Tent-Plate AlN PMUT With a Piston-Like Shape Under Liquid Operation

In this work, a waterproof tent-plate piezoelectric micromachined ultrasonic transducer (PMUT) with enhanced performance as actuator and sensor in comparison with standard clamped PMUT is presented. The squared AlN PMUT has four linear holes that are sealed by the passive layer allowing to increase the movement and giving the capability to work in liquid environment. The dimension of the holes was optimized to increase the PMUT displacement at least twice in relation with the regular clamped device. The acoustic performance of the PMUT was simulated in COMSOL Multiphysics and the results were experimentally verified under liquid operation. The experimental transmitting sensitivity, 3.9 kPa/V, as well as the sensor sensitivity, 13.4 V/MPa, provide a 2x factor improvement in contrast with the clamped PMUT with competitive values. Additionally, the presented tent-plate PMUT provides advantages in relation with the area, cost, power consumption and imaging quality thanks to the capability to be monolithically integrated over CMOS substrates.

I. Introduction

Ultrasound is a non-invasive diagnostic tool widely used in a large number of applications: from medical imaging, non-destructive testing in industrial applications to biometric applications as fingerprints or gesture recognition systems [1], [2]. In this sense, Micromachined Ultrasonic Transducers (MUTs) appear as a promising solution due to small size, low cost, possibility to be integrated with CMOS circuitry and good acoustic impedance matching in comparison with conventional ultrasonic transducers [3]–[5].