Residual Stress Analysis in ScAlN Micro-Diaphragm for High Sensitivity and Wide Range Pressure Sensing

Compared to conventional Lead Zirconate Titanate (PZT) micro-diaphragm, Scandium Aluminum Nitride (ScAlN) micro-diaphragm’s inherent piezoelectricity and absence of obvious ferroelectric hysteresis render it an optimal choice for resonance sensing. Given the flexibility of a thin elastic membrane, ScAlN micro-diaphragm can potentially be highly sensitive for pressure sensing. However, it is found that the micro-diaphragm with tensile residual stress impact will not work as expected at a low-pressure range (0-0.5 bar). The resonance characteristic of the micro-diaphragm is severely affected by the initial condition and residual stress. To address this challenge, we have investigated the impact of residual stress and initial membrane deformation and propose a desirable membrane condition. Eventually, we achieve a high-sensitivity (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Sen</inf> = 112 kHz/bar, FOM = f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Sen</inf>/f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> = 98×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ppm/bar) and a wide range (0-3 bar) Sc<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf>.<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</inf>Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf>.<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">85</inf>N micro-diaphragm pressure sensor well-suited for tire pressure monitoring in vehicles.