Highly Uniform and Stable n-Type Carbon Nanotube Transistors by Using Positively Charged Silicon Nitride Thin Films

Abstract

Air-stable n-doping of carbon nanotubes is presented by utilizing SiN(x) thin films deposited by plasma-enhanced chemical vapor deposition. The fixed positive charges in SiN(x), arising from (+)Si ≡ N3 dangling bonds induce strong field-effect doping of underlying nanotubes. Specifically, an electron doping density of ∼ 10(20) cm(-3) is estimated from capacitance voltage measurements of the fixed charge within the SiN(x). This high doping concentration results in thinning of the Schottky barrier widths at the nanotube/metal contacts, thus allowing for efficient injection of electrons by tunnelling. As a proof-of-concept, n-type thin-film transistors using random networks of semiconductor-enriched nanotubes are presented with an electron mobility of ∼ 10 cm(2)/V s, which is comparable to the hole mobility of as-made p-type devices. The devices are highly stable without any noticeable change in the electrical properties upon exposure to ambient air for 30 days. Furthermore, the devices exhibit high uniformity over large areas, which is an important requirement for use in practical applications. The work presents a robust approach for physicochemical doping of carbon nanotubes by relying on field-effect rather than a charge transfer mechanism.

Efficient and Reversible Electron Doping of Semiconductor-Enriched Single-Walled Carbon Nanotubes by Using Decamethylcobaltocene

“…Figure 1c shows the transfer curves ( I ds - V gs ) of the as-made CNFET device (W/L = 100 μm/20 μm) before any doping process at V ds  = −5 V, confirming its excellent p-channel transistor behaviors with large on current (~20 μA) and high on/off current ratio (~10 5 ). The p-channel characteristics can be attributed to the electron withdrawal effects by the absorbed oxygen on nanotubes in air ambient consistent with the reported results 4, 6 . Moreover, Fig.…”

Fabrication of air-stable n-type carbon nanotube thin-film transistors on flexible substrates using bilayer dielectrics

“…The output characteristics are also shown in Fig. 20 To elucidate the validity of our proposed n-type transistor structure, we compared the electrical transport characteristics of devices with our proposed bilayer MgO/Al 2 O 3 dielectric structure and devices with only an ALD Al 2 O 3 single layer as the top gate dielectric. The drain voltage was applied from zero to 3 V, with the top gate voltage stepped from −5 V to 5 V. The linear transport property at low V DS indicates a small contact barrier.…”

“…However, whether for TFTs or individual-SWNT-based transistors, fabricating air-stable n-type devices is challenging because the as-made devices are p-type under ambient conditions. Recently, several groups have reported air-stable n-type transistors by vacuum annealing followed by passivation with Si 3 N 4 film 19,20 or atomic layer deposited (ALD) high-κ dielectrics. One approach is doping the SWNT channel or the metal-SWNT contacts with alkali metal atoms such as potassium, 11,12 or organic polymers such as polyethylene imine 13 and viologen.…”

All‐Carbon Thin‐Film Transistors as a Step Towards Flexible and Transparent Electronics

“…[185] Ha et al reported a method to fabricate n-type CNT TFTs using SiN x thin films deposited by plasma enhanced CVD to introduce fixed positive charges around CNTs. [186] The devices with a good uniformity over a large area are stable without any noticeable change in electrical properties upon exposure to ambient air for 30 days. Gao et al used thin passivation layers of Al 2 O 3 and Si 3 N 4 to realize p-and n-type CNT TFTs, respectively, and further demonstrated a series of logic gates and ring oscillators.…”