Influence of a Tailored Oxide Interface on the Quality Factor of Microelectromechanical Resonators

Piezoelectric microelectromechanical systems (MEMS) are used as sensors, actuators, energy harvesters, accelerometers, and communication modules. Aluminum nitride (AlN) is an especially attractive piezoelectric material because its fabrication process allows it to be integrated into semiconductor circuitry to deliver a fully integrated solution. Microelectromechanical resonators with AlN sandwiched between n-type silicon (Si) and top metal electrode with and without a silicon oxide layer are designed and fabricated. The effect of the oxide film is up to a fourfold increase in quality factor (Q) that is consistent from very high frequency (VHF) to super high frequency (SHF). This effect is demonstrated using thin plate bulk acoustic wave modes from 70-80 MHz using the second contour mode and first width extensional mode and from 9.5-10.5 GHz using high overtone thickness modes. To explore potential applications of AlN-transduced Q-enhanced MEMS devices in harsh environments, measurements from -200 degrees C to +200 degrees C are performed. The Q enhancement is persistent across a wide temperature range for both VHF and SHF resonators with the added oxide layer. Furthermore, AlN-on-Si resonators that have a comparable temperature coefficient of frequency to silicon carbide-based resonators in commercial applications are demonstrated.

Automated summary

Piezoelectric microelectromechanical systems (MEMS) are versatile devices used for various applications such as sensing, actuation, and energy harvesting. Aluminum nitride (AlN) is an attractive material for these systems due to its integration capability with semiconductor circuitry. This study investigates the use of AlN in MEMS resonators and demonstrates the enhancement of quality factor (Q) through the addition of a silicon oxide layer. The Q enhancement is consistent across different frequencies and is maintained over a wide temperature range.