Millimeter-wave Devices Research Articles

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

Transformation optics for the validation of a time-domain full-wave model of linear complex media

Complex media have gained interest in microwave and millimeter-wave devices. They display some interesting characteristics such as, for instance, tunability and controlled filtering capacity. However, such media are generally very complex as they can be fully nonhomogeneous; frequency dependent, anisotropic, time dependent, or chiral. This requires simulation techniques capable of solving Maxwell’s equations accounting for such media. Also, apart comparison with rather difficult measurement, canonical solutions are not available for validation. In this paper, the concept of transformation optics (TO) is presented as a systematic tool to construct computational problems involving complex media for which the analytical solution is known. Several examples are shown for validation of a new transmission-line matrix (TLM) cell that model complex media.

Novel high Curie temperature Ba2ZnSi2O7 ferroelectrics with low-permittivity microwave dielectric properties

Ba2ZnSi2O7 ceramics with a monoclinic structure (C 2/c) were prepared using the conventional solid-state method at 1200°C for 3h in air. The as-prepared ceramics show signs of weak ferroelectricity from the P-E loop and ferroelectric domains with 90° and 103° directions. Although an εr anomaly appears at approximately 510°C, the Curie temperature (Tc) of the Ba2ZnSi2O7 ceramics is 750°C or higher. The ceramics also display low-permittivity microwave dielectric properties (εr=8.09, Q×f=26,634GHz, and τf=−51.46ppm/°C). Therefore, the coexistence of high-Tc ferroelectricity and good microwave dielectric properties is beneficial to develop Ba2ZnSi2O7 ceramics into tunable-microwave and millimeter-wave devices such as capacitors, phase shifters, and oscillators.

Magnetoelectric Effect for Rotational Parameters Detection

The magnetoelectric (ME) effect has been successfully demonstrated in the potential device applications of energy harvesters, magnetic sensors, current sensors, microwave and millimeter-wave multiferroic devices, miniature antennas, and even medical applications. To further investigate the role of ME effect in rotational parameters detection, this paper presents an ME rotational parameter sensor consisting of a magnetostrictive/piezoelectric laminated composite (MPLC) and a multi-pole magnetic ring. The relationship between the proposed sensor’s output signal and the rotational parameters has been analyzed. The output frequency is directly proportional to the rotational speed, and the waveform has a good sin property. In a word, based on the proposed sensor, the rotational speed can be measured by determining the frequency of the output signal, and the rotational position can be detected by the phase discrimination. As the MPLC has the characteristics of high sensitivity and quick response, the starting and stopping times and the eccentricity of rotating pieces can also be measured by the proposed ME rotational parameter sensor.

Antipodal Linear Tapered Slot Antenna Based Radio Link Characterization in Narrow Hallway Environment at 60 GHz

The performance of wireless communication systems is predominantly dependent on propagation environment and respective radiating antennas. Due to the shorter wavelength at millimeter wave (MmW) frequencies, the propagation loss through the objects in indoor environments is typically very high. To improve the channel capacity and to reduce inter-user interference, a high gain directional antenna is desired at MmW frequencies. Traditional antennas used in MmW devices are not suitable for low-cost commercial devices due to their heavy and bulky configurations. This paper focuses on design and development of a very compact (44.61 × 9.93 × 0.381 mm) high gain antipodal linear tapered slot antenna (ALTSA) utilizing substrate integrated waveguide (SIW) technology at 60 GHz. Received signal strength (RSS), path loss, and capacity are studied for MmW indoor applications utilizing ALTSA with radio frequency (RF) measurement equipment in narrow hallway environment.

A dual-mode operation overmoded coaxial millimeter-wave generator with high power capacity and pure transverse electric and magnetic mode output

An overmoded coaxial millimeter-wave generator with high power capacity and pure transverse electric and magnetic (TEM) mode output is designed and presented, by using a kind of coaxial slow wave structure (SWS) with large transversal dimension and small distance between inner and outer conductors. The generator works in dual-mode operation mechanism. The electron beam synchronously interacts with 7π/8 mode of quasi-TEM, at the meanwhile exchanges energy with 3π/8 mode of TM01. The existence of TM01 mode, which is traveling wave, not only increases the beam-wave interaction efficiency but also improves the extraction efficiency. The large transversal dimension of coaxial SWS makes its power capacity higher than that of other reported millimeter-wave devices and the small distance between inner and outer conductors allows only two azimuthally symmetric modes to coexist. The converter after the SWS guarantees the mode purity of output power. Particle-in-cell simulation shows that when the diode voltage is 400 kV and beam current is 3.8 kA, the generation of microwave at 32.26 GHz with an output power of 611 MW and a conversion efficiency of 40% is obtained. The power percentage carried by TEM mode reaches 99.7% in the output power.

Analysis of Dynamic Response of Permittivity in a Liquid Crystal Cell with Flow

Microwave and millimeter-wave devices including a liquid crystal (LC) are increasingly attractive for the use in adaptive and controllable devices. Various types of microwave phase shifters having an LC transmission line have been studied (e.g. microstripline, coplanar waveguide, and rectangular waveguide). In conventional microwave devices, the response time after removal of voltage is slow because the LC layer in the devices is usually thick. In this study, the time response of the LC permittivity is studied experimentally and theoretically. Experimentally measured response curves having two time constants for decay are examined by using Frank’s continuum theory with and without the backflow effect.

High Electron Confinement under High Electric Field in RF GaN-on-Silicon HEMTs

We report on AlN/GaN high electron mobility transistors grown on silicon substrate with highly optimized electron confinement under a high electric field. The fabricated short devices (sub-10-nm barrier thickness with a gate length of 120 nm) using gate-to-drain distances below 2 µm deliver a unique breakdown field close to 100 V/µm while offering high frequency performance. The low leakage current well below 1 µA/mm is achieved without using any gate dielectrics which typically degrade both the frequency performance and the device reliability. This achievement is mainly attributed to the optimization of material design and processing quality and paves the way for millimeter-wave devices operating at drain biases above 40 V, which would be only limited by the thermal dissipation.

Low Side-Lobe Substrate-Integrated-Waveguide Antenna Array Using Broadband Unequal Feeding Network for Millimeter-Wave Handset Device

A low side-lobe substrate-integrated-waveguide (SIW) antenna array is presented at the 28-GHz band using broadband unequal feeding network for millimeter-wave (mm-wave) handset devices. The ground-plane size of the proposed antenna is fixed to half of the size of the Samsung Galaxy Note 4. The antenna array has been implemented with a multilayer structure created by stacking three substrates and a copper plate. An 8-way SIW feeding network with broadband 4-stage T-junction dividers and a cavity-backed antenna are investigated to obtain broadband performance. The proposed unequal T-junction dividers with phase compensation are introduced and designed for various output ratios. Applying Taylor beam-pattern synthesis in the 8-way SIW feeding network, low side-lobe performance is achieved. The measured result of the fabricated antenna has 2.3 GHz bandwidth within $\text{S}_11\,{ . The fabricated antenna can be performed with a gain up to 13.97 dBi with a low cross-polarization and symmetrical fan beam radiation patterns with low side-lobe levels. Most of the measured results are validated with the simulated results. The proposed antenna array provides low cost, broadband performance, and good radiation performances with low side-lobe levels for mm-wave handset devices.

Performance Analysis of Outdoor mmWave Ad Hoc Networks

Ad hoc networks provide an on-demand, infrastructure-free means to communicate between soldiers in war zones, aid workers in disaster areas, or consumers in device-to-device (D2D) applications. Unfortunately, ad hoc networks are limited by interference due to nearby transmissions. Millimeter-wave (mmWave) devices offer several potential advantages for ad hoc networks including reduced interference due to directional antennas and building blockages, not to mention huge bandwidth channels for large data rates.. This paper uses a stochastic geometry approach to characterize the one-way and two-way signal-to-interference ratio distribution of a mmWave ad hoc network with directional antennas, random blockages, and ALOHA channel access. The interference-to-noise ratio shows that a fundamental limitation of an ad hoc network, interference, may still be an issue. The performance of mmWave ad hoc networks is bounded by the transmission capacity and area spectral efficiency. The results show that mmWave networks can support much higher densities and larger spectral efficiencies, even in the presence of blockage, compared with lower frequency communication for certain link distances. Due to the increased bandwidth, the rate coverage of mmWave can be much greater than lower frequency devices.

Design of a 170 GHz Notch Filter for the KSTAR ECE Imaging Sensor Application

A planar, light-weight, and low-cost notch filter structure is required for the KSTAR ECEI (Electron Cyclotron Emission Imaging) system to protect the mixer arrays from spurious plasma heating power. Without protection, this heating power can significantly degrade or damage the performance of the mixer array. To protect mixer arrays, a frequency selective surface (FSS) structure is the suitable choice as a notch filter to reject the spurious heating power. The FSS notch filter should be located between the lenses of the ECEI system. This paper presents a 170 GHz FSS notch filter for the KSTAR ECEI sensor application. The design of such an FSS notch filter is based on the single-sided square loop geometry, because that makes it relatively insensitive to the incident angle of incoming wave. The FSS notch filter exhibits high notch rejection with low pass-band insertion loss over a wide range of incident angles. This paper also reviews the simulated and measured results. The proposed FSS notch filter might be implemented in other millimeter-wave plasma devices.

A facile hydrothermal route to self-assembled ZnGa2O4 particles and their microwave application

Self-assembled porous ZnGa2O4 particles were synthesized through a facile hydrothermal route in this work. The phase evolution and microstructure of specimens were identified by XRD and SEM. Various morphologies (i.e. porous, nanorods or spherical particles) and size (nano or micro-sized) could be rationally designed through altering the reaction conditions. Hydrothermal ZnGa2O4 particles exhibited an outstanding microwave dielectric performance, i.e. a dielectric constant of 9.93, a Q×f value of 73 000GHz, and a τf value of –68.7ppm/°C. What is more, the ZnGa2O4 ceramics displayed a stable quality factor in the high temperature region (1400–1500°C) due to the unique frame-structured ZnGa2O4 particles. Therefore, they can be regarded as potential candidate materials for millimeter-wave device.

Effect of magnetic field on the RF performance of millimeter-wave IMPATT source

In this paper, a two-dimensional (2-D) large-signal model has been presented to study the effect of steady magnetic field on the RF performance of millimeter-wave (mm-wave) double-drift region impact avalanche transit time device. Magnetic field sensitivities of various static and large-signal parameters of the device designed to operate at W-band have been calculated and discussed in detail. Results show that the frequency tuning of the source of around 3.64 GHz is achievable with maximum sensitivity of about $$-$$-1.59 GHz $$\hbox {T}^{-1}$$T-1 for the application of transverse magnetic field varying from 4.0 to 5.0 T. The nature of both frequency and power tuning of the device due to application of transverse magnetic field is in good agreement with the experimental results carried out earlier.

Integrated Magnetic Nanoinductors

This paper demonstrates the feasibility of the realization of on-chip inductors for use in microwave and millimeter-wave devices using ultraminiaturized on-chip vertical nanohelices. The inductors are constructed by depositing a thin film of closely packed, vertically aligned Nickel nanohelices. The film is fabricated using a CMOS-compatible glancing angle physical vapor deposition method. The resulting nanostructured inductors are characterized from 10 to 70 GHz and are found to have inductances of 6 pH/ $\mu \text{m}^{2}$ , 60 times larger than conventional on-chip planar spiral inductors. A quality factor of three is measured and the results indicate that it continues to improve above 70 GHz, while inductance values remain relatively constant. The proposed nanostructured inductors can significantly reduce the chip area, and consequently the cost, of radio frequency and millimeter-wave integrated circuits. In addition, the nanostructured inductors offer significantly larger operation bandwidth than on-chip planar structures operating at frequencies above 100 GHz.

Synthesis and microwave dielectric properties of 2ZnO⋅3B2O3-doped ZnAl2O4 low-permittivity ceramics

2ZnO⋅3B2O3-doped ZnAl2O4 ceramics were synthesized via solid-state method. Influence of different 2ZnO⋅3B2O3 additions on the microstructure, sintering behavior and microwave dielectric properties has been investigated. The results showed that zinc borate could effectively improve the densification and expand the sintering temperature range. Microwave dielectric properties of 2ZnO⋅3B2O3-doped ZnAl2O4 ceramics were exhibited as follow: εr=8.32, Q×f=93,600GHz (at 14.0GHz) and τf=−68.5ppm/°C. Spinel-structured zinc borate-doped ZnAl2O4 ceramics possessed comparatively low sintering temperatures, wide temperature regions (about 100°C), simultaneously, high Q×f and stable τf values. These outstanding performance make them promising candidate materials for millimeter-wave devices at high frequency.

Analysis of the Photonic Bandgaps for Gyrotron Devices

The global bandgaps of photonic crystal are theoretically analyzed in this paper. The electromagnetic-wave propagation characteristics of photonic bandgap (PBG) structures, which is used in the the millimeter-wave, submillimeter-wave, and terahertz regime vacuum electronic devices and accelerators, were numerically simulated using the finite-element method software high-frequency structural simulator. The dispersion curves of the lattices in different rod radius to-rod spacing ratios and the global bandgaps for the general 2-D PBG structures formed by triangular and square arrays of metal rods were simulated. A mode map that shows the relationship between the structures and the contained modes was plotted and a 220-GHz metallic PBG resonator operating in TE $_{\mathrm {\mathbf {04}}}$ mode was designed for a gyrotron device to verify the theoretical and numerical simulations, and a comparison of mode density and quality factor between the PBG resonator and the equivalent cylindrical resonator has been carried out.

Microfabricated Thick-Cu PZT-MEMS Millimeter-Wave Topologies and Devices

This letter reports the design, fabrication, and performance of millimeter-wave transmission lines and devices in a tri-layer thick-copper (Cu) process. Beneath the Cu layers is a low-voltage lead zirconium titanate (PZT) MEMS stackup atop a nitride membrane, on high-resistivity silicon. The 10 μm thick Cu layers enable several transmission-line topologies, and the PZT-MEMS functionality enables tunability. We designed transmission lines and un-optimized noncontact distributed MEMS transmission line (DMTL) phase shifters for 75-110 GHz, and present static measurements here. Simulation and measurements are in close agreement, with measured CPW line loss 0.15 dB greater than simulated (0.27 dB/mm at 95 GHz). Excess loss is attributed to Cu roughness, conductivity, and membrane/strap supports. Measured noncontact DMTL phase shifters exhibit a mean of 40 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /dB when intrinsic line loss is subtracted.

Electrical detection of millimeter-waves by magnetic tunnel junctions using perpendicular magnetized L10-FePd free layer.

Spin dynamics excited by spin-polarized current in magnetic tunnel junctions (MTJs) is potentially useful in nanoscale electrical oscillation sources and detection devices. A spin oscillator/detector should work at a high frequency, such as that of a millimeter-wave, where the quality of a semiconductor device is restricted by carrier mobility, the CR time constant, and so on. Developers of spin systems for practical use need to find out how to excite spin dynamics (i) in the millimeter-wave region, (ii) with low power consumption (ex: no external magnetic field, low damping material), and (iii) for broad frequency modulation. Here L10-ordered FePd alloy with perpendicular magnetocrystalline anisotropy (PMA) and a low damping constant, 0.007, was used for the free layer in the MTJs, and a homodyne-detected ferromagnetic resonance (FMR) signal was obtained at around 30 GHz together with the possibility of one-octave frequency modulation. The FMR signal in out-of-plane magnetized L10-ordered FePd free layer could be excited without an external magnetic field by injecting in-plane spin polarized alternating current. This study shows the potential utility of L10-ordered alloy materials such as FePt, CoPt, MnAl, and MnGa in a variety of millimeter-wave spin devices.

PERFORMANCE INVESTIGATIONS WITH ANTIPODAL LINEAR TAPERED SLOT ANTENNA ON 60 GHZ RADIO LINK IN A NARROW HALLWAY ENVIRONMENT

The performance of wireless communication systems is predominantly dependent on propagation environment and respective radiating antennas. Due to the shorter wavelength at Millimeter Wave (MmW) frequencies, the propagation loss through surroundings in indoor environments is typically very high. To improve the channel capacity and to reduce inter-user interference, a high gain directional antenna is desired at MmW frequencies. Traditional antennas used in MmW devices are not suitable for low-cost commercial devices due to their heavy, bulky and expensive configurations. This paper focuses on design and development of a very compact (44.61 mm × 9.93 mm × 0.381 mm) high gain Antipodal Linear Tapered Slot Antenna (ALTSA) utilizing Substrate Integrated Waveguide (SIW) technology at 60 GHz. Received signal strength (RSS), path loss (PL) and capacity are studied for MmW based wireless applications utilizing electromagnetic (EM) computations and Radio Frequency (RF) experiments in narrow hallway environment.

Permittivity and Loss Characterization of SU-8 Films for mmW and Terahertz Applications

The dielectric permittivity measurement of thick SU-8 film is presented for the entire frequency band of 1 GHz to 1 THz. SU-8 is a high-resolution UV-patternable photoresist that can be used for fabrication of high-aspect-ratio 3-D structures for millimeter-wave and terahertz devices. Here, we report the measured dielectric constant and loss tangent of SU-8 films using terahertz time-domain spectroscopy. A quadratic polynomial model is established for the accurate calculation of complex permittivity up to 1 THz. The loss tangent of fully cross-linked 430- $\mu\hbox{m}$ -thick SU-8 film was measured to be 0.015, 0.027, and 0.055 at 1, 200, and 1000 GHz, respectively. Similarly, relative permittivity was found to be 3.24, 3.23, and 2.92. The fabrication process and level of cross-linking were demonstrated to have significant impact on the loss behavior of this material and the impact of cross-linking on dielectric permittivity is quantified across a wide frequency band. The characterization results reported in this letter are a platform for developing next-generation millimeter-wave and terahertz devices.