Material Design Strategy for Enhancement of Readback Signal Intensity in Ferroelectric Probe Data Storage

Ferroelectric probe data storage (FPDS) based on scanning nonlinear dielectric microscopy is expected as a next-generation data storage method with its large potential for improvement of the recording density. However, this novel method has a problem of low reading speed. To overcome this problem, a novel ferroelectric recording medium with large nonlinear permittivity is required because this data storage method uses the nonlinear dielectric response induced by small-amplitude ac bias to detect the bit data recorded in the form of polarization direction. Therefore, this article discusses nonlinear permittivity enhancement from the viewpoint of data storage application in the framework of the phenomenological theory. We reveal that the Curie-point control is one of the key techniques in material design for FPDS because nonlinear permittivity increases precipitously as the Curie temperature is approached, as with the linear permittivity and piezoelectric constants. A similar conclusion is also obtained through actual measurements of nonlinear permittivity in LiTaO₃ single crystals. On the other hand, we also reveal that there is a tradeoff relationship between nonlinear permittivity and polarization stability. To avoid this undesirable situation in data storage applications, pinning-site control will also be important. We also propose to employ a double-layer structure in the ferroelectric recording media for further improvement.