Sub-Millimetre Wave MMICs and Modules for Radiometer Applications up to 664 GHz

A strong need for global remote sensing still persists today in the field of earth observation activities such as weather forecast and climate studies. This is especially the case for the study of water vapour and ice cloud. Ice clouds play a
significant role in the hydrological cycle and in the atmosphere energy budget. However, cloud ice remains a large source of uncertainty in climate models. It is therefore of prime importance to develop the required sensor systems addressing the studies of water vapour and ice cloud.
Because they feature low-power consumption, small dimensions and do not necessarily require high-frequency signal or clock distribution, radiometers are becoming an essential tool for such applications.
For vertically integrated cloud mass studies, the radiometers need to operate at frequencies exceeding 300 GHz since appropriate water vapour lines exist at e.g. 448 GHz and above.
In a radiometer receiver chain, the low-noise amplifier (LNA) is a crucial element that amplifies the incoming signal to overcome the noise contribution of the detector while minimising its own contribution to the system noise temperature.
The challenge is therefore to find a suitable semiconductor technology that reaches the tremendous requirements in terms of fT and fmax to cover these extreme frequencies while additionally providing a low-noise performance.
Recent advances in III-V based high electron mobility transistors (HEMTs) have made fabrication of monolithic microwave integrated circuits (MMICs) in the submillimetre-wave frequency domain possible. In Europe and worldwide,
the InGaAs metamorphic HEMT (mHEMT) technologies of the Fraunhofer Institute for Applied Solid-state Physics (IAF) are extremely strong contenders for such purpose. Not only the very latest mHEMT technologies achieve a maximum frequency of oscillation (fmax) exceeding 1 THz, but also novel and advanced technological innovations to improve further the speed and low-noise performance of the MMICs have been recently initiated.
In the Low Noise Amplifier at 600 GHz ESA activity that was initiated in 2021, LNA MMICs and modules addressing the typical submillimetre-wave radiometer frequencies 325 GHz, 448 GHz and 664 GHz will be designed, fabricated and
tested. Two different State-of-the-Art technologies from Fraunhofer IAF will be used for the project: A 35 nm mHEMT technology as well as a novel 20 nm InGaAs HEMT on Silicon technology. The authors will present the latest results that were achieved among others in the frame of this activity.