In-line small high-pressure sensors in anodically bonded microfluidic restrictors

High-pressure microflow chemistry is advancing due to its potential advantages of being rapid, inexpensive, and accessible. However, as microfluidic devices gain popularity in areas such as synthesis and analysis, there is still a lack of control over thermodynamic parameters during high-pressure processes. This is an effect of existing external sensors causing an excessive increase in the system's internal and dead volumes. To avoid this, more sensors need to be integrated into high-pressure-resistant microfluidic channels. Herein, a proposed approach for integrating an in-line pressure-flow-temperature sensor is provided, where the flow is calculated from the pressure drop over a restrictor. An anodically bonded Si-glass microfluidic chip was constructed with wet-etched glass channels, boron-doped piezoresistors, and dry-etched diaphragms. The pressure sensors showed a precision of +/- 0.07% of full scale (70 bar) and the chip can withstand more than 210 bar. The internal volume was 25 nL and the diaphragms measured 72 x 108 mu m. With this work, improved control of high-pressure microfluidics has been accomplished.