Department of Applied Physics

Cognitive Computing

Using a variety of memristive electronic and optoelectronic oxide elements we emulate the functions of synapses and neurons in the brain.
Multilevel resistance switching and spike-timing dependent plasticity of a tunnel junction memristor

Energy efficiency, parallel information processing, and unsupervised learning make the human brain a model computing system for unstructured data handling. Different types of programmable resistors (memristors) integrated into an artificial neural network can be used to mimic essential brain functions. Our work focuses on tunnel junctions with ferroelectric tunnel barriers or active ionic interfaces and optoelectronic oxide films. We have demonstrated synaptic behaviors such as programmable synaptic weight, long and short-term potentiation and depression, paired-pulse facilitation and depression, and Hebbian and anti-Hebbian learning through spike shape and timing-dependent plasticity. Currently, we are working on the realization of artificial neurons and bioinspired optoelectronic tactile devices.

Representative Publications

1. Q.H. Qin, L. Äkäslompolo, N. Tuomisto, L. Yao, S. Majumdar, J. Vijayakumar, A. Casiraghi, S. Inkinen, B. Chen, A. Zugarramurdi, M. Puska, S. van Dijken. Resistive switching in all-oxide ferroelectric tunnel junctions with ionic interfaces. Advanced Materials 28, 6852 (2016).

2. N. Tuomisto, S. van Dijken, M. Puska. Tsu-Esaki modeling of tunneling currents in ferroelectric tunnel junctions. Journal of Applied Physics 122, 234301 (2017).

3. S. Majumdar, B. Chen, Q.H. Qin, H.S. Majumdar, S. van Dijken. Electrode dependence of tunneling electroresistance and switching stability in organic ferroelectric P(VDF-TrFE)-based tunnel junctions. Advanced Functional Materials 28, 1703273 (2018).

4. S. Majumdar, H.W. Tan, Q.H. Qin, S. van Dijken. Energy-efficient organic ferroelectric tunnel junction memristors for neuromorphic computing. Advanced Electronic Materials 5, 1800795 (2019).

5. H. Tan, S. Majumdar, Q. Qin, J. Lahtinen, S. van Dijken. Mimicking neurotransmitter release and long-term plasticity by oxygen vacancy migration in a tunnel junction memristor. Advanced Intelligent Systems 1, 1900036 (2019).

6. S. Majumdar, H. Tan, I. Pande, S. van Dijken. Crossover from synaptic to neuronal functionalities through carrier concentration control in Nb-doped SrTiO3-based organic ferroelectric tunnel junctions. APL Materials 1, 091114 (2019).

7. H.W. Tan, Q.Z. Tao, I. Pande, S. Majumdar, F. Liu, Y.F. Zhou, P.O.A. Persson, J. Rosen, S. van Dijken. Tactile sensory coding and learning with bio-inspired optoelectronic spiking afferent nerves. Nature Communications 11, 1369 (2020).

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