Micro-Scale 2D Thermal Gradiometer

We investigate thin film thermocouples (TFTC) as thermal gradient sensors at the micro-scale and using thermocouples perpendicular to each other with separation distances of 20- $100~\mu \text{m}$. Pairs of ${x}$ -direction and $y$ -direction thermocouples sense the thermal gradient while another calibrates the Seebeck coefficient to be S = 22.27 ± .01\mu$ V/K. The smallest detectable temperature difference is 10mK, and the sensitivity is 0.5/ $\mu$ m. The minimal Johnson-noise limited performance for thermocouple devices with typical integrated-circuit dimensions is 1.4 nV/ $\sqrt{{\mathrm {Hz}}}$. Our design further reduces the number of leads L needed to measure N thermocouples to $L=N$ and allows direct measurement of thermal gradient instead of interpolation. Our design implements a local metal layer A at the gradiometer distinct from an extended metal layer B. This design is robust against any erroneous Seebeck contribution caused by minor film thickness variations in the extended leads. This device can be applied for embedded thermal management systems that require high resolution and rapid-response thermal management, such as stacked three-dimensional (3D) integrated circuits.