Design and Development of GaN-based Vertical Transistors for Increased Power Density in Power Electronics Applications PDF Download

Author: Dong Ji
Publisher:
ISBN: 9780355764284
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Languages : en
Pages :

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Book Description
Gallium nitride (GaN)-based devices have entered the power electronics market and shown excellent progress in the medium power conversion applications. For power conversions applications > 10 kW, devices with vertical geometry are preferred over lateral geometry, since the former allows more current for a given chip area, thus provides a more economical solution for high-voltage and high-current applications. Moreover, the vertical geometry is attractive for its dispersion-free performance without passivation, a phenomenon that causes high dynamic on-state resistance (R[subscript on]) in lateral geometry high electron mobility transistors (HEMTs). In this study, GaN-based vertical transistors, which include trench current aperture vertical electron transistors (CAVETs) and in-situ oxide, GaN interlayer based trench field-effect transistors (OGFETs), have been studied both theoretically and experimentally. In order to model the devices for DC and switching performances, a device/circuit hybrid simulation platform was developed based on Silvaco ATLAS. The validation of the model was obtained by calibrating it against commercially available HEMT data. Using this hybrid model, one can start with a two-dimensional (2D) drift-diffusion model of the device and build all the way up to its circuit implementation to evaluate its switching performance. The hybrid model offers an inexpensive and accurate way to project and benchmark the performance and can be extended to any GaN-based power transistors.In the experimental portion of this study, a high voltage OGFET was designed and fabricated. An OGFET shows improved characteristics owing to a 10 nm unintentionally doped (UID) GaN interlayer as the channel. A normally-off (V[subscript th] = 4 V) vertical GaN OGFET with 10 nm UID-GaN channel interlayer and 50 nm in-situ Al2O3 was successfully demonstrated and scaled for higher current operation. By using a novel double-field-plated structure for mitigating peak electric field, a higher off-state breakdown voltage over 1.4 kV was achieved with a significantly low specific on-state resistance (R[subscript on,sp]) of 2.2 m[omega] cm2. The metal-organic chemical vapor deposition (MOCVD) regrown 10 nm GaN channel interlayer enabled a channel resistance lower than 10 [omega] mm with an average channel electron mobility of 185 cm2/Vs. The fabricated large area transistor with a total area of 0.4 mm × 0.5 mm offered a breakdown voltage of 900 V and an Ron of 4.1 [omega]. Results indicate the potential of vertical GaN OGFET for greater than 1 kV range of power electronics applications.In addition to the OGFET, the CAVET with a trench gate structure was studied in this work. By taking advantage of the two-dimensional electron gas (2DEG) in the AlGaN/GaN structure, the trench CAVET can secure an even higher channel electron mobility compared to the OGFET. The first functional trench CAVET with a metal-insulator-semiconductor (MIS) gate structure was fabricated in this work with a breakdown voltage of about 225 V. With the improvement in the fabrication process, an 880 V device with an R[subscript on,sp] of 2.7 m[omega] cm2 was demonstrated. One of the notable features of the fabricated trench CAVET is that it requires a standard MOCVD growth condition for HEMT epilayers. The simplification of the growth process is a significant achievement. Finally, a regrowth-free CAVET was demonstrated and patented. The transformative approach was realized using Si ion implantation based doping compensation in the aperture.