A new dual-sided chip that combines its photonic and electronic functions simultaneously has been developed by Cornell University researchers in the US.
The researchers made a functional device in which the electronics integrated on one side drive LEDs on the other – a feat never before achieved in any material, according to the Cornell team.
The innovation could reduce the fabrication steps required for optical devices such as microLEDs, which could speed-up manufacturing and reduce costs.
GaN surfaces exhibit different physical and chemical properties
Gallium nitride (GaN) is unique among wide-bandgap semiconductors because it has a large electronic polarisation along its crystal axis, which gives each of its surfaces dramatically different physical and chemical properties. The gallium, or cation, side has proved useful for photonic devices such as LEDs and lasers, while the nitrogen, or anion, side can host transistors.
Cornell’s Jena-Xing Laboratory made a functional device in which a high electron mobility transistor (HEMT) on one side drives LEDs on the other.
“To our knowledge, nobody has made active devices on both sides, not even for silicon,” said doctoral student Len van Deurzenvan. “One of the reasons is that there’s no additional functionality you get from using both sides of a silicon wafer because it’s cubic; both sides are basically the same. But gallium nitride is a polar crystal, so one side has different physical and chemical properties than the other, which gives us an extra degree in designing devices.”
Advance could lower manufacturing costs of microLEDs
Currently, LED displays have a separate transistor and independent fabrication processes. An immediate application for the dual-sided chip is microLEDs: fewer components, occupying a smaller footprint and requiring less energy and materials, and manufactured quicker for lower cost.
“Now you may not require the different processors to perform different functions, reducing the energy and speed lost in the interconnections between them that requires further electronics and logic,” explained Professor Debdeep Jena, who led the project. “Many of those functionalities shrink into one wafer with this demonstration.”
In addition, because the GaN substrates have a high piezoelectric coefficient, they can be used as bulk acoustic wave resonators for filtering and amplifying radio frequency signals in 5G and 6G communications. The semiconductors could also incorporate lasers instead of LEDs for LiFi – transmissions.
“You could essentially extend this to enable the convergence of photonic, electronic and acoustic devices,” van Deurzen said. “You’re essentially limited by your imagination in terms of what you could do, and unexplored functionalities can emerge when we try them in the future.”
The research was recently published in Nature.
