Critical Impact of Gate Dielectric Interfaces on the Contact Resistance of High-Performance Organic Field-Effect Transistors

Extensive research on organic field-effect transistors (OFETs) performed to date investigated separately the electronic contact and the gate dielectric interfaces but rarely probed the relation between the two. In this report, the strong impact of the gate dielectric on the contact resistance (R-c) is revealed. With the same semiconductor dioctylbenzothienobenzothiophene (C8-BTBT) and the same device configuration, the R-c value varies greatly from 10 to 66 k Omega.m depending on the gate dielectric interfaces. Also, the gate-voltage dependency of R-c exhibits an unexpectedly large discrepancy when different dielectrics are used. Intuitive comprehension points to the possibility that the gate dielectric interface affects the morphology of semiconductor and thus the charge injection. However, from microstructure study, albeit the semiconductor film exhibits structural defects on certain dielectrics, the impact on the injection is not crucial. Instead, bias-stress test correlates well with the contact resistance on different dielectric interfaces. At a quantitative level, gate-voltage-dependent R-c can be described by taking into account the different charge trapping induced by the gate dielectrics. The origin of the varied R-c is thus attributed to the trapped charges, which screen the gate field and reduce the carrier mobility simultaneously. A general method is proposed to examine whether the charge injection is significantly influenced by the charge trapping effect due to the gate dielectrics.