ION MODULATED ORGANIC TRANSISTORS - Doria

Nikolai Kaihovirta3. RESULTS AND DISCUSSIONSincreased roughness, the OFET displays expected deterioration, such as alower on/off ratio, a lower subthreshold slope (S) and a decreasedmobility. The change in mobility (µ) is interpreted from the slope (k) ofthe curves in Figures 3.2 (e) and (f). According to Equation (1.9), andwhen assuming that W, L, C i and (V G - V T) are constant, the change in k isgoverned by the change in µ.(a)48 nm(b)280 nmabs(I d)[A]sqrt(I d)[10 -3 A 1/2 ]10 -510 -610 -710 -82.01.51.00.520 µmV d=-1.5VPET 505Mylar A20 µm(c)PVP(e)PVPV d=-1.5V0.0-3 -2 -1 0 1V g[V]abs(I d)[A]sqrt(I d)[10 -3 A 1/2 ]10 -810 -910 -1010 -1110 -120.20.120 µmV d=-25V20 µm(d)PMMA(f)0.0-30 -20 -10 0 10 20V g[V]PMMAV d=-25VFigure 3.2. AFM pictures of (a) PET 505 and (b) Mylar A. Typical transfercharacteristicsfor (c) HIFETs and (d) OFETs manufactured on both substrates.The transfer-characteristics are measured in the saturated region. The squarerootof I DS for (e) HIFETs and (f) OFETs.Table 3.1 summarizes the statistical results for both the OFET and theHIFET. These results support the observations made in Figure 3.2. Alsothe yields of functioning devices (i.e., devices that are comparable to thetypical I-V curves in Figure 3.2) are shown. For the OFETs, the yieldreflects the change in the substrate roughness. A higher RMS roughnessincreases the risk for electrical breakdown for the PMMA dielectric. ThePVP is, however, almost twice the thickness of the PMMA. Moreover, theHIFET operates at substantially lower gate voltages. These two factorsaffect the higher yield of HIFETs on both substrates. The yield remainsunaffected by the increasing substrate roughness. Another indicator, infavor for the HIFET, is the calculated standard errors. For the OFET, the23