A Sensitivity-Enhanced Film Bulk Acoustic Resonator Gas Sensor with an Oscillator Circuit and Its Detection Application

Mengying Zhang,Zhan Zhao,Zhen Fang,Lidong Du

doi:10.3390/mi8010025

Abstract

This paper presents a sensitivity-enhanced gas sensor based on a film bulk acoustic resonator (FBAR). It was designed and fabricated with micro through-holes in its top electrode for sensitivity enhancement. The sensor was driven by a Colpitts oscillator circuit, and the output signal had characteristics of a power of −2.6 dBm@3 V and a phase noise of −90 dBc/Hz@100 kHz. In order to test the performance of the sensor, it was used for the detection of relative humidity (RH) and ethanol. When the relative humidity ranged from 25% to 88%, the frequency shift of the sensor was 733 kHz, which was 3.2 times higher than that of the existing FBAR sensor with a complete top electrode. Fitting results of the frequency shift and the relative humidity indicated that the measurement error was within ±0.8% RH. When the ethanol concentration ranged from 0 to 0.2355 g/L, the frequency shift of the sensor was 365 kHz. The effect of the oscillator circuit on the adsorption reaction and temperature response of the FBAR sensor device was analyzed to optimize its detection application.

Highlights

Sensors based on a film bulk acoustic resonator (FBAR) have attracted plenty of attention because of their highly sensitive resonance frequency to various parameters, such as mass [1], pressure [2], temperature [3] and light [4,5]
A sensitivity-enhanced gas sensor based on a FBAR was designed and fabricated in this work
Sensor samples consisting of the FBAR sensor and the oscillator circuit were fabricated and detected

Summary

Introduction

Sensors based on a film bulk acoustic resonator (FBAR) have attracted plenty of attention because of their highly sensitive resonance frequency to various parameters, such as mass [1], pressure [2], temperature [3] and light [4,5]. The quartz crystal microbalance (QCM) is another bulk acoustic resonator, and it has been widely used as a mass sensor. Decided by the piezoelectric layers, the resonance frequency of the QCM is usually from 5 to 10 MHz, while that of the FBAR reaches GHz. With a similar adsorption reaction, the mass sensitivity and discernibility of FBAR sensors are much higher than those of QCM sensors. For example, with ZnO nanostructures or some organic materials as sensitive layers [6,7,8,9,10]; the sensitivity of the QCM sensor was enhanced to

Methods

Discussion

Conclusion