Abstract
This paper reports on a significant further improvement of the high temperature stability of RuAl thin films (110 nm) on the piezoelectric CaTaGaSiO (CTGS) and LaGaSiO (LGS) substrates. RuAl thin films with AlN or SiO cover layers and barriers to the substrate (each 20 nm), as well as a combination of both were prepared on thermally oxidized Si substrates, which serve as a reference for fundamental studies, and the piezoelectric CTGS, as well as LGS substrates. In some films, additional Al layers were added. To study their high temperature stability, the samples were annealed in air and in high vacuum up to 900 °C, and subsequently their cross-sections, phase formation, film chemistry, and electrical resistivity were analyzed. It was shown that on thermally oxidized Si substrates, all films were stable after annealing in air up to 800 °C and in high vacuum up to 900 °C. The high temperature stability of RuAl thin films on CTGS substrates was improved up to 900 °C in high vacuum by the application of a combined AlN/SiO barrier layer and up to 800 °C in air using a SiO barrier. On LGS, the films were only stable up to 600 °C in air; however, a single SiO barrier layer was sufficient to prevent oxidation during annealing at 900 °C in high vacuum.
Highlights
The development of sensors working at high temperatures is an important research field since the knowledge of process parameters at high temperatures is required to control and optimize high temperature processes
The experiments revealed that an oxidation barrier between the substrates and the RuAl film was required to prevent a chemical reaction between the Al and the Ca3 TaGa3 Si2 O14 (CTGS) or La3 Ga5 SiO14 (LGS) if the samples were annealed at 800 ◦ C in high vacuum (HV) [10,11]
This paper reports on the further significant improvement of high-temperature stable RuAl thin films on the piezoelectric CTGS and LGS in comparison to reference thermally oxidized Si substrates
Summary
The development of sensors working at high temperatures is an important research field since the knowledge of process parameters at high temperatures is required to control and optimize high temperature processes. Several metallization systems have been investigated during the last few years concerning their high temperature stability, e.g., Pt- or Ir-based materials [1,2,3,4], oxide dispersion hardened materials [5,6], or refractory metals [7]. Another alternative material for high temperature stable electrodes is the RuAl alloy with its high melting temperature of 2050 ◦ C [8] and strong oxidation and corrosion resistance [9]. It was shown that this reaction was suppressed if a 10 nm thick sputtered
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