III-Nitride MEMS drum resonators on flexible metal substrates.

We present a simple and efficient process for fabricating III-Nitride (III-N) mechanical resonators on flexible metal substrates. This method combines Van der Waals epitaxy of III-N epilayers with the deposition of a thick metal stressor atop the III-N layers. During thermal treatment, the 30 μm thick metal stressor deposited on a 300 nm AlGaN/500 nm GaN layer grown on a 3 nm two-dimensional hexagonal-Boron Nitride (2D h-BN) release layer, initiates a one-step Self-Lift-Off and Transfer (SLOT) process. This process effectively transfers the III-N heterostructure from the h-BN/Sapphire growth wafer to the flexible metal stressor substrate. Additional local etching of the metal stressor and deposition of front electrodes allow for releasing self-standing III-N layers with integrated actuation. Fabricated III-N MEMS drum resonators were analyzed using optical profilometry and laser Doppler vibrometer, enabling the observation of static deflections and distinct vibration modes. Finite element method (FEM) simulations were also performed to further understand experimental observations and assess the mechanical properties of the released III-N layers, particularly enabling the estimation of stress in the GaN and AlGaN released layers. This straightforward approach not only provides a practical solution for cost-effective III-N MEMS resonators but also ensures flexibility, and crack-free structures.