Chia-Ching Wu

Developing high-transmittance heterojunction diodes based on NiO/TZO bilayer thin films

In this study, radio frequency magnetron sputtering was used to deposit nickel oxide thin films (NiO, deposition power of 100 W) and titanium-doped zinc oxide thin films (TZO, varying deposition powers) on glass substrates to form p(NiO)-n(TZO) heterojunction diodes with high transmittance. The structural, optical, and electrical properties of the TZO and NiO thin films and NiO/TZO heterojunction devices were investigated with scanning electron microscopy, X-ray diffraction (XRD) patterns, UV-visible spectroscopy, Hall effect analysis, and current-voltage (I-V) analysis. XRD analysis showed that only the (111) diffraction peak of NiO and the (002) and (004) diffraction peaks of TZO were observable in the NiO/TZO heterojunction devices, indicating that the TZO thin films showed a good c-axis orientation perpendicular to the glass substrates. When the sputtering deposition power for the TZO thin films was 100, 125, and 150 W, the I-V characteristics confirmed that a p-n junction characteristic was successfully formed in the NiO/TZO heterojunction devices. We show that the NiO/TZO heterojunction diode was dominated by the space-charge limited current theory.

Measuring the microwave frequency relative permittivity of polyetherimide/BaTi4O9 composites by using a rectangular cavity resonator

In this paper, high glass transition temperature (Tg) of polyetherimide (PEI) is used to mix with different weight percent (0–80wt%) of BaTi4O9 (BT4) ceramic powder to form a flexible PEI/BT4 composite. The relative permittivity of PEI/BT4 composites is developed from 1to16GHz using the “rectangular cavity resonator” method. The relative permittivity of PEI/BT4 composites is calculated by observing the frequencies of resonant cavity modes. From the results of dielectric properties, the relative permittivity of PEI/BT4 composites is almost unchanged as the measured frequency is changed. It conjectures that the polarization mode does not exist in BT4 ceramic powder.

Measuring the relative permittivity of polyetherimide/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites from 10 kHz to 12 GHz

The relative permittivity of polyetherimide-(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (PEI-BSTZ) composites is measured from 10 kHz to 1 MHz using plate method. As the content of BSTZ filler is less than 18 vol %, the experimental values are fitted to the values predicted by Lichtenecker equation. As the content is more than 18 vol %, the measured relative permittivity of PEI-BSTZ composites is higher than the predicted values. The relative permittivity of PEI-BSTZ composites is measured at 1–12 GHz using “square cavity resonator” method. Measured at gigahertz, the relative permittivity of PEI-BSTZ composites is almost unchanged.

The Dielectric Properties of PEI / ( Ba0.8Sr0.2 ) ( Ti0.9Zr0.1 ) O3 Composites

Polyetherimide/(Ba 0.8 Sr 0.2 )(Ti 0.9 Zr 0.1 )O 3 (PEI/BSTZ) composites are fabricated using PEI, dispersant, solvents, and BSTZ powder. The effects of the content of BSTZ filler on the physical and dielectric properties of PEI/BSTZ composites are studied in this paper. At the same loading ratio, the room temperature dielectric constants of PEI/BSTZ composites are higher than those of polymer/BaTiO 3 composites. In addition, the dielectric constants of PEI/BSTZ composites stay flat at temperatures higher than the Curie temperature of BSTZ (40°C). As the content of BSTZ powder increases from 10 to 70 wt %, the dielectric constants of PEI/BSTZ composites at 1 MHz increase from 2.52 to 20.28. However, when the content of BSTZ is more than 45 wt %, the measured dielectric constants of PEI/BSTZ composites are higher than theoretical values. The results indicate that the finer BSTZ ceramic particles can fill the interstitial sites of coarser BSTZ ceramic particles as indicated by scanning electron microscopy images.

Development of the α-IGZO/Ag/α-IGZO Triple-Layer Structure Films for the Application of Transparent Electrode

We investigated the structural, optical, and electrical properties of amorphous IGZO/silver/amorphous IGZO (α-IGZO/Ag/α-IGZO) triple-layer structures that were deposited at room temperature on Eagle XG glass and flexible polyethylene terephthalate substrates through the sputtering method. Thin Ag layers with different thicknesses were inserted between two IGZO layers to form a triple-layer structure. Ag was used because of its lower absorption and resistivity. Field emission scanning electron microscopy measurements of the triple-layer structures revealed that the thicknesses of the Ag layers ranged from 13 to 41 nm. The thickness of the Ag layer had a large effect on the electrical and optical properties of the electrodes. The optimum thickness of the Ag metal thin film could be evaluated according to the optical transmittance, electrical conductivity, and figure of merit of the electrode. This study demonstrates that the α-IGZO/Ag/α-IGZO triple-layer transparent electrode can be fabricated with low sheet resistance (4.2 Ω/□) and high optical transmittance (88.1%) at room temperature without postannealing processing on the deposited thin films.

Developing the dielectric mechanisms of polyetherimide/multiwalled carbon nanotube/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites

Various amounts of multiwalled carbon nanotubes [MWNTs] were embedded into polyetherimide [PEI] to form PEI/MWNT composites, and their dielectric properties were measured at 1 MHz. The Lichtenecker mixing rule was used to find a reasonable dielectric constant for the MWNTs used in this study. The dielectric constants of the developed composites were significantly increased, and the loss tangents were significantly decreased as 2.0 wt.% (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 ceramic powder [BSTZ] was added to the PEI/MWNTs to form PEI/MWNT/BSTZ composites. The Lichtenecker and Yamada mixing rules were used to predict the dielectric constants of the PEI/MWNT and PEI/MWNT/BSTZ composites. Equivalent electrical conduction models of both composites were established using the two mixing rules. In addition, the theoretical bases of the two mixing rules were used to explain the measured results for the PEI/MWNT and PEI/BSTZ/MWNT composites.

The Development of High-Density Vertical Silicon Nanowires and Their Application in a Heterojunction Diode

Vertically aligned p-type silicon nanowire (SiNW) arrays were fabricated through metal-assisted chemical etching (MACE) of Si wafers. An indium tin oxide/indium zinc oxide/silicon nanowire (ITO/IZO/SiNW) heterojunction diode was formed by depositing ITO and IZO thin films on the vertically aligned SiNW arrays. The structural and electrical properties of the resulting ITO/IZO/SiNW heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and current−voltage (I−V) measurements. Nonlinear and rectifying I−V properties confirmed that a heterojunction diode was successfully formed in the ITO/IZO/SiNW structure. The diode had a well-defined rectifying behavior, with a rectification ratio of 550.7 at 3 V and a turn-on voltage of 2.53 V under dark conditions.

Dielectric Behavior of Epoxy/(Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 Composites

The (Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 (BSTZ) dielectric ceramic powder is mixed with O-Cresol Novolac (OCN) epoxy resin to form epoxy/BSTZ composites. As the content of BSTZ ceramic powder increases from 0 to 70 wt%, the dielectric constants of epoxy/BSTZ composites increase from 5.72 to 25.23 and the loss tangents are almost unchanged as measured frequency increases. The dielectric constants of epoxy/BSTZ composites first increase as measured temperature increases and are unchanged as measured temperature is higher than the Cure temperature of BSTZ ceramic. This research proves that we can develop the epoxy/BSTZ composites with stable temperature- and frequency-dependent characteristics.

Crystalline Indium-Doped Zinc Oxide Thin Films Prepared by RF Magnetron Reactive Sputtering

The characteristic of indium-doped zinc oxide (IZO) thin films are closely related with the composition of the target, the deposition technique, and various process parameters such as the substrate temperature, the deposition pressure, the distance from target to substrate, and so on. In this study, IZO thin films have been deposited onto glass substrates with different deposition pressures by using the radio frequency magnetron reactive sputtering method. The structural, optical, and resistivity properties of IZO thin films were investigated using a field emission scanning electron microscope (FE-SEM), X-ray diffraction patterns (XRD), UV-visible spectroscopy, and Hall-effect analysis. XRD analysis on IZO thin films showed that only the (002) diffraction peak was observable, indicating that the IZO films showed a good c-axis orientation perpendicular to the glass substrates. As the deposition pressure of IZO thin films change from 5 × 10−3 to 5 × 10−2 Torr, the thickness decreased from 220 to 72 nm, the grain size increased from 74 to 23 nm, and the resistivity increased from 2.03 × 10−3 to 1.65 × 10−1 Ω cm. The lowest resistivity value of 2.03 × 10−3 Ω m was obtained for a deposition pressure of 5 × 10−3 Torr.

Preparation and Properties Investigation of Polyetherimide/Bamboo Charcoal Composites with High Dielectric Constant

The physic and dielectric properties of the polyetherimide/bamboo charcoal (PEI/BC) composites were studied by using bamboo charcoal as the conductive filler. The PEI/BC composites are fabricated using PEI, dispersant, solvents, and BC powder (BCP). The effects of the content of BCP on the physical and dielectric properties of PEI/BCP composites are studied in this research. Two different electric conductivity of BCP (BCP1 and BCP2) were used as the filler mixing with the polyetherimide, and the electric conductivity of BCP1 is higher than the BCP2. As the content of BCP1 and BCP2 increases from 10 to 70 wt%, the dielectric constants of PEI/BC1 and PEI/BC2 composites at 1 MHz increases from 5.06 to 19.73 and 4.7 to 18.9, respectively. All loss tangents of PEI/BC1 and PEI/BC2 composites are less than 0.04 at measured frequencies from 1 kHz to 1 MHz.