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 pull- in," 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 Techniques, Vol. 54, No. 5, pp. 2211-2219, 2006. 2 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 [email protected].
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 Deposit and pattern structural layer sacrificial layer
Some Substrate
1 2 3
Etch away sacrificial layer to get free standing structures Repeat steps 2 and 3 again
5 4 8 Foundry – Standard vs. Non-standard
• The PolyMUMPS process from MEMSCAP, NC, USA.
• 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 IC’s Resistors
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 Better performance ICs electronics High volume fabrication
Less power consumption Off-chip Better performance MEMS passives and filters 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
20μm ) -86 Q = 10,100 (air)
-88
(dB
Polysilicon -90 Electrode -92 -94 -96 -98 CVD Diamond Transmission -100 mMechanical Disk Ground 1507.4 1507.6 1507.8 1508 1508.2 Resonator Plane 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 16 MEMS,” IEEE Microelectromechanical Systems, pp. 673-676, 2002. Varactors: CMOS vs. MEMS
CMOS Varactors MEMS Varactors (reverse biased diodes)
Leakage currents exists No leakage current
Typical Q is 30-40, but can reach to Q can reach up to 200 – 300 50-60 Due to continuous downscaling, the Tuning ranges are high (~5 for tuning range (C /C ) is max min varactors and ~50 for switches and decreasing – Maximum ratio is 3 at even higher) millimeter-wave range. Good at low frequency (inductor loss dominates for LC tank), but No real concern lossy at millimeter-wave range
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 RF MEMS Publications 884 882 900 862 814 826 Variable Capacitor Publications 782 800 737 750
700
600 537
500 378 400 358 349 368 324 342 313 316 298 305 300 253 197 200 157 Number of of Number Publications 147 113 135 116 82 100 59
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
2750 2627
2500
2250
2000
1750
1500
1250 1000 808 750 621 462 450 500 400 Number of of Number Publications 299 272 240 250 189
0 United China France Japan Korea Germany Canada Italy India Belguim States 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 No Concern Concern Warping Availability of Metal No Concern Concern Layers Parasitics/balanced Concern Concern capability
26 Etching Holes
When a sacrificial layer is present between two structural layers, it has to be removed. One way is to do wet- etching: 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 holes and access holes.
• 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 Faraday Technology Corporation metal layers both capacitor www.design-reuse.com terminals can be metal and hence not affect Q.
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, What about CMOS? No. 3, pp. 538-547, 2010.
31 Residual Stress – 1
•What is it? MATERIAL 1 •First kind is: bending, or warping, taking place when two materials α1 > α2 with different thermal expansion coefficients, are on top of each other.
•During fabrication, heating then MATERIAL 2 cooling!
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 34 Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 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 35 Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 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 36 Plate Variable Capacitors,” Journal of Micromechanics and Microengineering, Vol. 18, No. 4, 2008 Closed Form Expressions
37 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 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 39 Conference, 256-257, 1998. 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 40 Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 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 41 Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 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 44 Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 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 45 Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. Addressing ‘Balance-ness’
• Black: Signal Terminal Almost same area for both • Gray: Ground Terminal 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 46 Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. Measurements
A. M. Elshurafa, A. Radwan, A. Emira, K. N. Salama, “RF MEMS Fractal Capacitors with High Self Resonant Frequencies,” IEEE 47 Journal of Microelectromechanical Systems, Vol. 21, No. 1, pp. 10-12, 2012. 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 50 Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012 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 51 Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012 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 52 Micro & Nano Letters, Vol. 7, No. 5, pp. 419-421, May 2012 Interwoven Design
Amro M. Elshurafa and K. N. Salama, "Differential RF MEMS Interwoven Capacitor Immune to Residual Stress Warping," IET Micro & 53 Nano Letters, Vol. 7, No. 7, pp. 658-661, July 2012. Interwoven Design
54 J. de Jong and S. Baler, “Integrated Capacitor with Alternating Layered Segments,” US Patent 7,944,732, 2011. 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 5.5 10 10 >20 >20 (GHz) * 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 Interleaved Woven Interwoven Moore’s
Could be created in a ✗ ✔ ✗ ✗ ✔ Single Layer?
Balanced ✗ ✔ ✗ ✔ ✔
Capacitance ✔✔ ✔ ✔ ✗ ✗ Value
High SRF ✗ ✔ ✔ ✔✔ ✔✔
Could it be ✔ ✔ used in a ✔ ✔ ✗ not in two layers* varactor? readily* 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 58 Integrated Circuits Conference, pp. 365-368, 2001. 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 Two distinct capacitances only Analog tunability (Linearity) (digital: High and Low) High Tuning Range (>~50:1 for Low Tuning Range (~5:1) switches and ~15:1 for switched capacitors) Mostly an insulator layer in Usually air separates both terminals addition to air separates both only terminals Dielectric charging is not a concern Dielectric charging is a concern because no physical contact occurs because physical contact occurs usually 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 xo x 2 Electrostatic Force 1 C 2 1 AV DC Fe V DC 2 2 x 2 (xo x) 2 Electrostatic F CV DC k e Spring Constant e 2 x (xo x) 2 CV DC 1 k x k (x x) Mechanical Force m e o 2(xo x) 2 2k x k m What if x = (1/3)xo? e (xo x) 66 Deriving Pull–in: 2
2 Electrostatic and 1 AV DC FE 2 kM x FM Mechanical Forces 2 (xo x) 2k x(x x)2 Solve for the Voltage V M o A 1 1 2k 2 V x 2 (x x) o A 1 1 1 V 1 2k 2 x 2 (x x) x 2 0 1. Take the derivative o x 2 A 1 1 2. Equate to 0 1 2 2 x (xo x) x 3. Solve for x 2 x x o 3 67 Maximum TR
eps.A C min d eps.A Ideally: C max 2 d 3 C 3 TR max 1.5 Cmin 2
C C C 0.4C Practically however: max f max max TR1 1.3125 Cmin C f Cmin 0.4Cmax
68 How to increase TR – 1
TR = 2.83
69 A. Dec and K. Suyama, “Micromachined Varactor with Wide Tuning Range,” Electronics Letters, Vol. 33, No. 11, pp. 922-944, 1997. 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 70 Transactions on Microwave Theory and Techniques, Vol. 46, No. 12, 1998. 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 71 Beams,” IEEE Conference on Microelectromechanical Systems, pp. 666-669, 2006. 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 72 Beams,” IEEE Conference on Microelectromechanical Systems, pp. 666-669, 2006. 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,” 73 IEEE International Electron Device Meeting, pp. 403-406, 2000. 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 74 Applications,” IEEE VLSI Symposium, pp. 33-36, 2003. 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 75 Microelectromechanical Systems, pp. 29-32, 2001. 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 78 .Structure,” ّ ّ IEEE J. Microelectromechanical Systems, Vol. 20, No. 6, pp. 1345-1354, 2011 How to increase TR – 6
79 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 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 80 Miroelectromechanical Sytems, Vol. 18, No. 1, pp. 147-153, 2009. 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 81 Ratio,” IEEE J. of Miroelectromechanical Sytems, Vol. 18, No. 1, pp. 147-153, 2009. 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 82 and Systems – ISCAS, 2013. 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 83 suppressing pull-in," IET Micro & Nano Letters, Vol. 7, No. 9, pp. 965-969, September 2012. 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 87 Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 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 88 Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. Close-up
89 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. Performance
A. M. Elshurafa, P. H. Ho, and K. N. Salama, "A Low Voltage RF MEMS Variable Capacitor with a Linear C-V Response," 90 IET/IEEE Electronics Letters, Vol. 48, No. 7, pp. 392-393, March 2012. 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 Generally, the results • Periodic Steady State acquired from Cadence are • Digital Flow • Layout reasonably accurate, and • LVS/DRC simulations do predict the • System Level Simulation behavior of the fabricated • Temperature Analysis chip very well. • Inductor design • Capacitors • Frequency Response • Filter Design • Noise Analysis • Leakage • Monte Carlo 92 Modeling of MEMS
Let’s look at a typical MEMS problem – a thermal actuator:
Pad – Anchored
Thin Arm – Suspended
5V Current
GND Current
Pad – Anchored Thick Arm – Suspended Movement Direction
93 Modeling of MEMS
• In thermal actuators: three physics are involved: a. Electric currents COMSOL © b. Thermal losses c. Structural interaction
• 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 Coventorware Multiphysics MEMS Sugar Modeling Intellisuite HFSS MatLab/Simulink Equations Maple Mathematica SolidWorks 3D Drawing 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 Fixed Boundaries Physics: structural
DC Voltage Ground Physics: Electrical 98 Physics: Electrical Tips and Tricks
• Start with a coarse mesh first, then refine. More elements, better accuracy, but more time and memory.
• 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. Vector network analyzer (VNA) b. DC Voltage source c. Appropriate Probe (1 or 2) d. Calibration Impedance Substrate e. Contact Substrate f. Bias-T network g. Correct Layout/Pads h. 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. S G G
102 Source: Gavin Fisher; Cascade Microtech Preparing Probes - Planarity
Not planarized
Use contact substrate to perform this task.
Planarized
103 Source: Gavin Fisher; Cascade Microtech 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 Stay in air! shorts all tips
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
DC
No DC No RF No
RF RF+DC
107 Setup
VNA VDC
+ _ GND
DC To Check: 1. Connectors (male or female, size, etc) 2. Cables RF 3. Frequency range 4. Max Power RF+DC 5. Max voltage
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. Pitch • 70um is reasonable or use an insulator substrate.
110 Smith Chart Considerations
• Top half of the Smith Chart is Inductive, and bottom half is capacitive.
L • Resonance is the middle horizontal line.
• 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 114 and Techniques, Vol. 61, No. 1, pp. 587-595, 2013. 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 form- factor smartphone or tablet products.
115 Omron and Radant Switches
•Omron’s switch. Professor Rebeiz •Radant Switch. describes it as ‘amazing’. ‘The best RF MEMS switch in the world’.
•Difference DC requirement between handheld devices and base stations 116 Classic CMOS MEMS-VCOs (0.5um)
A. Dec and K. Suyama, “A 1.9GHz CMOS VCO with Micromachined A. Dec and K. Suyama “Micromachined Electro-mechanically Tunable Electromechanically Tunable Capacitors,” IEEE Journal of Solid Capacitors and their Applications to RF IC’s” IEEE Transactions on State Circuits, Vol. 35, No. 8, pp. 1231-1237, 2000. Microwave Theory and Techniques, Vol. 46, No. 12, 1998.
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 High- Q 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 119 Transactions on Microwave Theory and Techniques, Vol. 59, No. 5, pp. 1238-1248, 2011. CMOS-MEMS Variable Capacitor
• Maskless, post-CMOS etching. • TR = 63:1! • Q = 160 at 1 GHz.
120 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. CMOS-MEMS Variable Capacitor
M. Bakri-Kassem, S. Fouladi, and R. Mansour, “Novel High Q MEMS Curled-Plate Variable Capacitors Fabricated in 0.35um 121 CMOS Technology,” IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 2, pp. 530-541, 2008. CMOS-MEMS Variable Capacitor
• Maskless, post-CMOS etching. • TR = 6:1! • Q = ~300 at 1.5 GHz.
122 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. 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 123 Sensitivity,” IEEE International Microwave Symposium, pp. 1254-1257. 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 125 Transactions on Microwave Theory and Techniques, Vol. 58, No. 6, pp. 1629-1637, 2010. 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. 764- 767, 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. 33. A. Dec and K. Suyama, “Micromachined Varactor with Wide Tuning Range,” Electronics Letters, Vol. 33, No. 11, pp. 922-944, 1997. 135 References: Fixed Capacitors
1. 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. 2. 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. 3. H. Samavati, A. Hajimiri, A. Shahani, G. Nasserbakht, and T. Lee, “Fractal Capacitors,” IEEE International Solid State Circuits Conference, 256- 257, 1998. 4. J. de Jong and S. Baler, “Integrated Capacitor with Alternating Layered Segments,” US Patent 7,944,732, 2011. 5. R. Aparicio and A. Hajimiri, “Capacity Limits and Matching Properties of Lateral Flux Integrated Capacitors,” Custom Integrated Circuits Conference, pp. 365-368, 2001. 6. A. M. Elshurafa and K. N. Salama, “Differential RF MEMS Interwoven Capacitor Immune to Residual Stress Warping,” IET Micro and Nano Letters, Vol. 7, No. 7, pp. 658-661, 2012.
136 References: Resonators and Filters
1. 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. 2. 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. 3. F. Bannon, J. Clark, and C. Nguyen, “High Frequency Microelectromechanical IF Filters,” IEEE International Electron Device Meeting, pp. 773-776, 1996. 4. V. Sekar, M. Armendariz, and K. 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. Agner et al., "Advancements of MEMS in RF-filter Applications," IEEE International Electron Device Meeting, pp. 897-900, December 2002. 10. M. El-Tanani and G. Rebeiz “High Performance 1.5-2.5GHz RF MEMS Tunable Filters for Wireless Applications,” IEEE TMTT, Vol. 58, No. 6, pp. 1629-1637, 2010. 11. C. Nguyen and R. Howe, “An Integrated CMOS Micromechanical Resonator High-Q Oscillator,” IEEE Journal of Solid State Circuits, Vol. 34, No. 4, pp. 440-455, 1999.
137 References: General
1. C. T. C. Nguyen, “RF MEMS for Wireless Applications,” Device Research Conference Digest, pp. 9-12, June 2002. 2. J. Smith, “Embedded Micromechanical Devices for the Monolithic Integration of MEMS with CMOS,” Proceedings of the IEEE International Electron Device Meeting, pp 609-612, December 1995. 3. K. Van Caekenberghe, "Modeling RF MEMS Devices," IEEE Microwave Magazine, Vol. 13, No. 1, pp. 83-110, 2012. 4. K. 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.
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