The Influence of a Chrome Film Bonding Layer on SAW Resonator Performance

Abstract

We have been working to make low aging rate, low phase noise SAW resonator oscillators for systems applications. These resonators are normally made using A1 electrodes, frequently including a Cr film bonding layer, and the resonators are often secured to a header u sing an adhesive. Here we report the results of tests to determine the i nfluence of a Cr bonding layer on device n oise levels and the effect of the high temperature bake (needed for adhesive cure) on a resonator frequency r esponse. It was found that a Cr film bonding caused an increase in the single side band phase noise (measured and the 1Hz intercept) of 15 dBc on average. High temperature b aking (35OoC) resulted in a significant and variable frequency shift as well a small changes in loss and Q. Physical analyses show Cr to be highly mobile, and significant oxidation of the A1 occurs when heated in air.