S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 1

RF MEMS Technology and Its Applications for Wireless Communication Systems

Shu-Ang ZHOU (周叔昂)Email: shuang.zhou@hotmail.com

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 2

MicroElectroMechanical Systems (MEMS)

Features:

• Small physical size (μm, sub-μm).

• Combination of electrical & mechanical components.

• Capable of being fabricated in mass production using, for instance, IC batch-processing techniques.

Other names: Microsystems, Micromachines

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 3

Will RF MEMS be the important /critical technology to our future wireless (radio) communication systems?

Could it be useful to radio base stations?

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 4

MEMS2TUNE Project supported by European Commission

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 5

Tuning ranges for these variable MEMS capacitors (the ratio between maximum and minimum capacitance) as high as 17, and Q-factors (Quality Factors) as high as 500, outperforming virtually all other types so far reported.

Philips News (February 2004)Microscope image of MEMS capacitor made by PASSI™ process

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 6

- Capable for wideband (broadband) operation

Trends in RF Component Technology

- High linearity for RF signal transmission & amplification

- Low loss and high Q factor design vs. bandwidth

- Adjustable (tunable, switchable, and intelligent)

- Enhanced power handling capability

- Miniaturization and Integration

- Large volume manufacturing

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 7

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 8

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 9

• ADC bottleneck, against future bandwidth expansion• Highly linear & wideband RF components required• High performance DSPs required

Issues

Wideband radio receiver architecture (SDR)

~~~~

A/D

LNA

B-BPF

B-RF-LO

B-MIX

~~~

B-IF-Amp

~~~

B-IRF

B-BPF

IF: 2~3 times BW (~ 140 MHz for WCDMA)Full dynamic range (SFDR): ~ 110 dB

...

Carrier/Channelin digital domain

Intermodulation issuesStrong in-band block signals

14 bit 105 MSPS100 dB SFDRNot adequate !

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 10

Some Interference Issues with Wideband RF FilterBroadband Pass

Filter

BIR-Filter

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 11

ADC Performance Limitations

(Ref. R.H. Walden, HRL, 1999)* Effective number of bits

0

2

4

6

8

10

12

14

16

18

20

22

1E+4 1E+5 1E+6 1E+7 1E+8 1E+9 1E+10 1E+11Sample Rate (Samples/s)

SNR

bits

ADC dataaperture (1 ps)aperture (0.5 ps)aperture (0.2 ps)regen (50 GHz)regen (250 GHz)thermal (50 ohms)thermal (2000 ohms)Heisenberg (.09fs)

thermal aperture

ambiguity

Heisenberg

Hypres(6/99)

Maxim(5/99)

HP(97)

Lucent(98)

HP(97)ADI (02)

*

Aperture (uncertainty in sampling time).

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 12

Analog-to-Digital Converters: A Few ApplicationsMilitary, Commercial

0

2

4

6

8

10

12

14

16

18

20

22

1E+4 1E+5 1E+6 1E+7 1E+8 1E+9 1E+10 1E+11Sample Rate (Samples/s)

Stat

ed R

esol

utio

n (B

its)

telephony

consumermedical imaging

software radio, HDTV

samplingoscilloscopes

FPAs

radar

EW

satellite

commercialexperimental/military

R.H. Walden, HRL (1999)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 13

What about Multi-Standard Radio ?

Tunable / switchable / separate RF / IF hardwares may be necessary for multi-standard radio !

890 915

1710 1785

1850 1910

1920 1980

GSM900 Rx

GSM1800 Rx

GSM1900 Rx

UMTS Rx

MHz

... 270 MHz

Q: What is the optimal & cost-effective solution?

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 14

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 15

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 16

Shrinking of tapeduring the firing:10-15 % in x/y axis10-45 % in z axis.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 17

Advantages of LTCC• 3D passive integration (number of signal layers almost unlimited).• Fabrication techniques are relatively simple and inexpensive.• Reduced size (compared to PCB) and low cost ?

Some Issues• Delamination from stressed structures during build.build• Relatively coarse fabrication geometry: limits accuracy & range.• Relatively high co-fire temperature (850 oC) − limited materials.• Different passives perform best with different dielectrics.• Relatively bad thermal conductivity (Thermal vias required).• 3D design tools not yet mature − long time for prototypes.• Still a ‘dummy’, inflexible passive assembly.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 18

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 19

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 20

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 21

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 22

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 23

Conventional (narrow-band) superheterodyne receiver arch.

WCDMA: 1920−1980 MHz 1714−1769 MHz 162 MHz 46 MHz (Example)

Intermodulation issues; strong ín-band block signals; high requirements for synthesizers; due to wideband, nonlinearity, ...

Extra-IF stage necessary for the archi-tecture causes further degradation of signal quality, and increase costs.

~~~

PS

LNA

B-BPF

~

~

...

B-RF-LO

B-MIX1

~~~

B-IRF ~~~

~~~IF1-IR/BPF

IF1-Amp

A/D

A/D

~

~~~

~~~~

...

IF2-IR/BPF

IF2-Amp

IF-LO

MIX2

Other issues: Inflexible, many RF/IF components, high-cost, large size, ...

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 24

Reconfigurable radio architecture with single-IF & filter banks

Generic Example

1920 1980 MHz

fLO Signal Band of Interest

~~~...

~~~ ~

~~~

~

...

Channel/carrier selectionIF-BPF/B

IF-Amp

A/DDSP(DDS)

LNA

B-BPF

Bandwidthpartition (N)

RF-LO

MIX

A/D DSPIQ

A/D DSPIQ

Channel selection

~~~~~~~~~

RF filter bank

M −ro

u tes

(M <

N)

IF (ex. 60 MHz)Advantages:

• Eliminate bottleneck of ADC• Relaxed DSP requirements• Reconfigurable multi-carrier radio• High performance and low-cost (potential)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 25

5% change of delay in feedforward

Feedforward MCPA(Powerwave Technologies, Inc. USA)

Broadband & linearadaptive TT-delay lines desirable!

High Efficient & Linear RF Power Amplifiers

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 26

RFTune Inc. (start-up, April 2002)

Claim:Best smart antenna architecture isRFTune’s low-cost RF front-end chip rather than existing complex DSP solutions.

Need of investigation !

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 27

Smart 4G radio head for MIMO systems

Main Objective:

To demonstrate the feasibility of a smart 4G radio head for MIMO (Multiple Input Multiple Output) wireless systems using RF MEMS (coarse-switching and fine-tuning) • to perform patten and/or polarization changes in radio signals, • to enable multi-mode operation, and• to optimize performance of the multiple antenna arrays in environment with multi-paths.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 28

Question and Comment

• Should performance (selectivity, sensitivity, dynamicrange ...) be traded for flexibility especially for RBS transceivers ? (No need for “full” programmability)

• By RF MEMS together with digital techniques, wemay achieve optimal radio architectures with bothhigh-performance and reconfigurability (flexibility)in a cost-effective way and capable of handling future bandwidth expansion. (No ADC bottleneck)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 29

Reconfigurable Multi-Carrier Radio ReceiverMain Objective:

Demonstrate the feasibility of novel receiver architectures byRF MEMS technology for future “Software Radio” systems.

Main Advantages:• Eliminate the bottleneck of ADCs in usual SDR architecture

• Relaxed requirements for both ADCs and DSPs• Reduced number of RF components required in conventional

narrow-band receiver architectures

• Reconfigurable radio with multi-carriers (software define & hardware (RF analog +DSP) implementation)

• High performance and low cost (high potential)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 30

Comments

A number of system architectures can be studied according to customer’s needs with the use of RF MEMS technology.

By RF MEMS together with digital techniques, it is possible to achieve optimal radio architectures with both high-performance & reconfigurability (flexibility) in a cost-effective way and be capable of handling future bandwidth expansion (No ADC bottleneck).

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 31

RF MEMS COMPONENT TECHNOLOGY

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 32

Yole Devel. Mag. (2004)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 33

Series Switch and Shunt Switch

FET swtich

PIN switch

series

shunt

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 34Coventor, Inc. (2001)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 35

Lincoln lab (reliability: 100 billion switching cycles at 1-10 mW, ~ 30 years lifetime for continuous 100 sw-cycl./s)

Raytheon, Rockwell, Analog Device (Radant MEMS) (source: UoM), ...

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 36

RF MEM Switches- Low insertion loss (< 0.1 dB)

- High isolation (> 40 dB at 1 GHz)

- Low power consumption (μW)

- High linearity & broadband op.

- Switching time (~ 1 μs)

- Actuation voltage (~ 1−10 V)

- Power handling capability (> 1 W)

- Reliability (> 10 switching cycles?)

A piezoelectric actuated switch witha low driving voltage ~ 3V (Marconi).

8

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 37

Phase Shifter

λ/n

Asin(ωt) Asin(ωt + φ)

Individual Phase Bit

MEMS-Based Phase Shifters

- Ultralow insertion loss

- Broadband operation

- High linearity

- High electric isolation

- Low power loss

- Power handling (?)

- Low weight & low cost

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 38

(IMS 2001)

Unm

atch

ed

Mat

ched

Insertion loss~ 2.5 dB at 10 GHz

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 39

Smart Antennas with MEMS Switches− Switch/tune relative phases

of the element excitation currents.

− Switch distribution of currents.

Dual-Band Dipole AntennaE. Brown, UCLA

E-tenna

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 40

MEMS Bulk Acoustic Wave Resonators

AIN - Aluminium Nitride

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 41

(a) Diagram and (b) Typical implementation of FBAR

Equivalent circuit for a piezoelectric crystal.

Thin Film Bulk Acoustic Wave Resonators

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 42

Agilent FBAR Duplexer

Agilent FBAR duplexer

Ceramic duplexer ´99

(Q > 1000)

Agilent Technologies ships one millionth FBAR duplexerPALO ALTO, Calif., Feb. 20, 2002.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 43

Feasibility of RF filters:Ex. Thin-Film Bulk Acoustic Resonator (FBAR) Filters

Image rejection~ 120 dB achievable together with the 1stRF bandpass filter

Half-IF suppression~ 110 dB achievabletogether with the mixer

Insertion lossTypical 2.2 dB

US PCS band (Agilent 2002)

fLO 15 MHz

60 MHz

* Other types RF filters could also be used to examine just the concept.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 44

Comparison of some filter technologies

Source: Agilent Technologies, Inc. (2001)

Note: This is just the beginning of the RF MEMS technology. Much improvement can be expected, and new filters may emerge with tunability & full integration capability.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 45

"By-band" front-end modules that are partitioned by frequency band (e.g., 1900 MHz and 850 MHz) provide the flexibility to be used in any phone that has a CDMA-1900 MHz PCS band.

Agilent News (March 2004): Industry's first combined CDMA duplexer/power amplifier front-end module for use in dual-band and U.S. PCS mobile phones and wireless data cards.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 46

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 47

Discera micro communication technologies

Technology based on work of Dr. Clark T.-C. Nguyen,University of Michigan and UCB

Current activity:

• 13 - 60 MHz VCO (0.25 ppm/K)

• 40 - 60 MHz filters on chip(discussed during SAZH visit).

Issue:• High input/output impedance (~ kΩ)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 48

The first commercial micromachined RF device (FBAR) is already vibrating inside Samsung's miniscule(CDMA-based) Watch Phone(Feb. 2002).

Newly established US company, DISCERA, believes that their (beam) resonators will be 80,000 times smaller than FBAR, and have Q-value of 10 times higher than FBAR. (Already demonstrated in lab: Q ~ 8,000 at 100 MHzIntel: beam resonator at 2 GHz, no Q-value is reported)

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 49

Some Notes

For extremely small MEM resonators aiming for highresonance frequency applications, the relative mass of the molecules populating the atmosphere in whichthe structure is immersed is no longer negligible, causing first the phenomenon of mass loading.

Secondly, the air/gas molecules that simply impingeupon the structure, without being absorbed, exert arandom force on it, known as the Brownian force,which manifests itself as noise, causing fluctuationof the resonance frequency.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 50

RF MEMS Inductors

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 51

High-Q inductor applications

• Impedance matching networks

• Low noise amplifiers

• Voltage-controlled oscillators...

CMOS RF amplifier withsuspended MEM inductorJ.Y.-C. Chang, et al, IEEE EDL, vol. 14 (1993).

Improvement of ~ 12 dB in gain

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 52

RF MEMS Tunable Capacitors*Main Advantages:

• Wide tuning ranges (ex. 8:1 turning ratio realized at Rockwell Sci.)

• High-quality Q factors (a few hundreds at 1 GHz)• Good linearity performance• High self-resonance frequencies• Reliable operation of ~ 10 billion cycles demonstrated.

Possible applications:

• Tunable filters• Voltage controlled oscillators• Matching circuits …

Tuning range of the device measured at 500 MHz.(Rockwell Scientific (2003)).

* Nokia Research is working on the subject among others.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 53

Failure modes:- Wear (humidity, lubricant, friction theory, …)- Adhesion and sticking (Van der Waals force,

capillary force, electrostatic force, hot weld, …)- Temperature, vibration, contamination, fracture,...

Reliability of RF MEMSIdentify Failure

ModesStatistical

CharacterizationDesign TestStructures

Develop PredictiveReliability Models Qualification

of MEMS

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 54

Some Issues & Challenges to MEMS Technology

Mass loading & resonance frequency fluctuation(relative mass of molecules populating atmosphere and their impact on MEMS structures may no longer be negligible).

Acoustic radiation/energy loss(air/gas molecules’ motion excited by structure vibration cause losses)

Adhesion, sticking, and wear(humidity, friction, lubricant, hot weld, …).

Thermal stability, aging, fracture, reliability test, ...Hermetic & vacuum packaging on chip, and environment control on chip

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 55

10-9

10-8

10-7

10-6

10-16

10-14

10-12

10-10

10-8

10-6

10-4

10-2

Magnetic (I = 5 mA)

Magnetic (I = 1 mA)

Casimir

Van der WaalsElectrostatic (1V)

Electrostatic (30V)

Capillary (θ = 10o)

Distance l (m)

Capillary (θ = 85o)

Comparison of Forces in MEMS (1 μm2)

Gold (1 μm3)

Earth gravityforce

Electrostatic 17 mV

Forc

e (N

)

S.-A. Zhou, Int. J. Eng. Sci. 41 (2003) 313.

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 56

System Integration of MEMS with ICs

• Hybrids: build of electronics industry manufacturinginfrastructure

- Simpler integration, larger size, low performance

• Flip chip / Advanced hybrids & packaging- Flexible integration with any RF substrates orfunctional materials

- Medium size, good RF performance, reliability?

• Monolithic: embedding of MEMS in IC wafers- Complex fabrication sequence, possible processincompatibilities, limited types of materials

- Small size, high performance, low cost

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 57

Integrated MEMS

A tiny "smart" machine (a three-axis accelerometer),combining microcircuits, sensors, and actuators on a single computer chip. (UCB, Sandia Nat Lab, Analog Device)

Digital Light Processing with DMD having 1.31 million hinged micro-mirrors (TI).

MEMS based atomic clock

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 58

MEMS Packaging

- Cap-on-Chip

- Flip Chip Package

- Atmosphere Control Agents: Getters (O, H2, H2O, …)

- Surface Control: Friction, Stiction, and SolutionsPolymer vacuum coating, ...

- Hermetic (Vacuum) Packaging

- Wafer Dicing Concern: Vibration, Shaking, Dirty ...

- Interface between sensor and environment

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 59

Why now RF MEMS, not decades ago?

RF device size ~ Wavelength λ

Electromagnetic: λ ~ 1 m at 100 MHz

Acoustic: λ ~ 10 μm at 100 MHz

IC technology Technology is now available to fabricate μ−machines!

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 60

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 61

Shift from Processing & Access to Interaction

Microprocessor

Microelectronics

1980 1990 2000 2010IFTF (1997)

Processing

Personalcomputer

Access

Laser

Optical, RadioInternetWWW

Interaction

SmartifactsHuman-machine

...

Sensor & Actuator

MEMS

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 62

Potential Applications of RF MEMS for RBS

Smart Antennas

Multi-bit TTD & phase shiftersAuto-gain/attenuation adjusters

Miniaturized filters andtunable/switchable filters

Smart RF matching networkVCO, signal process, MCPA, …Reconfigurable architectures

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 63

Potential Applications of RF MEMS for Terminals

Reconfigurable antennasMicro-switchesTunable capacitors andhigh-Q inductors

Miniaturized filters andtunable/switchable filtersMicrophone, Smart sensors Batteries, DisplaysIntegrated ...

S.-A. Zhou, Invited lecture presented in Kista (2001) and Shanghai (2004) (partial slides). 64

Summary

− Novel RF systems concepts need to be explored with respect to applications of RF MEMS

components and sub-systems.

− Technology challenges exist to bring RF MEMS from laboratory-scale experiments to production-worthy

prototypes, as well as to cost-effective, reliable, and high performance commercial products.

− RF MEMS may find interesting and perhapsunique applications in future radio communication

systems and mobile terminals.