Kaigham J. Gabriel

Integrated fabrication of polysilicon mechanisms

The integrated fabrication of planar polysilicon mechanisms incorporating lower and higher kinematic pairs (or joints) is described. The two lower kinematic pairs (revolute and prismatic) commonly used in macrorobotic systems are compatible with silicon microfabrication technology. The mechanisms are fabricated by surface micromachining techniques using polysilicon as the structural material and oxide as the sacrificial material. Turbines with gear and blade rotors as small as 125 mu m in diameter and 4.5 mu m in thickness were fabricated on 20- mu m-diameter shafts. A clearance as tight as 1.2 mu m was achieved between the gear and the shaft. Gear trains with two or three sequentially-aligned gears were successfully meshed. A submillimeter pair of tongs with 400- mu m range-of-motion at the jaws was fabricated. This structure incorporates a single prismatic joint and two revolute joints, demonstrating linear-to-rotary motion conversion. >

Silicon micromechanics: sensors and actuators on a chip

The techniques used to fabricate micromechanical structures are described. Bulk micromachining is routinely used to fabricate microstructures with critical dimensions that are precisely determined by the crystal structure of the silicon wafer, by etch-stop layer thicknesses, or by the lithographic masking pattern. Silicon fusion bonding has been used to fabricate micro silicon pressure sensor chips. Surface micromachining, based on depositing and etching structural and sacrificial films, allows the designer to exploit the uniformity with which chemical vapor deposition (CVD) films coat irregular surfaces as well as the patterning fidelity of modern plasma etching processes. Silicon accelerometers, resonant microsensors, motors, and pumps made by these techniques are discussed. Measuring the mechanical properties of silicon, which are important to these applications, is examined.<<ETX>>

Design, fabrication, and operation of submicron gap comb-drive microactuators

Making submicron interelectrode gaps is the key to reducing the driving voltage of a micro comb-drive electrostatic actuator. Two new fabrication technologies, oxidation machining and a post-release positioning method, are proposed to realize submicron gaps. Two types of actuator (a resonant type and a nonresonant type) with submicron gaps were successfully fabricated and their operational characteristics were tested experimentally. The drive voltage was found to be lower than that of existing actuators. The stability of comb-drive actuators is discussed. >

Interaural correlation discrimination: I. Bandwidth and level dependence

Measurements of interaural cross-correlation jnds from two reference correlations at several bandwidths were obtained for constant-total-power and constant-spectral-power Gaussian noise. At a reference correlation of 1, the results indicate that for bandwidths less than or equal to 115 Hz the jnd remains at a constant value of approximately 0.004, and monotonically increases (discrimination performance degrades) to approximately 0.04 as bandwidth increases above 115 Hz. At a reference correlation of 0, the jnd decreases (discrimination performance improves (from approximately 0.7 to 0.35 as the bandwidth increases from 3 to 115 Hz, and remains at a constant value of approximately 0.35 for bandwidths greater than 115 Hz. A decrease in the spectral level causes an increase in the jnds at a reference correlation of 1, and no change in the jnds at a reference correlation of 0. Of the three models tested, none is able to completely describe all of the empirical results.

CMOS-MEMS membrane for audio-frequency acoustic actuation

Using CMOS-MEMS micromachining techniques we have constructed a prototype earphone that is audible from 1 to 15 kHz. The fabrication of the acoustic membrane consists of only two steps in addition to the prior post-CMOS micromachining steps developed at CMU. The ability to build a membrane directly on a standard CMOS chip, integrating mechanical structures with signal processing electronics will enable a variety of applications including economical earphones, microphones, hearing aids, high-fidelity earphones, cellular phones and noise cancellation. The large compliance of the CMOS-MEMS membrane also promises application as a sensitive microphone and pressure sensor.

High-resolution digital integral photography by use of a scanning microlens array

We suggest what we believe is a new three-dimensional (3-D) camera system for integral photography. Our method enables high-resolution 3-D imaging. In contrast to conventional integral photography, a moving microlens array (MLA) and a low-resolution camera are used. The intensity distribution in the MLA image plane is sampled sequentially by use of a pinhole array. The inversion problem from pseudoscopic to orthoscopic images is dealt with by electronic means. The new method is suitable for real-time 3-D imaging. We verified the new method experimentally. Integral photographs with a resolution of 3760 pixels x 2560 pixels (188 x 128 element images) are presented.

A fully-integrated CMOS-MEMS audio microphone

We report on the construction of a microphone and associated electronics fabricated entirely within a standard CMOS (complementary metal oxide semiconductor) die. An A-weighted noise level of 46 dB SPL was achieved with a total diaphragm area of 0.61 mm/sup 2/. Because the microphone uses the same processing sequence as CMOS-MEMS (microelectromechanical systems) microspeakers it is now possible to create acoustic systems-on-chip for applications in such areas as hearing aids, in-ear translators, and active noise cancellation. Because electret materials are not used, the microphone can withstand temperatures up to 250/spl deg/C with no degradation in performance. The frequency-modulated output provides a convenient, low-noise way to transmit the signal off chip, and is directly compatible with digital circuitry and FM radios.

Micro gears and turbines etched from silicon

Abstract Using silicon etching techniques, free-standing micro gears and turbines were fabricated from silicon. Silicon gears with geometries similar to those of standard watch gears were fabricated, but with outer diameters as small as 300 μm. A micro air-turbine was built out of discrete, silicon micro-mechanical components and operated at speeds of approximately 400 rps (24000 rpm). Limitations to further size reduction are not the photolithographic or etching processes, but the difficulty in handling such small components without loss or damage. Micro-mechanical structures, on the scales of tens of microns, can be fabricated inexpensively, accurately and repeatedly. Once these micro-structures are cut free from their silicon substrates, these silicon components can be used to build a wide array of micro-mechanical systems. Moreover, the use of silicon processing technology makes possible the eventual fabrication and integration of sensors, actuators, mechanical structures and control circuitry on the same substrate.

Frequency dependence of binaural performance in listeners with impaired binaural hearing

Binaural performance was measured as a function of stimulus frequency for four impaired listeners, each with bilaterally symmetric audiograms. The subjects had various degrees and configurations of audiometric losses: two had high-frequency, sensorineural losses; one had a flat sensorineural loss; and one had multiple sclerosis with normal audiometric thresholds. Just noticeable differences (jnds) in interaural time, interaural intensity, and interaural correlation as well as detection thresholds for NoSo and NoS pi conditions were obtained for narrow-band noise stimuli at octave frequencies from 250-4000 Hz. Performance of the impaired listeners was generally poorer than that of normal-hearing listeners, although it was comparable to normal in a few instances. The patterns of binaural performance showed no apparent relation to the audiometric patterns; even the two subjects with similar degree and configuration of hearing loss have very different binaural performance, both in the level and frequency dependence of their performance. The frequency dependence of performance on individual tests is irregular enough that one cannot confidently interpolate between octaves. In addition, it appears that no subset of the measurements is adequate to characterize the performance in the rest of the measurements with the exception that, within limits, interaural correlation discrimination and NoS pi detection performance are related.

A micro rotary actuator using shape memory alloys

Abstract A thin (100 μm diameter) rod of shape memory alloy (Nitinol)_wire was clamped at two ends under torsional strain and used as a micro, rotary actuator less than 0.04 cm 3 in volume. Using three electrical connections (the two ends of the wire and a contact in the middle of the wire), the two halves of the wire were differentially heated, which caused repeatable, continuous and directional angular dflections of the wire about its longitudinal axis. In addition, this configuration allows the shape memory alloy to serve as both the actuating mechanism and the mechanical bias (which restores the deformation in the wire after shape recovery). Thus, the biasing takes place with the activation time constant of the wire and not with the thermal cooling time constant in most previous designs. The present actuator achieves operating bandwidths of approximately 4 Hz, two to three times higher than that of actuators of similar size that rely on bias springs. A micro fluid-valve and a pair of micro-tongs are presented as some applications of such an actuator.