Breakdown Field Measurements Research Articles

Impact of Threading Dislocations in GaN Power Switching Devices

Thick epitaxial (3-15 microns) GaN power switching devices are known to contain a high density of crystal defects, and especially threading dislocations in the epitaxial layer. The impact of these defects on device performance and reliability is a topic of ongoing research. This paper presents state-of-the-art methods for analyzing threading dislocation density, growth, and quantification of their impact on leakage current, blocking voltage, and peak E field. The effects of substrate type, epitaxial thickness, and processing techniques on dislocation density have been investigated to provide a roadmap for design and performance optimization of switching two terminal devices. Experimental and simulated data are used in conjunction to model dislocation impact on electrical performance characteristics and to identify techniques to minimize defect density.The experimental results have been achieved for 3 and 10 micron thick epitaxy as well as initial results for 15 micron epitaxy. The substrate was bulk GaN, and the epitaxy was grown by HPVPE by Kyma Corporation. The DMOS test structure investigated showed state of the art current voltage characteristics for a 10 micron n- epitaxy. Significant deviations were observed between the measured doping profile and the simulated profile, using a critical field of 3 MV/cm. For the DMOS device with epi doping of 8 × 1015 \U0001d450\U0001d45a−3 and epi thickness of 8 \U0001d707\U0001d45a. The device breaks down at approximately 2020 \U0001d449. At 2000 \U0001d449, the peak field is roughly 3.11 \U0001d440\U0001d449/\U0001d450\U0001d45a. For a device with epi doping of 8 × 1015 \U0001d450\U0001d45a−3 and epi thickness of 15 \U0001d707\U0001d45a. The device breaks down at approximately 3020 \U0001d449. At 3000 \U0001d449, the peak field is roughly 3.14 \U0001d440\U0001d449/\U0001d450\U0001d45a. The observed trend is significant since it shows that by increasing the epi thickness, also results in an increase in the peak field. For thin GaN epi of 3 microns, a peak breakdown field of 2.77 MV/cm was measured. These three date points will allow one to determine a relationship between peak critical field and epi thickness, which is a major requirement for designing vertical GaN high voltage switches.We report images from transmission x-ray topographs and TEM investigations as well as the correlation with critical breakdown field measurements. The transmission x-ray topograph shows that the GaN is characterized by a nearly uniform distribution of strain centers which are likely bundles of threading screw and edge dislocations. Strain free centers are then regions of relatively low dislocation densities. The threading dislocations are part of dislocation loops which are present in the GaN substrate and migrate through the interface. The cross-sectional TEM image shows partial dislocation loops through the thickness of the GaN sample.Figure: X-Ray Topography of GaN/GaN showing a nearly uniform distribution of strain centers. The Grazing incidence topograph is similar to the transmission image, the grazing image also shows the nearly uniform distribution of strain centers. The X ray image shows that individual threading dislocations are not resolved showing a relatively low dislocation density in those regions. Figure 1

A comparative study on atomic layer deposited oxide film morphology and their electrical breakdown

Transition metal oxide films HfO2, ZrO2, Ta2O5, TiO2, Nb2O5, and Y2O3, together with Al2O3 and SiO2 for reference, were deposited by atomic layer deposition (ALD) and investigated. For all the films ALD process was performed within the same reactor at two temperature ranges 100–125∘C and 250–300∘C. Both water and ozone were used as oxygen sources if processes were available. Most films are amorphous as-deposited, but HfO2, ZrO2, and Y2O3 can be crystalline, depending on deposition temperature and oxygen source.After deposition and initial characterization, the films were annealed to different temperatures up to 1200∘C, depending on the material, to observe the crystallization process.When crystalline phases were observed, grain sizes have been derived from the X-ray diffractograms and compared with feature sizes in SEM images. RMS analysis revealed a general tendency - an increase of roughness with the appearance of crystallization.The temperature-dependent morphological investigations were supported by breakdown field measurements. Those are also strongly affected when a film becomes crystalline. Most values observed for break down fields agree with literature, some values exceed previously reported numbers.

Changes induced in the properties of dielectric silicone elastomers by the incorporation of transition metal complexes

Three new, cheap, and easily obtained complexes of triethanolamine with Cu(II), Ni(II), and Co(II) were incorporated in a high-molecular-weight polydimethylsiloxane-α,ω-diol (number-average molecular weight = 440,000 g mol−1) together with silica nanoparticles. While silica has a well-known mechanical reinforcing role, adding the metal complexes with high dielectric permittivity aims to increase values for this characteristic of the prepared silicone composites in order to be useful for electromechanical applications. A simple procedure was employed for the incorporation of fillers by mechanical mixing in bulk without a solvent. The composites were processed as films and stabilized by curing initiated with 2,4-dichlorobenzoyl peroxide at high temperature (180°C) and pressure. The cross-linking yield was estimated on the basis of swelling in chloroform, while the cross-linking density was calculated from differential scanning calorimetry traces. The filler’s effect on mechanical and dielectric properties was assessed by appropriate measurements (tensile testing and dielectric spectroscopy). Changes in dielectric behavior as a result of the repeated deformation by stretching were also highlighted. Electromechanical sensitivity and ultimate tensile toughness values were estimated on the basis of these results as primary indices on suitability of these materials in transducers. The dielectric strength of the composite films was also evaluated by electrical breakdown field measurements.

Dielectric features of two grades of bi‐oriented isotactic polypropylene

ABSTRACTThe dielectric properties of two grades of bi‐oriented isotactic polypropylene were studied with a variety of techniques: breakdown field measurements, dielectric spectroscopy, thermally stimulated depolarization currents (Is), and direct‐current (dc) conduction I values. Standard polypropylene (STPP) and high‐crystallinity polypropylene (HCPP) films were investigated. Measurements were carried out over a wide temperature range (−150°C/+125°C). The breakdown fields in both materials showed a very small difference. On the other hand, the dielectric losses and dc conduction I values were significantly lower in HCPP. Both materials showed a decrease in the dielectric loss versus temperature in the range 20–90°C; this is favorable for application in alternating‐current power capacitors. The analysis of the dc I value allowed us to find evidence of two main conduction mechanisms: (1) below 80°C in both materials, a hopping mechanism due to the motion of electrons occurred in the amorphous phase, and (2) above 80°C, ionic conduction occurred in HCPP, and hopping conduction occurred in STPP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42224.

Electrical property dependence on thickness and morphology of nanocrystalline diamond thin films

In this study, we investigate the influence of nanocrystalline diamond (NCD) thin film morphology and thickness on their electrical properties. NCD films are grown on p-type Si substrates with varied thicknesses from 250 to 788nm. Electrical contacts are formed from combination of Ti/Au metal layers (100nm thick each). The I–V and breakdown field measurements are used to analyze the electrical properties of metal/NCD/Si sandwich structure. In addition, NCD films are analyzed by scanning electron microscopy and Raman spectroscopy for better interpretation of the I–V measurements.

Measurements of Breakdown Field and Forward Current Stability in 3C-SiC pn Junction Diodes Grown on Step-Free 4H-SiC

This paper reports on initial fabrication and electrical characterization of 3C-SiC p+n junction diodes grown on step-free 4H-SiC mesas. Diodes with n-blocking-layer doping ranging from ~ 2 x 1016 cm-3 to ~ 5 x 1017 cm-3 were fabricated and tested. No optimization of junction edge termination or ohmic contacts was employed. Room temperature reverse characteristics of the best devices show excellent low-leakage behavior, below previous 3C-SiC devices produced by other growth techniques, until the onset of a sharp breakdown knee. The resulting estimated breakdown field of 3C-SiC is at least twice the breakdown field of silicon, but is only around half the breakdown field of <0001> 4H-SiC for the doping range studied. Initial high current stressing of 3C diodes at 100 A/cm2 for more than 20 hours resulted in less than 50 mV change in ~ 3 V forward voltage.

Elaboration, characterization and dielectric properties study of amorphous alumina thin films deposited by r.f. magnetron sputtering

The r.f. magnetron sputtering of alumina in pure Ar and Ar–O 2 mixtures was investigated to determine the best conditions for the elaboration of Al–O films. These thin films were analyzed for chemical composition, thickness, density, refractive index, O/Al ratio and dielectric properties in order to know the effect of the inclusion of oxygen or argon in the sputter gas on these alumina layers. The O/Al ratios for these films, as determined by Rutherford backscattering spectrometry and X-ray fluorescence, were higher than or equal to the ratio expected from stoichiometric alumina (1.5). In general, higher partial pressures of oxygen in the sputter plasma produced oxygen-rich films. For a given partial pressure, the inclusion of argon in the films increases when the sputtering pressure decreases. The inclusion of oxygen in the sputtered Al–O is found to correlate with the breakdown field measurements, with the oxygen-rich films proving to be better insulators. The experimental results indicate the dependence of dielectric properties on films sputtering conditions.

Damage to Si substrates during SiO 2 etching: Opportunities of subsequent removal by optimized cleaning procedures

Surface residues present at the surface and in the near surface region of Si substrates after reactive ion etching (RIE) of SiO 2 on Si with CHF 3 C 2F 6 were investigated with Auger electron spectroscopy and atomic force microscopy. A thin fluorocarbon film was found to develop on all etched samples. The efficiency of different ex situ cleaning procedures was examined. A cleaning treatment without Si consumption was unable to remove the residue layer in the required manner. In contrast, post-RIE treatments characterized by oxidation/SiO 2 wet etch, respectively, by a Cl 2-N 2 RIE step yield surfaces suitable for further device processing. This was confirmed by capacitance-voltage (C-V) and breakdown field measurements ( E BD) at metal-oxidesemiconductor (MOS) capacitors. The results demonstrate, there is no universal post-RIE cleaning treatment for damage elimination, but optimized procedures with regard to special technological demands are realizable.

Comparison of Thermal Gate Oxides on Silicon and Carbon Face P-Type 6H Silicon Carbide

ABSTRACTMonocrystalline 6H silicon carbide samples (n-type and p-type) with both carbon face and silicon face have been used to investigate gate oxide quality. The oxides were thermally grown in a dry oxygen ambient at 1523 K with or without the addition of TCA (Trichloroethane), or in wet pyrogenic steam at 1473 K. POCI3 doped polysilicon gates were used for electrical characterisation by capacitance-voltage measurements and breakdown field measurements. Large flatband voltage shifts indicate fixed oxide charges up to 1013 cm-2. The incorporation of aluminum in the oxides was monitored using SIMS (Secondary Ion Mass Spectrometry). Surprisingly high signals were interpreted as evidence of an aluminum-Oxygen compound having been formed (ie Al2O3).

AC breakdown strength of aromatic polymers under partial discharge reducing conditions

Partial discharge occurring at HV in AC electric breakdown field measurements on insulating polymeric films strongly reduces the breakdown field strength of the material and conceals the intrinsic breakdown process. By performing AC electric breakdown field measurements on polymer films in phthalic diesters, it was possible to suppress partial discharge and obtain breakdown field data of more intrinsic character. This is valuable for the evaluation of the influence of the structure and the properties of polymers on their insulating behavior. The AC electric breakdown field strength of five aromatic polymers at different film thicknesses was measured in dibutyl phthalate. The results from these measurements showed about a twofold increase in the breakdown field strength at sample thicknesses >50 /spl mu/m, compared to data obtained in transformer oil. The breakdown field strength for thick samples showed a linear decrease with increasing sample thickness for all polymers except PEEK, which showed a constant breakdown field strength in the thickness range investigated. The breakdown field strength of thin samples was independent of the polymer structure. Measurements of the breakdown field strength of the polymers under dc conditions show no obvious correlation between chemical structure or polymer property and the breakdown field strength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Aromatic polyimides: Synthesis, characterization, and evaluation of electric strength

AbstractAromatic polyimides have been synthesized via the formation of polyamic acids in solution. This solution was cast into films that were thermally imidized. The imidization process was monitored using FTIR. The degree of imidization was also determined with thermo‐gravimetric analysis. The electric breakdown field strength was tested under ac and dc conditions. Ac electric breakdown field strength measured in transformer oil was shown to follow a power‐law dependence on film thickness. This dependence was not affected by the molecular mass of the polymer but changed with the degree of imidization and the electron‐accepting properties of the diamine. High ac breakdown field values of polymides were obtained in dibutyl phthalate medium due to the suppression of partial discharges that occurs under these conditions. Measurements on films with thicknesses up to 60 μ showed no thickness dependence. No significant influence of the chemical structure on the break‐down field strength was observed under these conditions. Breakdown field measurements under dc conditions showed high values, which were in good agreement with the peak values of the ac measurements in dibutyl phthalate. This indicates similarities in the intrinsic ac and dc breakdown processes. © 1993 John Wiley &amp; Sons, Inc.

Low pressure chemical vapor deposition of silicon dioxide below 500 °C by the pyrolysis of diethylsilane in oxygen

Low pressure chemical vapor deposition (LPCVD) of SiO2 in a horizontal LPCVD furnace using liquid diethylsilane and oxygen has been studied. A temperature deposition window ranging from 425–500 °C was observed resulting in a maximum deposition rate of ∼275 Å/min. The pressure dependence of the deposition rate revealed a threshold of ≳950 mTorr for gas phase reactions at a deposition temperature of 450 °C. Analysis of the films by Rutherford backscattering spectroscopy has indicated that as-deposited films are stoichiometric SiO2 for deposition temperatures ≤450 °C. Best case across wafer uniformity was ±5% for a caged boat. Wet chemical and reactive ion etch rates were found to be comparable to those of thermal oxides after annealing. Cross-sectional scanning electron microscopy images of the SiO2 films deposited on 2 μm deep 1 μm wide silicon trenches revealed a conformality of ∼80%. The electrical properties of films deposited at 450 °C were studied. The electrical properties of the films were studied as-deposited and after annealing the films in a cold-wall rapid thermal annealing (RTA) system. RTAs were performed at temperatures ranging from 950 to 1100 °C in Ar, N2, or O2 ambients. Current–voltage, current–temperature, and capacitance–voltage measurements were performed for the electrical characterization. Catastrophic breakdown field measurements have shown electric field strengths of 9.5 MV/cm for as-deposited 500 Å films. A study of the leakage current conduction mechanisms has indicated that as-deposited films exhibit trap conduction mechanisms at high electric fields and temperatures. However, if deposition is followed by a RTA in Ar or O2, the leakage current follows closely the Fowler–Nordheim mechanism and yields a leakage-current electric field dependence comparable to a thermal oxide. Results have shown that values as low as 6 × 1010/cm2 for fixed charge density can be obtained if oxide deposition is followed by a RTA in Ar or N2.

Removing the Barriers to Next Generation'S Dielectric Films: In Situ Void-Free Planarized Films

ABSTRACTIn the next generation of semiconductor devices, minimum dimensions will be smaller, aspect ratios (height to width) of devices features will be larger, and BPSG dielectrics will be challenged to deal with these changes. A new process, which integrates deposition, flow, and anneal of BPSG films, and allows void-free filling of high-aspect-ratio trenches with excellent surface planarization, is presented in this paper. Scanning electron micrographs are used to show the extent of film coverage and planarization. Additional characterization includes ion chromatography, ellipsometry, stress measurements, and breakdown field measurements.

Alumina films by sputter deposition with Ar/O2: Preparation and characterization

rf bias sputtered alumina thin films were produced under a variety of sputter conditions and analyzed for composition, thickness, density, and dielectric strength (breakdown field) in order to assess the affect of the inclusion of oxygen in the sputter gas on these films. All of the Al:O ratios for these films, as determined by Rutherford backscattering spectrometry, were lower than or equal to the ratio expected from stoichiometric considerations (0.67). In general, higher partial pressures of oxygen in the sputter system produced oxygen rich films. The Al:O ratios were found to vary from a high of 0.66 to a low of 0.54. These were found to correlate with the breakdown field measurements, with the oxygen rich films proving to be better insulators. Sputter bias was found to have the second greatest influence on dielectric strength. A sputter bias of −40 V in our sputtering system produced the best insulating films both in the presence and absence of oxygen in the sputter gas, with breakdown fields dropping off at lower and higher biases.

Characteristics of Polyethylene Thin Films Deposited by Ionized Cluster Beam

ABSTRACTPolyethylene thin films were deposited by the ionized cluster beam (ICB) method. The dielectric, resistivity, and breakdown field measurements showed that the ICB polyethylene films have excellent properties as an electrical insulator. The characteristics of Au/polyethylene/Si MIS diodes and MISFErs indicated that the ICB method can control the film-substrate interface property. The SIMS and ESCAan alyses showed that the ICB films have pure and stable chemical structure.