UTMF-Based Transparent Electrode Incorporating a Metallic Grid

Abstract

Among all the alternatives to ITO, UTMFs can overcome the high cost of raw materials and can be grown using a simple processing [1–4]. The electrical resistivity (ρ) of UTMFs can be lower than that of TCOs. However, if one wants to achieve high optical transmission, the thickness of UTMFs should be limited to several nanometers, at the expense of sheet resistance (R_S). This implies that the R_S, which is given by ρ/t, of UTMFs is relatively high compared to TCOs [5]. For example the R_S of 2 and 10 nm thick Ni films are in the range of 1000 and 50 Ω/sq, respectively, while R_S of 100 nm ITO film is in the 15–20 Ω/sq range. If the thickness of Ni is further increased, lower R_S values can be achieved at the expense of the optical transmission. In fact 40 nm films can achieve R_S values of about 5 Ω/sq but it becomes opaque. The larger the R_S value of a TE the higher the Ohmic (resistive) loss in the devices using the TE, thus the larger the power (energy) loss, consequently the probability that the device fails due to thermal loading in the TE area increases [6, 7]. Ohmic losses become critical for high current devices (e.g. laser sources and solar cells) while they are less critical for low current devices (e.g. integrated modulators and displays, which rely on capacitive charging) (Fig 3.1).