Characterisation of Schottky diodes and dielectric materials for millimeter wave and THz applications

Abstract

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.