Micromachined silicon electrolytic conductivity probes with integrated temperature sensor

Electrolytic conductivity measurements of fluids currently require sample volumes greater than a milliliter. Many applications would benefit from accurate measurements of nano- to microliter sample volumes. However, polarization and nonlinear electrode impedance effects, along with stray impedance and temperature effects, strongly affect measurements of the solution conductance for microliter and smaller sample volumes. MEMS-based silicon electrolytic conductivity probes, down to 100-μm wide, with integrated temperature sensors, have been designed and fabricated to overcome these effects. Several electrode configurations were tested: plain electrode pairs, electrode pairs plated with platinum black, plain four electrode sets, and four electrode sets plated with platinum black were investigated. The same accuracy as normal scale probes has been achieved with these sensors over almost three orders of magnitude in solution concentration and electrolytic conductivity ranges.