Investigation of brittle failure in transparent conductive oxide and permeation barrier oxide multilayers on flexible polymers

Abstract

An oxide multilayer structure—consisting of an indium zinc oxide (IZO) conductive layer, a silicon oxide (SiO x , x = 1.8) water vapor permeation barrier, and an aluminum oxide (Al 2O 3) interlayer—coated on polyethylene terephthalate (PET) is proposed as a transparent flexible substrate for display and photovoltaic applications. Vital properties of the multilayer, such as the low water vapor impermeability of the SiO x barrier and the high conductance of the IZO film, degraded considerably because of the crack formation in bend geometries, attributed to the large difference between elastic properties of the oxide films and polymers. In order to suppress the crack formation, a 10-nm-thick Al 2O 3 interlayer was sputtered on Ar ion-beam treated PET surfaces prior to a SiO x plasma-enhanced chemical vapor deposition (PECVD) process. Changes in the conductance and water vapor impermeability were investigated at different bending radii and bending cycles. It was found that the increases in resistance and water vapor transmission rate (WVTR) were significantly suppressed by the ion-beam PET pretreatment and by the sputtered Al 2O 3 interlayer. The resistance and WVTR of IZO/SiO x /Al 2O 3/PET systems could be kept low and invariable even in severely bent states by choosing the SiO x thickness properly. The IZO (135 nm)/SiO x (90 nm)/Al 2O 3 (10 nm)/PET system maintained a resistance of 3.2 × 10 − 4 Ω cm and a WVTR of < 5 × 10 − 3 g m 2 d − 1 after 1000 bending cycles at a bending radius of 35 mm.