Measuring out-of-plane permittivity of dielectric thin films at millimeter-wave frequencies

Accurate permittivity data is critical for the design of next-generation microelectronics. Whether for quantum computing or advanced communications, industry needs to measure broadband, out-of-plane permittivity up to millimeter-wave frequencies. The current state-of-the-art for measuring out-of-plane permittivity of thin films involves either scanning microwave microscopy, which has limited accuracy, or a metal-insulator-metal (MIM) capacitor method, which is limited by large uncertainty at frequencies above 5 GHz. Here, I will discuss our approach to extend the MIM capacitor method to millimeter-wave frequencies. First, I will discuss how we built on the existing method to remove parasitics, increase accuracy, and extend the applicable frequency range by updating the device design. Next, I will detail synthesis and measurements of SiN, a material with well-documented permittivity that we used to validate the method. Lastly, I will discuss data from a set of dielectric thin-film materials with different microstructures and chemical compositions. These materials provide a case study for extracting out-of-plane permittivity at millimeter-wave frequencies.