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Noise in nanoscale biosensors. Experimental results of (a) S 0.5 q and (b) S V G taken at 10 Hz as a function of gate area A obtained by different research groups: C. Schönenberger 13 , M. Reed 28 , A. van den Berg 14 , C. Dekker 26 , N. Clement 10 , S. Vitusevich (see SI). The dashed horizontal lines illustrate the notion of noise suppression indicating the noise level related to the results shown in Fig. 5(d). Scaling trend of S V G noise on (c) gate capacitance and (d) oxide thickness calculated for different conditions indicated in the figure.

Noise in nanoscale biosensors. Experimental results of (a) S 0.5 q and (b) S V G taken at 10 Hz as a function of gate area A obtained by different research groups: C. Schönenberger 13 , M. Reed 28 , A. van den Berg 14 , C. Dekker 26 , N. Clement 10 , S. Vitusevich (see SI). The dashed horizontal lines illustrate the notion of noise suppression indicating the noise level related to the results shown in Fig. 5(d). Scaling trend of S V G noise on (c) gate capacitance and (d) oxide thickness calculated for different conditions indicated in the figure.

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Article
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Transistor biosensors are mass-fabrication-compatible devices of interest for point of care diagnosis as well as molecular interaction studies. While the actual transistor gates in processors reach the sub-10 nm range for optimum integration and power consumption, studies on design rules for the signal-to-noise ratio (S/N) optimization in transisto...

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... we stress that considering a double-layer capacitance of 0.2 F m -2 and tg δ = 5 × 10 -3 Eq. (2a) could also provide a quantitative agreement to the charge noise measured for liquid-gated carbon nanotube transistor sensors 26 (see Fig. 2a). www.nature.com/scientificreports/ noise suppression in nanoscale ...
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... a lower noise level than N-type devices due to lower N ot for P-type structures in relation to different tunneling parameters (e.g. carriers effective mass) for electrons and heavy holes. Our experiments performed with nanoscale devices fabricated in the same technological run show that this is not necessarily the case for sub-µm devices (see Fig. 2a,b). One reason could be that the energy distribution of the few traps in scaled devices is pretty similar for both N-and P-type structures performed with the same fabrication protocol. Another one would be that the Coulomb repulsion effect between traps could be more effective for P-type devices. Such an effect is seen only when a ...
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... to Eq. (5), RTS noise tends to increase with capacitance decrease showing a stronger dependence than DP noise. RTS noise is typically above DP noise (see Fig. 2b,c). Such behavior demonstrates the effect of the presence of a single trap on the nanotransistor biosensor performance. However, as we discuss below, RTS noise can be suppressed by considering the single-carrier trapping-detrapping process as a signal rather than a parasitic effect. Moreover, better performance of nanobiosensors ...
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... devices. The second noise suppression effect due to the "nanometer dimension" is the fact that there are statistically no oxide traps for devices of a few tens of nanometers (see Fig. 2b). The gain compared to devices with traps (at fixed capacitance) is about a factor 12 (1200%) 19 . One could have expected a gain of several orders of magnitude in S V G , but it is restricted due to the presence of the thermal DP noise (see Fig. 2b,d). As Eqs. (1b) and (2b) have different dependence on C G , S V G is relatively lower ...
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... the fact that there are statistically no oxide traps for devices of a few tens of nanometers (see Fig. 2b). The gain compared to devices with traps (at fixed capacitance) is about a factor 12 (1200%) 19 . One could have expected a gain of several orders of magnitude in S V G , but it is restricted due to the presence of the thermal DP noise (see Fig. 2b,d). As Eqs. (1b) and (2b) have different dependence on C G , S V G is relatively lower for DP noise with thicker oxides when compared to the trapping/detrapping noise (see Fig. ...
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... a factor 12 (1200%) 19 . One could have expected a gain of several orders of magnitude in S V G , but it is restricted due to the presence of the thermal DP noise (see Fig. 2b,d). As Eqs. (1b) and (2b) have different dependence on C G , S V G is relatively lower for DP noise with thicker oxides when compared to the trapping/detrapping noise (see Fig. ...
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... phenomena as a stochastic resonance effect. The third noise suppression effect, as introduced in 21,22 , aims to exploit the presence of a single active trap in a gate dielectric layer of a nanotransistor, where RTS noise is observed (see Fig. 3a,b). Such an RTS effect is usually avoided as it increases the noise level (see Fig. 2b,c), but if RTS parameters (i.e. trap occupancy probability, time constants) are monitored (see Fig. 3b), then RTS noise becomes a signal. Intuitively, one could expect that the use of RTS as a signal would provide a gain corresponding to the difference between a single-trap and a trap-free device, e.g. between one and two orders of ...
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... but if RTS parameters (i.e. trap occupancy probability, time constants) are monitored (see Fig. 3b), then RTS noise becomes a signal. Intuitively, one could expect that the use of RTS as a signal would provide a gain corresponding to the difference between a single-trap and a trap-free device, e.g. between one and two orders of magnitude (see Fig. 2a,b). Below, we show that the potential of single-trap phenomena for the noise suppression is even larger and that it is similar to the SR effect observed in biology 31 , enabling here to overpass the thermal DP noise limit. The idea beyond this is that the addition of white noise to a signal that is nonmeasurable below a given threshold ...
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... discrete number of traps in nanoscale devices offers a rich toolbox for optimizing the S/N ratio. In the case of the absence of traps, the dielectric loss of the gate oxide can be a tunable parameter in addition to the oxide thickness (see Fig. 2c,d). For single-trap phenomena, the RTS frequency is the main parameter as the best performance is obtained for a trap occupancy probability averaged over many events. The trap operation frequency is not easy to control, even though progress has been reported towards "on-demand" trap generation 23 . Instead, a simple way to increase the ...

Citations

... We have used lightly doped thin device layer SOI wafers to demonstrate their suitability for detecting small changes in charge at the electrolyte-oxide surfaces (i.e., caused by the interaction of the proteins with peptides immobilized on the gate surface, which is the long-term goal of this work). A larger planar surface area allows a better signal-to-noise ratio and also less stringent requirements to counter reliability issues, e.g., from pin-holes, as compared to the nanowire counterparts [21]. Figure 1 shows the schematic of the proposed device design ( Figure 1A) and the cross-sectional view of the device layout ( Figure 1B). ...
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Label-free field-effect transistor-based immunosensors are promising candidates for proteomics and peptidomics-based diagnostics and therapeutics due to their high multiplexing capability, fast response time, and ability to increase the sensor sensitivity due to the short length of peptides. In this work, planar junctionless field-effect transistor sensors (FETs) were fabricated and characterized for pH sensing. The device with SiO2 gate oxide has shown voltage sensitivity of 41.8 ± 1.4, 39.9 ± 1.4, 39.0 ± 1.1, and 37.6 ± 1.0 mV/pH for constant drain currents of 5, 10, 20, and 50 nA, respectively, with a drain to source voltage of 0.05 V. The drift analysis shows a stability over time of −18 nA/h (pH 7.75), −3.5 nA/h (pH 6.84), −0.5 nA/h (pH 4.91), 0.5 nA/h (pH 3.43), corresponding to a pH drift of −0.45, −0.09, −0.01, and 0.01 per h. Theoretical modeling and simulation resulted in a mean value of the surface states of 3.8 × 1015/cm2 with a standard deviation of 3.6 × 1015/cm2. We have experimentally verified the number of surface sites due to APTES, peptide, and protein immobilization, which is in line with the theoretical calculations for FETs to be used for detecting peptide-protein interactions for future applications.
... A time trace of the 4-nanowire one and its amplitude evolution versus Vds and Vg are shown in Figure 2. The relative amplitude was as high as 15% of the overall current (Ids vs. Vg in the inset of Figure 3a), i.e., as high as 60% of the current flowing in the nanowire holding the defect. This RTS amplitude was extremely large when compared to 6 the RTS usually obtained in nanotransistors 33,34 . The evolution of the time spent in the up state (up) or down state (down) showed no correlation with Vg ( Figure S5) but demonstrated a clear ...
Article
The role of a single defect on the performance of transistors must be better understood to improve the design and fabrication process of nanotransistors. Capacitive networks on 18 nm long gate junctionless (JL) vertical gate-all-around nanowire transistors are studied through random telegraph signals, with amplitudes as high as 60% for a single nanowire. Defect densities extracted from both JL and accumulation-mode transistors allows one to discuss number fluctuation-based noise models, questioning the significance of defect densities of less than one defect per nanodevice. It is shown that the consideration of an effective charge in the models solves this issue.
... The advancement of semiconductor technology has led to mass production of low cost sensors with advantages such as real-time detection [115], high sensitivity at low concentrations [116], portable and convenient read out circuitry [117]. Over the time researches have experimentally demonstrated various architectures of chemically sensitive FETs for sensing of multiple analytes with considerable improvement in figure of merits (FOMs) for sensors such as sensitivity, linearity, limit of detection (LOD) and signal to noise ratio (SNR) [118,119]. ...
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The interest in biologically sensitive feld-effect transistors (BioFETs) is flourishing explosively due to their potential as biosensors in biomedical, environmental monitoring, and security applications. Recently, the adoption of silicon nanowires in BioFETs has enabled the enhancement of sensing fgure of merits, and device miniaturization. However with the advent of nanoscale BioFETs, reliability issues due to difculty in controlling the fabrication parameters at nanoscale dimensions hamper the sensing performance. Recently, junctionless (JL) approach has been incorporated in feld effect transistors to overcome the fabrication complexities where, current is governed by bulk conduction process. The absence of steep doping profles in JL transistors eases the fabrication complexities, reduces device variability and thermal budget. Imperatives of the performance requirements for next generation biosensors to detect the target chemical and biological molecules with higher sensitivity, small response times, and lower detection limit. However the potential of junctionless transistors as BioFETs still needs to be investigated. In the thesis we investigate different junctionless BioFET design strategies from simulation, analytical, and fabrication perspectives. This dissertation focuses on two types of junctionless BioFETs: the ion-sensitive and dielectric modulated. First we developed the surface potential based analytical models for ion-sensitive junctionless BioFET for pH sensing applications. We propose a new simulation equivalent model for electrolyte taking into account the site binding model (SBM) where the electrolyte is considered to be a stacked structure of stern layer, ion permeable layer and bulk electrolyte. Then a poly-Si based boron in-situ doped junctionless BioFET is fabricated by generic CMOS approach and tested for pH detection. Further for the detection of weakly charged biomolecules, the design considerations of junctionless embedded cavity dielectric modulated BioFET was investigated through surface potential based analytical and simulation model. Lastly, we report a novel biosensing scheme comprising two stages (the sensing and amplifying stages) based on the gate all around dielectric modulated junctionless BioFET.
... The advancement of semiconductor technology has led to mass production of low cost sensors with advantages such as real-time detection [2], high sensitivity at low concentrations [3], portable and convenient read out circuitry [4]. sensitive FETs for sensing of multiple analytes with considerable improvement in figure of merits (FOMs) for sensors such as sensitivity, linearity, limit of detection (LOD) and signal to noise ratio (SNR) [5], [6]. Majority of biomolecule sensing experiments take place in aqueous environments in polar solvents such as water. ...
... (a) Equivalent density of states (conduction band and valence band) for 3 molar concentrations of phosphate buffer solutions in(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) pH range (b) Experimental calibration of simulation model[24]. ...
Article
Herein this paper we propose a surface potential based analytical model for planar junctionless field effect transistor (JL-FET) for pH sensing. The electrolyte considered is phosphate buffer saline (PBS) solution which has been modeled as three layered stacked structure consisting of stern layer, ion-permeable membrane and bulk electrolyte. The proposed model has been deduced considering Poisson's equation in the channel region. Relative shift in threshold voltage ( $\rm V_{Th}$ ) and maximum drain current ( $\rm I_{DS,max}$ ) have been used as sensitivity metrics. The low concentrations of electrolyte (0.01), yielded higher $\rm V_{Th}$ sensitivity of $\text{63}\;mV/pH$ and $\text{59}\;mV/pH$ for bottom and liquid gate respectively as compared to higher molar concentrations of electrolyte. For 0.01 PBS the aggregate drain current shift has been found to be $52.8\ \mu A/pH$ and is larger for liquid gate operation while as for bottom gate, shift of $18.9\ \mu A/pH$ is observed. Further considering pH range of 1-14, we computed various figure of merits (FOMs) that include sensitivity, linearity and signal to noise ratio for the device. The FOMs were computed and analyzed for independent operation of liquid and bottom gate for three different molarities of PBS (1, 0.1, 0.01) each with pH range from 1 to 14. Signal to noise ratio of drain current is found maximum for low molar concentrations of electrolyte and also is highest at point of maximum transconductance. The results obtained from analytical model are in good coherence with the TCAD simulation model.
Article
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In small‐area transistors, the trapping/detrapping of charge carriers to/from a single trap located in the gate oxide near the Si/SiO2 interface leads to the discrete switching of the transistor drain current, known as single‐trap phenomena (STP), resulting in random telegraph signals. Utilizing the STP‐approach, liquid‐gated (LG) nanowire (NW) field‐effect transistor biosensors have recently been proposed for ultimate biosensing with enhanced sensitivity. In this study, the impact of channel doping concentration on the capture process of charge carriers by a single trap in LG silicon NW structures is investigated. A significant effect of the channel doping concentration on the single‐trap dynamic is revealed. To understand the mechanism behind unusual capture time behavior compared to that predicted by the classical Shockley–Read–Hall theory, an analytical model based on the rigorous description of the additional energy barrier that charge carriers have to overcome to be captured by the trap at different gate voltages is developed. The enhancement of the sensitivity for single‐trap phenomena biosensing with an increase of the channel doping concentration is explained within the framework of the proposed analytical model. The results open prospects for the development of advanced single trap‐based devices. Single‐trap phenomena (STP) are revealed and studied in liquid‐gated nanowire field‐effect transistors with different doping concentrations. Enhanced capture behavior is registered in the structures compared to the conventional Shockley–Read–Hall theory. Underlying mechanisms of the enhanced STP dynamic processes are explained within a proposed model and have to be considered for the development of ultrasensitive nanobiosensors utilizing STP.
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With the fast-shrinking of the transistor dimensions, the low-frequency noise level considerably increases emerging as an important parameter for the design of advanced devices for information technologies. Single-trap phenomena (STP) is a promising approach for the low-frequency noise suppression technique in nanotransistor biosensors by considering trapping/detrapping noise as a signal. We show a noise reduction mechanism offered by STP in nanoscale devices making the analogy with stochastic resonance effect found in biological systems by considering a single trap as a bistable stochastically driven nonlinear system which transmits and amplifies the weak signals. The STP noise suppression effect is experimentally demonstrated for the fabricated liquid-gated nanosensors exploiting STP. We found the optimal conditions and parameters including optimized gate voltages to implement a stochastic switching effect for the extraction of useful signals from the background noise level. These results should be considered for the development of reliable and highly sensitive nanoscale biosensors.