Rf Mems Theory, Design, and Technology by Gabriel M. Rebeiz - PowerPoint

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					RECONFIGURABLE MEMS
     ANTENNAS

     SUBMITTED BY

    AMIT KUMAR SINGH
        07007038
     HIMANSHU BAGRI
        07D07039
      AMIT BANSOD
        07D07041
                 WHAT IS ANTENNA?

   ANTENNAS  An antenna is a Transducer designed to
    transmit or receive electromagnetic waves. In other
    words, antennas convert electromagnetic waves into
    electrical currents and vice versa.

   An antenna is an arrangement of conductors that
    generate a radiating electromagnetic field in response to
    an applied alternating voltage.
      WHY MEMS IN ANTENNAS?
•   TO ACHIEVE RECONFIGURABILITY EASILY.

 CHANGING SHAPE OF EFFECTIVE RADIATING
• CHANGING SHAPE OF EFFECTIVE
               STRUCTURE
  RADIATING STRUCTURE.




      CHANGE IN               CHANGE IN
      RADIATION               FREQUENCY
       PATTERN                OPERATION
                  RECONFIGURABLE MEMS
                       ANTENNAS
       A reconfigurable antenna is one which alters the radiation, polarization
        and frequency characteristics by morphing its physical structure.

       MAJOR TYPES

1   .   PATTERN RECONFIGURABLE ANTENNAS :: Its implemented by changing
         Shape of effective radiating structure.

2.      MECHANICALLY ACTUATED MEMS ANTENNAS :: Implemented by
         changing orientation of antenna with respect to substrate.

3.      CAPACITIVE MEMS ANTENNAS :: It can be implemented by modifying
         impedance of antennas.




 •
    WHY MEMS ANTENNAS OVER OTHERS?

   Linearity: Low Signal Distortion.

   Low Power Consumption.

   Compatibility with Integrated Circuits.

   RESULT : High Performance compared to
    Semiconductors.
      MERITS OF MEMS DEVICES IN
              ANTENNAS

   Very low insertion Noise

   High Q factor upto frequencies of 120 GHz
    It indicates a lower rate of energy dissipation relative to the
    oscillation frequency, so the oscillations die out more slowly.

    Easy integration with substrates for high performance
•   It can be integrated on low dielectric-constant substrates which
    is important for high-efficiency antennas.
    PATTERN RECONFIGURABLE ANTENNAS
   Pattern reconfigurable antennas uses MEMS
    switches that connects different elements to make
    up antenna structure

   It can be implemented using :
        1. MEMS DC contact switches
        2. Lateral DC contact switches
FABRICATION OF SERIES DC
SWITCHES
    Substrates : Glass , Silicon

1.Deposition of Adhesive layer and Gold                    3.Patterning of wafer
o    Deposition of sacrificial layer of copper




o    Thickness of sacrificial copper Layer : 1.0 to 1.2
     µm                                                       The wafer is patterned with photoresist and the
                                                               cantilever and t-lines are electroplated with gold to a
                                                               thickness of 6–9 mm.

2.Etching – Two separate etches                            4. Removal of sacrificial layer




                                                           o     The highest temperature attained during the
                                                                 process is 250C.
   Two separate etches, a partial etch that defines the
    contact region and a complete etch that defines the    o     The MEMS switch is released using standard wet
    anchor, are then performed on the copper level.              etching of the copper layer
          PATCH ANTENNA
A TYPE OF PATTERN RECONFIGURABLE
             ANTENNA
                      FIGURE
                      (a) Layout of the original
                          patch antenna.(10
                          GHz)


                      (b) Antenna being
                          reconfigured by use
                          of MEMS
                          switches.(12.5 GHz)
                      SPIRAL ANTENNA
      A TYPE OF PATTERN RECONFIGURABLE
                   ANTENNA
•   A single turn square spiral antenna working at a nominal frequency
    of 3.7 GHz.

•   The outer end of the spiral is shorted to ground whilst the inner one
    forms the feed to the SMA probe.

•   In axial mode, switch 1 is closed while switch 2 is open. This creates
    a single turn spiral antenna working at 3.7 GHz.

•   With switch 1 open and switch 2 closed it reconfigures the antenna
    to the broadside configuration working at 6 GHz

•   Hence it successfully demonstrates the two features of a
    reconfigurable antenna using frequency and pattern reconfigurability
               SPIRAL ANTENNA
A) A SINGLE TURN SQUARE ANTENNA   B)   RECTANGULAR SPIRAL
                                       ANTENNA
A RECTANGULAR SPIRAL ANTENNA
   A set of MEMS switches which are monolithically
    integrated and packaged on the same substrate.

    The antenna is printed on a PCB and fed through a
    via hole, which is placed at the centre of the
    antenna.

   The antenna is made up of multiple lines which are
    connected via the MEMS switches, and by activating
    these switches the overall length of the antenna is
    changed which modifies its radiation pattern.
         RECTANGULAR SPIRAL ANTENNA
•   As shown in Figure , the rectangular
    spiral antenna is fed through a
    coaxial feed. The spiral consists of
    five sections connected with four
    MEMS switches (S1-S4).
•   The operating frequency of the
    antenna is chosen to be 6 GHz, and
    switching on the different sections
    of the radiating structure creates a
    tilted beam.
•   The maximum beam direction in the
    azimuth angle tilts from 18˚ to 104˚
    and a maximum tilt angle of 30˚ in
    the elevation plane as the length of
    the antenna changes.
•    The gain varies between 4-6 dBi
    depending on the length of the
    antenna.
     MECHANICALLY ACTUATED MEMS
             ANTENNAS
•   Ability to mechanically actuate the antenna with
    Electrostatic force .
•   Antenna suspended on a flexible spring.
•   Bias voltage is applied between patch and
    antenna
•   Creation of Electrostatic force attracts patch
    towards ground plate ,thus, changing height of
    antenna w. r. t ground plane.
•   Result is change in frequency operation of
    antenna.
MECHANICALLY ACTUATED MEMS
        ANTENNAS
   RESULTS SHOW THAT, WITH THE PULL DOWN VOLTAGE SET TO
   76V FOR THE PATCH, AS THE BIAS VOLTAGE IS ALTERED THE
 RESONANT FREQUENCY OF THE ANTENNA STARTS CHANGING FROM
46.3 GHZ TO 38.8 GHZ DEPENDING ON THE HEIGHT OF THE PATCH
    VBIAS=0                       VBIAS APPLIED
CAPACITIVE MEMS ANTENNAS
             The antenna is fabricated on
              a Pyrex 7740 glass
              substrate, and the MEMS
              bridge is suspended 1.5μm
               above the CPW.
             The resonant frequency of
              the antenna shifts down
              from 16.05 GHz to 15.75
              GHz as the actuation
              voltage is increased from 0
              to 11.9 V as the height of the
              capacitive gap changes from
              1.5 to 1.4 μm.
FABRICATION OF MEMS CAPACITIVE
           SWITCHES
 Substrate   : High resistivity silicon

1.Defining Bottom electrode

   A thin layer of tungsten (≤0.5 µm) is
    sputtered and patterned to define the bottom
    electrode.

 1000-    to 1500-A˚ -thick layer of PECVD
    nitride is deposited and patterned to insulate
    the electrode
     FABRICATION OF MEMS CAPACITIVE
                SWITCHES
2.Fabrication of Bridge Anchors and t- lines      3. Deposition of Sacrificial Layer
                  a. Aluminium evaporation
                  b. Wet Etching




                                                       A thick photo resist or polyimide
       Height of the Bridge anchors : 4 – 6 µm        sacrificial layer is spun on the wafer,
                                                       and a special planarization technique is
                                                       used to result in a planar and smooth
                                                       layer.


    4. Deposition of Aluminum membrane             5. Removal of Sacrificial Layer




                                                       An array of 2- to 3-µm-diameter
         The aluminum membrane is                      holes is defined in the bridge
          deposited and alloyed, and the                membrane to accelerate the
          bridge is released using an O2                removal of the polyimide layer from
          reactive ion etching process                  underneath the bridge.
BIBLIOGRAPHY
   RF MEMS Theory, Design, and Technology - GABRIEL
    M. REBEIZ.
   Reconfigurable MEMS Antennas :Camelia Dunare,
    Alan Gundlach, Jon Terry, Petros Argyrakis, Kevin
    Tierney, Alan Ross, and Tony O’Hara.School of
    Engineering and Electronics, University of
    Edinburgh,UK
   B.A. Cetiner, H. Jafarkhani, J. Qian, H.J. Yoo, A.
    Grau, F. De Flaviis, Multifunctional Reconfigurable
    MEMS Integrated Antennas For Adaptive MIMO
    Systems, University of California, Irvine, IEEE
    Communication Magazine.

				
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