Microstructure technology in silicon, quartz, and diamond

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: Microstructure technology can be defined as a set of fabrication processes enabling three-dimensional structures featuring dimensions in the micrometer to millimetre range, with micrometer accuracy. Microstructures can be assembled or manufactured integrated with other structures and/or microelectronics forming complex microsystems.The thesis includes articles presenting different fabrication processes and microstructures in three completely different materials: silicon, quartz, and diamond. Only single crystalline silicon and quartz, and polycrystalline chemical vapour deposited diamond are considered.An introduction is given to the field of microstructure technology in relation to crystal structure and wafer fabrication. Material properties are listed and commented, followed by an overview of relevant fabrication processes.A major part of the thesis is related to silicon. A system based on a capacitive pressure sensor, followed by an electrostatic actuator, both made in single crystalline silicon, are presented. The use of electrodeposited photoresist as a non-planar lithography technique is also demonstrated on silicon aiming at an optoelectronicmodule.Two papers treat fundamental fabrication processes on single crystalline quartz. Experiments and simulation of wet etching in quartz as well as a novel quartz-to-quartz direct wafer bonding technique are presented. The process compatibility of wet etching and quartz direct bonding is demonstrated by a hermetically sealed cavity.A microstructure technology for thick film diamond replicas, using hot filament chemical vapour deposition on microstructured silicon has been developed. Demonstrator structures for different application areas, especially microfluidics, are shown.Finally, the concept of a miniature X-ray source based on field emission is presented. A tentative medical application is discussed and candidate field emission structures in metal, silicon, and diamond are investigated. X-ray spectra from different anode materials have been collected using diamond cold cathodes, thereby providingexperimental verification of the device concept.Silicon is without competition the most mature material for microstructures. The properties of quartz are well known but this material is lagging far behind in the number of fabrication techniques. Diamond is the most recent material to be considered for microstructure technology. Although the possibilities to sculpture diamond are more limited, the extreme material properties are very attractive in many applications.

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