Top-gate/bottom-contact SWCNT network
transistors were fabricated on cleaned glass slides (sodium-free aluminum
borosilicate glass, Schott AF32 eco, 20 × 25 mm2,
thickness 0.3 mm). The interdigitated bottom electrodes (channel length L = 10 and 20 μm with channel width W = 10 mm or L = 40 μm with W = 5 mm) were patterned by photolithography using a double-layer
photoresist (LOR5B (MicroChem)/ MICROPOSIT S1813 (Dow Chemical)).
An adhesion layer of 2 nm of chromium and 30 nm of gold was deposited
by electron beam evaporation, followed by lift-off in N-methyl-2-pyrrolidone (NMP, Sigma-Aldrich, 99%) and a cleaning step
with ultrasonication in acetone and 2-propanol. Prior to deposition
of (6,5) SWCNTs, the substrates were treated in a UV/ozone cleaner
for 10 min, rinsed with 2-propanol, blow-dried with nitrogen, and
annealed for 5 min at 100 °C. To obtain homogeneous networks,
the (6,5) SWCNTs were spin-coated onto the substrates three times
(30 s, 2000 rpm). After each spin-coating step, the substrates were
heated for 2 min at 90 °C. To remove excess polymer, the samples
were washed with tetrahydrofuran (VWR International, analytical grade)
and 2-propanol and subsequently heated for 4 min at 90 °C. The
linear density of the resulting SWCNT networks was 30 nanotubes/μm
with an average SWCNT length of 1.2 ± 0.4 μm, as determined
by atomic force microscopy (AFM, Bruker Dimension Icon). SWCNTs outside
the channel area were removed by oxygen plasma etching while SWCNTs
within the channel were protected with photolithographically patterned
photoresist as described above. After the subsequent lift-off in NMP
and annealing for 45 min at 300 °C in dry nitrogen, selected
samples were doped by submerging the substrates in a 3 or 6 g·L–1 solution of 1,2,4,5-tetrakis(tetramethylguanidino)benzene
(ttmgb)52 (link) in anhydrous toluene for 20 min,
followed by annealing for 20 min at 150 °C. Polymeric dielectric
films with thicknesses of about 50 nm were deposited in a dry nitrogen
atmosphere by spin-coating and successive annealing: Teflon AF2400
(poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene], Sigma-Aldrich, 53 nm from 20 g·L–1 solution in FluorInert FC-40 (3M)); P(VDF-TrFE-CTFE)
(poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) Piezotech RT TS, Piezotech Arkema,
52 nm from 10 g·L–1 in n-butanone); PMMA (poly(methyl
methacrylate), PolymerSource, MW = 315
kg·mol–1, syndiotactic, 50 nm from 20 g·L–1 in n-butyl acetate); PS (polystyrene, Mw = 230.4 kg·mol–1, atactic,
50 nm from 20 g·L–1 in n-butyl
acetate). 60 nm of HfOx were deposited
via atomic layer deposition (ALD, Ultratech Savannah S100) at 100
°C with tetrakis(dimethylamino)hafnium (Strem Chemicals Inc.)
and water as precursors either as the top layer of a hybrid dielectric
or as a single dielectric layer directly on the SWCNTs. Thermal evaporation
of 30 nm thick silver gate electrodes through a shadow mask completed
the devices. Due to the conformal encapsulation with ALD-HfOx, all devices were air-stable.
transistors were fabricated on cleaned glass slides (sodium-free aluminum
borosilicate glass, Schott AF32 eco, 20 × 25 mm2,
thickness 0.3 mm). The interdigitated bottom electrodes (channel length L = 10 and 20 μm with channel width W = 10 mm or L = 40 μm with W = 5 mm) were patterned by photolithography using a double-layer
photoresist (LOR5B (MicroChem)/ MICROPOSIT S1813 (Dow Chemical)).
An adhesion layer of 2 nm of chromium and 30 nm of gold was deposited
by electron beam evaporation, followed by lift-off in N-methyl-2-pyrrolidone (NMP, Sigma-Aldrich, 99%) and a cleaning step
with ultrasonication in acetone and 2-propanol. Prior to deposition
of (6,5) SWCNTs, the substrates were treated in a UV/ozone cleaner
for 10 min, rinsed with 2-propanol, blow-dried with nitrogen, and
annealed for 5 min at 100 °C. To obtain homogeneous networks,
the (6,5) SWCNTs were spin-coated onto the substrates three times
(30 s, 2000 rpm). After each spin-coating step, the substrates were
heated for 2 min at 90 °C. To remove excess polymer, the samples
were washed with tetrahydrofuran (VWR International, analytical grade)
and 2-propanol and subsequently heated for 4 min at 90 °C. The
linear density of the resulting SWCNT networks was 30 nanotubes/μm
with an average SWCNT length of 1.2 ± 0.4 μm, as determined
by atomic force microscopy (AFM, Bruker Dimension Icon). SWCNTs outside
the channel area were removed by oxygen plasma etching while SWCNTs
within the channel were protected with photolithographically patterned
photoresist as described above. After the subsequent lift-off in NMP
and annealing for 45 min at 300 °C in dry nitrogen, selected
samples were doped by submerging the substrates in a 3 or 6 g·L–1 solution of 1,2,4,5-tetrakis(tetramethylguanidino)benzene
(ttmgb)52 (link) in anhydrous toluene for 20 min,
followed by annealing for 20 min at 150 °C. Polymeric dielectric
films with thicknesses of about 50 nm were deposited in a dry nitrogen
atmosphere by spin-coating and successive annealing: Teflon AF2400
(poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene], Sigma-Aldrich, 53 nm from 20 g·L–1 solution in FluorInert FC-40 (3M)); P(VDF-TrFE-CTFE)
(poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) Piezotech RT TS, Piezotech Arkema,
52 nm from 10 g·L–1 in n-butanone); PMMA (poly(methyl
methacrylate), PolymerSource, MW = 315
kg·mol–1, syndiotactic, 50 nm from 20 g·L–1 in n-butyl acetate); PS (polystyrene, Mw = 230.4 kg·mol–1, atactic,
50 nm from 20 g·L–1 in n-butyl
acetate). 60 nm of HfOx were deposited
via atomic layer deposition (ALD, Ultratech Savannah S100) at 100
°C with tetrakis(dimethylamino)hafnium (Strem Chemicals Inc.)
and water as precursors either as the top layer of a hybrid dielectric
or as a single dielectric layer directly on the SWCNTs. Thermal evaporation
of 30 nm thick silver gate electrodes through a shadow mask completed
the devices. Due to the conformal encapsulation with ALD-HfOx, all devices were air-stable.
