Neuromorphic integration and real-time programmability of temporally-coded phase-change plasmonic platforms for on-chip multilevel optical memory and adaptive logic systems

Abstract

This research reports the operation, architecture of a neuromorphic-compatible and real-time, programmable optical memory device, through temporally encoded femtosecond laser excitation of phase-change plasmonic nanomaterials. High-quality Ge₂Sb₂Te₅ (GST) thin films with sub-nanometer roughness (0.46–0.61 nm) were fabricated over rigid substrates using RF-magnetron sputtering that provided a smooth phase transition. Bowtie antennas produced under electron beam lithography showed a local maximum electric field enhancement of |E/E₀| ≈ 18.2, with resonance peaks at wavelengths of ∼1270 nm. The amorphous, partially crystalline, and crystalline state transitions using a femtosecond laser, leading to reflectance modulations of 8.5–35.2 percent, were used to achieve 2-bit memory encoding (00–11) on a stable basis. Electrical characterization showed single-crystal conductivity deviations of more than four orders between the states, with switching times less than 180 ps measured by pump-probe. The finite-Difference Time-Domain (FDTD) and COMSOL simulations verified the photothermal triggered efficient activation and interface-limited crystallization with an Avrami exponent of ∼2.0 and the thermal hotspot temperature of ∼465 K. The write/erase drift was less than 5 percent at over 10,000 write/erase cycles, and optical logic gates (AND, OR, XOR) success rates of 97–100 percent were obtained. This system integrates memory and logic on one nanoscale platform and is reconfigurable, high-density, ultrafast, and low-power, with potential scalability to in-memory photonic computing and neuromorphic applications.