Investigations of gold films on quartz crystals

Changes at the interface between the metal electrode and the quartz plate have been identified as possible instability mechanisms in high-precision resonators. This study was undertaken to investigate the nature of the gold-quartz interface, if gold diffuses into quartz under "normal" conditions, and whether or not the adhesion of gold electrodes changes with time. Various metal adhesion tests, etching tests, heating tests, and surface analyses were used during the investigations. Resonators fabricated in 1973 were compared with those processed nearly 20 years later. The results showed no evidence of electrode diffusion. The electrodes of 20-year old resonators could be removed with Scotch Magic tape as easily as those from recently fabricated resonators. Testing for gold in the quartz with Rutherford backscattering and SIMS (secondary ion mass spectroscopy) analysis indicated no more gold in the 1973 samples than in the recently fabricated ones. Gold electrodes on quartz have been found to consist of a weakly adhering central area and a strongly adhering narrow rim. The narrow rim is a <40 nm thick film that results from shadowing by the evaporation mask. The strong adhesion of this rim can be reproduced by depositing 10 nm to 40 nm thick pure gold films onto quartz plates