On-chip liquid and gas flow rate sensing via membrane deformation and bistability probed by microwave resonators

Abstract

Abstract Precise monitoring of fluid flow rates constitutes an integral problem in various lab-on-a-chip applications. While off-chip flow sensors are commonly used, new sensing mechanisms are being investigated to address the needs of increasingly complex lab-on-a-chip platforms which require local and non-intrusive flow rate sensing. In this regard, the deformability of microfluidic components has recently attracted attention as an on-chip sensing mechanism. To develop an on-chip flow rate sensor, here we utilized the mechanical deformations of a 220 nm thick Silicon Nitride membrane integrated with the microfluidic channel. Fluid flow induces deformations on the membrane, which is electronically probed by the changes in the capacitance and resonance frequency of an overlapping microwave resonator. By tracking the resonance frequency, both liquid and gas flows were probed with the same device architecture. For liquid flow experiments, a secondary sensing mechanism emerged when it was observed that steady liquid flow induces periodic deformations on the membrane. Here, the period of membrane deformation depends on the flow rate and can again be measured electronically by the microwave sensor. Flow rate measurements based on the deformation and instability of thin membranes demonstrate the transduction potential of microwave resonators for fluid-structure interactions at micro and nanoscales.