Fluid-FET: An Ionic Controller for Lab-on-a-Chip

A highly sensitive ions flow controller, for lab-on-a-chip devices, operating through the nanochannels and low external potentials is demonstrated. The ion concentration can be modulated upto 50% while working in sub-micro molar range. The device is a fluidic-field-effect transistor (Fluid-FET) which has nanodimensional fluidic channel, connecting two fluid reservoirs and is capped with high quality thermal SiO2 (i.e., low surface charges compared with plasma enhanced chemical vapor deposition SiO2), which is used as gate oxide; analogous to a channel between source-drain of a conventional FET. The ionic conductance modulation in the range of 40%-50% is demonstrated at low voltages (<= 2 V) through an external gate potential, providing a simpler way to modulate the surface charges of the channel. The conductance of nanochannel is modeled as a function of gate voltage and gate electrode position (symmetrical and asymmetrical with respect to nanochannels). The precise movement of the ions in one preferred direction (diodic behavior) is achieved by asymmetrically positioned external gate electrode. Fluid-FETs are realized using standard silicon process techniques with polysilicon as sacrificial material, allowing thermally grown silicon oxide as capping layer with low surface charges. The devices are analyzed using 3-D optical imaging, scanning electron microscopy, and electrical characterization in the presence of various ionic solutions.