Thermal Management Challenges in Military Systems
Military systems, ranging from ruggedized handheld devices to advanced weapon systems, are often subjected to harsh environmental conditions and intensive computational workloads. As the demand for higher processing power increases, so does the heat generated by electronic components. Inadequate thermal management can lead to system failures, reduced performance, and compromised mission success. Additionally, SWaP constraints in military applications call for compact and lightweight thermal management solutions that do not compromise system capabilities.
There’s increasing recognition that 3DHI – which integrates different circuit types and materials in a 3D stack of tiers – promises tremendous performance advantages. However, thermal management technologies currently limit implementation. While stacking chips will be a critical part of the future of computing, challenges in dissipating the heat of internal processing components remains a barrier to significant progress.
The DARPA MiniTherms3D Program: A Vision for the Future
As the future of microsystems technology converges around three-dimensional heterogeneous integration (3HDI) microelectronics, the scientists, researchers, and engineers working to advance the state of the art – including at DARPA – are arriving at the same challenge: How can we pack the maximum computing into the smallest-possible space, and how can we manage the heat inherently generated by high-powered processing, especially in such a small space?
To overcome these challenges, DARPA launched Miniature Integrated Thermal Management Systems for 3D Heterogeneous Integration (MiniTherms3D) program in Jan 2023.
The DARPA MiniTherms3D program is a visionary initiative aimed at revolutionizing thermal management solutions for high-performance military systems. Its primary goal is to develop cutting-edge technologies that efficiently dissipate heat, enhance system performance, and improve overall reliability—all while adhering to stringent SWaP limitations.
Innovative Solutions for Enhanced Performance
The MiniTherms3D program seeks to address these challenges by fostering innovation in thermal management technologies. Researchers and engineers within the program are exploring novel materials, advanced cooling techniques, and three-dimensional integration to design compact, efficient, and reliable cooling solutions.
- Advanced Materials: The program explores the use of advanced materials with superior thermal conductivity, such as carbon nanotubes and graphene, to efficiently dissipate heat from electronic components. These materials enable high thermal conductivity in compact form factors, ideal for military systems with limited space.
- Microfluidic Cooling: Microfluidic cooling involves integrating micro-scale fluid channels directly into electronic components. This innovative approach enhances heat transfer efficiency and reduces system temperatures, even in confined spaces.
- Three-Dimensional Integration: The MiniTherms3D program leverages 3D integration to stack electronic components vertically, reducing interconnect lengths and optimizing heat transfer pathways. This approach not only enhances thermal performance but also minimizes overall system size.
“This is a key problem that we’ll be trying to address, developing cooling technologies that will enable the 3DHI systems that are absolutely the key direction for continued growth in microelectronics,” said Dr. Yogendra Joshi, program manager of DARPA’s MiniTherms3D program.
“In any high-functional computing system, particularly as you make them more compact, there is heat you must get rid of. In a stack today, heat is transmitted to the top and/or bottom, transported away, and ultimately rejected – typically to ambient air. High-powered 3D stacks are not currently possible, because the interior temperatures would become unacceptably high, and exterior heat rejection systems would be unacceptably large.”
Joshi likened the stacks to high-rise buildings in which one floor is stacked on top of the other. The new cooling technology would allow for cooling not just on the top and bottom floors, but throughout every floor of the “building.”
MiniTherms3D aims to address this problem from multiple perspectives – and if successful, would enable countless high-powered, multi-tiered 3DHI applications. For the Department of Defense, that could include advanced, concurrent radar processing for unmanned aerial vehicle platforms, as well as high-speed, high-volume data analysis on the move and at the edge.
Continued rapid growth of compact high-performance microsystems is limited by inadequate
integrated thermal management, including acquisition of heat from semiconductor devices, to its
transport, and ultimate rejection to the ambient environment. For example, the SOTA 3DHI
employed in high performance computing (HPC) systems typically utilizes a single tier of logic
and multiple tiers of high-bandwidth memory. Stacking of logic is currently limited to lowpower tiers.
Three-dimensional (3D) stacking of multiple tiers of high-power logic and other
functional blocks, including radio frequency devices, promises to allow significant further
advancement in capabilities of future microsystems, but is currently infeasible due to insufficient
in-plane and out of plane heat acquisition capabilities from each tier, and poor thermal isolation
between functional blocks. Unoptimized heat transmission and rejection also result in large
overall size of thermal management hardware. This limits growth in system capabilities,
particularly in radio frequency systems, image analysis, and high-performance computing,
including artificial intelligence and machine learning applications, in size, weight, and power
(SWaP) constrained applications at the edge.
The Minitherms3D program seeks to develop a compact thermal management technology
scalable to an arbitrarily large number of high-power tiers in a 3D stack. The program will
culminate in a demonstration with:
3D stacking of five tiers with total heat dissipation > 6.8 kW
Heat rejection system < 0.006 m3
The Minitherms3D program has one technical area (TA) with three phases (18 months, 18
months, 12 months for Phases 1, 2, and 3, respectively).
The Minitherms3D TA will focus on multi-scale thermal management technologies within and
outside a high-power 3DHI stack. In order to meet the program goals (Table 1), it is imperative
that all thermal resistances be addressed simultaneously to achieve optimal solutions across the
range of length scales of interest. Proposers should specifically address how they will de-risk the
pitfalls of addressing a specific thermal resistance within the overall chain and neglecting some
During Phase 1, performers will focus on hot spot mitigation approaches for a stack of three
equally-powered tiers with total thermal dissipation of 4 kW, while establishing approaches for
thermal isolation and large tierwise heat removal. This capability demonstration will be
performed for a stand-alone stack, with the target for hot spot mitigation met.
In Phase 2, successful approaches are expected to demonstrate the thermal management of a stack of five equally-powered tiers, with total dissipation of 6.8 kW, along with targets for thermal isolation, inside the stack thermal resistance reduction, as well as reduction in the thermal link resistance to the ambient heat rejection component.
In Phase 3, the overall system level thermal resistance and volumetric heat rejection targets will be demonstrated in a simulated application environment.
The focus of Phase 1 (18 months) is on achieving the hot spot heat flux mitigation target. But
improvements in other metrics will also be made to achieve the targeted 4 kW, three-tier stack
heat dissipation and volumetric heat rejection goals.
The goal of Phase 2 (18 months) is to demonstrate all the inside stack target metrics for a fivetier stack, with total heat dissipation of 6.8 kW. Significant improvement in outside the stack
thermal performance will also be demonstrated for a constant ambient environment temperature
of 20 oC at atmospheric pressure.
The goal of Phase 3 (12 months) is to demonstrate the multi-scale thermal management approach
within and outside the stack in a compact enclosure under realistic tactical environmental
conditions for both steady-state and transient operations. Proposers will define this scenario of
environmental conditions unique to their concept.
Benefits for High-Performance Military Systems
The advancements made through the MiniTherms3D program offer numerous benefits to high-performance military systems:
- Enhanced Performance: Efficient thermal management ensures that military systems can operate at peak performance levels, even during intense computational tasks, without risking overheating or performance degradation.
- Increased Reliability: Improved thermal management solutions lead to enhanced system reliability, minimizing the risk of failures during critical missions and operations.
- SWaP Optimization: By developing compact and lightweight thermal management solutions, the program enables military systems to meet strict SWaP constraints while retaining their full capabilities.
- Versatility: The innovative thermal management technologies developed under the program have applications across a wide range of military systems, from infantry equipment to unmanned aerial vehicles.
The program’s efforts align with the broader Electronic Resurgence Initiative (ERI) 2.0, DARPA’s sweeping effort to collaboratively advance state-of-the-art, next-generation electronics, benefiting national security and industry alike.
“MiniTherms3D is a central part of what we’re trying to do under ERI 2.0,” Joshi said. “Making systems more functional, more powerful, able to do more things – in all of these endeavors, thermal management is a fundamental challenge. Our goal is to overcome these challenges to enable growth in systems capabilities, including in radio frequency systems, image analysis, and high-performance computing for applications at the tactical edge.”
The DARPA MiniTherms3D program represents a significant leap forward in thermal management solutions for high-performance military systems. By exploring cutting-edge materials, microfluidic cooling, and three-dimensional integration, the program aims to revolutionize thermal management and address SWaP constraints simultaneously. As the advancements from this program find their way into military applications, we can expect to see more robust, efficient, and reliable systems that empower our armed forces and enhance national security.
The DARPA MiniTherms3D program’s commitment to pushing the boundaries of thermal management reflects the agency’s dedication to fostering innovation and empowering our military with state-of-the-art technology. As researchers and engineers continue to innovate within this program, we are poised to witness a new era of thermal management solutions that unleash the full potential of high-performance military systems.