SPICE modelling of liquid capacitance in micromachined silicon capillaries

This paper investigates modeling of the conductance of liquid in a microchannel, using SPICE. When more than one liquid is present, conductance monitoring is an effective technique to measure electroosmotic flow rates. In micromachined silicon capillaries, the technique is hampered by the capacitance that exists between the bulk fluid and the silicon substrate, and leakage currents due to the thin insulating oxide layer. A SPICE model is used to simulate conductance waveforms, by using MOS transistors to model the time dependant resistance of the channel. The simulation results are used to determine the capacitance and explain the conductance waveforms measured for micromachined silicon channels.