Extended-gate Field-effect Transistor Research Articles

A Porous Silicon P-Type Interdigitated Extended-Gate Field Effect Transistor pH Sensor

We report on a porous silicon (PSi) p-type interdigitated extended-gate field effect transistor (IEGFET) pH sensor. Two types of crystalline orientation substrates were utilized, namely, p-type and p-type . PSi was prepared by an electrochemical etching method with an etching current density of 20 mA/cm2 and an etching time of 20 min. The scanning electron microscopy investigation revealed that the pore sizes of the p-type were smaller and deeper than those of the p-type for the same etching conditions. The average pore sizes of the p-type ranged from 0.2 to 1 μm with a depth of 19 μm. The p-type pore size and depth were found to be 1 to 4.5 μm and 14 μm, respectively. The proposed devices were tested in real time in a pH range of 3 to 11 at room temperature. The PSi p-type pH sensor exhibited enhanced pH sensitivity and linearity compared to the PSi p-type sensor. The voltage and current sensitivities of the p-type sensor were found to be approximately 43.75 mV/pH and 104 μA/pH, respectively. The PSi p-type exhibited comparatively weak voltage and current sensitivities of 7.5 mV/pH and 27.5 μA/pH, respectively. The performance enhancement of the PSi p-type sensor was due to a higher surface area to volume ratio. The crystal orientation steered the etching direction. The study produced all solid-state semiconductor efficient PSi p-type IEGFET pH sensors without the need for a bulky, fragile and liquid filled reference electrode.

Achieving enhanced pH sensitivity using capacitive coupling in extended gate FET sensors with various high-K sensing films

Sensing properties of various high-k sensing membrane, such as SnO2, HfO2, ZrO2, and Ta2O5, in dual gate extended-gate field-effect transistor (EGFET) were investigated. By adapting the dual-gate structure, high sensitivity exceeding the conventional Nernstian limit on sensitivity (59.15 mV/pH at 25 °C) was realized due to capacitive coupling effect. As a results, it was confirmed that dual-gate EGFET with Ta2O5 sensing membrane which has high permittivity shows the highest sensitivity of 478.0 mV/pH as well as excellent hysteresis voltage and drift rate characteristics.

EGFET-Based Sensors for Bioanalytical Applications: A Review.

Since the 1970s, a great deal of attention has been paid to the development of semiconductor-based biosensors because of the numerous advantages they offer, including high sensitivity, faster response time, miniaturization, and low-cost manufacturing for quick biospecific analysis with reusable features. Commercial biosensors have become highly desirable in the fields of medicine, food, and environmental monitoring as well as military applications, whereas increasing concerns about food safety and health issues have resulted in the introduction of novel legislative standards for these sensors. Numerous devices have been developed for monitoring biological processes such as nucleic acid hybridization, protein–protein interaction, antigen–antibody bonds, and substrate–enzyme reactions, just to name a few. Since the 1980s, scientific interest moved to the development of semiconductor-based devices, which also include integrated front-end electronics, such as the extended-gate field-effect transistor (EGFET) biosensor, one of the first miniaturized chemical sensors. This work is intended to be a review of the state of the art focused on the development of biosensors and chemosensors based on extended-gate field-effect transistor within the field of bioanalytical applications, which will highlight the most recent research reported in the literature. Moreover, a comparison among the diverse EGFET devices will be presented, giving particular attention to the materials and technologies.

Effect of gamma irradiation dose on the structure and pH sensitivity of ITO thin films in extended gate field effect transistor

Abstract Even though several studies have demonstrated the use of Indium Tin Oxides (ITO) as an extended gate field effect transistor (EGFET), the effect of different doses of gamma radiation on the intrinsic properties of the ITO films has not been considered. This study investigates the effect of gamma irradiation on the structural, optical, morphological and electrical properties as well as pH sensitivity (as an extended gate field effect transistor) of ITO thin films. ITO thin films with thickness of 400 nm were prepared using a radio frequency sputtering technique. The samples were then subjected to various doses of gamma radiation from a Co-60 radio-isotope (0.5 kGy, 1 kGy, 1.5 kGy, and 2 kGy). The structural and morphological changes as well as transmission and absorption of the thin films were analyzed using X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Field-Emission Scanning Electron Microscope (FESEM) and UV–Vis spectrophotometry, before and after irradiation. The irradiated ITO thin films were then used as an extended gate field effect transistor to determine its ability to improve sensitivity as pH sensors. The grain size and transmittance in the range 300–900 nm of the ITO films were found to decrease with increasing gamma irradiation dose. In contrast, the uniformity and surface roughness of ITO thin films increased with increasing gamma radiation dose due to the formation of lattice defects. Moreover, the electrical resistance of the thin films increased with increasing dose because of the low current density and high number of surface defects associated with irradiation. The pH sensitivity of the ITO thin films improved after irradiation, possibly due to the concomitant increase in surface roughness with increasing radiation dose. The improvements in the pH sensitivity of ITO thin films after irradiation justify their potential use as pH sensors.

Indium tin oxide coated PET for differential pH‐sensing using field‐effect transistor based sensor

Indium tin oxide (ITO) on polyethylene terephthalate (PET) substrate is characterised in terms of pH-sensitivity. Commercial ITO/PET sheet was cut in a shape of electrode and was connected to the gate-terminal of a metal–oxide–semiconductor field-effect transistor as the sensory part, creating an extended gate field-effect transistor (EGFET) pH-sensor. The quality of laser micromachining as well as the moulded ITO/PET electrode is investigated. The pH-sensitivity and linearity of the sensor signal are studied over time for a single hanging ITO/PET electrode. With the help of a constant-charge amplifier circuitry, the reference electrode, dipped in the measurement cell, is grounded. Therefore, the noise level, coupled into the sensor signal from environment, is decreased and also integration of the second sensor to the measurement cell becomes possible. The pH-measurement is carried out while EGFET pair, immersed into a buffer solution next to a pseudo-reference electrode, is working in differential mode to compensate for the high drift signal rate which is common for this type of sensors. As the result, a very low-cost EGFET-based pH-sensor is achieved based on commercially available products independent of costly cleanroom processes.

Fabrication of integrated solid state electrode for extended gate-FET pH sensor

To realize the miniaturization of an extended gate field effect transistor (EGFET) based sensor, an all solid state phase electrodes are needed. This paper presents the facile fabrication of an integrated solid state electrode (ISSE) consisting a solid state silver/silver chloride (Ag/AgCl) reference electrode (RE) and ZnO nanostructures sensing electrode (SE) on a single 2 × 2 cm2 indium tin oxide (ITO) substrate. The RE and SE was fabricated by thermal evaporation (TE) and simple immersion process respectively. The ISSE was then tested by applying it to an EGFET pH sensor setup and compared with commercialized Ag/AgCl RE; and it was found that the sensor sensitivity for both electrodes are comparable (commercial RE: 52.4 mV pH−1, ISSE: 53.4 mV pH−1).

Development of an aptamer-based field effect transistor biosensor for quantitative detection of Plasmodium falciparum glutamate dehydrogenase in serum samples

There has been a continuous strive to develop portable, stable, sensitive and low cost detection system for malaria to meet the demand of effective screening actions in developing countries where the disease is most endemic. Herein, we report an aptamer-based field effect transistor (aptaFET) biosensor, developed by using an extended gate field effect transistor with inter-digitated gold microelectrodes (IDµE) for the detection of the malaria biomarker Plasmodium falciparum glutamate dehydrogenase (PfGDH) in serum samples. A 90 mer long ssDNA aptamer (NG3) selective to PfGDH was used in the aptaFET to capture the target protein. The intrinsic surface net charge of the captured protein led to change in gate potential of the aptaFET device, which could be correlated to the concentration of the protein. This biosensor exhibited a sensitive response in broad dynamic range of 100 fM −10 nM with limits of detection of 16.7 pM and 48.6 pM in spiked buffer and serum samples, respectively. The high selectivity of the biosensor for PfGDH was verified by testing relevant analogous human and parasitic proteins on the device. Overall, the results validated the application potential of the developed aptaFET for diagnosis of both symptomatic and asymptomatic malaria.

A Protocol to Characterize pH Sensing Materials and Systems

AbstractAlthough significant progress is made in identifying pH sensing materials and device configurations, a standard protocol for benchmarking performance of next‐generation pH devices is still lacking. In particular, key properties of characterization systems, such as inherent component contributions, time plots for extended‐gate field‐effect transistor (EGFET) measurements, and the input resistance (Rin), often go unreported in studies of pH sensing systems. These properties strongly influence the characterization system and can lead to mistaken attribution of properties to the device. In this paper, a series of essential characterization tests and parameters are reported to evaluate pH systems, such as the zinc oxide EGFET, in a standardized protocol. This EGFET ZnO sensor has a sensitivity of −58.1 mV pH−1, drift range from 2.5 to 14.2 µA h−1, and response time of 136 s. By using a ZnO sensing electrode, it is demonstrated that i) intrinsic contributions of reference electrode and commercial transistor (for EGFET) are not negligible; ii) time plots for EGFET configuration and defining a critical point at the onset of drift are essential for accurate sensitivity, response time, and drift reporting; and iii) the results of the pH sensing system are strongly dependent on the input resistance of the used characterization instruments.

In-plane-gate a-IGZO thin-film transistor for high-sensitivity pH sensor applications

In this paper, we propose a thin-film transistor (TFT) with an in-plane-gate (IPG) structure, in which the channel and bottom-gate electrodes are located on the same plane to enhance the sensitivity of the pH sensor. The transistor was applied to an extended-gate field-effect transistor (EGFET) system for disposable sensor implementation. The fabricated IPG pH sensor exhibited amplified pH sensitivity owing to the improved capacitive coupling effects. Moreover, we measured the dependence of the pH sensitivity on the IPG area and evaluated the performance of the pH sensor with the IPG structure. The fabricated IPG pH sensor showed a linearity of 99% or more even for a small IPG area, and the amplification of the sensitivity was improved with further reduction in the area. Notably, we achieved a high sensitivity of 387.58 mV/pH, which is significantly greater than the Nernst limit (59 mV/pH), at the lowest IPG area. To evaluate the stability and reliability of the fabricated IPG pH sensor, non-ideal effects, such as hysteresis and drift characteristics, were considered. The IPG structure exhibited enhanced stability and reliability. Accordingly, we believe that EG-type biosensors with an IPG structure can be useful for biomedicine, clinical diagnosis, environmental monitoring, and point-of-care-testing (POCT) systems.

PH Sensing Characteristics of CuS/ZnO Thin Film Implemented as EGFET

Copper sulphide (CuS) is one of the most important semiconductor materials used in many applications for its semiconducting characteristics. CuS nanoscale thin films were deposited on various substrates using various methods of deposition; recently CuS thin films were used as extended gate field effect transistor (EGFET) and implemented as a pH sensor. In this work, CuS thin film was deposited on ZnO layer using spray pyrolysis deposition (SPD). CuS solution (0.4 M) was prepared from copper(II) chloride and sodium thiosulfate dissolved in deionised water. the precursors used to prepare CuS solution were copper chloride and sodium thiosulfate with 0.4 M concentration, and these precursors were solved using deionized water. The structural characteristics of this thin film show two phases for CuS; covellite and chalcocite with grain size of 31.2 nm. Nanoplate structure with a lot of aggregations was achieved from this deposition and it is confirmed by morphological examination, which estimates the roughness of the film to be 0.145 μm. CuS/ZnO thin film was used as EGFET and applied as pH sensor; the sensitivity and hysteresis were measured for this sensor to be 23.3 mV/pH and 17.5 mV, respectively.

Determination of Selectivity Coefficients of Sodium and Potassium Ion-Selective Electrode Using Porous Silicon N-Type (100) Based Extended Gate Field Effect Transistor

Ion-selective electrode (ISE) was able to accurately detect the ions, precisely for laboratory analysis purposes. The selection of the material varies to select a particular ion, according to the electrode response, and the decisive factor for the optimal selection of ISE for specific ion is the selectivity coefficient. This study used porous silicon (PSi) (100) as an ISE based on extended gate field effect transistor (EGFET) to characterize the selection's preference for sodium (Na+) as a target ion and potassium (K+) is an interference ion. The potential response in the linear region of the EGFET sensor between the detection electrode (PSi) and a reference electrode Ag/AgCl was measured in NaCl, KCl, and a mixed solution of the two salts along ions’ concentration (10-4-1 M) under drain-source voltage 0.3 V at temperature room. The potentiometric selectivity coefficient was calculated by two methods: (1) separate solution method (SSM) at the same activity (0.1 M) and (2) two solution method (TSM). The SSM method, KpotNa,K was 0.581, while the result of TSM method was 0.743. The results showed a slight superiority of Na+ selectivity and acceptable interference resistant for K+.

Thermal Chemically Deposited Zno Nanostructures: Influence of Post-Deposition Annealing Temperature on Ph Sensor Performance

Zinc oxide (ZnO) nanostructures were synthesized via thermal chemical deposition (TCVD) method and applied as the sensing membrane of an extended-gate field effect transistor (EGFET) pH sensor. The ZnO nanostructures undergone a post-deposition heat treatment with the temperature ranging from 200-500 °C for 15 min in air ambient. The influence of the post-deposition heat treatment on the physical and pH sensing characteristics was investigated. The FESEM images showed that the surface morphology of the samples were dependent on post-annealing treatment. The as-deposited sample showed the biggest grain size and non-uniformed structures. Applying the post-annealing heat treatment caused the surface morphology to become denser and uniform. The most ideal temperature for the heat treatment for EGFET pH sensor application was found at 300 °C resulting in a pH sensitivity of 48.2 mV/pH with 0.9646 linearity.

Preparation of V2O5/GOx onto a Screen-Printed Electrode for Sensing Surface of Glucose

Glucose oxidase (GOx) was immobilized on vanadium pentoxide xerogel (V2O5) onto a carbon-based screen-printed electrode to evaluate the possibility of constructing a V2O5/GOx biosensor. Structural characterizations of V2O5/GOx demonstrated a weak interaction between the species. Cyclic voltammetry results for V2O5/GOx after immobilization in 4.4 mmol/L of glucose, pH 5, in PBS medium indicated a stability tendency after several cycles and also an increase of total charge. The use of an electrochemical quartz crystal microbalance technique evidenced a mass loss after several cycles. Experimental studies using variations of glucose concentration and electrical characterization by extended gate field effect transistors is also discussed.

(Invited) Point-of-Care Based System Development for Urolithiasis Recurrence Prevention

Point-of-care (POC) based system becomes more important for aging society and modern life. In Taiwan or globally, most of patients who have a history of urinary stone, the chance of recurrence is about 70 – 80% within 7 years. So, the cost of urinary stone treatment consumes a significant percent of health care insurance. A platform for measuring key parameters of morning spot urine (random urine) to predict the onset of urolithiasis was implemented in this study. This research presents a POC test system developed for urolithiasis recurrence prevention. The system can be used to assist a patient in assessing the condition of his urinary system through urine quality indicators pH, Ca2+, uric acid, conductivity, color and crystallization, etc. Several major types of sensors were used to monitor core parameters in human’s urine. Ion Sensitive Field Effect Transistor and Extended Gate Field Effect Transistor potentiometric-type sensors are used for pH and Ca2+ monitoring, the enzyme based two or three-electrode amperometric type sensor is used for urine’s uric acid sensing, and the self-developed electrodes are used for conductivity measuring. The wireless based prototype with these sensors and CMOS readout circuits were integrated and tested in the laboratory and clinically. In this research, the integrated circuit designs for sub-sensing system implementation were fabricated through TSMC 0.35um and 0.18um CMOS processes. The test results on key parameters monitored by the proposed prototype and fabricated integrated circuits show an acceptable and promising performance referred to corresponding commercial meters for individual parameter sensing. In addition, the prototype system with blue tooth transceiver was developed for wireless communication. Through the data analysis and risk assessment made by urologists, this system can provide a regular urine quality monitoring to patients with urinary stone, the eating and life styles can be consulted or adjusted according to the data base collected from the proposed system and patient individually. The development of this POCT platform will be also useful for improving the life quality of patient with urolithiasis, extending applications in aging societies and reducing an unnecessary cost of health care insurance. Figure 1

Three-Dimensional Polymeric Biointerface for Ultra-Sensitive and Selective Detection of Low-Molecular-Weight Biomarker Using Semiconductor-Based Biosensor

Selective molecular sensing is of great importance in clinical applications. Due to the background noises caused by impurities in physiological samples, realization of selective detection of biomarkers, especially of small biomolecules, remains a great challenge. Herein, we propose a novel biosensing platform based on the extended-gate field-effect transistor (EG-FET) biosensors, particularly targeting glucose in physiological samples. Glucose is one of the most well-known and important biomolecules as a relation to various diseases and the index of health conditions. Moreover, further sensitive and selective detection enables non-invasive monitoring in biological fluids such as tears. FET biosensors can directly detect small biomolecules when they have intrinsic molecular charges, which are recognized inside the Debye length around a gate/solution interface. In particular, the extended-Au gate enables an ultra-sensitive detection of various biomolecules such as glucose, based on the electrochemical and catalytic reactions of glucose with the Au gate surface. If a chromatographic effect is supplied with polymeric membranes on the Au gate surface, only a small biomolecule as target reaches the sensing surface through the polymeric membrane, while the polymeric membrane as a filter captures various impurities outside the Debye length. In a case of glucose, uric acid (UA) and albumin will be the major impurities in tears or serum samples. In this study, we would like to show the impact of filtering effect by particularly utilizing dopamine as a model sample of small molecules, a well-known neurotransmitter, and phenylboronic acid (PBA) as a receptor. To investigate the filtering effect, we prepared the FET sensors, of which surface was modified by the polymeric membrane with or without PBA. Polymerization was carried out using visible light mediated atom transfer radical polymerization (ATRP). After the modification of a Au electrode with ATRP initiator using diazonium salt chemistry, co-polymerization of methacrylic acid, 2-hydroxyethyl methacrylate, and N,N’-methylenebisacrylamide was carried out. Finally, PBA was introduced into the polymeric structure through carboxyl-amino chemical reaction between methacrylic acid and m-aminophenylboronic acid. The gate surface potential was monitored using the FET real-time monitoring system while continuously adding dopamine in it. While the detection limit of the polymer-coated FET sensor without PBA was as low as in nM order, the detection sensitivity of the sensor with PBA polymer decreased significantly to a µM order. This result indicated that dopamine was captured by the PBA-based polymer membrane. Thus, the possibility of both an ultra-sensitive detection of small biomolecules and a filtering effect was clearly verified in this study. The sensor is further applied to the glucose sensor by designing an UA-capturing polymeric membrane above the Au sensing surface. The results will be discussed in the talk.

Full length histone H3 conjugated electrochemical biosensor for extracellular proteolytic Cathepsin L activity detection

Timely and accurate detection of proteolytic extracellular Cathepsin L (CTSL) activity is vital for assessing the metastatic potential of cancer. In this article, extracellular CTSL activity was detected using biotinylated full length histone H3 (BFLH3) treated extended gate (EG) field effect transistors (FETs) with 104 times the sensitivity of fluorometric CTSL activity assays. Upon active reaction by CTSL, the treated BFLH3 is cleaved after amino acid 21, inducing a significant charge change on the EG surface due to the large size and charge of the cleaved BFLH3. This change in EG surface charge can be detected by FET, enabling the quantification of proteolytic extracellular CTSL activity. Moreover, self-normalized quantification of CTSL activity was achieved in heterogeneous LNCaP and PANC-1 cultured cell media, which accurately represented higher CTSL levels in LNCaP derived from metastatic lesion of human prostatic adenocarcinoma. CTSL activity detection with EG FET allows multiple measurements of CTSL activity with one FET and opens up the possibility of detecting other proteolytic enzymes for cancer diagnosis and prognosis.

(Invited) Point-of-Care Based System Development for Urolithiasis Recurrence Prevention

This research presents a Point-Of-Care Test (POCT) system developed for urolithiasis recurrence prevention. The system can be used to assist a patient in assessing the condition of his urinary system through urine quality indicators pH, Ca2+, uric acid, conductivity, etc. Several major types of sensors were used to monitor key parameters in human’s urine. Ion Sensitive Field Effect Transistor and Extended Gate Field Effect Transistor potentiometric-type sensors are used for pH and Ca2+ monitoring, the enzyme based two or three-electrode amperometric type sensor is used for urine’s uric acid sensing, and the self-developed electrodes are used for conductivity measuring. The prototype with these sensors and CMOS readout circuits were integrated and tested in the laboratory and clinically. The test results show the acceptable and promising performance referred to corresponding meters for individual parameter sensing. Through the following data analysis and risk evaluation by urologists, the developed POCT system has a potential value and contribution to kidney stone of urolithiasis recurrence prevention.

Super-Nernstian pH sensors based on WO3 nanosheets

The effects of the surface morphology of hydrothermally grown WO3 nanosheets (NSs) and sputtering WO3 film on the performance of pH sensing electrodes are presented and compared in the pH range of 2–12. Using a separated electrode of an extended-gate field-effect transistor (EGFET) configuration, the WO3 nanosheet (NS) pH sensor shows a sensitivity of 63.37 mV/pH, a good linearity of 0.9973, a low voltage hysteresis of 4.79 mV, and a low drift rate of 3.18 mV/h. In contrast, the film-type one shows a typical sensitivity of only 50.08 mV/pH and a linearity of 0.9932. The super-Nernstian response could be attributed to the significant increase in the number of surface ion adsorption sites of the NS structure and the occurrence of local electric field enhancement over the sharp edges and corners of WO3 NSs.

Annealing Temperature Dependence of ZnO Nanostructures Grown by Facile Chemical Bath Deposition for EGFET pH Sensors

Zinc Oxide (ZnO) nanostructures were deposited using chemical bath deposition (CBD) technique in water bath at 95 °C for 4 h. Post-deposition heat treatment in air ambient at various temperature ranging from 200-600 °C for 30 min was applied in order to enhance the electrical properties of ZnO nanostructures as the sensing membrane of extended-gate field effect transistor (EGFET) pH sensor. The as-deposited sample was prepared for comparison. The samples were characterized in terms of physical and sensing properties. FESEM images showed that scattered ZnO nanorods were formed for the as-deposited sample, and the morphology of the ZnO nanorods changed to ZnO nanoflowers when the heat treatment was applied from 200-600 °C. For sensing properties, the samples heated at 300 °C showed the higher sensitivity which was 39.9 mV/pH with the linearity of 0.9792. The sensing properties was increased with the increasing annealing treatment temperature up to 300 °C before decreased drastically.

Drying Temperature Dependence of Sol-gel Spin Coated Bilayer Composite ZnO/TiO2 Thin Films for Extended Gate Field Effect Transistor pH Sensor

This study presents an investigation on zinc oxide (ZnO) and titanium dioxide (TiO2) bilayer film applied as the sensing membrane for extended-gate field effect transistor (EGFET) for pH sensing application. The influences of the drying temperatures on the pH sensing capability of ZnO/TiO2 were investigated. The sensing performance of the thin films were measured by connecting the thin film to a commercial MOSFET to form the extended gates. By varying the drying temperature, we found that the ZnO/TiO2 thin film dried at 150°C gave the highest sensitivity compared to other drying conditions, with the sensitivity value of 48.80 mV/pH.