一种新型体硅谐振加速度计的设计.pdf

第26卷第2期2005年2月半导体学报C~I NESE J OURNAL OF SEM ICONDUCTORSVol .26 No .2Feb . 2005% Pro ect supported by National ~igh Technology Research and Develop ment Progra m of ChinaCNo .2002 AA430020>Jia Yubin male Was born in 1964 associate professor .~is main research interests include MEMS MOEMS and integrated optics .Email:yb-ia @ i me .pku .edu .cn~ao Y ilong male Was born in 1963 professor .~is research interests include MEMS and its neW devices and neW processes .Zhang Rong male Was born in 1968 associate professor .~is research interests include m icromachined gyroscope and accelerometer .Received 23 June 2004 revised manuscript received 16 Septe mber 2004 2005 Chinese Institute of ElectronicsBulk-s ilicOn ResOnant AccelerOmeter%Jia Yubin1 ~ao Yilong1 and Zhang Rong2C1Institute of \ icroelectronics Peking UniUersitS Beijing100871 China>C2DePart ment of Precision \easure ment TechnologS and Instrument Tsinghua UniUersitS Beijing100084 China>Abstract:Resonant accelerometer is designed Which includes t Wo double-ended tuning forks a proof mass four-le-verage syste m a mplif ying inertial force and drive/sense combs . Each tuning fork is electrostatically actuated andsensed at resonance using comb electrodes .The device is fabricated using MEMS bulk-silicon technology Whose sen-sitive degree is 27. 3 ~z/g and the resolution is 167. 8*g .Key WOrds:MEMS accelerometer;resonant driving and sensing;bulk-silicon process;freCuency shiftEEACC:2520C;2560FCLC nu mber:TN304. 12 DOcu ment cOde:A Article ID:0253-4177C2005>02-0281-06l IntrOductiOnAccelerometers are used f or diverse areas ran-ging from inertial navigation to vibration monito-ring . M icromachinedaccelerometersareWidelyused f or automotive industry because of their loWcost s mall size and broad freCuency response[1].Various accelerometers based on a nu mber of dif-ferent techniCues and principles[2 ~7]have been de-signed and i mple mented .In the ma ority the accel-eration to be measured is converted into a displace-ment of movable proof mass .This displace ment canbe picked up by optical capacitive piezoresistive ortunneling methods[4 ~7]. ~oWeverthe resonant ac-celerometers are operated by detecting freCuencyshift due to the inertial f orce Which is caused bythe applied acceleration in the resonant characteris-tics of the devices .For a direct freCuency output resonant sensors have many advantages over con-ventional type such as high resolution Wide dy-na m ic range Cuasi-digital nature and the inherentcontinuous self-test capability[8].The Cuartz-basedresonant accelerometers have been used f or naviga-tion-grade sensing[9].During last feW yearsbasingon resonant principle several resonant accelerome-ters have been reported including surface[10 11] bulk[12] andm ixedCbulkandsurface>[8]m i-cromaching process .In 1997 Roessiget al. de-signed and fabricated a DETFCdouble-ended tun-ing f ork>resonant accelerometerWith a 45 ~z/gscale factor using a lever syste mto magnif y the in-ertial f orce applied to the tuning f ork[10].In 2002Seshiaet al. i mproved lever structure and fabrica-ted a DETF accelerometer With a 17 ~z/g scale fac-tor and a noise floor of 40*g/~z1/2f or input accel-erometer freCuency of 300 ~z[11].Resonant sensor monitors the measurand as af unction ofresonant freCuency ofthe vibratingstructure or resonator . A key deter m inant of theperf or mance of the device is the a mount of energycoupled through the resonator s supports to the半导体学报第26卷surroundings .The level of coupling can be reducedby designing a dyna m ically balanced resonator .DE-TF resonator mentioned above is the si mplest f or mofstresssensitivedyna m icallybalancedstruc-ture10 11J.In order to elevate the sensitivity andstability of resonant accelerometer i mproving thestructure of resonant accelerometer is essential . W edesign and fabricate a resonant accelerometer Witha 27. 3 ~z g scale factor and a 167. 8*g resolutionusing bulk-silicon process .2 s tructure descriptiOnThe structure of the resonant accelerometer isshoWn in Fig .1 .This accelerometer consists of t Wodouble-ended tuning f orks a proof mass surround-ing t Wo tuning f orks and extending around f our le-verage syste ms and drive sense combs .Fig .1 Structure of the resonant accelerometerThe proof mass is attached to t Wo double-en-ded tuning f ork resonators via f our mechanical-le-verage ar ms .In order to maxi m ize the scale factor the f our leverage syste ms are used to magnif y theinertial f orce applied to the tuning f orks .Each tun-ing f ork is electrostatically actuated and sensed atresonance using comb electrodes . When an externalacceleration is applied to the device one tuningf ork is sub ected to a tensile f orce Which raises itsnatural freCuency and the other tuning f ork expe-riences a compressive f orce loWering its freCuency .TWo double-ended tuning f orks provide f or a dif-ferential outputWhich is t Wice sensitivity of theone double-ended tuning f ork and avoid or loWerthe a mbient noise .3 Fre。