Memcapacitive characteristics defined to be a memorized capacitance change has been recently suggested and experimentally demonstrated. Di Ventra et al. noted that the memcapacitive characteristics involve the capacitance change in metal-oxide resulting from microscopic geometry change or history-dependent permittivity change [1]. Wang et al. reported the memcapacitive characteristics in ionic transport through SiO₂ conical nanopore in KCl solution caused by redistribution of mobile ions [2]. We previously reported the analog memcapacitive characteristics in pn junction diode structures [3]. The pn heterojunction with the assembly of n-type Fe₂O₃ nanoparticles having Pt core (called Pt-Fe₂O₃ core-shell nanoparticles) on p⁺-Si substrate exhibited gradually changing capacitance as repeating the application of voltage with respect to the polarity of voltage. The analog memcapacitive characteristics also emulated the biological synaptic potentiation and depression motions, which is indicative of potential application to neuromorphic devices as well as analog nonvolatile memory and circuits. Since the memcapacitive phenomenon exhibits the memorized capacitance change, the memcapacitor has a potential to modulate the forward and reverse current in diode structure through altering the barrier height and depletion width at the interface.

Also, the memcapacitance can modulate the drain current in MOSFETs and TFTs as variable gate stack capacitor, named memcapacitor, which gives the functions of memory, logic, neuromorphic operation, and so on. In this presentation, we discuss the memcapacitive characteristics in metal-oxide-semiconductor (MOS) capacitor structure consisting of reactive electrode (Mo, Al) and hafnium oxide (HfO_X) on n-type Si and indium-gallium-zinc-oxide (IGZO) semiconductor substrates. The capacitance-voltage curves exhibited sequentially changing capacitance as repeating the voltage sweeps. The saturation capacitance was decreased as repeating +V application, while the depletion capacitance was barely changed as –V application. Also, the capacitance-time curves disclosed the same tendency of capacitance change. On the other hand, the MOS structure with inert electrode (Pt) did not show the capacitance change. These memcapacitive behaviors were induced by the migration of oxygen ions between reactive electrodes (Mo, Al) and HfO_X, which modulated the permittivity and effective capacitor area. These results demonstrated the memcapacitive characteristics in MOS structure through voltage-driven oxygen migration for the application to memory, logic, and neuromorphic devices.

[1] M. Di Ventra, Y. V. Pershin, and L. O. Chua, Proc. IEEE 97 1717 (2009).

[2] D. Wang, M. Kvetny, J. Liu, W. Brown, Y. Li, and G. Wang, J. Am. Chem. Soc. 134,  3651 (2012).

[3] Y. J. Noh, Y.-J. Baek, Q. Hu, C. J. Kang, Y. J. Choi, H. H. Lee, and T.-S. Yoon, IEEE Trans. Nanotechnol. 14, 798 (2015)