Electrolyte-insulator-semiconductor Research Articles

Enhanced pH sensing with Ce-doped YTixOy sensing membrane in high-performance electrolyte–insulator–semiconductor devices

Electrolyte-insulator-semiconductor (EIS)-based sensors are a novel class of electronic chips designed for biochemical sensing that offer a direct electronic readout, making them part of a new generation of sensing technologies. To enhance the pH sensitivity, in this research we fabricated the CeYTixOy-based EIS sensors with different Ce concentrations (1 %, 5 %, and 10%) by the solution-processing method. The crystal orientation, surface topography, and chemical composition of the sensing film were examined by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy, respectively. The CeYTixOy-based EIS sensor treated with an optimal 5% Ce concentration displays a Super-Nernstian pH response of 66.59 mV/pH with an excellent linearity of 0.99. In the context of reliability, the device exhibited a smaller hysteresis voltage of 7 mV and a lower drift rate of 0.75 mV/h. This result may be attributed to the optimal Ce content in the CeYTixOy leads to the formation of redox couple Ce4+/Ce3+ resulting in less than one electron transferred per proton in the redox reaction.

Electrolyte-Insulator-Semiconductor (EIS) Device with Hafnium Dioxide (HfO2) for pH Detecting

In this work Electrolyte-Insulator-Semiconductor (EIS) device has been developed for pH measurements. This device operates as a Metal-Oxide-Semiconductor capacitor but instead of having the metal contact electrode, an electrolyte solution and a reference electrode are used to apply voltage. As dielectric material and sensitive membrane was chosen hafnium dioxide (HfO2). This film was obtained by RF sputtering, and was structurally characterized by Raman and Ellipsometry. The structural characterization of HfO2 thin film shows the presence of tetragonal phase, physical thickness of 50 nm and refractive index of 1.89, close to stochiometric of 1.91. Was developed MOS capacitors to make the electrical characterization of HfO2 thin films in order to determine the thin film properties, defined by high dielectric constant value (high-k), lower charge density (Q0/q) and flat-band voltage (VFB) around -0.9V. The electrical characterization done by Capacitance x Voltage (CxV) curves revealed high dielectric constant, VFB of 0.02V and Q0/q in the order of -10+12/cm2. The Current x Voltage (IxV) curve shows that the current through the dielectric is approximately 1x10-9A. With dielectric characterized it was possible to develop the EIS device. From electrical characterization it was possible to test the integrity of the electrodes and determined the sensitivity of the device. For electrical measurement of EIS was used Normalized Capacitance x Voltage curve (CxV curve) using different pH (3, 4, 5, 7, 9, 10 and 12) solutions. From the flat band voltage (VFB) of the Normalized CxV curves was possible to determine the sensitivity of the device of 78mV/pH. This result is greater than the Nernst level and greater than results found in the literature.

(Invited) ISFET-Based Sensors

The big difference between an ISFET (Ion Sensitive Field Effect Transistor) and a conventional MOSFET (Metal Oxide Semiconductor FET) is contained in the absence of the upper electrode on the gate oxide of the device, as shown in Figures 1 (a) and 1(b), respectively. In the case of an ISFET (Figure 1(a)), the gate reference electrode with the solution (of chemical or biological materials), which is in contact with the gate oxide (dielectric), work as the upper electrode, inducing the channel in the semiconductor and enabling the conduction of electric current between source and drain terminals. On these two terminals, there are the polymer layers as barrier against chemical or biological solutions. Therefore, the choice of the gate oxide is of great importance, since it must present chemical stability when in contact with the solution that will be measured. The solution pH is the main parameter which is measured. The gate dielectric chosen for application as a pH sensor must carry out measurements in acidic and basic media and be capable of forming hydrogen bonds. This ability is associated with atoms that have greater electronegativity such as fluorine, oxygen and nitrogen. Furthermore, the water contamination metals, DNA, RNA, enzymatic, antigen-antibody and cell related detections can be obtained by ISFETs.Thus, thin films of SiNx, TiOx, TaOx, AlOx and AlN were chosen as gate dielectrics because are compatible to chemical or biological substances. Various results from literature will be present. For example, pH ISFET devices with silicon nitride (SiNx) as gate dielectric were fabricated [2]. Silicon nitride (SiNx) films have been obtained by Low Pressure Chemical Vapor Deposition (LPCVD) at temperature of 720oC for 30 min, using different ratios of [SiH2Cl2]/[NH3] reagent gases. These films been used as ISFET gate dielectric. Figure 2 presents a characteristic of the current between source and drain (IDS) versus voltage between source and gate (VGS) of ISFETs (for voltage VDS of 2V) in related to the four values of pH solution. In this case, sensibility of S=51mV/pH [2]. was estimated, which is close to the expected 59mV/pH determined by the Nernst limit. Other application: Controlling the water quality has become an important issue nowadays, especially due to its contamination along the years which may cause significant damage to human health and in this context, phosphate in water reuse or lead deserves a great attention. The Electrolyte-Insulator-Semiconductor (EIS) structure, which is similar to the gate structure of ISFETs, with TiO2 thin films as gate dielectric, were fabricated and Capacitance x Voltage (CxV) curves to estimate the sensitivity values through the flat-band voltage variation for each curve. In order to enhance the Pb+ detection an additional cerium phosphate layer (TiO2 surface functionalization) was deposited over the TiO2 thin film as selective membrane for Pb+ measurements and the device presented 40 mV/100 ppm sensitivity. For the case of phosphate detection in waste water, EIS devices with TiO2 films as gate dielectric, without functionalization layer, were used and the good sensitivity to phosphate ions of 66 mV/ppm was obtained. Most of results with ISFET devices are based on Si semiconductor conduction channel between the source and drain regions. Others materials have been used as conduction channels of transistors, such as 2D layer, mainly graphene. One example is the biosensor based on Graphene Field Effect Transistor (GraFET), using the TiO2 dielectric gate, capable of being applied effectively for early diagnosis of COVID-19. The graphene channel has ten parallel ribbons, and the virus of SARS-Cov-2 interacts with the unprotected TiO2 gate dielectric. Unlike rapid tests, which depend on the body's immune response (production of IgM and/or IgG antibodies), this project seeks to detect components of the infectious agent itself. It makes graphene-based biosensors very advantageous compared to current tests available since there will be no dependence on the immune response to infection by COVID-19 but only on the presence of the virus in the tested samples. Thus, these devices can reduce the time involved in the analyses.In conclusion, as observed in this review, the ISFET devices are mandatory sensors to develop the future instrumentation, because allow the detection of various chemical and biological species, using different materials as gate dielectrics or electrodes, and conduction channels. Figure 1

Layer-by-Layer Film Based on Sn3O4 Nanobelts as Sensing Units to Detect Heavy Metals Using a Capacitive Field-Effect Sensor Platform

Lead and nickel, as heavy metals, are still used in industrial processes, and are classified as “environmental health hazards” due to their toxicity and polluting potential. The detection of heavy metals can prevent environmental pollution at toxic levels that are critical to human health. In this sense, the electrolyte–insulator–semiconductor (EIS) field-effect sensor is an attractive sensing platform concerning the fabrication of reusable and robust sensors to detect such substances. This study is aimed to fabricate a sensing unit on an EIS device based on Sn3O4 nanobelts embedded in a polyelectrolyte matrix of polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) using the layer-by-layer (LbL) technique. The EIS-Sn3O4 sensor exhibited enhanced electrochemical performance for detecting Pb2+ and Ni2+ ions, revealing a higher affinity for Pb2+ ions, with sensitivities of ca. 25.8 mV/decade and 2.4 mV/decade, respectively. Such results indicate that Sn3O4 nanobelts can contemplate a feasible proof-of-concept capacitive field-effect sensor for heavy metal detection, envisaging other future studies focusing on environmental monitoring.

EIS capacitor sensor, with TiO2 dielectric, applied in the evaluation of phosphate in wastewater

This work presents the development of an Electrolyte-Insulator-Semiconductor (EIS) device with a built-in reference electrode to detect phosphate in wastewater. The idea of developing this device comes from the need to improve the use of water processed by the effluent treatment plant. After treatment process, a fraction of the water can be used as wastewater, this water cannot be consumed, however it can be used for other purposes including cleaning public spaces, such as streets and squares. In the fabrication process of the EIS device, titanium oxide (TiO2) deposited on a silicon substrate was used as a sensor element, and titanium nitride (TiN) was used for the reference electrode. Both materials were deposited by the reactive sputtering process. Aluminum (Al) was used for the electrode on the back of the slide deposited by evaporation. Preliminary results of structural and electrical characterizations indicate that the manufactured device has good sensitivity to phosphate ions (66 mV/ppm). This sensitivity is due to the good quality of the film, which is shown using Raman spectroscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques, in addition to electrical measurements.

Flat band voltage (VFB) drift by integrated reference electrode work function in Electrolyte Insulator Semiconductor (EIS) devices

Electrolyte-insulator-semiconductor (EIS) devices were fabricated using titanium nitride (TiN), gold (Au) and platinum (Pt) as integrated reference electrodes. Here, Au and Pt were deposited by RF sputtering and TiN was deposited by DC sputtering. The devices were developed with different geometries and using silicon (Si) n and p type wafers. A titanium oxide (TiO2) film was used as a pH sensitive membrane in all EIS devices. Capacitance versus voltage (C-V) measurements were used to determine the sensitivity of the devices from their interaction with solutions of pH: 1, 3, 4, 7, 9, 10 and 12. From the analysis of the C-V curves for the EIS capacitors with integrated Pt and Au reference electrodes, two well-defined sensitivity regions are observed: one for acidic and neutral pH solutions, and one for basic pH solutions. This type of behavior is due to the difference between the values of the work functions of Au and Pt, in relation to that of Si. This difference between the work functions causes an increase in the curvature of the energy bands, as the pH value of the solution to be analyzed increases. As a result, leakage currents are generated by Schottky emission and Fowler-Nordheim (F-N) tunneling, causing incorrect displacements in C-V responses when interacting with different pH solutions, and with this, the formation of two regions of sensitivity. For EIS capacitors with TiN as an integrated reference electrode, this effect is not observed because the value of its work function is remarkably close to that of Si.

Comparison of Sb2O3 and Sb2O3/SiO2 Double Stacked pH Sensing Membrane Applied in Electrolyte-Insulator-Semiconductor Structure.

In this study, electrolyte-insulator-semiconductor (EIS) capacitors with Sb2O3/SiO2 double stacked sensing membranes were fabricated with pH sensing capability. The results indicate that Sb2O3/SiO2 double stacked membranes with appropriate annealing had better material quality and sensing performance than Sb2O3 membranes did. To investigate the influence of double stack and annealing, multiple material characterizations and sensing measurements on membranes including of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were conducted. These analyses indicate that double stack could enhance crystallization and grainization, which reinforced the surface sites on the membrane. Therefore, the sensing capability could be enhanced, Sb2O3/SiO2-based with appropriate annealing show promises for future industrial ion sensing devices.

Efficient Illumination for a Light-Addressable Potentiometric Sensor.

A light-addressable potentiometric sensor (LAPS) is a chemical sensor that is based on the field effect in an electrolyte–insulator–semiconductor structure. It requires modulated illumination for generating an AC photocurrent signal that responds to the activity of target ions on the sensor surface. Although high-power illumination generates a large signal, which is advantageous in terms of the signal-to-noise ratio, excess light power can also be harmful to the sample and the measurement. In this study, we tested different waveforms of modulated illuminations to find an efficient illumination for a LAPS that can enlarge the signal as much as possible for the same input light power. The results showed that a square wave with a low duty ratio was more efficient than a sine wave by a factor of about two.

Magnesium-Doped ZnO Nanorod Electrolyte–Insulator–Semiconductor (EIS) Sensor for Detecting Organic Solvents

Electrolyte–Insulator–Semiconductor (EIS) chemical sensor based on vertically aligned Mg doped ZnO nanorod is fabricated to detect different organic solutions at room temperature. The Mg doped ZnO nanorod was prepared by hydrothermal method over Si substrate. The X-ray diffraction (XRD) patterns and field emission scanning electron microscopy (FESEM) images confirm the Mg doped ZnO nanorods have good crystal quality and grow along with the (0 0 2) direction. Additionally, X-ray photoelectron spectroscopy (XPS) results suggest the existence of the Mg into ZnO crystal lattice. The sensing characteristics of Mg-doped ZnO nanorod toward detecting different organic solvents exhibit an excellent response to 2-methoxyethanol with a high sensitivity of 694 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}$ </tex-math></inline-formula> /ppm, low drift rate of 0.062 mV/h and low limit of detection of 185 ppm. The selectivity results shows that the Mg doped ZnO nanorod is most selective to 2-methoxyethanol against acetone, ethanol and methanol.

Detection of Acetoin and Diacetyl by a Tobacco Mosaic Virus-Assisted Field-Effect Biosensor

Acetoin and diacetyl have a major impact on the flavor of alcoholic beverages such as wine or beer. Therefore, their measurement is important during the fermentation process. Until now, gas chromatographic techniques have typically been applied; however, these require expensive laboratory equipment and trained staff, and do not allow for online monitoring. In this work, a capacitive electrolyte–insulator–semiconductor sensor modified with tobacco mosaic virus (TMV) particles as enzyme nanocarriers for the detection of acetoin and diacetyl is presented. The enzyme acetoin reductase from Alkalihalobacillus clausii DSM 8716T is immobilized via biotin–streptavidin affinity, binding to the surface of the TMV particles. The TMV-assisted biosensor is electrochemically characterized by means of leakage–current, capacitance–voltage, and constant capacitance measurements. In this paper, the novel biosensor is studied regarding its sensitivity and long-term stability in buffer solution. Moreover, the TMV-assisted capacitive field-effect sensor is applied for the detection of diacetyl for the first time. The measurement of acetoin and diacetyl with the same sensor setup is demonstrated. Finally, the successive detection of acetoin and diacetyl in buffer and in diluted beer is studied by tuning the sensitivity of the biosensor using the pH value of the measurement solution.

High sensitivity and rapid detection of KRAS and BRAF gene mutations in colorectal cancer using YbTixOy electrolyte-insulator-semiconductor biosensors

The KRAS and BRAF genes are attractive for a predictive biomarker to determine whether the colorectal cancer (CRC) patient predicts response to anti-epidermal growth factor receptor treatment. The detection of KRAS and BRAF mutation statuses has to be considered as a diagnostic and prognostic factor for the treatment of metastatic CRC patients because the targeted therapy may be expensive as well as toxic. In this work, we develop an YbTixOy electrolyte-insulator-semiconductor (EIS) biosensor to detect the KRAS and BRAF gene mutations in CRC. X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry were used to explore the structural features of YbTixOy films prepared under three Ti plasma power conditions. We found that the YbTixOy-based EIS sensor fabricated at the 80 W condition exhibited a higher sensitivity of 69.54 mV/pH (in pH range 2–12), a lower hysteresis voltage of 1 mV (in pH loop of 7→4→7→10→7), and a smaller drift rate of 0.15 mV/h (in pH 7) than those of the other Ti plasma power conditions. Furthermore, we successfully demonstrated that the single strain DNA probe-immobilized YbTixOy EIS biosensors functionalized with 3-aminopropyl triethoxysilane followed by glutaraldehyde were screened for the KRAS and BRAF gene mutations in CRC. High sensitivity and rapid detection of the YbTixOy-based EIS biosensor are expected to serve as the diagnostic tool for clinical examination and screening with CRC.

Label-Free Detection of Saxitoxin with Field-Effect Device-Based Biosensor.

Saxitoxin (STX) is a highly toxic and widely distributed paralytic shellfish toxin (PSP), posing a serious hazard to the environment and human health. Thus, it is highly required to develop new STX detection approaches that are convenient, desirable, and affordable. This study presented a label-free electrolyte-insulator-semiconductor (EIS) sensor covered with a layer-by-layer developed positively charged Poly (amidoamine) (PAMAM) dendrimer. An aptamer (Apt), which is sensitive to STX was electrostatically immobilized onto the PAMAM dendrimer layer. This results in an Apt that is preferably flat inside a Debye length, resulting in less charge-screening effect and a higher sensor signal. Capacitance-voltage and constant-capacitance measurements were utilized to monitor each step of a sensor surface variation, namely, the immobilization of PAMAM dendrimers, Apt, and STX. Additionally, the surface morphology of PAMAM dendrimer layers was studied by using atomic force microscopy and scanning electron microscopy. Fluorescence microscopy was utilized to confirm that Apt was successfully immobilized on a PAMAM dendrimer-modified EIS sensor. The results presented an aptasensor with a detection range of 0.5–100 nM for STX detection and a limit of detection was 0.09 nM. Additionally, the aptasensor demonstrated high selectivity and 9-day stability. The extraction of mussel tissue indicated that an aptasensor may be applied to the detection of STX in real samples. An aptasensor enables marine toxin detection in a rapid and label-free manner.

An electrochemical PAH-modified aptasensor for the label-free and highly-sensitive detection of saxitoxin.

Saxitoxin (STX), is one of the most dangerous and widespread paralytic shellfish toxins, causing a severe threat to the ecosystem and human health. So, it is important and highly essential to develop novel techniques for STX detection in a convenient, desirable, and low-cost manner. Herein, this study developed an electrolyte-insulator-semiconductor (EIS) sensor covered with a layer-by-layer prepared, positively-charged weak polyelectrolyte layer of poly (allylamine hydrochloride) (PAH) for the label-free detection of STX. The specific aptamer (Apt) sensitive to STX was electrostatically adsorbed onto the PAH layer. This leads to a preferentially flat orientation of the Apt within the Debye length, thus yielding a reduced charge-screening influence and a higher sensor signal. Each step of sensor surface modification, i.e. PAH adsorption, immobilization of Apt, and attachment of STX, was monitored by capacitance-voltage (C-V) and constant-capacitance (ConCap) measurements. Furthermore, atomic force microscopy (AFM) was employed to characterize the surface morphology and roughness of the PAH layer. Fluorescence microscopy was used to confirm the effective immobilization of Apt onto the PAH-modified EIS sensor. The results showed that the detection range of this aptasensor for STX detection was 0.5-100nM and the detection limit was as low as 0.05nM. Furthermore, this aptasensor showed good selectivity and 9 days' stability. The mussel tissue extraction test suggested that this aptasensor can be used to detect STX in real samples. This aptasensor provides a convenient approach for moderate, rapid, and label-free detection of marine biological toxins.

Comparison of NH3 and N2O Plasma Treatments on Bi2O3 Sensing Membranes Applied in an Electrolyte-Insulator-Semiconductor Structure.

In this study, bismuth trioxide (Bi2O3) membranes in an electrolyte–insulator–semiconductor (EIS) structure were fabricated with pH sensing capability. To optimize the sensing performance, the membranes were treated with two types of plasma—NH3 and N2O. To investigate the material property improvements, multiple material characterizations were conducted. Material analysis results indicate that plasma treatments with appropriate time could enhance the crystallization, remove the silicate and facilitate crystallizations. Owing to the material optimizations, the pH sensing capability could be greatly boosted. NH3 or N2O plasma treated-Bi2O3 membranes could reach the pH sensitivity around 60 mV/pH and show promise for future biomedical applications.

Miniaturized pH‐Sensitive Field‐Effect Capacitors with Ultrathin Ta2O5 Films Prepared by Atomic Layer Deposition

Miniaturized electrolyte–insulator–semiconductor capacitors (EISCAPs) with ultrathin gate insulators have been studied in terms of their pH‐sensitive sensor characteristics: three different EISCAP systems consisting of Al–p‐Si–Ta2O5(5 nm), Al–p‐Si–Si3N4(1 or 2 nm)–Ta2O5 (5 nm), and Al–p‐Si–SiO2(3.6 nm)–Ta2O5(5 nm) layer structures are characterized in buffer solution with different pH values by means of capacitance–voltage and constant capacitance method. The SiO2 and Si3N4 gate insulators are deposited by rapid thermal oxidation and rapid thermal nitridation, respectively, whereas the Ta2O5 film is prepared by atomic layer deposition. All EISCAP systems have a clear pH response, favoring the stacked gate insulators SiO2–Ta2O5 when considering the overall sensor characteristics, while the Si3N4(1 nm)–Ta2O5 stack delivers the largest accumulation capacitance (due to the lower equivalent oxide thickness) and a higher steepness in the slope of the capacitance–voltage curve among the studied stacked gate insulator systems.

Comparison of ZnO, Al2O3, AlZnO, and Al2O3-Doped ZnO Sensing Membrane Applied in Electrolyte-Insulator-Semiconductor Structures.

In this study, ZnO, AlZnO, Al2O3, and Al2O3-doped ZnO-sensing membranes were fabricated in electrolyte–insulator–semiconductor (EIS) structures. Multiple material analyses indicate that annealing at an appropriate temperature of 500 °C could enhance crystallizations, passivate defects, and facilitate grainizations. Owing to their material properties, both the pH-sensing capability and overall reliability were optimized for these four types of membranes. The results also revealed that higher Al amounts increased the surface roughness values and enhanced larger crystals and grains. Higher Al compositions resulted in higher sensitivity, linearity, and stability in the membrane.

Excellent physicochemical and sensing characteristics of a Re x O y based pH sensor at low post-deposition annealing temperature.

pH monitoring in clinical assessment is pivotal as pH imbalance significantly influences the physiological and extracellular functions of the human body. Metal oxide based pH sensors, a promising alternative to bulky pH electrodes, mostly require complex fabrication, high-temperature post-deposition treatment, and high expenses that inhibit their practical applicability. So, there is still room to develop a straightforward and cost-effective metal oxide based pH sensor comprising high sensitivity and reliability. In this report, a novel solution-processed and low-temperature annealed (220 °C) mixed-valence (vii/vi) oxide of rhenium (RexOy) was applied in an electrolyte–insulator–semiconductor (EIS) structure. The annealing effect on morphological, structural, and compositional properties was scrutinized by physical and chemical characterizations. The post-annealed RexOy exhibited a high pH sensitivity (57.3 mV pH−1, R2 = 0.99), a lower hysteresis (4.7 mV), and a reduced drift rate (1.7 mV h−1) compared to the as-prepared sample for an analytically acceptable pH range (2–12) along with good stability and reproducibility. The magnified sensing performance originated due to the valence state of Re from Re6+ to Re7+ attributed to each electron transfer for a single H+ ion. The device showed high selectivity for H+ ions, which was confirmed by the interference study with other relevant ions. The feasibility of the sensor was verified by measuring the device in real samples. Hence, the ease-of-fabrication and notable sensing performance of the proposed sensor endorsed its implementation for diagnosing pH-related diseases.

Comparison of Magnesium and Titanium Doping on Material Properties and pH Sensing Performance on Sb2O3 Membranes in Electrolyte-Insulator-Semiconductor Structure.

In this research, electrolyte-insulator-semiconductor (EIS) capacitors with Sb2O3 sensing membranes were fabricated. The results indicate that Mg doping and Ti-doped Sb2O3 membranes with appropriate annealing had improved material quality and sensing performance. Multiple material characterizations and sensing measurements of Mg-doped and Ti doping on Sb2O3 sensing membranes were conducted, including of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These detailed studies indicate that silicate and defects in the membrane could be suppressed by doping and annealing. Moreover, compactness enhancement, crystallization and grainization, which reinforced the surface sites on the membrane and boosted the sensing factor, could be achieved by doping and annealing. Among all of the samples, Mg doped membrane with annealing at 400 °C had the most preferable material properties and sensing behaviors. Mg-doped Sb2O3-based with appropriate annealing are promising for future industrial ionsensing devices and for possible integration with Sb2O3-based semiconductor devices.

Field-Effect Sensors Using Biomaterials for Chemical Sensing.

After millions of years of evolution, biological chemical sensing systems (i.e., olfactory and taste systems) have become very powerful natural systems which show extreme high performances in detecting and discriminating various chemical substances. Creating field-effect sensors using biomaterials that are able to detect specific target chemical substances with high sensitivity would have broad applications in many areas, ranging from biomedicine and environments to the food industry, but this has proved extremely challenging. Over decades of intense research, field-effect sensors using biomaterials for chemical sensing have achieved significant progress and have shown promising prospects and potential applications. This review will summarize the most recent advances in the development of field-effect sensors using biomaterials for chemical sensing with an emphasis on those using functional biomaterials as sensing elements such as olfactory and taste cells and receptors. Firstly, unique principles and approaches for the development of these field-effect sensors using biomaterials will be introduced. Then, the major types of field-effect sensors using biomaterials will be presented, which includes field-effect transistor (FET), light-addressable potentiometric sensor (LAPS), and capacitive electrolyte–insulator–semiconductor (EIS) sensors. Finally, the current limitations, main challenges and future trends of field-effect sensors using biomaterials for chemical sensing will be proposed and discussed.

Super-Nernstian pH sensitivity of TbTaO4 sensing film for a solid-state pH sensor

In this work, a super-Nernstian pH sensitivity of TbTaO4 sensing film was developed for an electrolyte-insulator-semiconductor (EIS) solid-state pH sensor. The TbTaO4 sensitive films deposited on the Si substrates through radio-frequency magnetron co-sputtering were prepared under three various Ta plasma powers (80, 120, and 160 W) and then annealed at 800 °C. To investigate the impact of tantalum plasma power, multiple material analyses including X-ray diffraction, secondary ion mass spectrometry, atomic force microscopy, and X-ray photoelectron spectroscopy were performed. Results indicate that the film processed with the 120 W condition might form a stoichiometric TbTaO4 structure and possess a rough surface. Therefore, the best sensing performance was observed for the TbTaO4-based EIS sensor fabricated at the 120 W. In addition, the TbTaO4-based EIS also showed good selectivity for H+ ion over other ions (Na+, K+, Mg2+, and Ca2+). The proposed film fabrication process and analysis may represent a promising approach for the exploration of a novel pH-sensitive TbTaO4 film.