Minimum Breakdown Field Research Articles

Design of compositionally graded contact layers for MOCVD grown high Al-content AlGaN transistors

In this letter, we design and demonstrate an improved metalorganic chemical vapor deposition (MOCVD) grown reverse Al-composition graded contact layer, whereby the Al-composition of AlxGa1−xN in the contact layer is graded from the higher Al-composition as in the channel to lower Al-composition, to achieve a low resistance contact to MOCVD grown ultrawide bandgap Al0.70Ga0.30N channel metal-semiconductor field-effect transistors. Increasing the thickness of the reverse graded layer was found to improve contact layer resistance significantly, leading to a contact resistivity of 3.3 × 10−5 Ω cm2. Devices with a gate length, LG, of 0.6 μm and a source-drain spacing, LSD, of 1.5 μm displayed a maximum current density, IDS,MAX, of 635 mA/mm with an applied gate voltage, VGS, of +2 V. Breakdown measurements on transistors with a gate to drain spacing, LGD, of 770 nm had breakdown voltage greater than 220 V, corresponding to a minimum breakdown field of 2.86 MV/cm—almost 3× higher than that exhibited by lateral GaN channel devices with similar dimensions. This work provides a framework for the design of low resistance contacts to MOCVD grown high Al-content AlxGa1−xN channel transistors.

Electric field strength of charged conducting balls and the breakdown of the air gap between them

Field amplification factors at the surfaces of two charged conducting balls are calculated numerically. It is shown that as the balls are brought closer together, except when their potentials are equal, the amplification factors go to infinity, and in the case of like-charged balls the field at the surface of one of them changes sign. Breakdown field strengths for the air gap between balls of a different diameter are calculated using the experimental data of other authors as the base. The results suggest that the minimum breakdown field strength is 26 kV cm−1 . The author's earlier results on the interaction force between the balls are revised.

Modified distributed electron cyclotron resonance ion source for the production of large diameter ion beams

The work presented in this article concerns the conception and the study of a multiantenna electron cyclotron resonance (ECR) ion source at 2.45 GHz dedicated to the surface treatment of large area materials. In this original device, a microwave plasma is created in a 20 cm in diameter ionization chamber. The 15 cm in diameter extracted ion beam has a current density of about 1 mA/cm2. The applicator is an N-way coaxial power divider in which the N=20 antennas are individually magnetized by internal SmCo bars in order to produce ECR zones in their vicinity. Moreover, the microwave plasma is confined by a multicusp magnetic structure surrounding the ionization chamber. The choice of the source geometry has been guided by the study of some theoretical considerations such as the characteristic diffusion length, the minimum breakdown field, and the penetration depth of the wave into the plasma. Simulations both of the electromagnetic field and the static magnetic field distribution have been carried out in order to validate the final choice of the source geometry. A full characterization of the ECR plasma and of the extracted ion beam was made with different experimental techniques. These results allow us to localize the plasma creation zones inside the ionization chamber. A 120 mA singly charged argon ion beam with a profile homogeneity better than ±5% over 10 cm was obtained 5 cm downstream the extraction system with a 300 W microwave power and a neutral argon pressure of 10−3 mbar in the ionizing chamber.

Problems of the application of N2/SF6 mixtures to gas‐insulated bus

AbstractIn designing a gas‐insulated bus (GIB) using N2/SF6 mixtures, there are many application problems, such as the mixture pressure needed in order to maintain the required dielectric and heat transfer performance. Problems of recycling SF6 are also essential in applying N2/SF6 mixtures. This paper presents the minimum breakdown field strength at lightning impulse and the temperature rise of the conductor and enclosure as measured for N2/SF6 mixtures. Considering the dielectric and heat transfer properties, we clarify the problems of application of mixtures to a GIB and discuss the appropriate mixture ratio of SF6 in designing a GIB comparable to the present dimensions. In addition, the lowest limit of SF6 content in a liquefied recovering method is theoretically estimated for reference in practical SF6 recovery from mixtures. It is important for design to consider both breakdown phenomena, including the area effect of electrode, and the heat transfer properties of mixtures. © 2001 Scripta Technica, Electr Eng Jpn, 137(4): 25–31, 2001

ガス絶縁母線へのN<sub>2</sub>/SF<sub>6</sub>混合ガス適用に関する検討

In designing a Gas insulated bus (GIB) using N2/SF6 mixtures, there are many application problems such as the mixtures pressure to maintain the required dielectric and heat transfer performance. The problems on recycling SF6 are also essential in applying N2/SF6 mixtures. In this paper, the minimum breakdown field strength at lightning impulse and temperature rise of conductor and enclosure have been measured for N2/SF6 mixtures. Considering the dielectric and heat transfer properties, we clarify the application problems of mixtures to a GIB and discuss the appropriate mixture ratio of SF6 in designing the GIB comparable to the present dimension. And also the lowest limit of SF6 content in a liquefied recovering method is theoretically estimated for the reference of practical SF6 recovery from mixtures. It is important for the design to consider both breakdown phenomena including area effect of electrode and heat transfer properties of mixtures.

The effect of aluminium inclusions on the dielectric breakdown of polyethylene

A narrow size distribution of irregular aluminium particles was blended into power cable insulation grade polyethylene. Some batches of the resulting material were then melt-filtered to reduce the size of particles present and narrow the distributions further. The failure statistics of the loaded polymers were then determined under AC ramped stress. The data have been fitted to extreme value statistics, and trends with size and density of defect can clearly be identified. In addition, for the filtered material, a minimum breakdown field can be associated with a given filter size: a result of commercial importance. Some indications exist to suggest that different modes of failure operate at high and low fields. Candidates for these modes are analysed and discussed in terms of the distributions of defects present. Local field enhancement due to the included flaws were calculated using finite-element techniques. The results are compared with a percolation model of breakdown. Predictions are found to quantify accurately the reduction in the characteristic strength of the material over the narrow range of defect concentrations examined.

Microwave multiple-pulse breakdown in nitric oxide

The minimum value of the peak RMS electric field for the TE11 mode resulting in the breakdown of pure nitric oxide has been measured in the pressure range 0·5-10 Torr. The microwave frequency was 9·361 GHz. For each pressure selected, the breakdown formation time τ was found as a function of the electric field. For all breakdown formation times, the minimum breakdown field occured at a pressure of 3-4 Torr, the pulse repetition frequency and pulse length being 100 pps and 4·7 ms respectively.

A pre-breakdown phenomenon in the liquid dielectric hexane

The paper describes the observation, recording, and interpretation of a pre-breakdown phenomenon occurring in the liquid dielectric hexane. The effect is seen as a region of changed refractive index, and an optical Schlieren system and a high speed streak camera have been constructed and used to investigate its nature and in particular its rates of growth and decay. From the results obtained a theory of breakdown of the point-plane electrode system is deduced and shown to explain the observed phenomena remarkably well. The region of disturbance itself is interpreted as a local heating which marks the extent of a weak plasma. This plasma forms at the point cathode, grows in size with time to span most of the electrode gap, and breakdown indicated by an arc finally ensues. From the plasma geometry it is estimated that the minimum field existing at the plasma boundary during breakdown is about five times greater than the mean applied field. Measurements of the rate of movement of the plasma boundary suggest that at these high fields electron mobilities are becoming field dependent and rising rapidly. The minimum breakdown field is estimated as about 620 kv cm-1 and the average electron mobility at this field is estimated as about 0.03 cm2 v-1 sec-1.

Formative Processes in Pulsed Microwave Discharges in Mixtures of Neon and Argon

In connection with studies for developing a microwave discharge chamber which detects tracks of charged particles, a number of important properties of a pulsed microwave discharge have been investigated. A pulsed microwave field of variable pulse widths, τ p =0.1∼2 µ sec, has been applied to a mixture of neon and argon at a total pressure of 100 mm Hg, but with various mixture ratio. The results are; a) the breakdown field strengths are approximately by one order of magnitude higher than those in continuous RF discharges and are less sensitive to the relative concentration of argon in neon, r , for smaller τ p , b) the breakdown field strength decreases with increasing r , reaches a minimum and increases again with a further increase of r , and c) the optimum value of r for the minimum breakdown field strength increases with decreasing τ p . These properties can be explained in teams of the direct ionization whose relative contribution becomes predominant as E / p increases and/or τ p decreases. The so-ca...