A film bulk acoustic resonator oscillator based humidity sensor with graphene oxide as the sensitive layer

Abstract

A film bulk acoustic wave resonator (FBAR) is a type of resonator with high frequency and small dimensions, particularly suitable for use as a sensor for physical and biochemical sensing with high sensitivity. FBAR-based sensors have been extensively studied, however they commonly use discrete devices and network analyzers for evaluation, and therefore are far from being able to be used in practical applications. This paper reports the design and analysis of an FBAR-based Pierce oscillator and a field-programmable gate array (FPGA)-based frequency counter, and the use of the oscillator as a humidity sensor with the frequency counter as the measuring circuit. Graphene oxide (GO) is used as the sensitive film to improve the sensitivity. The resonant frequency of the oscillator with a GO film shows a linear decrease with an increase in relative humidity, with a sensitivity of ca. 5 kHz per %RH (relative humidity) in the range of 3%RH to 70%RH, and a higher frequency shift is induced above 70%RH. The FBAR oscillator sensor shows excellent stability and repeatability, demonstrating the feasibility and potential sensing application using the integrated FBAR chip and simple frequency counter, particularly suitable for portable electronics.

Selective multiple analyte detection using multi-mode excitation of a MEMS resonator

“…The coating of selective materials on the resonator surface is essential for the adsorption of a particular analyte to significantly improve the sensitivity and selectivity of the device 31 , 32 . Particularly, for humidity detection, various methods have been used including surface acoustic waves (SAW), quartz crystal membranes (QCM), and MEMS resonators, which are coated with different materials such as graphene oxide, metal–organic frameworks (MOF), and polymers composite 33 – 36 . In our previous work 37 , we showed, based on heated buckled micro-beam, a selective identification for some gases without the need for the material coating.…”

Polyimide-Based High-Performance Film Bulk Acoustic Resonator Humidity Sensor and Its Application in Real-Time Human Respiration Monitoring

“…A lot of effort has been invested to realize high-performance FBAR humidity sensors. Hygroscopic materials such as polymers [ 26 ], graphene dioxide (GO) [ 27 ] and carbon nanomaterials are added to the surface of the resonators to increase the adsorption of water molecules and thus improve the sensitivity of the humidity sensors. Under the help of hygroscopic polymer polyvinylpyrrolidone (PVP) [ 26 ], the sensitivity was improved apparently for the thin PVP sample (−25 kHz/%RH) and thick PVP sample (−110 kHz/%RH) from 20%RH to 60%RH.…”

Fabrication and Characterization of Flexible Capacitive Humidity Sensors Based on Graphene Oxide on Porous PTFE Substrates

“…Graphene oxide (GO) as the derivative of two-dimensional material graphene, contains a large number of oxygen-containing groups [ 8 ], which enhances the hydrophilicity and sensitivity to water molecules. Various humidity sensors using GO as the sensitive material with different structures and sensing principles have been proposed, such as the GO-Si bi-layer stress-based sensor [ 9 ], the CMOS interdigital capacitive humidity sensors [ 10 ], QCM humidity sensors [ 11 ], SAW humidity sensors [ 12 ], FBAR humidity sensors [ 13 ], humidity sensors based on GO foam [ 14 ], etc. The humidity sensors with the sensitive material of GO exhibit high sensitivity, wide range, and fast response/recovery time [ 15 , 16 ].…”