Piezoelectric and ferroelectric device technologies for microwave oscillators

Doctoral thesis, 2009

The purpose of this thesis is to investigate piezoelectric and ferroelectric thin film device technologies for application in microwave oscillators. Thin film varactors based on ferroelectric materials are considered. Experimental development of practical varactors based on paraelectric phase BaxSr1−xTiO3, in terms of layout design and model extraction, is presented in the thesis. Experimental results of voltage-controlled oscillators based on ferroelectric varactors operating at 16 GHz and 19 GHz are also presented. The ferroelectric device technology is furthermore compared to traditional varactor technologies, and discussed from the perspective of oscillator applications. Thin film bulk acoustic resonators based on piezoelectric materials and biased electrostrictive materials are considered. Specifically, fixed-frequency resonators based on AlN and tunable resonators based on paraelectric phase BaxSr1−xTiO3 are investigated in the thesis. An integration concept is developed for AlN resonators, and experimentally demonstrated by 2 GHz oscillators. Additionally, modelling and measurement techniques for resonators based on AlN and BaxSr1−xTiO3 are developed. The investigated technologies are compared to traditional planar resonator technologies.