Effect of thickness of polymer electret on charge trapping properties of pentacene-based nonvolatile field-effect transistor memory

In this report, a set of pentacene-based organic field-effect transistor (OFET) memory devices using different thicknesses (ranged from 17.8 to 100.4 nm) of Poly (N-vinylcarbazole) (PVK) as charge trapping layers were fabricated, and the dependences of thickness on charge trapping behaviors were systematically investigated. As the thickness increased, the charge trapping capacity shows a Gaussian distributed growth behavior while the surface tunneling distance demonstrates the property of exponential decrease, which is ascribed to the synergistic effects of potential redistribution of trapped charge carriers and the co-existence of direct tunneling and Fowler–Nordheim (FN) tunneling. The optimum thickness (d_ot) to possess the most efficient charge trapping properties, which means a reasonably low programming voltage and high charge trapping capacity with good bias stress stability, is approximately 40 ± 5 nm. By calculating the threshold thickness (d_th) of PVK for an ultrathin memory, we proposed a model of superficial tunneling distance to deconstruct the continuous chargeable polymer electret-based OFET memory. Our work provided a quantitative evaluation method and can improve the understanding of charge trapping process from the aspect of electret thickness.