Short communicationControl of liquid crystal alignment by deposition of silicon oxide thin film
Introduction
Amorphous SiOx (a-SiOx) is a useful material for various industrial applications, such as protective layers, coal-like modifications, semiconductor technology, and heat shielding [1]. SiOx layers play a key role in determining the performance of electro-optical devices. In particular, a-SiOx layers deposited on indium-tin-oxide (ITO)-coated glass substrates have been incorporated into liquid crystal displays, plasma display panels, thermal control windows, solar cells, etc. Studies on the Si-SiO2 interface were reported in many previous publications [2], [3], [4], [5]. Despite many intensive studies, the dependence of SiOx film surface characteristics on the deposition temperature and the target-to-substrate distance has not been studied widely.
In this paper, the radio-frequency (rf) magnetron sputtering technique, which is very common and versatile, is used to study the effects of deposition temperature and target-to-substrate distance on the liquid crystal alignment of deposited a-SiOx thin film layers. We studied the dependence of SiOx film surface characteristics on the deposition temperature and the target-to-substrate distance using X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) apparatuses.
Section snippets
Experiments
We deposited a thin film of a-SiOx on ITO-coated glass substrates with an rf magnetron sputtering system at a frequency of 13.56 MHz. Silicon oxide molecules were sputtered from a circular polycrystalline SiO2 target with the diameter of 5 cm. Argon plasma was applied at an rf power of 100 W. The applied magnetic field of the magnetron was approximately 6.0 × 10− 2 T at the target surface. The base pressure of the deposition chamber was around 10− 3 Pa, while the working process pressure was around
Results and discussion
Dependence of the growth speed of the a-SiOx film layer on the deposition temperature, which was measured using cross-sectional scanning electron microscope images, is shown in Fig. 2. For d = 10 cm, the growth speed was decreased from 1.4 nm/min to 0.7 nm/min as the deposition temperature increased from 30 °C to 300 °C. For d = 8 cm, the growth speed decreased from 2.1 nm/min to 1.0 nm/min as the deposition temperature increased from 30 °C to 300 °C.
Surface morphologies of the SiOx film as a
Conclusions
We investigated dependence of the liquid crystal alignment in a-SiOx film on the deposition temperature and the target-to-substrate distance by using AFM, XRD, XPS, and a UV/VIS/NIR spectrometer. We found from AFM measurements that the RMS roughness of a-SiOx is not connected with liquid crystal alignment. Instead, whether liquid crystals can be aligned vertically or homogeneously on a-SiOx film can be predicted simply by measuring XRD data, XPS data, or the change in the optical transmittance.
Acknowledgements
This work was partly supported by the Next-Generation Growth Engine Project of the Ministry of Commerce, Industry and Energy of the Korean Government.
References (13)
- et al.
Mater. Sci. Rep.
(1986) - et al.
Appl. Surf. Sci.
(2004) - et al.
J. Non-Cryst. Solids
(2006) - et al.
Mater. Sci. Eng., B
(2000) - et al.
Nature
(1996) - et al.
Phys. Rev., B
(1988)
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Present address: Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, CA 90095, USA.