Pure Premium Quartz (PPQ) Synthesis for SAW Resonators Beyond the State of the Art

Until last years, filters for mobile operated in the 70-350 MHz frequency range with a quality factor times frequency (Q×f) product reaching values of around 9×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup>. The aim is now to reach a Q×f of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup>. Progress on quartz material is a key factor success. We worked on the synthesis of quartz to get higher purity and larger size (100mm/4-inches) to exceed characterization standard values (IEC 60 758 and JIS C 6704). Our Pure Premium Quartz (PPQ) AT wafers were compatible with fabrication of SAW devices. Multiple resonance resonators were manufactured, based on 2 interdigitated transducers, Bragg mirrors and a central cavity. The device measurements have been compared with theoretical prediction, yielding an excellent agreement between both curves. Same for the Temperature Coefficient of Frequency (TCF). Further analysis identified an attenuation constant of 1 mdB/λ providing the measured Q factors and therefore a Q×f product of 8.96×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> at air. Works in progress on our quartz should reach a Q×f product of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> on 150mm (6-inches) AT wafers.