N. J. Cronin

Fabrication and characterization of micromachined rectangular waveguide components for use at millimeter-wave and terahertz frequencies

The fabrication and characterization of micromachined reduced-height air-filled rectangular waveguide components suitable for integration is reported in this paper. The lithographic technique used permits structures with heights of up to 100 /spl mu/m to be successfully constructed in a repeatable manner. Waveguide S-parameter measurements at frequencies between 75-110 GHz using a vector network analyzer demonstrate low loss propagation in the TE/sub 10/ mode reaching 0.2 dB per wavelength. Scanning electron microscope photographs of conventional and micromachined waveguides show that the fabrication technique can provide a superior surface finish than possible with commercially available components. In order to circumvent problems in efficiently coupling free-space propagating beams to the reduced-height G-band waveguides, as well as to characterize them using quasi-optical techniques, a novel integrated micromachined slotted horn antenna has been designed and fabricated, E-, H-, and D-plane far-field antenna pattern measurements at different frequencies using a quasi-optical setup show that the fabricated structures are optimized for 180-GHz operation with an E-plane half-power beamwidth of 32/spl deg/ elevated 35/spl deg/ above the substrate, a symmetrical H-plane pattern with a half-power beamwidth of 23/spl deg/ and a maximum D-plane cross-polar level of -33 dB. Far-field pattern simulations using HFSS show good agreement with experimental results.

A new micro-machined millimeter-wave and terahertz snap-together rectangular waveguide technology

A novel technique for micro-machining millimeter and submillimeter-wave rectangular waveguide components is reported. These are fabricated in two halves which simply snap together, utilizing locating pins and holes, and are physically robust, and cheap, and easy to manufacture. In addition, S-parameter measurements on these structures are reported for the first time and display lower loss than previously reported micro-machined rectangular waveguides.

Active micromachined integrated terahertz circuits

Schottky barrier diodes have been integrated into on-chip rectangular waveguides. Two novel techniques have been developed to fabricate diodes with posts suitable for integration into waveguides. One technique produces diodes with anode diameters of the order of microns with post heights from 90 to 125 microns and the second technique produces sub-micron anodes with post heights around 20 microns. A method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.F. output in a mixer circuit. Devices have been fabricated and D.C. characterized.

W-band measurements of 100 /spl mu/m height micro-machined air-filled rectangular waveguides

The first S-parameter measurements of micro-machined 100 /spl mu/m high air-filled rectangular waveguides are reported, which have been performed at W-band using a specially designed test fixture connected to a standard vector network analyser. The results obtained show low loss and demonstrate propagation in TE/sub 10/ mode.

Integrated micro-machined antenna for 200 GHz operation

A new integrated micro-machined slotted horn antenna is reported which has been fabricated on a GaAs substrate. The far-field pattern has been simulated and measured showing good agreement, and the antenna has been used to successfully couple power in and out of a micro-machined rectangular waveguide.

Millimeter and submillimeter detection using Ga1−xAlxAs/GaAs heterostructures

We have shown that a Ga1−xAlxAs/GaAs heterostructure can be used as a sensitive tunable detector of mm-wave/sub-mm-wave radiation. The mechanism for detection requires the application of a magnetic field varying from approximately 0.2T at 94GHz (3.2mm wavelength) to 6.2T at 2500GHz (119μm wavelength). The responsivity and N.E.P. at 3.2mm have been roughly estimated at 200V/W and 5×10−11W/✓Hz respectively. The speed of such a detector could be several orders of magnitude greater than comparable InSb detectors.

Use of novel photoresists in the production of submillimeter-wave integrated circuits

A new technique is reported for micro-machining millimeter and submillimeter-wave rectangular waveguide components using an advanced thick film UV photoresist known as EPONTM SU-8. The recent introduction of this resist has been of great interest to the millimeter-wave and terahertz micro-machining communities, as it is capable of producing features up to 1 mm in height with very high aspect ratios in only a single UV exposure. It therefore represents a possible low-cost alternative to the LIGA process. S-parameter measurements on the new rectangular waveguides show that they achieve lower loss than those produced using other on-chip fabrication techniques, they have highly accurate dimensions, are physically robust, and cheap and easy to manufacture.

Fabrication and characterization of integrated waveguide for use at G-band

The fabrication of air-filled rectangular metal-pipe waveguide using a lithographically-based technique has recently been reported. This type of waveguide, together with other passive components such as antennas, couplers, mixers and filters may offer a realistic route to terahertz frequency integrated circuits in view of the compatibility of the fabrication technique with those of standard semiconductor processing. In this contribution, we report the fabrication of a range of waveguide components for operation at frequencies of up to 300 GHz. These measurements represent the highest frequency characterization study so far reported for a micromachined passive structure of this type and provide proof of TE10 propagation with the expected cut-off frequency. Numerous measurements have been taken using G-band (WR-F) guide which show an attenuation loss of approximately 0.6 dB per guide wavelength at 200 GHz. This low value of attneuation shows that these micromachined waveguide are viable components for use in integrated circuits at terahertz frequencies. The insertion loss repeatability (due to mismatch effects at the ports of the waveguides) has been measured and has been shown to be better than plus or minus 0.5 dB. Preliminary results are presented for J-band (WR-3) waveguide which clearly shows the cut off frequency.