One of the most widespread effects of the COVID-19 pandemic has been the ongoing global semiconductor chip shortage. Pandemic-induced supply chain disruptions coupled with surging demand have stymied OEMs and automotive manufacturers from procuring chips in the quantities needed.
The price of silicon metal has soared in recent years. Image used courtesy of Refinitiv Datastream and Reuters
Semiconductor materials such as silicon, germanium, and gallium arsenide have historically been used to create chips. One of several causes of the chip shortage has been skyrocketing silicon metal prices due to production cuts by the Chinese government and other factors.
While silicon and other common semiconductor metals will likely remain essential for years to come, researchers are investigating alternative semiconductor materials for certain types of chips.
Penn State and MIT Zero In on Tin Selenide
With funding from the U.S. Office of Naval Research and the National Science Foundation, researchers at Penn State University, in collaboration with MIT, are looking into a new type of semiconductor material for photonic chips.
Layers of tin selenide (SnSe) grown on a substrate. Image used courtesy of Wouter Mortelmans/MIT and Penn State University
Tin selenide is a binary compound material consisting of tin and selenium in a 1:1 ratio—just a few atoms thin. Tin selenide (SnSe) displays two different colors—each visible depending on the orientation of the material. This orientation-dependent optical property makes it suitable for photonic applications, particularly to compute, transmit, or store information using light. The Penn State researchers suggest that tin selenide offers these capabilities using less energy than current electronic devices.
Epitaxy: The Building Blocks to Precise Manufacturing
To produce tin selenide, however, a precise manufacturing methodology is critical. Specifically, SnSn production relies on a process called epitaxy. In simple terms, epitaxy is the process of depositing a layer of material on top of a crystalline substrate.
Various aspects of 2D materials development. Image courtesy of Penn State University
To understand how to properly fabricate a tin selenide chip using epitaxy, MIT professor Rafael Jaramillo worked with the 2D crystal consortium (2DCC) at Penn State University. The 2DCC offers cutting-edge facilities and resources to research crystallized materials. In the case of tin selenide, the researchers used rectangular-shaped unit cells assembled on a base plate made of aluminum oxide.
The Merits of Photonic Chips
Since photonic chips use light instead of electrons to communicate, they offer some benefits over conventional chips. Photonic chips can be vastly more efficient than electronic chips. In fact, a photonic chip devised by MIT in 2019 was estimated to be 10 million times more efficient than its electrical counterpart.
When used in data centers, for example, photonic chips can significantly reduce the total power consumption. On a larger scale, photonics may reduce the total amount of greenhouse gasses required to power modern technological infrastructure.
Additionally, photonic optoelectronic devices avoid many of the problems associated with electrical crosstalk in cabling. Crosstalk in conventional electronic circuits—for example, between traces on a PCB or between cables—is caused by induced EMI as current flows through a trace. There are a variety of ways that these effects can be mitigated in a conventional chip, which often require additional engineering resources to solve.
Crosstalk between cables in conventional electrical communication. Image used courtesy of Actelis
By leveraging novel materials such as tin selenide, researchers have taken one step closer to finding better ways to manufacture photonic devices.
