Factors affecting the properties of highly conductive flexible ultrathin ITO films in confined large area magnetron sputtering in three dimensions

Abstract

A large area magnetron source with the strongly confined magnetic field from all direction is applied for the deposition of flexible ultrathin ITO (UT-ITO) films of thickness 30 nm at room temperature for their applications as transparent electrodes. The films show a minimum resistivity of ∼5.0 x 10-4 Ωcm and high transmittance >80% at wavelengths of 400-700 nm. Measurements and data reveal that a high plasma density, high energy flux, and a relatively low concentration of negative oxygen ions (NOIs) to the flux of positive ions (PIs) induce lower mechanical stress to the growing films, which enables a lower resistivity and superior crystallinity with the smooth surface. The capability of the magnetron source and the characteristic plasma properties are studied in light of the resulting film properties. The considerably lower resistivity with higher carrier concentration and mobility of the UT-ITO films prepared at a high power density of 3 W/cm2 and a low O2 gas flow can be attributed to the growth of crystallized UT-ITO films, resulting in the combination of the oxygen vacancy and substitution of Sn4+ to In3+ site through the deposition of a high energy flux and a low flux ratio of NOIs to PIs.

Overall aspect for designing magnetron sputtering plasma sources and their applications in the deposition of ITO films

“…223 Apart from ionizing the sputtered atoms and controlling the plasma properties, the ion energy at the substrate can be controlled with the help of biasing the substrate and a directional deposition or collimation of these ions with the plasma sheath adjacent to the substrate surface. 104,130,189 Self-ion bombardment of the growing film causes it to crystallize more. 224 However, there are various issues involved with the MS.…”

“…The data, as presented in Table I, are collected from various works of literature. 99,[101][102][103][104][105][106][107][108]113,129,[238][239][240] Figure 3(b) represents a dual MS (DMS) 102,113 system, which utilizes two PMS systems. The targets are aligned in an inclined position to create a confined magnetic field.…”

“…99 The presence of a magnetic field near the substrate enables a high-density plasma near the film-growing substrate (Table I). [99][100][101][102][103][104][105][106][107][108][109]…”

“…Interestingly, the compressive stress in the films prepared by the FTMS was substantially lower than that of CMS films. 244 Sahu et al 104 reported the dependency of deposition rate and electrical properties (resistivity, mobility, and carrier concentration) on the discharge current.…”

“…Based on the geometry and orientation of the cathodes, the design of MS devices is known as conventional MS (CMS) or planar MS, 99,108 dual MS (DMS), 102,113 facing target MS (FTMS), 105 cylindrical MS (CYMS), 107 and three-dimensional MS (3DMS). [99][100][101]103,104,106,107 Furthermore, MS devices utilize a closed magnetic field geometry. The MS devices are divided into balanced and unbalanced configurations based on the formation of magnetic fields.…”