Abstract

The development of millimeter/submillimetre wave Schottky diode technology, as well as the technology of monolithic integrated direct receivers and mixers based on Schottky diodes, is an essential objective of ESA, especially to guarantee European independence in terms of future Earth observation, radiometers and other scientific instruments functioning at millimetre and submilllimetre wave frequencies. State of the art technologies regarding Schottky diodes for millimeter/submillimetre wave and THz applications have been developed in the USA, both at research as well at commercial level. The purchase of such Schottky diodes chips from the USA providers is not an easy task, because of their multiple applications. This is the reason why ESA has strongly encouraged the development of high performance Schottky diodes, working in the millimeter /submillimetre wave frequency range, as well as monolithic integrated detectors, mixers and multiplier devices based on Schottky diodes, in European facilities.

The present project intends to develop Schottky diodes with a cut-off frequency higher than 3 THz. If the critical technological processes involved in their fabrication will be developed successfully there are big chances to obtain cut-off frequencies higher than 3 THz.

Major technological challenges, like advanced nanolithographic process to obtain Schottky diodes with an area smaller than 1μm2, very narrow air bridges development, manufacturing very thin self-sustainable GaAs membranes supporting the circuits, will be targeted in the frame of this project.

Membrane technology will be used to develop the device. To extract the diode echivalent circuit parameters (including the series resistance, Rs, and junction capacitance, Cj which determinate the cut-off frequency), test structures in CPW will be manufactured and transmission and reflection parameters will be measured in the 65-110 GHz frequency range The Schottky diode chip will be one of the end products of this project.

A direct, video-type receiver module (detector) working at a frequency of about 100 GHz will be manufactured and characterized. The Schottky diode will be integrated monolithically with an antenna designed for this frequency and both will have as support the same thin GaAs membrane.

The development of frequency converter circuit will be initially based on discrete Schottky diodes inserted in external structures containing all other structures – filters, signal dividers/combiners, phase shifters – required by mixing applications. The results of this proof-of-concept activity will be followed by an integration stage level, aiming to design and manufacture a class of monolithic integrated circuits containing both Schottky diode(s) and their functionally associated transmission line parts, in order to obtain the mixers, with an operating frequency of 100 GHz, the other major task of this project.

The direct receiver module as well as the mixer will demonstrate the quality of the developed technology for the Schottky diodes (usable for much higher frequencies) but in the same time will represent real devices for space applications (their operating frequency range is allocated for satellite to satellite communications). The detector and the mixer will also use innovative technologies and design concepts.

The envisaged work is based on our expertise in microwave and millimeter wave devices and our contribution to the actual state of the art in Schottky diodes, detectors and mixers (see the reference list).
The TRL will arrive to the 4-th level, components (demonstrators) validation in laboratory environment; new modern technologies for Schottky diodes, mixers and detectors will be developed and state of the art results, at least at European level, will be obtained.