Carbon Nanotube Electronics Research

Additionally, aligned monolayers are a key building block for advanced electronics. A published paper co-authored in 2016 by Dr. Evensen, demonstrated the first CNT transistor that out-performed traditional transistors, built upon these aligned films.*

Carbon nanotubes are also expected to be valuable as sensors.  This is because every atom in a CNT is exposed to the surrounding environment, and therefore their electronic properties can be very sensitive to interactions with the environment. Because CNTs are on the same size scale as molecules and biological structures, it is expected that they will be an ideal means to detect trace amounts of gases or various proteins and enzymes in solution.

Our group works in collaboration with the Advanced Materials for Energy and Electronics Group at UW-Madison, which provides purified CNTs and aligned CNT films. UW-Platteville students have:

• Constructed working transistors on their own, using equipment entirely in our nano lab in Engineering Hall
• Created a proof-of-principle oxygen sensor
• designed a “nano-scale vacuum tube,” or vacuum-channel FET

The nanoscale vacuum-channel FET (VCFET) is an updated version of the “classic” vacuum-tube:  electrons travel through space between two electrodes, in a chamber (bulb) from which the air has been removed. At the nano-scale size, the gap between the electrodes can be made significantly smaller than the distance between adjacent molecules found in the air, effectively enabling the device to operate under vacuum without the challenge of actually creating a vacuum! 

There are other advantages: the nano-scale size means the device can operate at low voltages without getting hot, thus surmounting two other shortcomings of macro-scale vacuum tubes.

What are the advantages of a nano-scale vacuum tube? For one, they are expected to be radiation-resistant and therefore to find a niche in space applications. For another, they also have promise for high-power and high-frequency operation, as compared with traditional transistors.

The design, fabrication, and testing effort of the VCFET has been led by students, who again are doing the entire process in our nano lab in Engineering Hall.

All of this work is built upon a common set of skills that students have learned:

• Preparation of surfaces that are clean at the nano-scale
• Deposition of thin films of CNTs, polymers, and metals
• Design of patterns for these films
• Creation of these patterns via selective etching (removal) of the materials
• Electronic testing of the completed devices. 

This effort has required additional work to be done in instrumentation: building test chambers, writing software for data collection and analysis, etc.

*[Brady, G.J., Way, A.J., Safron, N.S., Evensen, H.T., Gopalan, P., & Arnold, M.S. (2016). Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs. Science Advances 2 (9), e1601240 (2016).]

Application and Career Opportunities

There are many career opportunities for students with experience in microfluidics-based medical devices, as well as in sensor development. More broadly, however, the thin-film industry encompasses companies in electronics, from computing to displays and sensors, and the skills used in our group are broadly transferable.

Importantly, it should be noted that past students have found success even if they did not seek employment in these specific fields. They made themselves stand out by virtue of their experience in "leading" their own aspect of a project, and by demonstrating an ability to not only apply what they're learning in their classes, but to also gain additional knowledge and skills and apply it to the work described here.

Academic Areas of Focus

Engineering
This project requires an understanding of fabrication methods, electronics, and electrical measurements. It also utilizes design skills for apparatus and software. In addition, future work in biochemical sensors would likely involve microfluidics: understanding fluid handling and motion at the micro-scale.

Engineering Physics & Electrical Engineering
Understanding why the CNTs behave as they do when in transistors and sensors which involves an understanding of semiconductor electronics. Additionally, the common fabrication methods are building blocks used in any micro-scale or nano-scale fabrication.

Chemistry & Biology
Building a sensor that detects only “Molecule A” or “Protein B” requires an understanding of chemistry or biochemistry, which is used to modify the CNT and to determine a valid means of detection.