Mr. Robert D. White Profile

Robert D. White

Graduate Student at Univ of Michigan

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Proceedings Article | 22 January 2005 Paper

Capacitively sensed micromachined hydrophone with viscous fluid-structure coupling

Robert White, Lei Cheng, Karl Grosh

Proceedings Volume 5718, (2005) https://doi.org/10.1117/12.591376

KEYWORDS: Silicon, Microfluidics, Electrodes, Sensors, Semiconducting wafers, Etching, Motion models, Acoustics, Motion measurement, Deep reactive ion etching

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This work presents a novel design for a micromachined, capacitively sensed hydrophone. The design consists of a fluid-filled chamber constrained by two sets of membranes. The "input" membranes are arrayed around the outside of the circular chamber. Incoming sound generates a trapped cylindrical wave, creating mechanically amplified motion of the 1 mm diameter central "sensing" membrane. The membrane material is a LPCVD nitride/oxide/nitride triple-stack with respective film thickness 0.1/0.65/0.1 micron. The chamber is filled with 200 cSt viscosity silicone oil. Fluid-filling eases design constraints associated with submerging the sensor, especially with respect to exterior mass loading. Both silicon-glass anodic bonding and tin-gold solder bonding are used to form the structure, including the 5 micron sensing gap. The fluid-structure system is computationally modeled using both approximate analytic and numerical techniques. Model results indicate a 28 dB displacement gain between the motion of the "input" membranes and the "sensing" membranes. An off-chip charge amplifier, with a 10 pF integrating capacitor, is used to convert membrane motion into an electrical signal. Mean measured system sensitivity is 0.8 mV/Pa (-180 dB re 1 V/microPa) from 300 Hz-15 kHz with a 1.5 volt applied bias and a 26 dB preamplifier gain. The predicted low frequency sensitivity is 0.3 mV/Pa. The measured sensitivity exhibits considerable scatter below 7 kHz, with a standard deviation of 80%. Laser vibrometry measurements indicate that this scatter may be caused by compliance of the chip mounting scheme. Above 10 kHz, the quiescent noise is -100 dB re 1 V/rtHz. Noise characteristics exhibit a 1/f character below 10 kHz, rising to a maximum of -50 dB re 1 V/rtHz at 100 Hz.

Proceedings Article | 11 July 2002 Paper

Micromachined cochlear-like acoustic sensor

Robert White, Karl Grosh

Proceedings Volume 4700, (2002) https://doi.org/10.1117/12.475020

KEYWORDS: Semiconducting wafers, Silicon, Epoxies, Etching, Acoustics, Wafer bonding, Oxides, Microfluidics, Adhesives, Transducers

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The mammalian cochlea achieves remarkable acoustic transduction characteristics in a compact and robust design. For this reason, its mechanics have been extensively studied, both mathematically and experimentally. Recently, a number of researchers have attempted to mimic the cochlear function of the basilar membrane in micromachined mechanical devices. This paper presents a design for a silicon cochlea which extends previous work by utilizing a micromachined liquid-filled two duct structure similar to the duct structure of the biological cochlea. Design issues related to both mechanical structure and electrical transduction will be discussed, particularly with regard to optimization of transducer performance. A parallel beam array structure is proposed as a model for an orthotropic membrane. Fabrication procedures and results are also presented. Challenging Fabrication issues related to through-wafer etching, adhesive wafer bonding, device release, and fluid injection are emphasized.

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