Umbrella-shaped gate field-effect transistor for biosensing measurements
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Based on previous CMOS-compatible biosensor designs and the flash memory technology, a novel Umbrella-Shaped Field-Effect Transistor (UGFET) is realized as a biochemical charge sensor in the MOSIS AMIS 1.5 um standard CMOS process. The devices show high scalability and versatility needed for VLSI application. The UGFET device architecture is modified from previous CvMOS (Shen et al. 2003) and CMFET (Barbaro et al. 2006) designs and is scaled down to maximize the charge sensing area and drastically improve the chip density. The device simulation results show an approximate 1 volt increase in floating gate voltage for every 10 nC/cm^2 charge density increase on the sensing electrode. The designed UGFET devices are quite stable and very sensitive to the gate potential change. Two methods based on shifts in the threshold voltage and drifts in the subthreshold voltage slope are developed to sense and detect miniscule charges in charged poly electrolytes and poly amino acids. All the measured results are consistent and show the applicability of using UGFET devices as charge-modulated biosensors. Array implemented sensor chips are also taped out and tested with biochemical solutions.