Observation of Large Threshold Voltage Shift Induced by Pre-applied Voltage to SiO₂ Gate Dielectric in Organic Field-Effect Transistors

Field-effect transistors based on organic semiconducting materials (OFETs) have unique advantages of intrinsically mechanical flexibility, simple preparation process, low manufacturing cost, and large-area preparation. Through the innovation of new material design and device structures, the performance of device parameters such as mobility, on-off current ratio, and the threshold voltage (V-TH) of OFETs continues to improve. However, the V-TH shift of OFETs has always been an important problem restricting their practical applications. In this work, we observe that the V-TH of polymer OFETs with the widely investigated device structure of a SiO2 bottom-gate dielectric is noticeably shifted by pre-applying a large gate voltage. Such a shift in V-TH remains to a large extent, even after modifying the surface of the SiO2 dielectric using a hexamethyldisilazane (HMDS) self-assembled monolayer. This behavior of V-TH can be ascribed to the charge trappings at the bulk of the SiO2. In addition, the generality of this observation is further proven by using two other conjugated polymers including p-type PDPP3T and n-type PTzNDI-2FT, and a similar trend is obtained.