A Large 'Small' Project
Moore’s Law predicts that the number of transistors per square inch on integrated circuits will double every year (later revised to 18 months), and it has held true ever since Intel cofounder Gordon Moore announced it in 1965.
But as microelectronics researchers try to pack more and more circuits into increasingly tiny packages, they’re colliding with the peculiar physics that take place on the nanoscale. When things get exceedingly small, the risk of short-circuiting soars and the very flow of electrons makes them too hot to function.
Philip Liu (Macaulay Honors College at City College, B.E. in chemical engineering, 2012) intends to pursue a solution thanks to a 2013 National Science Foundation Graduate Research Fellowship. This $126,000 three-year grant is the most prestigious award for graduate research in the science, technology, engineering and mathematics (STEM) fields.
Guided by two professors in the chemical engineering doctoral program at the University of Texas at Austin, Liu is working to create a material that will insulate electrical circuits and conduct heat efficiently away from them – two seemingly incompatible functions that have never been combined before. He hopes to do this with a polymer composite, which would enable more silicon chips to be stacked upon one another than is now possible. And that would allow adherence to Moore’s Law.
“My first project is to synthesize boron nitride nanotubes, which are long skinny tubes with nanometer diameters,” Liu says. (A nanometer is 1 billionth of a meter; a human hair is about 100,000 nanometers wide. Boron nitride is a chemical that is electrically insulating and heat conducting.) But, he explains, the method used so far to create boron nitride nanotubes yields few tubes: brute-force fragmenting chunks of the material. So Liu’s initial hurdle is to come up with a more elegant and efficient manufacturing process.
“The next step would be to functionalize the nanotubes by attaching organic functional groups such as ketones or alcohols, which will serve as sites where we can attach long-chain polymers,” he says.
The functionalized nanotubes would then be dispersed in a polymer, which would latch onto the nanotubes in the designated places. That would form a composite that would have high heat conductivity and would electrically insulate the tiny copper wires that run vertically between stacked silicon integrated circuits.
Liu decided to pursue this project after hearing a presentation at the University of Texas by C. Grant Willson, who holds the Rashid Engineering Regents Chair. He also studies with Brian Korgel, the Matthew Van Winkle Regents Professor of Chemical Engineering.
“I work with Doctor Korgel, who has the equipment and knowledge to make the nanomaterials, and with Doctor Wilson to incorporate these materials into commercially viable products,” he says.
Liu switched into this project after having worked on batteries at CUNY’s Energy Institute at City College.
“I worked on zinc batteries, trying to understand the morphologies of dendrites that form when they are charged,” he says. Dendrites are crystallized minerals that collect on battery terminals and eventually interfere with their functioning. “The experience inspired me to pursue research, because you tinker with novel ideas and apply them.”
As an undergraduate, Liu had an NSF-funded Research Experience for Undergraduates at Columbia University, where he worked with mechanical engineering associate professor Chee Wei Wong on modeling nanoparticles and determining their influence on the optical properties of thin films. He also worked on artificial eye research at the Lawrence Livermore National Laboratory one summer; his tasks included preparing electrodes that would carry images from the artificial eye into the subjects’ brains.
Liu intends to work in industry after earning his doctorate.