Characterization of IrOx sputtering for IrO2 and IrO2/Pt bottom-electrode piezoelectric micro-electro-mechanical systems applications

This study examines the effects of sputter deposition growth conditions on IrO2 thin films developed as electrode layers for Pb(ZrxTi1-x)O3 piezoelectric Micro-Electro-Mechanical Systems applications. For IrO2 thin-film bottom electrodes sputter deposited on {100}-textured, rutile structure, TiO2 template layers, the effects of substrate temperature, Ar and O2 flow rates, and post-deposition anneal were studied. Additionally, the impact of various IrO2/Pt bilayer structures on electrode properties were investigated. IrO2 bottom electrodes grown on 100-oriented TiO2 at 500 °C with an Ar flow rate of 100 sccm, O2 flow rate of 60 sccm, and a nominal 100 nm thickness exhibited a film sheet resistance of 9.2 ± 0.2 Ω/sq., surface roughness of 2.3 ± 0.1 nm measured over a 2 μm × 2 μm area, and a rutile structure, preferred-{100} crystalline fiber texture normal to the substrate plane. Furnace-anneal treatments on this electrode at 650 °C for 30 min in 3 SLM O2 improved its sheet resistance to 7.5 ± 0.2 Ω/sq., and surface roughness was 4.0 ± 0.1 nm. Bilayers of IrO2/Pt grown on TiO2, with IrO2 and Pt thicknesses in the 0-100 nm range, were sputter deposited at 500 °C. The electrodes had composite sheet resistances in the range of 1.34 ± 0.03 Ω/sq. to 9.92 ± 0.25 Ω/sq., and surface roughnesses ranging from 1.5 ± 0.1 nm to 2.0 ± 0.1 nm for 2 μm × 2 μm measurement areas. Scanning Transmission Electron Microscopy verified preferred IrO2 and Pt crystalline fiber textures of {100} and {111}, respectively.