Abstract
A piezoelectric AlN-on-SOI structured MEMS Lamb wave resonator (LWR) is presented for high-temperature strain measurement. The LWR has a composite membrane of a 1 μm thick AlN film and a 30 μm thick device silicon layer. The excited acoustic waves include Rayleigh wave and Lamb waves. A tensile strain sensor has been prepared with one LWR mounted on a uniaxial tensile plate, and its temperature characteristics from 15.4°C to 250°C and tensile strain behaviors from 0 με to 400 με of Rayleigh wave and S4 mode Lamb wave were tested. The temperature test verifies the adaptability of the tensile strain sensor to temperature up to 250°C, and S4 mode Lamb wave and Rayleigh wave represent almost the same temperature characteristics. The strain test demonstrates that S4 mode Lamb wave shows much higher strain sensitivity (-0.48 ppm/με) than Rayleigh wave (0.05 ppm/με) and confirms its advantage of strain sensitivity. Finally, for this one-LWR strain sensor, a method of beat frequency between S4 mode Lamb wave and Rayleigh wave is proposed for temperature compensation and high-sensitivity strain readout.
Highlights
Strain sensors operating at temperatures above several hundred degrees Celsius are demanded for industrial process monitoring and control, steel and refractory material manufacturing, in power plant environments, aerospace and defense.[1,2,3,4] The current high-temperature strain sensors include resistance strain gauge,[5] Fiber Bragg Grating (FBG) optical strain sensor[6] and surface acoustic wave (SAW) strain sensor.[7]
Most of SAW strain sensors can only work below 150◦C due to the limit of the conventional piezoelectric materials such as quartz, lithium niobate (LN) and zinc oxide (ZnO).[8,9,10,11]
Aluminum nitride (AlN) film can be grown on various substrates such as Si, SiC, sapphire and diamond, and the growth processes are compatible with the micro-fabrication process.[14,15,16,17]
Summary
Strain sensors operating at temperatures above several hundred degrees Celsius are demanded for industrial process monitoring and control, steel and refractory material manufacturing, in power plant environments, aerospace and defense.[1,2,3,4] The current high-temperature strain sensors include resistance strain gauge,[5] Fiber Bragg Grating (FBG) optical strain sensor[6] and surface acoustic wave (SAW) strain sensor.[7]. High-temperature high-sensitivity AlN-onSOI Lamb wave resonant strain sensor We design and fabricate a piezoelectric AlN-on-SOI structured MEMS Lamb wave resonator (LWR) for high-temperature strain measurement.
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