Innovation in Transistor Design with Carbon Nanotubes

The New York Times article “IBM Scientists Find New Way to Shrink Transistors” by John Markoff focuses on the goal of the semiconductor industry to create smaller transistors in order to remain competitive while emphasizing cutting-edge design strategies with the use of carbon nanotubes. By switching from traditional methods to carbon nanotubes, IBM’s Physicist Wilfried Haensh, of the research group, highlights the improvements in power saving and ultimately increasing the speed of IBMs microprocessors sevenfold.

The transistor industry constantly faces what is known as the “Red Brick Wall”, or the inability to shrink the transistor due to technical limitations. In the mid-1980s, technical limitations surrounded ways to break the one-micron barrier in which methods using optical technology proved to be the solution. Early in 2000, these technical limitations changed to include gate stack, interconnects, and others. Still, the transistor industry discovered new ways to adapt to these crises and continue. Today, IBM faces technical limitations include a variety of factors such as electrical resistance, temperature, and materials.

Electrical resistance refers to the difficulty of passing electrical current through conductive material and with more resistance less electricity will flow. Electrical resistance also refers to the relationship between voltage and current. In essence, higher resistance will limit the electric current able to flow through the wire. Reducing electrical resistance will also increase processor chip speed while shrinking the physical limitations.

Along with electrical resistance, as transistor temperature increases, so will the collector current. A continual increase in heat will cause thermal runaway to occur, ultimately breaking the transistors. Limiting both electrical resistance and heat becomes a priority in order to maintain transistor stability as well as higher performance gains. All of these technical limitations compound to impact processor chip speed and pose challenging design choices for chip designers.

For a little over a decade, multi-core technology has been implemented for more efficient power consumption as opposed to increasing the processing speed, due to resistance and heat increases in smaller transistors sizes in conventional silicon transistors. In response to these technical barriers, IBM has chosen to switch from silicon to carbon nanotubes because of its useful properties in its transistors. Carbon nanotubes are strong, light, and conductive tubular cylinders of carbon atoms which form a one atom thick matrix. Carbon nanotubes also have none of the major physical degradation common to other metals, making it more stable as well as 15 times more conductive and with 1000 times more current capacity than copper. Dario Gil at IBM recognizes the clear advantages of carbon nanotubes over other materials, stating: “Of all the possible materials, this one is at the top of the list by a long shot.”

Another key innovation with the use of carbon nanotubes involves IBM’s new design approach towards the placement of the carbon nanotubes in transistors. The new design features the use of carbon nanotubes in parallel rows to connect ultrathin metal wires together, all the while focusing on decreasing the contact size to metal wires. By finding ways to align the carbon nanotubes close together, IBM can shrink the size of each transistor. In this way, the carbon nanotube will be used for electrical switching and help perform the essential functions of a transistor. IBM proposes future enhancement to design in the next decade by decreasing the contact size from 40 to 28 atoms in width.

Zach Allen & Parun Thamutok

References
J. Markoff, “IBM Scientists Find New Way to Shrink Transistors,” The New York Times, 01-Oct- 2015. [Online]. Available at: http://www.nytimes.com/2015/10/02/science/ibm- scientists-find-new-way-to-shrink-transistors.html?_r=1. [Accessed: 10-Mar-2016].
“Nanocomp Technologies | What Are Carbon Nanotubes?,” Nanocomp Technologies | What Are Carbon Nanotubes?, 2014. [Online]. Available at: http://www.nanocomptech.com/what-are-carbon-nanotubes. [Accessed: 10-Mar-2016].
M. Lapels, “Has The IC Industry Hit A ‘Red Brick Wall’?,” Semiconductor Engineering, 09-Jun-2014. [Online]. Available at: http://semiengineering.com/will-ic-industry-hit-red-brick-wall/. [Accessed: 10-Mar-2016].