This letter reports for the first time on a very low loss silicon micromachined waveguide technology, implemented for the frequency band of 220–325 GHz. The waveguide is realized by utilizing a double H-plane split in a three-wafer stack. This ensures very low surface roughness, in particular on the top and bottom surfaces of the waveguide, without the use of any surface roughness reduction processing steps. This is superior to previous micromachined waveguide concepts, including E-plane and single H-plane split waveguides. The measured average surface roughness is 2.14 nm for the top/bottom of the waveguide, and 163.13 nm for the waveguide sidewalls. The measured insertion loss per unit length is 0.02–0.07 dB/mm for 220–325 GHz, with a gold layer thickness of 1 $\mu$m on the top/bottom and 0.3 $\mu$m on the sidewalls. This represents, in this frequency band, the lowest loss for any silicon micromachined waveguide published to date and is of the same order as the best metal waveguides.

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 providing a simulated field of view of 56°. The design is based on a dielectric filled parallel-plate waveguide (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 x 16 large perforated membranes, which are only 30 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 and a maximum gain of 28.5dBi with an input reflection coefficient below –10. The overall frequency beam steering frontend is extremely compact (24 × 24 × 0.9) 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.

At the end of the 19th century, researchers observed that biological substances have frequency- dependent electrical properties and that tissue behaves "like a capacitor" [1]. Consequently, in the first half of the 20th century, the permittivity of many types of cell suspensions and tissues was characterized up to frequencies of approximately 100 MHz. From the measurements, conclusions were drawn, in particular, about the electrical properties of the cell membranes, which are the main contributors to the tissue impedance at frequencies below 10 MHz [2]. In 1926, a study found a significant different permittivity for breast cancer tissue compared with healthy tissue at 20 kHz [3]. After World War II, new instrumentation enabled measurements up to 10 GHz, and a vast amount of data on the dielectric properties of different tissue types in the microwave range was published [4]-[6].

Two high-gain flat array antenna designs operating in the 320 – 400 GHz frequency range are reported in this paper. The two antennas show measured gains of 32.8 dBi and 38 dBi and consist of a 16 × 16 (256) element array and a 32 × 32 (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), 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 SOI micromachining technology used in this work. The total height of the antennas is 1.1mm (1.2 λ at the center frequency), with sizes of 15mm × 18mm and 27mm × 30mm 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 paper and the performance of the antennas compared to the simulated data, as well as manufacturability and fabrication repeatability are reported in detail.

This paper presents a ruthenium metal-contact RF microelectromechanical system switch based on a corrugated silicon oxide/silicon nitride diaphragm. The corrugations are designed to substantially reduce the influence of the fabrication-induced stress in the membrane, resulting in a highly insensitive design to process parameter variations. Furthermore, a novel multilayer metal-contact concept, comprising a 50-nm chromium/50-nm ruthenium/500-nm gold/50-nm ruthenium structure, is introduced to improve the contact reliability by having a hard-metal surface of ruthenium without substantial compromise in the contact and transmission-line resistances, which is shown by theoretical analysis of the contact physics and confirmed by measurement results. The contact resistance of the novel metallization stack is investigated for different contact pressures and is compared to pure-gold contacts. The contact reliability is investigated for different dc signal currents. At a measurement current of 1.6 mA, the Ru-Au-Ru contacts have an average lifetime of about 100 million cycles, whereas the Au-Au contacts reach 24 million cycles only. For larger signal currents, the metal contacts have proven to be more robust over the Au-Au contacts by a factor of ten. The measured pull-in voltage is reduced significantly from 61 V for flat diaphragm to 36 V for corrugated diaphragm with the introduction of corrugation. The measured RF isolation with a nominal contact separation of 5 mum is better than -30 dB up to 4 GHz and still -21 dB at 15 GHz, whereas the insertion loss of the fully packaged switch including its transmission line is about -0.7 dB up to 4 GHz and -2.8 dB at 15 GHz.