University of Houston Cullen College of Engineering


In Nanotech, It's Hip to be Square


Toby Weber

New nano-fabrication technique enables the creation of squares and other features that hold promise for the future of computing.

A team of professors with the Center for Nanomagnetic Systems at the University of Houston Cullen College of Engineering has developed a method of fabricating tightly packed nano-sized features with sharp corners, such as squares and honeycomb patterns, that could result in more more powerful and reliable computing devices for everything from music storage to computational research. The results have been published in the latest issue of Nano Letters.

The research team is led by Dmitri Litvinov, an associate professor in the Departments of Electrical & Computer Engineering and Chemical & Biomolecular Engineering. Other members include Paul Ruchhoeft, an associate professor in the Department of Electrical & Computer Engineering; and Stanko Brankovic, an assistant professor in that same department. Vishal Parekh, who recently received his Ph.D. from the Cullen College, and graduate student Ariel Ruiz also contributed significantly to the research efforts.

The nanofabrication method used by this group is based on electron-beam (or e-beam) lithography. E-beam lithography uses a small stream of electrons to create nano-scale patterns of openings in a thin film of material. That thin film is then used as a stencil to transfer patterns of nano-scale features onto a layer of, in this case, magnetic material.

Typically, only circular features or features with round corners can be defined with traditional e-beam lithography techniques. In the method developed by this team of researchers, though, the thin film material erodes during the pattern transfer in such a way that the circles turn into tightly packed squares or form a honeycomb pattern.

According to Litvinov, such shapes would be of great use in the areas of computing that rely on magnetic materials, such as magnetic cellular logic and magnetic recording. “This will allow for more memory and more computing power on a smaller space,” he said.

For example, bit patterning is seen as the next phase in magnetic data recording. This method stores data on nano-sized circular features that are systematically written in set spots on a magnetic recording surface. Each nano-circle holds one bit of data. Squares defined on a recording surface through this method, however, would have a larger surface area than the circles from which they are derived. That larger surface area would produce a stronger magnetic signal, allowing computers to more easily retrieve the information the bits hold and hence yielding faster and more reliable data storage devices. Furthermore, the larger bit size resulting from the increase surface area holds higher amounts of magnetic energy, which improves long-term data stability.

In addition to providing stronger magnetic signals, these squares offer larger points of contact between one another—think of two blocks touching versus two balls touching—thereby enabling stronger, more reliable interaction between magnetic features. This interaction is especially important for emerging magnetic cellular logic systems, which hold enough potential computing power that they could end up rivaling semiconductor technology. Such systems utilize the interactions of a series of magnetic nanocells in order to combine logic functions, random access memory and data storage in a single nanomagnetic computing system. Since square features provide extremely strong interaction, they are highly desirable for the development of this technology.

“There is a wide array of applications in nanomagnetics and beyond that could utilize the features that we can now fabricate,” said Litvinov. “Researchers and engineers who rely on computer simulations could benefit. So could consumers, who could have access to smaller, more powerful and more reliable electronic devices.”



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