Realizing Controllable Carbon Nanotube Arrays for Soft Devices by Asymmetric Langmuir–Blodgett and Hydrophilization Process

Well-aligned Carbon nanotube (CNT) arrays are expected by flexible and stretchable devices. In this paper, an asymmetric Langmuir-Blodgett (LB) method and inorganic hydrophilization method have been proposed, with which well-aligned CNT arrays on soft substrates like polyethylene naphthalate, polyimide and polydimethylsiloxane have been realized. After depositing 50 nm SiO2 for hydrophilization, the water contact angle has been significantly reduced for different substrates. The surface roughness and flexibility have also been characterized to analyze their effect on device performance. The nanotube density in the arrays can be controlled to 10-25 tubes/μm
²
, 25-35 tubes/μm
²
or 35-45 tubes/μm
²
by tuning the surface pressure during the LB process. With aligned semiconducting CNT arrays as channel and anisotropic metallic CNT network as gate/source/drain electrodes, all-carbon nanotube transistors on PI substrate have been fabricated for demonstration. The fabricated devices show a subthreshold swing of 92.9 mV/dec, a carrier mobility of 15.32 cm
²
/Vs, and an on/off current ratio of 4.51 × 10
²
. More importantly, with 50 nm thick gate dielectrics, the changes of threshold voltage and carrier mobility are within 16.62% and 28.78%, respectively, even after bending 1000 times under a curvature radius of 3.66 mm.