The time dependent dissolution of silicon nitride is studied in a simulated eye environment (controlled saline solution) as a function of temperature and pressure. Silicon nitride films manufactured by plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD), respectively, were tested. The results revealed that both film types showed evidence of dissolution i.e., the films dissolved in the saline solution over time. At 37°C, PECVD and LPCVD silicon nitride membranes dissolved at a rate of 1.3 nm/day and 0.3 nm/day, respectively. It was found that at 23°C, the dissolution rate of the PECVD samples reduced to just 0.2 nm/day. Dissolution was not observed in samples tested in deionized water at 37°C. Titanium oxide layers (TiO2) were tested as protective layers to stop the dissolution. The results are important for implantable MEMS devices where silicon nitride is used as a functional membrane or as a protective layer.

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