RF MEMS for Low-Power Communications Clark T.-C. Nguyen Center for - - PowerPoint PPT Presentation

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RF MEMS for Low-Power Communications Clark T.-C. Nguyen Center for - - PowerPoint PPT Presentation

Nov 06, 2023 262 likes •590 views

MEMS for Wireless Communications RF MEMS for Low-Power Communications Clark T.-C. Nguyen Center for Wireless Integrated Microsystems Dept. of Electrical Engineering and Computer Science University of Michigan Ann Arbor, Michigan 48109-2122

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SLIDE 1

MEMS for Wireless Communications

RF MEMS for Low-Power Communications

Clark T.-C. Nguyen

Center for Wireless Integrated Microsystems

  • Dept. of Electrical Engineering and Computer Science

University of Michigan Ann Arbor, Michigan 48109-2122 http://www.eecs.umich.edu/~ctnguyen

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MEMS for Wireless Communications

Outline

  • Miniaturization of Transceivers

the need for high-Q

  • High-Q Micromechanical Resonators
  • Micromechanical Circuits

micromechanical filters micromechanical mixer-filters micromechanical switch micromechanical C’s & L’s

  • Using MEMS in Comm. Receivers

direct replacement of passives trade Q (or selectivity) for power MEMS-based receiver architecture

  • Conclusions
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SLIDE 3

MEMS for Wireless Communications

Miniaturization of Transceivers

  • High-Q functionality

required by oscillators and filters cannot be realized using standard IC components use

  • ff-chip mechanical

components

  • SAW, ceramic, and

crystal resonators pose bottlenecks against ultimate miniaturization

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SLIDE 4

MEMS for Wireless Communications

So Many Passive Components!

  • The total area on a printed circuit board for a

wireless phone is often dominated by passive components passives pose a bottleneck on the ultimate miniaturization of transceivers

Transistor Chips Transistor Chips Quartz Crystal Quartz Crystal IF Filter (SAW) IF Filter (SAW) Inductors Capacitors Resistors Inductors Capacitors Resistors IF Filter (SAW) IF Filter (SAW) RF Filter (ceramic) RF Filter (ceramic)

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MEMS for Wireless Communications

Need for High-Q: Selective Low-Loss Filters

  • In resonator-based filters: high

tank Q ⇔ low insertion loss

  • At right: a 0.3% bandwidth filter

@ 70 MHz (simulated) heavy insertion loss for resonator Q < 5,000

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SLIDE 6

MEMS for Wireless Communications

Surface Micromachining

  • Fabrication steps compatible with planar IC processing
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MEMS for Wireless Communications

Post-CMOS Circuits+μMechanics Integration

  • Completely monolithic, low phase noise, high-Q oscillator

(effectively, an integrated crystal oscillator) [Nguyen, Howe]

  • To allow the use of >600oC processing temperatures,

tungsten (instead of aluminum) is used for metallization

Oscilloscope Output Waveform

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MEMS for Wireless Communications

Target Application: Integrated Transceivers

  • Off-chip high-Q mechanical components present bottlenecks

to miniaturization replace them with μmechanical versions

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SLIDE 9

MEMS for Wireless Communications

Micromechanical Resonators

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MEMS for Wireless Communications

Vertically-Driven Micromechanical Resonator

  • To date, most used design to achieve VHF frequencies
  • Smaller mass higher frequency range and lower series Rx
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MEMS for Wireless Communications

HF μMechanical CC-Beam Resonator

  • Surface-micromachined, POCl3-doped polycrystalline silicon
  • Extracted Q = 8,000 (vacuum)
  • Freq. and Q influenced by

dc-bias and anchor effects

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SLIDE 12

MEMS for Wireless Communications

92 MHz Free-Free Beam μResonator

  • Free-free beam μmechanical resonator with non-intrusive

supports reduce anchor dissipation higher Q

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SLIDE 13

MEMS for Wireless Communications

92 MHz Free-Free Beam μResonator

  • Free-free beam μmechanical resonator with non-intrusive

supports reduce anchor dissipation higher Q

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SLIDE 14

MEMS for Wireless Communications

156 MHz Radial Contour-Mode Disk μMechanical Resonator

  • Below: Balanced radial-mode disk polysilicon μmechanical

resonator (34 μm diameter)

μmechanical Disk Resonator Metal Electrode Metal Electrode R Anchor

Design/Performance: R=17μm, t=2μm d=1,000Å, VP=35V fo=156.23MHz, Q=9,400 [Clark, Hsu, Nguyen IEDM’00] fo=156MHz Q=9,400

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SLIDE 15

MEMS for Wireless Communications

Micromechanical Circuits

  • A single mechanical beam can’t really do much on its own
  • But use many mechanical beams attached together in a

circuit, and attain a more complex, more useful function

Input Force Fi Output Displacement xo

t xo t Fi Key Design Property: High Q

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SLIDE 16

MEMS for Wireless Communications

HF Spring-Coupled Micromechanical Filter

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SLIDE 17

MEMS for Wireless Communications

High-Order μMechanical Filter

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SLIDE 18

MEMS for Wireless Communications

Nonlinear Micromechanical Circuits

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MEMS for Wireless Communications Electrical Signal Input Mechanical Signal Input

ωRF ωLO ωRF ωLO ωIF ω ω

Filter Response

Electromechanical Mixing

ωIF ωo=ωIF

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SLIDE 20

MEMS for Wireless Communications

Micromechanical Mixer-Filter

[Wong, Nguyen 1998]

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MEMS for Wireless Communications

Micromechanical Switch

[C. Goldsmith, 1995]

  • Operate the micromechanical beam in an up/down binary

fashion

  • Performance: I.L.~0.1dB, IIP3 ~ 66dBm (extremely linear)
  • Issues: switching voltage ~ 20V, switching time: 1-5μs
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SLIDE 22

MEMS for Wireless Communications

Phased Array Antenna

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SLIDE 23

MEMS for Wireless Communications

Voltage-Tunable High-Q Capacitor

  • Micromachined, movable, aluminum plate-to-plate capacitors
  • Tuning range exceeding that of on-chip diode capacitors and
  • n par with off-chip varactor diode capacitors
  • Challenges: microphonics, tuning range truncated by pull-in
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SLIDE 24

MEMS for Wireless Communications

Suspended, Stacked Spiral Inductor

  • Strategies for maximizing Q:

15μm-thick, electroplated Cu windings reduces series R suspended above the substrate reduces substrate loss

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MEMS for Wireless Communications

MEMS-Based Receiver Architectures

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MEMS for Wireless Communications

MEMS-Based Receiver Architecture

  • Most Direct Approach: replace off-chip components (in
  • range) with μmechanical versions (in green)
  • Obvious Benefit: substantial size reduction

Replace with MEMS

L1~0.3dB L1~0.3dB L1~2dB L1~2dB NF = 8.8dB NF = 8.8dB NF = 2.8dB NF = 2.8dB L3~6dB L3~6dB L5~12dB L5~12dB L3~0.5dB L3~0.5dB L5~1dB L5~1dB Antenna Diversity for resilience against fading Antenna Diversity for resilience against fading

Higher Q

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MEMS for Wireless Communications

MEMS-Based Receiver Front-End

  • Extremely high-Q insertion loss no longer a problem

LNA not needed LNA not needed Pre-Select Filter not needed Pre-Select Filter not needed

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MEMS for Wireless Communications

MEMS-Based Receiver Front-End

Single High-Order μMechanical RF Image-Reject Filter @ 1.8 GHz Single High-Order μMechanical RF Image-Reject Filter @ 1.8 GHz No LNA Power Reduction No LNA Power Reduction

  • Problem: RF local oscillator

synthesizer (w/ PLL and pre-scaler) is a power hog!

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SLIDE 29

MEMS for Wireless Communications

MEMS-Based Receiver Front-End

Single High-Order μMechanical RF Image-Reject Filter @ 1.8 GHz Single High-Order μMechanical RF Image-Reject Filter @ 1.8 GHz No LNA Power Reduction No LNA Power Reduction Solution: μMechanical IF Channel-Selecting Mixer- Filter Bank @ 70 MHz; One Mixler Per Channel Solution: μMechanical IF Channel-Selecting Mixer- Filter Bank @ 70 MHz; One Mixler Per Channel No longer need

  • freq. tunable LO

No longer need

  • freq. tunable LO
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SLIDE 30

MEMS for Wireless Communications

MEMS-Based Receiver Front-End

Single High-Order μMechanical RF Image-Reject Filter @ 1.8 GHz Single High-Order μMechanical RF Image-Reject Filter @ 1.8 GHz No LNA Power Reduction No LNA Power Reduction Solution: μMechanical IF Channel-Selecting Mixer- Filter Bank @ 70 MHz; One Mixler Per Channel Solution: μMechanical IF Channel-Selecting Mixer- Filter Bank @ 70 MHz; One Mixler Per Channel Single-Frequency μMechanical RF Local Oscillator @ 1.73GHz No Tuning Very Low Power Single-Frequency μMechanical RF Local Oscillator @ 1.73GHz No Tuning Very Low Power Size Reduction Size Reduction

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MEMS for Wireless Communications

Conclusions

  • Via enhanced selectivity on a massive scale,

micromechanical circuits using high-Q elements have the potential for shifting communication transceiver design paradigms, greatly enhancing their capabilities

  • Advantages of Micromechanical Circuits:
  • rders of magnitude smaller size than present off-chip

passive devices better performance than other single-chip solutions potentially large reduction in power consumption alternative transceiver architectures that maximize the use

  • f high-Q, frequency selective devices for improved

performance … but there is much work yet to be done …

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MEMS for Wireless Communications

Acknowledgments

  • Former and present graduate students, especially Kun

Wang, Frank Bannon III, and Ark-Chew Wong, who are largely responsible for the micromechanical filter work, and Wan-Thai Hsu and John Clark, who are largely responsible for the resonator work

  • My government funding sources: mainly DARPA and an

NSF Engineering Research Center on Wireless Integrated Microsystems (WIMS)