Thermal Vias in 3D-IC Stacks for Heat Removal
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Solution Overview
Problem
Three Dimensional Integrated Circuits (3D-ICs) face significant challenges in heat removal due to increased power density and high thermal resistance, particularly in stacked configurations where transistors are far from heat sinks and wiring dielectric regions do not conduct heat well, leading to inefficient heat transfer.
Innovation Solution
The implementation of thermal contacts and thermally conductive paths, including through-layer vias and power/ground distribution networks, to connect transistors directly to heat sinks, utilizing materials with low electrical conductivity but high thermal conductivity, such as copper or aluminum, to facilitate efficient heat transfer and reduce thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistors are stacked in 3D configuration to reduce wire lengths, then transistor density and performance improve, but heat removal becomes significantly more difficult due to increased power density and thermal resistance
Solution Approach 1:
The patent introduces thermal management functionality in the vertical dimension by stacking heat sinks beneath transistor layers. This vertical heat dissipation path addresses the thermal accumulation problem caused by 3D stacking by utilizing the z-axis for heat removal, complementary to the planar transistor arrangement.
Solution Approach 2:
The patent employs intermediate thermal management layers including heat spreaders and thermal interface materials positioned between the transistor layers and heat sinks. These intermediary components facilitate efficient heat transfer from high-density transistor regions to heat dissipation structures, overcoming the thermal resistance barrier.
2Ease of operation
If through-silicon vias are used to connect stacked device layers, then interlayer connectivity improves, but thermal resistance to heat sink increases
Solution Approach 1:
The patent designs through-silicon via structures that serve dual functions: electrical interconnection between layers and thermal conduction pathways to heat sinks. By making the via structures multi-functional, the patent simultaneously achieves connectivity and heat removal without requiring separate dedicated thermal paths.
Solution Approach 2:
The patent utilizes composite via structures filled with thermally conductive materials or lined with thermally conductive coatings. These composite via structures combine electrical conductivity for signal transmission with enhanced thermal conductivity for heat dissipation, addressing both connectivity and thermal management requirements.
3Power
If power density is increased in stacked layers to maintain performance, then transistor functionality is preserved, but thermal management becomes more challenging
Solution Approach 1:
The patent divides the 3D integrated circuit into multiple stacked layers, each with its own heat generation and heat dissipation characteristics. This segmentation allows for distributed thermal management where each layer can be independently cooled, preventing thermal accumulation that would occur in a monolithic high-power structure.
Solution Approach 2:
The patent incorporates heat sinks and thermal management structures directly within the 3D IC stack, allowing the device to self-manage its thermal load. The heat sinks are positioned to directly receive heat from adjacent transistor layers, creating a self-contained thermal management system that actively dissipates heat at the source.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces thermal resistance and enhances heat removal capabilities in 3D-ICs, allowing for the maintenance of transistors within desirable temperature limits and improved mechanical stability, even in high-power configurations.
Implementation Method 1
the through-layer via includes material whose co-efficient of thermal expansion is within about 50 percent of the second layer coefficient of thermal expansion
Implementation Method 2
a thermal connection to at least one of the second transistors, where the thermal connection is electrically isolated from at least one of the second transistors, and the thermal connection provides a thermally conductive path between at least one of the second transistors and the top or bottom surface of the device
Data Source
AI summary
A device, including: a first layer of first transistors, overlaid by at least one interconnection layer, wherein the interconnection layer includes metals such as copper or aluminum; a second layer including second transistors, the second layer overlaying the interconnection layer, wherein the second layer is less than about 0.4 micron thick; and a connection path connecting the second transistors to the interconnection layer, wherein the connection path includes at least one through-layer via, and the through-layer via includes material whose co-efficient of thermal expansion is within about 50 percent of the second layer coefficient of thermal expansion.