Engineering researchers work to improve performance of transistors

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Several researchers, including a UT professor and graduate student, have found a molecular-scaled “Band-Aid” to fix nanotube defects on transistors.

Ananth Dodabalapur, electrical and computer engineering professor, and Seonpil Jang, electrical and computer engineering graduate student, are using carbon nanotubes and polar molecular polymers to improve the conductivity of transistors.  

“There is a great deal of interest in making new kinds of transistors with new material,” Dodabalapur said. “The transistor we would be creating would be good for display drivers and larger electronics like sensors. Silicon — the more commonly used material — is good but has some limitations, so we are looking at all kinds of new material.”

Dodabalapur and several UT students are working with Mark Hersam, materials science and engineering professor from Northwestern University, who is able to sort the nanotubes and get 99 percent semiconducting fractions. Hersam then sends the purified nanotube transistors to UT.

“My lab specializes in low dimensional electronic materials, including highly purified semiconducting carbon nanotubes,” Hersam said in an email. “My lab utilizes a method called density gradient ultracentrifugation to separate carbon nanotubes by their physical and electronic structure.”

The nanotubes work efficiently, but they still have defects that hurt the properties of the material, according to Dodabalapur.

“The defect causes the nanotubes to not behave as well, and we’ve found molecules that can detach that defect,” Dodabalapur said. “We’ve found a molecular scale ‘Band-Aid’ to fix the defects and impurities and essentially neutralize them. As a result, they behave a lot better. This ‘Band-Aid’ is hard to find, and it’s hard to apply to most semiconductors. The reason it worked for nanotubes is because they are either a flat sheet or rolled up flat sheet of carbon.”

According to Dodabalapur, this “Band-Aid” can be any polar molecule. The molecular structure goes to the defects in nanotubes and repairs them.

Jang said the polymer made the transistors better conductors.

“Our lab is focused on instant-printing electronic devices, but there are challenges from the process,” Jang said. “We tried to overcome the limitation utilizing that polymer. So, now we are focusing on flexible display because we can apply instant printing.”