We fabricated a terahertz (THz) polarization converter using a twisted nematic (TN) liquid crystal (LC) cell. Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films coated on quartz glass substrates were used as electrode layers in the TN LC cell. The PEDOT/PSS films were rubbed unidirectionally using a rayon cloth to align the nematic LC, thereby also serving as an alignment layer. The azimuthal surface anchoring strength of the PEDOT/PSS films was measured to be 5 × 10−4 J/m2 using the Néel wall method, which is similar to that of typical polymeric alignment layers. The optical constants of the PEDOT/PSS film in the THz range were also characterized using the Drude-Smith model, and the results indicated that the PEDOT/PSS films could be used both as transparent electrodes in the THz range and as alignment layers for the LC. The electro-optical properties of the fabricated TN LC cell were also investigated using a polarized visible laser and THz time-domain spectroscopic system. In particular, the transmission spectra and polarization conversion property of the TN LC cell in the THz range were theoretically analyzed based on a stratified model that considers optical anisotropy, absorption, and multiple interference. This work substantiates the advantages of TN LC cells with rubbed PEDOT/PSS films useful for THz polarization converters with electrical tunability.

Despite superior compatibility to mass-production, magnetic tunnel junction (MTJ) with MgO barrier prepared by oxidation process (MgO x ) has shown unacceptable magnetotransport properties for proper operation of spintronics devices because poor crystalline MgO x cannot properly provide a template for crystallization of amorphous CoFeB layers, thus lack of pseudo-epitaxy in overall. We report novel stack structure for MgO x -based MTJ to assure acceptable magnetotransport properties: insertion of preferred-grain-growth-promotion (PGGP) seed layer and bi-layered ferromagnetic pinned layer (bi-PL) to induce preferred grain growth in MgO x and crystallization of CoFeB layers at higher temperature annealing. Microstructure analysis confirms highly crystalline MgO x in pseudo-epitaxy with fully crystallized CoFeB via PGGP by high temperature annealing, attributed to enhanced thermal stability of bi-PL. Tunneling magnetoresistance (TMR) 132.6% at resistance-area product (RA) 1.2 mm 2 and 253% at 5.9 mm 2 from novel MTJ stack successfully satisfy specifications for spintronics devices.

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We fabricated submicron magnetic tunnel junctions (MTJs) using natural oxidation of thin Mg layers deposited by dc sputtering. The MTJs exhibited magnetoresistance (MR) ratios of up to about 150% with a low resistance-area product (RpA) of 8 Ω μm2, which are comparable to those for radio-frequency-sputtered MgO barriers. The submicron MTJs had highly variable MR and RpA values due to a high pinhole density (20 μm−2) in the barriers, whereas current-in-plane-tunneling (CIPT) measurements on the same MTJ films revealed highly reproducible MR and RpA values. This indicates that reproducible CIPT measurements do not necessarily give accurate results of MR and RpA at high pinhole densities.

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