Study On Micro-machined Resonant Electrometer With Single-Electron Charge Resolution In Room Temperature

Charge sensing measurement is the fundamental of electricity measurement and mechanical testing.If the resolution of charge sensing is reached to the charge of single electron,the original source of electrical signal will be revealed and the mechanism of electrical signal occurring could be understand well,as well as bring a revolution to the modern industries.This paper proposed a micro-machined resonant electrometer based on the mode localization of weakly coupled resonators(WCRs),resulting in single-electron charge resolution under room temperature.This study mainly focused on four aspects of the electrometer listed as follows:the operating principle,the structure design and the fabrication process,the circuit design,open-loop and closed-loop test.Firstly,the mode localization phenomena based on multi-degree-of-freedom(DoF)WCRs and its contribution to the improvement of sensitivity are analyzed.An equivalent electrical model of WCRs was established to simulate the magnitude-frequency responses of the mechanical structure.By analyzing the noises and resolutions of the WCRs,the feasibility of realizing WCRs based electrometer with single-electron charge resolution was proved.Secondly,a 3-DoF WCRs structural were proposed to overcome the shortcomings of previous mode localized electrometer,and the working principle of the 3-DoF WCRs based electrometer was expatiated.The software COMSOL is utilized for optimization of micro structure of electrometer.Then the electrometer was fabricated using MEMS-SOI technology.Thirdly,the measurement setup of electrometer were studied,and a closed-loop control scheme based on automatic gain control combined with phase-locked loop which is suitable for WCRs was proposed.With the promoted closed-loop control circuit,the resonant frequency of the WCRs can be locked and the amplitude of resonator can be stabilized.Finally,the electrometer was tested and estimated under room temperature.The test results show that:on one hand,the amplitude-ratio-based sensitivity is 7.29×106 ppm/fC,which is 2557 times higher than the frequency-based sensitivity(2.85×103 ppm/fC);on the other hand,the noise of the output signal is reduced by nearly 1 order of magnitude under the promoted control scheme compared with the previous self-oscillation circuit and the bandwidth of the electrometer is increased from 1.6Hz to 10Hz.Based on the test results,the resolutions of different output metrics were also compared,and it’s been proved that the highest resolution can be obtained with amplitude ratio.At last,the resolution of the electrometer based on the amplitude ratio output reaches 1.6e/√Hz under room temperature.