Liquid Crystal Aligning Capabilities in Solution-Processed HfZrO Layers Created via Ion-Beam Irradiation

Recently, rubbing-free methods have been studied for liquid crystal (LC) alignment; layers generated via such methods have excellent electrical and optical characteristics compared with those obtained using the rubbing method. 1‐3 The rubbing method is a very simple process; however, this process leads to degradation of the surface quality of the alignment layer because of the direct contact of the rubbing machine fabric with the layer and the generation of electrostatic charges and debris between the sample and the rubbing machine fabric. 4‐6 In contrast, alternative methods based on non-contact process such as the ultraviolet (UV) photoalignment technique, 7 oblique deposition, 8 andion-beamirradiation 9‐12 inducefewsurfacedefectsof LC alignment layer compared with that fabricated using the rubbing method. Ion-beam irradiation is commonly used for both inorganic and organic materials; however, this technique is especially useful for inorganic alignment layers. Previously, our research group studied inorganic-based LC alignment layers using ion-beam irradiation; Ta2O5, 13 Al2O3, 14 and HfO2 15 were used for the LC alignment layer rather than rubbed-polyimide. ZrO2 has been studied for use in diverse applications such as gate insulators, sensors, and displays because of its high dielectric constant (∼25), large bandgap (∼5.1 eV), and low standard electrode potential (SEP) (−1.45 V). It has been reported that adding HfO2 to ZrO2 enhances the insulating characteristics of the material by reducing the amount of oxygen vacancies. Furthermore, ZrO2 and HfO2 have the same structure, are located in the same column in the periodic table, and have almost the same atomic radius; thus, their mixture causes no structural defects. 16 Conventional inorganic-based alignment layers typically require the use of sputtering equipment in a vacuum environment. 13‐15,17 In contrast, a solution-process offers the advantages of a relatively simple process, low cost, and easy composition ratio control of the multicomponent materials. 18 Especially, multicomponent materials with variousmoleratioscanbeeasilydepositedthroughtheirsimultaneous addition to the solvent under solution process. In addition, solutionprocessed ZnO has already been evaluated for use as an LC alignment layer in previous study and its performance was similar to that of ZnO deposited by sputtering. 19 In this study, we introduce solution-processed HfZrO-based LC cells created via ion-beam irradiation. The surface of the HfZrO film and optical characteristics of the LC cells for various Hf atomic mole ratios were investigated.