N-type Carbon Nanotube Field-effect Transistors Research Articles

High-performance n-type carbon nanotube field-effect transistors with estimated sub-10-ps gate delay

High-performance top-gated n-type single-walled carbon nanotube (CNT) field-effect transistors (FETs) have been fabricated using scandium contacts and HfO2 gate oxide and are benchmarked against the state-of-the-art n-type Si metal-oxide semiconductor FETs. Two key device metrics, the intrinsic gate-delay (CV∕I) and energy-delay product (CV∕I⋅CV2) per unit width, of the n-type CNT FETs are found to show significant improvement over the Si devices. In particular, the gate-delay time is estimated to be 2.1ps for an n-type CNT FET which is based on a CNT with a diameter of 1.1nm and a channel length of 220nm.

Fabrication of high performance top-gate complementary inverter using a single carbon nanotube and via a simple process

High performance complementary inverters have been fabricated using single-walled carbon nanotubes. The Al2O3 top-gate dielectric is grown via first depositing an Al film followed by complete oxidation of the film. It is shown that the quality of the Al2O3 film can be significantly improved by annealing at 400°C, and stable p-type and n-type carbon nanotube field-effect transistors (CNTFETs) may be fabricated using either Pd (p-type) or Al (n-type) electrodes. High performance complementary inverter is demonstrated by integrating the p-type and n-type CNTFETs on the same carbon nanotube, and a gain of about 3.5 is achieved.

Nanoelectronic logic circuits with carbon nanotube transistors

We demonstrate logic circuits with carbon nanotube field-effect transistors (CNTFETs). The p-type CNTFETs are fabricated based on single-walled carbon nanotubes and n-type CNTFETs are fabricated based on nitrogen-doped multiwalled carbon nanotubes. To be specitic, we demonstrate three types of logic circuits with CNTFETs, which include an inverter (a p-type CNTFET), a complementary inverter (a p-type CNTFET and an n-type CNTFET in a single clip), and a logic NOR (two p-type CNTFETs).

Modeling and Simulation of n-Type Carbon Nanotube Field Effect Transistors Using Ca as Contact Electrodes

AbstractIn this research work, a model has been proposed in view of the recent experimental demonstration using Calcium (Ca) as a contact metal to realize the n-type carbon nanotube field effect transistors (CNTFET). In order to fully optimize this proposed device model, effects of different parameters like the work function, oxide thickness, the oxide capacitance and the source velocity limits were studied. Among all the parameters, the work function of the contact metal plays an important role for controlling the flow of carriers through the carbon nanotube channel and to reduce the threshold voltage. A semi-classical simulation of the proposed n-type CNTFET has been performed. Results show an excellent subthreshold swing value of 62.91 mV/decade, close to the International Technology Roadmap for Semiconductor (ITRS) specifications.

Fabrication of n-type carbon nanotube field-effect transistors by Al doping

We report the effect of an Al layer, covering the central part of the nanotube channel, on the electrical transport properties of carbon nanotube field-effect transistors (CNFETs). The CNFETs, consisting of single-walled carbon nanotube or double-walled carbon nanotube between two Pd electrodes on top of SiO2 layer, which showed p-type or ambipolar transport behaviors, exhibit clear n-type characteristics after the Al deposition. We ascribe such conversions into n-type behaviors to the electron doping in the Al-covered nanotube region, which results in the bending of the nanotube bands nearby the edges of the Al layer. This technique, Al deposition under a high vacuum, may give rise to a practical fabrication method for the n-type CNFET, which may enable us to develop complementary logic nanotube electronic devices.

Air-stable n-type carbon nanotube field-effect transistors with Si3N4 passivation films fabricated by catalytic chemical vapor deposition

Air-stable n-type carbon nanotube field-effect transistors (CNTFETs) were fabricated, with Si3N4 passivation films formed by catalytic chemical vapor deposition (Cat-CVD). Electrical measurements reveal that the p-type characteristics of CNTFETs are converted to n-type after fabricating Si3N4 passivation films at 270°C. This indicates that adsorbed oxygen on the CNT sidewalls was removed during the formation process of the Si3N4 passivation films. In addition, the source-drain current of the n-type CNTFETs does not change over time under vacuum, or in air. Consequently, the n-type CNTFETs are completely protected by the Si3N4 passivation film from further effects of ambient gases. Therefore, Cat-CVD is one of the best candidates to fabricate Si3N4 passivation films on CNTFETs.

Carbon nanotube transistors and logic circuits

We discuss our recent efforts to develop high performance carbon nanotube field effect transistors (CNTFETs) and logic circuits. By improving the metal nanotube contacts the characteristics of the CNTFETs are greatly enhanced. Analysis shows that the performance of p-type CNTFETs is already competitive to that of silicon p-MOSFETs. In addition to the p-CNTFETs, we present techniques by which ambipolar and pure n-type CNTFETs can be fabricated. A particulary simple process involving the annealing in vacuum of a p-CNTFET is shown to convert it to an n-CNTFET. This conversion is reversible, and re-exposure to oxygen leads to a p-CNTFET. Evidence is found that the key effect of oxygen involves modification of the contact barriers. Having complementary CNTFETs (i.e. p- and n-type) allows us to build the first integrated circuits. We present results on a NOT logic gate. Both an inter-molecular gate involving two separate CNTFETs, and an intra-molecular gate where the logic function is encoded along the length of a single tube are demonstrated.