Large RF Power Research Articles

Bias-free operational monolithic symmetric-connected photodiode array

We have designed and fabricated zero-bias operational two-element symmetric-connected photodetector arrays (SC-PDAs). The designed SC-PDAs have higher saturation currents, larger RF power, and better frequency responses than the single photodetector (PD) under zero bias. The bias-free SC-PDA with 15 μm diameter of each PD demonstrated a 3 dB bandwidth of 19.4 GHz at 0.5 mA. The RF saturation photocurrent and maximum RF output power of the SC-PDA with 40 μm, 50 μm, and 60 μm diameters under zero bias are over 9.31 mA and −5.86 dBm at 3 GHz, 14.52 mA and 1.17 dBm at 1 GHz, and 13.72 mA and −1.76 dBm at 1 GHz, respectively.

Integrated microwave photonic phase shifter with full tunable phase shifting range (> 360°) and RF power equalization.

We report a novel microwave photonic phase and amplitude control structure based on a single microring resonator with a tunable Mach Zehnder interferometer reflective loop, which enables the realization of a continuously tunable microwave photonic phase shifter with enhanced phase tuning range while simultaneously compensating for the RF power variations. The complimentary tuning of the phase and amplitude presents a simplistic approach to resolve the inherent trade-off between maintaining a full RF phase shift while eliminating large RF power variations. Detailed simulations have been carried out to analyze the performance of the new structure as a microwave photonic phase shifter, where the reflective nature of the proposed configuration shows an effective doubling of the phase range while the amplitude compensation module provides a parallel control to potentially reduce the RF amplitude variations to virtually zero. The phase range enhancement, which is first verified experimentally with a passive only chip, demonstrates the capability to achieve a continuously tunable RF phase shift of 0-510° with an RF amplitude variation of 9 dB. Meanwhile, the amplitude compensation scheme is incorporated onto an active chip with a continuously tunable RF phase shift of 0-150°, where the RF power variations is shown to be reduced by 5 dB while maintaining a constant RF phase shift.

Monolithic Symmetric-Connected Photodiode Array

We demonstrate a two-element symmetric-connected photodiode array (SC-PDA) for high-power and high-speed applications. A traditional traveling-wave photodiode array (TW-PDA), an SC-PDA, and a single PD with the same epitaxial structure were fabricated and tested. Both the TW-PDA and SC-PDA have higher saturation currents, larger RF power, and better high-power and high-frequency responses than the single PD. However, the results show that the SC-PDA has a higher responsivity (0.32 A/W), a smooth frequency response (14.0 GHz), and a higher saturation current (66 mA) than the TW-PDA (0.24 A/W, periodically patterned frequency response and 42 mA) without using phase matching techniques.

Numerical calculations and RF characteristics measurement of complex-conjugate impedance antenna system for ICRF heating and current drive

Characteristics of a complex-conjugate impedance antenna system for ion cyclotron resonance frequency (ICRF) heating and current drive (H & CD) are discussed in this paper. Large RF power is reflected in such transitions as that of ELMy H–L mode due to the large change in plasma resistance during the ICRF H & CD. In such a case the RF power injection to the plasma must be ceased in order to protect the tetrode vacuum tubes. The idea of a complex-conjugate impedance antenna system to mitigate the large reflected RF power, referred to as ELM tolerance, has recently been proposed. It has been proved that the reflected RF power fraction can be reduced even during a large change in plasma resistance. But it is not reduced to the level allowable for the tetrode tubes. Therefore, an improved system adding a single stub tuner is proposed. Using it, the reflected RF power fraction can be reduced to the allowable level. Numerical calculations and experiments are carried out for this system. It is found that the experimental data agree with numerical calculations.

Large signal RF power transmission characterization of InGaP HBT for RF power amplifiers

The large signal RF power transmission characteristics of an advanced InGaP HBT in an RF power amplifier are investigated and analyzed experimentally. The realistic RF powers reflected by the transistor, transmitted from the transistor and reflected by the load are investigated at small signal and large signal levels. The RF power multiple frequency components at the input and output ports are investigated at small signal and large signal levels, including their effects on RF power gain compression and nonlinearity. The results show that the RF power reflections are different between the output and input ports. At the input port the reflected power is not always proportional to input power level; at large power levels the reflected power becomes more serious than that at small signal levels, and there is a knee point at large power levels. The results also show the effects of the power multiple frequency components on RF amplification.

Characterization of reactive ion etching of benzocyclobutente in SF 6/O 2 plasmas

This paper reports the reactive ion etching (RIE) characteristics of benzocyclobutene (BCB) in sulfur hexafluoride/oxygen (SF 6/O 2) plasmas. The dependence of etching rate and etch anisotropy on the processing parameters, including RF power, chamber pressure, and SF 6 concentration, are investigated comprehensively ranging from 50 to 200 W, 22.5 to 270 mTorr, and 0% to 80%, respectively. The BCB etching rate increases with chamber pressure and RF power in spite of nonlinearity, but decreases with the increase in SF 6 concentration. Anisotropic etching can be achieved using low chamber pressure, large RF power, and high SF 6 concentration. To avoid grass-like residue that happens at low pressure and large power fluorine-poor conditions, processing parameters with respect to residue-free etching are recommended. The etching mechanisms of the dependence of the etching characteristics on the processing parameters are discussed. Optimal processing parameters are presented as a guideline for isotropic etching of BCB as sacrificial layers to release structures and for anisotropic etching of BCB to precisely control etching dimensions and profiles.

Effect of Plasma Conditions on the Growth of GaNAs by Plasma-Assisted Molecular-Beam Epitaxy

We undertake an exclusive study on the plasma-assisted molecular-beam epitaxy of GaNAs, focusing on plasma conditions. We investigate the effects of species contributing to growth and the ions produced on the resulting structural and optical characteristics of the epitaxial layer, and the effect of rapid thermal annealing on the layer. The larger the RF power, the larger the amount of both atomic N and metastable molecule N2* are produced, resulting in a monotonic increase in nitrogen incorporation. An increase in the nitrogen gas flow rate leads to the saturation of nitrogen incorporation, followed by a reduction in atomic N. Both atomic N and metastable molecule N2* contribute to the growth. The number of ions produced is larger at a larger RF power and lower nitrogen gas flow rate, but is almost negligible near the border of the plasma mode transition. The sample exposed to fewer ions during growth shows better optical properties.

Power handling limits and degradation of large area AlGaN/GaN RF-HEMTs

We investigate the influence of the device geometry of large scale RF power AlGaN/GaN-HEMTs on the RF output power density. Multifinger-RF-HEMTs with different device geometries were fabricated on comparable epilayers grown on both sapphire and SiC substrates. Thermal impedances of the different FETs were measured and simulated. We discuss the correlation between the thermal device impedance and the RF output power, measured at 2 GHz. Degradation phenomena under high temperature and high current conditions are reported. As a result, we show that the thermal device impedance can be used as a design rule for the optimization of AlGaN/GaN-RF-HEMTs.

Comparison of an in-line asymmetric directional coupler modulator with distributed optical loss to other linearized electrooptic modulators

The transfer function of an external modulator is the critical factor that determines the spurious free dynamic range, signal power gain, and noise figure of a wide-band analog RF-photonic link. We present an in-line asymmetric directional coupler modulator with distributed optical loss capable of providing a transfer function linearized to the fourth order for multioctave bandwidths. This modulator compares favorably with multiple modulator suboctave linearization techniques consisting of series symmetric directional coupler and series Mach-Zehnder modulators and superoctave parallel Mach-Zehnder, and cascaded sections containing series Mach-Zehndersymmetric directional coupler modulators. The optimum bias point for the asymmetric directional coupler modulator is determined by device dimensions and material parameters with relative insensitivity to errors introduced during fabrication. Optical insertion loss imposes significant limitations on modulator performance. An implementation of an in-line asymmetric directional coupler modulator is discussed that eliminates excess loss due to fiber coupling in order to achieve a large RF power gain and competitive noise figure compared to the linearization configurations.

大気圧プラズマＣＶＤ法によるアモルファスＳｉの高速成膜に関する研究 （第１報） 回転電極型大気圧プラズマＣＶＤ装置の設計・試作

A new technique for high speed a-Si deposition using the atmospheric pressure plasma with the cylindrical rotary electrode was developed. The advantages of using rotary electrode are as follows; 1) the reactant gases can be introduced efficiently into the small gap between the electrode and the substrate and 2) a large rf power can be supplied without thermal damage of the electrode. A 150 MHz VHF power supply was employed to avoid the ion bombardment of the electrode and the substrate. In the consequence of these advantages, high density radicals are produced and high quality amorphous silicon films can be deposited with high growth rate. The silicon films were fabricated in gas mixtures containing helium, hydrogen and monosilane. They were investigated by Raman spectroscopy and scanning electron microscopy (SEM). The results showed that amorphous silicon films with uniform structure were grown on the glass substrates. The maximum deposition rate was 38nm/s, which was extremely faster than those of the previous techniques. It was also found from the SEM obsevation that the thickness of the silicon films were uniform and no particles were observed inside the films.

Plasma‐Enhanced Chemical Vapor Deposition of Silicon Dioxide Deposited at Low Temperatures

Thin silicon dioxide films are commonly used as insulating layers in metal‐insulator structures, such as integrated circuits and multichip modules. These films are either thermally grown or deposited by thermal or plasma‐enhanced chemical vapor deposition (PECVD). The advantage of PECVD is that lower deposition temperatures can be used avoiding defect formation, diffusion, and degradation of the metal layer. However, the low deposition temperature of the PECVD process has a negative effect on the quality of the silicon dioxide. Oxides produced at low temperatures contain more silanol and water impurities and are more porous than those deposited at higher temperatures. The deposition parameters, including substrate temperature, RF power, pressure, and reactant gas flow rate, affect the silanol and water concentration. The substrate temperature has the largest effect on the silanol concentration of the oxide. Using a large RF power, high pressure, and low nitrous oxide to silane ratio will minimize the silanol concentration at a given temperature. This will minimize the dielectric constant and maximize the etch resistance of the oxide produced.

Influence of radio-frequency sputtering and crystallization parameters on the structure of the BiGa-DyIG garnet films for magneto-optical recording

The dependence of the crystalline structure on crystallization temperature, argon pressure, and rf power have been investigated in detail. Three ranges of annealing temperature were found. In the first and second ones, the film structures are, respectively, amorphous and perfectly polycrystalline, while in the last case an evolution to a textured state occurs. It has been observed that although for large rf power the formation of spurious phases is observed, there is only a small change in the overall composition of the films. On the contrary, for different values of the argon pressure only the garnet phase is observed, but with large stoichiometry changes.

ＲＦ‐スパッタ法によって作製したＹ‐Ｂａ‐Ｃｕ‐Ｏ系薄膜の結晶化

Micro structures and electrical properties were investigated on thin films crystallized from amorphous Y-Ba-Cu-O film prepared by rf-sputtering. Effects of fluorine or CuO addition to the amorphous film were also studied on these properties. An elevation of crystallization temperature enhanced both platy YBCO crystal growth and its orthorhombic c-axis preferred orientation in the crystallized film on MgO substrate. Sputtering power was more important on the film / SrTiO3. No preferred orientation was observed on the film prepared at 100W power. Larger rf-power and fluorine addition to sputter target elevated substrate temperature (Ts). Epitaxially preferred oriented films were obtained at Ts≥350°C. Amorphous films containing fluorine or excess CuO gave c-axis preferred orientations at annealing temperature of 50°C lower than that of Y-Ba-Cu-O film. CuO added film showed the best result on superconducting transition (Tc zero≥70 K) in the present investigations.

LAMPF II

We present a plan for two rapid-cycling synchrotrons — a 45 GeV, 40 μA proton synchrotron with a 9 GeV, 200 μA booster. These machines can provide simultaneously 45 GeV slow-extracted beam for the production of kaons, antiprotons, and other secondary particles, and 9 GeV fast-extracted beam for neutrino and pulsed muon physics. The LAMPF II machines are compared with existing and proposed kaon factories. Relative to the Brookhaven AGS as it exists today, LAMPF II will provide 90 tmes as many neutrino events per year and 300 times as many kaons per year. Some design features of the LAMPF II accelerators that are important for reducing beam losses and increasing beam availability are discussed. Because of the large rf power and voltage required, an innovative design of the ferrite-tuned cavities is necessary. A commercially available Mg-Mn ferrite with perpendicular bias has been shown to raise the available ferrite Q by more than a factor of 10 when compared with materials now in use at other accelerators. The 45 GeV LAMPF II synchrotron would produce far more neutrinos, kaons, and antiprotons per unit cost than an upgraded conventional machine. The LAMPF II booster by itself, which can provide 100 μA at 12 GeV, is a very interesting option at moderate cost.

High Power Integral RF Linac Cavities

Accelerating a long train of high current pulses requires a very large power flow from cavity to beam. Several advantages exist when this large rf power is supplied to the accelerating cavities at the same high rate at which the beam is extracting it. A particular approach to accomplishing this, the wake field transformer concept of Voss and Weiland, as applied to the parameter regime of interest is examined here. Several high current, low energy (few MeV) beams injected offaxis into the cavity are decelerated by their own and preceding fields. The resulting rf energy in the proper mode accelerates a lower current, high energy beam on-axis. Mode generation by an idealized annular beam is calculated as a function of driving current pulse width, cavity length, and radius of the annulus. Optimal pulse width is about half the wavelength of the TM/sub 010/ accelerating mode, and the efficiency (the fraction of the energy going into the TM/sub 010/ mode) is maximized for annulus radius equal to about two-thirds the cavity radius. The modest transformer ratio of about three (ratio of accelerating potential on-axis to decelerating potential on the driving beam) can be increased by making the annulus larger and sacrificingmore » efficiency. Analysis of the beam dynamics shows that an axial magnetic field of the order of 1 kG is adequate to guide the annular power beam.« less

Heating processes in the ionosphere

Heating of the ionosphere by radio waves has been of interest in two main fields. The first is in artificial heating experiments where a large RF power is fed mainly into the F region by a directive aerial. This leads to many effects including turbulence and bulk movement of the plasma. The second field is in the phenomenon of wave interaction of the Luxembourg effect, in which the modulation of a 'disturbing wave' is impressed on the electron temperature and thence transferred as modulation to a 'wanted wave' traversing the heated region. In both these fields the plasma electrons acquire ordered motion from the heating wave. This is converted, through collisions, to disordered motion so that the electrons are heated first. They then share their acquired energy, again through collisions, with the other particles of the plasma. In this subject, therefore, the study of electron collision processes is of great importance. In the ionosphere, electron collisions are predominantly with neutral particles. The problem of finding how the electron velocity distribution function is modified by a heating wave is still not satisfactorily solved. It is connected with the velocity dependence of the electron collision frequency, which also is not known with certainty.