Ultra Low-Power CMOS Featuring FBARs
Jan M. Rabaey, Michael Mark, Jesse Aaron Richmond and Nathan Pletcher
This project focuses on increasing the reliability and level of integration of Film Bulk Acoustic Resonators (FBAR) based ultra-low power radios for wireless sensor networks (WSN). FBARs provide very high-Q resonances and offer the possibility to achieve a high level of integration and are therefore a key enabling technology to achieve ultra-low power WSN radios. However, there are some limitations associated with FBARs, both at the circuit as well as on the integration side.
The high-Q of the FBARs enables ultra-low power high quality oscillators and excellent RF filters, however it also limits the achievable tuning range of these oscillators, which restricts the radios to operate at a more or less fixed frequency. This restriction makes the narrowband radios susceptible to channel fading and interference, which could prevent the radios from reliably communicating with each other.
Another issue is the temperature drift of the resonances of the FBARs, which might also prevent the radios from communicating with each other. Further, achieving the ultimate integration of high quality FBARs with CMOS circuits in one single package in a reliable and economical way is something that hasn't been accomplished yet.
The purpose of this project is to come up with circuit and process solutions to overcome some of these limitations. Currently, a first set of test chips has been produced, and characterization is about to start.