Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Patent
1996-09-23
1998-07-14
Mai, Huy
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
349 52, G02F 1136
Patent
active
057812560
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a nonlinear resistance element and a fabrication method thereof, together with a liquid crystal display device, and, in particular, it relates to an element having a metal-insulator-metal (MIM) structure (hereinafter called a MIM element) that is used as a switching element in an active matrix liquid crystal display device, and a fabrication method thereof.
BACKGROUND OF ART
A MIM element is a switching element that is configured of a thin insulator film sandwiched between two thin conductive films, making use of the fact that the voltage-current characteristic between the thin conductive films is nonlinear.
In order to provide a high level of image quality, a liquid crystal panel using a MIM element must satisfy the following conditions: the liquid crystal. small. nonlinearity, and the ratio of the on-current to the off-current must be sufficiently large. drive voltage periodically changes, the voltage-current characteristic must be symmetrical on the positive voltage side and the negative voltage side.
Note that the drive method in which the polarity of the drive voltage periodically changes is hereinafter called an "inverting drive."
One of the present inventors and two other persons have developed a technique of first forming on a glass substrate a first metal film having tantalum (Ta) as a main component to which is added tungsten (W), then forming an insulating film by anodization of the first metal film, to satisfy the above described conditions demanded of a MIM element, and have applied for patents thereon (International Application No. PCT/JP94/00204 and International Laid-Open No. WO 94/18600).
Use of this technique can greatly reduce time-dependent variations in the characteristics of the MIM element.
The present inventors continued their research into even further satisfying the conditions of the MIM element. This research concentrated on further reducing time-dependent variations in the characteristics of the MIM element, and also on establishing a technique of reducing the "polarity difference" by making the voltage-current characteristic on the positive voltage side and negative voltage side symmetrical when the MIM element is used in an inverting drive.
This "polarity difference" is the potential difference .DELTA.V (=V1-V2) between the voltage V1, necessary for a current (Poole-Frenkel current) of 1 A/cm.sup.2 to flow from the first conductive film through the insulating film and into the second conductive film, and the voltage V2, necessary for a current of 1 A/cm.sup.2 to flow from the second conductive film through the insulating film and into the first conductive film, when the MIM is subjected to an inverting drive as shown in FIG. 16. Note that the absolute value of current concentration (logarithmic scale) is plotted along the vertical axis in FIG. 16 and the absolute value of voltage (linear scale) is plotted along the horizontal axis. Reference number 1100 and reference number 1200 in FIG. 16, respectively, denote the characteristics on the positive voltage side and the negative voltage side of the MIM element.
When the display is switched to a new screen after the same pattern has been displayed for a long time on the liquid crystal screen, the previous display pattern will remain clearly visible if the "polarity difference" is large, generating a phenomenon called "sticking" and thus causing the display quality of the liquid crystal display device to deteriorate. The generation of this "sticking phenomenon" is caused by polarization of the liquid crystal elements by the DC component generated by the non-symmetry of the MIM element during inverting drive. Therefore, it is important to reduce the polarity difference of the MIM element to improve the display quality of the liquid crystal display device.
This invention was made on the basis of results obtained by the above described research performed by the inventors.
DISCLOSURE OF INVENTION
An objective of this invention is to provide a novel MIM element that enables a further redu
REFERENCES:
patent: 5128784 (1992-07-01), Suzuki et al.
Inoue Takashi
Ono Nagamasa
Mai Huy
Malinowski Walter
Seiko Epson Corporation
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