Effect of Substrate Bias on the Structural and Electrical Properties of Sputtered Mo Thin Films on Flexible Substrates

Abstract

The metal molybdenum (Mo) thin films deposited on flexible substrates can act as the contact electrode of flexible Cu(In,Ga)Se2 or Cu2ZnSn(S,Se)4 solar cells. In this work, in order to enhance the structural and electrical characteristics of flexible Mo thin films, a negative substrate bias was applied during the direct current sputtering of Mo thin films. The flexible substrates used for growing the Mo films were stainless steel foils and polyimides. The characteristics of Mo thin films were studied by x-ray diffraction and sheet resistance measurements. The measured results reveal that an optimal value of negative substrate bias can be found for improving the electrical and structural characteristics of Mo thin films on flexible substrates. The minimum sheet resistances of Mo thin films are 2.50 Ω/sq and 2.73 Ω/sq for the stainless steel foil and polyimide substrates, respectively.

Negative substrate bias induced modifications of the physical properties of DC sputter deposited nano-crystalline Mo thin films

“…The room temperature sheet resistance of the films was found to increase from 2.5 /□ to 7.2 /□ at -50 V which subsequently decreases to 4.6 /□ at -150 V bias. The sheet resistance values of our Mo thin films compares well with the reported values [17,23]. The room temperature resistivity () of the films has been estimated using the sheet resistance and film thickness.…”

“…al. [17]. The substrate bias induced coalescence of the nano-crystallites may have an impact on the sheet resistance and the RMS surface roughness of the films.…”

“…The aim was also, to produce nano-crystalline Mo films with low sheet resistance, low RMS roughness and good adhesion with small tensile stress which can be used in place of graded Mo back contacts deposited at varying Ar pressures [6]. The negative bias on substrate is known to significantly alter the physical properties of the films [17,18]. There are only a few reports on the use of substrate bias for modification of the morphological, transport and superconducting properties of particularly the nano-crystalline Mo films [19,20].…”

“…The marginal effect of substrate bias on the grain size of Mo films has already been reported by Xu et. al [17]…”