What Is Quartz Crystal Healing?

The chemical composition of quartz crystal is SiO2. The crystal belongs to the trigonal oxide mineral, namely low-temperature quartz (a-quartz). Broadly defined quartz also includes high temperature quartz (b-quartz).

quartz crystal

Quartz crystal is an important electronic material. A quartz wafer cut in a certain direction, when subjected to

General index of quartz crystal

Nominal frequency: The frequency specified by the crystal component specification.

Adjust frequency difference: the maximum allowable deviation of the operating frequency from the nominal frequency at the reference temperature. Usually expressed in ppm (1/10).

· Temperature frequency difference: The allowable deviation of the operating frequency from the reference temperature in the entire temperature range. Usually expressed in ppm (1/10).

· Resonance resistance (Rr): The resistance value of the crystal element at the series resonance frequency Fr.

· Load capacitance (CL): The effective external capacitance that determines the load resonance frequency FL together with the crystal element

· Static capacitance (C0)

The capacitance in the static arm of the equivalent circuit. Its size mainly depends on the electrode area, wafer thickness and wafer processing technology. Its common calculation formula is:

C0 = KC0 × Ae × F0 + C constant

KC0Capacitance constant, its value is related to the form of the rack and the shape of the wafer;

Aeelectrode area, unit mm;

F0Nominal frequency, unit is KHz;

C constant-constant, unit pF;

· Dynamic capacitance (C1)

Capacitance in a dynamic arm in an equivalent circuit. Its size mainly depends on the electrode area, and it is also related to the degree of wafer parallelism and fine-tuning. Its common formula is:

C1 = KC1 × Ae × F0 + C constant

KC1Capacitance constant;

Aeelectrode area, unit mm;

F0Nominal frequency in KHz;

C constant-constant, unit pF;

· Dynamic inductance (L1)

Inductance in a dynamic arm in an equivalent circuit. Dynamic inductance and dynamic capacitance are a pair of related quantities. Its common formula is:

L1 = 1 / (2F0) 2C1 (mH)

· Series resonance frequency (Fr)

The electrical impedance of the crystal element is the lower of the two resistive frequencies.

· Load resonance frequency (FL)

The crystal element is connected in series or in parallel with a load capacitor, and its combined impedance is one of the two resistive frequencies.

· Quality factor (Q)

The quality factor is also called the mechanical Q value. It is an important parameter that reflects the performance of the resonator. It has the following relationship with L1 and C1

Q = wL1 / Rr = 1 / wRrC1

As shown in the above formula, the larger R1 is, the lower the Q value is, the larger the power dissipation is, and it will also cause frequency instability. Conversely, the higher the Q value, the more stable the frequency.

· Relative load frequency offset (DL)

The change amount of the crystal load resonance frequency relative to the series resonance frequency DL = (FL-Fr) / Fr can be approximated by the following formula:

DLC1 / 2 C0 + CL

· Relative frequency traction range (DL1, L2)

The amount of frequency change of the crystal between two fixed loads.

D (L1, L2) = (FL1-FL2) / Fr = C1 (CL2-CL1) / 2 (C0 + CL1) (C0 + CL2)

Traction sensitivity (TS)

The rate of change of crystal frequency under a fixed load.

TS-C1 * 1000/2 * C0 + CL 2

· Excitation level correlation (DLD)

Due to the piezoelectric effect, the excitation level forces the oscillator to generate mechanical oscillations. In this process, acceleration work is converted into kinetic and elastic energy, and power consumption is converted into heat. The latter conversion is caused by internal and external friction of the quartz resonator.

Friction loss is related to the velocity of the vibration particle. When the oscillation is no longer linear, or when the tensile or strain, displacement or acceleration inside the quartz oscillator or its surface and the mounting point reaches a critical value, the friction loss will increase. This causes changes in frequency and resistance.

Major causes of poor DLD during processing

There is particulate pollution on the surface of the resonator. The main reason is that the production environment is unclean or the wafer surface is illegally contacted;

-Mechanical damage of the resonator. The main cause is the scratches generated during the grinding process.

There are particles or silver balls in the electrode. The main reasons are that the vacuum chamber is not clean and the coating rate is inappropriate.

The mounting is caused by poor electrode contact;

Mechanical stress exists between the bracket, the electrode and the quartz plate.

Quartz Crystal Parasitic Response

In addition to the main response (frequency required), all crystal elements have other frequency responses. The method to reduce the parasitic response is to change the geometry of the wafer, the electrodes, and the wafer processing technology, but at the same time, the dynamic and static parameters of the crystal will be changed.

· Measurement of parasitic response

SPDB uses DB to represent the difference between the amplitude of Fr and the maximum parasitic amplitude;

SPUR resistance at maximum parasitics;

(3) The distance between the SPFR minimum resistance parasitics and the resonance frequency, expressed in Hz or ppm.