Formation of Silicon-Based Molecular Electronic Structures Using Flip-Chip Lamination

Abstract

We report the fabrication of molecular electronic test structures consisting of Au-molecule-Si junctions by first forming omega-functionalized self-assembled monolayers on ultrasmooth Au on a flexible substrate and subsequently bonding to Si(111) with flip-chip lamination by using nanotransfer printing (nTP). Infrared spectroscopy (IRS), spectroscopic ellipsometry (SE), water contact angle (CA), and X-ray photoelectron spectroscopy (XPS) verified the monolayers self-assembled on ultrasmooth Au were dense, relatively defect-free, and the -COOH was exposed to the surface. The acid terminated monolayers were then reacted with a H-terminated Si(111) surface using moderate applied pressures to facilitate the interfacial reaction. After molecular junction formation, the monolayers were characterized with p-polarized backside reflection absorption infrared spectroscopy (pb-RAIRS) and electrical current-voltage measurements. The monolayer quality remains largely unchanged after lamination to the Si(111) surface, with the exception of changes in the COOH and Si-O vibrations indicating chemical bonding. Both vibrational and electrical data indicate that electrical contact to the monolayer is formed while preserving the integrity of the molecules without metal filaments. This approach provides a facile means to fabricate high-quality molecular junctions consisting of dense monolayers chemically bonded to metal and silicon electrodes.

Metal-Molecule-Silicon Junctions Produced by Flip Chip Lamination of Dithiols: Effect of Molecular Length and Backbone

“…The observation of similar molecular conformation within the junction following FCL is consistent with previous studies of COOH-terminated alkyl molecules used in FCL (14,19). Bonding of the thiol-linkage to the H-terminated silicon surface is thought to occur through a Si-S linkage.…”

“…In order to address these concerns a novel fabrication technique, flip-chip lamination (FCL), was developed to create ordered, dense organic monolayers covalently bound between gold and semiconductor electrodes (14). This procedure takes advantage of well established thiol-gold chemistry and combines it with nanotransfer printing (nTP) in order to make reliable molecular junctions.…”

(Invited) Metrology of Molecular Devices Made by Flip Chip Lamination

“…During this transition, the molecular chain orientation retains the same d -C-H peak position, indicating the monolayer remains highly ordered. The C-O and Si-O spectral regions change with increasing pressure indicating bonding between the carboxyl groups and the H-terminated silicon surface (4). Evolution of this spectral region has been attributed to bonding of the oxygen atoms within the carboxyl group to the silicon surface through a symmetric bidentate coordination.…”

Bottom‐Up Molecular Tunneling Junctions Formed by Self‐Assembly

“…[159] As shown in Figure 15, Coll et al formed SAMs of carboxylic acid terminated alkanethiols on Au TS on poly(ethylene terephthalate) (PET). [159] They then inverted these films and applied them to passivated silicon wafers, forming SiÀO linkages. The properties of the junctions were verified by observing reasonable values of V trans and magnitudes of I.…”