# Ultra‐Tough Copper–Copper Bonding by Nano‐Oxide‐Dispersed Copper Nanomembranes

## TL;DR

A new method for bonding copper surfaces using copper nanomembranes achieves ultra-strong, eco-friendly, and cost-effective results.

## Contribution

A novel copper nanomembrane bonding technique that overcomes the strength-ductility trade-off and enhances bonding strength.

## Key findings

- Copper nanomembranes exhibit ultra-low elastic modulus, high yield strength, and excellent ductility.
- The bonding method achieves an interfacial shear strength of up to 73 MPa, 35 times stronger than conventional methods.
- The technique is cost-effective, environmentally friendly, and scalable for large-area applications.

## Abstract

Metal–metal bonding has played a pivotal role in advancing human technologies across various industrial sectors. As devices continue to miniaturize, there is an increasing need for efficient bonding techniques capable of achieving metal–metal bonds at smaller length scales. In this study, a facile but effective bonding technique is developed that enables the bonding of randomly oriented copper with copper nanomembranes under low temperatures and pressures. The fabricated copper nanomembranes, with a thickness of ≈50 nm and a width of 1 cm or above, exhibit a unique heterogeneous nanostructure, comprising copper nanocrystals along with nano‐copper‐oxide dispersions. Consequently, these copper nanomembranes display exceptional mechanical properties, including an ultra‐low elastic modulus of ≈35 GPa, a remarkable yield strength of ≈1 GPa, and excellent ductility of ≈40%, overcoming the conventional strength‐ductility trade‐off observed in various copper alloys. Most importantly, these ultra‐soft copper nanomembranes serve as metallic “glues”, promoting grain growth across the bonding interface between randomly oriented copper surfaces. This process leads to an average interfacial shear strength of up to 73 MPa at room temperature, representing an approximate 35 times increase in bonding strength compared to direct copper–copper bonding achieved under identical temperature and pressure conditions.

Conventional copper–copper bonding methods are typically costly and environmentally detrimental due to the use of various chemicals. In this study, a copper nanomembrane (NM) bonding approach is developed specifically designed for copper–copper bonding. This approach is marked by the large‐scale fabrication of flexible yet strong copper NMs using the polymer surface buckling enabled exfoliation method. Notably, this nanomembrane bonding approach is characterized by its cost‐effectiveness, environmental friendliness, and remarkable bonding strength.