Dynamic moderation of an electric field using a SiO2 switching layer in TaOx ‐based ReRAM

ReRAMs using oxygen vacancy drift in their resistive switching are promising candidates as next generation memory devices. One remaining issue is degradation of the on/off ratio down to 10² or less with an increased number of switching cycles. Such degradation is caused by a local hard breakdown in a set process due to a very high electric field formed just before the completion of a conductive filament formation. We found that introducing an ultra‐thin SiO₂ layer prevents the hard breakdown by dynamical moderation of the electric field formed in the TaO_x matrix, resulting in repeated switching while retaining a higher on/off ratio of about 10⁵. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A novel partial silicon on insulator high voltage LDMOS with low-k dielectric buried layer

A novel partial silicon-on-insulator (PSOI) high voltage device with a low-k (relative permittivity) dielectric buried layer (LK PSOI) and its breakdown mechanism are presented and investigated by MEDICI.At a low k value the electric field strength in the dielectric buried layer (E I) is enhanced and a Si window makes the substrate share the vertical drop,resulting in a high vertical breakdown voltage;in the lateral direction,a high electric field peak is introduced at the Si window,which modulates the electric field distribution in the SOI layer;consequently,a high breakdown voltage (BV) is obtained.The values of EI and BV of LK PSOI with kI=2 on a 2 μm thick SOI layer over 1 μm thick buried layer are enhanced by 74% and 19%,respectively,compared with those of the conventional PSOI.Furthermore,the Si window also alleviates the self-heating effect.     

Pre-stressing effect on DC breakdown in low-density polyethylene

Polyethylene is widely used in electrical wires and power cables. The pre-stressing effect, which restricts the applications of polyethylene, has not yet been investigated in depth. We studied the breakdown of low-density polyethylene (LDPE) films pre-stressed by direct current (DC) electric field. The results showed some conformity, as reported in many other papers, that the DC breakdown strength E_B+ with the same polarity to that of the pre-stressing field was higher than the DC breakdown strength E_B of thin LDPE films without pre-stressing, while the DC breakdown strength E_B? with the opposite polarity was lower than E_B. Such phenomena could be explained by the hetero effects of accumulating space charges, which enhanced the electrical field when the polarity was reversed. However, as a further increase in pre-stressing electrical field, both E_B+ and E_B? were found higher than E_B. We investigated the space charge behavior in LDPE films and found that when applied with a higher electrical field, space charge packet initialized and traveled through the specimen. The results suggest that the space charge packet behavior may contribute to the pre-stressing effects on electrical breakdown in LDPE films.     

De Haas-van Alphen effect in rare-earth hexaborides (RE=Pr,Nd, Gd)

The de Haas-van Alphen (dHvA) effect has been measured for antiferromagnetic PrB₆, NdB₆, and GdB₆. The dHvA data of PrB₆ and NdB₆ show paramagnetic Fermi surfaces which arise from magnetic breakdown through the small antiferromagnetic gaps in high fields very similar to those of LaB₆. In contrast, the antiferromagnetic Fermi surfaces which arise from new magnetic Brillouin zone boundaries introduced by the magnetic order seem to be very different in PrB₆ and NdB₆, respectively. In GdB₆ dHvA oscillations could be observed for the first time. In all three compounds magnetic phase transitions have been observed in the dHvA measurements in the field range of 10–12 T.Dedicated to Professor Hund on the occasion of his 95th birthday     

Avalanche breakdown in narrow gap semiconductors in crossed fields

The paper presents the results of experimental and theoretical investigations of interband breakdown in narrow gap Bi_1?xSb_x and Hg_1?xCd_xTe semiconductors in crossed electric and magnetic fields. Both these alloys show an increase of breakdown electric field in sufficiently strong magnetic field. In the case of Hg_1?xCd_xTe the breakdown field changes nonmonotonically with H. This is interpreted as being due to the transverse breakdown.     

三氯乙烯氧化硅膜推迟破坏性击穿的机理研究

本文对三氯乙烯(TCE)氧化推迟SiO₂膜的破坏性击穿及其机理进行了研究。结果表明,随着TCE流量的增大、处理时间的增加、温度的升高和氧分压的降低,SiO₂膜的击穿电流耐量增大。但过大的TCE流量和过长的处理时间,将使击穿特性变坏。结果还表明,击穿电流耐量的增大与膜内电子陷阱密度的增大有关。文中提出包括三种恶性循环在内的“低势垒点-电场增强”击穿模型,并考虑氧化气氛中的H₂O对击穿特性的影响,引入电子陷阱抑制低势垒点-电场增强的作用,分析T 关键词：     

Reversibler Gleichfeld- und Mikrowellen-Durchschlag in n-Typ-Germanium bei 4,2 °K

The microwave induced breakdown characteristic inn-type germanium at 4.2 °K has been observed and compared with the d.c. induced breakdown characteristic obtained from the same sample. The effective microwave breakdown field intensity is nearly equal to the field intensity observed in d.c. induced breakdown. However, in the breakdown region with conductivities greater than 0.1 ohm^?1 cm^?1 a relaxation effect was found and interpreted qualitatively as momentun relaxation. In the initial breakdown the relaxation time τ _m is small,ω ²τ _m ² being ?1 whereω/2π=9·10⁹s^?1 is the microwave frequency. The relaxation time is determined by predominant neutral impurity scattering with at last 5·10¹⁴ impurities per cm³. This scattering mechanism becomes ineffective when the impurities are ionized by hot carriers. Ionized impurity scattering or acoustic phonon scattering will then be predominant with increased and energy dependent values of τ _m . The increased phase shift between carriers and field causes a decreased energy transfer from the field to the carriers, an accordingly smaller ionization rate, and finally results in a nearly constant a.c. conductivity. The observed anisotropy of the breakdown field intensity is in qualitative agreement with the assumption that only carriers in “hot” valleys of the conduction band initiate the breakdown by impact ionization. The unsufficient quantitative agreement may be due to an inhomogeneity of doping which is suggested by comparing the values of the ohmic low temperature conductivity of the samples.     

An AlGaN/GaN HEMT with reduced surface electric field and improved breakdown voltage

A reduced surface electric field in AlGaN/GaN high electron mobility transistor (HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas (2-DEG) channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional source-connected field plate and double field plate, the HEMT with Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, L_m, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with V_GS=-5 V, L_m=1.5 μm, a peak Mg doping concentration of 8× 10¹⁷ cm^-3 and a drift region length of 10 μm, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.     

Fabrication of gas ionization sensor based on titanium oxide nanotube arrays

Gas sensors have been fabricated based on field ionization from titanium oxide nanotubes grown on titanium foil. Ordered nanaotube arrays of titanium oxides were grown by the anodization method. We measured breakdown voltages and discharge currents of the device for various gases. Our gas ionization sensors (GIS) presented good sensitivity, selectivity, and short response time. The GISs based on TiO₂ nanotube arrays showed lower breakdown voltage, higher discharge current, and good selectivity. An excellent response observed for Ar compared to other gases. Besides, by introducing 2 % CO and 4 % H₂ to N₂ flow gas, the amount of breakdown voltage shifts about 20 and 70 volts to the lower values, respectively. The GIS works at room temperature and has the ability of detect inert gases with high stability and good linearity. Besides, short response time of about 1 second for the GISs based on TiO₂ nanotube arrays makes them excellent for gas sensing applications. Sharp edges of the nanotubes, through enhancing the applied electric field, reduce operating voltage to the reasonable values and power consumption.     

Frequency combinations in the magnetoresistance oscillations spectrum of a linear chain of coupled orbits with a high scattering rate

The oscillatory magnetoresistance spectrum of the organic metal (BEDO)₅Ni(CN)₄. 3C₂H₄(OH)₂ has been studied up to 50 T, in the temperature range from 1.5 K to 4.2 K. In high magnetic field, its Fermi surface corresponds to a linear chain of quasi-two-dimensional orbits coupled by magnetic breakdown (MB). The scattering rate consistently deduced from the data relevant to the basic α and the MB-induced β orbits is very large which points to a significant reduction of the chemical potential oscillation. Despite of this feature, the oscillations spectrum exhibits many frequency combinations. Their effective masses and (or) Dingle temperature are not in agreement with either the predictions of the quantum interference model or the semiclassical model of Falicov and Stachowiak.     

Dielectric breakdown phenomena in Al2O3 filled DGEBA/MDA/SN composite system

Dielectric breakdown phenomena by electrical treeing deterioration was investigated in the new epoxy resin system DGEBA/MDA/SN filled with Al₂O₃. As the filler content increased, the maximum electric field at breakdown increased and then decreased with increase of defects such as voids, impurities and delamination or peeling between filler and matrix. As the electrode separation increased, the breakdown voltage increased, but the breakdown strength decreased and then saturated to 17 kV/mm. Also, the maximum electric field at the tip when the system was failed increased. The electrical tree initiated from the side of the needle electrode was not from the tip where the reinforced field is the highest. The electrical tree was blocked by the filler. The interface condition of filler and polymer matrix played an important role in the electrical treeing resistance. The final breakdown phenomena showed fan-type crack as observed in the non-filled system.     

Untersuchungen über die Entwicklung des Kanaldurchschlags in Gasen

The temporal development of the current of a discharge leading to breakdown was investigated under static and homogeneous field conditions with wide band oscilloscopic techniques. The discharges were started by 10³ to 10⁵ electrons released within some 10^?9 sec along traces of single α-particles parallel to the electric field. Measurements have shown that streamer mechanism occurs in gases as CH₄ and CO₂ at static breakdown, if a sufficient density of space charge is produced by a great number of overlapping avalanches. The gas amplification of thesingle avalanche only has a value of about 10⁵. Also in O₂ and dry air at highpd-values breakdown develops with streamer mechanism. — In electronegative gases as freon 12 and O₂ a prolongation of the time necessary for streamer formation is caused by the reduction of the effective total space charge by the negative ions. The results of a detailed study of the time necessary for streamer development and the time constant of the increase of the current leading to breakdown confirm the model of streamer mechanism.     

Control of electric field in 4H-SiC UMOSFET: Physical investigation

In this paper, we show how breakdown voltage (V_BR) and the specific on-resistance (R_on) can be improved simply by controlling of the electric field in a power 4H-SiC UMOSFET. The key idea in this work is increasing the uniformity of the electric field profile by inserting a region with a graded doping density (GD region) in the drift region. The doping density of inserted region is decreased gradually from top to bottom, called Graded Doping Region UMOSFET (GDR-UMOSFET). The GD region results in a more uniform electric field profile in comparison with a conventional UMOSFET (C-UMOSFET) and a UMOSFET with an accumulation layer (AL-UMOSFET). This in turn improves breakdown voltage. Using two-dimensional two-carrier simulation, we demonstrate that the GDR-UMOSFET shows higher breakdown voltage and lower specific on-resistance. Our results show the maximum breakdown voltage of 1340 V is obtained for the GDR-UMOSFET with 10 µm drift region length, while at the same drift region length and approximated doping density, the maximum breakdown voltages of the C-UMOSFET and the AL-UMOSFET structures are 534 V and 703 V, respectively.     

Electrical breakdown of dysprosium oxide films

The principal laws governing the electrical breakdown of dysprosium oxide films in silicon metal — insulator — semiconductor structures are investigated. The dependence of the breakdown field E_br on the rise rate of the voltage on the structure K_v, the temperature, the material and area of the electrode, and the humidity of the environment is studied. The dependence of the time delay of breakdown on the amplitude of a rectangular voltage pulse is investigated. It is established that the breakdown field increases linearly with log K_v for all insulator thicknesses, and the saturation of E_br is observed at K_v>10⁵ V/sec. It is found that E_br does not depend on the electrode material and decreases as the area of the electrode or the temperature is increased. The maximum breakdown field is determined: E _br ^max =14 MV/cm. The mechanism of the precursory stage of breakdown, i.e., the period of transient buildup of critical charge in the insulator, is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 95–101, August, 1995.     

Empirical analysis of picosecond breakdown in sulfur hexafluoride

Using state of the art equipment and multiple simultaneous data acquisition systems, breakdown in sulfur hexafluoride (SF₆) is examined in high resolution. Recorded risetimes can be as fast as 50 ps. Influential parameters of breakdown are identified, recorded, and categorized. Methods for removing the impact of the measurement system are implemented in efforts to distinguish the physical phenomenon from influential external factors. Observed waveforms and breakdown characteristics are categorized into three types. Each type is particular to a specific parameter range – i.e. electric field E/p or the product of pressure and distance pd.     

Electric field induced avalanche breakdown and non-volatile resistive switching in the Mott Insulators AM4Q8

The Mott insulator compounds AM₄Q₈ exhibit a new type of volatile and non volatile resistive switchings that are of interest for RRAM application. We found that above a threshold electric field E _TH of the order of a few kV/cm these compounds undergo a volatile resistive switching based on an avalanche process. For electric field much higher than the threshold avalanche breakdown field, the resistive switching turns non volatile. Our EDXS and STEM analyses show that the non volatile resistive switching originating from the avalanche breakdown can neither be ascribed to local chemical modifications nor to a local phase change with symmetry breaking at a resolution better than a few nanometer. This is in strong contrast with non volatile resistive switching reported so far that are all based on chemical or structural changes. Conversely, our results suggest that the avalanche breakdown induce the collapse of the Mott insulating state at the local scale and the formation of a granular conductive filament formed by compressed metallic domains and expanded “superinsulating” domains.     

High-Power GaN Electronic Devices

Gallium Nitride (GaN) and related materials (especially AlGaN) recently have attracted a lot of interest for applications in high-power electronics capable of operation at elevated temperatures and high frequencies. The AlGaInN system offers numerous advantages. These include wide bandgaps, good transport properties, the availability of heterostructures (particularly AlGaN/GaN), the experience base gained by the commercialization of GaN-based laser and light-emitting diodes and the existence of a high growth rate epitaxial method (hydride vapor phase epitaxy, HVPE) for producing very thick layers or even quasisubstrates. These attributes have led to rapid progress in the realization of a broad range of GaN electronic devices. Al_xGa_1-xN (x=0 ～.25) Schottky rectifiers were fabricated in a lateral geometry employing p⁺-implanted guard rings and rectifying contact overlap onto an SiO₂ passivation layer. The reverse breakdown voltage (V_B) increased with the spacing between Schottky and ohmic metal contacts, reaching 9700 V for Al_0.25Ga_0.75N and 6350 V for GaN, respectively, for 100-µm gap spacing. Assuming lateral depletion, these values correspond to breakdown field strengths of <9.67×10⁵ Vcm^?2, which is roughly a factor of 5 lower than the theoretical maximum in bulk GaN. The figure of merit (V_B)²/R_ON, where RON is the on-state resistance, was in the range 94 to 268 MWcm^?2 for all the devices. Edge-terminated Schottky rectifiers were also fabricated on quasibulk GaN substrates grown by HVPE. For small-diameter (75?µm) Schottky contacts, Vs measured in the vertical geometry was ～700?V, with an on-state resistance (RON) of 3?mΩcm², producing a figure-of-merit V_B ²/R_ON of 162.8?MW-cm^?2. GaN p-i-n diodes were also fabricated. A direct comparison of GaN p-i-n and Schottky rectifiers fabricated on the same GaN wafer showed higher reverse breakdown voltage for the former (490?V vs. 347?V for the Schottky diodes), but lower forward turn-on voltages for the latter (～3.5?V vs. ～5?V for the p-i-n diodes). The forward I-V characteristics of the p-i-n rectifiers show behavior consistent with a multiple recombination center model. The reverse current in both types of rectifiers was dominated by surface perimeter leakage at moderate bias. Finally, all of the devices we fabricated showed negative temperature coefficients for reverse breakdown voltage, which is a clear disadvantage for elevated temperature operation. Bipolar devices are particularly interesting for high current applications such as microwave power amplifiers for radar, satellite, and communication in the l～5?GHz range, powers >l00?W, and operating temperatures >425°C. pnp Bipolar Junction Transistors and pnp Heterojunction Bipolar Transistors were demonstrated for the first time. For power microwave applications, small area self-aligned npn GaN/AlGaN HBTs were attempted. The devices showed very promising direct current characteristics.     

Kinetic parameters,collision rates,energy exchanges and transport coefficients of non-thermal electrons in premixed flames at sub-breakdown electric field strengths

The effects of an electric field on the collision rates, energy exchanges and transport properties of electrons in premixed flames are investigated via solutions to the Boltzmann kinetic equation. The case of high electric field strength, which results in high-energy, non-thermal electrons, is analysed in detail at sub-breakdown conditions. The rates of inelastic collisions and the energy exchange between electrons and neutrals in the reaction zone of the flame are characterised quantitatively. The analysis includes attachment, ionisation, impact dissociation, and vibrational and electronic excitation processes. Our results suggest that Townsend breakdown occurs for E/N = 140 Td. Vibrational excitation is the dominant process up to breakdown, despite important rates of electronic excitation of CO, CO₂ and N₂ as well as impact dissociation of O₂ being apparent from 50 Td onwards. Ohmic heating in the reaction zone is found to be negligible (less than 2% of peak heat release rate) up to breakdown field strengths for realistic electron densities equal to 10¹⁰ cm^?3. The observed trends are largely independent of equivalence ratio. In the non-thermal regime, electron transport coefficients are insensitive to mixture composition and approximately constant across the flame, but are highly dependent on the electric field strength. In the thermal limit, kinetic parameters and transport coefficients vary substantially across the flame due to the spatially inhomogeneous concentration of water vapour. A practical approach for identifying the plasma regime (thermal versus non-thermal) in studies of electric field effects on flames is proposed.     

Partial-SOI high voltage P-channel LDMOS with interface accumulation holes

A new partial SOI (silion-on-insulator) (PSOI) high voltage P-channel LDMOS (lateral double-diffused metal-oxide semiconductor) with an interface hole islands (HI) layer is proposed and its breakdown characteristics are investigated theoretically. A high concentration of charges accumulate on the interface, whose density changes with the negative drain voltage, which increase the electric field (E_I) in the dielectric buried oxide layer (BOX) and modulate the electric field in drift region . This results in the enhancement of the breakdown voltage (BV). The values of E_I and BV of an HI PSOI with a 2-μm thick SOI layer over a 1-μm thick buried layer are 580V/μm and -582 V, respectively, compared with 81.5 V/μm and -123 V of a conventional PSOI. Furthermore, the Si window also alleviates the self-heating effect (SHE). Moreover, in comparison with the conventional device, the proposed device exhibits low on-resistance.     

Energy gap of a charge density wave in NbSe3 induced by a high magnetic field above the Peierls transition temperature

The effect of a magnetic field on the energy gap of the charge density wave (CDW) in NbSe₃ near the temperature T _p2 of the lower Peierls transition has been investigated using interlayer tunneling spectroscopy. It has been shown that the magnetic field increases the energy gap and can even induce it at temperatures higher than T _p2 by 15–20 K. As the field strength increases, the peak amplitude of the gap singularity of the tunneling spectrum first increases, reaches its maximum at 20–30 T, and then decreases. The increase in the gap peak amplitude is attributed to the field-induced improvement of the condition of the CDW nesting, while the decrease in the amplitude in high fields, to the breakdown of the ground state caused by its Zeeman splitting.