Platinum thin film electrodes for high-temperature chemical sensor applications

Platinum–zirconium composite thin film electrodes for high-temperature micro-chemical sensor applications

“…The initial work was then used to compare against an alternative DC sputtering process used to manipulate the microstructure and thickness of the Zr adhesion layer, where a gradient in Zr concentration was varied throughout the thickness of the Pt film. By manipulating the deposition parameters (such as sputtering power and primary deposition gas pressure) during the adhesion layer deposition a functionally gradient composite Zr/Pt film was formed that demonstrated similar stability as the Zr-Pt layer-by-layer structure demonstrated by Cunha et al [43] and Ç iftyürek et al [26]. After a high-temperature stable, composite Zr/Pt film was proven, a method for fabricating the required micro-IDE pattern for sensor applications was demonstrated; this development was important since both Zr and Pt are not easily etched, especially through wet-chemical techniques.…”

“…1b shows the SEM micrograph of the Pt film with the Zr adhesion layer (Zr/Pt) after 5 h at 1200 • C. The resulting microstructure consisted of micron-size Pt grains with a low degree of percolation across the microstructure. Detailed studies regarding the effect of different annealing conditions can be found by the current authors' previous paper regarding Zr/Pt high-temperature films [26].…”

“…A strategy is required to control the migration of the adhesion layer away from the substrate interface and to limit the migration of the Pt grain boundaries, which results in unwanted grain growth. One method recently demonstrated for controlling the later mechanism is through the introduction of Zr metal into the Pt layer through a co-sputtering of Zr and Pt, or through sequential depositions of each of these constituents [26,[41][42][43]. The dispersion of refractory particles (such as nano-or micro-ZrO 2 or Zr/Pt intermetallics) drastically reduces the low-and high-angle grain boundary mobility within the polycrystalline film.…”

“…materials of choice for this application, since it possesses a high melting point and is resistant to oxidation and chemical reaction. However, Pt has several drawbacks especially processed or operated at high temperatures (≥800 • C), where the metal demonstrates a high level of coarsening/agglomeration and weak adhesion when deposited on oxide or nitride surfaces, such as those typically utilized in microsensor and MEMS designs (such as Al 2 O 3 , SiO 2 , Si 3 N 4 ) [25,26]. In other words, upon exposure to high temperature processing or operation, thin Pt films uncover the underlying oxide or nitride substrate, and the film separates into a discontinuous array of islands.…”

“…In addition, researchers investigated methods of incorporating alternating metal and metal oxide layered compositions into the bulk Pt thin film in order to limit sintering/coarsening processes by pinning the Pt grain boundaries [40][41][42]. More recently, Ç iftyürek et al utilized 35 nm thick Hf as an adhesion promoter with multiple 10 nm thick Zr as a grain pinning phase for Pt thin films for high temperature chemical sensor applications; the adhesion layer enhanced Pt bonding through the formation of intermetallic phases, and the layer-by-layer deposited Pt thin film showed a durable microstructure up to 48 h at 1200 • C [26].…”