Memcapacitive elements for cognitive devices


Neuromorphic computing devices aim to mimic biological systems and are expected to dramatically improve performance and efficiency, enabling the development of advanced information technology, including complex data analysis and pattern recognition. Brain synapses can be emulated by memristors, displaying a reversible and non-volatile electrical resistance change upon the application of electrical stimulus. Other potential applications of memristors include nanoelectronic memories and logic gates. Memristive behavior is ubiquitously found in transition metal oxides, including perovskite manganites. Proposed memristive mechanisms for metal/manganite systems include the modulation of metal/insulator Schottky barriers due to oxygen vacancies (OV) drift-diffusion, or the interfacial redox reaction occurring when a reactive electrode (Ti or Al) is used. In the former case, the movement of a small number of OV within the manganite is usually assumed, and oxygen exchange with the environment is neglected. Alternatively, a robust memristive effect can be anticipated for perovskites displaying topotactic redox ability, i.e. the capability of reversibly storing and releasing oxygen without structural change. In this case, the memristive effect would rely on the electrical switch between oxidized and reduced phases with different electrical conductivities. In this scenario, significant exchange of oxygen with the surrounding atmosphere can be expected.

Memcapacitance –non-volatile change of a device capacitance, C, upon electrical stress- is an additional functionality of memristors that has scarcely been explored. Proposed mechanisms include creation and annihilation of conducting nanofilaments, Schottky barriers modulation or changes in the oxide permittivity upon OV electromigration. While applications for memcapacitance, including neuromorphic computing devices, have been proposed, the interest in this phenomenon has been hampered by the small reported performance to date (C_HIGH/C_LOW ≤ 10). Nielen et al. reported that associated capacitive networks, suitable for efficient pattern recognition, can be build from cells able to switch their capacitance between C_HIGH and C_LOW, where the device computing capability scales with C_HIGH/C_LOW ratio[24]. This evidences the high technological interest of novel memcapacitive systems with large response.

Rubi’s group recently showed that the interface between the perovskite manganite with topotactic redox ability La0.5Sr0.5Mn0.5Co0.5O3-δ (LSMCO, 0 ≤ δ ≤ 0.62, p-type) and Nb:SrTiO3 (NSTO, 0.05 wt%, n-type) behaves as a switchable n-p diode with memristive and giant memcapacitive behavior. Memcapacitance figures were CHIGH/CLOW ~ 10^4 for the NSTO/LSMCO interface and > 300 for the complete NSTO/LSMCO/Pt device, that is a factor >30 in comparison with already reported devices. The multi-mem behavior is related to the electrical switch between LSMCO oxidized and reduced phases, which produce large changes in the donor/acceptor balance at the NSTO/LSMCO interface. However, it was observed that during the electroforming process a strong O2 release takes place, producing structural damage on the devices. This imposes some limitations to the reliability and miniaturization possibilities of these devices. The visit intends to explore multi-mem LSMCO-based devices with engineered nanostructures that include by-design channels for easy oxygen migration in and out of the device, in order to avoid the damage linked to the forming process and ease their integration in practical neuromorphic circuits.





Prof. dr. B. Noheda

Verbonden aan

Rijksuniversiteit Groningen, Faculty of Science and Engineering (FSE), Zernike Institute for Advanced Materials


15/12/2019 tot 15/03/2020