ION MODULATED ORGANIC TRANSISTORS - Doria

Nikolai Kaihovirta3. RESULTS AND DISCUSSIONSstandard errors reveal larger fluctuations in quality between the OFETs,while the HIFETs show more consistency between each other.Device Substrate On/off S[V/decade]k[A 1/2 /V]Yield[%]HIFET PET 505 10 2 0.80±0.05 -(9.2±0.3)×10 -4 > 70HIFET Mylar® A 10 2 0.70±0.05 -(9.1±0.3)×10 -4 > 70OFET PET 505 10 3 -10 4 3.9±0.3 -(7.4±1.2)×10 -6 ~ 40OFET Mylar® A 10 2 -10 3 7.0±0.8 -(4.9±0.6)×10 -6 ~ 20Table 3.1. Average values of the on/off ratio, the subthreshold slope (S) and theslope of the square-root of I DS (k) for all devices on respective substrate. Thestandard error has been calculated for S and k. Also the yields of functioningdevices are shown.Two arguments are pointed out to explain the higher stability inHIFETs. Firstly, it has earlier been shown that the HIFET is governed bythe potential difference rather than by the electric field [27]. The ionmigration at applied gate voltages causes the operation of the HIFET (aswell as other electrolyte gated OFETs) to be independent to the insulatorthickness. Thus, the thickness of the PVP layer does not alter the lowvoltagebehavior. Likewise, a similar smoothening effect could bepossible at the rough semiconductor/insulator interface. Secondly, thehigher capacitance that is gained by the hygroscopic PVP (as discussed inSection 1.2.3) generates more charges to the active channel to efficientlyfill all the deeper trap states.Besides the demonstrated all-printed HIFET on the Mylar A substrate[59], this work inspired to proceed towards even more challengingsubstrates, such as paper. Indeed, our group managed to demonstrateone of the first low-voltage polymeric transistors manufactured on apaper substrate [42]. After the publication of this work, other groups haveindependently also acknowledged the electrolyte gated OFET as beinginsensitive to an increased roughness [60, 61].24