高性能MEMS射频无源器件与三维硅微机械加工技术

1、附件5论文中英文摘要作者姓名：顾磊论文题目：高性能MEMS射频无源器件与三维硅微机械加工技术作者简介：顾磊，男1980年4月出生，2004年4月师从中国科学院上海微系统与信息技术研究所李昕欣研究员，于2007年7月获博士学位。中 文 摘 要片上集成电感、互感和可调电容是射频集成电路中三种最重要的射频无源元件，在整个电路系统中起着决定性的作用，是单片RF集成电路如压控振荡器（VCOs）、低噪声放大器(LNAs)及无源滤波器中的关键性部件，在个人移动通讯、全球定位系统（GPS）以及卫星信号接收等高频电路系统中占有重要的地位。利用微机械技术研究射频无源器件是目前MEMS研究领域的热点之一。体微机械、

2、表面微机械以及LIGA技术是MEMS领域重要的三种加工手段，几种加工方式的融合与实现片上集成也是目前MEMS加工领域的发展方向。本论文工作主要研究硅基三维微机械结构制造及射频关键器件的研制技术。一方面针对目前电讯用RFIC的高性能无源元件，如电感、互感和可变电容。所开发的低温工艺可以与射频CMOS工艺相兼容，同时利用MEMS技术解决了硅衬底损耗等问题，实现了高性能的RF电感、互感和可变电容等关键元件，另一方面还针对微纳操纵和精确定位系统需求的X-Y微移动平台，用深沟侧壁隔离（Trench-sidewall） MEMS工艺形成具有微米级移动范围和纳米级定位精度的高性能X-Y微移动载台，为微米电子

3、机械系统进入到纳米电子机械系统研究提供了基本的操作平台，同时新型的电绝缘技术使该微平台可以在普通硅片上制作实现，替代SOI硅片，大大降低了制造成本。主要研究工作和成果分项归纳为：1）在国际上首次报道一种采用低温CMOS兼容工艺制造的嵌入式悬浮螺管 (Concave-Suspended Solenoid) 结构电感和互感（L.Gu, X.Li, IEEE Trans. Electron Devices 54，2007，pp.882；L.Gu, X.Li,IEEE Trans. Microwave Theory Tech. 55，2007，pp.1237）。为了便于封装以及后续加工，电感或互感线圈

4、嵌入在硅片内部，电感线圈周围的硅材料被XeF2气体各向同性腐蚀去除，整个线圈结构通过两边伸出的二氧化硅薄膜支撑（发明专利CN200610029276.8李昕欣,顾磊）。由于线圈周围的硅都被腐蚀移除，电感的衬底损耗极低，大大提高器件的高频性能。而采用铜电镀工艺又显著降低线圈的欧姆损耗。上面两个 1因素使得新型电感和互感的Q值和谐振频率得到显著提高。两边二氧化硅膜支撑也使得整个悬浮结构更加结实，制作的器件在10000g加速度冲击试验下完好无损。利用有限元分析软件ANSYS仿真100g的环境加速度以及80摄氏度环境温度改变下的电感值变化，分析得到的变化值比目前国际上报道最好的悬浮结构还要低一个量级。

5、针对该创新结构嵌入式悬浮螺管电感和互感，建立了集总和准分布两种电路模型，模型与测量结果相吻合，能够指导电感或互感的优化设计 (L.Gu, X.Li, IEEE J-MEMS 16，2007，pp.1162)。电感高频性能测量结果表明2.47nH电感的Q值在2GHz时高达54，自谐振频率超过15GHz，优于已发表的各种CMOS兼容微机械片上电感。在电感制造基础上进一步工艺创新，设计制造出双螺旋结构悬浮互感，建立了器件模型（L.Gu, X.Li,IEEE Trans. Microwave Theory Tech. 55，2007，pp.1237）。互感有效带宽测量值为14Ghz到16GHz，有效增

6、益（可以作为评价互感性能的综合指标）为0.89，在国际报道的片上集成互感中性能最好。该电感和互感创新技术2006年入选著名的国际电子器件大会（IEDM）作报告 (L.Gu, X.Li, IEEE IEDM 2006，pp.521) 。2）针对该创新结构，提出并实现了各种经常使用的电感或互感设计方法 (L.Gu, X.Li,IEEE MEMS 2007，pp.771)，针对更大的电感值，为节省芯片面积，首尾串联的紧密型电感结构是合适的选择；反之如果希望进一步提高性能但对芯片面积要求不高，则“S”型结构更加合适；为避免电感线圈形成的电磁场对周围电路的影响，提出并实现了一种闭合回路结构，HFSS软件

7、分析表明该结构能够将磁力线几乎全部限制在线圈内部(L.Gu, X.Li, Microelectron. Eng.85，2008，pp.697)。此外，为了进一步提高电感或互感的性能及一致性，提出并实现了一种带有绝缘沟槽的微结构，通过精确限制XeF2气体腐蚀区域的技术，显著提高了器件性能的一致性。通过在焊盘底部放置厚二氧化硅层减少引线焊盘引入的寄生效应，使得器件在满足片上集成需要的之外还可以作为高性能分立器件倒装焊封装到SiP射频电路中 (L.Gu, X.Li, Microw. Opt. Technol. Lett. 50,2008,pp.2442)。3）针对射频集成电路用微机械可变电容存在的问

8、题，提出了一系列的解决办法和创新技术。为了减少串联电阻、降低工艺复杂度并与Post-CMOS工艺兼容，发明一种低应力多层金属电镀技术来制造悬浮可变面积及可变间距梳齿电容 (L.Gu, X.Li, Microw. Opt. Technol. Lett. 50,2008,pp.2469)。利用金属镍优异的机械性能，我们采用镍制作器件结构，在金属镍的表面电镀一薄层金用来降低串联电阻并防止镍在空气中氧化。为降低衬底损耗，可变电容结构底部硅用干法腐蚀去除，可动结构通过周围的二氧化硅锚点支撑固定。整个制造过程温度不超过120摄氏度，仅需两块光刻版 （发明专利CN200710044283.3，李昕欣、顾磊）

9、。器件测量结果为：4V电压驱动下，电容值的可调比高达2.98:1，1GHz时的Q值为103，2GHz时的Q值为46.2，优于目前报道的各种CMOS兼容片上集成微机械可变电容。为了避免驱动电压端口对射频信号端口的影响，提出并实现了一种新的相互绝缘式可变电容结构(L.Gu, X.Li, Electronics Lett. 43,2007,pp.808)。电容驱动端与敏感电容端通过二氧化硅薄膜桥实现机械上相连，但电学上相互绝缘。该结构消除了直流偏置电路对可变电容性能的影响，提高了可变电容在电路布局中的灵活性，测量得到4V电压驱动下，电容的可调比高达3.18:1，Q值在1GHz时为115.0，在2GH

10、z时为40.2。4）国际上首次提出并实现一种旋转式微结构可变电容，能够抵抗外界环境振动或冲击对可变电容稳定性的影响 (L.Gu, X.Li, IEEE Electron Device Letters 29,2008,pp.195)。当施加静电驱动力时，梳齿电容的运动方向是沿着器件中心轴旋转。这种结构只有受到轴向力才会产生明显形变，而外界环境加速度的影响几乎都为水平单一方向，很少会产生沿中心轴旋转加速度的干扰，故该结构能够有效抑制移动通讯系统应用时环境振动冲击对器件的影响，显著提高了可靠性(发明专利CN200710045457.4,李昕欣、顾 磊)。该旋转结构在10g环境加速度下，电容的变化值比

11、传统微机械可变电容（直向运动）的电容变化值低两个量级以上。性能测试得到12V电压下，可变电容可调比为2.1:1，Q值在2GHz时仍高达35.2。以上MEMS片上可调谐电容的相关成果又一次入选2007年国际电子器件大会（IEDM）做报告(L.Gu, X.Li, IEEE IEDM 2007，pp.427)。本论文在射频电路用高性能MEMS器件方面的研究成果得到国际同行高度重视，作为中国学者，首次被邀请在2008年IEEE RFIC国际会议做特邀报告（X.Li, L.Gu，IEEE RFIC-2008，pp.163）。5) 首次采用深沟侧壁（Trench-sidewall）MEMS集成工艺技术在单

12、一硅片上成功制造微移动平台 (L.Gu,et al, J Micromech. Microeng. 85,2008,pp.697)。采用的Trench-sidewall MEMS技术能够取代价格昂贵的SOI衬底，将静电驱动，电容、压阻信号检测部分集成在单硅片上，并且能够对一些功能进行自检和反馈控制，提高的器件的精度和可靠性，降低制造成本 (X.Li，L.Gu，IEEE Sensors Journal, 8,2008,pp.1992)。显微镜测量制造出的两维微位移载台，在23V驱动电压下载台移动范围为20×20微米2。为车辆载台的移动定位精度，一种加热SPM探针纳米压印方法被设计和用于

13、测量。测量结果显示位移精度优于18nm，为将来的微电子机械系统研究进入到纳电子机械系统研究提供了必要的操作和测试平台工具。本论文工作用原始创新的关键技术解决了三维MEMS结构集成制造的复杂难题。特别是与CMOS集成电路工艺兼容的片上集成高性能射频无源器件技术，所取得的成果获得国际学术界的认可，所开发的可实用化技术也在微电子产业界获得转让和推广应用。论文的相关学术成果两度发表在国际电子器件领域论文录取最为困难的“国际电子器件会议”（International 3Electron Device Meeting,简称IEDM，在IEDM五十多年历史中我国被录取发表的论文仅寥寥数篇）。此外，论文多次发

14、表在包括IEEE E-D Lett., IEEE T-ED, IEEE J-MEMS, IEEE T-MTT等电子信息领域国际核心期刊上，引起了国际同行的重视。相关成果受2008年领域国际著名会议IEEE International RFIC Symposium邀请作特邀报告，是我国首次在该会议获邀作邀请报告。另外包括IEEE ED Society的副主席和IEEE Fellow等国际著名学者纷纷主动就该成果进行高性能RF集成电路技术合作研发。论文成果中包括三项核心发明专利（一项授权，两项公开）。香港主版上市公司上海先进半导体制造有限公司（ASMC）等企业就本论文的成果已经与我们展开了专利技术

15、转让来实现微电子制造产品技术。根据该技术应用研发内容，上海市科委近期确立了重点项目进行支持。这种用自主创新的技术来提升我国微电子企业的产业技术水平对推动我国微电子事业的发展具有重要意义。本文所作的研究工作，在MEMS三维复杂集成结构制造方面取得了突破性成果，对于实现高性能射频集成电路、通讯系统以及纳米操纵等具有重要的学术价值和应用价值，有助于我国在信息技术领域取得突出的、有特色的进展，获得重大经济效益。规定期限内相关成果形成的论文和专利列表如下：论文：1. Lei Gu, Xinxin Li, Variable Capacitors and Tunable LC-Tanks Formed by

16、 CMOS-Compatible Metal MEMSfor RF ICs, IEDM 2007 - 53th IEEE International Electron Device Meeting, Washington DC，USA, 10-13 Dec., 2007, pp.427-430.2. Lei Gu, Xinxin Li, A Post-CMOS Concave-Suspending MEMS Process in Standard Silicon Wafers forHigh-Performance Solenoidal-DNA-Configured Micro-Transfo

17、rmers, IEDM 2006 - 52th IEEE International Electron Device Meeting 2006, San Francisco, CA, USA, Dec. 11-13, 2006, pp. 521-524.3. Lei Gu, Xinxin Li, Rotational-driven RF Variable Capacitors with Post-CMOS Processes, IEEE ElectronDevice Letters, Vol.29, No.2, 2008, pp.195-197.4. Lei Gu, Xinxin Li, Hi

18、gh-Q Solenoid Inductors With a CMOS-Compatible Concave-Suspending MEMSProcess, IEEE Journal of Microelectromechanical Systems, VOL. 16, NO. 5, 2007, pp.1162-1172.5. Lei Gu, Xinxin Li, High-Performance CMOS-compatible Solenoidal Transformers with aConcave-suspended Configuration, IEEE Transactions on

19、 Microwave Theory and Techniques, VOL. 55, NO. 6, 2007, pp.1237-1245.6. Lei Gu and Xinxin Li, Concave-suspended High-Q Solenoid Inductors with an RFIC-compatibleBulk-micromachining Technology, IEEE Transactions on Electron Devices, Vol.54, 2007, pp.882-885.7. Lei Gu, Xinxin Li, Haifei Bao, Bin Liu,

20、Yuelin Wang, Min Liu, Zunxian Yang, Baoluo Cheng,Single-Wafer-Processed Nano-Positioning XY-Stages with a Trench-Sidewall Micromachining Technology, J. Micromech. Microeng., 16 (2006) 13491357.8. L. Gu and X. Li, Post-CMOS micromachined RF varactor with mutual-isolated large-tuning capacitor andlow-

21、voltage actuator, Electronics Letters, Vol. 43, No. 15, 2007, pp.808-809.9. Lei Gu, Xinxin Li, On-chip embedded toroidal-solenoid inductors and transformers formed by post-CMOSmicromachining techniques, Microelectronic Engineering, Vol. 85, 2008, pp.697-703.10. Lei Gu, Zhengzheng Wu, Xinxin Li, Post

22、-CMOS compatibly micromachined high-performance on-chipair-core solenoidal inductors, Microwave and Optical Technology Letters, Vol. 50, 2008, pp.2442 2446.11. Lei Gu, Zhengzheng Wu, Xinxin Li, Post-CMOS micromachined nickel tunable-capacitors with a large 4tuning-range under low actuating voltage,

23、Microwave and Optical Technology Letters, Vol. 50, 2008, pp.2469 2472.12. Lei Gu, Xinxin Li, An wide-range tunable on-chip radio-frequency LC-tank formed with a post-CMOS13. Lei Gu, Xinxin Li, CONCAVE-SUSPENDED HIGH-Q SOLENOID INDUCTORS WITH A POST-CMOSMEMS PROCESS IN STANDARD SILICON WAFERS, IEEE M

24、EMS-07 - the 20th IEEE International Conference on Micro Electro Mechanical Systems, Kobe, Japan, Jan. 21-25, 2007, pp.771.14. Lei Gu, Xinxin Li, Haifei Bao, Bin Liu, Yuelin Wang, Min Liu, Zunxian Yang, Baoluo Cheng, ASingle-Wafer-Processed XY-Stage Fabricated with Trench-sidewall Doping and Refille

25、d-Trench Isolating Technology, IEEE NEMS-06 - the 1st IEEE International Conference on Nano/Micro Engineered and Molecular Systems, Jan. 18-21, 2006, Zhuhai, China, pp.860-863.15. (邀请报告) Xinxin Li, Lei Gu, (INVITED) Hi-Performance RF passives Using Post-CMOS MEMSTechniques for RF SoC, IEEE RFIC-2008

26、 - 2008 IEEE Radio Frequency Integrated Circuits Symposium, June 15-17, 2008, Atlanta, GA, USA, pp.163-166. (注：第一作者为申请者的导师)16. Xinxin Li, Lei Gu, Yuelin Wang, Heng Yang, Single-wafer-processed Self-testable High-g Accelerometerswith Both Sensing and Actuating Elements Integrated on Trench-sidewall,

27、IEEE Sensors Journal, Vol. 8, 2008, pp.1992-1999. (注：第一作者为申请者的导师)17. Xinxin Li, Baoluo Chen, Yuelin Wang, Lei Gu, Jian Dong, Xiaohong Ge，A trench-sidewallsingle-wafer-MEMS technology and its typical application in high-performance accelerometers，IEDM 2004-50th IEEE International Electron Device Meet

28、ing, San Francisco, CA ,13-15 Decmber，2004，pp.43-46. (注：第一作者为申请者的导师)18. Xinxin Li, Wei Xu, Ying Chen, Le Luo, Lei Gu, Min Liu, Baoluo Cheng, and Yuelin Wang,Single-wafer-processed trench-sidewall integration and its application in a micro resonant detector for vacuum monitoring, J. Vac. Sci. Technol

29、. B 24 (1), Jan/Feb 2006, pp16-19. (注：第一作者为申请者的导师) 专利：1. 一种CMOS工艺兼容的嵌入悬浮螺管结构电感或互感的制作方法, CN200610029276.8, 李昕欣、顾磊（已授权）2. 一种CMOS工艺兼容的悬浮式可变电容的制作方法，CN200710044283.3，李昕欣、顾磊 （法律状态：实质审查的生效；公开（公告）号：101110354；公开（公告）日：2008-01-23）3. 一种抗环境振动的适用于移动电信的MEMS片上可变电容，CN200710045457.4, 李昕欣、顾 磊 （法律状态：实质审查的生效；公开（公告）号：101

30、154505；公开（公告）日：2008-04-02）关键词：微电子机械系统，射频无源器件，电感，互感，可变电容,可调谐谐振器，X-Y两维微移动平台，微机械加工High-performance MEMS RF passive components and siliconmicromachined technologyLei GuABSTRACTOn-chip inductors, transformers and tunable capacitors are most important passive components in RF integrated circuits and play

31、key roles for designing VCO (voltage control oscillator), LNA (low noise amplifier) and passive filter or resonator. Besides, personal mobile communication, GPS (global position system), and satellitic signal receiver also need these high-performance devices, namely high Q-factor of inductors/tunabl

32、e capacitors and high available gain of transformers. Presently, it is a hotspot for studying RF passive components by using MEMS technology. Bulk, surface micromachining and LIGA technique are three essential method of fabrication. Several kinds of processes infused and integrated are also the dire

33、ction for further MEMS research.In this dissertation, we mainly study the 3-D micromachined process based on silicon substrate and research of key RF passive components. On the one hand, some high performance RF components are implemented for telecommunications by using a concise process, such as in

34、ductors, transformers and tunable capacitors. The novel process could be compatible with CMOS process with low temperature. Moreover, the substrate loss is suppressed deeply by selective removing silicon surrounding the devices. On the other hand, a nano-precision XY-stage is designed and fabricated

35、 with trench-sidewall technology. Moreover, the XY-stage is formed on a single wafer instead of SOI wafer to reduce the cost of the fabrication. The stage is an elementary operation method for further research from MEMS (microelectricmechanical system) to NEMS (nanoelectricmechanical system) researc

36、h. The main work and contributions are as follows:1) In order to improve the performance of inductors and transformers, concave-suspended solenoid structures are proposed and formed by low temperature CMOS compatible process. To our best knowledge, these structures are reported firstly in the world.

37、 To facilitate the package and post-fabrication, the coils of inductors or transformers are embedded into the silicon substrate. The silicon surrounding the 6coils are etched and removed by gaseous XeF2. Therefore, the substrate loss of thedevice is suppressed due to the silicon surrounding coils re

38、moved. Moreover, the ohmic loss also reduced by using the copper plated process. Both factors improve the Q-factor and resonant frequency. The whole structure is sustained with protruding silicon oxide film on the both sides of the structure. The robust structure can be survived even under a shock o

39、f 10000g acceleration. By using finite element software ANSYS, the deformation of coil is one order smaller than other suspended inductors under 100g acceleration and 80 centigrade temperature changed. According to these proposed concave-suspended solenoid inductors and transformers, lumped and quas

40、i-distributed circuit models are given. The simulated results based on circuit model can agree well with the measurement and be used to design and optimize the inductors and transformers. The measured Q-factor, the inductance and resonant frequency of the concave-suspended solenoid inductor are 542G

41、Hz, 2.47nH at low frequency and more than 15GHz, respectively. These performances are better than most of other micromachining inductors. We also fabricate some transformers which formed with the similar process. For the transformer, available gain can be defined as the ratio between the power deliv

42、ered to the load and the power input to the network. It can be considered as an important figure-of-merit for overall evaluation of the RF transformers. The available gain of our present transformer is as high as 0.89 which is better than all other reported transformers. The available bandwidth is f

43、rom 14 to 16GHz.2) Different layouts of inductors and transformers are proposed for different applications. For the high inductance with small area occupation, a compact structure made by connecting several one column inductors in series is better choice. For the high inductance with high performanc

44、e, an “S”shaped structure is a suitable choice with a little bigger area occupation. In order to eliminate the effect of electromagnetic interference and noise coupling with neighboring RF components, several closed loop solenoid inductor are implemented. With simulation of HFSS (Ansoft company soft

45、ware), these structure can confine the magnetic flux into a close-path. The structure can also avoid the flux intersecting with metals and semiconductor materials where eddy currents are easily induced. In order to improve the uniformity of the performance, a kind of structure with silicon oxide ref

46、illed trenches is given, which can define the region for XeF2 gaseous etching. The oxideblock beneath the test pad can suppress the substrate parasitics. This structure can be used not only on-chip integration but as an off-chip for flip-chip package.3) Some new structures and process are presented

47、for solving problems existed in conventional MEMS tunable capacitors. In order to reduce the series resistance 7and simply the fabrication, low stress multi-metal electroplated technology (also called metal MEMS technology) is proposed and used to fabricate the suspended tunable capacitor with comb

48、drivers. Electroplated nickel is used as the structure material due to its excellent mechanical properties. A thin gold film is covered on the surface of the nickel for long-term antioxidation in the air. After finishing the whole structure, the silicon substrate beneath the capacitive combs is also

49、 removed by XeF2 dry etching to for the same reason of suppressing the substrate loss. The structures are sustained by surrounding silicon oxide anchors. A suspension gap distance from the silicon substrate is formed. The temperature during the whole fabrication is below 120 centigrade. Only two mas

50、ked are required. Under 4V driving voltage, the tuning ratio is 2.98:1. The Q-factor is 103 at 1GHz and 46.2 at 2GHz, which is better than most of micromachining tunable capacitor.Most of the previously reported MEMS tunable capacitors share a common electric terminal with the electrostatic actuator

51、. This common-ground configuration confines the flexibility of RFIC design. Moreover, the DC driving voltage interferes with the input RF signal especially in high power application. To overcome this limitation, the present technique electrically isolates the two parts at the middle of the linking b

52、ars with a patterned SiO2 bridge. The bridge just connects the two terminals mechanically but isolates each other electrically. This allows a greater flexibility in RF circuit layout. Under 4V driving voltage, the tuning ratio is 3.18:1. The Q-factor is 115 at 1GHz and 40.2 at 2GHz4) To date, a draw

53、back of the developed micromachined tunable capacitors lies in the mechanical instability induced by the straight-line-driven comb structures. For achieving a large tuning ratio under a low driving voltage, the researches have always designed the suspension springs as flexible as possible. When used

54、 in a mobile system like cell phone, such a mechanically instable capacitor will be inevitably influenced by the environmental vibratory/acceleration. On the contrary, rigid suspended beams require high driving voltage for getting wide tuning range. This is a dilemma in the design of micromaching tu

55、nable capacitors. To solve this problem, this dissertation develops, for the first time, a rotationally driven tunable capacitor. The rotational structure features a low stiffness in tangential direction for capacitance tuning but a much higher stiffness along radial directions for anti-vibration, t

56、hereby, exhibiting both high tuning-range under low-voltage and high resist against the axial vibration and acceleration. Generally, the environmental acceleration is applied along the straight direction. Therefore, the rotational structure can effectively suppress the environmental vibratory/accele

57、ration. By using ANSYS simulation, the comb moving distance along 8the electrostatic driving direction is about two orders of magnitude lower than that of the conventional straight-moving tunable capacitors. Under 12V driving voltage, the tuning range of rotational capacitor is 2.1:1. The Q-factor i

58、s 35.2 at 2GHz.5) Besides the RF passive components, a XY-stage is firstly presented on a single silicon wafer with trench-sidewall MEMS integrated technology. The trench-sidewall technology can be used to integrated piezoresistive, capacitive sensing and electrostatic actuator on a single silicon w

59、afer instead of expensive SOI or SOG wafer. Moreover, the reliability of device can be improved by self-testing and feed back control. By using measured microscope, the moving range of the XY-stage is tested as 20×20m2 under a driving voltage of 23V. In order to get a precision of movement, a nano-print system is designed and used to measure the XY-stage. Limited by the radius of the nanometric tip, the resolution of the tip position