Hao-Yen Tang

Ultrasonic fingerprint sensor using a piezoelectric micromachined ultrasonic transducer array integrated with complementary metal oxide semiconductor electronics

This paper presents an ultrasonic fingerprint sensor based on a 24 × 8 array of 22 MHz piezoelectric micromachined ultrasonic transducers (PMUTs) with 100 μm pitch, fully integrated with 180 nm complementary metal oxide semiconductor (CMOS) circuitry through eutectic wafer bonding. Each PMUT is directly bonded to a dedicated CMOS receive amplifier, minimizing electrical parasitics and eliminating the need for through-silicon vias. The array frequency response and vibration mode-shape were characterized using laser Doppler vibrometry and verified via finite element method simulation. The arrays acoustic output was measured using a hydrophone to be ∼14 kPa with a 28 V input, in reasonable agreement with predication from analytical calculation. Pulse-echo imaging of a 1D steel grating is demonstrated using electronic scanning of a 20 × 8 sub-array, resulting in 300 mV maximum received amplitude and 5:1 contrast ratio. Because the small size of this array limits the maximum image size, mechanical scanning was used to image a 2D polydimethylsiloxane fingerprint phantom (10 mm × 8 mm) at a 1.2 mm distance from the array.

Pulse-echo ultrasonic fingerprint sensor on a chip

A fully-integrated ultrasonic fingerprint sensor based on pulse-echo imaging is presented. The device consists of a 24×8 Piezoelectric Micromachined Ultrasonic Transducer (PMUT) array bonded at the wafer level to custom readout electronics fabricated in a 180-nm CMOS process. The proposed top-driving bottom-sensing technique minimizes signal attenuation due to the large parasitics associated with high-voltage transistors. With 12V driving signal strength, the sensor takes 24μs to image a 2.3mm by 0.7mm section of a fingerprint.

3D Ultrasonic Rangefinder on a Chip

An ultrasonic 3D rangefinder uses an array of AlN MEMS transducers and custom readout electronics to localize targets over a ±45° field of view up to 1 m away. The rms position error at 0.5 m range is 0.4 mm, 0.2 °, and 0.8 ° for the range, x-angle, and y-angle axes, respectively. The 0.18 μm CMOS ASIC comprises 10 independent channels with separate high voltage transmitters, readout amplifiers, and switched-capacitor bandpass ΣΔ ADCs with built-in continuous time anti-alias filtering. For a 1 m maximum range, power dissipation is 400 μW at 30 fps. For a 0.3 m maximum range, the power dissipation scales to 5 μW/ch at 10 fps.

Versatile CMOS-MEMS integrated piezoelectric platform

We present the extension of the InvenSense fabrication platform to piezoelectric transduction. The newly proposed CMOS-MEMS Integrated Piezoelectric Platform inherits the wafer bonding advantages of its predecessor, leverages existing semiconductor infrastructure, and is applicable to a wide range of applications.

11.8 Integrated ultrasonic system for measuring body-fat composition

An accurate, low-power, and highly integrated solution for accurate assessment of body fat is presented that addresses a growing consumer interest in economical and easy-to-use solutions for monitoring personal health and fitness. Unlike the prevalent present solution that estimates body fat percentage from an impedance measurement integrated in a weight scale and gives only a global index with accuracy compromised by a host of factors including skin moisture and metabolic activity, the reported approach uses ultrasound for an accurate measure of the actual thickness of the fat and muscle layers [1].

Short-range and high-resolution ultrasound imaging using an 8 MHz Aluminum Nitride PMUT array

Ultrasound imaging uses costly bulk piezoelectric transducers and high voltage (200V+) electronics. Low-cost and low-voltage ultrasound transducers would enable many new applications in healthcare, biometrics, and personal health-monitoring. Here, we demonstrated short-range (~mm) and high-resolution (<;100 μm) imaging based on piezoelectric micromachined ultrasonic transducers (PMUTs) and a 1.8 V interface ASIC. The PMUTs use piezoelectric Aluminum Nitride (AlN), which has the advantages of low-temperature (<;400 °C) deposition and compatibility with CMOS fabrication but has a relatively low piezoelectric constant (e31=-0.5 C/m2), making detection of ultrasound signals from tiny (50 μm) PMUTs a challenging task. To solve this problem, we developed an ASIC with a low-noise analog front-end pre-amplifier that is impedance matched to the PMUT. Furthermore, a novel beam-forming and scanning method was demonstrated to achieve a sub-100μm focus size and 70 μm scanning step. Pressure map measurement from phased PMUT array and pulse echo imaging results were demonstrated using 1-D and 2-D phantoms.

Pulse-Echo Ultrasound Imaging Using an AlN Piezoelectric Micromachined Ultrasonic Transducer Array With Transmit Beam-Forming

This work demonstrates short-range and high-resolution ultrasonic imaging using 8 MHz aluminum nitride (AlN) piezoelectric micromachined ultrasonic transducer (PMUT) arrays, which are compatible with complementary metal-oxide semiconductor circuitry and wafer-level mass manufacture. Because AlN has a low dielectric constant, the PMUTs have low capacitance and a custom 1.8 V interface application-specified integrated circuit with on-chip charge-pump (1.8 to 32 V) is capable of providing sufficient output current to drive the PMUT array. Transmit beam-forming is used to produce a 90 μm focused acoustic beam-width. A pressure map measured with a needle hydrophone agrees with finite element method-simulations. Finally, 1-D and 2-D pulse-echo imaging was conducted using metal targets.

Ultrasonic beamforming system for interrogating multiple implantable sensors.

In this paper, we present an ultrasonic beamforming system capable of interrogating individual implantable sensors via backscatter in a distributed, ultrasound-based recording platform known as Neural Dust [1]. A custom ASIC drives a 7 × 2 PZT transducer array with 3 cycles of 32V square wave with a specific programmable time delay to focus the beam at the 800mm neural dust mote placed 50mm away. The measured acoustic-to-electrical conversion efficiency of the receive mote in water is 0.12% and the overall system delivers 26.3% of the power from the 1.8V power supply to the transducer drive output, consumes 0.75μJ in each transmit phase, and has a 0.5% change in the backscatter per volt applied to the input of the backscatter circuit. Further miniaturization of both the transmit array and the receive mote can pave the way for a wearable, chronic sensing and neuromodulation system.

3-D Ultrasonic Fingerprint Sensor-on-a-Chip

A fully integrated 3-D ultrasonic fingerprint sensor-on-a-chip is presented. The device consists of a 110× 56 piezoelectric micromachined ultrasonic transducer (PMUT) array bonded at the wafer level to custom readout electronics fabricated in a 180-nm CMOS process with a HV (24 V) transistor option. With the 24 V driving signal strength, the sensor consumes 280 μJ to image a 4.73 mm × 3.24 mm section of a fingerprint at a rate of 380 fps. A wakeup mode that detects the presence of a finger at 4 fps and dissipates 10 μW allows the proposed sensor to double as a power switch. The sensor is capable of imaging both the surface epidermal and subsurface dermal fingerprints and is insensitive to contaminations, including perspiration or oil. The 3-D imaging capability combined with the sensors sensitivity to the acoustic properties of the tissue translates into excellent robustness against spoofing attacks.

Miniaturizing Ultrasonic System for Portable Health Care and Fitness

We present a miniaturized portable ultrasonic imager that uses a custom ASIC and a piezoelectric transducer array to transmit and capture 2-D sonographs. The ASIC, fabricated in 0.18 μm 32 V CMOS process, contains 7 identical channels, each with high-voltage level-shifters, high-voltage DC-DC converters, digital TX beamformer, and RX front-end. The chip is powered by a single 1.8 V supply and generates 5 V and 32 V internally using on-chip charge pumps with an efficiency of 33% to provide 32 V pulses for driving a bulk piezoelectric transducer array. The assembled prototype can operate up to 40 MHz, with beamformer delay resolution of 5 ns, and has a measured sensitivity of 225 nV/Pa , minimum detectable signal of 622 Pa assuming 12 dB SNR ( 4σ larger than the noise level), and data acquisition time of 21.3 ms. The system can image human tissue as deep as 5 cm while consuming less than 16.5 μJ per pulse-echo measurement. The high energy efficiency of the imager can enable a number of consumer applications.