Integrated membrane-free thermal flow sensor for silicon-on-glass microfluidics

Area of Science:

• Microfluidics
• Sensor Technology
• Analytical Instrumentation

Background:

• Lab-on-a-chip (LOC) systems require precise control of ultralow liquid reagent flows for multistep reactions.
• Existing flow meters often introduce dead volume and are incompatible with microfluidic chip fabrication.
• A need exists for integrated, robust flow sensors for advanced portable analytical devices.

Purpose of the Study:

• To develop and characterize a novel membrane-free microfluidic thermal flow sensor (MTFS) for seamless integration into LOC devices.
• To propose design rules for optimizing MTFS sensitivity and measurement range.
• To demonstrate the compatibility of the MTFS with corrosive liquids and its long-term stability.

Main Methods:

• Fabrication of a membrane-free MTFS using a 4'' wafer silicon-glass process, integrating thin-film thermo-resistive elements isolated from microchannels.
• Development of design rules for maximizing sensor performance.
• Implementation of an automated calibration method for the thermo-resistive elements.
• Experimental validation against a Coriolis flow sensor over extended periods.

Main Results:

• Successful integration of the MTFS into silicon-glass microfluidic chips.
• Demonstrated compatibility with corrosive liquids, crucial for biological applications.
• Achieved a relative flow error of less than 5% for flow rates between 2-30 μL min⁻¹.
• Exhibited a sub-second time response and stability over hundreds of hours of testing.

Conclusions:

• The developed membrane-free MTFS is a viable, integrated solution for precise liquid flow control in LOC devices.
• This technology enhances the capabilities of portable analytical systems, particularly for applications involving corrosive reagents.
• The MTFS offers a robust, accurate, and fast alternative to conventional external flow meters in microfluidic applications.