Method and instrumentation for the measurement and characterization of MEMS fabricated electrical contacts

Abstract

MEMS fabricated electrical contacts consist of two MEMS fabricated surfaces which are physically separated and brought together for the purpose of carrying current. MEMS fabricated electrical contacts are used in a wide variety of applications including MEMS relays, wafer probing applications, and the packaging and assembly of MEMS devices. In all of these devices, low, stable contact resistance is desired. Modeling these contacts is difficult because much of traditional contact resistance theory was derived for macro scale contacts and relies on assumptions not valid at the MEMS scale. A large variety of factors affect contact resistance including contact force, contact scrub, contact material, and contact geometry. Additionally, electrical characteristics of these contacts can change over many cycles. The result of this is that the MEMS fabricated electrical contacts used in a variety of devices are often designed using a trial and error approach to determine which contact materials and geometries work best. Since these devices are often expensive and timely to manufacture, this method of design is far from ideal. The objective of my research is to develop a system for measuring and characterizing a wide variety of MEMS fabricated electrical contacts. The system consists of two silicon coupons which can be assembled and disassembled with a positional repeatability of less than one micron. This system allows any combination of contact force and contact scrub to be imparted on a pair of MEMS fabricated electrical contacts. The contacts themselves can consist of a wide variety of materials fabricated in a wide variety of ways including sputtering contact material, plating contact material, unconventional contact materials, plated tips, and three-dimensional tips. The repeatable assembly and disassembly of the coupons allows the contacts to be tested, observed using metrology such as an SEM or AFM, and then reassembled for further testing. This allows the changes in the contact surface to be observed as the contact is cycled. The instrumentation to impart force, scrub and measure contact resistance has also been developed. This system is used to measure the contact resistance between flat-on-flat contacts, plated tip contacts, and spherical contacts. The results of these tests offer fundamental (cont.) insights into the contact resistance between two thin films as well as compile a variety of data regarding multiple contact materials and contact geometries.

The results of these tests are used to create guidelines for designers of MEMS fabricated electrical contacts. Additionally, this platform can be used as a method of measurement and characterization for designers of MEMS fabricated electrical contacts to test any new contact geometries and materials in a quick cost effective manner. This method can also be used by research scientists investigating the fundamental physics of MEMS scale electrical contacts.