New Transistor Could Shrink Communications Devices on Smartphones

University of Michigan, Ann Arbor, MI

Electrical and Computer Engineering Research Scientist Ding Wang and Graduate Student Minming He from Professor Zetian Mi’s group are working on the epitaxy and fabrication of high electron mobility transistors based on a new nitride material, ScAlN, which has been demonstrated recently as a promising high-k and ferroelectric gate dielectric that can foster new functionalities. (Image: Marcin Szczepanski/Lead Multimedia Storyteller, Michigan Engineering)

After announcing a ferroelectric semiconductor at the nanoscale thinness required for modern computing components, a University of Michigan team has demonstrated a reconfigurable transistor using that material. The study is featured in Applied Physics Letters.

“By realizing this new type of transistor, it opens up the possibility for integrating multifunctional devices, such as reconfigurable transistors, filters, and resonators, on the same platform — all while operating at very high frequency and high power,” said lead author and U of M’s Zetian Mi. “That’s a game changer for many applications.”

At its most basic level, a transistor is a kind of switch, letting an electric current through or preventing it from passing. This one demonstrated at U of M is known as a ferroelectric high-electron mobility transistor (FeHEMT) — a twist on the HEMTs that can increase the signal as well as offer high switching speed and low noise. This makes them well-suited as amplifiers for sending out high-speed signals to cell towers and Wi-Fi routers.

Ferroelectric semiconductors stand out from others because they can sustain an electrical polarization, like the electric version of magnetism. But, unlike a fridge magnet, they can switch which end is positive and which is negative. In the context of a transistor, this capability adds flexibility.

“We can make our ferroelectric HEMT reconfigurable,” said first author Ding Wang. “That means it can function as several devices, such as one amplifier working as several amplifiers that we can dynamically control. This allows us to reduce the circuit area and lower the cost as well as the energy consumption.”

Areas of particular interest for this device are reconfigurable radio frequency and microwave communication, as well as memory devices in next-generation electronics and computing systems.

“By adding ferroelectricity to an HEMT, we can make the switching sharper. This could enable much lower power consumption in addition to high gain, making for much more efficient devices,” said co-corresponding author Ping Wang.

The ferroelectric semiconductor is made of aluminum nitride spiked with scandium — a metal sometimes used to fortify aluminum in performance bicycles and fighter jets. It is the first nitride-based ferroelectric semiconductor, enabling it to be integrated with the next-gen semiconductor gallium nitride. Offering speeds upward of 100 times that of silicon, as well as high efficiency and low cost, these semiconductors are contenders to displace silicon as the preferred material for electronic devices.

“This is a pivotal step toward integrating nitride ferroelectrics with mainstream electronics,” Mi said.

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