Nanoimprint lithography allows flexible transistor dev't

A team of engineers at the University of Wisconsin-Madison have pioneered a method that could enable manufacturers to easily and cost-effectively develop high-performance transistors with wireless capabilities on huge rolls of flexible plastic.

The researchers, led by Zhenqiang (Jack) Ma, the Lynn H. Matthias Professor in Engineering and Vilas Distinguished Achievement Professor in electrical and computer engineering, and research scientist Jung-Hun Seo, has made significant headway by fabricating a transistor that operates at a record 38GHz, though their simulations show it could be capable of operating at a mind-boggling 110GHz. In computing, that translates to lightning-fast processor speeds.

It's also very useful in wireless applications. The transistor can transmit data or transfer power wirelessly, a capability that could unlock advances in a whole host of applications ranging from wearable electronics to sensors.

The researchers' nanoscale fabrication method upends conventional lithographic approaches, which use light and chemicals to pattern flexible transistors, overcoming such limitations as light diffraction, imprecision that leads to short circuits of different contacts, and the need to fabricate the circuitry in multiple passes.

Figure 1: Using a unique method they developed, a team of UW-Madison engineers has fabricated the world's fastest silicon-based flexible transistors, shown here on a plastic substrate.

Using low-temperature processes, Ma, Seo and their colleagues patterned the circuitry on their flexible transistor, single-crystalline silicon ultimately placed on a polyethylene terephthalate (more commonly known as PET) substrate, drawing on a simple, low-cost process called nanoimprint lithography.

In a method called selective doping, researchers introduce impurities into materials in precise locations to enhance their properties, in this case, electrical conductivity. But sometimes the dopant merges into areas of the material it shouldn't, causing what is known as the short channel effect. However, the UW-Madison researchers took an unconventional approach: They blanketed their single crystalline silicon with a dopant, rather than selectively doping it.

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