SiC PiN Diodes Research Articles

Characterization of Packaged 6.5 kV SiC PiN-Diodes up to 300 °C

Silicon Carbide bipolar diodes offer unique ultrafast switching behavior for high voltage and high power applications [1]. But due to the small chip size it is required to parallel a lot of dice and therefore it is necessary to get detailed information about the electrical and thermal behavior of single diodes. For the characterization in the full current and voltage regime we have developed a molded leadframe package. The package was designed with a lateral contact geometry and a high creepage distance of 20 mm, which enable us to characterize these diodes for high voltage applications. Forward and reverse I-V characteristics and turn-off behavior under hard switching conditions up to 300 °C are reported. Additionally the forward voltage stability and power cycling tests are discussed.

High-Performance Smoothly Tapered Junction Termination Extensions for High-Voltage 4H-SiC Devices

A novel taper-doping anode termination method is introduced for high-voltage silicon carbide devices. The method employs a subresolution two-tone termination mask to achieve a gray-scale exposure and a smoothly tapered photoresist profile. Using the tapered profile as an implantation mask, self-aligned 6-kV SiC PiN diodes are demonstrated with 90% of the parallel-plate breakdown voltage. The avalanche breakdown for the design is controlled and reversible. This one-step technique allows wide design control over the width and shape of the termination profile and has wide device and material applicability.

An Experimental Study of High Voltage SiC PiN Diode Modules Designed for 6.5 KV / 1 KA

The paper describes first results of 6.5 kV SiC PiN diode modules which are designed as neutral point valves for medium-voltage power inverters rated for 1000 A. The power module consists of 4 AlN DCB substrates soldered on an AlSiC base plate. Each DCB is equipped with 20 SiC PiN diodes operating in parallel. The total active area of all 80 diode chips is 5.68 cm². At the rated current of 2 x 500A the forward voltage drops from 4.1 V at room temperature to 3.9 V at an averaged junction temperature of 125°C. The switching experiments show a very low reverse recovery charge of about 30 µC only. The conduction loss is comparable to the corresponding 6.5 kV silicon diode whereas the dynamic loss is marginal with respect to the forward conduction loss if the switching frequency is held below 10 kHz.

A Molded Package Optimized for High Voltage SiC-Devices

We present first results on power cycling of 6.5 kV SiC PiN-diodes mounted into a molded package. The geometry of this lateral package was designed to fulfill the specifications of the electrical isolation and the creepage distances in the high voltage region of 6.5 kV. To evaluate the suitability of this package we used high voltage SiC PiN-diodes. The diodes were soldered onto a copper lead frame, wire bonded and covered by molding compound. The packaged diodes were characterized by electrical measurements before and during a power cycling test with a temperature swing of 90 K. These results showed long term stable behavior of the I-V characteristics of the diodes as well as the suitability of the package for high temperature and high voltage application of SiC devices.

6.5 kV SiC PiN Diodes with Improved Forward Characteristics

The paper compares static and dynamic characteristics of 6.5 kV SiC PiN diodes fabricated with different p-emitters. The version with the thickest p-emitter (4 µm) showed the lowest forward voltage (3.4 V at 100 A/cm²) and the lowest (negative) temperature coefficient. Forward voltage DC stress tests revealed a stability within the measurement error of the test apparatus (<50 mV). The dynamic performance showed a soft recovery even at 4 kV. The reverse recovery charge Qrr is analyzed for different forward currents and junction temperatures. The dynamic losses of the SiC PiN diode are marginal with view to the application in industrial inverters.

On the Luminescence and Driving Force of Stacking Faults in 4H-SiC

Since it was determined that the formation and expansion of intrinsic stacking faults (SFs) induced a drift in the forward voltage (Vf) in 4H-SiC bipolar devices, significant effort has been made to understand the driving force causing SF motion as well as the various associated luminescence processes. The observation that annealing of faulted SiC devices and epilayers induced SF contraction and a recovery of the Vf drift enabled the studying of the impact of various parameters such as temperature, injection level and operation time upon SF motion, the Vf drift and luminescence within the same device. However, these observations in many cases contradicted the previously reported driving force models. Here we report on a basic driving force model explaining SF expansion in hexagonal SiC as well as discuss the observation of green luminescence from C-core partial dislocations bounding the SFs that may indicate an enhanced mobility of point defects within forward biased SiC pin diodes.

高過負荷１００ｋＶＡ級ＳｉＣインバータの開発

High overload inverters were developed by using SiC devices for the first time, although its realization by using Si devices had been difficult because of Si's low maximum Tj. High resistive SiC pin diodes with heavy electron irradiation are proposed for the turn-on snubber circuit as an alternative to the conventional resistor and diode. The inverter circuit was greatly miniaturized by mounting the high resistive SiC pin diode in a SiCGT (SiC Commutated Gate turn-off Thyristor) module and using no heat sink for the resistor. The newly developed 100 kVA overload SiC inverter provides an overload capability rate of 200 % and can supply 300 kVA for up to 3 seconds.

Silicon Carbide UV Based Photovoltaic for Hostile Environments

The development of silicon carbide technologies has allowed for the development of sensors and electronics to measure the changes in a variety of hostile environments. A problem has been identified with reliable and efficient ways to power such sensors in these hostile environments. It is likely to be impractical to run power cables to these sensors and battery power has a finite lifetime. Recent research has demonstrated many energy scavenging techniques but to date none have been developed with a view of operation in hostile environments. To investigate the power density achievable from a SiC based energy scavenging device a SiC pin diode was exposed to both broad spectrum light form a tungsten halogen bulb and a 255 nm UV source. IV and CV measurements were used to determine the structural properties and photovoltaic response of the device, dark saturation current, induced photo current and the fill factor. We present the characteristics and maximum power density of these devices at temperatures between 300 K and 600 K. We demonstrate that the maximum power density achievable decreases with temperature. This is mostly due to the reduction in the built in potential from the pn junction, and the reduction of the generated photocurrent.

Recent progress in 3.3 kV SiC diodes

The electrical performance of 3.3 kV SiC Schottky, JBS and PiN diodes are compared. In forward mode, the 25 mm 2 Schottky exhibits better performances than the 2.6 mm 2 JBS and PiN diodes. On the other hand, due its very large active area, the Schottky diode show a leakage current of 1 mA, which is 100× and 1000× higher than that of the JBS and PiN diodes, respectively. In switching mode, the Schottky and JBS diodes show similar reverse current peaks (2 A at 300 °C), whereas it is 5× higher for the PiN diode. Concerning the surge current capability, the three diodes present similar surge current capability (around 55 A) at 25 °C. At 225 °C, we have observed a 50% decrease in the surge current of the Schottky diode whereas it is almost the same for the PiN and JBS diodes.

Improved Properties of AlON/4H SiC Interface for Passivation Studies

Aluminium oxynitride (AlON) films of variable composition were grown by reactive sputter deposition in a N2/O2 ambient at room temperature and studied for device passivation. The films were deposited on Si and 4H-SiC substrates as well as on SiC PiN diodes. The AlON/SiO2/SiC stack provided superior interface properties compared to the AlON/SiC structure. Samples with 8% oxygen content, in the AlON film, and subjected to a UV exposure prior to deposition, exhibited the smallest net positive interface charge. A large net negative interface charge was observed for samples with 10% oxygen content and for the samples with 8% oxygen content and subjected to a RCA1 surface clean, prior to deposition. Diodes passivated with AlON films demonstrated reduced leakage current compared to as-processed diodes.

Numerical Evaluation of Forward Voltage in SiC Pin Diode with Non-Ohmic Current Component in Contact to p-Type Layer

Forward voltage of SiC pin diodes is evaluated by device simulation, where a p-type contact is described by Schottky barrier to a p-type surface region. The contact resistance is calculated from the comparison to I-V characteristic of Schottky structure to a p-SiC layer with a sufficiently low Schottky barrier height. Even in the relatively low contact resistance rc of 10-4 Wcm2, non-ohmic current component is observed in Schottky structure to p-SiC and the increase of forward voltage of pin diodes is fairly small. Forward voltage of pin diodes increases in the pin diodes with contact resistance rc over 10-4 Wcm2. The same behavior is also observed irrespective of a time constant of carriers, and doping concentration and thickness of a drift layer.

Bevel Mesa Combined with Implanted Junction Termination Structure for 10 kV SiC PiN Diodes

A 10 kV 4H-SiC PiN diode with an improved junction termination structure has been fabricated. An improved bevel mesa structure, nearly vertical side-wall at the edge of pn junction and rounded corner at mesa bottom, has been formed by reactive ion etching (RIE). The junction termination extension (JTE) region has been optimized by device simulation, and simulated breakdown voltage has been compared with experimental results. The locations of electric field crowding and diode breakdown have been discussed.

Characterization, Modeling, and Application of 10-kV SiC MOSFET

Ten-kilovolt SiC MOSFETs are currently under development by a number of organizations in the United States, with the aim of enabling their applications in high-voltage high-frequency power conversions. The aim of this paper is to obtain the key device characteristics of SiC MOSFETs so that their realistic application prospect can be provided. In particular, the emphasis is on obtaining their losses in various operation conditions from the extensive characterization study and a proposed behavioral SPICE model. Using the validated MOSFET SPICE model, a 20-kHz 370-W dc/dc boost converter based on a 10-kV 4H-SiC DMOSFET and diodes is designed and experimentally demonstrated. In the steady state of the boost converter, the total power loss in the 15.45-mm2 SiC MOSFET is 23.6 W for the input power of 428 W. The characterization study of the experimental SiC MOSFET and the experiment of the SiC MOSFET-based boost converter indicate that the turn-on losses of SiC MOSFETs are the dominant factors in determining their maximum operation frequency in hard-switched circuits with conventional thermal management. Replacing a 10-kV SiC PiN diode with a 10-kV SiC JBS diode as a boost diode and using a small external gate resistor, the turn-on loss of the SiC MOSFET can be reduced, and the 10-kV 5-A SiC MOSFET-based boost converter is predicted to be capable of a 20-kHz operation with a 5-kV dc output voltage and a 1.25-kW output power by the PSpice simulation with the MOSFET model. The low losses and fast switching speed of 10-kV SiC MOSFETs shown in the characterization study and the preliminary demonstration of the boost converter make them attractive in high-frequency high-voltage power-conversion applications.

Electric and Physical Chacteritics of a SiC-PiN Diode for High-Power Devices

Electric and Physical Chacteritics of a SiC-PiN Diode for High-Power Devices Nam-Oh Kim and Wan-Ki Min Department of Electricity, Chosun College of Science & Technology, Gwangju 501-759 Kyung-Min Sung Department of Electrical and Electronic Systems Engineering, Ibaraki National College of Technology, Ibaraki 312-8508, Japan Kazuma Suzuki Department of Arti cial System Science, Chiba University, Japan Yasunori Tanaka and Hiromichi Ohashi National Institute of Advanced Industrial Science and Technology Power Electronics Research Center, Japan (Received 26 February 2008) This paper is presented on a 2.5-kV silicon-carbide (SiC) PiN diode with a silicon injection enhancement gate transistor (IEGT) in an inductively loaded chopper circuit. The experimental switching characteristics of the SiC-PiN diode are presented under a DC 1200 V bias voltage and 40 A cuto current. Experimental results show that the reverse recovery time and the IEGT turn-on loss are signi cantly reduced by the combination of the SiC-PiN diode and the IEGT. To reduce switching losses and investigate the limitation of the switching frequency in high power converters, we newly present the design concept of an IEGT combined with a SiC-PiN diode. The proposed design concept is evaluated based on a device simulation. The result of the device simulation yields the possible switching frequency by using the comprehensive total devices loss in the test circuit. PACS numbers: 78.40.F, 78.55.F, 73.40.V

Influence of Temperature on Shockley Stacking Fault Expansion and Contraction in SiC PiN Diodes

While Shockley stacking fault (SSF) creation and expansion within 4H-SiC bipolar devices is well known, only recently was it observed that this expansion and the associated increase in the forward voltage drop (V f) could be completely reversed via low-temperature annealing. Here we report the temperature dependence of the recovery rate of the V f drift via annealing, reporting an activation energy of 1.3 ± 0.3 eV. The V f drift was observed to saturate following extended electrical stressing, and it was observed that the value of V f at this saturation was inversely proportional to the stressing temperature. We also observed that SSF and V f drift recovery could occur in highly stressed diodes at elevated temperatures even under high current injection conditions (14 A/cm2).

Influence of Temperature on the Saturation of the Forward Voltage Drift in SiC Pin Diodes

Shockley stacking faults (SSFs) in hexagonal SiC are known to induce an increase in the forward voltage drop of bipolar devices, such as pin diodes. Recent annealing studies have illustrated that propagated SSFs can not only propagate under current or optical injection conditions, but under low temperature (210-7000C) annealing can contract completely. Associated with this contraction is the complete and repeatable recovery of the drift. These observations have brought about questions as to the driving force for SSF propagation and contraction. Here we report that following extended periods of forward bias operation, the drift of 4H-SiC 10kV pin diodes increased until an eventual saturation occurred. At this point, further current injection no longer induced any further SSF propagation or increases in . Furthermore, the maximum attainable drift was inversely proportional to the stressing temperature, meaning that at elevated temperatures, the degree to which the SSFs may propagate is significantly limited.

Propagation and Shrinking of Shockley Stacking Faults in SiC PiN Diodes

not Available.

ELECTRICAL CHARACTERISTICS AND CARRIER LIFETIME MEASUREMENTS IN HIGH VOLTAGE 4H-SIC PIN DIODES

The key material and device parameters governing the electrical performance of high voltage 4 H - SiC PiN diodes have been investigated using experimental results and numerical simulations. Reverse recovery characteristics show an increase in both carrier lifetime and anode injection efficiency at elevated temperature. Open circuit voltage decay measurements are used to estimate carrier lifetimes (τ≈0.6μ s at T =25° C increasing to τ≈2μ s at T =225° C ) that are comparable to values measured on starting material prior to fabrication using micro-wave photoconductivity decay techniques.

Demonstration of High-Voltage 4H-SiC Bipolar RF Power Limiter

We present the design and fabrication of the first high-voltage 4H-SiC RF power limiter. First, Schottky and PiN diodes are compared for power limiter applications by numerical simulations. Small-signal S-parameters and large-signal operation are then simulated based on our device design. The fabrication is based on a SiC PiN diode with at least 900V blocking capability and packaged into a 50 microstrip transmission line fixture. Small signal insertion and return losses are measured in the frequency band from 100MHz to 3GHz after packaging and agree well with our simulation. The limiter has an insertion loss of only 0.6dB at 1GHz. This is believed to be the first 4H-SiC high-voltage RF power limiter, as well as one of the best SiC limiters in terms of low small-signal transmission loss up to gigahertz frequencies.

Laser Direct Write Doping and Metallization Fabrication of Silicon Carbide PIN Diodes

A novel laser direct write doping and electrical property conversion technique has been used to fabricate prototype SiC PIN diodes on n-type 4H-SiC wafers. Two different diode structures are fabricated: (1) a laser aluminum doped top p + /p region on a n-type 4H-SiC wafer segment with a low doped n-type SiC epitaxial layer; and (2) the same laser doped top p - /p region on the same substrate and a laser heavily nitrogen doped n' region at the bottom. A simple Schottky diode fabricated on the same substrate medium was used for a comparison. In the laser doped n + region conductors are directly fabricated by the formation of electrically conductive surface carbon rich phase. The results show that laser fabrication of PIN diodes, having a 10 μm epilayer, exhibits higher dopant concentrations and indicate promising breakdown voltages and forward voltage drops without edge tcrmination.