Ring electrode design for spurious suppression in piezoelectric resonators

Researchers in the Stanford University Power Electronics Research Lab developed an effective ring electrode that removes spurious modes in piezoelectric resonators. Spurious modes, secondary resonances in a bulk acoustic material, disrupt efficient piezoelectric-based power converter operation and worsen performance of other piezoelectric resonator applications, such as RF filters. By introducing a metallized, concentric ring, separated from the active electrode by a thin gap, the boundary conditions for supporting spurious lateral modes are changed such that these modes experience zero coupling coefficient and are not supported. (See comparison with reference designs in figure 1.) The SUPER Lab bulk lithium niobate acoustic resonator design is the first method that removes spurious modes in piezoelectric resonators tailored for power electronics and telecommunications applications like acoustic filters, oscillators, and transformers.

Figure 1 Simulated impedances (Z) and resistances (R) of the rectangular reference design (a), the circular reference design (c), and the novel grounded ring design (e). Displacement at resonance of all three designs, marked by triangles in the impedance plots, are illustrated in (b, d, f).

Stage of Development – Prototype
The SUPER Lab working prototype achieved a high Q of 4000, k_t² of 30%, and a large fractional suppressed region of 62%. Research continues to extend the design to applications like filters, oscillators, and transformers .