On intermittent-contact mode sensing using electrostatically-actuated micro-cantilevers with integrated thermal sensors

Ultrahigh data storage densities on the order of 1 Tb/in
²
or higher can be achieved by using scanning-probe microscopy techniques to write, read back and erase data on very thin polymer films. The written information is usually read back in contact mode because it is simple to implement and analyze. However, the physical contact between the probe-tip and the media leads to wear of the tip due to abrasive and adhesive forces. Tip wear has adverse effects on the read and write performance at ultrahigh data storage densities. In this paper, an intermittent-contact mode read operation is presented that has been developed to improve the durability of probe-based devices by significantly reducing tip wear. The electrostatic pull-in force between the cantilever and the silicon substrate underneath the polymer medium is used as the actuating force for intermittent-contact operation. The cantilever response is highly nonlinear because of the large adhesion between the tip and the soft polymer medium, which forces the cantilever to remain in contact with the medium for significant fraction of its periodic orbit. For fast and noninvasive reading a feedback controller is designed to ensure reliable small-amplitude operation. Significant improvements in both of the read-lifetime and the rate of signal amplitude-loss were achieved using the intermittent-contact read method compared with the contact read method because of substantial reduction in tip wear rate.