Dual-gate Ion-sensitive Field-effect Transistors Research Articles

Self-sensitivity amplifiable dual-gate ion-sensitive field-effect transistor based on a high-k engineered dielectric layer

In this study, we propose a self-sensitivity amplifiable pH-sensor platform based on a dual-gate (DG) structure ion-sensitive-field-effect-transistor (ISFET) by applying a high-k engineered dielectric layer. We implement amplification according to the capacitance ratio of top and bottom gate dielectric layers through the capacitive coupling effect of DG structure, which exceeds the Nernst limit of the existing ISFET, and maximizes device sensitivity by extracting the change in current based on a reference voltage. In repeated and continuous pH sensitivity measurements and reliability evaluations under external noise conditions, the proposed sensor platform demonstrated excellent linearity and stability. Because the proposed sensor platform significantly exceeds the Nernst limit and has excellent reliability, it is expected to be a promising technology for use as a biosensor platform for detecting analytes with micro potentials.

Fabrication of high-performance dual-gate ISFET pH sensors using In2O3 nano-channel

Here, a high-performance dual-gate ionsensitive field-effect transistor (ISFET) was designed for pH detection based on the high carrier mobility and chemical stability of In2O3. To optimize the structural parameters of the ISFET, the ISFET model with a dual-gate structure was constructed using the Silvaco TCAD. The effects of the channel layer and gate dielectric layer parameters on the performance of the ISFET model were investigated in the dual-gate structure. Following the optimal parameters of the simulation, the dual-gate ISFET chip was fabricated by microfabrication techniques. The pH sensitivity of the fabricated chip was 321.54 mV/pH and exhibited good stability with low drift and hysteresis voltage. In addition, we also tested the pH change caused by the hydrogen peroxide oxidation reaction under catalysis by horseradish peroxidase. The sensitivity was up to 103.28 µA/mM, verifying this high-performance ISFET can be used to detect pH changes of trace substances in the biosensing field.

A proton-selective membrane (PSM)-deposited dual-gate ion-sensitive field-effect transistor (DG-ISFET) integrating a microchamber-embedded filter membrane for bacterial enrichment and antimicrobial susceptibility test

The antimicrobial susceptibility test (AST) is one of the most common methods to evaluate bloodstream infections (BSI). Currently, AST methods usually required prolonged sample preparation processes and bulky systems, making it difficult to provide timely information for clinical decisions. In this paper, we integrated a proton-selective membrane (PSM)-deposited dual-gate ion-sensitive field-effect transistor (DG-ISFET) with a microchamber-embedded filter membrane to perform bacterial enrichment and incubation followed by on-chip AST. The DG-ISFET sensor consists of a high-k dielectric hafnium oxide (HfO2) sensing surface and dual gate, enabling high ion sensitivity, and low drifting and hysteresis issues. By depositing a PSM on DG-ISFET, the sensor has higher proton sensitivity and selectivity, preventing interference from other ion signals in the bacterial culture medium. To further shorten the bacterial culture time, we integrated a microchamber-embedded filter membrane on top of the DG-ISFET sensor to enrich the amount of bacteria and place seeded bacteria close to DG-ISFET’s sensing surface. As a proof of concept, we first evaluated the proton sensitivity and selectivity of DG-ISFET under various PSM deposition thicknesses. Then, we demonstrated that the PSM-deposited DG-ISFET system can successfully distinguish kanamycin-susceptible and resistant Escherichia coli strains treated with various kanamycin concentrations in 30 min based on the continuous drain-source current (Ids) pattern. We envision that this fully integrated system can perform rapid, real-time, continuous AST, which can potentially be applied in resource-limited environments or point-of-care settings.

Dual‐gate ion‐sensitive field‐effect transistors: A review

AbstractIon‐sensitive field‐effect transistors (ISFETs) are electrochemical sensors that work on the principle of metal‐oxide field‐effect transistors. Dual‐gate ion‐sensitive field‐effect transistors (DGISFETs) are an advanced version of ISFETs with an additional gate dielectric, resulting in sensitivity enhancement on account of the coupling of the capacitances of the two gate dielectrics. ISFETs were demonstrated first in 1970 and there are several review articles available on various aspects of ISFETs; although DGISFETs were first demonstrated in 2010, there are no focused review articles on this subject and this is the motivation of present work. This review has explored the understanding of the basic platform, the working principle, different structures, and various applications of DGISFETs. Further, types of DGISFETs are elaborated based on their architecture, material used for fabrication, and substrates used for such devices with utilization of different semiconductor and gate dielectric materials, rigid and flexible substrates. The state‐of‐the‐art of rigid and flexible DGISFETs is discussed for various applications. Challenges in the fabrication and utilization of DGISFETs in various fields and further advances are discussed.

Super-Nernstian ion sensitive field-effect transistor exploiting charge screening in WSe2/MoS2 heterostructure

Ion-sensitive field-effect transistors (ISFETs) have gained a lot of attention in recent times as compact, low-cost biosensors with fast response time and label-free detection. Dual gate ISFETs have been shown to enhance detection sensitivity beyond the Nernst limit of 59 mV pH−1 when the back gate dielectric is much thicker than the top dielectric. However, the thicker back-dielectric limits its application for ultrascaled point-of-care devices. In this work, we introduce and demonstrate a pH sensor, with WSe2(top)/MoS2(bottom) heterostructure based double gated ISFET. The proposed device is capable of surpassing the Nernst detection limit and uses thin high-k hafnium oxide as the gate oxide. The 2D atomic layered structure, combined with nanometer-thick top and bottom oxides, offers excellent scalability and linear response with a maximum sensitivity of 362 mV pH−1. We have also used technology computer-aided (TCAD) simulations to elucidate the underlying physics, namely back gate electric field screening through channel and interface charges due to the heterointerface. The proposed mechanism is independent of the dielectric thickness that makes miniaturization of these devices easier. We also demonstrate super-Nernstian behavior with the flipped MoS2(top)/WSe2(bottom) heterostructure ISFET. The results open up a new pathway of 2D heterostructure engineering as an excellent option for enhancing ISFET sensitivity beyond the Nernst limit, for the next-generation of label-free biosensors for single-molecular detection and point-of-care diagnostics.

A handheld testing device for the fast and ultrasensitive recognition of cardiac troponin I via an ion-sensitive field-effect transistor

Cardiac troponin I (cTnI) is an efficient and specific biomarker for the accurate diagnosis of acute myocardial infarction (AMI), one of the diseases with the highest mortality worldwide. Due to the short course and high fatality of this disease, a rapid, accurate and portable device for quantitative detection is urgently needed for early diagnosis and treatment. In this work, we designed a handheld device based on a dual-gate ion-sensitive field-effect transistor (ISFET) for early and accurate warning of AMI through cTnI detection. A one-step enzyme-linked immunosorbent assay strategy was proposed for use in this device to recognize trace cTnI in serum, converting the cTnI concentration to a drain-source current generated by an ultrasensitive ISFET. This portable device exhibited an ultrahigh sensitivity of 132 pA pg−1·mL−1, a wide linear range from 1 to 1000 pg/mL that enabled coverage far exceeding the threshold level (280 pg/mL), and a low detection limit of 0.3 pg/mL for the cTnI assay, which was much lower than the current diagnostic cut-off for a healthy control level for AMI (40 pg/mL). In addition, this handheld device showed satisfactory selectivity and reliable results in the analysis of real serum within 20 min, indicating its potential applications in early screening and diagnosis for the clinical evaluation of AMI.

High sensitivity In-Ga-Zn-O nanofiber-based double gate field effect transistors for chemical sensing

Herein, a high sensitivity In-Ga-Zn-O (IGZO) nanofiber channel double gate (DG) field-effect transistor (FET)-based chemical sensor is described. Transparent and flexible IGZO nanofiber channels were fabricated by electrospinning, and IGZO film channels were prepared for comparison via spin coating. We connected a separative extended gate (EG) with a chemical sensing membrane to the fabricated IGZO FETs to test their applicability to pH sensing applications. The effectiveness of the IGZO nanofiber channel was verified by comparing the pH sensitivity and non-ideal effects such as drift and hysteresis voltage with the IGZO film channel. The nanofiber channel showed much higher sensitivity in the dual gate ion-sensitive field-effect transistor (DG ISFET) than the film channel as it has an increased capacitive coupling effect due to an increase in the upper channel surface area and a decreased channel bottom surface area. The sensitivity of the DG ISFET with an IGZO nanofiber channel was 998 mV/pH at room temperature, surpassing the 384 mV/pH of the IGZO film channel, which itself far exceeded the Nernstian limit of 59.16 mV/pH. Furthermore, the nanofiber channel had a lower hysteresis voltage and drift rate compared to its amplified sensitivity, and exhibited a more stable performance than the film channel. Therefore, IGZO nanofiber-based DG FET chemical sensors are expected to be promising for use in transparent and wearable biosensor applications.

Interfacial charge regulation of protein blocking layers in transistor biosensor for direct measurement in serum

Ion-sensitive field-effect transistor (ISFET) as a biosensor facilitates a process of data-acquisition through label-free and real-time monitoring. Direct quantification of a biomarker in serum is challenging in ISFET biosensor since charged proteins in serum interfere transduction to electrical signals. Here, we report the fabrication of protein blocking layers (PBLs) with intended interfacial charges to minimize non-specific protein bindings on ISFET. Use of charged protein precursors enables to regulate the interfacial charge of PBLs, preserving their intrinsic electric features (neutral: hemoglobin, positively charged: lysozyme, negatively charged: BSA). The effect of this interfacial charge on the signal was demonstrated through PSMA (prostate cancer biomarker) sensing using a dual-gate ISFET biosensor. The neutral PBL showed the minimum noise compared to the negatively and positively charged PBLs, enabling the ISFET to exhibit the same detection range in untreated serum as with pre- or post-treatment (1 fg/ml to 100 ng/ml). The introduction of neutral PBLs to ISFET biosensors would allow the application of the ISFET biosensor as a point-of-care device.

Stacked Top Gate Dielectrics in Dual Gate Ion Sensitive Field Effect Transistors: Role of Interfaces

Dual gate ion sensitive field effect transistors (DGISFETs) have elicited interest due to the capability to provide pH sensitivity values several times the Nernst limit. The interfaces in the devic...

A pH/Light Dual-Modal Sensing Isfet Assisted By Artificial Neural Networks

Multi-modal sensing system is essential in healthcare and internet-of-things (IoT) [1]. Making the sensor systems small, low power and cost effective is the ultimate goal to fulfill the growing needs. To achieve this requirement, we present a single-device-dual-sensor by transforming a conventional dual-gate ion sensitive field-effect transistor (DG-ISFET) [2] to a pH/light bi-functional sensing device. In addition to pH sensing ability, since photocurrent in DG-ISFET has been proved to be controllable by gate voltages [3], it is possible to detect light by a DG-ISFET. However, the signals of pH and light are coupled together in a complicated manner. Therefore, in order to realize an effective dual-sensor, we introduce a sequential re-configuration method and back-propagation neural network (BPNN) to DG-ISFET in order to distinguish and quantify the signal from pH and light generated by the same device. The sequential re-configuration (SRC) method used in this work aims to mimic the function of sensor array in a multi-sensing system. To achieve this goal, the gate bias of DG-ISFET is intentionally configured in a sequential manner by tuning top and bottom gate voltages. In other words, we virtually generate a number of sensors with different sensitivities to light and pH from a single DG-ISFET device to replace the sensor array in the multi-sensor system. Afterwards, the output signals are processed by machine learning algorithms to quantify the actual value of the analytes. To quantify the pH value and light intensity, BPNN serving as a regression machine learning algorithm are employed. The regression results given in the form of boxplot of pH value and light intensities is shown in figure1. Based on the results, the error between calculated and true intensity is smaller than 10 μW/cm2 or 1.1% of every level of light intensity. pH values, on the other hand, have smaller calculation error of 0.5%. Based on these results, BPNN models are capable for practical applications to measure pH value and light intensity. Furthermore, the algorithm-calculated results have smaller variation than the direct-measured data does. It indicates the process variation of different sensors can be mitigated by the proposed SRC method with algorithms. This SRC based DG-ISFET reduces the need of sensor array and improves data consistency compared with a real sensor array. At the same time, back-propagation neural networks are employed to construct the data processing models to realize multi-signal quantification. Based on this work, the light interference of DG-ISFET can be transformed into effective illumination sensing quantity. And the proposed SRC-based single-chip-dual-sensing technique has good potential to be applied to sensor fusion technologies for healthcare and environmental monitoring.

A pH/Light Dual-Modal Sensing ISFET Assisted by Artificial Neural Networks

Multi-modal sensing system is essential in internet-of-things (IoT). Making the sensor systems small, low power and cost effective is the ultimate goal to fulfill the growing needs. To achieve this requirement, we present a single-device-dual-sensor by transforming a conventional dual-gate ion sensitive field-effect transistor (DG-ISFET) to a pH/light bi-functional sensing device. In order to realize an effective dual-sensor, we introduce a sequential control method and back-propagation neural network (BPNN) to DG-ISFET in order to distinguish and quantify the signal from pH and light generated by the same device. The BPNN models are capable for practical applications to measure pH value and light intensity. Based on the results, the light interference of DG-ISFET can be transformed into effective illumination sensing quantity for dual-modal sensing applications.

Role of deposition and annealing of the top gate dielectric in a-IGZO TFT-based dual-gate ion-sensitive field-effect transistors

The deposition of the top gate dielectric in thin film transistor (TFT)-based dual-gate ion-sensitive field-effect transistors (DG ISFETs) is critical, and expected not to affect the bottom gate TFT characteristics, while providing a higher pH sensitive surface and efficient capacitive coupling between the gates. Amorphous Ta2O5, in addition to having good sensing properties, possesses a high dielectric constant of ∼25 making it well suited as the top gate dielectric in a DG ISFET by providing higher capacitive coupling (ratio of Ctop/Cbottom) leading to higher amplification. To avoid damage of the a-IGZO channel reported to be caused by plasma exposure, deposition of Ta2O5 by e-beam evaporation followed by annealing was investigated in this work to obtain sensitivity over the Nernst limit. The deteriorated bottom gate TFT characteristics, indicated by an increase in the channel conductance, confirmed that plasma exposure is not the sole contributor to the changes. Oxygen vacancies at the Ta2O5/a-IGZO interface, which emerged during processing, increased the channel conductivity, became filled by optimum annealing in oxygen at 400 °C for 1 h, which was confirmed by an x-ray photoelectron spectroscopy depth profiling analysis. The obtained pH sensitivity of the TFT-based DG ISFET was 402 mV pH−1, which is about 6.8 times the Nernst limit (59 mV pH−1). The concept of capacitive coupling was also demonstrated by simulating an a-IGZO-based DG TFT structure. Here, the exposure of the top gate dielectric to the electrolyte without applying any top gate bias led to changes in the measured threshold voltage of the bottom gate TFT, and this obviated the requirement of a reference electrode needed in conventional ISFETs and other reported DG ISFETs. These devices, with high sensitivities and requiring low volumes (∼2 μl) of analyte solution, could be potential candidates for utilization as chemical sensors and biosensors.

Back-Channel Electrolyte-Gated a-IGZO Dual-Gate Thin-Film Transistor for Enhancement of pH Sensitivity Over Nernst Limit

A dual-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) was studied to obtain a pH sensitivity of $\sim 160$ mV/pH, which is above Nernst limit (59 mV/pH) with a low value of operating voltage (−5 to 5 V). The utilization of the active layer itself as the sensitive surface constitutes the dual-gate TFT structure with the back-channel gated with the electrolyte. The TFT characteristics were optimized by annealing the IGZO film in varying temperatures in oxygen ambience. A double-layered a-IGZO was used to sandwich the source/drain electrodes to eliminate the issues related with the high contact resistance and critical passivation of source/drain electrodes to protect from the exposure of the electrolyte. The single-gate electrolyte-gated thin film transistor showed the pH sensitivity of 24 mV/pH, which was enhanced by 6.7-fold by its dual-gate operation. The operation of dual-gate TFT ion-sensitive field-effect transistors (ISFETs) with varying only bottom gate voltage eliminates the requirement of a reference electrode necessary in single-gate ISFETs. Such dual-gate ISFETs obviate the need of an additional high- $K$ dielectric needed for the dual-gate TFT ISFETs and could also be fabricated on flexible substrates. These structures with the high sensitivity of $\sim 160$ mV/pH and requiring low ( $\sim 2~\mu \text{L}$ ) analyte solution could be the potential candidates for utilization as chemical and bio-sensors.

유연한 폴리이미드 기판 위에 구현된 확장형 게이트를 갖는 Silicon-on-Insulator 기반 고성능 이중게이트 이온 감지 전계 효과 트랜지스터

유연한 폴리이미드 기판 위에 구현된 확장형 게이트를 갖는 Silicon-on-Insulator 기반 고성능 이중게이트 이온 감지 전계 효과 트랜지스터

SOI dual-gate ISFET with variable oxide capacitance and channel thickness

A dual-gate (DG) ion sensitive field effect transistor (ISFET) using capacitance coupling effect has recently been proposed to overcome the Nernst limitation as 59mV/pH. In this study, we focus on the analysis of sensing characteristics by various oxide capacitances and channel thickness using intensive measurement on conventional fully depleted (FD) silicon-on-insulator (SOI) based DG ISFET. The enlarged oxide capacitance and reductive channel thickness enhance the capacitive coupling effect and increase sensitivity of DG ISFET. And also, the thin channel thickness reduced the leakage current in the DG operation. These will be very promising techniques for high performance biosensor application.

Improved sensing performance of polycrystalline-silicon based dual-gate ion-sensitive field-effect transistors using high-k stacking engineered sensing membrane

Improved sensing performance, larger pH sensitivity that breaches the Nernst response limit with excellent stability, was realized on polycrystalline silicon based dual-gate (DG) ion-sensitive field-effect transistors. The capacitive coupling between the top and bottom gate oxides for a DG operation amplified its sensitivity to as high as 325.8 mV/pH. In particular, the SiO2/HfO2/Al2O3 (OHA) layer, proposed as an engineered sensing membrane, significantly reinforced the sensing margin of devices as well as the chemical stability for long-term use. The sensing characteristics of the OHA and conventional SiO2 layer were evaluated for single gate and DG operation modes, respectively.

Fabrication of high-performance fully depleted silicon-on-insulator based dual-gate ion-sensitive field-effect transistor beyond the Nernstian limit

High-performance dual-gate (DG) ion-sensitive field-effect transistors (ISFETs) beyond the Nernstian limit of 59 mV/pH were realized using the fully depleted (FD) silicon-on-insulator (SOI) substrate. The FD SOI-based DG ISFET exhibited a significantly enhanced pH sensitivity of 379.2 mV/pH for DG operation amplified by capacitive coupling, while it exhibited a relatively poor sensitivity of 47.9 mV/pH for single-gate (SG) operation. Meanwhile, the non-ideal effects for long-term use slightly increased by the DG operation compared to the SG operation. Therefore, the FD SOI-based DG ISFETs compatible with the complementary metal-oxide-semiconductor process are considered to be very promising bio-chemical sensors.