On-Wafer Microfabricated Test Structures for Characterizing RF Breakdown in Narrow Gaps

Plasmas formed in microscale gaps at DC and plasmas formed at radiofrequency (RF) both deviate in behavior compared to the classical Paschen curve, requiring lower voltage to achieve breakdown due to unique processes and dynamics, such as field emission and controlled rates of electron/ion interactions. Both regimes have been investigated independently, using high precision electrode positioning systems for microscale gaps or large, bulky emitters for RF. However, no comprehensive study of the synergistic phenomenon between the two exists. The behavior in such a combined system has the potential to reach sub-10 V breakdown, which combined with the unique electrical properties of microscale plasmas could enable a new class of RF switches, limiters and tuners.This work describes the design and fabrication of novel on-wafer microplasma devices with gaps as small as 100 nm to be operated at GHz frequencies. We used a dual-sacrificial layer process to create devices with microplasma gaps integrated into RF compatible 50 Ω coplanar waveguide transmission lines, which will allow this coupled behaviour to be studied for the first time. These devices are modelled using conventional RF simulations as well as the Sandia code, EMPIRE, which is capable of modelling the breakdown and formation of plasma in microscale gaps driven by high frequencies. Synchronous evaluation of the modelled electrical and breakdown behaviour is used to define device structures, predict behaviour and corroborate results. We further report preliminary independent testing of the microscale gap and RF behaviour. DC testing shows modified-Paschen curve behaviour for plasma gaps at and below four microns, demonstrating decreased breakdown voltage with reduced gap size. Additionally, preliminary S-parameter measurements of as-prepared and connectorized devices have elucidated RF device behaviour. Together, these results provide baseline data that enables future experiments as well as discussion of projected performance and applications for these unique devices.