Dynamics of High-Speed Electrical Tree Growth in Electron-Irradiated Polymer

We present the results from an experiment to image dielectric breakdown sequences in electron-irradiated polymethyl methacrylate. While dielectrics are integral to the functioning of modern society, there remain many open questions regarding the failure mechanisms of these materials when exposed to charged particle radiation, such as in space environments. Dielectric materials can fail catastrophically in these environments through an electrostatic discharge (ESD) event following the charging of the material’s bulk. During the ESD event, the breakdown of the material coincides with a rapid evacuation of the implanted charged particles, leaving behind permanent dendritic structures known as electrical trees. The images we acquired with nanosecond temporal resolution of the formation of these electrical trees revealed the propagation dynamics of the breakdown channels, including two distinct modes. We measured the propagation speed of branch-type channels and found it to exceed 10⁶ m/s. We measured the channel formation speed of a previously unclassified mode of breakdown, called the ivy-type, and found it to exceed 10⁷ m/s—almost 4% the speed of light in the material. The ivy-type mode sheds light on gaps in existing dielectric breakdown models, which will be outlined in this presentation.