Thermal, mechanical and chemical effects in the degradation of the plasma-deposited α-SiC:H passivation layer in a multilayer thin-film device
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Amorphous, hydrogenated silicon carbide (α-SiC:H) deposited by a plasma-enhanced-chemical-vapour-deposition (PECVD) process has been used as the topmost passivation layer in a multilayer thin-film device, namely, a thermal ink-jet printhead. Normal operations of the device involve rapid heating of the multilayer structure at several kHz, repetitively forming vapour bubbles that grow and collapse in an otherwise liquid environment. During such operations, the α-SiC:H layer is subjected to a variety of thermal, mechanical and chemical stresses that are detrimental to its integrity. It is found that thermally activated failures may occur when the multilayer structure is driven for extended periods of time or by pulses of excessive magnitude or duration, or when the α-SiC:H film is so thick as to store excessive elastic energy due to large differential thermal expansion effects. It is also found that severe mechanical (namely, cavitation) effects associated with bubble collapse cause early device failures if the surface of the device is exposed to an unlimited liquid reservoir; however, such adverse effects are greatly mitigated by the presence of a nozzle plate in the vicinity of the top surface. Finally, it is shown that high pH and various chemicals tend to etch the α-SiC:H thin film through an oxidation-dissolution process, removing the passivating material rapidly and leading to device failures.
KeywordsCavitation Multilayer Structure Passivation Layer Vapour Bubble Expansion Effect
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