Measuring Out-of-Plane Permittivity of Thin Films to Millimeter Wave Frequencies

Published

April 22, 2025

Author(s)

Florian Bergmann, Meagan Papac, Benjamin Jamroz, Nicholas Jungwirth, Bryan Bosworth, Anna Osella, Tomasz Karpisz, Lucas Enright, Eric Marksz, Angela Stelson, Christian Long, Nathan Orloff, Robert Jones

Abstract

Modern microchips utilize multilayer stack-ups with many interstitial layers of dielectrics. Optimizing device performance and maximizing yield requires precise measurements of the out-of-plane permittivity of these dielectric layers. At the same time, high-performance microchips are pushing operating frequencies into the millimeter-wave range, requiring precise materials property knowledge at these frequencies to perform as intended. With this context, one outstanding challenge is to accurately measure the out-of-plane permittivity of thin films. Unfortunately, the conventional method to extract this property, the metal-insulator-metal (MIM) capacitor technique, produces inconsistent and therefore unreliable material data for frequencies above a few gigahertz. To address these inconsistencies, we designed an experiment with on-wafer devices of varying topology and varying geometry. We chose to study silicon nitride for this experiment because it is a ubiquitous dielectric in microchips, widely accepted as approximately dispersionless, and available with established processes in our cleanroom. Our experiment resulted in an out-of-plane permittivity of thin film silicon nitride of εr=7.0 ± 0.1 and a loss tangent of tanδ<0.03 up to 90 GHz. Our key findings about improving on-wafer calibrations and modeling of the MIM devices will help material scientists and microchip designers obtain reliable permittivity data on thin films at millimeter wave frequencies.

Citation

IEEE Transactions on Microwave Theory and Techniques

Pub Type

Journals

Download Paper

https://doi.org/10.1109/TMTT.2025.3558477

Local Download

Keywords

Microwave, mmWave, Wafer, Thin film, Permittivity, MIM

Citation

Bergmann, F. , Papac, M. , Jamroz, B. , Jungwirth, N. , Bosworth, B. , Osella, A. , Karpisz, T. , Enright, L. , Marksz, E. , Stelson, A. , Long, C. , Orloff, N. and Jones, R. (2025), Measuring Out-of-Plane Permittivity of Thin Films to Millimeter Wave Frequencies, IEEE Transactions on Microwave Theory and Techniques, [online], https://doi.org/10.1109/TMTT.2025.3558477, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958735 (Accessed June 15, 2025)