THESIS
2010
xiv, 60 p. : ill. ; 30 cm
Abstract
With the ever-increasing demand for high-performance RF/microwave power amplifiers and power switches, the wide bandgap AlGaN/GaN high electron mobility transistor (HEMT) technology has received special attention in recent years owing to the device’s unique capabilities of achieving high breakdown voltage, high driving current, and high-frequency operation simultaneously. Despite the tremendous progress made in material growth and device processing techniques during the last decade, the suppression of the adverse effects induced by the surface states remains to be a challenging issue....[
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With the ever-increasing demand for high-performance RF/microwave power amplifiers and power switches, the wide bandgap AlGaN/GaN high electron mobility transistor (HEMT) technology has received special attention in recent years owing to the device’s unique capabilities of achieving high breakdown voltage, high driving current, and high-frequency operation simultaneously. Despite the tremendous progress made in material growth and device processing techniques during the last decade, the suppression of the adverse effects induced by the surface states remains to be a challenging issue.
In general, silicon nitride layer grown by chemical vapor deposition (CVD) techniques has been used to passivate the device’s surface and protect the device from contaminations. However, additional leakage path could occur in the SiN layer deposited by conventional PECVD (plasma enhanced CVD), degrading the devices’ off-state performance. In this work, various dielectric materials including parylene-C, SiOF and F-SiN are investigated for passivation of AlGaN/GaN HEMT. Very low off-state leakage can be achieved with parylene-C layer, but smaller ON-state current density and even more severe current collapse occur with such passivation technique. SiOF deposited by PECVD, although initially exhibiting lower dielectric constant, is found to be unstable in air due to water absorption. Besides, the technique suffers from large off-state leakage current. F-SiN passivation that features PECVD grown SiN followed by fluorine ion implantation was found to deliver low leakage current and reasonable current collapse suppression. Detailed electrical characterizations including DC, pulsed I-V and small signal S-parameter tests were conducted to evaluate the devices’ performance. Material characterization techniques such as FTIR, XPS and SIMS were carried out to analyze the material’s physical properties. Finally, a physical model is proposed to explain the effectiveness of F-SiN as a passivation material in AlGaN/GaN HEMT.
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