60 GHz Optimised Nickel-free Gold-plated Enclosed Coplanar Waveguide Liquid Crystal Phase Shifter

Abstract

A novel nickel-free gold-plated enclosed coplanar waveguide is experimentally demonstrated for a liquid crystal tunable delay line phase shifter at 60 GHz. By numerical investigations, we find that conventional surface impedance model (without meshing inside metals) fails to accurately characterise the effect of gold-plating thickness on conductor loss, especially when the plating thickness is smaller than 4 times of the gold's skin depth. To address this, adaptive meshing inside metals is performed for accurate modelling of the device. The gold-plating thickness is then experimentally optimised and tailored for the liquid crystal-based device-making procedures, i.e. taking into account the accelerated copper migration into gold problem during the alignment agent baking process at 200˚C. Measurement results of assembled phase shifters at 60 GHz verify that a direct gold plating of 2µm on Cu can reduce the insertion loss by 1.79 dB and 2.85 dB as compared with that with a thinner plating of 50 nm, and no plating, respectively. The maximum insertion loss of-2.996 dB demonstrated at 60 GHz for the 0-π phase shifter delivers a figure-of-merit of 60˚/dB, an improvement of 42˚/dB as compared with up-to-date literature.

Liquid Crystal-Filled 60 GHz Coaxially Structured Phase Shifter Design and Simulation with Enhanced Figure of Merit by Novel Permittivity-Dependent Impedance Matching

“…Notably, with the proposed coaxial approach, the conventional LC-filled MW devices fabrication and assembling process (which is time-consuming and cost-prohibitive in materials and clean-room facilities) can be dramatically simplified. To be more specific, the following conventionally key steps can all be eliminated, including the spin-coating of polyimide (PI) as an alignment agent (wherein spin-coater and PI are required), the 200 • C baking of the PI layer for solvent evaporation (time consuming and prone to tarnishing [41] of the plated gold), and the mechanical rubbing of the coated PI (wherein high-precision roller and pressure control systems are required). The removal of the above steps not only significantly speeds up the prototyping, reducing costs (materials and facilities), but also mitigates the vulnerabilities of performance degradation due to fabrication errors and manufacturing tolerances issues, hence improving yields.…”

Electroplated waveguides to enhance DNP and EPR spectra of silicon and diamond particles

“…Mode converters can also be utilized to exploit propagation modes that experience less attenuation through certain waveguide geometries (Yu and Chang, 2005). Electroplating the inside of the waveguide is another common solution to reduce transmission losses and subsequently improve EPR sensitivity (Albannay et al, 2019;Li, 2020). In our current DNP polarizer setup (Jähnig, 2018), we found electroplating to be the simplest solution, due to ease of adoption into the existing probe design (Jähnig et al, 2017).…”

Electroplated waveguides to enhance DNP and EPR spectra of silicon and diamond particles

“…Mode converters can also be utilized to exploit propagation modes that experience less attenuation through certain waveguide geometries (Yu and Chang, 2005). Electroplating the inside of the waveguide is another common solution to reduce transmission losses and subsequently improve EPR sensitivity (Albannay et al, 2019;Li, 2020). In our current DNP polarizer setup (Jähnig, 2018) we found this to be the simplest solution, due to ease of adoption into the existing probe design (Jähnig et al, 2017).…”