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3D-ICs and the Importance of Heat Transfer Models

Published Date
Author Cadence System Analysis

Key Takeaways

  • Reducing the total area of integrated circuits is the main objective of 3D-IC technology.

  • Developing heat transfer models of 3D-ICs can help in addressing thermal challenges in the early phases of design and development. 

  • There are two main techniques used for developing heat transfer models of 3D-ICs: the analytical approach and the numerical computation approach.  

 3D-IC

3D-IC designs experience severe thermal challenges due to high power dissipation and heat density

Traditional single die planar integrated circuit (IC) designs are unable to match the high power density, high bandwidth, and low power consumption requirements of the electronics market. Three-dimensional (3D) IC technology offers somewhat better advantages by utilizing vertical stacking of multiple chips, which are electrically interconnected. The small form factor of 3D-ICs, with advanced functionalities such as better integration, reduced signal delay, and heterogeneous integration, establishes excellent electrical performance.

However, 3D-IC designs experience severe thermal challenges due to high power dissipation and heat density. 3D-IC heat transfer models were developed to address the thermal feasibility limitations of 3D-ICs. The heat transfer models of 3D-ICs help in developing new packaging. Let’s discuss 3D-ICs and their heat transfer model in this article. 

3D-IC Technology

Reducing the total area of integrated circuits is the main objective of 3D-IC technology. A 3D-IC is formed by vertically stacking conventional device layers or chips that are interconnected electrically. 3D-IC technology enhances the functionalities, performance, and packaging density of integrated devices. It reduces signal delays, enabling faster on-chip communications. The shortened interconnects between the logic and memory chips in 3D-IC packages provide faster signal transmission speeds. 3D-ICs exhibit better vertical integration density and heterogeneous integration, which showcases advantages over alternatives such as system-on-single chip and package-on-package. The integration in 3D-IC can be face-to-face integration or back-to-face integration.

3D-ICs can be classified into two types:

  1. 3D stacked ICs - formed by stacking IC chips and interconnecting them using through silicon vias (TSV). TSVs are the basic elements that enable the fabrication of 3D-SICs. The holes created by the etch process in the TSV are filled with conductive materials such as tungsten, copper, or polysilicon. TSV interconnects offer shortened paths between layers and chips, thereby improving the interconnect density and power consumption. 

  2. True 3D-ICs - multiple device layers are stacked on a single chip using fab processes. This type of IC is ideal for incorporating more transistors in a given footprint area. This technology helps to overcome the limits of the single die at the most advanced node. 

Advantages of 3D-ICs

The advantages of 3D-IC technology include:

  1. Low-cost design - All the functionalities do not need to move to advanced process nodes in 3D-ICs and this reduces the cost of design.

  2. Easy to achieve high transmission speed - 3D-IC technology has shortened interconnects, which decreases signal delays and offers high-speed communication and transmission.

  3. Circuit miniaturization - The stacking of layers helps to incorporate numerous transistors in 3D-ICs. Transistor densification saves space and makes 3D-ICs suitable for compact devices. 

  4. Low power consumption - 3D-ICs do not require high power-consuming drivers. Instead, they rely on low-power small input-output drivers. The low impedance of 3D-ICs also helps to reduce internal power losses. 

  5. Higher bandwidth - 3D-ICs can deliver higher bandwidth features. In 3D-IC technology, stacking cache memory on top of the processor increases bandwidth. 

  6. Flexibility - The stacking of heterogeneous technologies introduces flexibility in 3D-ICs. Different manufacturing processors and nodes can be intermixed using heterogeneous integration in 3D-ICs. This helps to reuse the existing chips without redesigning, thus providing risk-free cost reduction. 

Heat Transfer Models in 3D-IC Technology

Thermal challenges pose one of the biggest hurdles in 3D-IC technology. To achieve high power density in a given footprint, device layers are stacked up one over the other. Applying power in the given footprint of stacked up layers leads to high dissipation of heat. The complex architecture and high level of integration add to increased heat dissipation and heat density. 3D stacked IC technology inherently produces high temperatures and causes disastrous failures in 3D-IC integration.

Heat needs to be dissipated properly for the efficient working of 3D-ICs. Conventional air cooling is not sufficient for 3D-ICs, and sophisticated thermal management systems need to be designed to dynamically control the 3D-IC temperature. Developing heat transfer models of 3D-ICs can help address thermal challenges in the early phases of design and development. The heat transfer models of 3D-ICs can answer fundamental heat transfer questions that are critical in the successful implementation of 3D-IC technology.

The heat transfer models of 3D-ICs investigate the limitations of the thermal feasibility of 3D-IC designs. It is a supporting tool to implement a suitable thermal management approach for IC cooling and packaging styles to accommodate 3D-ICs. There are two main techniques used for developing heat transfer models of 3D-ICs.

  1. Analytical approach - Analytical heat transfer models derive the temperature fields of the 3D-IC architecture by solving energy conservation equations along with boundary conditions. These models can be used for investigating the impact of various geometric and thermophysical parameters on the thermal performance of 3D-ICs. 

  2. Numerical computation approach - When 3D-ICs have complex architecture and temperature-dependent properties, it becomes difficult to derive the exact solutions for the heat transfer equations. In such cases, numerical computational heat transfer models are developed by approximately solving the equations by discretizing the geometry. The numerical computation technique can predict the temperature with acceptable accuracy. 

The heat transfer model of 3D-ICs can determine the junction temperatures and peak temperatures generated in the internal structure. Heat transfer models can also identify hotspots in 3D-IC architecture and help engineers design proper thermal management techniques.

Cadence software can generate heat transfer models that can be used for determining the temperature distribution for each die. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts. 

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