Piezoelectric Characterization in an AFM

1. Piezoelectric Characterization in an AFM Joe T. Evans, Jr, Radiant Technologies, Inc.

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.

3. Foundation Process One half of a micrometer of PZT, TiOx, & glass as protection Bottom Electrode Top Electrode • Radiant has an established process for thin PZT film capacitors with platinum electrodes, top glass passivation, and chrome/gold metal interconnect (not shown). Ferroelectric material Half of a micrometer of Silicon Dioxide as a foundation Silicon wafer

4. 20/80 PZT • Typical hysteresis loop for Radiant 0.26 20/80 PZT with platinum electrodes.

5. Reference Process Bottom Electrode Top Electrode Ferroelectric material Silicon wafer • The reference is fabricated without the ILD passivation layer to allow electrical access directly to the top electrode.

6. The Reference Die The completed die has multiple capacitors ranging from 10x10 up to 100,0002. The film is 0.26 20/80 PZT.

7. Packaging The die is mounted on a TO-18 transistor header without a lid. The bottom electrode is bonded to the COMM pin. Any of the other capacitors may be bonded to the other two free pins.

8. TO-18 Top view COMMON CAP A CAP B CASE Cap A Common Cap B Packaging The TO-18 package provides a convenient format for handling and connecting to the integrated capacitors. The packages shown above have lids. The PFM references do not.

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.

10. Electrical Connection With a conductive cantilever tip, the PZT over the bottom electrode without a top electrode my be scanned and poled.

11. PFM of Un-electroded PZT The un-electroded PZT over bottom electrode as made exhibits the theoretical distribution of 50:50 polarization orientation.

12. PFM of Un-electroded PZT The un-electroded PZT over bottom electrode as made exhibits the theoretical distribution of 50:50 polarization orientation.

13. PFM of Un-electroded PZT Using a conductive tip, the exposed PZT over bottom electrode can be poled UP or DOWN with the application of a bias voltage. In the image above, the rim outside the poled region is virgin and was not poled in the opposite direction.

14. PFM of Electroded PZT The electroded PZT may be electrically stimulated either with a conductive tip or through one of the TO-18 package pins.

15. TO-18 Cap A Common Cap B Electrical Connection Bottom electrode PFM Stimulus Signal The common is the bottom electrode connection. The PFM signal can be applied to one of the capacitor top electrodes through a package pin. In this situation, the cantilever tip provides displacement information only.

16. TO-18 Cap A Common Cap B Electrical Connection Bottom electrode PFM Stimulus Signal The common is the bottom electrode connection. The PFM signal can be applied to one of the capacitor top electrodes through a package pin. In this situation, the cantilever tip provides displacement information only.

17. PFM of Electroded PZT Phase maps of the same region poled UP and DOWN yields information about the presence and distribution of defects.

18. PFM of Switching Polarization All of the new PFM tools may be applied to the reference.

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.

20. Reference Applications • With its high signal-to-noise ratio, a reference may be used for 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

21. Other Measurements AFM Output Signal AFM By connecting the Z-output of an AFM to a polarization tester, a large array of other tests may be executed to parallel the PFM measurements. Conductive Tip Polarization Tester Insulator SENSOR DRIVE RETURN Chuck A wire must run directly between system grounds.

22. Butterfly Loop 1.0 PNZT with platinum electrodes, shown above, moves approximately 15 Angstroms at 20 volts. The 0.26 20/80 PZT is expected to move approximately 3 Angstroms at 9 volts.

23. Electrical Properties • 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.

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.

25. Acknowledgements An Asylum Research MFP-3D AFM with an Arc2 controller were used to capture the images in this presentation. Radiant would like to acknowledge Asylum Research and its employees for their assistance in this work.