A novel low-temperature method to fabricate MEMS resonators using PMGI as a sacrificial layer

A method to fabricate microelectromechanical systems (MEMS) clamped-clamped resonators using polymethylglutarimide (PMGI) as a sacrificial release layer has been developed. Control of the critical air-gap dimension between the resonator beam and drive electrode was maintained by varying the sacrificial PMGI thickness, allowing fabrication of devices with resonator-to-electrode gaps as small as 100 nm. The resonator beam was constructed by depositing a low stress, low temperature bi-layer alpha-TaN/SiON (50/2000 nm) film over the PMGI layer, followed by a multi-step etch process. Physical characterization of devices with varying beam lengths was performed via focused ion beam and scanning electron microscopy analyses to verify complete release of the resonator structures. Electrical testing showed a resonant frequency of 11.3 MHz, which agreed well with simulated results. The measured RF characteristics are fitted with a lumped element model that used Young's modulus and the device quality factor as adjustable parameters. Young's modulus of the individual components of the TaN/SiON bi-layer was measured and found to be in good agreement with the values used to fit the measured resonance.