عنوان

First Developments of AlSiO Gate Dielectrics by MOCVD:

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انگلیسی

First Developments of AlSiO Gate Dielectrics by MOCVD:

[Thesis]

Chan, Silvia Huiting

A Pathway to Efficient GaN Electronics

Mishra, Umesh KDenBaars, Steven P

2018

Mishra, Umesh KDenBaars, Steven P

2018

High-quality gate dielectrics are key to securing the performance and reliability needed in GaN-based electronics to drive widespread adoption. GaN has emerged as a strong contender to serve a range of applications in the rapidly growing field of power electronics due to its attractive wide-bandgap and high mobility. As power devices regularly experience high levels of current and high fields, a robust gate dielectric offers the only gating solution that can permit long-term, stable switching operations under these strenuous electrical conditions. However, GaN does not possess a high-quality native oxide, and despite more than a decade of research efforts, a definitive agreement on a preferred gate dielectric material and its deposition technique have yet to be reached. As it currently stands, the long-term performance of GaN transistors is limited by the gate dielectric and its interface with GaN. Hence, the technical development of high-quality gate dielectrics, such as the work illustrated here, will be a prerequisite to the success of GaN for energy-efficient power electronics. This dissertation documents the material selection, growth, and characterization of gate dielectrics, as well as the development of the gate integration process into GaN power transistors. This work describes the first uses of metalorganic chemical vapor deposition (MOCVD) to explore the growth design space of in situ gate oxides on III-nitride epitaxy. In addition, MOCVD growth was used to tune the crystallinity and interfacial/bulk properties of the gate oxides. Metal-oxide-semiconductor (MOS) capacitors served as test structures for electrically characterizing various MOCVD gate oxides for the following features: oxide leakage current, breakdown field, fixed charge, interface and border trap density, charge-to-breakdown, and time-to-breakdown capabilities. MOCVD growth studies commenced with Al2O3 gate dielectrics on GaN and tuning of their electrical properties. A turning point came in the technical development of Al2O3 when the growth space of amorphous Al2O3 was found to be limited. Investigations progressed to AlSiO dielectrics, which was formed by supplying Si into the Al2O3 growth process. This alloying growth strategy extended the amorphous stability as well as improved the electrical properties. Amorphous Al2O3 and AlSiO exhibited superior characteristics over crystalline Al2O3 dielectrics, with lower leakage, higher breakdown, and reduced interface-state and border trap densities. Moreover, AlSiO excelled with a predicted lifetime of 20 years for high electric fields >3 MV/cm based on time-dependent dielectric breakdown measurements. A gate regrowth process was developed to integrate MOCVD dielectrics into vertical GaN trench MOSFETs. The process consisted of an annealing treatment to repair processing damage, followed by a GaN regrowth prior to dielectric deposition to recreate the in situ, high-quality dielectric/GaN interface. This work reports the first growth developments of AlSiO gate dielectrics for GaN-based devices and concludes with the first demonstration of a high-performance AlSiO-gated GaN power FET.

Sacks, Michael

Chan, Silvia Huiting

UC Santa Barbara

p

[Thesis]

276903

a

Y