Low forward drop JBS rectifiers fabricated using submicrontechnology

This paper demonstrates the impact of using submicron technology (0.5 μm design rules) on JBS Rectifiers to achieve very low forward voltage drops while maintaining good high temperature reverse blocking characteristics. Two dimensional numerical simulations show that decreasing P⁺-junction width and depth improves the on-state voltage drop by improved utilization of the active area for the Schottky region and improved spreading of majority carrier current from the Schottky contact. Experimental results that demonstrate the capability to reduce the forward drop from 0.5 V to 0.25 V, while operating at up to 125°C-175°C with good reverse blocking capability, are presented. The tradeoff curves between forward drop and reverse leakage current show 45× reduction in leakage current for the same forward drop as compared to previous reports on JBS rectifiers. Power dissipation analysis indicates higher operating temperatures, (100°C for Ti-JBS and 175°C for Cr-JBS rectifiers) with reduced heat sink sizes for the JBS Rectifiers when compared to the conventional Schottky Barrier Diode (SBD)     

The pinch rectifier: A low-forward-drop high-speed power diode

A new concept for reducing the forward voltage drop of Schottky rectifiers without incurring excessive reverse leakage currents is introduced. In this concept, a junction grid is incorporated beneath the Schottky barrier to pinch off current flow during reverse blocking. Experimental results that demonstrate the capability to reduce the forward drop from 0.6 to 0.4 V without incurring an increase in leakage current are presented.     

Design, fabrication, and characterization of low forward drop, low leakage, 1-kV 4H-SiC JBS rectifiers

The 1-kV 4H-SiC planar junction barrier Schottky (JBS) rectifiers were designed, fabricated, and characterized. Different p+ implantation dosages and activation anneal methods were used to determine an optimum baseline process. Using the optimized process, the forward drop of our JBS rectifiers is <1.5 V while the reverse leakage current density is <1/spl times/10/sup -5/ A/cm/sup -2/. Blocking voltage>1 kV was achieved using a single-zone junction termination extension termination. It was shown experimentally that 4-/spl mu/m p-type implantation window spacing gives an optimum tradeoff between forward drop voltage and leakage current density for these rectifiers, yielding a specific on-resistance of 3 m/spl Omega//spl middot/cm/sup 2/.     

Gallium arsenide Schottky power rectifiers

This paper discusses the development of high-performance gallium arsenide Schottky rectifiers for power switching applications. These diodes are shown to exhibit superior turn-on and turn-off dynamic switching characteristics when compared with silicon p-i-n rectifiers. The theoretical analysis presented in the paper indicates that the gallium arsenide Schottky power rectifier will be attractive for high-frequency power switching circuits operating at 1.00-300 V.     

Reverse recovery processes in silicon power rectifiers

The present review gives an account of a number of investigations that have been recently carried out in the Semiconductor Laboratory Pretzfeld, Siemens AG. The switching processes in power rectifiers from the forward into the reverse state differ greatly from the corresponding process predicted by low-level theory. This result is caused not only by the fact that the conditions are different for high injection, but in addition, the sweeping out of the charge carriers takes place from two sides, owing to the nearly uniform concentration distribution in the forward state. Because of the unequal electron and hole mobilities, the impurity distribution on the side of the p contact is of much greater importance than at the n contact; if there is no p-n junction on this more important side, then the stored change can be swept out without much voltage buildup (example: rectifiers from uniformly doped p material). If, on the other hand, a p-n junction lies before the p contact (example: rectifiers from uniformly doped n material) then tbe reverse recovery current decays soon but slowly, and the switching process takes a longer time. This fact also contributes to the relatively long turn-off time of the thyristors.     

Analytical solution for reverse recovery of power rectifiers

The reverse recovery of power rectifiers is analyzed solving the one-dimensional ambipolar diffusion equation for any given current waveform, with the aid of the Fourier cosine series in respect to space coordinate. Applications of the method to linear ramp and sine-wave recovery are given.     

Band-to-band auger recombination and carrier-carrier scattering in power rectifiers

It is shown that band-to-band Auger recombination has a profound influence on the carrier-concentration profile and on the forward characteristic of p-s-n rectifiers (and thyristors) at high current densities, particularly when the diffusivity is decreased at high carrier concentrations by carrier-carrier scattering.     

Dual metal SiC Schottky rectifiers with low power dissipation

Nickel and titanium are the most commonly used metals for Schottky barrier diodes on silicon carbide (SiC). Ti has a low Schottky barrier height (i.e. 0.8 eV on 6H-SiC), whilst Ni has a higher barrier (i.e. 1.25 eV). Therefore, the first metal allows to achieve a low forward voltage drop V_F but leads to a high leakage current. On the other hand, the second one presents the advantage of a lower reverse leakage current but has also a high value of V_F. In this work, dual-metal-planar (DMP) Schottky diodes on silicon carbide are reported. The rectifying barrier was formed by using an array of micrometric Ti and Ni₂Si (nickel silicide) stripes. This low/high Schottky barrier allowed to combine the advantages of the two metals, i.e. to fabricate diodes with a forward voltage drop close to that of a Ti diode and with a level of reverse current comparable to that of a Ni₂Si diode. Under the application point of view, using this kind of barrier can lead to a reduction of the device power dissipation and an increase of the maximum operating temperature.     

Comparison of gold, platinum, and electron irradiation for controlling lifetime in power rectifiers

Recombination statistics based upon a single dominant level have been used to predict the relative characteristics of gold-diffused, platinum-diffused, and electron-irradiated silicon power rectifiers and thyristors. These calculations indicate that gold-diffused devices will have the best trade-off curve between forward voltage drop and reverse recovery time, while exhibiting the highest leakage currents. Electron-irradiated devices are predicted to have the worst trade-off curve among the three cases and twice the leakage current of platinum-diffused devices. The leakage current of platinum-diffused devices is shown to be an order of magnitude lower than gold-diffused devices. The measured characteristics of gold-diffused, platinum-diffused, and electron-irradiated power rectifiers are shown to be in good agreement with these calculations. The results are also shown to be applicable to power thyristors.     

High power factor PWM rectifiers with an analog pulsewidthprediction controller

A single-phase PWM bridge rectifier controlled by a pulsewidth prediction (PWP) method to operate switching devices to realize a high power factor and to reduce the AC-side current harmonics is proposed. The PWP controller provides instantaneous current control with either a constant frequency carrier or a piecewisely fixed multiple-frequency carrier in one source-voltage cycle. The paper describes the control methods and implementation of analog PWP controllers, and performance characteristics of the rectifier. Unity displacement power factor was obtained and the AC-side current harmonics were reduced. Experimental results show the usefulness of the proposed method and applicability to rectifiers in UPS systems, etc     

State variable decoupling and power flow control in PWMcurrent-source rectifiers

Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line-commutated rectifiers as a source of variable DC power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2 kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations     

Notes on the theory of the forward characteristic of power rectifiers

The forward characteristic of power rectifiers has often been the subject of calculation and experimental studies^(1–10) and was so again only recently⁽¹¹⁾. A treatment of this problem without applying numerical methods is possible only by making strong and even precarious simplifications, and above all by neglecting the concentration dependences of the carrier mobilities and lifetimes in the middle region of these psn or pin† structures. But even with such simplifications the mathematical apparatus provides but little insight into the actual physical relationships, and it would therefore appear appropriate to consider, like Enrico Fermi, the ‘hydrogen case’ of this problem.

Section 1 of this didactic paper, which should be considered as a supplement to 's work,⁽¹¹⁾ deals with a completely symmetrical structure. In Section 2 it will be shown that the asymmetries encountered in practice lead to dependences which do not differ markedly from those obtained in Section 1. If one wishes to consider these differences one must be consistent and take into account also the concentration dependence of carrier mobilities and lifetimes already mentioned (see also the end of Section 3).     

Behaviour of 1.2 kV SiC JBS diodes under repetitive high power stress

A methodology and a dedicated test-bench to evaluate the behaviour of SiC JBS diodes under repetitive high power stresses and surge currents have been developed and illustrated with JBS and Schottky 1.2 kV SiC diodes. The concept of dissipated energy versus the number of cycles is introduced to characterize the degradation evolution of the tested device. The sweeping current pulse technique offers the possibility to evaluate the effect of the self-heating on the I (V). This is especially relevant for JBS SiC diodes whose series resistance highly depends on the junction temperature. JBS diodes show a ×2.66 (×4.16) higher surge current capability at 25 °C (225 °C) than the pure Schottky diodes. The fabricated SiC JBS and Schottky diodes have been submitted to more than 300,000 power cycles at a dissipated energy of 0.7 J, showing no relevant degradation.     

A hybrid structure using phase-controlled rectifiers andhigh-frequency converters for magnet-load power supplies

Thyristor rectifiers are still the preferred choice for large magnet power supplies. However, large harmonic voltages, resulting in large current ripple, and slow dynamic response are major drawbacks of these converters. This paper presents a topology and a control technique for hybrid large-power high-precision magnet power supplies. The system consists of a phase controlled rectifier connected in series with a high-frequency PWM converter. The rectifier is designed to handle the main output power and the PWM converter is used only for harmonics cancellation and error compensation. A feedforward control scheme is proposed to ensure that the desired power sharing is maintained during both the steady state and transient operations. The operating principles of the proposed structure are discussed in the paper, and the results from a 1 kVA experimental setup are provided to validate the proposed topology     

2700V4H-SiC结势垒肖特基二极管

在76.2 mm 4H-SiC晶圆上采用厚外延技术和器件制作工艺研制的结势垒肖特基二极管(JBS).在室温下,器件反向耐压达到2700 V.正向开启电压为0.8V,在VF=2V时正向电流密度122 A/cm2,比导通电阻Ron=8.8 mΩ·cm2.得到肖特基接触势垒qφв=1.24 eV,理想因子n=1.     

High-current snapback characteristics of MOSFETs

The high-current snapback characteristics of MOSFETs with different channel lengths and widths, gate oxide thicknesses, and substrate dopings were studied to determine their effectiveness in electrostatic discharge stress protection. Filamentary conduction was not observed for currents up to 7 mA/μm of channel width for a pulsewidth of 500 ns. MOSFETs with shorter channel lengths require lower voltages to sustain the same current, independent of gate oxide thickness. Increasing the substrate doping does not necessarily reduce the high current voltage. These trends can be explained using a simple lateral n-p-n bipolar transistor snapback model     

Measurement and analysis of carrier distribution and lifetime in fast switching power rectifiers

Charge distributions in fast switching rectifiers are measured by free-carrier infrared absorption in both steady state and during transient operation. The results are compared to curves generated by an exact simulation of the carrier-flow equations and it is determined that the carrier lifetime varies inversely as the 0.3 power of the doping. A study is also made on the effect that gold doping, platinum doping, and electron irradiation have on the carrier distributions under both steady-state and open-circuit decay conditions. These results are analyzed in view of measurements of the switching behavior in these devices made at the device terminals.     

Reduced-parts-count multilevel rectifiers

Multilevel power converters have gained much attention in recent years due to their high power quality, low switching losses, and high-voltage capability. These advantages make the multilevel converter a candidate topology for the next generation of naval ship prolusion systems. The primary disadvantage of these systems is the large number of semiconductors involved. This paper presents a reduced-parts-count rectifier which is well suited for naval rectifier applications where bidirectional power flow is not required. The proposed converter is analyzed and experimentally verified on an 18-kW four-level rectifier/inverter system.     

Organic molecular rectifiers

In the field of molecular scale electronics the drive is towards the fabrication of self-assembled, organic, nanoscale architectures which will have an active role to play in novel electronic devices. As a formative step towards this goal the creation of an organic analogue to the p–n junction was proposed by Aviram and Ratner in the 1970s. In their proposal a monomolecular layer of a charge transfer species controls current flow between a pair of metal electrodes, allowing easy flow for only one polarity of the applied voltage. Such metal/molecular layer/metal structures have now been fabricated, utilising the self-ordering properties of Langmuir–Blodgett films to form the organic layer, with one dimension of the device being reduced to the molecular scale. The fabrication techniques involved in the generation of these M/LB/M junctions are now described along with the present understanding of conduction mechanisms through such nanoscale thickness junctions. These structures clearly show that the organic molecular layers can control current passage in electronic devices emulating some of the characteristics of an inorganic semiconducting p–n junction.