Submillimeter-wave Frequencies Research Articles

Multiplier and Harmonic Generator Technologies for Terahertz Applications

Harmonic generation based on frequency multipliers has proven to be the most successful and widely used solid-state technology for generating power at submillimeter wavelengths. Over the last several years, the development of new device technologies, implementation of innovative circuits, and application of advanced integrated-circuit processing techniques to frequency multiplier design have resulted in unprecedented levels of performance throughout the submillimeter-wave frequency band. This paper reviews the technological innovations, device options, circuit architectures, and fabrication technologies that have made harmonic generation such a successful approach to source development in the submillimeter spectrum.

Bilan des saignements d'origine digestive par microcapsule

Following the introduction of metamorphic high electron mobility transistors (MHEMTs) 30 years back, there has been a rapid growth in their use in advanced MMIC (monolithic microwave integrated circuit) and TMIC (Terahertz monolithic integrated circuit) applications in sub-millimetre wave (S-MMW) and terahertz (THz) frequency regime. Undoubtedly, they are capable of making a great impact in applications such as deep space, cryogenic, biomedical instrumentation, military, high speed communication networks etc, in the years to come. This review article not only studies the progress of depletion mode (D-Mode), enhancement mode (E-Mode) type MHEMTs in the last 30 years, extensively but also critically and systematically analyzes the fabrication challenges, reliability issues and their use in cryogenic fields. Yet another highlight is that the work also carefully examines the utility of MHEMTs in deep space, biomedical, scientific, military, communication areas and so forth.

A submillimetre-wave SIS mixer using NbN/MgO/NbN trilayers grown epitaxially on an MgO substrate

We have designed, fabricated and tested a quasi-optical superconductor–insulator–superconductor (SIS) mixer employing distributed NbN/MgO/NbN tunnel junctions and NbN/MgO/NbN microstriplines at submillimetre-wave frequencies. These trilayers were fabricated by dc- and rf-magnetron sputtering on an MgO substrate at ambient temperature so that the NbN and MgO films were grown epitaxially. Our SIS mixer consists of an MgO hyperhemispherical lens with an antireflection cap and a self-complementary log-periodic antenna made of a single-crystal NbN film, on which the distributed SIS junctions and the two-section impedance transformers were mirror-symmetrically placed at the feed point of the antenna. As designed, the junctions are 0.6 μm wide and 15.5 μm long, which is sufficient to absorb the incoming signal along this lossy transmission line, assuming a current density of 10 kA cm−2. The mixer showed good I–V characteristics, with subgap-to-normal resistance ratios of about 13, although weak-link breaks were observed above the gap voltage. The minimum double side band receiver noise temperature was 334 K at 678 GHz, including the input noise of about 200 K as estimated by the standard technique. The noise temperature gradually rose to 672 K at 820 GHz. This behaviour may be caused by RF losses from the weak-link parts, due to the steps between the distributed junctions and the microstriplines being less than 1 μm wide.

Parametric analysis of micromachined reflex klystrons for operation at millimeter and submillimeter wavelengths

A tool for the simulation of high frequency reflex klystrons is presented. Based on the Monte Carlo technique, this simulation includes loss mechanisms (due to the opacity of the grids) and takes into account the main peculiarities expected for device operation at millimeter and submillimeter wave frequencies. The tool has been used to study the effects of device parameters which are critical to the optimization of output power in a prototype 100 GHz micromachined structure based on a field emission electron source, namely, the electric field in the drift region and the grid distance. The results also show that this device can be used for direct generation of useful amounts of power at these frequencies.

A low-cost fabrication technique for symmetrical and asymmetrical layer-by-layer photonic crystals at submillimeter-wave frequencies

This paper presents a rapid, versatile, and practical technique for the manufacture of layer-by-layer photonic crystals in the millimeter- and submillimeter-wave regions. Mechanical machining is used to derive a rugged layer-by-layer structure from high-resistivity silicon wafers. Unlike traditional anisotropic etching techniques, this method does not rely on any particular crystal orientation of the substrate and allows greater flexibility in the photonic crystal design. Automatic alignment of alternating layers is achieved via careful placement of the separation cuts. Using this ability, two configurations of photonic crystals are realized and their RF characteristics are measured and presented. Firstly, a symmetrical photonic crystal is studied as an initial demonstration of the technique. This is followed by an asymmetrical example, where a different frequency response is observed for the two orthogonal polarizations of the incident radiation. Two measurement techniques are used to characterize the photonic crystals and the merits of each are discussed. Theoretical predictions are seen to agree well with the measured behavior.

Fabrication of niobium superconductor–insulator–superconductor junctions with a magnetic tunneling barrier NiOx for millimeter and submillimeter mixer applications

A thin-film superconductor-insulator-superconductor junction with a magnetic barrier, NiOx, and superconducting electrode, Nb, was fabricated. It is shown that the Josephson current was strongly suppressed without external magnetic field. The tunneling barrier was formed by plasma oxidation and or thermal oxidation. The junction with thermal oxidation showed low specific resistance and current–voltage characteristics with a clear energy gap structure. It is shown that this junction has the potential for quasiparticle mixer working at higher submillimeter wave frequency region above ∼700 GHz, especially suited for making an imaging array.

Submillimeter wave generation through optical four-wave mixing using injection-locked semiconductor lasers

This paper presents a comprehensive analysis of submillimeter wave generation through optical four-wave mixing (FWM) in an injection-locked semiconductor laser. The probe wave introduces pump-probe difference frequency amplitude modulation (AM) and phase modulation (PM) of the slave laser injection locked to the pump wave. The AM and PM indexes of the locked laser output lightwave modulated at the submillimeter wave frequency have been calculated. The submillimeter wave power generated through this technique has also been calculated theoretically. The analysis predicts a submillimeter wave power of -3.7 dBm at 300-GHz frequency for a free-running slave laser output power of 30 mW. In the presence of amplitude modulation of the probe wave, the same modulation is transferred to the submillimeter wave. The suppression of output lightwave amplitude noise relative to the pump, probe, or free-running slave laser amplitude noise has also been estimated in this analysis. At a submillimeter wave frequency of 300 GHz and a probe power equal to the pump power, typical amplitude noise reduction occurs by 7 dB.

Series connection of resonant tunneling diodes for eliminating spurious oscillations

AbstractResonant tunneling diodes, which have the highest operating frequencies among solid‐state oscillating devices at millimeter and submillimeter wave frequencies, generate spurious low‐frequency oscillations easily. As a method of suppressing spurious oscillation of negative resistance devices, the oscillation devices may be connected in series. In this paper, this approach is applied to resonant tunneling diodes. If two diodes are connected in series, no spurious oscillation is observed in the oscillation output spectrum. The effect of suppression of spurious oscillation is experimentally confirmed. Further, from the output characteristic, it is found that the devices are useful as low‐noise high‐ frequency amplifiers and frequency multipliers. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(12): 17–25, 2001

Membrane-supported CPW with mounted active devices

This paper reports the fabrication of printed circuit lines on a 5 μm thick membrane that minimizes dielectric loss and effectively eliminates surface modes, both of which are important for operation at millimeter-wave and submillimeter-wave frequencies. The relatively low-cost low-temperature process uses a photosensitive resin (SU-8) to form the membrane and enables devices to be mounted on it.

Model of thin-film microstrip line for circuit design

An equivalent-circuit model for the thin-film microstrip line (TFMSL) is presented in this paper. Its elements are calculated using closed-form expressions and, thus, this model can easily be implemented in common circuit design tools. For typical TFMSL dimensions, it holds from DC up to the submillimeter-wave frequency range. The model is validated by comparison to electromagnetic full-wave simulation data. Typical errors of phase constant and characteristic impedance are below 2% and 3%, respectively. Regarding attenuation, deviations below 8% are found.

Anomalies in the temperature dependence of the microwave dielectric properties of Ba6−xSm8+2x/3Ti18O54

Measurements of the microwave dielectric properties of Ba6−xSm8+2x/3Ti18O54 solid solutions revealed the existence of a broad maximum in the temperature dependence of the permittivity as well as the dielectric loss. Submillimeter-wave frequency measurements confirmed the intrinsic origin of the observed anomaly, which could possibly be ascribed to phase transition with unknown nature in the Ba6−xSm8+2x/3Ti18O54 solid solution. The temperature of the anomaly, which is in the range of 90–120 °C, depends on composition of Ba6−xSm8+2x/3Ti18O54 and decreases with an increase in x.

Optical mixing with difference frequencies to 552 GHz in ultrafast high electron mobility transistors

The technology of optical mixing in three-terminal devices has been extended, for the first time, to submillimeter-wave frequencies. Using a new generation of 50-nm gate InP-based high electron mobility transistors (HEMT's), optically mixed signals were detected to 552 GHz with a signal-to-noise ratio of approximately 5 dB. A novel harmonic three-wave mixing scheme was used for the detection of the optically generated signals. The technique involved downconversion of the signal in the device by the second harmonic of a gate-injected millimeter-wave local oscillator. Measurements were also done at 212 and 382 GHz to estimate the absolute signal strength and conversion losses. Finally, new interesting features in the bias dependence of the optically mixed signal are reported.

Modeling and design aspects of millimeter-wave and submillimeter-wave Schottky diode varactor frequency multipliers

Design and optimization of Schottky varactor diode frequency multipliers for millimeter and submillimeter wavelengths are generally performed using harmonic balance techniques together with equivalent-circuit models. Using this approach, it is difficult to design and optimize the device and multiplier circuit simultaneously. The work presented in this paper avoids the need of equivalent circuits by integrating a numerical simulator for Schottky diodes into a circuit simulator. The good agreement between the calculated and published experimental data for the output power and conversion efficiency originates from the accurate physical model. The limiting effects of multiplier performance such as breakdown, forward conduction, or saturation velocity are discussed in view of the optimum circuit conditions for multiplier operation including bias point, input power, and loads at different harmonics. It is shown that the onset of forward or reverse current flow is responsible for the limitation in the conversion efficiency.

Potential of GaN Gunn Devices for High Power Generation Above 200 GHz

ABSTRACTThis paper investigates the potential of Gallium Nitride (GaN) Gunn diodes for generating high power radiation at millimeter and sub-millimeter wave frequencies. Simulations were carried out based on an ensemble Monte Carlo computer model. This model accounts for thermal effects, series resistance, and device circuit interaction through the harmonic balance technique. The accuracy of the model has been validated in the case of InP Gunn devices at frequencies above 100 GHz[1]. Initially uniform and linearly graded doping profiles in the active region were considered. It is found that, similar to devices based on InP, the graded profile resulted in a much improved performance in terms of power, efficiency, and operating temperature. In particular, a GaN Gunn structure consisting of a 1 μm thick active region with a graded doping profile increasing from 6 × 1015 cm−3 at the cathode terminal to 4.6×1016cm−3 at the anode terminal yielded promising results. The DC bias voltage was estimated from the calculated velocity-electric field data to be about 25 V. With this bias, it was found that oscillations in the fundamental mode could be obtained over the frequency range from 220 GHz to 330 GHz subject to a load resistance of 1 Ohm and a maximum operating temperature of 800 K. The maximum output power was 30 mW at 290 GHz with a corresponding conversion efficiency of 0.25 %. Considerable improvement was obtained from a device with a heterojunction at the cathode. For a 1 μm device, an optimum power level close to 150 mW was predicted at 215 GHz with an efficiency of 2 %. This estimated power level is about an order of magnitude higher than what can be achieved from InP Gunn oscillators at the same frequency.

Rovibrational Spectroscopy of the v5 = 1 Level of 28SiDF3

The ν5 fundamental band of trifluorosilane-d (SiDF3) at 627 cm−1 was studied for the first time by high-resolution FTIR spectroscopy at a resolution of 2.4 × 10−3 cm−1. The analysis was performed simultaneously with available microwave and newly measured submillimeter-wave data in the approximation of an isolated degenerate fundamental level of a C3Kv symmetric top molecule leading to a standard deviation of 0.22 × 10−3 cm−1 for the reproduction of the infrared wavenumbers, 36 kHz for the microwave, and 198 kHz for the submillimeter-wave frequencies, respectively. The unitary equivalence between the two reductions (Q and D) of the effective Hamiltonian applied in the analysis is demonstrated.

Novel high-Q waveguideE-plane resonators using periodic metallic septa

A novel class of waveguide E-plane resonator structures using periodic metal septa for use at millimeter-wave, submillimeter-wave, and terahertz frequencies has been proposed. It aims to show that this type of resonator can be easily realized with a single metal insert within a rectangular waveguide. One type of resonator which used quarter-wavelength metallic septa was employed. The simulated results for an air-filled metal pipe rectangular waveguide resonator using periodic metallic septa at 37.80 GHz is presented. The measured frequency response of a rectangular waveguide E-plane resonator shows 30 dB rejection at 36 GHz. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 311–312, 1999

Novel high‐Q waveguide E‐plane resonators using periodic metallic septa

A novel class of waveguide E-plane resonator structures using periodic metal septa for use at millimeter-wave, submillimeter-wave, and terahertz frequencies has been proposed. It aims to show that this type of resonator can be easily realized with a single metal insert within a rectangular waveguide. One type of resonator which used quarter-wavelength metallic septa was employed. The simulated results for an air-filled metal pipe rectangular waveguide resonator using periodic metallic septa at 37.80 GHz is presented. The measured frequency response of a rectangular waveguide E-plane resonator shows 30 dB rejection at 36 GHz. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 311–312, 1999

Quasi-Optical Power Combining Techniques

This paper brings about the past and recent trends in the design of solid-state transmitter in the millimeter and submillimeter-wave frequencies using quasi-optical techniques where many devices are efficiently combined to give moderately high power useful for radar applications. In quasi-optics, the cavity dimension can be of many wavelengths, thereby allowing large number of solid-state devices to be integrated without any moding problem usually present in waveguide combiner circuits. Combining efficiency is quite high since combination takes place in the space. Some work carried out at SAMEER is also reported.

Generation and detection of coherent terahertz waves using two photomixers

A general technique has been demonstrated at microwave and submillimeter-wave frequencies for photoconductive sampling in the frequency domain using photomixers and continuous-wave laser diodes. A microwave version in which two photomixers were coupled by a transmission line was developed to quantitatively test the concept from 0.05 to 26.5 GHz. A quasioptical version using antenna-coupled photomixers was demonstrated from 25 GHz to 2 THz. Such a system can outperform systems based on time-domain photoconductive sampling in frequency resolution, spectral brightness, system size, and cost.

Integrated modified rectangular loop slot antenna on substrate lenses for millimeter- and submillimeter-wave frequencies mixer applications

A coplanar waveguide (CPW)-fed rectangular-loop slot antenna with built-in tuning and DC-return capabilities on extended hemispherical lenses is examined. The proposed configuration is scalable up to the submillimeter-wave frequencies. For designing and analyzing the impedance characteristics of the proposed antenna, a multilayer method of moments (MoM) solver has been developed based on the mixed potential integral equation (MPIE) formulation. The corresponding patterns through the lens are obtained using geometrical optics and the surface equivalence principle. Three models have been simulated and one of them has been built and tested at 65 GHz. The integrated antenna exhibits tuning capability, rotationally symmetric patterns, high directivity, good Gaussian coupling efficiency, and a reasonable bandwidth. In addition, computed results agree well with measurements and are used to characterize the input impedance and pattern behavior of the antenna.