MEMS/NEMS Nano Technology

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Authors: Li Qun Du, Qi Jia Wang, Xiao Lei Zhang
Abstract: SU-8 photoresist has received a lot of attention in the MEMS field because of its excellent lithography properties. However, its high internal stress affects the overall pattern quality of the micro structures. The purpose of this work is to reduce the internal stress in SU-8 micro structure by ultrasonic stress relief technology. The stress relief mechanism of SU-8 micro structure was presented. The effect of ultrasonic stress relief on SU-8 micro structure was studied by experiments. The experimental results show that the internal stress in SU-8 micro structures can be reduced by ultrasonic stress relief technology.
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Authors: Zheng Yi Niu, Xue Zhong Wu, Pei Tao Dong, Ding Bang Xiao, Zhan Qiang Hou, Zhi Hua Chen, Xu Zhang
Abstract: Anisotropic wet etching is a key processing step for the fabrication of microstructures. In general, convex corner structures and non {111} crystal planes will be undercut during wet anisotropic etching. This characteristic of Si is an obstacle to the fabrication of structures in various applications. Among a number of silicon etchants, TMAH is becoming popular for low toxicity and CMOS compatibility. In this paper, a new design of compensation structure has been proposed to solve the undercutting problem with 25%wt TMAH solution. The new compensation structure is made up by squares which are connected to the convex corner. An empirical expression between the parameters of the new compensation structure and etching depth is derived. The changes of the compensation structure in different etching process are shown by photographs. Experimental results prove the high accuracy of this method. Compared to two widely used compensation structures, the new structure is more space efficient.
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Authors: Jian An Lv, Zhen Chuan Yang, Gui Zheng Yan, Yong Cai, Bao Shun Zhang, Kevin J. Chen
Abstract: In this article, integrated AlGaN/GaN cantilevers on (111) silicon substrate are fabricated and characterized. The process started with AlGaN/GaN HEMTs fabrication followed by a series of dry-etch-only MEMS process. To characterize the residual stress distribution, Micro-Raman spectroscopy is used and the residual stress in suspended GaN cantilever is found ~ 90% lower after releasing. A type of micro-bending test is used to characterize the piezoresponse of AlGaN/GaN HEMT on the GaN cantilever. An output current modulation greater than 20% can be observed when the cantilever is vertically downward deflected ~ 30 µm.
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Authors: Dong Sheng She, Xiao Dong Wang, Xi Wen Zhang, Li Ding Wang
Abstract: The dynamic testing system for MEMS in low temperature environment has been developed. A thermoelectric cooling refrigerator was utilized to generate the low temperature environment. The base excitation device was established using the piezoelectric ceramic as the driving source. A vacuum chamber was designed to protect the micro-structure from the humid air. Through the base impact excitation, the resonance frequencies are obtained by analyzing the impulse response signals. The frequency response of micro-cantilever was obtained by using both BIST method and laser Doppler vibrometer. The dynamic testing experiments for the silicon micro-cantilever were carried out from -50°C to room temperature. The result shows that the resonance frequency slightly increases with the decreasing temperature. The measurement device is effective to carry out dynamic testing of microstructure from -50°C to room temperature.
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Authors: Jin Tang Shang, Jun Wen Liu, Di Zhang, Bo Yin Chen, Chao Xu, Xin Hu Luo, Hui Yu, Jing Dong Liu, Qin Gan Huang, Jie Ying Tang, Ming Qin
Abstract: Many MEMS devices including accelerometer and gyroscopes, having moving parts, requires hermetic and low cost packaging. In this paper we propose a low cost fabricating process to prepare micro glass cavity arrays for wafer-level and hermetic packaging of MEMS. First, the fundamental of the process was discussed. Then, the process for preparing cavity arrays in Pyrex7740 glass wafer was studied experimentally. After that, the defects of the fabrication were discussed. Results show that wafer-level packaged cavities were prepared, whose diameter was controllably between 200 microns and 2000 microns. It is also disclosed that the defects could be avoided by controlling the process parameters. Results also show that the leakage rate of the single packaged cavities is below 5Χ10-9 Pa.m/s which could meet the hermetic packaging standard.
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Authors: Qi Fang Hu, Cheng Chen Gao, Yi Long Hao, Yang Xi Zhang
Abstract: This work focuses on the etching characteristic of (100) silicon wafer in surfactant added tetramethyl-ammonium-hydroxide (TMAH:( CH3)4NOH) solution. The experimental result shows that under etching effect in TMAH achieves a significant reduction by adding fatty alcohol ethoxylate (R-O (CH2-CH2)n-OH) in the solution. Synperonic-A series fatty-alcohol-ethoxylate with increasing length of ethylene oxide segments are used to carry out the experiment. Comparing with the pure TMAH, the maximum under etching rate in the surfactant added TMAH is reduced to three quarters. The etching loss of convex corners is negligible for shallow to medium-deep etching (<30μm).
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Authors: Le Guan, Jia Li Gao, Jin Kui Chu
Abstract: The methods of on-chip integrated testing have a wide application with the development of the study for MEMS materials properties measurement in microscale. A novel on-chip integrated micro-tensile testing system is designed through system-level simulation based on macromodels to measure the fracture strength and fatigue mechanical properties of polysilicon thin films. The structure of testing instrument consists of V-beam electrothermal actuator, differential capacitance sensor, supporting spring and specimen. The capacitance signal is sensed and controlled by a second sigma-delta modulator circuit. The analytic macromodel of polysilicon thin film specimen considering geometric nonlinearity and the numerical reduced-order model of V-beam electrothermal actuator based on Krylov subspace projection are created separately and described in the MAST hardware language. The mechanical structure dimension size and circuit components parameters are determined and optimized according to system-level simulation. The computing result has shown that the self-build macromodels and the on-chip integrated test system are efficient and reliable.
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Authors: Jian Cui, Zhong Yang Guo, Qian Cheng Zhao, Zhen Chuan Yang, Yi Long Hao, Gui Zhen Yan
Abstract: This paper proposed an effective approach for extending the bandwidth of MEMS vibratory gyroscope by employing the electrostatic force feedback control. The mathematical model for the bandwidth is established through the dynamic model of the gyroscope, which indicates that the bandwidth of the sensor depends on the difference between the resonant frequencies of the two working modes. The system bandwidth can be enlarged by utilizing electrostatic force rebalance control to null Coriolis force caused by external angular rate which can also improve the performance of the transient response. Simulation results forecast a satisfactory performance of the control system with suggested control method.
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Authors: Fan Tao Meng, Jin Kui Chu, Gang Luo, Zhi Tao Han, Zhi Wen Wang
Abstract: Flexible polymer stamps are considered as an attractive alternative to rigid, brittle and expensive stamps made of inorganic materials because of their low cost and ease of fabrication. In this paper, we present a nanoimprint process to fabricate large area, high-resolution nanograting patterns using flexible polymer stamp made from fluoropolymer. The flexibility and low surface energy of polymer stamp provide a clean release without fracture or deformation of the stamp and of the replicated nanograting. Large-area, high-density nanograting patterns with good shape homogeneity and size uniformity have been successfully fabricated using the flexible polymer stamp with advantages of its good conformal contact and low adhesion. Using flexible polymer stamps can resolve many serious issues in NIL and therefore can bring it to real industrial applications.
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