Mechanical properties of amorphous indium–gallium–zinc oxide thin films on compliant substrates for flexible optoelectronic devices

Abstract

Amorphous indium-gallium-zinc-oxide (a-IGZO) thin films were deposited using RF magnetron sputtering on polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) flexible substrates and their mechanical flexibility investigated using uniaxial tensile and buckling tests coupled with in situ optical microscopy. The uniaxial fragmentation test demonstrated that the crack onset strain of the IGZO/PEN was ~2.9%, which is slightly higher than that of IGZO/PET. Also, uniaxial tensile crack density analysis suggests that the saturated crack spacing of the film is strongly dependent on the mechanical properties of the underlying polymer substrate. Buckling test results suggest that the crack onset strain (equal to ~ 1.2%, of the IGZO/polymer samples flexed in compression to ~ 5.7 mm concave radius of curvature) is higher than that of the samples flexed with the film being in tension (convex bending) regardless whether the substrate is PEN or PET. The saturated crack density of a-IGZO film under the compression buckling mode is smaller than that of the film under the tensile buckling mode. This could be attributed to the fact that the tensile stress encouraged this crack formation originating from surface defects in the coating. It could also be due to the buckling delamination of the thin coating from the substrate at a lower strain than that at which a crack initiates during flexing in compression. These results provide useful information on the mechanical reliability of a-IGZO films for the development of flexible electronics.

Flexible and stretchable metal oxide nanofiber networks for multimodal and monolithically integrated wearable electronics

“…To understand this aspect quantitatively, FEA simulations were next carried out. Figure 3d shows the computed relationship of the angle between a fiber long axis vs. the tensional direction (α) and strain (ɛ) exerted on the substrate to achieve a 1.1-GPa stress on the fiber, by assuming the IGZO fiber forms a crack at 0.8% strain 44,45 . Clearly ɛ increases polynominally with α.…”

“…A convergence test of the mesh size was performed to ensure accuracy, where the minimal element size was 1/20 of the diameter of the fiber. The elastic modulus (E) and Poisson's ratio (ν) of inorganic fibers are 110 GPa and 0.34, respectively 44,45 . The crack strain is taken as 0.8%.…”

Flexible Photonic Sensors: Investigation of an Approach Based on Ratiometric Power in Few-Mode Waveguides for Bending Measurement

“…The obtained results show that this novel approach could be exploited for the development of innovative optical sensors, allowing the simultaneous temperature and curvature monitoring, or, more in general, multiparameter monitoring. Progress in this domain is expected to influence fields including soft robotics, medicine, and the monitoring of engineered structures [4], [16]- [18], [22], [23].…”

Versatile Solution‐Processed Organic–Inorganic Hybrid Superlattices for Ultraflexible and Transparent High‐Performance Optoelectronic Devices

“…Although crystalline metal oxides typically show superior optoelectronic performance, owing to their wide optical bandgaps and high electrical conductivities, they are vulnerable to mechanical stress, which hinders their use in the emerging flexible optoelectronic applications. [ 1d,3a,5 ] Amorphous metal oxides have the potential to address the problem of mechanical deformation; [ 6 ] however, these oxides have poor electrical properties because of their limited mechanical stability. [ 7 ] When very thin amorphous IGZO was used for flexible electronics, [ 8 ] the devices generally demonstrated moderate electrical performance with a mobility of ≈5 cm 2 V –1 s –1 and limited mechanical stability after 1000 cycles of bending with a radius of 5–10 mm.…”