Memristive synaptic devices which can be reliably programmed to a continuum of resistance states at low energy cost (<100pJ per write operation is competitive with CMOS) are highly desirable for neuromorphic computing. Nevertheless, most memristors to date can be programmed to only a few resistance states (typically 2-3). In addition, despite recent progress in demonstrating memristor-based neuromorphic arrays, no architecture to date can operate with the projected energy efficiency while maintaining high accuracy. For example, filament forming metal-oxide (FFMO) and phase-change memristors (PCM) suffer from excessive write noise and non-linearities, mostly due to their stochastic switching mechanism.
Here, we demonstrate polymer-based synaptic devices based on organic mixed-ionic-electronic-conductors (MIECs) where the resistance of a transistor-like channel can be continuously tuned (over >100 distinct states) by low-voltage (<1V) potentiation/depotentiation pulses, enabling low-power operation (~pJ range). These devices show extremely low write noise (<1%) and close-to-symmetric resistance tunning in response to pulsed inputs. Reversible switching relies on controlled insertion/extraction of ions which couple to conjugated polymer chains. The ions dope/de-dope the transistor-like channel, altering its resistance.
High resistances are instrumental for building large neuromorphic arrays, and we demonstrate polymer-based synaptic devices which operate at resistances of the order ~10MΩ when scaled down to ~10µm dimensions. We show that the resistance switching mechanism above is general and can be exploited in several organic MIECs. As such, polymer-based synaptic devices offer a promising and yet to be fully exploited alternative to conventional memristive devices.