Structural and Electrical Properties of Flip Chip Laminated Metal–Molecule–Silicon Structures Varying Molecular Backbone and Atomic Tether

Abstract

Formation of electrical contacts to organic molecules by using a scalable technique that preserves molecular integrity is a key development toward reliable fabrication of nanoscale molecular architectures. Here we report the structural and electrical properties of metal–monolayer–silicon junctions fabricated by using Flip Chip Lamination (FCL), a novel, low cost, and nondestructive approach. The effect of junction formation is studied with both aliphatic and aromatic molecular backbones. The ω-functionalized monolayers are first formed on ultrasmooth gold via a thiol linkage and then laminated to H–Si via a thiol or alkene linkage. The application of pressure and temperature enables formation of the nanoscale molecular junctions chemically tethered to two electrodes. The molecular structure and interfacial chemistry within the electrical structure are investigated by using polarized backside-reflection absorption infrared spectroscopy (pb-RAIRS) and current–voltage (I–V) measurements. The confined organic monolayers maintain an overall structure similar to the original self-assembled monolayers (SAMs) on gold with small changes in the configuration of the molecular backbone attributed to lamination and bonding of the molecular terminal group to silicon and exhibiting electrical dielectric integrity. The optimal lamination conditions for each monolayer are dependent on the surface free energy, monolayer conformation, ambient conditions, and reaction of the molecular functionality with the silicon substrate. We demonstrate the structural and electrical integrity at the monolayer level of a variety of organic molecules bonded to both silicon and metal electrodes by probing the effect of molecular backbone (aliphatic vs aromatic) and molecule–electrode interface. FCL enables formation of an extended variety of molecular junctions to identify the critical factors in charge transport across metal–molecule–silicon nanoelectronic architectures.