Organic Synaptic Transistors and Printed Circuit Board Defect Inspection with Photonic Stimulation: A Novel Approach Using Oblique Angle Deposition.

This study introduces a photonic stimulation-based synaptic transistor utilizing oblique angle deposition (OAD) of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). While OAD enables advanced nanostructures, its application to organic materials remains largely unexplored. Here, the electrical characteristics and photoinduced trap behavior of obliquely deposited DNTT transistors are systematically investigated, successfully replicating key synaptic functions. OAD-controlled grain size and spacing in the DNTT channel yield distinct performance metrics compared to conventional devices. The introduced trap regions enable stable synaptic behavior across diverse gate voltage (V) conditions. By adjusting presynaptic photonic pulse intensity, duration, and repetition, a robust transition is achieved to long-term memory (LTM). The device further demonstrates reliable optoelectronic synaptic operation over 52 durability cycles. Concurrent photonic stimulation enables parallel potentiation-depression dynamics, enhancing processing speed and performance, highlighting its promise for next-generation neuromorphic computing. Its application is also showed in printed circuit board (PCB) defect inspection, successfully mimicking biological synapses under simultaneous photonic stimulation.