Design and fabrication of reference saw oscillator using polylithic integration of electronic and acoustic devices on quartz-on-silicon wafer

Abstract

This paper presents an methods to integrate high Q passives and integrated circuits on a chip using our proposed PolyLithically Integrated Circuit(PLIC) technology. The electro-acoustic devices such as high Q SAW resonator and filters can be fabricated on Quartz directly bonded on the processed Silicon wafer (QoS), whose process are compatible with conventional Si IC process. We first fabricated a prototype of SAW resonator and oscillator on thick QoS instead of existing crystal oscillator. The crystal cannot be integrated on QoS with thin film process, but SAW devices are compatible with photolithographic process and easily realizable on QoS. Our SAW resonator on QoS shows Q about 10,000 and 11 dB insertion loss at 289 MHz, and BJT integrated on Si wafer is used as the active transistor of SAW oscillator. The measured phase noise of oscillator is as small as -120 dBc at 10 kHz offset, which is sufficient for most reference oscillator applications. For more advanced work to show the feasibility of single chip RF system on QoS, a digitally temperature compensated SAW reference oscillator(DTCSO) is designed and fabricated in this work. The SAW device has some dependency on variation of temperature and process. In so far, analog temperature compensation method using varactor is adopted in every previous works, where the varactor is hardly integrable on Si IC. But our digital compensation circuits contains the circuits such as CMOS controller, digital capacitor bank, temperature sensor using bipolar transistor, and PROM, which are all integrable on cheap CMOS IC. The achieved compensated results shows the frequency stability of 3ppm against variation of temperature and process. Moreover, to improve the accuracy and thermal hysteresis of sensor, a SAW itself is employed as a temperature sensor and its characteristics is investigated. The sensitivity of SAW sensor to temperature is about 19ppm/℃ and using frequency counter very accurate and non hysteric temperature ...