Optical-Interferometry-Based CMOS-MEMS Sensor Transduced by Stress-Induced Nanomechanical Deflection.

Satoshi Maruyama,Kazuaki Sawada,Kazuhiro Takahashi,Takeshi Hizawa

doi:10.3390/s18010138

Abstract

We developed a Fabry–Perot interferometer sensor with a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for chemical sensing. The novel signal transducing technique was performed in three steps: mechanical deflection, transmittance change, and photocurrent change. A small readout photocurrent was processed by an integrated source follower circuit. The movable film of the sensor was a 350-nm-thick polychloro-para-xylylene membrane with a diameter of 100 µm and an air gap of 300 nm. The linearity of the integrated source follower circuit was obtained. We demonstrated a gas response using 80-ppm ethanol detected by small membrane deformation of 50 nm, which resulted in an output-voltage change with the proposed high-efficiency transduction.

Highlights

Microelectromechanical systems (MEMS)-based sensors allow the real-time detection of various parameters such as pressure, acceleration, force, and surface stress, which contributes to the Internet of Things (IoT) realm
We propose a method to convert the displacement of the movable film into a light intensity change by using optical interference, in which the flexible movable film on the photodiode has a hollow structure, and to convert the light-intensity change into an opto-electric signal with a photodiode
The movable film of this sensor consists of polychloro-para-xylylene, which has a Youngs’ modulus two orders lower than that of silicon, and the amount of deformation with respect to surface stress is expected to be greater with this film compared to that with conventional movable films

Summary

Introduction

Microelectromechanical systems (MEMS)-based sensors allow the real-time detection of various parameters such as pressure, acceleration, force, and surface stress, which contributes to the Internet of Things (IoT) realm. As a sensor for measuring physical quantities and biomolecules and chemical substances, MEMS sensors that capture the mechanical response to the adsorption of molecules are used to detect various molecules as well as the mechanical and electrical changes in structures due to adsorption, which can be observed in real time. A chemical and bio sensor using MEMS structures including a system for detecting a static deflection of the dynamic system and a micro-mechanical structure to detect a change in the mechanical resonance frequency has been proposed [14,15,16,17,18,19]. In a resonant chemical sensor, a functional film that absorbs a molecule is formed on a silicon resonator, and the change in resonance frequency after the absorption of molecules is captured.

Methods

Results

Conclusion