mechanical?exibility,environmental stabil-
reasonable inverting behavior upon connect-transistors.Accordingly,the coplanar-gate
transistors provide a novel and simple route achieving low-cost printed?exible graphene elec-
a high device performance.
AND DISCUSSION
illustrates the fabrication of coplanar gate
transistors with an ion gel gate dielectric on a substrate.To begin with,high-quality mono-
graphene was synthesized via CVD over a large-as described previously.19Multiple strips arms of graphene were then formed on the Cu
photolithography and oxygen plasma etching.
between the split arms and the graphene
300μm.Note that we introduced the split
electrode instead of a single arm structure
more uniform charge accumulation across
channel.A supporting polymer layer used transfer-printing was spin-coated onto the gra-patterns on the Cu foil,and the Cu foil was
electrochemical etching.The graphene were then transfer-printed onto a polyeth-terephthalate(PET)substrate,and the supporting removed.Subsequently,an ion gel gate di-consisting of poly(styrene-methyl methacry-
(PS-PMMA-PS)triblock copolymer and 1-ethyl-3-methylimidazolium bis(tri?uoromethylsulfonyl)-completely from the channel(main strip)
tioned to be coplanar with the channel.The
strip segment in contact with the ion gel functioned the channel of the transistor with a conductance could be tuned by the bias applied at the
gate electrode,while the remainder of the
the source/drain electrodes.The length(L
(W)of the channel were500and10μm,respectively. photograph of the as-prepared coplanar-gate phene transistor array is displayed in Figure coplanar gate graphene transistors also exhibit optical transparancy.Figure2displays the
tance of the layered?lms over the visible infrared spectral range.The transparency of
?lm depended weakly on the wavelength approximately92%,for example,at550nm. transparency was reduced after transferring phene monolayer onto PET and slightly patterning the ion gel on the graphene layer
still above80%(84%optical transparency
Typical drain current(I D)àdrain voltage acteristics of a coplanar-gate graphene
?ve di?erent gate voltages(V G)are plotted demonstrating reasonable gate modulation.
large drain currents were obtained at low
gate voltages(I D≈30μA at V G=à2V and
with a L/W ratio of50).These results were
to the very large capacitance of the ion dielectrics.A speci?c capacitance of8.1
Schematic diagram showing the fabrication of an ion gel-gated graphene transistor array in a coplanar on a?exible plastic substrate.(b)Photograph of the coplanar-gate graphene transistor array.The microscopy image of a coplanar-gate graphene transistor(scale bar:200μm).
Transmittance of a PET substrate(black)
(red)and an ion gel layer(blue).
Output characteristics(I D vs V D)of a coplanar-gate graphene transistor at?ve di?erent V G values.
the speci?c capacitance of the ion-gel capacitor in graphene/ionàgel/graphene coplanar characteristics(I D vs V G)of a coplanar-gate graphene transistor at V D=à0.1V and the corresponding Distribution of the hole and electron mobilities from50coplanar-gate graphene transistors.