Thermal management of chips by a device prototype using synergistic effects of 3-D heat-conductive network and electrocaloric refrigeration

Modern microelectronics such as 5G chips exhibit high power density and heat generation, making efficient thermal management critical. Conventional passive cooling (air/liquid forced convection to heat sinks/cold plates) suffers from multilayer thermal resistances and limited performance at low temperature differentials, even with thermal interface materials or microfluidic heat pumping. Electrocaloric (EC) cooling offers active, solid-state, environmentally benign refrigeration by exploiting reversible dipolar entropy changes under applied electric fields. Polymeric ferroelectrics are attractive for EC cooling due to flexibility and scalable fabrication, but their inherently low thermal conductivity and interfacial resistances limit heat penetration and high-frequency operation, leading to reduced cooling performance at higher switching frequencies. This work demonstrates a practical approach that combines a relaxor-type ferroelectric polymer with a continuous 3-D ferroelectric ceramic thermal-conductivity network to synergistically enhance EC performance at low fields and enable rapid heat transport, targeting precise fixed-point cooling for next-generation chips.

The study situates itself amid efforts to improve thermal management for high-power microelectronics. Conventional approaches (forced air/liquid cooling to external sinks) face interfacial thermal resistances and require auxiliary cooling for low temperature differentials. Directed liquid microfluidic heat pumps improve efficiency but still contend with layered thermal paths. Electrocaloric refrigeration has emerged as an efficient, solid-state, zero-GWP alternative. Polymeric ferroelectrics have shown promising EC performance and manufacturability, yet their low thermal conductivity—stemming from chain conformation and amorphous entanglement—hampers rapid heat transfer, especially at elevated operation frequencies where earlier reports observed declining cooling performance. Building continuous 3-D thermal networks in polymers is known to boost passive thermal transport; however, integrating such networks to simultaneously enhance EC effects under low fields and improve heat extraction in EC cycles has received limited attention.

Materials and composite design: A 3-3 polymer/ceramic composite (3-3 PCC) was fabricated by integrating a continuous 3-D Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic network into a relaxor-type ferroelectric terpolymer matrix, P(VDF-TrFE-CFE). The 3-D ceramic network serves as both a polar nucleation scaffold and a high-thermal-conductivity pathway. The network continuity was confirmed by cross-sectional SEM elemental mapping. Polymer film preparation: P(VDF-TrFE-CFE) (62.1/30.1/7.8 mol%) was dissolved in DMF (4 wt%) and stirred 12 h. Solutions were cast onto glass and dried at 60 °C for 24 h to remove solvent, then annealed under vacuum at 106 °C for 10 h. Final film thickness was 15–20 µm. 3-D ceramic network fabrication: A BCZT sol was prepared by mixing ethanol, acetylacetone, and glacial acetic acid as co-solvent, then dissolving tetrabutyl titanate, barium hydroxide, calcium hydroxide, and zirconium acetylacetonate. Polyurethane foam templates were immersed in the sol for 10 min, excess sol squeezed out, dried at 55 °C, and calcined at 1200 °C for 2 h to obtain the free-standing 3-D BCZT network. Characterization and measurements: EC properties (isothermal entropy change ΔS, adiabatic temperature change ΔT, and isothermal cooling energy density Q) were measured using an in situ calibrated setup. Polarization–electric field (P–E) loops were recorded to assess polarization (Pmax). Temperature-dependent dielectric permittivity and loss were measured to identify relaxor behavior and polar nano-regions. In situ XRD under increasing electric fields monitored phase evolution between nonpolar and polar phases and quantified polar phase volume fraction. Thermal transport behavior was investigated using finite element simulations comparing discontinuous fillers vs continuous 3-D networks. Passive heat transfer experiments monitored temperature evolution using an IR imager for samples transferred between hot and cold plates; heating/cooling rates were derived from first-order time derivatives. Through-thickness thermal conductivity was measured by flash DSC. Device prototype and performance testing: An EC cooling device was built with electromagnet actuation to shuttle an EC stack between a heat sink and a heat source within a 3-D printed frame, minimizing interference between drive and cooling modules. Control relays (R1, R2) sequenced mechanical contact and field application (with a 0.1 s delay for R2 to ensure contact before field application/removal). Heat fluxes at the heating and cooling sides were measured with a heat flux sensor at varying electric fields and operating frequencies. A CPU-like heating plate simulated a chip; surface temperatures were measured by IR thermography to evaluate cooling under practical conditions (supply voltage U1 = 12 V, actuation at 1 Hz, field E ≈ 30 MV m−2).

- Integration of a continuous 3-D BCZT ceramic network into P(VDF-TrFE-CFE) produced an interpenetrating 3-3 PCC with enhanced electrocaloric response and thermal conductivity while maintaining flexibility for good chip contact. - Electrocaloric performance at low fields was significantly enhanced: at 60 MV m−1, Q reached 14.72 MJ m−3 with electrocaloric strength Q/ΔE = 245.3 kJ m−2 MV−1; ΔS = 26.76 J kg−1 K−1; ΔT = 5.94 K; ΔS/ΔE = 446 J mm−1 kg−1 K−1 MV−1; ΔT/ΔE = 99 K mm MV−1. Overall EC performance was increased by about 240% relative to the neat polymer at the same field. - Polarization enhancement: Pmax of the 3-3 PCC was 6.08 µC cm−2 at 60 MV m−1, approximately twice that of the neat polymer, consistent with ΔS ∝ P2 scaling. - Field-induced phase evolution: In situ XRD showed polar phase volume fraction in the composite increased from ~32% at zero field to ~43% at 40 MV m−1, whereas the neat polymer reached only ~3.5% increase under similar conditions, evidencing facilitated nucleation and growth of polar domains. - Thermal transport improvement: Through-thickness thermal conductivity increased from 0.21 W m−1 K−1 (neat polymer) to 0.84 W m−1 K−1 (3-3 PCC), a 300% enhancement. Passive heating/cooling experiments showed faster thermal response: average heating was 11.9 s faster and cooling 16.1 s faster than the neat polymer, with larger initial temperature time-derivatives (rates). - Device-level performance at low fields compatible with chip voltages: With E ≈ 30 MV m−2 (supply U1 = 12 V) at 0.1 Hz, maximum heat fluxes were 288 W m−2 (heating) and −272 W m−2 (cooling). Average cooling heat flux reached −213 W m−2 at 1 Hz and −236 W m−2 at 1.25 Hz; an ideal temperature span of ~1.1 K was observed at 1 Hz and 30 MV m−2. - Chip cooling demonstration: On a heated CPU surrogate, activating the EC cooler (U1 = 12 V at 1 Hz, E = 30 MV m−2) reduced surface temperature from 71.4 °C to 63.0 °C, moving the operating point away from the high-risk failure range (70–80 °C).

The study demonstrates that embedding a continuous 3-D ferroelectric ceramic network within a relaxor polymer simultaneously addresses two key barriers to polymer-based EC cooling: low thermal conductivity and the need for high electric fields. The 3-D network acts as polar nucleation centers that pre-form polar nanodomains, lowering the energy barrier for domain growth and boosting polarization under low fields, thereby enhancing dipolar entropy modulation and EC strength. Concurrently, the percolated ceramic provides high-speed phonon pathways that rapidly evacuate heat from localized hot spots during field application and deliver cooling during field removal, improving thermal penetration and enabling higher operational frequencies. This synergy allows effective heat pumping at electric fields compatible with typical semiconductor supply voltages, enabling precise, localized, and scalable chip cooling. The findings directly address the challenge of efficient fixed-point thermal management in high-power 5G electronics.

In summary, integrating a 3-D lead-free ferroelectric ceramic interpenetrating network into a relaxor-type ferroelectric polymer substantially enhances both electrocaloric performance (≈240% increase) and thermal conductivity (≈300% increase). The network increases polar nanodomains and interfacial areas, augments manipulable entropy at low fields, and provides fast thermal pathways for rapid heat/cold transfer. A scaled-up, electromagnet-driven EC device prototype achieved significant heat fluxes at low fields and successfully cooled a heated chip surrogate from 71.4 °C to 63.0 °C under a 12 V supply, demonstrating feasibility for precise fixed-point thermal management in next-generation microelectronics.