GaN C-Band HPA for Phased-Array Applications
In the UMS GH25-10 GaN MMIC technology a C-band high power amplifier (HPA) has been realized. The current design is primarily intended for use in a space-based SAR system with a center frequency of 5.4 GHz and a sweep bandwidth of 100 MHz. To enable reuse of the amplifier in other radar systems such as weather radar, a large bandwidth is required. A design bandwidth from 5 to 6 GHz has been used. Simulation and measurement data from on-wafer and mounted samples will be shown. Showing more than 50 W output power with 45% efficiency the HPA shows sufficient performance to be used in a module for state-of-the-art active electronically scanned arrays. The measured output power and efficiency are a record for MMIC amplifiers.
High Voltage Breakdown pHEMTs for C-band HPA
High Voltage Breakdown (HVB) HPA MMIC based on GaAs pHEMTs technology represents a useful way for high power RF application. To increase the breakdown voltage respect to conventional device, a field-plate (FP) gate structure is implemented in our standard 0.5 µm process. With this solution the off-state breakdown voltage of the device has been improved from 18V to 28V, while keeping constant the drain current. As expected, FP devices showed smaller drain current collapse than standard devices under pulsed DC measurement conditions and a significant increase in power density, i.e. 1.4 W/mm. To guaranty a full advantage for real HPA applications we have carried out numerical simulations, to optimise device thermal behaviour as a function of GaAs thickness and gate pitch. On the basis of this technology development, reliable and reproducible HPA have been fabricated with an output power of circa 30 W and power added efficiency (PAE) of circa 35% in the 4.9–6.1GHz frequency range. Therefore this proposed technological solution enables the realization of very high power T/R modules with reliable GaAs technology, waiting for more disruptive and less mature GaN HEMT one.
Fabrication, Characterization and Numerical Simulation of High Breakdown Voltage pHEMTs
High breakdown voltage pHEMTs have been successfully developed by implementing a field-plate (FP) structure. Devices with and without FP have been fabricated on the same wafer in order to compare the improvements induced by adopting the FP. Both kinds of devices showed little or no current dispersion under pulse measurement conditions. Moreover the off-state breakdown voltage improved from 23V, for the devices without FP, to 38V for the field-plated devices. At 4GHz an output power as high as 1.6W/mm was measured for a FP device, resulting in a 60% improvement with respect to the device without FP. The fabricated structures were also evaluated by carrying out 2D numerical simulations. Experimental results on MIS pHEMTs have been explained by means of a donor trap at the SiN/GaAs interface located at 0.18eV from the GaAs conduction band. Finally, a good agreement between experimental and simulated device characteristics was obtained