Publications

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This paper reports on a near-zero power inertial wakeup sensor system supporting digital weighting of inputs and with protection against false positives due to mechanical shocks. This improves upon existing work by combining the selectivity and sensitivity (Q-amplification) of resonant MEMS sensors with the flexibility of digital signal processing while consuming below 10 nW. The target application is unattended sensors for perimeter sensing and machinery health monitoring where extended battery life afforded by the low power consumption eliminates the need for power cables. For machinery health monitoring, the signals of interest are stationary but may contain spurious mechanical shocks.

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Fingerprint sensing is pervasive in the cellular telecommunications market. Current commercial fingerprint sensors utilize capacitive scanning. This work focuses on the design, fabrication and characterization of post-complementary-metal-oxide-semiconductor (CMOS) compatible piezoelectric micro-machined ultrasonic transducers for use as ultrasonic pixels to improve robustness to contamination and allow for sub-epidermis scans. Ultrasonic pixels are demonstrated at frequencies ranging from 100 kHz to 800 kHz with several electrode coverages and styles to identify trends.

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The Defense Advanced Research Project Agency has identified a need for low-standby-power systems which react to physical environmental signals in the form of an electrical wakeup signal. To address this need, we design piezoelectric aluminum nitride based microelectromechanical resonant accelerometers that couple with a near-zero power, complementary metal-oxide-semiconductor application specific integrated circuit. The piezoelectric accelerometer operates near resonance to form a passive mechanical filter of the vibration spectrum that targets a specific frequency signature. Resonant vibration sensitivities as large as 490 V/g (in air) are obtained at frequencies as low as 43 Hz. The integrated circuit operates in the subthreshold regime employing current starvation to minimize power consumption. Two accelerometers are coupled with the circuit to form the wakeup system which requires only 5.25 nW before wakeup and 6.75 nW after wakeup. The system is shown to wake up to a generator signal and reject confusers in the form of other vehicles and background noise.

The defense community desires low-power sensors deployed around critical assets for intrusion detection. A piezoelectric microelectromechanical accelerometer is coupled with a complementary metal-oxide-semiconductor comparator to create a near-zero power wakeup system. The accelerometer is designed to operate at resonance and employs aluminum nitride for piezoelectric transduction. At a target frequency of 160 Hz, the accelerometer achieves sensitivities as large as 26 V/g. The system is shown to require only 5.4 nW of power before and after latching. The combined system is shown to wake up to a target frequency signature of a generator while rejecting background noise as well as non-target frequency signatures.

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With the advent of the internet-of-things, sensors that are constantly alert yet consuming near-zero power are desired. Remote sensing applications where sensor replacement is costly or hazardous would also benefit. Piezoelectric micro-electro-mechanical systems (MEMS) convert mechanical or acoustic energy into electrical signals while consuming zero power. When coupled with low-power complementary metal-oxide-semiconductor (CMOS) circuits, a near-zero power sensing system is formed. This work describes piezoelectric MEMS microphones based on aluminum nitride (AlN). The microphones operate as passive acoustic filters by placing their resonant response within bandwidths of interest. Devices are demonstrated with operational frequencies from 430 Hz to greater than 10 kHz with quality factors as large as 3,000 and open-circuit voltages exceeding 600 mV/Pa.

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