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

Abstract

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 (VTH) of OFETs continues to improve. However, the VTH shift of OFETs has always been an important problem restricting their practical applications. In this work, we observe that the VTH 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 VTH remains to a large extent, even after modifying the surface of the SiO2 dielectric using a hexamethyldisilazane (HMDS) self-assembled monolayer. This behavior of VTH 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.

Dissecting the Interplay between Organic Charge-Modulated Field-Effect Transistors and Field-Effect Transistors through Interface Control Engineering

“…In particular, V th is affected by two main factors: the intrinsic electric field generated by the permanent dipole of the dielectric surface and the electrochemical reaction between the semiconducting active molecules and the surface functional groups . Previous studies related to OFET devices indicate that dielectric surfaces with a strong electron affinity tend to preferentially attract electrons toward the interface region between the dielectric and active layers, preventing the accumulation of holes that balance the charge and negatively shift V th . − Therefore, regulating the surface potential of a dielectric is critical for modulating the charge and electrical performance of a device. The relationship between μ FET /μ OCMFET or V th and the surface potential was explored by collecting the secondary electron emission spectra of various SAM-controlled AlO x gate dielectrics, as shown in Figure a.…”