Sara Rigante

Sensing with Advanced Computing Technology: Fin Field-Effect Transistors with High-k Gate Stack on Bulk Silicon

Field-effect transistors (FETs) form an established technology for sensing applications. However, recent advancements and use of high-performance multigate metal-oxide semiconductor FETs (double-gate, FinFET, trigate, gate-all-around) in computing technology, instead of bulk MOSFETs, raise new opportunities and questions about the most suitable device architectures for sensing integrated circuits. In this work, we propose pH and ion sensors exploiting FinFETs fabricated on bulk silicon by a fully CMOS compatible approach, as an alternative to the widely investigated silicon nanowires on silicon-on-insulator substrates. We also provide an analytical insight of the concept of sensitivity for the electronic integration of sensors. N-channel fully depleted FinFETs with critical dimensions on the order of 20 nm and HfO2 as a high-k gate insulator have been developed and characterized, showing excellent electrical properties, subthreshold swing, SS ∼ 70 mV/dec, and on-to-off current ratio, Ion/Ioff ∼ 10(6), at room temperature. The same FinFET architecture is validated as a highly sensitive, stable, and reproducible pH sensor. An intrinsic sensitivity close to the Nernst limit, S = 57 mV/pH, is achieved. The pH response in terms of output current reaches Sout = 60%. Long-term measurements have been performed over 4.5 days with a resulting drift in time δVth/δt = 0.10 mV/h. Finally, we show the capability to reproduce experimental data with an extended three-dimensional commercial finite element analysis simulator, in both dry and wet environments, which is useful for future advanced sensor design and optimization.

Finfet with fully PH-responsive HFO 2 as highly stable biochemical sensor

In this work, highly scaled FinFETs (Fin Field Effect Transistors) are proposed as both sensing and circuit units of a lab-on-a-chip platform. The FinFET-based sensors with an HfO₂ gate oxide demonstrate full pH-response with ΔV_th ≈ 56 mV/pH. High readout sensitivity S_out = ΔI_d/I_d ≈ 43% is achieved in combination with excellent device electronic properties, i.e. SS = 77 mV/dec and I_on/I_off =1.5×10⁶. High long-term stability is proven over 4.5 days with a drift in time limited at 0.14 mV/h.

Low power finfet ph-sensor with high-sensitivity voltage readout

Low power n-channel fully depleted local-SOI FinFET integrated sensors have been developed and validated for the amplification of pH sensing signals. A simple architecture with one FinFET connected as depletion-mode load and another one as driving sensor, provides a maximum readout gain of 6.6 V/V with a maximum pH readout sensitivity of 185 mV/pH, at 2 V operation. By comparing the proposed amplifier with a single sensing FinFET the threshold voltage shift readout is shown to be 4.4 times larger. High-k dielectric HfO2 has been used to maximize both sensing and electronic performances. The FinFETs have been fabricated on bulk silicon by a local-SOI technique. FinFET thickness (TFin) and height (HFin) achieved are in the range of 20 nm ≤ T Fin ≤ 40 nm and 65 nm ≤ HFin ≤ 120 nm.

A simulation study of N-shell silicon nanowires as biological sensors

Two different silicon nanowire (SiNW) based devices are discussed as potential ion and biological sensors. Three-dimensional TCAD simulations are used to investigate and compare the efficiency of such devices upon applying an external voltage difference of ΔVg = 50 mV. The simulation results presented in this work reveal that an n-doped shell acts as sensitivity booster for uniformly doped SiNWs. It is demonstrated that a 10 nm n-type shell surrounding a p-type core can produce a sensitivity enhancement of more than 50%.