The DARPA COSMOS and ELASTx Programs: Towards Next Generation Linearized Microwave/Mm-Wave Transmitters

The COmpound Semiconductor Materials On Silicon (COSMOS) program of the U.S. Defense Advanced Research Projects Agency (DARPA) focuses on developing transistor-scale heterogeneous integration processes to intimately combine advanced compound semiconductor (CS) devices with high-density silicon circuits. The technical approaches being explored in this program include high-density micro assembly, monolithic epitaxial growth, and epitaxial layer printing processes. Through heterogeneous integration of advanced InP HBTs with commercially fabricated CMOS circuits, the program has successfully demonstrated world-record differential amplifiers and is currently developing complex wideband, large dynamic range, high-speed digital-to-analog converters (DACs) employing sophisticated in situ digital correction techniques enabled by CMOS integration. This paper will also discuss future directions of technical approaches, for example integration of high power CS devices such as GaN transistors with silicon-based linearization techniques developed under DARPA's Efficient Linearized All-Silicon Transmitter ICs (ELASTx) program to realize next-generation microwave/mm-wave transmitters. In these future transmitters, the high breakdown voltage CS devices will be used to implement efficient, although non-linear, power amplifiers while the required linearity for complex waveforms will be recovered through integrated linearization architectures.