In the relentless pursuit of performance and miniaturization, the semiconductor industry has increasingly turned to 3D integrated circuits (3D-ICs) as a cutting-edge solution. Stacking dies in a 3D assembly offers numerous benefits, including enhanced performance, reduced power consumption, and more efficient use of space. However, this advanced technology also introduces significant thermal dissipation challenges that can impact the electrical behavior, reliability, performance, and lifespan of the chips (figure 1). For automotive applications, where safety and reliability are paramount, managing these thermal effects is of utmost importance.

Fig. 1: Illustration of a 3D-IC with heat dissipation.

3D-ICs have become particularly attractive for safety-critical devices like automotive sensors. Advanced driver-assistance systems (ADAS) and autonomous vehicles (AVs) rely on these compact, high-performance chips to process vast amounts of sensor data in real time. Effective thermal management in these devices is a top priority to ensure that they function reliably under various operating conditions.

The thermal challenges of 3D-ICs in automotive applications

The stacked configuration of 3D-ICs inherently leads to complex thermal dynamics. In traditional 2D designs, heat dissipation occurs across a single plane, making it relatively straightforward to manage. However, in 3D-ICs, multiple active layers generate heat, creating significant thermal gradients and hotspots. These thermal issues can adversely affect device performance and reliability, which is particularly critical in automotive applications where components must operate reliably under extreme temperatures and harsh conditions.

These thermal effects in automotive 3D-ICs can impact the electrical behavior of the circuits, causing timing errors, increased leakage currents, and potential device failure. Therefore, accurate and comprehensive thermal analysis throughout the design flow is essential to ensure the reliability and performance of automotive ICs.

The importance of early and continuous thermal analysis

Traditionally, thermal analysis has been performed at the package and system levels, often as a separate process from IC design. However, with the advent of 3D-ICs, this approach is no longer sufficient.

To address the thermal challenges of 3D-ICs for automotive applications, it is crucial to incorporate die-level thermal analysis early in the design process and continue it throughout the design flow (figure 2). Early-stage thermal analysis can help identify potential hotspots and thermal bottlenecks before they become critical issues, enabling designers to make informed decisions about chiplet placement, power distribution, and cooling strategies. These early decisions reduce the risks of thermal-induced failures, improving the reliability of 3D automotive ICs.

Fig. 2: Die-level detailed thermal analysis using accurate package and boundary conditions should be fully integrated into the ASIC design flow to allow for fast thermal exploration.

Early package design, floorplanning and thermal feasibility analysis

During the initial package design and floorplanning stage, designers can use high-level power estimates and simplified models to perform thermal feasibility studies. These early analyses help identify configurations that are likely to cause thermal problems, allowing designers to rule out problematic designs before investing significant time and resources in detailed implementation.

Fig. 3: Thermal analysis as part of the package design, floorplanning and implementation flows.

For example, thermal analysis can reveal issues such as overlapping heat sources in stacked dies or insufficient cooling paths. By identifying these problems early, designers can explore alternative floorplans and adjust power distribution to mitigate thermal risks. This proactive approach reduces the likelihood of encountering critical thermal issues late in the design process, thereby shortening the overall design cycle.

Iterative thermal analysis throughout design refinement

As the design progresses and more detailed information becomes available, thermal analysis should be performed iteratively to refine the thermal model and verify that the design remains within acceptable thermal limits. At each stage of design refinement, additional details such as power maps, layout geometries and their material properties can be incorporated into the thermal model to improve accuracy.

This iterative approach lets designers continuously monitor and address thermal issues, ensuring that the design evolves in a thermally aware manner. By integrating thermal analysis with other design verification tasks, such as timing and power analysis, designers can achieve a holistic view of the design’s performance and reliability.

A robust thermal analysis tool should support various stages of the design process, providing value from initial concept to final signoff:

1. Early design planning: At the conceptual stage, designers can apply high-level power estimates to explore the thermal impact of different design options. This includes decisions related to 3D partitioning, die assembly, block and TSV floorplan, interface layer design, and package selection. By identifying potential thermal issues early, designers can make informed decisions that avoid costly redesigns later.
2. Detailed design and implementation: As designs become more detailed, thermal analysis should be used to verify that the design stays within its thermal budget. This involves analyzing the maturing package and die layout representations to account for their impact on thermally sensitive electrical circuits. Fine-grained power maps are crucial at this stage to capture hotspot effects accurately.
3. Design signoff: Before finalizing the design, it is essential to perform comprehensive thermal verification. This ensures that the design meets all thermal constraints and reliability requirements. Automated constraints checking and detailed reporting can expedite this process, providing designers with clear insights into any remaining thermal issues.
4. Connection to package-system analysis: Models from IC-level thermal analysis can be used in thermal analysis of the package and system. The integration lets designers build a streamlined flow through the entire development process of a 3D electronic product.

Tools and techniques for accurate thermal analysis

To effectively manage thermal challenges in automotive ICs, designers need advanced tools and techniques that can provide accurate and fast thermal analysis throughout the design flow. Modern thermal analysis tools are equipped with capabilities to handle the complexity of 3D-IC designs, from early feasibility studies to final signoff.

High-fidelity thermal models

Accurate thermal analysis requires high-fidelity thermal models that capture the intricate details of the 3D-IC assembly. These models should account for non-uniform material properties, fine-grained power distributions, and the thermal impact of through-silicon vias (TSVs) and other 3D features. Advanced tools can generate detailed thermal models based on the actual design geometries, providing a realistic representation of heat flow and temperature distribution.

For instance, tools like Calibre 3DThermal embeds an optimized custom 3D solver from Simcenter Flotherm to perform precise thermal analysis down to the nanometer scale. By leveraging detailed layer information and accurate boundary conditions, these tools can produce reliable thermal models that reflect the true thermal behavior of the design.

Automation and results viewing

Automation is a key feature of modern thermal analysis tools, enabling designers to perform complex analyses without requiring deep expertise in thermal engineering. An effective thermal analysis tool must offer advanced automation to facilitate use by non-experts. Key automation features include:

1. Optimized gridding: Automatically applying finer grids in critical areas of the model to ensure high resolution where needed, while using coarser grids elsewhere for efficiency.
2. Time step automation: In transient analysis, smaller time steps can be automatically generated during power transitions to capture key impacts accurately.
3. Equivalent thermal properties: Automatically reducing model complexity while maintaining accuracy by applying different bin sizes for critical (hotspot) vs non-critical regions when generating equivalent thermal properties.
4. Power map compression: Using adaptive bin sizes to compress very large power maps to improve tool performance.

5. Automated reporting: Generating summary reports that highlight key results for easy review and decision-making (figure 4).

Fig. 4: Ways to view thermal analysis results.

Automated thermal analysis tools can also integrate seamlessly with other design verification and implementation tools, providing a unified environment for managing thermal, electrical, and mechanical constraints. This integration ensures that thermal considerations are consistently addressed throughout the design flow, from initial feasibility analysis to final tape-out and even connecting with package-level analysis tools.

Real-world application

The practical benefits of integrated thermal analysis solutions are evident in real-world applications. For instance, a leading research organization, CEA, utilized an advanced thermal analysis tool from Siemens EDA to study the thermal performance of their 3DNoC demonstrator. The high-fidelity thermal model they developed showed a worst-case difference of just 3.75% and an average difference within 2% between simulation and measured data, demonstrating the accuracy and reliability of the tool (figure 5).

Fig. 5: Correlation of simulation versus measured results.

The path forward for automotive 3D-IC thermal management

As the automotive industry continues to embrace advanced technologies, the importance of accurate thermal analysis throughout the design flow of 3D-ICs cannot be overstated. By incorporating thermal analysis early in the design process and iteratively refining thermal models, designers can mitigate thermal risks, reduce design time, and enhance chip reliability.

Advanced thermal analysis tools that integrate seamlessly with the broader design environment are essential for achieving these goals. These tools enable designers to perform high-fidelity thermal analysis, automate complex tasks, and ensure that thermal considerations are addressed consistently from package design, through implementation to signoff.

By embracing these practices, designers can unlock the full potential of 3D-IC technology, delivering innovative, high-performance devices that meet the demands of today’s increasingly complex automotive applications.

For more information about die-level 3D-IC thermal analysis, read Conquer 3DIC thermal impacts with Calibre 3DThermal.

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