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.     

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 C.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.     

Temperature-dependent characteristics of 4Hben 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.     

A1/Ti/4H-SiC Schottky barrier diodes with inhomogeneous barrier heights

This paper investigates the current-voltage （I-V） characteristics of Al/Ti/4H-SiC Schottky barrier diodes （SBDs） in the temperature range of 77 K-500 K, which shows that Al/Ti/4H SiC SBDs have good rectifying behaviour. An abnormal behaviour, in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature （T）, has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the A1/Ti/4H-SiC interface. The effective Richardson constant A＊ = 154 A/cm2 . K2 is determined by means of a modified Richardson plot In（I0/T2） - （qσ）2/2（κT）2 versus q/kT, which is very close to the theoretical value 146 A/cm2 · K2.     

Edge termination study and fabrication of a 4Hben SiC junction barrier Schottky diode

The 4H-SiC junction barrier Schottky (JBS) diodes terminated by field guard rings and offset field plate are designed, fabricated and characterized. It is shown experimentally that a 3-μm P-type implantation window spacing gives an optimum trade-off between forward drop voltage and leakage current density for these diodes, yielding a specific on-resistance of 8.3 mΩ·cm². A JBS diode with a turn-on voltage of 0.65 V and a reverse current density less than 1 A/cm² under 500 V is fabricated, and the reverse recovery time is tested to be 80 ns, and the peak reverse current is 28.1 mA. Temperature-dependent characteristics are also studied in a temperature range of 75 ℃-200 ℃. The diode shows a stable Schottky barrier height of up to 200 ℃ and a stable operation under a continuous forward current of 100 A/cm².     

套刻偏差对4H-SiC 浮动结结势垒肖特基二极管的影响研究

4H-SiC浮动结结势垒肖特基二极管与常规结势垒肖特基二极管相比在 相同的导通电阻条件下具有更高的击穿电压. 由p⁺埋层形成的浮动结与主结p⁺区 之间的套刻对准是实现该结构的一项关键技术. 二维模拟软件ISE的模拟结果表明, 套刻偏差的存在会明显影响器件的击穿特性, 随着偏差的增大击穿电压减小. 尽管主结和埋层的交错结构与对准结构具有相似的击穿特性, 但是当正向电压大于2 V后, 交错结构的串联电阻更大.     

Analysis and simulation of a 4H-SiC semi-superjunction Schottky barrier diode for softer reverse-recovery

In this paper,a 4H-SiC semi-superjunction (SJ) Schottky barrier diode is analysed and simulated.The semi-SJ structure has an optimized design and a specific on-resistance lower than that of conventional SJ structures,which can be achieved without increasing the process difficulty.The simulation results show that the specific on-resistance and the softness factor depend on the aspect and thickness ratios,and that by using the semi-SJ structure,specific on-resistance can be reduced without decreasing the softness factor.It is observed that a trade-off exists between the specific on-resistance and the softness of the diode.     

Analysis and simulation of a 4H-SiC semi-superjunction Schottky barrier diode for softer reverse-recovery

In this paper, a 4H-SiC semi-superjunction (SJ) Schottky barrier diode is analysed and simulated. The semi-SJ structure has an optimized design and a specific on-resistance lower than that of conventional SJ structures, which can be achieved without increasing the process difficulty. The simulation results show that the specific on-resistance and the softness factor depend on the aspect and thickness ratios, and that by using the semi-SJ structure, specific on-resistance can be reduced without decreasing the softness factor. It is observed that a trade-off exists between the specific on-resistance and the softness of the diode.     

Experimental and numerical analyses of high voltage 4H-SiC junction barrier Schottky rectifiers with linearly graded field limiting ring

This paper describes the successful fabrication of 4H-SiC junction barrier Schottky(JBS) rectifiers with a linearly graded field limiting ring(LG-FLR). Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2(about 80% of the theoretical value). Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termination, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.     

Characterization of ion-implanted 4H-SiC Schottky barrier diodes

Ion-implantation layers are fabricated by multiple nitrogen ion-implantations (3 times for sample A and 4 times for sample B) into a p-type 4H-SiC epitaxial layer. The implantation depth profiles are calculated by using the Monte Carlo simulator TRIM. The fabrication process and the I--V and C--V characteristics of the lateral Ti/4H-SiC Schottky barrier diodes (SBDs) fabricated on these multiple box-like ion-implantation layers are presented in detail. Measurements of the reverse I--V characteristics demonstrate a low reverse current, which is good enough for many SiC-based devices such as SiC metal--semiconductor field-effect transistors (MESFETs), and SiC static induction transistors (SITs). The parameters of the diodes are extracted from the forward I--V and C--V characteristics. The values of ideality factor n of SBDs for samples A and B are 3.0 and 3.5 respectively, and the values of series resistance R_\rm s are 11.9 and 1.0~kΩ respectively. The values of barrier height φ _\rm B of Ti/4H-SiC are 0.95 and 0.72 eV obtained by the I--V method and 1.14 and 0.93 eV obtained by the C--V method for samples A and B respectively. The activation rates for the implanted nitrogen ions of samples A and B are 2\% and 4\% respectively extracted from C--V testing results.     

Al/Ti/4H-SiC Schottky barrier diodes with inhomogeneous barrier heights

This paper investigates the current-voltage (I-V) characteristics of Al/Ti/4H-SiC Schottky barrier diodes (SBDs) in the temperature range of 77 K-500 K,which shows that Al/Ti/4H-SiC SBDs have good rectifying behaviour.An abnormal behaviour,in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature (T),has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the Al/Ti/4H-SiC interface.The effective Richardson constant A =154 A/cm 2 · K 2 is determined by means of a modified Richardson plot ln(I 0 /T 2)-(qσ) 2 /2(kT) 2 versus q/kT,which is very close to the theoretical value 146 A/cm 2 · K 2.     

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.     

4H-SiC Schottky barrier diodes with semi-insulating polycrystalline silicon field plate termination

Based on the theoretical analysis of the 4H-SiC Schottky-barrier diodes(SBDs) with field plate termination, 4H-SiC SBD with semi-insulating polycrystalline silicon(SIPOS) FP termination has been fabricated. The relative dielectric constant of the SIPOS dielectric first used in 4H-SiC devices is 10.4, which is much higher than that of the SiO2dielectric,leading to benefitting the performance of devices. The breakdown voltage of the fabricated SBD could reach 1200 V at leakage current 20 μA, about 70% of the theoretical breakdown voltage. Meanwhile, both of the simulation and experimental results show that the length of the SIPOS FP termination is an important factor for structure design.     

Simulation study of a mixed terminal structure for 4H-SiC merged PiN/Schottky diode

In this paper, a mixed terminal structure for the 4H-SiC merged PiN/Schottky diode (MPS) is investigated, which is a combination of a field plate, a junction termination extension and floating limiting rings. Optimization is performed on the terminal structure by using the ISE-TCAD. Further analysis shows that this structure can greatly reduce the sensitivity of the breakdown voltage to the doping concentration and can effectively suppress the effect of the interface charge compared with the structure of the junction termination extension. At the same time, the 4H-SiC MPS with this termination structure can reach a high and stable breakdown voltage.     

Fabrication and characteristics of lateral Ti/4H-SiC Schottky barrier diodes

This paper describes the fabrication and characteristics of the lateral Ti/4H-SiC Schottky barrier diodes (SBDs). SBDs are fabricated by nitrogen ion implantation into p-type 4H-SiC epitaxial layer. The implant depth profile is simulated using the Monte Carlo simulator TRIM. Measurements of the reverse I－V characteristics demonstrate a low reverse current, that is good enough for many SiC-based devices such as SiC metal-semiconductor field-effect transistors, and SiC static induction transistors. The parameters of the diodes are extracted from the forward I－V characteristics. The barrier height φ_b of Ti/4H-SiC is 0.95 eV.     

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·cm 2 and breakdown voltage increases 422 V with an additional floating junction for the given structure.     

Barrier height homogeneity for 4.5 kV 4H-SiC Schottky diodes

4.5 kV SiC Schottky diodes have been fabricated using Ni as the Schottky contact. A manufacturing yield of 40% is reached for the bigger area diodes (1.6×1.6 mm²) and of 70% for the smaller ones (0.4×0.4 mm²). The measured variations of barrier height and ideality factor with temperature do not agree with the thermionic model. This has been interpreted in terms of barrier height inhomogeneities using the Werner model. We extracted an average barrier height and its standard deviation . These two parameters are almost independent of the diode size. The variation of the barrier height distribution with field has also been investigated and shows a dependence similar to that of Schottky diodes realized from other semiconductor materials.     

A 4H-SiC merged P-I-N Schottky with floating back-to-back diode

A novel 4H-SiC merged P-I-N Schottky (MPS) with floating back-to-back diode (FBD), named FBD-MPS, is proposed and investigated by the Sentaurus technology computer-aided design (TCAD) and analytical model. The FBD features a trench oxide and floating P-shield, which is inserted between the P+/N-(PN) junction and Schottky junction to eliminate the shorted anode effect. The FBD is formed by the N-drift/P-shield/N-drift and it separates the PN and Schottky active region independently. The FBD reduces not only the V_turn to suppress the snapback effect but also the V_on at bipolar operation. The results show that the snapback can be completely eliminated, and the maximum electric field (E_max) is shifted from the Schottky junction to the FBD in the breakdown state.     

Study of a double epi-layers SiC junction barrier Schottky rectifiers embedded P layer in the drift region

<正>This paper proposes a double epi-layers 4H—SiC junction barrier Schottky rectifier(JBSR) with embedded P layer (EPL) in the drift region.The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process.The electric field and potential distribution are changed due to the buried P-layer,resulting in a high breakdown voltage(BV) and low specific on-resistance(R_(on,sp)).The influences of device parameters,such as the depth of the embedded P+ regions,the space between them and the doping concentration of the drift region,etc.,on BV and R_(on,sp) are investigated by simulations,which provides a particularly useful guideline for the optimal design of the device.The results indicate that BV is increased by 48.5%and Baliga's figure of merit(BFOM) is increased by 67.9%compared to a conventional 4H-SiC JBSR.