High coupling coefficient Temperature compensated FBAR resonator for oscillator application with wide pulling range

Abstract

This paper demonstrates two variations of Temperature compensated (TempCo) FBAR resonators with high Kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . One 1.5 GHz non-symmetric stack design TempCo FBAR resonator has a Kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 4.28% and linear TCF of 0 ppm/°C. A second, quasi-symmetric stack design 1.5GHz TempCo FBAR resonator has Kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> as high as 5.6% and linear TCF of -6 ppm/°C. Significant Kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). High Kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> TempCo FBAR resonator is ideal for FBAR oscillator application with wide frequency pulling range.