A research team at Tsinghua University, led by Shoushan Fan, has fabricated single-wall carbon nanotube (SWCNT) thin films with different nanotube densities and transferred them to flexible substrates serving as electrodes and channel materials, respectively. Using this method they obtained all-carbon nanotube thin-film transistors (TFT) with an on/off ratio as high as 105. They fabricated inverters on top of the flexible substrates with symmetric input/output behavior.
The team reported their findings in Advanced Materials (“Fabrication of All-Carbon Nanotube Electronic Devices on Flexible Substrates Through CVD and Transfer Methods”).
Schematic showing the configuration of an all-carbon nanotube based thin film transistor that uses a SWCNT metallic network (SWCNT M-network) as source, drain and gate electrodes, and a SWCNT semiconducting network (SWCNT S-network) as the channel material. These two kinds of SWCNT network were fabricated by controlling the density of the network through CVD method and then transferred to the flexible substrate successively to construct the SWNT-TFT. (© Wiley-VCH Verlag)
The density of the network was successfully controlled by tuning the concentration of catalysts and the growth time.
The researchers obtained two kinds of SWCNT thin films and used them for the electrode and channel materials of the TFT. To obtain the all-carbon nanotube flexible TFTs, they transferred thin films of SWCNT with different sheet resistance from silicon to a flexible substrate through a series of transfer processes using PMMA and Cr/Au as adhesive layers.
Furthermore, they fabricated inverters demonstrating an application of such full carbon nanotube devices. They report achieving symmetric input/output behavior at supply voltages lower than 5V.
Moreover, they find that by cutting the SWCNT electrodes of the diodeload transistor into several stripes, the properties of all-carbon nanotube inverters can be tuned efficiently.
These results highlight the importance of controlling both the fabrication process and control over SWCNT material properties to achieve fabrication of all carbon nanotube thin film flexible circuits.
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