A mode-localized MEMS electrical potential sensor based on three electrically coupled resonators

We report a new class of MEMS resonant potential sensor based on the mode localization effect using a 3-degree-of-freedom (DoF) electrically weakly coupled resonator system. As opposed to previously reported electrically coupled 2DoF mode-localized resonant sensors, it can be shown in theory that the 3DoF structure has an improved sensitivity without sacrificing signal transduction, in addition to a reduced nonideal effect with regard to the vibration amplitudes and the motional currents. Experimentally, it has also been shown that several orders of magnitude higher sensitivity can be achieved compared to frequency shift and 2DoF mode-localized sensor. In the best case, we are able to demonstrate over 4 orders of magnitude improvement in sensitivity compared to frequency shift as an output signal. Compared to current state-of-the art 2DoF mode-localized sensor, the highest sensitivity improvement is over 123 times. An estimation of the noise floor of the sensor is 614 µV / √Hz for potential sensing, or an equivalent 57.6e / √Hz for charge sensing, and a dynamic range of 66.3 dB can be achieved. Furthermore, two different approaches for detection were investigated, perturbing the stiffness in the form of either an axial electrostatic force or a change in electrostatic spring. We were able to demonstrate that the approach of changing electrostatic spring is more sensitive than its counterpart.