PhD Defense: "InP DHBTs in a refractory emitter process for THz Electronics"

Vibhor Jain

July 6th (Wednesday), 2:00pm
Elings Hall, Room 1601

High speed InP double heterojunction bipolar transistors (DHBTs) have potential applications in 0.3 – 1.0 THz ICs for imaging, sensing, radio astronomy and spectroscopy; in 2 – 20 GHz mixed signal ICs like wideband, high-resolution analog to digital converters, digital to analog converters, and direct digital frequency synthesizers; and in 100 – 500 GHz digital logic. The efforts pursued to increase the bandwidth of InP based DHBTs through improved processing techniques and design changes are presented in this talk. Lithographic and epitaxial scaling of critical device dimensions and reduced access resistances have decreased the transit delays and RC delays associated with the device thereby improving device bandwidth. A new emitter process for high yield emitters, scalable to 64nm node, has been demonstrated and device results at 110nm and 220nm junction nodes are presented. The emitter stack incorporates all refractory metals to sustain high current density without problems of electromigration and contact diffusion under stress. Emitter space charge region was redesigned to overcome problems of source starvation and high space charge region resistance. New and improved surface preparation techniques were developed to achieve low contact resistivity. Reduction in base access resistance was achieved through modified epitaxial design and process optimization. Improved RF performance at smaller emitter junction widths can be achieved with improved lithographic procedures for base contact and base mesa definitions.
A theoretical analysis of the abrupt InP/InGaAs emitter base junction was performed to study significant contributors to transconductance degradation at high current density. These include modulation of the electron injection barrier at emitter base heterojunction by the applied bias, drop in the electron quasi Fermi level in the emitter space charge region and degenerate electron injection and quantum mechanical reflection at the hetero-interface.

Host: Professor Mark Rodwell

Hosted by: Professor Mark Rodwell