Finite element analysis of the effect on employing thermal through vias and heat fingers to increase heat transfer to fluid in calorimetric flow sensors

Measurement results of a robust silicon calorimetric flow sensor with a 25 μm thick silicon dioxide membrane with thermal silicon vias have been compared with results obtained from three-dimensional Finite Element Analysis (FEA). Based on the fabricated device, the sensor has been further developed to include heat-exchanging fingers extending down into the integrated flow channel for increased heat transfer. Using FEA, different designs of the fingers have been compared with respect to signal strength, sensitivity, power consumption and pressure loss in the channel at flow rates from 0 to about 650 sccm. Using heat fingers, the sensor signal was improved by a factor of five. The sensor signal, i.e. the temperature difference between downstream and upstream elements, was more than 60 °C when the central heater was heated 300 °C above room temperature, which was comparable to a thin-membrane device modeled. The maximum sensitivity using the finger design was about 1.4 °C sccm−1, and the maximum power consumption was almost 700 mW, which is considerably higher than for thin-membrane sensors. A figure of merit used for evaluation, was the ratio of signal strength to power consumption. The results show that the device design is a promising concept that is suitable in systems requiring robust monolithically integratable flow sensors.