Vendredi 10 Fevrier 2023 à 11h00, Anouk Goossens donnera un séminaire sur le Memristive Memory Enhancement by Device Miniaturisation for Neuromorphic Computing.
Abstract :
Designing materials and devices for energy-efficient hardware is a crucial aspect for developing novel applications and for computing schemes beyond von Neumann. Devices on complex oxide platforms, such as SrTiO3 (STO), bring in functionalities that are relevant for this purpose.These functionalities are largely derived from the temperature and electric field dependence of its dielectric permittivity. As a result, such devices possess transport characteristics that can be controllably changed by external stimuli such as temperature, voltage, current, electric and magnetic fields, and spin-orbit torque. In this context, we have exploited the rich phase space, intrinsic to complex oxides, to build devices capable of brain-like physical computing. I will discuss two memristive device types, where tailoring of the energy landscape enables multistate resistance states.
The first work is based on interface based memristive Schottky devices on semiconducting Nb-doped STO (Nb:STO). These memristors require no forming process and show continuous conductance modulation akin to synapses[1] ; we have shown that this behaviour can be described by a power-law which can successfully be implemented as a learning algorithm[2]. Given that these memristors meet both hardware and software requirements, they serve as a strong candidate for material-based physical computing. The scalability of memristors is an important consideration for integration into novel architectures. For example, limitations in device stability, endurance and associated enhanced power of operation when device areas are reduced are major roadblocks in the successful implementation of filamentary memristors in large-scale architectures. In this work, we developed a reliable process to fabricate Co contacts on Nb:STO of variable device dimensions and performed electrical measurements on devices of areas spanning three orders of magnitude. We show the ability to achieve analogue switching with remarkably high resistive windows by downscaling, high endurance and low device and cycle variation integrated directly on a semiconducting platform. We were able to verify the results by measuring across a range of devices showing minimal device-to-device variation. By combining an ionic semiconductor possessing unconventional properties with an appropriate device design, local enhancement of the electric field around the devices’ edges tunes the dielectric constant and increases the concentration of defects leading to improved resistive switching.[3]
In the second type of devices, we utilise the crystal orientation and show that magnetic anisotropy in tailored SrRuO3 (SRO) ferromagnetic layers can be tuned to either exhibit a perfect or slightly tilted perpendicular magnetic anisotropy (PMA). We show that the strong magnetocrystalline anisotropy in SRO not only allows for the design of a perpendicular magnetic anisotropy in such devices but enables the tailoring of easy axes at controlled tilt angles from the surface normal, for probabilistic as well as deterministic switching, with relative ease.[4]
References :
1. Goossens, A., Das, A. & Banerjee, T. Electric field driven memristive behavior at the Schottky interface of Nb-doped SrTiO3. Journal of Applied Physics 124, 152102 (2018).
2. Tiotto, T. F., Goossens, A. S., Borst, J. P., Banerjee, T. & Taatgen, N. A. Learning to approximate functions using Nb-doped SrTiO3 memristors. Frontiers in neuroscience 14, 627276 (2021).
3. Goossens, A. et al. Unpublished 2022.
4. Goossens, A. S., Leiviskä, M. & Banerjee, T. Anisotropy and Current Control of Magnetization in SrRuO3/SrTiO3 Heterostructures for Spin-Memristors. Frontiers in Nanotechnology 3, 680468 (2021).
