The Fluidic-Field Effect Transistor (Fluid-FET) has a nano-dimensional fluidic channel, connecting two fluid reservoirs and is capped with high-quality thermal SiO2 (i.e. low surface charges compared to PECVD SiO2) which is used as gate oxide; analogous to a channel between source-drain of a conventional Field Effect Transistor (FET). The ionic conductance modulation in the range of 40-50% is demonstrated at low voltages (≤ 2V) 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
Fig. 1: (a) Angular SEM micrograph of Fluid-FET (Inset showing the released channel) (b) Experimentally measured conductance as a function of KCl concentration of nanochannel of dimension (120μm × 7.5μm × 200nm) at the floating gate (V= 0V) terminal. The error bars correspond to multiple measurements
an asymmetrically positioned external gate electrode. Fluid-FETs (Fig.1) are realized using standard silicon process techniques with polysilicon as a sacrificial material, allowing thermally grown silicon oxide as capping layer with low surface charges.
Particle Separation Chip:
Particle Separation Chip (Fig.2) provides size based separation of particles using physical filters. Numerous filters were used and the direction of flow is kept perpendicular to the flow direction in order to reduce channel clogging (cross-flow filtration). Pillar type filters were used for separation of particles size greater than 6μm diameter. Another filter design Weir type filters were used for Plasma and particles below the size of 2 μm diameter. Polystyrene beads of sizes 5 μm and 10 μm were separated. Almost all 10 μm diameter beads got filtered out. The device is also used to separate blood cells from plasma in blood.
Fig. 2: (a) Cell separator & Counting Micro-Fluidic Chip (b) White Blood Cells (WBCs) Filtration Efficiency