Layered memristive and memcapacitive switches for printable electronics (original) (raw)

Novel computing technologies that imitate the principles of biological neural systems may o er low power consumption along with distinct cognitive and learning advantages 1,2. The development of reliable memristive devices capable of storing multiple states of information has opened up new applications such as neuromorphic circuits and adaptive systems 3,4. At the same time, the explosive growth of the printed electronics industry has expedited the search for advanced memory materials suitable for manufacturing flexible devices 5. Here, we demonstrate that solution-processed MoO x /MoS 2 and WO x /WS 2 heterostructures sandwiched between two printed silver electrodes exhibit an unprecedentedly large and tunable electrical resistance range from 10 2 to 10 8 combined with low programming voltages of 0.1-0.2 V. The bipolar resistive switching, with a concurrent capacitive contribution, is governed by an ultrathin (<3 nm) oxide layer. With strong nonlinearity in switching dynamics, di erent mechanisms of synaptic plasticity are implemented by applying a sequence of electrical pulses. Memristors were postulated as electrical resistance switches retaining a state based on the history of applied voltage and passed charge, followed by the introduction of the memcapacitor and meminductor 6. Inspired by Strukov's TiO 2 memristor concept 7 , a large class of metal oxides-along with less numerous halides, chalcogenides and organic polymers-have been studied as switching materials 3,4. Depending on the switching mechanism, these materials can be grouped into chemical switches, with anions or cations as mobile species producing a compositional gradient 8 , or physical switches, where only physical changes such as magnetic, ferroelectric, electron/hole trapping and phase-change processes are involved 3. State-of-the-art memristive devices exhibit programming times of nanoseconds, high switching ratios with multiple states, low energy consumption, high cycling endurance and retention times of several years 2,4. However, their flexible 9,10 , printable 11,12 and organic 13,14 counterparts show less impressive characteristics, with relatively high operating voltages above 2 V, small dynamic ranges limited to 10 2 , and insufficient electrical and mechanical reliability. Therefore, a strong need for high-performance memristors which fulfil the requirements imposed by system-in-foil technologies still remains. The emerging field of the characterization of two-dimensional (2D) materials has the potential to identify materials and composites with memory features that will outperform conventional bulk metal oxides. Layered transition metal dichalcogenides (TMDs) and transition metal oxides (TMOs) have attracted much attention