Abstract-High-Transmittance 2π Electrically Tunable Terahertz Phase Shifter with CMOS-Compatible Driving Voltage Enabled by Liquid Crystals

Chan-Shan Yang  Chun Kuo, Po-Han Chen, Wei-Ta Wu, Ru-Pin Pan, Peichen Yu, Ci-Ling Pan,

Figure 1. (a) Schematic diagrams of three different configurations of indium–tin–oxide-nanowhiskers (ITO-NWhs)-based phase shifters, type A, B, and C, respectively. The cross-sectional images of (b) the substrate of ITO NWhs, (c) ITO NWhs coated with polyimide, and (d) ITO NWhs treated with the rubbing process.

https://www.mdpi.com/2076-3417/9/2/271/htm

We have investigated tunable terahertz (THz) phase shifters that are based on a sandwiched liquid crystal (LC) cell with indium–tin–oxide (ITO) nanowhiskers (NWhs) as transparent electrodes. More than 360° of phase shift at 1.0 THz was achieved at a driving voltage as low as ~2.6 V (rms). This is approximately 40 times smaller than that reported in previous works using an electrically tuned LC device. Significance of the NWhs in reducing the required voltage is demonstrated. Overall transmittance of the device is as high as 30%, which is accountable by absorption losses of ITO NWhs, quartz substrate and LC. Experimental results are in good agreement with a theoretical formulism while taking into account super-thick LC cells (~1 mm) and pretilt angles. We also propose and demonstrate a novel THz technique for measuring pretilt angles of liquid crystals.

Abstract-Voltage-controlled liquid-crystal terahertz phase shifter with indium–tin–oxide nanowhiskers as transparent electrodes

Chan-Shan Yang, Tsung-Ta Tang, Po-Han Chen, Ru-Pin Pan, Peichen Yu, and Ci-Ling Pan  »View Author Affiliations

Optics Letters, Vol. 39, Issue 8, pp. 2511-2513 (2014)
http://dx.doi.org/10.1364/OL.39.002511

http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-39-8-2511

Indium–tin–oxide nanowhiskers were employed as transparent electrodes in a liquid-crystal terahertz phase shifter. Transmittance of the device was as high as ∼75%. Phase shift exceeding π/2 at 1.0 THz is achieved in a ∼500  μm-thick cell. The driving voltage required for the device operating as a quarter-wave plate was as low as 17.68 V (rms), an improvement of nearly an order of magnitude over previous work.

© 2014 Optical Society of America

Abstract-Liquid crystal terahertz phase shifters with functional indium-tin-oxide nanostructures for biasing and alignment

Chan-Shan Yang^1,2, Tsung-Ta Tang³, Ru-Pin Pan⁴, Peichen Yu⁵ and Ci-Ling Pan^1,6,a)

1 Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
2 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3 Taiwan Semiconductor Manufacturing Company, Hsinchu, Taiwan
4 Department of Electrophysics, National Chiao Tung University, Hsinchu 30078, Taiwan
5 Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
6 Frontier Research Center on Fundamental and Applied Science of Matters, Hsinchu 30013, Taiwan
a) Author to whom correspondence should be addressed. Electronic mail: clpan@phys.nthu.edu.tw
Appl. Phys. Lett. 104, 141106 (2014); http://dx.doi.org/10.1063/1.4871255

Indium Tin Oxide (ITO) nanowhiskers (NWhs) obliquely evaporated by electron-beam glancing-angle deposition can serve simultaneously as transparent electrodes and alignment layer forliquid crystal (LC) devices in the terahertz (THz) frequency range. To demonstrate, we constructed a THz LC phase shifter with ITO NWhs. Phase shift exceeding π/2 at 1.0 THz was achieved in a ∼517 μm-thick cell. The phase shifter exhibits high transmittance (∼78%). The driving voltage required for quarter-wave operation is as low as 5.66 V (rms), compatible with complementary metal-oxide-semiconductor (CMOS) and thin-film transistor (TFT) technologies.

Abstract-Realization of Metal-Insulator Transition and Oxidation in Silver Nanowire Percolating Networks by Terahertz Reflection Spectroscopy

Yao-Jiun Tsai,  Chi-Ying Chang, Yi-Chun Lai, Peichen Yu,  Hyeyoung Ahn
http://pubs.acs.org/doi/abs/10.1021/am404717j

Metal nanowires (NWs) enable versatile applications in printed electronics and optoelectronics by serving as thin and flexible transparent electrodes. The performance of metal NWs as thin electrodes is highly correlated to the connectivity of NW meshes. Percolation threshold of metal NW films corresponds to the minimum density of NWs to form the transparent, yet conductive metal NW networks. Here, we determine the percolation threshold of silver NW (AgNW) networks by using morphological analysis terahertz (THz) reflection spectroscopy. From the divergent behavior of carrier scattering time and the increase of carrier backscattering factor, the critical NW density at which crossover from Drude to non-Drude behavior of THz conductivity occurs can be unambiguously determined for AgNW thin films. Furthermore, the natural oxidation of AgNWs which causes the gradual reduction of the connectivity of AgNW network is also realized by the THz spectroscopy. The selective oxidation of NW-to-NW junctions weakens the ohmic contact and for AgNWs near a critical density, it can even lead to metal-insulator transition. The presented results offer invaluable information to accelerate the deployment of metal nanowires for next-generation electronics and optoelectronics on flexible substrates.