Origin of microplasma instabilities during DC operation of silicon based microhollow cathode devices

Abstract

The failure mechanisms of micro hollow cathode discharges (MHCD) in silicon have been investigated using their I-V characteristics, high speed photography and scanning electron microscopy. Experiments were carried out in helium. We observed I-V instabilities in the form of rapid voltage decreases associated with current spikes. The current spikes can reach values more than 100 times greater than the average MHCD current. (The peaks can be more than 1 Ampere for a few 10's of nanoseconds.) These current spikes are correlated in time with 3-10 μm diameter optical flashes that occur inside the cavities. The SEM characterizations indicated that blister-like structures form on the Si surface during plasma operation. Thin Si layers detach from the surface in localized regions. We theorize that shallow helium implantation occurs and forms the 'blisters' whenever the Si is biased as the cathode. These blisters 'explode' when the helium pressure inside them becomes too large leading to the transient micro-arcs seen in both the optical emission and the I-V characteristics. We noted that blisters were never found on the metal counter electrode, even when it was biased as the cathode (and the Si as the anode). This observation led to a few suggestions for delaying the failure of Si MHCDs. One may coat the Si cathode (cavities) with blister resistant material; design the MHCD array to operate with the Si as the anode rather than as the cathode; or use a gas additive to prevent surface damage. Regarding the latter, tests using SF 6 as the gas additive successfully prevented blister formation through rapid etching. The result was an enhanced MHCD lifetime.

Characteristics of a novel nanosecond DBD microplasma reactor for flow applications

“…One of the serious problems of microplasma devices is their often short lifetime due to surface and internal damages. This is due to the frequent loss of plasma confinement due to vaporization and ablation, which cause significant surface erosion and structural failure [34,35]. Reactor lifetime is very sensitive to many parameters, e.g.…”

Direct current microhollow cathode discharges on silicon devices operating in argon and helium

“…In order to get a better understanding of the mechanism, some characterization after the first minutes of plasma operation was carried out. First, using the high-speed camera, small bright (10 μm diameter) spots appearing simultaneously with the high current spikes were evidenced [19]. Such an intensive spot is shown in figure 5(a) where an array of 16 microplasmas having a cavity geometry with a diameter of 150 μm was ignited in helium at 350 mbar.…”

“…In figure 3(b), the resulting V-I characteristic is shown with oscillations of the V-I curve following a slope corresponding to the ballast resistor (here 300 kΩ). For a lower ballast resistor, much higher intensity current peaks can be produced where typical values in the order of 1 A for current spikes could be obtained [19]. After plasma operation of about 1 min (about 6 signal periods), the device was destroyed.…”

“…Even if arrays containing 1024 microplasmas were successfully ignited, the device operation is unstable and produces many current spikes that significantly damage the microcavities and lead to device failure. The mechanism responsible for this unstable operation and short lifetime was investigated in [19]. In this paper, we discuss different possibilities to enhance the stability of microdischarges made from silicon wafers, limit the damage and increase their lifetime for currents above 1 mA.…”

On the validity of neutral gas temperature by emission spectroscopy in micro-discharges close to atmospheric pressure

“…The electrode pattern around the cavity opening is defined with lithography techniques before the plasma vapor deposition (PVD) process. Newly introduced in [20,19], a metallic layer covers the inner surface of the isotropic cavity giving the advantage of a better electrical conductivity of the plasma material interface while protecting the Si surface from ion bombardment, strong implantation and a potential oxidation of Si. The second electrode consists of a metal layer (typically Ni) formed at the back of the wafer by a PVD process.…”