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This article presents a new, very compact silicon-micromachined two-port waveguide platform that features axial ports but allows to integrate waveguide devices, which is enabled by integrated broadband, back-to-back, stepped E- and H-plane bends. This approach of rotating the waveguide plane in two axes enables devices of complex geometry to be directly mounted between two waveguide flanges. A prototype transition operating at 220–320 GHz has experimentally demonstrated an insertion loss of less than 0.2 dB and a return loss of better than 18.5 dB throughout the entire WM-864 waveguide band, characterized by an integrated on-chip waveguide calibration kit. Two 5th-order waveguide filters have been designed as complex demonstrator devices and co-fabricated with the proposed axial integration platform, demonstrating a direct-coupled filter at 270 GHz and a cross-coupled filter at 300 GHz with three transmission zeros. The filters with 1.85% and 2% fractional bandwidths demonstrate a measured insertion loss of 1.92 and 1.50 dB, respectively, to which the two transitions combined add a total of 0.3 dB, and a return loss of 19 and 15 dB in the passbands, respectively. The unloaded $Q$ -factors for the resonator cavities of the two filters were extracted to 750 and 900, respectively. These results are so far unparalleled for filters of similar complexity in this frequency range. The sensitivity to fabrication tolerances is analyzed. [ABSTRACT FROM AUTHOR]

This article presents precision silicon micromachined waveguide calibration standards for use with terahertz vector network analyzers. This enables the creation of precise, highly repeatable, and traceable terahertz waveguide standards, surpassing the limits of current metrology techniques. A single silicon-on-insulator wafer with the appropriate device and handle layer thicknesses is used to implement a wide range of calibration and verification standards. The design of the standards is discussed from mechanical, electrical, and end-user perspectives. Silicon is shown to be the most promising material for the realization of precision metrology standards. We outline the potential to scale the presented design to at least 2.6 THz. Eight types of WM-570 standard, totaling 15 prototypes, are fabricated and characterized between 325 and 500 GHz. Despite some fabrication anomalies, all devices offer excellent performance. The best micromachined standards offer a return loss in excess of 40 dB, an insertion loss of below 0.1 dB, and a phase error of less than 1°. The standards are utilized in both one- and two-port calibrations, including the multiline through-reflect-line algorithm. These are benchmarked against calibrations performed using conventional metallic standards, with a high degree of agreement observed between error-corrected measurements of a range of test devices. [ABSTRACT FROM AUTHOR]

We report on the development of a non-galvanic transition from a silicon micromachined to metallic rectangular waveguide for use in integrated waveguide systems at D-band (110–170 GHz). This transition overcomes the limitations of current solutions that require proper ohmic (galvanic) contact between both waveguides, and thus relaxes tolerance requirements in assembly and manufacturing. The transition uses an in-plane design which enables low-loss integration of micromachined waveguide components, as it eliminates the need for waveguide bends and complex multi-layer structures. We describe the RF design, analyze the EM simulation results, and explain the operating principle of the transition. To verify the concept, dedicated silicon micromachined and metallic waveguides are designed and fabricated. Characterization of the assembled samples shows good agreement with simulation. The transition achieves a typical insertion loss of 0.3 dB and return loss above 20 dB over most of the D-band. Measurement of multiple samples and repeated assemblies results in a variation of S21 of less than ±0.1 dB over the whole band, demonstrating good robustness and repeatability. By removing the need for galvanic connection, automated tools can then be used during system assembly, which enables industrial scale applications such as wireless communications. [ABSTRACT FROM AUTHOR]

In this work, we propose a new concept of phase shifting by tuning the coupling distance between two parallel silicon slabs that support the propagation of an in-phase supermode. A prototype device was implemented in the 220–330-GHz band by integrating the micro-electro-mechanical system (MEMS)-actuated phase-shifting mechanism, based on two moveable parallel-coupled high-resistivity silicon slabs, inside a metallized hollow rectangular waveguide in silicon-on-insulator (SOI) micromachining technology. The prototype device has been characterized to a maximum continuous phase tunability of 550° with a maximum insertion loss of 1.87 dB achieved at 330 GHz. A maximum figure-of-merit (FOM) of 375°/dB is achieved at around 320 GHz, which presently is the highest FOM value reported for any phase shifter in the subterahertz (sub-THz) frequency range. The bandwidth covers the whole waveguide band with an average and worst case insertion loss of 1.94 and 2.5 dB, respectively, a worst case insertion-loss variation of 0.7 dB and a phase error better than 4° for all phase states. A large displacement of MEMS electrostatic comb-drive actuators that are co-fabricated in the micromachined waveguide platform is achieved by a driving voltage of 50 V. The prototype footprint is $7.3 \times 5.3$ mm2. [ABSTRACT FROM AUTHOR]

In this article, we present a new technology platform for creating compact and loss-efficient wafer-scale integrated micromachined substrate-integrated waveguides with silicon-core (Si-SIWs) for the 230–330-GHz frequency range. The silicon dielectric core enables highly integrated sub-millimeter-wave systems, since it allows for downscaling the waveguide’s cross section by a factor of 11.6, and the volume of components by a factor of 39.3, as compared to an air-filled waveguide. Moreover, geometrical control during fabrication of this type of waveguides is significantly better as compared to micromachined hollow waveguides. The measured waveguide’s insertion loss (IL) is 0.43 dB/mm at 330 GHz (0.14 dB/ $\lambda _{g}$ , normalized to the guided wavelength). A low-loss ultrawideband coplanar-waveguide (CPW) transition is implemented to enable direct measurements of devices and circuits in this waveguide platform, and this is also the very first CPW-to-SIW transition in this frequency range. The measured IL of the transition is better than 0.5 dB (average 0.43 dB above 250 GHz), which is lower than for previously reported CPW-to-SIW transitions even at 3 times lower frequencies; the return loss is better than 14 dB for 75% of the band. As devices examples implemented in this platform, a filter and H-plane waveguide bends are shown. The waveguides and the devices are manufactured by deep-silicon etching using a cost-efficient two-mask micromachining process. [ABSTRACT FROM AUTHOR]

A D-band waveguide diplexer, implemented by silicon micromachining using releasable filling structure (RFS) technique to obtain high-precision geometries, is presented here for the first time. Prototype devices using this RFS technique are compared with devices using the conventional microfabrication process. The RFS technique allows etching large waveguide structures with nearly 90° sidewall angles for the 400- $\mu \text{m}$ -tall waveguides. The diplexer consists of two direct-coupled cavity six-pole bandpass filters, with the lower and the upper band at 130–134 and 141–148.5 GHz, respectively. The measured insertion loss of the two bands is 1.2 and 0.8 dB, respectively, and the measured return loss is 20 and 18 dB, respectively, across 85% of the passbands. The worst case adjacent channel rejection is better than 59 dB. The unloaded quality factors of a single cavity resonator are estimated from the measurements to reach 1400. Furthermore, for the RFS-based micromachined diplexer, an excellent agreement between measured and simulated data was observed, with a center frequency shift of only 0.8% and a bandwidth deviation of only 8%. In contrast to that, for the conventionally micromachined diplexer of this high complexity, the filter poles are not well controllable, resulting in a large center frequency shift of 3.5%, a huge bandwidth expanding of over 60%, a poor return loss of 6 and 10 dB for the lower and the upper band, respectively, and an adjacent channel rejection of only 22 dB. [ABSTRACT FROM AUTHOR]

Two high-gain flat array antenna designs operating in the 320–400 GHz frequency range are reported in this article. The two antennas show the measured gains of 32.8 and 38 dBi and consist of a $16\times16$ (256) element array and a $32\times32$ (1024) element array, respectively, which are fed by a corporate H-tree beamforming network. The measured operation bandwidth for both antennas is 80 GHz [22% fractional bandwidth (FBW)], and the total measured efficiency is above −2.5 dB and above −3.5 dB for the two designs in the whole bandwidth. The low measured loss and large bandwidth are enabled by optimizing the designs to the process requirements of the silicon on insulator (SOI) micromachining technology used in this article. The total height of the antennas is 1.1 mm ($1.2~\lambda $ at the center frequency), with sizes of 15 mm $\times $ 18 mm and 27 mm $\times $ 30 mm for both arrays. The antennas are designed to be directly mounted onto a standard WM-570 waveguide flange. The design, fabrication, and measurements of eight prototypes are discussed in this article and the performance of the antennas compared to the simulated data, as well as manufacturability and fabrication repeatability are reported in detail. [ABSTRACT FROM AUTHOR]

A very low-profile sub-THz high-gain frequency beam steering antenna, enabled by silicon micromachining, is reported for the first time in this paper. The operation bandwidth of the antenna spans from 220 to 300 GHz providing a simulated field of view of 56°. The design is based on a dielectric filled PPW leaky-wave antenna fed by a pillbox. The pillbox, a two-level PPW structure, has an integrated parabolic reflector to generate a planar wave front. The device is enabled by two extreme aspect ratio, 16 $\times$ 16 mm large perforated membranes, which are only 30 $\mu \text{m}$ thick, that provide the coupling between the two PPWs and form the LWA. The micromachined low-loss PPW structure results in a measured average radiation efficiency of −1 dB and a maximum gain of 28.5 dBi with an input reflection coefficient below −10 dB. The overall frequency beam steering frontend is extremely compact (24 $\times$ 24 $\times$ 0.9 mm) and can be directly mounted on a standard WM-864 waveguide flange. The design and fabrication challenges of such high performance antenna in the sub-THz frequency range are described and the measurement results of two fabricated prototypes are reported and discussed. [ABSTRACT FROM AUTHOR]

This letter presents an under-etching prevention method for an aqueous hydrofluoric acid (HF) releasing process by adding a single-side low-pressure chemical vapor deposition (LPCVD) silicon protection layer. The proposed method enables advanced silicon-on-insulator (SOI) based millimeter-wave/terahertz (mmW/THz) MEMS waveguide devices, which require for RF performance a complete metallization film over the SOI buried-oxide (BOX) layer, and simultaneously need a locally under-etched BOX layer for implementing MEMS actuators reconfiguring the devices. A comparison between the WR-3.4 waveguide (220-330 GHz) using the proposed under-etching prevention method and the one without using it proves the effectiveness and feasibility during HF releasing processes. A MEMS tunable phase shifter driven by comb-drive actuators has been successfully implemented by applying this method in a micromachined waveguide. [2021-0036] [ABSTRACT FROM AUTHOR]

This paper investigates the fabrication accuracy and repeatability of micromachined quadruplet filters designed at a center frequency of 270 GHz with a 5-GHz bandwidth using a versatile multilayer chip platform which allows for axially arranged waveguide ports. A large number of narrowband silicon-micromachined filters arranged on multiple chips are investigated for fabrication imperfections, assembly misalignment, and fabrication yield, employing fabrication-prediction and different chip-to-chip self-alignment feature strategies. A numerical technique for characterization of the entire fabrication process of the filters through extracting the error statistics for coupling coefficients of a large number of different samples from separately assembled chips is proposed. A total of 47 test filters in effectively 15 different design variants have been fabricated in two fabrication runs, evaluated, and analyzed. The most critical sources of errors are determined. The expected accuracy of the entire filters fabrication process is demonstrated through the yield analysis based on the collected error statistics. [ABSTRACT FROM AUTHOR]

This letter reports on a new low-loss and high-linearity 3-D wafer-level interposer technology enabled by through glass vias (TGVs) with an inverted via configuration. The proposed TGV utilizes a tapered via sidewall profile to achieve a void-free conformal metal coverage with lower process time and fewer fabrication steps than a fully filled conventional TGV. Measurement results for a single 100- $\mu \text{m}$ -tall TGV show an insertion loss of 0.014 dB at 10 GHz and a dc resistance of 28 $\text{m}\Omega$. Finally, this letter reports, for the first time, on nonlinearity measurements of TGVs. Single-tone measurements show that the third-harmonic level for a coplanar waveguide (CPW) TGV test structure is only 2 dB higher than a reference CPW through line without TGVs, indicating an overall excellent linearity performance. [ABSTRACT FROM AUTHOR]

This paper presents a detailed technical characterization of a micromachined millimeter-wave near-field probe developed for skin cancer diagnosis. The broadband probe is optimized for frequencies from 90 to 104 GHz and consists of a dielectric-rod waveguide, which is metallized and tapered towards the tip to achieve high resolution by concentrating the electric field in a small sample area. Several probes with different tip sizes were fabricated from high-resistivity silicon by micromachining and were successfully characterized using silicon test samples with geometry-defined tailor-made permittivity. The probes show a high responsivity for samples with permittivities in the range of healthy and cancerous skin tissue at 100 GHz (from 3.2-j2.3 to 7.2-j8.0, loss tangent of approximately 1.26). The sensing depth was determined by simulations and measurements from 0.3 to 0.4 mm, which is adapted for detecting early-stage skin tumors before they metastasize. The lateral resolution was determined to 0.2 mm for a tip size of 0.6\,\times\,0.3 mm, which allows for resolving small skin tumors and inhomogeneities within a tumor. [ABSTRACT FROM PUBLISHER]

This study presents a design study of a novel concept of a three-dimensional (3D) micromachined square helical antenna designed for 75 GHz, which is completely integrated into a semiconductor silicon substrate. In contrast to conventional on-chip integrated antennas which typically are built on top of the substrate surface, the proposed antenna concept utilises, for the first time to the knowledge of the authors, the whole volume of the wafer by building the helical structure inside the substrate, which results in a very area-efficient high-gain radiating element for a substrate-integrated millimeter-wave system. The effective permittivity of the antenna core and the surrounding substrate can be tailor-made by 3D micromachining, for optimising the maximum antenna performance with this design study it was found, that such an antenna concept can achieve a maximum gain of 13.2 dBi, a radiation efficiency of 95.3% at the axial ratio of 0.94 and a half-power beamwidth (HPBW) of smaller than 40°, and a return loss S11 of -22.3 dB at the nominal frequency of 74.5 GHz, with a 15-GHz bandwidth with a reflection coefficient better than -10 dB. A 16-element substrate-integrated helical line array is demonstrated and achieves a maximum gain of 24.2 dBi with a HPBW of 6.3° in the y-z-plane. This study also studies intensively the influences of the surrounding silicon substrate and dielectric-core etching, the matching transition between the helical structure and a coplanar-waveguide feeding, as well as size and geometry of the ground structure. [ABSTRACT FROM AUTHOR]

This paper demonstrates a very robust and fabrication-parameter insensitive concept of full stress compensation in metallized monocrystalline silicon membranes by symmetrical antidirectional metal deposition on both sides of a transfer-bonded silicon membrane. This concept results in previously unmatched near-perfectly flat, temperature-compensated, and high-reliability metal-coated membranes, independent on the thickness, residual stress, and material of the metal layers. Application examples are high-performance optical mirror devices and quasi-optical tunable microwave surfaces, the latter being presented in this paper. The influence of the thickness ratio of the metal films on the membrane curvature is investigated, demonstrating a controllable curvature range from -0.3 to 0.1 \mm^-1 for the investigated devices by varying the top-to-bottom metal thickness ratio from 0.38 to 3.5 using metal thicknesses from 200 to 800 nm. Near-zero curvature down to 0.004 \mm^-1 is also demonstrated. Theoretical analysis of the stress-compensated multilayer structures and characterization results of fabricated test devices are included in this paper, as well as the influence of unsymmetrically etched structures in the two metallization layers on the stress-induced curvature. Reliability tests up to 100 million cycles showed no detectable change in curvature or plastic deformation, proving the robustness and repeatability of this new design concept of zero-curvature temperature-compensated monocrystalline silicon-core membranes with thick metal coating.\hfill[2012-0230] [ABSTRACT FROM AUTHOR]

This paper analyzes the power handling capability and the thermal characteristics of an all-silicon dielectric-block microelectromechanical-system (MEMS) phase-shifter concept, which is the first MEMS phase-shifter type whose power handling is not limited by the MEMS structures but only by the transmission line itself and by the heat-sink capabilities of the substrate, which enables MEMS phase-shifter technology for future high-power high-reliability applications. The power handling measurements of this concept are performed up to 43 dBm (20 W) at 3 GHz with an automatic gain-controlled setup, assisted by a large-signal network analyzer, and the temperature rises of the devices were measured with an infrared microscope camera. The measurement results are extended to 40 dBm at 75 GHz by calibrating electrothermal simulations with the measurements. A comparative study to conventional state-of-the-art MEMS phase-shifter concepts based on thin metallic bridges is carried out. The simulated results show that the all-silicon phase-shifter designs have the maximum temperature rise of only 30 ^\circ\C for 40 dBm at 75 GHz, which is 10–20 times less than conventional MEMS phase shifters of the comparable RF performance. [ABSTRACT FROM PUBLISHER]

This paper reports on design, fabrication, and characterization of a novel multistage all-silicon microwave MEMS phase-shifter concept, based on multiple-step deep-reactive- ion-etchedmonocrystalline-silicon dielectric blocks which are transfer bonded to an RF substrate containing a 3-D micromachined coplanar waveguide. The relative phase shift of 45° of a single stage is achieved by vertically moving the λ/2-long blocks byMEMS electrostatic actuation. The measurement results of the first prototypes show that the return and insertion loss of a 7 × 45° multistage phase shifter over the whole frequency spectrum from 1 to 110 GHz are better than -12 and -5.1 dB, respectively. The monocrystalline high-resistivity silicon blocks are acting as a dielectric material from an RF point of view, and at the same time as actuation electrodes for dc electrostatic actuation. The mechanical reliability was investigated by measuring life-time cycles. All tested phase shifters with three-meander 36.67-N/m mechanical spring and a pull-in voltage of 29.9 V survived 1 billion cycles after which the tests were discontinued, no indication of dielectric charging could be found, neither caused by the dielectric block nor by the Si3N4 distance keepers to the bottom electrodes. Finally, it is investigated that, by varying the fill factor of the etch hole pattern, the effective dielectric constant of the block can be tailor made, resulting in 45°, 30°, and 15° phase-shifter stages fabricated out of the same dielectric material by the same fabrication process flow. [ABSTRACT FROM AUTHOR]