Development of a High-Density Piezoelectric Micromachined Ultrasonic Transducer Array Based on Patterned Aluminum Nitride Thin Film.

Eunjung Shin,Hongsoo Choi,Changzhu Jin,Wonki Park,Sung-Chul Lee,Hong Goo Yeo,Ara Yeon

doi:10.3390/mi11060623

Abstract

This study presents the fabrication and characterization of a piezoelectric micromachined ultrasonic transducer (pMUT; radius: 40 µm) using a patterned aluminum nitride (AlN) thin film as the active piezoelectric material. A 20 × 20 array of pMUTs using a 1 µm thick AlN thin film was designed and fabricated on a 2 × 2 mm2 footprint for a high fill factor. Based on the electrical impedance and phase of the pMUT array, the electromechanical coefficient was ~1.7% at the average resonant frequency of 2.82 MHz in air. Dynamic displacement of the pMUT surface was characterized by scanning laser Doppler vibrometry. The pressure output while immersed in water was 19.79 kPa when calculated based on the peak displacement at the resonant frequency. The proposed AlN pMUT array has potential applications in biomedical sensing for healthcare, medical imaging, and biometrics.

Highlights

Compared with conventional bulk ultrasound transducers made with piezoelectric ceramics, micromachined ultrasonic transducers (MUTs) based on thin films can provide more advanced array design, lower power consumption, and better acoustic coupling [1,2,3,4,5]
MUT-based systems integrated with complementary metal-oxide semiconductor (CMOS) circuits are suitable for portable devices
An ultrasound fingerprint sensor consisting of an MUT array and CMOS signal processing electronics was demonstrated by Jiang et al [10]

Summary

Introduction

Compared with conventional bulk ultrasound transducers made with piezoelectric ceramics, micromachined ultrasonic transducers (MUTs) based on thin films can provide more advanced array design, lower power consumption, and better acoustic coupling [1,2,3,4,5]. Lu et al developed an integrated MUT array with a CMOS using wafer-level conductive eutectic bonding for short-range pulse-echo imaging [9]. An ultrasound fingerprint sensor consisting of an MUT array and CMOS signal processing electronics was demonstrated by Jiang et al [10]. In fingerprint sensing, MUTs provide improved image quality even when there are moisture and contamination on the target surface, unlike a capacitive fingerprint sensor. According to the operating principle of MUT, the MUT is divided into two types: A capacitive micromachined ultrasonic transducer (cMUT) and a piezoelectric micromachined ultrasonic transducer (pMUT)

Methods

Results

Conclusion