At the University of Duisburg-Essen (UDE), a Terahertz Integration Centre, unique in Germany, is currently being built, which is being funded by the state of North Rhine-Westphalia and the EU with 6.5 million euros. Under the direction of Prof. Dr. Nils Weimann, scientists at the Center for Semiconductor Technology and Optoelectronics (ZHO) at UDE are already working on the necessary semiconductor materials, such as indium phosphide (InP).
This semiconductor material is well suited for high-frequency components, but can currently only be produced in very complex and small quantities. To change this, the ZHO has purchased a new production facility – for the Terahertz Integration Center.
The semiconductor experts at UDE are now contributing their know-how to the newly founded »Joint Lab InP Devices«, in which the Ferdinand Braun Institute, Leibnitz Institute for High Frequency Technology (FBH), in Berlin is also participating. Together, semiconductor materials, components and circuits for mm wave and terahertz applications are to be developed.
High frequency semiconductors
The terahertz range (0.1–3 THz) is still largely untapped, as electronic components are currently only commercially available for frequencies below 100 GHz. In order to open up the highest frequency range, suitable semiconductor materials, such as indium phosphide (InP), and component structures optimized for maximum frequency must be researched and developed.
Since January 2017, research in the department on THz components is funded by the Collaborative Research Center / Transregional Collaborative Research Center (SFB/TRR) 196 - Mobile Material Characterization by Electromagnetic Scanning (MARIE). This Collaborative Research Center of the German Research Foundation, DFG, was established at the UDE.
The outstanding material properties of InP – high electron velocity combined with high breakdown field strength – allow the realization of components with highest cut-off frequencies and high output power. The material system InP is being studied in detail at the UDE: epitaxial processes accurate to one atomic layer are used to create structures for resonant tunnel diodes (RTD) and heterostructure bipolar transistors (HBT).
For this purpose, the Department of High-Frequency Electronics Devices (BHE) has two epitaxy systems at its disposal in the laboratories of the Center for Semiconductor Technology and Optoelectronics (ZHO) at the UDE: molecular beam epitaxy (MBE) and metal organic gas phase epitaxy (MOVPE). The MOVPE system was newly procured as part of the BMBF initiative ForLab SmartBeam.
At UDE, RTD and HBT are developed and optimized for highest frequency and performance. The necessary manufacturing processes are carried out in the clean room of the ZHO. Here, critical component structures are defined using electron beam lithography, which allows structure widths far below 1 μm.
The semiconductor components RTD and HBT form the building blocks for complex circuits and modules. The InP wafers with HBTs for THz applications developed at UDE are further processed at FBH to form complex circuits. Both partners in the new Joint Lab InP Devices use the same wafer diameter and compatible processes – this enables a fast implementation of new fundamental research results of the university in the application-oriented development of the FBH.
At the UDE, THz RTDs with integrated antennas are produced which are integrated into modules using chip assembly technology. This work takes place in the new Terahertz Integration Center of the UDE at the ZHO.