Masataka Fukuyama

Selective Detection of Antigen-Antibody Reaction Using Si Ring Optical Resonators

Si ring optical resonators have been fabricated by the Si LSI technology using electron beam lithography and reactive ion etching. The resonator is applied for sensing receptor-analyte reaction using silicon-binding protein, Si-tag, which enables receptors immobilized on a Si dioxide surface with a controlled orientation. For the receptor, the major house-dust mite allergen called Der f 2 was used, and for the analyte anti-Der f 2 immunoglobulin type G (IgG), which is selectively bound to Der f 2, was used. Antiserum against Der f 2, which contains anti-Der f 2 IgG, was diluted to 1/100 with the pure water, and exposed to the resonator on which the Der f 2 was adsorbed with the Si-tag. Then the resonance wavelength was shifted by 0.18 nm, while exposure of the normal rabbit serum containing no Der f 2 IgG resulted in the peak shift less than half (0.07 nm). These results indicate the selective reaction between Der f 2 and anti-Der f 2 IgG.

Silicon Ring Optical Modulator with p/n Junctions Arranged along Waveguide for Low-Voltage Operation

For low-voltage and high-speed operation, a Si ring optical modulator, where p/n junctions are arranged along the waveguide of the ring resonator, is proposed. In this device, a switching speed of over 30 GHz and a modulation of 3 dB are estimated at a low operation voltage of 1 V by simulation. Optimum design parameters are obtained: the carrier concentration is 1×1018 cm-3 and the length of the p- and n-type regions is 0.4 µm. The modulators were fabricated and the performance was evaluated. The modulation is 1.25 dB at 6 V, which is lower than the simulated value. This is explained by the unexpected low carrier concentration. It is suggested that the optimization of the fabrication process will yield better performance.

Study of charge retention mechanism for DNA memory FET

The charge retention mechanism of the λ-DNA molecules with 400 bp (136 nm) are examined. The DNA solution was dropped on the Si source and drain electrodes with the gap of 120 nm. The change of the refresh characteristics by applying the negative voltage to the gate was measured. As a result, it was found that the electron trap remarkably influenced on the hole conduction of the DNA channel. In addition, the DNA has memory ability because the trap and detrap of the electrons can be controlled by the refresh voltage.

Reduction in Operation Voltage of Silicon Ring Optical Modulator Using High-k (Ba,Sr)TiO3 Cladding Layer

Electric-field drive Si ring optical modulators with a (Ba,Sr)TiO3 (BST) cladding layer have been fabricated. A lateral electric field is applied across the Si ring using the side Pt electrodes, and the optical output from the drop port is measured. It is estimated that an operation voltage of less than 10 V is possible when the relative dielectric constant of the cladding layer is larger than 150 and the quality factor is 5×104. The operation voltage of the fabricated optical modulator with a BST cladding layer is reduced to <1/8 relative to that of the SiO2 and Si3N4 cladding layers. One reason for the still high operation voltage (125 V for 75% modulation) is the low quality factor, which is limited by the light propagation loss of the BST film. It is also estimated that an operation voltage of less than 10 V is achievable when the propagation loss of the cladding layer is improved to less than 28 dB/cm.

Detection of Antigen–Antibody Reaction Using Si Ring Optical Resonators Functionalized with an Immobilized Antibody-Binding Protein

We propose the integrated biosensor chip using Si ring resonators, where different receptor is immobilized on each sensor. Signal detection is carried out by the matrix of light-input and detection waveguides, which are respectively connected to laser diodes and photodetectors. The Si rings are arranged at the cross points. The unique point of our work is to use the silicon-binding protein (designated Si-tag), which binds to SiO2 surface, as an anchoring molecule to immobilize bioreceptor on the Si rings in an oriented manner. In the integrated biosensor chip, many kinds of Si-tag-receptor fusions are required for high-throughput detection of analyte. In this paper, the Si ring biosensors were functionalized with various antibodies using the Si-tagged protein A as an intermediate binder, and the label-free detection of antigen have been achieved. We have developed the rapid functionalization method of Si-ring resonators with antibodies using Si-tagged protein A. Since various kinds of antibody can be used as receptors for biosensing, this method promises to realize the integrated biosensors for high-throughput analyte detection.

Low-voltage high-speed Si Mach-Zehnder optical modulator with multi-cascade p/n junctions along waveguides

We propose a Si Mach-Zehnder interferometer (MZI) optical modulator with multi-cascade p/n junctions along waveguides. So far a single p/n junction is set horizontally across the waveguide or vertically in the thickness direction. Compared with these types of MZIs, the newly proposed structure operates at low voltage because the depletion region expands from the p/n junctions at the both edges of the p or n type neutral region along the waveguide and the reverse bias voltage required to deplete the whole region becomes low. Furthermore, the doping concentration of the p and n regions can be reduced because there is no constraint on the width of the depletion region, while in the case of the horizontal or vertical junction type, the doping concentration must be high so that the depletion-region width is within the width or the height of the waveguide. The low doping concentration results in the low junction capacitance and leads to the higher operation speed. In this paper the detailed characteristics of the newly proposed MZI modulator have been simulated. The operation voltage of the proposed device is only 1.5V at 13dB (95%) modulation for the arm length of 5mm, while in the case of vertical junction, the operation voltage is 8V at the same modulation and for the same arm length.

Detection of Antigen-Antibody Reaction Using Si Ring Optical Resonators Functionalized with an Immobilized Antibody-Binding Protein

We propose the integrated biosensor chip using Si ring resonators, where different receptor is immobilized on each sensor. Signal detection is carried out by the matrix of light-input and detection waveguides, which are respectively connected to laser diodes and photodetectors. The Si rings are arranged at the cross points. The unique point of our work is to use the silicon-binding protein (designated Si-tag), which binds to SiO2 surface, as an anchoring molecule to immobilize bioreceptor on the Si rings in an oriented manner. In the integrated biosensor chip, many kinds of Si-tag-receptor fusions are required for high-throughput detection of analyte. In this paper, the Si ring biosensors were functionalized with various antibodies using the Si-tagged protein A as an intermediate binder, and the label-free detection of antigen have been achieved. We have developed the rapid functionalization method of Si-ring resonators with antibodies using Si-tagged protein A. Since various kinds of antibody can be used as receptors for biosensing, this method promises to realize the integrated biosensors for high-throughput analyte detection. # 2011 The Japan Society of Applied Physics

Charge retention and conduction mechanism of DNA memory transistor

The carrier behavior m DNA was examined using the DNA channel/SiO2/Si gate structure. In this case, electrodes with a gap of 120 nm using a substrate Si was prepared and DNA was fixed between the electrodes. The dID/dVD shows the maximum value at the drain voltage of 0.7 V. This phenomenon relates to the trapped and detrapped electrons in DNA. The electrons were trapped by guanine-base, and they were detrapped by the electric field in the channel. In the case of p-Si, the holes of majority earriers are emitted from the drain electrodes by recombination of electrons and holes in the DNA channel.

Study of the conduction mechanism of the DNA memory FET

The carrier behavior in DNA was examined using the DNA channel/SiO2/Si gate structure. The source/drain electrodes with a gap of 120 nm etching a SOI film was prepared and DNA was fixed between the electrodes. The dID/dVD shows the maximum value at the drain voltage of 0.3 V. This phenomenon relates to the trapped and detrapped electrons in DNA. The electrons were trapped by guanine-base, and they were detrapped by the electric field in the channel.

Slot ring biosensors using silicon nitride waveguides with small temperature coefficient

We propose the biosensor chip using optical ring resonators. Although the detection of biomarkers for the diagnosis of diseases generally requires high sensitivity of the order of 10-9 g/ml, the detection sensitivity of our device was of the order of 10-7 g/ml. In this paper, we show that 10 or 100 times higher sensitivity than the previous biosensor is accomplished by the following three strategies; (1) using slot-type waveguides, (2) using silicon nitride (SiN) as the waveguide core, (3) improvement of measurement system.