Showing papers by "John W. Palmour published in 1999"

High-power microwave GaN/AlGaN HEMTs on semi-insulating silicon carbide substrates

Abstract: Record performance of high-power GaN/Al/sub 0.14/-Ga/sub 0.86/N high-electron mobility transistors (HEMTs) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12/spl times/125 /spl mu/m), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the -2 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-nitride HEMT under RF drive.

Insulator investigation on SiC for improved reliability

Abstract: Significant improved high-temperature reliability of SiC metal-insulator-semiconductor (MIS) devices has been achieved with both thermally grown oxides and by using a stacked dielectric consisting of silicon oxide-nitride-oxide (ONO). Capacitors of p-type 6H-SiC, n-type 6H-SiC and n-type 4H-SiC were fabricated with a variety of insulators. The best performance was accomplished only with insulators incorporating silicon dioxide. A new thermal oxidation process of growing a dry oxide then following with a wet re-oxidation anneal produces an oxide with the dielectric strength of a dry oxide and the high-quality interface of a wet oxide. MIS field effect transistors (MISFETs) with an ONO gate insulator had surface channel mobilities similar to MISFETs with thermal gate oxides, and demonstrated a lifetime of 10 days at 335/spl deg/C and 15 V bias. The lifetime of the ONO MISFET was a factor of 100 higher than for devices fabricated with deposited oxides, which had been the prior state of the art for high-temperature MISFETs on SiC.

Progress in SiC : from material growth to commercial device development

Abstract: Silicon carbide technology has made tremendous strides in the last several years, with a variety of encouraging device and circuit demonstrations in addition to volume production of nitride-based blue LEDs being fabricated on SiC substrates. The commercial availability of relatively large, high quality wafers of the 6H and 4H polytypes of SiC for device development has facilitated these exciting breakthroughs in laboratories throughout the world. These have occurred in numerous application areas, including high power devices, short wavelength optoelectronic devices, and high power/high frequency devices. This paper will describe progress made in increasing the quality and size of SiC wafers, advances in SiC epitaxy and some of the resulting device demonstrations and commercialization by Cree Research.

Self-aligned methods of fabricating silicon carbide power devices by implantation and lateral diffusions

Abstract: Silicon carbide power devices are fabricated by implanting p-type dopants into a silicon carbide substrate through an opening in a mask, to form a deep p-type implant. N-type dopants are implanted into the silicon carbide substrates through the same opening in the mask, to form a shallow n-type implant relative to the p-type implant. Annealing is then performed at temperature and time that is sufficient to laterally diffuse the deep p-type implant to the surface of the silicon carbide substrate surrounding the shallow n-type implant, without vertically diffusing the p-type implant to the surface of the silicon carbide substrate through the shallow n-type implant. Accordingly, self-aligned shallow and deep implants may be performed by ion implantation, and a well-controlled channel may be formed by the annealing that promotes significant diffusion of the p-type dopant having high diffusivity, while the n-type dopant having low diffusivity remains relatively fixed. Thereby, a p-base may be formed around an n-type source. Lateral and vertical power MOSFETs may be fabricated.

Steady-state and transient forward current-voltage characteristics of 4H-silicon carbide 5.5 kV diodes at high and superhigh current densities

Abstract: Steady-state and transient forward current-voltage I-V characteristics have been measured in 55 kV p/sup +/-n-n/sup +/ 4H-SiC rectifier diodes up to a current density j/spl ap/55/spl times/10/sup 4/ A/cm/sup 2/ The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, /spl tau//sub ph/, has been estimated from transient characteristics At low injection level, the hole diffusion length L/sub pl/ has been measured by photoresponse technique For a low-doped n-base, the hole diffusion lengths are L/sub pl//spl ap/2 /spl mu/m and L/sub ph//spl ap/6-10 /spl mu/m at low and high injection levels respectively Hole lifetimes for low and high injection levels are /spl tau//sub pl//spl ap/15 ns and /spl tau//sub ph//spl ap/140-400 ns The calculated and experimental results agree well within the wide range of current densities 10 A/cm/sup 2/ 5 kA/cm/sup 2/, the experimental values of residual voltage drop V is lower than the calculated ones In the range of current densities 5/spl times/10/sup 3/ A/cm/sup 2/ 25 kA/cm/sup 2/, R/sub d/ increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic The possible role of Auger recombination is also discussed

High hole lifetime (3.8 [micro sign]s) in 4H-SiC diodes with 5.5 kV blocking voltage

Abstract: The hole lifetime /spl tau//sub p/ in the n-base of 4H-SiC diodes with 5.5 kV blocking voltage has been measured in the temperature range 300-550 K. The /spl tau//sub p/ increases monotonically in this temperature range from 0.6 to 3.8 /spl mu/s. Forward current-voltage characteristics demonstrate a very high level of base modulation by minority carriers.

Recent Progress in SiC Microwave MESFETs

Abstract: SiC MESFET’s have shown an RF power density of 4.6 W/mm at 3.5 GHz and a power added efficiency of 60% with 3 W/mm at 800 MHz, demonstrating that SiC devices are capable of very high power densities and high efficiencies. Single devices with 48 mm of gate periphery were mounted in a hybrid circuit and achieved a maximum RF power of 80 watts CW at 3.1 GHz with 38% PAE.

High temperature, high current, p-channel UMOS 4H-SiC IGBT

Abstract: Commercial silicon Insulated Gate Bipolar Transistors (IGBTs) offer an excellent balance in terms of on-state voltage drop, speed, I-V safe operating area and MOS gate control. A p-channel UMOS IGBT is suitable for fabrication in 4H-SiC because: (a) extremely low resistivity p-type substrates are not considered feasible in SiC; (b) the inherent PMOS transistor offers superior high temperature reliability; (c) a UMOS structure offers a much higher channel packing density than other structures; and (d) lower micropipe density substrates are available in 4H-SiC as compared to 6H-SiC. This paper reports the design, fabrication and high temperature characterization of the first 4H-SiC IGBT with a high current rating (1.5 A) and excellent high temperature characteristics (operating up to 350/spl deg/C).

Progress in SiC and GaN microwave devices fabricated on semi-insulating 4H-SiC substrates

Abstract: The two technologies being studied are SiC MESFETs based on homoepitaxially grown epilayers, primarily targeted for applications from UHF up to 10 GHz, and GaN/AlGaN HEMTs that are grown via heteroepitaxial MOCVD which can operate at frequencies potentially up to 35 GHz. As a result of the use of 4H-SiC semi-insulating substrates, impressive demonstrations of microwave power have been made in both types of devices. This paper will describe progress made in SiC substrates, and some of the resulting microwave device demonstrations in both SiC MESFETs and in GaN/AlGaN devices grown on SiC.

Frequency properties of 4H-SiC thyristors at high current density

Abstract: Frequency properties of 4H-SiC thyristors with forward blocking voltages of 400 V and 700 V have been investigated. The limiting operating frequency exceeds 500 kHz up to current densities of for 400 V structures and 750 A for 700 V structures. The experimentally measured limiting frequencies of 4H-SiC devices are compared with the theoretical estimations and the experimental data for rated Si thyristors.

Characterization of Thick 4H-SiC Hot-Wall CVD Layers

Abstract: Epitaxial 4H-SiC layers suitable for high power devices have been grown in a hot-wall chemical-vapor deposition (CVD) system. These layers were subsequently characterized for many parameters important in device development and production. The uniformity of both thickness and doping will be presented. Doping trends vs. temperature and growth rate will be shown for the p -type dopant used. The n -type dopant drops in concentration with increasing temperature or increasing growth rate. In contrast, the p -type dopant increases in concentration with decreasing temperature or increasing growth rate. A simple descriptive model for this behavior will be presented. The outcome from capacitance-voltage and SIMS measurements demonstrate that transitions from n to n − , or p to p − , and even n to p levels can be made quickly without adjustment to growth conditions. The ability to produce sharp transitions without process changes avoids degrading the resulting surface morphology or repeatability of the process. Avoiding process changes is particularly important in growth of thick layers since surface roughness tends to increase with layer thickness. Device results from diodes producing two different blocking voltages in excess of 5 kV will also be shown. The higher voltage diodes exhibited a breakdown behavior which was near the theoretical limit for the epitaxial layer thickness and doping level grown.