Application of GaAs Device Technology to Millimeter-Waves

The firstly commercialized millimeter-wave application was the automotive radar, which appeared nearly 10 years ago, for driving safety support. The market size has been growing year by year and is expected to reach a level of around five million units per year in 2016. With the progress in popularity, the radar has been expected to spread even to general cars, therefore, development of lowcost and mass-productive technology for related components has become vital. In this situation, mass-productive SiGe hetero-junction bipolar transistor (HBT)(1), (2) and complementary metal oxide semiconductor (CMOS)(3)‐(5) technologies have been competing with GaAs PHEMT technology. However, the discussion on “Si or GaAs” has not been settled because the radar unit is installed peculiarly near the engine room. Si and GaAs devices have been sharing the market recently. In addition, the market still requests flexible and speedy production methodologies to meet a marginal production volume per a type of radar. Sumitomo Electric Device Innovations, Inc. (SEDI) and Sumitomo Electric Industries, Ltd. have launched a novel wafer-level chip size package (WLCSP) technology(6)‐(8) by innovatively modifying three-dimensional (3-D) GaAs monolithic microwave integrated circuit (MMIC) technology. This 3-D WLCSP MMIC technology actualizes reliable flip-chip assembly on a printed circuit board (PCB) via tiny solder balls arranged on the surface pads and ground metal of MMIC, where neither package, wire bonding, nor tuning are necessary and a 3-D high integration is provided. Therefore, the GaAs 3-D WLCSP is a promising technology to meet the requirements for both simple assembly and mass production. These advantages have already been adapted to point-to-point communication MMICs between 13 GHz and 38 GHz. Various MMICs in the range of between microwave and millimeter-wave can be produced in the same form and design manners, resulting in easier development of 76 GHz/79 GHz-band automotive radar MMICs and 80 GHz-band (E-band) MMICs. This paper introduces our research and development on millimeter-wave devices using the 3-D WLCSP MMIC technology. Firstly, commercialized millimeter-wave radar modules will be described. Secondly, the structure and the features of the low-cost and mass-production basis 3-D WLCSP will be explained. Thirdly, various functional circuit designs with the 3-D WLCSP MMIC for the millimeterwave radar and the E-band communication devices will be illustratively introduced. Advantages and benefits of our technology against other technologies will be additionally discussed.