Novel continuously tunable and miniaturized passive "slow-wave" phase shifters with fast response time for millimeter wave applications based on a combined Liquid Crystal (LC) and Nanowire-filled Membrane (NaM) technology

• Applicants: Professor Dr.-Ing. Rolf Jakoby; Professor Dr.-Ing. Holger Maune
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2016 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 314460176

• Final Report Year: 2018

Final Report Abstract

Within this project, the LC characterization at 60 GHz was extensively studied and a reliable setup based on higher order modes was established. The slow-wave effect of the LC-NaM phase shifter was comprehensively studied, hence, the line length could be reduced by a factor of 1.5 to 2.0. Moreover, with the LC-NaM concept it was further possible to reduce the LC cavity height by a factor of 3 to 5, while keeping the line impedance at 50 Ω. The critical switch-off response time of the LC-NaM phase shifter of 𝜏off = 1.3 s is far above our goal of 30 ms, because of technological challenges, which could not be all solved within the project. For example, processing of the polyimide film turned out to be incompatible with the SU-8 process for the cavity walls. But, this polyimide film is crucial for strong surface anchoring forces, required for fast re-orientation of the LC. The FoM of 37°/dB is better than for SiGe, GaAs or BST passive phase shifters, but worse than for MEMS and definitely below our goal of 70°/dB. The reasons for the lower FoM are manifold, mainly by the higher dielectric loss of the NaM than expected. Due to this and the missing polyimide layer, we intentionally did not use the best performing LC mixture (highest anisotropy accompanied with much lower dielectric loss – GT5- 28004), because of limited availability. Despite we could not reach all our project goals, the LC-NaM concept is feasible to realize miniaturized phase shifters. The technological challenges within this project took more time than planned and some of them could not be solved yet. The working demonstrator was finished in M20, hence, measurements were primarily focused on basic parameters as presented above. Further planned characterizations, IP3 and T-dependent measurements, were prepared but not conducted by the end of the project. These measurements are postponed until the above-mentioned technological issues are sufficiently solved. These challenges will be addressed in a new PhD project, started in August 2018.

Publications

• "Miniaturized Liquid Crystal Slow Wave Phase Shifter Based on Nanowire Filled Membranes," in IEEE Microwave and Wireless Components Letters, vol. 28, no. 8, pp. 681-683, Aug. 2018
  M. Jost, J. S. K. Gautam, L. G. Gomes, R. Reese, E. Polat, M. Nickel, J. M. Pinheiro, A. L. C. Serrano, H. Maune, G. P. Rehder, P. Ferrari, and R. Jakoby
  
• Liquid Crystal Mixed Beam-Switching and Beam-Steering Network in Hybrid Metallic and Dielectric Waveguide Technology, Shaker Verlag, 2018, ISBN: 978-3-8440-6042-3
  M. Jost