Andrew L. Robinson

Process Integration for active polysilicon resonant microstructures

Abstract Microsensors based on active polysilicon resonant microstructures are attractive because of their wide dynamic range, high sensitivity and frequency shift output. In this paper, we discuss processing issues for integrating electrostatically-driven and -sensed polysilicon microstructures with on-chip nMOS device. Surface-micro-machining using sacrificial spacer layers is used to obtain relased microstructures. A novel feature is the use of rapid thermal annealing (RTA) for strain relief of the ion-implanted, phosphorous-doped polysilicon. Resonance frequencies of cantilever beams indicate a lower-bound Youngs modulus of about 90 GPa and an upper-bound compressive residual strain of only 0.002%, indicating that RTA is potentially useful for strain relief.

One-port active polysilicon resonant microstructures

Theoretical and experimental characteristics of a two-terminal, or one-port, resonant microstructure are discussed. An equivalent circuit model that is useful for design and analysis of these devices is presented. This model is verified by experimental measurements, with a worst-case error between model and experimental parameters of 30%. A process for integrating polysilicon resonant microstructures with on-chip NMOS (N-metal oxide semiconductor) circuitry is also described. A novel feature of this process is the use of rapid thermal annealing (RTA) for strain-relief of the non-implanted phosphorus-doped polysilicon. The RTA-strain-relieved polysilicon has a Youngs modulus of 0.9.10/sup 12/ dynes/cm/sup 2/ and residual strain of 0.002% as measured by resonant frequency techniques. This low value of strain indicated that RTA is a useful strain-relief technique.<<ETX>>

Micromachining for improvement of integrated ultrasonic transducer sensitivity

A micromachined diaphragm structure for integrated ultrasonic transducers is discussed. The micromachining significantly reduces a large parasitic capacitance, resulting in improved sensitivity compared with identical transducers on solid substrates. For the particular geometry tested, sensitivity improved 8.9 dB; this result matches a prediction of 10.9 dB, based on a simple model, reasonably well. This level of improvement is considered significant for the applications under consideration (medical imaging and nondestructive evaluation). >

A Mobile-Phone-Based Breath Carbon Monoxide Meter to Detect Cigarette Smoking

INTRODUCTION Mobile phones hold considerable promise for delivering evidence-based smoking cessation interventions that require frequent and objective assessment of smoking status via breath carbon monoxide (Breath CO) measurement. However, there are currently no commercially available mobile-phone-based Breath CO meters. We developed a mobile-phone-based Breath CO meter prototype that attaches to and communicates with a smartphone through an audio port. We then evaluated the reliability and the validity of Breath CO measures collected with the mobile meter prototype and assessed the usability and acceptability of the meter. METHODS Participants included 20 regular smokers (≥10 cigarettes/day), 20 light smokers (<10 cigarettes/day), and 20 nonsmokers. Expired air samples were collected 4 times from each participant: twice with the mobile meter and twice with a commercially available Breath CO meter. RESULTS Measures calculated by the mobile meter correlated strongly with measures calculated by the commercial meter (r = .96, p < .001). Additionally, the mobile meter accurately distinguished between smokers and nonsmokers. The area under the receiver-operating characteristic curve for the mobile meter was 94.7%, and the meter had a combined sensitivity and specificity of 1.86 at an abstinence threshold of ≤6 ppm. Responses on an acceptability survey indicated that smokers liked the meter and would be interested in using it during a quit attempt. CONCLUSIONS The results of our study suggest that a mobile-phone-based Breath CO meter is a reliable, valid, and acceptable device for distinguishing between smokers and nonsmokers.

A silicon-on-insulator circuit for high-temperature, high-voltage applications

The authors previously proposed the concept of a composite high-voltage device using series-connected low-voltage SOI (silicon-on-insulator) MOSFETs. In the present work, they demonstrate how the composite device can circumvent the fundamental materials limitations of bulk devices for high-voltage, high-temperature applications. Experimental circuits were fabricated on SIMOX (separation by implanted oxygen) substrates using an SOI NMOS process. For the purpose of demonstrations, external resistors were used as the bias elements. Individual transistor breakdown voltages were about 6-7 V, and did not vary significantly from 24 degrees C to 400 degrees C. The composite device characteristics closely resemble those of the individual MOSFETs. In particular, the breakdown voltage (typically 26-30 V) is nearly constant over the temperature range studied. Drain characteristics of a typical five-transistor composite device are shown for several stage temperatures.<<ETX>>

AudioDAQ: turning the mobile phone's ubiquitous headset port into a universal data acquisition interface

We present AudioDAQ, a new platform for continuous data acquisition using the headset port of a mobile phone. AudioDAQ differs from existing phone peripheral interfaces by drawing all necessary power from the microphone bias voltage, encoding all data as analog audio, and leveraging the phones built-in voice memo application (or a custom application) for continuous data collection. These properties make the AudioDAQ design more universal, so it works across a broad range of phones including sophisticated smart phones and simpler feature phones, enables simple analog peripherals without requiring a microcontroller, requires no hardware or software modifications on the phone itself, uses significantly less power than prior approaches, and allows continuous data capture over an extended period of time. The AudioDAQ design is efficient because it draws all necessary power from the microphone bias voltage, and it is general because this voltage and a voice memo application are present on most mobile phones in use today. We show the viability of our architecture by evaluating an end-to-end system that can capture EKG signals continuously for hours and send the data to the cloud for storage, processing, and visualization.

Characterization of a needle hydrophone array for acoustic feedback during ultrasound hyperthermia treatments

A prototype 16-element needle hydrophone array has been designed, fabricated, and characterized. The primary use of this array is to provide acoustic feedback during ultrasound hyperthermia treatments. This feedback is necessary to compensate phase array heating patterns for patient motion and tissue inhomogeneities in real time. The array consists of a polyvinylidene fluoride (PVDF) covered silicon substrate carrier which contains the signal electrodes of the individual acoustic sensors. Tests show that the array is sensitive to both pulsed and continuous ultrasound (943-kHz) excitation and can be used in tissue media. A complete description of the needle array, element cross-coupling measurements, beam profile measurements, calibration procedures, and sensitivity analyses in both water and tissue is presented.<<ETX>>

Applications of microelectronics and microfabrication to ultrasound imaging systems

Recent work on techniques for applying microelectronics and related microfabrication technology to different aspects of ultrasound imaging systems is described. Particular topics addressed include integrated transducer arrays, acoustic crosstalk, microelectronics for front-end interface circuits, microelectronic preamplifiers, microelectronic design flexibility, microfabrication techniques for 2-D arrays, and 3-D interconnects for 2-D arrays.<<ETX>>

A composite high-voltage device using low-voltage SOI MOSFETs

A circuit is described that uses low-voltage transistors to form a high-voltage composite device. The circuit is a series string of SOI (silicon-on-insulator) MOSFETs and associated biasing elements fabricated using a modified nMOS process on a SIMOX (separation by implantation of oxygen) substrate. The circuit voltages higher than the breakdown voltage of a single transistor by dividing the applied voltage among the transistors in the string. MOSFET-like characteristics with breakdown voltage up to 60 V are demonstrated using a string of 25 SOI MOSFETs, each with a breakdown voltage of 6-7 V.<<ETX>>

AudioDAQ: turning the mobile phone's headset port into a universal data acquisition interface

Smartphone peripherals like the Square card reader, Red-Eye mini, and HiJack platform suggest a growing interest in using the headset port for more than just headsets. How-ever, these peripherals only support sporadic activities in an efficient manner. Continuous sensing applications - like monitoring EKG signals - is possible but remains too inefficient for many realistic usage scenarios. We present Au-dioDAQ, a new sensor data acquisition platform. In contrast with prior work, AudioDAQ requires no hardware or software modifications on the phone, uses significantly less power, and allows continuous data capture over extended periods of time. The design is efficient because we draw all necessary power from the microphone bias voltage, and it is general because this voltage is present in every headset port. Data is modulated within the audible range, captured with the built-in voice recording app, and sent to a server for processing and storage. We show the viability of this approach by demonstrating an EKG monitor that can capture data continuously for hours.