Experimental Study of Fine Frequency Selection Techniques for Piezoelectric Aluminum Nitride Lamb Wave Resonators

Experimental Study of Fine Frequency Selection Techniques for Piezoelectric Aluminum Nitride Lamb Wave Resonators by Ting-Ta Yen Master of Science, Plan II in Electrical Engineering and Computer Sciences University of California, Berkeley Professor Albert P. Pisano, Chair Strong demand for high-Q resonators and filters in mobile wireless communication systems has initiated various research on radio frequency microelectromechanical systems (RF MEMS). Several CMOS-compatible RF MEMS resonator technologies, either electrostatic or piezoelectric, can provide multi-frequency operation on a single substrate and have the potential to realize a channel-select RF front-end architecture. However, utilizing a narrowband filter bank in such an architecture as the key component for frequency selection leads to a major challenge: fine frequency control. Depending upon the standard, it may entail the simultaneous fabrication of tens to hundreds of filters with 0.05 to 0.1% bandwidth, and spacing. Aluminum nitride (AlN) Lamb wave resonators (LWRs) utilize piezoelectric transduction to ensure low motional resistance. The resonance frequency of a LWR is defined by interdigital transducer (IDT) pitch and is thus decoupled from the overall device dimensions. This fine frequency selection technique is enabled by adjusting the so-called AlN "overhang" dimension allowing control of relative frequency of Lamb wave resonators in an array to 0.1%. Experimental results suggest the center frequency of LWRs can be linearly adjusted by up to 5% with no significant effect on other resonator parameters including Q, Rm, C0, and kt . Closely and evenly spaced AlN Lamb wave resonators, without post-process trimming, demonstrate the potential to realize a pure mechanical, high performance, yet low power RF front-end system. Albert P. Pisano Date