Yasuhisa Kayaba

Fabrication of Si Nanowire Field-Effect Transistor for Highly Sensitive, Label-Free Biosensing

We fabricated a biosensor based on a silicon nanowire field-effect transistor (SiNW FET) with a Si3N4 gate insulator for highly sensitive detection of target biomolecules. The fabricated SiNW FET acted as an ion-sensitive FET that could detect the charge density in solutions flowing along the gate surface by responding to the pH of the solutions. The SiNW FET also detected charged protein molecules in solution, suggesting that our device can be used in highly sensitive, label-free biosensing.

Confocal Imaging Using Ultra Wideband Antenna Array on Si Substrates for Breast Cancer Detection

A Si on-chip bow-tie antenna array was developed for transmitting Gaussian monocycle pulses (GMPs) whose center frequency was 15 GHz. The length and flare angle of the bow-tie antenna were 7.16 mm and 53°, respectively. GMPs were emitted from the antenna to the substrate whose dielectric constant was 7 and reflected at the target whose dielectric constant was 30. A minimum dielectric target size of 3×3 mm2 at a depth of 20 mm in the dielectric substrate was detected and a two-dimensional cross-sectional image of a dielectric target in a dielectric substrate was reconstructed by confocal imaging algorithm.

Mesoporous sol-gel silica cladding for hybrid TiO 2 /electro-optic polymer waveguide modulators

We report the efficient poling of an electro-optic (EO) polymer in a hybrid TiO(2)/electro-optic polymer multilayer waveguide modulator on mesoporous sol-gel silica cladding. The mesoporous sol-gel silica has nanometer-sized pores and a low refractive index of 1.24, which improves mode confinement in the 400-nm-thick EO polymer film in the modulators and prevents optical absorption from the lower Au electrode, thereby resulting in a lower half-wave voltage of the modulators. The half-wave voltage (Vπ) of the hybrid modulator fabricated on the mesoporous sol-gel silica cladding is 6.0 V for an electrode length (Le) of 5 mm at a wavelength of 1550 nm (VπLe product of 3.0 V·cm) using a low-index guest-host EO polymer (in-device EO coefficient of 75 pm/V).

Electrical Reliabilities of Highly Cross-Linked Porous Silica Film with Cesium Doping

A highly cross-linked porous silica dielectric (PoSiO) film was fabricated at a low temperature of 350°C. PoSiO films were derived by the sol-gel method and their pore surface silanol groups were silylated with 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) by vapor phase treatment. To promote the degree of siloxane cross-linkage of the film, cesium (Cs) was added to the precursor solution with the amount of 0, 5, 15, and 30 wt ppm as a base catalyst. Then, the amount of methyl-silicon-three oxygen (Me-Si T-type) and hydrogen-silicon-three oxygen (H-Si T-type) bridged structures of the chemisorbed TMCTS were increased, and the amount of surface silanol groups was decreased markedly with the increasing amount of Cs concentration. Leakage current and dielectric constant were measured under various humidity conditions, which were hardly degraded for the highly cross-linked PoSiO owing to its small amount of residual silanol groups and adsorbed water. It was also shown that the amount of mobile protons originated from the silanol groups became negligible. Time zero dielectric breakdown field strength was improved to 6.7 MV/cm and a projected time-dependent dielectric breakdown lifetime satisfied 10 years for Cs 30 ppm-doped PoSiO under a stress condition of 220°C and |E| = 1 MV/cm.

Effect of Water Adsorption on Electrical Characteristics of Porous Silica Films

The effects of water adsorption on the dielectric constant and leakage current of porous silica thin films were investigated. The films were prepared by the sol–gel method and their pore surfaces became hydrophobic with 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) or hexamethyldisilazane (HMDS) vapor phase treatment. Permittivity and leakage current were measured within the relative humidity condition range from 3 to 50%. The dielectric constant increased with increasing relative humidity, and water adsorption properties were calculated from the dielectric constant. Then, the number densities of water adsorption sites were nearly the same in the two films. Leakage current began to increase at a relative humidity of 8%. The slope of leakage current relative to electric field was described well by the Pool–Frenkel leakage current model above an electric field strength of 0.3 MV/cm. To consider the effect of water adsorption on the leakage current model, we used the Pool–Frenkel current equation for ionic conduction. This model revealed that the ionization energy of proton emission from the silanol group decreased with increasing relative humidity; thus, leakage current increased with increasing relative humidity.

Theoretical Investigation of Maximum Field Strength in Porous Silica Dielectric

The maximum magnitude of electrical field strength (Emax) in porous silica dielectrics is derived as a function of porosity in a theoretical approach. The cylindrical air pores assume the Hashin–Shtrikman (HS) structure, two-dimensional periodic square-array, and hexagonal-array structures. In the case of the HS structure, as porosity increases, the electric field strength decreases homogeneously in the silica skeleton; therefore, Emax decreases monotonically with increasing porosity. In the case of a square- or hexagonal-array structure, at low porosity, Emax is approximately equal to that of the HS structure; however, as porosity increases, the electric field strength around the pore surface deviates from the prediction of the HS model, and electric field strength becomes large at local spots; then Emax increases with increasing porosity. In addition similar studies are performed for coated cylindrical air pores.

Cu-Oxide-Assisted Selective Pyrolysis of Organic Nanolayer on Patterned SiO2–Cu Surface

Organic nanolayers attract much attention for the isolation and adhesion promotion of the Cu line and insulator in Cu interconnection of microelectronic devices. This paper proposes a strategy for selective formation of adhesion nanolayer on the insulator surface with etching it on Cu surface by Cu-oxide-assisted pyrolysis. After deposition of a uniform polyelectrolyte layer on both SiO2 and Cu surfaces, heat treatment at 350 °C in ambient nitrogen was applied. Then, a larger thickness decrease was observed on the polyelectrolyte layer on Cu when compared to that on SiO2. According to the TDS and XPS analysis, the polyelectrolyte layer was relatively stable on SiO2 up to the intrinsic decomposition temperature of the material, but on the Cu surface it decomposed to volatile small molecules at a lower temperature due to Cu2O-assisted oxidization. This substrate dependent selective pyrolysis was examined for 100 nm width Cu lines and SiO2 spaces, and then a patterned polyelectrolyte layer on the SiO2 surface was obtained with a single nanometer scale edge resolution.

Quantitative Determination of Complex Dielectric Function of Amorphous Silicon Dioxide on Silicon Substrate from Transmission Spectrum

Infrared spectroscopy is a powerful tool for characterizing the molecular bonding structures of oxide films. Using parametric analysis, we could determine both real and imaginary parts of the complex dielectric function of oxide thin films supported on a substrate. In this work, the complex dielectric function of a silicon dioxide thin film on a silicon substrate in the infrared region (400–1400 cm-1) was determined quantitatively by fitting an optical model for the transmittance of an air/silicon/insulator/air laminated structure to experimental data. The adsorption due to the ionic vibration of siloxane bonding was parameterized with the sum of Lorentz damping oscillators convoluted with a Gaussian distribution. The incidence angle of light was changed from nearly normal (5° off) to oblique (55–65° off), and all of the data was simultaneously fitted. Transverse optic and longitudinal optic functions were calculated from the dielectric function. Good agreement was found between the peak frequency of each function and that calculated by another method.

Electrical reliabilities of porous silica low-k films

Electrical reliability of self-assembled porous silica films was investigated. Vapor phase silylation by use of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) was developed to reduce silanol groups and enhance siloxane cross-linkage, resulting in achieving lower dielectric constant and higher elastic modulus. To promote siloxane cross-linkage, Cs ion was doped to its precursor solution. The self-assembled porous silica low-k film was integrated in Cu damascene interconnects with ultraviolet (UV) irradiation and TMCTS vapor treatment, resulting in the highest elastic modulus of 9 GPa with the dielectric constant of 2.1. Sidewall protection layer was formed in the trench for Cu interconnects to improve time-dependent dielectric breakdown (TDDB) lifetime of more than 10 years at the electric field of 2.3 MV/cm.

Selective formation of an ultra-thin pore seal on mesorporous low-k for a copper dual damascene structure

A strategy for the selective formation of a pore sealing layer on mesoporous low-k applicable for a Cu dual damascene interconnection process is herein proposed. An ultra-thin, adhesive, and conformal pore sealing layer was formed on mesoporous low-k by spin coating macromolecules. The pore sealant on the Cu surface was selectively decomposed with the help of Cu2O induced oxidization. This selective removal was also examined for patterned structure. Our simple and novel technique will help the integration of ulta-low-k materials in LSI devices.