Fabrication and characterization of an ultrasensitive acousto-optical cantilever

Abstract

A cantilever-type silicon device for sensing changes in pressure has been designed, fabricated and characterized. The microfabrication process is based on two-sided etching of silicon-on insulator (SOI) wafers. The rectangular cantilevers are 9.5 µm thick, and cover an area of a few square millimeters. The cantilevers are surrounded by thick and tight frames, since on the three free sides there are only narrow, micrometer sized air gaps between the cantilever and the frame. This design and excellent mechanical properties of single crystal silicon enable sensitive detection of time-dependent gas pressure variations, i.e. acoustic waves. The mechanical properties of the cantilever have been characterized by analyzing its dynamic behavior. The resonance frequency and the mechanical vibrational mode patterns have been determined using finite-element method (FEM) simulations and laser interferometry. These results are found to be in good agreement with each other. Initially this mechanical door-like cantilever was designed to be used in ultra-high sensitivity photoacoustic gas sensing, but it can also be applied quite generally in various kinds of sound wave detection schemes.

Fourier Transform Infrared Photoacoustic Multicomponent Gas Spectroscopy with Optical Cantilever Detection

“…Since, the membrane response is also dependent on temperature, the thermal stability of the membrane microphone is bad. 7 To overcome these limitations, Kauppinen, from the University of Turku, Finland, invented the optical readout cantilever microphone in the recent past. This optical microphone is not subject to the physical limitations of the condenser microphone, allowing improvements to the sensitivity and the dynamic range.…”

“…This optical microphone is not subject to the physical limitations of the condenser microphone, allowing improvements to the sensitivity and the dynamic range. 1,[5][6][7][8] Using the optical cantilever detection (OCD) technique, the photoacoustic method can be 100 times more sensitive than with conventional capacitive microphones. 2,9,10 So far, photoacoustic gas spectroscopy using optical cantilever detection (PAS-OCD) has only been set up with lasers, diode lasers, or blackbody radiators with filters.…”

Progress in cantilever enhanced photoacoustic spectroscopy

“…3). The fabrication and characterization of the cantilever sensor is described in detail elsewhere [6].…”

Robust Design of Horn Shaped Piezo-Resistive Mems Pressure Sensor

“…Incorporation of capacitive detection technique in cantilever beam makes the fabrication process of sensor complex owing to the requirement of counter electrode [12]. Cantilever based pressure sensor provides higher sensitivity for the reason of fact that only one side is fixed and all other three sides are freely movable which is not in case of diaphragm based pressure sensor [13]. The orientation of the p-type piezo-resistors along <110> direction of <100> Silicon wafer during bulk micro manufacturing contributes to improved sensitivity [14].…”