Design, fabrication and characterization of metal embedded thin film thermocouples with various film thicknesses and junction sizes

TLDR

Micro thin film thermocouples (TFTCs) can provide measurements with high spatial and temporal resolution. The study aims to investigate the performance of metal‑embedded TFTCs and how junction size and film thickness affect their temporal and spatial resolution. A novel batch microfabrication process using thin‑film transfer and wafer‑scale embedding was employed to embed TFTCs into electroplated nickel structures. Embedded TFTCs exhibit a faster dynamic response than conventional thermocouples, a linear static response up to 900 °C, and sensitivity comparable to K‑type thermocouples for films >100 nm; increasing junction size reduces temporal resolution without affecting sensitivity, while thinner films improve response speed at the cost of reduced sensitivity.

Abstract

Micro thin film thermocouples (TFTCs) can provide measurements with high spatial and temporal resolution. If these micro sensors can be embedded in metals, tremendous benefits can be achieved for real industrial applications. In this study, a novel batch microfabrication technique, based on the thin film transfer technique and wafer-scale embedding process, was developed to fabricate and embed thin film sensors into an electroplated nickel structure. To investigate the performance of metal embedded TFTCs and the effect of size on their temporal and spatial resolution, TFTCs with different junction sizes and film thicknesses were fabricated and characterized. The dynamic response time of the sensor on a metal substrate, as measured by the pulsed laser heating method, indicates that TFTCs have a significantly faster response than conventional thermocouples. The static response of the embedded sensor is found to be linear with temperatures up to 900 °C while the thermal sensitivity of the embedded TFTCs (film minimal thickness > 100 nm) matched well with that of a standard K-type thermocouple. As the junction size is incremented, no significant differences in the thermal sensitivity were observed, nevertheless the temporal resolution reduced. Thinner film thickness results in a faster response but reduced thermal sensitivity for embedded TFTCs.