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Electronic system layouts have increasingly become smaller and more compact. To address the growing demand for performance, dynamic thermal management with thermal energy storage has emerged as an attractive solution. Phase change materials (PCM) can store and release large amounts of heat through melting or solidification. However, they are limited by their thermal conductivity, which is several orders of magnitude lower than traditional heat sinks. To address this design weakness, we have developed a novel composite consisting of vertically aligned carbon nanotube arrays infiltrated with PCM to deliver a high thermal conductivity storage medium that also maintains the high latent heat capacity of the native PCM. This study numerically and experimentally investigates the design of an encapsulated CNT-PCM composite and its impact on the temperature rise and peak temperature of an electronic device. Different form factors have been experimentally tested. The composite's impact on a heating element is measured experimentally, and a numerical model is developed and verified using the experimental results. Additional models are designed to evaluate the effect of composite thickness on thermal response. 

Abstract This work reports important fundamental advancements in multiwall carbon nanotube (MWCNT) rectenna devices by creating and optimizing new diode structures to allow optical rectification with air‐stable devices. The incorporation of double‐insulator layer tunnel diodes, fabricated for the first time on MWCNT arrays, enables the use of air‐stable top metals (Al and Ag) with excellent asymmetry for rectification applications. Asymmetry is increased by as much as 10 times, demonstrating the effectiveness of incorporating multiple dielectric layers to control electron tunneling in MWCNT diode structures. MWCNT tip opening also reduces device resistance up to 75% due to an increase in diode contact area to MWCNT inner walls. This effect is consistent for different oxide materials and thicknesses. A number of insulator layers, including Al₂O₃, HfO₂, TiO₂, ZnO, and ZrO₂, in both single‐ and then double‐insulator configurations are tested. Resistance increases exponentially with insulator thickness and decreases with electron affinity. These results are used to characterize double‐insulator diode performance. Finally, for the most asymmetric device structure, Al₂O₃‐HfO₂(4/4 nm), optical rectification at a frequency of 470 THz (638 nm) is demonstrated. These results open the door for designing efficient MWCNT rectenna devices with more material flexibility, including air‐stable, transparent, and conductive top electrode materials.