微光机电加速度计的研究现状及发展

1、mems鸟传感器mems and sensorsresearch and development status ofmoems accelerometersfeng lishuang, chi yuanyuan, zhou zhen, yao baoyin(key laboratory of micro-nano measurement-manipulation and physics of the ministry ofeducation 9 school of instrumentation science and opto-electronics engineering 9 beihan

2、guniversity 9 beijing 100191» china)abstract： the principle and structural characteristics of micro-optical electronic mechanical system (moems) accelerometers attracting great attention are analyzed> and the classification and development trend of moems accelerometers are summarized. accord

3、ing to micro-nano grating accelerometers the principles and structures of micro-grating accelerometers based on interfe* rence effect and nano-grating accelerometers based on effective refractive index change for subwavelength structure are analyzed. the results show that the precision of those acce

4、lerometers can reach ng order and be applied in seismic monitoring successfully. the structure and performance of new optical waveguide accelerometers based on polymers are analyzed emphatically. the microring resonator accelerometer has the advantages of the high measurement precision and tailored

5、propertiest but the long term stability is the primal problem to restrict its application. the acceleration measurement by atoms through the light force accelerometer overcomes the shortcoming of poor long term stability and has a very high precision. the technical features and main indexes of these

6、 accelerometers are comparedt and the development direction and application prospect of moems accelerometers in the inertial field are also discussed preliminarily.key wo rds： moems accelerometer； micro-nano grating accelerometer； immunity to electromagnetic interference； high precision； inertial fi

7、eldclc number： th703 document code： a article id： 1671-4776 (2011) 09-0583-08doi： 1(). 3969/j. issn. 1671-4776. 2011. 09. 008 eeacc： 2575微光机电加速度计的研究现状及发展冯丽爽，迟媛媛，周 震，姚保寅(北京航空航天大学仪器科学与光电工程学院微纳测控与低维物理教育部重点实验室，北京100191)摘要：对目前正成为研究热点的微光机电(moems)加速度计的原理和结构特点进行分析，总 结了 moems加速度计的分类和发展趋势。针对微纳光栅加速度计，分析了基于干涉效应

8、的 微米光栅加速度计和基干亚波长结构有效折射率变化的纳米光栅加速度计的结构和原理，其精度 可达ng,并成功应用到地震监测中。重点分析了基于聚合物的新型光波导加速度计的结构和性received date： 2011-05-06corresponding author： chi yuanyuan, e-mail: chiyuanyuan 1021 126. com能。微环谐振式加速度计测量精度高，性能可“裁剪”，但长期稳定性是制约其应用的主要问题。 光力加速度计利用原子进行加速度测量，克服了传统悬臂梁结构长期稳定性差的缺点，具有极高 的测量精度。对这几种加速度计的技术特点和主要指标进行比较，并初步

9、探讨了用于惯性领域中 的moems加速度计的发展方向和应用前景。关键词：微光机电（moems）加速度计）微-纳光栅加速度计；抗电磁干扰；精度高；惯性 领域中图分类号：th703 文献标识码：a 文章编号：1671-4776 （2011） 09-0000-00itemsaccelerometerarrow waveguidemicroring resonatorlight forcemicro-gratingnano-gratingaccelerometeraccelerometeraccelerometeraccelerometeraccelerometerrepresentive insti

10、tutegeorgia institute oftechnology andsilicon audiosandia national labcentre nacional demicroelectronica barcelona t spainuniversity of southern californiamassachusetts institute of technologyprinciplefrauhofer diffractionnear field opticsijght intensity modulationthe physical elongation of the ring

11、 and strainoptic effectradiation pressure rebalancing against the accelerometersensitivity2 ng/ </hz17 ng/ 应13. 1 db/g31 pm/gv100 ng/ y/hzrestrictionrelatively small measuring rangehigh requirement for nanograting fabrica- tion> overall structure packagerelatively low sensitivityrelatively poo

12、r long term stabilityinstability caused by photophoretic effects etc. and high requirement for levitated particles fabricationihble 1 main targets and technology characteristics of the moems accelerometers 表1 moems加速度计的主要指标和技术特点micro-nano grating0 introductionaccelerometers have been a subject of re

13、search and development for many decades. for many navigation applications t the crucial issues concerned are not only improving the accuracy/ performance of the accelerometer t but also reducing cost and size1recently there has been considerable interest in the micro-optical electronic mechanical sy

14、stem (moems) accelerometers because of the significant advantages of optical sensors over the conventional counterparts. moems accelerometers have combined optical measurements with micro electronic mechanical system (mems) technology. moems technology has generated considerable interest in the scie

15、ntific community due to its wide variety of advantages t such as immunity to electromagnetic interferencet electrical insulating, corrosion-resistant 9 remote sensing 9 high-sensitivity and multiplexing ability1-3"53 these accelerometers have a wide range of applications in inertial navigation

16、with high accuracy f vibration sensing of vehicle t seismic sensing and oi 1-field applications1-6among present reports of moems accelerometer t they can roughly be classified into four categories by the detection principle. moems accelerometers include the micronano grating accelerometer t polymer

17、waveguide accelerometer, microring resonator accelerometer light force accelerometer and so on. the present state of the art regarding the development of several typical moems accelerometers is described the main targets and technology characteristics of moems accelerometers are indicated in table 1

18、.1 micro-nano grating accelerometermicro-nano grating accelerometers are novel moems accelerometers based on micro-grating and nanograting corresponding to fraunhofer diffraction accelerometers and nanophotonic grating accelerome- tersc，1.1 micro-grating accelerometermicro-grating accelerometers are

19、 based on optical gratings operated on frauhofer diffraction prin cipals. the original of micro-grating accelerometers was developed by the microsystems technology laboratories t mit and ginzton laboratory t stanford university in 20001°a novel micrograting displacement sensor is developed by g

20、eorgia institute of technology. the simple implementation is schematically shown in fig. 111 in fig. 19 zo is the intensity of the zeroth diffraction order,is the intensityofthe+ 1 st diffraction order>z43 is the intensityofthe+ 3 rd diffration order>z-iis the intensityofthe-1 st diffraction o

21、rder tis the inctensityofthe-3 rd diffraction order* 人 is the intensity of the light source« d is the gap thickness between the sensor membrane and the diffraction gratings the sensor comprises of an aluminum membrane surfaced on the quartz substrate, a back electrode shaped in the form of a di

22、ffraction grating and a vertical cavity surface emitting laser (vcsel) bonded to the surface of the electronics die containing the photodetectors. the distance between a reflective membrane and an optical grating would be changed 9 and the movement would change the optical path length for the constr

23、uctive and destructive interference. the changes in path length would cause variations in intensity of the diffracted light from the grating. the detectable membrane displacement is 2. 08x 10_5 nm hz-,/2 at 20 khz and 1.35x 105 nm 日矿山 at ioo kh/n3. further sensitive enhancements are obtained by intr

24、oducing a grating-assisted resonant-cavityenhanced ( garce ) structure > forming an asymmetric fabry-perot etaloa experiments show an 8 db increase in detection sensi tivity with the etalon structure. in addition > the em* bedded diffraction grating enables the integration of optoelectronics i

25、n a small volume1打.light source:iulsrr nr <»ptical fiberphotodetector arrayfig- 1 cross section schematic of the displacement sensorintegrated with optical detection device图1集成光学检测器件的位移传感器的微面图with the support of ldrd (laboratory directed research and development) funding in us, a great deal

26、of effective work about micro-grating accelerometers has been done by sandia national lab which is in a leading position in the design and fabrication of the micro-nano grating accelerometers, not only in theory research but also in experimental workdiffnujiori gratingfe<xil>ack electrodesi 5

27、nvnfig. 2 principle schematic of the micro-grating accelerometer 图2微米光栅加速度计的原理图smp housingjihown)they have designed and fabricated the high-precision micro-grating accelerometers in 20081 with the same principle of mirco-grating accelerometers for georgia institute of technology, as shown in fig. 2c

28、l3 the sensor architecture includes a mono- lithically integrated electrostatic actuation port that enables the application of precisely controlled broadband forces to the proof mass, while the displacement is simultaneously and independently measured optically. this approach enables several useful

29、features such as dc actuation for self-tuning of the interferometert dynamic self-characterization and self-calibration force-feedback modalities for altering device dynamics and enhancing dynamic range. the noise floor spectral density at 1 khz is measured as 24. 4 pg/ /hz and 20 - 40 ng/ -/hz reso

30、lution can be achieved in an open loop configuration from structures with approximately 100 hz mechanical resonance,3.through two years of hard effort, silicon audio has successfully built several prototypes of the integrated mirco-grating accelerometer made by san- di national lab and applied in a

31、3-axis seismometer t as shown in fig. 3( 14j. the compact design is roughly the size of a 12-oz coke can and incorpo- rates a sensor orientation > semi-closed loop force feedback operation, automatic mass centering, and clip level stabilization. the prototype accurately resolves the 2 ng/ /tiz ba

32、ckground noise. tested alongside a calibrated sts - 2 broadband seismometer > excellent matching among all three axes can be seen. to the best of our knowledge, these accelerometers are the most sensitive moems accelerometers built to datecu.fig. 3 prototype of 3-axis seismometer 图3三轴地震检波仪的原型1. 2

33、 nano-grating accelerometeran in-plane near-field resonant sensor based on multilayer sub-wavelength optical gratings was developed in 2007, as shown in fig. 4ns. this nanooptic sensor comprises of two sets of polysilicon nano-gratings separated by an air gap. they modulate the near-field intensity

34、and polarization of an incident light source in response to the relative lateral motion of the two gratings. electrostatic actuators are integrated into the sensor to control the nano-grating motion and characterize the displacement sensitivity.、 - t弋孑1 3lpjs 2.0r;缸kf_ 1() hlcn xl 600 jo <nn)fig.

35、 4 moems ncar-ficld resonant displacement sensor based on sub-wavelength nancrgratings图4基于亚波长纳米光栅的moems近场共振位移传感器using reference detection circuitry in conjunction with correlated double sampling method, the sensor resolution is improved dramatically by reducing mf noise limits in the reference detec

36、tion circuitry. the displacement sensitivity is as low as 12 fm/ vtlz at 1 khz, and 50 fm/y/hz at 10 mhz. these highly sensitive displacement sensors are converted to the highly sensitive acceleration sensors through a direct mass integration process. measurements with the integrated subwavelength o

37、ptical nano-grating accelerometers have shown the device sensitivities of 590 v/g and the noise floors corresponding to 17 ng/ a/hz (at1 hz) which is close to the theoretical thermal noise floor of 8 ng/hz1snano-gratings show some of the highest sensi tivities based on the optical method. however, i

38、tis really difficult to fabricate this kind of the structure. what's more, the roughness of the gratings may affect the sensitivity greatly. it is better to use the closed loop approach or integrated package to improve the robustness of the nano-grating accelerometers.2 arrow waveguide accelerom

39、eterthe antiresonant reflecting optical waveguides (arrow) have already been used in optical accelerometers as shown in fig. 516 it consists of a three-fold segmented waveguide the input and output segments are on the chip frame, and thefiguration assures that the light mostly is confined through th

40、e waveguide. two fishbone-shaped structures have been defined on both sides of a channel in order to solve the self-alignment problem of the optical fiber. the schematic of the selfalignment polymer accelerometer is depicted in fig.su 一 8 was used to fabricate high-sensitivity polymer optical accele

41、rometers by changing the mechanical and optical properties as a function of the process parameters. experimental results show optical sensitivities of 13. 1 db/g for negative and 17 5 db/g for positive accelerations193.electrodesensing part is on the principle is based on light intensity versus misa

42、lignment of thesmic mass. the working the variation of the output the acceleration due to the waveguides. the arrowintermediate waveguidestructures minimize the insertion losses and makeinput waveguideexternal beamsthe alignment easier. the cross-axis error has been reduced significantly by making t

43、he waveguides wider at each step). the mechanicalsensitivity of the device is 1 pm/g, and the optical sensitivity is 2 3 db/g for negative acceleration and 1. 7 db/g for positive acceleration116 17j.mass displarrmrntinertial massself-alignment structurefig 6 schcmnth of the sclpalignmcnt polymer acc

44、vlf-ronicicr图6自对准的聚合物光学加速度计原理图fig. 5 schematic diagram of the misalignment-based optical accelerometer图5基于波导的光学加速度计原理图an improved structure is proposed with periodic air gaps at both sides of the waveguide. this con3 microring resonator accelerometeran optical accelerometer based on a polymer micro

45、resonator fabricated on a flexible substrate is proposed by the university of southern california9 as shown in fig. 7(a)r2g1、 one end of the flexible device is attached to a fixed support and a proof mass is attached at the other end. fig. 7(b) and (c)20 shows the photograph of the final device and

46、its cross-sectional dimensions. the ring experiences a strain which causes its resonant wavelength shift because of the physical elongation. the shift in resonant wavelength of the ring resonator is directly proportional to the external acceleration. this accelerometer has a sensitivity of 31 pm/g a

47、nd a dynamic range offlexible ring resonator accelerometer(a) schematic diagram of accelerometer in a practical setup± 7 g. there is a tradeoff between the sensitivity and dynamic range, and the accelerometer properties can be tailored for a specific applica-(b) cross section digram of a ring r

48、esonator coupled vertically to a bus waveguide(c) photograph of a ring resonator coupled vertically to a bus waveguidefig. 7 schematic diagram of the accelerometer in a practical setup* the cross section and a photograph of a ring resonator coupled vertically to a bus waveguide图7实际的加速度计示意图、垂直耦合波导的 环

49、形谐撮腔侧面图和照片4 light force accelerometerwith the rapid development of microfabrication9 the accelerometers are approaching the fundamental limits of their noise performances. the limitation is mechanical constraint of the structure > such as the stability of cantilever beam, and multiple distinct de

50、vices required complex microfabrication.light force accelerometer (lfa) is a new kind of optical inertial sensor developed in the last several years. the lfa is composed of a micro dynamical system based on the orbital motion of a trapped particle； as illustrated in fig 822. acceleration is measured

51、 by the balance of inertial force on a levitated glass microsphere as proof mass and radiation pressure from a laser beam. from fig. it can be seen that the acceleration readout of the sensor is the difference between the power signals pa and pb on detectors pda and pdr. proof mass displacement is m

52、easured by focusing light scattered by the proof mass on a position-sensitive photodetector. the simple model estimates lfa could be capable of achieving a sensitivity of v100 ng/ /hz. lfa is very promising in the local gravitational field of an orbiting spacecraft. although the theory of lfa is dev

53、eloping quickly, much work still remains to be done in order to design and fabricate a practical lfac22_23j measurement p0a beamfig. 8 detection principle diagram of the lfa 图8光力加速度计的检测原理图besides t there are some very novel accelerometers. for example» the accelerometer based on atom interferom

54、eter has very high sensitivity which is io17 better than traditional optical interferome- ter. it，s very promising in the future.many research institutes in our country such as tsinghua univers让y, beihang university > zhejiang universityt north university of china, etc. have carried out the resea

55、rch of moems accelerometers recently. the simulation for mirccrnano grating accelerometers has been demonstrated by beihang university24 9 and the process of micrograting sensor has been designed and completed. beihang university is the only institute engaged in the study of nano-grating acceleromet

56、er domestically. the key component of the nano-grating accelerometer has been fabricated with grating period of 840 nm and depth of 400 nm via fib/sem dual beam systemc25 besides > the interferometric mi* cromachined accelerometer based on integrated grating has been devised with resolution of 4-

57、 4 pg and range of 10 mg by tsinghua university and zhejiang university1-263 a great progress has been made on the theoretical verification and design of moems accelerometers. however, there is still a great disparity between our country and foreign countries in terms of the accuracy and stability o

58、f the moems accelerometers.5 conclusion and prospectsthis paper has discussed the current state of the art regarding various aspects of moems accelerometers. moems technology has become an attractive research area due to its broad application and prospectsa though the great progress has been achieved in the research and exploration there are still lots of challenges for its practical applications*moems accelerometers depend exceedingly on the experience in practica