Materials Science Forum Vols. 717-720

Abstract: A fully electrically isolated package for a SiC temperature sensor, able to work at high temperature, is presented in this paper. The adopted packaging solution was tested under thermal stress by varying the temperature between 300C and 400C (for 500 cycles) and between 50C and 400C (for other 500 cycles). The thermal stress had negligible effect on the capsules leakage currents (measured from the sensor terminals to the package metal casing) and did not degrade the glass which ensures the sealing of the capsule. The measurements and microphysical investigations showed a stable operation of the package up to temperatures of 400C.

Abstract: The forward current distribution in SiC 600V merged pn-Schottky (MPS) diodes is visualized with the help of emission microscopy at various current densities. It is shown how the light emission develops with increasing current densities and extends from the Schottky contact areas into the pn junction areas. Large p⁺-regions e.g. in the edge termination contribute first by minority carrier injection, whereas the smaller p⁺ hexagonal cells and the p⁺ grid follow subsequently.

Abstract: This paper presents three different structures of Schottky diodes that were fabricated with low Schottky barrier heights. To reduce the forward voltage drop, the introduction of a lower Schttoky barrier is necessary. One of key issues associated with diodes having a low Schottky barrier height and a planar structure is an excessively high leakage current. By introducing the novel trench structure, the leakage current was reduced to a reasonable level. Furthermore it was confirmed that they have minimal switching time during turn-off and high avalanche capability. Thus trench structure Schottky diodes are able to reduce not only switching losses but also conductive losses and demonstrate sufficient robustness.

Abstract: Various layouts of the anode of Junction Barrier Schottky (JBS) diodes are compared theoretically and it is found that the hexagonal honeycomb structure with 3-D symmetry offers the best figure of merit (FOM). Proportional relationships between the various layouts are reported, using which we extend a fully analytical 2-D model for reverse biased field shielding in a JBS diode to the superior 3-D layouts. The effect of reducing implanted feature size is also analyzed as a trade-off between FOM and breakdown voltage capability.

Abstract: The performance of Junction Barrier Schottky (JBS) diodes developed for medium voltage hard-switched Naval power conversion is reported. Nominally 60 A, 4.5kV rated JBS freewheeling diodes were paired with similarly rated Si IGBTs and evaluated for temperature dependent static and dynamic characteristics as well as HTRB and surge capability. The SiC JBS/Si IGBT pair was also directly compared to Si PiN diode/Si IGBT with similar ratings. Compared to Si, the SiC freewheeling diode produced over twenty times lower reverse recovery charge leading to approximately a factor-of-four-reduction in turn-on loss. Alternatively, for equivalent total switching loss, the SiC JBS/Si IGBT hybrid configuration allows for at least a 50% increase in specific switched power density. Reliability testing showed the devices to be robust with zero failures.

Abstract: Novel device design and process innovations made at GeneSiC on SiC JBS rectifiers result in a significant increase in surge current capability with a 33% decrease in power dissipation at 10x rated current. On the 1200 V-class rectifiers, a clear signature of avalanche-limited breakdown with ultra-low leakage currents is observed at temperatures as high as 240 °C. Almost temperature independent Schottky barrier heights of 1.2 eV and ideality factors 2K² (for 4H-SiC) is directly extracted from the forward I-V characteristics. When compared with an off-the-shelf all-Si IGBT power co-pack, GeneSiC’s GA100XCP12-227 co-pack offers 88% and 47% reduction at 125 °C in the IGBT and free-wheeling diode switching energy losses, respectively. This results in an overall switching loss reduction of about 28% as compared to its silicon counterpart.

Abstract: Sharp avalanche breakdown voltages of 12.9 kV are measured on PiN rectifiers fabricated on 100 µm thick, 3 x 10¹⁴ cm-3 doped n- epilayers grown on n+ 4H-SiC substrates. This equates to a record high 129 V/µm for a > 10 kV device. Optimized epilayer, device design and processing of the SiC PiN rectifiers result in a > 60% blocking yield at 10 kV, ultra-low on-state voltage drop and differential on-resistance of 3.75 V and 3.3 mΩ-cm² at 100 A/cm² respectively. Open circuit voltage decay (OCVD) measured carrier lifetimes in the range of 2-4 µs are obtained at room temperature, which increase to a record high 14 µs at 225 °C. Excellent stability of the forward bias characteristics within 10 mV is observed for a long-term forward biasing of the PiN rectifiers at 100 A/cm2. A PiN rectifier module consisting of five parallel large area 6.4 mm x 6.4 mm 10 kV PiN rectifiers is connected as a free-wheeling diode with a Si IGBT and 1100 V/100 A switching transients are recorded. Data on the current sharing capability of the PiN rectifiers is also presented.

Abstract: This paper presents a study of performance and scalability of 8kV SiC PIN diodes focusing on area-dependent yield and sensitivity to material properties variation. Successfully fabricated 18 and 36 mm2 SiC-PiN diodes exhibited avalanche breakdown above 8 kV and < 5V forward voltage drop at 100 A/cm2 current density. The fast switching operation of these diodes up to ~5 kHz frequency is evidenced by reverse recovery measurements with by double-pulse inductive switching tests. The devices exhibit 0.142 and 0.169 uC/cm2 stored charge at room temperature and 125oC, respectively, when turned-off from Jf = 100A/cm2 to Vr = 2.1 kV. The measured diode breakdown voltage exhibited location and size dependent yield, indicating the necessity of material quality improvements for production.

Abstract: 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.

Abstract: To meet the large current handling requirements of modern power conditioning systems, paralleling of a large number of devices is required. This increases cost and complexity through dicing, soldering, and forming multiple wire bonds. Furthermore, paralleling discrete devices increases package volume/weight and reduces power density. To overcome these complexities, PiN diodes were designed, fabricated at high yields, tested, and interconnected on a three-inch 4H-SiC wafer to form an 11.72 cm² wafer-scale diode. The wafer-scale diode exhibited a breakdown voltage of 1790 V at an extremely low leakage current density of less than 0.002 mA/cm². Under pulsed conditions, the peak current through the wafer-scale diode is 64.3 kA with a forward voltage drop of 10.3 V. The dissipated energy was 382 J and the action exceeded 1.7 MA²-sec.