RF MEMS Circuits Applications of MEMS switch and tunable capacitor Dr. Jeffrey DeNatale, Manager, MEMS Department Electronics Division jdenatale@rwsc.com 85-373-4439 Panamerican Advanced Studies Institute MicroElectroMechanical Systems June 21-3, 24
Outline Motivation for RF MEMS circuits MEMS Tunable Filters Switch based Tunable capacitor based MEMS Phase Shifters Low-Loss Switching Networks Reconfigurable MMIC Circuits Summary / Acknowledgements Chart 2
MEMS for RF Communications Leverage small small mechanical motions motions for for large large RF RF property property excursions Chart 3 2-Pole MEMS Switched Filter MEMS is key enabling technology addressing pervasive trends in communications and radar systems: tunability / agility / modularity / reconfigurability increased functionality (component, system) Substantial performance improvements: Insertion loss, isolation, linearity, power consumption, bandwidth, size, integration Multi-band (X, Ku) amplifier S21, db -1-2 -3-4 S21, db -5-6 -1-2 -3-4 -5 Low band -6-7 Mid band High Band Low band -7 Mid band -8 High Band 8 9 1 11 12 13 14 15 16 17 18 Frequency (MHz) -8 8 9 1 11 12 13 14 15 16 17 18 Frequency (MHz) Range Range of of device device concepts under under development RF RF Switches // Relays Relays Tunable Tunable Capacitors Micromachined inductors Micromechanical resonators Building Blocks for for High-Performance Miniaturized RF RF Subsystems SP4T Routing Network X-Band Phase Shifter
RSC MEMS RF Switch Key Elements of of RSC MEMS RF RF Switch Low-temperature processing (circuit (circuit compatible) Broadband (DC- (DC-mmWave) Electrostatic drive drive for for low low power powerconsumption Low Low insertion loss loss (<.1dB) (<.1dB) High High isolation (<-4dB (<-4dB@ 1GHz) 1GHz) High High linearity linearity (IP3> (IP3> +8dBm) Chart 4 Switch insertion loss (db). -.2 -.4 Insertion Loss Switched Line (as measured) Switch Only (extracted) -.6 2 4 6 Frequency (GHz) Off-switch isolation (db). Isolation -2. -4. -6. 2 4 6 Frequency (GHz) Select circuits // applications to to exploit MEMS advantages
MEMS RF Switch Step-Tuned Filter Demo benchmark MEMS switch vs. PIN diode DARPA MTO MEMS VHF Filter Circuit VHF Step-tuned Bandpass Filter 116-152 MHz dual MEMS switch replaces 2 PIN dual diodes increased dynamic range, reduced parts count Filter Specifications (2-Pole VHF Filter) Center Freq. Tuning Range: 116-151.975 MHz Selectivity (fo 8 MHz) 13.4 db rejection Tune time: < 75 microseconds 2-pole midband loss < 4.5 db 2-pole 1 db compression pt. > +2 dbm Derived Component Requirements - RF Switch (Packaged) Max Rs (on): 1.8 Ohm (.5 GHz) Max Cs (off):.5 pf (.5 GHz) Min. 3rd Order IP: 5 dbm I RF, V RF (survive):.2 A, 1.4 V rms I RF, V RF (op):.3 A, 2.1 V rms Sw Time: 15 usec max. Chart 5 2-Pole Sub-section Switch Drivers 6-Pole Filter
VHF 2-Pole MEMS Switched Filter Prototype Step-Tunable Filter with MEMS Switches + Discrete Capacitors Packaged MEMS Switches (8X) Chart 6 2-Pole MEMS Switched Filter Prototype Future: Integrated Monolithic Switches + Capacitors Packaged circuit with 16 switched capacitors, in one monolithic die 5x Improvement in Linearity 42% Parts Count Reduction (123 vs 71 for 2 pole) Static Power Reduced from.5w to near-zero (2 pole)
VHF 2-Pole MEMS Switched Filter Test Data Chart 7-1 -2 Insertion Gain (db) -3-4 -5-6 -7-8 5 6 7 8 9 1 11 12 13 14 15 16 17 18 19 2 Frequency (MHz) Demonstrate Step-Tuning with good filter characteristics over full full band
VHF 2-Pole MEMS Switched Filter Intermodulation key parameter for cosite mitigation Chart 8 Output Tone Level +2 dbm IMR3 = -71.5 dbc IP3o = +55.75 dbm 3rd Order In-Band IM Distortion - 112.5 MHz Fc
RSC MEMS Tunable Capacitor (Varactor) 1 µm 3 µm Chart 9 SEM micrographs showing the high aspect ratio feature of the MEMS tunable cap. 5 µm Capacitance (pf) 14 12 1 8 6 4 2 Capacitor Tuning Range Tuning Tuning range range >8.4X >8.4X 1 2 3 4 5 6 7 8 9 Voltage (V) 8.4X Tuning Tuning range: range: >8:1 >8:1 Base Base capacitance: capacitance: 1.5 1.5 --2pF 2pF Electrical Electrical Q: Q: 3-15 3-15 Max Max tuning tuning voltage: voltage: 6-4V 6-4V Mechanical Mechanical Resonance Resonance ::.4.4 --2kHz 2kHz typ typ Electrical Electrical self-resonance: self-resonance: 6GHz 6GHz
Voltage Tunable Filter Demonstration benchmark MEMS vs. semiconductor varactor DARPA MTO MEMS Chart 1 UHF Filter Circuit UHF Voltage-tuned Bandpass Filter 225-4 MHz MEMS variable capacitor replaces varactor diode array increased dynamic range, drastically reduced parts count Filter Specifications (2-Pole UHF Filter) Center Freq.Tuning Range: 225-399.975 MHz Selectivity (fo 13 MHz) 1.75 db rejection Tune time: < 27 microseconds 2-pole midband loss < 5.5 db Derived Component Requirements - Variable Capacitor (Packaged) Cap. Range: 2.5-1 pf (4:1) Tune V Range: 1-6 VDC Max Rs: 1. Ohm @ 1 pf I RF, V RF (op):.18 A, 21 V rms Tune Time: 1 usec max. 16-diode 16-diode series-parallel series-parallel array array for for high high IP IP (1 (1 array array per per pole) pole)
UHF 2-Pole MEMS Capacitor Filter Schematic Chart 11 MEMS Filter, 2 tunable capacitors MEMS Capacitor Filter Schematic Existing Varactor Version 16-diode series-parallel arrays Dramatic (9%) parts parts count reduction validated for for MEMS circuit Slightly improved IP3 IP3 (+3 (+3 to to +37dBm)
UHF 2-Pole MEMS Capacitor Filter Test Data Chart 12-5 -1-15 -2 Insertion Gain (db) -25-3 -35-4 -45-5 -55-6 -65-7 -75 228 MHz Fo 312.5 MHz Fo 398 MHz Fo -8 15. 2. 25. 3. 35. 4. 45. Frequency (MHz) Nearly full full octave tuning achieved
Tunable Capacitor Improvements Required Results from tunable capacitor filter demo Initial filter insertion validated utility of MEMS tunable capacitor in filter tuning circuit, but issues noted: Device Q: series resistance ~1W (solution: improved metalization, device design) Tuning speed, Vibration Immunity: (solution: stiff flexures, reduced mass, package environment) Mechanical Ringing: settling time ~4msec (solution: package environment) Maximum capacitance value: ~12pF (solution:thicker device layer, package environment - up to 25pF demonstrated) Filtered Response Tunable Capacitor Response Time Chart 13 Tunable Capacitor with 8mm deep combs 1.2 4.5 1 4 3.5 Filtered Output.8.6.4.2 -.5.15.35.55.75.95 Time (sec) Air Damping Near Critical Damping Filtered response to step input Relative Capacitance (Arb) 3 2.5 2 1.5 1.5 -.5.5.15.25.35.45.55.65.75.85 Time (seconds) Effect of damping on device response time
MEMS TTD Phase Shifter Development Key Component for Steerable Phased Arrays Chart 14 MEMS Switch can enable significant advances in reconfigurable electronics Low insertion loss compatible with multiswitch implementation High isolation reduces resonant effects of off-state leakage Metal-Metal contacts enable broad band implementation Compatible with MMIC processing Exploit low-loss, broadband characteristics for for multi-bit True Time Delay (TTD) Circuit Switchable Delay Line d δ γ Phase shifter φ Power divider Steering of main lobe at φ = cos -1 (-δ/d) Antenna 2δ 3δ
MEMS-Based Phase Shifter Circuits RSC has demonstrated broad portfolio of MEMS-based phase shifter circuits Exploit low-loss, broadband nature of RSC MEMS switch Novel circuits demonstrated for low loss, compact size, broad bandwidth Chart 15 4-Bit Broad Band (2.4dB avg) Miniature 2-bit, 4-bit X-Band (.7dB 9.5GHz 3-Bit Ka-Band (2.2dB avg) 4-Bit Low Loss X-Band (1.2 db avg) 6-Bit Broad Band 2-Bit X-Band (1dB avg) 2-Bit Low Loss X-Band (.56 db avg)
4-Bit Broadband TTD Phase Shifter Circuit exploit broadband nature of RSC switch Added group delay (psec) 1 8-1 6-2 4-3 2-4 4 8 12-5 16 Switch position Insertion loss (db) Chart 16 32 2 Group delay (psec) 28 16 24 12 Type A 2 8 16 4 12 Type B 8-4 1 2 3 4 Frequency (GHz) 4-Bit 4-Bit TTD TTD circuits circuits implemented implemented (16 (16 MEMS MEMS switches switches per per circuit) circuit) 2.2 2.2 to to 2.6 2.6 db db insertion insertion loss loss at at 1GHz 1GHz Mismatch Mismatch loss loss below below 15 15 db db at at all all frequencies frequencies group group delay delay ripple ripple <5ps <5ps up up to to 3GHz 3GHz 5.8psec 5.8psec gap gap among among different different states states
Low-Loss SP4T-Based Phase Shifters (RSC/UofM) Address major elements of loss budget: Conductor loss, switch loss, long reference path Low-loss X-band TTD phase shifter developed Chart 17 star SP4T switch network, 8-mil GaAs mstrip process Compact circuit, short reference line Excellent performance characteristics: -.6dB avg insertion loss 8-12 GHz -23dB return loss 8-12GHz Wide operational bandwidth (RL<-14 db DC-14 GHz) Low phase error ( ± 2 deg @1 GHz)
Extension to 4-Bit Phase Shifter Circuit Chart 18 Phase Accuracy = ± 2 deg (1 GHz) Average Insertion Loss = -1.1 db (1 GHz) Return loss < -14 db DC-14 GHz Phase at 1GHz -5 Phase Shift [deg] -1-15 -2-25 -3-35 -4 5 1 15 State
Miniature (Mini-MEMS) Phase Shifters: UoM/RSC Chart 19 CLC phase shift networks with discrete capacitors, transmission-line inductors Compact 1x2 MEMS metal-contact switch designs RSC low-loss 8-mil GaAs microstrip process Phase Accuracy = ± 3 deg (9.5 GHz) Average Insertion Loss = -.7 db (9.5 GHz) Return loss < -14 db DC-14 GHz Area = 4.9 mm 2 (1.95x2.49mm) 4-bit Design: 7 mm 2 (not shown)
Measured 4-bit X-band Phase Shifters Size Comparison Raytheon Chart 2 RSC SP4T UoM/RSC Miniature UoM/RSC Size Substrate Thickness Average Loss Bandwidth Phase 8 mm 2 (Si, coupler area only) Silicon 5µm 1.4 db 7-1 GHz (S11 <-1 db) Linear 3 mm 2 GaAs or Si 75 µm (2 µm) 2.1 db (1.6 db)/1 db DC-4 GHz* Linear 17 mm 2 GaAs or Si 2 µm 1.2 db/1 GHz DC-18 GHz* Linear 7 mm 2 GaAs or Si 2 µm 1.45 db/1 GHz DC-14 GHz* Linear * S11 < -14 db. Stricter definition of bandwidth.
Capacitive Switch: Ka-Band Phase Shifters Raytheon membrane switch circuit Chart 21 Loss.65-.75 db/bit Courtesy Rebeiz, UofM
Low Loss SP4T MEMS Switch Networks Low-loss switch network ideal for signal routing, component selection circuits Tunable filters Band-select operation Reconfigurable I/O Chart 22 8-mil GaAs mstrip process, compact switch geometry for low loss Data FIL1L1 F24D1A Data FIL1L1 F24D1A -.1-1 -2 Isolation A Isolation B Isolation C Isolation D Insertion Loss (db) -.2 -.3 Isolation (db) -3-4 -5 Insertion Loss Loss < -.1dB -.1dB Isolation > -45dB -45dB -.4 -.5 Insertion A Insertion B Insertion C Insertion D.5 1 1.5 2 2.5 3 3.5 Frequency (GHz) -6-7 -8.5 1 1.5 2 2.5 3 3.5 Frequency (GHz)
MEMS/MMIC Integration RSC MEMS switch compatible with monolithic MMIC integration MEM relay allows reconfiguration of electronic circuit Efficiency-Optimized X-Band PA Chart 23 Input 8-mm Output Low on insertion loss Good off isolation 64-mm Switchable Gain Amplifier parameter db 3 2 1-1 -2-3 -4-5 -6-7 -8-9 2 4 6 8 1 12 14 16 18 2 22 GHz Multi-band (X, Ku) amplifier with MEMS
Summary and Conclusions MEMS RF switch highly attractive for tunable filter, phase shifter circuits: low loss, high isolation, high linearity, wide band, low power, integration compatible MEMS tunable capacitor enables wide tuning range operation for low-frequency applications Present efforts targeting improved tuning speed, damping, Q MEMS SP4T, DPDT switch elements provide ultra-low loss switching networks Integration compatibility of MEMS switch enables reconfigurable / agile / adaptable electronics Chart 24
Acknowledgements 6/24/24 Chart 25 Supporters and Collaborators: DARPA Air Force Research Lab NASA Rockwell Collins Lockheed Martin Jet Propulsion Lab The Aerospace Corp University of Michigan UC Santa Barbara THE AEROSPACE CORPORATION RSC RSC RF RF MEMS MEMS Team Team Switch: Rob RobMihailovich, Judy Judy Studer Studer Tunable Cap: Cap: Rob RobBorwick, Phil Phil Stupar, Stupar, Kathleen Garrett Garrett Collaboration with with University of of Michigan (Prof. (Prof. Gabriel Gabriel Rebeiz Rebeizand and G.L. G.L. Tan) Tan) gratefully acknowledged