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FALL 2008
VOL. 35, NO. 1

ENGINEERS' DAY 2009
Mark your calendars for Friday, Oct. 16, 2009, when the Badgers play the Hawkeyes.

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Self-assembling polymer arrays
improve data storage potential

Lithographically patterned surface (upper left panel), block copolymers (upper right panel) nanoscale silicon pillars (bottom panel)

Researchers from the University of Wisconsin-Madison and Hitachi Global Storage Technologies have reported a way to improve the quality and resolution of patterned templates such as those used to manufacture hard drives and other data storage devices. When added to lithographically patterned surfaces such as those shown in the upper left panel of this composite image, specially designed materials called block copolymers self-assemble into structures, shown in the upper right panel, with improved quality and resolution over the original patterns. These structures can be used to make templates with nanoscale elements like the silicon pillars shown in the bottom panel, which may be useful for manufacturing higher capacity hard disk drives. (large image)

A new manufacturing approach could help overcome technological limitations currently facing the microelectronics and data-storage industries, paving the way for smaller electronic devices and higher-capacity hard drives.

“In the past 20 to 30 years, researchers have been able to shrink the size of devices and the size of the patterns that you need to make those devices, following the use of the same types of lithographic materials, tools and strategies, only getting better and better at it,” says Smith-Bascom Professor of Chemical and Biological Engineering Paul Nealey, who directs the Nanoscale Science and Engineering Center (NSEC).

Now, those materials and tools are reaching their fundamental technical limits; in addition, extrapolating lithography (a process used to pattern manufacturing templates) to smaller and smaller dimensions may become prohibitively expensive. Advances will require a commercially viable approach that is capable of meeting demanding industry quality-control standards.

Nealey, Howard Curler Distinguished Professor of Chemical and Biological Engineering Juan de Pablo and NSEC colleagues partnered with researchers from Hitachi Global Storage Technologies to test a promising new twist on the traditional methods. In the August 15 issue of the journal Science, the team demonstrated a revolutionary patterning technology that offers performance improvements and reduces the time and cost of manufacturing.

The method combines lithography techniques traditionally used to pattern microelectronics with novel self-assembling materials called block copolymers. When added to a lithographically patterned surface, the long molecular copolymer chains spontaneously assemble into designated arrangements. “There’s information encoded in the molecules that results in getting certain size and spacing of features with certain desirable properties,” says Nealey. “Thermodynamic driving forces make the structures more uniform in size and higher density than you can obtain with the traditional materials.”

The block copolymers pattern the resulting array down to the molecular level, offering a precision unattainable by traditional lithography-based methods alone and even correcting irregularities in the underlying chemical pattern. Such nanoscale control also allows the researchers to create higher-resolution arrays capable of holding more information than those produced today.

In addition, the self-assembling block copolymers only need one-fourth as much patterning information as traditional materials to form the desired molecular architecture, making the process more efficient, Nealey says. “If you only have to pattern every fourth spot, you can write those patterns at a fraction of the time and expense,” he says.

The collaboration provided very clear objectives about creating a technology that is industrially viable. “This research addresses one of the most significant challenges to delivering patterned media—the mass production of patterned disks in high volume, at a reasonable cost,” says Richard New, director of research at Hitachi Global Storage Technologies.

In its current form, this method is very well-suited for designing hard drives and other data-storage devices, which need uniformly patterned templates—exactly the types of arrangements the block copolymers form most readily. With additional advances, the approach may also be useful for designing more complex patterns such as microchips.

In addition to support from the National Science Foundation, NSEC and Hitachi Global Storage Technologies, additional funding was provided by the Semiconductor Research Corp.

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