Tungsten as a Chemically-Stable Electrode Material on Ga-Containing Piezoelectric Substrates Langasite and Catangasite for High-Temperature SAW Devices

Abstract

Thin films of tungsten on piezoelectric substrates La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) have been investigated as a potential new electrode material for interdigital transducers for surface acoustic wave-based sensor devices operating at high temperatures up to 800 °C under vacuum conditions. Although LGS is considered to be suitable for high-temperature applications, it undergoes chemical and structural transformation upon vacuum annealing due to diffusion of gallium and oxygen. This can alter the device properties depending on the electrode nature, the annealing temperature, and the duration of the application. Our studies present evidence for the chemical stability of W on these substrates against the diffusion of Ga/O from the substrate into the film, even upon annealing up to 800 °C under vacuum conditions using Auger electron spectroscopy and energy-dispersive X-ray spectroscopy, along with local studies using transmission electron microscopy. Additionally, the use of CTGS as a more stable substrate for such applications is indicated.

High Temperature Behavior of RuAl Thin Films on Piezoelectric CTGS and LGS Substrates

“…For the application of such sensors at high temperatures, a suitable metallization with a high thermo-mechanical stability, a low electrical resistivity, and a high oxidation and corrosion resistance, as well as a high temperature stable piezoelectric substrate are required. 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].…”

Novel AlN/Pt/ZnO Electrode for High Temperature SAW Sensors

“…The major challenge of SAW sensors operating at high temperatures is to prepare stable high temperature film electrodes, since film electrodes such as Pt [7], Pt-Rh [8], Ir-Rh [9], Ru-Al [10], W/Mo [11], W [12], or Pt-Ni/Pt-Zr [13] film electrodes, always undergo rapid agglomeration and recrystallization above 700 °C, resulting in the discontinuity of film electrodes, an increase in resistance, and a failure of the SAW sensor. Until now, many researchers have made much effort to solve this problem.…”

“…Many efforts in recent years have been focused on surface acoustic wave (SAW) sensors [ 1 , 2 ], mainly due to their excellent wireless, passive, small, multifunctional quality, and their ability to be widely applied to systems sensing temperature [ 3 ], pressure [ 4 ], and strain [ 5 ] et al With the progress of science and technology, these SAW sensors, which work in high temperature, harsh environments, are in high demand [ 6 ]. The major challenge of SAW sensors operating at high temperatures is to prepare stable high temperature film electrodes, since film electrodes such as Pt [ 7 ], Pt-Rh [ 8 ], Ir-Rh [ 9 ], Ru-Al [ 10 ], W/Mo [ 11 ], W [ 12 ], or Pt-Ni/Pt-Zr [ 13 ] film electrodes, always undergo rapid agglomeration and recrystallization above 700 °C, resulting in the discontinuity of film electrodes, an increase in resistance, and a failure of the SAW sensor. Until now, many researchers have made much effort to solve this problem.…”

“…Taguetta [ 9 ] used Ir-Rh alloy electrodes with different compositions and found that the Ir-Rh film electrodes with optimum composition ratio can tolerate temperatures as high as 800 °C. Rane [ 12 ] used tungsten film electrodes to prevent the diffusion of Ga and O atoms from the substrate, into the tungsten film, and obtained stable electrodes up to 800 °C. Seifert [ 15 ] prepared RuAl film electrodes with a SiO 2 barrier, which was able to work stably at 800 °C for 10 h. However, the SAW electrode was unable to steadily work above 1000 °C because the recrystallization phenomenon of the electrode film was difficult to prevent.…”

Improvement of High-Temperature Stability of Al2O3/Pt/ZnO/Al2O3 Film Electrode for SAW Devices by Using Al2O3 Barrier Layer

“…Taguetta [8] used Ir-Rh alloy electrodes of different compositions and found that Ir-based film electrodes can withstand temperatures as high as 800 °C. Rane [9,10] used tungsten film electrodes to prevent the diffusion of Ga and O atoms from the substrate and obtained stable sensors up to 800 °C. Pereira da Cunha [11] investigated a Pt-Ni/Pt-Zr electrode containing an Al 2 O 3 interfacial layer that was used to reduce the degradation of the electrode layer by inhibiting the interdiffusion and interfacial reactions.…”