Abstract
Microelectromechanical system (MEMS)-based mass sensors are proposed as potential candidates for highly sensitive chemical and gas detection applications owing to their miniaturized structure, low power consumption, and ease of integration with readout circuits. This paper presents a new approach in developing micromachined mass sensors based on capacitive and piezoelectric transducer configurations for use in low concentration level gas detection in a complex environment. These micromachined sensors operate based on a shift in their center resonant frequencies. This shift is caused by a change in the sensor’s effective mass when exposed to the target gas molecules, which is then correlated to the gas concentration level. In this work, capacitive and piezoelectric-based micromachined sensors are investigated and their principle of operation, device structures and configurations, critical design parameters and their candidate fabrication techniques are discussed in detail.
Highlights
Microelectromechanical system (MEMS)-based sensors are introduced as high-performance detectors due to their sensing capabilities at the micro and nanoscale levels and their potential for integration with wearable electronics [1,2]
capacitive micromachined ultrasonic transducer (CMUT) and piezoelectric micromachined ultrasonic transducer (PMUT) can be configured as gas sensors, operating based on the change in mass of their sensing layer
CMUT gas sensors consist of a suspended membrane
Summary
The application of mechanical force on certain crystals and ceramics, which has no center of inversion symmetry, generates an electric charge. This phenomenon is known as the direct piezoelectric effect. The deformation of the crystal on an applied electric field generates ultrasound, is known as the indirect piezoelectric effect. This advantageous effect can be utilized to design a PMUT sensor. In the CMUT, as described, a high mass sensitivity and sensing performance can be achieved It presents issues, such as the requirement of a high bias voltage and the limitation imposed by the cavity structure. The ability to operate at lower voltages, flexibility in adapting to different sensing materials, and uncomplicated array configuration promises numerous applications in the fields of medicine, environmental monitoring and agriculture [43]
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