August 18, 2010

Radiant has created a new product to support the exploding interest in piezoresponse force microscopy (PFM) among ferroelectric and piezoelectric materials researchers. The new product consists of a die of integrated scale thin ferroelectric film capacitors mounted on a TO-18 transistor package header without a lid. The capacitors are made without glass passivation, exposing the top electrodes and making possible stimulation of the capacitors using a conductive cantilever tip. The bottom electrodes for all of the capacitors connect to one pin of the package, making electrical connection to the device-under-test much simpler. At customer request, Radiant will bond wires between any two of the capacitor top electrodes and the free pins on the TO-18 package. This arrangement allows the piezoresponse force stimulus signal to drive the larger capacitors through the package instead of a conductive tip, allowing the testing of capacitors much larger than can be driven through a conductive AFM tip. Additionally, the die has large areas of exposed PZT over bottom electrode so nanoscale poling and piezoelectric measurments can be made directly on PZT grains.

The PFM test die is shown below

The reference has 2600 Angstroms of 20/80 PZT film with platinum electrodes. The metal traces and bond pads are in chrome/gold metallization. The die is mounted on a TO-18 package header which itself can be soldered to a PC board or mounted on a socket for easy placement under the AFM cantilever.

Once under the cantilever, a researcher can test the PZT under the top electrode platinum, which is only 500 Angstroms thick, or test the exposed PZT over bottom electrode.

Using an AFM alone, the researcher may execute the full suite of PFM-type measurements, including phase/amplitude scans or d33 hysteresis loops. Using a Radiant tester in conjuction with the AFM on a capacitor with a top electrode, the researcher can also measure the IV, the polarization hysteresis loop simultaneously with the large signal butterfly displacement loop , and the small signal capacitance and small signal displacement simultaneously.

Below is the phase plot an area of bare 20/80 PZT over bottom electrode poled using a conductive AFM cantilever tip. The grain boundaries of the film are clearly visible as artifacts in the poled region. Prior to poling, the phase histogram of this region showed a 50% split between "up" and "down" polarization as would be expected for untouched thin PZT film. The outside band of PZT in the image was not poled and is in virgin state.

The two images below are phase plots of the same 2µ x 2µ region of top electroded PZT. The images show opposing saturated polarization states. This capacitor had a total area of 10µ x 10µ and was driven with the piezoresponse stimulus signal through a pin of the TO-18 header.

Regions of polarization that are "stuck" are clearly delineated between the two images above.

The 2µx2µ capacitor area shown above was switched through its full hysteresis loop overnight, stopping at partially switched states to capture the phase and amplitude maps at each state. The movie below shows the phase map of the tested area during switching around the loop. Above the phase map is the histogram of the phase information displaying the distribution of polarization orientation in that 2µx2µ area as the loop progressed.

A PFM Reference from Radiant may be used for a variety of purposes. First, one may be used to verify the installation and operation of the PFM equipment using a known-good sample with strong signal response. Secondly, a PFM Reference may be used for training on the operating procedures of the AFM and PFM. Third, new measurement concepts or test procedures may be developed and tested on the reference before being used on the researcher's samples, again because the Radiant PFM Reference represents a known-good sample with strong signal, . Finally, the 20/80 PZT process at Radiant has been in use since 1990 with consistent results. Different references separated by time and lot will be similar if not the same. Therefore, a Radiant PFM Reference will serve as a stable platform for long term materials research studies of grain/domain/electrode/switching properties.

Please contact Michelle Bell at Radiant Technologies, Inc. (1-505-842-8007 / radiant@ferrodevices.com ) with questions about this new product.

Radiant would like to thank Asylum Research (www.asylumresearch.com) in Santa Barbara, CA for working in conjunction with Radiant on these Measurements.

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