A 0.35 MM2 System on Chip Level Detector Based on An Annular Pmut-On-Cmos Array

This paper presents a 0.35 mm² multi-element annular piezoelectric micromachined ultrasonic transducer array monolithically integrated on CMOS (PMUT-on-CMOS) capable of monitoring fluid level changes and evaporation rates in very small quantities and with high sensitivity in a non-invasive and non-intrusive way. Each individual PMUT consists of a 40 μm square AlScN PMUT with a resonance frequency of 8.6 MHz. Using a pulse-echo scheme, the high-frequency ultrasound system provides an interesting solution for the determination of fluid level changes and evaluation of evaporation rates in containers with low ultrasound reflection. Demonstrations of the evaporation rates of acetone and ethanol are provided as proof-of-concept. The thickness variations are 82 μm/min and 18 μm/min for acetone and ethanol, respectively; these values correspond to an evaporation rate of 3.9 kg/(m²h) (Acetone) and 0.9 kg/(m²h) (Ethanol).

INTRODUCTION

Nowadays, industrial control in the pharmaceutical, food, and chemical fields requires frequently liquid-based operations. The detection of fluid levels, leaks and evaporation rates are some of the tasks that must be constantly verified. In this context, ultrasound could be an interesting solution due to it is safe, non-invasive, and relatively inexpensive technology. Both invasive and noninvasive approaches could be implemented where the first one offers a fast solution, and the second one avoids the risk of fluid contamination.