Three-Dimensional MMIC and Its Evolution to WLCSP

An exciting program on monolithic microwave integrated circuit (MMIC) technology was pursued on from nearly 1983 to 1991, including its design and fabrication equipments, mainly in USA and Europe. In the era, “MMIC” was a very new concept which meant integration of microwave and millimeter-wave circuits on a die. By incorporating the CAD and measurement tools developed in the program, Japanese researchers joined and contributed to the progress of the technology. The program was named “MIMIC Program” by Defense Advanced Research Project Agency (DARPA), USA. The title MIMIC means Monolithically Integrated Microwave Integrated Circuit. The author started his research on MMIC in 1983: same as the start of the program, hence, he is recognized as a starter in Japan. Four years later, he and his colleagues took part in challenges on highly integrated MMIC technology which was a target issue for both the program and his team. One of the main subjects was the Multi-layered MMIC. It had advanced, via its renewal to the three-dimensional MMIC (3-D MMIC), to the wafer level chip size package technology, WLCSP in short. The origin was first a really simple idea, but it became a big tree through a long-term technical evolution. This paper describes firstly a fruitless era with the passive multilayer MMICs, secondly an aggressive era with the active device-rich 3-D MMIC transceivers, and thirdly current fruitful era with the WLCSP concept by incorporating which package-less and low cost microwave components are pushed in to commercialization. This paper describes the author’s experience that an idea can be matured through changes in the way of thinking and engineering.