Twisted nematic liquid-crystal-based terahertz phase shifter using pristine PEDOT: PSS transparent conducting electrodes

Anup Kumar Sahoo, Chan Shan Yang, Chun Ling Yen, Hung Chun Lin, Yu Jen Wang, Yi-Hsin Lin, Osamu Wada, Ci Ling Pan*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

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 0.2-1.2 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° at 1 THz, 7.2 V RMS , and 0.5 V RMS , respectively. The thickness of the LC layer for the phase shifter was 250 μm, 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·dB·V -1 . This compared favorably with previously reported homogeneously aligned phase shifters with an FOM of 2.19 degree·dB -1 ·V -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.

Original languageEnglish
Article number761
JournalApplied Sciences (Switzerland)
Volume9
Issue number4
DOIs
StatePublished - 21 Feb 2019

Keywords

  • LC
  • Liquid crystals
  • PEDOT: PSS
  • Phase shifter
  • TCE
  • THz
  • TN
  • Terahertz
  • Transparent conducting electrode
  • Twisted nematic

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