Growth of high quality quartz crystal and its application to temperature sensors

Synthetic quartz crystal has been grown in a platinum lined autoclave measuring /spl phi/ 20 cm/spl times/300 cm. The seed, measured purity of the liquid solution and the nutrient are carefully selected to minimize impurities and dislocations in the "as grown" quartz crystal. The three-layer autoclave has been newly designed to grow a highly pure and inclusion free synthetic quartz crystal. The liner and the fixtures such as basket, frame and baffle plate for the autoclave are all made from platinum. Etch channels, etch pits and inclusions are not detectable in this synthetic quartz crystal using a detection limit of 10 /spl mu/m. A wide-range cryogenic temperature sensor is fabricated from this highly pure synthetic quartz crystal. An optimum Y cut plate is mounted in a hermetically sealed enclosure 2 mm in diameter and 6 mm in length to realize a cryogenic temperature sensor covering a wide temperature range from 4.2 K to 400 K. The sensor operates in fundamental mode at about 28 MHz through either an extended cable connection or wireless echo sensor system. Although degradation in crystal impedance and an abnormal frequency change of the temperature sensor was initially found at about 60 K, these disadvantages have been eliminated by applying a "sweeping method".<>