Scaling of contact metal induced hysteresis in solution processed organic thin film transistors

Contact effect in organic thin film transistor (OTFT) with bottom contact configuration has been considered as a serious issue that renders inferior device performance. In this article, the contact between metal and semiconductor is unveiled to be responsible for hysteresis in bottom gate bottom contact OTFT, consisting of poly(3-hexylthiophene) as semiconductor and cross-linked poly(4-vinylphenol) as polymer dielectric. The correlation between the contact effect and hysteresis is demonstrated by comparing gold contact and silver contact devices with having low and high contact resistances respectively. Negligible hysteresis in gold contact devices in contrary to sizable hysteresis in silver contact devices ensures contact-assisted trapping of charge carriers as the origin of hysteresis. Variation of hysteresis on scaling down the channel length of silver contact devices validates the contact induced hysteresis. A simplistic analysis based on charge trapping in the vicinity of source terminal is proposed to explain the scaling behavior of hysteresis with channel length.