James E. Baumgardner

Radio frequency analog electronics based on carbon nanotube transistors

The potential to exploit single-walled carbon nanotubes (SWNTs) in advanced electronics represents a continuing, major source of interest in these materials. However, scalable integration of SWNTs into circuits is challenging because of difficulties in controlling the geometries, spatial positions, and electronic properties of individual tubes. We have implemented solutions to some of these challenges to yield radio frequency (RF) SWNT analog electronic devices, such as narrow band amplifiers operating in the VHF frequency band with power gains as high as 14 dB. As a demonstration, we fabricated nanotube transistor radios, in which SWNT devices provide all of the key functions, including resonant antennas, fixed RF amplifiers, RF mixers, and audio amplifiers. These results represent important first steps to practical implementation of SWNTs in high-speed analog circuits. Comparison studies indicate certain performance advantages over silicon and capabilities that complement those in existing compound semiconductor technologies.

Inherent linearity in carbon nanotube field-effect transistors

The authors consider the suitability of carbon nanotubes for use in analog rf amplifiers, where the linearity of the device is critical. They show that in the limit of large electrostatic gate-channel capacitance, their theory predicts that an Ohmically contacted, ballistic carbon-nanotube-based field-effect transistor is inherently linear. While they have not achieved this limit in their experimental work, they compare the theory to experiment in the limit of small electrostatic gate-channel capacitance and find excellent agreement at virtually all bias conditions.

Carbon nanotube field-effect transistor operation at microwave frequencies

A top-gated carbon nanotube (CNT) field-effect transistor (FET) was fabricated on a quartz substrate. We used a novel measurement approach and demonstrated for the first time frequency-independent performance of a CNT FET for frequencies as high as 23GHz. This observed maximum operating frequency represents a significant breakthrough in the realization of carbon nanotube-based electronics for high frequency applications.

A 500 MHz carbon nanotube transistor oscillator

Operation of a carbon nanotube field effect transistor (FET) oscillator at a record frequency of 500 MHz is described. The FET was fabricated using a large parallel array of single-walled nanotubes grown by chemical vapor deposition on ST-quartz substrates. Matching of the gate capacitance with a series inductor enabled greater than unity net oscillator loop gain to be achieved at 500 MHz.

K-band Carbon Nanotube FET Operation

A top-gated carbon nanotube (CNT) field-effect transistor (FET) was fabricated on a quartz substrate using a single nanotube grown by CVD and a sputtered SixNy gate dielectric. Measurements of the mixing products produced by two closely spaced microwave input signals applied to the gate of the FET circumvented the problems associated with measuring high impedance RF devices in 50 Omega systems. The frequency-independent performance of a CNT FET, at frequencies as high as 23 GHz, was demonstrated for the first time. This observed operating frequency represents a significant breakthrough in the realization of carbon nanotube-based electronics for high frequency applications