5.4GHz, 0.35μm BiCMOS FBAR-Based Single-Ended and Balanced Oscillators in Above-IC Technology

Abstract

For the last few years, one of the main challenges in circuit design has been the integration of frequency references in applications where phase noise requirements are very stringent. To overcome the usual limitation of (Bi)CMOS integrated circuits (ICs) phase noise, mainly due to the low Q-factor of standard integrated passive devices (R, L, C) inherent to low resistivity substrate, a solution has been to use BAW resonators. Indeed, thin film BAW resonators based on piezoelectric material, generally AlN or ZnO, sandwiched between two metallic electrodes, exhibit a high Q-factor, can handle high power, and can operate at high frequencies (above 10 GHz Hz), while keeping a small size and being compatible with (Bi)CMOS IC processes. The very first oscillators using FBAR and SMR resonators were designed with separately wire-bonded resonators connected to the IC circuit. This chapter deals with the world premiere realization of two 5-GHz FBAR-based oscillators, where the FBAR is directly integrated above the IC with some further process steps, compatible with (Bi)CMOS. A single-ended and a balanced version were designed. The circuits were implemented in a 0.35-μm SiGe BiCMOS process from AMI Semiconductor. From the obtained results, we show that post-processing the FBAR directly over the IC eliminates much of the parasitics and modelling issues associated with bondwires. Furthermore, it reduces the circuit area. The single-ended and balanced oscillators are based on the Colpitts configuration and achieve respectively a state-of-the-art phase noise performance (at the time of design) of − 117. 7 d b c Hz and − 121 d b c Hz at 100 K Hz offset from the 5.4-GHz carrier frequency. The balanced version allows direct driving of balanced dividers and mixers without the need of a single-ended to balanced converter. Some comparisons are also made with standard LC balanced oscillators.