Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
1999-01-08
2001-05-22
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S347000
Reexamination Certificate
active
06236061
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor materials deposited and crystallized using a pulsed laser source on oxide and/or metal layers on polymeric and polymer composite substrates of low coefficient of thermal expansion (CTE). Applications related to such an invention are also addressed.
BACKGROUND OF THE INVENTION
New technology to fabricate semiconductor films on polymer substrates are needed in electronic industry for many applications. Semiconductor materials are particularly useful, if they can be crystallized with good structural integrity on polymer substrates so that the films can be used to function in electronic circuits, light detectors, light emitting diodes (LED), thin film transistors (TFT), CMOS and SRAMS. These have a variety of end uses as for example solar cells, display devices and electronic circuits.
One approach to making crystallized semiconductor films on any substrate is to deposit the semiconductor film on the substrate and anneal the semiconductor film using a pulsed laser source. Many have used laser annealing to achieve low temperature processing in making thin film transistors on glass substrates. See for example Kyung Ha Lee et al., IEEE Electron Device Lett. 17, 258 (1996). On polymer substrates this approach is difficult because the laser can heat the polymer substrate and damage both the polymer/semiconductor interface and the semiconductor film even when thermally insulating layers are introduced in between the polymer substrate and the semiconductor film. The polymer substrate must also be stable to changes in ambient moisture (humidity) and temperature. Resistance to elevated temperatures, as well as high mechanical strength, impact resistance and chemical resistance are also all desirable.
Various prior techniques for improving the crystallinity of semiconductor films by laser annealing and doping the films are exemplified by U.S. Pat. No. 4,059,461 issued Nov. 22, 1977 to J. C. C. Fan et al.; U.S. Pat. No. 4,309,225 issued Jan. 5, 1982 to J. C. C. Fan et al.; U.S. Pat. No. 4,400,715 issued Aug. 23, 1983 to S. G. Barbes et al.; U.S. Pat. No. 4,719,183 issued Jan. 12, 1988 to M. Maekawa; U.S. Pat. No. 4,751,193 issued Jun. 14, 1988 to J. J. Myrick, U.S. Pat. Nos. 5,346,850 issued Sep. 13, 1994 and 5,538,564 issued Jul. 23, 1996 to J. L. Kaschmitter et al. Various prior techniques for reducing the polymer substrate CTE are exemplified by U.S. Pat. No. 5,552,210 issued Sep. 1996 to Horn et al.; and U.S. Pat No. 5,739,193 issued Apr. 14, 1998 to Walpita et al.
In these prior developments and research efforts laser annealing have been done to improve crystallinity of crystalline or amorphous semiconductors, particularly silicon, deposited on insulator films on substrates such as PET, PES, PTFE at a range of processing temperatures from room temperature to 180° C. Semiconductor films deposited and laser annealed on deposited films of metal and oxide on these plastics does not retain film integrity under temperature cycling and during use over short and long time periods because large mismatch of the coefficient of thermal expansion (CTE) between the deposited films and the plastic substrates in the operating temperature ranges. Therefore the laser annealing technologies can not be effectively utilized for plastic substrates in practical applications.
The present invention permits the fabrication of inexpensive yet highly efficient electronic devices, such as photovoltaic cells, on the filled substrates by the use of laser annealing techniques.
SUMMARY OF THE INVENTION
The present invention overcomes the problem of CTE mismatch by reducing the difference in CTE of the deposited film and the substrate by introducing filler into the substrate. A filled polymeric substrate which has a low CTE is made by mixing a polymer of high thermal coefficient of expansion and fillers of low thermal coefficient of expansion and molding them into articles at above polymer melt temperature. One way of making such a substrate is melt extruding the mixed composition into strands and cutting the strands into pellets. Pellets so made are fed into a molding machine to form films, sheets or other shapes. The mixed composition can also be compressed molded or extruded into films, sheets or other shapes. One or two layers of thermally or electrically insulating or non insulating layers are deposited onto the surface of films, sheets and/or other shapes by standard vacuum techniques or laminated by thermal compression or during molding processes. Layers of semiconductors are further deposited onto the deposited layers by standard vacuum techniques and laser annealed selectively. Layers of oxide and/or metal are further deposited on to the semiconductor layers by standard vacuum techniques. All insulating, non-insulating, and semiconductor layers can be patterned before or after laser annealing.
It is the object of the present invention to provide a method or a process of fabricating crystallized semiconductor film on a metal and/or oxide film on a polymer substrate which will retain film integrity without cracks.
It is another object of the invention to provide examples of devices; such as solar cells and light emitting diodes
REFERENCES:
patent: 4059461 (1977-11-01), Fan et al.
patent: 4309225 (1982-01-01), Fan et al.
patent: 4400715 (1983-08-01), Barbee et al.
patent: 4719183 (1988-01-01), Maekawa
patent: 4751193 (1988-06-01), Myrick
patent: 5538564 (1996-07-01), Kaschmitter
patent: 5552210 (1996-09-01), Horn, III et al.
patent: 5739193 (1998-04-01), Walpita et al.
Botjer William L.
Meier Stephen D.
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