High‐Performance Inkjet Printed Carbon Nanotube Thin Film Transistors with High‐k HfO₂ Dielectric on Plastic Substrate

Abstract

Inkjet printing technology has been extensively studied for depositing thin fi lms of diverse materials for scalable, lowcost printable fl exible electronics. Inkjet printing of carbon nanotube thin fi lm transistors (CN-TFTs) on fl exible or plastic substrate has hitherto achieved relatively poor device performance, or has used uncommon materials as the dielectric. In this paper we report superior performance inkjet printed CN-TFTs using a common dielectric on fl exible substrate. On indium-tin-oxide-coated polyester fi lm, we deposited a thin ( ∼ 70 nm) fi lm of the commonly used stable and high dielectric constant (k) material Hafnium oxide (HfO 2 ) as gate dielectric. After patterning of Au electrodes, active channels were formed by inkjet printing of highly purifi ed (99%) semiconducting carbon nanotube (CN) ink. The resulting CN-TFTs have performance that is superior to other reported fl exible TFTs. We systemically studied the effect of areal density of carbon nanotubes in the active channel (controlled by the amount of printing) and channel length (L C ) on the TFT on-current density, effective mobility, on/off ratio, threshold voltage and gate hysteresis. The optimized inkjet printed CN-TFTs with L C = 160 μ m and channel width (W C ) = 60 μ m exhibit outstanding effective mobility of 43 cm 2 V − 1 s − 1 with on/off ratio ≥ 10 4 , threshold voltage of 4.1 V and gate hysteresis of 2.2 V. Our transistor performance is superior to other reported values using inkjet printing of CNs and common stable microelectronics materials. These demonstrated high-performance inkjet printed CN-TFTs are ready for scalable printable fl exible electronics in the near future.Inkjet printing technology is favored in electronics manufacturing for a wide variety of applications such as organic thin fi lm transistors, [1][2][3] light-emitting diodes, [ 4 , 5 ] solar cells, [6][7][8] memory devices, [ 9 ] and sensors [10][11][12] owing to its reduced material wastage, low cost and scalability to large area manufacturing. The most signifi cant advantage of inkjet printing is that it is a non-contact direct patterning method suitable for depositing diverse materials at precisely controlled position without the use of pre-patterned masks. It has been extensively used as a research tool for exploring various aspects of printed electronics and for realizing applications of novel materials, designs and systems at laboratory scale. Initial research efforts on inkjet printed fl exible electronics have been focused on organic semiconductors, [13][14][15][16][17] owing to their compatibility with plastic substrate and their carrier mobility being comparable to that of amorphous silicon. In recent years, inorganic nanowires and carbon nanotubes have emerged as competitors of organic semiconductors as the active material for electronic devices. [18][19][20][21] Single-walled carbon nanotubes (SWCNTs) are regarded as a potential semiconductor material for printed fl exible electronics but as-synthesized SWCNTs are mixtures containing metallic...

High‐Performance Partially Aligned Semiconductive Single‐Walled Carbon Nanotube Transistors Achieved with a Parallel Technique

“…Wang et al used 50 nm SiO 2 as the dielectric and achieved performance similar to ours here: mobility of about 30 cm 2 /Vs and on/off ratio of 10 5 with same channel length, L = 50 μm, and similar nanotube purity (98% semiconducting enriched) 69. We have also previously used HfO 2 (dielectric constant = 12 compared to 3.9 for SiO 2 here) and achieved similar device performance 70. It appears that partial alignment can improve device performance, to a degree comparable to that achieved by use of a superior dielectric.…”

Logic circuits composed of flexible carbon nanotube thin-film transistor and ultra-thin polymer gate dielectric

“…On the other hand, the inkjet printing technique may be the most promising alternative because of its mask-less process, high printing resolution, and low-temperature requirement 12 13 14 15 16 17 18 19 . Therefore, a number of studies on the inkjet-printed CNT-TFTs based on various gate dielectric layers, such as ion-gel materials 9 12 13 , barium titanate (BaTiO3-BTO) nanoparticles 6 11 14 , and polymethyl methacrylate (PMMA) 15 , have been extensively reported.…”

Engineering of the structures of carbon nanotubes and graphene-based materials for electronic applications

“…urn. Figure 5.4C&D show the performance of typical FET devices with onloffratio 10 4 -10 5 and mobility 15-30 cm 2 V-IS-I (mobility computed using the coupling model mobility equations [48,216] employed in our previous publications [247]). The good on-off switching ratio confirms the high purity of the sorted semi-SWNTs.…”