Browsing by Author "Mallat, Juha, Dr., Aalto University, Department of Radio Science and Engineering, Finland"

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    Characterisation of Schottky diodes and dielectric materials for millimeter wave and THz applications
    (Aalto University, 2017) Khanal, Subash; Kiuru, Tero, Dr., VTT Technical Research Centre of Finland, Finland; Mallat, Juha, Dr., Aalto University, Department of Radio Science and Engineering, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Räisänen, Antti, Prof., Aalto University, Department of Radio Science and Engineering, Finland
    This thesis work contributes to two fields of research: Schottky diode characterisation and dielectric material characterisation, both for millimeter wave and THz applications. Schottky diodes are characterised for their electrical, thermal, noise and RF properties with various measurement techniques, and an easy-to-use method is introduced for the extraction of the dielectric material properties at millimeter wave frequencies. In addition, the applications of the developed thermal characterisation method for THz Schottky diodes and of the material characterisation method are presented. Schottky diode is a key component in almost all non-cryogenic mixer and frequency multiplier applications at 100−3000 GHz. In this work, a novel thermal characterisation method suitable for small THz Schottky diodes is introduced. This method is based on the transient current measurement and it enables the extraction of thermal resistances, thermal time-constants, and peak junction temperatures. The accuracy of the transient measurement setup is ensured with a developed verification routine and the characterization results are compared against an in-house measurement-based method and also against simulation results of two commercial 3-D thermal simulators. As an application, the developed characterisation method is applied to obtain the thermal performance of the Schottky based mixer and multiplier prototypes for the MetOp-SG satellite instruments. Besides thermal performance, Schottky diodes are also characterised for their low-frequency noise and RF properties. Experimental investigations are carried out to study the indication of charge trapping in the THz Schottky diodes with a small anode area. Various measurement techniques are applied including I-V, capacitance and low-frequency noise measurements. Furthermore, low-barrier Schottky diodes from ACST GmbH are characterised to study their suitability for millimeter wave mixing applications because the low-barrier height enables low LO power requirement for the mixers. The performance of such diodes is evaluated, in terms of the conversion loss and the noise temperature, in a fundamental mixing configuration with measurements and simulations. The last part of this thesis work presents the characterisation of dielectric material at millimeter wave frequencies. An easy-to-use method is introduced for the extraction of the permittivity and the loss tangent of the material sample from reflection and transmission coefficient measurements. Extraction of the material parameters are performed with two approaches. First, by using the direct comparison with the simulated S-parameter results and second, from the analytical calculations. As an application, this extraction technique is used to characterise potential substrate materials for printing millimeter wave components, e.g., antennas.
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    Development of on-wafer calibration methods and planar Schottky diode characterisation at THz frequencies
    (Aalto University, 2014) Dahlberg, Krista; Mallat, Juha, Dr., Aalto University, Department of Radio Science and Engineering, Finland; Silvonen, Kimmo, Dr., Aalto University, Department of Radio Science and Engineering, Finland; Kiuru, Tero, Dr., Aalto University, Department of Radio Science and Engineering, Finland; Radiotieteen ja -tekniikan laitos; Department of Radio Science and Engineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Räisänen, Antti, Prof., Aalto University, Department of Radio Science and Engineering, Finland
    This thesis focuses on development of on-wafer calibration methods for S-parameter measurements and Schottky diode characterisation at millimeter wave and terahertz frequencies. The radio frequency characteristics of components at the wafer level are obtained using on-wafer S-parameter measurements with a vector network analyzer. In general an error network including eight error terms is used to calibrate the on-wafer S-parameter measurements, but in measurement configurations affected by leakage the use of full 16-term error network can be profitable. In this thesis a novel 16-term calibration method based on reciprocity conditions of the error network is introduced and demonstrated with simulations and practical on-wafer measurements. The developed calibration method enables the calibration of the full 16-term error network using only four calibration standards. The method is limited to second-tier calibration of reciprocal error networks with a pre-calibrated network analyzer, when the reciprocity assumption is valid. Also a novel method to determine Line-Reflect-Reflect-Match (LRRM) calibration standards for reciprocal 16-term error network is presented. The Line standard and the resistance of the Match standard need to be exactly known and the reactances of the two unknown lossless reflect standards (typically Short and Open) and the Match standard are solved using the raw S-parameter data of the calibration standard measurements. The accuracy of the known S-parameters or self-calibration results of the calibration standards can be verified as a by-product of the 16-term reciprocal calibration. LRRM is only one possible combination of the four calibration standards to solve the reciprocal 16-term error network. In this thesis all possible non-singular combinations are solved with a simulation approach. Schottky diodes are significant components in the millimeter wave and terahertz frequency applications. Traditionally Schottky diodes are characterised by current-voltage, capacitance-voltage, and S-parameter measurements. The design of the millimeter wave and terahertz diode mixers relies heavily on the extracted parameters from the traditional characterisation measurements. However, the diode operation in the final application such as a mixer cannot be completely predicted by using the extracted parameters. In this thesis a novel mixer-based characterisation method of discrete planar Schottky diodes is presented. A fundamental mixer test jig for single-anode Schottky diodes and a subharmonic mixer test jig for antiparallel Schottky diodes are developed to characterize and compare the mixer operation of different diodes at 183 GHz.