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Amro M. Elshurafa May 2013 RF MEMS Capacitors and Variable Capacitors – The Future of Wireless Communication Before we begin… You are free to use this presentation as you see fit. Any publications, in the form of slides, conference papers, journal articles, technical reports, or otherwise, in which these slides will be used (in their original or modified format) should cite one or more of the following references: [+] Amro M. Elshurafa et al., "Low voltage puzzle-like fractal MEMS variable capacitor suppressing pullin," IET/IEEE Micro & Nano Letters, Vol. 7, No. 9, pp. 965-969, 2012. [+] Amro M. Elshurafa et al., "Differential RF MEMS Interwoven Capacitor Immune to Residual Stress Warping," IET/IEEE Micro & Nano Letters, Vol. 7, No. 7, pp. 658-661, 2012. [+] Amro M. Elshurafa et al., "Two-Layer RF MEMS Fractal Capacitors in PolyMUMPS for S-Band Applications," IET/IEEE Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, 2012. [+] Amro M. Elshurafa et al., "A Low Voltage RF MEMS Variable Capacitor with a Linear C-V Response," IET/IEEE Electronics Letters, Vol. 48, No. 7, pp. 392-393, 2012. [+] Amro M. Elshurafa et al., "RF MEMS Fractal Capacitors with High Self Resonant Frequencies," IEEE JMEMS, Vol. 21, No. 1, pp. 10-12, 2012. [+] Amro M. Elshurafa et al., "MEMS Variable Capacitance Devices Utilizing the Substrate: I. Novel Devices with Customizable Tuning Range," Journal of Micromechanics and Microengineering, Vol. 20, No. 4, 045027 (8pp), 2010. [+] Amro M. Elshurafa et al., "Effects of Non-uniform Nanoscale Deflections on Capacitance in RF MEMS Parallel Plate Variable Capacitors," Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 040512 (11pp), 2008. [+] Amro M. Elshurafa et al., "Finite Element Modeling of Low Stress Suspension Structures and Applications in RF MEMS Parallel Plate Variable Capacitors,“ IEEE Transactions of Microwave Theory and 2 Techniques, Vol. 54, No. 5, pp. 2211-2219, 2006. Before we begin… This presentation was prepared in May 2013. Publications, research, and results reported afterwards will not be reflected herein. About the author: Amro Elshurafa obtained his PhD in 2008 in electrical engineering with a focus on RF MEMS variable capacitors. Amro is a registered professional engineer (PEng) and is a senior member of the IEEE. He can be contacted via email at elshurafa@ieee.org. 3 Agenda What is MEMS and RF MEMS RF MEMS Capacitors RF MEMS Variable Capacitors Simulation Measurements State of the Art 4 What is MEMS? • MEMS abbreviates Micro Electro Mechanical Systems • Integrating sensors and actuators possessing dimensions ranging from 1mm to 1μm and relying on electrical, mechanical, optical, chemical, etc, phenomena. • You can hear NEMS, (similar to RF, it is no longer radio frequencies; microelectronics also is nano now!). • Hair diameter thickness is ~100μm. • Strong emphasis on fabrication. • If coupled with IC, the sky is the limit. 5 Most Famous Applications • Printer Ink Jet Nozzles • Inertial sensors – Accelerometers (1D acceleration meter) – Gyroscope (rotation rate meter) – Applications in: air bags, Wii, game arcades, iPhones, Samsung phones, satellites, missiles, etc. • Biomedical medication dispensers (microfluidics). • RF switch array in mobile phones (2012). 6 Most Famous Companies • • • • • • • • • • • • • • • AD HP TI Siemens Bosch Xerox GE STMicroelectronics Qualcomm Cavendish WiSpry Omron Raytheon Intel (classified) This list is different than pure MEMS design, fab, and fabless companies. 7 Fabrication – Briefly Deposit and pattern sacrificial layer Deposit and pattern structural layer Some Substrate 1 2 Etch away sacrificial layer to get free standing structures 5 3 Repeat steps 2 and 3 again 4 8 Foundry – Standard vs. Non-standard • The PolyMUMPS process MEMSCAP, NC, USA. from • Has been in business since 1992. • Very reliable and robust. • Used by hundreds of groups throughout the world in countless applications. • What about CMOS? Can we have that? 9 Foundry – Standard vs. Non-standard 10 Why RF MEMS? Inductors Capacitors Resistors IC’s It is the high-Q passive components that are hindering miniaturization! Slide by Dr. Clark Nguyen at University of California at Berkeley. 11 Why RF MEMS? • Ceramic filters: • Made of piezoelectric ceramics • Frequency is adjusted by thickness and size of the ceramic element • Typical dimensions are: ~20mm × ~10mm × ~5mm • Extremely dimensions sensitive: a ±0.1mm dimension tolerance yields a frequency accuracy of ±220MHz → Expensive • No further opportunities for further miniaturization 12 MEMS Benefit: General Less power consumption Discrete electronics Better performance ICs High volume fabrication Less power consumption Off-chip passives and filters Better performance MEMS High volume fabrication 13 What Can MEMS Offer? High Q filters: fo = 8.5MHz Qvac = 8,000 Qair ~ 50 Lr = 40μm F. Bannon, J. Clark, and C. Nguyen, “High Frequency Microelectromechanical IF Filters," IEEE International Electron Device Meetings, pp. 773-776, 1996. 14 What Can MEMS Offer? High Q resonators: -84 Transmission (dB) 20μm Polysilicon Electrode CVD Diamond mMechanical Disk Resonator Ground Plane -86 -88 Q = 10,100 (air) -90 -92 -94 -96 -98 -100 1507.4 1507.6 1507.8 1508 1508.2 Frequency (MHz) J. Wang, J. Butler, T. Feygelson, and C. Nguyen, “1.51GHz nanocrystaline Diamond Micromechanical Disk Resonator with Material Mismatched Isolating Support,” IEEE Conference on Microelectromechanical Systems, pp. 641-644, 2004. 15 What Can MEMS Offer? High Q inductors: J. Zou, J. Nickel, D. Trainor, C. Liu, and J. Schutte-Aine, “Development of Vertical Planar Coil Inductors Using Plastic Deformation Magnetic Assembly,” IEEE International Microwave Symposium, pp. 193-196, 2001. Jun-Bo Yoon, Byeong-I1 Kim, Yun-Seok Choi, and Euisik Yoon, “3-D Lithography and Metal Surface Micromachinig for RF and Microwave MEMS,” IEEE Microelectromechanical Systems, pp. 673-676, 2002. 16 Varactors: CMOS vs. MEMS CMOS Varactors (reverse biased diodes) MEMS Varactors Leakage currents exists No leakage current Typical Q is 30-40, but can reach to 50-60 Q can reach up to 200 – 300 Due to continuous downscaling, the tuning range (Cmax/Cmin) is decreasing – Maximum ratio is 3 at millimeter-wave range. Tuning ranges are high (~5 for varactors and ~50 for switches and even higher) Good at low frequency (inductor loss dominates for LC tank), but lossy at millimeter-wave range No real concern K. Kwok and J. Long, “A 23-to-29 GHz Transconductor-Tuned VCO MMIC in 0.13um CMOS,” IEEE Journal of Solid State Circuits, Vol. 42, No. 12, pp. 2878-2886, 2007. 17 Why MEMS Varactors? • Internal antenna, form factor, touch screens, etc, pose real challenges (remember the death grip in iPhone4). • Technologies changing rapidly, 2.5G, 3G, 4G: many carriers and bands. Hence, antennas, filters, power amplifiers need to tune to these bands. • Dennis Yost, CEO of Cavendish, states: Theoretical 4G limit is 80Mbps, though testing shows ~8Mbps at best. • Gabriel Rebeiz: a tunable front end is the holy grail of advanced multi-mode multi-frequency mobile devices. • Paratek shipped a tunable device to Samsung (thin-film based varactor). Interestingly, RIM bought Paratek in 2012! 18 Why MEMS Varactors • The RF filters are mostly ceramic or SAW filters, and are very bulky and expensive (off-chip). • Typical dimensions are 2cm x 1cm x 0.5 cm! 19 Why MEMS Varactors • Add MEMS filters and receive whatever you want (no size limitation). You can add many filters or a tunable filter. • Quality factors > 15,000 at 1.4GHz BW = 100kHz; better than the current BW of 35MHz found in today’s phones. 20 The Ultimate Goal is: A complete MEMS-based transceiver: 21 However… • Fabrication and integration challenges: CMOS and MEMS. • Actuation voltages for MEMS varactors: 10V ~ 40V. • Lifetime and reliability despite tests have been performed for billions of cycles in lab conditions. • Temperature stability and drift. • Modeling vs. trial and error fabrication. C. T. C. Nguyen, “Mechanical Radio,” IEEE Spectrum, December 2009. 22 Publications: Numbers 1000 Number of Publications 900 800 RF MEMS Publications 884 882 862 814 826 Variable Capacitor Publications 782 750 737 700 600 537 500 400 313 358 300 200 100 253 113 59 157 316 298 305 349 135 147 82 324 368 342 378 197 116 0 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Year Source: Engineering Village 23 Publications – Where? 3000 Number of Publications 2750 2627 2500 2250 2000 1750 1500 1250 1000 808 750 621 500 462 450 400 299 272 240 189 Canada Italy India Belguim 250 0 United States China France Japan Korea Germany Country Source: Engineering Village. 24 Agenda What is MEMS and RF MEMS RF MEMS Capacitors RF MEMS Variable Capacitors Simulation Measurements State of the Art 25 A MEMS Perspective • Typical capacitors in MEMS are of the parallel-plate type: Criterion CMOS MEMS Etching Holes No Concern Concern Residual-Stress Warping No Concern Concern Availability of Metal Layers No Concern Concern Parasitics/balanced capability Concern Concern 26 Etching Holes When a sacrificial layer is present between two structural layers, it has to be removed. One way is to do wetetching: submerge wafer in an etcher. How much time will the etching take for the example here if we assume that the etching rate is 10μm/min? 27 Etching Holes • Now, by adding etching holes throughout the large structure, the etchant will have more opportunities to penetrate through the structure. Hence, reducing the etching time required significantly. • Also called release access holes. holes and • Concerns: affect capacitance, mechanical performance, and optical performance. • What about CMOS? 28 Metal Layer Scarcity • Self explanatory! • Most MEMS processes possess several polysilicon layers but a single metal layer obtaining high Q is difficult. • What about CMOS? • In CMOS processes, there are ~9 metal layers both capacitor terminals can be metal and hence not affect Q. Faraday Technology Corporation www.design-reuse.com 29 Substrate Parasitics: Balanced/Differential Capability • In a typical parallel-plate capacitor, the bottom-plate/substrate parasitic is larger than the top-plate/substrate parasitic. • Connecting transistors to capacitors is very strict (TSMC) – many prohibited configurations. • The output of the circuit is NOT the same if the terminals of the capacitor are swapped (similar to a polarized capacitor). •Exists also in discrete capacitors. • For both MEMS and CMOS. So, what to do? 30 Residual Stress – Examples http://mems.ece.dal.ca/research.php R. Al-Dahleh and R. Mansour, “High Capacitance Ratio Warped-Beam Capacitive MEMS Switch Designs,” IEEE Journal of Microeletromechanical Systems, Vol. 19, No. 3, pp. 538-547, 2010. What about CMOS? 31 Residual Stress – 1 •What is it? •First kind is: bending, or warping, taking place when two materials with different thermal expansion coefficients, are on top of each other. •During fabrication, heating then cooling! MATERIAL 1 α1 > α2 MATERIAL 2 32 Residual Stress – 2 •Second kind is: bending, or warping, taking place in a single layer while cooling. •During cooling, the molecules reorient themselves in such a way that the Young’s Modulus is not the same everywhere within the material (moving parts). •Different for fixed-free, fixed-fixed, etc beam/plate orientations. •Severe in larger plates and longer beams. 33 Calculate Capacitance with Warping A. M. Elshurafa and E. I. El-Masry, “Effects of Nonuniform Nanoscale Deflections on Capacitance in RF MEMS Parallel Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 34 Calculate Capacitance with Warping Elliptic paraboloid Hyperbolic paraboloid A. M. Elshurafa and E. I. El-Masry, “Effects of Nonuniform Nanoscale Deflections on Capacitance in RF MEMS Parallel Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 35 Calculate Capacitance with Warping Capacitance evaluation in 2D Capacitance evaluation in 3D A. M. Elshurafa and E. I. El-Masry, “Effects of Nonuniform Nanoscale Deflections on Capacitance in RF MEMS Parallel Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 36 Closed Form Expressions A. M. Elshurafa and E. I. El-Masry, “Effects of Nonuniform Nanoscale Deflections on Capacitance in RF MEMS Parallel Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 37 What are Fractals? http://www.evl.uic.edu/aej/488/lecture13.html http://www.bathsheba.com/gallery/assorted/ http://www.evl.uic.edu/aej/488/lecture13.html Fractal Capacitors • Initially introduced in 1998 in ISSCC by Samavati et al. while working with Tom Lee at Stanford. • Main Concern in capacitance density. • Benefit from the lateral downscaling. • Obtain lateral and vertical capacitances (if two layers are used). • Increase fringing. H. Samavati, A. Hajimiri, A. Shahani, G. Nasserbakht, and T. Lee, “Fractal Capacitors,” IEEE International Solid State Circuits Conference, 256-257, 1998. 39 One Solution: Fractals Moore’s Fractal A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 40 4th and 5th Iteration These capacitors are single-layer capacitors A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 41 Addressing Etching Holes A separation exists already throughout the structure! 42 Addressing Residual Stress The segments are small, and when long they can be easily anchored. 43 Residual Stress Warping Parallel Plate 5th order fractal A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 44 Addressing Metal Scarcity Use the only available metal layer. A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 45 Addressing ‘Balance-ness’ • Black: Signal Terminal • Gray: Ground Terminal Almost same area for both terminals, hence it is balanced. A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 46 Measurements A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 47 SRF Measurements Self resonant frequency: the frequency at which the impedance of the capacitor becomes purely real (resistive). C Band: 4 – 8 GHz. X Band: 8 – 12 GHz. Ku Band: 12 – 18 GHz. 48 Parallel Plate vs. Fractal 49 More Designs – in 2 Layers Woven Design Interleaved Design A. M. Elshurafa and K. N. Salama, "Two-Layer RF MEMS Fractal Capacitors in PolyMUMPS for S-Band Applications," IET Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012 50 More Designs – in 2 Layers Woven Design Interleaved Design A. M. Elshurafa and K. N. Salama, "Two-Layer RF MEMS Fractal Capacitors in PolyMUMPS for S-Band Applications," IET Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012 51 Measurements Woven Design Interleaved Design A. M. Elshurafa and K. N. Salama, "Two-Layer RF MEMS Fractal Capacitors in PolyMUMPS for S-Band Applications," IET Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012 52 Interwoven Design Amro M. Elshurafa and K. N. Salama, "Differential RF MEMS Interwoven Capacitor Immune to Residual Stress Warping," IET Micro & Nano Letters, Vol. 7, No. 7, pp. 658-661, July 2012. 53 Interwoven Design J. de Jong and S. Baler, “Integrated Capacitor with Alternating Layered Segments,” US Patent 7,944,732, 2011. 54 Interwoven Design A. M. Elshurafa and K. N. Salama, "Differential RF MEMS Interwoven Capacitor Immune to Residual Stress Warping," IET Micro & Nano Letters, Vol. 7, No. 7, pp. 658-661, July 2012. Comparison* Criterion PP Interleaved Woven Interwoven Moore’s C, pF 4.7 1.2 1.1 0.7 0.58 Q 7 3.5 6 9 10 SRF (GHz) 5.5 10 10 >20 >20 * Measurement results at 2GHz A. M. Elshurafa and K. N. Salama, "Differential RF MEMS Interwoven Capacitor Immune to Residual Stress Warping," IET Micro & Nano Letters, Vol. 7, No. 7, pp. 658-661, July 2012. A. M. Elshurafa and K. N. Salama, "Two-Layer RF MEMS Fractal Capacitors in PolyMUMPS for S-Band Applications," IET Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012. A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 56 Fractal Cookbook Criterion PP Could be created in a Single Layer? ✗ ✔ ✗ ✗ ✔ Balanced ✗ ✔ ✗ ✔ ✔ Capacitance Value ✔✔ ✔ ✔ ✗ ✗ High SRF ✗ ✔ ✔ ✔✔ ✔✔ ✗ ✔ Could it be used in a varactor? ✔ Interleaved Woven Interwoven ✔ ✔ not readily* Moore’s in two layers* Capacity Limits Cmax = Cmax,x + Cmax,y + Cmax,z R. Aparicio and A. Hajimiri, “Capacity Limits and Matching Properties of Lateral Flux Integrated Capacitors,” IEEE Custom Integrated Circuits Conference, pp. 365-368, 2001. 58 Agenda What is MEMS and RF MEMS RF MEMS Capacitors RF MEMS Variable Capacitors Simulation Measurements State of the Art 59 Variable Capacitors • What are they? Simply capacitors with a varying capacitance! •They could be called variable capacitor, varactor, or varicap. • For a capacitor, figures of merit (FOM): C, Q, SRF. • For a varactor actuated electrostatically, we add: • actuation voltage (VDC) • linearity (R2) • tuning range (TR) 60 Variable Capacitor vs. Switch! Variable Capacitor Switch or Switched Capacitor Analog tunability (Linearity) Two distinct capacitances only (digital: High and Low) Low Tuning Range (~5:1) High Tuning Range (>~50:1 for switches and ~15:1 for switched capacitors) Usually air separates both terminals only Mostly an insulator layer in addition to air separates both terminals Dielectric charging is not a concern because no physical contact occurs usually Dielectric charging is a concern because physical contact occurs usually Pull-in limits performance Pull-in is not a real limitation Actuation Voltage • A DC voltage is used to achieve movement, i.e. actuation. • The change in the separating distance governs the change in capacitance. • Ideally, want VDC to be as low as possible. Typically however, it is at least 10V, but can reach 50V and more, and very few designs use low voltage (~4V). 62 Linearity: C-V • The capacitance-voltage relation in a parallel plate capacitor when d is varying is inherently nonlinear; C = εA/d. • One of the solutions is to use a comb-drive capacitor. • The catch: requires area to obtain usable C and V for actuation. Rockwell Labs Varactor 63 Tuning Range (TR) • Definition: the ratio of the maximum capacitance to the minimum capacitance; i.e. TR = Cmax/Cmin • Ideally, want TR to be as high as possible. • Usually, minimum capacitance takes place when V = 0. • Usually, maximum capacitance takes place when V = VDC:pull-in 64 TR – Pull In • Parallel plate variable capacitors suffer from the pull-in phenomenon, or snap-in phenomenon. 65 Deriving Pull–in: 1 A Initial Capacitance C Electrostatic Force 1 C 2 1 AV 2 DC Fe V DC 2 x 2 ( xo x ) 2 Electrostatic Spring Constant Mechanical Force What if x = (1/3)xo? xo x Fe CV 2 DC ke x ( xo x ) 2 CV 2 DC 1 km x ke ( xo x ) 2( xo x ) 2 2km x ke ( xo x ) 66 Deriving Pull–in: 2 Electrostatic and Mechanical Forces 1 AV 2 DC FE k M x FM 2 2 ( xo x) Solve for the Voltage 2k M x( xo x) 2 V A 1 2 1 2k 2 V x ( xo x) A 1. Take the derivative 2. Equate to 0 3. Solve for x 1 2 2k V 1 x ( xo x) x 0 x 2 A 1 2 1 2 1 1 12 x ( xo x) x 2 2 x x o 3 67 Maximum TR eps.A d eps.A Cmax 2 d 3 Cmax 3 TR 1.5 Cmin 2 Cmin Ideally: Practically however: TR1 C max C f C min C f C max 0.4C max 1.3125 C min 0.4C max 68 How to increase TR – 1 TR = 2.83 A. Dec and K. Suyama, “Micromachined Varactor with Wide Tuning Range,” Electronics Letters, Vol. 33, No. 11, pp. 922-944, 1997. 69 How to increase TR – 1 TR = 2.83 1. Dec and K. Suyama, “Micromachined Varactor with Wide Tuning Range,” Electronics Letters, Vol. 33, No. 11, pp. 922-944, 1997. 2. A. Dec and K. Suyama “Micromachined Electro-mechanically Tunable Capacitors and their Applications to RF IC’s” IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 12, 1998. 70 How to increase TR – 2 TR = 4.1 Maher Bakri-Kassem and R. R. Mansour, “High Tuning Range Parallel Plate MEMS Variable Capacitors with Arrays of Supporting Beams,” IEEE Conference on Microelectromechanical Systems, pp. 666-669, 2006. 71 How to increase TR – 2 TR = 4.1 Maher Bakri-Kassem and R. R. Mansour, “High Tuning Range Parallel Plate MEMS Variable Capacitors with Arrays of Supporting Beams,” IEEE Conference on Microelectromechanical Systems, pp. 666-669, 2006. 72 How to increase TR – 3 Theoretical TR = ∞ J. Zou, J. Aine, J. Chen, and S. Kang, “Development of a Wide Tuning Range MEMS Tunable Capacitor for Wireless Communication,” IEEE International Electron Device Meeting, pp. 403-406, 2000. 73 How to increase TR – 3 Theoretical TR = ∞ T. Tsang and M. El-Gamal, “Very Wide Tuning Range Microelectromechanical Capacitors in the MUMPS Process for RF Applications,” IEEE VLSI Symposium, pp. 33-36, 2003. 74 How to increase TR – 4 TR = 1.5 G. Ionis, A. Dec, and K. Suyama, “A Zipper Action Differential Micromechanical Tunable Capacitor,” IEEE Conference on Microelectromechanical Systems, pp. 29-32, 2001. 75 How to increase TR – 5 A. M. Elshurafa and E. I. El-Masry, "MEMS Variable Capacitance Devices Utilizing the Substrate: I. Novel Devices with Customizable Tuning Range," Journal of Micromechanics and Microengineering – JMM, Vol. 20, No. 4, 045027 (8pp), April 2010. 76 How to increase TR – 5 A. M. Elshurafa and E. I. El-Masry, "MEMS Variable Capacitance Devices Utilizing the Substrate: I. Novel Devices with Customizable Tuning Range," Journal of Micromechanics and Microengineering – JMM, Vol. 20, No. 4, 045027 (8pp), April 2010. 77 How to increase TR – 6 TR = 2.2 C. Han, D. Choi, and J. Yoon, “Parallel Plate MEMS Variable Capacitor with Superior Linearity and Large Tuning Ratio using a Levering Structure,”ّّ IEEE J. Microelectromechanical Systems, Vol. 20, No. 6, pp. 1345-1354, 2011. 78 How to increase TR – 6 C. Han, D. Choi, and J. Yoon, “Parallel Plate MEMS Variable Capacitor with Superior Linearity and Large Tuning Ratio using a Levering Structure,”ّّ IEEE J. Microelectromechanical Systems, Vol. 20, No. 6, pp. 1345-1354, 2011. 79 How to increase TR – 7 • Make use of residual stress •After fabricating the varactor, use ALD • Tuning range: 5:1 • Q= 29 at 1GHz M. Bakri-Kassem and R. R. Mansour, “Linear Bilayer ALD Coated MEMS Varactor with High Tuning Capacitance Ratio,” IEEE J. of Miroelectromechanical Sytems, Vol. 18, No. 1, pp. 147-153, 2009. 80 How to increase TR – 7 •A comment on the relatively high quality factor: the substrate was etched under the bottom plate M. Bakri-Kassem and R. R. Mansour, “Linear Bilayer ALD Coated MEMS Varactor with High Tuning Capacitance Ratio,” IEEE J. of Miroelectromechanical Sytems, Vol. 18, No. 1, pp. 147-153, 2009. 81 How to Increase TR – 8 A. M. Elshurafa, P. H. Ho, and K. N. Salama, "Modeling and Fabrication of an RF MEMS Variable Capacitor with a Fractal Geometry," IEEE International Symposium on Circuits and Systems – ISCAS, 2013. 82 How to increase TR – 8 F = Force F subscript = Fringing V Subscript = Vertical H Subscript = Horizontal S Subscript = Substrate A. M. Elshurafa, A. G. Radwan. P. H. Ho, M. H. Ouda, K. N. Salama, "Low voltage puzzle-like fractal MEMS variable capacitor suppressing pull-in," IET Micro & Nano Letters, Vol. 7, No. 9, pp. 965-969, September 2012. 83 Actuation Before Actuation After Actuation A. M. Elshurafa, P. H. Ho, and K. N. Salama, "Modeling and Fabrication of an RF MEMS Variable Capacitor with a Fractal Geometry," IEEE International Symposium on Circuits and Systems – ISCAS, 2013. 84 Optical Profiler and CV Curve 85 Comparison 86 Other Requirements: Linearity A. M. Elshurafa, P. H. Ho, and K. N. Salama, "A Low Voltage RF MEMS Variable Capacitor with a Linear C-V Response," IET Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 87 Other Requirements: Linearity A. M. Elshurafa, P. H. Ho, and K. N. Salama, "A Low Voltage RF MEMS Variable Capacitor with a Linear C-V Response," IET Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 88 Close-up A. M. Elshurafa, P. H. Ho, and K. N. Salama, "A Low Voltage RF MEMS Variable Capacitor with a Linear C-V Response," IET/IEEE Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 89 Performance A. M. Elshurafa, P. H. Ho, and K. N. Salama, "A Low Voltage RF MEMS Variable Capacitor with a Linear C-V Response," IET/IEEE Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 90 Agenda What is MEMS and RF MEMS RF MEMS Capacitors RF MEMS Variable Capacitors Simulation Measurements State of the Art 91 Modeling of MEMS Before that, how is CMOS modeling performed: Cadence: Virtuoso, Hspice, Spectre, Encounter: One stop shop! • DC/AC/Transient analysis •Steady State • Periodic Steady State • Digital Flow • Layout • LVS/DRC • System Level Simulation • Temperature Analysis • Inductor design • Capacitors • Frequency Response • Filter Design • Noise Analysis • Leakage • Monte Carlo Generally, the results acquired from Cadence are reasonably accurate, and simulations do predict the behavior of the fabricated chip very well. 92 Modeling of MEMS Let’s look at a typical MEMS problem – a thermal actuator: Pad – Anchored Thin Arm – Suspended 5V Current Current GND Pad – Anchored Thick Arm – Suspended Movement Direction 93 Modeling of MEMS • In thermal actuators: three physics are involved: a. Electric currents b. Thermal losses c. Structural interaction COMSOL © • Electrostatic problems: a. Electrostatic force b. Mechanical deflection • Microfluidic problems • Magnetic actuation • Gyroscopes/accelerometers • RF performance! 94 Modeling of MEMS LEdit Layout Cadence Clewin ANSYS COMSOL Multiphysics MEMS Modeling Coventorware Sugar Intellisuite HFSS MatLab/Simulink Equations Maple Mathematica 3D Drawing SolidWorks AutoCAD 95 Typical Flow 96 Finite Element Modeling • Given the interdisciplinary nature of MEMS, the FEM method seems to be the most suitable way of solving problems. • Divide the structure to elements (i.e. mesh the structure). • Specify boundary conditions for each physics. • Know the solution for one element, then add all independent solutions for a global solution. 97 Real Example Heat Flux Physics: Thermo DC Voltage Physics: Electrical Fixed Boundaries Physics: structural Ground 98 Physics: Electrical Tips and Tricks • Start with a coarse mesh first, then refine. More elements, better accuracy, memory. but more time and • Start with a single physics first, then add. • Verify with a known simple problem to verify your model, then do yours. • Make use of Symmetry. •Do you always get a more accurate result with more elements? 99 Agenda What is MEMS and RF MEMS RF MEMS Capacitors RF MEMS Variable Capacitors Simulation Measurements State of the Art 100 Measurements • In order to characterize RF MEMS varactors and/or switches, we can do a 1-port or a 2-port measurement, and for that we need: a. b. c. d. e. f. g. h. Vector network analyzer (VNA) DC Voltage source Appropriate Probe (1 or 2) Calibration Impedance Substrate Contact Substrate Bias-T network Correct Layout/Pads Cables and adapters (VERY IMPORTANT). • Can I use an LCR meter? 101 Microwave Probes •The most popular probe is a ground-signal-ground probe, or a GSG probe. G Source: Gavin Fisher; Cascade Microtech S G 102 Preparing Probes - Planarity Not planarized Use contact substrate to perform this task. Planarized Source: Gavin Fisher; Cascade Microtech 103 Probe Preparation - Alignment Recommended over-travel (skidding or skating) Pitch (150μm usually) In addition to planarization, we need to perform alignment: • Arrive at the reference (not landed yet). • Land (vertical) • Skid/skate (horizontal) • Repeat to adjust 104 Source: Gavin Fisher; Cascade Microtech Probes are ready – Calibrate! •We can now calibrate. Let’s start with a 1-port calibration, also could be named SOL calibration. We will: Define a short Define an Open Define a load (50Ω) Land on load Land on a line that shorts all tips Stay in air! This is done using a calibration substrate. 105 For a 2-port Calibration: •The only difference is that you need a Thru and you do calibration for both probes (hence SOLT). • For SOL, you will obtain information regarding S11 only (i.e. reflection), while for the SOLT you obtain information for S11 and S21 (i.e. reflection and transmission). •You need calibration only for RF frequencies. 106 Setup VNA VDC + _ GND No DC RF No RF DC RF+DC 107 Setup VNA VDC + _ GND DC To Check: 1. Connectors (male or female, size, etc) 2. Cables 3. Frequency range 4. Max Power 5. Max voltage RF RF+DC 108 A Few Tips on Pads • Too much current, and you blow your probes away! • Your boss will not be happy. 109 A Few Tips on Pads • Ensure you design pitch is the same as the probes you have! • Small pads: less parasitics. • Big pads mean: easier landing. • 70um is reasonable or use an insulator substrate. Pitch 110 Smith Chart Considerations • Top half of the Smith Chart is Inductive, and bottom half is capacitive. • Resonance is the middle horizontal line. L • Be on the outer sides for high quality factor Q = imaginary/real. • Reasonable method up to Qs of 100 or maybe 200. C 111 A Real Measurement 112 Agenda What is MEMS and RF MEMS RF MEMS Capacitors RF MEMS Variable Capacitors Simulation Measurements State of the Art 113 WiSpry – Tuner Board •Published in January 2013 in IEEE TMTT by Gu and Morris. •Built using MEMS tunable capacitors •Operates from 300MHz to 500MHz. Q. Gu and A. Morris, “A New Method for Matching Network Adaptive Control,” IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 1, pp. 587-595, 2013. 114 WiSpry – Antenna Tuner •World’s smallest antenna tuning developers’ kit for smart phones and tablets. •Designed for optimization during the development stages. •Fits inside a true formfactor smartphone or tablet products. 115 Omron and Radant Switches •Omron’s switch. Professor Rebeiz describes it as ‘amazing’. ‘The best RF MEMS switch in the world’. •Radant Switch. •Difference DC requirement between handheld devices and base stations 116 Classic CMOS MEMS-VCOs (0.5um) A. Dec and K. Suyama “Micromachined Electro-mechanically Tunable Capacitors and their Applications to RF IC’s” IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 12, 1998. A. Dec and K. Suyama, “A 1.9GHz CMOS VCO with Micromachined Electromechanically Tunable Capacitors,” IEEE Journal of Solid State Circuits, Vol. 35, No. 8, pp. 1231-1237, 2000. 117 Classic CMOS-MEMS Oscillator •Developed at UC Berkeley. •Wang developed the resonator first circa 1989. •Nguyen integrated both in circa 1994 (PhD dissertation) but published later in 1999. C. Nguyen and R. Howe, “An Integrated CMOS Micromechanical Resonator HighQ Oscillator,” IEEE Journal of Solid State Circuits, Vol. 34, No. 4, pp. 440-455, 1999. CMOS-MEMS Variable Capacitor •Benefit from Residual Stress. • Thermal actuation first, then electrostatic. J. Reinke, G. Fedder, T. Mukherjee, “CMOS MEMS 3-bit Digital Capacitors with Tuning Ratios Greater Than 60:1,” IEEE Transactions on Microwave Theory and Techniques, Vol. 59, No. 5, pp. 1238-1248, 2011. 119 CMOS-MEMS Variable Capacitor • Maskless, post-CMOS etching. • TR = 63:1! • Q = 160 at 1 GHz. J. Reinke, G. Fedder, T. Mukherjee, “CMOS MEMS 3-bit Digital Capacitors with Tuning Ratios Greater Than 60:1,” IEEE Transactions on Microwave Theory and Techniques, Vol. 59, No. 5, pp. 1238-1248, 2011. 120 CMOS-MEMS Variable Capacitor M. Bakri-Kassem, S. Fouladi, and R. Mansour, “Novel High Q MEMS Curled-Plate Variable Capacitors Fabricated in 0.35um CMOS Technology,” IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 2, pp. 530-541, 2008. 121 CMOS-MEMS Variable Capacitor • Maskless, post-CMOS etching. • TR = 6:1! • Q = ~300 at 1.5 GHz. M. Bakri-Kassem, S. Fouladi, and R. Mansour, “Novel High Q MEMS Curled-Plate Variable Capacitors Fabricated in 0.35um CMOS Technology,” IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 2, pp. 530-541, 2008. 122 Temperature Insensitivity • Tuning Range: 3 • Q is very high > 100! • Stable up to +125 C and processed in a university. R. Mahameed and G. Rebeiz, “Electrostatic RF MEMS Tunable Capacitors with Analog Tunability and Low Temperature Sensitivity,” IEEE International Microwave Symposium, pp. 1254-1257. 123 UCSD: 10W Switch! • Tuning Range: 7 • Q is very high: >>200! • Could handle 10W of power. H. Zareie and G. M. Rebeiz, “High Power (>10W) RF MEMS Switched Capacitors,” IEEE International Microwave Symposium, 2012. 124 Tunable Filter •Bandwidth from 1.5GHz to 2.5GHz. •Q is around 100 using variable devices. M. El-Tanani and G. Rebeiz “High Performance 1.5-2.5GHz RF MEMS Tunable Filters for Wireless Applications,” IEEE Transactions on Microwave Theory and Techniques, Vol. 58, No. 6, pp. 1629-1637, 2010. 125 Tunable Filters - Michigan A. Abbaspour-Tamijani, L. Dussopt, G. M. Rebeiz, “Miniature and Tunable Filters Using MEMS Capacitors,” IEEE Transactions on Microwave Theory and Techniques, Novl. 51, No. 7, pp. 1878-1885, 2003. 126 To Integrate or Not to Integrate -1 • IMEC: (Interuniversity Microlectronics Center) provide the SiGe-MEMS process. www.imec.be • Same wafer processing • Why SiGe? 127 To Integrate or Not to Integrate - 2 • Invensense Nasiri Fabrication Platform: www.invensense.com • Different wafers – superb bonding (their competitive edge). 128 To Integrate or Not to Integrate - 3 • DALSA MEMS process with CMOS 0.8: www.dalsa.com • Same wafer, achieved through wafer packaging, vias, bonding. • Structural layer is metal. 129 Future Outlook • Challenges that need to be overcome are: – Packaging: SiP, SoC, SoP, Bonding, Seamless, Hermetic. – Temperature Drift: Material selection and optimization. – Mechanical Reliability: Material selection, actuation techniques, and fatigue. – Voltage Actuation Requirement: intelligent MEMS designs or high performance charge pumps*. – CMOS Opportunities: MEMS interface circuits. * A. Emira, M. AbdelGhany, M. Elsayed, A. M. Elshurafa, S. Sedky, and K. N. Salama, "50V All-PMOS Charge Pumps Using Low-Voltage Capacitors," IEEE Transactions on Industrial Electronics, 2013, (10.1109/TIE.2012.2213674). 130 Conclusion • Variable/Tunable devices are needed for next generation wireless communication, and RF MEMS variable capacitance devices can satisfy the requirements. • To integrate seamlessly or not to integrate: two views and I like to stand in the middle. 131 Further Reading 1. RF MEMS: Theory, Design, and Technology (Textbook). 2. Tuning in to RF MEMS, IEEE Microwave Magazine, 2009. 3. Handling RF Power: The Latest advances in RF MEMS Tunable Filters, IEEE Microwave Magazine, 2013. 4. RF MEMS-CMOS Device integration: An Overview of the Potential for RF Researchers, IEEE Microwave Magazine, 2013. 5. The Search for a Reliable MEMS Switch???: Metal-Contact Switches, IEEE Microwave Magazine, 2013. 6. Mechanical Radio, IEEE Spectrum, 2009. 7. MEMS Technology for Timing and Frequency Control, IEEE Transactions on Ultrasonics, Ferroelectrics, & Frequency Control, 2007. 8. RF MEMS for Ubiquitous Wireless Connectivity: Parts I and II, IEEE Microwave Magazine, 2004. 132 Thank You References: Variable Capacitors 1. A. M. Elshurafa, P. H. Ho, and K. N. Salama, "A Low Voltage RF MEMS Variable Capacitor with a Linear CV Response," IET/IEEE Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 2. A. M. Elshurafa and E. I. El-Masry, "MEMS Variable Capacitance Devices Utilizing the Substrate: II. Zipping Varactors," Journal of Micromechanics and Microengineering, Vol. 20, No. 4, 045028 (7pp), April 2010. 3. A. M. Elshurafa and E. I. El-Masry, "MEMS Variable Capacitance Devices Utilizing the Substrate: I. Novel Devices with Customizable Tuning Range," Journal of Micromechanics and Microengineering, Vol. 20, No. 4, 045027 (8pp), April 2010. 4. A. M. Elshurafa and E. I. El-Masry, "Effects of Non-uniform Nanoscale Deflections on Capacitance in RF MEMS Parallel Plate Variable Capacitors," Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 040512 (11pp), April 2008. 5. A. M. Elshurafa and E. I. El-Masry, "Finite Element Modeling of Low Stress Suspension Structures and Applications in RF MEMS Parallel Plate Variable Capacitors," IEEE Transactions of Microwave Theory and Techniques, Vol. 54, No. 5, pp. 2211-2219, May 2006. 6. A. M. Elshurafa and E. I. El-Masry, "A Novel 3-in-1 MEMS Variable Capacitance Device with Customizable Tuning Ranges," IEEE International Device and Test Workshop, November 2009. 7. A. M. Elshurafa and E. I. El-Masry, "Design Considerations in MEMS Parallel Plate Variable Capacitors," IEEE Midwest Symposium on Circuits and Systems (INVITED), pp. 1173-1176, August 2007. 8. A. M. Elshurafa and E. I. El-Masry, "Effects of Etching Holes on Capacitance and Tuning Range in MEMS Parallel Plate Variable Capacitors," IEEE International Workshop on System on Chip, pp. 221-224. December 2006. 9. A. M. Elshurafa and E. I. El-Masry, "Quality Factor Estimation of Fabricated MEMS Parallel-Plate Variable Capacitors in MUMPS," IEEE Proceedings of the 2nd Northeast Workshop on Circuits and Systems, pp. 109-112, June 2004. 10. Y. Shim, Z. Wu, and M. Rais-Zadeh, "A Multimetal Surface Micromaching Process for Tunable RF MEMS Passives," IEEE Journal of Microelectromechanical Systems, pp. 867-874, 2012. 11. J. Gauvin, F. Barriere et al., "Design, Fabrication, and Measurements of Reliable Low Voltage RF MEMS Switched Varactors," IEEE Microwave Integrated Circuits Conference, pp. 434-437, 2011. 12. R. Stefanini, B. Chen, A. Yu, and J. Shi, "Miniature RF MEMS Metal Contact Switches for DC – 20GHz Applications," IEEE Solid State Sensors, Actuators, and Microsystems Conference, pp. 406-409, 2011. 13. U. Shah, M. Sterner, and J Oberhammer, "Basic Concepts of Moving Side Tuneable Capacitors for RF MEMS Reconfigurable Filters," IEEE European Microwave Conference, pp. 1087-1090, 2011. 14. Maher Bakri-Kassem and R. R. Mansour, “An Improved Design for Parallel Plate MEMS Variable Capacitors,” IEEE International Microwave Symposium, pp. 865-868, 2004. 15. Maher Bakri-Kassem and R. R. Mansour, “High Tuning Range Parallel Plate MEMS Variable Capacitors with Arrays of Supporting Beams,” IEEE Conference on Microelectromechanical Systems, pp. 666-669, 2006. 16. H. Hsu and D. Peroulis "A CAD Model for Creep Behavior of RF-MEMS Varactors and Circuits," IEEE Transactions on Microwave Theory and Techniques, Vol. 59, No. 7, pp. 1761-1768, 2011. 134 References: Variable Capacitors 17. U. Shah, M. Sterner, and J Oberhammer, "Basic Concepts of Moving Side Tuneable Capacitors for RF MEMS Reconfigurable Filters," IEEE European Microwave Conference, pp. 1087-1090, 2011. 18. J. Reinke, G. Fedder, T. Mukherjee, “CMOS MEMS 3-bit Digital Capacitors with Tuning Ratios Greater Than 60:1,” IEEE Transactions on Microwave Theory and Techniques, Vol. 59, No. 5, pp. 1238-1248, 2011. 19. Maher Bakri-Kassem and R. R. Mansour, “An Improved Design for Parallel Plate MEMS Variable Capacitors,” IEEE International Microwave Symposium, pp. 865-868, 2004. 20. A. Abbaspour-Tamijani, L. Dussopt, and G. Rebeiz, “Miniature and Tunable Filters using MEMS Capacitors,” IEEE Transactions on Microwave Theory and Techniques, Vol. 51, No. 7, pp. 1878-1885. 21. I. Reines and G. Rebeiz, “A Robut Power Handling (>10W) RF MEMS Switched Capacitor,” IEEE Microelectromechanical Systems, pp. 764767, 2011. 22. M. Bakri-Kassem, S. Fouladi, and R. Mansour, “Novel High Q MEMS Curled-Plate Variable Capacitors Fabricated in 0.35um CMOS Technology,” IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 2, pp. 530-541, 2008. 23. A. Dec and K. Suyama, “A 1.9GHz CMOS VCO with Micromachined Electromechanically Tunable Capacitors,” IEEE Journal of Solid State Circuits, Vol. 35, No. 8, pp. 1231-1237, 2000. 24. H. Zareie and G. M. Rebeiz, “High Power (>10W) RF MEMS Switched Capacitors,” IEEE International Microwave Symposium, pp. 1-3, 2012. 25. Z. Yao et al, “Micromachined Low-loss Microwave Switches,” Journal of Microelectromechanical Systems, Vol. 8, No. 2, pp. 129-134, June 1999. 26. A. Dec and K. Suyama, “Micromachined Electro-mechanically Tunable Capacitors and Their Applications to RF IC’s,” IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 12, pp. 2587-2596. 27. Q. Gu and A. Morris, “A New Method for Matching Network Adaptive Control,” IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 1, pp. 587-595, 2013. 28. M. Bakri-Kassem and R. R. Mansour, “Linear Bilayer ALD Coated MEMS Varactor with High Tuning Capacitance Ratio,” IEEE J. of Miroelectromechanical Sytems, Vol. 18, No. 1, pp. 147-153, 2009. 29. C. Han, D. Choi, and J. Yoon, “Parallel Plate MEMS Variable Capacitor with Superior Linearity and Large Tuning Ratio using a Levering Structure,”ّّ IEEE J. Microelectromechanical Systems, Vol. 20, No. 6, pp. 1345-1354, 2011. 30. G. Ionis, A. Dec, and K. Suyama, “A Zipper Action Differential Micromechanical Tunable Capacitor,” IEEE Conference on Microelectromechanical Systems, pp. 29-32, 2001. 31. T. Tsang and M. El-Gamal, “Micromechanical Variable Capacitors for RF Applications,” IEEE Midwest Symposium on Circuits and Systems, pp. 25-28, 2002. 32. J. Zou, J. Aine, J. Chen, and S. Kang, “Development of a Wide Tuning Range MEMS Tunable Capacitor for Wireless Communication,” IEEE International Electron Device Meeting, pp. 403-406, 2000. 135 33. A. Dec and K. Suyama, “Micromachined Varactor with Wide Tuning Range,” Electronics Letters, Vol. 33, No. 11, pp. 922-944, 1997. References: Fixed Capacitors 1. 2. 3. 4. 5. 6. A. M. Elshurafa and K. N. Salama, "Two-Layer RF MEMS Fractal Capacitors in PolyMUMPS for S-Band Applications," IET Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012. A. M. Elshurafa, A. G. Radwan, A. Emira, and K. N. Salama, "RF MEMS Fractal Capacitors with High Self Resonant Frequencies," IEEE J. Microelectromechanical Systems - JMEMS, Vol. 21, No. 1, pp. 10-12, February 2012. H. Samavati, A. Hajimiri, A. Shahani, G. Nasserbakht, and T. Lee, “Fractal Capacitors,” IEEE International Solid State Circuits Conference , 256257, 1998. J. de Jong and S. Baler, “Integrated Capacitor with Alternating Layered Segments,” US Patent 7,944,732, 2011. R. Aparicio and A. Hajimiri, “Capacity Limits and Matching Properties of Lateral Flux Integrated Capacitors,” Custom Integrated Circuits Conference, pp. 365-368, 2001. A. M. 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Entesari, "A 1.2 – 1.6 GHz Substrate integrated Waveguide RF MEMS Tunable Filter," IEEE Transactions on Microwave Theory and Techniques, Vol. 59, No. 4, pp. 866-876, 2011. 5. K. Chan, S. Fouladi, R. Ramer, and R. Mansour, "RF MEMS Switchable Interdigital Bandpass Filter," IEEE Microwave and Wireless Components Letters, Vol. 22, No. 1, pp. 44-46, 2012. 6. K. Chan, S. Fouladi, R. Ramer, and R. Mansour, "RF MEMS Switchable Interdigital Bandpass Filter," IEEE Microwave and Wireless Components Letters, Vol. 22, No. 1, pp. 44-46, 2012. 7. W. Chen, W. Fang, and S. Li, "High Q Integrated CMOS MEMS Resonators With Submicrometer Gaps and Quasi-Linear Frequency Tuning," IEEE Journal of Microelectromechanical Systems, Vol. 21, No. 3, pp. 688-701, 2012. 8. F. Bannon, J. Clark, and C. Nguyen, “High Frequency microelectromechanical IF Filters," IEEE International Electron Device Meetings, pp. 773-776, 1996. 9. R. 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Van Caekenberghe, "RF MEMS on the Radar," IEEE Microwave Magazine, Vol. 10, No. 6, pp. 99-116, 2009. 5. E. Lourandakis, R. Weigel, H. Mextorf, R. Knoechel, "Circuit Agility," IEEE Microwave Magazine, Vol. 13, No. 1, pp. 111-121, 2012. 6. C. T. C. Nguyen, "Micromechanical Circuits for Communication Transceivers," IEEE Proceedings of the BiCMOS Circuits and Technology Meeting, pp. 142-149, 2000. 7. Interuniversity Microelectronic Center: www.imec.be 8. Yole Dévelopoment. Website: www.yole.fr. 9. WiSpry. Website: www.wispry.com. 10. Invensense: www. Invensense.com 11. RF MEMS Magazine. Website: www.scoop.it. 1. 2. 138