  This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on
characterize resistance switching (RS), polarization rotation (PO) and surface
potential changes in copper doped ZnO (ZnO:Cu) thin films. The bipolar RS
behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PO
with almost 180{\deg} phase angle is confirmed by using the vertical and
lateral Piezoresponse Force Microscopy (PFM). In addition, it elucidates that
obvious polarization rotation behavior can be observed in the sample with
increasing Cu concentration. Furthermore, correlation of the RS behavior with
PO behavior has been studied by performing various mode SPM measurements on the
same location. The electric field resulted from the opposite polarization
orientation are corresponded to the different resistance states. It is found
that the region with the polarization in downward direction has low resistance
state (LRS), whereas the region with upward polarization has high resistance
state (HRS). In addition, the Piezoresponse Force Spectroscopy (PFS) and
Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the
existence of the built-in field due to the uncomplemented polarization may
affect the depletion region and hence contribute to the RS behavior. In
addition, Kelvin Probe Force Microscopy (KPFM) results show that, when
ZnO-based thin films is subjected to negative and then followed by positive
sample bias, injection charge limit current is dominated.
