Nanotribology and nanomechanics of AFM probe-based data recording technology

Abstract

With the advent of scanning probe microscopes, probe-based data recording technologies are being developed for ultrahigh areal density recording, where the probe tip is expected to be scanned at velocities up to 100 mm s −1. In one technique, a conductive atomic force microscope (AFM) tip is scanned over a phase change chalcogenide medium and phase change is accomplished by applying either a high or low magnitude of current which heats the interface. Another technique is ferroelectric data storage, where a conducting AFM tip is scanned over a lead zirconate titanate (PZT) film, a ferroelectric material. Ferroelectric domains can be polarized by applying short voltage pulses between the AFM tip and the bottom electrode layer that exceed the coercive field of the PZT film, resulting in nonvolatile changes in the electronic properties. Tip wear is a serious concern in both data storage methods. The understanding and improvement of tip wear, particularly at the high velocities needed and at high interface temperatures for high data rate recording, is critical to the commercialization of these data storage technologies. This paper presents a review of nanotribological and nanomechanical studies on the materials used in phase change and ferroelectric probe-based recording. Although this work is aimed at probe-based data recording, it is also relevant to the development of robust AFM probes and to the study of nanocontacts in general.

Ultrahigh Density Probe-based Storage Using Ferroelectric Thin Films

“…Another technological bottleneck is that the high data access rate requires a probe-tip sliding velocity on the order of 5 to 10 mm/ s, over a lifetime of 5 to 10 years, corresponding to probe-tip sliding distances of 5 to 10 km. The bit size, and thus the storage density, mainly depends on the radius of the probe-tip that is prone to rapid mechanical wear and dulling due to the high-speed contact mode operation of the system (Cho et al, 2006;Knoll et al, 2006;Bhushan et al, 2008;Gotsmann et al, 2008). This tip wear causes serious degradation of the write-read resolution over the device lifetime.…”

MEMS-based storage devices

“…MEMS-based storage devices have two main types of wear: (1) probe wear and (2) medium wear [72,73,74]. Note that MEMS-based storage devices have no rubbing surfaces, so that wear of bearing does not exits, unlike in disk drives.…”

“…Usually, wear is caused by friction at high load on the probe tip, high temperature, and high velocity. In addition, Bhushan et al [73] indicate that tribochemical reactions can take place. Likewise, the medium wears due to several factors including high temperature, and contact with the probe.…”

“…In these techniques a probe tip wears due to high temperature and high velocity. Bhushan et al [73] give an extensive study of the causes of wear in these two techniques. Probes and medium might be lubricated to reduce probe wear.…”

“…Based on the literature [72,73,74] and discussions with physicists, we assume the following in our work:…”