Modeling of Dual-Backplate based Airborne CMUTs with Enhanced Bandwidth

This work presents a lumped element based model of an airborne capacitive micromachined ultrasonic transducer (CMUT) based on a dual-backplate MEMS technology. The model is derived from analytical equations of a deflected circular membrane and includes physical effects occurring in the electrical, mechanical and acoustical energy domain and their bidirectional coupling. The resulting model considers a nonlinear capacitive transduction and hence accounts for electrostatic spring-softening while allowing an implementation and simulation in standard circuit simulation tools supporting behavioural modeling via hardware description languages (HDL), such as Verilog-A. A verification by Laser-Doppler vibrometry (LDV) of dual-backplate CMUT prototypes shows a good agreement between measurement and simulation. Moreover, a wide fractional bandwidth of 29% and high peak displacement amplitudes of 259 nm/V at low bias voltages of 8V are confirmed for the fabricated CMUT samples. Finally it is shown, that the transducer bandwidth can be changed by adjusting the perforation density of the transducer backplates.