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Magnetic Actuator - Magnetostatic Actuator

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Magnetic Actuator - Magnetostatic Actuator Powered By Docstoc
					            Micromachining for Integrated Electronics


                                  Chang Liu
                Micro Actuators, Sensors, Systems Group
                University of Illinois at Urbana-Champaign

              Power and Energy Systems Seminar, ECE 490 I
                              9/24/2001
                                                             MASS
Chang Liu
                                                             UIUC
                                    Outline

      •     Overview - MEMS for circuit applications
      •     Micromachined tunable capacitors
      •     Micromachined high-Q inductors
      •     Conclusions




                                                       MASS
Chang Liu
                                                       UIUC
            MEMS Applications




                                MASS
Chang Liu
                                UIUC
                       A Future Wireless World …
                     Small, Low Power and Low Cost




      Wireless LAN       Collision avoidance radar




                                                     MASS
Chang Liu
                                                     UIUC
                      Ultimate Miniaturization

    GPS
    Cellular Phone
    30 GB memory
    True color display
    DC-200KHZ microphone
    Pressure sensor
    Pulse sensors
    Heart monitor
    Personal digital assistance
    Digital camera and movie
    Large screen projection display
                                                 MASS
Chang Liu
                                                 UIUC
                        MEMS for Integrated Electronics
      • RF Circuits
            – high performance, integrated components including
                 •   capacitors,
                 •   inductors,
                 •   resonators,
                 •   filters,
                 •   switches.
            – High performance integrated probes for circuit characterization
                 • ability to interrogate sub-micrometer structures
      • Power electronics and energy systems
            –   Capacitors
            –   Inductors
            –   Relays and switches
            –   Transformers



                                                                                MASS
Chang Liu
                                                                                UIUC
            MASS
Chang Liu
            UIUC
            Integrated Power Generation and Conversion




   Portable generation
   and conversion
   for
   High power density
   High voltage
   applications


                                                         MASS
Chang Liu
                                                         UIUC
      BioMicrofluidics Applications for Integrated Lab-on-
                            a-Chip




                               s




                                                       MASS
Chang Liu
                                                       UIUC
                                    Outline

      •     Overview - MEMS for circuit applications
      •     Micromachined tunable capacitors
      •     Micromachined high-Q inductors
      •     Conclusions




                                 Moore’s law for integrated circuits
                                                                  MASS
Chang Liu
                                                                  UIUC
            •   Background & Motivation
                   Current tunable capacitors
                   Performance limiting “pull-in” effect in micromachined
                    parallel-plate tunable capacitors

            •   Design, Fabrication and Testing
                   Design How to overcome the “pull-in” effect and
                    achieve a wide tuning range?
                   Fabrication How to make it ?
                   Testing and measurement

            •   Conclusions


                                                                        MASS
Chang Liu
                                                                        UIUC
                           Existing Tunable Capacitor Overview


            •   Solid-state Varactors
                                                                                      Diode
                      High substrate resistive loss
                      Limited tuning range (<10%)
                                                                                       MOS
            •   MEMS tunable capacitors                                              Capacitor
                      Lower loss
                      Wider tuning range
                      Typical example – electrostatically actuated
                       parallel-plate tunable capacitor


                                                     Suspended plate
                                              VDC             C
                                                                       Fixed plate




                                                                                      MASS
Chang Liu
                                                                                      UIUC
            Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable
                                         Capacitors




             Pull-in effect is an intrinsic phenomenon to
            electrostatically actuated devices, which greatly
            limits the tuning range of the tunable capacitor.




                                                                                  MASS
Chang Liu
                                                                                  UIUC
                 Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable
                                              Capacitors


                                           Suspended plate

                                           x0
                                                      C
                                                                   Fixed plate



        Spacing                                           Capacitance

            x0


                                                          A
                                                          x0


                 0                              VDC            0                        VDC




                                                                                       MASS
Chang Liu
                                                                                       UIUC
                 Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable
                                              Capacitors

                                               Suspended plate

                                  VDC               C
                                                                 Fixed plate




        Spacing                                         Capacitance

            x0


                                                        A
                                                        x0


                 0                            VDC            0                          VDC




                                                                                       MASS
Chang Liu
                                                                                       UIUC
                   Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable
                                                Capacitors

                                                  Suspended plate

                                     VPI
                                                                  Fixed plate



                           Controllable
             Spacing                                     Capacitance
                           displacement

              x0                           Unstable    3A
                                           Snap-in
                                                       2 x0
            2 x0
             3                                         A
                                                       x0


                   0                                                               VPI
                                           VPI   VDC          0
                                                                                          VDC
                                Max. controllable tuning range = 50%

                                                                                         MASS
Chang Liu
                                                                                         UIUC
                           To Extend Tuning Range …



      • Require full-gap positioning




                                         Capacitance
      Spacing

      x0                                3A
                                        2 x0
    2 x0
     3                                  A
                                        x0


            0              VPI   VDC           0       VPI




                                                             MASS
Chang Liu
                                                             UIUC
                                    Design of the Novel Tunable Capacitor


            Conventional design                                       New design
                         Suspended plate                                                      Suspended plate
                     x
      VDC                                                VDC=0V          d2              d1
                             C                                                   C
                                      Fixed plate                                                   Fixed plates




                  x0/3   Suspended plate                                                      Suspended plate

      VPI                                                    VPI                                2d2/3
                            C                                                                           Fixed plates
                                     Fixed plate
                                                                              d1 -d2/3



                                                                    A                           A
             A                  3A                         C0          Cm ax 
     C0             Cm ax            1.5C0                      d1                     (d1  d 2 / 3)
             x0                  2 x0
                                                             d1  2m         d 2  3m
              Max. C/C0 = 50%                                     Max. C/C0 = 100%

                                                                   US Patent Pending                      MASS
Chang Liu
                                                                                                         UIUC
                                 Fabrication Process



                                                        Cu
                 Gold (0.5m)
                                                            2m     3m
            E3   E2         E3
                                     (a)                                       (d)
                                                             Ni-Fe (2m)
                 Cu (1m)


                                     (b)                                       (e)


                                                       E1
                                                        d1(2m)     d2(3m)

                                                  E3   E2           E3
                                     (c)                                       (f)




                                                                              MASS
Chang Liu
                                                                              UIUC
                            SEM Micrograph of the Tunable Capacitor




                                                                        E1

                                                                      2m          3m
            Contact Pads      Cantilever beam
                              Suspension                              d1 -x
                                                             E3          E2        E3


                                            To E3
                           Top Plate
                              E1
    To E2
                                                                              E1
                                                                  Etch hole




                                                                                         MASS
Chang Liu
                                                                                         UIUC
                                   Simulation/Optimization




   •        Electromechanically coupled simulation (MEMCAD*)
                  Base capacitance (C0)
                  Pull-in voltage (VPI)
                  Maximum Tuning range (C/C0)
                  Dynamic characteristic of the movable plate suspension

   •        High frequency performance (Sonnet em Suite*)
                  Loss
                  Capacitive behavior


               * MEMCAD - Microcosm Inc, MA
               * Sonnet em Suit - Sonnet Software, Inc, NY




                                                                       MASS
Chang Liu
                                                                      UIUC
                           MEMCAD Model for C-V Simulation

                                                                    Suspended plate
                                                             x

                                                                         Fixed plates



                      E1

                     E2     E3




     MEMCAD model showing 3 plates of         Travel distance (x) of the top plate
     the wide tuning range tunable            (E1) when a DC driving voltage (VDC)
     capacitor (See from the bottom)          is applied between E1 and E3


                                                                              MASS
Chang Liu
                                                                              UIUC
                                                                              -0.6
            Model used in SonnetSimulation                                                     Simulated




                                                        S11 Magnitude in dB
                                                                              -0.5
                                                                                                Measured
                                                                              -0.4

                                                                              -0.3
                         E1
                                                                              -0.2
                                     E2                                       -0.1 0        1       2       3       4       5       6       7       8       9    10
                                                                                    0
                                                                                                                Frequency (GHz)

                                                                              -50
                                                                                                Simulated
               Measured
                               45MHz                                          -40               Measured




                                                   Phase (degree)
               Simulated                                                      -30

                                                                              -20

                                                                              -10
                                                                                    0   1       2       3       4       5       6       7       8       9       10
                                                                               0
                                                                                                            Frequency (GHz)


                    10GHz                        Return loss < 0.6dB@10GHz
                                                 Linear phase-frequency relationship

                                                                                                                                                                     MASS
Chang Liu
                                                                                                                                                                     UIUC
                      Experiment




                                                              Pull-in


            VDC=0V




                          d1 decreases continuously from 2 m to
                           1.2 m. Then d1 decreases abruptly from
                           1.2 m to 0.6m at VDC=17.2V.
                          The top plate travels 0.8 m (>d1/ 3)
                           before the Pull-in occurs.
            VDC=16V


                                                               MASS
Chang Liu
                                                               UIUC
            Results achieved
                  A new design concept for parallel-plate tunable
                   capacitor to achieve arbitrary tuning range

                  A maximum tuning range of 70% achieved
                   experimentally

                  Low loss (<0.6dB@10GHz) and excellent capacitive
                   behavior at high frequencies




                                                                      MASS
Chang Liu
                                                                      UIUC
                                    Outline

      •     Overview - MEMS for circuit applications
      •     Micromachined tunable capacitors
      •     Micromachined high-Q inductors
      •     Conclusions




                                                       MASS
Chang Liu
                                                       UIUC
                             Conventional Spiral Inductors




                                           2nd Metal layer        1st Metal layer

                                                 SiO2

                                                  Si




               Occupy relatively large substrate space (~100100m2)
               Suffer loss and parasitics from lossy substrate
                       Limited quality factor (Q)
                       Limited self-resonant frequency



                                                                               MASS
Chang Liu
                                                                               UIUC
                  Limitations of Current Micromachined Planar Coil Inductors




            Si                           Si
                                                                  Si
            Completely removing substrate         Partially removing substrate material
             material underneath (Ozgur)                     underneath (Yeh)


                        Polyimide                      Air Gap

                          Si                                     Glass

            Applying a thick polyimide layer        Levitating the inductor structure
                   underneath (Kim)                 above the substrate (Park, Yoon)


                 Still requiring relatively large substrate real estate
                  (~100100m2)
                 Involving complex microfabrication steps, possibly
                  incompatible with IC fabrication foundry
                                                                                        MASS
Chang Liu
                                                                                        UIUC
            Fabrication Process of Vertical Spiral Inductors


                   •   Fabrication                             •       Deposition of
                       begun with a                                    Permalloy
                       IC chip




                                                                   •    Sacrificial
                   •   Deposition of
                                                                        layer etching
                       sacrificial layer




                   •   Fabrication of
                       spiral inductor                         •       Inductor
                                                                       assembly using
                                                                       PDMA




                                                                            MASS
Chang Liu
                                                                            UIUC
                                   Assembly Using Micro Hinged Structures




                     Main flap

                Secondary flap




                                                                                 Cantilever beam spring
                                                                                  loading mechanism


                 Require additional substrate estate for
                  supporting structures or actuators
                 Difficult to create electrical path between the
                  3D structures and the substrate                                              Electrical connection to
                                                                                                       substrate
                 Major application: Optical MEMS
  **-Yong Yi and C. Liu, IEEE J. Microelectromechanic. Syst. vol. 8, no. 1, pp .10-17, 1999.

                                                                                                                 MASS
Chang Liu
                                                                                                                 UIUC
                                  Assembly Using Phase Changing Materials




            Phase changing material
                                    Micro flap


                                                               Heat


                   Phase changing material: solder or photo resist
                   Requires heating to melt bulky phase changing material
                   Requires delicate control to attain uniform assembly


    **- R. R. A. Syms, IEEE J. Microelectromechanic. Syst. vol. 4, no. 4, pp. 177-184, 1995.
    **- K. F. harsh, V. M. Bright, and Y. C. Lee, Sensors & Actuators A., vol. 77, pp. 237-244, 1999.

                                                                                                        MASS
Chang Liu
                                                                                                        UIUC
                           Motivation of This Work




            To develop an alternative general-
              purpose 3D assembly process

                High density, uniform and efficient assembly
                Solid electrical path between the 3D structure
                 and the substrate
                Room temperature assembly
                Compatible with IC Foundry


                                                                MASS
Chang Liu
                                                                UIUC
                              Plastic Magnetic Deformation Assembly




                        Magnetic
                        material                                           
                                  Micro flap                    Flexible
                                                                region


                      Substrate                (a)                             (b)

                                                               Hext

            (a1) Surface-micromachining of the structure to be assembled
            (a2) Deposition of the magnetic material piece
            (b)   Application of an external magnetic field (strength & direction)
                  to create required plastic deformation in the flexible region
            Magnetic material can be removed afterwards if necessary.


                                                                                     MASS
Chang Liu
                                                                                     UIUC
                          Plastic Magnetic Deformation Assembly




                       Before PDMA                     After PDMA


               Supporting structure not required  High density
               Magnetic actuation  Room temperature process
               3D structures aligned to the external magnetic filed  Uniformity
               Metal used as bending material  Solid electrical path
               IC compatible

                                                                           MASS
Chang Liu
                                                                           UIUC
            Plastic Magnetic Deformation Assembly




                                                         
             Flexible
             region


                            (b)                                 (c)


            Hext
                                        Structures may fall back
                                         to a certain angle () after
                                         Hext is removed due to the
                                         elastic energy stored in
                                         microstructure during the
                                         bending.


                                                                 MASS
Chang Liu
                                                                UIUC
                      Theoretical Analysis




        For a specific PDMA implementation, we
        need to know the relationship between
             Hext and the bending angle ()
         beforehand, so that the targeted final
             rest angle () can be achieved.



                                              MASS
Chang Liu
                                              UIUC
                                                    Theoretical Analysis


                                        tp
                   Permalloy
                                                                                 Tm
                                                                                tg
                         lp
                                                                           lg         
            Gold
                    lg              
                               tg


                                             Hext

            Magnetic Force: Tm = MwptplpHextcos=MVpHextcos
   The magnetic force tries to align the cantilever beam to the magnetic field

            M - Magnetization of Permalloy
            wp, tp and lp – width, thickness and length of Permalloy

                                                                                      MASS
Chang Liu
                                                                                      UIUC
                                                Theoretical Analysis


    When Hext is increased, the bending experiences two phases.

    Phase 1: Elastic bending (at small s)                                                         Tm
                                                                                                  tg

                                               Eg I g                                        lg         
        Tm  Mwpt pl p H ext cos                      
                                                lg
                          Eg I g               Eg I g      
            H ext                         
                      l g Mwpl pt p cos       l g MVp cos        Eg   – Young’s Modulus of gold
                                                                   M    – Magnetization of the Permalloy piece
                                                                   y   – Yield stress of gold
    Phase 2: Plastic bending (at large s)                         Ig   – Moment of inertia of the gold beam

                                      y wg t g
                                              2                    lg   – Length of the gold beam
      Tm  Mw p t p l p H ext cos                                wg   – Width of the gold beam
                                         4                         tg   – Thickness of the gold beam
                                                                   lp   – Length of the Permalloy
                       y wg t g
                               2
                                1      y wg t g 1
                                               2
                                                                   wp   – Width of the Permalloy
        H ext                      
                  4Mwp l p t p cos    4MVp cos                   tp   – Thickness of the Permalloy
                                                                   Vp   – volume of the Permalloy piece



                                                                                                        MASS
Chang Liu
                                                                                                     UIUC
                                                Theoretical Analysis


    When Hext is increased, the bending experiences two phases.

    Phase 1: Elastic bending
                                               Eg I g
        Tm  Mwpt pl p H ext cos                                        Plastic
                                                lg
                          Eg I g               Eg I g      
            H ext                         
                      l g Mwpl pt p cos       l g MVp cos

    Phase 2: Plastic bending
                                      y wg t g
                                              2

      Tm  Mw p t p l p H ext cos                                    Elastic
                                         4
                       y wg t g
                               2
                                1      y wg t g 1
                                               2

        H ext                      
                  4Mwp l p t p cos    4MVp cos


                                                                                     MASS
Chang Liu
                                                                                     UIUC
                                  Theoretical Analysis




                                        Plastic
                                  Yielding



                                       Elastic


               The bending is first elastic and then plastic.
               The bending angle () saturates when Hext increases since
                the magnetic force tries to align the cantilever beam to the
                magnetic field.
               The final rest angle () is determined by the bending angle
                occurring in the plastic regime.
                                                                          MASS
Chang Liu
                                                                          UIUC
            Measured Displacement Vs. Hext




            80


            60


            40
                                M easured
                                M odel
            20


             0
                 0    10000    20000        30000




                                                    MASS
Chang Liu
                                                    UIUC
                       Experimental Results




                                                         Tm
                                                        tg

                                                   lg         



            80

                                  Measured
            60
                                  Model

            40


            20


            0
                 10   30     50      70       90



                                                              MASS
Chang Liu
                                                              UIUC
                                 Other Issues

                       Creating vertical structure


                              > 90
                                  o


                                                        90
                                                           o



            Flexible
            region


                                      (a)                      (b)

                       Hext

                       Post-assembly Strengthening
                                                     3 m Parylene coating




                                                                         MASS
Chang Liu
                                                                        UIUC
             Scanning Electron Micrographs of Fabricated Prototype Devices




     Test pads              Gold Bottom
                            conductor



                            CYTOP
                            Dielectric Bridge


     Copper Top
     conductor



                  Before PDMA                              After PDMA




                                                                             MASS
Chang Liu
                                                                             UIUC
                                                         Experimental Results


                5
                        Inductor on Silicon                                              Vertical inductor
                                                                               14
                                                                                           Model
                4                                                              12
                                                                               10          Measurement
    Q Factor




                                                                    Q Factor
                3
                                                                               8
                2                                                              6
                        Model                                                  4
                1
                        Measurement                                            2
                0                                                              0
                    0   0.2       0.4    0.6       0.8    1                         0       1          2        3   4
                               Frequency (GHz)                                                  Frequency (GHz)


                         Inductor on Glass
               14                                                                      Inductance = 4.5nH
                         Model
               12
               10        Measurement
     Q Factor




                8                                                              Max Q inductor on Silicon = 3.5
                6
                4                                                              Max Q vertical inductor = 12
                2
                0                                                              Max Q inductor on glass = 12
                    0         1       2        3          4
                               Frequency (GHz)

                                                                                                                        MASS
Chang Liu
                                                                                                                        UIUC
            3D Solenoid




                          MASS
Chang Liu
                          UIUC
            3D Solenoid




                          MASS
Chang Liu
                          UIUC
                                    Outline

      •     Overview - MEMS for circuit applications
      •     Micromachined tunable capacitors
      •     Micromachined high-Q inductors
      •     Conclusions




                                                       MASS
Chang Liu
                                                       UIUC
                                  Conclusions

      • Potentials for applying micromachining technology to circuit
        and power electronics applications
      • Developed variable gap tunable capacitor architecture and
        demonstrated large tuning range;
      • Developed three-dimensional assembly technique and realized
        high qualify factor inductor elements;

      • Current and future work:
            – Develop integrated power convertors for on-chip power regulation.
            – Develop tunable, lockable and resettable micro capacitors.
            – Develop high-Q inductors and demonstrate integration onto IC
              chips.




                                                                           MASS
Chang Liu
                                                                           UIUC
                          Acknowledgements

      • This research is supported by the Grainger Center and DARPA.

      • Thanks for discussions from Professor Krein and Professor
        Chapman.




                                                                    MASS
Chang Liu
                                                                    UIUC

				
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