THz Circuits Research Articles

An Assessment of Available Models for the Design of Schottky-Based Multipliers Up to THz Frequencies

This paper evaluates the ranges of application and physical limitations of lumped equivalent circuits and drift-diffusion models for the design of THz circuits. The predictions of these models have been compared with a Monte Carlo model, which was considered as a reference, and with measurements from doublers and triplers designed and fabricated by the Jet Propulsion Laboratory. Additionally, the usefulness of Schottky diodes as frequency multipliers above 3 THz is analyzed with the Monte Carlo model.

Plasmonic terahertz detector response at high intensities

Recent work on plasmonic terahertz detection using field effect transistors (FETs) has yielded detectors with high responsivity. Therefore, deviation from small signal mode of operation, when the detector signal is simply proportional to the THz intensity, must be considered. This work presents a new analytical model to predict terahertz response in a FET at arbitrary intensity levels. The proposed analytical model was experimentally validated using a 0.13 μm InGaAs high electron mobility transistor and optically pumped CO2 gas laser operating at 1.63 THz of varying output intensities. The model is suitable for implementation in circuit simulators and might be used for device optimization and THz circuit design.

All-metal micromachining for the fabrication of sub-millimetre and THz waveguide components and circuits

A novel technology for the manufacturing of micromachined all-metal waveguide circuits and structures for frequency bands ranging from 200 up to 7000 GHz (sub-millimetre and THz) is presented. The waveguide circuits are formed by using metal electroplating with preceding sputtering of a thin metal film seed layer over a photo-lithographically patterned thick SU-8 photoresist. The process provides the possibility of making three-dimensional structures via facilitating multi-level (layered) designs. The surface roughness of the THz waveguide structure was demonstrated to be as low as 30 nm. This technology was used to build a state-of-the-art waveguide balanced 1.3 THz hot electron bolometer mixer and other applications for radio astronomy instrumentation.

Complex permittivity characterization of benzocyclobutene for terahertz applications

High-quality polymers such as the benzocyclobutene polymer (BCB) provide interesting dielectric feature for terahertz applications. Already used in silicon integrated circuit technologies, this material could become one of the most promising candidates for the realization of future THz waveguides and interconnections on a silicon substrate but also after active devices process on the top of any other technology (GaAs, InP, GaN…). A frequency-dependent complex permittivity of spin-coated thick layers of this low-k dielectric is obtained from transmittance spectra measured with Fourier transform spectroscopy in the frequency range of 0.5–5.4 THz. The dielectric constant and the loss tangent are discussed according to curing conditions of the photosensitive resin used. A low loss tangent value of 7 − 9 × 10 -3 at 1 THz is obtained with polymerisation in oxygen-free atmosphere. An incomplete curing and a high dose UV exposure have a weak impact on losses. These results associated with the high compatibility of this polymer with silicon and metals make BCB layers well suited for the design of microelectronic THz devices and circuits.

Planar plasmonic terahertz guided-wave devices

We describe the experimental realization of planar plasmonic THz guided-wave devices using periodically perforated metal films. These perforated films behave as effective media for which the dielectric function can be broadly engineered. We initially use transmission measurements to measure the complex dielectric constants of these effective media and show experimentally that the effective plasma frequency corresponds to the cutoff frequency of the rectangular apertures. Using these structures, we demonstrate not only straight planar THz waveguides, but also more complex devices such as Y-splitters and 3-dB couplers. In each of these embodiments, we demonstrate that the propagating THz radiation is well confined in both the in-plane and out-of-plane axes. This approach opens exciting new avenues for both passive and active THz guided-wave devices and circuits.

New concept of RF functions by microfluidic coupling

We present a new concept that combines microfluidic circuits designed inside planar waveguides for advanced ultra-wide band functions. Feasibility of such approach is demonstrated on a broadband variable delay line operating in the microwave region. We also show that this approach is very well fitted for the future THz circuits. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1912–1916, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21812