Kazuo Sanada

Rewritable Capacitance Disk Memory with Ferroelectric-Semiconductor Structure

This paper presents a new rewritable capacitance disk memory with a ferroelectric-semiconductor structure. The ferroelectric film of the medium was poled in the perpendicular direction to generate depletion capacitance for data recording. Capacitance between the stylus head and the medium was detected for data reproduction. The amount of change in capacitance due to the poling direction showed that the recording density of this memory system could be more than 1 Gbit/cm2. Evaluation equipment was constructed for dynamic bit recording and reproduction, in which the mobile stylus head was in contact with the medium surface. It was confirmed that data bits with 0.4 µm spatial wavelength could be recorded and reproduced. In our experiment, recording density was mostly determined by the stylus size, and its limit was also estimated by the numerical simulation of ferroelectric semiconductor structure.

Noncontact Evaluation of Capacitance Disk Memory with Ferroelectric/Semiconductor Structure

Noncontact evaluation of capacitance disk memory with ferroelectric semiconductor (FS) structure was performed in order to avoid wear of the head and medium. Head-medium spacing was actively controlled using differential capacitance between the head and medium as the active feedback signal. Using this system, head-medium spacing could be stably controlled to be as low as 30 nm, which is less than that of a magnetic hard disk. Ferroelectric film of the medium was poled, which corresponded to recording in memory application, while head-medium spacing was kept constant using the active spacing control system. Change in capacitance due to poling direction, which corresponded to the reproduction signal in memory application, could be observed at the spacing below 100 nm. As a result, we confirmed that ferroelectric/semiconductor disk memory could function without head-medium contact. The surface image was also obtained using the capacitance signal while differential capacitance was kept constant.