Presentation on theme: "Piezoelectric Characterization in an AFM Joe T. Evans, Jr, Radiant Technologies, Inc."— Presentation transcript:
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 Radiant has an established process for thin PZT film capacitors with platinum electrodes, top glass passivation, and chrome/gold metal interconnect (not shown). Silicon wafer Half of a micrometer of Silicon Dioxide as a foundation One half of a micrometer of PZT, TiOx, & glass as protection Top Electrode Bottom Electrode Ferroelectric material
4 20/80 PZT Typical hysteresis loop for Radiant 0.26 20/80 PZT with platinum electrodes.
5 Reference Process The reference is fabricated without the ILD passivation layer to allow electrical access directly to the top electrode. Silicon wafer Top Electrode Bottom Electrode Ferroelectric material
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 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. Top view COMMON CAP A CAP BCASE Cap A Cap B Common TO-18
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 In the image above, the rim outside the poled region is virgin and was not poled in the opposite direction. Using a conductive tip, the exposed PZT over bottom electrode can be poled UP or DOWN with the application of a bias voltage.
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 Electrical Connection 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. Cap A Cap B Common TO-18 PFM Stimulus Signal Bottom electrode
16 Electrical Connection 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. Cap A Cap B Common TO-18 PFM Stimulus Signal Bottom electrode
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 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. Polarization Tester RETURN SENSOR DRIVE Insulator Chuck Conductive Tip AFM A wire must run directly between system grounds. AFM Output Signal
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 d 33 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.