Takafumi Fukushima

Synthesis and positive-imaging photosensitivity of soluble polyimides having pendant carboxyl groups

Polyimides having pendant carboxyl groups were prepared by a direct one-pot polycondensation of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 3,5-diaminobenzoic acid (DABz) and bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) in the presence of a γ-valerolactone/pyridine catalyst system using N-methyl-2-pyrrolidone (NMP)/toluene mixture as a solvent at 180 °C. The obtained polyimides were soluble in dipolar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and NMP as well as in tetrahydrofuran and aqueous basic solution. The solubility of the polyimides was dependent on the diamine composition. Photosensitve polyimide (PSPI) systems composed of the polyimides and diazonaphthoquinone compound as a photosensitive material gave positive-tone behavior by UV irradiation, followed by development with aqueous tetramethylammonium hydroxide (TMAH) solution. The scanning electron microscopic photograph of the resulting image showed 10-μm line/space resolution with about 15 μm of film thickness. The PSPIs baked at 350 °C for a short time had excellent thermal resistance comparable to the original polyimides.

Photosensitive Polyarylates Based on Reaction Development Patterning

Films of a commercially available polyarylate (U polymer®) containing a photosensitive agent were prepared by means of spin-coating onto copper foil, which showed positive-tone behavior after UV irradiation and development with an ethanolamine/N-methyl-pyrrolidone/H 2 O mixture. Scanning electron microscope photographs of the images exhibited fine patterns ( 10 μm line/space resolution) with 9-14 μm film thickness. The pattern-forming mechanism is based on the reaction development patterning (RDP) process, where the main pattern-forming reaction occurs during development.

Ionic-bonded negative photosensitive polyimides having pendant aminoalkyl (meth)acrylamide groups

Abstract Soluble polyimides having pendant carboxyl groups were prepared by a direct one-pot polycondensation of various acid dianhydrides with 3,5-diaminobenzoic acid and bis[4-(3-aminophenoxy)phenyl]sulfone in the presence of γ-valerolactone/pyridine catalyst in 1-methyl-2-pyrrolidone (NMP)/toluene mixture at 180xa0°C. The pendant carboxyl groups were blocked with photopolymerizable (meth)acrylamides, N -[3-(dimethylamino)propyl]acrylamide (DMAPAA), N -[3-(dimethylamino)propyl]methacrylamide (DMAPMA), or N -[3-(diethylamino)propyl]methacrylamide (DEAPMA), through ionic bonding at room temperature. The ionic-bonded photosensitive polyimide films containing photosensitizer Michler’s ketone (MK) and ethylene glycol dimethacrylate (EGDMA) as an external multifunctional cross-linker gave negative-tone behavior by near-UV irradiation followed by development with 10% aqueous NaOH at 25xa0°C. The SEM photograph of the resultant images showed fine patterns (line/space 20/20 μm) with ∼15 μm in film thickness. The sensitivity of photosensitive polyimides with DMAPAA or DMAPMA was higher than that of photosensitive polyimides with (meth)acrylate esters such as 2-(dimethylamino)ethyl acrylate (DMAEA), 3-(dimethylamino)propyl acrylate (DMAPA), 2-(dimethylamino)ethyl methacrylate (DMAMA), and 2-(diethylamino)ethyl methacrylate (DEAMA).

Heat-resistant photoresists based on new imaging technique: reaction development patterning

Spin-coated films of nonphotosensitive engineering thermoplastics mixed with photosensitive agent diazonaphthoquinone (DNQ) can be clearly imaged with near-UV light. The selected engineering thermoplastics are commercially available poly(bisphenol A carbonate), polyarylate (U polymer®) and polyetherimide (Ultem®), and synthesized fluorinated polyimide, which have no specific functional groups. Development with a solution including ethanolamine dissolves the irradiated areas to give positive fine patterns. The two-component photosensitive systems shows good photosensitivity and resolution (line/space 10/10 μm) with about 10 to 15 μm in thickness. Gel-permiation chromatography (GPC) and 1H-NMR measurements that can give information on the structure of components dissolved from the irradiated regions are carried out to make clear the imaging mechanism, which we call reaction development patterning (RDP). RDP-based photosensitive polymers showed high heat resistance up to their glass transition temperature (Tg) or above.

Ultrafast Active Transmission Lines with Low-k Polyimide Integrated with Ultrafast Photoconductive Switches

We fabricated the first ultrafast active transmission lines with low dielectric constant (low-k) polyimide integrated with ultrafast photoconductive switches formed by the nano-anodization process. Electrical pulses as short as 290 fs were measured on this transmission line by an electrooptic sampling system based on a femtosecond laser. P-n junctions were inserted in the transmission line to control dispersion in lines, and low-k polyimide was introduced to reduce dielectric and radiation losses.

Heat-resistant photoresists based on new imaging technique: reaction development patterning (RDP)

Spin-coated films of non-photosensitive engineering thermoplastics mixed with photosensitive agent diazonaphthoquinone (DNQ) can be imaged with near-UV light. The engineering thermoplastics selected for study are commercially available poly(bisphenol A carbonate), polyarylate (U polymer) and polyetherimide (Ultem), and synthesized fluorinated polyimide, which have no specific functional groups. Development with a solution including ethanolamine dissolves the irradiated areas to give positive fine patterns. The two-component photosensitive systems showed good photosensitivity and resolution (line/space 10/10 µm) with about 10-15 µm in thickness.

Ultrafast photoconductive switches integrated with electrical waveguides of low-k polyimide

We have fabricated ultrafast electrical waveguides with low-k polyimide integrated with ultrafast photoconductive switches formed by nano-anodization process for the first time. Electrical signals are affected by nonlinear capacitance of p-n junctions in this waveguides, and pass through the low-k polyimide, so the dielectric loss and the radiation loss are dramatically reduced. The electrical pulses as short as 290 fs were measured on this waveguide by an electro-optic sampling system based on a femtosecond laser.