PT-PT Bonding for High-Temperature Integrated Resonant Pressure Sensors

This work introduces, for the first time, the use of flip chip Pt-Pt bonding to form microelectromechanical systems (MEMS) suspended resonators, integrated on top of electronics, and targeted for 1 hour survival at 800°C. We show a bonding method using Platinum (Pt) metal which guarantees a strong bond and achieves a crack free interface along with a uniform cavity. The bond is formed between AlN bulk substrate (where the electronics will be fabricated) and sputtered AlN-based stack on Si (MEMS die), surviving the high temperature annealing at 800°C for 1 hour, and maintaining the symmetrical gap. Bond quality was evaluated using focused ion beam (FIB) analysis and shear test. By eliminating the need of sacrificial layer or refilled cavities, a more versatile process is introduced, for integration of AlN MEMS with Electronics. We demonstrate a resonant pressure sensor on this platform, with a high and linear frequency vs. pressure sensitivity of 1.53 ppm/Pa. We also demonstrate thickness extensional resonance modes at 3.2 GHz measured on the same platform, showing minimal quality factor degradation up to 40 min annealing at 800°C.