Aluminum nitride piezoelectric microphones as zero-power passive acoustic filters

With the advent of the internet-of-things, sensors that are constantly alert yet consuming near-zero power are desired. Remote sensing applications where sensor replacement is costly or hazardous would also benefit. Piezoelectric micro-electro-mechanical systems (MEMS) convert mechanical or acoustic energy into electrical signals while consuming zero power. When coupled with low-power complementary metal-oxide-semiconductor (CMOS) circuits, a near-zero power sensing system is formed. This work describes piezoelectric MEMS microphones based on aluminum nitride (AlN). The microphones operate as passive acoustic filters by placing their resonant response within bandwidths of interest. Devices are demonstrated with operational frequencies from 430 Hz to greater than 10 kHz with quality factors as large as 3,000 and open-circuit voltages exceeding 600 mV/Pa.