The crystal unit/crystal oscillator with high stability is mainly divided into three types according to the cut type:

     (1) The kHz-level crystal unit adopts a tuning fork structure vibrator;

     (2) The MHz-level crystal unit adopts AT-type structural vibrator;

     (3) The 100 MHz ultra-high frequency crystal unit adopts SAW type vibrator, and its temperature characteristic curve is similar to tuning fork type vibrator. As downstream products demand higher and higher requirements for crystal vibration resistance, phase noise, etc., size miniaturization and other parameters, the limitations of traditional machining are gradually revealed.

     Tuning fork crystal defect: it will be difficult to obtain good oscillation characteristics after the unit size is reduced. When the size of the quartz vibrator is reduced from 1.2×1.0mm to 1.0×0.8mm, the series resistance value (CI value) will increase by about 30%, which means that it will be difficult to obtain good oscillation after the size of the tuning fork crystal unit is reduced. characteristic.

     AT-cut crystal defects: Traditional machining is difficult to meet strict tolerance requirements. AT cutting is currently one of the most commonly used types of quartz crystals, and is often used for high-frequency crystal oscillators. The size of a typical ultra-small blank is less than 3.5*0.63mm, and the processing difficulty is greatly increased. When large-scale production of small crystals, it is necessary to control the tolerance within 2um, while traditional machining is difficult to meet the strict tolerance requirements.

     Ultra-high frequency crystal defect: repeated frequency multiplication causes serious phase noise loss. The operating frequency of the crystal oscillator is usually inversely proportional to the thickness of the wafer. The most suitable frequency range for traditional machining is 1-40MHz (corresponding to the thickness of the wafer 0.04mm). Consuming a 100 MHz crystal oscillator in the traditional way requires processing the wafer to be ultra-thin, resulting in poor stability and easy breakage. Therefore, consumer high-frequency crystal oscillators of 100 MHz usually use mature products of 10MHz as the reference frequency source, and obtain the required signal after repeated frequency multiplication. However, this leads to complex circuits and serious phase noise losses.