JP2005070789A - Optical modulator device or display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical modulator device and a display device wherein a modulation medium operates in an optically isotropic state. <P>SOLUTION: The optical modulator device or the display device using a liquid crystal modulation medium that is in the optically isotropic state at the temperature at which the device operates can be addressed even in any combination of conditions by overdriving addressing wherein voltage higher than first and last switching voltages is applied during driving. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to light modulation elements and electro-optic displays, and relates to response times, respective response behaviors of these light modulation elements and displays, and media for these light modulation elements and displays, in particular optical isotropy BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light modulation element and a display using a mesogenic modulation medium that is in a liquid crystal blue phase at the operating temperature of the light modulation element and display.

  Light control elements and displays using mesogenic modulation media, which are optically isotropic at the operating temperature of the display, have recently been described. DE10217273A1, and unpublished patent applications DE10241301, DE10253325, and DE10252250 describe optical controlling elements using a modulation medium that is isotropic at the operating temperature of the element, but DE10313979, which is still unpublished, operates. Sometimes, an element using a modulation medium that is an optically isotropic blue phase is described. However, to date, for these light modulation elements and displays, the operating temperature range is not sufficiently wide and the temperature dependence of the operating voltage is very high, allowing easier addressing over a wider temperature range. In order to do so, it must be lowered.

  In addition, light modulation elements and display types are characterized by excellent contrast with very fast response times and minimum viewing angle dependence. However, unfavorable response times are observed, especially in this new type of light modulation element and display. This undesirable effect consists of a change in the electric field, not as a desired state, ie, a single exponential relaxation type response, but as a response with two different characteristic response times. In these cases, preferably the extremely fast attenuation of the relative contrast is typically achieved when the modulation element is switched off in response times of a few ms, for example 5 ms or less, and only 1 ms or less at high temperatures. Only a portion of the relative contrast change is observed, eg, a remaining relative contrast change of about 10%. This fast response then becomes a very low response to 0% relative contrast or at least close to 0% for the remaining relative contrast decay. This slower response time constant is often more than an order of magnitude higher than the fast response time constant, for example in the order of 60 ms, or in the range of several hundred msec. This means that the prominently fast response times of promising new types of light modulation elements and displays cannot be fully exploited, and in some cases even impractical.

  Thus, improved light that operates or is operable at a temperature in which the modulation medium is in an optically isotropic state, eg, a liquid crystal in a blue phase, and does not suffer from, or at least not interfere with, an undesirable dual response There is a significant demand for modulation elements and displays.

  Surprisingly, to achieve an improved light modulation element and display operating at or operable at a temperature at which the modulation medium is in an optically isotropic state, for example similar to those disclosed in DE 10217273 A1 and in particular DE 10313979 It does not show the disadvantages of the prior art materials or at least shows them to a very small extent.

The present invention relates to a light modulation medium that is optically isotropic at the operating temperature of the device,
a) pulsed addressing having a continuous addressing time of 2.000 ms or less, or b) having a pulse width shorter than 4 msec and having timely separation between pulses of 10 msec or more Or c) having a horizontal spatial distribution of operating voltage, or d) having a vertical spatial distribution of operating voltage, or e) overdriven addressing, a high voltage between the first and last switching voltage Apply while driving,
f) Increase the temperature until an optically isotropic phase first appears, at an operating temperature at least 3 degrees higher than the transition temperature, or a), b), respectively, and from c) to f) It is characterized by being addressed by any combination of two or more conditions.

  In the first aspect of the present invention, the light modulation element and the display are put into practical use by driving the light modulation element with an improved addressing method. In this method, a continuous drive voltage (eg, square wave, triangle or other continuous waveform) is applied for a limited time period, preferably 500 s or less, more preferably 100 ms or less, and most preferably. Applies to the light modulation element without interruption in 50 ms or less.

  In another aspect of the invention, the drive voltage is applied with voltage pulses rather than continuous wave, and these pulses are applied in time periods while the voltage is not addressed or a sufficiently low voltage is addressed. It is divided. A typical voltage pulse width is 10 msec or less, preferably 8 msec or less, more preferably 4 msec or less. The time period between such pulses, where the voltage is not addressed, is between 20 msec and 1 msec, preferably between 15 msec and 2 msec. In a preferred embodiment, the sum of the pulse width and time period without applied voltage is 16 msec or less.

In this embodiment, the light modulation element must maintain the change in operating state until the voltage, the next refreshment pulse. Accordingly, these light modulation elements preferably have a voltage holding ratio of 90% or higher, more preferably 95% or higher, and most preferably 98% or higher, and preferably at the operating temperature. Has under high temperature and / or light irradiation.
The time limit at which the voltage is actually applied to the modulation medium with this addressing method is preferably realized by the spatial distribution of the voltage applied to the modulation element over the area of the display. This spatial distribution may be either horizontal or vertical with respect to the main surface of the display, or both at the same time.

  Here, horizontal distribution application across the display of addressing voltages is considered to mean the distribution of the addressing voltages for the light modulation elements in different regions, for example pixels or groups of pixels distributed over the region of the display. The different address areas then change over time.

  In contrast, a vertical distribution application of addressing voltage comprises two or more layers of conductive material, and includes light that includes electrode structures that substantially overlap each other as described in DE10241301, for example. It means that the modulation elements are addressed with different voltages or kept at different potentials for at least some time. These electrode structures having two or more layers of electrically conductive material and substantially overlapping one another include electrode pairs to which the light modulation cells correspond, each electrode pair being a modulation element or display This is realized in such a way that they are mutually positioned in a direction perpendicular to the main surfaces of the first and second surfaces and are separated from one another by a dielectric over at least a substantial part of the respective region. When the corresponding part of the electrode pair is located on the opposing substrate of the modulation element or display, this dielectric is the modulation medium itself. If they are located on one and the same substrate, the dielectric can be a solid dielectric, preferably a solid dielectric.

Another preferred embodiment of the present invention is the use of so-called over or step driving to overcome response time problems. Overdriving means switching with an intermediate higher voltage without directly switching from the start voltage to the desired final voltage. For example, without switching from V ₁₀₀ to 0 V, the switching is first performed to 1.3 times V ₁₀₀ and then returns to 0 V. Surprisingly, this can significantly accelerate switching time and overcome the switching time limitations described above.

This overdriving is preferably applied to the off switching from start voltage between V ₁₀ and V ₁₀₀ to 0V.

In a further preferred embodiment of the invention, for a 100% relative contrast (V ₁₀₀ ), a light modulating medium with a characteristic voltage as low as possible is used, resulting in an undesirable response behavior with a dual response time. It has been found to reduce and effectively suppress responses with longer time constants (constants). Preferably, the light modulation element of the present invention, 40V or less, and more preferably 35V or less, and most preferably 30V or less characteristic voltage V _100.

  Furthermore, the (electrical) capacity of each pixel of the light modulation element of the present invention and the display of the present invention is high. Preferably it is a factor of 2 or more, more preferably 3 or more, and most preferably 5 or more of the pixels of a comparable TFT display operating in TN-mode.

  For capacity comparison, typical reference cells and their layout can include “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status Nov. 1997, Merck KGaA, Germany.

Particularly preferred are light modulation elements comprising a liquid crystal medium that is optically isotropic in the operating temperature range, for example a blue phase.
Another aspect of the invention is that the transition temperature from a phase present at a lower temperature, such as a chiral nematic phase (referred to herein as a cholesteric phase) to a blue phase, preferably 4 ° or more, more preferably 6 °. Or more, and most preferably, the operation of the light modulation element, the display, respectively, at a temperature of 10 ° or more.

  The liquid crystal compounds of the present invention also include compounds that themselves have a liquid crystal phase, compounds that are compatible with the mesogenic phase, particularly the nematic phase, without unacceptably decreasing the clearing point. The latter compound has a mesogenic structure and is also called a mesogenic compound.

As used herein, “comprising” refers to an entity considered to be a vehicle or component, for example, that the compound is preferably 10% or more, and most preferably 20% or more of the whole It means to contain by concentration.
"Mainly consisting of" means that the entity referred to herein contains 80% or more, preferably 90% or more, and most preferably 95% or more of the compound. Means.
“Completely comprised” means that the entity referred to herein contains 98% or more, preferably 99% or more, and most preferably 100.0% of the compound. To do.

  In this specification, the term dielectrically positive compound describes a compound with Δε> 1.5, and the dielectrically neutral compound is a compound with −1.5 ≦ Δε ≦ 1.5, Negative compounds are those with Δε <−1.5. The same applies to the components. Δε is determined at 1 kHz and 20 ° C. The dielectric anisotropy of the compound is determined from the result of a 10% solution of the individual compound in the nematic host mixture. The volume of these test mixtures is determined in both homeotropic and homogeneous orientation within the cell. Both types of cell gaps are about 10 μm. The applied voltage is a square wave with a frequency of 1 kHz and typically an average double root of 0.1 V (0.5 V) to 1.0 V, which is the capacity threshold of the respective test mixture. The following are selected.

Mixture ZLI-4792 for dielectrically positive compounds and both mixture ZLI-3086, Merck KGaA, Germany for dielectric neutral compounds as well as dielectric negative compounds, respectively, as host mixture It is done. The dielectric constant of the compound is determined from the change in value when the compound of interest is added to the host mixture and extrapolated to a concentration of 100% of the compound of interest.
Ingredients having a nematic phase at a measuring temperature of 20 ° C. are measured as such, and everything else is treated like compounds.

In this specification, the term threshold voltage refers to the optical threshold and is given for 10% relative contrast (V ₁₀ ), the term saturation voltage means optical saturation, unless otherwise specified. Is given for a 90% relative contrast (V ₉₀ ). Capacitive threshold voltage (V ₀ , also called Fredericks threshold VFr) is used only when explicitly stated.
The ranges of parameters used herein are all including the limit values unless explicitly stated.

In this specification, unless stated otherwise, concentrations are percentages by weight, and for each complete mixture, all temperatures are given in degrees Celsius, and all temperature differences are also in degrees Celsius. All physical properties are determined as described in “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status Nov. 1997, Merck KGaA, Germany, and are indicated for a temperature of 20 ° C. unless otherwise stated. It is. The optical anisotropy (Δn) is determined at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) is determined at a frequency of 1 kHz. The threshold voltage as well as other electro-optical properties are determined in a test cell made in Merck KGaA, Germany. The test cell for the determination of Δε had a cell gap of 22 μm. The electrode was a circular ITO electrode having a protective ring and an area of 1.13 cm2. The alignment layer was lecithin for homeotropic alignment (ε ||) and polyamide AL-1054 from _{Japanese synthetic rubber} for homogeneous alignment (ε _┴ ). The capacity was determined with a frequency response analyzer Solatron 1260 using a sine wave with a voltage of 0.3 V _rms . The light used in the electro-optical measurement was white light. The setup used was a commercially available equipment from Otsuka, Japan. The characteristic voltage was determined under vertical observation. The threshold (V ₁₀ ) —intermediate gray (V ₅₀ ) — and saturation (V ₉₀ ) voltages were determined for relative contrasts of 10%, 50% and 90%, respectively.

  The liquid crystal medium according to the invention can contain further additives and chiral dopants in conventional amounts. The total concentration of these additives is 0 to 10% as a whole, preferably 0.1 to 6%, based on the total amount of the mixture. The individual compound concentration used is preferably 0.1 to 3%. In the present specification, these and similar additive concentrations are not taken into account when referring to the concentration values and concentration ranges of the liquid crystal component and the compound of the liquid crystal medium.

  The liquid crystal medium of the present invention consists of a plurality of compounds, preferably 3-30, more preferably 5-20, and very preferably 6-14. These compounds are mixed by a usual method. In general, the desired amount of the compound used in the smaller amount is dissolved in the compound used in the larger amount. When the temperature is higher than the clearing point of the compound used at higher concentrations, it is easy to observe complete dissolution. However, the medium is prepared using other conventional methods such as premixes, which are eutectic mixtures of homologues or compounds, or using so-called multi-bottle systems, components that can be used as mixtures on their own. It is also possible to do.

Melting point T (C, N) of liquid crystal and mesogenic material, transition T (S, N) and clearing point T (N, I) from smectic phase (S) to nematic (N) phase and all other transition temperatures In degrees Celsius.
In the present specification and the following examples, the structure of the liquid crystal compound is indicated by an abbreviation called an acronym. The conversion of abbreviations to the corresponding structures is performed according to the following two tables A and B. All groups of C _n H _{2n + 1} and C _m H _{2m + 1} are straight chain alkyls having n and m carbon atoms, respectively. The interpretation of Table B is self-explanatory. Table A shows only abbreviations for the structural cores. Individual compounds are designated by the abbreviation for the core, followed by a hyphen and a code for the substituents R ¹ , R ² , L ¹ and L ² .

Table A:

Table B:

The liquid crystal medium of the present invention is preferably
-6 or more compounds selected from the group of compounds in Tables A and B-containing 5 or more compounds selected from the group of compounds in Table B.

Example:
The following examples illustrate the present invention without limiting it.
However, among other things, the physical data of the compounds explains to the expert what properties can be achieved in which range. In particular, the combination of the various properties that can preferably be achieved is clear.

Example 1
Mixture A, a mesogenic mixture, has the following composition:

This mixture has the following properties:
The transition temperature from the cholesteric phase to the blue phase is 33 ° C.
This medium is introduced into a test cell having interdigital electrodes on only one substrate. The thickness of the mesogenic layer in the cell is 10 μm. The width of the electrodes is 10 μm, and the distance between the electrodes is also 10 μm.
The test cell is investigated for response behavior at several fixed temperatures. The optically isotropic phase is investigated at 35 ° C, 37 ° C, 39 ° C.
The results are shown in Table 1.

次に、３７℃の温度で、様々のアドレッシング時間、および１００％相対的コントラストから、それぞれ１０％、５％相対的コントラストへの相対的コントラストの変化に対する応答時間で、テストセルを調査する。結果を表２に示す。 Table 1: Response behavior for switching from 52 V to 0 V (V _rms , rectangular wave, 100 Hz, addressing time: 100 msec)

The test cell is then examined at a temperature of 37 ° C. with various addressing times and response times for changes in relative contrast from 100% relative contrast to 10% and 5% relative contrast, respectively. The results are shown in Table 2.

この表から、１０％相対的コントラストまでの減少に対する応答時間が、調査されたすべてのアドレッシング時間より極めて速く、アドレッシング時間の増大に伴いわずかに増大することが明らかである。対照的に、５％相対的コントラストまでの減少に対する応答時間は、著しいアドレッシング時間依存性を示す。 Table 2: Response time at various temperatures for switching from V ₁₀₀ to 0 V (square wave, 100 Hz) with an addressing time of 100 ms (t _adr .)

From this table it is clear that the response time to a reduction to 10% relative contrast is much faster than all the addressing times investigated and increases slightly with increasing addressing time. In contrast, the response time to a reduction to 5% relative contrast shows a significant addressing time dependence.

変調媒体が光学的に等方性の相であり、ブルー相への遷移温度より充分に高い場合、すなわちここでは３５℃以上、好ましくは３６℃以上、より好ましくは３７℃以上であるときに、Ｖ_１００から１０％相対的コントラストまでおよび５％相対的コントラストまでのスイッチングバックに対する、双方の応答時間が早いことが、この表から明らかである。これらの比較的高温下、これらのアドレッシング条件下で、双方の応答時間が、昇温に伴うわずかの非常に小さい増大を示すだけであることが更に明らかである。 Table 3: Response time at different temperatures for switching from V ₁₀₀ to 0 V (square wave, 100 Hz) with different (t _adr .) Addressing times

When the modulation medium is an optically isotropic phase and is well above the transition temperature to the blue phase, ie here 35 ° C. or higher, preferably 36 ° C. or higher, more preferably 37 ° C. or higher, It is clear from this table that both response times are fast for switching back from V ₁₀₀ to 10% relative contrast and 5% relative contrast. It is further clear that under these relatively high temperatures, under these addressing conditions, both response times show only a very small increase with increasing temperature.

Claims (10)

A light modulation element or display using a liquid crystal modulation medium that is optically isotropic at the operating temperature of the element,
a) with a continuous addressing time of 2.000 ms or less, or b) with pulsed addressing with a pulse width shorter than 4 msec and a timely separation of 10 msec or more between these pulses, Or c) in the horizontal spatial distribution of the operating voltage, or d) in the vertical spatial distribution of the operating voltage, or e) in overdriving addressing, which applies a voltage higher than the first and last switching voltage during driving.
f) While raising the temperature to the first optically isotropic phase, at least 3 degrees higher than the transition temperature, or a), b), and c) to f) Said light modulation element or display, characterized in that it is addressed in any combination of two or more conditions.   Light modulation or display element according to claim 1, characterized in that the modulation medium is blue phase at operating temperature.   3. Light modulation or display element according to claim 1 or 2, characterized in that it has a temperature range with a small temperature dependence of a characteristic voltage of 10 degrees or more. The switching response time from V ₁₀₀ to 0 V to reach a relative contrast of 10% is more than 70% of the switching response time to reach a relative contrast of 5%. The light modulation or display element according to any one of .about.3.   5. A light modulation or display element according to claim 1, having a voltage holding ratio of 90% or more at the operating temperature.   6. The light modulation or display element according to claim 1, wherein the light modulation or display element has a capacity twice or more than that of a normal TN-TFT-LCD that can be compared.   An electro-optic display comprising one or more light modulation elements according to claim 1. A method of operating a light modulation element or display comprising:
a) with a continuous addressing time of 2.000 ms or less, or b) with pulsed addressing with a pulse width shorter than 4 msec and a timely separation of 10 msec or more between these pulses, Or c) in the horizontal spatial distribution of the operating voltage, or d) in the vertical spatial distribution of the operating voltage, or e) in overdriving addressing, which applies a voltage higher than the first and last switching voltage during driving.
f) While raising the temperature to the first optically isotropic phase, at least 3 degrees higher than the transition temperature, or a), b), and c) to f) Said method, characterized in that it is addressed in any combination of two or more conditions.   9. The method of operating a light modulation element or display according to claim 8, wherein the modulation medium is in an optically isotropic phase at the operating temperature of the light modulation element or display.   The liquid crystal modulation medium according to claim 1, wherein the liquid crystal modulation medium exhibits a blue phase at an operating temperature.