Fabrication of ceramic microstructures from polymer compositions containing ceramic nanoparticles

A method is provided for fabricating ceramic microstructures, i.e., microcomponents of micron or submicron dimensions. A polymer composition is prepared containing a polymer, typically a thermally or chemically curable polymer, and nanometer size (1 to 1000 nm in diameter) ceramic particles. A mold, such as a lithographically patterned mold, preferably a LIGA mold, is filled with the polymer composition and the polymer is then cured or otherwise hardened. The elevated segments of the mold are then removed. The surface-attached ceramic microstructures so provided may then be removed from the substrate and, if desired, pyrolyzed and sintered.

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 be a
 curable polymer as such.
 In a further aspect of the invention, a process is provided for preparing
 ceramic microstructures that are permanently locked in place on a
 substrate surface, i.e., are mechanically locked thereon, eliminating the
 need for adhesives or other fastening means. The method involves curing
 and/or hardening a polymer composition comprising ceramic nanoparticles,
 as described above, using a substrate having one or more recesses in which
 the interior diameter or width of the recess is smaller on the substrate
 surface and larger within the substrate interior (as in a dovetail
 recess), such that a ceramic component fabricated therein cannot be
 mechanically extracted from the substrate surface. In some cases, it may
 be advantageous for the locked-in microstructure to be free to rotate
 about a central axis. This may be readily accomplished by deposition of a
 decomposable or otherwise removable release layer on the substrate
 surface, including on the interior of the surface recess or recesses,
 prior to fabrication of the ceramic microstructure. The release layer is
 removed following microstructure fabrication, leaving a gap between the
 substrate surface, including the interior surface of the recess or
 recesses, and the exterior of the newly fabricated microstructure.
 In an additional aspect of the invention, certain ceramic microstructures
 are prepared as novel compositions of matter. The novel ceramic
 microstructures comprise a compressed solid of (1) a matrix of a cured or
 hardened polymer, and (2) ceramic nanoparticles dispersed throughout the
 matrix, wherein the aspect ratio of the microstructure is greater than
 about 20:1, preferably greater than about 40:1.

DETAILED DESCRIPTION OF THE INVENTION
 Definitions:
 It is to be understood that unless otherwise indicated, this invention is
 not limited to specific materials (e.g., specific polymers or ceramic
 materials), processing conditions, manufacturing equipment, or the like,
 as such may vary. It is also to be understood that the terminology used
 herein is for the purpose of describing particular embodiments only and is
 not intended to be limiting.
 It must be noted that, as used in the specification and the appended
 claims, the singular forms "a," "an" and "the" include plural referents
 unless the context clearly dictates otherwise. Thus, for example,
 reference to "a curable polymer" includes mixtures of curable polymers,
 reference to "a ceramic material" includes mixtures of ceramic materials,
 and the like.
 The term "ceramic material" is used to refer to material that contains
 ceramic material or is wholly ceramic in nature, wherein the term
 "ceramic" is used in its conventional sense to indicate a nonmetallic,
 inorganic material such as a metal oxide. Thus, the term "ceramic
 materials" as used herein encompasses composites, containing both ceramic
 and nonceramic material, as well as materials that are entirely ceramic
 and do not contain any nonceramic material.
 The term "polymer" is used herein in its conventional sense to refer to a
 compound having two or more monomer units, and is intended to encompass
 homopolymers as well as copolymers, including, for example, graft
 copolymers. Those polymers herein that are referred to as "curable" are
 capable of becoming crosslinked, either thermally, chemically or
 photolytically, so that a cured polymeric matrix may be provided.
 The terms "microstructure" and "microcomponent" are used interchangeably
 herein to refer to a three-dimensional solid structure whose height, width
 (or diameter) or length is less than about 100 microns, i.e., at least one
 dimension of the three-dimensional structure is less than about 100
 microns.
 The term "aspect ratio" is used herein in its conventional sense to refer
 to the ratio of an object's height to its width (or diameter). High aspect
 ratio structures are thus prepared using molds (such as LIGA molds) having
 very voids, or recesses, that are extremely narrow relative to their
 height.
 "Optional" or "optionally" means that the subsequently described
 circumstance may or may not occur, so that the description includes
 instances where the circumstance occurs and instances where it does not.
 For example, the phrase "optionally sintered" means that a material may or
 may not be sintered, and the description thus includes sintered materials
 as well as nonsintered materials. Similarly, a microstructure fabrication
 method or system that includes an "optionally present" release layer
 encompasses methods and systems that make use of a release layer as well
 as methods and systems that do not make use of a release layer.
 Preparation of Ceramic Microstructures:
 The invention thus features a process for preparing ceramic microstructures
 which involves, initially, providing a substrate having a patterned relief
 structure on its surface to serve as a mold, wherein the microstructures
 are to be formed within the recesses present within the pattern, i.e.,
 around and between corresponding elevated segments on the substrate
 surface. The mold is filled with a curable polymer composition containing
 ceramic nanoparticles and a curable binder polymer, and external pressure
 is applied to press the composition into the mold. The polymer composition
 is then cured to provide a hardened ceramic material, i.e., the "ceramic
 microstructures," in the recesses of the mold. Preferably, the surface is
 then planarized. At this point, the elevated segments of the mold can be
 removed, leaving the ceramic microstructures on the substrate surface. If
 desired, the ceramic microstructures can then be removed from the surface
 as well. In an alternative embodiment, the binder polymer is not
 necessarily cured or curable. Rather, a paste is formed comprising ceramic
 nanoparticles, binder polymer and solvent, and following compression of
 the paste into the recesses of the mold, the solvent is removed under
 vacuum and/or by heating, to harden but not cure the polymer.
 The mold is typically although not necessarily a lithographically patterned
 mold, prepared, for example, using optical, X-ray, electron-beam, or
 ion-beam methods, but preferably fabricated using LIGA technology. As will
 be appreciated by those skilled in the art, preparation of a LIGA mold
 involves deposition of a layer of an X-ray resist on a substrate having a
 conductive surface, which may or may not be pretreated with an
 adhesion-promoting layer such as a metal oxide (e.g., oxides of titanium
 and/or copper) or with a silanization reagent such as methacryloxypropyl
 trimethoxysilane, to facilitate adhesion of the resist to the substrate
 surface. Metallized silicon is a preferred substrate.
 Suitable X-ray resists may comprise, for example, poly(methyl methacrylate)
 ("PMMA") or copolymers thereof such as poly(methyl
 methacrylate-co-t-butylmethacrylate), a poly(lactide) such as
 poly(lactide-co-glycolide), polymethacrylamide, polyoxymethylene,
 polyalkenesulfone, or poly(glycidylmethacrylate-co-ethyl acrylate). The
 resist is deposited using any of a number of conventional techniques,
 e.g., sequential spin coating or the like. The deposited resist is
 irradiated using X-ray radiation, such as from a synchrotron, and an X-ray
 mask to provide the desired mold pattern. Following exposure, the resist
 is developed using a suitable solvent to remove the irradiated areas. The
 resulting mold, then, is comprised of a substrate having a patterned
 relief structure on the substrate surface comprised of elevated segments
 (i.e., the undeveloped resist) with corresponding voids therebetween. In a
 preferred embodiment, the remaining surface is treated so that removal of
 ceramic microstructures fabricated thereon is facilitated; suitable
 surface treatments include, but are not limited to, polishing, application
 of a low adhesion coating comprised of a material-releasing agent such as
 poly(tetrafluoroethylene), silicones, waxes or the like, and deposition of
 a decomposable or otherwise removable release layer (as may also be termed
 a "sacrificial" layer) such as a poly(methyl methacrylate).
 The molds that can be used in conjunction with the present invention may
 also be fabricated using other techniques, as alluded to above. LIGA molds
 are preferred, however, insofar as such molds can be prepared so as to
 have very high aspect ratios, and can thus provide high aspect ratio
 ceramic microstructures. The the aspect ratio of the ceramic
 microstructures prepared herein, using LIGA molds, can be 20:1 or even
 40:1 or higher.
 After the mold is fabricated or otherwise obtained, a polymer composition
 is prepared comprising a binder polymer and ceramic nanoparticles.
 Preferred binder polymers are curable, and include thermally curable
 polymers, chemically curable polymers, and photolytically curable
 polymers. If a thermally curable polymer is used, the temperature to which
 the polymer composition is heated, during microcomponent fabrication, is
 kept to the minimum necessary to bring about cure, so as to avoid
 deformation of the mold and shrinkage. If a chemically curable polymer is
 used, an appropriate curing agent is typically required. Binder polymers
 useful in conjunction with the invention include, but are not limited to:
 vinyl and acrylic polymers such as poly(vinyl alcohol), poly(vinyl amine),
 poly(vinyl acetate), poly(vinyl halides) including poly(vinyl chloride)
 and poly(vinyl fluoride), poly(vinylidene halides) including
 poly(vinylidene chloride) and poly(vinylidene fluoride), polystyrene,
 poly(o-bromostyrene), poly(m-methylstyrene), poly(p-methylstyrene),
 poly(o-hydroxystyrene), poly(m-hydroxystyrene), poly(p-hydroxystyrene),
 poly(vinyl phosphate), poly(vinyl pyrrolidone), poly(methyl vinyl ether),
 poly(ethyl vinyl ether), poly(methyl vinyl ketone), poly(acrylonitrile),
 vinyl-pyrrolidone-vinyl acetate copolymers, vinyl acetate-acrylic acid
 copolymers, vinyl alcohol-vinyl acetate copolymers, vinyl
 pyrrolidone-styrene copolymers, poly(acrylic acid), poly(acrylamide),
 poly(methacrylic acid), poly(methyl acrylate), poly(ethyl acrylate),
 poly(butyl acrylate), poly(acrylonitrile-acrylic acid),
 poly(styrene-acrylic acid), poly(butadiene-acrylonitrile acrylic acid),
 poly(butylacrylate-acrylic acid), poly(methyl methacrylate), poly(ethyl
 methacrylate), poly(ethyl acrylate-acrylic acid),
 poly(methacrylate-acrylic acid), poly(methyl methacrylate-acrylic acid)
 and poly(methyl methacrylate-styrene-acrylic acid); silicone resins such
 as polyhydridosiloxane, poly(methylsiloxane), poly(dimethylsiloxane),
 poly(ethylsiloxane), poly(diethylsiloxane), poly(phenylsiloxane),
 poly(methylphenylsiloxane), poly(ethylphenylsiloxane) and
 poly(diphenylsiloxane); other inorganic, preferably silicon-containing,
 polymers such as polysilazanes and polysiloxazanes; epoxy resins, i.e.,
 polymers formed by step polymerization of an epoxide such as
 epichlorohydrin and a dihydroxy compound, wherein suitable dihydroxy
 compounds include bisphenol A (2,2-bis(4-hydroxyphenyl)propane),
 hydroquinone, resorcinol, novolacs, and the like; polyesters such as
 poly(ethylene terephthalate), poly(butylene terephthalate), poly(lactic
 acid), and copolymers of substituted and/or unsubstituted styrene monomers
 and ester moieties; polyethers such as polyacetal, poly(ethylene glycol),
 poly(oxyethylene), poly(oxypropylene) and poly(tetrahydrofuran); and
 copolymers and blends of any of the foregoing.
 The ceramic nanoparticles may be obtained commercially (e.g., from TPL
 [Technologies to Products], Albuquerque, N. Mex.; Materials Modification,
 Incl, Fairfax, Va.; and Nanophase Technologies Corporation, Burr Bridge,
 Ill.) or fabricated using techniques known to those skilled in the art
 and/or described in the pertinent texts and literature (see, e.g., R. A.
 Andrievsky (1998), "State-of-the-Art and Perspectives in the Field of
 Particulate Nanostructured Materials," J. Mater. Sci. Technol. 14:97-103).
 Generally, the nanoparticles will be approximately 1 to 1000 nm in
 diameter, preferably 1 to 500 mn in diameter, and most preferably 1 to 100
 nm in diameter. Typical ceramic materials used in conjunction with the
 invention include: metal oxides such as Al.sub.2 O.sub.3, ZrO.sub.2,
 TiO.sub.2, ZnO, SiO.sub.2, BaTiO.sub.3, BaZrO.sub.3, SrTiO.sub.3,
 WO.sub.2, WO.sub.3, Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Ca.sub.5
 (PO.sub.4)OH, MnFe.sub.2 O.sub.4, PbZr.sub.0.5 Ti.sub.0.5 O.sub.3,
 BaFe.sub.12 O.sub.19, CrO.sub.2, Cr.sub.2 O.sub.3, MoO.sub.2 and MoO.sub.3
 ; silicon-containing ceramics such as SiC, Si.sub.3 N.sub.4 and Si.sub.2
 ON.sub.2 ; aluminum nitride; tungsten carbide; samarium cobalt
 (SmCo.sub.5); neodymium iron boride (NdFeB); TiC; TiN; MoSe.sub.2 ;
 MoSe.sub.3 ; MoS.sub.2 ; and MoS.sub.3. Any ceramic material can be used,
 and the process of the invention is not in any way limited with regard to
 a specific ceramic material or materials. However, as certain ceramic
 materials can provide a specific function in a particular context, the
 context may dictate choice of material. That is, when the final ceramic
 microstructure is to be magnetic, a magnetic ceramic material such as
 MnFe.sub.2 O.sub.4 is used, when a piezoelectric ceramic microstructure is
 desired, a piezoelectric ceramic material such as PbZr.sub.0.5 Ti.sub.0.5
 O.sub.3 or BaFe.sub.12 O.sub.19 is used, etc. The following table sets
 forth preferred ceramic materials according to their properties and the
 intended function of the ceramic microstructure:
 TABLE 1
 Intended Function Class Ceramic Material
 Magnetic Soft MnFe.sub.2 O.sub.4
 Hard SmCo.sub.5, NdFeB
 Electrical Insulation Al.sub.2 O.sub.3
 Piezoelectric PbZr.sub.0.5 Ti.sub.0.5 O.sub.3,
 BaFe.sub.12 O.sub.19
 Ferroelectric BaTiO.sub.3, SrTiO.sub.3
 Optical Transparent Al.sub.2 O.sub.3
 Photochromism MoO.sub.3, WO.sub.3
 Mechanical Refractory Al.sub.2 O.sub.3, SiC, Si.sub.3 N.sub.4
 Wear-Resistant Al.sub.2 O.sub.3, SiC, Si.sub.3 N.sub.4,
 ZrO.sub.2
 Cutting Al.sub.2 O.sub.3, ZrO.sub.2, Si.sub.3
 N.sub.4
 Lubrication MoS.sub.2
 Thermal Insulation Al.sub.2 O.sub.3, ZrO.sub.2, SiO.sub.2
 Radiator ZrO.sub.2, TiO.sub.2
 Chemical Gas Sensor ZnO, ZrO.sub.2, Fe.sub.2 O.sub.3
 Filters SiO.sub.2, Al.sub.2 O.sub.3
 Biological Biocompatible Ca.sub.5 (PO.sub.4).sub.3 OH
 The ceramic nanoparticles generally represent on the order of 5 wt. % to 95
 wt. % of the polymer composition, preferably about 15 wt. % to 90 wt. % of
 the composition, while the polymeric component per se typically represents
 about 5 wt. % to 95 wt. %, preferably about 5 wt. % to 30 wt. % of the
 composition, and the remainder of the polymer composition is comprised of
 solvent. The solvent is such that the binder polymer dissolves therein; a
 preferred solvent is water, but lower alkanols (C.sub.1 -C.sub.6 alkanols,
 preferably C.sub.1 -C.sub.4 alkanols) such as ethanol, isopropanol and the
 like may be also used. The polymer composition is typically prepared by
 simple admixture of the components, with the solvent added last in an
 amount sufficient to provide the composition in the form of a paste of a
 desired viscosity, suitable for application to the mold described above.
 The polymer composition may contain other components as well, such as
 additional binder polymers, catalysts, metal powders, flexibilizers,
 surfactants, nanoparticle surface modifying primers, etc.
 The polymer composition so prepared is then applied to the mold, and
 pressure is applied to ensure that the mold is completely filled.
 Typically, the applied pressure is at least about 1000 lb/in.sup.2,
 preferably at least about 5000 lb/in.sup.2. For compositions containing
 thermally curable polymers, heat is applied along with pressure, such as
 by using a combined hydraulic press and heater. The heating temperature
 and time will depend on the polymer used, but generally temperatures
 higher than about 50.degree. C., more typically higher than about
 70.degree. C., are employed, with heating times of 30 minutes or more. For
 photolytically curable polymers, the applied polymer composition is
 irradiated with light of a suitable wavelength (e.g., ultraviolet light)
 rather than heated. In some cases, i.e., with some curable polymers,
 irradiation with an electron beam is particularly effective in bringing
 about curing. For chemically curable polymers, a curing agent is present
 in the polymer composition that brings about curing during the compression
 step. With binder polymers that are not cured and are not necessarily
 curable, heating temperature and time are selected simply to effect
 solvent removal; solvent may also be removed by vacuum, instead of or in
 addition to heating. Solvent removal results in a hardened ceramic
 composition.
 Following compression, the mold surface is planarized using conventional
 equipment and techniques to remove excess polymer composition. The
 elevated segments of the mold are then removed, e.g., by stripping with a
 suitable solvent or ashing in an oxygen plasma. If one or more sacrificial
 mold release layers is present on the substrate surface (e.g., formed from
 poly(methyl methacrylate) or the like), the elevated mold segments and
 newly formed ceramic microcomponents can be freed from the substrate
 surface by removal of the sacrificial layer or layers; see, e.g., U.S.
 Pat. No 5,576,147 to Guckel et al., cited earlier herein. The
 surface-attached ceramic microcomponents can also be removed mechanically.
 Alternatively, the ceramic microcomponents may, if desired, be retained on
 the substrate on which they are fabricated. The process is thus
 advantageous in those contexts where microcomponents would otherwise need
 to be affixed to a substrate surface.
 The microstructures prepared as just described will comprise a cured or
 hardened polymer, and, dispersed therein, ceramic material deriving from
 the ceramic nanoparticles. Such a structure is in effect a "composite,"
 i.e., an admixture of a ceramic material and a nonceramic material. If
 desired, the composite microstructures can be subjected to a pyrolysis
 step to remove organic material and convert all inorganic material present
 to ceramic material. Pyrolysis may be conducted on the substrate, or,
 alternatively, the free, i.e., removed, microstructures may be pyrolyzed.
 Pyrolysis temperatures are generally in the range of about 300.degree. C.
 to 700.degree. C., preferably in the range of about 400.degree. C. to
 600.degree. C. Generally, although not necessarily, pyrolysis is conducted
 in an oxygen-containing atmosphere. The microstructures may also be
 sintered, i.e., heated to a temperature of at least about 1200.degree. C.,
 preferably at least about 1500.degree. C., with the preferred temperature
 typically approximating 75% of the melting temperature of the ceramic
 body. As will be appreciated by those skilled in the art, sintering is
 carried out to bring about densification and grain growth of the ceramic
 material.
 The method of the invention is illustrated schematically in FIG. 1, where
 the patterned mold is shown generally at 10, comprised of substrate 12 and
 voids 16 between corresponding elevated segments 18. The polymer
 composition, having been introduced into the mold and the mold then
 planarized, is shown at 20. Following curing and/or hardening of the
 polymer composition and subsequent removal of the elevated segments, a
 substrate having ceramic microstructures 20 affixed thereto is provided,
 indicated at 22.
 A preferred variation on the aforementioned method is illustrated in FIG.
 2, wherein substrate 12 is provided with an overlying decomposable or
 otherwise removable release layer 14 as may be formed, for example, from
 poly(methyl methacrylate). As in the method of FIG. 1, the polymer
 composition comprised of a binder polymer, ceramic nanoparticles and
 solvent is compression molded into the surface recesses or "voids"
 indicated at 16, between corresponding elevated segments 18. Following
 curing and/or hardening of the polymer composition and subsequent removal
 of the elevated segments, surface-bound ceramic microstructures are
 provided in which the microstructures 20 are affixed to release layer 14.
 The microstructures may be removed from the substrate surface, e.g.,
 mechanically, chemically, and/or by removal of the release layer 14. A
 poly(methyl methacrylate) release layer can be removed, for example, by
 immersion in a PMMA solvent such as acetone.
 In an alternative embodiment, ceramic microcomponents are prepared that are
 permanently affixed to a substrate. This process is illustrated in FIG. 3.
 Initially, substrate 24 is etched, using either chemical or plasma
 etching, to provide a dovetail-shaped recess 26. A sacrificial filling 28
 is introduced into recess 26, followed by application of a photoresist
 layer 30. The photoresist is patterned using conventional means, i.e., is
 irradiated through a mask and subsequently developed, to provide elevated
 resist segments 32. The sacrificial filling 28 in dovetail recess 26 is
 then removed, leaving a mold consisting of the elevated resist segments
 32, voids 34 therebetween, and dovetail recess 26. A polymer composition
 as prepared herein, containing ceramic nanoparticles and a binder polymer,
 is introduced into the mold, pressure is applied and the composition is
 cured and/or hardened as described previously, resulting in ceramic
 microstructure 36. Removal of elevated resist segments 32 results in a
 substrate having ceramic microstructure 36 "locked in" to the substrate
 surface, as shown in the figure. A given substrate may have more than one
 recess, such that two or more ceramic microstructures can be prepared
 simultaneously.
 A variation on the aforementioned method is illustrated schematically in
 FIG. 4. In this alternative method, the final microstructure is also
 locked in to the substrate surface as a result of having been fabricated
 in a dovetail-shaped recess; however, a gap between the finished
 microstructure and both the substrate surface and the interior of the
 recess allows the microstructure to rotate about a central axis. This is
 accomplished by deposition of a release layer 38 prior to filling the
 recess with the polymer composition. As may be seen in the figure, the
 release layer is present throughout microstructure fabrication, and is
 removed along with or subsequent to dissolution of the photoresist.
 Removal of the release layer 38 results in a gap 40, resulting in a
 locked-in microstructure that is free to rotate about a central axis,
 while maintained in place on the substrate surface.
 The processes of the invention thus provide ceramic microstructures, i.e.,
 ceramic components having micron or submicron dimensions. The present
 method is readily scaled up to provide a viable manufacturing process for
 fabricating ceramic microstructures. The method makes use of available
 equipment and commonly used reagents and materials, and involves
 relatively mild processing conditions (e.g., relatively low temperatures
 are need to cure most "thermally curable" polymers). The invention is
 useful in a host of applications and technical fields, including MEMS
 fabrication and semiconductor processing, information storage, medical
 diagnostics, optics, and the manufacture of structural materials.
 It is to be understood that while the invention has been described in
 conjunction with the preferred specific embodiments thereof, that the
 foregoing description as well as the examples which follow are intended to
 illustrate and not limit the scope of the invention. Other aspects,
 advantages and modifications within the scope of the invention will be
 apparent to those skilled in the art to which the invention pertains.
 All patents, patent applications, and publications mentioned herein are
 hereby incorporated by reference in their entireties.
 Experimental:
 The following examples are put forth so as to provide those of ordinary
 skill in the art with a complete disclosure and description of how to
 carry out the method of the invention. Efforts have been made to ensure
 accuracy with respect to numbers (e.g., quantities, temperature, etc.) but
 some errors and deviations should be accounted for. Unless indicated
 otherwise, parts are parts by weight, temperature is in .degree.C. and
 pressure is at or near atmospheric. Additionally, all starting materials
 were obtained commercially or synthesized using known procedures.
 EXAMPLE 1
 This example describes preparation of Al.sub.2 O.sub.3 microstructures
 using poly(vinyl alcohol) and poly(acrylic acid) as binder polymers.
 An aqueous slurry of Al.sub.2 O.sub.3 nanoparticles was prepared with 1.36
 g Al.sub.2 O.sub.3, 201 mg poly(vinyl alcohol), 22 mg poly(acrylic acid)
 and 10.05 g water. An SEM photograph of the starting material (FIG. 5)
 shows the individual grains of Al.sub.2 O.sub.3, tending to aggregate into
 chains. Initially, the water and polymers were admixed and placed in a
 74.degree. C. oven for one hour; the Al.sub.2 O.sub.3 was then added and
 the solution was stirred. The mixture was returned to the oven for 40
 minutes, stirred again, and then placed in a 100.degree. C. oven for one
 hour. As some of the water had evaporated, a paste formed. The paste was
 pressed into a PMMA mold fabricated using LIGA technology, having a groove
 pattern with groove width of 40 microns and depth of 500 microns. 5000
 lbs/in.sup.2 pressure was applied using a Carver hydraulic laboratory
 press. To eliminate the remaining water from the polymer composition, the
 mold was heated to 100.degree. C. for thirty minutes, and then, to
 pyrolyze the PMMA mold and the polymer binder, the sample was heated to
 500.degree. C. for forty-five minutes. Subsequently, to sinter the
 microstructure, the mold was heated to 1130.degree. C. for 6 hours. The
 resulting ceramic microstructures were approximately 400 microns in
 height, and 35 microns wide; FIG. 6 is an optical micrograph of the grid
 pattern of the microstructures formed (the scale bar on the figure is 100
 microns). The microstructures were removed mechanically by shearing off of
 the substrate surface, and a TEM photograph of the fractured product shows
 the nanometer size ceramic grains (FIG. 7).
 EXAMPLE 2
 This example describes preparation of magnetic ceramic microstructures
 using an epoxy resin as a binder polymer.
 A paste of MnFe.sub.2 O.sub.4 nanoparticles was prepared with 2.99 g
 MnFe.sub.2 O.sub.4 and 1.53 g epoxy formulation (prepared by mixing 50 g
 Epon 862 epoxy resin, 5 g "736" flexibilizer, and 16 g D230 curing agent).
 FIG. 8 is an SEM photograph of the starting material, and individual
 grains of MnFe.sub.2 O.sub.4, 5 nm or less in diameter, can be seen. The
 paste was pressed into a cylindrical PMMA mold on a metallized silicon
 substrate, and 9000 lbs/in.sup.2 pressure was applied using a Carver
 hydraulic laboratory press. The mold was heated to 140.degree. F. for five
 hours, allowed to cool, and immersed in acetone to dissolve the PMMA. The
 ceramic microparts so prepared were then sheared off of the substrate
 surface. FIGS. 9, 10, 11 and 12 are SEM photographs of the microparts,
 magnified 25.times., 75.times., 100.times. and 200.times., respectively,
 and illustrate the sharp edges of the product. FIG. 13 is a high
 resolution (50,000.times.) SEM photograph of the product illustrating the
 nanometer size MnFe.sub.2 O.sub.4 grains therein.