17 May 2013 MEMS-based silicon cantilevers with integrated electrothermal heaters for airborne ultrafine particle sensing
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Abstract
The development of low-cost and low-power MEMS-based cantilever sensors for possible application in hand-held airborne ultrafine particle monitors is described in this work. The proposed resonant sensors are realized by silicon bulk micromachining technology with electrothermal excitation, piezoresistive frequency readout, and electrostatic particle collection elements integrated and constructed in the same sensor fabrication process step of boron diffusion. Built-in heating resistor and full Wheatstone bridge are set close to the cantilever clamp end for effective excitation and sensing, respectively, of beam deflection. Meanwhile, the particle collection electrode is located at the cantilever free end. A 300 μm-thick, phosphorus-doped silicon bulk wafer is used instead of silicon-on-insulator (SOI) as the starting material for the sensors to reduce the fabrication costs. To etch and release the cantilevers from the substrate, inductively coupled plasma (ICP) cryogenic dry etching is utilized. By controlling the etching parameters (e.g., temperature, oxygen content, and duration), cantilever structures with thicknesses down to 10 - 20 μm are yielded. In the sensor characterization, the heating resistor is heated and generating thermal waves which induce thermal expansion and further cause mechanical bending strain in the out-of-plane direction. A resonant frequency of 114.08 ± 0.04 kHz and a quality factor of 1302 ± 267 are measured in air for a fabricated rectangular cantilever (500x100x13.5 μm3). Owing to its low power consumption of a few milliwatts, this electrothermal cantilever is suitable for replacing the current external piezoelectric stack actuator in the next generation of the miniaturized cantilever-based nanoparticle detector (CANTOR).
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Hutomo Suryo Wasisto, Hutomo Suryo Wasisto, Stephan Merzsch , Stephan Merzsch , Andreas Waag , Andreas Waag , Erwin Peiner , Erwin Peiner , } "MEMS-based silicon cantilevers with integrated electrothermal heaters for airborne ultrafine particle sensing", Proc. SPIE 8763, Smart Sensors, Actuators, and MEMS VI, 87632L (17 May 2013); doi: 10.1117/12.2016938; https://doi.org/10.1117/12.2016938
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