Resistive switching in tunable Pt–C granular metals

The charge-transport properties of nanogranular metals, comprising arrays of metallic nanoparticles embedded in an insulating matrix, are governed by the average tunneling conductance g between neighboring particles. In the weak-coupling limit (g ≪ 1), a transition from a high-resistive state (HRS) to a low-resistive state (LRS) occurs for bias voltages exceeding the global Coulomb-blockade threshold Vt. In this work, we investigate the charge-transport properties of Pt–C granular metals fabricated by focused electron beam induced deposition, across a bias voltage range spanning from the low-voltage regime (V ≪ Vt) up to the global Coulomb-blockade threshold (V ∼ Vt). Current–voltage characteristics (I–V), measured between room temperature and 2 K, reveal ohmic behavior at low bias voltages and field-assisted ohmic conduction at intermediate biases. Approaching Vt, the I–V curve exhibits a steep, non-linear increase in current, indicative of an avalanche-like charge carrier multiplication process. Above Vt, ohmic behavior is again observed. The resistive switching mechanism is hysteretic, exhibiting distinct transition voltages for the HRS-to-LRS and LRS-to-HRS transitions. Temperature-dependent conductivity measurements for V ≪ Vt reveal transport characterized by correlated variable-range hopping (c-VRH), indicative of cotunneling. At higher bias voltages, a field-assisted c-VRH regime is observed at low temperatures, which culminates in an abrupt transition to a low-resistance state at Vt. Finally, as the coupling strength between particles in Pt–C can be precisely controlled via electron curing, the switching temperature between HRS and LRS is adjustable from a few Kelvin to 60 K.