Effect of different temperatures to remove reduction gas on the photoluminescence properties of Eu-doped Li2 (Ba1-x Srx )SiO4 phosphors.

In this study, Eu-doped Li2 (Ba1-x Srx )SiO4 powders (x = 0, 0.2, 0.4, and 0.6) were synthesized at 850°C in a reduction atmosphere (5% H2 + 95% N2 ) for a duration of 1 h using a solid-state reaction method. The reduction atmosphere was infused as the synthesis temperature reached 850°C, and was removed as the temperature dropped to 800-500°C. Li2 (Ba1-x Srx )SiO4 (or Li2 BaSiO4 ), (Ba,Sr)2 SiO4 (or BaSiO4 ), and Li4 SiO4 phases co-existed in the synthesized Eu-doped Li2 (Ba1-x Srx )SiO4 powders. A new finding was that the reduction atmosphere removing (RAR) temperature of the Li2 (Ba1-x Srx )SiO4 phosphors had a large effect on their photoluminescence excitation (PLE) and PL properties. Except for the 800°C-RAR-treated Li2 BaSiO4 phosphor, PLE spectra of all other Li2 (Ba1-x Srx )SiO4 phosphors had one broad emission band with two emission peaks centred at ~242 and ~283 nm; these PL spectra had one broad emission band with one emission peak centred at 502-514 nm. We showed that the 800°C-RAR-treated Li2 BaSiO4 phosphor emitted a red light and all other Li2 (Ba1-x Srx )SiO4 phosphors emitted a green light. Reasons for these results are discussed thoroughly.

Electric Characteristic Enhancement of an AZO/Si Schottky Barrier Diode with Hydrogen Plasma Surface Treatment and AlxOx Guard Ring Structure.

In this study, the design and fabrication of AZO/n-Si Schottky barrier diodes (SBDs) with hydrogen plasma treatment on silicon surface and AlxOx guard ring were presented. The Si surface exhibited less interface defects after the cleaning process following with 30 w of H2 plasma treatment that improved the switching properties of the following formed SBDs. The rapid thermal annealing experiment also held at 400 °C to enhance the breakdown voltage of SBDs. The edge effect of the SBDs was also suppressed with the AlxOx guard ring structure deposited by the atomic layer deposition (ALD) at the side of the SBDs. Experimental results show that the reverse leakage current was reduced and the breakdown voltage increased with an addition of the AlxOx guard ring. The diode and fabrication technology developed in the study were applicable to the realization of SBDs with a high breakdown voltage (>200 V), a low reverse leakage current density (≤72 µA/mm²@100 V), and a Schottky barrier height of 1.074 eV.

Developments of the Physical and Electrical Properties of NiCr and NiCrSi Single-Layer and Bi-Layer Nano-Scale Thin-Film Resistors.

In this study, commercial-grade NiCr (80 wt % Ni, 20 wt % Cr) and NiCrSi (55 wt % Ni, 40 wt % Cr, 5 wt % Si) were used as targets and the sputtering method was used to deposit NiCr and NiCrSi thin films on Al2O3 and Si substrates at room temperature under different deposition time. X-ray diffraction patterns showed that the NiCr and NiCrSi thin films were amorphous phase, and the field-effect scanning electronic microscope observations showed that only nano-crystalline grains were revealed on the surfaces of the NiCr and NiCrSi thin films. The log (resistivity) values of the NiCr and NiCrSi thin-film resistors decreased approximately linearly as their thicknesses increased. We found that the value of temperature coefficient of resistance (TCR value) of the NiCr thin-film resistors was positive and that of the NiCrSi thin-film resistors was negative. To investigate these thin-film resistors with a low TCR value, we designed a novel bi-layer structure to fabricate the thin-film resistors via two different stacking methods. The bi-layer structures were created by depositing NiCr for 10 min as the upper (or lower) layer and depositing NiCrSi for 10, 30, or 60 min as the lower (or upper) layer. We aim to show that the stacking method had no apparent effect on the resistivity of the NiCr-NiCrSi bi-layer thin-film resistors but had large effect on the TCR value.

Porous SiO2/MgF2 broadband antireflection coatings for superstrate-type silicon-based tandem cells.

The purpose of this study is to reduce the glass substrate reflectivity over a wide spectral range (400-1200 nm) without having high reflectivity in the near-infrared region. After making porous SiO2/MgF2 double-layer antireflection (DLAR) thin film structure, the superstrate-type silicon-based tandem cells are added. In comparison to having only silicon-based tandem solar cells, the short-circuit current density has improved by 6.82% when porous SiO2/MgF2 DLAR thin film is applied to silicon-based tandem solar cells. This study has demonstrated that porous SiO2/MgF2 DLAR thin film structure provides antireflection properties over a broad spectral range (400-1200 nm) without having high reflectivity at near-infrared wavelengths.

A compact bandpass filter with enhanced stopband characteristics by an asymmetric cross-shape defected ground structure.

In this paper, we present an effective technique to enhance stopband bandwidth for a bandpass filter by using an asymmetric, cross-shape defected ground structure (CSDGS). A single CSDGS can provide a higher attenuation rate near passband and broader stopband bandwidth. Moreover, with the asymmetric CSDGS, two different resonant frequencies can be excited and controlled independently, resulting in synthesizing a passband. The synthesized bandpass filter can be modeled by parallel LC resonant circuits in connection with T-networks. The bandwidth and insertion loss of this bandpass filter at 4.2 GHz is 28.6% and -1.44 dB, respectively, and 20 dB rejection in the stopband is up to four times the central frequency. All the synthesized bandpass filters have been measured and are in good agreement with simulated results.

Spurious suppression of a microstrip bandpass filter using three types of rectangular PBG loops.

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with and without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stopband; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.

Direct bonding of recessed-structure SAW filter on silicon substrate.

A procedure for fabricating a recessed surface acoustic wave (SAW) device coupled with silicon substrate is reported. The recessed structure is stable and rugged enough against the bonding process, and it can be applied to integrate a semiconductor device into one chip by a direct bonding technique. In this paper, the tensile strength of silicon (Si)-to-recessed-SAW filter is measured, and the performance of the device is discussed.

Proton-exchanged wet etching of recessed-structure SAW filter.

An improved method for fabricating recessed-structure surface acoustic wave (SAW) filters is reported. The relation between proton-exchanged duration and etched depth are studied, as well as the relation between internal reflection, etched depth, and thickness of the aluminum electrode. Experimental results show that the devices have superior performance, and ideas for further improvement of the fabricated SAW device are discussed.