Eugene H. Cook

A MEMS diamond hemispherical resonator

In this paper we report the fabrication of hemispherical polycrystalline diamond resonators fabricated on a novel high-temperature glass substrate. The hemispherical resonator gyroscope is one of the most accurate and rugged of the mechanical gyroscopes, and can be operated in either rate or whole-angle mode due to its high degree of symmetry. A fabrication sequence for creating extremely symmetric 3D MEMS hemispheres is presented. Mode shapes and frequencies obtained with a laser vibrometer are shown, as well as curves of Q versus pressure, and the dependence of frequency on anchor size. Fundamental mode frequency matching to <0.1% in as-fabricated devices has been achieved, which is essential to gyroscope operation in whole-angle mode.

High Q diamond hemispherical resonators: fabrication and energy loss mechanisms

We have fabricated polycrystalline diamond hemispheres by hot-filament CVD (HFCVD) in spherical cavities wet-etched into a high temperature glass substrate CTE matched to silicon. Hemispherical resonators 1.4 mm in diameter have a Q of up to 143 000 in the fundamental wineglass mode, for a ringdown time of 2.4 s. Without trimming, resonators have the two degenerate wineglass modes frequency matched as close as 2 Hz, or 0.013% of the resonant frequency (~16 kHz). Laser trimming was used to match resonant modes on hemispheres to 0.3 Hz. Experimental and FEA energy loss studies on cantilevers and hemispheres examine various energy loss mechanisms, showing that surface related losses are dominant. Diamond cantilevers with a Q of 400 000 and a ringdown time of 15.4 s were measured, showing the potential of polycrystalline diamond films for high Q resonators. These resonators show great promise for use as hemispherical resonant gyroscopes (HRGs) on a chip.

MEMS process compatibility of multiwall carbon nanotubes

While carbon nanotubes (CNT) have been proposed and used as structural elements (e.g., cantilevers, bearings, nanofluidic channels, etc.) in microsystems, knowledge of the compatibility of CNTs with a broad range of standard microelectromechanical system (MEMS) fabrication processes is incomplete. This work investigates the effect of 23 common MEMS processes and chemicals on catalytically-grown and arc-discharge-produced multiwall nanotubes (MWNT) and compares the observed effects with those reported in the literature. Specific individual nanotubes are observed using scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM) before and after the application of each process. This allows detection of process-induced changes to the nanotube from the bulk scale down to the nanometer and even atomic scales. Various thin-film deposition techniques are used to deposit common MEMS materials on MWNTs. A variety of wet chemicals and dry etching techniques are applied to MWNTs. Many processes prov...

Fabrication of a rotary carbon nanotube bearing test apparatus

Carbon Nanotubes (CNTs) are attractive elements for bearings in Micro-Electro-Mechanical Systems (MEMS), because their structure comprises nested shells with no bonding and sub-nanometre spacing between them, enabling relative motion with low friction and wear. A reliable bearing technology is critical to bringing rotating MEMS machines from laboratory demonstrations to common use. We report here the design and fabrication of a test rotor, a testing apparatus and testing attempts, and integration of CNTs with MEMS. The device improves on existing CNT bearing demonstrators by establishing a vertical bearing orientation (enabling superior rotor balance and speed, and drive mechanism placement flexibility) and a manufacturable process (employing CNTs grown in place by chemical vapour deposition (CVD)). The main outstanding challenge to demonstrating rotation is available CVD CNT quality.