Heat Assisted Ferroelectric Reading for High Speed Ferroelectric Probe Data Storage

We previously proposed ferroelectric data storage that uses scanning nonlinear dielectric microscopy (SNDM), called SNDM probe memory, as a next-generation ultrahigh-density information recording method. We confirmed an extremely high recording density and high-speed writing using LiTaO₃ single crystal media [1][2]. <br/>However, since reading is based on the detection of very small nonlinear dielectric constants of ferroelectric materials using SNDM technique, slow playback speed (actually 2Mbps) hinders the practical use of SNDM probe memory [3]. <br/>To solve this problem, a material with a large nonlinear dielectric constant is required. Our basic experiments revealed that a nonlinear dielectric constant has an extremely large temperature dependence and is proportional to (T₀-T)^-3.5, where T is the medium temperature and T₀ is the Curie temperature[4]. This means that an increase in the nonlinear dielectric constant, which would enable ultrahigh-speed reading (Gbps or faster), can be easily obtained even in LiTaO₃ crystal by making T close to T₀. However, simply increasing the medium temperature closer to the Curie temperature under thermal equilibrium degrades the polarization retention characteristics. <br/>Therefore, we propose a heat-assisted ferroelectric reading (HAFeR) method that increases the reading speed while maintaining the polarization retention characteristics. This is achieved by locally heating the medium for a very short time at the data reading position using laser pulse irradiation. We conducted a basic experiment and confirmed that laser pulse irradiation increased the SNDM signal strength much more. <br/>We also discuss the relationship between the maximum number of laser irradiation pulses and the optical pulse width for a medium heated to 550 °C (equivalent to a reading speed of 5 Gbps).<br/>The proposed method overcomes the fundamental problems of next-generation ultrahigh-density ferroelectric data storage.<br/> <br/>References: <br/>[1] Kenkou Tanaka and Yasuo Cho, ”Actual information storage with a recording density of 4 Tbit/in.² in a ferroelectric recording medium”, Appl. Phys. Lett,Vol.97, 092901 (2010) .<br/>[2] Kenkou TANAKA, Yuichi KURIHASHI, Tomoya UDA, Yasuhiro DAIMON, Nozomi ODAGAWA, Ryusuke HIROSE, Yoshiomi HIRANAGA, and Yasuo CHO:“Scanning Nonlinear Dielectric Microscopy Nano-Science and Technology for Next Generation High Density Ferroelectric Data Storage”, Jpn. J. Appl. Phys, Vol.47, 3311 (2008).<br/>[3] Yoshiomi Hiranaga, Tomoya Uda, Y. Kurihashi, H. Tochishita, M. Kadota and Y. Cho, “Nanodomain Formation on Ferroelectrics and Development of Hard-Disk-Drive-Type Ferroelectric Data Storage Devices”, Jpn.J.Appl. Phys. Vol.48, 09KA18 (2009).<br/>[4] Yoshiomi Hiranaga and Yauo Cho, “Material Design Strategy for Enhancement of Readback Signal Intensity in Ferroelectric Probe Data Storage”, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, Vol.68, 859 (2021).