Rohanieza Abdul Rahman

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 Post Deposition Annealing Process on the pH Sensitivity of Spin-Coated Titanium Dioxide Thin Film

This paper presents an investigation on titanium dioxide (TiO2) thin film, which is used as sensing membrane for Extended-Gate Field Effect Transistor (EGFET) for pH sensing application. TiO2 thin films were deposited using sol-gel spin coating method on indium tin oxide (ITO) substrates. After the deposition, the thin films were annealed at 300 °C for 10 and 15 min, while another sample was annealed at 400 °C for 15 min. The sensitivity measurement was taken using the EGFET setup equipment with constant-current (100 μA) and constant-voltage (0.5 V) biasing interfacing circuit. TiO2 thin film as the pH-sensitive membrane and the working electrode was connected to a commercial metal-oxide semiconductor FET (MOSFET). The MOSFET then was connected to the interfacing circuit. 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. For comparison, a sample of bare-ITO was also tested to see its sensitivity. We found that the TiO2 thin film annealed at 400 °C for 15 min gave the highest sensitivity compared to other annealing conditions and also compared to the bare ITO substrate with the value of 44.30 mV/pH. This showed that TiO2 thin film can be used for pH sensing and the post-deposition treatment of the thin film can influence the sensing ability. We also measured the TiO2 thin films’ current – voltage (I-V) characteristics. Relating the I-V characteristic of the thin films and sensitivity, the sensing membrane with higher conductivity gave better sensitivity.

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.

The effect of dip-coating speed on Graphene decorated ZnO films for memristor application

ZnO-Graphene material has been proven to show the effect of memristive behaviour. Consequently, a good memristive performance in devices of such materials has the potential in non-volatile memory applications. However, little is known about the significance of nanostructure in making the devices more conductive, thereby improving their performance. Here, we show the electrical, optical and morphological properties of ZnO decorated Graphene film for memristive device by using dip-coating method. Nanoflake structure was observed in samples that had been immersed 5 times for 30 seconds and annealed each time at 250°C for 10 minutes. These samples have higher current than that of samples without the nanostructure. The overall results demonstrate that the nanostructure ZnO and Graphene have greatly improved the current by 16 × 106 order of magnitude, thereby giving rise to improved memristive behaviour with resistance ratio of 1.18.

Characteristics of TiO2/ZnO bilayer film towards pH sensitivity prepared by different spin coating deposition process

In this study, titanium dioxide (TiO2) and zinc oxide (ZnO) bilayer film for pH sensing application will be presented. TiO2/ZnO bilayer film with different speed of spin-coating process was deposited on Indium Tin Oxide (ITO), prepared by sol-gel method. This fabricated bilayer film was used as sensing membrane for Extended Gate Field-Effect Transistor (EGFET) for pH sensing application. Experimental results indicated that the sensor is able to detect the sensitivity towards pH buffer solution. In order to obtained the result, sensitivity measurement was done by using the EGFET setup equipment with constant-current (100 µA) and constant-voltage (0.3 V) biasing interfacing circuit. TiO2/ZnO bilayer film which the working electrode, act as the pH-sensitive membrane was connected to a commercial metal-oxide semiconductor FET (MOSFET). This MOSFET then was connected to the interfacing circuit. The sensitivity of the TiO2 thin film towards pH buffer solution was measured by dipping the sensing membrane in pH4,...

Post-deposition annealing temperature dependence TiO2-based EGFET pH sensor sensitivity

EGFET pH sensor is one type of pH sensor that is used to measure and determine pH of a solution. The sensing membrane of EGFET pH sensor plays vital role in the overall performance of the sensor. This paper studies the effects of different annealing temperature of the TiO2 sensing membranes towards sensitivity of EGFET pH sensor. Sol-gel spin coating was chosen as TiO2 deposition techniques since it is cost-effective and produces thin film with uniform thickness. Deposited TiO2 thin films were then annealed at different annealing temperatures and then were connected to the gate of MOSFET as a part of the EGFET pH sensor structure. The thin films now act as sensing membranes of the EGFET pH sensor and sensitivity of each sensing membrane towards pH was measured. From the results it was determined that sensing membrane annealed at 300 °C gave the highest sensitivity followed by sample annealed at 400 °C and 500 °C.

Annealing time dependence of the physical, electrical and pH response characteristics of spin coated TiO2 thin films

Titanium dioxide (TiO2) thin film was deposited on indium tin oxide (ITO) substrate and used as sensing membrane of EGFET pH sensor. The thin film was fabricated using sol- gel spin coating method. All samples were annealed at 400 °C but the annealing time was varied. This is done to study the effects of annealing time on physical and electrical properties of titanium dioxide thin film. The sensitivity of each sample towards H+ ion was measured and result shows that sample annealed for 45 minutes has the highest sensitivity (52.6 mV/pH). It is found that increasing annealing duration will increase the pH sensitivity but a limit will be reached at certain point. Longer annealing processes done beyond this point will results in lower pH sensitivity.

Annealing temperature effect on the electrical characteristics and pH sensitivity of TiO 2 /ZnO bilayer films

The effect of annealing temperature on the surface morphology and electrical properties of composite bilayer, TiO2/ZnO were studied in this investigation. The composite thin films were applied as the sensing membrane of an Extended Gate Field-Effect Transistor (EGFET) based pH sensor. TiO2 and ZnO were deposited on Indium Tin Oxide (ITO) by using sol-gel spin-coating process. The effects of the varied parameter on the sensor sensitivity and linearity were also investigated. 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. In addition, these thin films were characterized by using Field Emission Scanning Electron Microscope (FESEM) to obtain the surface morphology of the composite thin films. Meanwhile, I-V measurement was done in order to determine the electrical properties of the thin films. According to the result obtained in this experiment, thin film that annealed at highest temperature, which is 500°C produced highest sensitivity, 53.3 mV/pH. Relating the I-V characteristic of the thin films and sensitivity, the sensing membrane with higher conductivity gave better sensitivity.

Sensing capability of TiO 2 thin films with different thicknesses as sensing membrane of EGFET pH sensor

For this research, titanium dioxide (TiO2) is used as the sensing membrane and the thickness of the sensing membrane is varied to study the influence of thickness of sensing membrane towards EGFET pH sensor sensitivity. TiO2 sensing membrane in form of thin film was deposited on an indium tin oxide (ITO) substrate where sol-gel spin coating technique was chosen as the depositing technique. Result shows that increasing thickness will increase the thin film surface roughness. All samples have linearity approximately 1 which indicates that TiO2 is suitable and stable to be used to detect hydrogen ion in solution with different pH values. The sample sensitivity was measured and the result shows that the thinnest sample has the highest sensitivity with value of 56 mV/pH. This value is close to Nernstian theoretical value of 59 mV/pH.