Thermal Reliability and Electrical Properties of Integrated Copper Inverse Opal Structures

Abstract

Templating with self‐assembled colloidal crystals has enabled fabrication of porous materials with potential for sensing, heat transfer, and energy storage applications. Herein, electrical, thermal, and mechanical properties of templated electroplated metallic copper inverse opals (CIO) containing close‐packed 500 nm pores are evaluated via a four‐point probe, eddy current, lap shear measurements, thermal cycling, and finite‐element analysis (FEA). CIOs are found to have an electrical conductivity of ≈4 × 106 S m−1, about 15% of pure copper, about the expected value based on the measured electroplated copper conductivity and the CIO pore structure. The good electrical and thermal properties of this structure, coupled with its connected porosity, make it attractive for two‐phase cooling applications. However, the thermal reliability of this structure raises questions about its integrity. It is found that this structure fails around 150 cycles when cycled between −40 and 200 °C at 10 °C min−1. Scanning electron micrograph (SEM) images of failed samples show that the failure plane lies within the CIO and generally at the thinnest interconnects in the structure, which agrees with FEA of the CIO structure, which shows stress concentrations at thin regions of the interconnects in the structure.

Achieving Functionality and Multifunctionality through Bulk and Interfacial Structuring of Colloidal-Crystal-Templated Materials

“…Although 3DOM metals have also been successfully used as current collectors together with other active materials (e.g., Si), it should be noted that the conductivity of a 3DOM metal is lower than that of corresponding bulk metals, as a result of reduced dimensions and grain boundaries between nanoparticles that compose the walls. For example, the conductivity of 3DOM copper is between 5% and 15% of the value for bulk copper . Similar conductivity behavior was also observed in colloid-imprinted mesoporous carbon where thinner walls resulted in increased electronic resistance .…”

“…For example, the conductivity of 3DOM copper is between 5% and 15% of the value for bulk copper. 67 Similar conductivity behavior was also observed in colloid-imprinted mesoporous carbon where thinner walls resulted in increased electronic resistance. 68 Thermal conductivity of 3DOM copper is also reduced significantly, especially with smaller pore sizes, as a result of increased surface scattering as the conduction length scales become comparable to the bulk mean free path of electrons (∼tens of nm in metals).…”

“…When a 3DOM material is supported on a substrate, mismatch of thermal expansion coefficients can result in thermal stresses that lead to failure. For example, thermal cycling (−40 to 200 °C) or thermal shocks (250 to −78 °C) cause delamination and structural failure of 3DOM copper layers that are supported on silicon substrates . The failure planes are located within the 3DOM skeleton at the narrowest struts where stresses are highly concentrated.…”

“…For example, thermal cycling (−40 to 200 °C) or thermal shocks (250 to −78 °C) cause delamination and structural failure of 3DOM copper layers that are supported on silicon substrates. 67 The failure planes are located within the 3DOM skeleton at the narrowest struts where stresses are highly concentrated. While this behavior becomes a limitation in applications in which the operating temperature fluctuates over wide ranges, such as microfluidic heat exchangers, 144 it has been used to advantage in the preparation of uniform, shaped nanoparticles.…”

Shape Control of Metal Nanostructures by Electrodeposition and their Applications in Electrocatalysis

“…87 Polystyrene particles for inverse opal structures.-Another template-assisted 3D fabrication method is based on the use of spherical monodisperse polystyrene (PS) particles. [88][89][90][91][92][93][94][95][96][97][98] The procedure for assembling metal inverse opal (IO) structures is depicted in Fig. 5a.…”