New method for accurate transmission line characterization on low-loss silicon substrate at millimiter-wave frequencies
(2019) The Microwave Technology and Techniques Workshop 2019 — Location: ESA-ESTEC in Noordwijk (The Netherlands) (2.April.2019)
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- Abstract
- The technological downscaling has improved the figures of merit of silicon-based technology, enabling a progressive replacement of conventional technologies at millimeter wave frequencies. The calibration and de-embedding techniques that involve on-chip transmission lines (TLs) were traditionally developed for non-conductive substrates. They need to be revised when applying them to silicon-based substrates at millimeter-wave frequencies. The importance of accurate on-wafer probing pad de-embedding is twofold. First, their de-embedding requires the use of many dummy structures during FET characterization at high frequency (above 40 to 70 GHz depending on the device dimension), unless an accurate on-wafer calibration scheme is performed [1]. Second, different flavors of substrate are used in silicon-based technology. Their characteristics are not necessarily known after an industrial process. On-chip TLs provide a cheap and convenient method to extract those characteristics [2],[3], as long as the probing pads are accurately de-embedded. A TL is characterized by two parameters: its propagation constant (γ) and its characteristic impedance (Zc), which enable us to calculate the lineic RLGC parameters. While the propagation constant is accurately extracted over a wide frequency range with the multiline TRL (mTRL) algorithm [4], it is very challenging to extract Zc of a TL that is mounted on a substrate of unknown conductive losses. This paper reviews the most popular methods [5]-[13] to characterize TLs and presents a new method to extract Zc using only the measurements of lines of different lengths. The different methods are compared on the measurement of a coplanar waveguide (CPW) line. An explanation for the origin of the incorrect extraction of the imaginary part of Zc is determined based on a simulation-based analysis comparing the different methods. It is shown that the assumption of symmetric transmission elements is at fault.
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Citations
Nyssens, L., Rack, M., & Raskin, J.-P. (2019). New method for accurate transmission line characterization on low-loss silicon substrate at millimiter-wave frequencies. The Microwave Technology and Techniques Workshop 2019, ESA-ESTEC in Noordwijk (The Netherlands). https://hdl.handle.net/2078.5/228069