How Multiphysics Is Powering The Future Of 3D-ICs

It’s surprising to learn that the idea of 3D integrated circuits (3D ICs) has been kicking around for over sixty years. Not long after the first MOS IC emerged in 1960, researchers were already thinking vertically. By 1983, Fujitsu manufactured the first 3D IC prototype using through-silicon via (TSV) technology, using laser beam recrystallization. That’s a long time for a good idea to catch on, but now that the technology has caught up, 3D IC is having a moment.

True 3D architectures are accelerating progress in AI, mobile devices and beyond. However, this progress brings significant new technical challenges. Ask any engineer involved with 3D ICs and they’ll point to familiar hurdles like stress, electrical parasitics, and timing closure.

Yet in many projects, it’s thermal effects that present the most urgent and complex issues. In 3D structures, heat doesn’t dissipate as easily as in planar ICs. The increased density traps thermal energy between stacked layers, and if these thermal phenomena go unchecked, they can trigger electromigration, signal degradation, timing errors or even mechanical warpage—cascading into reliability threats for the entire product.

Addressing 3D IC design complexity through multiphysics

With these new demands, how do we get ahead of the challenges? The answer lies in a multiphysics approach—one that integrates electrical, thermal and mechanical analysis throughout the workflow. We need to treat the stack as a coupled physical system, where every force and effect is interrelated.

This philosophy forms the foundation for Siemens’ collaborative approach with ecosystem partners, including TSMC. With holistic, interoperable workflows, design and manufacturing teams can work together across the full spectrum of the 3D IC lifecycle, from early concept and verification through assembly and tape-out.

A central piece of this workflow is a holistic EDA (electronic design automation) platform like the Calibre platform (figure 1). It includes tools to bring robust physical and circuit verification to heterogeneous 3D ICs, regardless of chiplet supplier or stack complexity. Coupled with high-accuracy cross-die extraction, designers can pinpoint and mitigate signal integrity issues caused by parasitics at the die-to-die interface. This flexibility supports both standard and highly customized projects, while enabling open integration with the broader EDA ecosystem.

Fig. 1: Siemens holistic 3D IC multiphysics workflow (diagram showing design, verification, manufacturing and multiphysics engines).

A holistic portfolio includes a comprehensive multiphysics cockpit for 3D IC design, verification and manufacturing, like Siemens’ Innovator3D IC. Through the cockpit, or standalone, a series of tools helps 3D IC designers perform digital implementation (Aprisa), package layout (Xpedition Package Designer) and multiphysics analysis. The multiphysics analysis tools run detailed, iterative simulations to map thermal gradients, identify mechanical stress concentrations and predict how these factors ripple across the stack. This comprehensive approach empowers teams to systematically identify and remedy risks, long before fabrication.

Understanding multiphysics in the context of 3D ICs

But what exactly does “multiphysics” mean? At its core, it is an acknowledgment that nothing in a 3D IC exists in isolation. Each layer, material and design choice is subject to a combination of electrical currents, heat transfer and mechanical stresses. The classic Newtonian principle—that all objects are influenced by external forces—applies here on a microscopic scale, across millions or billions of stacked devices.

For example, delivering power across chiplets leads to current flows that generate heat. This heating impacts transistor performance, alters resistivity, shifts timing and can drive electromigration. But it doesn’t end there—each material in the die stack expands and contracts with temperature changes, introducing mechanical stresses that, unchecked, can cause warpage or even microfractures (figure 2). In sensitive circuits, these deformations can induce parameter drift and reduce long-term reliability.

Fig. 2: Stress hotspots in a 3D stack involve thermal, electrical and mechanical effects.

Because all these forces interact, 3D IC designers must consider every relevant domain in their analysis: electrical, thermal and mechanical behaviors are tightly coupled. This is where a multiphysics analysis engines shine: by running coupled, iterative analyses across these domains, they capture both direct and secondary effects, map them across the layout and drive design refinements that ensure signoff confidence.

The impact of early, “shift-left” multiphysics analysis

The biggest risk in advanced design is waiting too long to check for coupled effects. If thermal or stress issues are discovered late—at final signoff—making changes is expensive and may jeopardize project schedules. That’s why the industry is embracing a “shift left” methodology: run powerful multiphysics simulations from the earliest architectural studies.

For example, with the Siemens’ multiphysics flows, teams can simulate candidate chiplet placements, experiment with various power delivery strategies, and locate potential hotspots—even before finishing the first floorplan (figure 3). These early insights enable proactive risk mitigation. As the project matures, designers can update placements, models and loading conditions incrementally—feeding in real block locations, material choices and actual power budgets—without needing to restart or rework each time requirements change.

Fig. 3: A shift-left approach runs multiphysics simulations starting at the conceptual phase.

A closer look at the modern 3D IC multiphysics flow

So, how does the multiphysics analysis workflow come together in practice? Here’s a stepwise overview using Siemens tools:

1. 3D floorplanning and connectivity: Begin with placement and initial interconnect planning in Innovator3D IC or your chiplet planning tool. Capture proposed block locations, define inter-die links and input early estimates for power delivery.
2. Physical verification: Use Calibre 3DStack to perform comprehensive physical and circuit correctness checks, ensuring complete stack integrity before moving forward.
3. Multiphysics analysis: mPower, Calibre 3DThermal and Calibre 3DStress tools analyze power integrity, temperatures and mechanical loads. The solvers provide actionable feedback—such as optimal placement for thermal dissipation, or stress minimization strategies for sensitive analog blocks.
4. Incorporate findings and iterate: Feed thermal and mechanical data back into placement and routing steps, and continuously refine timing, power and stress performance through iterative runs.
5. Iterative timing and closure: Keep refining analysis with each design refinement, so that by the time you reach DRC, LVS and final timing closure, most major issues have already been spotted and addressed.

By deploying this flow, challenges like stress hotspots, thermal bottlenecks and parasitic impacts become manageable and predictable—reducing the late-stage surprises that can derail complex projects.

The future: scaling reliability through multiphysics innovation

As 3D ICs move to ever larger and more diverse stacks, multiphysics analysis will only grow in importance. The next generation of devices will present new materials, denser interconnects and more sophisticated architectures—all increasing the urgency for coupled, domain-aware verification. Design teams will find value in EDA tools and methodologies that enable early, reliable multiphysics analysis, and EDA providers who are dedicated to their customers’ success.

3D ICs have matured from a longstanding theory into the new normal for heterogeneous integration. Only by embracing holistic multiphysics approaches can we achieve the reliability, scalability and performance required for tomorrow’s electronic systems.