Tapani Närhi

Fabrication and performance of InP-based heterostructure barrier varactors in a 250-GHz waveguide tripler

High-performance InGaAs-InAlAs-AlAs heterostructure barrier varactors (HBVs) have been designed, fabricated, and RF tested in a 250-GHz tripler block. The devices with two barriers stacked on the same epitaxy are planar integrated with coaxial-, coplanar-, and strip-type configurations. They exhibit state-of-the-art capacitance voltage characteristics with a zero-bias capacitance C/sub 3//sup 0/ of 1 fF//spl mu/m/sup 2/ and a capacitance ratio of 6:1. Experiments in a waveguide tripler mount show a 9.8-dBm (9.55-mW) output power for 10.7% conversion efficiency at 247.5 GHz. This is the highest output power and efficiency reported from an HBV device at J-band (220-325 GHz).

A Single-Waveguide In-Phase Power-Combined Frequency Doubler at 190 GHz

This work represents the first demonstration of in-phase power-combined frequency multipliers above 100 GHz based on a dual-chip single-waveguide topology, which consists of two integrated circuits symmetrically placed along the E-plane of a single transmission waveguide. This strategy increases by a factor of 2 the maximum sustainable input power with regard to traditional waveguide multipliers. A biasless 190 GHz Schottky doubler based on this novel concept has been designed and tested with a 6-10% conversion efficiency measured across a 177-202 GHz band when driven with a 50-100 mW input power at 300 K.

Schottky Diode Series Resistance and Thermal Resistance Extraction From

A new method for extracting the series resistance and thermal resistance of a Schottky diode is presented. The method avoids the inaccuracies caused by the temperature dependence of the saturation current and ideality factor. These are a major concern for traditional extraction methods, especially when the diode under test has a submicrometer anode diameter and is significantly heated up by the bias current. The method uses theoretical models validated with measurements for the temperature-dependent saturation current and ideality factor, and the series resistance values extracted from low-frequency scattering parameter measurements in the high bias current regime. The main focus of this paper is the accurate extraction of the series resistance. For example, the series resistance value extracted with our method for a discrete diode with a 0.8-μm anode diameter is 88% larger than the series resistance extracted using traditional techniques. As a by-product from the extraction algorithm, an estimate for the thermal resistance of the diode is obtained. The method is validated with extensive current-voltage (I-V) and scattering parameter measurements of two different commercially available discrete single anode mixer diodes optimized for terahertz operation. I-V measurements are performed at several controlled ambient temperatures and scattering parameter measurements at one known ambient temperature.

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For use in a millimeter-wave direct detection radiometer for earth remote sensing, we have developed a low-noise amplifier (LNA) module with a small-signal gain of 19.5 dB at 243 GHz and a 3 dB bandwidth of 40 GHz. The implemented three-stage LNA MMIC has been manufactured using a 50 nm gate length metamorphic HEMT (mHEMT) technology on 50 μm thick GaAs substrates. Each of the two on-chip integrated E-plane probe waveguide transitions offers a transmission loss of only 0.5 dB at 243 GHz including a 7.5 mm long WR-3.4 waveguide. Due to the low-loss packaging, the LNA module achieves a low noise figure of only 6.0 dB at room temperature.

-Parameter and Temperature Controlled I–V Measurements

Recent developments in the fabrication of GaAs integrated Schottky structures for applications above 100 GHz are presented. Two approaches are discussed; the fabrication of integrated circuits using a GaAs foundry service, coupled with the research based post-processing of these structures, and the fabrication of discrete and integrated Schottky structures using a bespoke research laboratory.

A 243 GHz LNA Module Based on mHEMT MMICs With Integrated Waveguide Transitions

A new analysis method for nonlinear circuits is presented. By representing nonlinear components with one- or two-dimensional series of orthogonal polynomials, circuits are analyzed solely in frequency domain. Improvement in computing efficiency is such that microwave circuits with multiple independent excitation frequencies can be analyzed on a microcomputer. As an example, intermodulation analysis of a MESFET mixer is presented.

Integrated Schottky Structures for Applications Above 100 GHz

We report upon the development of a 190 GHz MMIC frequency doubler and 380 GHz sub-harmonic mixer using foundry planar Schottky diodes. The devices have been fabricated by the company UMS using their BES process, and post-processed afterwards to transfer the GaAs circuit membranes onto a quartz substrate. This novel substrate transfer technique is presented. Preliminary measurements give a doubler output power over 3 mW in the frequency range 170-205 GHz.

Multi-Frequency Analysis of Nonlinear Circuits using One and Two-Dimensional Series Expansions

To improve the performance of G-band equipment for humidity sounding of the atmosphere, a high-gain and low-noise amplifier is needed. Here, the performances of 165 and 183 GHz low-noise amplifier microchips intended for atmospheric water vapor profiling application are reported. The microchips are manufactured in metamorphic high-electron mobility transistor technology having a gate length of 50 nm. The on-wafer measured results show noise figures of 4.4-7.4 dB and 16-25 dB gain at the operating frequencies. In addition, two of the amplifiers were assembled in waveguide packages and the measured results show a gain of 19-20 dB and 7 dB noise figure at both 165 and 183 GHz.

Application of substrate transfer to a 190 GHz frequency doubler and 380 GHz sub-harmomic mixer using MMIC foundry Schottky diodes

This paper presents a new method for thermal characterization of THz Schottky diodes. The method is based on the transient current behavior, and it enables the extraction of thermal resistances, thermal time-constants, and peak junction temperatures of THz Schottky diodes. Many typical challenges in thermal characterization of small-area diode devices, particularly those related to self-heating and electrical transients, are either avoided or mitigated. The method is validated with measurements of commercially available single-anode Schottky varactor diodes. A verification routine is performed to ensure the accuracy of the measurement setup, and the characterization results are compared against an in-house measurement-based method and against simulation results of two commercial 3-D thermal simulators. For example, characterization result for the total thermal resistance of a Schottky diode with an anode area of 9 μm2 is within 10% of the average value of 4020 K/W when using all four approaches. The new method can be used to measure small diode devices with thermal time constants down to about 300 ns with the measurement setup described in the paper.

MHEMT G-band low-noise amplifiers

A large-signal black-box model for nonlinear microwave devices is presented. The model is directly constructed from measured small-signal s-parameters and DC characteristic curves of the device without complicated parameter extraction procedures. Separate determination of device parasitics is not necessary. The model is self-consistent, very general and device-and technology-independent. Black-box model of a MESFET and its implementation in a frequency-domain analysis program is described, and measured and calculated results are compared.