Gate Ion-sensitive Field-effect Transistor Research Articles

Application of Double Gate Ion Sensitive Field Effect Transistor for Detection of Fluid Flow Rate in Micro-Channel

In this work a micro flow sensor, using a double gate Ion Sensitive Field Effect Transistor (ISFET) and two metal electrodes, for fluid flow rate measurement in micro-channels were fabricated and demonstrated. By the channel fabrication the molds were patterned reversely on a silicon wafer using Deep Reactive Ion Etcher (DRIE). The double gate ISFET and two metal electrodes were placed on the mold in the distance 15 millimeters. The channels were formed using polydimethylsiloxane (PDMS) from the mold with the width 1000 and 2000 micrometer and the depth of 250 micrometer. After removing PDMS from the mold the channel was bonded with glass substrate by RF plasma technique. By the verification of flow sensors working range water and one mole of sodium nitrate solution were alternated in flow channel. The fluid flow rate were compared with the flow rate from weighing. It found from the comparison that the high deviation was found at low flow rate. Furthermore, the deviation depends also on the dimension of the flow channel.

Body effect minimization using single layer structure for pH-ISFET applications

In this study, the hafnium oxide (HfO 2) thin film deposited by using radio frequency (r.f.) sputter was used as the sensing membrane of ion sensitive field-effect transistor (ISFET) for pH detection. For low cost and easy fabrication, the single HfO 2 gate ISFET without SiO 2 as buffer layer have been developed to compare with the conventional ISFETs with HfO 2 or Si 3N 4 on SiO 2 buffer layer in same process. Electrical characteristics including off current, transconductance, subthreshold swing and body effect of metal–insulator–semiconductor field-effect transistor (MISFET) devices and pH sensing properties including sensitivity, linearity, drift coefficient and body effect of ISFET devices were investigated in detail. The single HfO 2 gate MISFET exhibits better electrical performance like higher transconductance, smaller subthreshold swing and lower body effect than the stack HfO 2/SiO 2 gate MISFET and Si 3N 4/SiO 2 gate MISFET. In pH sensing properties, both the single HfO 2 gate ISFET and the stack HfO 2/SiO 2 gate ISFET show better sensing performance than the stack Si 3N 4/SiO 2 gate ISFET. Due to the concern of exact pH detection and high operation speed for commercial product application, the single HfO 2 gate ISFET with lower body effect on pH detection and higher transconductance is a potential candidate to integrate with an analog readout circuit.

Design and Fabrication of pH Detecting System Using Lead Titanate Series Gate Ion-Sensitive Field Effect Transistors

The amorphous sol-gel-derived lead titanate (PbTiO 3 ) series membranes were prepared as the pH-sensing gate on the ion-sensitive field effect transistor. In this study, the hardware architecture of pH detecting system is built up. The system makes use of constant current and voltage bias technique to ensure that the variations of the output voltage can give directly the variations of pH value. For the purpose of achieving the function of data calibration and driving the liquid crystal display, the 8051 microprocessor is adopted. The pH sensing values of 2.0, 4.0, 6.1, 7.2, 8.0, 9.7 and 11.6 are directly obtained in relation to the standard values of 2.0, 4.0, 6.0, 7.0, 8.0, 10.0 and 12.0 in the buffer solutions, respectively. This shows that the PbTiO 3 -series membrane is successfully applied as an excellent pH-sensing gate.

Characteristics of Cost-Effective Ultrathin HfTiOx Film as Sensitive Membrane in ISFET Fabricated by Anodization

A cost-effective technique was introduced to prepare hafnium-titanium dioxide thin film, which was fabricated by anodic oxidation (anodization) of stacked Hf and Ti metals at room temperature in deionized water. Using the anodization method, the linearity of -gate ion-sensitive field-effect transistor (ISFET) was excellent between the pH 2 and 10 range. In addition, capacitor structure is prepared to characterize the capacitance-voltage and current-voltage curves using high-frequency and measurements, as well as X-ray photoelectron spectroscopy, was also examined to characterize the structural composition.

CMOS-based programmable gate ISFET

A CMOS-based PG-ISFET (programmable gate-ion sensitive field effect transistor) is presented, which compensates for large threshold voltage and device mismatch observed with ISFETs fabricated in an unmodified CMOS process. The proposed device uses a capacitively coupled floating gate to allow tunability of its operating point to counteract the presence of trapped charge, thus allowing the device to operate within a tolerable gate voltage range. Fabricated in a 0.35 µm CMOS process, the device shows good weak-inversion operation for low-power chemical sensing.

Temperature effects on the characteristics of hydrogen ion-sensitive field-effect transistors with sol–gel-derived lead titanate gates

The temperature effects on the characteristics of PbTiO 3 gate ion-sensitive field-effect transistors (ISFETs) operated in the nonsaturation and saturation regions are investigated. The origin of this effect is explained by the ISFET model theory, operating in 5–65 °C range. According to the experimental results, as operated in the nonsaturation region, the pH response increases monotonically as the temperature increases with a temperature coefficient of about 0.106 mV pH −1 ° C −1. However, the linearity drops abruptly above 55 °C. The isothermal point, affected by both the electron mobility and threshold voltage, can be obtained at about I DS =40 μA . Conversely, as operated in the saturation region, the drain-source current is dominated mainly by the electron mobility. The pH response decreases monotonically with an increase in temperature with a temperature coefficient of about −0.071 μA pH −1 ° C −1 . The linearity also becomes worse at higher temperature.

Temperature effects on the characteristics of hydrogen ion-sensitive field-effect transistors with sol?gel-derived lead titanate gates

The temperature effects on the characteristics of PbTiO3 gate ion-sensitive field-effect transistors (ISFETs) operated in the nonsaturation and saturation regions are investigated. The origin of this effect is explained by the ISFET model theory, operating in 5–65 °C range. According to the experimental results, as operated in the nonsaturation region, the pH response increases monotonically as the temperature increases with a temperature coefficient of about 0.106 mV pH−1°C−1. However, the linearity drops abruptly above 55 °C. The isothermal point, affected by both the electron mobility and threshold voltage, can be obtained at about IDS=40μA. Conversely, as operated in the saturation region, the drain-source current is dominated mainly by the electron mobility. The pH response decreases monotonically with an increase in temperature with a temperature coefficient of about −0.071μApH−1°C−1. The linearity also becomes worse at higher temperature.

Preparation and properties of hydrogen ion-sensitive field effect transistors with sol–gel-derived Mg-modified lead titanate gate

A sol–gel-derived Mg-modified lead titanate (PMT) membrane has been applied successfully as a novel hydrogen ion-sensitive layer. The fabrication parameters and characteristics of the amorphous PMT membrane are determined at a firing temperature of 350–450 °C and Mg content below 7 mol% via differential thermal, thermogravimetric and X-ray diffraction analyses. The optimized fabrication parameters of the PMT membrane for hydrogen ion-sensitive field effect transistors (ISFETs) include a Mg content of 4–5 mol%, thickness of 0.5 μm and firing temperature of 400 °C. These parameters were determined via capacitance–voltage measurements of the electrolyte–insulator–semiconductor structure. These membranes exhibit a quasi-Nernstian response of 58–59 mV/pH, good surface adsorption and corrosion resistant characteristics. The output characteristics of the PMT gate ISFET are very similar to those of metal oxide field effect transistors at a specific pH concentration. In the saturation region, the pH response and linearity can be controlled by adjusting the gate–source voltage ( V GS), e.g. the pH responses of −8.4, −24.3 and −32.7 μA/pH and the correlation coefficients of 0.99067, 0.99959 and 0.99963 at V GS=1, 3 and 5 V can be obtained, respectively. In the non-saturation region, a linear pH response exists at about 59 mV/pH.

Drift and Hysteresis Effects on AlN/SiO2 Gate pH Ion-Sensitive Field-Effect Transistor

The nonideal and unstable factors of AlN-based ion-sensitive field-effect transistor (ISFET) devices including the drift and hysteresis effects have been investigated in this study. The drift and hysteresis of AlN-based pH-ISFET devices have been measured using a constant current constant voltage (CCCV) readout circuit. The drift rates were obtained by long-time monitoring for 12 h in pH = 1, 3, 5, 7, 9, and 11 buffer solutions, which indicated that the drift rate increased with the pH value. The hysteresis effect was investigated by exposing the AlN gate ISFET in pH = 7–3–7–11–7 loop cycles with loop times of 960 s, 1920 s and 3840 s, and the magnitudes of hysteresis of 1.0, 1.5 and 4.5 mV were obtained, respectively. The temperature coefficient of hysteresis was found to be approximately 0.234 mV/°C. In addition, it was also found that the hysteresis width with pH started from acid side is smaller than that started from basic side, which results in an asymmetric hysteresis effect.

Characteristics of the hydrogen ion-sensitive field effect transistors with sol–gel-derived lead titanate gate

Abstract The sol–gel-derived lead titanate (PbTiO 3 ) membrane has been successfully applied as a pH sensitive layer to form the PbTiO 3 gate ion-sensitive field-effect transistor (ISFET). There exhibit the excellent quasi-Nernstian response of 56–59 mV pH −1 , good surface adsorption and anticorrosion characteristics via the C – V measurement of the EIS structure. At a specific pH concentration, the output and transfer characteristics are very similar to the behaviours of MOSFETs, and the ISFET model can be derived by the modified MOSFET model. As it operated in the nonsaturation region, there exhibits a linear pH response of about 56–59 mV pH −1 . On the other hand, as it operated in the saturation region, the pH response and linearity can be controlled by adjusting the V GS values, e.g. the pH responses of −4.2, −24.8 and −31.3 μA pH −1 and the correlation coefficients of 0.9491, 0.9995 and 0.9996 at V GS =1, 3 and 5 V can be obtained, respectively. Besides, in order to get the best pH response and the minimized leakage current, the heat treatment temperature of the PbTiO 3 membrane must be limited between 350 and 450 °C.

Nonideal Factors of Ion-Sensitive Field-Effect Transistors with Lead Titanate Gate

Sol–gel-derived lead titanate (PbTiO3) membranes have been successfully applied as H-ion-sensitive layers onto ion-sensitive field-effect transistors (ISFETs), yielding the quasi-Nernstian responses of 56–59 mV/pH. The effects of nonideal factors, such as stable response time, drift, hysteresis, lifetime and temperature, on the characteristics of the PbTiO3 gate ISFET have been investigated. Experimental results show a stable response time of 2–4 min, a drift of 0.5–1 mV/h and a hysteresis of 3–5 mV. Moreover, the PbTiO3 gate ISFET is long-lived, which has a lifetime of more than one year and a reduced pH sensitivity of about -10 µV/pH-day. The thermal effect on the PbTiO3 gate ISFET can mainly be attributed to the buffer solution and semiconductor because the PbTiO3-senstive membrane is unsusceptible to ambient temperature.

Temperature Effect on AlN/SiO2 Gate pH-Ion-Sensitive Field-Effect Transistor Devices

The temperature effect was investigated for the ion-sensitive field-effect transistor (ISFET) devices with an aluminum nitride (AlN) gate insulator. The AlN thin film was prepared on the reference electrode/electrolyte/AlN thin film/SiO2/p-Si substrate structure by radio frequency sputtering technology. The current–voltage characteristics of the AlN/SiO2 gate ISFET were obtained at various temperatures and the pH sensitivities were calculated in the buffer solutions range of pH=1-11. The experimental results show that the pH sensitivities were 48.38, 52.5, 53.83, 54.46, 56.0, 56.36, and 57.25 mV/pH for 5-65±0.1°C (step 10°C). The temperature coefficient of sensitivity (T.C.S.) was determined to be 0.130 mV/pH°C. In addition, the constant voltage constant current (CVCC) readout circuit was used to measure the gate versus source output voltage in various pH buffer solutions at different ambient temperatures, which reveals the same temperature-dependent characteristics of the ISFET.

Preparation and Properties of Lead Titanate Gate Ion-Sensitive Field-Effect Transistors by the Sol–Gel Method

An ion sensitive layer dominates the behavior of the ion-sensitive field-effect transistor (ISFET). In this study, the first proposed PbTiO3 (lead titanate) membrane has been prepared by the sol-gel method as a H ion sensitive layer. Relative permittivity of about 17.0 is obtained by the capacitance–voltage (C–V) measurement of an Al/PbTiO3 metal-insulator-semiconductor (MIS) structure. The fabrication parameters of the PbTiO3 membrane included a thickness of 0.5 µm and a firing temperature between 350°C and 400°C. The pH response is the quasi-Nernstian response of 56–59 mV/pH via the C–V measurement of an electrolyte-insulator-semiconductor (EIS) structure. The pHPZC (the point of zero charge) is about 1.8 calculated by means of the MOS theory and site-binding model. Finally, with the sample PbTiO3 gate ISFET, excellent pH responses of about 56.6 mV/pH and -24.8 µA/pH were achieved, operated at IDS = 37 µA (constant drain-source current) and VDS = 3 V (constant drain-source voltage), respectively.

Study of indium tin oxide thin film for separative extended gate ISFET

Abstract In this study, the indium tin oxide (ITO) was used as a sensitive film for H + ion sensitive field effect transistor (ISFET). The sensitive characteristics of ITO glass structure for separative extended gate ion sensitive field effect transistors (EGFET) were studied. ITO thin film is used for the first time as a H + ion sensitive film which has a linear pH sensitivity of Nerstern response, about 58 mV/pH, between pH 2 and pH 12.

Study on the amorphous tungsten trioxide ion-sensitive field effect transistor

In this study, the pH-sensitive properties of the amorphous tungsten trioxide (a-WO 3) thin films by the RF sputtering system from a WO 3 target have been investigated. The electrolyte–insulator–semiconductor (EIS) structure with a-WO 3 thin film can be used to detect the sensitivity of ion and can be explained by the C– V curve in the different acidic buffer solutions (pH=1–7) using the C– V measurement. In addition, the tungsten trioxide thin films were also deposited on the double layer structure of a-WO 3/SiO 2 gate ion-sensitive field effect transistor (ISFET), and could obtain the shift of the linear region threshold voltage (Δ V T) of the ISFET devices in the acidic solutions. The a-WO 3 materials exhibit a fairly high response, and the sensitivity is obtained at about 50 mV/pH.

The influence of isothermal annealing on tin oxide thin film for pH-ISFET sensor

The aim of this paper is to investigate pH sensitivity of tin oxide thin films prepared by thermal evaporation, and the influences of isothermal annealing on its characteristics. A series of capacitance–voltage ( C– V) curves of SnO 2/SiO 2/Si electrolyte insulator semiconductor (EIS) diodes are used to evaluate pH sensitivity of tin oxide thin films. The results show that tin oxide thin films (as grown) have linear pH sensitivities of approximately 58 mV/pH in a concentration range between pH 2 and pH 10. However, pH sensitivity decreases after the isothermal annealing processes at 300°C, 400°C, and 500°C in N 2 ambiance for 1 h; and pH sensitivity goes further down to only 33 mV/pH, after annealing in N 2 ambiance for 15 h. This phenomenon influences the structure of tin oxide thin films, which will undergo phase transition from amorphous to polycrystal after the isothermal annealing process. Moreover, the characteristics of the tin oxide gate ion-sensitive field-effect transistor (ISFET) (SnO 2/SiO 2 gate ISFET), where the tin oxide is formed under optimum condition, is also presented in this paper.

Platinum-Platinum Oxide Gate pH ISFET

Platinum-platinum oxide gate ISFETs (ion sensitive field effect transistors) have been designed and fabricated for a stable pH microsensor. The platinum oxide layer, formed by a new fabrication process using an RF sputtering technique, was identified as PtO2 by X-ray photoelectron spectroscopy. The pH response of the platinum-platinum oxide gate ISFET was linear in the pH range between 1 and 10, and a sensitivity of 40.5±4.0 mV/pH was obtained. The ISFET developed had better stability than a conventional Si3N4 bare gate ISFET.

Ion-sensitive field-effect transistor with silicon nitride gate for pH sensing

An ion-sensitive field-effect transistor (ISFET) has been fabricated with silicon nitride as the gate to provide a pH-sensing membrane. Measurements of pH sensitivity, selectivity, hysteresis effect and long-term stability have been made. The pH sensitivity is 46 mV per pH. The chemical response to the K+ ion is higher than that for the Na+ ion for this device. The long-term drift is about 1 mV per hour after a ten-hour immersion. Results for an oxide gate ISFET are also shown for comparison.

A CMOS-integrated 'ISFET-operational amplifier' chemical sensor employing differential sensing

The ISFET (ion-sensitive field-effect transistor) pH sensor is first matched with a MOSFET at the differential input stage of a CMOS operational amplifier (called the ISFET-operational amplifier) to cancel out the temperature sensitivity. Then, the output of an ISFET-operational amplifier with a Ta/sub 2/O/sub 5//SiO/sub 2/ gate (58-59 mV/pH) ISFET is differentially amplified against the output of another on-chip ISFET-operational amplifier with a SiO/sub x/N/sub y//Si/sub 3/N/sub 4//SiO/sub 2/ gate ISFET (18-20-mV/pH). An on-chip noble metal counterelectrode serves as the electrical contact to define the electric potential of the electrolyte. No external reference electrode is required. The difference measurement technique achieves (1) common-mode rejection of the solution potential, and (2) relaxation of the requirement that the on-chip reference electrode be ideal. The CMOS-compatible ISFET process is modified from a standard self-aligned polysilicon gate CMOS process with minimal process redesign. The standard CMOS sequence is unaltered until the contact windows are opened. The complete sensor has 40-43-mV/pH pH sensitivity and demonstrates common-mode rejection to ambient light and noise from the electrolyte.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The fabrication and characterisation of ion-sensitive field-effect transistors with a silicon dioxide gate

The ion-sensitive field-effect transistor (ISFET) is a new type of miniaturised semiconductor chemical sensor. It is based on the structure of the metal-insulator-semi-conductor field-effect transistor (MISFET) in which a metal gate is replaced by an ion selective membrane, an electrolyte and a reference electrode. In this paper, an ISFET is fabricated with silicon dioxide as a gate for a pH selective membrane. The measurement of pH sensitivity, selectivity and long-term characteristics of this device have been made. A pH sensitivity can be reached of 40 mV per pH. The oxide gate ISFET device has a significant response to K+ and Na+ ions even at the low concentration of 0.01 mol 1-1. The response to K+ ion is much higher than Na+ ion. The long-term stability of the silicon dioxide gate ISFET is also studied. The long-term drift is about 1 mV per hour after a ten hour immersion.