http://www.raytheon.com/news/technology_today/2014_i1/semiconductor.
Semiconductors for Combined RF and Logic Functionality Traditionally, gallium arsenide (GaAs) has been the semiconductor of choice for efficiently amplifying and phase shifting RF signal in radars. Throughout the 1990s, Raytheon was a pioneer in inserting GaAs-based MMICs into the first modern phased array radars. As the performance requirements of these military systems have increased to meet ever-growing threats, so too have the power, efficiency and low noise requirements on these MMICs. During that time, Raytheon has continued to customize and optimize its semiconductor processes for each specific radar function (Table 1). One such Raytheon GaAs pseudomorphic high electron mobility transistor (pHEMT) technology, customized for multifunction MMICs containing phase shifters, attenuators and gain stages, combines RF and logic functions on the same MMIC, providing a serial or parallel logic interface to a separate silicon (Si) controller chip. By designing a process that allowed the combining of some logic functions on the RF MMIC circuitry, the number of off-chip components and interfaces between chips was minimized, reducing size and cost while improving radar manufacturability. During the past six years under independent research and development (IRAD) and Defense Advanced Research Projects Agency (DARPA) funding, Raytheon has taken the integration of RF and logic functions to the next level. Raytheon has developed technology to directly integrate GaAs, indium phosphide (InP) or gallium nitride (GaN) RF devices with high density Si complementary metal oxide semiconductor (CMOS) logic on a common Si substrate. This heterogeneous integration technology enables greater levels of functionality and digital control of RF circuits as well as a reduction in cost over using the traditional separate RF and logic chips. Using this integration approach, Raytheon demonstrated the world’s first GaN HEMT and Si CMOS heterogeneously integrated chip; a GaN RF amplifier with in-situ Si CMOS gate bias control (Figure 2). This circuit was a proof of concept that demonstrated that GaN HEMT and Si CMOS devices could be integrated on the same Si substrate with minimal performance impact to the Si CMOS and GaN HEMT technologies. The circuit also serves as a building block for digitally assisted RF and mixed signal circuits, such as amplifiers with on-chip digital control and calibration, reconfigurable or linearized PAs with in-situ adaptive bias control, high-power digital-to analog converters (DACs) and on-chip power distribution networks. - See more at: http://www.raytheon.com/news/technology_today/2014_i1/semiconductor.html#sthash.5l4iwZuE.dpuf
