Single-cell system using monolithic PMUTs-on-CMOS to monitor fluid hydrodynamic properties

Abstract

In this work, a single cell capable of monitoring fluid density, viscosity, sound velocity, and compressibility with a compact and small design is presented. The fluid measurement system is formed by a two-port AlScN piezoelectric micromachined ultrasonic transducer (PMUT) with an 80 μm length monolithically fabricated with a 130 nm complementary metal-oxide semiconductor (CMOS) process. The electrode configuration allows the entire system to be implemented in a single device, where one electrode is used as an input and the other as an output. Experimental verification was carried out by exploiting the features of piezoelectric devices such as resonators and acoustic transducers, where a frequency shift and amplitude variation are expected because of a change in density and viscosity. A sensitivity of 482 ± 14 Hz/kg/m3 demonstrates the potential of the system compared to other dual-electrode PMUTs. In addition, according to the acoustic measurement, the sound velocity, fluid compressibility, and viscosity coefficient can be extracted, which, to the best of our knowledge, is novel in these PMUT systems.

Monolithic Sensor Integration in CMOS Technologies

“…For example a chemical sensor can be fabricated by depositing an absorbing material sensitive to a specific chemical over a resonator, and then detecting its mass change [29], [30]. If we add piezoelectric materials to the manufacturing process, like the SilTerra MEMS-on-Top PMUT MEMS process [31], we can build Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) for applications like fluid properties monitoring [32], micron-range distance measurements [33] or for microimaging [34].…”

Fabrication and DC-Bias Manipulation Frequency Characteristics of AlN-Based Piezoelectric Micromachined Ultrasonic Transducer

“…An ultrasound imaging system can provide real-time, high-resolution images, and it is a more affordable medical imaging solution than magnetic resonance imaging and computed tomography. Ultrasonic imaging has also been widely used in other areas of research beyond medical applications, including rangefinders [ 3 , 4 ], fingerprint sensing [ 5 , 6 ], fluid density sensing [ 7 , 8 ], communication links [ 9 ], underwater 3D imaging [ 10 , 11 ], nondestructive testing [ 12 ], and wireless power supply for implantable microdevices [ 13 ]. As one of the typical ultrasonic imaging devices, piezoelectric micromechanical ultrasound transducers (PMUTs) are particularly attractive due to their affordability, compact size, and compatibility with Complementary Metal Oxide Semiconductor (CMOS) manufacturing processes [ 5 , 7 ].…”

A High Sensitivity AlN-Based MEMS Hydrophone for Pipeline Leak Monitoring

“…However, PMUTs do not require high DC bias voltage for low-power operation and have high sensitivity and good linear response [ 25 ]. Due to these advantages, PMUTs have been widely used in fluid density monitoring [ 26 , 27 , 28 , 29 , 30 ], ultrasonic positioning [ 31 ], intravascular ultrasound (IVUS) [ 32 ] fingerprint sensors [ 33 ] and hydroacoustic monitoring. Among the studies for hydroacoustic monitoring, Xu et al proposed a hydrophone based on a PMUT with a resonant frequency of 1.086 MHz, and the sensitivity of the hydrophone was measured to be −182.5 dB [ 34 ].…”