Inline and Real-Time Microfluidic Relative Permittivity Sensor Using Highly Doped Silicon Sidewall Electrodes

This paper reports an inline sensor for the real-time measurement of the relative permittivity of a continuously flowing fluid, with electrodes that are electrically isolated from the fluid. The sensor has been characterised for relative permittivity values ranging from 1 to 80 – including water and water-containing mixtures – showing an accuracy within 3% of full scale. The proposed sensor contains multiple parallel microchannels, each of which has parallel electrodes in the sidewall, resulting in a low pressure drop and high sensitivity while the internal volume is only 50 nL. The fabrication technology is scalable: equally deep microchannels with widths of 5, 10, 20, and 40 μm are demonstrated. The technology is also compatible with other inline sensors, enabling further on-chip integration.