Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-03-24
2001-12-11
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C345S087000, C345S091000, C257S059000, C257S072000
Reexamination Certificate
active
06330099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to liquid crystal-based video and graphics display devices, and, in particular, to increasing manufacturing yields for such display devices.
2. Description of the Related Art
A substantial need exists for various types of video and graphics display devices with improved performance and lower cost. For example, a need exists for miniature video and graphics display devices that are small enough to be integrated into a helmet or a pair of glasses so that they can be worn by the user. Such wearable display devices would replace or supplement the conventional displays of computers and other devices. In particular, wearable display devices could be used instead of the conventional displays of laptop and other portable computers. Potentially, wearable display devices can provide greater brightness, better resolution, larger apparent size, greater privacy, substantially less power consumption and longer battery life than conventional active matrix or double-scan liquid crystal-based displays. Other potential applications of wearable display devices are in personal video monitors, in video games and in virtual reality systems.
Miniaturized displays based on cathode-ray tubes or conventional liquid crystal displays have not been successful in meeting the demands of wearable displays for low weight and small size. Of greater promise is a micro display of the type described in U.S. Pat. No. 5,596,451 of Handschy et al. (digital pixel driver) and in European patent application no. 98122934.7 of Walker et al. (analog pixel driver), the disclosures of which are incorporated into this disclosure by reference. This type of micro display includes a reflective spatial light modulator that uses a liquid crystal (LC) material as its light control element. Typically, a ferroelectric liquid crystal (FLC) material is used as the light control element.
When manufacturing the spatial light modulator of the LC-based micro display just described, internal short circuits can develop that lower manufacturing yields, thereby increasing production costs. In order to keep yields high, it is necessary to insure that shorts between the transparent electrode on the cover glass and the top metal on the edge of the spacial light modulator chip will not have adverse circuit consequences,. Previous solutions to this problem have involved connecting this metal to the driving circuit for the transparent (typically made of ITO (Indium Tin Oxide)) electrode, or leaving this metal completely floating. However, the first solution can cause ESD (electrostatic discharge) damage to the ITO circuit, as well as shorts to ground, while the second solution violates manufacturing assumptions required for consistent plasma etching of the metal.
Thus, it can be seen that modern spatial light modulator manufacturing techniques impose manufacturing yield and production cost limits upon LC-based micro displays, and hinder the use of these micro displays in many applications.
Therefore, there is an unresolved need for an improved spatial light modulator manufacturing technique that can increase LC-based micro display manufacturing yields and lower production costs.
SUMMARY OF THE INVENTION
A spatial light modulator manufacturing technique is described that increases LC (Liquid Crystal)-based micro display manufacturing yields and thereby lowers production costs.
Adverse circuit consequences caused by shorts between the transparent electrode on the cover glass and the top metal on the edge of the spatial light modulator chip are avoided during manufacture. First, metal on the edge of the chip is connected to the substrate by way of a reverse-biased diode. This insures that the metal will be correctly biased during plasma etching. Alternatively, the metal on the edge of the chip is connected to the substrate by way of another solid-state device such as a FET (Field Effect Transistor) which can be turned on during power-on-reset (and which has an implicit diode to the substrate).
Second, all other metal layers in this region are also connected only to the substrate in the same fashion as the top metal.
Third, all metal in this region of the chip is segmented into several regions, so that if one segment shorts to one signal or supply, and another shorts to a different signal or supply, those two signals or supplies remain separate. Thus, a short will only occur if a single segment shorts to multiple signals.
Finally, the metal under the fill area, and the metal under the “skirt” (peripheral top metal) on either side of the fill area, are all treated as separate regions in the division just described. This minimizes the chances that a metal short will affect the circuit driving the “apron” (top metal surrounding the array and covered with LC material) will short to the skirt or any other signals or supplies.
By manufacturing liquid crystal on silicon micro displays in this way, one can avoid problems caused by prior isolation techniques, such as ESD (Electro-Static Discharge) damage to the transparent electrode circuit, shorts to ground, and violation of manufacturing assumptions required for consistent plasma etching of the metal.
REFERENCES:
patent: 5019002 (1991-05-01), Holmberg
patent: 5596451 (1997-01-01), Handschy et al.
patent: 5610738 (1997-03-01), Sasano et al.
patent: 5712528 (1998-01-01), Barrow et al.
patent: 5971538 (1999-10-01), Heffner
patent: 5995071 (1999-11-01), Mertz
patent: 6175394 (2001-01-01), Wu et al.
patent: 0311979 (1989-04-01), None
patent: 0897128 (1999-02-01), None
patent: 0953959 (1999-11-01), None
patent: 0953960 (1999-11-01), None
Lawrence Kren, Associate Editor; “Microdisplays Loom Larger”; Electronic—Machine Design, Apr. 8, 1999; pp. 92, 94, 96, & 98; -http://www.machinedesign.com.
Patrick Mannion; “Microdisplays to Enable Portable, High-Information-Content Viewing”; Power, Packaging & Components—pp. 89, 90, 92, 94 & 96. Aug. 9, 1999.
Lewis Harold Dean
Robson Craig
Sojourner Douglas
Agilent Technologie,s Inc.
Epps Georgia
Lester Evelyn A.
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