Modeling of microdischarge devices: Pyramidal structures

Abstract

Microdischarge (MD) devices are plasma sources typically operating at 100s Torr to atmospheric pressure with dimensions of 10s–100s μm. Their design in based on $\mathrm{pd}$ $(\mathrm{pressure}\times \mathrm{characteristic}$ dimension) scaling; smaller dimensions are enabled by higher operating pressures with typical devices operating with $\text{pd=1–10\hspace{0.17em}}\mathrm{Torr} \mathrm{cm}.$ MD devices have exhibited behavior that resemble both Townsend and hollow-cathode discharges, with bulk and beam electrons providing the dominant excitation, respectively. In this article, results from a two-dimensional computational study of MD devices operating in neon using a pyramidal cathode structure are discussed. Pressures of 400–1000 Torr and device dimensions of 15–40 μm are investigated. The onset of behavior resembling negative glow discharges with decreasing pressure correlates with an extension of cathode fall accelerated beam electrons into the bulk plasma. For constant applied voltage, peak electron densities increase with increasing pressure as the beam electrons are slowed in more confined regions. The MD devices typically require higher applied voltages to operate at lower pressures, and so resemble discharges obeying Paschen’s curve for breakdown. MD devices having similar magnitudes and spatial distributions of plasma and excited state densities can be obtained to dimensions of $\text{<15\hspace{0.17em}μ}\mathrm{m}$ by keeping $\mathrm{pd}$ and current density constant, and having a cathode fall thickness small compared to the characteristic dimension.