Nanobelt Field-effect Transistors Research Articles

Solution-Induced Degradation of the Silicon Nanobelt Field-Effect Transistor Biosensors.

Field-effect transistor (FET)-based biosensors are powerful analytical tools for detecting trace-specific biomolecules in diverse sample matrices, especially in the realms of pandemics and infectious diseases. The primary concern in applying these biosensors is their stability, a factor directly impacting the accuracy and reliability of sensing over extended durations. The risk of biosensor degradation is substantial, potentially jeopardizing the sensitivity and selectivity and leading to inaccurate readings, including the possibility of false positives or negatives. This paper delves into the documented degradation of silicon nanobelt FET (NBFET) biosensors induced by buffer solutions. The results highlight a positive correlation between immersion time and the threshold voltage of NBFET devices. Secondary ion mass spectrometry analysis demonstrates a gradual increase in sodium and potassium ion concentrations within the silicon as immersion days progress. This outcome is ascribed to the nanobelt's exposure to the buffer solution during the biosensing period, enabling ion penetration from the buffer into the silicon. This study emphasizes the critical need to address buffer-solution-induced degradation to ensure the long-term stability and performance of FET-based biosensors in practical applications.

Quantitative measurement of local conductivity of SnO2 nanobelt field effect transistor utilizing microwave atomic force microscopy

A non-contact quantitative method for measuring the electrical conductivity of a SnO2 nanobelt field-effect transistor (FET) with nanometer-scale spatial resolution is reported. The topography and microwave images of the nanobelt FET were measured by microwave atomic force microscopy (M-AFM) under a constant source voltage and different back-gate voltages. The output characteristics of the nanobelt FET were measured using a two-probe measurement method. The local conductivity of the SnO2 nanobelt FET measured by M-AFM concurred with that obtained by the two-probe measurement. Therefore, M-AFM is a promising method for measuring the local conductivity of nanomaterial FETs.

Effects of Buffer Concentration on the Sensitivity of Silicon Nanobelt Field-Effect Transistor Sensors.

In this work, a single-crystalline silicon nanobelt field-effect transistor (SiNB FET) device was developed and applied to pH and biomolecule sensing. The nanobelt was formed using a local oxidation of silicon technique, which is a self-aligned, self-shrinking process that reduces the cost of production. We demonstrated the effect of buffer concentration on the sensitivity and stability of the SiNB FET sensor by varying the buffer concentrations to detect solution pH and alpha fetoprotein (AFP). The SiNB FET sensor was used to detect a solution pH ranging from 6.4 to 7.4; the response current decreased stepwise as the pH value increased. The stability of the sensor was examined through cyclical detection under solutions with different pH; the results were stable and reliable. A buffer solution of varying concentrations was employed to inspect the sensing capability of the SiNB FET sensor device, with the results indicating that the sensitivity of the sensor was negatively dependent on the buffer concentration. For biomolecule sensing, AFP was sensed to test the sensitivity of the SiNB FET sensor. The effectiveness of surface functionalization affected the AFP sensing result, and the current shift was strongly dependent on the buffer concentration. The obtained results demonstrated that buffer concentration plays a crucial role in terms of the sensitivity and stability of the SiNB FET device in chemical and biomolecular sensing.

Investigation of the Mechanism for Ohmic Contact Formation in Ti/Al/Ni/Au Contacts to β-Ga2O3 Nanobelt Field-Effect Transistors.

The issue of contacts between the electrode and channel layer is crucial for wide-bandgap semiconductors, especially the β-Ga2O3 due to its ultra-large bandgap (4.6-4.9 eV). It affects the device performance greatly and thus needs special attention. In this work, the high-performance β-Ga2O3 nanobelt field-effect transistors with Ohmic contact between multilayer metal stack Ti/Al/Ni/Au (30/120/50/50 nm) and unintentionally doped β-Ga2O3 channel substrate have been fabricated. The formation mechanism of Ohmic contacts to β-Ga2O3 under different annealing temperatures in an N2 ambient is systematically investigated by X-ray photoelectron spectroscopy. It is revealed that the oxygen vacancies at the interface of β-Ga2O3/intermetallic compounds formed during rapid thermal annealing are believed to induce the good Ohmic contacts with low resistance. The contact resistance (Rc) between electrodes and unintentionally doped β-Ga2O3 reduces to ∼9.3 Ω mm after annealing. This work points to the importance of contact engineering for future improved β-Ga2O3 device performance and lays a solid foundation for the wider application of β-Ga2O3 in electronics and optoelectronics.

Optimization of Nanobelt Field Effect Transistor with a Capacitive Extended Gate for Use as a Biosensor

In this study, various types of extended gate field effect transistor (EGFET) biosensors were compared and then a model based on potential coupling between a disposable extended gate (EG) capacitor and the gate–source/drain capacitor of a nanobelt field effect transistor (NBFET) was developed and optimized for biosensor applications. Several parameters, including the dielectric thicknesses and the EG gate area coverage, the ionic strength of buffer solution, and the charge density of specific binding biomolecules, were included in the model. The potential coupling efficiency between the potential induced by surface charge on the EG and the gate voltage of the FET was analyzed and verified through pH detection. Biotin–streptavidin/avidin sensing was demonstrated with the optimized EG and NBFET. In addition, real-time measurements of the detection of botulinum neural toxin (BoNT) type-A were also performed using the EG NBFET, which could detect an extremely low concentration (20 fM) of BoNT type-A. Because the nanoelectronic field effect transistor does not need to be sacrificed after detection, the optimized EG NBFET biosensor has great potential for use in bio/chemical and point-of-care applications.

High-Response Identifiable Gas Sensor Based on a Gas-Dielectric ZnPc Nanobelt FET

Gas sensors based on organic semiconductor have recently attracted much attention due to their inherent advantages, especially excellent flexibility and good selectivity. However, the gas species identification with high sensing response remains a key subject for organic gas sensors. Herein, a ZnPc single nanobelt field-effect transistor with the gas dielectric was fabricated and exhibited excellent gas sensing performance at room temperature. The sensors show the high response with 220% to 10 ppm NO2 and 3566% to 20 ppm H2S, and the low detection limit down to 50 ppb towards NO2/H2S, which surpass most reported room-temperature organic-based NO2/H2S sensors. Further, our single device realized accurate gas selective identification among NO2, SO2 and H2S with 92% success ratio in LDA feature space.

Ultra-fast and sensitive silicon nanobelt field-effect transistor for high-throughput screening of alpha-fetoprotein

In this paper, we described a novel fabrication technique for Silicon nanobelt field-effect transistors (SiNB FETs) based on the Local Oxidation of Silicon (LOCOS) process widely utilized in the manufacturing of microelectronics components and explore it to screened alpha-fetoprotein (AFP). LOCOS process is used as it enables thorough compatibility with complementary metal oxide semiconductor (CMOS) technology. Thus, the need for expensive lithography tools to define the nanoscale pattern is avoided. The SiNB FETs emerges as a powerful biosensor for ultrasensitive, label-free for biological/chemical detection and direct electrical readout. The analytical sensing results of the fabricated SiNB FETs employed as a biomolecular sensor for the early, real-time, and label-free screening of AFP can be understood in term of the change in charge density at the silicon nanobelt surface after functionalization. It is observed that, by tuning the gate voltage, the electrical linearity response of the system towards AFP extends its concentration range from 3ng/mL to 100ng/mL, allowing the screening of hepatocellular carcinoma (HCC). These results indicate that the detection of AFP under our direct, label-free, and ultrasensitive biosensor in a microfluidic channel could be one of the promising state-of-the-art techniques applicable as an AFP detector in real samples.

Effect of front and back gates on β-Ga2O3 nano-belt field-effect transistors

Field effect transistors (FETs) using SiO2 and Al2O3 as the gate oxides for the back and front sides, respectively, were fabricated on exfoliated two-dimensional (2D) β-Ga2O3 nano-belts transferred to a SiO2/Si substrate. The mechanical exfoliation and transfer process produced nano-belts with smooth surface morphologies and a uniform low defect density interface with the SiO2/Si substrate. The depletion mode nanobelt transistors exhibited better channel modulation with both front and back gates operational compared to either front or back-gating alone. The maximum transconductance was ∼4.4 mS mm−1 with front and back-gating and ∼3.7 mS mm−1 with front-gating only and a maximum drain source current density of 60 mA mm−1 was achieved at a drain-source voltage of 10 V. The FETs had on/off ratios of ∼105 at 25 °C with gate-source current densities of ∼2 × 10−3 mA mm−1 at a gate voltage of −30 V. The device characteristics were stable over more than a month for storage in air ambient and the results show the potential of 2D β-Ga2O3 for power nanoelectronics.

Control of the threshold voltage in ZnO nanobelt field-effect transistors by using MoOx thin film

We report on the feasible control of the threshold voltage (Vth) in ultra-thin ZnO nanobelt FETs by using substoichiometric molybdenum trioxide (MoOx, x < 3) either as a modification layer on the surface of ZnO nanobelts or as electrodes instead of the widely used Ti/Au. ZnO nanobelt FETs using Ti/Au as the electrodes usually exhibit a negative threshold voltage, indicating n-channel depletion mode behavior, whereas ZnO FETs with MoOx/Au electrodes instead of Ti/Au show a positive shift of threshold voltage, exhibiting an n-channel type enhancement mode, which can be explained by a high Schottky barrier created at the interface of MoOx and the ZnO channel. In contrast, the decoration on the surface of ZnO channel by MoOx significantly increases the zero-bias conductivity and electron carrier concentration, and then negatively shifts the threshold voltage. We propose that MoOx thin film may play a passivation effect role, much more so than the doping effect role, due to the large amount of adsorbed species on as-grown ZnO nanobelts, especially oxygen species.

Exfoliated β-Ga2O3 nano-belt field-effect transistors for air-stable high power and high temperature electronics.

This study demonstrated the exfoliation of a two-dimensional (2D) β-Ga2O3 nano-belt and subsequent processing into a thin film transistor structure. This mechanical exfoliation and transfer method produces β-Ga2O3 nano-belts with a pristine surface as well as a continuous defect-free interface with the SiO2/Si substrate. This β-Ga2O3 nano-belt based transistor displayed an on/off ratio that increased from approximately 10(4) to 10(7) over the operating temperature range of 20 °C to 250 °C. No electrical breakdown was observed in our measurements up to VDS = +40 V and VGS = -60 V between 25 °C and 250 °C. Additionally, the electrical characteristics were not degraded after a month-long storage in ambient air. The demonstration of high-temperature/high-voltage operation of quasi-2D β-Ga2O3 nano-belts contrasts with traditional 2D materials such as transition metal dichalcogenides that intrinsically have limited temperature and power operational envelopes owing to their narrow bandgap. This work motivates the application of 2D β-Ga2O3 to high power nano-electronic devices for harsh environments such as high temperature chemical sensors and photodetectors as well as the miniaturization of power circuits and cooling systems in nano-electronics.

Conductive SnO2:Sb nanobelts as electrodes for detection of NO2 in ppb level with ultrahigh sensitivity

We report a SnO2 nanobelt field effect transistor sensor, with the SnO2:Sb nanobelts serving as the source and drain electrodes. An anomalous feature of the device is that the threshold voltage shows the negative shift upon exposure to NO2. The comparative results from the other two types of devices, including SnO2 nanobelt with metal film electrodes and SnO2:Sb nanobelt with metal film electrodes, reveal that the interface between the SnO2:Sb nanobelt electrodes and the SnO2 nanobelt is responsible for the improved carrier injection efficiency and the negative shift in the threshold voltage. Such a response mechanism results in the detection limit for NO2 down to 10 ppb, with a sensitivity as high as 7.16 × 105 % at room temperature.

Electrical characteristics of individual In-doped ZnO nanobelt field effect transistor

Back-gate field effect transistors based on In-doped ZnO individual nanobelts have been fabricated using the low-cost microgrid template method. The output (Ids-Vds) and transfer (Ids-Vgs) characteristic curves for the transistors are measured, and the mobility is derived to be 622 cm2· V-1· s-1. This value is obviously superior to those for most of materials including pure ZnO in the literature, and possible influence factors have also been discussed.

Enhancement of detection by selective modification of silicon nanobelt field-effect transistors via localized Joule heating

We utilized localized Joule heating to ablate methoxy-poly (ethylene-glycol)-silane (mPEG-sil) modified on the p− region of an n+–p−–n+ silicon nanobelt field-effect transistor (SNFET). SNFETs with selective modifications of 3-aminopropyltrimethoxysilane (APTMS) and NHS-biotin on the ablated region exhibited a faster sensing response rate and a higher sensitivity in real-time detection of Streptavidin (SA). Characterization of the ablated region via lateral force microscopy and the fluorescence image show that the ablation region occurs only in the p− region near the drain side and is believed to be a result of the impact ionization mechanism during Joule heating. Moreover, a bias of 20V pulse voltage for 1ms successfully ablates mPEG-sil and reduces the device off leakage current by 1 order after Joule heating. However, Joule heating with a pulse voltage larger than 20V (1ms) yielded an increase of device off leakage owing to damage to gate dielectrics during Joule heating. A comparison of real-time detection of SA between selectively and non-selectively modified chips shows that selectively modified ones exhibit a better limit of detection (LOD) that is one order lower than non-selectively modified ones, and a sensing response rate twice as fast as the non-selectively modified one for every target concentration.

Characterizing individual SnO2 nanobelt field-effect transistors and their intrinsic responses to hydrogen and ambient gases

The intrinsic electrical properties of individual single-crystalline tin dioxide nanobelts, synthesized via catalyst-free physical vapor deposition, were studied and correlated to the surface oxygen deficiency with the presence of various ambient gases, especially hydrogen. Four-terminal field-effect transistor (FET) devices based on individual SnO2 nanobelts were fabricated with SiO2/Si as back gate and RuO2/Au as contacts. Four-probe I–V measurements verify channel-limited transistor characteristics and ensure that the hydrogen gas sensing reflect electrical modification of the nanobelt channel. The demonstrated results of the intrinsic SnO2 nanobelt based hydrogen sensor operating at room temperature provide useful information on the synthesis of room temperature chemo-resistive gas sensors with good sensitivity and stability. To evaluate the impact of surface gas composition on the electrical properties of SnO2 nanobelts, their temperature-dependent resistivity (ρ), effective carrier mobility (μeff) and effective carrier concentration (ne) were determined under different oxygen concentrations.

Real-time and Ultra-sensitive detection of Cancer Marker Using a Novel Silicon Nanobelt Field Effect Transistor

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Functionalized SnO 2 nanobelt field-effect transistor sensors for label-free detection of cardiac troponin

Real-time label-free electrical detection of proteins, including cardiac troponin (cTn), is demonstrated using functionalized SnO 2 nanobelt field-effect transistors (FETs) with integrated microfluidics. Selective biomolecular functionalization of the active SnO 2 nanobelt channel and effective passivation of the substrate surface were realized and verified through fluorescence microscopy. The validation/verification of the sensing scheme was initially demonstrated via detection of biotin–streptavidin binding: devices with single biotinylated SnO 2 nanobelts showed pronounced conductance changes in response to streptavidin binding. Importantly, the pH-dependence of the conductance changes was fully consistent with the charged states of streptavidin at different pH. Moreover, the specificity of the sensors’ electrical responses was confirmed by co-labeling with quantum dots. Finally, the sensing platform was successfully applied for detection of the cardiac troponin I (cTnI) subunit within cTn, a clinically important protein marker for myocardial infarction.

Electrical Transport and High‐Performance Photoconductivity in Individual ZrS2 Nanobelts

Individual ZrS(2)-nanobelt field-effect transistors were fabricated using a photolithography process. Temperature-dependent electrical transport revealed different electrical conductivity mechanism at different working temperature regions. ZrS(2)-nanobelt photodetectors demonstrated a high-performance visible-light photoconductivity.

High-performance CdS nanobelt field-effect transistors with high-κ HfO2 top-gate dielectrics

We have fabricated high-performance enhancement and depletion mode (E- and D-mode) top-gate metal-insulator-semiconductor field-effect transistors (T-G MISFETs) using two kinds of CdS nanobelts (NBs), labeled as NB A and NB B, respectively. High-κ HfO2 dielectric is used as the insulator layer. The thicknesses of NBs A and B are about 60 and 180 nm, respectively. The threshold voltage and subthreshold swing of the CdS NB A T-G MISFET are about 0.15 V and 62 mV/dec, respectively. The on/off ratio is about 6 × 104, which is the best result for E-mode CdS nanoFETs reported so far. The threshold voltage, on/off ratio and peak transconductance of the CdS NW B T-G MISFET are about −3.4 V, 2 × 109, and 11 µS, respectively. The on/off ratio, to the best of our knowledge, is the highest reported for nanoFETs so far. Both of the two kinds of T-G MISFETs have quite small hysteresis in their transfer characteristics. The mechanisms for the different gate transfer characteristics are discussed. Corresponding Si back-gate CdS NB MISFETs each with a 600 nm SiO2 film as the insulator layer are also measured for comparison.

Logic gates constructed on CdS nanobelt field-effect transistors with high-κ HfO2 top-gate dielectrics

A high-performance NOT logic gate (inverter) was constructed by combining two identical metal-insulator-semiconductor field-effect transistors (MISFETs) made on an individual CdS nanobelt (NB). The MISFETs, which used high-κ HfO2 dielectrics as the top-gate insulator layer, show excellent performance, such as low threshold voltage (∼ −0.1 V), a high on/off ratio (∼108), small subthreshold swing (∼65 mV dec−1) and threshold voltage hysteresis (∼30 mV). The supply voltage for the inverter can be as low as 1 V with a voltage gain as high as 14. When the supply voltage is 7 V, the voltage gain is 72, which is the best reported value, as far as we know, for the inverters based on NB/NW n-channel MISFETs. Besides, the inverter can work in a larger input range with highly stable output voltages. Their high output voltages can make full use of the supply voltages, and their low output voltages can be close to zero. NAND and NOR logic gates have been constructed by assembling three such CdS NB MISFETs, which show high performances as well. The operating principle of the inverter is discussed in detail.

Mechanism and optimization of pH sensing using SnO2 nanobelt field effect transistors.

We report a systematic investigation about the mechanism of pH sensing using SnO2 nanobelt field effect transistors (FETs). The FETs, based on single SnO2 nanobelts, are channel-limited and with proper contact passivation; the pH sensing was conducted with sodium phosphate solutions through integrated microfluidics. The responses of the FET channel conductance to pH were measured at different gate voltages: a linear pH dependence was observed in the linear transport "on" state, while an exponential dependence was observed in the subthreshold regime. Measurements at the same pH but different ion concentrations demonstrated that the FET's pH sensitivity decreases logarithmically with the ion concentration. The effect of APTES-functionalization was evaluated by comparing the pH responses of the same device with and without the surface modification. The APTES functionalization results in a slight enhancement of the pH sensitivity and a large suppression of the noise level, leading to marked improvement in the signal-to-noise ratio. The results indicate that the pH sensing is based on a screened field-effect response of the FETs to the surface protonation/deprotonation on the nanobelt. This study provides several useful guidelines for optimizing the sensor performance for chemical and biomolecular detection.