The modified design of ring electrode quartz crystal resonator for uniform mass sensitivity distribution.

The mass sensitivity distribution curve of quartz crystal resonators (QCRs) with common circular electrodes is bell-shaped; however, a uniform mass sensitivity distribution is expected for highly accurate and repeatable measuring results. Pioneers designed a ring electrode QCR with a bimodal distribution curve of mass sensitivity, and an obvious concavity is presented between two peak points for a fundamental operating frequency of 10 MHz. The concavity is an obstacle to uniform mass sensitivity distribution, so eliminating the concavity is the goal of this study; two methods-changing overtone order and designing electrode geometry-are proposed to do so. An analytical theory for sensitivity distribution is introduced in this paper first. Analysis results show that the fifth overtone of 10 MHz is desirable for eliminating the concavity but with a drawback of sacrificing absolute mass sensitivity. The method of designing the electrode geometry can overcome this drawback and dot-ring and double-ring electrode geometries are proposed. When electrode parameters were selected properly, the maximum difference of mass sensitivity between two peak points was reduced by about 42.21% for dot-ring electrode QCR and 77.63% for double-ring electrode QCR compared with that of ring electrode QCR.