Quantized conductance behaviour observed in an atomic switch using triptycene-based polymers

A novel triptycene-based azo polymer (TBAP) was explored as a switching material in an atomic switch showing resistive change under voltage sweep and pulse. Current atomic force microscopy (C-AFM) measurements on a TBAP film on a Ag electrode revealed that a TBAP atomic switch shows volatile and nonvolatile switching, depending on the amplitude of the bias voltage and sweep cycles, in which low-resistance states are attributed to quantized conductance with integer multiples of a single atomic point contact in a Ag filament formed between a C-AFM tip and the Ag electrode. The switch also exhibited a longer retention time with increased conductance states. Switching time from high-resistance to low-resistance states was found to decrease exponentially with an increase in the amplitude of voltage pulses, implying that the nucleation of metal atoms is likely to be the rate-limiting process. Repeated voltage sweeping with varying interval times resulted in a transition from volatile to nonvolatile switching behaviours, mimicking the learning process of the human brain. These results indicate that the TBAP atomic switch has great potential for organic neuromorphic electronics.