Effects of ion source etching on the impedance performances of quartz component

Abstract

Quartz element (i.e., active quartz crystal oscillator or resonator) is coated on the quartz crystal with an Ag/Ni double-layer film. An ion source etching system is used to etch the Ag film surface of the quartz crystal through masks of different sizes. Three groups of masks were adopted for quartz crystal etching, the sizes of which are A (1.30×1.10 mm2), B (1.70×1.30 mm2), and C (2.42×1.62 mm2) with the remaining area not being etched. During the etching process, a frequency counter was connected to monitor the load resonance frequency (FL, MHz), load resonant frequency difference (FLD, ppm), resistance at series resonant frequency (RR, Ω, related to impedance performance). After ion source etching, the quartz element (mask A) corresponds to FLD (-385.5 ~ -256.8 ppm), and load resonant impedance RR ranges from 8.7 to 9.1 Ω, representing a 6.32% average impedance reduction. Using masks C, the quartz element corresponds to FLD (-282.9 ~ -241.1 ppm), and load resonant impedance RR ranges from 10.0 to 21.1 Ω. The average impedance divergence is 13.04 Ω. It is speculated that the size of the etching area of the quartz crystal using mask B or mask C was too large, and some remaining zones have been etched improperly, which led to an increase in impedance and also caused crystal frequency instability or oscillation failure. Precise etching and mask selection when producing quartz components is essential to maintain their functionality and stability.