Piezoelectric Quartz Wafer for SAW Components
1. Quartz Crystal Properties
The quartz, a very important piezoelectric material, is raw material for making quartz crystal resonators. Its main feature is that its atoms or molecules are arranged regularly, which reflects the symmetry of the shape on a macroscopic scale. Under the action of an electric field, the crystal generates stress and deforms, thereby generating mechanical vibration and obtaining a specific frequency. Quartz crystal resonators are manufactured by using its inverse piezoelectric effect characteristics.
2. Quartz Substrate Properties
Quartz crystal is currently the most used crystal and is an important electronic material. When a quartz wafer cut in a certain direction is subjected to mechanical stress, an electric field or charge proportional to the stress will be generated. This phenomenon is called the positive piezoelectric effect. Conversely, when the quartz crystal wafer is subjected to an electric field, it will produce a strain proportional to the electric field. This phenomenon is called the inverse piezoelectric effect. The positive and inverse effects are collectively called the piezoelectric effect. Quartz single crystal wafer not only has piezoelectric effect, but also has excellent mechanical, electrical and temperature characteristics. Resonators, oscillators and filters designed and manufactured with single crystal quartz wafer have outstanding advantages in frequency stabilization and frequency selection.
3. Production Process for Z-cut and ST-cut Quartz Wafer
To produce a quartz crystal resonator with good performance, in addition to a reasonable design and excellent raw materials, the production process for single crystal quartz substrate will play a decisive role. The specific production steps are as follows:
Firstly, the raw pieces are sorted. Because of the large cutting angle error of the quartz raw pieces, the X-ray directional instrument must be used for angle sorting before rough processing. Then select the appropriate angle of the raw piece for processing according to the needs, that is, sticking strips, cutting seed crystals, rounding and so on.
Then, the quartz substrate grinding process is carried out, which is generally divided into coarse grinding, intermediate grinding and fine grinding. Coarse grinding is mainly to cut the angle and thickness of the quartz wafers, while middle grinding and fine grinding are to finely adjust the thickness of the quartz single crystal wafer.
After grinding, in order to ensure the surface quality of the wafer and the stability and reliability of the crystal in use, the quartz wafer is polished and cleaned. The thicker the wafer, the greater the impact on the vibration performance and resistance of the crystal. Therefore, the deep etching method to remove the loose surface layer of the single crystal quartz wafers caused by grinding is more effective.
Mounting and dispensing is to slowly put the quartz plate with the electrode plated between the two metal plates of the ribbon support. Let the two metal plates with slots tightly clamp the quartz plate, and then apply the coating on the contact between the electrode and the metal plate. The upper layer of conductive glue makes the electrode film contact with the metal sheet through the conductive glue on the edge to produce an electrical connection.
Frequency modulation is a key step in the production of crystal oscillators, that is, adjusting the resonant frequency of the crystal oscillator to meet the design requirements. The frequency modulation methods of different types of crystal oscillators are different. The methods are vacuum coating frequency modulation and polishing wafer frequency modulation. For the production of crystal oscillators with low technical added value and relatively high cost requirements, the polishing wafer frequency modulation process is often used.
Finally, the shell packaging, printing and finished product measurement processes are carried out.
4. Quartz Wafer Application and Development
Electronic parts made of the physical properties of quartz wafers have high frequency stability and are widely used in digital circuits, computers, communications and other fields. Quartz wafer is to serve as a frequency source and frequency reference in electronic circuits.
As the scale of the information industry and electronics industry in various countries continues to expand, the application scope of crystal oscillators is still expanding, driving the continuous growth of its market scale. At present, the market has a great demand for high-precision, high-frequency, high-stability, and low-power crystal oscillator products. At the same time, with the development of electronic products in the direction of ultra-thin, miniaturization, and functional integration, crystal oscillator products have also been upgraded to miniaturization, chip-type, and integration. Therefore, there should be a lot of room for improvement in the production technology of the quartz wafer industry.