Quartz, a kind of crystallized Silicon Dioxide, SiO2, 32 symmetry group of trigonal system (Fig.1), exhibits piezoelectric property, which is the operating base of the electromechanical products. With its intrinstic high Q-value, the quartz based resonator and oscillator are the most wildly adopted as the reference signal source in circuitry for frequency control applications. Quartz frequency control products can be categorized into bulk acoustic wave application devices, such as crystals/resonators, monolithic crystal filters and clock oscillators, and surface accoustic wave application devices, such as SAW resonators and SAW filters. A piece of quartz crystal in a specific orientation cut, shape and dimensions is named crystal wafer (blank). Such a crystal wafer with two deposited electrodes on both sides and housed in a holder is a crystal unit (one-port resonator). By using the one-port resonators as impedance elements, crystal bandpass filters can be obtained. By incorporating the crystal resonator into a kind of electric circuit, one could get different kind of clock crystal oscillators (CXO), for example, Pierce Oscillator, Colpitts Oscillator, Simple Package Crystal Oscillator, Voltage Controlled Crystal Oscillatos, Temperature Compensated Crystal Oscillator, Oven Controlled Crystal Oscillator, and so on. Instead of bulk vibration of quartz crystals, a shorter wavelength (higher frequency) vibration can be achieved by surface wave propergation with inter-digital-transducer (IDT) electrodes on the surface of quartz material. This vibration mechanism can be used for resonator and filter applications .

Fig.1 Crystallized quartz material