External Dc Bias Research Articles

Beam steering characteristics of strip line fed printed array antenna on magnetized ferrite

In this study, beam steering characteristics of strip line fed printed array antenna on magnetized ferrite substrate due to structural parameter and operating frequency variations are analyzed depending on the simple cavity analysis. Possibility of tuning on these characteristics via external DC bias field control providing full range beam steering and the alignment of the main beam to a specific direction are discussed. The obtained results indicate that the effects of structural parameter and operating frequency variations on the beam steering characteristics of the antenna can be tuned by varying the external bias field strength without changing the antenna configuration.

Density-controlled carbon nanotubes

We demonstrate that the field emission efficiency was greatly improved by reducing the density of carbon nanotubes (CNTs). In this study, catalyst composed of gold and nickel was deposited by e-gun evaporation before pre-treatment of furnace annealing. Carbon nanotubes were then grown on silicon substrate using bias-assisted microwave plasma chemical vapor deposition. Vertical aligned carbon nanotubes were grown with gas mixture of methane and hydrogen under external DC bias. The surface morphology and the tubular structure of carbon nanotubes were confirmed by electron microscopy and the density of carbon nanotubes could be controlled by the composition of the catalyst. The field emission properties were investigated through I– V measurement and the effects are discussed.

Effect of electric field on dielectric response of PMN–PT thin films

Electric field (ac and dc) induced complex dielectric properties of 0.7 Pb(Mg 1/3 Nb 2/3 )O 3 –0.3 PbTiO 3 (PMN–PT) thin films were studied as a function of frequency at different temperatures. A non-linear behavior of dielectric susceptibility, with respect to the amplitude of the ac drive, was observed at lower temperatures. The magnitude of the dielectric constant measured at 1 kHz was increased from 2000 to 6000 with increasing ac signal amplitude from 0.5 to 10 kV/cm, while temperature of maximum dielectric constant ( T m ) was observed to follow reverse trend at all frequencies. The relaxor nature of PMN–PT thin films was studied in terms of diffused phase transition along with frequency dispersion of temperature of dielectric maximum ( T m ). Vogel–Fulcher relationship was used to analyze the frequency dependence of temperature of dielectric maximum ( T m ). The dielectric constants (both real and imaginary) of PMN–PT thin films were observed to reduce with the application of external dc field. The external dc bias suppressed the frequency dispersion and increased the ferroelectric stability by increasing the transition temperature ( T m ). The disappearance of relaxor nature in PMN–PT (70/30) films was attributed to manifestation of long-range order at higher bias voltage.

Effect of electric field on dielectric response of PMN–PT thin films

Electric field (ac and dc) induced complex dielectric properties of 0.7 Pb(Mg 1/3Nb 2/3)O 3–0.3 PbTiO 3 (PMN–PT) thin films were studied as a function of frequency at different temperatures. A non-linear behavior of dielectric susceptibility, with respect to the amplitude of the ac drive, was observed at lower temperatures. The magnitude of the dielectric constant measured at 1 kHz was increased from 2000 to 6000 with increasing ac signal amplitude from 0.5 to 10 kV/cm, while temperature of maximum dielectric constant ( T m) was observed to follow reverse trend at all frequencies. The relaxor nature of PMN–PT thin films was studied in terms of diffused phase transition along with frequency dispersion of temperature of dielectric maximum ( T m). Vogel–Fulcher relationship was used to analyze the frequency dependence of temperature of dielectric maximum ( T m). The dielectric constants (both real and imaginary) of PMN–PT thin films were observed to reduce with the application of external dc field. The external dc bias suppressed the frequency dispersion and increased the ferroelectric stability by increasing the transition temperature ( T m). The disappearance of relaxor nature in PMN–PT (70/30) films was attributed to manifestation of long-range order at higher bias voltage.

Na0.5K0.5NbO3 Film Microwave Varactors

Na0.5K0.5NbO3 (NKN) and Pb(Zr0.53Ti0.47)O3 (PZT) films have been grown by rf-magnetron sputtering and pulsed laser deposition techniques, correspondingly, on sapphire (Al2O3-0112, r-cut), quartz (Y+36°-cut) and YAlO3 + 1% Nd (Nd:YAlO3-001) single crystal substrates with Interdigital Capacitor (IDC) of Coplanar Waveguide (CPW) structure. Photolithography and metal lift-off technique was used for processing of the tunable microwave capacitor. Microwave network analyzer with G-S-G Picoprobe and probe station performed microwave measurement with external DC bias. NKN film interdigital capacitors on Nd:YAlO3 show superior performance in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40 V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor from 152% @10 GHz to 46% @40 GHz, voltage independent C p was about 230 fF, tan δ p changes from 0.14 @10 GHz to 0.36 @40 GHz, real and imaginary part of interconnect impedance increases with frequency from 0.13 Ω @10 GHz to 0.50 Ω @40 GHz and from 1.9 Ω @10 GHz to 5.9 Ω @40 GHz respectively.

A novel low-cost high-conversion-efficiency microwave power detector using GaAs FET

A novel simple microwave power detector using a GaAs MESFET is developed at 5.8 GHz. The FET detector has good noise characteristics, temperature stability, and dynamic range. Since the availability of FET is more flexible and the price is lower, the FET detector can be more cost effective than the GaAs Schottky diode. The detector circuit is self-biased and no external DC bias network is required. The detector converts microwave power to DC power with a conversion efficiency of 62.06% and a DC output voltage of 7.35 V at an input power of 29.4 dBm. This is the highest conversion efficiency and DC output voltage ever reported for a self-biased FET detector. The experimental results agree well with the simulation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 29–31, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20537

High rate sapphire (Al 2O 3) etching in inductively coupled plasmas using axial external magnetic field

BCl 3/HBr inductively coupled plasmas magnetized by external magnetic fields was used to achieve high etch rate of sapphires and high etch selectivities over photoresist. The etch characteristics such as etch rates of sapphire and photoresist, etch selectivity over photoresist, plasma density, and etch profiles etc. were investigated as functions of applied external magnetic field strength, working pressure, and dc bias voltage. The obtained highest etch rate of sapphire was approximately 7700 Å/min at −800 V of dc bias voltage and 20 Gauss (G) of external magnetic field, when 1400 W of inductive power, 10 mTorr of 90% BCl 3/10% HBr were used. The etch selectivities over photoresist were varied from approximately 0.6 to 0.8, where, it increased up to 0.8 with an increasing external magnetic field, however, it decreased with an increasing dc bias voltage.

Chaotic transport in low-dimensional superlattices

We predict that in arrays of quantum dots (0D superlattice) and arrays of one-dimensional quantum wires (1D superlattice) chaotic transport should be observed in the presence of an ac field and for a wide range of physical parameters, like the external dc bias, contact charge, doping levels, and disorder in the array. Time-dependent current oscillations set in the array due to the formation of electric domain walls when sequential resonant tunneling is the main transport mechanism between adjacent units. Such oscillations can then be forced into spatiotemporal chaos. A similar phenomenon has been predicted and demonstrated for solid-state superlattices. However, contrary to the latter case, the domain walls move across a larger number of units in the superlattice the lower the dimensionality, due to the different spatial distribution of the electric-field across the array in the three cases.

A Phenomenological Explanation to the Dielectric Aging Mechanism of a Lead Magnesium Niobate-Based Ceramic

We measured the dielectric permittivity (ε) of a Pb(Mg1/3Nb2/3)O3-based ceramic as a function of aging time (t) and external dc bias (field strength E up to 20 kV/cm). By comparing the ε–t and ε–E relationships, we obtained an E–t relationship that assumedly reflects the evolution of the internal field in the ceramics during aging. The internal field was found to gradually increase during aging and keep a nonlinear relationship with logarithm of aging time. A phenomenological model was proposed to semi-quantitatively explain why and how the internal bias causes the decrease in the dielectric permittivity and consequently the aging effect.

Nonlinear dielectric properties of barium strontium titanate ceramics

In barium strontium titanate (Ba x Sr 1− x TiO 3) ceramics, obvious tunabilities of both dielectric permittivity and loss tangent under external DC bias field were observed. The temperature and frequency dependences of nonlinear dielectric properties were studied. Polarizing process was carried out to evaluate the influence of domain reorientation on dielectric nonlinearity in the ferroelectric polycrystalline samples. The nonlinear variation of dielectric properties under external DC bias field was tentatively explained.

Dynamics of Quantized Photon and Electron Field in Semiconductor Multi-Subbands Superlattices

We study time evolution of the interacting system consisting of quantized photon field and electron field in semiconductor superlattices analytically/numerically. In the single-subband condition, the electron dynamics is able to generate several nonclassical photon states depending on the external dc bias. Effects of the intersubband transition for the quantized photon states is investigated in the multi-subband condition. Competition of two-kinds of intersubband electron dynamics, Rabi oscillation and Zener tunneling, is discussed.

Effective laser ultrasonic detection with biased GaAs photoelectromotive force detectors

Improvement of the sensitivity of laser-induced ultrasonic detection by GaAs adaptive photoelectromotive force (photo-EMF) devices under external dc bias is reported. The gain in responsivity of the detector about 7× in ≈10 MHz frequency band was observed under application of an external dc field ≈50 V/mm at λ=633 nm. Detailed experiments show that this growth is paid by proportional shift of maximum of the photo-EMF response to lower spatial frequencies and by appearance of a relatively broad resonance pick located at modulation frequencies lower than the cutoff frequency of the unbiased GaAs photo-EMF detector. These results are consistently interpreted using a theoretical model of the photo-EMF effect in bipolar photoconductor with large lifetime of one type of the photocarriers.

Microwave Phase Shifters Using Ferroelectric (Ba,Sr)TiO3 Films

AbstractThe ferroelectric (Ba0.6Sr0.4)TiO3 (BST) films were prepared on (001) MgO single crystals by pulsed laser deposition. Coplanar waveguide (CPW) type phase shifters controlled by external dc bias field were fabricated on BST films using a 2 μm thick metal layer to reduce metal loss. Microwave properties of the CPW phase shifter were measured using a HP 8510C vector network analyzer from 0.1 – 20 GHz. The fabricated CPW phase shifters (8 mm long) exhibited differential phase angle of 100 ° at 10 GHz with a dc bias field of less than 80 kV/cm between center and ground conductors. Furthermore, a stable differential phase angle (102 ± 3.5 o) was observed from another CPW while changing the power of incident microwave from -10 to +30 dBm. Gap size dependent dielectric constant of the BST film was observed and a simple correction method was suggested in the paper. These results demonstrate the possible application of ferroelectric tunable devices on a high power tunable wireless telecommunication.

Hybrid model for the calculation of ion distribution functions behind a direct current or radio frequency driven plasma boundary sheath

A hybrid fluid dynamic/kinetic model is presented which describes the sheath and the presheath regions of dc or rf driven low pressure gas discharges in a realistic and self-consistent way. The model assumes an infinite extended sheath parallel to the electrode, allowing a one-dimensional spatial description. It provides for the presence of multiple positive ion species and their collisional interactions with the neutral background, and takes into account the possibility of a nonharmonic modulation of the sheath potential and the application of an external dc bias; in this work, the model is applied to a two-species capacitively coupled argon and oxygen plasma. The input required by the model consists of the fluxes of the incoming ions, of the modulating current, and of the pressure, the composition, and the temperature of the background gas. On output, the model provides the values of the electric field and of the particle densities within the sheath and the presheath, the total voltage drop across the sheath, and also the energetically and angularly resolved distributions of the positive ions and the energetic neutrals which impinge the material substrate at the boundary. In general, the model is able to treat dc discharges as well as capacitively and/or inductively coupled rf discharges, it thus covers most of the plasmas used in very large scale integration microelectronics manufacturing and other surface modification techniques. Using the model, studies of the energy distributions of the incoming ions have been performed for a wide range of parameters, and the effects of varying process conditions have been investigated. At low and intermediate pressures (p<50 mTorr), the distribution functions of rf driven discharges exhibit a characteristic bimodal structure; this structure disappears with increasing pressure as ion-neutral collisions become significant. A comparison of calculated ion energy distributions with experimental measurements on capacitively coupled argon and oxygen discharges shows excellent quantitative agreement. In addition to the ion energy distribution, the angular distributions of the incident ions at various energies are also discussed as a function of the neutral gas pressure. It turns out that the details of the angular distribution not only depend on the field structure of the sheath itself but also on that of the presheath. The results of the presented model are therefore more reliable than those of previous models which restricted themselves to the sheath region. This high physical accuracy of the presented model, together with its flexibility and its high execution speed, allows its use as a tool for technology-oriented computer-aided design in the microelectronics industry.

Alternating current electrical properties of antiferroelectric lead zirconate thin films by pulsed excimer laser ablation

In situ crystalline lead zirconate (PZ) thin films were deposited on platinum metallized silicon substrates, using a 248 nm KrF pulsed excimer laser ablation technique. The antiferroelectricity in PZ thin films was confirmed by means of P vs E and C vs V measurements. The maximum observed saturated polarization (Ps) was 44 μC/cm2 at an applied field of 200 kV/cm. The calculated forward and backward switching fields were 71 and 154 kV/cm, respectively. The dielectric phase transition temperature was at ∼219 °C with zero dc bias and was increased to 290 °C in the presence of 4 V dc bias. Detailed comprehensive study was done on PZ thin films to understand the charge carrier transport with respect to frequency domain of dielectric and ac conductivity measurements. Effect of simultaneous dc bias on the frequency response of the dielectric dispersion and ac conductivity studies were done to understand the nature of charge carrier transport and their activation energies. The calculated activation energies, from ac conductivity and conductance measurements, in the absence of external dc bias were 0.42 and 0.37 eV, respectively. Measurements with the simultaneous application of 4 V dc bias gave two activation energy values 0.38 and 1.76 eV, respectively. The lower and higher activation energies were attributed to the shallow and deep trap energies respectively.

Electroabsorption studies of phthalocyanine/perylene solar cells

We report electroabsorption (EA) studies of electric fields in bilayer molecular organic solar cells made from zinc phthalocyanine (ZnPc) and a methyl substituted perylene pigment (MPP). We have detected an electric field at the metal/organic interface which is sensitive to the external DC bias. The interface field has a different spectral signature from that of the bulk of the two layers, which we attribute to interface species such as charge transfer-induced dipoles. The electric field is proportional to the applied bias in devices containing only ZnPc or MPP, but rectifying behavior is observed in the bilayer solar cell.

Electroreflectance measurements of electric fields in ordered GaInP2

Ordered Ga0.52In0.48P alloys (GaInP2 for simplicity) grown on miscut [001] GaAs resemble monolayer superlattices with alternating Ga- and In-rich layers along either the [1̄11] or [11̄1] directions. Recent calculations suggest that, in fully ordered GaInP2, an intrinsic ordering-induced electric field of order 1600 kV/cm should exist. In partially ordered samples, as can actually be grown, the expected field is reduced to 400 kV/cm. For such a strong internal electric field, clear Franz–Keldysh Oscillations (FKOs) would be expected in an electroreflectance measurement. We report electroreflectance measurements of ordered GaInP2 layers measured at T=100 K. For all samples measured, no FKOs are observed in the absence of an additional external dc bias voltage. At the lowest bias voltages for which FKOs are seen, the internal electric field in the GaInP2 layer, determined from the FKOs, is ∼60 kV/cm along the [001] direction corresponding to ∼100 kV/cm along the ordering direction. Hence, we conclude that, at least in the organometallic vapor phase epitaxy grown samples studied here, any net macroscopic internal electric field in the GaInP2 layer is less than ∼100 kV/cm along the ordering direction.

Giant enhancement of low frequency non-steady-state photo-EMF signal in Bi 12SiO 20 crystal under external DC bias

We present experimental results which demonstrate that non-steady-state photo-EMF, induced by vibrating interference fringes in Bi 12SiO 20 photorefractive crystal can be dramatically (by a factor of 10 3 in our experimental conditions) enhanced in a resonance regime under application of an external DC field. We show that for increasing applied electric field the resonance maximum moves from the dielectric relaxation frequency towards the low frequency end. Its magnitude grows as E 0 2 for low values of the field, for high external field significant broadening of the resonance peak and linear growth of the signal resonance amplitude is observed. This effect and non-trivial dependence of the resonance signal amplitude on the spatial frequency of the pattern is explained by saturation of the space charge grating. Finally, the sensitivity of the biased resonance adaptive photo-EMF detector is estimated.

Control of quantized photon states with external dc bias in semiconductor superlattices

We show that the Bloch oscillation in semiconductor superlattices under the external dc bias is able to generate nonclassical photon states. The time development operator of the photon field in such systems is obtained and is shown to be equivalent approximately to the displacement operator, the phase-quadrature amplitude squeezing operator, or the optical Kerr operator, depending on the external dc bias. Such equivalence is discussed also in terms of Stark-ladder formation.

Tunable intersubband Raman laser in GaAs/AlGaAs multiple quantum wells

A new tunable source of infrared radiation based on intersubband electron Raman scattering in semiconductor quantum wells is studied theoretically. The structure consisting of three levels in two coupled GaAs/AlGaAs quantum wells is optimized for a maximum Raman gain at zero bias. Raman gain as large as 400/cm can be achieved according to our calculations. Lasing wavelengths are tuned when an external dc bias field is applied along the growth direction. An infrared tuning range of 8–12 μm with moderate Raman gain is predicted as the electric field is varied from -40 to 40 kV/cm.