FinFET integrated low-power circuits for enhanced sensing applications

This work presents different circuit architectures that combine sensing and signal readout functions. The basic building block is a Fin Field-Effect Transistor (Fin-FET) used as both sensor and metal gate transistor. Moreover, a hybrid partially gated FinFET is proposed as a unique device enabling the integration of digital gates with biosensing. Each device has been modeled using Verilog-A to explore different designs through Electronic Design Automation (EDA) simulations. A common-source amplifier has been demonstrated to be a simple circuit for the amplification of a threshold voltage shift upon, e.g., a pH change at the sensor surface. Using an enhancement-mode n-MOS transistor as load, an input variation ΔVth ≈ 60 mV/pH can be amplified up to ΔVout ≈ 1 V/pH with good linearity between pH 6 and 10. A depletion-mode n-MOS transistor load has been used to obtain a steeper transition in DC characteristics. By using a hybrid partially gated FinFET as a driving transistor a sensing NOR logic gate has been shown. The use of such hybrid FinFETs allows for building multi-stage circuits. Two examples of such circuits, capable of both sensing and signal conditioning, have been explored and discussed here. The first circuit is a ring oscillator whose oscillating frequency depends on the analyte concentration, i.e., on the voltage drop in the liquid. The second is a pseudo-differential amplifier for differential measurements with tunable gain. The linearity and the sensitivity of the different designs are analyzed for various applications. To the best of our knowledge, no FinFET-based circuits featuring both sensing and readout capabilities have been previously reported.