고감지전압 및 가지전극을 이용한 고정도 정전용량형 미소가속도계의 전기적 잡음 감소 및 자율균형력 발생에 의한 강성 증가Electrical Noise Reduction and Stiffness Increase with Self Force-Balancing Effect in a High-Resolution Capacitive Microaccelerometer using Branched Finger Electrodes with High-Amplitude Sense Voltage
high-amplitude sense voltage. From the fabricated microacceleromcter, the total noise is obtained as 9 ㎍/√Hz at the sense voltage of 16.5V, while the conventional microaccelerometers have shown the noire level of 25~800 ㎍/√Hz. We reduce the mechanical noise level of the microaccelerometer by increasing the proof-class based on deep RIE process of an SOI wafer. We reduce the electrical noise level by increasing the amplitude of AC sense voltage. The nonlinearity problem caused by the high-amplitude sense volage has been solved by a new electrode design of branched finger type, resulting in self force-balancing effects for the enhanced linearity and bandwidth. The fabricated microaccelerometer shows the electrical noise of 2.4 ㎍/√Hz at the sense voltage of 16.5V, which is an order of magnitude reduction of the electrical noise of 24.3 ㎍/√Hz measured at 0.9V. For the sense voltage higher than 2V, the electrical noise of the microaccelerometer is lower than the voltage-independent mechanical noise of 11 ㎍/√Hz. Total noise, composed of the electrical noise and the mechanical noire, has been measured as 9 ㎍/√Hz at the sense voltage of 16.5V, which is 31% of the total noise of 28.6 ㎍/√Hz at the sense voltage 0.9V. The self force-balancing effect in the blanched finger electrodes increases the stiffness of the microaccelerometer from 1.1N/m to 1.61N/m as the sense voltage increases from 0V to 17.8V, thereby generating additional stiffness at the rate of 0.0016±0.0008 N/m/V2.