Supplementary Section
About 4 wt % and 10 wt % of poly (methyl methacrylate) (PMMA) (Mw = 996,000 g/mol)
were dissolved in butylacetate (BTAc) and propylene carbonate (PC), respectively and
subsequently spincoated on pre-cleaned thermally-evaporated aluminum-coated (60 nm) glass
substrates in a nitrogen-filled glove box. The PMMA dielectric films were baked for 1 h at 100
°C. The dielectric film thicknesses were approximately 210 nm and 200 nm for the PMMABTAc and PMMA-PC films, respectively. One of the advantages of using PC over BTAc in
dissolving PMMA is that it is relatively easier to realize thinner PMMA films with PC than it is
with BTAc, as could be seen from their concentrations above. A 60 nm thick pentacene layer
(without any purification) was thermally evaporated onto the dielectric surface at a rate of 0.1 –
0.3 Å/s at room temperature. Top contact source/drain (40 nm) gold electrodes which define a
channel length (L) and width (W) of 500 µm and 50 µm, respectively were thermally evaporated
onto the pentacene film via a shadow mask.
Shown in Fig. S1 are the capacitance-voltage curves obtained at a frequency of 5 kHz for
PMMA-PC and PMMA-BTAc-based MIS capacitors. The devices show typical p-type MIS
behavior, which is characterized by an accumulation region at negative bias, a depletion region at
less negative bias and a deep depletion region at positive bias. The device fabricated from
PMMA-PC (Fig. S1(a)) exhibits a smaller hysteresis with flat band voltage shift ΔVFB, of 0.45
V when the gate bias is continuously swept from -10 V, passing through 10 V and back to -10 V
at a step voltage of 0.05 V, while the device from PMMA-BTAc solution (Fig. S1(b)) exhibits a
more prominent hysteresis with ΔVFB of 2.17 V under same applied voltage range. This shows
that hysteresis is lower in PMMA-PC devices than in PMMA-BTAc devices and corroborates
our earlier observations in Fig 2, where no hysteresis was observed in our thinner PMMA-PC
film, which is more desirable for practical and low-power applications. As mentioned in Refs. 9
and 12, OFETs have been achieved with very low PMMA thicknesses via cross-linking, yet they
operated at gate voltages that are about three – four times higher than our PMMA-PC OFET.
Fig. S1. (a) C-V curve of Al/PMMA-PC/Pentacene/Au MIS diode at a frequency of 5 kHz. (b)
C-V curve of Al/PMMA-BTAc/Pentacene/Au MIS diode at a frequency of 5 kHz.
Figures S2 (a) and (b) show the output and transfer characteristics of PMMA-BTAc-based
OFET measured under ambient conditions. Our OFET exhibited good linear and saturation
-7
-4.8V
-10
10
-6.4V
1.2
-9
0.8
-10
-11
0
1.6
10
VT = 0.43 V
-6
-4
-2
Drain voltage (V)
1/2
VDS = - 8V
-8
10
-13
-16
-8
2.0
10
-8
-6
-4
-2
Gate voltage (V)
0.4
0.0
0
-4
-3
(b)
1/2
Drain current, -ID (A)
Drain current, ID (nA)
-7
10
0V, -1.6V
-3.2V
Drain current, ID
(a)
0
(x10 A )
behaviors in the output characteristics and could be operated below -8 V.
Fig. S2. Representative (a) output and (b) transfer characteristics of a pentacene PMMA-BTAc
OFET