Michael J. Daneman

Monolithic 591×438 DPI ultrasonic fingerprint sensor

This paper presents a 591×438 DPI ultrasonic fingerprint sensor. The sensor is based on a piezoelectric micromachined ultrasonic transducer (PMUT) array that is bonded at wafer-level to complementary metal oxide semiconductor (CMOS) signal processing electronics to produce a pulse-echo ultrasonic imager on a chip. To meet the 500 DPI standard for consumer fingerprint sensors, the PMUT pitch was reduced by approximately a factor of two relative to an earlier design. We conducted a systematic design study of the individual PMUT and array to achieve this scaling while maintaining a high fill-factor. The resulting 110×56 PMUT array, composed of 30×43μm2 rectangular PMUTs achieved a 51.7% fill-factor, three times greater than that of the previous design. Together with the custom CMOS ASIC, the sensor achieves 2 μV/Pa sensitivity, 13 kPa pressure output, 75μm lateral resolution, and 150μm axial resolution in a 4.6 mm × 3.2 mm image.

Ultrasonic fingerprint sensor based on a PMUT array bonded to CMOS circuitry

This paper describes a single-chip 591×438 DPI ultrasonic fingerprint sensor. The sensor is based on a piezoelectric micromachined ultrasonic transducer (PMUT) array that is bonded at wafer-level to complementary metal oxide semiconductor (CMOS) signal processing electronics to produce a pulse-echo ultrasonic imager on a chip. To meet the 500 DPI standard for consumer fingerprint sensors, the PMUT pitch was reduced by approximately a factor of two relative to an earlier design. We conducted a systematic design study of the individual PMUT design and array to achieve this scaling while maintaining a high fill-factor. The resulting 110×56 PMUT array, composed of rectangular PMUTs achieved a 51.7% fill-factor, three times greater than that of the previous design. Together with the custom CMOS ASIC, the sensor achieves 75 micron lateral resolution and 150 micron axial resolution over a 4.6 mm × 3.2 mm image.

Theory and experimental analysis of scratch resistant coating for ultrasonic fingerprint sensors

Ultrasonic imaging for fingerprint applications offers better tolerance of external conditions and high spatial resolution compared to typical optical and solid state sensors respectively. Similar to existing fingerprint sensors, the performance of ultrasonic imagers is sensitive to physical damage. Therefore it is important to understand the theory behind transmission and reflection effects of protective coatings for ultrasonic fingerprint sensors. In this work, we present the analytical theory behind effects of transmitting ultrasound through a thin film of scratch resistant material. Experimental results indicate transmission through 1 μm of Al2O3 is indistinguishable from the non-coated cover substrate. Furthermore, pulse echo measurements of 5 μm thick Al2O3 show ultrasound pressure reflection increases in accordance with both theory and finite element simulation. Consequently, feasibility is demonstrated of ultrasonic transmission through a protective layer with greatly mismatched acoustic impedance when sufficiently thin. This provides a guide for designing sensor protection when using materials of vastly different acoustic impedance values.

Monolithic ultrasound fingerprint sensor

This paper presents a 591×438-DPI ultrasonic fingerprint sensor. The sensor is based on a piezoelectric micromachined ultrasonic transducer (PMUT) array that is bonded at wafer-level to complementary metal oxide semiconductor (CMOS) signal processing electronics to produce a pulse-echo ultrasonic imager on a chip. To meet the 500-DPI standard for consumer fingerprint sensors, the PMUT pitch was reduced by approximately a factor of two relative to an earlier design. We conducted a systematic design study of the individual PMUT and array to achieve this scaling while maintaining a high fill-factor. The resulting 110×56-PMUT array, composed of 30×43-μm2 rectangular PMUTs, achieved a 51.7% fill-factor, three times greater than that of the previous design. Together with the custom CMOS ASIC, the sensor achieves 2 mV kPa−1 sensitivity, 15 kPa pressure output, 75 μm lateral resolution, and 150 μm axial resolution in a 4.6 mm×3.2 mm image. To the best of our knowledge, we have demonstrated the first MEMS ultrasonic fingerprint sensor capable of imaging epidermis and sub-surface layer fingerprints.

High performance MEMS-based 8x8-port optical switch

This paper presents the design and measured optical performance of a MEMS-based 8/spl times/8-port fiberoptic switch. The device uses a novel two-chip construction to achieve precise MEMS mirror positioning, resulting in insertion loss uniformity within 1 dB and repeatability of less than 0.12 dB. Measurements of six representative 8/spl times/8 switches show a worst-case insertion loss of 2 dB, while typical insertion loss is better than 1.4 dB.