Comparative Study of the Hexagonal Structure of the SiC JBS Source Region

A 2-dimensional fully analytical model for design of high voltage junction barrier Schottky (JBS) diodes

The Junction Barrier Schottky (JBS) diode in silicon carbide is a promising candidate for a low-leakage power rectifier for high switching frequencies and elevated temperature operation. It has the advantage of a low forward voltage drop while keeping a low leakage current at high blocking voltage. JBS devices have been fabricated in 4H SiC and 6H SiC and then electrically characterised in comparison with pn and Schottky diodes on the same wafer. The JBS devices reached blocking voltages up to 1.0 kV at a leakage current density of 13 IŒA/cm2 and the forward conduction was limited by an on-resistance close to the theoretical value.

4H-SiC Schottky Barrier Diodes (SBD) have been developed using p-type buried grids (BGs) formed by Al implantation. In order to reduce on-state resistance and improve forward conduction, the doping concentration of the channel region between the buried grids was increased. The fabricated diodes were encapsulated with TO-254 packages and electrically evaluated. Experimental forward and reverse characteristics were measured in the temperature range from 25 °C to 250 °C. On bare die level, the forward voltage drop was reduced from 5.36 V to 3.90 V at 20 A as the channel doping concentration was increased, which introduced a low channel resistance. By the encapsulation in TO-254 package, the forward voltage drop was decreased approximately 10% due to a lower contact resistance. The on-state resistance of the identical device measured on bare die and in TO-254 package increased with increasing temperature due to the decreased electron mobility in the drift region resulting in higher resistance. The incremental contact resistances of the bare dies were larger than in the packaged devices. One key issue associated with conventional Junction Barrier Schottky (JBS) diodes is a high leakage current at high temperature operation over 200 °C. The developed Buried Grid JBS (BG JBS) diode has significantly reduced leakage current due to a better field shielding at the Schottky contact. The leakage current of the packaged BG JBS diodes is compared to pure SBD and commercial JBS diodes.

A physics based compact model for SiC Junction Barrier Schottky (JBS) diodes is presented which features a comprehensive physical description of the DC and CV behavior of SiC JBS diodes. For the first time, modeling of leakage current for JBS diode in circuit simulation is done. The model includes temperature scaling of its parameters to enable modeling of the diodes over a wide range of temperature (25 °C to 175 °C). The model has been validated using characterization data from a 1200 V, 3 A SiC JBS diode from GeneSiC. Excellent agreement is shown between device measurements and simulation for all regimes of operation of the diode.

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.

The Transformerless Intelligent Power Substation (TIPS) is being developed as an alternative to the conventional line frequency transformers at the 13.8 kV distribution grid - 480 V utility grid interface. The Front End Converter (FEC) of TIPS is composed of newly developed 15 kV/20 A Silicon Carbide (SiC) IGBTs and series connected 10 kV/10 A SiC Junction Barrier Schottky (JBS) diodes. The low device current ratings open up a big challenge in the protection of these devices in the event of faults on the a.c side or on the d.c bus as well as during high surge voltage on the line. This paper covers a detailed study of the various components of the fault protection system in terms of their breaking time, breaking current and fault coordination. The evaluation is also done with respect to different fault types like 3-phase to ground fault and single phase to ground fault at various points of the system. The effect of fault on passive elements is also considered.

4H-SiC junction barrier Schottky (JBS) diodes with four kinds of design have been fabricated and characterized using two different processes in which one is fabricated by making the P-type ohmic contact of the anode independently, and the other is processed by depositing a Schottky metal multi-layer on the whole anode. The reverse performances are compared to find the influences of these factors. The results show that JBS diodes with field guard rings have a lower reverse current density and a higher breakdown voltage, and with independent P-type ohmic contact manufacturing, the reverse performance of 4H-SiC JBS diodes can be improved effectively. Furthermore, the P-type ohmic contact is studied in this work.

High-performance gallium oxide (Ga2O3) junction barrier Schottky (JBS) diodes were fabricated using planar and trench junction barrier designs. Their electrical transport mechanisms were systematically studied. The JBS integration strengthens interfacial depletion via p–n junction-induced Ga2O3 conduction band elevation, whereas the trench design forms a higher interfacial barrier and expands lateral depletion, effectively modulating carrier transport. Additionally, the JBS structure reduces the electric field at the Schottky interface which not only suppresses Schottky barrier lowering to reduce reverse leakage current but also mitigates surface field crowding to prevent premature device breakdown. The forward current density ratios of Schottky barrier diodes (SBDs) with a JBS reached an impressive 8.0 × 1010, demonstrating exceptional switching characteristics. The reverse breakdown voltage of the SBDs with trench JBS increases from 310 V in the SBDs to a remarkable 1150 V, representing roughly a 3.7-time. The leakage current is simultaneously reduced by two orders of magnitude to an ultra-low value of 1.1 × 10−9 A cm−2. A comparative analysis of device performance between planar and trench JBS structures is presented, offering a theoretical foundation and reference for future innovations in Ga2O3-based SBDs.

This paper reports the detailed design, fabrication, and characterization of two sets of high-power 4H-silicon carbide (4H-SiC) junction barrier Schottky (JBS) diodes - one with a 1500-V, 4-A capability and another with 1410-V, 20-A capability. Two-dimensional (2-D) device simulations show that a grid spacing of 4 /spl mu/m results in the most optimum trade-off between the on-state and off-state characteristics for these device ratings. JBS diodes with linear and honeycombed p/sup +/ grids, Schottky diodes and implanted p-i-n diodes fabricated alongside show that while 4H-SiC JBS diodes behave similar to,Schottky diodes in the on-state and switching characteristics, they show reverse characteristics similar to p-i-n diodes. Measurements on 4H-SiC JBS diodes indicate that the reverse-recovery time (/spl tau//sub rr/) and associated losses are near-zero even at a high reverse dI/dt of 75 A//spl mu/s. A dc/dc converter efficiency improvement of 3-6% was obtained over the fastest, lower blocking voltage silicon (Si) diode when operated in the 100-200 kHz range.

This work explores the effects of extended epitaxial defects on 4H-SiC power devices. Advanced defect mapping techniques were used on large quantities of power device wafers, and data was aggregated to correlate device electrical characteristics to defect content. 1200 V class Junction Barrier Schottky (JBS) diodes and MOSFETs were examined in this manner; higher voltage 3.3 kV class devices were examined as well. 3C inclusions and triangular defects, as well as heavily decorated substrate scratches, were found to be device killing defects. Other defects were found to have negligible impacts on device yield, even in the case of extremely high threading dislocation content. Defect impacts on device reliability was explored on MOS-gate structures, as well as long-term device blocking tests on both MOSFETs and JBS diodes. Devices that passed on-wafer electrical parametric tests were found to operate reliably in these tests, regardless of defect content.

Power electronic devices are crucial components of power converter systems. The evolution of power devices drives the development of power converters, including improvements in performance, reliability, and power capacity. In this chapter, the author expounds the structure, working principle, and static and dynamic characteristics of the conventional PN junction diode. And the silicon carbide (SiC) Schottky barrier diode (SBD), junction barrier Schottky (JBS) diode, trench JBS (T-JBS) diode, and sidewall-enhanced trench JBS (SET-JBS) diode are also discussed and compared. Also, the structures and properties of the gallium oxide (Ga2O3) SBD and heterojunction diode are also summarized. Next, the author gives a detailed analysis and discussion of the silicon power metal-oxide-semiconductor field-effect transistor (MOSFET), superjunction MOSFET, and the SiC MOSFET and JFET, and the Ga2O3 MOSFET. Then, the device structure and operating principle, switching characteristics, and current tailing mechanism of the insulated gate bipolar transistor (IGBT) are also analyzed and summarized in detail. Finally, the energy band structure, working principle, and switching characteristic of the gallium nitride (GaN) high-electron mobility transistor (HEMT), one of the hot devices in the current market, are also described. Finally, the summary and prospect of power electronic devices are also presented in this chapter.

It is known that a Schottky barrier height (b) of metal/C-face 4H-SiC Schottky barrier diode (SBD) differ from b of metal/Si-face 4H-SiC SBD. Furthermore, b of metal/4H-SiC SBD varies with annealing temperature. We fabricate 0.231mm2 SBD with Ti/SiC interface using Si-face and C-face 4H-SiC. These SBDs are annealed at several temperatures after a formation of the Ti/SiC interface. As a result, b of Ti/C-face 4H-SiC interface annealed at 400 oC is nearly equal to b of Ti/Si-face 4H-SiC interface annealed at 500 oC and the n-values of these SBDs are nearly equal to the ideal value (unity). Using that annealing condition, we fabricated 25mm2 junction barrier Schottky (JBS) diodes with Ti/SiC interface on Si-face and C-face 4H-SiC epitaxial substrate. b of Si-face and C-face JBS diodes are 1.26eV and 1.24eV, respectively. The leakage currents for both Si-face and C-face JBS diodes are less than 1mA/cm2. The current of 100A is obtained at the forward bias voltage of 1.95V and 2.16V for the Si-face JBS and the C-face JBS.

The static and dynamic characteristics of 13-kV class 4H-SiC junction barrier Schottky (JBS) diodes with a three-zone junction termination extension (JTE) are presented. Using an anisotropy breakdown model, technology computer-aided design simulation of devices with a three-zone JTE agrees well with the obtained experimental results, correctly predicting a sharp drop in blocking voltage at high JTE acceptor concentrations. The forward voltage of the JBS diode at 75°C and a forward current of 500 mA is reduced to approximately one-ninth by that of 13 series-connected 1000-V Si PiN diodes. This suggests that conduction losses of traditional high-voltage circuits which conventionally use series-connected devices can be drastically reduced by replacing the series-connected devices with a single 13-kV class SiC JBS diode. Moreover, the reverse recovery current waveform of the 13-kV class SiC JBS diode shows that these diodes have lower reverse recovery losses than a 13-kV SiC PiN diode.

The dv/dt switching limitations of power semiconductor devices are evaluated in a boost (PFC) power converter using circuit simulations. State-of-the-art commercial silicon CoolMOS devices, commercial Silicon Carbide (SiC) Junction Barrier Schottky (JBS) diodes, and emerging Gallium Nitride (GaN) lateral power transistors are considered. It is shown that although SiC and GaN power devices have low stored charge and small capacitances, they experience high switching dv/dt stresses which may pose serious switching limitations especially in high-frequency power converters. This problem is likely to be further exacerbated by the presence of a high density of crystal defects in SiC and GaN materials which will manifest in the form of poor field-reliability. Specific guidelines for device selection are recommended in order to optimize both performance and field-reliability.

Robustness of 4H-SiC 1200V Schottky diodes under high electrostatic discharge like human body model stresses: An in-depth failure analysis