Electrical Breakdown in Gases with Electrode Gap at the Nanometer Scale

Electrical breakdown in gases is a critical aspect for applications relying on electrical insulation such as circuit breakers or contactors. The voltage breakdown (VK) can be estimated in a reasonable order using the Paschen’s law1. Theoretically based on ideal assumptions ‒e.g. perfectly uniform electric field, infinitely large electrode size, …‒ this analytical approach has shown remarkable capability to predict VK in an innumerable quantity of systems. Centered around the product pressure times inter-electrode distance (p·d), the Paschen’s law scales a large pressure range coupled with the gap distance which makes it very convenient to use. The robustness of the Paschen’s law to predict consistent values of VK clearly fails at gap distances shorter than a micrometer at atmospheric pressure. Many studies have brought experimental2, theoretical3 and simulation4 evidences of such limitations which seriously questions the insulation properties of gases at short distances.

This study focuses on the experimental investigation of VK in very short electrode gap ranging from 100 nm to 1 µm. The  system consist on a silicon plane coated with gold or aluminum and connected to the ground. The anode is a sharp  tungsten needle of 10 µm or 20 µm radius of curvature mounted on a piezo-transductor. The needle is coated with gold. Conventionally, air gas is used at atmospheric pressure. The experiments are realized in ambient conditions to compared with data from the literature and in a controlled chamber. The later is used to set the pressure which will be varied from 10-4 mbar to 3.0 bar and the purity of the gas. A specific attention is paid to the control of the humidity which is a parameter investigated in this study. The evolution of VK depending on the electrode distance evidences a clear deviation from the prediction of the Paschen’s law. In some conditions, VK values were found below 30V and open new opportunities in industrial applications.