By Kate Kurtin
High-tech industries are always looking for ways to improve their products– trying to make things that are fast, faster; things that are low powered, lower powered; and things that are small, smaller. Many of these improvements are enabled by semiconductor technology. By continuously improving electronic device design and introducing new materials, new technologies are advancing at an incredible rate. The second part of this two-pronged improvement plan is at the heart of Dr. Brian Willis’ research. Dr. Willis is an associate professor and director of the Chemical Engineering Program who joined UConn in 2008.
“For every application there is a material that is performing some function and you can always improve that function and make it better at what it does,” he explained. Dr. Willis received a National Science Foundation Early Career (CAREER) Development Award in 2003, with continued funding this year, for his work involving the integration of oxide materials with the semiconductor industry standard, silicon. “Crystalline oxides will add new capabilities to future electronic devices,” Dr. Willis explained. The age of using silicon as the primary functional material in electronic devices has run its course. As semiconductor devices near the limits of miniaturization and speed new ideas are necessary to add value. However, because silicon is so widely used and is the industry standard, Dr. Willis explained, it is likely that silicon will remain as the platform or support material, and therefore, the way to improve its functionality is to integrate it with another material. Looking at oxides has allowed Dr. Willis to expand the functionality of semiconductor research. “Oxides have unique functional properties that would enable you to make interesting devices from that you can’t make from silicon,” he explained.
“Technologically, because silicon is such an established platform in nano-electronics, the most practical applied way forward is to somehow integrate the oxides with the silicon,” Dr. Willis continued. How? To do so, Dr. Willis explained that researchers must “go around Mother Nature to grow oxides materials atom by atom on top of a silicon wafer.” But Mother Nature impedes this process because, when silicon is mixed with oxygen — an element needed to form oxides — we can inadvertently make silicon dioxide, experienced more widely as a major component of sand, and very stable. “You have sort of a ‘Catch-22’ or a paradox,” Dr. Willis continues. “You want to grow an oxide on top of silicon, but you have to avoid forming silicon dioxide.” That is where the real trick comes.
The process of layering silicon with oxide materials is relatively untapped, and there is good reason for this: oxides and silicon are very different materials, with widely different structural properties. To explain this concept Dr. Willis turned to a memorable high school chemistry lesson, “like mixes with like” and these materials are so unlike that integrating them is like trying to mix oil and water.
This dilemma is solved by the introduction of alkaline earth metals. Calcium, barium, and strontium have special properties that enable the oxides to be grown on the silicon without forming silicon dioxide. Essentially, they love oxygen more than silicon. “They facilitate the integration of the oxides with the silicon substrate,” Dr. Willis further explained. This layering using the alkaline earth metals has been done before in a laboratory setting and, therefore, has been proven possible. What is lacking is any real-world analysis. To make this a practical technology that could be integrated into everyday processes, the technique must have manufacturability. This is the crux of Dr. Willis’ research — making this process real-world applicable and cost effective.
With his graduate student and post-doctoral research assistants, Han Wang and Changbin Zhang, Dr. Willis has passed the first milestone in discovering the steps necessary for this integration of oxides and silicon, and now it may be only a matter of time before they are integrated in a manufacturable way and ready to be adopted by the industry. The importance of this research is at the very core of the technology industry. If this integration is successful, it will “make devices better in the future, so that you can have new functionalities 10 years from now that you wouldn’t be able to think of right now,” Dr. Willis explained.
As an academic, Dr. Willis is also involved in educational initiatives. Next summer, he will host high school science teachers in his lab and teach them about basic characterization tools that are used in nanotechnology. The goal of this workshop is for the teachers to take the lessons they learn back to their classrooms. One simple experiment might involve having the teachers look at silicon devices, learn how they work and then conduct experiments aimed at unveiling the component makeup of the wafers. The teachers would be able to see the individual atoms in the lattice, and be able to reconstruct the experiment in their classrooms to teach students about silicon technology, atomic structures and how the wafers are used in everything from cell phones or video game consoles.
The future of the semiconductor industry is boundless. “The semiconductor industry is a fun industry because they are driven very strongly by new products and new ideas,” Dr. Willis said. “Companies like Intel are investing in new technologies that I originally thought were too far out, too academic, or too high risk. They’re doing it because nanotechnologies are the driving force for future projects.” It is for this reason that technology companies are very open to new ideas, even crazy and difficult new ideas. “If the industry doesn’t innovate, it will die,” Dr. Willis finished.