Basic Knowledge of Crystal Sensor

1. What is a crystal Sensor?

The thin circular crystal sensor comes from the polyhedral quartz rod, which is cut into shiny hexahedral rod, then cut and grinded repeatedly. The quartz rod is finally made into a pile of thin (0.23mm thick, 13.98mm diameter) wafers. Each wafer is trimmed, polished and cleaned, and finally coated with metal electrodes (full plated on the front and keyhole plated on the back), tested, packaged. It can be used out of the factory. The quality and lifetime of crystals not only affect the accuracy of measurement of velocity and thickness, but also determine whether the controlled process can be successfully completed.

2. Principle of Crystal Sensor

If mechanical pressure is applied on both sides of the wafer, an electric field will be generated in the corresponding direction of the wafer. This physical phenomenon is called piezoelectric effect. If the alternating voltage is applied to the two poles of the wafer, the wafer will produce mechanical vibration, and the mechanical vibration of the wafer will produce alternating electric field.

3. Classification of Crystal Sensor

There are two kinds of frequency points commonly used in the market. The nominal frequency is 5.000MHz and 6.000MHz respectively. Different electrode shapes are adopted according to the design of the probe of the film thickness controller.

4. Application of Crystal Sensor

Quartz crystal oscillator is a speed and thickness sensor in the crystal film thickness control system. These crystals are used for vacuum applications of all standard monitors or controllers and single, double or multiple crystal sensors.

5. Electrode Material of Crystal Sensor

The electrode of crystal sensor is very important to monitor the film thickness. At present, there are three kinds of standard electrode materials on the market: gold, silver and alloy. Users plated different materials, need to choose different electrode material products.

Gold: It is the most widely used traditional material. It has low contact resistance, high chemical stability and is easy to deposit. Suitable for low stress coating, such as Al Au Ag Cu.

Silver: Suitable for plating high stress film materials, such as Ni, Cr, Mo, Zr, Ni-Cr, Ti, stainless steel, etc.

Silver-aluminium alloy: suitable for dielectric optical coating, MgF2, SiO2, Al2O3, Titanium dioxide and other film materials.

6. Principle of monitoring film thickness of Crystal Sensor

The piezoelectric effect and mass loading effect of quartz crystal are used to monitor the film thickness by quartz crystal method. When a film is coated on the crystal sensor, the thickness of the crystal sensor increases, the natural frequency of the crystal sensor will change accordingly.

The higher the fundamental frequency of the crystal is, the higher the sensitivity of the control is. However, when the fundamental frequency is too high, the crystal sheet will be very thin and fragile. The AT cut frequency is usually used for 5-10MHz. Using AT chip, its vibration frequency is extremely sensitive to the change of mass, but not sensitive to the change of temperature. It has unique advantages such as high accuracy and good sensitivity, and is very suitable for the monitoring of film thickness in vacuum film deposition.

7. Recycling of Crystal Sensor

(1) Silver or silver-aluminium alloy is soluble in various acids and is not suitable for reuse. It is necessary to completely remove the film and electrodes on the crystal oscillator and send them back to our company for electroplating.

(2) Gold is insoluble in sulphuric acid. Users can dispose of it by themselves, remove the film layer on the crystal sensor, clean and reuse it, but it is not easy to reuse too many times, otherwise the quality stability will be reduced and the use will be affected.

8. Cleaning formula of Crystal Sensor:

20% ammonium hydrogen fluoride solution, soaked for more than 6 hours, after soaking, put into alcohol wipe, then water removed.

The related film materials produced by ATS are as follows:

At the same time, we cooperate with professional crystal sensor manufacturers to supply high quality crystal sensor. Welcome to contact us!