Sukreen Hana Herman

Fabrication and Characterization of PZT Thin Film Capacitors for MMIC Applications

This paper reports on the use of thin lead zirconate titanate (PZT) films for monolithic microwave integrated circuit (MMIC) capacitors to replace existing materials for better size-reduction. The films were sputtered on Pt/Ti/SiO2 coated, undoped silicon wafers. Square Pt electrodes with sides ranging from 10 mum to 50 mum were patterned on the PZT layers to form the capacitors. Results of this study show that PZT thin films can be utilized for efficient size reduction in MMIC. The linewidth obtained for a 50 Omega transmission line is merely 300 nm - this results in a size reduction of approximately five times compared to conventional MMIC. For a 50 times 50 mum electrode area, capacitance values ranging from 5 to 20 pF were obtained at frequencies up to 20 GHz. Suitable de-embedding of S parameters using Cascade microwave probes revealed films with relative permittivities of the order of 100 to 500

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.

Effect of film thickness on the memristive behavior of spin coated titanium dioxide thin films

The paper presents the memristive behavior of spin-coated titania thin films. The spin speed during the deposition was varied and their effect on the film thickness and thus, to the memristive behavior was studied. Sample deposited at 5000 rpm produced thinner film thickness which result in better switching behavior. The sample showed larger OFF to ON resistance ratio of 5. All samples were measured 3 times for each positive and negative bias. It was found that the memristive behavior was repeatable for 2nd and 3rd measurement. The crystallinity of the films was characterized using Raman spectroscopy. In our work, it was observed that the film thickness mainly affects the switching behavior of memristive device instead of the crystallinity of the films.

Influence of Doping Concentration on Dielectric, Optical, and Morphological Properties of PMMA Thin Films

PMMA thin films were deposited by sol gel spin coating method on ITO substrates. Toluene was used as the solvent to dissolve the PMMA powder. The PMMA concentration was varied from 30 ~ 120 mg. The dielectric properties were measured at frequency of 0 ~ 100 kHz. The dielectric permittivity was in the range of 7.3 to 7.5 which decreased as the PMMA concentration increased. The dielectric loss is in the range of 0.01 ~ –0.01. All samples show dielectric characteristics which have dielectric loss is less than 0.05. The optical properties for thin films were measured at room temperature across 200 ~ 1000 nm wavelength region. All samples are highly transparent. The energy band gaps are in the range of 3.6 eV to 3.9 eV when the PMMA concentration increased. The morphologies of the samples show that all samples are uniform and the surface roughness increased as the concentration increased. From this study, it is known that, the dielectric, optical, and morphology properties were influenced by the amount of PMMA concentration in the solution.

Optical and Electrical Characteristic of Layer-by-Layer Sol-Gel Spin Coated Nanoparticles ZnO Thin Films

Transparent nanoparticles ZnO thin films have been deposited on glass substrates using sol-gel spin coating technique. 0.35M sol were prepared by dissolving zinc acetate dehydrate in 2-methoxyethanol with monoethanolamine as the stabilizer. In this paper, a novel method called layer-by-layer is introduced, where the thin film is not only dried after each layer is spin-coated, but also directly annealed at 500°C to improve the electrical and optical properties of the films. Samples without annealing were also prepared as the reference sample. ZnO thin films were characterized using current-voltage measurement, UV-Vis spectroscopy and photoluminescence spectroscopy. The results revealed that layer-by-layer ZnO thin films have lower resistivity compared to the reference samples with a maximum value of 0.77Ω.cm for ZnO films deposited with 2 layers. Transmittance spectra show that the films were transparent in the visible range above 400nm with range of 86%-98% for the layer-by-layer ZnO films. The optical band gaps were between 3.2 to 3.3eV for both layer-by-layer and the reference samples. PL spectra indicate that layer-by-layer method improves the crystallinity of the films.

Optical Properties and Surface Morphology of PMMA: TiO2 Nanocomposite Thin Films

Sol-gel spin coated PMMA:TiO2 nanocomposite thin films on glass substrates were studied by comparing two types of the sol-gel solutions. Two types of PMMA:TiO2 nanocomposite sol-gel solutions were prepared; one using Degusa (P25), and the other one is using self-prepared TiO2 powder. The self-prepared nanosized TiO2 powder is obtained by drying the TiO2 sol-gel using solvothermal method followed by grinding the TiO2 crystal using ball miller. Triton-X was used as surfactant to stabilize the composite. Besides comparing the nanocomposite solution, we also studied the effect of the thin films thickness on the optical properties and their surface morphology. The optical properties and surface morphology were measured with UV-VIS spectrometer and atomic force microscopy (AFM). The result showed that nanocomposite PMMA with self-prepared TiO2 give high optical transparency than that of with Degusa (P25). The results also indicate that as the thickness is increased the optical transparency are decreased. Both AFM images showed that the agglomerations of TiO2 particles occurred on top of the thin film and the surface roughness increased when the thickness is increased. AFM results show that nanocomposited PMMA with P25 has high agglomeration particles compared to the other one.

Effect of Post-Deposition Annealing Process on the Resistive Switching Behaviour of TiO2 Thin Films by Sol-Gel Method

The paper presents the memristive behaviour of spin-coated titania thin films on ITO substrate. The sample was annealed in air ambient at different annealing temperature and duration of 250 and 450 °C for 20 and 60 min. The effect of post-annealing process to the physical thickness and crystallinity of the films towards switching behaviour was studied. It was found that the thickness and crystallinity of the films increases as the post annealing process increases. Sample annealed at 250 °C for 20 min with thinner film showed better switching behaviour even though the sample is still in amorphous form. Thus, in our work, we believed that the crystallinity of the films does not affect the switching behaviour of the sample. The reliability of device performance was studied by repeating the measurement for three times.

Self-Catalyzed Thermal Chemical Vapor Deposited ZnO Nanotetrapods

ZnO in various nanostructures forms have been widely studied for the application such as in solar cells, light emitting diodes, UV sensors and so on. In this paper, we have successfully deposited ZnO nanotetrapods using thermal chemical vapour deposition (TCVD) technique on layer-by-layer ZnO seeded catalyst, with Zn powder and O2 gas as source materials. We demonstrate that by using double furnace TCVD system, ZnO nanotetrapods can be deposited at lower temperature than the vapour temperature of the Zn powder. In this paper we report the effect of different deposition temperature (450 °C to 600 °C) on the surface morphologies, crystalline structure and optical properties of the ZnO nanotetrapods. FE-SEM micrographs show that the length of the nanotetrapods arms decreases with the increase of the deposition temperature. PL spectra show that the visible emission are very low compared to the UV emission which indicates that the ZnO tetrapod have very low intrinsic defect. The highest UV emission intensity is given by the sample deposited at 500 °C.

Sputtered titanium dioxide thin film for Extended-Gate FET sensor application

This paper presents an investigation on sputtered titanium dioxide (TiO2) thin film for application in the Extended-Gate Field Effect Transistor (EGFET) sensor application for pH detection. The TiO2 thin film was fabricated on conductive indium-tin oxide (ITO) covered glass by using RF Sputtering method. An EGFET proof-of-concept setup was constructed using a commercial FET as the transducer and the TiO2/ITO structure was used for the extended gate. The sensor measurement was taken using semiconductor device parametric analyzer, constant-current constant-voltage biasing interfacing circuit and data logger to obtain the sensitivity and the characteristics for output voltage with respect to time. TiO2 thin film on ITO glass as the sensing membrane was compared with a bare ITO glass substrate for the extended gate. The TiO2/ITO glass exhibited the sensitivity of 42.1 mV/pH and good linearity of 0.9997 in the sensing range pH4, pH7 and pH10 which was better than the bare ITO glass sensitivity of 31.3 mV/pH and the linearity of 0.9868.

Hybrid organic-inorganic light emitting diode using ZnO nanorods as electron transport layer

We have successfully synthesized hybrid organic-inorganic light emitting diode using ZnO nanorods as the electron transport layer and MEH-PPV as the emitting layer. The ZnO nanorods were synthesized using self-catalyzed thermal chemical vapor deposition method. The current density-voltage curves prove that the conductivity of the ZnO nanorods was improved. The turn on voltage was reduced from 2V to 0.4V with the insertion of ZnO nanorods between the cathode and emissive layer. Sharp visible emissions centred at 540 and 580 nm were observed from the electroluminescence spectra under forward biasing. A broad emission at 590 nm with a shoulder peak at 640 nm was also detected.