Study of dc micro-discharge arrays made in silicon using CMOS compatible technology

Abstract

In this paper we present the fabrication technology used to make micro-discharge ‘reactors’ on a silicon (Si) substrate. For the fabrication of these reactors we have used Si wafers with 4 inch diameter and standard cleanroom facilities. The fabrication technology used is compatible with standard CMOS device fabrication and the fabricated micro-discharge reactors can be used to produce dc discharges. These micro-discharges operate at near atmospheric pressure. They were given ring-shaped anodes separated from the cathode by a SiO2 dielectric with a thickness of approximately 5–6 µm rather than the much more common ∼100 µm. The micro-discharge reactors can consist of either a single hole or multiple holes and we have built devices with holes from 25 to 150 µm in diameter. The micro-discharge measurements were obtained for helium and argon dc plasmas between 100 and 1000 Torr. We used a single ballast resistor to produce micro-discharges in multi-hole array. This resistor also acted to limit the discharge power. An average current density of 0.8 A cm−2 was calculated for the 1024 holes array with 100 µm diameter holes. In addition, we will report on stability of micro-discharges depending on the cavity configuration of the micro-reactors and the ignition trends for the micro-discharge arrays. Finally, we discuss the life time of micro-discharge arrays as well as the factors affecting them (cathode sputtering, thermally affected zones, etc).

Surface-engineered silicon nanocrystals

“…At this stage the industrial scalability of these processes does not represent a limiting factor. Nonetheless it should be noted that both laser-based processes and microplasma technology have demonstrated the potential for scaled-up congurations 31,109,110 to achieve large scale surface engineering as would be required for applications such as photovoltaics.…”

Kinetic modeling of the electronic response of a dielectric plasma-facing solid

“…How the fluxes are annihilated, radiatively or non-radiatively, is beyond the present model. Solving the Poisson equation( 3) together with the Boltzmann equations (23) for the four species subject to the matching conditions ( 5), ( 16), ( 17), (19), and (20) gives the species' distribution functions and eventually the density and potential profiles of the double layer across the interface. The source and the reservoir can be made self-consistent by enforcing additional conditions to fix the boundary densities n b * , n bh , n se , and n si , which depend however on what kind of collisions are included.…”

“…In particular, solid-state based integrated microdischarges [21,22,23,24] can be expected to soon reach the sub-micron range where the electron transit time τ transit e through the sheath of the discharge approaches the electron energy relaxation time τ relax * inside the solid. In this case, the electronic subsystem of the wall remains out-of-equilibrium between subsequent electron encounters from the plasma and surface parameters have to be obtained for a solid in strong electronic non-equilibrium.…”

Electron kinetics at the plasma interface

“…Characterizing charge transfer across the plasma interface by a set of (energy-and angle-dependent) surface parameters is justified as long as the scales of charge transport/relaxation inside the plasma and inside the solid are well separated. In situations, however, where they approach each other, as we expect it to occur soon in arrays of integrated microdischarges [24,25], because of the continuing miniaturization efforts in this field [26], it is no longer sufficient to treat electron deposition and extraction across the plasma interface as elementary surface collision processes. Instead it will be necessary to describe the charge transport across the interface selfconsistently with the charge dynamics on both sides of it.…”

“…Motivated primarily by the prospects of solid-based opto-electronic plasma devices [24,25,26,27], but also with an eye on dielectric barrier discharges [28,29,30], we initiated in the framework of the Transregional Collaborative Research Center SFB/TRR24 a still on-going effort to understand the charge transport, that is, the electron kinetics across the plasma interface from a microscopic point of view. Part of our work is devoted to the calculation of surface parameters (which may be also functions of energy and angle).…”