Components for Wireless Communication Mechanical/Electrical … · 2017-12-14 · Wireless Communication Components [Nguyen et al., 1998] Texas Christian University Department of

11

Texas Christian University Department of Engineering Ed Kolesar

Introduction toMicroeletromechanical Systems

(MEMS)Lecture 12 Topics

• MEMS for Wireless CommunicationComponents for Wireless CommunicationMechanical/Electrical Systems

Mechanical Resonatorso Quality Factor

OscillatorsVoltage-Tunable CapacitorsMicromachined InductorsFiltersSwitchesAntennas


MEMS Overview

Micromachining: lithography, deposition, etching, …

Processes & Foundries

Devices & Structures

Methodology

History & Market

Introduction &

Background

22


MEMS for Wireless Communication

Why microfabrication?• Process integration• Mass fabrication• Beyond cell phones: combine sensing, actuation,

computation, and communication → intelligent sensor/actuator network (“smart dust”)

Why mechanical components?• High-frequency oscillators (GHz range and more)• Stability w.r.t. temperature, aging• Low loss oscillators (high quality factor)• Tunable oscillators (voltage controlled)


Components for Wireless MEMS• Antennas• Amplifiers

• SwitchesResistively coupledCapacitively coupled

• Resonators• Filters• Oscillators

It is difficult to build integrated high quality electronic resonators for high-frequency applications (»1MHz)

→ Use discrete components, or→ Use corresponding micromechanical devices instead

33


Mechanical / Electrical Systems

Vi

L

C Vo

R

mK

mbm

ssFxsH

KbmFtKxtxbtxmxF

++==

=++

2

1

)(

:functionTransfer stiffness damping, mass,

)()()(nt displaceme :Output force external :Input

&&&

LCLRLC

i

o

iC

o

i

ssVVsH

CRLVtqtqRtqL

VV

12

1

1

)(

:functionTransfer capacit. resist., induct.,

)()()(

voltage :Output voltage :Input

++==

=++ &&&

x

F

b

Km


Mechanical / Electrical Systems

Vi

L

C VoR

LCRC

LC

i

o

iCRCL

o

i

ssVVsH

CRLVtqtqtqL

VV

112

1

1

)(

:functionTransfer ecapacitanc ,resistance ,inductance

)()()(

voltage :Output voltage :Input

++==

=++ &&&

Alternative circuit:

44


Resonators

• Analogy between mechanical and electrical system:Mass m - inductivity LSpring K - capacitance CDamping b - resistance R (depending where R is placed in circuit)

• Solution to 2nd order differential equation:

factorquality

system electrical system, mechanical

frequency natural 2

)(

100

00

20

2

20

0

Q

ωω

πfω

sssH

LCmK

Q

==

=

++=

ωωω


Mechanical Resonator

• Frequency and phase shift under damping:

• Energy dissipation:

shift phase 4

-14

1-1

timedamping

)cos()(

2

0220

01

12

ϕ

ωτω

ωω

τ

ϕωτ

Kmb

bm

tAetxt

==

=

+= −

τt

eEtE −= 0)(

55


Quality Factor

• How fast does energy dissipate?• What is the maximum amplitude for a given frequency?

Definition: Quality factor (Q factor)Ratio of stored energy

and lost energy:

Mechanical system:

Similar for electric systems: (a)

(b)

bKm

bmQ == 0ω

CL

RRLQ 1

0 ==ω

τωτππ 022 ==∆

=TE

EQ

LCRRCQ == 0ω


Quality Factor

• How fast does energy dissipate?

• What is the maximum amplitude for a given frequency?At resonance, amplitude is Q times the DC response

l)(mechanica 0 b

mQ== τ

ωτ

ω (1/s)

Gain (dB)

0

ω0

66


Summary: Mechanical/Electrical Resonator

Mechanical resonator:

Torsional resonator:

Electrical resonator:

) small(for frequency natural

stiffness damping, mass, 0)()()(

0 bmK

KbmtKxtxbtxm

=

=++

ω

&&&

Ik

kbItktbtI

=

=++

0frequency natural

stiffness damping, inertia, ofmoment 0)()()(

ω

θθθ &&&

LC

CRL

tqC

tqRtqL

1frequency natural

ecapacitanc ,resistance y,inductivit

0)(1)()(

0 =

=++

ω

&&&


Wireless Communication

Frequency Spectrum

2015105

RF

VLFLF

MFHF

VHFUHF

SHFEHF

IR

visible

UV X-rays

10n Hz

cm µmwavelength

77


Wireless Communication Components

[Nguyen et al., 1998]


Oscillators for Wireless Communication

• Current Technology:Quartz crystalSurface acoustic wave (SAW)Discrete elements (variable capacitors and inductors)

• Advantages:High quality factor: > 10,000Extremely high stability against thermal variations and agingExtremely selective filtering (small channel bandwidth)

• Problem: requires incompatible materials (e.g.,GaAs) → assembly necessary

88


Oscillators for Wireless Communication

• Goals:High Q oscillatorsIntegrated VCO’s (voltage controlled oscillators)Compatibility with micromachining processesLow cost

• Challenges:Q is proportional to L (inductivity) or m (mass)Tunable devicesMEMS devices with sufficiently high C and LNoise from temperature changes, vibrations, agingInductor losses: eddy currents in substrate


Oscillator Stability


99


Voltage-Tunable Capacitors

[Young and Boser 1996]200µm


Voltage-Tunable Capacitors

[Young and Boser 1996]

4 tunable parallel capacitors 2.04pF … 2.35pF3V tuning voltage, Q=62 at 1GHz

1010


Micromachined Inductors

[Najafi et al., 1997]

NiFe core under planar metal spiral

2.7 µH inductanceQ=6.6 at 4MHz

Spiral inductor on substrate-isolating platform/membrane

1.2 nH inductanceQ=60-80 at 40GHz


Micromachined Inductors

[Young and Boser 1997]

Electroplated 3D coil inductors with 4nH, Q=30 at 1GHz

1111


Thin-Film Bulk Acoustic Resonators

[Lakin, Kline and McCarron 1995]

Thin-film bulk-acoustic mode piezoelectric resonator (FBAR)

Q > 100f0 = 1.5 - 7.5 GHz

Thin-film resonator on substrateAcoustic isolation by strategic

selection of separating layers


Comb-Drive Resonator

Vp DC biasVd drive signal at ωd

I0 output current ∝ VpdC/dt

feedback via transimpedance amplifier

Vc carrier signal at ωc

output signal:frequency spectrum includes ωd , ωc , but also ωc±ωd

basis for frequency transfer (heterodyning)

[Figure: Maluf 2000]

1212


Bandpass Filters

Intuition:• Two resonance modes• Loosely coupled

resonators: resonance modes are close and effectively form bandpass

• Additional coupled resonators widen frequency bandpass

[Figure: Maluf, 2000]


Resonators and Filters


1313


MEMS Medium Frequency Filters



Cantilever Beam Switches

Issues:• Maxium current when ON, max. voltage when OFF• Impedance for DC to GHz frequency range• Speed, stiction, lifespan, contact deterioration

[de los Santos 1999]

1414


Mercury Switches

• Side-driven mercury switch [Saffer et al. 1996]• Curved electrodes achieve small gap size (large el.stat. force)

over larger actuation range• Bumpers prevent electrode contact / short• Mercury drop (selectively deposited only on Au patches)• Originally fabricated in MUMPs

[S. Saffer et al., 1996]


Capacitive Switches

• Metal membrane• Electrostatic actuation• Avoid stiction with

dielectric layer • Capacitive, not resistive

coupling • No DC component,

which is ok for microwave frequencies

[Goldsmith et al., 1996]

1515


Antennas

[Gauthier, Courtay and Rebeiz 1997]

Documents

Components for Wireless Communication Mechanical/Electrical … · 2017-12-14 · Wireless Communication Components [Nguyen et al., 1998] Texas Christian University Department of