Vapor-deposited vertical organic field-effect transistors with optimized geometry for unrivaled transition frequencies (Conference Presentation)

Future flexible consumer electronic devices require powerful organic field-effect transistors (OFETs) to fulfill the demanding performance targets for, e.g., flexible RFID tags or active-matrix display driving. To achieve the required switching speed and current density (e.g. for display driving), it is firstly important to improve the charge carrier mobility of the organic semiconductors but secondly, it is also essential to reduce the channel length. In this context, optimizing the geometry of OFETs led to the development of novel approachs for vertical organic field-effect transistors (VOFETs) [1] where the vertical channel can be scaled down to the range of <50 nm. Here we present VOFETs produced by a new, highly reliable integration process which allows to push the cutoff frequency, a main figure of merit, to new limits. In particular, geometrical aspects of the VOFET such as gate-source overlap and charge carrier injection/ extraction length are investigated to derive scaling laws allowing to predict dynamic device properties. Furthermore, we present an advanced patterning technique helping to maximize on/off ratio and leakage current. These improvements on device performance allow for alternating current operation above 10 MHz. Moreover, to evaluate the role of the organic semiconductor in these highly contacted limited devices, we investigate how semiconductor properties such as HOMO-LUMO gap, intrinsic doping, and mobility affect the VOFET performance and in particular device stability. Combining these finding on the device scaling and the influence of the semiconductor properties, we can provide a roadmap for future device improvement strategies.