A team at the University of Wisconsin-Madison led by Jack Ma, assistant professor of electrical and computer engineering, has developed a method of making flexible, thin-film transistors (TFTs) that are not only inexpensive to produce, but also capable of operating at a world-record speed of 7.8 GHz, more than 50 times faster than previous flexible TFTs.

Until now, flexible TFTs have been relatively slow, operating in the 0.5 GHz range. This is fine for applications such as LCD, but not for applications such as military surveillance antennas that require high-performance but flexible circuitry for easy storage.

Several factors contribute to the record-breaking speed of their TFTs:
Nanoscale-thin membranes of single-crystal silicon, which has greater electron mobility and greater speed, are used, while previous TFTs are usually made of organic materials or amorphous or poly silicon.
2. Low-resistance electrode contacts, which has been rather challenging because the high temperatures needed to activate low-resistance contact connections melt the polymer substrates on which the transistors are fabricated. The team overcame this obstacle by using two steps. First, they made the contact connectors on a bulk silicon substrate to achieve low resistance, and then transferred the single-crystal nanomembranes to the flexible substrate to continue fabrication.
3. The TFT gates are made of silicon monoxide, not the usual silicon dioxide. Silicon monoxide has lower processing temperatures, higher electric capacity, thus can be made thinner than the dioxide. As a result, the device speed becomes even faster.

This research has been published in Applied Physical Letters.

(Image credit: Jack Ma)
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