PhD Defense: "Design and Fabrication of Sub-100 nm Base-Emitter Junctions of THz InP DHBTs"

Han-Wei Chiang

October 16th (Thursday), 11:30am
Elings Hall, Room 1601

Because of their wide RF bandwidth and high breakdown voltages, npn-InGaAs/InP double heterojunction bipolar transistors (DHBTs) have extensive applications in monolithic microwave integrated circuits (MMICs) such as high performance transceivers, near-terabit optical fiber link, and THz amplifiers in radar/imaging systems. The improvements in the performance of DHBTs were made possible because of device scaling. Two important issues regarding the design and fabrication of the sub-100nm base-emitter junction of DHBTs will be addressed.

First, the process flow for the refractory emitter metal stack developed for DHBTs with 250-100nm emitter width is not feasible for device with <100nm emitter width. In order to further scale DHBT to below 100 nm emitter width, the existing process flow has been re-calibrated. A composite dielectric sidewall process has also been developed for DHBTs to protect the exposed base semiconductor region. With the improved process features, DHBTs with a 85 nm-wide base-emitter junction can be reliably fabricated. Second, a reduction in DC-current gain (β) associated with device scaling has been observed experimentally. In order to assess the causes of the reduction, the electron transport in the DHBT base region was emulated by a commercial simulator. A model for DC-β at high injection current density was established and verified against the experimental results. The model allows the estimation of β, which benefits the design of the future scaling generations of DHBTs. Moreover, new geometries for the base-emitter junction have been designed in order to suppress the Auger recombination and lateral electron diffusion in the bulk base region. According to our simulation, the new designs could potentially improve the DC-β of THz DHBTs to >50 if the process flow required by the designs could be adequately integrated into the DHBT fabrication.

About Han-Wei Chiang:

Han-Wei Chiang received the B.S. degree in Materials Science and Engineering from National Taiwan University, Taiwan, in 2007. After joining UCSB in 2009, he received his M.S. degree in Electrical and Computer Engineering in 2011, and is currently a PhD candidate in the same department. He has worked with Prof. Mark Rodwell on the development of THz InGaAs/InP DHBT since 2009.

Hosted by: Professor Mark Rodwell