Study Of High-voltage Junction Barrier Schottky Rectifiers

With the rapid development of power electronic technology, the conventional Schottky Barrier Diodes (SBD) has the shortcomings of low breakdown voltage and high leakage current, while the charge-storage effect of PiN rectifiers restricts its applications in high freguency field. Those disadvantages make SBD and PiN rectifiers are unable to meet the demands of high-frequency, high-power and low-power-loss. To avoid these deficiencies, Junction Barrier Schottky rectifiers (JBS) which ingeniously combined the SBD and PiN structure has been proposed. JBS rectifiers have the advantages of high breakdown voltage, low voltage drop, low leakage current, high-frequency response and strong anti-overvoltage and surge current capability. JBS devices are widely used in Switched-Mode Power Supply (SMPS) circuit, Power Factor Correction (PFC) circuit, and Transformer Secondary (TS) circuit, Residual Current Device (RCD) circuit and some other circuits. Therefore, it is of broad market prospects and research value.In order to further improve the performance of JBS rectifier, based on the basic theory of the device, floating-limiting ring (FLR) terminal structure has been adopted, and JBS rectifiers with breakdown voltage high to650V have been designed and prepared. This thesis is mainly focused on the following three aspects:1. The advantages and disadvantages of SBD and PiN rectifier are compared and analyzed. In addition, forward and reverse current-voltage characteristics, as well as transient characteristics of the JBS rectifier are further expounded. And it’s focused on researching the influence of epitaxial materials on device performance. The results indicate that to obtain certain reverse breakdown voltage, punchthrough designed epitaxial material optimized device conduction properties.2. JBS rectifiers can be classified as active area striped and concentric circled stuctures.The terminal JBS structure consisting of several floating-limiting-rings and one cutting-ring are studied and designed. Breakdown voltage high to650V has been obtained in our device. The correspnding leakage current of the device is less than 20μA. When the current is large as10A (current density33.3A/cm2), the voltage drop on the device is approximately1V. And the device shows a good operating characteristics at the temperature of125℃, indicating that thermal stability of the device is good. The measured barrier height is0.668-0.681eV, which is very close to the theoretical value. C-V tests found that the capacitance of device at zero bias is370pF. And the value increases rapidly as the reverse bias decreases, which indicating that the device capacitance has small impact on the reverse recovery characteristics.Therefore, the device has a good frequency characteristic.3. In order to further improve the device performance and yield, Silvaco-TCAD simulation software was used to optimize the device structure parameters and technological process, and a novel device structure with four-limit-ring terminal structure was presented. Simulation results show that with given epitaxial materials, Three-floating-limiting-ring terminal structure instead of two-floating-limiting-ring terminal structure can achieve the designed requiments. Howerver, taking the low yield reasulted from instability of process conditions into account, four-floating-limit-ring terminal structure with reverse breakdown voltage high to680V is adopted, which leaves enough margin for the production process. At the low forword current condition, the current of JBS is formed by unipolar majority carriers. While at the condition of large current, the current conducting mechanism is similar to the current transport mechanism of PiN bipolar. The current density at the edge of P+bars is the largest, whereas the current density at the center line of the schottky channel is the smallest. At the applied voltage of1V, the current density can reach127A/cm2.