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15 Apr 2012

Volume 111, Issue 8, Articles (08xxxx)

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J. Appl. Phys. 111, 084701 (2012); http://dx.doi.org/10.1063/1.3698319 (11 pages)

Xerxes Lopez-Yglesias, Jason M. Gamba, and Richard C. Flagan
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back to top Plasmas and Electrical Discharges

Breakdown voltage reliability improvement in gas-discharge tube surge protectors employing graphite field emitters

Marko Žumer, Bojan Zajec, Robert Rozman, and Vincenc Nemanič

J. Appl. Phys. 111, 083301 (2012); http://dx.doi.org/10.1063/1.4704699 (6 pages)

Online Publication Date: 19 April 2012

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Gas-discharge tube (GDT) surge protectors are known for many decades as passive units used in low-voltage telecom networks for protection of electrical components from transient over-voltages (discharging) such as lightning. Unreliability of the mean turn-on DC breakdown voltage and the run-to-run variability has been overcome successfully in the past by adding, for example, a radioactive source inside the tube. Radioisotopes provide a constant low level of free electrons, which trigger the breakdown. In the last decades, any concept using environmentally harmful compounds is not acceptable anymore and new solutions were searched. In our application, a cold field electron emitter source is used as the trigger for the gas discharge but with no activating compound on the two main electrodes. The patent literature describes in details the implementation of the so-called trigger wires (auxiliary electrodes) made of graphite, placed in between the two main electrodes, but no physical explanation has been given yet. We present experimental results, which show that stable cold field electron emission current in the high vacuum range originating from the nano-structured edge of the graphite layer is well correlated to the stable breakdown voltage of the GDT surge protector filled with a mixture of clean gases.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
79.70.+q Field emission, ionization, evaporation, and desorption
84.47.+w Vacuum tubes

Plasma potential mapping of high power impulse magnetron sputtering discharges

Albert Rauch, Rueben J. Mendelsberg, Jason M. Sanders, and André Anders

J. Appl. Phys. 111, 083302 (2012); http://dx.doi.org/10.1063/1.3700242 (12 pages) | Cited 4 times

Online Publication Date: 23 April 2012

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Pulsed emissive probe techniques have been used to determine the plasma potential distribution of high power impulse magnetron sputtering (HiPIMS) discharges. An unbalanced magnetron with a niobium target in argon was investigated for a pulse length of 100 μs at a pulse repetition rate of 100 Hz, giving a peak current of 170 A. The probe data were recorded with a time resolution of 20 ns and a spatial resolution of 1 mm. It is shown that the local plasma potential varies greatly in space and time. The lowest potential was found over the target’s racetrack, gradually reaching anode potential (ground) several centimeters away from the target. The magnetic presheath exhibits a funnel-shaped plasma potential resulting in an electric field which accelerates ions toward the racetrack. In certain regions and times, the potential exhibits weak local maxima which allow for ion acceleration to the substrate. Knowledge of the local E and static B fields lets us derive the electrons’ E×B drift velocity, which is about 105 m/s and shows structures in space and time.
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52.80.Pi High-frequency and RF discharges
52.40.Kh Plasma sheaths
52.70.Ds Electric and magnetic measurements

High electronegativity multi-dipolar electron cyclotron resonance plasma source for etching by negative ions

E. Stamate and M. Draghici

J. Appl. Phys. 111, 083303 (2012); http://dx.doi.org/10.1063/1.4704696 (6 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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A large area plasma source based on 12 multi-dipolar ECR plasma cells arranged in a 3 × 4 matrix configuration was built and optimized for silicon etching by negative ions. The density ratio of negative ions to electrons has exceeded 300 in Ar/SF6 gas mixture when a magnetic filter was used to reduce the electron temperature to about 1.2 eV. Mass spectrometry and electrostatic probe were used for plasma diagnostics. The new source is free of density jumps and instabilities and shows a very good stability for plasma potential, and the dominant negative ion species is F−. The magnetic field in plasma volume is negligible and there is no contamination by filaments. The etching rate by negative ions measured in Ar/SF6/O2 mixtures was almost similar with that by positive ions reaching 700 nm/min.
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52.77.Bn Etching and cleaning
52.70.Nc Particle measurements
81.65.Cf Surface cleaning, etching, patterning
52.70.Ds Electric and magnetic measurements
52.50.Dg Plasma sources

rf-power and the ring-mode to red-mode transition in an inductively coupled plasma

J. G. Coffer and J. C. Camparo

J. Appl. Phys. 111, 083304 (2012); http://dx.doi.org/10.1063/1.4705469 (7 pages)

Online Publication Date: 25 April 2012

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The optical output of an alkali-metal inductively coupled plasma (alkali-ICP) plays an important role in both atomic magnetometers and atomic clocks, producing these devices’ atomic signals through optical pumping. Unfortunately, though the alkali-ICP’s optical pumping efficiency grows exponentially with temperature, at relatively high temperatures (∼140 °C) the discharge transitions from “ring mode” to “red mode,” which is a spectral change in the plasma’s output that corresponds broadly to a transition from “good emission” for optical pumping to “poor emission.” Recently, evidence has accumulated pointing to radiation trapping as the mechanism driving the ring-mode to red-mode transition, suggesting that the phenomenon is primarily linked to the alkali vapor’s temperature. However, observations of the transition made in the 1960 s, demonstrating that the ICP temperature associated with the transition depended on rf-power, would appear to cast doubt on this mechanism. Here, we carefully investigate the influence of rf-power on the ring-mode to red-mode transition, finding that rf-power only affects the transition through discharge heating. Thus, the present work shows that the primary effect of rf-power on the ring-mode to red-mode transition can be understood in terms of the radiation trapping mechanism.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Resonant planar antenna as an inductive plasma source

Ph. Guittienne, S. Lecoultre, P. Fayet, J. Larrieu, A. A. Howling, and Ch. Hollenstein

J. Appl. Phys. 111, 083305 (2012); http://dx.doi.org/10.1063/1.4705978 (6 pages)

Online Publication Date: 27 April 2012

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A resonant planar antenna as an inductive plasma source operating at 13.56 MHz inside a low pressure vacuum vessel is presented for potential plasma processing applications. Its principle consists in interconnecting elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna shows a set of resonant modes associated with peaks of the real input impedance. Each of these modes is defined by its own current and voltage distribution oscillating at the frequency of the mode. A rectangular antenna of 0.55m×0.20m has been built, and first results obtained with argon plasmas are presented. Plasma generation is shown to be efficient as densities up to 4·1017m-3 at 2000 W have been measured by microwave interferometry at a distance of 4 cm from the source plane. It is also demonstrated that the plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. A non-uniformity of less than ±5% is obtained at 1000 W at a few centimeters above the antenna over 75% of its surface.
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52.50.Dg Plasma sources
52.25.-b Plasma properties
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
84.40.Ba Antennas: theory, components and accessories

Space charge effects on externally injected current in planar diodes: Existence of multiple stationary states

A. Rokhlenko and J. L. Lebowitz

J. Appl. Phys. 111, 083306 (2012); http://dx.doi.org/10.1063/1.4706567 (7 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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We study the effects of space charge on the properties of a system with a specified steady current. The problem is solved exactly for a planar one dimensional geometry, but we expect similar results for more realistic systems. We find that in many cases, the stationary current density cannot exceed some fixed value Jmax and in other cases be lower than a fixed Jmin depending on the method of injection. There are also intervals of intermediate current densities, which cannot exist in the stationary conditions. In general, there are values of J in some range where there are two different stationary regimes, which correspond to two different electric fields at the emitter surface. Connection with results obtained from numerical simulations and possible applications are also considered.
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85.45.Bz Vacuum microelectronic device characterization, design, and modeling
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