本研究的目標將設定在以微機電技術設計並製造新穎、具高性能的微振動計，並結合CMOS積體電路製程完成整合型感測器晶片。設計創新之處在於以靜電力變化率（Electrostatic force gradient）來調降機械彈簧係數，使微振動計在合理面積下達成低共振頻率的需求。從訊號濾波的角度而言，此一振動計亦可作為極低頻濾波器的基本建構元件，解決在積體電路中製造大電容與電阻而佔大量面積的問題。
　　以微機電方式製作振動計雖因質量較小而有較高的布朗寧噪聲底限（預估10-7 (m/s)/□Hz），但可藉電容式感測增加感測度。應用頻率範圍在數十至數千Hz之間，可作為工具機的故障檢驗，常用的方式即是經由振動訊號的模式判斷--例如偵測軸承磨損所導致轉動頻率的變化，在即時觀測下提供故障預防診斷。另外在數百Hz的應用，目前振動計的使用在尖端磁碟機已成為趨勢，主要原因在於磁碟儲存密度的提昇，需要更精密的GMR（Giant MagnetoResistive）讀寫頭伺服控制。
　　因此我們提出設計及製作一新穎、具低噪聲μg解析度的微加速度計，與同感測度的加速度計比較，其特色在於其更微小化的體積。我們將使用CMOS微機電技術完成感測器及電容式感測電路的直接整合、以大幅降低非直接整合時所帶來的大量寄生電容。一特殊CMOS相容的體加工方式可製作高深寬比結構及感測電極以提昇感測度；並且利用靜電的軟化彈簧效應配合穩定迴授控制，更增加感測度以達到μg解析度目標。

　This work develops a post-CMOS (Complementary Metal Oxide Semiconductor) bulk-micromachining process for fabrication of a capacitive accelerometer and its dedicated high-performance for applications with target value: µG resolution. The important feature of the post-CMOS process is to control the thickness of proof mass by e deep anisotropic backside etch and electroless plating without an additional mask. And of course a capacitive sensing circuit will be designed to measure the acceleration. For this CMOS capacitive accelerometer, The DRIE (Deep RIE) accelerometer structure is 0.65mm by 0.65 mm in size and has a 44 μm-thick silicon and 50 μm-thick proof mass. The 　Brownian noise floor is around 6 μg/rtHz. which a post-CMOS bulk-micromachining process using composite microstructures made from combinations of aluminum.
In this study, The CMOS MEMS has been developed for TSMC 0.35 μm CMOS processes. The released microstructure consists of multiple layers of metal, SiO2, and silicon. 　　The microstructures have large mass in the order of 10-7 kg, resulting in high sensitivity to outside force, and several orders of magnitude higher Brownian noise than surface micromachining devices. we will design a accelerometer with standard CMOS process. The readout IC will be composed of a pre-amp, sample circuit and low-pass filter. The circuit system will help us converting the displacement of proof-mass into electrical signal.
　We propose to design and fabricate a novel low-noise accelerometer with a μg resolution, which compares favorably with other low-g inertial sensors in its small size. The CMOS-MEMS technology is used for monolithic integration of the sensor and the capacitive readout, in order to minimize the parasitic capacitances if implemented otherwise. A special CMOS-compatible bulk micromachining process helps to promote the capacitive sensitivity with the resultant thicker micromechanical structures. 　　　　　　Additional sensitivity increasing is obtained via the use of a feedback control scheme, in which the accelerometer is operated in a spring-softening regime and stabilized in a controlled loop.

[1]S.S. Rao, Mechanical vibrations, Addison-Wesley, 1990.
[2]J. Bernstein, R. Miller, W. Kelley, and P. Ward, “Low-noise MEMS vibration sensor for geophysical application,” J. of Microelectromechanical Systems, vol.8, no. 4, pp. 433-438, December, 1999.
[3]J. Thomas, R. kuhnhold, R. Schnupp, H. Ryssel, “A silicon vibration sensor for tool state monitoring working in the high acceleration range,” Sensors and Actuators A, 85, pp. 194-201, 2000.
[4]Y.H. Huang, M. Banther, P.D. Mathur, and W.C. Messner, “Design and analysis of a high bandwidth disk drive servo system using an instrumented suspension,” IEEE-ASME Trans. on Mechatronics, vol. 4, no. 2, pp. 196-206, June, 1999.
[5]H.K. Rockstad, T.W. Kenny, P. Kelly, and T. Gabrielson, “A micro-fabricated electron-tunneling accelerometer as a directional underwater acoustic sensor,” in Proc. Acoustic Particle Velocity Sensors: Design, Performance, and Applications, pp. 57-68, 1996.
[6]C. Burrer, J. Esteve, E. Lora-Tamayo, “Resonant silicon accelerometers in bulk micromachining technology – an approach,” J. of Microelectromechanical Systems, vol. 5, no. 2, pp. 122-130, June, 1996.
[7]A. Partridge et al., “A high-performance planar piezoresistive accelerometer,” J. of Microelectromechanical Systems, vol. 9, no. 1, pp. 58-66, March, 2000.
[8]S. Butefisch et al., “Three-axis monolithic silicon low-g accelerometer,” J. of Microelectromechanical Systems, vol. 9, no. 4, pp. 551-556, December, 2000.
[9]Analog Devices, “ADXL05/50/105/202 signal chip accelerometer with signal conditioning,” Datasheets, Cambridge, MA.
[10]T. Smith et al., “A 15-bit electromechanical sigma-delta converter for acceleration measurements,” IEEE Int. Solid-State Circuits conf. Digest of Technical Papers, pp. 160-161, 1994.
[11]C. Lu, M. Lemkin, and B. Boser, “A monolithic surface micromachined accelerometer with digital output,” IEEE Int. solid-State Circuits Conf. Digest of Technical Papers, pp. 160-161, 1995.
[12]Geospace, Inc., GS-14 geophone, Houston, TX 77040, USA.
[13]Motorola, XMMAAS40G10D micromachined accelerometer data sheet, Phoenix, AZ, USA.
[14]L.S. Fan and L. Crawforth, “Spring-softening effect in MEMS microstructures,” 7th Int. Conf. Solid-State Sensors and Actuators, (Transducers’93), pp. 767-769, 1993.
[15]C. T.-C. Nguyen and R.T. Howe, “Microresonator frequency control and stabilization using an integrated micro oven,” 7th Int. Conf. Solid-State Sensors and Actuators, (Transducers’93), pp. 1040-1043, 1993.
[16]J.J. Yao and N.C. MacDonald, “A micromachined, single-crystal, tunable resonator,” J. Micromech. Microeng., vol. 5, pp. 257-264, 1995.
[17]S.G. Adams, F.M. Bertsch, K.A. Shaw, P.G. Hartwell, N.C. MacDonald, F.C. Moon, “Capacitance based tunable micromechanical resonator,” 8th Int. Conf. Solid-State Sensors and Actuators, (Transducers’95), Stockholm, Sweden, pp. 438-441, 1995.
[18]C. T.-C. Nguyen and R.T. Howe, “Design and performance of CMOS micromechanical resonator oscillators,” Proc. of IEEE 48th Frequency Control Symposium, pp. 127-134, 1994.
[19]J.P. Yang and S.X. Chen, “Vibration predictions and verifications of disk drive spindle system with ball bearings,” Computers and Structures, vol.80, pp. 1409-1418, 2002.
[20]S. Valoff and W.J. Kaiser, “Presettable micromachined MEMS accelerometers,” Proceedings of the 12th IEEE Int. Conf. on Micro Electro Mechanical Systems (MEMS’99), pp. 72-76, 1999.
[21]A. Barzilai, Improving a geophone to produce an affordable, wideband seismometer, Ph.D. Thesis, Stanford University, CA, 2000.