UT-Dallas helps develop smallest circuit transistor

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Photo Credit: Lex Rojas | Daily Texan Staff

Researchers have broken boundaries and created the smallest circuit transistor ever developed. The transistor, at 1 nanometer in diameter, is about 1/50,000 the size of a strand of human hair.

Professors from The University of Texas at Dallas, University of California, Berkeley and Stanford University worked together to build this transistor, which sends controlled electrical signals to a source and can be switched on or off to trigger different features. It was previously thought that transistors could not be smaller than 5 nanometers when set on silicon-based circuit boards. 

“This is the smallest transistor ever fabricated and characterized,” said Moon Kim, a material science professor at UT-Dallas. “It’s a glimpse of what we can expect for the pushing down of the size of silicon based technology.”

The researchers built the transistor using a new base compound: a chemical called molybdenum disulfide. This new compound is part of a larger family of transition metals called dichalcogenides, which can form semiconductor sheets only three atoms thick. 

“A particular material that we’d been looking for was transition metal and dichalcogenide materials,” Kim said. “It’s a combination of those materials with conventional materials that determines how well they behave in terms of the transistor behavior.”

Transistors are composed of three functioning terminals: the source, where electrons travel from; the drain, where electrons travel to; and the gate, which controls how many electrons pass through the transistor. Sujay Desai, an electrical engineering and computer science doctorate student at the University of California, Berkeley, said that the researchers were able to create such a small gate by developing carbon nanotubes, each with a diameter of 1 nanometer.

“We used a carbon nanotube [which] can be naturally used as a 1-nanometer diameter use,” Desai said. “This offers us a significant advantage.”

According to Desai, if a silicon gate has less than a 5-nanometer diameter, it becomes nearly impossible to control the flow of electrons through the transistor, leading to electron leakage. This is due to the weight and density of the silicon material; silicon is a lighter material than molybdenum disulfide. 

“For silicon devices, there’s high [electron] leakage, so we wanted to try a new material,” said Qingxiao Wang, an electro-science doctorate student at the University of Texas at Dallas. 

The breakthrough of this transistor size defied what is known as Moore’s Law, which declares that the number of electric transistors on an electronic chip will double every two years until stopped at the threshold of 5 nanometers, according to Desai.

“Using the conventional processing which [the] industry uses today, it is not possible to make a 1-nanometer feature.” Desai said. 

However, the smaller the transistors get, the faster and more efficient they become, according to Desai. 

“First, it offers better performance,” Desai said. “Second, the cost of operation goes down, and third is that you have higher linkage, which means that you can have more circuits and thereby more functionality.”

Though the future integration of this compound material remains a long way off, this invention is a glimpse of what is yet to come, Kim said. 

“At the moment, this is a great achievement in terms of providing the future feasibility,” Kim said. “Whether you can actually have this in your mobile device or computer device is another story.”