Real-Time Frequency Tracking of an Electro-Thermal Piezoresistive Cantilever Resonator with ZnO Nanorods for Chemical Sensing

Andi Setiono,Michael Fahrbach,Wilson Nyang’Au,Erwin Peiner,Maik Bertke,Hutomo Wasisto,Jiushuai Xu

doi:10.3390/chemosensors7010002

Andi Setiono, Michael Fahrbach + Show 5 more

Open Access

https://doi.org/10.3390/chemosensors7010002

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Abstract

The asymmetric resonance response in electro-thermal piezoresistive cantilever resonators causes a need of an optimization treatment for taking parasitic actuation-sensing effects into account. An electronic reference circuit for signal subtraction, integrated with the cantilever resonator has the capability to reduce the effect of parasitic coupling. Measurement results demonstrated that a symmetric amplitude shape (Lorentzian) and an optimized phase characteristic (i.e., monotonically decreasing) were successfully extracted from an asymmetric resonance response. With the monotonic phase response, real-time frequency tracking can be easier to implement using a phase-locked loop (PLL) system. In this work, an electro-thermal piezoresistive cantilever resonator functionalized with self-assembled monolayers of chitosan-covered ZnO nanorod arrays as sensitive layers has been investigated under different relative humidity (rH) levels. Enhancement of resonance phase response has been demonstrated by implementing the reference signal subtraction. Subsequently, a lock-in amplifier integrated with PLL system (MFLI, Zurich Instruments, Zurich, Switzerland) was then employed for continuously tracking the resonant frequency. As a result, we find a good correlation of frequency shift (∆f0) with change in rH monitored using a commercial reference sensor.

Highlights

Silicon micro-electro-mechanical system (MEMS)-based cantilevers combined with nanorod arrays are a versatile platform integrating micro and nano-components (Figure 1), which can be used in multiple sensing applications of physical, chemical, and biological targets [1]
Tracking of the resonance frequency is performed by implementing the phase-locked loop (PLL) technique, as shown in Tracking of the resonance is performed by implementing thein technique,amplitude as shown
Asymmetric resonance in electro-thermal piezoresistive cantilever sensors with ZnO NRs and chitosan has been successfully suppressed by subtracting a reference signal from the sensor output

Summary

Introduction

Silicon micro-electro-mechanical system (MEMS)-based cantilevers combined with nanorod arrays are a versatile platform integrating micro and nano-components (Figure 1), which can be used in multiple sensing applications of physical, chemical, and biological targets [1]. Resonance tracking cannot work can guarantee utmostthere suppression of parasitic on electro-thermal piezoresistive cantilever properly ,an because is an ambiguity in effects the phase response, which subsequently leads to sensors. Hereby we apply an external reference piezoresistive cantilever sensors, realizing the similar effect of direct thermal-parasitic coupling signal in order to obtain a is symmetric amplitude shape and a and monotonic phase response bywhich subtracting between two cantilevers complicated as the heat supply the boundary condition, cause itthe from the outputs of the electro-thermal piezoresistive cantilever sensor [14]. We resonance expect thattracking the implementation of reference signal cantilever subtractionsensors can expedite resonance tracking based on the PLL technique and reduce instabilities during the locking process of Chemosensors 2019, 7, x FOR PEER REVIEW. (VOCs) [15,16] and gases [17,18]

Self-Actuating

V DC voltage at input of the shows there is temperature centeraof the

Reference Signal Subtraction

Real-Time Resonant Frequency Tracking

Conclusions