Xu's novel double heterojunction biopolar transistor earns Best Student Paper at CSICS

Improved transistor reliability research wins award

ECE graduate student Huiming Xu won the 2014 Compound Semiconductor Integrated Circuit Symposium (CSICS) Best Student Paper Award for his research on a novel double heterojunction bipolar transistor (DHBT). Xu’s advisor, Professor Milton Feng, received the award last week at the 2015 CSICS conference.

ECE Professor Milton Feng (right) and coauthor Barry Wu (left), who works at Keysight Technologies (formerly Agilent), receive the 2014 CSICS Best Student Paper award for colleague Huiming Xu from CSICS symposium chair Chuck Campbell.
ECE Professor Milton Feng (right) and coauthor Barry Wu (left), who works at Keysight Technologies (formerly Agilent), receive the 2014 CSICS Best Student Paper award for colleague Huiming Xu from CSICS symposium chair Chuck Campbell.
Xu’s work demonstrated the effectiveness of adding an emitter ledge to a Type-II GaAsSb/InP DHBT to improve the transistor’s performance and reliability. For years, engineers would reduce the width of a transistor’s emitter in order to improve its speed. However, shrinking the emitter width causes the transistor’s current gain to drop, which, in turn, makes the device less reliable.

“Image a square, when the square becomes smaller and smaller, the square’s area to the square’s peripheral length ratio will reduce,” explained Xu. “So, as the emitter area reduces, the emitter peripheral surface recombination current becomes very important. If the peripheral is really leaky (high emitter peripheral surface recombination current density), then lots of electrons will be leaked out through peripheral, leading to reduced current gain.”

As Xu demonstrated, the ledge passivates the emitter peripheral surface, making it less leaky, which improves the current gain. In fact, his approach improved the current gain by 50% over existing DHBTs, which are used for high-speed instrumentation and communication systems.

“This type of device could be a key enabler of next-generation communication technology, such as 5G mobile networks and 100G Internet,” said Xu, who earned his PhD in late 2014 as a member of Professor Feng’s High-Speed Integrated Circuits group.

Today, Xu works as a senior electrical engineer at Skyworks Solutions, a leading supplier of analog semiconductor communication components. In addition to Feng, Xu’s co-authors on the paper were Illinois graduate student Ardy Winoto and Barry Wu, who works at Keysight Technologies, formerly known as Agilent Technologies.