S. Biber

Design and Testing of Frequency-Selective Surfaces on Silicon Substrates for Submillimeter-Wave Applications

A new class of frequency-selective surfaces (FSSs), to be used as quasi-optical filters for harmonic suppression in submillimeter-wave frequency multipliers, is proposed and experimentally verified. The FSSs consist of two-dimensional aperture arrays and are made from microstructured aluminum on electrically thick, high-resistivity silicon substrates. This leads to a very good mechanical stability, reasonably low insertion loss, and permits manufacture of the structure by using standard processes available from the semiconductor industries. This paper presents the design, fabrication, and testing of two sets of prototypes, the former with a passband at 300 GHz and a stopband at 450 GHz and the latter with a passband at 600 GHz and a stopband at 750 GHz. For both frequency ranges, FSSs with rectangular slots and with dogbone-shaped holes have been designed by using the method of moments/boundary integral-resonant mode expansion method. The effect of ohmic and dielectric losses has been determined by using the commercial code HFSS. Several prototypes have been fabricated, and measured by terahertz time-domain spectroscopy and continuous wave measurements, showing high reproducibility of the machining process, insertion loss between 1.0 and 1.6 dB, and stopband attenuation larger than 30 dB. Finally, we demonstrate that the incidence angle can be used as a degree of freedom for fine tuning the stopband, without practically changing the frequency response in the passband

Design and measurement of a bandpass filter at 300 GHz based on a highly efficient binary grating

A bandpass filter for 300 GHz with a stopband at 450 GHz based on a highly efficient binary grating as a frequency-selective element was developed and optimized. The geometry of the grating was carefully designed for a maximum difference angle between reflected beams at 300 and 450 GHz and for maximum efficiency at 300 GHz. The grating efficiency was optimized using a rigorous theory of diffraction, yielding a maximum efficiency of over 99.5% neglecting conductor losses. Antennas and elliptical mirrors are used for optimum quasi-optical illumination of the grating and Gaussian beam shaping. After an optimization and a comprehensive examination of the grating in an experimental heterodyne measurement setup at 300 GHz, the filter was implemented fixed tuned into a small housing with waveguide flanges. The fixed tuned setup with corrugated feed horns results in an overall flange-to-flange insertion loss of only 2.8 dB.

Design of artificial dielectrics for anti-reflection-coatings

With the increasing interest in new artificial materials ranging from meta-materials to photonic bandgap materials there is a growing need for accurate models of artificial materials. We examine the design of a three-layer structure with an artificial dielectric as an anti-reflection-coating on both sides of a dielectric slab. We present a field-equivalent circuit theory to calculate the effective dielectric constant of the structured dielectric. The materials discussed in this paper have a lateral periodicity smaller than ¿/10 and can easily be manufactured from high density polyethylene (HDPE) for frequencies up to 20 GHz. The field-analog circuit theory can also be used to calculate the polarization dependence of the artificial dielectric. Theoretical results of three geometrically different structures were compared with waveguide measurements at X-band and showed excellent agreement. Applications such as the design of new components at millimeter and submillimeter wave frequencies are discussed, considering the X-Band measurements as a scaled model.

A novel system for systematic microwave noise and DC characterization of terahertz Schottky diodes

An automated system is developed to evaluate a large number Schottky diodes for terahertz applications with respect to their dc and noise characteristics using a highly sensitive noise measurement technique for one port devices. An extensive RF switching matrix allows noise characterization of one port devices at selected frequency points over a bandwidth from 2 to 8 GHz. The measurement principle also accounts for the impedance mismatch between the system and the device under test (DUT). Furthermore, the setup includes an automated three-axis nanopositioning system capable of consecutively contacting many Schottky diodes arranged in a honeycomb array. The highly accurate positioning of the DUT allows to create reproducible contacts with the diodes using electrochemically etched whisker tips. The smooth contacting procedure enables several hundred contacts with the same whisker tip. With this system, we evaluate the statistical distribution of dc and noise parameters of Schottky diodes with an anode diameter of 1 /spl mu/m within one honeycomb chip. The system helps in optimizing the production parameters of Schottky diodes for terahertz frequencies.

Design of new passive THz devices based on micromachining techniques

We present an overview on the latest results using micromachining techniques for the fabrication of THz-components. Different machining techniques was discussed with respect to their capability to generate complex 3-dimensional geometries with high aspect ratios and to meet the high mechanical requirements for THz-components. Exemplary results for the application of micromachining techniques for the design of new components were reviewed. We emphasizes the potential of silicon based microstructures for the manufacturing of new devices.

Micromachined split-block Schottky-diode mixer for 600 GHz

This paper presents simulation results for a 600 GHz micromachined waveguide mixer with integrated horn antenna, a hybrid-integrated planar Schottky diode and IF filter structures on a quartz substrate. In addition to the simulated electrical performance we show approaches for the manufacturing of the split-block mixer by both micro-mechanical milling and silicon etching technology.

600 GHz GaAs Schottky diode mixer in split-block technology

In this paper we present measurement results of a micro-machined split-block waveguide mixer for 600 GHz. The mixer implements a planar GaAs Schottky diode on a quartz substrate. Two different diode designs used for this mixer design are compared. The overall performance of the waveguide mixer is demonstrated by measurements of the mixer in a quasi-optical setup at 600 GHz. In this setup we are able to measure single sideband conversion losses of 9-14 dB at 600 GHz and voltage responsivities of 421-1690 mV/mW.

Design and testing of frequency selective surfaces on thick silicon substrate operating at 600 GHz

This paper describes the design and experimental verification of frequency selective surfaces, to be used as quasi-optical filters in the sub-millimeter wave range. They consist of a thin metal layer perforated periodically with rectangular or dogbone-shaped holes, and supported by a thick silicon substrate. A set of filters with pass-band at 600 GHz and stop-band at 750 GHz have been designed and tested. The design procedure based on the MoM/BI-RME method, the manufacturing of prototypes by standard processes available from the semiconductor industries, and their measurement by CW and THz time-domain spectroscopy are reported in this work. This class of filters is mechanically robust, presents low losses (1.4 dB), exhibits good reproducibility, and permits a fine tuning of the stop-band frequency by slightly changing the incidence angle.

Low loss silicon window material for submillimeter waves using micromachined artificial dielectrics for anti-reflection coating

A high-resistivity silicon wafer was used to design a broad-band low loss window material for 600 GHz by micromachining an artificial dielectric as a quarter wave transformer on the front and rear side of the wafer. The artificial dielectric is made from a 2-dimensional periodic structure to ensure the same transmission characteristics for horizontally and vertically polarized waves.

Technological issues for micromachining of new passive THz-components based on deep-trench silicon etching

We present a survey of the application of micromachining techniques for the fabrication of THz-components. Micro-machining of new THz- devices based on deep trench etching of silicon is discussed with respect to its capability to generate complex 3-dimensional geometries with high aspect ratios (ARs) and to meet the high mechanical requirements for THz-components. First results for the application of deep trench etching for the design of a branch-line coupler for 600 GHz is discussed. We emphasize the potential of silicon based microstructures for manufacturing new devices and focus on technological issues.