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Piezo Responce Force Microscopy

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Piezo Responce Force Microscopy

  1. 1. PiezoelectricCharacterization in an AFM Joe T. Evans, Jr, Radiant Technologies, Inc. Radiant Technologies, Inc.
  2. 2. Introduction• Radiant has developed a special packaged die containing thin PZT film capacitors constructed to aid piezoelectric characterization in an AFM.• The capacitors have exposed top electrode and exposed PZT surfaces over bottom electrode to allow PFM characterization.• The devices may also be used to execute more conventional piezoelectric measurements such as the butterfly loop.• All of the characterization techniques that may be executed on one of these reference devices will be described in the following presentation. Radiant Technologies, Inc. 2
  3. 3. Foundation Process One half of a micrometer of PZT, Top Bottom TiOx, & glass as Electrode Ferroelectric Electrode protection material Half of a micrometer of Silicon Dioxide as Silicon wafer a foundation• Radiant has an established process for thin PZT film capacitors with platinum electrodes, top glass passivation, and chrome/gold metal interconnect (not shown). Radiant Technologies, Inc. 3
  4. 4. 20/80 PZT 80 P o la r iz a tio n (µ C /c m 2 ) 70 60 50 40 30 20 10 0 -1 0 -7 .5 -5 .0 -2 .5 0 .0 2 .5 5 .0 7 .5 V o lt a g e• Typical hysteresis loop for Radiant 0.26µ 20/80 PZT with platinum electrodes. Radiant Technologies, Inc. 4
  5. 5. Reference Process Top Bottom Electrode Ferroelectric Electrode material Silicon wafer• The reference is fabricated without the ILD passivation layer to allow electrical access directly to the top electrode. Radiant Technologies, Inc. 5
  6. 6. The Reference DieThe completed die has multiple capacitors ranging from10µx10µ up to 100,000µ2. The film is 0.26µ 20/80 PZT. Radiant Technologies, Inc. 6
  7. 7. PackagingThe die is mounted on a TO-18 transistor header without a lid. Thebottom electrode is bonded to the COMM pin. Any of the othercapacitors may be bonded to the other two free pins. Radiant Technologies, Inc. 7
  8. 8. Packaging TO-18 Cap A Common Cap B Top view COMMON CAP A CAP B CASEThe TO-18 package provides a convenient format for handling andconnecting to the integrated capacitors. The packages shown abovehave lids. The PFM references do not. Radiant Technologies, Inc. 8
  9. 9. Mounted in the AFM• The header (package without a lid) can be soldered to an experiment board or placed in a socket for alignment under the AFM cantilever. Radiant Technologies, Inc. 9
  10. 10. Electrical ConnectionWith a conductive cantilever tip, the PZT over the bottom electrodewithout a top electrode my be scanned and poled. Radiant Technologies, Inc. 10
  11. 11. PFM of Un-electroded PZTThe un-electroded PZT over bottom electrode as made exhibits thetheoretical distribution of 50:50 polarization orientation. Radiant Technologies, Inc. 11
  12. 12. PFM of Un-electroded PZTThe un-electroded PZT over bottom electrode as made exhibits thetheoretical distribution of 50:50 polarization orientation. Radiant Technologies, Inc. 12
  13. 13. PFM of Un-electroded PZTUsing aconductive tip,the exposedPZT overbottomelectrode canbe poled UP orDOWN withthe applicationof a biasvoltage.In the image above, the rim outside the poled region is virgin andwas not poled in the opposite direction. Radiant Technologies, Inc. 13
  14. 14. PFM of Electroded PZTThe electroded PZT may be electrically stimulated either with aconductive tip or through one of the TO-18 package pins. Radiant Technologies, Inc. 14
  15. 15. Electrical Connection TO-18 Bottom electrode Cap A Common Cap B PFM Stimulus SignalThe common is the bottom electrode connection. The PFM signalcan be applied to one of the capacitor top electrodes through apackage pin. In this situation, the cantilever tip providesdisplacement information only. Radiant Technologies, Inc. 15
  16. 16. Electrical Connection TO-18 Bottom electrode PFM Stimulus Signal Cap A Common Cap BThe common is the bottom electrode connection. The PFM signalcan be applied to one of the capacitor top electrodes through apackage pin. In this situation, the cantilever tip providesdisplacement information only. Radiant Technologies, Inc. 16
  17. 17. PFM of Electroded PZTPhase maps of the same region poled UP and DOWN yieldsinformation about the presence and distribution of defects. Radiant Technologies, Inc. 17
  18. 18. PFM of Switching Polarization 80 70 60 P o la r iz a tio n (µ C /c m 2 ) 50 40 30 20 10 0 -10 -7 .5 -5 .0 -2 .5 0 .0 2 .5 5 .0 7 .5 V o lt a g eAll of the new PFM tools may be applied to the reference. Radiant Technologies, Inc. 18
  19. 19. PFM of Switching Polarization Asylum Research tested a new software protocol to capture this movie. The data took three hours to collect. The software protocol used landmark recognition to correct any X:Y drift of the stage between scans. Radiant Technologies, Inc. 19
  20. 20. Reference ApplicationsWith its high signal-to-noise ratio, a reference may be usedfor a variety of applications: • Activation at less than 10 volts. • Verification of equipment operation • Verification of procedures • Evaluating test procedures on a known-good sample • Materials and polarization switching studies Radiant Technologies, Inc. 20
  21. 21. Other Measurements AFM Output Signal AFMBy connecting the Z-output of an ConductiveAFM to a polarization tester, a large Tiparray of other tests may be executedto parallel the PFM measurements. Polarization Tester SENSOR Insulator DRIVE RETURN Chuck A wire must run directly between system grounds. Radiant Technologies, Inc. 21
  22. 22. Butterfly Loop1.0µ PNZT with platinum electrodes, shown above, movesapproximately 15 Angstroms at 20 volts. The 0.26µ 20/80 PZT isexpected to move approximately 3 Angstroms at 9 volts. Radiant Technologies, Inc. 22
  23. 23. Electrical Properties Hysteresis Parameters 50 40 uC/cm^2, uA/cm^2, uF/cm^2 30 20 10 Rhyst 0 -6 -4 -2 0 2 4 6 SW CV*10 -10 nSW CV*10 -20 SW IV*2.5 -30 nSW IV*2.5 -40 Volts• Using the AFM as a probe station, the polarization, remanent polarization, small signal capacitance, and leakage vs voltage may be measured on the same sample as are the piezoelectric measurements. Radiant Technologies, Inc. 23
  24. 24. Conclusion• It is now possible to measure all electrical and piezoelectric properties on a single capacitor. – Polarization hysteresis – Small signal capacitance hysteresis – Current vs Voltage – Butterfly loop – Small signal displacement – PFM amplitude and phase maps – PFM d33 loop• Measurement and comparison of these measurements on a single sample will improve our understanding of the nature of piezoelectric materials. Radiant Technologies, Inc. 24
  25. 25. AcknowledgementsAn Asylum Research MFP-3D™ AFM with an Arc2™ controllerwere used to capture the images in this presentation. Radiantwould like to acknowledge Asylum Research and its employees fortheir assistance in this work. Radiant Technologies, Inc. 25

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