Fabrication of a Bilayer Structure of Cu and Polyimide To Realize Circuit Microminiaturization and High Interfacial Adhesion in Flexible Electronic Devices

Abstract

With commercialization of the fifth-generation mobile communication system and the further spread of the Internet of Things, industrial innovation is arriving with new business fields related to concepts such as high-speed communication, self-driving vehicles, and remote medicine. One of the challenges is the realization of flexible devices with high-definition circuits, which requires new fabrication techniques for Cu films on polymer substrates to meet demands and an understanding of Cu/polymer interfacial nanostructure to assure product quality. We have developed a promising technique for the fabrication of Cu film on polyimide (PI), which consists mainly of very simple semiconductor device processes. This technique allows for control of the Cu thickness with nanometer precision to form miniaturized Cu circuits with potential advantages in terms of interfacial adhesion and material/production costs. The Cu/PI interfaces fabricated by conventional vapor deposition and the new technique are systematically analyzed using synchrotron hard X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and time-of-flight secondary ion mass spectroscopy. With conventional vapor deposition, it was discovered that evaporated Cu atoms decompose the PI and an oxidation layer with a thickness of several nanometers that deteriorates the interfacial adhesion could be visualized at the Cu/PI interface. With the new technique, the decomposition of PI and interfacial oxidation are significantly suppressed. Furthermore, the proposed technique can be broadly applied to the investigation of metal/polymer interfaces fabricated by polymer coating on a metal substrate, which has so far been impossible.

Immobilization of Air-Stable Copper Nanoparticles on Graphene Oxide Flexible Hybrid Films for Smart Clothes

“…However, compared with precious metal materials such as gold and silver, CuNPs have the advantage of being inexpensive and simple to prepare. CuNPs have attracted considerable research attention for various applications, including in electrical and thermal conductivity materials [12], semiconductor components [13], solar cells [14,15], capacitors [16,17], buildings [18], and electronic devices [19,20]. The most common methods for preparing CuNPs include the gas phase method [21,22], the solid phase method [23,24], and the liquid phase method [25,26].…”

High-Energy Electron-Irradiated Fluorinated Ethylene Polypropylene Copolymer Coatings on Al Substrates for Enhanced Metal Adhesion and Protection

“…For decades, metal–polymer composites have played an important role in a wide range of industrial fields, including microelectronics, medical equipment, automobiles, and aerospace. − Among commercial polymers, fluorocarbon polymers (FPs) have excellent nonadhesiveness and low friction, in addition to high heat and chemical resistances. − These properties make FPs an ideal coating material for metal sliding parts in various industrial products. However, their nonadhesiveness also makes it extremely difficult for them to adhere to or combine with metals, which has prevented their wider application.…”

“…In this study, we developed a novel analytical approach to link the morphology, diffusion, and chemical interactions to the adhesion at the interface between the FP coating and metal substrate. First, a cryogenic setup was employed to reduce the electron beam damage during TEM observation. , In addition, the samples were fabricated by an improved process to model the FP–metal interface for analysis by synchrotron hard XPS (HAXPES). ,,− The fabrication process is based on that previously proposed for a Cu/PI bilayer structure, which can control the Cu film thickness to a precision of 1 nm, and has been used to laminate flexible printed circuits with Cu . We used these techniques to clarify the changes in the elemental diffusion and chemical bonding state at the interface between a fluorinated ethylene–polypropylene (FEP) coating and Al substrate due to the 1000 keV electron irradiation.…”

Chemical Interactions at the Al/Poly-Epoxy Interface Rationalized by DFT Calculations and a Comparative XPS Analysis

“…Design and tuning of the metal–polymer interface have enabled many technological advancements in the fields of microelectronics, automobile, aerospace, catalysis, and nanomedicine. − In general, metals and polymers have contrasting properties inducing curiosity about nature of bonds at the interface . From the past few decades, combined research efforts (both experiment and theory) have been converged on understanding polymer deposition on metal or metal-oxide surfaces. − On the other hand, metal deposition on polymer surfaces at nanoscale for low regime coverage is still not entirely understood. , A useful dimensionless parameter that characterizes the metal–polymer interaction is the condensation coefficient, C = n ads / n tot , which is defined as the number of adsorbed atoms ( n ads ) per total number of impinging atoms ( n tot ).…”