Viability of Piezojunction Effect for Microresonator Applications

This paper presents a study on the application of piezojunction transduction for the detection of vibrations of resonant microdevices. The piezojunction effect refers to the dependence of the electrical characteristics of a p-n junction to mechanical stress. It is shown that the piezojunction signal is proportional to the bias current of the diode, which can be adjusted as needed. A simple model that accounts for both capacitive and piezojunction currents and the equivalent electrical representations of the microdevice are developed and verified. A bulk-mode extensional resonator with an integrated p-n junction was designed and fabricated to serve as a proof-of-concept device. The static and dynamic responses of the fabricated devices were measured and compared against the models. The extensional-mode frequency of the resonator was measured to be ~7 MHz with a mechanical quality factor of ~1400. Capacitive and piezojunction signals at the output of the device were isolated and studied. It is shown that even with diode bias currents on the order of a few microamperes, the piezojunction and capacitive currents are comparable. Experimental verification demonstrates that piezojunction effect is a promising addition to the existing detection techniques in the resonance-based applications, where small chip area, integration, and power consumption are key requirements.