Document Type

Honors Thesis


Engineering Physics


Robert J. Lad

Committee Members

Carl P. Tripp, Jordan LaBouff, Samuel T. Hess

Graduation Year

May 2023

Publication Date

Spring 2023


Wireless sensors that can operate in temperatures up to 1000°C are widely needed for real time monitoring of large-scale industrial processes. Such sensors will improve efficiency and prevent component failure. Under previous work at UMaine, Surface Acoustic Wave Resonator (SAWR) sensors fabricated on piezoelectric langasite (La3Ga5SiO14) wafers have shown promise for wireless strain measurements at high temperatures. However, there is a major technical challenge in attaching SAWR langasite based sensors to metal parts because the large differences in the coefficient of thermal expansion (CTE) between langasite and metals leads to large thermal stresses and fracture of the associated materials during thermal cycling. Preliminary work resulted in the development of a multilayered adhesive containing graded CTE values using platinum, silicon, zirconium, and copper which showed promising adhesion between langasite and steel. However, problems with the multilayered adhesive include non-uniform bonding leading to irreproducible behavior, film delamination, weakening through oxidation, and lack of thermal stability. This thesis reports on results of experiments performed using facilities in UMaine’s Frontier Institute for Research in Sensor Technologies (FIRST). The thermal stability of PtxSi1-x alloy films deposited on langasite substrates was investigated to create a uniform, reproducible layer to reliably adhere langasite to a copper overlayer. The PtxSi1-x films were deposited to a thickness of ~150nm using an electron beam evaporation technique carried out in ultra-high vacuum. Several PtxSi1-x films were synthesized by co-deposition from elemental Si and Pt sources and then subjected to annealing treatments up to 850°C in vacuum, air, or N2 process gases. The PtSi alloy composition was identified to be the most promising for creating a uniform, thermally stable film as determined from X-ray diffraction and scanning electron microscopy analysis. A 500 nm thick copper layer deposited on a PtSi film using a sputter deposition technique yielded a thermally stable film configuration due to a chemical reaction across the PtSi/Cu interface.

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