Influence of Molecular Weight of Polymer Electret on the Synaptic Organic Field-Effect Transistor Performance

Chargeable polymer electret-based organic field-effect transistor (OFET) memory devices are attractive for intrinsically flexible artificial synapse. However, the effects of molecular weight (Mw) of polymer electret on the charge trapping properties, especially the implementation of synaptic functions, are not yet well-understood. In this work, the authors study pentacene-based synaptic OFET memory made from two different molecular weight polymer electrets, with poly(N-vinylcarbazole) (PVK) as the case study. Utilizing the synergistic effect of smooth surface morphology, higher polymer chain-end density and lower dielectric constant, OFET memory device with lower Mw PVK electret showed a larger memory window (28.2 V) and faster write speed (1 ms) compared to that with higher Mw PVK. Benefiting from its charge-trapping ability, the synaptic OFETs with lower Mw PVK delivered a better modulation of synaptic weight. The co-modulation of photonic and electric operations enabled the reconfigurable short-term plasticity and long-term plasticity (LTP) in lower Mw PVK devices, further leading to the STP-based emulation of visible color recognition and LTP-based neural network simulation. This work enlightens a detailed understanding of the molecular weight-dependent charge trapping behavior for the future integration of visible information sensing-memory-processing in optoelectronic OFET memory.