Lowering motional resistance by partially HfO2 gap filling in double-ended tuning fork MEMS resonators

This paper reports a 80nm air gap double-ended tuning fork (DETF) resonator partially filled with 20nm of HfO
₂
. The device operates at 10.7 MHz with a quality Q-factor of 7930 and a motional resistance, R
_m
, x18 better than for the measured counterparts in air-gaps. An enhancement of the S
₂₁
transmission signal of 6dB in addition to the reduction of the R
_m
have been achieved thanks to the improvement of the electromechanical coupling factor by partially filling the electrode-to-resonator-gap with an atomic layer deposition (ALD) of 20nm of HfO
₂
high-k dielectric (ε
_r
~19). This result proves an outstanding enhancement in the detection signal while keeping all the desired properties of flexural resonators for future mechanical sensing applications.