Scalable and Highly Stable Laser‐Fabricated Piezoresistive Flow Sensor for On‐Chip Microfluidic Application

Abstract

Accurate pressure monitoring is crucial for stable fluid manipulation in microfluidic systems. However, the development of microfluidic sensors involves a complex fabrication process and a multistep lithographic method. In this study, we demonstrate a laser‐based fabrication of a piezoresistive flow sensor for on‐chip microfluidic applications. A CO 2 laser is employed to engrave microfluidic channels, create a deformable PDMS membrane, and graphitize polyamic acid film deposited on the membrane, which functions as a piezoresistive sensor. Due to intrinsic interfacial incompatibility between PDMS and PAA, the membrane surface was silanized using APTES, enabling robust chemical bonding and efficient strain transfer during membrane deformation. To obtain a precise electrical readout, the piezoresistive sensor was integrated into a Wheatstone bridge configuration, which measures the voltage at various flow rates. The sensor exhibited a gauge factor of 8.48, with stable, repeatable voltage output across 1000 cycles. Device demonstrated a linear response within a flow range of 10–200 µL/min with a sensitivity of 0.014 mV/μL/min, a minimum detectable flow rate of 10 µL/min, and a resolution of 2 µL/min. The device demonstrates low hysteresis (≤3%) within the linear range and stable operation over 90 days with a response time of 12 s.