Khairul Aimi Yusof

TiO 2 -based extended gate FET pH-sensor: Effect of annealing temperature on its sensitivity, hysteresis and stability

In this study, titanium dioxide (TiO₂) thin films have been investigated as a sensing membrane of the extended gate field effect transistor (EGFET) for pH detection application. The sol-gel TiO₂ has been prepared and spin coated onto the indium tin oxide (ITO) coated glass as a substrate. Then the TiO₂/ITO test structures thin films were annealed for 15 min at different temperatures; 300 °C and 400 °C under ambient atmosphere. The pH sensing characterizations of TiO₂ thin films were measured by Semiconductor Parametric Device Analyzer in different pH buffer solutions of pH 4, 7, 10 and 12. The sensitivity of TiO₂ thin film annealed at 400 °C exhibited a higher sensitivity that is 51 mV/pH compared to the thin film annealed at 300 °C gave slightly lower sensitivity of 49 mV/pH. The hysteresis and drift effect for TiO₂ thin films also being investigated in this study. TiO₂ thin films annealed at 400 °C obtain better hysteresis and drift value compared to the TiO₂ thin films annealed at 300 °C.

pH sensing characteristics of silicon nitride thin film and silicon nitride-based ISFET sensor

The pH sensing characterizations of silicon nitride (Si₃N₄) thin film, and Si₃N₄-based ISFET sensor were discussed in this paper. The Si₃N₄ thin film was fabricated with to form silicon/silicon dioxide/silicon nitride (Si/SiO₂/Si₃N₄) structure while Si₃N₄-based ISFET was fabricated and packaged as a pH sensor. Both thin film and ISFET packaged device have low pressure chemical vapor deposited silicon nitride as sensing layer. Source measure unit (SMU), the semiconductor device analyzer model Agilent B1500A and a custom made test jig was used to investigate the electrical properties for both Si₃N₄ thin film and Si₃N₄-based ISFET sensor. The measurements were carrying out in three different buffer solutions with various pH levels of 4, 7 and 10 at room temperature. The pH sensitivity of thin film and ISFET packaged device with silicon nitride were 66.9 mV/pH and 53.6 mV/pH respectively. Both have shown good linearity in chosen pH range.

EGFET pH Sensor Performance Dependence on Sputtered TiO2 Sensing Membrane Deposition Temperature

Titanium dioxide (TiO2) thin films were sputtered by radio frequency (RF) magnetron sputtering method and have been employed as the sensing membrane of an extended gate field effect transistor (EGFET) for pH sensing detection application. The TiO2 thin films were deposited onto indium tin oxide (ITO) coated glass substrates at room temperature and 200°C, respectively. The effect of deposition temperature on thin film properties and pH detection application was analyzed. The TiO2 samples used as the sensing membrane for EGFET pH-sensor and the current-voltage (I-V), hysteresis, and drift characteristics were examined. The sensitivity of TiO2 EGFET sensing membrane was obtained from the transfer characteristic (I-V) curves for different substrate heating temperatures. TiO2 thin film sputtered at room temperature achieved higher sensitivity of 59.89 mV/pH compared to the one deposited at 200°C indicating lower sensitivity of 37.60 mV/pH. Moreover the hysteresis and the drift of TiO2 thin film deposited at room temperature showed lower values compared to the one at 200°C. We have also tested the effect of operating temperature on the performance of the EGFET pH-sensing and found that the temperature effect was very minimal.

Spin Speed and Duration Dependence of TiO2 Thin Films pH Sensing Behavior

Titanium dioxide (TiO2) thin films were applied as the sensing membrane of an extended-gate field-effect transistor (EGFET) pH sensor. TiO2 thin films were deposited by spin coating method and the influences of the spin speed and spin duration on the pH sensing behavior of TiO2 thin films were investigated. The spin coated TiO2 thin films were connected to commercial metal-oxide-semiconductor field-effect transistor (MOSFET) to form the extended gates and the MOSFET was integrated in a readout interfacing circuit to complete the EGFET pH sensor system. For the spin speed parameter investigation, the highest sensitivity was obtained for the sample spun at 3000 rpm at a fixed spinning time of 60 s, which was 60.3 mV/pH. The sensitivity was further improved to achieve 68 mV/pH with good linearity of 0.9943 when the spin time was 75 s at the speed of 3000 rpm.

Effect of Annealing Time Process on the pH Sensitivity of Spin-coated TiO2/ ZnO Bilayer Film

This paper presents an investigation on titanium dioxide (TiO2) and zinc oxide (ZnO) bilayer film, which is used as sensing membrane for extended-gate field effect transistor (EGFET) for pH sensing application. TiO2/ZnO thin films were deposited using sol-gel spin coating method on indium tin oxide (ITO) substrates. After the deposition, the bilayer films were annealed at constant temperatures which is 400 °C for 15, 30, 40 and 60 minutes. The sensitivity of the TiO2 thin film towards pH buffer solution was measured by dipping the sensing membrane in pH4, pH7 and pH10 buffer solution. By varying the annealing time, we found that the TiO2/ZnO thin film annealed at 400°C for 15 minutes gave the highest sensitivity compared to other annealing conditions, with the value of 64.87 mV/pH.

Light effect characterization of ISFET based pH sensor with Si 3 N 4 gate insulator

The performance of ISFET based pH sensor device in testing and characterization process of light effect has been successfully done. The experimental setup was carried out by Agilent Technologies B1500A Semiconductor Device Analyzer with an additional readout interfacing circuit (ROIC). This paper reports the electrical characterization test i.e. current-voltage (I-V) measurement and sensitivity, drift and hysteresis test of the fabricated sensor. The I-V measurement was done in light and dark conditions but the drift and hysteresis characterizations were done in dark condition to avoid the influence of light. This experiment used the standard buffer solution to observe the characteristic of the device. From the experimental result, it found that the sensor performance has a light effect due to the light exposure. Drift and hysteresis test using the ROIC showed a good performance in term of the durability, reliability and accuracy of the sensor. The discussion of the light effect on the sensor performance is presented.

Influence of TEOS/Si 3 N 4 passivation layer on the performance of MOSFET/ISFET structure

This paper presents an investigation of dual passivation layer deposition on the characteristic of MOSFET/ISFET structure. PECVD TEOS oxide and LPCVD Silicon nitride (Si3N4) has been used as the passivation layer and deposited on the metal shield layer of ISFET. The Keithley 236 Parameter Analyzer and Semi-auto prober micromanipulator system was used to measure the drain-source current (IDS) versus gate to source voltage (VGS) characteristics. In this study, unpassivated and passivated structure were characterized and compared. The negative shift of threshold voltage, VTH is observed after passivation layer was deposited. This might be due to the charge trapping of electrons or deposition process of passivation layer.

Effect of source-drain metal shield in FET structure on drain leakage current

This study presents the effect of source-drain metal shield in FET structure on drain leakage current. The FET structure was fabricated on the wafer by using MIMOSs standard fabrication process. Aluminum (Al) was sputtered with thickness of 400 nm as metal shield layer at the source and drain area of FET structure. There are four different layout designs of source-drain metal shield that were tested by Keithley 236 current-voltage sourcing under light and dark conditions. The measurements were carried out in a dark box with controllable light intensity. Besides the drain leakage current investigation, this study also investigates the light effect of various layout designs with source-drain metal shield on FET structure. It was found that the layout design with source-drain metal shield has lower drain leakage current compared to the layout design without source-drain metal shield. However, the various layout design of source-drain metal shield cannot eliminate the light effect.

Effect of channel width-to-length ratio on isothermal point of MOSFET-ISFET structure

The effect of channel width-to-length (W/L) ratio on MOSFET-ISFET structures was investigated from simulation and experimental approach. A metal-oxide-semiconductor field-effect-transistor (MOSFET) has been adopted to investigate the isothermal point of an ion-sensitive FET (ISFET), which is needed to suit the readout interfacing circuit of an ISFET sensor. The MOSFET structure with different W/L ratio has been characterized in order to see the effect of W/L ratio to the isothermal point. The Keithley 236 Parameter Analyzer and Semi-auto prober micromanipulator system were used to measure the drain-source current (IDS) versus gate to source voltage (VGS) curves at various temperatures from 30 °C to 60 °C. The simulation result showed that the reduction of W/L ratio can decrease the isothermal point and this was proven by the actual measurement.