Hiroshi Itatani

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.

New fabrication process for Josephson tunnel junctions using photosensitive polyimide insulation layer for superconducting integrated circuits

Photosensitive polyimide, synthesized by block copolymerization, is expected to be an excellent insulation layer in LSI circuits in the future. This polyimide has a higher thermal resistance than those of the other organic polymers. It also has good electric properties such as a high break down voltage and a low dielectric constant. We propose a new fabrication process for the Josephson tunnel junction using a photosensitive polyimide. It is possible to simplify the fabrication process of the Josephson tunnel junction, because the photosensitive polyimide is used as the insulation layer instead of conventional inorganic insulation films without an etching process. We fabricated Nb/Al-AlOx/Nb Josephson tunnel junctions using this new process. The junctions show excellent current-voltage (I-V) characteristics with V/sub m/ values more than 80 mV.

Interlayer dielectric process for LSI circuits using positive photosensitive polyimide synthesized by block-copolymerization

Photosensitive polyimide is expected as a future interlayer dielectric material in LSI circuits. In this paper, we propose a new interlayer dielectric process using a positive photosensitive polyimide directly synthesized from aromatic dianhydride and aliphatic diamine by block-copolymerization. Photosensitive polyimide solution was prepared with N-methyl-2-pyrrolidone (NMP) solvent. A diazonaphthoquinone PC-5 was used as a photosensitizer. The thin film was spin-coated with changing polyimide concentration and rotation speed. The uniformity of the coated film was achieved less than +/- 0.9 % on a 3-inch wafer of silicon. A 0.5 micrometers line and space pattern was obtained by i-line lithography. The (gamma) value of the contrast was evaluated to 1.05. The dielectric constant of the base polyimide was measured for a thick film by the cavity perturbation method. The values from 2.4 to 3.0 were obtained within the frequency range from 1 GHz to 20 GHz. The break down voltage was measured to be 107 kV/mm without high-temperature heat treatment.

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.

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.

Fabrication of fine wiring structure by electrodeposited polyimide for high density packaging and interconnection

For packaging and interconnection of a high performance electronic system, a fine high-density wiring structure is required. We have developed a new fabrication technology of a fine wiring structure using electrodeposited polyimide and electroless plated copper. The electrochemical properties of the electrodeposition process for polyimide were investigated. A fine copper wiring structure was formed by electroless plating on a trench in an electrodeposited polyimide layer. A 2 /spl mu/m wide copper wiring structure on an electrodeposited polyimide layer was successfully demonstrated. It is expected that the practical application of this new fabrication technology for high-density packaging and interconnection will be developed.

RADIATION-INDUCED cis AND trans ISOMERIZATION OF POLYISOPRENES AND TEMPERATURE DEPENDENCE OF THE EQUILIBRIA.

Abstract The cis and trans interconversion of polyisoprenes in solutions induced by γ-radiation in the presence of a sensitizer, which is any one of organic bromides or n-butyl mercaptan, was studied by using hevea and gutta percha as starting substances. The percentage cis remaining or converted after irradiation was determined by the infrared absorption. The equilibrium constants for the interconversion at 22, 60, and 100° C were found to be 3.00, 5.25, and 7.33, respectively. The firstorder rate constants for as cis → trans and trans → cis isomerizations at 22° C were calculated to be 9.05 and 2.91, respectively. The results were interpreted by the mechanism proposed by Golub, according to which the double bonds from π complexes with radiolytic fragments from sensitizers give a radical transition state capable of interconversion. However, our results showing that heating shifts the equilibrium toward trans isomer are not in accord with the mechanisms of the radiation-induced isomerization of polybutadi...