response time of 20 to 100 ms, and when applied to a low speed FSC, the display quality is greatly degraded due to flickering. to be.

In addition, there is a problem that the response time of the STN (Super Twist Nematic) is even later to 50 to 300 ms.

On the other hand, ferroelectric liquid crystals have a fast response time but hardly exhibit half-tone images, have a very small cell spacing, and are difficult to be used because of various difficulties in orientation. There is a problem.

In order to solve this problem, US Patent No. 6,108,058 attempts to solve the above problem by using a liquid crystal oriented bent and a phase compensation plate.

However, the patent also has a problem that it is difficult to apply sufficiently to high resolution Field-Sequential Color Dispaly (FSC) with a cell interval of 8 μm and a response time of 2 to 8 ms.

In addition, the viscosity of the used liquid crystal is higher than 20 mPa · s, and the OCB mode driving method has a voltage burden in the driving sector because the V _C voltage is usually 2 to 3 V and the driving voltage V _H is usually high at 6 to 20 V. There is a problem that this is large.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems described above, and an object of the present invention is to apply a liquid crystal cell with a narrow interval and a low viscosity to the OCB mode, thereby providing a short response time and excellent contrast for a 1-panel LCoS engine for an FSC display. It is about.

1 is a view showing the configuration of a 1-panel LCoS engine according to an embodiment of the present invention.

2 is a view showing the change of the liquid crystal state according to the voltage.

3 is a graph illustrating a change in free energy of a bend state and a splay state according to a voltage change.

4 is a graph showing a relationship between t ₀ , which is a time at which a transient effect is maintained at 0 V under a constant driving voltage.

FIG. 5 is a graph illustrating a change in rising time and falling time according to a change in pretilt angle under a constant applied voltage.

6 is a graph showing the relationship between the response time according to the pretilt angle when the applied voltage is V _H = ± 4.0 V.

The present invention to achieve the above object, the present invention

Compensation film is disposed in front of the liquid crystal cell, polarizing beam splitter and projection lens are sequentially arranged in front of the compensation film, and the optical compensation birefringence (OCB) mode is provided with a reflection mirror attached on the substrate. In the LCoS engine employed, there is provided a 1-panel LCoS engine for an FSC display, wherein the liquid crystal cell interval in the OCB mode is 2 to 3 µm and the response speed is 0.5 ms or less.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in detail.

1 shows a schematic structure of a 1-panel LCoS engine according to the present invention.

Referring to FIG. 1, the LCoS engine is configured such that a compensation film 5 is disposed in front of the liquid crystal cell 3, and a polarizing beam splitter 7 and a projection lens 9 are disposed in front of the retardation film. ) Sequentially. The light source 11 is provided outside.

It is preferable that the liquid crystal cell 3 uses a liquid crystal of nematic structure as a liquid crystal oriented bent.

In the LCoS engine driving method, the light (white light) 11 emitted from the light source is incident on the bend cell 3 through the PBS 7.

The incident light is controlled by a liquid crystal cell 3 which acts as a light gate, reflected back from a reflecting mirror 1 attached to a silicon substrate, and then passed through a PBS 7 to a projection lens. Through (9).

Here, the retardation film or the compensation film 5 serves to improve the contrast of the display by making the contrast dark black through phase compensation of the liquid crystal cell 3. Do it.

The retardation film preferably has a phase difference of 20 to 500 nm.

The most important part in the development of 1-panel LCoS engine is the field-sequential color (FSC) implementation method, so the response speed of the liquid crystal panel of less than 1 ms is essential. .

In the present invention, the response speed can be remarkably improved by improving the cell gap, the viscosity of the liquid crystal, and the driving method.

In order to improve the response speed, the cell gap was reduced to 2.0 to 3.0 μm, and liquid crystals having improved viscosity of the liquid crystal to 7.5 to 8.0 mPa · s, which is 1/3 of the materials used, are used.

Equation 1 below shows the relationship between the response time, the cell spacing, and the physical properties of the liquid crystal material.

Equation 1

Where γ is the viscosity of the liquid crystal material, d is the cell spacing, v is the driving voltage, v ₀ is the threshold voltage, Δε is the dielectric anisotropy, and K is the elastic modulus.

In the above formula, the response time tau _r depends on the viscosity of the liquid crystal material and the cell spacing. Therefore, a method of reducing the response time is to reduce the viscosity and the cell spacing of the liquid crystal material.

In addition, in the nematic structure of the liquid crystal, as shown in FIG. 2, in the conventional case, the state of 21 is turned off and the state of 25 is turned on. However, in the present invention, the state of 25 is turned off and the state of 23 is turned off. Design to ON. The response time of the liquid crystal can be significantly improved by applying the state of 23 to 0 V as the V _C voltage and the state of 25 to ± 3.0 to ± 5.0 V as the driving voltage.

In the state of 23, when a voltage is applied, a bias is selected by selecting a place where bend free energy and splayfree energy intersect according to a change in voltage. ) State.

Reduces the relaxation time by eliminating the stopping force caused by the V _C voltage when the liquid crystal is relaxed by increasing the biased common voltage (V _C ) voltage to 0 V to reduce the falling time. Can be.

Conventionally, trans-Difluorostilbene (DFS) is used as the liquid crystal. DFS has excellent viscosity and is advantageous for high-speed response, but the trans and sheath forms continuously change with energy. The isomerization reaction occurs, which causes deterioration in liquid crystal properties, which is not preferable.

In the present invention, for the photoisomerization reaction, liquid crystal properties and light resistance are improved by substituting one end group of DFS with another substituent, or by replacing cyclohexane group in place of phenyl group in DFS structure, viscosity, T_ni And the response time can be secured by increasing the elastic modulus K and decreasing Δn.

The liquid crystal used in the present invention is preferably DFS-F (Difluorostilbene-Fluoride) represented by Formula 1 or DFS-C (Difluorostilbene-Chloride) represented by Formula 2 below.

Formula 1

R ₁ -A-CF = CF-Ph-R ₂

In the above formula, R ₁ is selected from the group consisting of an ethyl group, a propyl group, a butyl group, a pentyl group, and a pentene group, A is a phenyl group, and R ₂ is fluorine (F).

Formula 2

R ₁ -A-CF = CF-Ph-R ₂

Wherein R ₁ is a propyl group or a pentyl group, A is cyclohexane, and R ₂ is fluorine (F) or chlorine (Cl).

Meanwhile, as shown in FIG. 4, when a constant driving voltage V _H is applied, the state of FIG. 3 in FIG. 3 in the liquid crystal cell depends on time t ₀ when a 0 V voltage is applied. Thus, the state of 23 is called a transient effect, and t ₀ is the maximum time that the curved state can be maintained in the liquid crystal cell without interruption.

The minimum driving voltage at which the temporary state can be maintained is preferably ± 3.0 to 5.0 V, more preferably ± 3.0 V, and t ₀ may be 3 to 5 ms.

In addition, the relationship between the pretilt angle and the response speed of the liquid crystal can be experimentally confirmed that the higher the pretilt angle, the faster the response speed through the response speed change experiment according to the pretilt angle.

As can be seen in FIG. 5, it can be seen that as the pretilt angle increases, the rising time and the falling time are both faster.

The rising time tends to saturate somewhat at angles above 10 °, while the falling time continues to increase even at angles above 10 °.

Therefore, the higher the pretilt angle, the faster the response speed of the liquid crystal.

When the pretilt angle is about 15 °, the rise time is 80 ms, and in the case of the polling time, a very fast response speed is obtained, such as 350 ms.

Therefore, the pretilt angle of the liquid crystal is preferably about 8 ° to 30 °.

In addition, the refresh rate of the 1-panel LCoS engine is preferably at least 270 Hz (sub-frame time = 1/270 = 3.7 ms) without color breakup problem.

Hereinafter, a preferred embodiment of the present invention. However, the following examples are only presented to better understand the present invention, but the present invention is not limited to the following examples.

Example 1

The liquid crystal of SEIMI Chemical Co., Ltd. of Japan (SEIMI Chemical Co., Ltd.) whose (DELTA) n is 0.212, _Tni is 83.1 degreeC, viscosity ((gamma)) is 7.9 mPa * s at 25 degreeC, and (DELTA) epsilon is 10.2 was used. The cell spacing was designed to be 2 μm, and driving voltage V _H was applied to ± 3.5 V and V _C to 0 V. As a light source, the ON (rising) and the OFF (falling) times were measured while changing the pretilt angle of the OCB cell from 5 ° to 15 ° using a He-Ne laser. The results are shown in FIG.

As can be seen in Figure 5, the rising time decreases as the pretilt angle increases and it can be seen that the saturation occurs when a certain angle or more, and in the case of polling time, as the pretilt angle increases It can be seen that the decrease continues.

Therefore, it can be seen that the response time decreases as the pretilt angle increases.

In general, the equation used to calculate the throughput of the LCoS engine in the optical system is as follows.

Equation 1

Throughput = light irradiation efficiency x aperture ratio x mirror reflectance x polarization efficiency in liquid crystal mode

to be.

Throughput of the LCoS engine according to the embodiment of the present invention and the throughput of the existing LCoS engine was calculated. The calculation result is as follows (the aperture ratio was 0.9, the mirror reflectance 0.9, and the polarization efficiency was 0.85).

Throughput according to an embodiment of the present invention = (3.7-0.43) / 3.7 × 0.9 × 0.9 × 0.85 = 0.61 (about 61%),

In the conventional case, throughput = (3.7-1.5) /3.5 × 0.9 × 0.9 × 0.85 = 0.41 (about 41%).

As can be seen from the above calculation, in the case of the 1-panel LCoS engine according to an embodiment of the present invention, the throughput was improved by about 50% from 41% to 61%.

Comparative example

Using the liquid crystal as shown in the following table, the response speed was measured. V_H = ± 3.5 V, V_C= 0 V, R / F = 100 nm, pretilt angle (θ) was 11.5 ° and cell spacing was 2.0 µm.

Tni Δn (589 nm) Rotational Viscosity (25 ℃) Δε ε _⊥ V ₁₀ SSF-2080 (Seimi Chemical Co., Ltd.) 96.0 ℃ 0.218 15.3 mPas 18.0 4.9 1.64 V MDA-99-3480 (Merck Korea) 98.5 ℃ 0.200 22.0 mPas 13.0 4.5 2.25 V

When the SSF-2080 is used, the rise time is 160 ms, the polling time is 650 ms, the response time is 810 ms (0.81 ms), and the MDA-99-3480 is rated at 250 ms and polling time 950 ms. (1.20 ms), it turned out that response time is slower than the liquid crystal (response time 320 microseconds) used by this invention.

Example 2

The change of the response speed according to the pretilt angle was measured at an applied voltage of ± 4.0 V. The measurement conditions are OCB- mode, and _{V C = 0 V, R /} F = 100 nm, d = 2.0 ㎛, the liquid crystal was used as a trade name: SSF-1576 (Japan three already Chemical Corp.).

The results are shown in FIG.

Referring to FIG. 6, it can be seen that the response speed is faster than that when the applied voltage V _H is ± 3.5 V. As can be seen from Equation 1, which is a response speed relation, the applied voltage is applied under the same conditions. Increasing it can be seen that the response speed of the liquid crystal decreases.

In addition, as in the applied voltage condition of ± 3.5 V, it was found that the response speed increases as the pretilt angle increases.

Example 3

V_H = ± 4.0 V, V_C = 0 V, R / F = 160 nm, d = 3.0 µm, and the liquid crystal used DSF-F series SSF-1576 (Seimi Chemical Co., Ltd.), and the pretilt angle was 11.5 °, and the response according to the cell spacing The speed was measured.

As a result of the measurement, the rising time τ _r was 0.27 ms and the polling time τ _t was 0.52 ms.

As can be seen from the response rate measurement results, it was found that when the cell interval was increased from 2.0 μm to 3.0 μm, the rising time decreased from 0.1 ms to 0.27 ms and the polling time decreased from 0.36 ms to 0.52 ms.

In the cell spacing of 2.0 μm, the bend could be maintained even with a voltage of ± 3.5 V. However, in the cell spacing of 3.0 μm, the bend could only be maintained by applying a voltage of ± 4.0 V. The voltage was also raised.

In the case of using the 1-panel LCoS engine according to the present invention, since it shows a fast response speed of 0.5 ms or less even at a cell spacing of 2.0 μm, it is not necessary to lower the cell spacing anymore to improve the response speed, thereby ensuring sufficient process productivity. Drive voltage is low from ± 3.0 to ± 5.0 V, the driving safety of the backplane is excellent, and because the V _C voltage is 0 V, there is no need to apply additional voltage. There is an advantage.

Claims (10)

Compensation film is disposed in front of the liquid crystal cell, polarizing beam splitter and projection lens are sequentially arranged in front of the compensation film, and optical compensation birefringence (OCB) having a reflecting mirror attached to the substrate. An LCoS engine employing a Compensated Bend) mode, wherein the liquid crystal cell interval of the OCB mode is 2 to 3 µm and the response speed is 0.5 ms or less. delete The method of claim 1, The 1-panel LCoS engine for FSC displays whose viscosity of the said OCB mode liquid crystal is 7.5-8.0 mPa * s. The method of claim 3, The liquid crystal is a 1-panel LCoS engine for an FSC display, which is a material represented by Chemical Formula 1 or 2 below: [Formula 1] R ₁ -A-CF = CF-Ph-R ₂ Wherein R ₁ is selected from the group consisting of ethyl group, propyl group, butyl group, pentyl group and pentene group, A is phenyl group, R ₂ is fluorine (F), [Formula 2] R ₁ -A-CF = CF-Ph-R ₂ Wherein R ₁ is a propyl group or a pentyl group, A is cyclohexane, and R ₂ is fluorine (F) or chlorine (Cl). The method of claim 1, 1-panel LCoS engine for FSC display, wherein V _C in OCB mode is 0 V and drive voltage V _H is ± 3.0 to 5.0 V. The method of claim 1, The 1-panel LCoS engine for FSC displays, wherein the refresh rate of the 1-panel LCoS engine is at least 270 Hz. The method of claim 1, 1-panel LCoS engine for FSC display, wherein the retardation film of the OCB mode is 50-200 nm. The method of claim 1, 1-panel LCoS engine for FSC display, wherein the pretilt angle of the OCB mode is 8 ° to 30 °. The method of claim 1, The LCoS engine further comprises a 1 or 2-panel 1-panel LCoS engine for FSC display. Compensation film is disposed in front of the liquid crystal cell, polarizing beam splitter and projection lens are sequentially arranged in front of the compensation film, and optical compensation birefringence (OCB) having a reflecting mirror attached to the substrate. In the LCoS engine employing the Compensated Bend mode, the liquid crystal cell interval of the OCB mode is 2 to 3 µm, the response speed is 0.5 ms or less, and the viscosity of the liquid crystal in the OCB mode is 7.5 to 8.0 mPa · s. Features 1-panel LCoS engine for FSC displays.