Temperature-dependent characteristics of 4H-SiC junction barrier Schottky diodes

The current-voltage characteristics of 4H-SiC junction barrier Schottky （JBS） diodes terminated by an offset field plate have been measured in the temperature range of 25-300℃. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H-SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.

Study and optimal simulation of 4H-SiC floating junction Schottky barrier diodes' structures and electric properties

This paper stuides the structures of 4H SiC floating junction Schottky barrier diodes. Some structure parameters of devices are optimized with commercial simulator based on forward and reverse electrical characteristics. Compared with conventional power Schottky barrier diodes, the devices are featured by highly doped drift region and embedded floating junction layers, which can ensure high breakdown voltage while keeping lower specific on-state resistance, and solve the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with optimized structure parameter, the breakdown voltage can reach 4.36 kV and the specific on-resistance is 5.8 mΩ.cm2 when the Baliga figure of merit value of 13.1 GW/cm2 is achieved.

Modeling of 4H-SiC multi-floating-junction Schottky barrier diode

This paper develops a new and easy to implement analytical model for the specific on-resistance and electric field distribution along the critical path for 4H-SiC multi-floating junction Schottky barrier diode. Considering the charge compensation effects by the multilayer of buried opposite doped regions, it improves the breakdown voltage a lot in comparison with conventional one with the same on-resistance. The forward resistance of the floating junction Schottky barrier diode consists of several components and the electric field can be understood with superposition concept, both are consistent with MEDICI simulation results. Moreover, device parameters are optimized and the analyses show that in comparison with one layer floating junction, multilayer of floating junction layer is an effective way to increase the device performance when specific resistance and the breakdown voltage are traded off. The results show that the specific resistance increases 3.2 mΩ.cm2 and breakdown voltage increases 422 V with an additional floating junction for the given structure.

Study of 4H-SiC junction barrier Schottky diode using field guard ring termination

This paper reports that the 4H-SiC Schottky barrier diode, PiN diode and junction barrier Schottky diode terminated by field guard rings are designed, fabricated and characterised. The measurements for forward and reverse characteristics have been done, and by comparison with each other, it shows that junction barrier Schottky diode has a lower reverse current density than that of the Schottky barrier diode and a higher forward drop than that of the PiN diode. High-temperature annealing is presented in this paper as well to figure out an optimised processing. The barrier height of 0.79 eV is formed with Ti in this work, the forward drop for the Schottky diode is 2.1 V, with an ideality factor of 3.2, and junction barrier Schottky diode with blocking voltage higher than 400 V was achieved by using field guard ring termination.

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky （JBS） diodes with a high-temperature annealed resistive termination extension （HARTE） are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm^2 with a total active area of 2.46× 10 ^-3 cm^2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250 ℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9× 10^-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

Design of vertical diamond Schottky barrier diode with junction terminal extension structure by using the n-Ga_(2)O_(3)/p-diamond heterojunction

A novel junction terminal extension structure is proposed for vertical diamond Schottky barrier diodes(SBDs) by using an n-Ga_(2)O_(3)/p-diamond heterojunction. The depletion region of the heterojunction suppresses part of the forward current conduction path, which slightly increases the on-resistance. On the other hand, the reverse breakdown voltage is enhanced obviously because of attenuated electric field crowding. By optimizing the doping concentration, length, and depth of n-Ga_(2)O_(3), the trade-off between on-resistance and breakdown voltage with a high Baliga figure of merit(FOM)value is realized through Silvaco technology computer-aided design simulation. In addition, the effect of the work functions of the Schottky electrodes is evaluated. The results are beneficial to realizing a high-performance vertical diamond SBD.

High performance trench diamond junction barrier Schottky diode with a sidewall-enhanced structure

The trench diamond junction barrier Schottky(JBS)diode with a sidewall enhanced structure is designed by Silvaco simulation.Comparing with the conventional trench JBS diode,Schottky contact areas are introduced on the sidewall of the trench beside the top cathode.The sidewall Schottky contact weakens the junction field-effect transistor effect between the trenches to realize a low on-resistance and a high Baliga's figure of merit(FOM)value.In addition,the existence of the n-type diamond helps to suppress the electric field crowding effect and enhance the reverse breakdown voltage.With the optimal parameters of device structure,a high Baliga's FOM value of 2.28 GW/cm^(2) is designed.Therefore,the proposed sidewall-enhanced trench JBS diode is a promising component for the applications in diamond power electronics.

Design optimization of high breakdown voltage vertical GaN junction barrier Schottky diode with high-K/low-K compound dielectric structure

A vertical junction barrier Schottky diode with a high-K/low-K compound dielectric structure is proposed and optimized to achieve a high breakdown voltage(BV).There is a discontinuity of the electric field at the interface of high-K and low-K layers due to the different dielectric constants of high-K and low-K dielectric layers.A new electric field peak is introduced in the n-type drift region of junction barrier Schottky diode(JBS),so the distribution of electric field in JBS becomes more uniform.At the same time,the effect of electric-power line concentration at the p-n junction interface is suppressed due to the effects of the high-K dielectric layer and an enhancement of breakdown voltage can be achieved.Numerical simulations demonstrate that GaN JBS with a specific on-resistance(R_(on,sp)) of 2.07 mΩ·cm^(2) and a BV of 4171 V which is 167% higher than the breakdown voltage of the common structure,resulting in a high figure-of-merit(FOM) of 8.6 GW/cm^(2),and a low turn-on voltage of 0.6 V.

具有圆形P+区的1200 V SiC JBS二极管的研究

【目的】通过改变碳化硅(silicon carbide,SiC)结势垒肖特基二极管(junction barrier Schottky diode,JBS)的P+掺杂区的形状,将常规SiC JBS条形分布的P+掺杂区优化为圆形P+掺杂区,并两两之间以正三角形分布于肖特基接触之间。【方法】通过三维结构有限元仿真方法模拟以上两种SiC JBS结构的正反向特性,优化P+掺杂区宽度和外延层掺杂浓度,并进行对比分析。【结果】仿真结果显示,两种结构的反向击穿电压均高于1500 V,圆形P+掺杂区JBS二极管的正向导通压降比条形P+掺杂区JBS二极管的低:在正向电流密度为400 A/cm^(2)时,导通压降由条形P+结构的2.37 V降低至圆形P+结构的2.05 V,降低了13.5%;圆形P+结构在经过优化外延层掺杂浓度后,其在正向电流密度为400 A/cm^(2)时的导通压降为1.97 V,较条形P+结构的降低了16.9%。相较于条形SiC JBS,圆形P+结构具有更大的肖特基接触面积,在保证击穿电压的同时可以获得更低的导通压降,并通过优化器件的外延层掺杂浓度进一步降低器件的导通压降。【结论】本文将P+掺杂区形状由条形调整为圆形,并以正三角形分布排列。这种调整增大了器件的肖特基接触面积,优化了正向导通特性,并通过优化器件的外延层掺杂浓度进一步提高了导通特性,获得了更低的导通压降。

4H-SiC SBD和JBS退火研究

在4H-SiC外延材料上制备了SBD和JBS器件,研究并分析了退火温度对这两种器件正反向特性的影响。结果表明,低于350℃退火可同时提高SBD和JBS的正反向特性。当退火温度高于350℃时,二者的正向特性都出现退化,SBD退化较JBS更为严重。JBS阻断电压随退火温度升高而增大,在退火温度高于450℃时增加趋势变缓。SBD阻断电压随退火温度升高先升后降,在500℃退火时达到一个最大值。可见一定程度的退火有助于提高4H-SiCSBD和JBS器件的正反向特性,但须考虑其对正反向特性的不同影响。综合而言,退火优化后JBS优于SBD器件性能。

3.3kV/50 A SiC JBS二极管及混合功率模块研制

通过理论计算、仿真与实验验证的方式研制出3.3 kV/50 A 4H-碳化硅(SiC)结势垒肖特基(JBS)二极管芯片。芯片漂移区厚度33μm,掺杂浓度2×1015 cm-3,p+结区深度0.6μm,p+结区掺杂浓度5×1018 cm-3。芯片终端采用非均匀场限环结构。芯片静态测试表明,反向电压3.3 kV时漏电流低于100μA,正向电流50 A时压降小于2.4 V,与设计目标相符。基于该SiC JBS芯片完成了3.3 kV/400 A Si IGBT/SiC JBS混合功率模块研制,测试结果表明混合功率模块降低开关损耗明显,为实现变流装置高效化、小型化及轻量化打下了基础。

6500 V 15 A 4H-SiC JBS二极管的研制

基于有限元仿真的方法对6 500 V15 A4H-SiC肖特基二极管开展了材料结构、有源区结型势垒肖特基（JBS）结构和终端保护结构的优化设计。基于4英寸（1英寸=2.54 cm）n型4H-SiC导电衬底,采用厚度为55μm、杂质浓度为9×1014 cm-3的外延材料、48个宽度为3.0μm浮空场限环实现了一款反向击穿电压大于6 500 V的4H-SiC JBS二极管。电特性测试结果表明,室温下正向电流为15 A时,正向电压为2.9 V,开启电压为1.3 V;150℃下正向电流为15 A时,正向电压为5.2 V,开启电压为1.2 V。

1200 V/100 A高温大电流4H-SiC JBS器件的研制

基于SiC结势垒肖特基（JBS）二极管工作原理及其电流/电场均衡分布理论,采用高温大电流单芯片设计技术及大尺寸芯片加工技术,研制了1 200 V/100 A高温大电流4H-SiC JBS二极管。该器件采用优化的材料结构、有源区结构和终端结构,有效提高了器件的载流子输运能力。测试结果表明,当正向导通压降为1.60 V时,其正向电流密度达247 A/cm^2（以芯片面积计算）。在测试温度25和200℃时,当正向电流为100 A时,正向导通压降分别为1.64和2.50 V;当反向电压为1 200 V时,反向漏电流分别小于50和200μA。动态特性测试结果表明,器件的反向恢复特性良好。器件均通过100次温度循环、168 h的高温高湿高反偏（H3TRB）和高温反偏可靠性试验,显示出优良的鲁棒性。器件的成品率达70%以上。

1200 V 4H-SiC JBS二极管的研制

通过理论分析与计算机仿真方法对1 200 V 4H-碳化硅(SiC)结势垒肖特基(JBS)二极管进行了设计与研究,实现了1 200 V/2 A,1 200 V/5 A及1 200 V/30 A三种等级管芯的研制。鉴于非均匀场限环(FLR)保护效率存在对工艺偏差敏感的问题,所设计各电流等级的管芯均采用均匀FLR作为终端结构。经测试,所研制管芯在反偏压为1 200 V时,漏电流均不大于3μA,且1 200 V/2 A,1 200 V/5 A及1 200 V/30 A三种等级管芯的通态电阻分别为790mΩ,360 mΩ及59.3 mΩ。

650V/50A 4H-SiC JBS二极管的设计与验证

对肖特基区宽度不同的4H-碳化硅(SiC)结势垒肖特基(JBS)二极管进行了仿真与实验研究。根据研究结果设计了一款兼具高功率处理能力与超低漏电流的4H-SiC JBS二极管并进行实验验证。实验结果显示所设计器件通态电阻为36 mΩ,反向耐压650 V时漏电流小于10 nA,功率处理能力大于30 kVA。

SiC JBS二极管和SiC MOSFET的空间辐照效应及机理

基于第六代650 V碳化硅结型肖特基二极管(SiC JBS Diode)和第三代900 V碳化硅场效应晶体管(SiC MOSFET),开展SiC功率器件的单粒子效应、总剂量效应和位移损伤效应研究。20~80 MeV质子单粒子效应实验中,SiC功率器件发生单粒子烧毁(SEB)时伴随着波浪形脉冲电流的产生,辐照后SEB器件的击穿特性完全丧失。SiC功率器件发生SEB时的累积质子注量随偏置电压的增大而减小。利用计算机辅助设计工具(TCAD)开展SiC MOSFET的单粒子效应仿真,结果表明,重离子从源极入射器件时,具有更短的SEB发生时间和更低的SEB阈值电压。栅-源拐角和衬底-外延层交界处为SiC MOSFET的SEB敏感区域,强电场强度和高电流密度的同时存在导致敏感区域产生过高的晶格温度。SiC MOSFET在栅压偏置(U_(GS)=3 V,U_(DS)=0 V)下开展钴源总剂量效应实验,相比于漏压偏置(U_(GS)=0 V,U_(DS)=300 V)和零压偏置(U_(GS)=U_(DS)=0 V),出现更严重的电学性能退化。利用中带电压法分析发现,栅极偏置下氧化层内的垂直电场提升了陷阱电荷的生成率,加剧了阈值电压的退化。中子位移损伤会导致SiC JBS二极管的正向电流和反向电流减小。在漏极偏置下进行中子位移损伤效应实验,SiC MOSFET的电学性能退化最严重。该研究为空间用SiC器件的辐射效应机理及抗辐射加固研究提供了一定的参考和支撑。

POP型SiC JBS二极管结构的改进与性能优化

为了进一步提高SiC JBS的反向击穿特性和BFOM值,对POP型SiC JBS结构进行了重要改进。虽然它们都是采用外延的方法在一个较窄的轻掺杂P阱上面再制作一个较宽的重掺杂P区,但是改进的结构在二者的界面附近存在一段等宽区,即P阱的上半部分与重掺杂P区同宽,从而大幅度降低重掺杂P区的边缘电场集中效应以提高击穿电压。通过理论分析与MEDICI软件仿真,深入探讨了这种结构变化对器件性能的影响。结果表明,在不增加额外工艺的情况下,改进的结构可大幅度提高BFOM和击穿电压。

表面缺陷对SiC JBS二极管特性影响研究

由于碳化硅(SiC)外延材料中缺陷的影响,目前SiC结势垒肖特基(JBS)二极管实际性能仍低于理论预期。通过4H-SiC外延材料生长和表征、4H-SiC JBS二极管制作和器件特性测试分析,研究了表面缺陷对4H-SiC JBS二极管反向特性的影响。结果表明,当金属接触区或场限环区有彗星形缺陷或彗核存在时,器件击穿电压较低。胡萝卜缺陷会造成反向偏压较低时器件漏电流的增大,对器件的击穿电压影响不大。生长坑对器件的击穿电压和漏电流影响相对较小。三角形缺陷的存在会导致反向击穿电压降低约50%,漏电流增大4个数量级,对器件的反向特性有较严重的影响。分析认为,表面缺陷所导致的4H-SiC JBS二极管肖特基势垒高度的降低和缺陷处局部电场的增大是产生上述实验现象的主要原因。

4H-SiC浮动结JBS器件的设计方法

研究了4H-SiC浮动结(FJ)结势垒肖特基(JBS)二极管的设计方法。提出在上外延层厚度一定的情况下得到外延层最佳掺杂浓度,然后以器件的功率优值(BFOM值)为依据确定出最佳下外延层厚度,进而设计出浮动结和表面结的最佳结构参数。否定了文献中认为浮动结位于器件中部为最佳设计的结论。仿真结果表明浮动结和表面结线宽比不仅影响器件导通特性,还会影响反向特性。浮动结线宽比在一定范围内会略微影响器件击穿电压,而表面结线宽比主要影响器件的反向泄漏电流。

Optimized design of 4H-SiC floating junction power Schottky barrier diodes

SiC floating junction Schottky barrier diodes were simulated with software MEDICI 4.0 and their device structures were optimized based on forward and reverse electrical characteristics. Compared with the conventional power Schottky barrier diode, the device structure is featured by a highly doped drift region and embedded floating junction region, which can ensure high breakdown voltage while keeping lower specific on-state resistance, solved the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with opti- mized structure parameter, the breakdown voltage can reach 4 kV and the specific on-resistance is 8.3 mΩ·cm2.