David B. Hicks

Resonant-bridge two axis microaccelerometer

A resonant bridge two-axis microaccelerometer is disclosed comprising polysilicon resonant bridges orthogonally attached to a silicon proof mass, such that the silicon proof mass is suspended by the resonant bridges. Acceleration in the plane of the substrate causes differential axial loads on the opposing microbridges in each pair, thereby shifting their resonant frequencies. The acceleration component aligned with a pair is measured by the difference in resonant frequencies.

Characterization of electroformed nickel microstructures

Electroformed nickel resonators were constructed and tested in the temperature range of - 40 to 110 degrees C. The temperature sensitivities of the resonant frequencies are - 150 ppm/degrees C, - 200 ppm/degrees C, and - 3000 ppm/degrees C for cantilever beams, ring structures, and clamped-clamped bridges, respectively. The built-in stress for the bridge was estimated to be approximately 2 X 109 dyne/cm2. No resonant frequency shift was detected after long-term (over 60 days), large amplitude vibration. This implies that the electroformed nickel is a viable material for the construction of resonant mechanical sensors.

Bonding of silicon to silicon by solid-phase epitaxy

Using concepts of solid‐phase epitaxy, a sealed and structurally sound bond between two silicon wafers has been achieved with aluminum, platinum silicide, or germanium as the transport medium. Only in the case of aluminum did microprobe analysis show an interface clear of the bonding medium. The bond quality was tested by bonding wafers of different crystal orientation and then intentionally cleaving and fracturing the bonded wafers. A clean fracture was obtained without the wafers falling apart. Leak test of sealed cavities suggests that a hermetically sealed enclosure can be achieved with this technique.

The Formation Of Electroplating Molds By Reactive Ion Etching

Polyimide, polymethylmethacrylate (PMMA) and polyester-based polymers were investigated as potential electroplating mold materials. They showed high tensile stress (/spl equiv/10/sup 8/ dyne/cm/sup 2/) after heat treatment at temperatures /spl ges/ 200/spl deg/C. Conventional reactive ion etching techniques together with a trilevel masking scheme was used to delineate the polymer layers. The etch mask used was either spin-on glass or aluminum, and the etch gas was oxygen. With proper power density and etch gas pressure, aspect ratios >5 were obtained. Compatibility issues between RIE and the etch mask materials, as well as between RIE and the plating base materials are discussed.