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Compact single-stage 90 GHz power amplifier for terahertz applications

FBH research: 23.01.2023

Fig. 1: SEM image of a fully processed 850 nm transistor.

Fig. 2: Microscope image of fully processed PA.

Fig. 3: High signal performance of PA at 87 GHz.

InP-based transistors offer superior performance in the sub-/THz range. Due to their material properties, higher output powers are achieved at higher frequencies. This facilitates the design process and minimizes the complexity of the layout. We have designed and fabricated a compact single-stage power amplifier (PA) using our 850 nm triple-mesa InP HBT process (displayed in Fig. 1). The process is based on a standard triple-mesa transistor architecture with three metallization layers for interconnects in addition to MIM capacitors and NiCr resistors. The triple mesa process allows for better thermal coupling of the transistors to the substrate which in turn helps in maintaining acceptable operation temperature of the devices at higher output powers.

The PA is designed based on a common emitter (CE) single finger 850 nm transistor with separate bias pads for base and collector, respectively. The input and output are 50 Ohm, matched to a thin-film microstrip stack. The chip photograph of the realized PA with a chip area of 0.7 x 0.75 mm²is depicted in Fig. 2. Large signal measurements show a gain of 6 dB with the 1 dB gain compression at 3 dBm input power level. A saturated output power of 12.5 dBm is achieved with 45 mW DC power consumption and results in a power-added efficiency (PAE) of 17% at 87 GHz. The chip also offers flip-chip indium/gold pillars, which enables flip chip mounting to a larger CMOS or BiCMOS integration. The pad frame of the circuit offers mechanical stability as well as a thermal path for the flip-chip process with minimal RF losses at the frequency of operation [1].

This work is part of the T-KOS project and partially funded by the Research Fab Microelectronics Germany (FMD) initiative.


[1] M. Rausch, T. Flisgen, C. Stölmacker, A. Stranz, A. Thies, R. Doerner, H. Yacoub, W. Heinrich, “Technology for the Heterointegration of InP DHBT Chiplets on a SiGe BiCMOS Chip for mm-wave MMICs”, Proc. 52nd European Microwave Conference (EuMC 2022), Milan, Italy, 2022, pp. 28-31, doi: 10.23919/EuMC54642.2022.9924451.