High Coupling Coefficient Temperature Compensated FBAR Resonator for Oscillator Application with Wide Pulling Range

This paper demonstrates two variations of Temperature compensated (TempCo) FBAR resonators with high Kt(2). One 1.5 GHz non-symmetric stack design TempCo FBAR resonator has a Kt(2) of 4.28% and linear TCF of 0 ppm/degrees C. A second, quasi-symmetric stack design 1.5GHz TempCo FBAR resonator has Kt(2) as high as 5.6% and linear TCF of -6 ppm/degrees C. Significant Kt(2) improvement comes from optimal design of stack film, interposer electrode effect and novel process development of a sealant for the oxide to protect it from HF etching. This paper also discusses the trade-off between two parameters (linear TCF vs. Kt(2)). High Kt(2) TempCo FBAR resonator is ideal for FBAR oscillator application with wide frequency pulling range.