High-performance low-cost phase-shifter design based on ferroelectric materials technology

A novel approach to ferroelectric phase-shifter design using Ba/sub x/Sr/sub 1-x/TiO/sub 3/ (BSTO) films in a multilayer dielectric coplanar waveguide structure is described. By including a low-loss dielectric layer (SiO/sub 2/) between the coplanar waveguide conductors and a layer of ferroelectric materials, significant reduction in insertion loss can be achieved in conjunction with a threefold increase in figure of merit (/spl deg//dB).     

Electrical properties of HgCdTe epilayers doped with silver using an AgNO3 solution

We employed AgNO₃ solutions for doping Ag in liquid phase epitaxy (LPE) grown Hg_0.78Cd_0.22Te epilayers and found that the minority carrier lifetimes became longer so that the diode properties improved. After annealing LPE grown Hg(1-x)Cd(x)Te layers (x=0.22) in Hg atmosphere, the epilayers were immersed in an AgNO₃ solution at room temperature. The typical carrier concentrations of holes was 3 × 10¹⁶ cm⁻³ at 77K. These values were almost the same as for the nondoped wafers. Also, its acceptor level was 3 to 4 meV. This shows that the Ag was activated. The doped crystals have lifetimes several times longer than those of the nondoped crystals. Numerical fitting showed the lifetime was limited mostly by the Auger 7 process. The Shockley-Read-Hall recombination process was not effective. To examine the Ag-doped wafer, we fabricated photodiodes using standard planar technology. The diodes have an average zero-bias resistance of several MΩ and a shunt resistance of about 1 GΩ for a 10 μm cutoff wavelength at 78K. These values are about four times higher than those of nondoped diodes. The photo current is also two times higher at the same pixel size. This shows that the quantum efficiency is increased. The extension of the lifetime contributes to the high resistance and the high quantum efficiency of the photodiode.     

Still image transmission using ARQ over Rayleigh fading channels

The authors propose a new ARQ scheme suitable for image transmission over radio channels. The proposed scheme detects only serious degradation and so attains higher throughput performance than the conventional ARQ scheme     

CuPc/PbZr0.2Ti0.8O3/(La,Ba)MnO3 field effect transistor heterojunction photomemory

We investigated a photoconductor(PC)/ferroelectric oxide(OF)/semiconductor oxide(SO) POS-FET structure photomemory consisting of organic photoconductor CuPc/inorganic ferroelectric PbZr_0.2Ti_0.8O₃ heterojunction gate and a ferromagnetic oxide semiconductor La_0.87Ba_0.13MnO₃ channel. Visible light information detected by photoconductor CuPc can be memorized in ferroelectric PbZr_0.2Ti_0.8O₃, and non-volatile and non-destructive reading out process of light information memorized in this ferroelectric layer were achieved by reading out the resistance modulation of ferromagnetic semiconductor oxide La_0.87Ba_0.13MnO₃ channel under the photoconductor/ferroelectric gate.     

Wideband and compact folded loop antenna

A simple and successful design method that yields a wideband and compact antenna without a ground plane is proposed. The antenna, referred to as the folded loop antenna, can, with the right parameters, achieve wideband characteristics. Calculated and measured results agree well and more than 50% bandwidth (return loss /spl les/-10 dB) is obtained.     

Amorphous structures of buried oxide in SiC-on-insulator

A buried amorphous layer in high-dose oxygen ion-implanted silicon carbide (SiC) has been characterized by transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), and energy dispersive x-ray spectroscopy. Single crystalline (0001)-oriented 6H-SiC wafers were irradiated with 180 keV oxygen ions at 650°C to a fluence of 1.4 ×10¹⁸/cm². A fully amorphous SiO₂ layer was formed insido the irradiated crystal, while the surrounded 6H-SiC exhibited minimal damage. This SiO₂ layer included self-bonded carbon atoms and showed a layered structure due to compositional variations of silicon, carbon, and oxygen.     

Analysis and discussion on conduction current based on simultaneousmeasurement of TSC and space charge distribution

A new analysis of conduction current distributed in dielectrics based on simultaneous measurements of thermally stimulated current (TSC) and time dependent space charge distribution is proposed. A new system pulsed electro-acoustic (PEA) method has been developed to enable simultaneous measurement of the TSC and the dynamic space charge and electric field distributions as a function of temperature within insulators. With the new system, the relationship between the TSC and the time dependent electric field distribution in electron beam (e-beam) irradiated PMMA has been investigated. From the time dependent electric field, the displacement current in dielectrics is obtained. The TSC is a typical external current which is represented as an addition of the displacement current and a conduction current in dielectrics. This paper makes it clear that the conduction current as a function of position is determined by the simultaneous measurement of the external current and the dynamic space charge distribution     

Formation of uniform GaAs multi-atomic steps with 20–30 nm periodicity and related structures on vicinal (111)B planes by MBE

We studied morphology of GaAs surfaces and the transport properties of two-dimensional electron gas (2DEG) on vicinal (111)B planes. Multi-atomic steps (MASs) are found on the vicinal (111)B facet grown by molecular beam epitaxy, which will affect electron transport on the facet. We also studied how the morphology of GaAs epilayers on vicinal (111)B substrates depends on growth conditions, especially on the As₄ flux. The uniformity of MASs on the substrates have been improved and smooth surfaces were obtained when the GaAs was grown with high As₄ flux, providing step periodicity of 20 nm. The channel resistance of the 2DEG perpendicular to the MASs is reduced drastically with this smooth morphology. These findings are valuable not only for fabricating quantum devices on the (111)B facets but also those on the vicinal (111)B substrates.     

Blue electroluminescent devices withSrGa2S4:Ce for full-color display

In order to realize full-color electroluminescent (EL) displays, which are expected as a dominant candidate for the future multimedia flat panel display, blue EL devices with SrGa₂S₄:Ce have been prepared by molecular beam epitaxy (MBE). This paper proposes a novel deposition method employing Sr metal and Ga₂S₄ compound as the source materials. A single-phase SrGa₂S₄ layer is obtained in a Ga₂S₃/Sr flux ratio of 60 and at the growth temperature of 560°C. We have obtained the well-saturated blue with CIE color coordinates of x=0.14, y=0.14 and brighter blue EL devices made by optimizing the growth conditions in MBE. The maximum luminance of 70 cd/m² in comparison with the 3 cd/m₂ of our previous EL devices, is achieved at a driving frequency of 1 kHz