Project Introduction and Motivation

MVE MURI 99 Kick-off Meeting R. Barker, Technical Monitor

Started 1 May 99 October 1999

Project Introduction and Motivation

•Millimeter-wave switches may be used in a variety of applications, including

Millimeter-wave imaging system and collision avoidance systems.

Millimeter-wave power control systems.

Moderate pulse radar reflectometry for plasma diagnostics.

.

• Beam control array technology offers the possibility of achieving high speed and

high power handling capability with increased dynamic range.

• Silicon based microelectromechanical system (MEMS) switches have the potential

to form low cost, high performance, ultrawide quasi-optical control elements for

advanced defense and commercial applications.



High Speed Switching System Design

The high speed switch consists of a quasi-optical beam control array, matching system, and high speed bias circuitry. Quasi-optical power combining techniques are utilized to obtain high output power by combining the power of thousands of diodes. The control speed is limited by three factors: the quasi-optical array physical dimensions, bias circuitry, and diode grid layout.

CW Mmwave Input

Switch Array

Switched Mmwave Output

Bias

Matching PlateMatching Plate

Microstrip Wilkison Power DividerMicrostrip to CPW TransitionWirebond from Bias Board to GaAs Wafer

E



Introduction to High Speed Quasi-Optical Arrays



Equivalent Circuit Model of the Diode Grid Unit Cell

R sC p

Ld

VaractorDiodeCgrid

Equivalent Circuit for Diode Grid Unit Cell

SEM photo of Unit cell

E-Field Distribution of Top View of Schottky Varactor



High Speed Switch Array with Bias Control Board



High Speed Beam Control Switch Testing Setup

BWO

PowerDetector

Trigger Signal

Pulse CircuitSignal Generator

Atten. Directional Coupler

V-K Trans.

Overmode Waveguide

Mounting Fixture

K-V Trans

Isolator Diode Detector

Frequency Meter

Sampling Oscilloscope



High Speed Switch Testing Results

<1.5 dB insertion loss and 16.8 dB on/off contrast ratio measured at 60 GHz.The switch

fall time is <127 psec, rise time is 168 psec with pulse width (FWHM) 317 psec limited by bias pulse.

> 10 dB on/off contrast ratio for the frequency band from 55 GHz to 66 GHz.The measured

results are very close to the simulation results.

0

5

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54 56 58 60 62 64 66

MeasuredSimulated

Co

ntr

ast

Rat

io (

dB

)

Frequency (GHz)

Comparison Between Measured and Simulated Contrast Ratio



New High Speed Switch Performance

High speed, monolithic millimeter wave switch arrays, which will operate

at V-band and W-band, have been designed and are being fabricated

In the new class high speed switch system, a new 1:8 wilkinson power

divider and a new optimized overmoded K-band mounting fixture will be used.

The grid switch array size is 0.4 x 1 cm2. There are around 400 Schottky

varactor diodes on the wafer, and it can handle power levels in excess of 1 W.

Lower insertion loss and higher contrast ratio is expected:

V-band switch array: < 1 dB insertion loss and 27 dB ON/OFF contrast ratio.

W-band switch array: < 2.5 dB insertion loss and > 25 dB ON/OFF contrast ratio.



Introduction: Microelectromechanical System (MEMS)

•MEMS stands for Micro-Electro-Mechanical System, where the physical dimensions are on the order of a few or tens of microns.

•There are two advantage of RF MEMS devices compared to traditional semiconductor devices:

a. Electromechanical isolation

b. Power consumption

• Developments in MEMS technologies have facilitated exciting advancements in the fields of sensors (accelerometers and pressure sensors), micromachines (microsized pumps and motors), and control components (high definition TV displays and spatial light modulators).



Silicon Wafer

V+

V-

4 m Metal

0.3 m Al

0.3 m AlMembrane

Microwave / Millimeter Wave MEMS Switch Operation

The MEMS switch consists of two metal plates, a fixed base plate and a movable thin film membrane.

Electrically, the MEMS switch is a nonlinear function of the DC bias applied to the switch.

Through the application of a DC electrostatic field, the MEMS membrane is attracted towards a metalized

bottom contact.



SEM Photo of MEMS Switch

•The top metal with holes is a movable membrane, which is supported by Al post.

•The holes are employed to etch the sacrificial layer using a plasma etcher. The unit cell size is 1200 x1200 µm2, and membrane is 120 x120 µm2.



MEMS Switch Array Layout



MDS Simulation of MEMS Power Control Array

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Cmax (Off)

Cmin (On)

Inse

rtion

Los

s in

Off

Mod

e (dB

)

Insertion Loss in On M

ode (dB)

Frequency (GHz)

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Cmax (Off)

Cmin (On)

Ref

lect

ion

Loss

in O

ff M

ode

(dB

)

Reflection Loss in O

n Mode (dB

)

Frequency (GHz)

The MDS simulation tool has been used to simulate the MEMS switch array.

The contrast ratio is > 20 dB over a 20 GHz bandwidth.



MEMS Tunable QO filter consists of sevearl pieces, an LC resonant circuit is fabricated on each of the wafer surfaces.

QO MEMS Tunable Filter System

Transmission Line

LCCircuit

Transmission Line

LCCircuit

Equivalent circuit of the Tunable Filter

Design of MEMS Tunable Filters



Simulation Result of W-band Tunable Filter

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Phase of W-band Tunable filter

Tune 1Tune 2

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Pass-Band of Tunable Filter

Tune 1Tune 2

S21 (

dB

)

Frequency(GHz)

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25 30 35 40 45

Stop-Band of Tunable Filter

Tune 1Tune 2

S2

1 (

dB

)

W-band tunable filter can tune ~30 degree phase shift From 30GHz---40GHz.



•A new class of GaAs based V-band and W-band high speed monolithic millimeter

wave switch array has been designed and is being fabricated.

•MEMS Switch array technology is being developing. MEMS based quasi-optical

arrays will be employed as quasi-optical power control, quasi-optical phase shifters,

and tunable quasi-optical filters.

Ongoing Activities

Documents

Project Introduction and Motivation