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Twisted Nematic Liquid-Crystal-Based Terahertz Phase Shifter using Pristine PEDOT: PSSTransparent Conducting Electrodes

Authors
  • sahoo, anup kumar
  • yang, chan-shan
  • yen, chun-ling
  • lin, hung-chun
  • wang, yu-jen
  • lin, yi-hsin
  • wada, osamu
  • pan, ci-ling
Publication Date
Feb 21, 2019
Source
MDPI
Keywords
Language
English
License
Green
External links

Abstract

For this study, we demonstrated three different types of twisted nematic (TN) liquid crystal (LC) terahertz (THz) phase shifters using pristine poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) thin films as transparent conducting electrodes (TCEs). The transmittance of spin-coated pristine PEDOT: PSS thin film was as high as 92% in the frequency range of 0.2&ndash / 1.2 THz. This is among the highest reported. Several TN-LC cells were constructed in a comparative study, which confirmed the reliability of pristine PEDOT: PSS as a TCE layer for THz phase shifter applications. The highest phase shift, required root-mean-square (RMS) driving voltage, and threshold voltage achieved by devices tested were 95.2&deg / at 1 THz, 7.2 VRMS, and 0.5 VRMS, respectively. The thickness of the LC layer for the phase shifter was 250 &micro / m, approximately half as thick as previous designs. In addition, the pristine PEDOT: PSS-based TN-LC phase shifter exhibited a figure-of-merit (FOM) value of approximately 6.65 degree&middot / dB&minus / 1&middot / V&minus / 1. This compared favorably with previously reported homogeneously aligned phase shifters with an FOM of 2.19 degree&middot / dB&minus / 1&middot / V&minus / 1. Our results indicated that a twisted nematic LC cell with pristine PEDOT: PSS thin films as electrodes is a good combination for a THz phase shifter and wave plates as well as other LC-based THz devices.

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