Mechanical integrity of thin inorganic coatings on polymer substrates under quasi-static, thermal and fatigue loadings

Abstract

The interplay between residual stress state, cohesive and adhesive properties of coatings on substrates is reviewed in this article. Attention is paid to thin inorganic coatings on polymers, characterized by a very high hygro-thermo-mechanical contrast between the brittle and stiff coating and the compliant and soft substrate. An approach to determine the intrinsic, thermal and hygroscopic contributions to the coating residual stress is detailed. The critical strain for coating failure, coating toughness and coating/substrate interface shear strength are derived from the analysis of progressive coating cracking under strain. Electrofragmentation and electro-fatigue tests in situ in a microscope are described. These methods enable reproducing the thermo-mechanical loads present during processing and service life, hence identifying and modeling the critical conditions for failure. Several case studies relevant to food and pharmaceutical packaging, flexible electronics and thin film photovoltaic devices are discussed to illustrate the benefits and limits of the present methods and models.

The role of the gradient film properties in silica moisture barriers synthesized in a roll‐to‐roll atmospheric pressure plasma enhanced CVD reactor

“…The stress relaxation may be induced by the fissuring of the layer as portrayed in the AFM micrographs of Figure . Similarly the wavy structure between positions 2 and 9 mm can be an indication of stress relaxation as the film is very loosely adhered to the polymeric substrate which can lead to the formation of a buckled structure …”

Subcritical crack growth in SiNx thin-film barriers studied by electro-mechanical two-point bending

“…In order to plot them both along the same time scale, dynamic failure times were converted in expected static equivalents, according to Eq. (11). By the combination of dynamic and static failure, failure times over a much larger range, more than four decades, are realized.…”

“…The cracking phenomenon is influenced by many factors, such as defect size and location, 5,7-9 internal stress, 10,11 layer thickness, 12,13 and loading type. 11,14 It is important to indicate that crack extension in barrier layers is greatly affected by environmental conditions, due to the fact that the brittle inorganic material is susceptible to environmentally assisted subcritical crack growth. 15 In addition, the considerable hydro-thermal-mechanical contrast between the inorganic barrier layer and the polymer substrate also contributes to the cracking.…”

Instrument for evaluating the electrical resistance and wavelength-resolved transparency of stretchable electronics during strain

“…Transparency continues to fall steadily with increasing strain as a greater fraction of the incident light is scattered, presumably by cracks that develop in the brittle ITO film. 6,7 The other key features of note in Fig. 4(b) are the periodic gaps in the data.…”

“…ITO is currently the most prevalent TC material; 1-4 however, ITO is also known to suffer irreversible damage when subjected to moderate bending or stretching. 6,7 While this does not represent a major problem for rigid electronics, it does render ITO incompatible with the flexible or stretchable electronic devices that are presently under intense development. [8][9][10][11] As a result, research efforts are also underway to identify strain-tolerant TCs, and many publications now highlight TC performance under strain by tracking the evolution of electrical resistance during either linear or cyclic strain processes and in either bending or stretching modes.…”