Through-wafer 3-D micromachining and its applications for neural interfaces and microrelays

Citation

Wright, John A. (1999) Through-wafer 3-D micromachining and its applications for neural interfaces and microrelays. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/g4sj-2q41. https://resolver.caltech.edu/CaltechETD:etd-11092006-110012

Abstract

The relatively new field of Micro Electro Mechanical Systems (MEMS) is proving to be a very powerful technology capable of producing devices beneficial to a wide range of disciplines. Instruments once impossible to fabricate can now made with relative ease opening up new possibilities in experimental research as well as commercial applications. Through-wafer, 3-D micromachining techniques used to produce two families of such devices are presented. A functional silicon micromachined device that permits non-invasive, bi-directional, highly specific communication with cultured mammalian neurons is discussed. The mechanical and electrical nature of the system is reported and experimental data presented. In arriving at the present design, an iterative approach was used to create a structure that allows normal growth of neurons and permits the formation of functional neural networks while preventing cell body escape. The set of low-temperature (< 400°C) fabrication steps that have been used to develop two types of magnetically actuated MEMS relays are presented. Designed to be potentially compatible with CMOS substrates, the fabrication uses thick electroplated metal films (> 10 µm) including Au, Cu and Ni80Fe20, and insulating material deposited at low temperatures. Millinewton force, variable-reluctance actuators have been realized with this technology and used as the basis of a miniature electromagnetic relay. Prototypes utilize > 5 µm contact gaps and produce 200 µN of force with a coil power of only 320 mW. Initial electrical tests show contact resistances of less than 1°. For a second application, magnetostatic relays have been designed to commutate miniature DC brushless motors. Large contact closure forces (> 5 mN) are generated to produce contact resistance of less than 35 milliohms. Commutation of a three-phase, four-pole DC brushless motor by three of the MEMS relays has been successfully demonstrated.

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