High-voltage SiC and GaN power devices

The recent progress in the development of high-voltage SiC and GaN power switching devices is reviewed. The experimental performance of various rectifiers and transistors, which have been demonstrated, is discussed. Material and processing challenges and reliability concerns on SiC and GaN power devices are also described. The future trends in device development and commercialization are pointed out.     

Die-attachment solutions for SiC power devices

Silicon carbide has become a very attractive material for high temperature and high power electronics applications due to its physical properties, which are different than those of conventional Si semiconductors. However, the reliability of SiC devices is limited by assembly processes comprising die attachment and interconnections technology as well as the stability of ohmic contacts at high temperatures.The investigations of die to substrate connection methods which can fulfill high temperature and high power requirements are the main focuses of the paper. This work focuses on die attach technologies: solder bonding by means of gold-germanium alloys, adhesive bonding with the use of organic and inorganic conductive compositions, as well as die bonding with the use of low temperature sintering with silver nanoparticles. The applied bonding technologies are described and obtained results are presented. Of the methods tested, the best solutions for high temperature application are two die attach technologies: silver glass die attach and die bonding with the use of low temperature sintered Ag nanopowders.     

Some aspects of SiC CVD epitaxy

A brief comparative analysis of techniques for the CVD epitaxy of SiC is made. Two tendencies in the use of inner reactor equipment are distinguished. Irrespective of the design features and the active gases used, chemical reactions of hydrogen with the interior of the reactor occur concurrently with the epitaxial growth. These reactions control the actual [C]/[Si] ratio in the gas phase and in part determine the background impurity concentration in pure epilayers.     

Unipolar SiC power devices and elevated temperature

The paper discusses the limitations and perspectives of unipolar SiC devices for the use in high temperature applications. After clarifying the requirements for the next generation high temperature semiconductor components, these data are reflected to the performance of devices available or in development today. For Schottky barrier diodes, the limits of today’s standard technology are shown and the strategy for developing an improved device is sketched. For switching devices, the two competing concepts - normally on JFETs and normally off MOSFETs - are compared. Advantages for JFET structure are worked out, mainly based on the fact that no oxide interface is involved. The theoretical considerations are checked by experiments.     

Trade-off analysis of the p-base doping on ruggedness of SiC MOSFETs

Reliability represents a very important factor for the design of Silicon Carbide (SiC) power metal oxide semiconductor field effect transistors (MOSFETs). Ruggedness of the device during abnormal operating conditions like the short circuit (SC) and avalanche conduction (during unclamped inductive switching - UIS) is an important aspect of reliability. Often, variation in design parameters to improve ruggedness during SC and UIS shows negative impact on the nominal operating performance. This paper presents a comprehensive analysis of the impact of modification of p-base doping on the performance of a 1.2 kV SiC MOSFET during SC and UIS by means of TCAD simulations. The improvement in MOSFET ruggedness by optimizing the p-base doping and its influence on the nominal operating performance is evaluated.     

SiC devices for advanced power and high-temperature applications

Silicon carbide (SiC) process technology has made rapid progress, resulting in the realization of very promising electronic devices and sensors, enabling advanced solutions in power industry and mobile systems. In particular, for electronics working under harsh environmental conditions, SiC devices reach unprecedented performance. Transfer to production has already started for some applications     

Reliability and performance limitations in SiC power devices

Despite silicon carbide’s (SiC’s) high breakdown electric field, high thermal conductivity and wide bandgap, it faces certain reliability challenges when used to make conventional power device structures like power MOS-based devices, bipolar-mode diodes and thyristors, and Schottky contact-based devices operating at high temperatures. The performance and reliability issues unique to SiC discussed here include: (a) MOS channel conductance/gate dielectric reliability trade-off due to lower channel mobility as well as SiC–SiO₂ barrier lowering due to interface traps; (b) reduction in breakdown field and increased leakage current due to material defects; and (c) increased leakage current in SiC Schottky devices at high temperatures.Although a natural oxide is considered a significant advantage for realizing power MOSFETs and IGBTs in SiC, devices to date have suffered from poor inversion channel mobility. Furthermore, the high interface state density presently found in the SiC–SiO₂ system causes the barrier height between SiC and SiO₂ to be reduced, resulting in increased carrier injection in the oxide. A survey of alternative dielectrics shows that most suffer from an even smaller conduction band offset at the SiC–dielectric interface than the corresponding Silicon–dielectric interface and have a lower breakdown field strength than SiO₂. Thus, an attractive solution to reduce tunneling such as stacked dielectrics is required.In Schottky-based power devices, the reverse leakage currents are dominated by the Schottky barrier height, which is in the 0.7–1.2 eV range. Because the Schottky leakage current increases with temperature, the SiC Schottky devices have a reduction in performance at high temperature similar to that of Silcon PN junction-based devices, and they do not have the high temperature performance benefit associated with the wider bandgap of SiC.Defects in contemporary SiC wafers and epitaxial layers have also been shown to reduce critical breakdown electric field, result in higher leakage currents, and degrade the on-state performance of devices. These defects include micropipes, dislocations, grain boundaries and epitaxial defects. Optical observation of PN diodes undergoing on-state degradation shows a simultaneous formation of mobile and propagating crystal stacking faults. These faults nucleate at grain boundaries and permeate throughout the active area of the device, thus degrading device performance after extended operation.     

Calculation of lattice heating in SiC RF power devices

Silicon carbide MESFET devices are suitable for high-speed and high-power applications. In this paper we are studying thermal effects in 4H-SiC RF power devices. The simulations are based on a combination of 2D device simulations for the electrical transport, and 3D thermal simulations for the lattice heating. We show that the method gives good accuracy, efficiency, flexibility and capacity dealing with tasks, where a 2D coupled electrical–thermal simulation is not sufficient. We also present an improvement of Roschke and Schwierz mobility model, based on Monte Carlo simulations for the temperature dependencies of the mobility parameters β and v_sat.     

Current SiC technology for power electronic devices beyond Si

Recent big progress in SiC technology for power electronic devices beyond Si is reviewed. Historical aspects in SiC development are described. Current subjects such as bulk crystal growth, epitaxial growth, device processes for new generation of SiC power devices are briefly explained. Commercially available Schottky diodes and possible switching devices are introduced.     

SiC power devices packaging with a short-circuit failure mode capability

The failure mode of press-pack-type packages dedicated to SiC devices is experimentally analyzed in order to investigate their use for HVDC applications. Single SiC Schottky diode samples have been submitted to short-circuit conditions and continuous current flow test. The samples have been then characterized with optical and scanning electronic microscopy. Results from the experiments reveal that the press-pack structure offers a short-circuit failure mode with SiC devices, as it does for Si devices. The metallurgy involved is, however, quite different. Cu, Ni, Ag or Al foils are found to be suitable interface material between the package and the die to achieve a stable a short-circuit failure mode, providing the die is properly attached to a substrate.     

On the short-circuit and avalanche ruggedness reliability assessment of SiC MOSFET modules

This paper provides an insight into the operational robustness of commercially available SiC MOSFET power modules, during short-circuit (SC) and unclamped inductive switching (UIS) test environments. A set of five different power modules from three vendors rated from 1.2–1.7 kV and with various current ratings have been evaluated, where the possible failure mechanisms that cause the breakdown of the modules have been addressed. The SC pulse duration of the modules was gradually increased until the failure occurred. A critical short circuit energy in the order of 4.0–8.0 J was observed at a supply voltage of 800 V and a pulse duration of 4.0 μs. At lower supply voltage of 500 V, all modules survived until 10.0 μs. One of the modules, rated at 1.7 kV, survived SC tests at voltages up to 1000 V for a pulse duration of 4 μs, but failed when the supply voltage was increased to 1100 V. Prior to failure, a gate-source voltage drop has been recorded, which is associated with a high G-S leakage current. The main failure mechanism, however, is the thermal runaway which leads the devices into avalanche breakdown mode. During the UIS tests, multiple samples from the three vendors of the power modules failed. The failure of the modules was always caused by the external diode connected in parallel with the MOSFETs. One of the modules from the same vendor which does not have external diode and another module from a different vendor with external diode survived the UIS tests under nominal test conditions.     

The potential of diamond and SiC electronic devices for microwaveand millimeter-wave power applications

The potential of SiC and diamond for producing microwave and millimeter-wave electronic devices is reviewed. It is shown that both of these materials possess characteristics that may permit RF electronic devices with performance similar to or greater than what is available from devices fabricated from the commonly used semiconductors, Si, GaAs, and InP. Theoretical calculations of the RF performance potential of several candidate high-frequency device structures are presented: the metal semiconductor field-effect transistor (MESFET), the impact avalanche transit-time (IMPATT) diode, and the bipolar junction transistor (BJT). Diamond MESFETs are capable of producing over 200 W of X-band power as compared to about 8 W for GaAs MESFETs. Devices fabricated from SiC should perform between these limits. Diamond and SiC IMPATT diodes also are capable of producing improved RF power compared to Si, GaAs, and InP devices at microwave frequencies. RF performance degrades with frequency and only marginal improvements are indicated at millimeter-wave frequencies. Bipolar transistors fabricated from wide bandgap material probably offer improved RF performance only at UHF and low microwave frequencies     

SiC材料与器件

介绍了碳化硅材料和器件的最新进展     

Reliability aspects of copper metallization and interconnect technology for power devices

The introduction of thick copper metallization and topside interconnects as well as a superior die attach technology is improving the performance and reliability of IGBT power transistor technologies significantly.The much higher specific heat capacity and higher thermal conductivity increases the short circuit capability of IGBTs, which is especially important for inverters for drives applications. This opens the potential to further optimize the electrical performance of IGBTs for higher energy efficiency.The change in metallization requires the introduction of a reliable barrier against copper diffusion and copper silicide formation. This requires the development of an efficient test method and reliability assessment according to a robustness validation approach.In addition, the new metallization enables interconnects with copper bond wires, which yield, together with an improved die attach technology, a major improvement in the power cycling capability.     

SiC power modules emerging

Cree Inc has agreed with Advanced Power Technology, to purchase all of its SiC Zero Recovery Schottky Diode die to be packaged and sold as finished products under the APT brand name. APT intends to primarily address market segments not currently served by Cree, mainly by using alternative packaging and innovative engineering and use its expertise in high power semiconductor manufacturing to offer multi-die parallel discrete devices in a variety of packages, as well as in hermetic packages with and without military screening.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

SiC microwave power technologies

Two SiC transistors that are investigated for microwave power applications are the 4H-SiC static induction transistor (SIT) and the 4H-SiC metal-semiconductor field-effect transistor (MESFET). Ultrahigh frequency 4H-SiC SITs have demonstrated record-breaking pulsed power per package (900 W) with excellent associated power-added efficiency (PAE) of 78%. S band 4H-SiC MESFETs have shown a record power-density of 5.6 W/mm and 36% PAE, as well as 80 W continuous-wave (CW) power (1.6 W/mm), with an associated PAE of 38%. X-band MESFET power density of 4.3 W/mm was obtained for exploratory CW devices. These performance gains are afforded by the advantageous material properties of silicon carbide. SiC SIT technology offers many military system advantages including lower cost, lower weight, higher power and high temperature of operation and higher efficiency transmitters with minimal cooling requirements. SiC RF MESFET's and circuits are candidates for use in efficient linear transmitters for commercial and military communications.     

SOI power devices

This paper provides an introduction to silicon-on-insulator (SOI) technology and the operating principles of high-voltage SOI devices, reviews the performance of the available SOI switching devices in comparison with standard silicon devices, discusses the reasoning behind the use of SOI technology in power applications and covers the most advanced novel power SOI devices proposed to date. The impact of SOI technology on power integrated circuits (PICs) and the problems associated with the integration of high-voltage and low-voltage CMOS are also analysed     

Evaluation of the ruggedness of power DMOS transistor from electro-thermal simulation of UIS behaviour

High-voltage power MOSFETs have been widely used in switching mode power supply circuits as output drivers for industrial and automotive electronic control systems. However, as the device size is reduced, the energy handling capability is becoming a very important issue to be addressed together with the trade-off between the series on-resistance R_ON and breakdown voltage V_BR. Unclamped inductive switching (UIS) condition represents the circuit switching operation for evaluating the “ruggedness”, which characterizes the device capability to handle high avalanche currents during the applied stress. In this paper we present an experimental method which modifies the standard UIS test and allows extraction of the maximum device temperature after the applied standard stress pulse vanishes. Corresponding analysis and non-destructive prediction of the ruggedness of power DMOSFETs devices supported by advanced 2-D mixed mode electro-thermal device and circuit simulation under UIS conditions using calibrated physical models is provided also. The results of numerical simulation are in a very good correlation with experimental characteristics and contribute to their physical interpretation by identification of the mechanism of heat generation and heat source location and continuous temperature extraction.     

Gate leakage-current analysis and modelling of planar and trench power SiC MOSFET devices in extreme short-circuit operation

The purpose of this paper is to present a complete analysis of the gate leakage-current behaviour during short-circuit (SC) fault operation of 1200 V SiC MOSFETs from five different manufacturers including planar and trench-gate structures. Ruggedness and gate leakage level are evaluated in function of the chip size. Finally, the gate leakage current is modelled and the robustness tested.     

SiC field-effect devices operating at high temperature

Field-effect devices based on SiC metal-oxide-semiconductor (MOS) structures are attractive for electronic and sensing applications above 250°C. The MOS device operation in chemically corrosive, high-temperature environments places stringent demands on the stability of the insulating dielectric and the constituent interfaces within the structure. The primary mode of oxide breakdown under these conditions is attributed to electron injection from the substrate. The reliability of n-type SiC MOS devices was investigated by monitoring the gate-leakage current as a function of temperature. We find current densities below 17 nA/cm² and 3 nA/cm² at electric field strengths up to 0.6 MV/cm and temperatures of 330°C and 180°C, respectively. These are promising results for high-temperature operation, because the optimum bias point for SiC MOS gas sensors in near midgap, where the field across the oxide is small. Our results are valid for n-type SiC MOS sensors in general and have been observed in both the 4H and 6H polytypes.