Passive Device Integration from Silicon Technology

Passive components are indispensible parts used in electronics circuits for various functions, such decoupling, biasing, resonating, filtering, matching, transforming, etc. These passive components can be made on chips, or in PCBs, or in SMDs. SOC (system-on-chip) solutions where all passives are implemented may be long-term goals, but suffer high cost and long development cycle times at the time being. Making passive components embedded inside laminate substrates is limited on passive density. SMD solutions are by far the most popular approaches in the industry, and may still be dominant for some times. Passive components consume 70%–80% area of an electric package in a SiP solution, and therefore it is a great deal to reduce the area of passive components, in order to reduce the size of entire package. We have developed an IPD (integrated passive device) process from silicon technology to make these passive components of high-Q performance, preferably to be used in RF packages. Low-loss substrate material is used in this process, and thick Cu layer is used for high-Q inductors. From this process, we can make capacitors in 330pF/mm sq density, and the Q-factor is around 30–35 peak for a 3nH–5 nH inductor. Most importantly, the thin-film IPD process has better tolerance control than other commonly available ones, such as PCB and LTCC technologies, which may results in very repeatable electrical performance, and provides packages in high integration. For a passive function block, using BPF (band-pass-filter) as an example, an IPD filter is typically two times smaller in X-Y size and half thinner in Z-height. This makes such IPD very suitable to be integrated in a SiP package. Using some case studies (individual IPD and chip-scale-module-package), we will present how high integration can be achieved, and where are the right spots to use IPD approaches other than SAW, or SMD, or LTCC solutions for RF SiP applications.