Date of Award

3-3-2008

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering

Department

Department of Electrical and Computer Engineering

First Advisor

James Fellows, PhD

Abstract

A sensitivity analysis of AlGaN/GaN HEMT performance on material and process variations was performed. Aluminum mole fraction, barrier thickness, and gate length were varied ± 5% over nominal values to determine how sensitive simulated device performance was to changes in these 3 parameters. Simulated data was generated with the Synopsys TCAD software suite using a physics-based HEMT model. To validate model performance, simulated data was correlated with experimental data, which consisted of wafer epilayer characterization data as well as DC and small-signal RF device performance data from 1-26 GHz. Trends were observed in the experimental data due to variations in the fabrication process. Epilayer data showed cross-wafer trends in sheet resistance, barrier thickness and Al mole fraction but didn’t show any discernable trends in mobility or sheet carrier concentration. Maximum output current was the only measured performance metric that showed a strong trend across the wafers. Data from two different device geometries on the same wafers were compared to determine whether performance variations across a wafer could be attributed to epilayer variation or device geometry. Variation in power and current gain cutoff frequencies was attributed to differences in the device geometry whereas variations in maximum output current was correlated to sheet resistance and barrier thickness variation. Simulated device performance showed varying sensitivities when ± 5% changes in aluminum mole fraction, barrier thickness, and gate length were made. Al mole fraction and barrier thickness had a large effect on DC output up to 40%, while the gate length only moderately effected DC output by 2-3%. However, of all 3 parameters, changes in gate length had the greatest effect on the RF performance (1-3%) while RF performance was negligibly affected by changes in Al mole fraction and barrier thickness. Although varying these three parameters affects device performance, variation in these three parameters alone is insufficient to accurately account for variations in measured device performance.

AFIT Designator

AFIT-GE-ENG-08-17

DTIC Accession Number

ADA482821

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