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. 2021 Nov 17;6(47):32297–32303. doi: 10.1021/acsomega.1c05469

Fabrication of a Mesoporous Multimetallic Oxide-based Ion-Sensitive Field Effect Transistor for pH Sensing

Tingke Rao †, Jialin Li †, Wen Cai ‡, Min Wu †, Jie Jiang †, Peng Yang †, Yuanliang Zhou †, Wugang Liao †,*
PMCID: PMC8638296  PMID: 34870050

Abstract

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Sensitive and reliable noninvasive sensors are in demand to cope with an increasing need for robust working conditions and fast results. One of the leading potential technologies is field-effect transistor (FET)-based sensors to improve response time, sensitivity, and stability. Here, a sol–gel method fabricates an ion-sensitive field-effect transistor with a high current and output sensitivity for electrochemical sensing, solving binary device design, component regulating, and long-term stability, while maintaining the promoted sensitivity. Metal oxide-based devices with single and binary contents are fabricated and characterized for monitoring pH changes, with performance fitted to a Nernst–Poisson model. After detecting the performance, the result was compared with devices in different components and ratios to obtain excellent performance and high stability. In addition, these extended gate FETs with multimetallic oxide promise efficiency and stability optimization in terms of a flexible component design, demonstrating the feasibility of the novel sol–gel fabrication method to achieve efficient and reliable FET sensors.

1. Introduction

Field-effect transistor (FET)-based biosensors attract researchers’ attention as a promising probing method in various fields such as health,1 building,2 food,3 and electronics4 with advantages including high integration degree, fast response, accuracy, robustness, simplicity and noninvasiveness.5 First proposed by Bergveld in the 1970s, ion-sensitive FETs (ISFETs) based on conventional metal-oxide-semiconductor FETs (MOSFETs), consisting of a gate electrode, instead of the gate electrode of the MOSFETs, as well as chamber and electrolyte, can be used to probe ion concentration by monitoring electrical property change according to the surface potential change which is caused by ionic reactions happened at the sensing membrane.6 Shortages including quenching of the sensing membrane can be avoided by introducing an extended gate FET (EGFET) to separate the sensing and measuring membrane, EGFET.7 Moreover, advantages including flexible assembly, disposability, light, simple package, and light response endow EGFET even wider applications.8

Current sensing membranes are coated via traditional thermal evaporation and radiofrequency magnetron sputtering methods, which might bring up more problems, including uneven thickness, difficulty regulating component, and so forth. In comparison, sol–gel methods can adapt various substrates and modulate the membrane film by simply adjusting parameters such as method, heating temperature, concentration, and so forth. However, few reports regard the production of a metal oxide-based active layer using urea as sol–gel precursors. Organic ligands decompose under high temperature, leaving the metal oxide film with high homogeneity films with low roughness values.9 Moreover, this sol–gel route has advantages over traditional preparation methods because urea decomposes fast, generates high porosity, and increases the substrate surface area. However, it is necessary to take into account that the processing parameters, such as spin-coating speed, precursor concentration, and substrate, as well as the annealing process have a strong influence on the properties and performance of the films. In this work, the authors demonstrated that these properties could be tuned by the growth parameters with pH-sensitive metal oxide-based FET.

Several metal oxide materials have been investigated as suitable pH sensing layers for ISFET-based pH sensors, such as WO3,10 MoO3,11 ZnO,12 HfO2,13 and so forth, according to their electron affinity and wide band gap.14 However, these devices suffer from a number of drawbacks such as drift and ionic interference, which have never been solved to a satisfactory degree. Also, meal oxide-based ISFET devices face bottleneck transcending Nernstian magnitudes15 with units between 50 and 59 mV/pH. Parameters including gate length,16 thickness,17 and topography18 of the transition metal oxide membrane have been demonstrated to have a decisive promotion on the device characteristics, highlighting the importance of the sensing membrane fabrication methods.19

EGFET with sensing metal oxides was fabricated via a novel sol–gel route in a simple method in this paper. Furthermore, it exhibited a pH sensitivity of 63.15 mV/pH and linearity of 0.999 and an output sensitivity of 9.20 (μA)1/2/pH with an outstanding linearity of 0.999 in the saturation region. Moreover, the effects of gate extension and hybrid nanostructured design are investigated. This study confirms that performance is promoted by introducing a binary component. The experimental findings suggest that sensitivity is strongly related to defects, which facilitate charge transfer and trapping, and is favored when photogenerated minority carriers (holes) become available in the n-type metal oxide transistor. We suggest that intrinsic defects such as interfacial states, resulting in effective positive charge trapping, are a fundamental cause of hysteresis.

2. Result and Discussion

2.1. Sensing Film Characterization

The crystal structure of the MoO3, WO3, and ZnO sensing membrane were examined by X-ray diffraction (XRD) using the grazing incidence mode, as shown in Figure 1a. The XRD result confirms that the average grain size is 41.3, 58.9, and 55.1 for MoO3, WO3, and ZnO, respectively. A good example to start characterization is MoO3, the finest grain size among the three as-synthesized materials. Scanning electron microscopy (Figure 1b) shows a uniform ∼200 nm thick MoO3 film (Figure 1c) and the highly-porous morphology as a result of organic ligands decomposition. A relatively lower melting point21 probably causes this. The surface structure of the MoO3 film was uniform, smooth, and small-grained, as shown from corresponding atomic force microscopy (AFM) shown in Figure 1e. The surface roughness of the MoO3 sensing membrane was evaluated to be 1.65 nm. High porosity of the MoO3 extend gate, which derives from the sol–gel precursor decomposition during thermal treatment,22 facilitates charge distribution with a large surface area and splendid sensing sites,23 thus benefits the sensing performance. Additionally, metal oxide sensing membrane transparency endows them other uses such as energy harvesting or optical regulation devices, as given in Figure 1f.

Figure 1.

Figure 1

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(a) XRD pattern of MoO3 film. (b) SEM and (c) Cross-section SEM images of MoO3 membrane. (d) SEM images of W0.5Mo0.5O3 membrane. (e) AFM images of MoO3 film. (f) Transparent single MoO3 device on ITO glass.

Figure 2b,e shows X-ray photoelectron spectroscopy (XPS) of the Mo 3d spectra of WxMo1–xO3 before and after sensing measurement. At the initial state before the probing test, the WxMo1–xO3 film showed Mo 3d3/2 and Mo 3d5/2 peaks in 236.0 and 232.9 eV separately, which fit Mo6+ states well. Whereas, the two fitted peaks remain and no other peaks are adapted after the UV illumination. Similarly, in the W 4f spectrum of the WxMo1–xO3 membrane, the two peaks at binding energies of 35.8 and 37.8 eV correspond to the spin–orbit doublet peaks of W 4f7/2 and W 4f5/2, indicating the presence of oxide (WO3), as given in Figures 2a and 4d. In addition, as shown in Figure 2c,f, O 1s peaks can be divided into μ (530.1 eV) and μ′ (531.8 eV) for the oxide membranes both before and after probing tests. The abiding binding energy states suggest that the semiconducting characteristics remain after 1000 min’ tests in pH solution for several cycles, different from a metal oxide sensing membrane applied in UV24 and electrochemical tests. The stable valence state of Mo ions indicates protons that exist in acid solution does not incorporate into the membrane,25 thus guarantee high stability.

Figure 2.

Figure 2

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XPS spectra of the (a,d) W 4f, (b,e) Mo 3d and (c,f) O 1s peak for the WxMo1–xO3 membrane (a–c) before and (d–f) after UV illumination.

Figure 4.

Figure 4

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(a) Transfer characteristics and (b) output characteristics of W0.5Mo0.5O3-based EGFET sensor measured at gradient pH buffer. (c) Voltage sensitivity and (d) current sensitivity of series of metal oxide-based EGFET sensors.

2.2. Single Metal Oxide EGFET Response

Further investigations were carried out by recording the corresponding sweeping voltage when they were placed in the Britton–Robinson buffer over the pH range from 4 to 9.18. The transfer characteristic is shown in Figure 3a, with VDS = 0.1 V. Modulation of the conductance of the oxide-based EGFET sensors upon the binding of the target depends on the concentration.26 Native n-doping is commonly attributed to the omnipresent electron-donating oxygen vacancies, especially in metal oxide,27 even though the n-doping character of oxygen vacancies has been disputed.28 Surface potential change leads to the gradient shift in threshold voltage of the IDS–VGS curve when a MoO3 sensing membrane exposed in different aqueous buffer solutions.

Figure 3.

Figure 3

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(a) Transfer and (c) output characteristics of MoO3-based EGFET sensor measured at gradient pH buffer. (b) Voltage sensitivity and (d) current sensitivity of MoO3-based EGFET sensor in IDS–VGS and IDS–VDS measurement under linear and saturation region.

Two types of sensitivities are extracted to evaluate the figures of merit of the sensor. Voltage sensitivity or output sensitivity, which is Inline graphic, corresponds to the variation of the applied reference voltage to obtain the same drain current for different pH values. Current sensitivity, or the transfer sensitivity, corresponds to Inline graphic , where Ii is the current value at fixed gate voltage for a given pH and I0 is the current at a baseline lower concentration.

The obtained voltage sensitivity from transfer characteristics and linearity of the MoO3-based EGFET sensor are 53.21 mV/pH and 0.99, as given in Figure 3a,b. Compared with other devices, a relatively higher sensitivity gives a clue of smaller grain size and smoother topography. Previous results revealed that a smoother surface morphology endows a better sensitivity due to better carrier mobility inside a sensing-active membrane.29 A relative lower pH sensitivity was obtained for devices prepared with the abovementioned sol–gel method (47.03 and 46.14 mV/pH for WO3 and ZnO devices separately) compared with that of MoO3 calculated line given in Figure S1 and sensitivities shown in Figure 4c.

Keeping VGS as constant at 0.1 V and VDS scanned from 0 to 0.5 V, IDS increases till threshold, which varies with the pH value, as given in Figure 3c with the square root of IDS plotted in order as functions of pH. An output characteristic (IDS–VDS) of −8.58 (μA)1/2/pH for MoO3 was obtained by calculation in Figure 3d. Similarly, 6d predicts output sensitivities of −11.46 (μA)1/2/pH and −10.37 for WO3 and ZnO, respectively. The characteristic calculation is given in Figure S2 and sensitivity calculation is given in Figure 4d.

Alternatively, WO3 impurities, introduced in natural MoO3, have been proposed as another method for enhancing n-type dopants. The binary structure endows the EGFET with a significant pH response and preserves the electronic quality of graphene that is commonly characterized by the charge carrier mobility. The W0.5Mo0.5O3 (Figure 4a), W0.5Zn0.5O2.5 (Figure S1c), and Zn0.5Mo0.5O2.5 device provides a promoted pH sensitivity (63.15, 55.15 and 49.38 mV/pH separately) and compared with that of single content devices, as summarized in Table 1, both close to that of Nernstian response30 (∼59.2 mV/pH). These results suggest that this kind of metal oxide film can be a pH sensor through a wide pH range.

Table 1. Summarization of Metal Oxide EGFET Devices’ pH Sensitivity, Current Sensitivity and Corresponded Linearities.

content pH sensitivity (mV/PH) linearity current sensitivity (μA1/2/pH) linearity refs
ZnO 46.14 0.99 –10.37 0.94 this work
WO3 47.03 0.97 –11.46 0.93  
MoO3 53.21 0.99 –8.58 0.99  
W0.5Mo0.5O3 63.15 0.99 –10.56 0.98  
W0.5Zn0.5O2.5 55.15 0.99 –10.16 0.99  
Zn0.5Mo0.5O2.5 49.38 0.99 –9.20 0.97  
W0.2Mo0.8O3 55.86 1.00 –14.29 0.99  
W0.4Mo0.6O3 61.86 1.00 –19.94 1.00  
W0.5Mo0.5O3 63.15 1.00 –9.20 0.97  
W0.6Mo0.4O3 57.63 0.99 –20.36 0.97  
W0.8Mo0.2O3 50.96 1.00 –17.32 0.99  
W0.2Zn0.8O2.2 45.28 0.98 –14.53 0.88  
W0.4Zn0.6O2.4 42.94 1.00 –14.06 0.95  
W0.5Zn0.5O2.5 55.15 0.99 –10.16 1.00  
W0.6Zn0.4O2.6 44.73 1.00 –11.50 0.99  
W0.8Zn0.2O2.8 46.54 1.00 –10.73 1.00  
ZnO 15.4 N/A 0.26 N/A (31)
ZnO 64 N/A N/A N/A (32)
ZnO Nanorods 24.67 0.986 21.4 0.994 (33)
Al2O3/In2O3 61.9 0.986 N/A N/A (34)
Na3BiO4/Bi2O3 49.63 N/A N/A N/A (35)
WO3 44.9 N/A N/A N/A (36)
CuO Nanowires 48.34 0.998 N/A N/A (37)
ITO 60.18 0.993 N/A N/A (38)
TiO2 Nanoflower 46 0.999 2.7 0.999 (39)
ITO 52.31 0.995 N/A N/A (40)
WO3/C 41.38 N/A N/A N/A (41)
RuOx 65.11 0.999 N/A N/A (42)
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Output characteristics of W0.5Mo0.5O3 and W0.5Zn0.5O2.5 EGFETs at VGS = 0.1 V and IDS versus VDS varying the electrolyte pH are given in Figures 4b and S2c, with each curve corresponding to different pH values represented with sensitivity shown in Figure 4d. The output characteristics of the wires remained linear through all tested pH exhibiting a good ohmic behavior for all devices between 0 and 500 mV. The conductance through the wire increases with low pH due to the repulsion of positive charge carriers H+ adsorbed on the surface at the subsequent increase of the depleted region. The conductance values were valued from the slope of the IDS versus VDS curves in different pH buffer solutions. Output characteristics show a decrease in conductance of the devices with increasing VGS due to the positive charge carriers and attracting field experienced. Increasing pH values of the electrolyte plays an equivalent role with increasing VGS, resulting in increased conductance and current with a nearly linear response. This is coherent with what was observed in the transfer characteristics.

Further characteristics of the binary metal oxide EGFET have been investigated with gradient metal oxide ratios. Sensing performances show volcano peaks for both components including WxMo1–xO3 and WxZn1–xO2+x, as the details given in Table 1. Both contents show an all-around performance of sensitivities and linearities near the molar ratio of 1:1, implying the importance of evenly mix. Degree of mixing nanoparticles in a matrix directly influences interface area, carrier mobility, and density of defects. Physical studies of EGFET devices are needed with future perspectives for further advancements.

3. Conclusions

In summary, a high cost-effective EGFET pH sensor was manufactured via a facile thermal sol–gel process, and the metal oxide sensing membrane fabricated with urea and metal chloride was revealed to be dense and uniform with a flexible component ratio. It demonstrates a nearly Nernstian pH response of 63.15 mV/pH with a good linearity of 0.999. Properties including uniform, small grains, and binary microstructure of the metal oxide sensing membrane have a decisive influence on the performance by offering high conductivity and increasing ion adsorption sites on the sensing membrane. The novel synthesis approach of the EGFET sensor is a new pattern for ion probing and noninvasive diagnostics.

4. Experimental Details

4.1. Sensing Membrane Preparation and Characterization

In this study, W1–xMoxO (x = 0.00, 0.02, 0.04, 0.05, 0.06, 0.08, 0.10), W1–xZnxO (x = 0.00, 0.02, 0.04, 0.05, 0.06, 0.08, 0.10), and Zn0.5Mo0.5O2.5 thin films were prepared by the sol–gel method at 3000 rpm for 40 s on ITO substrates. A schematic illustration is given in Figure 5. The precursor solutions were prepared in stoichiometric ratios using MoCl6, WCl6, zinc acetate dehydrates (Zn(CH3COO)2·2H2O), WO3 nanoparticles, ZnO nanoparticles, and urea. The chemical solution was ultrasonicated for 1 h. After each coating step, the thin films were pyrolyzed for 5 min at 300 °C on a hot plate. After cooling down, the metal oxide thin films were annealed at 400 °C for 2 min in the atmosphere.

Figure 5.

Figure 5

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Schematic illustration of the sol–gel preparation process for a metal oxide active layer.

4.2. Sensor Fabrication and Measurement

The EGFET structure with several types of metal oxide sensing membranes was fabricated on an ITO/glass substrate, which was later connected to the gate of a commercial MOSFET (FDC6320C), as shown in Figure 6. For pH sensing, the sensing membrane of the EGFET sensor was submerged in different pH solutions with a gate bias applied to a reference electrode (Ag/AgCl). All sensing characteristics, including pH sensitivity and stability, were measured using a semiconductor parameter analyzer (Keithley 2636).

Figure 6.

Figure 6

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Schematic of the metal oxide-based EGFETs.

The drain-source current IDS of the EGFET was measured versus electrolytic gate potential VGS regulated through Ag/AgCl reference electrode at VDS = 0.1 V. The VGS sweeps at a small range (0–1.5 V) during measurements to avoid analytic electrolysis and to limit the gate leakage IGS.

The EGFET device was initially placed in a beaker containing 50 mL buffer solution (pH = 4.00/6.86/9.18). Once the sensor was cleaned thoroughly with acetone and deionized water, the sensing measurement was performed in real time with pH values in the following order: 6.86 → 9.18 → 4.0. The ion concentrations were obtained by solving the series of the Nikolskii–Eisenman equations,20 where the constants were extracted from the calibration tests.

Acknowledgments

The work was partially supported by the financial supports from National Natural Science Foundation of China (grant no. 61904110) and Young Teachers’ Startup Fund for Scientific Research of Shenzhen University (grant no. 860-000002110426).

Glossary

Abbreviations

FETs

field-effect transistors

ISFETs

ion-sensitive FETs

EGFETs

extended-gate FETs

MOSFETs

metal-oxide-semiconductor FETs

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c05469.

  • Further information on transfer and output characteristics of WO3, ZnO, and W1–xMoxO-based EGFET sensor with a gradient W/Mo ratio measured at different pH buffers (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao1c05469_si_001.pdf (494.6KB, pdf)

References

  1. Cho W.-J.; Lim C.-M. Sensing Properties of Separative Paper-Based Extended-Gate Ion-Sensitive Field-Effect Transistor for Cost Effective PH Sensor Applications. Solid. State. Electron. 2018, 140, 96–99. 10.1016/j.sse.2017.10.025. [DOI] [Google Scholar]
  2. Mittag T.; Rabe M.; Gradert T.; Kühn A.; Dumitrescu R. Building Blocks for Planning and Implementation of Smart Services Based on Existing Products. Procedia CIRP 2018, 73, 102–107. 10.1016/j.procir.2018.04.010. [DOI] [Google Scholar]
  3. Bhardwaj H.; Rajesh; Sumana G. Recent Advances in Nanomaterials Integrated Immunosensors for Food Toxin Detection. J. Food Sci. Technol. 2021, 73, 102. 10.1007/s13197-021-04999-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Larpant N.; Pham A. D.; Shafaat A.; Gonzalez-Martinez J. F.; Sotres J.; Sjöholm J.; Laiwattanapaisal W.; Faridbod F.; Ganjali M. R.; Arnebrant T.; Ruzgas T. Sensing by Wireless Reading Ag/AgCl Redox Conversion on RFID Tag: Universal, Battery-Less Biosensor Design. Sci. Rep. 2019, 9, 12948. 10.1038/s41598-019-49245-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Rollo S.; Rani D.; Leturcq R.; Olthuis W.; Pascual García C. High Aspect Ratio Fin-Ion Sensitive Field Effect Transistor: Compromises toward Better Electrochemical Biosensing. Nano Lett. 2019, 19, 2879–2887. 10.1021/acs.nanolett.8b04988. [DOI] [PubMed] [Google Scholar]
  6. Yuqing M.; Jianrong C.; Keming F. New Technology for the Detection of pH. J. Biochem. Biophys. Methods 2005, 63, 1–9. 10.1016/j.jbbm.2005.02.001. [DOI] [PubMed] [Google Scholar]
  7. Pullano S.; Tasneem N.; Mahbub I.; Shamsir S.; Greco M.; Islam S.; Fiorillo A. Deep Submicron EGFET Based on Transistor Association Technique for Chemical Sensing. Sensors 2019, 19, 1063. 10.3390/s19051063. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Rao L.; Wang P.; Qian Y.; Zhou G.; Nötzel R. Comparison of the Extended Gate Field-Effect Transistor with Direct Potentiometric Sensing for Super-Nernstian InN/InGaN Quantum Dots. ACS Omega 2020, 5, 32800–32805. 10.1021/acsomega.0c05364. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Giordano C.; Corbiere T. A Step Forward in Metal Nitride and Carbide Synthesis: From Pure Nanopowders to Nanocomposites. Colloid Polym. Sci. 2013, 291, 1297–1311. 10.1007/s00396-012-2865-x. [DOI] [Google Scholar]
  10. Jung G.; Jeong Y.; Hong Y.; Wu M.; Hong S.; Shin W.; Park J.; Jang D.; Lee J.-H. SO2 Gas Sensing Characteristics of FET- and Resistor-Type Gas Sensors Having WO3 as Sensing Material. Solid. State. Electron. 2020, 165, 107747. 10.1016/j.sse.2019.107747. [DOI] [Google Scholar]
  11. Xu K.; Liao N.; Xue W.; Zhou H. Predicting Gases Sensing Performance of α-MoO3 from Nano-Structural and Electronic Properties. Appl. Surf. Sci. 2020, 509, 144913. 10.1016/j.apsusc.2019.144913. [DOI] [Google Scholar]
  12. Fathil M. F. M.; Md Arshad M. K.; Ruslinda A. R.; Gopinath S. C. B.; Nuzaihan M.N M.; Adzhri R.; Hashim U.; Lam H. Y. Substrate-Gate Coupling in ZnO-FET Biosensor for Cardiac Troponin I Detection. Sens. Actuators, B 2017, 242, 1142–1154. 10.1016/j.snb.2016.09.131. [DOI] [Google Scholar]
  13. Jankovic V.; Chang J. P. HfO2 and ZrO2–Based Microchemical Ion Sensitive Field Effect Transistor (ISFET) Sensors: Simulation & Experiment. J. Electrochem. Soc. 2011, 158, P115. 10.1149/1.3623421. [DOI] [Google Scholar]
  14. Yin Z.; Tordjman M.; Vardi A.; Kalish R.; Del Alamo J. A. A Diamond:H/WO3 Metal-Oxide-Semiconductor Field-Effect Transistor. IEEE Electron Device Lett. 2018, 39, 540–543. 10.1109/LED.2018.2808463. [DOI] [Google Scholar]
  15. Denisenko A.; Jamornmarn G.; El-Hajj H.; Kohn E. PH Sensor on O-Terminated Diamond Using Boron-Doped Channel. Diamond Relat. Mater. 2007, 16, 905–910. 10.1016/j.diamond.2006.12.050. [DOI] [Google Scholar]
  16. Das A.; Ko D. H.; Chen C.-H.; Chang L.-B.; Lai C.-S.; Chu F.-C.; Chow L.; Lin R.-M. Highly Sensitive Palladium Oxide Thin Film Extended Gate FETs as PH Sensor. Sens. Actuators, B 2014, 205, 199–205. 10.1016/j.snb.2014.08.057. [DOI] [Google Scholar]
  17. Chang S. P.; Yang T. H. Sensing Performance of EGFET PH Sensors with CuO Nanowires Fabricated on Glass Substrate. Int. J. Electrochem. Sci. 2012, 7, 5020–5027. 10.1149/ma2012-02/35/2770. [DOI] [Google Scholar]
  18. Li H.-H.; Yang C.-E.; Kei C.-C.; Su C.-Y.; Dai W.-S.; Tseng J.-K.; Yang P.-Y.; Chou J.-C.; Cheng H.-C. Coaxial-Structured ZnO/Silicon Nanowires Extended-Gate Field-Effect Transistor as PH Sensor. Thin Solid Films 2013, 529, 173–176. 10.1016/j.tsf.2012.05.045. [DOI] [Google Scholar]
  19. Gill E.; Arshak K.; Arshak A.; Korostynska O. Mixed Metal Oxide Films as PH Sensing Materials. Microsyst. Technol. 2008, 14, 499–507. 10.1007/s00542-007-0435-9. [DOI] [Google Scholar]
  20. Tian B.; Cohen-Karni T.; Qing Q.; Duan X.; Xie P.; Lieber C. M. Three-Dimensional, Flexible Nanoscale Field-Effect Transistors as Localized Bioprobes. Science 2010, 329, 830–834. 10.1126/science.1192033. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Enneti R. K.; Wolfe T. A. Agglomeration during Reduction of MoO 3. Int. J. Refract. Met. Hard Mater. 2012, 31, 47–50. 10.1016/j.ijrmhm.2011.09.004. [DOI] [Google Scholar]
  22. Rao T.; Saladino M. L.; Fang Y.; Wang X.; Giordano C. Multimetallic Oxynitrides Nanoparticles for a New Generation of Photocatalysts. Chem.—Eur. J. 2019, 25, 16676–16682. 10.1002/chem.201904033. [DOI] [PubMed] [Google Scholar]
  23. Mahdavi M.; Samaeian A.; Hajmirzaheydarali M.; Shahmohammadi M.; Mohajerzadeh S.; Malboobi M. A. Label-Free Detection of DNA Hybridization Using a Porous Poly-Si Ion-Sensitive Field Effect Transistor. RSC Adv. 2014, 4, 36854–36863. 10.1039/c4ra07433e. [DOI] [Google Scholar]
  24. Zhou F.; Zhou Z.; Chen J.; Choy T. H.; Wang J.; Zhang N.; Lin Z.; Yu S.; Kang J.; Wong H.-S. P.; Chai Y. Optoelectronic Resistive Random Access Memory for Neuromorphic Vision Sensors. Nat. Nanotechnol. 2019, 14, 776–782. 10.1038/s41565-019-0501-3. [DOI] [PubMed] [Google Scholar]
  25. Wang S.; Fan W.; Liu Z.; Yu A.; Jiang X. Advances on Tungsten Oxide Based Photochromic Materials: Strategies to Improve Their Photochromic Properties. J. Mater. Chem. C 2018, 6, 191–212. 10.1039/c7tc04189f. [DOI] [Google Scholar]
  26. Sheibani S.; Capua L.; Kamaei S.; Akbari S. S. A.; Zhang J.; Guerin H.; Ionescu A. M. Extended Gate Field-Effect-Transistor for Sensing Cortisol Stress Hormone. Commun. Mater. 2021, 2, 10. 10.1038/s43246-020-00114-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Zhang M.; Averseng F.; Krafft J.-M.; Borghetti P.; Costentin G.; Stankic S. Controlled Formation of Native Defects in Ultrapure ZnO for the Assignment of Green Emissions to Oxygen Vacancies. J. Phys. Chem. C 2020, 124, 12696–12704. 10.1021/acs.jpcc.0c01078. [DOI] [Google Scholar]
  28. Ngamwongwan L.; Fongkaew I.; Jungthawan S.; Hirunsit P.; Limpijumnong S.; Suthirakun S. Electronic and Thermodynamic Properties of Native Point Defects in V2O5 : A First-Principles Study. Phys. Chem. Chem. Phys. 2021, 23, 11374–11387. 10.1039/d0cp06002j. [DOI] [PubMed] [Google Scholar]
  29. Yao P.-C.; Chiang J.-L.; Lee M.-C. Application of Sol-Gel TiO2 Film for an Extended-Gate H + Ion-Sensitive Field-Effect Transistor. Solid State Sci. 2014, 28, 47–54. 10.1016/j.solidstatesciences.2013.12.011. [DOI] [Google Scholar]
  30. Chen S.; Bomer J. G.; Carlen E. T.; Van Den Berg A. Al2O3/Silicon NanoISFET with near Ideal Nernstian Response. Nano Lett. 2011, 11, 2334–2341. 10.1021/nl200623n. [DOI] [PubMed] [Google Scholar]
  31. Van Thanh P.; Nhu L. T. Q.; Mai H. H.; Tuyen N. V.; Doanh S. C.; Viet N. C.; Kien D. T. Zinc Oxide Nanorods Grown on Printed Circuit Board for Extended-Gate Field-Effect Transistor PH Sensor. J. Electron. Mater. 2017, 46, 3732–3737. 10.1007/s11664-017-5369-0. [DOI] [Google Scholar]
  32. Jakob M. H.; Gutsch S.; Chatelle C.; Krishnaraja A.; Fahlteich J.; Weber W.; Zacharias M. Flexible Thin Film PH Sensor Based on Low-Temperature Atomic Layer Deposition. Phys. Status Solidi RRL 2017, 11, 1700123. 10.1002/pssr.201700123. [DOI] [Google Scholar]
  33. Young S.-J.; Chu Y.-J.; Chen Y.-L. Enhancing PH Sensors Performance of ZnO Nanorods with Au Nanoparticles Adsorption. IEEE Sens. J. 2021, 21, 13068–13073. 10.1109/JSEN.2021.3062857. [DOI] [Google Scholar]
  34. Ren H.; Liang K.; Li D.; Zhao M.; Li F.; Wang H.; Miao X.; Zhou T.; Wen L.; Lu Q.; Zhu B. Interface Engineering of Metal-Oxide Field-Effect Transistors for Low-Drift PH Sensing. Adv. Mater. Interfaces 2021, 8, 2100314. 10.1002/admi.202100314. [DOI] [Google Scholar]
  35. Sharma P.; Gupta S.; Singh R.; Ray K.; Kothari S. L.; Sinha S.; Sharma R.; Mukhiya R.; Awasthi K.; Kumar M. Hydrogen Ion Sensing Characteristics of Na3BiO4–Bi2O3 Mixed Oxide Nanostructures Based EGFET PH Sensor. Int. J. Hydrogen Energy 2020, 45, 18743–18751. 10.1016/j.ijhydene.2019.07.252. [DOI] [Google Scholar]
  36. Chiang J.-L.; Jan S.-S.; Chou J.-C.; Chen Y.-C. Study on the Temperature Effect, Hysteresis and Drift of PH-ISFET Devices Based on Amorphous Tungsten Oxide. Sens. Actuators, B 2001, 76, 624–628. 10.1016/S0925-4005(01)00657-8. [DOI] [Google Scholar]
  37. Mishra A. K.; Jarwal D. K.; Mukherjee B.; Kumar A.; Ratan S.; Jit S. CuO Nanowire-Based Extended-Gate Field-Effect-Transistor (FET) for PH Sensing and Enzyme-Free/Receptor-Free Glucose Sensing Applications. IEEE Sens. J. 2020, 20, 5039–5047. 10.1109/JSEN.2020.2966585. [DOI] [Google Scholar]
  38. Mokhtarifar N.; Goldschmidtboeing F.; Woias P. Indium Tin Oxide Coated PET for Differential PH-Sensing Using Field-Effect Transistor Based Sensor. Micro Nano Lett. 2018, 13, 1525–1530. 10.1049/mnl.2018.5240. [DOI] [Google Scholar]
  39. Yang C.-C.; Chen K.-Y.; Su Y.-K. TiO 2 Nano Flowers Based EGFET Sensor for PH Sensing. Coatings 2019, 9, 251. 10.3390/coatings9040251. [DOI] [Google Scholar]
  40. Mokhtarifar N.; Goldschmidtboeing F.; Woias P. ITO/Glass as Extended-Gate of FET: A Low-Cost Method for Differential PH-Sensing in Alkaline Solutions. J. Electrochem. Soc. 2019, 166, B896. 10.1149/2.0401912JES. [DOI] [Google Scholar]
  41. Jamal M.; Razeeb K. M.; Shao H.; Islam J.; Akhter I.; Furukawa H.; Khosla A. Development of Tungsten Oxide Nanoparticle Modified Carbon Fibre Cloth as Flexible PH Sensor. Sci. Rep. 2019, 9, 4659. 10.1038/s41598-019-41331-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Singh K.; Lou B.-S.; Her J.-L.; Pang S.-T.; Pan T.-M. Super Nernstian PH Response and Enzyme-Free Detection of Glucose Using Sol-Gel Derived RuOx on PET Flexible-Based Extended-Gate Field-Effect Transistor. Sens. Actuators, B 2019, 298, 126837. 10.1016/j.snb.2019.126837. [DOI] [Google Scholar]

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