Yoshiteru Amemiya

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.

Si Ring Optical Resonators for Integrated On-Chip Biosensing

Si ring optical resonators were fabricated for integrated on-chip biosensing, and tested for their sensing ability using sucrose solution. Resonance wavelength shifts were observed depending on the concentration of the solution. By detecting the output intensity change at a fixed wavelength, the detection sensitivity of the resonator became ten times larger than that obtained by detecting a resonance wavelength shift directly. Si ring optical resonators were applied to biomaterial sensing such as streptavidin and bacterial cells using the silicon-binding protein Si-tag, which enables receptors to be immobilized directly on the Si dioxide surface. For biosensing in aqueous solutions, the simulation results show that a wavelength of 1.3 µm is suitable. The results of this work indicate the possibility of further increasing sensing ability.

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.

Photoelastic Effect in Silicon Ring Resonators

The photoelastic effect of Si was measured in a real optical device, a racetrack ring resonator. The sample holder that can induce strain mechanically was fabricated and the strain dependence of resonance wavelength was investigated. The holder can induce a 10-4 order strain and a 0.1 nm order shift of resonance wavelength induced by this strain was observed. By subtracting the contribution of change in the circumference of the racetrack ring resonator from the resonance wavelength shift, the photoelastic effect was estimated. As a result, the obtained photoelastic coefficient was consistent with that of bulk Si.

Silicon photonic crystal resonators for label free biosensor

We report the fabrication and characterization of a two-dimensional (2D) silicon photonic crystal biosensor consisting of waveguides and cavity-type and defect-type resonators for enhancing the interactions between light and biomaterials. Sensitivity was measured using sucrose solution and the sensor showed the highest sensitivity [1570 nm/RIU (refractive index unit)] ever reported. We also investigated cavity size effects on resonance wavelength shift, and we observed that a large cavity exhibits a greater resonance wavelength shift. The fabricated sensor has shown a high Q of ~105 in water and a device figure of merit of 1.2 × 105, which represent the improvements of the device performance over other photonic-crystal-based sensors.

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.

Design and Simulation of Silicon Ring Optical Modulator with p/n Junctions along Circumference

A Si ring optical modulator, where a low operation voltage is expected, is proposed. In this device, p/n junctions are arranged along the circumference of the ring resonator. By simulation, the propagation loss 95% modulation at 1 V, where the length of the p/n region is 150 nm. Multi-interference occurs between the light reflections at the interfaces of neutral and depletion regions. When the resonance wavelength of multi-interference is equal to that of the ring resonator, the effect of multi-interference is simulated. Moreover, it is shown that the multi-interference effect is not the problem when a different resonance wavelength is used as an input optical signal.

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.

Influence of surface smoothing on spin Seebeck effect of Ce1Y2Fe5O12 deposited by metal organic decomposition

Thus far, Bi1Y2Fe5O12 (Bi:YIG) films deposited by metal organic decomposition (MOD) are mainly used for magnetic insulation film of spin Seebeck devices. In order to increase the power conversion efficiency of these devices, we focused on Ce1Y2Fe5O12 (Ce:YIG), which has a larger Faraday rotation than Bi:YIG. Since there has been no report, except for the patent document, concerning the deposition of Ce:YIG films by MOD, we investigated the appropriate annealing temperatures, and we found that Ce:YIG films are crystallized when the annealing temperature is over 800 °C. However, since no electromotive force has been observed, we checked the surface roughness of Ce:YIG films by atomic force microscopy (AFM). Since their surfaces of Ce:YIG films were very rough, it was mechanically polished (MP). Then, an electromotive force of, at most, 11.3 µV was generated. This is the first report concerning the spin Seebeck effect of Ce:YIG deposited by MOD.