Threshold voltage and turn-on voltage in organic transistors: Sensitivity to contact parasitics

Threshold voltage and turn-on voltage of organic field effect transistors are very sensitive to the fabrication process. Their knowledge and control are required for design and fabrication of OFET based circuits. A simple gradual channel OFET model is not appropriate close to threshold, and even fails to describe turn-on voltage. Therefore a distributed model has been developed, based on a numerical calculation of the accumulated charge along the channel, allowing the calculation of the transistor output characteristics both below and above threshold. Also, uneven source contact carrier injection can be modelled, based on physical parameters. In the present work, in-depth analysis of contact influence is carried-out, both below and above threshold, and impact on threshold voltage and turn-on voltage is outlined. Besides, surface Fermi level pinning effects and influence of the semiconductor layer thickness is also discussed.

Injection barrier impact on threshold voltage (a) and turn-on voltage (b).Figure optionsDownload as PowerPoint slideResearch highlights
► A numerical model was developed to study OFETs both below and above threshold.
► Injection barrier at the source contact will shift the threshold voltage.
► The onset voltage is insensitive to both linear and non-linear contact contributions.
► The sub-threshold slope is influenced by the semiconductor thickness.
► Surface Fermi level pinning will shift the threshold voltage.