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Piezoelectric MEMS Resonator Measurement and Characterization

Piezoelectric MEMS Resonator Measurement and Characterization. April 6, 2004. Joung-Mo Kang, David Carter, Doug White, and Amy Duwel The Charles Stark Draper Laboratory. Presentation Overview. Background and device models Filter design L-Bar measurements Parasitic investigations

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Piezoelectric MEMS Resonator Measurement and Characterization

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  1. Piezoelectric MEMS Resonator Measurement and Characterization April 6, 2004 Joung-Mo Kang, David Carter, Doug White, and Amy Duwel The Charles Stark Draper Laboratory

  2. Presentation Overview • Background and device models • Filter design • L-Bar measurements • Parasitic investigations • Conclusion

  3. Device Overview and Goals 18 x 5.5 mm bar with 3.5 mm tethers • Desired: a high performance RF channel-select filter bank on a chip • 0.3-3 GHz frequencies • high selectivity  high Q • compatible with silicon IC technologies • small size  high density • low loss • device characteristics defined by lateral geometry 10 x 5 mm bar with 1 mm tethers

  4. Device Structure Circuit Model resonator Ctethers

  5. Longitudinal Resonance Longitudinal Mode Shape • tethers placed at displacement node • longitudinal displacement amplitude on the order of nm • other types of mechanical resonances cancel out in charge at lower frequencies

  6. Butterworth Van-Dyke Model MTO MEMS DARPA DARPA C L R C 0 e r wl 2 t l r c 8 we l p t = = = z = C L C R 0 2 2 t tc p Q 8 we 8 we 2

  7. BVD Impedance Function 8 10 6 10 Impedance Magnitude (W) 4 10 2 10 860 865 870 875 880 885 890 895 900 905 910 90 45 Impedance Phase (degrees) 0 -45 -90 860 865 870 875 880 885 890 895 900 905 910 l = 5.5 mm w = 3.0 mm t = 0.5 mm Q = 10,000 L = 342 mH C = 0.096 fF R = 189 W C0 = 2.98 fF

  8. Filter Design Primary Objectives: • Review existing crystal filter topologies and assess performance metrics. • Down-select a filter topology based on specifications set by RF group. • Define fabrication requirements and tolerances to achieve desired performance with each topology

  9. Dual Resonator Ladder Zs RS Vout Vin Zp RL

  10. Lattice Filter Impedance of Za and Zb Za R Za Zb wa wb Vin Vout R Zb Full filter response Zb Za

  11. Lattice Filter

  12. Simple Ladder Filter Z=sL+1/sC Z=sL+1/sC RS Vin RL Vout C12 Wideband Response -20 -40 -60 Magnitude (dB) -80 -100 -120 -140 102 103 104 105 106 Frequency (MHz)

  13. Simple Ladder Filter 0 -10 -20 Filter Transmission (dB) -30 797.5 798 798.5 799 799.5 800 800.5 801 801.5 802 802.5 90 no mismatch data1 0.1 % 0 data2 0.3 % data3 -90 Phase (degrees) -180 -270 797.5 798 798.5 799 799.5 800 800.5 801 801.5 802 802.5 Effect of bar length mismatch on filter characteristic Nominal values: l = 6.04 mm w = 3.22 mm t = 0.5 mm RS, RL = 1758 W C12 = 113.2 fF

  14. Mechanically Coupled Devices RS Vout Vin RL C12 RS Vout Vin RL C12

  15. Device Measurement Primary Objectives: • Confirm successful operation of resonators and accuracy of the analytic model (f vs. l, spurious modes) • Fit measurements to a discrete circuit model, adjust model if necessary, and extract resonator parameters (ie, determine resonator Q) • Use resonator performance results and analysis of parasitics to guide process and design improvements

  16. Device Measurement 3 mm 5 mm ~800 MHz resonator structure Device (GSG configuration) L C R Co RS RL

  17. First Round Devices Longitudinal axis contact contact AlN 5 mm Bar, Q=104 0 Cthru=2pF 50 L C R S21 (dB) Cthru=0 100 675 800 MHz 925 Co 25 mm Bar, Q=103 Rs 10 Cthru RL Cthru=2pF S21 (dB) 20 30 140 180 160 MHz

  18. First Round L-Bar Resonance -15.5 -15.6 -15.7 S21 (dB) -15.8 -15.9 -16 73 72 Phase (degrees) 71 70 69 150 147 148 149 146 Frequency (MHz) Cthru ~ 2 pF

  19. Measurement Results 800 -15 Fundamental Length Resonances -6 600 -16 Frequency (MHz) -7 25 mm bar -17 400 ~ 3.8 GHz - mm -8 E S21 (dB) 1 = × -18 2 r 200 -9 -19 600 700 800 900 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 30 mm bar 1 / mm -20 Fundamental Width Resonances -21 120 130 140 150 160 Frequency (MHz) Frequency (MHz)

  20. Second Round L-Bar 10 mm x 5 mm device showing length and width modes -40 -50 S21 Magnitude (dB) -60 -70 -80 110 100 90 Phase (degrees) 80 70 60 100 200 300 400 500 600 700 800 900 1000 Frequency (MHz)

  21. Fit to Model S21 data from 10mm x 5mm device • Parasitics modeled as • port capacitance and • resistance • BVD circuit parameters • R= 35 kW • L= 1 mH • C=0.047 fF • C0=12.7 fF • Q of ~125

  22. Metal-Oxide-Silicon Structures 0 -20 -40 S21 Magnitude (dB) -60 -80 -100 0 100 200 300 400 500 600 700 800 900 1000 200 100 Phase (degrees) 0 -100 -200 0 100 200 300 400 500 600 700 800 900 1000 Frequency (MHz)

  23. Glass Substrate OP6 on Glass • OP6 fit parameters: • pure open to ground • 1.43fF thru capacitance -60 S21 Magnitude (dB) -80 data simulation -100 0 500 1000 1500 2000 2500 3000 150 100 Phase (degrees) 50 0 0 500 1000 1500 2000 2500 3000 Frequency (MHz)

  24. Glass Substrate OP1 on Glass • OP1 fit parameters: • pure open to ground • 2.6fF thru capacitance -60 S21 Magnitude (dB) -80 data simulation -100 0 500 1000 1500 2000 2500 3000 150 100 Phase (degrees) 50 0 0 500 1000 1500 2000 2500 3000 Frequency (MHz)

  25. Conclusions • Filter designs will be implemented on upcoming mask layout. Mechanically coupled device will be used. • An accurate model of parasitics is vital for obtaining useful device measurements. • Ongoing work to define explanation for the 100 MHz resonance on silicon substrate, and the wideband phase noise

  26. Acknowledgements Draper Engineering Amy Duwel, David Carter, Doug White Draper Fellows Paul Calhoun, Luke Hohreiter Draper Program Manager James Sitomer Acknowledgements: Draper:Connie Cardoso, Mert Prince, Mark April, Mark Mescher and Mathew Varghese MIT:Prof. Charles Sodini DARPA: Contract # DAAH01-01-C-R204

  27. S-parameters - V = i S i j + V = ¹ V 0 , k j j k

  28. Z-parameters V1 = Z11I1 + Z12I2 V2 = Z21I1 + Z22I2

  29. Two-port p model ( ) ( ) + + Z Z Z Z Z Z Z Z = = = a b c a c c a b Z Z Z 11 12 22 + + + + + + Z Z Z Z Z Z Z Z Z a b c a b c a b c Z = Z11Z22-Z122 Z Z Z = = = Z Z Z a b c Z - Z Z Z - Z 22 12 12 11 12

  30. Transformed Zb Impedance Data Zb Magnitude and Phase 3 10 |Zp| 2 10 Impedance Magnitude (W) 1 10 |Zs| 0 10 fs fp 1.5 2 2.5 3 2 1 Impedance Phase (radians) 0 -1 -2 1.5 2 2.5 3 Frequency (GHz) 1 = = w 2 π f s s LC C = = + w 2 π f w 1 p p s C 0 R = » Z R s + 1 j w RC s 0 1 - j w RC 1 p 0 = » Z p 2 2 2 2 w RC w RC p 0 p 0

  31. BVD Model Fitting Zb Magnitude and Phase 60 50 40 30 Impedance Magnitude (dB) data data 20 model 10 0 2 1 0 Impedance Phase (radians) - 1 - 2 1.5 2 2.5 3 Frequency (GHz) R = 2.76 W, L = 91.6 nH, C = 0.061 pF, C0 = 1.54 pF

  32. Filter Design Constraints Constraints placed on equivalent circuit parameters by bar geometry: • Q assumed to be a function of the process and static • Two degrees of freedom, l and w/t • Resonant frequency fixes l uniquely • For a given frequency, the other degree of freedom controls the “impedance level” • C/C0 fixed by piezoelectric materials parameters

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