Gate-Voltage Modulation in Graphene - Graphene and Its Fascinating Attributes - page 183

Fig. 3. (a) Optical microscope image of the graphene transistor fabricated on
substrate. After forming the source and drain electrodes,
evaporated onto the graphene surface. Although this process has no intentional insulator
layer at the interface between the graphene and the aluminum film, the int
aluminum can be partially oxidized in air. Because the oxidation is only around the
surface of the film and the interface and the inside of the aluminum film remains as the
conductive aluminum, the aluminum film evaporated on the graphene can be use
gate electrode. (b) Schematic of the transistor structure with measurement circuit system.
(c) Schematic of the ambipolar semiconductor film with a top
the experiment, the ambipolar semiconductor was the graphene channel.
separated from the back
insulator SiO 2 film (dielectric constant
with a self-assembled insulating layer

(a) Optical microscope image of the graphene transistor fabricated on
substrate. After forming the source and drain electrodes, the aluminum gate was directly
evaporated onto the graphene surface. Although this process has no intentional insulator
layer at the interface between the graphene and the aluminum film, the int
aluminum can be partially oxidized in air. Because the oxidation is only around the
surface of the film and the interface and the inside of the aluminum film remains as the
conductive aluminum, the aluminum film evaporated on the graphene can be use
gate electrode. (b) Schematic of the transistor structure with measurement circuit system.
Schematic of the ambipolar semiconductor film with a top-gate and a back-
the experiment, the ambipolar semiconductor was the graphene channel. The channel was
back gate by a distance D b ( D b =300 nm in the experiment) with a gate
dielectric constant Ε t =3.9Ε 0 ), and from the top-gate by a distance
assembled insulating layer (Ε t ).

(a) Optical microscope image of the graphene transistor fabricated on SiO 2 /Si
aluminum gate was directly
evaporated onto the graphene surface. Although this process has no intentional insulator
layer at the interface between the graphene and the aluminum film, the interface
aluminum can be partially oxidized in air. Because the oxidation is only around the
surface of the film and the interface and the inside of the aluminum film remains as the
conductive aluminum, the aluminum film evaporated on the graphene can be used as the
gate electrode. (b) Schematic of the transistor structure with measurement circuit system.
-gate. In
The channel was
=300 nm in the experiment) with a gate
gate by a distance D t

between the source
contact formation
layer was not introduced
Al electrode and the graphene were naturally insu
device to air for several hours [
the source (or drain) electrodes
the interior remains intact because the Al electrode remains conductive.
The most possible oxidation source is
could diffuse into the interface layer between the Al and the graphene
due to the fairly weak
The oxygen gas absorbed on the graphite surface cou
the oxidization process. However, the amount of oxygen atoms adsorbed
on the graphene surface would be insufficient to form the nm
oxidation layer (the thickness is estimated below). Thus, we speculate
that the oxygen was mainly
dielectric layer is formed, the current from the
graphite can hardly
The proposed top gate

the source-drain electrodes using the process similar to the
contact formation (Figs. 3(a) and (b)). Although an intentional insulator
layer was not introduced between the Al top gate and the graphene, the
Al electrode and the graphene were naturally insulated after exposing the
device to air for several hours [8]. The resistance between the gate and
the source (or drain) electrodes automatically far exceeds 100 MΩ
the interior remains intact because the Al electrode remains conductive.
ible oxidation source is the atmospheric oxygen,
could diffuse into the interface layer between the Al and the graphene
fairly weak physical contact between Al and graphite [16
The oxygen gas absorbed on the graphite surface could also contribute to
the oxidization process. However, the amount of oxygen atoms adsorbed
on the graphene surface would be insufficient to form the nm
oxidation layer (the thickness is estimated below). Thus, we speculate
that the oxygen was mainly supplied from the air. Once the top
is formed, the current from the top gate electrode to the
hardly be measured, thus exhibiting insulating propert
top gate fabrication method is superior to other methods

using the process similar to the
Although an intentional insulator
the graphene, the
lated after exposing the
he resistance between the gate and
Ω, and
the interior remains intact because the Al electrode remains conductive.
oxygen, which
could diffuse into the interface layer between the Al and the graphene,
16-18].
ld also contribute to
the oxidization process. However, the amount of oxygen atoms adsorbed
on the graphene surface would be insufficient to form the nm-thick
oxidation layer (the thickness is estimated below). Thus, we speculate
top gate
electrode to the
nsulating properties.
methods