A hypersensitive pressure sensor array for phase change microfluidics analysis

This work presents for the first time an innovative solution for measuring small pressure changes as a pressure front moves along a surface at the micro-scale, targeting applications in microfluidics. Pump-less flow boiling is an attractive method of improving heat removal from electronic devices for its lack of additional pump and the efficiency gained from phase-change cooling over conventional pumped single-phase cooling. Efforts to characterize the mechanisms of boiling at the micro-scale to effect pump-less flow has primarily focused on taking pressure measurements at the entry and exit of the channel, not within it, limiting the ability of current computer models to scale this technology. A pressure sensor array designed to operate in boiling conductive fluids is proposed in this paper to create a map of the pressure front on channel surfaces from nucleating gas-phase bubbles within a tapered micro-gap. 8 200mm piezoresistive transducers are fabricated on a 0.9mm by 20mm chip using a novel hybrid bulk- and surface-micromachining process to create 240nm thick diaphragms targeting a 1µV output for 20Pa of applied pressure, or a sensitivity of 50nVPa-1. Characterization of the fabricated devices yields a sensitivity of 155nVPa-1 with R2 = 0.90 at 5V input, and a high correlation with the diaphragm’s physical deformation.