Fumihiro Dasai

Fabrication of a 128

The charge transfer technique, which is capable of operating in charge accumulation-mode, is suitable for use in pH-imaging to detect small changes in potential. An advanced charge-transfer-type hydrogen ion image sensor consisting of 128 × 128 pixels with a 23-μm pixel pitch is fabricated. A new scanning system and high-performance drive buffer circuits are adopted to achieve high frame rates. For miniaturization of the sensor pixels, we developed an advanced new fabrication process. The pH sensitivity is 32.8 mV/pH when using standard pH solutions. Videos of the movement of hydrogen ions are clearly obtained with the 128 × 128 pixels display, and photo images are taken simultaneously with the videos of the movement of hydrogen ions. A frame rate of 58 frames per second is realized with this image sensor.

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Charge-transfer-type pH sensors can be used to improve pH sensitivity with enhanced signal-to-noise ratio by applying the charge-accumulation technique. Theoretically, the pH sensitivity improves directly with the accumulated count. However, in a conventional sensor structure, a quasi-signal resulting from low charge transfer efficiency limits the accumulated count. In this paper, an effective solution to the problem of the quasi-signal and the novel sensor structure are investigated.

128 Pixels Charge Transfer Type Hydrogen Ion Image Sensor

An integrated square wave voltammetry (SWV) redox sensor has been developed on the basis of a standard complementary metal–oxide–semiconductor (CMOS) process technology. The sensor consists of a square wave (SW) pulse generator, a voltage controller, and two electrodes for electrochemical analysis. Our proposed sensor is the first integrated sensor system of a SW pulse generator. Potassium ferricyanide solution was measured to obtain the characteristics of the proposed sensor. We confirmed that the dynamic ranges of potassium ferricyanide concentration and SW frequency were obtained from 0.6 to 6 mM and from 20 to 500 Hz, respectively. To verify the accuracy of the proposed sensor system, we performed a comparison between the fabricated sensor and an electrochemical analyzer.

High-Sensitivity Charge-Transfer-Type pH Sensor With Quasi-Signal Removal Structure

The improvement of a filter-less fluorescence sensor, by suppressing forward scattering in silicon by surface planarization is presented. A fluorescence microscope has been widely used in biochemical fields. However, it is difficult to miniaturize because optical filters and other parts are necessary. We previously developed a filter-less fluorescence sensor. The separation ability of excitation light and fluorescence in the previous device was 550:1. It is necessary to improve the separation ability. This study focuses on the suppression of forward-scattered incident light in silicon, through the enhanced surface planarization of polysilicon, which is the gate electrode material. The separation ability of the filter-less fluorescence sensor was increased from 550:1 to 1250:1 by the suppression of forward-scattered light.

Integrated Square Wave Voltammetry Redox Sensor System for Electrochemical Analysis

We have developed a CMOS-MEMS-based label-free protein sensor, which utilizes nonlinear optical transmittance change by the Fabry-Perot interference to enhance the sensitivity of surface-stress. Theoretical minimum detectable surface stress of the proposed sensor is predicted -1 μN/m which is two orders of magnitude above the peizoresistive type. A read-out tiny photocurrent from the multidimensional arrayed MEMS sensor is signal-processed by integrated source follower circuit, selector, and decoder. The integrated MEMS sensor array can be used for screening analysis for any cancers.

Filter-less fluorescence sensor with high separation ability achieved by the suppression of forward-scattered light in silicon

We developed a low-detection-limit filter-free fluorescence sensor by a charge accumulation technique. For charge accumulation, a floating diffusion amplifier (FDA), which included a floating diffusion capacitor, a transfer gate, and a source follower circuit, was used. To integrate CMOS circuits with the filter-free fluorescence sensor, we adopted a triple-well process to isolate transistors from the sensor on a single chip. We detected 0.1 nW fluorescence under the illumination of excitation light by 1.5 ms accumulation, which was one order of magnitude greater than that of a previous current detection sensor.

A CMOS-MEMS-based label-free protein sensor for high-sensitive and compact system

In this paper, the detection of fluorescence from the solution of a fluorescent dye with a submicromolar concentration by the filter-free fluorescence sensor is reported. The filter-free fluorescence sensor has a photo-gate structure and the intensities of excitation and fluorescent lights can be calculated from the photocurrents for different gate voltages. It makes it possible to measure various wavelengths even without optical filters and mirrors. The separation ability of excitation light (470 nm) and fluorescence (530 nm) in the developed filter-free fluorescence sensor was 1200:1 for LED light source. The fluorescent measurements were carried out for the dye of fluorescein isothiocyanate isomer. The excitation light with the wavelength of 470 nm was used, and the photocurrents were measured for the gate voltages of 1 V and 3 V, respectively. Based on the calculation, the fluorescence from fluorescein isothiocyanate isomer was detected for the solution with the concentration of as low as 100 nM (12 bases).

Improvements of low-detection-limit filter-free fluorescence sensor developed by charge accumulation operation

An advanced charge transfer type hydrogen image sensor consisting of 1024 × 1024 pixels with 12.1 μm pixel pitch, which contains the most pixels to date and half pitch compared to previous works, was fabricated. The new pixel layout of common ID electrodes and partition scanning system were designed for high-density image element (12.1 μm) and preventing a readout lag time. The pH sensitivity is 29.8 mV/pH using standard pH solutions. All 1024 × 1024 pixels are capable of measuring hydrogen ions, as demonstrated in the video of the hydrogen ion movement on the new sensor chip. To realize the high-density array sensor, observance of various movements of a cell can perform.

Fluorescence detection of submicromolar concentration using a filter-free fluorescence sensor

This paper presents a NEMS (Nano Electro Mechanical System) tunable color filter integrated with MOS driver circuits on an SOI (Silicon on Insulator) wafer. The NEMS electrostatic actuator could be designed a high mechanical resonance frequency with a relatively low drive voltage. The sub-wavelength grating and MOS driver circuits were made in a top and a substrate layer of the SOI wafer, respectively. The tiny anchors and pre-fabricated MOS transistors were covered by parylene N during the sacrificial release process using buffered hydrofluoric acid. Various structural colors depended on the pitch of the sub-wavelength grating were observed from integrated NEMS-LSI chip and NEMS TEG area. The color tuning from yellow to green was demonstrated at 20 V operation.

Realization of 1 million pixel charge transfer type ion image sensor with 12 µm pixel pitch

We have designed and fabricated a 2×4 electrochemical image sensor with CMOS signal processing circuits integrated on a single chip. Using a well-studied ferricyanide solution, a clear cyclic voltammetry curve was obtained from each working electrode of the array sensor. The external components used include a data generator and a data recorder. This sensor chip is an early prototype of a fully integrated system of a fast-scan electrochemical image sensor that uses microelectrodes.