Interstratum Connection Design Considerations for Cost-Effective 3-D System Integration

Emerging 3-D multistrata system integration offers the capability for high density interstratum interconnects that have short lengths and low parasitics. However, 3-D integration is only one way to accomplish system integration and it must compete against established system integration options such as system-on-a-chip (SoC) and system-in-a-package. We discuss multiple tradeoffs that need to be carefully considered for choosing 3-D integration over other integration schemes. The first step toward enabling 3-D design is characterizing the new interstratum connection elements, microconnects and through-Si vias, in a bonded 3-D technology. We have used both analytical- and simulation-based approaches to analyze the parasitic characteristics of interstratum connections between bonded 3-D stratum, and have compared the interstratum power and performance with SoC global interconnects, taking into account the impact of technology scaling. The specific elements in an interstratum connection and their electrical properties strongly depend on the choice of 3-D integration architecture, such as face-to-face, back-to-face, or the presence of redistribution layer for bonding. We present an adaptive interstratum IO circuit technique to drive various types of interstratum connections and thus enable 3-D die reuse across multiple 3-D chips. The 3-D die/intellectual property reuse concept with the adaptive interstratum IO design can be applied to design 3-D ready dice to amortize additional 3-D costs associated with strata design, test, and bonding process.