Improving the performance of thermal flow sensors by the integration of silica aerogels

Abstract Highly sensitive thermal flow sensors are usually fabricated with heaters and temperature sensors on fragile membranes. To expand the application areas of such sensors, the membranes can be supported by other materials to achieve a greater robustness. However, most supporting materials degrade the sensor performance because they provide an additional heat-transfer path through the chip. This effect is also demonstrated in this work by integrating the hybrid polymer ORMOCOMP, which causes a reduction in the output signal. In this work, a new approach is proposed to realize a more robust thermal flow sensor than one with a free-standing silicon nitride membrane, while simultaneously increasing sensitivity. To this end, the porous material silica aerogel is integrated beneath the membrane to prevent deformation under external loads. The maximum loads on these membranes can be enhanced by up to 40 %. Although an additional material is introduced into the sensor, measurements indicate that the output signal improves when a superhydrophobic silica aerogel is applied beneath the silicon nitride membrane. At the same time, the noise of the signal is reduced compared to a sensor with a membrane only. The aerogel flow sensors have a time response of less than 200 ms, making them suitable for a wide range of real-time flow measurement applications.