Zhongquan Wen

A novel MEMS field emission accelerometer based on silicon nanotips array

A novel MEMS field emission accelerometer based on silicon nanotips array with about 10000 silicon tips in total is proposed. It consists of a proof mass, four L-shaped springs, silicon nanotips array, anode and feedback electrodes. The sensor is fabricated on one N-type (1 0 0) single crystal silicon wafer and one #7740 glass wafer using bulk silicon micromachining technology. The silicon tip arrays are form by wet etching with HNA (HNO3, HF and CH3COOH) with I2 as additive. After oxidation sharpening, the curvature radius of the tips is smaller than 50nm, and the tip arrays are metalized by sputtering TiW/Au film. ICP process is utilized to release the sensor chip. In order to improve the linearity of the sensor, a feedback control circuit is used to rebalance the proof mass. The accelerometer is tested on a dividing head and test results show that the sensitivity is about 420mV/g and nonlinearity is about 0.7% over a range of -1g~1g.

Closed-loop control of a MOEMS mirror integrated with angle sensor

There is currently considerable interest in MOEMS mirrors because of their wide applications. As the majority of application systems require accurate control of reflection optical beams, We have developed a MOEMS mirror integrated with angle sensor. In this paper, a closed-loop control scheme for the MOEMS mirror integrated with angle sonser is proposed. Following establishment of theoretical model of the mirror, mathematical model of the closed-loop control system is presented and simulated using CAD software. Based on the study of the closed-loop control method, a closed-loop control circuit is developed. The circuit consists of signal producing module, angle detecting module, feedback control module and VGA module. The signal producing module is a frequency divider based on CPLD to provide driving signal with steady frequency. The signal frequency generated by the signal producing module is 542Hz, which matches the resonant frequency of the mirror, 543.22Hz. Key component of the circuit is variable gain amplifier made up of an analog multiplier. It controls the amplitude of the driving signal utilizing the measurement signal of the integrated angle sensor to achieve constant deflection angle of the mirror. We applied the circuit to the fabricated mirror, and experiment results show that, with the closed-loop control, the accurate control of the mirror is achieved.

A new method to eliminate the noise of vacuum microelectronic high precision accelerometer

The vacuum microelectronic high precision accelerometer was developed based on the vacuum field emission theory; it has many advantages such as high precision, good linearity in theory, but the inherent low frequency such as 1/f noise of the accelerometer decreases the signal-to-noise ratio greatly, and it is the main influencing factors to precision and linearity of accelerometer. In this paper a new method to eliminate noise of vacuum microelectronic high precision accelerometer was first bring forward by using modulation and demodulation and coherent detection technology. The system mainly includes AC signal generator, current obtain, phase shift, demodulator, differential amplification and feedback control. At last, the noise between 0 Hz and 200Hz contrast test experiment of the accelerometer was carried out by oscilloscope, the result shows the mean spectrum density of output signal is 29μV/√Hz between 0 Hz and 200Hz. Static gravitation field rolling experiment in ±1 g is also performed to measure the linearity of the accelerometer; the least-square linear fitting curve shows the maximum nonlinear is 0.41%. Through the results we can draw conclusion that the noise and linear performs have been greatly improved through eliminated noise.

A novel electromagnetically actuated MEMS scanning mirror integrated with rotation angle sensor

Aiming at application of micro-spectrometer systems, a novel electromagnetically actuated MEMS scanning mirror with large size and integrated rotation angle sensor is proposed for the application of micro-spectrometer. The size of the mirror plate is 6x5mm2, which is supported by two torsion beams. The scanning mirror is fabricated on a 500 μm-thick single crystal silicon wafer using bulk micromachining process. Two gold coils are deposited on back side of the mirror using electroplating technology. One of them is used to generate Lorentz force to drive the mirror, and the other is used to monitor the rotation angle by measuring the induced voltage which is proportional to the angular rate. The silicon substrate is heavily doped (0.02 ohm•cm) to connect the coil central end to outside pad. A 500 nm-thick aluminum film is sputtered on the front side of the mirror plate to form a high quality mirror surface. The whole structure is released by wet etching technology, and corner compensation structure is designed to avoid convex corner undercutting. In order to achieve large deflection angle, NdFeB permanent magnets are used to provide high magnetic field. Testing results show that maximum mechanical rotation angle of the scanning mirror can achieve ±10°at the resonant frequency of 344Hz with low driving voltage of less than 1Veff, corresponding to a Q-factor of 137 at atmospheric pressure, and the output voltage of the angle sensor has high linearity.

Synthesis of the System Modeling and Signal Detecting Circuit of a Novel Vacuum Microelectronic Accelerometer

A novel high-precision vacuum microelectronic accelerometer has been successfully fabricated and tested in our laboratory. This accelerometer has unique advantages of high sensitivity, fast response, and anti-radiation stability. It is a prototype intended for navigation applications and is required to feature micro-g resolution. This paper briefly describes the structure and working principle of our vacuum microelectronic accelerometer, and the mathematical model is also established. The performances of the accelerometer system are discussed after Matlab modeling. The results show that, the dynamic response of the accelerometer system is significantly improved by choosing appropriate parameters of signal detecting circuit, and the signal detecting circuit is designed. In order to attain good linearity and performance, the closed-loop control mode is adopted. Weak current detection technology is studied, and integral T-style feedback network is used in I/V conversion, which will eliminate high-frequency noise at the front of the circuit. According to the modeling parameters, the low-pass filter is designed. This circuit is simple, reliable, and has high precision. Experiments are done and the results show that the vacuum microelectronic accelerometer exhibits good linearity over -1 g to +1 g, an output sensitivity of 543 mV/g, and a nonlinearity of 0.94 %.