Buried Contouring PTCDI-C13 Layer for Interface Engineering in Dual-Function Optical Synaptic and Memory Transistors

We present a heterojunction based on the n-type organic semiconductor N,N'-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) with a PTCDI-C13/parylene/PTCDI-C13-layered structure, enabling dual functionality as both an optical synaptic and a memory transistor. The device exploits a buried contouring PTCDI-C13 layer, where the lower PTCDI-C13 and intervening parylene layers serve distinct functions in charge trapping and modulation. In memory mode, the buried PTCDI-C13 serves as a floating gate, while the parylene layer acts as a tunneling barrier, facilitating charge storage and controlled electron tunneling under combined optical and electrical stimulations. In synaptic mode, the thickness of the buried PTCDI-C13 dictates the surface roughness, which is transferred to the parylene layer, forming a textured interface with abundant charge trap sites that modulate the synaptic behavior. By tuning the PTCDI-C13 thickness, we controlled the interface roughness and trap density (nt), achieving optimal performance at 82 nm. The device successfully emulated synaptic plasticity and demonstrated transitions to long-term memory. To further verify its neuromorphic capabilities, our device achieved a recognition accuracy of 91.7% in a Modified National Institute of Standards and Technology-based classification simulation, successfully replicating biological synaptic behavior. Additionally, an electrocardiogram-based simulation demonstrated high classification accuracy while effectively processing dynamic, time-dependent signals. By reliably performing both static image recognition and dynamic biosignal processing, our device showcases its potential for real-time biomedical diagnostics, adaptive AI, and bioinspired computing applications.