Development of ALD Coatings for Harsh Environment Applications

Abstract

Atomic layer deposition (ALD) is a well-known technique for the fabrication of ultrathin and highly conformal barrier coatings which have extensively been used for the protection of electronic devices in open atmospheric conditions. Here, we extend the scope for the application of low-temperature-deposited plasma-enhanced ALD barrier coatings for the protection of devices in a variety of chemical environments. The chemical stability tests were conducted in 3.5% NaCl, sea water, HCl (pH 4), and H₂SO₄ (pH 4) solutions for ALD Al₂O₃, HfO₂, TiO₂, and ZrO₂, deposited at 100 °C on TiO₂-coated Au and ALD ZnO (photoactive)-coated Si substrates. Using electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) study, various aspects of the barrier properties and performance of ALD films in harsh chemical environments were explored. We demonstrate that the combined approach involving EIS and PL provides unique insights into the suitability of ALD films as barriers in harsh environments involving ionic solutions. The observations from EIS and PL tests are supported by the X-ray photoelectron spectroscopy analysis of ALD materials. Of the materials tested, ALD TiO₂ and ZrO₂ were found to be the most stable, chemically, in all four solutions, whereas TiO₂ was a better permeation barrier.