High-Voltage 4H SiC Pin Diodes Research Articles

High-voltage 4H-SiC PiN diodes with the etched implant junction termination extension**Project supported by the Science and Technology Development Foundation of China Academy of Engineering Physics (No. 2014A05011) and the Special Foundation of President of China Academy of Engineering Physics (No. 2014-1-100).

This paper presents the design and fabrication of an etched implant junction termination extension (JTE) for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multiple etching steps to achieve the optimum JTE concentration range. The simulation results show that the etched implant JTE method can improve the blocking voltage of SiC PiN diodes and also provides broad process latitude for parameter variations, such as implantation dose and activation annealing condition. The fabricated SiC PiN diodes with the etched implant JTE exhibit a highest blocking voltage of 4.5 kV and the forward on-state voltage of 4.6 V at room temperature. These results are of interest for understanding the etched implant method in the fabrication of high-voltage power devices.

Design, fabrication and characterization of mesa combined with JTE termination for high-voltage 4H–SiC PiN diodes

Mesa combined with JTE termination structures for high-voltage 4H–SiC PiN diodes are designed, fabricated, and characterized in this paper. Designs based on simulation are performed to investigate the influence of the mesa shape on breakdown for SiC PiN diodes. It is found that a deeper mesa height and a smaller mesa angle contribute to a higher breakdown voltage owing to a smoother and more uniform surface electric field distribution. A maximum reverse blocking voltage of 3.8 kV and an on-state voltage drop of 3.4 V at 100 A/cm2 are obtained from the fabricated diodes with a mesa height of 2.1 μm and a mesa angle of 22°, corresponding to about 80% of a parallel plane breakdown voltage for the drift layer with a thickness of 30 μm. Additionally, the dependence of the breakdown voltage on the JTE length observed in the fabricated diodes shows a good agreement with the simulated results in the trend.

1.4 kV 4H-SiC PiN diode with a robust non-uniform floating guard ring termination

This paper presents the design and fabrication of an effective, robust and process-tolerant floating guard ring termination on high voltage 4H-SiC PiN diodes. Different design factors were studied by numerical simulations and evaluated by device fabrication and measurement. The device fabrication was based on a 12 μm thick drift layer with an N-type doping concentration of 8 × 1015 cm−3. P+ regions in the termination structure and anode layer were formed by multiple aluminum implantations. The fabricated devices present a highest breakdown voltage of 1.4 kV, which is higher than the simulated value. For the fabricated 15 diodes in one chip, all of them exceeded the breakdown voltage of 1 kV and six of them reached the desired breakdown value of 1.2 kV.

Development of High-Voltage 4H-SiC PiN Diodes on 4° and 8° Off-Axis Substrates

13-kV 4H-SiC PiN diodes were fabricated on 4° and 8° off-axis substrates and their electrical properties were examined. Small test PiN diodes with various JTE concentrations were fabricated and the dependence of JTE concentration was examined. The highest breakdown voltages were 14.6 and 14.1 kV at a JTE1 concentration of 1.9 × 1017 cm−3 for both the 4° and 8° off-axis substrates. Based on the results, 4 mm × 4 mm SiC PiN diodes were successfully fabricated and exhibited avalanche breakdown voltages of 14.0 and 13.5 kV for the 4° and 8° off-axis substrates, respectively. Forward voltage degradation was larger for the 8° off-axis substrates.

Transient Electrical Characteristics of Electron Irradiated High Blocking Voltage 4H-SiC Pin Diode

The transient electrical characteristics of the forward recovery and reverse recovery characteristics of lifetime-controlled high blocking voltage 4H-SiC pin diodes by electron irradiation are investigated. Even at a heavy electron dose of 1×1014 cm-2, the forward voltage overshoot of a 4H-SiC pin diode is lower than that of a 2 kV/100 A class Si fast diode. As for the reverse recovery characteristics, small reverse recovery current and fast reverse recovery time are obtained by electron irradiation. The reduction ratio of recovery loss can therefore exceed the increase ratio of steady-state loss by electron irradiation.

High-Voltage 4H-SiC PiN Diodes With Etched Junction Termination Extension

Implantation-free mesa-etched 4H-SiC PiN diodes with a near-ideal breakdown voltage of 4.3 kV (about 80% of the theoretical value) were fabricated, measured, and analyzed by device simulation and optical imaging measurements at breakdown. The key step in achieving a high breakdown voltage is a controlled etching into the epitaxially grown p-doped anode layer to reach an optimum dopant dose of ~ 1.2 times 1013 cm-2 in the junction termination extension (JTE). Electroluminescence revealed a localized avalanche breakdown that is in good agreement with device simulation. A comparison of diodes with single- and double-zone etched JTEs shows a higher breakdown voltage and a less sensitivity to varying processing conditions for diodes with a two-zone JTE.

Comparative Evaluation of Anode Layers on the Electrical Characteristics of High Voltage 4H-SiC PiN Diodes

The impact of anode layers on the electrical characteristics of 10kV 4H-SiC PiN diodes has been evaluated in this work. Co-fabricated diodes with various epitaxial anode layer designs as well as those employing P+ implanted injecting layers are used to experimentally investigate the device conduction mechanisms. The role of the injecting layer is demonstrated via electrical characteristics and numerical simulations, showing the importance of maintaining sufficient carrier recombination lifetime in the device anode region.

Self-Heating of 4H-SiC PiN Diodes at High Current Densities

Self-heating in high-voltage 4H-SiC PiN diodes has been studied experimentally and theoretically in dc and 8-ms single pulse modes. To simulate the self-heating, an electro-thermal model was used to calculate non-isothermal current-voltage characteristics at dc and current-time dependences at pulsed measurements. The dynamic instability of N-type was observed: the current decreases in spite of increasing of bias applied to the structure. At dc, irreversible diode degradation was found to occur at a current density of about 1700 A/cm2. Under a single current surge 8-ms pulse, the loss of thermal stability has been found at a current density of approximately 9000 A/cm2. Comparison of experimental data and simulations showed that the local temperature in the diode base at the end of the 8-ms, 9000-A/cm2 pulse reaches 2000 – 2300 K.

Simulation and Experimental Study on the Junction Termination Structure for High-Voltage 4H-SiC PiN Diodes

Designing and fabrication of 10-kV 4H-SiC PiN diodes with an improved junction termination structure have been investigated. An improved bevel mesa structure and a single-zone junction termination extension (JTE) have been employed to achieve a high breakdown voltage (ges 10 kV). The improved bevel mesa structure, nearly a vertical sidewall at the edge of the p-n junction and a gradual slope at the mesa bottom, has been fabricated by reactive ion etching. The effectiveness of the improved bevel mesa structure has been experimentally demonstrated. The JTE region has been optimized by device simulation, and the JTE dose dependence of the breakdown voltage has been compared with experimental results. A 4H-SiC PiN diode with a JTE dose of 1.1 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> has exhibited a high blocking voltage of 10.2 kV. The locations of electric field crowding and breakdown are also discussed.

Forward Voltage Degradation of 4H-SiC pin Diodes and High Voltage 4H-SiC pin Diodes on the (000-1) C-Face with Reduced Forward Degradation

The dependence of forward voltage degradation on crystal faces for 4H-SiC pin diodes has been investigated. The forward voltage degradation has been reduced by fabricating the diodes on the (000-1) C-face off-angled toward . High-voltage 4H-SiC pin diodes on the (000-1) C-face with small forward voltage degradation have also been fabricated successfully. A high breakdown voltage of 4.6kV and ΔVF of 0.04V were achieved for a (000-1) C-face pin diode. A 8.3kV blocking performance, which is the highest voltage in the use of (000-1) C-face, is also demonstrated in 4H-SiC pin diode.

Electrical Characterization of High Voltage 4H-SiC pin Diodes Fabricated Using a Low Basal-Plane Dislocations Process

Forward current-voltage (I-V) characteristics and non-equilibrium carrier lifetime, τ were measured in 4H-SiC pin diodes (10-kV rated, 100 μm base width). The τ value was found to be 3.7 μs at room temperature by measurements of open circuit voltage decay. To the best of the authors' knowledge, the above lifetime value is the highest reported for 4H-SiC. The forward voltage drops were measured to be 3.44 V at current density of 100 A/cm2 and 5.45 V at 1000 A/cm2 showing a very deep modulation of the blocking base by injected carriers. Diodes operated well at elevated temperatures up to 400oC. No essential forward degradation was detected after 300- A×min current stress at 400oC.

CM-Wave Modulator with High-Voltage 4H SiC pin Diodes

The results of mathematical simulation, development and investigation of a modulator with 4H SiC pin diodes are presented. We simulated the effect of bias modes on isolation and transmission between the modulator input and output in the 1−20 GHz frequency range, for pin diodes with 6 μm long i-region. It was calculated that the isolation in a modulator with three diodes may run into –45 dB, the transmission losses being no more than 2 dB. The modulator was made as an integrated circuit (IC) on the basis of nonsymmetrical strip lines (characteristic impedance of 50 Ω) incorporating chips of high-voltage 4H SiC pin diodes with iregion 6 μm long, mesa diameter of 60 μm and calculated avalanche breakdown voltage of 1000 V. We studied the experimental parameters of this modulator as a function of forward current and reverse voltage in the 2.4−12 GHz frequency range, as well as the microwave signal switching behavior. It was determined that the modulator is characterized by transmission losses of 1.0−2.0 dB and isolation of 27−34 dB (in the 2.4−7 GHz frequency range). The formation of microwave pulses with leading (trailing) edge of 22 (29) ns was also observed.

Investigation of Packaged High-Voltage 4H SiC pin Diodes in the 20-700 °C Temperature Range

The packaged microwave 4H SiC pin diode chips (with i-region length of 6 μm, mesa diameter of 80 μm and blocking voltage of 1000 V) were investigated. We studied the parameters of diode I−V curve (in particular, the diode resistance RS at forward current) and the processes of diode switching from forward current of 50 mA to reverse voltage of 15 V, as well as C−V curves, in the 20−700 °C temperature range. At a voltage of 300 V, the diode reverse current was 10 (180) μA when temperature was 600 (700) °C. At a forward current of 40 mA, the diode resistance first decreases smoothly as temperature is increased from 20 up to 300 °C, and then grows up. As temperature is increased from 20 up to 700 °C, the effective lifetime τeff grows from 7 up to 50 ns, while the diode capacitance (in the 0−40 V reverse voltage range) grows smoothly as temperature is increased from 20 up to 400 °C.

Planar Edge Termination Design and Technology Considerations for 1.7-kV 4H-SiC PiN Diodes

This paper presents the design, fabrication, and comparison of different planar edge termination techniques on high-voltage 4H-SiC PiN diodes, including single- and double-junction termination extensions (JTE), floating guard rings, and a novel termination structure, the so-called "floating guard rings-assisted JTE." The influence of the anode metal edge location over different periphery regions on the breakdown voltage is also discussed, as well as the effect of a field plate and the passivation layer on the reverse characteristics. The terminations were studied by way of two-dimensional numerical device simulations and they are confirmed by fabricating and measuring 1.7-kV 4H-SiC aluminum implanted PiN diodes. It is shown that the novel termination structure provides the best results achieving the highest breakdown voltages with good production yield. The fabricated diodes also exhibited excellent forward current characteristics with a low on-state voltage drop of 3.0 V at 100 A/cm/sup 2/, thanks to the low specific contact resistivity achieved (/spl rho//sub C/=1/spl middot/10/sup -5/ /spl Omega/cm/sup 2/) after the high-temperature treatment of the anode contact. High-temperature reverse current-voltage measurements were also carried out and are presented and discussed.

8.3 kV 4H-SiC PiN Diode on (000-1) C-Face with Small Forward Voltage Degradation

The dependence of forward voltage degradation on crystal faces for 4H-SiC pin diodes has been investigated. The forward voltage degradation has been reduced by fabricating the diodes on the (000-1) C-face off-angled toward &lt;11-20&gt;. High-voltage 4H-SiC pin diodes on the (000-1) C-face with small forward voltage degradation have also been fabricated successfully. A high breakdown voltage of 4.6 kV and DVf of 0.04 V were achieved for a (000-1) C-face pin diode. A 8.3 kV blocking performance, which is the highest voltage in the use of (000-1) C-face, is also demonstrated in 4H-SiC pin diode.

Characterization of hard- and soft-switching performance of high-voltage Si and 4H-SiC PiN diodes

This paper presents a study of the performance of high-voltage Si and 4H-SiC diodes in a DC-DC buck converter. Device operation in both hard- and zero-voltage switching conditions is presented with the help of measurements and two-dimensional (2-D) mixed device-circuit simulations. Experimental results show that SiC PiN diodes have a strong potential for use in high-speed high-voltage power electronics applications operating at high temperature. A combination of low excess carrier concentration and low carrier lifetime results in superior switching performance of the 4H-SiC diode over ultrafast Si diodes. Soft switching is shown to minimize the switching loss and allow operation at higher switching frequencies using Si diodes. The power loss of 4H-SiC diodes is dominated by conduction loss. Consequently, soft-switching techniques result in a marginal reduction in power loss. However, the low overall power loss implies that SiC diodes can be used at very high switching frequencies even in hard-switching configurations.