High-power 4H-SiC JBS rectifiers

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.

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.

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 systematic experimental study is conducted on floating field rings (FFR) incorporated into 4H-SiC junction barrier Schottky (JBS) diodes across four voltage ratings 650, 1200, 1700 and 3300V, in pursuit of highly efficient FFR designs. 30 designs of FFR in 3 categories are studied for each voltage rating, and the measured breakdown voltage (Vbr) of JBS divided by ring system width (W) is taken as the figure of merit (FOM) of each design. The influence of ring spacing, ring width and number of rings on Vbr is studied in detail. It is found that the initial ring spacing (S1) is critical in determining the highest Vbr achievable by a certain design, and its optimum value increases as voltage rating increases. TCAD simulation verifies the importance of S1. For designs with a small ring system width, subsequent ring spacing can also become important. Ring width does not have a definitive effect, and Vbr saturates beyond a certain ring number. The design with the highest Vbr may not render the highest FOM. Even style designs with appropriate ring spacings can be advantageous likely due to less susceptibility to variation of field oxide charge, and more tolerance to fabrication error, as well as ease of design.

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.

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

This paper proposes a novel 4H-SiC diode---accumulation-mode MOS channel diode (AMMCD). Theoretical analyses of the operation principle of the AMMCD are carried out. The parameters of the AMMCD are optimized by Sentaurus TCAD tools. Finally, the 4H-SiC AMMCD with low forward voltage drop (VF) and reverse leakage current (IR) is obtained. Compared with 4H-SiC super barrier rectifier (SBR) and junction barrier Schottky diode (JBS) with the same breakdown voltage (650 V), the AMMCD proposed in this paper has superior static electrical characteristics. In addition, the current and electric field profiles of 4H-SiC SBR and AMMCD are analyzed as well.

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.

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.

Silicon carbide (SiC) junction barrier Schottky (JBS) diode has been widely used in power electronic systems due to its excellent physical characteristics and electrical performance, and the structural design of its source area has a particularly significant impact on the performance. This study provides a comparative analysis of the SiC JBS diode performance of different hexagonal structures, aiming to provide theoretical support and practical guidance for the optimization of JBS diode performance. Through theoretical derivation, experimental verification and data processing, the paper deeply analyzes the influence of hexagonal structure on JBS diode current distribution and breakdown voltage, and proposes a targeted optimization strategy.

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.

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.

The surge reliability and failure mechanisms of 1200-V/40-A 4H-SiC junction barrier Schottky diodes with different epilayer defect types have been studied in depth. Under 2500 surge current cycles with Ipeak = 190 A conditions, it is observed that the particle inclusions, triangular defects, surface particles, and stacking faults exhibit varying degrees of significant effects on the conduction, breakdown, and surge characteristics of the diodes. The results indicate the presence of three distinct failure mechanisms that are attributed to epilayer defects being activated and expanded at high current and high junction temperature, accelerating the premature failure of the devices in the iterative process of thermo-electric coupling. One mechanism involves defect-induced current paths damaging the Schottky barrier interface within the active region, directly leading to the loss of the device’s blocking and surge capabilities. The other mechanisms relate to defect-related damage in the termination region, which also triggers varying degrees of degradation in the breakdown voltage and surge capability.