Mechanically strengthened graphene-Cu composite with reduced thermal expansion towards interconnect applications

Abstract

High-density integration technologies with copper (Cu) through-silicon via (TSV) have emerged as viable alternatives for achieving the requisite integration densities for the portable electronics and micro-electro-mechanical systems (MEMSs) package. However, significant thermo-mechanical stresses can be introduced in integrated structures during the manufacturing process due to mismatches of thermal expansion and the mechanical properties between Cu and silicon (Si). The high-density integration demands an interconnection material with a strong mechanical strength and small thermal expansion mismatch. In this study, a novel electroplating method is developed for the synthesis of a graphene-copper (G-Cu) composite with electrochemically exfoliated graphenes. The fabrication and evaluation of the G-Cu composite microstructures, including the microcantilevers and micromirrors supported by the composite, are reported. We evaluated not only the micromechanical properties of the G-Cu composite based on in-situ mechanical resonant frequency measurements using a laser Doppler vibrometer but also the coefficients of thermal expansion (CTE) of the composite based on curvature radius measurements at a temperature range of 20–200 °C. The Young’s modulus and shear modulus of the composite are approximately 123 and 51 GPa, which are 1.25 times greater and 1.22 times greater, respectively, than those of pure Cu due to the reinforcement of graphene. The G-Cu composite exhibits a 23% lower CTE than Cu without sacrificing electrical conductivity. These results show that the mechanically strengthened G-Cu composite with reduced thermal expansion is an ideal and reliable interconnection material instead of Cu for complex integration structures.

Stability Assessment of p-i-n Perovskite Photovoltaic Mini-Modules Utilizing Different Top Metal Electrodes

“…The formation of these conductive particles can be avoided by using an extra layer (30 nm) of gold (Au) over the copper (Cu) (70 nm) metal electrode (Cu/Au) [ 21 ]. Gold has the capability to bind strongly to the bottom layer and thus protects the Cu layer from forming the flakes, due to its high degree of thermal expansion [ 26 , 27 ]. EDX images of P3 scribing of both Cu- and Cu/Au-based PSMs are shown in Figure S8 .…”

Advanced Electrical Conductors: An Overview and Prospects of Metal Nanocomposite and Nanocarbon Based Conductors

“…For example, nanocarbon-copper composites can potentially outperform copper in terms of maximum current-carrying capacity, [48,49] lower temperature coefficient of resistance (TCR), [50,51] and lower CTE. [52] The main challenge facing this field is to scale up and optimize the current fabrication technologies that are mostly developed on a lab scale.…”

“…Graphene in its plane and CNTs along their longitudinal axis possess a negative CTE (−8 μ −1 K −1 ) [ 52 ] compared with the relatively large and positive CTE of copper and Al (23 and 17 μ −1 K −1 ), and their addition to these metals can lower the overall CTE. [ 52 ] The reduction in CTE is commensurate with the volume fraction of the nanocarbon.…”

Electrochemical Deposition of Copper on Epitaxial Graphene

“…In the past decade, huge efforts have been made to conceptualize graphene-copper material hybridization for practical applications [8][9][10][11][12][13]. Particularly, it was discovered that the addition of graphene to the copper matrix can improve the mechanical and electrical properties of Cu, causing a significant increase in the electrical conductivity, Young's modulus, shear modulus, and Vickers hardness as well as a reduction in the thermal expansion coefficient [8][9][10][11]. The aforementioned advantages create excellent prerequisites for copper-graphene (Cu-Gr) composites to be used as reliable interconnection materials, electrical contact materials for ultrahigh-voltage circuit breakers and printed electronics.…”