Batch Fabrication and Characterization of Micro-Thin-Film Thermocouples Embedded in Metal

Abstract

Micro-thin-film sensors are promising for in situ monitoring of various processes in that they can provide measurements with high spatial and temporal resolution. It is desirable to embed microsensors into metals, which are used as functional structures in most hostile industrial environments. However, the fabrication and embedding of these sensors into metals are very challenging. In this study, a batch microfabrication technique based on SU-8 patterning, electroplating, and wet etching of silicon is developed to fabricate and embed thin-film thermocouples (TFTCs) into electroplated nickel and to separate each sensor unit without the need of additional cutting. A dielectric multilayer ( Al 2 O 3 ∕ Si x N y ∕ Al 2 O 3 ) provides insulation successfully for the embedded sensors from the nickel substrate and embedding layer. Study by using scanning electron microscopy and energy-dispersive spectroscopy line scan confirms that no significant interdiffusion occurs between different thin film layers after 10 h of annealing at 600 ° C . The embedded TFTCs provide a linear relationship between temperature and thermoelectric output. The sensitivity of the embedded sensors is almost identical to that of a standard K-type thermocouple. The fabricated TFTCs demonstrate a significantly faster response, approximately 46 ns , than conventional bulk thermocouples.