43.2: Parasitic Capacitance Model for BGTC TFTs and Verification Using C‐V Measurements from Devices with Various Channel Dimensions

Abstract

A model of the accumulation and depletion capacitance for a bottom gate top contact (BGTC) thin film transistors (TFT) with an etch stop layer (ESL) was presented. The model, which includes the parasitic capacitance due to device layout, was verified by comparison of measured data and modeled data for TFTs of various dimensions. Good agreement was seen between measured and modeled data, where the model underestimated the capacitance by 2% to 7%, depending on the device dimensions. The impact of the parasitic capacitance on estimates of the Debye length (λD ) are discussed and it is demonstrated that the relative error in the λD estimates is directly proportional to the ratio of the parasitic capacitance over the measured capacitance (CPAR/CM). The relative error was shown to increase as the ratio increases, leading to a larger underestimation of the λD. It was concluded that the parasitic capacitance to measured capacitance should be minimized for devices that are used for extraction of physical parameters from C‐V data. This is especially important in the case where the λD is a critical parameter in the optimization of TFT performance.