T. Tokuda

Laboratory investigation of microelectronics-based stimulators for large-scale suprachoroidal transretinal stimulation (STS)

This paper describes the technological developments underlying the realization of a reliable and reproducible microchip-based stimulator with a large number of stimulus electrodes. A microchip-based stimulator with over 500 electrodes for suprachoroidal transretinal stimulation (STS) is proposed in this paper, and an example is presented. To enhance reliability and reproducibility for such a large array, we introduce a flip-chip bonding technique and place microchips on the reverse side of a substrate. A square microchip of size 600 microm was fabricated using 0.35 microm standard CMOS process technology. Twelve microchips were flip-chip bonded on a polyimide substrate through Au bumps. To evaluate the feasibility of the proposed device, we successfully fabricated a stimulator with 12 microchips and 118 electrodes made of Pt/Au bumps, and demonstrated their operation in a saline solution for 2 weeks. Also, to evaluate the device operation in vivo, a stimulator with one active IrO(x) electrode was implanted into the scleral pocket of a rabbit and electrical evoked potential (EEP) signals with a threshold of 100 microA were obtained. We also fabricated a simulator with 64 microchips that has 576 electrodes (9 electrodes in a microchip times 64 microchips).

Pulse modulation CMOS image sensor for bio-fluorescence imaging applications

For wide dynamic range, compatibility with digital circuits, and low-voltage operation, the pulse modulation technique is suitable for an implanted bioimage sensor. We demonstrate bio-fluorescence imaging of the hippocampus in a sliced mouse brain using a pulse modulation-based image sensor. The sensor architecture and system configuration are discussed. In addition, we develop an imaging device for implantation into a mouse brain in order to measure the neural activity in the hippocampus. The device is composed of a pulse modulation image sensor with 128/spl times/128 pixels and a fiber illuminator on a polyimide substrate.

Effect of lower growth temperature on C incorporation in GeC epilayers on grown by MBE

Abstract Effect of lower growth temperature T s on C incorporation to substitutional sites in Ge 1−x C x / Si (0 0 1) grown by molecular beam epitaxy was investigated. To enhance the non-equilibrium growth condition, the temperature T s was lowered from 600°C down to 300°C. The C incorporation into substitutional sites of GeC epilayers was very sensitive to T s . X-ray diffraction (XRD) measurement indicated that the substitutional C composition x increased with decrease in T s from 600°C to 400°C. At T s ⩽350°C, the estimation of x by the XRD analysis was impossible because of polycrystallization. The Raman shift measurement enables to estimate x for T s ⩽350°C, as consequently larger x than that grown at T s =400°C was verified. The enhancement of non-equilibrium growth condition by decreasing T s was important to increase x .

Optimization of Sputtering Condition of IrOx Thin Film Stimulation Electrode for Retinal Prosthesis Application

We have optimized the sputtering condition of the RF sputtering deposition for the fabrication of the iridium oxide thin film used in retinal prosthesis applications. The deposited IrOx thin films were characterized by using the cyclic voltammetry method and the charge delivery capacity was calculated from the integral of the generic CV curve. From the experimental results, the charge delivery capacity of IrOx under the best sputtering condition was improved to more than 50 times that of Pt. We also verified from our in vivo experiment results that IrOx has a better charge delivery capacity than that of Pt. The in vitro and in vivo experimental results also show that IrOx is a promising candidate for retinal prosthesis applications.

CMOS-based smart-electrode-type retinal stimulator with bullet-shaped bulk Pt electrodes

A CMOS-based flexible retinal stimulator equipped with bullet-shaped bulk Pt electrodes was fabricated and demonstrated. We designed a new CMOS unit chip with an on-chip stimulator, single- and multi-site stimulation modes, and monitoring functions. We have developed a new structure and packaging process of flexible retinal stimulator with bullet-type bulk Pt electrode. We have confirmed the retinal stimulation functionality in an in vivo stimulation trial on rabbits retina.

Organic-Inorganic Hybrids for Bioinert Coating on Implantable Electronic Devices

For the purpose of bioinert coating on electronic devices, we developed the non-hydrolytic sol-gel derived organic-inorganic hybrid materials by addition of epoxy groups which can adhere strongly to the surface of electronic silicon device. The adhesion and chemical properties of hybrids were investigated as a function of epoxy group contents. The hybrids were prepared from 3-metacrloxypropyltrimethoxysilane (MPTS) and 3-glycidoxypropyltrimethoxysilane (GPTS) and diphenylsilanediol. The transparent hybrids were obtained after curing by UV irradiation. The adhesion properties of the hybrids were estimated by the maximum load to resist in a scratch test. The adhesion property of the hybrids increased with addition of GPTS and the highest adhesion was obtained from the hybrid with 5-10 mol% of GPTS. From the element analysis, Si concentrations of all the solutions were less than 2 mM after soaking for 7 d. The Si concentrations were not changed with increasing soaking period. The addition of epoxy groups is effective on improvement of adhesion property of the silica-based hybrid without loosening its chemical stability.

Toward 1000-ch electrode array based on distributed microchip architecture for retinal prosthesis

A smart stimulator for retinal prosthesis that is biocompatible and fully compatible with a standard LSI structure was developed towards the goal of 1000-ch electrodes. Our stimulator is based on multi-microchip architecture and offers mechanical flexibility as a result of the distributed architecture used for the micro-sized LSI chips, which are small enough that the array can be bent. The device should allow tight fitting to the eyeball and thus effective stimulation of retinal cells. In addition, our stimulator can reduce the number of electrical connections required between electrodes; inter-chip communication circuits incorporated in the micro-sized LSI chip help to reduce electrical wiring between the micro-nodes. Toward a 1000-ch electrode, we have improved the smart distributed microchip-based stimulator

A multi-chip-architecture based flexible stimulation device for retinal prosthesis with a flip-chip packaging technique

In the present work, we designed a multi-chip-architecture based flexible neural stimulation device for retinal prosthesis. Based on the multi-chip architecture, a novel CMOS stimulation device was successfully designed and characterized. A packaging technique for thin, flexible neural stimulation device was also proposed and demonstrated. Flip-chip bonding technology plays an essential role in the fabrication of the present thin and flexible neural stimulation device

Lensless imaging device for digital counting of fluorescent micro-droplet chambers

We developed a miniaturized lensless fluorescence imaging device for digital counting of micro-droplet chamber array, which is used in single molecule detection. Fluorescent beads in a droplet array were imaged with the device and its resolution was improved by using deconvolution method.

Polarization-analyzing image sensor based on standard CMOS technology

In this work, we propose and demonstrate a technology to realize polarization-analyzing CMOS image sensors. We developed a polarization-analyzing pixel with embedded polarizers. We characterize the performances of the sensor and demonstrate its functionality in polarimetric measurement of chiral solutions.