Platinum-coated probes sliding at up to 100 mm/s against lead zirconate titanate films for atomic force microscopy probe-based ferroelectric recording technology

Abstract

With the advent of scanning probe microscopes, probe-based data recording technologies are being developed for ultrahigh areal density. In alternative ferroelectric data storage, a conductive atomic force microscope (AFM) tip is placed in contact on a lead zirconate titanate (PZT) layer as the ferroelectric film. Ferroelectric domains can be polarized by applying short voltage pulses between the AFM tip and the bottom electrode that exceed the coercive field of the PZT layer, resulting in local, nonvolatile changes in the electronic properties of the underlying film. By monitoring the piezoelectric vibration of the ferroelectric film caused by an external ac voltage, the domain structure can be visualized. A degradation due to a voltage pulse to the PZT film occurs and is one reliability concern, called ferroelectric fatigue. Another important reliability concern is tip wear during tip-sample contact. The understanding and the improvement of tip wear, particularly at high velocities needed for high data rate recording, is critical to the commercialization of ferroelectric memories. In this study, wear experiments are performed using a Pt-coated tip sliding against a PZT layer at sliding velocities ranging from 0.1 to 100 mm/s. A silicon grating sample and software to deconvolute tip shape are used to characterize the change in the tip shape and evaluate the tip radius and its wear volume. The tip wear mechanism is dependent on the operating conditions. At velocities up to 1 mm/s, it is adhesive wear assisted with thermally activated stick slip and, at higher velocities, it is adhesive and impact wear. In wear life threshold experiments, the threshold reaches a smaller sliding distance at higher loads. In high-temperature experiments at 80 °C, the wear rate is high compared to that at 20 °C.