Fastest flexible silicon transistor developed

Scientists have pioneered a unique method to easily and cheaply fabricate high-performance transistors with wireless capabilities on huge rolls of flexible plastic.

Researchers from the University of Wisconsin-Madison in US created a transistor that operates at a record 38 gigahertz, though their simulations show it could be capable of operating at a mind-boggling 110 gigahertz. In computing, that translates to lightning-fast processor speeds, researchers said.

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, researchers said.

The 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.

Using low-temperature processes, Zhenqiang Ma, Jung-Hun Seo and 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.

Sometimes the dopant merges into areas of the material it should not, causing what is known as the short channel effect.

However, the researchers took an unconventional approach: They blanketed their single crystalline silicon with a dopant, rather than selectively doping it.

Then, they added a light-sensitive material, or photoresist layer and used a technique called electron-beam lithography – which uses a focused beam of electrons to create shapes as narrow as 10 nanometres wide – on the photoresist to create a reusable mold of the nanoscale patterns they desired.

They applied the mold to an ultrathin, very flexible silicon membrane to create a photoresist pattern. They finished with a dry-etching process – essentially, a nanoscale knife – that cut precise, nanometer-scale trenches in the silicon following the patterns in the mold, and added wide gates, which function as switches, atop the trenches.

With a unique, three-dimensional current-flow pattern, the high performance transistor consumes less energy and operates more efficiently.

Because the method enables them to slice much narrower trenches than conventional fabrication processes can, it also could enable semiconductor manufacturers to squeeze an even greater number of transistors onto an electronic device. The research was published in the journal Scientific Reports.