Integration of 60-GHz Microstrip Antennas with CMOS Chip

New emerging wireless systems that operate at millimeter wave frequencies, such as high data rate 60-GHz transceivers for wireless personal area networks (WPAN), use integrated antennas. The small wavelength at 60-GHz enables the antenna to be integrated either in the package or on the chip. However, on-chip integrated antennas for 60-GHz systems, built on a conductive substrate, such as complementary metal-oxidesemiconductor (CMOS) or silicon germanium (SiGe), results in poor radiation efficiency. Therefore, antennas for these systems are commonly implemented on in-package solutions. The integration of antenna-in-package can be achieved by using wire bonding or flip-chip bonding interconnections. Although bonding wires are typically employed to connect passive devices to chip modules since they are robust, inexpensive and tolerant of chip thermal expansion they increase reflections, impedance mismatches and power loss at millimeter wave frequencies. The flip-chip bonding of antenna to chip module can significantly reduce these effects as it uses metallic bumps for device connections which are kept small compared to the length of the bond wire that results in better impedance matching and reduced interconnection losses. In this chapter two types of antenna integration methods are presented; a microstrip antenna for flip-chip integration and a coplanar waveguide (CPW) fed antenna for wire bonding. The flip-chip integrated antenna compatible with CMOS technology achieves good performance and is mounted on the CMOS chip using standard printed circuit board and flip-chip bonding technology. This approach is compact and inexpensive. The microstrip patch is printed on one substrate layer with a CPW feeding line through the ground patch that permits direct attachment of the patch to the die. The use of low dielectric constant and low dissipation loss substrate material improves antenna radiation efficiency and input impedance bandwidth. The flip-chip approach does have some limitations. The flip-chip interconnection parameters, such as bump height and diameter, vary with the fabrication and cannot be accurately predicted in the design stage. The supporting under fill layer between the antenna and chip influences antenna performance. In this chapter we also investigate the effects of flip-chip interconnection on microstrip antenna performance and explore the relationship of the flip-chip interconnection parameters on bandwidth, radiation efficiency and gain. Our design methodology shows that microstrip antenna bandwidths of 15% can be achieved with careful flip-chip interconnection design and fabrication.