A self-assembled covalent nanoglue

Nano-glues rely on surface chemistry to intimately bond two surfaces together. The bond can be removable, which means it has to weaken, usually with temperature, or it can be a permanent bond, valued for strength, with a covalent bond yielding the highest strength. A practical covalent nanoglue based upon self-assembled monolayers (SAM) with amine and carboxyl termination is demonstrated, and applicable to any surface that bonds these SAM layers. For bonding flat or deformable layers, the SAM layers on each surface bond directly to each other with a peptide or nylon-like bond. For a removable bond or longer covalent structure, nylon chains are grown between the layers to bridge the gap for non-flat and non-flexible substrates. Bond strength and reliability are measured for several preparation schemes for the intermediate layer. A crystallization process is developed to pre-align the intermediate layer precursors and drive off the solvent to improve bond reliability and insure covalent bonding from wafer to wafer (W2W). Both covalent and removable bonds are created. Temperature dependence of the removable bond strength is measured, while the covalent bonds are stronger than our measurement process. The nanoglue does not bond until activated by (modest) heating, so alignment is enabled, and it is directly compatible with a wafer level fluid-self-alignment (FSA) process described elsewhere.