  We report the first direct measurements of the micro scale resistance profile
between the terminals of a two terminal symmetric thin film Pr0.7Ca0.3MnO3
electrical pulse induced resistance change device composed of a Pr0.7Ca0.3MnO3
active layer. The symmetric device is one in which the electrode shape, size,
composition, and deposition processing are identical. We show that under
certain limitations of pulse switching voltage, such a symmetric electrical
pulse induced resistance change device can exhibit either no net device
resistance switching at room temperature, or bipolar switching with the
resistance hysteresis curve exhibiting a "table leg" structure. The resistance
measurements are made using surface scanning Kelvin probe microscopy, which
allows for the measurement of the profile of resistance from one electrode,
across the Pr0.7Ca0.3MnO3 material and into the second electrode, both before
resistance switching and after switching. The results show that resistance
switching in the symmetric device occurs primarily in the interface region
within about 1 to 3 micron of the electrical contact surface. Resistance
switching is also observed in the bulk Pr0.7Ca0.3MnO3 material although at a
lower level. Symmetry considerations for a two terminal symmetric device that
can switch resistance are discussed, and the data reported here is consistent
with the symmetric model previously developed.
