Nicholas J. Kolias

GaN technology for microwave and millimeter wave applications

After many years of development to improve the material and devices, GaN technology is now in production and poised to revolutionize many of todays Radar and Communication systems. In this paper we present an overview of GaN development, focusing on reliability, affordability, and defense applications.

The development of T/R modules for radar applications

The last 40 years has seen the migration from mechanically steered radars to the active electronically steered arrays (AESAs) of today. The key enabler for the AESAs has been the development and improvement of the performance, manufacturing capability, and cost of the Transmit/Receive (T/R) modules that typically sit behind each radiating element of the array. These T/R modules typically contain a duplexer (circulator), a driver amplifier and power amplifier for transmit, a limiter and a low noise amplifier for receive, and a common-leg-circuit used for both transmit and receive consisting of T/R switches, a phase shifter (for beam scanning), an attenuator, and a gain block. The first T/R modules were hybrid silicon-based modules developed for the MERA program which started in 1964. This talk traces the evolution from these first T/R modules through the development of the GaAs MMIC based modules of the 1990s and 2000s that power todays systems to the emerging GaN and silicon based modules of future active phased array radars. The evolution of the MMIC technology and capabilities as well as the improvements in assembly and packaging will be highlighted.

MMIC pioneers: A historical review of MMIC development at Raytheon

The latter part of the 20th century saw the birth and rapid development of monolithic microwave integrated circuit (MMIC) technology which dramatically changed the microwave industry. Raytheon Company was at the forefront of this development. This presentation gives a historical review of the pioneering MMIC technology work done at Raytheon.

Device and packaging considerations for MMIC-based millimeter-wave quasi-optical amplifier arrays

Practical implementation of millimeter-wave quasi-optical amplifier arrays will require high device uniformity across the array, efficient coupling to and from each gain device, good device-to-device isolation, and efficient heat removal. This paper presents techniques that address these issues for a 44 GHz MMIC-based design. To improve device uniformity, a double selective gate recess approach is introduced which results in a demonstrated 3 - 5X improvement in uniformity when compared to Raytheons standard production pHEMT process. For packaging, direct backside interconnect technology (DBIT) is introduced as a bondwire-free scheme for connecting each amplifier to the array. This approach significantly reduces interconnect loss by reducing interconnect inductance. Measured insertion loss at 44 GHz for the DBIt transition is 0.35 dB compared to 2.3 dB for a typical bondwire transition produced on a manufacturing automated bonding machine. By eliminating bondwires which tend to radiate at millimeter wave frequencies, the DBIT approach also significantly improves the device-to-device isolation, thereby improving the array stability. The DBIT approach would not be viable if it could not effectively dissipate heat (a typical 25 watt array generates greater than 100 watts of heat). Finite element thermal analysis results are presented which show that the DBIT approach adds a tolerable 15.5 degree(s)C temperature rise over a standard solder-based MMIC die-attach to a heatsink. Thus, the DBIT approach, along with the double selective gate recess process, provides an attractive, low-loss, bondwire-free approach for producing uniform amplifier arrays.

Recent advances in Ga N MMIC technology

GaN MMIC technology is now in production and is revolutionizing microwave Radar and Communication systems. In this paper we present an overview of GaN MMIC technology, focusing on device characteristics, reliability, and high frequency performance. We also introduce emerging GaN technologies such as GaN-on-diamond and the heterogeneous integration of GaN with Silicon.