An Aluminum Nitride-Based Dual-Axis MEMS In-Plane Differential Resonant Accelerometer

A dual-axis in-plane resonant accelerometer based on aluminum nitride (AlN) has been developed, fabricated, and characterized. The performance of the constituent resonators in the resonant accelerometer has been fully assessed through its open and closed-loop responses, with detailed characterization results for one of the four resonators. The resonator features a low motional resistance (
${R}_{m}$
), eliminating the need for any board-level circuitry, unlike previous designs, while simply using a commercial lock-in amplifier with a phase lock loop (PLL) for oscillation. At an offset frequency of 1 kHz, the oscillator exhibits a phase noise of 100 dBc/Hz and an Allan deviation of subppm range. Acceleration of 1 g is induced by tilting the device by 90°, causing a corresponding frequency change in the beam resonator due to generated stress. All four resonators have been tested using a 45° step tilt to verify the results. At a frequency of 1.1 MHz, the accelerometer has an
${x}$
-axis sensitivity of 73 Hz/g (66 ppm/g) and a
${y}$
-axis sensitivity of 53 Hz/g (48 ppm/g), respectively, with a linear response exhibiting an
${R}^{{2}}$
value of 0.9995 and a minimum detectable angle of 0.67°. Despite using wider beams, the device’s sensitivity remains significant due to the use of a full substrate thickness for the proof mass and a slender resonator thickness of only
$3 \mu \text{m}$
.