Reliability characterization of a soot particle sensor in terms of stress- and electromigration in thin-film platinum

Reliability of platinum electrodes and heating elements on SiO2 insulation layers and membranes

“…The grain growth has also been observed in FIB/SEM images of "as deposited" and annealed platinum layers presented in [7]. In addition to these results, a platinum {100} peak emerges after the thermal annealing as shown in Fig.…”

“…These platinum films and their Ti or Ta adhesion layers are deposited by DC magnetron sputtering to typical thicknesses between 300 and 500 nm. Some results have been already presented in [6,7]. Here, additional results will be presented and the electromigration lifetime of the layers will be related to the material evolution at high temperature.…”

“…After the thermal anneal the resistivity-temperature characteristic becomes linear and the resistivity reduces. The titanium reacts with the oxygen diffusing into the platinum [7] and is, this way, removed from the solution, and its effect on the resistivity is strongly reduced [12]. The platinum samples with 10 vol.-% titanium addition have higher resistivity values, Fig.…”

“…7, where the cross-section of the multi-layer stripe is visible. Next to the large, abnormally grown crystallites, which have been studied in detail in our earlier publications [6,7], even larger, "bubble-like" structures are visible on the surface of the upper platinum thin film. They are presumably due to delamination caused by the difference in the coefficients of thermal expansion between the platinum and the silicon substrate leading to high compressive stress in the Pt layer [8].…”

“…This phenomenon can take place on a macroscopic scale due to temperature gradients or current density divergences or on a microscopic scale in the grain boundaries of the platinum. A detailed comparison between the electromigration-driven failure on a macroscopic and microscopic scale has been presented in [7]. Although it is almost impossible to fully avoid temperature gradients and current density divergences, the design of a heater element should aim to minimize them, since they are extremely critical for the device reliability and strongly reduce its lifetime.…”