Poly-SiGe: A High-Q Structural Material for Integrated RF MEMS

Abstract

This paper presents new material data for single-and multilayer CMOS compatible poly-SiGe films, including mechanical quality factor (Q), Young's modulus, and strain gradient. Using audio frequency folded-flexure comb-drive resonators, the mechanical quality factor of poly-SiGe was determined at 2Torr pressure. As-deposited poly-SiGe has Q = 20,000 -31,000. CMOS compatible rapid thermal annealing (RTA) at 525C for 60 seconds results in a quality factor between 40,000 and 44,000. We have measured the highest Q factor yet reported for poly-SiGe (Q 61,100), as a result of RTA at 600C for one minute. The measured resonant frequencies of the resonators were used to back-calculate the Young's modulus of poly-SiGe: E = 155 5GPa. The calculated elastic modulus is significantly higher than the metallurgical Young's modulus of 146GPa. The as-deposited strain gradient of the tri-layer poly-SiGe film was found to be 1.7510 -4 m -1 (curl-up). RTA at 600C for one minute drops the tri-layer strain gradient to 2.6710 -5 m -1 (curl-up). The graded Ge content multi-layer film was observed to induce a larger normalized strain gradient.