Project Introduction and Motivation

1
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.

2
High Speed Switching System Design
E
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.
3
Introduction to High Speed Quasi-Optical Arrays
4
Equivalent Circuit Model of the Diode Grid Unit
Cell
Equivalent Circuit for Diode Grid Unit Cell
SEM photo of Unit cell
E-Field Distribution of Top View of Schottky
Varactor
5
High Speed Switch Array with Bias Control Board
6
High Speed Beam Control Switch Testing Setup
7
High Speed Switch Testing Results
Comparison Between Measured and Simulated
Contrast Ratio

• lt1.5 dB insertion loss and 16.8 dB on/off
  contrast ratio measured at 60 GHz.The switch fall
  time is lt127 psec, rise time is 168 psec with
  pulse width (FWHM) 317 psec limited by bias
  pulse.
• gt 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.

8
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 18 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 lt 1 dB insertion loss and
  27 dB ON/OFF contrast ratio.
• W-band switch array lt 2.5 dB insertion loss and
  gt 25 dB ON/OFF contrast ratio.

9
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).

10
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.
11
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.

12
MEMS Switch Array Layout
13
MDS Simulation of MEMS Power Control Array
The MDS simulation tool has been used to simulate
the MEMS switch array. The contrast ratio is gt 20
dB over a 20 GHz bandwidth.
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Design of MEMS Tunable Filters
Equivalent circuit of the Tunable Filter
QO MEMS Tunable Filter System
MEMS Tunable QO filter consists of sevearl
pieces, an LC resonant circuit is fabricated on
each of the wafer surfaces.
15
Simulation Result of W-band Tunable Filter
W-band tunable filter can tune 30 degree phase
shift From 30GHz---40GHz.
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Ongoing Activities

• 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.