Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1998-01-16
2000-04-25
Baliato, Josie
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
3241581, G01R 3100
Patent
active
060548703
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
present invention relates to a liquid crystal device evaluation method and apparatus, and more particularly, to a method and apparatus for detecting impurities mixed in a liquid crystal device.
BACKGROUND ART
In a liquid crystal device, if impurities responsive to an electric field (hereinafter referred to as "field responsive impurities") are mixed in a liquid crystal, the device performance, such as a response speed and contrast, deteriorates and the service life of the device shortens. The field responsive impurities are defined as chemical species capable of moving or transporting electric charges within the device upon application of the electric field. The field responsive impurities include protons, organic ions, inorganic ions, compounds having a hydrogen bonding ability, compounds having an electron transporting ability, compounds having a large dipole moment, compounds having a large polarizability, and the like. It is therefore indispensable to improve the manufacturing process in order to prevent contamination of the device with the field responsive impurities by detecting, identifying, and determining them mixed in the device. At this time, to properly determine which one of processes should be modified and how to modify it, the identification of the mixed impurities will be important.
To evaluate impurities, a method of measuring a voltage retention ratio of the liquid crystal device at high temperature has been conventionally employed. This method enables to evaluate the liquid crystal device in the final state of the construction thereof. However, this method requires much time and labor. In addition, it is difficult to specify causative materials for impurities and a process in which impurities are mixed in the liquid crystal device.
It is an object of the present invention to provide a liquid crystal evaluation method capable of identifying field responsive impurities contained in a liquid crystal device simply and with high sensitivity, and an apparatus for realizing the evaluation method.
DISCLOSURE OF INVENTION
A method of evaluating a liquid crystal device according to the present invention, comprises the steps of: crystal layer between a pair of electrodes; wavelength while an AC pulsed electric field is being applied to the liquid crystal device after the DC electric field is removed to obtain a field response curve corresponding to time-dependent change of light intensity during a cycle of the AC pulsed electric field by time-resolved measurement of light passed through the liquid crystal layer; basis of specific quantitative change in the field response curve as a function of elapsed time after the functional electric field is removed.
A liquid crystal device evaluation apparatus of the present invention comprises: liquid crystal layer between a pair of electrodes; device; the DC electric field is removed; from the light radiated from the light source; range passed through the liquid crystal layer into an electric signal after the light is extracted by the spectroscopic means from the light radiated from the light source; change of light intensity during a cycle of the AC pulsed electric field by time-resolving and integrating the electric signal converted by the light detection means; and curve and analyzing the quantitative change as a function of elapsed time after the DC electric field is removed.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram showing an example of a liquid crystal device evaluation apparatus of the present invention;
FIGS. 2A and 2B are characteristic graphs respectively showing AC pulse electric field applied according to the method of the present invention and the measured field response curve; and
FIG. 3 is a characteristic graph showing change of transmitted light intensity with a passage of time, which is obtained from the field response curve of the liquid crystal cell measured according to the method of the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
First, the principle of the present invention will
REFERENCES:
patent: 5621334 (1997-04-01), Urano et al.
K. Iwata and H. Hamaguchi, "Construction of a Versatile Microsecond Time-Resolved Infrared Spectrometer", Applied Spectroscopy, vol. 44, Nov. 9, 1990, pp. 1431-1437.
Machida Shigeru
Sano Kenji
Urano Taeko
Baliato Josie
Kabushiki Kaisha Toshiba
Sundaram T. R.
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