Thermal management of 3-D heterogeneously integrated microelectronics: challenges and future research directions

Abstract

The increasing demand for high-performance computing, artificial intelligence, and advanced communication technologies has accelerated the development of compact, energy-efficient, and multifunctional three-dimensional heterogeneously integrated (3-DHI) microelectronics. While such integrated circuits offer significant improvements in functionality and integration density, the compact and vertical stacking of heterogeneous components introduce significant thermal challenges. These result in non-uniform power densities, hotspot proliferation, thermal expansion mismatch, and narrowing heat dissipation pathways—all of which compromise device reliability, longevity, and performance by hindering heat removal within the package and to the environment. This review critically examines the thermal bottlenecks inherent in 3-DHI architectures and evaluates the effectiveness of current thermal management strategies, including embedded microfluidic cooling, interlayer heat spreaders, and through-silicon vias. Additionally, the article outlines future research directions focused on overcoming existing limitations and advancing the development of thermally efficient 3-DHI chips.

Thermal management is becoming increasingly important as microelectronic devices grow smaller and more powerful. Manoj Kumar Sharma and Bladimir Ramos Alvarado review key challenges and design considerations for effective heat control in advanced microelectronics.

Introduction

Electronics play an essential role in almost every aspect of human life, including communication, healthcare, industrial automation, and transportation. The increasing demand for intelligent and efficient functionalities, particularly for artificial intelligence and machine learning, has placed unprecedented pressure on computing hardware¹. This demand has driven continuous innovation in semiconductor technology, with a focus on compact, high-speed, and energy-efficient processors capable of handling complex computational tasks². The development of the transistor in 1947 by John Bardeen, Walter Brattain and William Shockley was the first effort made toward today’s fast, reliable, and compact processors³. This invention led to the foundation for integrated circuits (ICs), first demonstrated by Jack Kilby in 1958⁴. Subsequent advancements during the late 1950s and 1960s (Fig. 1a, b) further refined the technology, enabling the miniaturization of electronic components and leading to the development of microprocessors⁴. Subsequent progress, including the evolution from single-core to multi-core architectures, has steadily improved computing capabilities³. However, with Moore’s Law nearing its practical limits, further enhancements in functionality now require alternative approaches to advance computing hardware^5,6.

Fig. 1. Demonstration of 3-DHI chip architecture.

a Photograph of a computer motherboard, with enlarged views of (b) a chip (or packaged integrated circuit) and (c) a 3-D heterogeneously integrated circuit, (d) heat generation and functionality increase as a function of time (BGA Ball Grid Array, DIP Dual In-line Package, FCBGA Flip Chip Ball Grid Array, QFP Quad Flat Package, SIP System in Package, TSV Through-Silicon Via).

Monolithic 3-dimensional integration (3-DI) is an advanced semiconductor packaging technique that vertically fabricates multiple device layers on a single wafer, enabling compact, high-density circuits with reduced footprint and latency^2,5. The performance, flexibility, and cost-effectiveness of monolithic 3-DI are further improved by integrating heterogeneous functional blocks (or dies) such as processors, logic units, memory, optoelectronic components, radio-frequency modules, and signal processing units, each differing in size, material properties, and often fabricated across various foundries (Fig. 1c)^5,7. These dies are vertically interconnected via through-silicon vias (TSVs), ensuring efficient inter-tier communication, higher integration density, and improved design compactness^5,7,8. By reducing signal delays and power consumption, 3-DHI emerges as a promising pathway for advanced applications in data centers, high-performance computing, communication electronics, and AI/ML applications.

Although 3-DHI significantly enhances computational performance, it also generates substantial heat due to the dense integration of transistors and packaging elements (Fig. 1d)^9,10. The stacked architecture comprises materials with diverse thermal properties and multiple interfaces, which increase overall thermal resistance and impede heat dissipation¹¹. This thermal bottleneck promotes heat accumulation between stacked layers, resulting in higher operational temperatures, which can surpass the thermal design limits of one or more components within the package^11,12. Suboptimal thermal design and inadequate heat dissipation strategies are key factors exacerbating overheating. As a result, temperature gradients within the stack become more pronounced, increasing the probability of hotspot development that can degrade device performance, induce thermal expansion mismatches, cause interconnect failures, and lead to delamination within the stack^10–14.

The reliability of electronic systems is highly sensitive to temperature; a rise of only 1 °C between 70–80 °C can reduce device reliability by ~5%¹⁵. Moreover, over 55% of electronic device failures are attributed to excessive operating temperatures^11,15. In some cases, a temperature rise of just 5 °C beyond the optimal threshold may halve the lifespan of sensitive electronic components¹⁶. These concerns highlight the urgent need for effective and reliable thermal management strategies in 3-DHI architectures, where inherent structural constraints, limited heat removal pathways, and high interfacial resistances pose unique challenges.

Thermal management approaches for electronics cooling are typically classified into interconnect-level, die/IC-level, and system/CPU-level solutions (Fig. 2). At the CPU level, conventional air- and liquid-cooled heat sinks and thermoelectric cooling remain effective^17,18 but are inadequate for internal heat extraction from stacked chips. This limitation has led to the development of IC-level cooling strategies, such as embedding high thermal conductivity materials in the chips to improve heat spreading^9,19–21. However, vertical heat transport across stacked layers is often limited. TSVs, made of high thermal conductivity materials such as copper and incorporated at the interconnect level, provide a promising route for vertical heat transfer between tiers. When combined with appropriate cooling solutions, TSVs can significantly improve heat distribution and enhance the overall thermal performance of 3-DHI microelectronics.

Fig. 2.

Schematic representation of electronic cooling strategies categorized by package architecture level.

Several studies^15,22–24 have explored the thermal management of microelectronics, primarily focusing on cooling mechanisms or power delivery challenges, performance degradation, or thermo-mechanical aspects. However, most of these studies are centered on 3-DI circuits, while the thermal management of 3-DHI remains relatively underexplored. Despite existing research^25–28 and a few review articles^5,29,30 on the related topics addressing disjointed aspects of 3-DHICs thermal challenges, no comprehensive review article presents a cohesive view of the field that addresses the limitations of thermal management techniques and also outlines possible future directions.

The present review article focuses on the thermal management of 3-DHI microelectronics, with a particular focus on the key constraints that influence the efficiency and effectiveness of the thermal management methods. As depicted in Fig. 3, these factors encompass both chip-level constraints and cooling system-level limitations. Each of them presents unique challenges that must be systematically addressed to achieve optimal thermal management of 3-DHI systems. In this article, firstly, we discuss the mechanisms of heat generation within 3-DHI systems, along with the associated issues arising from elevated and spatially non-uniform temperature distributions. Thereafter, a comprehensive analysis is presented, outlining the primary obstacles to effective thermal management of 3-DHI systems. This includes limitations at both the chip and cooling system levels, their impact on overall thermal performance, and potential strategies to address these challenges. Special attention is given to microscale thermal management techniques that enhance heat dissipation efficiency within the confined environments of 3-DHI structures.

Fig. 3.

Schematic illustration depicting the chip-level and cooling system-level constraints associated with the thermal management of 3-DHI microelectronics.

Heat generation mechanisms and their implication in microelectronics

The fundamental understanding of the heat generation mechanisms is critical in optimizing next-generation electronics performance and reliability, particularly in engineering thermal management systems. As electronic devices advance toward higher performance and miniaturization (i.e., 3-DHI), heat generation densities increase due to the proximity of interconnected functional blocks³¹. Heat generation in such integrated architectures may include resistive losses in interconnects, transistor switching losses, leakage currents, and dielectric losses in insulating materials (Fig. 4)^31,32. Resistive losses occur as electrical current encounters resistance in conductive interconnect pathways, resulting in Joule heating; switching losses are associated with transistor operations, particularly during their switch on and off; leakage currents, which persist even when transistors are nominally off and contribute to continuous heat generation; and dielectric losses emerge in insulating materials exposed to time-varying electric fields where polarization and conduction mechanisms result in energy being dissipated as heat^31,32. At the interconnect level, heat is often transported through TSVs and micro-bumps (µBumps) from the heating source to the heat sink²⁸. Although the presence of TSVs and µBumps enhances heat transfer in 3-DHI, they also introduce additional electrical resistance, further contributing to Joule heating.

Fig. 4.

Heat generation in the integrated circuits and temperature-driven issues in thermal-mechanical reliability.

Moreover, electromigration, a phenomenon where the flow of electric current may cause ion migration and develop voids within metal interconnects, can alter resistive pathways and intensify heat generation over time through Joule’s heating^33,34. Concurrently, the downscaling of chip dimensions has made the leakage currents a dominant source of heat generation³⁵. These currents are highly sensitive to temperature and tend to rise with device temperature. Elevated device temperature through heat generation also increases the resistivity of components, leading to augmented Joule heating³⁵. Together, these effects establish a thermal feedback loop that accelerates heat generation and raises the overall operating temperature of the microelectronic system (Fig. 4). In 3-DHI devices, such elevated operational temperatures can lead to a range of critical issues, including signal integrity degradation, mechanical and electrical failures, and, in extreme cases, thermal runaway (Fig. 4). This Section outlines these concerns in brief.

Communication issues

The electrical characteristics of integrated components, namely resistance, capacitance, and inductance, play a critical role in determining the performance of 3-DHI systems. These parameters can introduce challenges in maintaining communication efficiency and signal integrity, especially under high temperatures³⁶. Their impact becomes more significant in compact architectures, where longer interconnects experience greater resistance-capacitance delays³⁶. Additionally, phenomena such as signal crosstalk, signal attenuation, and inductive noise pose further challenges, especially in high-frequency, multilayer configurations. Collectively, these issues can degrade signal quality and cause signal delay. Beyond signal delay, hardware trojans represent a critical security threat in microelectronics, which may sometimes be activated in thermally constrained 3-DHI microelectronic devices³⁷. For example, operating temperatures as high as 158°C, potentially triggering temperature-sensitive Trojan payloads through induced timing shifts³⁸.

Mechanical and electrical reliability

Vertical integration in 3-DHI significantly enhances processing capabilities and reduces interconnect lengths. Nevertheless, such dense packaging intensifies localized heat generation, leading to steep temperature gradients within the stack. Consequently, thermo-mechanical reliability is compromised, primarily due to mismatched coefficients of thermal expansion (CTE) among neighboring components in the integration (i.e., silicon dies, solder joints, µBumps, TSVs, dielectric, underfill, and substrates), which cause the electrical and mechanical failure of the microelectronic device. CTE mismatch generates cyclic shear stresses during temperature fluctuations from uneven heat generation, leading to electrical failure through the fatigue of solder interconnects (Fig. 4)³⁹. For example, thermal cycling tests between −55 °C and 175 °C on flip chip assemblies revealed solder joint cracks due to accumulated plastic strain, exacerbated by underfill delamination at elevated temperatures³⁹. Substrate delamination and die lift also arise from interfacial stresses induced by CTE mismatches between the epoxy molding compound and passivation layers. Finite element simulations have revealed steep thermal gradients at material interfaces, contributing to this delamination phenomenon^39,40. Such delamination often precedes die cracking and warpage, as localized stress concentrations propagate through brittle silicon or passivation layers, particularly in structures incorporating high CTE polymers operating above their glass transition temperature^40,41. At temperatures exceeding 150 °C, the gradual decline in underfill adhesion strength further undermines mechanical stability, accelerating both interconnect fatigue and delamination³⁹. To mitigate these effects, strategies such as tailoring the CTE of underfills and dielectric, improving interfacial adhesion through appropriate material selection, and redistributing thermal stresses by employing advanced packaging architectures are used, as discussed later in this article.

Thermal runaway

In integrated circuits packaged within plastic or metallic cases, as shown in Fig. 1b, the enclosure provides mechanical and environmental protection but also introduces considerable thermal resistance, thereby impeding heat transfer to the ambient. As operating temperatures rise within the confined package, leakage currents in the semiconductor increase exponentially, generating additional heat that further elevates temperatures⁴². This feedback loop causes catastrophic failure, resulting in package deformation, interconnect melting, or die fracture^42,43. The metal pins, though providing electrical connectivity, offer minimal thermal relief paths compared to modern thermal management solutions like integrated heat spreaders. Addressing thermal runaway requires comprehensive package-level thermal design considerations, including appropriate die attachment materials, strategic pin placement for thermal dissipation, and careful power density management across the substrate.

Thermal crosstalk

Thermal crosstalk is another major concern in 3-DHI systems, posing challenges due to unintended heat transfer between vertically stacked or laterally adjacent components, leading to performance degradation and reliability risks⁴⁴. For example, in memory-processor stacks, low-power memory dice experience elevated temperatures from high-power logic layers due to thermal coupling through underfill and TSVs, degrading memory retention and increasing leakage power by up to 16%⁴⁵. Similarly, in photonic integrated electronics, microheaters in silicon photonic circuits suffer reduced efficiency ( ~ 43.3%) and increased crosstalk (~44.4%) when bonded to heat spreads through µBumps and interposer layers⁴⁶.

Several studies on thermal crosstalk mitigation strategies are focused on thermal isolation and path optimization. Optimizing floor planning may be an effective method to reduce the thermal crosstalk, where clustering TSVs away from temperature-sensitive regions and implementing thermal bridges with auxiliary microfluidic cooling can minimize lateral heat propagation^45,47. Additionally, co-design approaches integrating thermal-aware 3-D placement with crosstalk-optimized routing reduce peak temperatures and coupling noise by balancing wirelength, via density, and inter-layer spacing⁴⁷. These solutions highlight the critical need for geometric optimization and material and architectural innovations to decouple thermal domains in 3-DHI systems while maintaining electrical performance.

Key barriers in thermal management of 3-DHI microelectronics

Although 3-DHI offers enhancement in performance, functionality, form factor, and system-level efficiency, overcoming the limitations of 2.5 D and monolithic 3-D integration techniques, its high-power density, compact stacking, and thermo-mechanical stress cause various thermal management-related challenges. Moreover, the inherently heterogeneous architecture and narrow heat dissipation pathways in 3-DHI microelectronics constrain the effectiveness of conventional cooling methods¹. To elucidate the key obstacles hindering efficient thermal management in 3-DHI, we classified them into two categories: (a) architectural constraints, and (b) challenges associated with thermal management systems, as discussed in the subsequent Sections.

Architectural constraints

3-DHI chips have limited thermal pathways for heat removal, particularly for the tiers situated in the middle of the stack, which are the farthest from direct cooling interfaces. Additionally, inadequate thermal isolation between adjacent functional blocks within the 3-D stack further complicates effective thermal management. While strong thermal isolation is essential to reduce thermal crosstalk between neighboring functional blocks with different power densities and thermal sensitivities, it can hinder heat spreading, leading to localized hotspots and uneven temperature profiles. On the other hand, poor isolation may promote heat transfer between functional blocks, potentially degrading their performance and reliability. Hence, achieving an optimal balance between thermal isolation among functional blocks and efficient heat removal from intermediate layers is essential. Nonetheless, the dense integration of components, suboptimal placement of TSVs, non-uniform heat generation, and heterogeneous material properties within the stack collectively hinder the heat dissipation rate both within and from the package. These aspects are thoroughly discussed in the subsequent Sections.

Limited heat spreading

The vertical stacking of functional blocks along with packaged components possessing heterogeneous thermal properties and uneven power densities leads to heat accumulation within interior tiers of 3-DHI microelectronics, and results in steep thermal gradients in localized regions (Fig. 5a)⁴⁸. These hotspots are prominent in regions which are thermally isolated from the environment, such as components embedded within low thermal conductivity materials or those exhibiting intense heat generation. The lateral dimensions of the tiers also impact the distribution of hotspots. Thinner dies tend to experience elevated local temperatures due to their limited ability to laterally spread heat (Fig. 6)⁴⁹, whereas thicker layers may function as passive heat spreaders, aiding in temperature uniformity^1,50. In some cases, localized heat flux can exceed ~30 kW cm⁻²⁴⁹. Such non-uniform heat distributions lead to temperature variation across the integrated components (Fig. 6)⁴⁹ and can induce thermal crosstalk between neighboring functional units, potentially degrading their performance and compromising system reliability.

Fig. 5. Schematic illustrations depicting key thermal challenges in 3-DHI microelectronics.

a hotspots within a dense component package, (b) misalignment of TSVs, (c) elevated thermal resistance across heterogeneous interfaces (where α = 12–25 µm, β = 70–380 µm, γ = 2.7–5 µm, and δ = 0.3–10 µm)^{91,118,135–137}, and (d) interfacial air voids within TSV structures.

Fig. 6.

Temperature distribution of a Gallium Nitride-based high-power heterogeneously integrated chip (This figure has been adapted from ref. ⁴⁹. with permission from Elsevier Publications, Copyright 2023).

Most cooling systems are typically designed under the assumption of uniform power dissipation, where temperature gradients remain spatially and temporally predictable. However, in real conditions, non-uniform heat generation with the presence of localized hotspots poses a challenge for effective thermal management (Fig. 6)⁴⁹. Doubling the coolant flow rate in a liquid cooling device reduces the peak temperature in microelectronics by only about 8 °C, while affecting the temperature non-uniformity negligibly. This limitation becomes more critical when heat-generating regions are situated farther from the cooling interfaces, thereby reducing the effectiveness of cooling methods^51,52. For example, the peak GPU temperature rises by approximately 61.33% upon the integration of additional logic layers between the GPU and the cooling device⁵¹. Addressing this challenge requires the integration of targeted thermal management strategies that focus on reducing localized thermal resistance. These may include careful optimization of functional block placement and enhanced thermal coupling between heat-intensive areas and nearby heat spreaders or sinks to improve heat dissipation and maintain reliable operation.

Thermal-aware design strategies, including functional block replacement, optimizing wirelength, TSV counts, and peak temperatures, are essential in minimizing the hotspot formation⁵³. Advanced strategies, i.e., iterative thermal-force-directed approaches and discrete cosine transform models, are utilized to iteratively optimize die placement away from high temperature zones^1,48,53. These quadratic-based formulations aim to mitigate hotspot formation by promoting thermally balanced 3-D layouts, while simultaneously minimizing cell overlap and interconnect length^1,48. For example, redistributing the heat generation components while floor planning drops the temperature of components by 2.74 °C⁵¹; and an increase in TSV usage by 6% while increasing the wirelength by 8% lowers the maximum on-chip temperature by 37%⁵³.

Although the primary objective of floorplanning algorithms is to maintain a uniform thermal profile, the occurrence of thermal hotspots remains unavoidable. Material advancements are therefore critical to enhancing thermal management. For example, high-thermal-conductivity underfills can significantly improve heat transfer between tiers while offering promising solutions for hotspot mitigation¹. Beyond these passive solutions, solid-state thermal management devices—such as thermal diodes, regulators, and switches—introduce nonlinear and switchable control over heat flow^54,55. Unlike conventional spreaders and sinks, these components can actively regulate, rectify, or redirect heat, making them especially relevant for 3-DHI architectures that face localized hotspots and highly non-uniform thermal loads. Phase-change materials and metal–insulator transition systems (e.g., VO₂-based regulators) further extend this functionality by dynamically altering thermal conductivity at critical transition points⁵⁵. Integrating such advanced solid-state thermal management devices within 3-DHI stacks could enable both localized hotspot suppression and efficient global heat redistribution. Nonetheless, challenges related to nanoscale integration, parasitic thermal losses, and long-term reliability under cyclic operation remain open, necessitating continued research as needed for heterogeneous integration⁵⁶.

Constrained heat dissipation pathways

The compact integration of components restricts direct heat conductive pathways from the inner tiers to external heat sinks, which causes reduced cooling effectiveness^29,57. Moreover, vertical stacking of components in 3-DHI architectures significantly raises confined heat fluxes within intermediate tiers, leading to localized hotspots and steep temperature gradients (Fig. 5a)^58,59. Although the functional blocks (dies) in 3-DHI are physically stacked through interlayer dielectrics, vertical heat transfer through these components is restricted due to their heterogeneous properties. Hence, the effective extraction of the trapped heat within interlayers relies on lateral heat conduction through ultra-thin substrates and interlayer dielectrics⁵⁹. The choice of substrate materials (i.e., silicon, glass, or organic substrates) greatly influences the overall thermal resistance, as their anisotropic thermal conductivities and restricted lateral heat spreading capabilities pose additional constraints in densely packed ICs⁶⁰. For example, the very low thermal conductivity of an ultra-thin silicon layer (∼0.3 Wm^-1K^-1)⁶¹ limits heat conduction, while also restricting heat spreading to only ~200 W cm^-² for 1 mm² hotspots⁵⁹. Ultra-thin interlayer dielectrics (e.g., SiO₂, polymers, and Si₃N₄)^62,63 possessing low thermal conductivity further restrict effective heat transport due to narrow thermal pathways^64,65. To mitigate these high internal resistance challenges, several strategies, including material advancements and embedded cooling solutions, have been proposed. Replacing traditional silicon dioxide interlayer dielectrics with high-conductivity materials such as aluminum nitride (AlN, ~250 W⁻¹K⁻¹) and hexagonal boron nitride (hBN, ~600 Wm⁻¹K⁻¹) has demonstrated over 40% improvement in vertical heat conduction^66,67. Complementarily, these materials in 3-D integration can help redistribute the hotspots away from thermally resistive junctions⁶⁷. While replacing SiO₂ interlayer dielectrics with high-thermal-conductivity materials improves both lateral and vertical heat dissipation in 3-DHI architectures, these materials introduce thermo-mechanical challenges due to their high CTE, which are discussed later in this article.

Several factors, such as surface roughness, interfacial voids, and the presence of multiple contact layers in the 3-DHI package, further impede heat flow through increased interfacial thermal resistance in the order of ~0.05 °C W⁻¹⁶⁵. In addition, hybrid designs incorporating diamond-coated layers improve the effective thermal conductivity of chips^66,68; and embedded cooling technologies, such as 3-D printed pin fins, minimize interfacial resistances by integrating heat extraction devices directly into the die²⁹. For example, bonding diamond directly to the rear surface of silicon chips has demonstrated significant improvements in heat dissipation with a reduction in interfacial resistance by 28.5%⁶⁸. To fabricate the diamond-based heat spreaders on dies/chips, several methods have been explored, including direct deposition of polycrystalline diamond films via chemical vapor deposition and wafer bonding techniques. Although these approaches show great potential, their practical implementation is limited by the requirement for elevated operating temperatures (typically above 400 °C) and high pressures, which pose a risk of damaging the delicate die structures. Consequently, they are not well-suited for integration within standard semiconductor packaging processes⁶⁸. This highlights the need for alternative methods to enable diamond growth directly on-chip under low temperature/pressure conditions.

Suboptimal TSV placement

TSVs are the pillar of 3-DHI microelectronics, which play a dual role—serving not only as electrical interconnects but also as vertical thermal conduits within densely stacked assemblies where conventional heat dissipation routes are limited. Unlike in monolithic 3-D integration, where a combination of TSVs and metal interlayer vias may be employed, 3-DHI architectures predominantly utilize TSVs in conjunction with die-to-die µBumps to achieve a robust vertical interconnection. Hence, TSVs in combination with µBumps provide conductive routes for heat dissipation from intermediate dies toward the package exterior or heat sink (Fig. 5b, c). Typically formed by deep silicon etching followed by copper filling, TSVs benefit from copper’s high thermal conductivity, promoting effective heat extraction from densely populated regions³⁶. Similarly, µBumps, which are primarily intended for mechanical and electrical bonding, influence thermal transport by introducing localized conduction paths between dies.

Despite their promising role in enhancing vertical heat conduction, suboptimal placement of TSVs compromises the overall heat dissipation from 3-DHI microelectronics, resulting in heat accumulation within the stacked layers. To address this, several strategies have been explored for optimizing TSV distribution. Thermal-aware floorplanning has gained traction as a powerful strategy. By judiciously distributing TSVs, high-power modules, and heat-generating logic units across the chip layout, thermal gradients can be moderated while avoiding localized hotspots^1,69,70. Sophisticated co-design algorithms enable simultaneous optimization of TSV placement, electrical routing, and thermal behavior, taking into account factors such as TSV density, aspect ratio, and proximity to active regions^1,71. However, the total number of TSVs that can be integrated within a package is inherently constrained, as their placement is primarily dictated by electrical interconnection requirements. This limitation restricts the use of signal-carrying TSVs for targeted thermal management in high-heat flux regions. To address this issue, the integration of thermal through-silicon vias (TTSVs), which are specifically dedicated to conducting heat rather than electrical signals, has emerged as an effective strategy for improving heat dissipation in densely packed 3-DHI microelectronics. TTSVs provide additional thermal pathways and can substantially reduce peak junction temperatures when co-optimized with signal (or electrical) TSVs^70,72. For example, replacing just 10% of electrical TSVs with TTSVs can lead to a reduction in peak temperature by nearly 15 °C in 3-D integrated circuits⁷⁰. Nevertheless, this thermal advantage comes at the cost of reducing the available electrical TSVs. Hence, co-design strategies that simultaneously consider both thermal management and electrical functionality are implemented. These approaches typically involve the careful optimization of both signal-carrying and heat-dissipating TSVs to ensure a well-rounded system performance⁷³. Although the co-optimization of TSVs, TTSVs, and the placement of functional blocks of 3-DHI systems can facilitate a more uniform temperature distribution across the device, this approach often involves intricate computational procedures and extensive iterative simulations, which can substantially elevate the system development cost. Additionally, integrating TSVs and TTSVs consumes chip area that could otherwise accommodate functional blocks, potentially contributing to increased chip size. A large number of TSVs for effective thermal management also increases fabrication costs in the absence of a targeted optimization strategy. Therefore, strategic floorplanning is essential to refine TTSV placement techniques that effectively navigate the trade-offs among temperature uniformity, thermal and electric TSV count, device size, and interconnect length, while also minimizing the overall cost of interconnections.

Heterogeneous material properties

3-DHI assembles multiple functional blocks manufactured in different foundries, each with distinct electrical, mechanical, and thermal characteristics, to achieve enhanced system-level performance. Silicon remains the preferred candidate for high-speed logic circuits due to its well-established fabrication ecosystem and unique thermo-mechanical properties⁷⁴. In contrast, Gallium Nitride is often employed for high-frequency radio-frequency applications due to its superior electronic properties⁷⁵. These logic and radio-frequency units, along with other functional blocks (i.e., analog, photonics, and MEMS), are integrated in the same package consisting of a substrate which may have dissimilar thermo-physical properties. Vertical and lateral interconnections between dies are ensured through TSVs and µBumps, each consisting of different thermal properties. To physically connect all these components while maintaining the electrical, thermal and signal integrity, dielectric materials and underfill compounds are strategically employed within the package. However, the integration of such a diverse set of materials introduces mismatches in the thermal properties across the shared interfaces. For example, copper-based TSVs, which are critical for vertical heat and signal transfer, have high thermal conductivity ( ~ 385 Wm⁻¹K⁻¹) but are typically embedded within low-conductivity dielectric material such as silicon dioxide ( ~ 1.4 Wm⁻¹K⁻¹) or organic polymers for signal integrity⁵¹. This contrast in thermal properties creates pronounced interfacial thermal resistance, impeding heat dissipation (Fig. 5c). Moreover, the thermal pathway from µBumps to TSVs and eventually to external heat sinks is characterized by a series of thermally resistive interfaces, further limiting efficient heat removal in 3-DHI architectures (Fig. 5c).

The mismatch in the CTEs of neighboring components poses another challenge^39,40. For example, polymers or epoxy-based underfills used for insulation and bonding typically have CTEs an order of magnitude higher than semiconductor materials like Si (3 × 10⁻⁶ °C⁻¹)⁷⁶ or Gallium Nitride (3.17 × 10⁻⁶ °C⁻¹)⁷⁷. During thermal cycling, mismatches in the CTE between adjacent materials generate thermomechanical stresses at their interfaces. These stresses may damage the heat conductive pathways through warpage, delamination, structural misalignment, and cracking within TSV structures, which in turn lower the heat dissipation rate⁷⁸. A practical way to mitigate this issue is to choose neighboring materials with approximately the same CTE at each interface. While the material selection for functional blocks or dies is limited by their intended functions, the interlayer materials can be modified to meet thermal, electrical, and mechanical requirements. Consequently, ongoing research has focused on developing interlayer dielectric materials whose CTEs are compatible with those of neighboring semiconductor layers and substrates, thereby minimizing interfacial stress and enhancing long-term mechanical integrity. Compliant interlayers, such as stress-buffering adhesives infused with hexagonal boron nitride (k = 220–600 Wm⁻¹K⁻¹, CTE = −2.6 × 10⁻⁶ °C⁻¹)^79,80 or chemical vapor deposition diamond (k = 1200 Wm⁻¹K⁻¹, CTE=1.5–1.8 × 10⁻⁶ °C⁻¹)⁸¹ accommodate CTE mismatches while reducing interfacial thermal resistance.

Challenges associated with thermal management systems

The stacked-die architecture in 3-DHI introduces substantial thermal resistance, with assembly tolerances further compounding these bottlenecks and hindering heat dissipation. To mitigate these issues, a range of cooling strategies, such as embedded microfluidic systems, TSVs, thermal interface materials (TIMs), and advanced heat spreaders, are used. However, these strategies are subjected to design, performance, and reliability concerns. This Section examines the key challenges associated with various chip components that assist the thermal management of 3-DHI microelectronics.

TSV defects

The benefits of optimum placement of TSVs in terms of improved thermal management were discussed previously. While TSVs offer substantial advantages in vertical heat conduction, they may also face reliability concerns under manufacturing defects and operational stresses, which can introduce thermal and mechanical challenges hindering the effective heat dissipation in 3-D heterogeneous integration. One major concern arises from the fabrication process itself. Imperfections such as voids, seams, incomplete metal fill during electroplating, cracks, or impurities in copper filling can significantly increase the local thermal resistance, potentially leading to poor heat conduction across tiers and the formation of localized hotspots (Fig. 5d)¹. Moreover, sub-optimal wafer bonding or lithography inaccuracies lead to misalignment of TSVs and may disrupt thermal pathways by decreasing the effective heat transfer area, thereby affecting the heat dissipation from the 3-DHI stack (Fig. 5b)⁸².

To enhance heat dissipation through TSVs and mitigate the associated challenges, several solutions have been proposed at both the process and system design levels. On the fabrication front, advancements in copper filling techniques—such as void-free electrochemical deposition with controlled current density (7 mA cm^-2)⁸³, incorporating additives⁸⁴, optimized barrier layers⁸⁵, and improved via profile control¹—have demonstrated improvements in structural reliability. These methods aim to reduce internal voids and seam formations while ensuring consistent thermal conductance. Wafer alignment precision is another critical enabler of TSV performance⁸². Techniques including infrared alignment, intersubstrate alignment, and the use of semi-transparent or transparent substrates have been successfully applied to minimize TSV misalignment during die stacking processes¹.

In addition to the formation of air pockets, various forms of atomic migration-including stress-induced migration from thermo-mechanical stress gradients, current-induced migration from electron flow, temperature-induced migration due to thermal gradients, and migration driven by atomic concentration gradients, can lead to void formation in TSVs and µBumps⁸⁶. The increased resistance caused by these voids hinders the effective heat conduction through TSVs and µBumps over extended periods of operation^86,87. Such risk of void formation can be mitigated by ensuring a uniform temperature distribution across the stack, which in turn helps to minimize the potential for electromigration⁷⁰.

Thermal cycling further impedes effective heat dissipation through TSVs, primarily due to the mismatch in the CTEs between copper ( ~ 17.5 × 10⁻⁶ °C⁻¹) and silicon/dielectric ( ~ 0.5×10⁻⁶°C⁻¹)^88,89. This mismatch causes stress concentrations at TSV sidewalls that can exceed 1 GPa, resulting in interfacial delamination and microcracks in adjacent dielectric layers and TSVs, which disrupt established heat transfer pathways (Fig. 7)^88,90,91. These issues can be alleviated by selecting metal fillers with lower thermal expansion coefficients and by controlling the grain size at TSV boundaries^88,89. Additionally, introducing a buffer layer such as polymer-based liners between TSVs and the surrounding silicon can mitigate interfacial stress and improve the overall thermo-mechanical reliability of ICs⁹². Although grain size control during TSV filling and the introduction of buffer layers can improve thermo-mechanical reliability, implementing these strategies at the microscale level remains a manufacturing challenge. Consequently, there is growing interest in exploring alternative via-fill materials, such as carbon nanotubes and graphene-copper composites, which offer superior thermal conductivity and may help mitigate CTE mismatches more effectively than conventional copper⁹³.

Fig. 7.

Interfacial and cohesive cracks under Cu pad, on the TSV side wall and Cu/SiO₂ interface (This figure has been adapted from Ref. ⁹¹. with permission from Elsevier Publications, Copyright 2013).

Degradation of thermal interface materials

Thermal interface materials (TIMs) are critical for reducing thermal resistance at microscopically rough interfaces between heat-generating components (i.e., logic tiers, memory arrays, etc.) and heat-dissipation systems (i.e., heat spreaders and heat sinks)⁶⁵. For example, a reduction in contact thermal resistance by using epoxy-embedded silver nanowires as a TIM reduced the CPU operating temperature from 86.2 °C to 64.6 °C⁹⁴. Although TIMs play an essential role in facilitating heat transfer across contacting surfaces, they suffer from several limitations, including low thermal conductivity, degradation under thermal cycling, and the tendency to form interfacial voids, leading to high bulk thermal resistance.

Height mismatches and surface irregularities create additional contact thermal resistance and hinder proper interface conformity.⁵¹ Soft TIMs are often used to establish reliable contact and reduce interfacial air gaps; however, their naturally low thermal conductivity limits heat transport. Conversely, TIMs with high thermal conductivity, such as metallic fillers, are mechanically stiff, making them less adaptable to surface variations and more likely to form air gaps.^94,95 This trade-off requires TIMs to balance two conflicting needs: (a) minimizing interfacial resistance and (b) adapting to surface and height variations to prevent trapped voids. Unfortunately, materials with high thermal conductivity (e.g., metals) tend to be rigid, while softer materials (e.g., thermal pastes) do not have enough thermal transport capability.

In order to bridge this gap, hybrid TIMs have been developed to combine thermal efficiency with mechanical compliance (Fig. 8a). These include polymer matrices embedded with nanostructured fillers such as nanoplatelets, nanotubes, nanowires, etc., which significantly enhance the effective thermal conductivity⁶⁵. For example, epoxy infused with 25 vol.% graphite nanoplatelets achieves a thermal conductivity of 6.44 Wm⁻¹K⁻¹, representing a 3000% improvement compared to that of the base polymer⁹⁶. Similarly, silver nanowires embedded in polycarbonate exhibit an effective conductivity of 30.3 Wm⁻¹K⁻¹, markedly reducing conduction resistance⁹⁷. A summary of other comparable advancements in TIMs is provided in Table S1.

Fig. 8. Design, degradation, and performance factors influencing interfacial thermal resistance.

a Common strategies for designing thermally conductive and mechanically flexible TIMs suitable for microelectronic devices⁹⁵, (b) TIM degradation with (c) resulting increase in the thermal resistance with time¹⁰¹, and (d) impact of clamping pressure on the interface thermal resistance⁹⁹. (a−d) have been adapted from refs. ^95,99,101. with permission from ACS and Elsevier Publications, Copyrights 2017, 2013, and 2024, respectively).

Nonetheless, hybrid TIMs may also face issues with surface conformity. Their increased stiffness may promote void formation at the interface. One promising approach to resolving this issue involves integrating low-melting-point metals into high-temperature polymer matrices. These composites improve conformity to heterogeneous circuit topographies while maintaining thermal performance. For example, encapsulating low-melting-point metals such as indium (k∼70 W.m⁻¹K⁻¹) within thin polymer layers offers a compelling combination of thermal performance and mechanical compliance⁹⁸. This approach not only reduces the risk of intermetallic compound formation but also enhances reworkability, making it well-suited for advanced electronic packaging applications.

Despite these advances, TIMs still encounter persistent reliability issues in 3-DHI microelectronics. Repeated thermal cycling can accelerate oxidation⁹⁹, leading to an increase in the bulk thermal resistance. The coefficient of thermal expansion (CTE) mismatch further induces interfacial stresses that promote delamination and void formation, which disrupt heat transfer due to increased thermal resistance (Figs. 8b and 8c)^100,101. High clamping pressure is sometimes applied to minimize voids, improve conformity at the contact surfaces, and reduce the thickness of the TIM, thereby reducing the overall thermal resistance⁹⁹. For example, raising the clamping pressure from 0.1 MPa to 1.2 MPa decreases thermal resistance by ~20% (Fig. 8d)⁹⁹. However, fragile 3-DHI components cannot withstand excessive pressure, making this approach impractical. Long-term stability is further challenged by environmental factors such as humidity, which exacerbate corrosion, fouling, and interfacial reactions, leading to cracks and voids¹⁰². Addressing these interdependent thermal, mechanical, and environmental degradation mechanisms is critical for ensuring the reliable performance of TIMs in next-generation 3-DHI microelectronics.

Issues with interlayer micro heat spreaders

Interlayer micro heat spreaders are critical for the efficient thermal management of 3-DHI microelectronics. As device density and power dissipation increase in vertically stacked architectures, localized hotspots and elevated junction temperatures become key reliability and performance bottlenecks. By being positioned between adjacent functional blocks or dies, interlayer heat spreaders laterally redistribute heat from functional blocks and hotspots. They also direct heat toward the TSVs, thereby improving temperature uniformity across the stack.

The ideal interlayer material must simultaneously satisfy multiple requirements: (i) high thermal conductivity to enhance heat spreading, (ii) high electrical resistivity to avoid signal crosstalk, (iii) a low dielectric constant to ensure energy-efficient, high-speed signal transmission with minimal noise, and (iv) a CTE closely matched to that of neighboring functional blocks to prevent thermal expansion mismatch.

In conventional electronics, silicon dioxide (SiO₂) is commonly employed as a dielectric due to its balanced thermo-electric properties. However, its inherently low thermal conductivity restricts its effectiveness for heat dissipation in high-power 3-DHI devices. To overcome this limitation, materials such as AlN and hBN have been investigated because of their superior thermal transport characteristics¹⁶. A summary of the thermo-electric properties of these interlayer materials with their relevant properties is provided in Table 1.

Table 1.

Key considerable properties of widely used interlayer materials

	Plane type	Thermal Conductivity (Wm−1K−1)	Electrical Resistivity (Ω.cm)	Coefficient of Thermal Expansion (°C−1)	Dielectric Constant	References
SiO2	-	1.1–1.4	$3.2\times {10}^{15}\mathrm{to}1\times {10}^{18}$	$0.5\times {10}^{-6}\mathrm{to}0.64\times {10}^{-6}$	3.7–4.7	(Bartzsch et al., Institute of Microelectronics, Krosaki Harima, MEMSnet)121–124
AlN	In-plane	∼260 ± 40	$1\times {10}^{11}\mathrm{to}1\times {10}^{15}$	$2.56\times {10}^{-6}\mathrm{to}4.3\times {10}^{-6}$	8.5–8.8	(Hoque et al., Khor et al., Krosaki Harima, Morkoç, Pinto et al.)123,125–128
	Cross-plane	∼260 ± 40	-	-	-	Hoque et al125.
hBN	In-plane	~600	$1\times {10}^{13}\mathrm{to}1\times {10}^{15}$	$-2.57\times {10}^{-6}\mathrm{to}-2.83\times {10}^{-6}$	6.82–6.93	(Laturia et al., Liu et al., Steinborn et al., Yates et al., Yuan et al.)129–134
	Cross-plane	2.0–30	-	$35.6\times {10}^{-6}\mathrm{to}40\times {10}^{-6}$	3.29–3.76	(Laturia et al., Yates et al., Yuan et al.)129,130,134

Aluminum nitride offers high thermal conductivity, making it a promising heat spreader material. Nevertheless, its relatively low electrical resistivity and high dielectric constant can negatively affect signal crosstalk and speed. In contrast, hBN provides a unique thermal transport mechanism through volume-confined hyperbolic phonon polariton modes¹⁰³. Unlike conventional phonon-mediated conduction, hyperbolic phonon polariton modes enable ultrafast, radiative energy transfer across solid–solid interfaces, with experimentally measured interfacial thermal boundary conductances exceeding 500 MW·m⁻²·K⁻¹—nearly an order of magnitude higher than traditional phonon-phonon mechanisms¹⁰³. Such radiative coupling presents an exciting opportunity for rapidly dissipating localized heat in high-power 3-DHI microelectronics¹⁰³.

Despite these advantages, the widespread use of hBN is limited by its intrinsic anisotropy. hBN exhibits exceptionally high in-plane thermal conductivity ( ~ 600 W·m⁻¹·K⁻¹) but significantly lower cross-plane values (~2–30 W·m⁻¹·K⁻¹) (Table 1). While this anisotropy reduces thermal crosstalk—beneficial for 3-DHI applications—it can also lead to heat accumulation within the interlayer, causing hotspot formation. Additionally, the mismatch in CTE between hBN and silicon-based dies is problematic: hBN has a negative in-plane CTE and a positive cross-plane CTE, both of which deviate substantially from that of silicon. This contrast may cause cracking in the interlayer or adjacent dies, thereby worsening interfacial thermal resistance.

A further challenge lies in the fabrication of high-performance interlayer heat spreaders. Deposition typically requires high processing temperatures (often >1000 °C), which is incompatible with back-end-of-line (BEOL) integration and potentially damages to underlying circuitry¹⁶. To address this, low-temperature deposition methods for thin films (100 nm–1.7 μm) at temperatures below 100 °C have recently been developed, making them compatible with BEOL processes¹⁶. While such sputtering techniques enable integration without compromising delicate electronic structures, they can result in higher defect densities and reduced crystallinity, thereby lowering thermal performance and raising concerns about thermo-mechanical reliability¹⁶.

Finally, the rigid integration of micro heat spreaders within 3-DHI stacks exacerbates stresses during thermal cycling or under moisture exposure. CTE mismatches between the heat spreader and surrounding materials can cause delamination, cracking, or warpage^39,40 (a detailed discussion of these issues is provided in Section ‘Heterogeneous material properties’). Consequently, the long-term reliability of these systems remains an open challenge. Therefore, continued research into the development of micro heat spreader materials is essential, with particular focus on thermal conductivity and the coefficient of thermal expansion mismatch with neighboring dies, to ensure both thermal efficiency and mechanical reliability in integrated systems.

Challenges with embedded microfluidic heat sinks

While a range of cooling techniques (i.e., spray cooling, jet impingement, heat pipes, thermoelectric cooling, etc.) have been explored for microelectronics, these methods typically operate at the system level and often involve external thermal management structures. The integration of such conventional heat sinks introduces the physical separation between the chip and the cooling solution, which is often filled with TIMs. However, the inherently low thermal conductivity of TIMs, along with the risks of void formation and delamination, poses a challenge to managing the heat loads in high-performance computing systems¹⁰⁴. Various strategies to enhance the thermal performance of TIMs have been discussed previously (see section “Degradation of thermal interface materials”). While advancements in fabrication techniques can help lower the interfacial thermal resistance, it remains difficult to eliminate thermal resistance arising from micro-voids, surface imperfections, and time-dependent material degradation that inevitably occur at the contact surfaces in practical applications¹⁰⁵. To address these limitations, placing cooling solutions in closer proximity to the primary heat-generating dies can substantially enhance heat removal efficiency.

Embedded thermal management systems, such as microchannel cooling¹⁰⁶, are incorporated directly with or between active tiers (Fig. 9a) while eliminating TIMs insertion. To further enhance the heat dissipation rate through increased effective heat exchange surface, microchannel heat sinks incorporating monolithically integrated micro pin-fin structures have also been employed¹⁰⁷. Additionally, co-designed configurations employing optimized microstructure geometries and manifold layouts have reported exceptional thermal performance with very low thermal resistances (0.074 °C.W⁻¹), which also require minimal pumping power¹⁰⁸. For example, a state-of-the-art co-design has enabled the extraction of heat fluxes over 1700 W cm⁻² using just 0.57 W cm⁻² of pumping power, resulting in a coefficient of performance exceeding 10,000 for single-phase water cooling—approximately 50 times higher than that of conventional straight microchannel designs¹⁰⁹. Recent developments in embedded microfluidic cooling solutions and the associated issues are presented in Table S2.

Fig. 9. Mitigation of hotspots in 3-DHI microelectronics using embedded microfluidic cooling systems.

a Embedded microfluidic cooling of 3-DHI microelectronics with (b) gradient distributed micro pin-fin arrays for (c–e) hotspot mitigation, and (f) tier-specific thermal management. The legend in (c) corresponds to the data in (d, e). (b–e) have been adapted from ref. ¹²⁵ with permission from Elsevier Publications, Copyright 2016).

Hotspot-driven device failure was also addressed by novel embedded microfluidic cooling, which utilized gradient distribution micro pin-fin arrays within the chip substrate (Fig. 9b–e)^110,111. The study conducted by Fend et al.¹¹⁰ systematically investigated the effects of key design parameters, such as pin-fin diameter and array porosity, on the thermal performance of the cooling system. The gradient distribution micro pin-fin arrays design not only achieves lower overall thermal resistance but also significantly enhances temperature uniformity across the chip surface compared to conventional uniform micro pin fin arrays, effectively eliminating large temperature differences in hotspots¹¹¹. Optimal ranges for pin-fin diameter (100–200 μm) and porosity (0.65–0.85) are recommended to balance thermal resistance and pumping power for the design of next-generation embedded microfluidic cooling solutions¹¹⁰.

Although the temperature uniformity is maintained in a particular tier of the 3-DHI stack through gradient distribution micro pin-fin arrays, temperature nonuniformity may exist among neighboring vertical tiers. Practical approaches may be needed for addressing such challenges by optimizing the flow path. To maintain a uniform temperature in nearby tiers, tier-specific microfluidic architectures—where each layer holds an independently controlled coolant path—have shown promise in maintaining the thermal uniformity throughout the stack while mitigating overcooling of low-power layers, and ensuring targeted thermal regulation of power-dense regions (Fig. 9f)^112,113. This architecture enables precise thermal management intended for the distinct power profiles of each tier, effectively maintaining the safe operating temperatures of each tier, reducing thermomechanical stress, and preventing unnecessary overcooling. By regulating the coolant flow independently for each layer, the required pumping power can be reduced by up to 37.5% compared to applying a uniform flow rate throughout the stack, providing a more energy-efficient and adaptable cooling solution for next-generation high-performance heterogeneous 3-D integrated circuits¹¹². Moreover, such a cooling strategy to high-power tiers helps protect thermally sensitive layers, i.e., memory modules, photonic devices, sensors, etc. from thermal crosstalk^114,115.

Despite the evident advantages of embedded microfluidic cooling in 3-DHI systems, the practical deployment of these technologies remains constrained due to several critical issues. Foremost among these is the mechanical reliability of cooling structures subjected to elevated operational pressures. Peripheral epoxy bonding, which is frequently employed for the integration of micro-pin-fin structures, has demonstrated failure at pressures around 700 kPa, while anodic bonding provides only modest improvements, withstanding up to approximately 800 kPa¹⁰⁶. Although numerical simulations suggest that pressures nearing 1500 kPa may be tolerable with optimized bonding strategies¹⁰⁶, such mechanical integrity under cyclic thermal and fluidic stresses has yet to be experimentally validated.

Embedded microfluidic cooling in 3-DHI systems also introduces additional design and fabrication complexities. Sometimes, structural modifications necessary to incorporate fluidic channels can lead to increased mechanical stresses, which in turn affect TSV reliability and may cause chip deformation and capacitive delays. Hence, optimizing electrical and thermal performance through co-design remains a persistent challenge. In response, researchers have developed TSV-compatible microfluidic cooling systems for efficient thermal management without sacrificing interconnect density or electrical performance^116–118. One study demonstrated the successful integration of high-aspect-ratio (29:1) with small-diameter (5.2 µm) copper TSVs with micropin-fin heat sinks, which led to both effective electrical connection and high heat removal capacity¹¹⁸. Experimental and numerical analyses revealed that this design maintained average chip temperatures below 72 °C at a power density of 312 W cm⁻², with a minimum total thermal resistance of 0.286 °C cm² W⁻¹ at a flow rate of 117 mL min⁻¹¹¹⁸. Additionally, the optimized configuration supported a TSV density of 9025 mm⁻² and achieved a notable reduction in oxide capacitance, hence enabling low-latency, high-bandwidth interconnects along with robust thermal performance¹¹⁸.

From the manufacturing point of view, the integration of embedded microfluidics requires substantial deviations from standard semiconductor process flows. Essential steps such as wafer thinning, precision etching, and advanced bonding, which are crucial for microchannel fabrication, can adversely affect device yield and reworkability. Compatibility with BEOL processes further complicates the scenario, as embedded cooling structures must coexist with dense electrical interconnects and TSVs without compromising electrical performance¹⁶.

Prolonged direct exposure of cooling fluids to semiconductor chips can lead to moisture ingress within the packaging materials and silicon structures. This absorbed moisture expands when subjected to elevated temperatures inside the encapsulated die, a phenomenon commonly known as the popcorning effect¹¹⁹. The resulting internal pressure induces mechanical stresses that can cause delamination, and in severe cases, lead to package cracking¹²⁰. Despite the effectiveness of direct liquid cooling in dissipating heat, it may promote moisture ingress issues if the system design and material selection are inadequate. Therefore, further investigation is required to develop robust packaging solutions that ensure the long-term reliability of advanced microelectronic devices under direct liquid cooling.

Despite significant progress, several critical challenges associated with direct contact liquid cooling remain unresolved and call for further exploration. The long-term mechanical and thermal reliability of flexible interconnects and isolation layers under cyclic operational stresses is not yet fully understood. Key technical hurdles—including the complex fabrication of high-aspect-ratio TSVs, reliable wafer bonding, and ensuring long-term operational stability and leak prevention—continue to require focused development. Moreover, the co-design of electrical and fluidic interconnects in densely integrated 3-DHI microelectronic systems remains an important research direction.

Conclusions and perspectives for future research

Conclusions

The compact vertical stacking of next-generation 3-DHI microelectronics introduces high operational temperatures, which threaten system reliability and performance by introducing thermal and signal crosstalk, and thermo-mechanical-driven mechanical and electrical failures. To ensure stable and long-term device operation, robust thermal management strategies are indispensable. However, effective heat dissipation in such architectures remains challenging due to two primary constraints: (a) architectural and material complexity of the package and (b) limitations in the performance and integration of existing cooling solutions. Material heterogeneity within 3-DHI packages intensifies non-uniform heat generation and hotspot formation, as the varying thermal conductivities of diverse integrated components limit heat spreading. This intrinsic package heterogeneity not only contributes to greater heat buildup but also poses considerable challenges for effectively dissipating the accumulated thermal energy.

Mismatched coefficients of thermal expansion of neighboring components in the package further disrupt the existing heat transfer pathways, as repeated thermal cycling may induce thermo-mechanical stresses that lead to package delamination. Placement of TSVs, which serve as critical vertical heat conduits, often remains suboptimal, further restricting efficient thermal transport. While TSVs effectively transport heat from interior tiers to external heat sinks, their heat transfer efficiency is also limited by fabrication defects, alignment inaccuracies, and degradation under operational stresses, which elevate thermal resistance and compromise long-term performance.

Emerging solutions—such as high-conductivity interlayer heat spreaders, optimizing CTE of components at shared boundaries, advanced TIMs, thermal-aware TSV designs, and embedded microfluidic cooling—demonstrate the potential to address these thermal bottlenecks. Nevertheless, their widespread adoption is hindered by suboptimal design, high interfacial thermal resistance, integration complexity, manufacturing challenges, and uncertainties regarding durability over extended operational lifetimes. Overcoming these barriers requires an integrated research focus on material innovation for TIMs and micro heat spreaders, optimizing package architecture, insertion of thermal TSVs, co-optimized thermal-electrical design, and scalable fabrication techniques.

Perspectives for future research

To fully utilize the capabilities of next-generation 3-DHI microelectronics, it is essential to maintain the package operating temperature below safe limits through robust and efficient thermal management methods. Achieving this goal requires coordinated research in thermal design, material innovation, seamless process integration, and holistic system-level optimization. Based on our literature survey, key directions for future research are provided below.

Future research should prioritize scalable thermal management solutions that can adapt to increasing integration density and diverse functional block architectures in 3-DHI. Co-optimization of electrical, thermal, and mechanical design must be incorporated to balance TSV placement, signal integrity, and effective heat conduction. Hybrid approaches—such as combining dedicated thermal TSVs with electrical interconnects and leveraging embedded microfluidic networks tailored for tier-specific cooling demands—are vital. Thermal-aware floorplanning, advanced co-design algorithms, and real-time thermal monitoring should be further refined to support reliable large-scale integration without compromising computational performance.

The integration of advanced cooling methods into manufacturable products demands careful attention to process compatibility and cost-effectiveness. Low-temperature deposition methods for high-conductivity materials for heat spreaders, void-free TSV filling techniques, robust wafer bonding, and stress-tolerant interlayer structures must be systematically developed and standardized. Additionally, novel TIMs that combine high thermal conductivity with mechanical flexibility and long-term stability should be investigated. Collaborative efforts between materials scientists, thermal engineers, and packaging specialists are essential to ensure that innovative cooling technologies remain compatible with existing BEOL and packaging workflows.

Interlayer heat spreaders should prioritize the development of materials and fabrication strategies that simultaneously deliver high thermal conductivity, low dielectric constant, and mechanical compatibility with silicon-based dies. Hybrid or composite structures that integrate hBN with high cross-plane conductive fillers, or layered heterostructures combining AlN with other wide-bandgap ceramics, may help mitigate the challenges of anisotropy and CTE mismatch. The search for such advanced materials, such as isotopically engineered crystals, continues to be an active area of research to further enhance interlayer heat spreading. Low-temperature deposition techniques, such as atomic layer deposition, at reduced temperatures, and advanced sputtering methods, warrant further exploration to achieve BEOL-compatible integration without compromising crystallinity and thermal performance. Additionally, scalable nanomanufacturing approaches for defect-free large-area films and engineered interfaces could enhance interfacial thermal boundary conductance. Reliability studies under cyclic thermal and humidity stress are equally important to establish long-term stability. Collectively, these research directions can advance interlayer heat spreading technologies toward practical deployment in high-power 3-DHI microelectronics.

Emerging cooling strategies, including near-junction microfluidic cooling and micro-jet impingement cooling, need continued investigation. Exploring energy-efficient multi-phase flow cooling within stacked tiers could significantly advance thermal regulation capabilities with a focus on minimizing the interfacial resistance. Furthermore, robust system-level validation under realistic thermal loads and cyclic conditions is needed to establish the long-term reliability of these techniques.

Author contributions

Manoj Kumar Sharma: Conceptualization, literature analysis, visualization, writing—original draft. Bladimir Ramos-Alvarado: Supervision, resources, funding acquisition, writing—review and editing.

Peer review

Peer review information

Communications Engineering thanks Yuxin Ye and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editors: [SungHoon Hur] and [Philip Coatsworth]. A peer review file is available.

Data availability

No datasets were generated or analyzed during the current study.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s44172-026-00590-y.