Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-25
2002-10-22
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S189000, 43
Reexamination Certificate
active
06469761
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to microfabrication and integrated circuit techniques and, in particular, to a system and method for microfabricating liquid crystal displays by creating cavities within microfabricated devices and filling the cavities with liquid crystal.
BACKGROUND OF THE INVENTION
Conventional liquid crystal displays (LCDs) include a substrate with a transparent cover connected thereto and disposed thereover. A cavity is formed between the substrate and the transparent cover, and the cavity is filled with liquid crystal. Optical properties of the liquid crystal change as an electric field that is applied across the liquid crystal changes. Therefore, by controlling the electric field appearing across portions of the liquid crystal, the optical properties of the liquid crystal can be changed in order to display information in the form of characters or numbers, for example.
However, many prior art techniques of manufacturing a liquid crystal display individually connect the transparent cover to each substrate. Therefore, production of many substrates in parallel, at the wafer-scale, of liquid crystal displays is hindered. Furthermore, application of a separate transparent cover is subject to error in the thickness uniformity of the liquid crystal material, deriving from imperfect flatness or parallelism of the substrate and cover. Therefore, the process of individually connecting a transparent cover oftentimes requires precise tolerances, which can be difficult to obtain.
Furthermore, in creating conventional liquid crystal displays, as well as many other types of microfabricated devices, a sacrificial layer is oftentimes deposited and then later removed through conventional microfabrication techniques, such as etching. The deposition and later removal of the sacrificial layer enables cavities or other hollow areas to be formed during the manufacturing process.
One prior art method for forming hollow areas within microfabricated devices includes the step of forming a porous material to encapsulate sacrificial material. The porous material includes many thousands of tiny holes that allow gases to pass through the porous material. Oxygen or an oxygen-plasma is allowed to move through the porous material, thereby vaporizing the sacrificial layer when the device is exposed to high temperatures (e.g., greater than 100 degrees Celsius). The gaseous sacrificial material egresses through the pores of the porous material leaving a hollow area where the sacrificial material once resided. The opening is usually plugged during a subsequent deposition step in order to seal the microfabricated device.
However, this type of technique for removing a sacrificial layer through a porous material requires the extra steps of exposing the device to oxygen plasma. The exposure of the device to oxygen-plasma can be potentially damaging to other elements of the device. Furthermore, the process of forming a suitable porous material can be difficult, since thousands of tiny holes need to be formed in order to develop a porosity sufficient for allowing sacrificial material to escape. Furthermore, as the porosity of the material is increased, the mechanical stability of the material is typically decreased. Therefore, manufacturing a sufficiently porous material that can withstand the high pressures associated with dissipating sacrificial material can be very difficult and costly.
Due to many difficulties, including the difficulties of forming cavities for liquid crystal displays, prior art techniques of manufacturing liquid crystal displays are inefficient and do not usually integrate liquid crystal displays onto a single substrate where mechanical components, such as the covers mentioned hereinbefore, are not separately attached. Thus, a heretofore unaddressed need exists in the industry for providing a system and method to efficiently microfabricate a fully integrated liquid crystal display.
SUMMARY OF THE INVENTION
The present invention overcomes the inadequacies and deficiencies of the prior art as discussed herein. The present invention provides a system and method for efficiently microfabricating a fully integrated liquid crystal display.
The present invention utilizes a base, a conductive pad, permeable material, liquid crystal, a contact and a transparent conductor. The conductive pad is formed on the base, and the permeable material is formed on sacrificial material, which is configured to dissolve into and dissipate through the permeable material when the sacrificial material is heated. Liquid crystal is formed in the cavity which is between the conductive pad and permeable material. The transparent conductor is formed such that the liquid crystal resides between the transparent conductor and the conductive pad. The transparent conductor is coupled to a voltage contact, and the voltage difference between the transparent conductor and the conductive pad creates an electric field that appears across the liquid crystal. By varying the electric field applied across the liquid crystal, the optical properties of the liquid crystal can be changed in order to change the appearance of the liquid crystal to an observer.
In accordance with another feature of the present invention, the sacrificial material is preferably formed on the conductive pad and on exposed portions of the base prior to formation of the permeable material. The sacrificial material is preferably patterned in order to expose portions of the base. Once the permeable layer is formed, the sacrificial material is preferably dissipated through the permeable material in order to form a cavity. The cavity is then filled with the liquid crystal.
The present invention can also be viewed as providing a method for microfabricating a liquid crystal display. Briefly described, the method can be broadly conceptualized by the following steps: forming a conductive pad on a base; forming sacrificial material on the pad; patterning the sacrificial material to expose a portion of the base; forming permeable material on the sacrificial material and the exposed portion of the base; dissipating the sacrificial material through the permeable material in order to form a cavity; filling the cavity with liquid crystal; forming a transparent conductor; and creating a voltage difference between the transparent conductor and the conductive pad to apply an electric field across the liquid crystal.
The present invention has many advantages, a few of which are delineated hereafter, as mere examples.
An advantage of the present invention is that liquid crystal displays can be microfabricated on a wafer-scale.
Another advantage of the present invention is that liquid crystal displays can be efficiently microfabricated.
Another advantage of the present invention is that liquid crystal displays can be efficiently microfabricated without forming a multitude of openings to allow sacrificial material to dissipate.
Another advantage of the present invention is that cavities within liquid crystal displays can be formed and filled with liquid crystal with only one hole punctured into the liquid crystal display.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following detailed description, when read in conjunction with the accompanying drawings. It is intended that all such features and advantages be included herein within the scope of the present invention, as is defined by the claims.
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Drabik Timothy J.
Kohl Paul A.
Chung David
Georgia Tech Research Corp.
Thomas Kayden Horstemeyer & Risley
Ton Toan
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