SOS Diodes Research Articles

New SOS Diode Pumping Circuit Based on an All-Solid-State Spiral Generator for High-Voltage Nanosecond Applications

New SOS Diode Pumping Circuit Based on an All-Solid-State Spiral Generator for High-Voltage Nanosecond Applications

Stacked Diodes for Pulsed Power Applications: New Process Integration Scheme

Since Boff, Moll, and Shen’s discovery of the high-speed switching effect inherent in initially forward-biased silicon diodes that are suddenly reverse-biased in 1960 [1]; DSRD’s (as termed by Grekhov and Kardo-Sysoev in 1985 [2]) performance has not increased as their deep-diffusion manufacturing process remains the same as it was over 60 years ago. Albeit new pulse generator topologies which utilize diodes like DSRDs, i.e., SOS diodes (termed by Rukin in 1992 [3]) have shown improvement at circuit level given they operate under a higher direct-current density compared to that of DSRD-based pulsers – the voltage-to-risetime, dV/dt, of these silicon-based solid-state diodes remain on the order of 1012 V/s. Furthermore, all possible ways to improve pulse performance of DSRD made by deep diffusion have been extensively investigated and exhausted. To achieve the 1013 V/s (10 kV/ns) voltage-to-risetime required by an all-solid-state pulse generation utilized to support of the missions, improving DSRD manufacturing techniques must ensue.The process flow is schematically illustrated by Fig. 1. On starting degenerate doped wafer, two epitaxial layers are grown, first n- then p-type doped thus forming p-n junction of the diode.The doping profile is controlled by changing dopant flow into epi chamber. It allows getting an optimal diode doping profile predicted by simulation. Notice, the old diffusion process allows only predetermined doping profile (complementary error function) which is not optimal.After forming the blanket p-n junction structure on entire wafers, individual diode dies are separated by wafer patterning. Though the wafers remain intact. This is opposite to the old process where the wafers were cut into individual diode dies. In our technology, V-grooves are formed by anisotropic etching process resulting in structure shown on Fig. 2. Squares surrounded by the v-grooves will become diodes, Inner slopes of v-grooves become side walls of the diodes. Notice, in old technology side walls were usually vertical, which creates a weak point for electrical breakdown: it is limited by surfacee breakdown properties, not bulk silicon properties.Next is diode side surface insulation. It is achieved by thermal oxidation. Thus, the diodes get the best surface passivation (i.e., thermal SiO2). The p-n junction is located near middle of the V-groove slope. Thus, there is no local spike of electric field where avalanche breakdown starts. Eventually, the breakdown properties of this diode are much closer to bulk silicon limit – as compared to old technology where the breakdown was surface limited.At next stage the silicon dioxide layer is removed on top surface but remains on v-groove slopes. Now we have wafers with diode arrays, terminated and passivated by side surfaces.Further, selective electroplating of copper is performed to form electrical contacts. Also, it is a step in preparation to wafer stacking. In old technology, metallization was at much earlier stage of flow and thus it interfered with side insulation. In selective electroplating, copper is deposited only on silicon surfaces, and does not deposit on SiO2 surfaces of v-groove insulation.To finish preparation for wafer bonding, tin is selectively deposited over copper. Then, wafers are aligned and stacked. The wafer stack is heated above tin melting temperature. By solid-liquid interdiffusion, Cu/Sn intermetallic compound is formed. It has much higher melting point compared to tin. Bonding process continues until entire tin layer is consumed.Now the bonded wafer stack is ready for last step in the processing – cutting into stacked DSRDs. The cutting is regular mechanical sawing. The saw lines are along the lines of v-grove bottoms.The process and resulting device design are patented [4].On next step of this project, electrical performance of final stacked DSRDs will be compared to performance of stacked DSRDs manufactured by traditional deep diffusion-based technology. Boff, A., J. Moll, and R. Shen. "A new high-speed effect in solid-state diodes." in 1960 IEEE International Solid-State Circuits Conference. Digest of Technical Papers, vol. 3, pp. 50-51. IEEE, 1960. Grekhov, I. V., V. M. Efanov, A. F. Kardo-Sysoev, and S. V. Shenderey. "Power drift step recovery diodes (DSRD)." Solid-State Electronics 28, no. 6 (1985): 597-599..Rukin, S. N. "Pulsed power technology based on semiconductor opening switches: A review." Review of Scientific Instruments 91, no. 1 (2020): 011501.Bellinger, A.Caruso, A.Usenko, US Patent Application “Stacked Diode with Side Passivation and Method of Making the Same” filed 09/10/2021. Figure 1

Numerical and Experimental Study of an Optimized p-SOS Diode

We report on the results of experimental investigation and numerical simulation of switching of SOS diode with p+P0n+ structure and with reduced thickness of P0-base. The proposed 1D diffusion-drift model of electron–hole plasma dynamics is found to be in good agreement with the experiment. The reduction of the P0-base thickness has allowed us to double the output pulse voltage with the same switching current density. This has been reached by a considerable reduction of switching losses as well as due to the formation of the domain of a strong quasi-rectangular electric field at the P0n+ junction during the current interruption. As a result, output pulse amplitude considerably exceeds the static breakdown voltage of P0n+ junction. This effect has been observed for the first time for high-voltage semiconductor opening switches.

Численное и экспериментальное исследования оптимизированного p-SOS-диода

AbstractWe report on the results of experimental investigation and numerical simulation of switching of SOS diode with p ^+ P _0 n ^+ structure and with reduced thickness of P _0-base. The proposed 1D diffusion-drift model of electron–hole plasma dynamics is found to be in good agreement with the experiment. The reduction of the P _0-base thickness has allowed us to double the output pulse voltage with the same switching current density. This has been reached by a considerable reduction of switching losses as well as due to the formation of the domain of a strong quasi-rectangular electric field at the P _0 n ^+ junction during the current interruption. As a result, output pulse amplitude considerably exceeds the static breakdown voltage of P _0 n ^+ junction. This effect has been observed for the first time for high-voltage semiconductor opening switches.

POWERFUL GENERATORS OF HIGH-VOLTAGE PULSES WITH NANOSECOND FRONTS

Purpose. Purpose of the article is to show the possibility of joint efficient operation of semiconductor switches and spark arresters in high-powerful high-voltage generators for obtaining nanosecond and shorter pulse fronts on a high-voltage load. Methodology. The variants of generators of power high-voltage pulses with semiconductor switches in the form of IGBT-transistors, SOS-diodes and spark dischargers as pulse front peaking spark gaps are considered. A scheme is proposed for such a generator of high-voltage pulses with nanosecond front on the basis of a linear pulsed transformer in the Tesla scheme. Results. On the complex load of the generator in the form of a serial connection of a gas bubble in water with a discharge in it and a layer of water under the bubble, voltage pulses with an amplitude of 23 kV and current pulses with an amplitude of 15 A were obtained. In this case, the pulse front, both voltage and current, on the levels 0.1-0.9, was approximately 10 ns, and the repetition rate of pulses in the load ranged from 1200 to 5000 pulses per second. Originality. A scheme is proposed for a generator of high-voltage pulses with a nanosecond front. The difference of the proposed generator with a nanosecond front, high pulse repetition rate, using its high-voltage and low-voltage circuits in the discharge circuit, is the presence in its composition of a linear pulse transformer and a system of peaking of pulse front using SOS diodes and spark gaps. Practical value. These generators considered in this work can find wide application in high-voltage technologies, including decontaminating water treatment, water purification by electric discharges.

Development of a Cluster Burst Pulse Generator Based on a SOS Diode for Medical Applications

SUMMARYThis work focuses on the design of a compact high‐power pulsed electromagnetic wave generator using a nanosecond pulsed power generator for the cancer treatment. In the previous study, since the output voltage waveform of the pulsed power generator was damping oscillation, the duration of the burst pulse was under 100 ns. So the generator uses a magnetic switch instead of the gap switch and uses a SOS diode with current cutoff time of nanoseconds. The cluster pulse has six burst pulses that are repeated at 2 Mpps. The frequency of the burst pulse is 50 MHz. The peak output voltage is 7.5 kV.

Powerful diode nanosecond current opening switch made of p-silicon (p-SOS)

The nanosecond semiconductor diode-based opening switch (SOS-diode) capable of switching currents with densities up to several tens of kiloamperes per cubic centimeter represents a p+p’Nn+ silicon structure fabricated by the deep simultaneous diffusion doping (to about 200 μm) of n-Si by Al and B from one side and P from the other. In the SOS mode, first a short pulse of forward current passes through the diode and then a fast-growing pulse of reverse voltage is applied. A resulting pulse of reverse current carries away injected holes and thereby forms a plasma front in the p’ layer, which moves toward the p’N junction. When the hole concentration in the flow exceeds the dopant concentration in the p’ layer, a space charge region arises in this layer, the resistivity of the diode increases sharply, and the current switches to a load connected parallel to the diode. Early results concerning an alternative configuration of the SOS diode are presented. Here, the diode was made by the rapid simultaneous diffusion of B and P from the opposite sides of a p-Si wafer to a depth of 60-80 μm. If a short pulse of forward current is passed through such a p+pn+ structure and a pulse of reverse voltage is then applied, a plasma front arising in the p+ region moves toward the p+p interface through the heavily doped (i.e., low-resistivity) p+ region. Having crossed this interface, the front passes into a low-doped region, where the hole concentration in the flow becomes much higher than the dopant concentration and a space charge region causing the current to pass to the load forms at once. It is shown experimentally that, all other things being the same, the time of current breaking in the p-SOS-diode is roughly twice as short as in the conventional n-SOS-diode, switched currents are considerably lower, and the fabrication technique of p-SOS-diodes is much simpler. Ways of optimizing the design of the semiconductor structure of the p-SOS-diode to further raise the speed are outlined.

Analysis of nanosecond breaking of a high-density current in SOS diodes

Effect of a sharp (nanosecond) breaking of the reverse current with a density on the order of 103–104 A/cm2 in a silicon diode upon switching from direct to reverse bias voltage (so-called silicon opening switch, or SOS effect) is widely used in nanosecond technologies of gigawatt powers. For detailed analysis of the SOS effect, we constructed a special setup with small stray inductance, which makes it possible to test single SOS diodes with a working area of 1–2 mm2 in a wide range of current densities. Our experiments show, in particular, that the numerical model of the SOS effect developed at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences successfully described the experimental results. It is also shown that the charge extracted from the diode structure by the reverse current exceeds the charge introduced by a direct current pulse by not more than 10%, indicating a relatively small role of ionization processes. The possibility to carry out experiments on single samples with a small surface area allows us to study the SOS effect and considerably facilitates investigations aimed at the perfection of the design of SOS diodes.

SOSダイオードを用いた医療用クラスタバーストパルス発生装置の開発

This work focuses on the design of a compact high power pulsed electromagnetic wave generator using a nanosecond pulsed power generator for the cancer treatment. In previous study, since the output voltage waveform of the pulsed power generator was damping oscillation, the duration of the burst pulse was under 100 ns. So the generator uses a magnetic switch instead of the gap switch and uses a SOS diode with current cutoff time of nanoseconds. The cluster pulse has 6 burst pulses that are repeated at 2 Mpps. The frequency of the burst pulse is 50 MHz. The peak output voltage is 7.5 kV.

Operation of a semiconductor opening switch at ultrahigh current densities

The operation of a semiconductor opening switch (SOS diode) at cutoff current densities of tens of kA/cm2 is studied. In experiments, the maximum reverse current density reached 43 kA/cm2 for ∼40 ns. Experimental data on SOS diodes with a p +-p-n-n + structure and a p-n junction depth from 145 to 180 μm are presented. The dynamics of electron-hole plasma in the diode at pumping and current cutoff stages is studied by numerical simulation methods. It is shown that current cutoff is associated with the formation of an electric field region in a thin (∼45 μm) layer of the structure’s heavily doped p-region, in which the acceptor concentration exceeds 1016 cm−3, and the current cutoff process depends weakly on the p-n junction depth.

Subnanosecond 4H-SiC diode current breakers

Mesa epitaxial 4H-SiC-based p +-p-n 0-n + diodes have been fabricated and their reverse recovery characteristics have been measured in modes typical of fast semiconductor current breakers, drift step recovery diodes, and SOS diodes. It has been found that, after the short (∼10 ns) pulsed injection of nonequilibrium carriers by a forward current with a density of 200–400 A cm−2 and the subsequent application of a reverse voltage pulse (with a rise time of 2 ns), diodes can break a reverse current with a density of 5–40 kA cm−2 in a time of about (or less than) 0.3 ns. A possible mechanism for ultrafast current breaking is discussed.

High efficiency nanosecond generator based on semiconductor opening switch

On the base of novel circuitry approach a SOS-based (Semiconductor Opening Switch) all-solid-state repetitive generator has been developed for various technological and industrial applications. The generator is equipped with a circuit for recuperation of unused energy reflected back from the magnetic compressor. The SOS is pumped in a novel pumping regime that includes microsecond forward pumping and current pause before fast reverse pumping process. As a result, the total efficiency of the generator has been increased from usual value of around 40% up to 60-62%. The generator has the following output specifications: peak voltage is up to 60 kV; peak current is up to 6 kA; FWHM is around 40 to 50 ns; pulse repetition frequency in continuous mode is up to 1 kHz; output average power in matched load is up to 9 kW. Electrical circuit diagrams and principle of the generator operation as well as experimental and testing results obtained are described. The results of numerical simulation of the SOS diode operation are presented also.

A nanosecond SOS-generator with a 20-kHz pulse repetition rate

A nanosecond SOS-generator with a 20-kHz pulse repetition rate in the continuous operating mode and with a 100-kHz pulse repetition rate in the pulse burst mode is described. The generator contains a low-voltage module with a primary capacitive storage and a transistor switch, and a high-voltage module with a magnetic compressor and a semiconductor opening switch (SOS diode). The generator forms pulses with amplitudes of 40–100 kV with a 20- to 30-MW peak power and a 10- to 14-ns duration across a 50- to 500-Ω external load. The output average power in the continuous operating mode is 5 kW. The electric circuit, principle of operation, and design of the generator’s elements are described. The test results are given.

Effect of space charge on subnanosecond current cutoff in powerful semiconductor diodes

High-density current cutoff in an SOS diode is studied with a physicomathematical model including the space-charge effect. If the depth of the p-n junction exceeds 180 µm, the forward pumping time is less than 60 ns, and the backward pumping time is shorter than 20 ns, the subnanosecond cutoff of current with a density of several kiloamperes per square centimeter takes place. The cutoff mechanism is associated with the origination of three high-field zones at the stage of current cutoff: two zones on the p-side, which expand with a velocity close to the saturation value, and one on the n-side, which expands slowly. Taking the space charge into account reduces the role of avalanche multiplication and, as a consequence, improves the switching properties of the diode. It is found that a set of conditions for the electric circuit parameters that specify the pumping current duration and density and for the dopant profile in the semiconductor must be met for subnanosecond current cutoff to occur. The results are compared with experimental data and a model using a quasi-neutral approximation.

Operation of a semiconductor opening switch at the pumping time of a microsecond and low current density

The mechanism of operation of a semiconductor opening switch (a SOS diode) at the forward-pumping time of a microsecond and low current density was studied. The current’s cutoff time shorter than 10 ns at the voltage across the SOS diode as high as 80 kV was obtained experimentally at the reverse-pumping time ∼200 ns and the cutoff-current density of about 120 A/cm2. These are the results of numerical simulation of processes in the dynamics of the electron-hole plasma in the diode at the stages of pumping and current cutoff. It is shown that the stage of the current cutoff is similar to the conditions of the SOS effect observed at a high current density and is also related to motion of the concentration front of excess plasma along the heavily doped p-type region of the structure. In spite of the low density of current in the course of its cutoff, the switching process takes several nanoseconds. The reason is that the low current density is compensated by a low concentration of the excess plasma at the front, which retains the high velocity of motion of this front at the stage of the current cutoff.

Wide-aperture electric-discharge nitrogen laser

The parameters of a wide-aperture nitrogen laser pumped by a generator with the inductive energy storage and a SOS diode opening switch or a generator with the capacitive energy storage are studied. The gas preionisation was performed by soft X-rays. The size of the active volume of the laser was 10×6×100 cm. The output energy and power obtained at the 337.1-nm C 3Πu — B 3Πg transition are maximal for electric-discharge nitrogen lasers. The output energy in the second positive system of nitrogen in the N2—SF6 mixture achieved 110 mJ for a peak power of 6 MW. Due to an increase in voltage across the laser gap in nitrogen mixtures with NF3, the generation of ∼35-mJ, 100-ns pulses was obtained in the quasi-stationary stage of the discharge.

Production of an Atmospheric‐Pressure Glow Discharge Using an Inductive Energy Storage Pulsed Power Generator

AbstractSummary: An atmospheric‐pressure glow discharge has been generated using an inductive energy storage pulsed power generator. A pulsed high voltage with a short rise time of under 30 ns is employed to generate streamer discharges simultaneously at all tips of a needle‐array electrode in nitrogen. The large number of streamer discharges prevent glow‐to‐arc transitions caused by inhomogeneous thermalization. SOS diodes are used as an opening switch to shorten the rise time. Circuit parameters such as the capacitance of a primary energy storage capacitor and/or the inductance of a secondary energy storage inductor are determined by experimental results using dummy resistive loads. The results show that circuit parameters adequate for producing atmospheric glow discharges are different from those for producing corona discharges. The energy transfer efficiency of the pulsed power generator has a maximum value of 75% at 193 Ω dummy load resistance. Voltage‐current characteristics of the glow discharge show two regions: constant voltage (normal glow) and an increasing voltage with discharge current (abnormal glow). The glow current is drastically decreased by eliminating the SOS diodes, in which case the charging voltage is directly applied to the electrode. Spatial‐ and time‐averaged electron densities in a positive column are estimated from calculations based on nitrogen swarm data. The electron density is estimated to be 1.8 × 1011 cm−3, which is much larger than 9.7 × 109 cm−3 in the case without the SOS diodes.Photographs of atmospheric pressure nitrogen glow discharge generated using a needle‐array electrode at a 1.0 cm gap length.imagePhotographs of atmospheric pressure nitrogen glow discharge generated using a needle‐array electrode at a 1.0 cm gap length.

A nanosecond SOS generator with a peak power of 4 GW

A high-current nanosecond generator with a peak power of up to 4 GW, an output voltage of 0.4–1 MV, a pulse duration of 8–10 ns, and pulse repetition rates of 300 Hz in a continuous mode and up to 1 kHz in the burst mode is described. The average output power at a pulse repetition rate of 1 kHz reaches 30 kW. The generator has an all-solid-state energy-switching system. A semiconductor opening switch on SOS diodes forms output pulses. The electric circuit and design of the generator are described, and the experimental results are presented. A device for eliminating prepulses across the load is proposed. The results of its testing and numerical simulation are presented.

Efficient electric-discharge XeF laser pumped by a generator with an inductive energy storage

The parameters of discharge and laser radiation in an Ne—Xe—NF3 mixture excited by a double discharge from a generator with an inductive energy storage and a current interrupter based on semiconductor SOS diodes are studied. It is shown that a high-voltage prepulse formed by a generator with inductive energy storage increases considerably the stability and duration of volume discharge in mixtures with NF3, and also increases the emission energy and pulse duration of laser radiation at the B—X transition of XeF* molecules. In the case of spark preionisation, radiation pulses with a total duration of up to 200 ns and the full width at half-maximum up to 100 ns are obtained. The maximum output energy of an XeF laser (λ = 348, 351 and 353 nm) was 0.5 J for the electric efficiency up to 1.6%.

Pulsed gas lasers pumped by generators with inductive energy storage

A new method of pumping electric-discharge gas lasers and excimer lamps is proposed on the basis of generators with inductive energy storage and opening switches of various types (exploding wires, gas-discharge low-pressure devices, plasma erosion opening switches, and semiconductor SOS diodes). It is shown that the inductive energy storage provides a convenient way of varying the pump pulse parameters (primarily, the pulse duration and the input power) and obtaining optimal excitation pulses for various types of lasers. The potential of using generators with inductive energy storage for pumping gas lasers is demonstrated.