Angle- and Thickness-Dependent Response Characteristics of YBa2Cu3O7−δ-Based Atomic-Layer Thermopile Heat Flux Sensors

The atomic layer thermopile (ALTP) heat flux sensor has played an important role in the study of boundary layer transition. However, the response characteristics of the sensors still have not yet been clarified sufficiently. Herein, the angle- and thickness-dependent response characteristics of the ALTP heat flux sensors are investigated. Based on a 1-D thermal conductivity model, the anisotropic thermal conductivity (
$\kappa _{\textit {ab}}$
= 4.28 W/m
$\cdot $
K,
$\kappa _{c}$
= 0.53 W/m
$\cdot $
K) and anisotropic Seebeck coefficient (
$\Delta {S}$
=
$16.72 \mu \text{V}$
/K) of YBa2Cu3O7-δ (YBCO) thin films are obtained by fitting the angle-dependent sensitivities. As the inclined angle increases, the increased thermal conductivity
$\kappa _{z}$
along the normal direction of the thin film leads to a decrease in temperature difference
$\Delta {T}$
. Therefore, the sensitivity of the ALTP heat flux sensor only reaches the maximum value
$\sim 24.16 \mu \text{V}$
/(kW/
$\text{m}^{{2}}$
) at 18° even if the inclined angle continues to increase. The increased thermal conductivity
$\kappa _{z}$
results in a decrease in the response time of the ALTP heat flux sensor as the inclined angle increases. The results of static calibration experiments and simulations indicate that the sensitivity of the ALTP heat flux sensor is almost independent of the thickness of the thin film, but their response time gradually decreases with increasing thickness based on heat conduction theory. This work may provide a good design basis for the application of ALTP heat flux sensor.