Perpustakaan Digital ITB

Charge carrier mobility is one of the importantparameters to measure to compare the behavior of differentorganic transistors. A high carrier mobility is essential for theorganic transistors to operate at a high frequency. Recently,there have been discussions on the mobility overestimationdue to gate bias dependent Schottky contacts which lead tosevere nonlinearities in the current?voltage characteristics,i.e., the double-slope feature. In addition, an accurateevaluation of the carrier mobility from the transfer curvesrequires accurate parameters such as channel dimensions ordielectric capacitance. Many of the organicfield-effecttransistors (OFETs) reported in the literature employunpatterned semiconductor active layers or gate/gate dielectrics where the effective channel dimensions significantly deviatefrom the values defined by the source?drain electrodes due to the fringe effect. To reveal the importance of the fringe effect onthe mobility evaluation, here we perform a systematic investigation of OFETs with vacuum-deposited active layers in relation tothe fringe effect, followed by the same analysis of solution-processed OFETs with tunable crystal morphology. By continuouslynarrowing down the active layer toward the actual channel region defined by the source?drain electrodes, we show that thecarrier mobilities are 110% and 60% overestimated in the vacuum-deposited and solution-processed devices, respectively, evenwith ideal linearity in the transfer curves. Herein, we suggest a model to evaluate the degree of mobility overestimation in thesetwo families of OFETs and provide the guidelines for the design of the device geometry and channel dimensions to minimizemobility overestimation induced by the fringe effect. In our solution-processed OFETs, we conclude that a large channel widthto length ratio over 20 is essential to alleviate the fringe current outside the channel, while a channel ratio greater than 40 isneeded for the OFETs with vacuum-deposited semiconductor layers.