Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-06-02
2001-06-12
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S443000, C524S444000, C524S445000, C524S447000, C524S448000, C524S450000
Reexamination Certificate
active
06245849
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the preparation of ceramic microstructures. More specifically, the invention relates to the fabrication of ceramic components of micron or submicron dimensions using polymer compositions, preferably curable polymer compositions, containing ceramic nanoparticles and lithographically or otherwise patterned molds. The invention pertains to miniaturization and “nanotechnology,” and has utility in many fields, including microelectromechanical system fabrication, semiconductor processing, information storage, medical diagnostics, optics, materials science, and structural engineering.
BACKGROUND
“Nanotechnology” refers to nanometer-scale manufacturing processes, materials and devices, as associated with, for example, nanometer-scale lithography and nanometer-scale information storage. See, for example,
Nanotechnology,
ed. G. Timp (New York: Springer-Verlag, 1999), and
Nanoparticles and Nanostructured Films,
ed. J. H. Fendler (Weinheim, Germany: Wiley-VCH, 1998). Nanometer-scale components find utility in a wide variety of fields, particularly in the fabrication of microelectromechanical systems (commonly referred to as “MEMS”). Such systems include, for example, micro-sensors, micro-actuators, micro-instruments, micro-optics, and the like. Many MEMS fabrication processes exist, and tend to fall into the two categories of surface micro-machining and bulk-micromachining. The latter technique involves formation of microstructuring by etching directly into a bulk material, typically using wet chemical etching or reactive ion etching (“RIE”). Surface micromachining involves fabrication of microelectromechanical systems from films deposited on the surface of a substrate, e.g., from thin layers of polysilicon deposited on a sacrificial layer of silicon dioxide present on a single crystal silicon substrate (this technique is commonly referred to as the “thin film polysilicon process”).
An exemplary surface micro-machining process is known as “LIGA.” See, for example, Becker et al. (1986), “Fabrication of Microstructures with High Aspect Ratios and Great Structural Heights by Synchrotron Radiation Lithography Galvanoforming, and Plastic Moulding (LIGA Process),”
Microelectronic Engineering
4(1):35-36; Ehrfeld et al. (1988), “1988 LIGA Process: Sensor Construction Techniques via x-Ray Lithography,”
Tech. Digest from IEEE Solid
-
State Sensor and Actuator Workshop,
Hilton Head, S.C.; Guckel et al. (1991)
J. Micromech. Microeng.
1: 135-138. A related process is termed “SLIGA,” and refers to a LIGA process involving sacrificial layers. LIGA is the German acronym for X-ray lithography (“lithographie”), electrodeposition (“galvanoformung”) and molding (“abformtechnik”), and was developed in the mid-1970's. LIGA involves deposition of a relatively thick layer of an X-ray resist on a substrate, e.g., metallized silicon, followed by exposure to high-energy X-ray radiation through an X-ray mask, and removal of the irradiated resist portions using a chemical developer. The mold so provided can be used to prepare structures having horizontal dimensions—i.e., diameters—on the order of microns. The technique is now used to prepare metallic microcomponents by electroplating in the recesses (i.e., the developed regions) of the LIGA mold. See, for example, U.S. Pat. Nos. 5,190,637 to Guckel et al. and 5,576,147 to Guckel et al.
While metallic microcomponents are useful in a host of applications, nonmetallic components are obviously desirable as well. Ceramic microcomponents, i.e., microcomponents containing ceramic material (as in a ceramic/polymer composite) or that are entirely ceramic in nature, would clearly be useful in a number of applications, insofar as such materials can provide a host of advantageous properties, including increased toughness, thermal stability, chemical and biological compatibility, magnetism, piezoelectricity, ferroelectricity, photochromism, lasing, etc.
To date, however, no suitable method has been developed for the fabrication of ceramic microstructures. In general, ceramics are extremely difficult to machine, and even the most refined precision manufacturing techniques have failed to provide ceramic components of microscopic dimensions.
SUMMARY OF THE INVENTION
Accordingly, the invention is directed to the aforementioned need in the art and provides a method for making ceramic microstructures, i.e., ceramic components of micron or submicron dimensions.
It is another object of the invention to provide such a method which involves compressing, into a patterned mold, a curable polymer composition comprising a curable binder polymer and ceramic nanoparticles, and curing the polymer.
It is still another object of the invention to provide such a method wherein the patterned mold is a lithographically patterned mold such as a LIGA mold.
It is yet another object of the invention to provide such a method wherein the binder polymer is thermally, chemically or photolytically cured.
It is a further object of the invention to provide a method for making ceramic microstructures which involves compressing, into a patterned mold, a paste comprising an admixture of a binder polymer, ceramic nanoparticles and a solvent for the polymer, and wherein the composition is then hardened by removal of the solvent, e.g., by heating and/or vacuum.
It is still a further object of the invention to provide novel ceramic microcomponents fabricated using the methodology disclosed and claimed herein.
It is an additional object of the invention to provide ceramic microcomponents having an aspect ratio of at least about 20:1.
It is still an additional object of the invention to provide such microcomponents which, as fabricated, are affixed to the surface of a functional substrate such as a silicon wafer.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect of the invention, then, a process for preparing ceramic microstructures is provided which involves compression molding a curable polymer composition in a suitable mold, typically a lithographically patterned mold such as a LIGA mold, wherein the curable polymer composition is comprised of a curable binder polymer and nanoparticles of a ceramic material. The polymer composition is cured, thermally, chemically, photolytically, or otherwise, to provide ceramic microstructures within the voids of the patterned relief surface on the mold that is employed. Following planarization, the elevated segments of the mold are removed, leaving the ceramic microstructures on the substrate surface; at that point, the microstructures can, if desired, be removed from the surface, pyrolyzed to remove any organic material and convert any inorganic material to ceramic material, and sintered. Ceramic components of micron or submicron dimensions can be prepared in this manner. With a LIGA mold, such components may be prepared having high aspect ratios, i.e., greater than about 20:1, preferably greater than about 40:1. In addition, depending on the ceramic material selected, ceramic microstructures can be fabricated with desirable optical, structural, magnetic, piezoelectric or other properties.
In another aspect of the invention, a process is provided for preparing ceramic microstructures which involves initially compression molding a polymer composition in a suitable mold, as above, but wherein the polymeric component of the composition is not subsequently cured. Rather, after compression molding a paste comprising an admixture of a binder polymer, ceramic nanoparticles and a solvent for the polymer, the composition is then hardened by removal of the solvent, e.g., by heating and/or vacuum. Although the composition is hardened by solvent removal and thus forms a ceramic madrix, the binder polymer is not crosslinked, i.e., cured. In this embodiment, then, the binder polymer may or may not b
Chinn Douglas
Morales Alfredo Martin
Zhang Z. John
Cain Edward J.
Reed Dianne E.
Reed & Associates
Sandia Corporation
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