Simultaneous Lamination Research Articles

High-density vertical sidewall MoS2 transistors through T-shape vertical lamination

Vertical transistors, in which the source and drain are aligned vertically and the current flow is normal to the wafer surface, have attracted considerable attention recently. However, the realization of high-density vertical transistors is challenging, and could be largely attributed to the incompatibility between vertical structures and conventional lateral fabrication processes. Here we report a T-shape lamination approach for realizing high-density vertical sidewall transistors, where lateral transistors could be pre-fabricated on planar substrates first and then laminated onto vertical substrates using T-shape stamps, hence overcoming the incompatibility between planar processes and vertical structures. Based on this technique, we vertically stacked 60 MoS2 transistors within a small vertical footprint, corresponding to a device density over 108 cm−2. Furthermore, we demonstrate two approaches for scalable fabrication of vertical sidewall transistor arrays, including simultaneous lamination onto multiple vertical substrates, as well as on the same vertical substrate using multi-cycle layer-by-layer laminations.

Modification of poly(tetrafluoroethylene) and gold surfaces by thermal graft copolymerization for adhesion improvement

The adhesion between a poly(tetrafluoroethylene) (PTFE) film and a gold substrate was achieved by surface graft copolymerization of glycidyl methacrylate (GMA) on an argon plasma-pretreated PTFE film at elevated temperature with simultaneous lamination to a surface-modified gold substrate. The plasma pretreatment introduces peroxides which are thermally degraded into radicals to initiate the graft copolymerization of GMA on the PTFE surface. The gold surface, on the other hand, was first pretreated with 3-mercaptopropionic acid (MPA), 3-mercaptopropionic acid-2-ethylhexyl ester (MPAEE), or (3-mercaptopropyl)trimethoxysilane (MPTMS) to form self-assembled monolayers (SAMs) and then subjected to Ar plasma treatment. The simultaneous graft copolymerization and lamination of the PTFE film to the gold surface was carried out in the presence of GMA and an amine hardener at an elevated temperature under atmospheric conditions. The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The gold/GMA/PTFE assembly exhibited a T-peel adhesion strength above 10 N/cm and the joint delaminated by cohesive failure inside the bulk of the PTFE film. The strong adhesion of the Au/PTFE laminate is the result of concurrent graft copolymerization on both the Ar plasma-pretreated PTFE surface and the SAM of the Au surface to form a covalent network. The network is further strengthened by the crosslinking reaction promoted by the presence of the hardener.

Low-temperature graft copolymerization of 1-vinyl imidazole on polyimide films with simultaneous lamination to copper foils—effect of crosslinking agents

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) in the presence of a small amount of a crosslinking agent (XLA) on plasma-pretreated polyimide (PI or Kapton HN®) films with simultaneous lamination of copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80–150°C under atmospheric conditions and in the complete absence of a polymerization initiator. Significant improvement in adhesion was achieved by the presence of a XLA, such as 2,4,6-triallyloxy-1,3,5-triazine (TATZ), or 1,3,5-triallyl benzene tricarboxylate (TBTC), in VIDZ during the thermal graft copolymerization and lamination process. T-peel adhesion strength exceeding 17N/cm can be readily achieved for the polyimide–copper interface for grafting and lamination carried out at the reduced temperature of 100°C. The T-peel adhesion strengths are reported as a function of the cooling rate, the argon plasma pre-treatment time of the polyimide films, the thermal lamination temperature, and the thermal lamination time. The polyimide–copper interface graft copolymerized and laminated in the presence of a XLA also exhibited substantially improved resistance to moisture. The surface compositions of the polyimide films and copper foils from the delaminated interfaces were studied by X-ray photoelectron spectroscopy (XPS). The enhanced interfacial adhesion has resulted in cohesive failure deep inside the PI film as is also revealed by the scanning electron micrograph (SEM).

Low‐temperature thermal graft copolymerization of 1‐vinyl imidazole on fluorinated polyimide films with simultaneous lamination of copper foils

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) on pristine and argon plasma pretreated fluorinated polyimide (FPI) films with simultaneous lamination of copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80–140°C under atmospheric conditions and in the complete absence of a polymerization initiator. Three different FPI samples of different chemical structures were employed in the present study. An optimum T-peel strength about 15 N/cm was achieved for the copper/FPI laminate. The adhesion strength, however, decreased with increasing fluorine content in the FPI film. The onset of cohesive failure occurred in the FPI film for assemblies with T-peel strength greater than 6 N/cm. The T-peel strengths are reported as a function of the argon plasma pretreatment time of the FPI films and thermal lamination temperature. The adhesion strengths were compared to that of the similarly prepared copper/polyimide (Kapton HN) laminate. Time-dependent water contact angle (Θ) measurements indicated that the surfaces of FPI films are significantly more hydrophobic and more resistant to water diffusion or hydration than the Kapton HN films. The surface compositions of the pristine FPI films, as well as the delaminated FPI films and copper foils were studied by X-ray photoelectron spectroscopy. The thickness of the graft VIDZ polymer layer was in the order of 200 nm, as derived from the cross-sectional view of the scanning electron micrograph. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1478–1489, 1999

Thermally induced surface graft copolymerization with concurrent lamination of polyaniline films under atmospheric conditions

Simultaneous lamination of emeraldine base (EB) films of polyaniline (PANI) was achieved during thermally induced surface graft copolymerization with various monomers, such as N,N′-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS), sodium salt of styrenesulfonic acid (NaSS), 1-vinyl imidazole (VIDz) and acrylic acid (AAc). The simultaneous thermal grafting and lamination process can be carried out under atmospheric conditions, and in the complete absence of an added polymerization initiator and surface preactivation of the EB substrates. The structure and chemical composition of the graft copolymerized surfaces from the self-delaminated junction in water were investigated by X-ray photoelectron spectroscopy (XPS). The effects of monomer concentration, thermal grafting/lamination temperature, and the physicochemical attributes of the various monomers on the observed lamination strength were studied. The efficiency of surface graft copolymerization and the lamination strength were found to increase with increasing temperature in the temperature range of 80–120°C. Maximum lap shear adhesion strengths of greater than 350 N/cm 2 and exceeding the yield strength of the substrate EB film could be readily achieved for grafting/lamination carried out in the presence of DMAPS, VIDz and AAc monomer.

Surface Graft Copolymerization of Poly(vinylidene fluoride) Film with Simultaneous Lamination to Copper Foil

Surface thermal graft copolymerization with concurrent lamination was carried out between an Ar plasma pretreated poly(vinyh'dene fluoride) (PVDF) film and a copper foil in the presence of a small quantity of a N-containing monomer, such as 4-vinyl pyridine (4-VPN) and acryloyl morpholine (ACMO), under atmospheric conditions and in the complete absence of an added polymerization initiator and system degassing. The adhesion strength, as reported by T-peel strength, was dependent on the argon plasma pretreatment time of the PVDF film, the thermal lamination temperature and the type of monomer. An optimum T-peel adhesion of about 10 N/cm was readily achieved in the Cu/PVDF laminate for grafting and lamination carried out in the presence of 4-VPN. A lower adhesion strength was obtained using ACMO and other N-containing monomers. The chemical compositions of the graft copolymerized and delaminated sample surfaces were studied by X-ray photoelectron spectroscopy (XPS). The failure mode of the Cu/4-VPN/PVDF assembly was a combined adhesional and cohesive failure. The strong adhesion between the Cu foil and the PVDF film arises from the strong charge transfer interaction between Cu and the pyridine ring, as well as the fact that the graft chains are covalently tethered on the PVDF films surfaces as a result of surface graft copolymerization.

Low-temperature thermal graft copolymerization of 1-vinyl imidazole on fluorinated polyimide films with simultaneous lamination of copper foils

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) on pristine and argon plasma pretreated fluorinated polyimide (FPI) films with simultaneous lamination of copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80–140°C under atmospheric conditions and in the complete absence of a polymerization initiator. Three different FPI samples of different chemical structures were employed in the present study. An optimum T-peel strength about 15 N/cm was achieved for the copper/FPI laminate. The adhesion strength, however, decreased with increasing fluorine content in the FPI film. The onset of cohesive failure occurred in the FPI film for assemblies with T-peel strength greater than 6 N/cm. The T-peel strengths are reported as a function of the argon plasma pretreatment time of the FPI films and thermal lamination temperature. The adhesion strengths were compared to that of the similarly prepared copper/polyimide (Kapton HN) laminate. Time-dependent water contact angle (Θ) measurements indicated that the surfaces of FPI films are significantly more hydrophobic and more resistant to water diffusion or hydration than the Kapton HN films. The surface compositions of the pristine FPI films, as well as the delaminated FPI films and copper foils were studied by X-ray photoelectron spectroscopy. The thickness of the graft VIDZ polymer layer was in the order of 200 nm, as derived from the cross-sectional view of the scanning electron micrograph. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1478–1489, 1999

Adhesion improvement of polytetrafluoroethylene/metal interface by graft copolymerization

Copper-poly(tetrafluoroethylene) (PTFE) and gold-PTFE laminates were prepared by surface graft copolymerization of glycidyl methacrylate (GMA) on argon plasma-pretreated PTFE films at an elevated temperature with simultaneous lamination to copper foils or gold substrates. The plasma pretreatment introduces peroxides, which are thermally degraded into radicals to initiate the graft copolymerization of GMA on the PTFE surface. Before lamination, the gold surface was pretreated with alkanethiols to form self-assembled monolayers and then subjected to an Ar plasma treatment. The modified surfaces and interfaces were characterized by x-ray photoelectron spectroscopy and the adhesion strength was assessed by the T-peel test method. By this technique, the Cu-PTFE or Au-PTFE laminates exhibit significantly improved adhesion strengths and the joints are delaminated by cohesive failure inside the bulk of the PTFE film.

Surface graft copolymerization of poly(tetrafluoroethylene) film with simultaneous lamination to copper foil

A simple, one-step process of surface thermal graft copolymerization of argon plasma-pretreated poly(tetrafluoroethylene) (PTFE) films with simultaneous lamination of copper foils, or with similarly plasma-pretreated PTFE films, was demonstrated. The simultaneous thermal grafting and lamination process was carried out at 120°C under atmospheric conditions. The monomers used for the graft copolymerization were 1-vinyl imidazole (VIDz), 4-vinyl pyridine (4VP), and 2-vinyl pyridine (2VP). The adhesion strengths are reported as lap shear adhesion strengths and T-peel adhesion strengths. The adhesion strength between the polymer and the metal was further enhanced by the presence of a crosslinking agent in the monomer. Adhesion strengths exceeding 7 N/cm were achieved for the Cu foil/PTFE laminates. X-ray photoelectron spectroscopic (XPS) studies of the delaminated Cu foil/PTFE assembly revealed that the joint failed by cohesive failure inside the PTFE film. The strong adhesion between PTFE and Cu arises from the charge-transfer interaction between the nitrogen moiety of the grafted polymer and the Cu atom, as well as from the fact that the graft chains are covalently tethered on the PTFE film surface as a result of the graft copolymerization process.

Low-temperature graft copolymerization of 1-vinyl imidazole on low-density polyethylene films with simultaneous lamination of copper foils

Surface modification of argon plasma-pretreated low-density polyethylene (LDPE) films by graft copolymerization with 1-vinyl imidazole (VIDz) and with concurrent lamination of copper foils at room temperature and at an elevated temperature were carried out. The adhesion strengths were reported as lap shear adhesion strengths and T-peel strengths. The surfaces of the graft copolymerized films and the mechanically delaminated LDPE and Cu surfaces were characterized by X-ray photoelectron spectroscopy (XPS). It was found that plasma pretreatment of LDPE alone, and in the absence of VIDz, could give rise to strong lap shear adhesion between the polymer and copper. Significant T-peel strengths, however, were obtained only for LDPE/Cu laminates obtained from the simultaneous graft copolymerization and lamination technique. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1977–1983, 1998

Thermal graft copolymerization with concurrent lamination of low density polyethylene and poly(tetrafluoroethylene) films

A simple technique of thermal graft copolymerization of glycidyl methacrylate (GMA) on argon plasma pretreated poly(tetrafluoroethylene) (PTFE) films or low density polyethylene (LDPE) films with simultaneous lamination of the two films was demonstrated. The effect of crosslinking agent on the adhesion strength of the PTFE/PTFE interface was also investigated. The simultaneous thermal grafting and lamination process was carried out under atmospheric conditions and in the complete absence of a polymerization initiator. The surface structure and composition of the graft copolymerized PTFE and LDPE films from either self-delamination in acetone or mechanical delamination were studied by X-ray photoelectron spectroscopy (XPS). The efficiency of surface graft copolymerization and lamination was found to be strongly dependent on the plasma pretreatment time of the substrate, graft concentration, thermal grafting/lamination temperature and time. T-peel adhesion strengths of about 0.9 and 1.7 N cm −1 were achieved for the PTFE/GMA/PTFE assemblies in the absence and presence, respectively, of the crosslinking agent, triallyl-1,3,5-benzenetricarboxylate (TBTC). The T-peel adhesion strength of the LDPE/GMA/LDPE assembly, on the other hand, can reach about 2.6 N cm −1 in the absence of TBTC. XPS analysis of the mechanically delaminated surfaces suggests that the failure mode of the PTFE/GMA/PTFE assembly and the PTFE/GMA + 2 vol% TBTC/PTFE assembly is adhesional in nature, and that of the LDPE/GMA/LDPE assembly is cohesive.

Low-temperature thermal graft copolymerization of 1-vinyl imidazole on polyimide films with simultaneous lamination to copper foils

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) on pristine and argon plasma-pretreated polyimide (PI or Kapton HN®) films with simultaneous lamination to copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80-160°C under atmospheric conditions and in the complete absence of a polymerization initiator. The adhesion strength was found to be strongly dependent on the rate of cooling after the thermal grafting and lamination, with the adhesion substantially improved by annealing. An ultimate T-peel strength greater than 14 N/cm and a lap shear adhesion strength approaching 2000 N/cm2 were achieved for the polyimide-copper interface for grafting and lamination carried out at 120°C before cohesive failure occurred in the polyimide film. The T-peel and lap shear adhesion strengths are reported as a function of the cooling rate after thermal grafting and lamination, the argon plasma pretreatment time of the polyimide films, the thermal lamination temperature, and the thermal lamination time. The effect of moisture on the lamination strength was also investigated. The surface compositions of the polyimide films and copper foils after delamination were studied by X-ray photoelectron spectroscopy (XPS). The thickness of the graft interfacial layer was of the order of 200 nm, as derived from the cross-sectional view of the scanning electron micrograph.

Adhesion improvement of a poly(tetrafluoroethylene)- copper laminate by thermal graft copolymerization

Poly(tetrafluoroethylene) (PTFE)-copper laminates were achieved by surface graft copolymerization of glycidyl methacrylate (GMA) on an argon plasma-pretreated PTFE film at elevated temperature with simultaneous lamination of a copper foil in the presence of an epoxy resin adhesive. The plasma pretreatment introduces peroxides which are thermally degraded into radicals to initiate the graft copolymerization of GMA on the PTFE surface. The graft copolymerization with concurrent lamination of copper was carried out in the complete absence of a polymerization initiator or system degassing. The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The adhesion strength between the PTFE film and copper was assessed by the T-peel test method. The adhesion strength was affected by the plasma pretreatment time, as well as by the grafting and curing temperatures. The PTFE/GMA-epoxy resin/Cu assembly exhibits a significantly higher measured adhesion strength, compared with those of the PTFE/epoxy resin/Cu and PTFE/GMA/Cu assemblies. The PTFE/GMA-epoxy resin/Cu joint delaminated by cohesive failure inside the bulk of the PTFE film. This suggests that the enhanced adhesion between the graft-modified PTFE film and the copper surface is attributable to the formation of covalent bonds between the tethered GMA graft chains on PTFE and the epoxy resin network.