Microelectronics Center, Belgium reported the co‐design of circular‐polarized slotted patch antenna with a wireless local area network (WLAN) transceiver in a multilayer package [17]. Popov et al. at the Institute of Microelectronics, Singapore reported the design of part of an RF chip package as a dielectric resonator antenna with a high dielectric constant when the antenna feed was integrated with the rest of the circuitry [18]. Leung at City University of Hong Kong independently proposed adding the chip package function to a dielectric resonator antenna in 2004 [19].
In 2005, Castany et al. at Fractus, Spain filed a patent about the integration of fractal antennas in a chip package [20]. They claimed that fractal antennas could provide very good antenna performance while allowing a high degree of miniaturization and an enhancement of isolation between the antenna and the die in the package.
In 2006, Brzezina et al. at Carleton University reported planar antennas with transceiver integration capability for ultra‐wideband (UWB) radios [21]. Sun et al. devised a novel technique that reduces the size of a conventional planar antenna by 40% and used it as a package to house a single‐chip UWB radio [22].
In 2007, Wi et al. at Yonsei University, Korea presented an antenna‐integrated package [23]. A modified U‐shaped slot antenna was designed and measured, showing bandwidth of 180 MHz at 5.8 GHz. A parametric study was conducted with a full‐wave electromagnetic solver to determine the critical factors in design and fabrication, as well as to estimate the performance accuracy of the antenna‐integrated package.
1.3.2 60‐GHz Radio and Other Millimeter‐wave Applications
In early March 2005, Zhang met Brian P. Gaucher and Duixian Liu from the IBM Thomas J. Watson Research Center for the first time at the First International Workshop on Small Antenna Technology in Singapore and invited them to visit Nanyang Technological University. Gaucher gave a talk about the IBM 60‐GHz radio SiGe chipsets, antennas, packages, and measurement setup. Figure 1.5 shows the chip‐scale package for proof of concept [24]. The chip‐scale package had a size of 13 × 13 × 1.25 mm3. Note that the radio dies were flip‐chip bonded with the antennas and assembled together as an land grid array (LGA) package. The package required a dedicated opening for an antenna and an encapsulation prior to the mounting of the antenna. Thus, it was difficult to fabricate and assemble this chip‐scale package for mass production. With that in mind, Zhang briefed the visitors about antennas designed for 2.4 and 5 GHz as chip packages in LTCC, and a collaboration plan for a feasibility study for developing LTCC packages embedded with antennas for the IBM 60‐GHz radio SiGe chipset was agreed. Zhang paired up with Mei Sun to lead the design effort, a team of researchers from Singapore Institute of Manufacturing Technology (Chee Wai Lu, Kai Meng Chua, and Lai Lai Wai) was responsible for fabrication, and Duixian Liu did the evaluation and feedback.
In June 2005, Naoyuki Shino, Hiroshi Uchimura, and Kentaro Miyazato from the Kyocera research and development center reported the unification of antenna with a package based on laminated waveguides, coupling slots, and open cavity radiating elements in LTCC for short‐range car radar operating in the 77‐GHz band [25].
Even after all of the early attempts at integration of antennas onto or into packages, there is not yet an all‐encompassing term to describe this process. Inspired by SiP, Zhang coined the term AiP to promote the idea [26]. In early March 2006, Zhang attended the Second International Workshop on Small Antenna Technology in New York and visited the IBM Thomas J. Watson Research Center. The visit strengthened the collaboration for integrating antennas in packages and accelerated AiP development. Figure 1.6 shows images captured in the design stage and photos of fabricated AiP samples for IBM 60‐GHz SiGe transmitter and receiver dies. The AiPs for the transmitter and receiver dies measured 12.5 × 8.6 × 1.265 mm3 and 12.5 × 8 × 1.265 mm3, respectively. The transmitter AiP integrated a Yagi‐Uda antenna and the receiver AiP a novel coplanar waveguide (CPW)‐fed quasi‐cavity‐backed, guard‐ring‐directed, substrate‐material‐modulated slot antenna. The measured antenna results were promising and were recognized with the Best Paper Award in the third International Workshop on Small Antenna Technology held on 21–23 March 2007 in Cambridge, UK [27].
In August 2007, Sibeam put the first CMOS 60‐GHz phased array radio in an LTCC AiP [28]. It made board and system design much easier by containing all high‐frequency routing within the CMOS die and chip package, and enabled products in the market for wireless transmission of high‐definition video content. It is worthwhile mentioning that after Zhang's keynote address at the Antenna Systems and Short‐Range Wireless Conference 2005 held on 22–23 September in Santa Clara, California, USA, in the break Zhang enthusiastically discussed some issues about integration of antennas in LTCC with Doan, one of founders of SiBeam and pioneers in mmWave CMOS [29].
1.4 Developing the Idea into a Mainstream Technology
The success of the idea of AiP is largely due to the renewed interest in 60‐GHz radios. In 2007 a new phase of 60‐GHz radios began as the Institute of Electrical and Electronics Engineers (IEEE) initiated development of a new standard for the unlicensed 60‐GHz band and many companies started to get involved in the development of 60‐GHz radio chipsets with multiple antennas in chip packages. Since then, there have been numerous AiP designs reported by industry for applications at 60 GHz and other mmWave frequencies. Clearly, the idea of AiP has been developed into a mainstream antenna and packaging technology. The milestones in the development are described here.
The first and perhaps most important milestone was to break the boundaries between antenna and circuit fields, and to implement the design considerations for both antenna and circuit in a single design platform. It was stressed by the design strategy that the AiP should be co‐simulated with the radio frequency integrated circuit (RFIC) in a circuit simulator with compact models extracted from full‐wave electromagnetic simulations of the antenna and package for optimum results. The co‐design platform with software tools from different vendors had been built before Cadence released the RF‐SiP methodology kit in 2006 [30]. It runs the Advanced Design System from Agilent for two‐dimensional (2D) electromagnetic simulation, the High Frequency Structure Simulator (HFSS) and ePhysics from Ansoft for three‐dimensional (3D) electromagnetic simulation as well as 3D steady‐state thermal, transient thermal and linear stress analyses coupling to HFSS.
The
