Design, implementation and characterization of temperature compensated SAW resonators in CMOS technology for RF oscillators.

摘要

Surface Acoustic Wave (SAW) resonators, are vastly popular in local oscillators for RF transceiver designs. With the advent of miniaturization and integration of mobile wireless systems, there is motivation to implement the SAW resonator as a monolithic block, fabricated using standard IC process technology. This work describes the design, implementation and characterization methods of integrating GHz SAW resonators in CMOS technologies. Progression of several different designs implemented in standard CMOS (0.6 mum) and RF-CMOS (0.18 mum) technologies are presented. The design of the resonators is equipped with the development of an equivalent circuit model specifically for SAW resonators employing CMOS layers. Simulations using 3D-FEM tools were also performed to obtain the devices' resonant frequencies and transducer capacitance.;The major challenge of realizing GHz acoustic wave resonators is the requirement of manufacturing submicron, high aspect ratio IDTs. This was surmounted by fabricating the thin IDTs in commercial CMOS process technology and implementing a unique fabrication post-CMOS process sequence to realize the device. Three micromachining processes namely reactive-ion-etching, zinc oxide deposition and region definition through wet-etching, were implemented. Extensive characterization of both the device and deposited piezoelectric material was carried out. Measurement results revealed resonators operating at frequencies between 600 MHz to 3.12 GHz, insertion losses ranging from 30 to 50 dB and quality factors ranging between 30 and 255.;Two different techniques had been introduced to improve the performance of CMOS SAW resonators. Enhanced device quality factors were obtained by increasing the reflectors' height using stacked CMOS metal-oxide layers. The second approach employs matching networks coupled to the packaged resonator and provided approximately 30 dB reduction in insertion losses.;The temperature sensitivity of ZnO necessitates a means of attaining resonant frequency stability with varying ambient temperatures. This unique temperature compensation scheme, complete with a micro-hotplate and an on-chip calibration thermistor demonstrated capabilities of reducing the TCF from -97.2 ppm/°C to -23.19 ppm/°C. Finally, the application of the CMOS SAW resonator as an RF oscillator was demonstrated. Oscillation was achieved at 626 MHz when the CMOS SAW resonator, a commercial amplifier and a phase shifter was connected and mounted on a PCB.