A Technical Seminar Report

Submitted in Partial Fulfilment of the academic requirements

For the award of degree of

Bachelor of Technology

In

Electronics and Communication Engineering

BY

P.VIVEK 11C71A04A0

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERINGELLENKI COLLEGE OF ENGINEERING AND TECHNOLOGY

(Affiliated to Jawaharlal Nehru Technological University-Hyderabad)

ELLENKI COLLEGE OF ENGINEERING AND TECHNOLOGY

(Affiliated to Jawaharlal Nehru Technological University-Hyderabad)

2014-15

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

CERTIFICATE

This is to certify that the seminar entitled “ARTIFICIAL RETINA USING THIN FILM

TRANSISTOR” is a Presentation given by,

P.VIVEK 11C71A04A0

In partial fulfilment of the academic requirements of the award of the degree of Bachelor of

Technology in Electronics and Communications Engineering, submitted to the Department of

Electronics and Communications Engineering, Ellenki College of Engineering and Technology,

Hyderabad during the period 2014-15.

T. SRAVAN KUMAR

HOD(ECE) EXTERNAL EXAMINER

DECLARATION

I hereby declare that the SEMINAR entitled “ARTIFICIAL RETINA USING THIN FILM

TRANSISTOR” is the Technical seminar by me at “ECET” during the academic year 2014-15 and is

submitted in partial fulfilment of the requirement for the award for degree of Bachelor of Technology in

Electronics and Communication Engineering from JAWAHARLAL NEHRU TECHNOLOGICAL

UNIVERSITY, HYDERABAD.

P.VIVEK

(11C71A04A0)

ACKNOWLEDGEMENT

With great pleasure I want to take this opportunity to express my heartfelt gratitude to all the

people who helped in making this seminar work a grand success.

I am highly indebted to Principal Dr. SUKDEO SAHO for giving me the permission to carry out

this seminar.

And with deep sense of gratitude and I would like to thank Mr. T. SRAVAN KUMAR, Head of

the Department of Electronics and Communications Engineering, for his constant support throughout the

period of our study in ECET.

I would like to thank the Teaching & Non-teaching staff of Department of Electronics & Communication

Engineering for sharing their knowledge with us.

I would also like to express my heartfelt and sincere thanks to my parents who have been

constantly backing us at every stage of my life.

P.VIVEK

ABSTRACT

For those millions of us whose vision is not perfect, there are glasses. But for those hundreds of

thousands who are blind devices that merely assist the eyes just aren’t enough, what they need

are alternative routes by which the sights of world can enter the brain .Technology has created

many path ways for the mankind. Now technology has improved to that extent where in the body

can be controlled using a single electronic chip. Now it is the turn of artificial vision through

artificial retina. Chips designed specially to imitate the characteristics of retina and the cones

rods of organs of sight are implanted with a microsurgery

Artificial retinas have been desired to recover the sight sense for sight handicapped people.

Recently, artificial retinas using external cameras, stimulus electrodes, and three dimensional

large scale integrations (LSIs) have been actively developed for patients suffering from retinitis

pigmentosa and age related muscular degeneration. So in this seminar, we will discuss about the

possibilities of artificial retina using thin film transistors (TFTs), which can be fabricated on

transparent and flexible substrates. Electronic photo devices and circuits are integrated on the

artificial retina, which is implanted on the inside surface of the living retina at the back part of

the human eyeballs. In addition wireless power supply is used to drive the object. This helps to

eliminate the connection wires and to realize complete artificial internal organs to improve the

quality of life.

CONTENTS

CHAPTER 1

INTRODUCTION…………………………………………………………………............. ……09Visual SystemRetinaArtificial retinaRetinal implantEpiretinal ImplantSubretinal Implant

CHAPTER 2

ARTIFICIAL RETINA USING THIN FILM TRANSISTOR……………………………. 12Thin-film transistorArtificial retina using thin film transistorFabrication of thin film phototransistorsION Doping TechniquesSelf Aligned structure and TFT characteristicsNew Masking technique and CMOS ProcessDevice characterization of p/i/n Thin- film phototransistors for photo sensor applications Electrooptical Measurement

CHAPTER 3

WIRELESS POWER SUPPLY USING INDUCTIVE COUPLING……………………………16IntroductionWorking

CHAPTER 4

SUMMARY……………………………………………………………………………………...xx

CHAPTER 5

CONCLUSION…………………………………………………………………………………..56

CHAPTER 6

REFERENCES…………………………………………………………………………………45

LIST OF FIGURES

1.1VISUAL SYSTEM

1.2 RETINA

2.1RETINAL ARRAY

2.2RETINAL ARAY WITH RETINA PIXEL

2.3WORKING OF ARTIFICIAL RETINA

2.4MODEL OF THE ARTIFICIAL RETINA FABRICATED ON A TRANSPARENT AND

FLEXIBLE SUBSTRATE AND IMPLANTED USING EPIRETINAL IMPLANT

2.5SCHEMATIC DIAGRAM OF THE NEW ION DOPING SYSTEM

2.6SCHEMATIC CROSS SECTIONAL VIEWS OF A SELF ALIGNED AND A NON SELF

ALIGNED TFT

2.7THE CHARACTERISTICS OF S/A TFT ALIGNED AND A NON SELF ALIGNED TFT

P/I/N TFPT

2.8ELECTRO OPTICAL MEASUREMENT

2.9ELECTROOPTICAL CHARACTERISTIC

3.1POSSIBLE COIL LOCATIONS

3.2WIRELESS POWER SUPPLYWITH INDUCTIVE COIL

4.1 DETECTED RESULT OF IRRADIATED LIGHT

Chapter 1

INTRODUCTION

The ability to interpret the surrounding environment by processing information that is contained

in visible light is called eyesight, sight, or vision The various components involved in vision are

referred to collectively as the visual system

VISUAL SYSTEM

The act of seeing starts when the lens of the eye focuses an image of its surroundings onto a

light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of

the brain that is isolated to serve as a transducer for the conversion of patterns of light into

neuronal signals. The lens of the eye focuses light on the photoreceptive cells of the retina, which

detect the photons of light and respond by producing neural impulses. These signals are

processed in a hierarchical fashion by different parts of the brain, from the retina upstream to

central ganglia in the brain.

fig1.1

RETINA

The  retina (/ ̍ r ɛ t ɪ n ə /  RET -i-nə, pl. retinae, / ̍ r ɛ t i n i ː/; from Latinrēte, meaning "net") is a light-

sensitive layer of tissue, lining the inner surface of the eye. The optics of the eye create an image

of the visual world on the retina (through the cornea and lens), which serves much the same

function as the film in a camera. Light striking the retina initiates a cascade of chemical and

electrical events that ultimately trigger nerve impulses. These are sent to various visual centers of

the brain through the fibers of the optic nerve The only neurons that are directly sensitive to light

are the photoreceptor cells. These are mainly of two types: the rods and cones. Rods function

mainly in dim light and provide black-and-white vision, while cones support daytime vision and

the perception of colour.

fig1.2

ARTIFICIAL RETINA

Artificial retina may refer to functioning implant designed to restore sight or this is an electronic

device that could translate images and electrical pulses that could restore vision. These have been

designed to recover the sight sense for sight handicapped people. Here electronic photo devices

and circuits substitute for deteriorated photoreceptor cells. These devices are implanted inside

the eyes which is called retinal implant or retinal prothesis

RETINAL IMPLANTATION

A retinal implant is a biomedical implant technology currently being developed by a research

institutions worldwide The implant is meant to restore useful vision to people who have lost their

vision due to degenerative eye conditions such as retinitis pigmentosa (RP) or macular

degeneration. There are three types of retinal implants currently in clinical trials: epiretinal

Implants (on the retina), subretinal Implants (behind the retina), and suprachoroidal

implants (above the vascular choroid). Retinal implants provide the user with low resolution

images by electrically stimulating surviving retinal cells. Such images may be sufficient for

restoring specific visual abilities, such as light perception and object recognition.

The Argus II retinal implant has received market approval in the USA in Feb 2013 and in Europe

in Feb 2011, becoming the first approved implant. The device may help adults with RP who have

lost the ability to perceive shapes and movement to be more mobile and to perform day-to-day

activities. The subretinal device is known as the Retina Implant and was originally developed in

Germany. It completed a multi-centre clinical trial in Europe and was awarded a CE Mark in

2013, making it the first wireless subretinal device to gain market approval

EPIRETINAL IMPLANT

Epiretinal implants sit in the inner surface of the retina The epiretinal implant requires an

external video camera to acquire images The camera receives an image of the surrounding

environment, processes the image, and communicates the image information to the implanted

electrode array wirelessly via telemetry. An external transmitter is also required to provide

continuous power to the implant via radio-frequency induction coils or infrared lasers. The

external camera and image processing chip are generally mounted onto eyeglasses for the

patient.[3] The image processing involves reducing the resolution of the image and converting the

image into a spatial and temporal pattern of stimulation to activate the appropriate retinal cells. [4]

[12] The epiretinal implant system must be capable of processing images in real time to prevent

any noticeable delays between the camera input and retinal stimulation, which could confound

visual perception. Epiretinal implants are advantageous as they bypass a large portion of the

retina. The epiretinal implants could provide visual perception to individuals with retinal

diseases extending beyond the photoreceptor layer The majority of electronics can be

incorporated into the associated external components, allowing for a smaller implant and simpler

upgrades without additional surgery. The external electronics also allow a doctor to have full

control over the image processing and adapt the processing for each patient. Additionally, the

location of epiretinal implants allows the vitreous humor to serve as a heat sink for the implant

SUBRETINAL IMPLANT

Subretinal implants sit on the outer surface of the retina, between the photoreceptor layer and the

retinal pigment epithelium, directly stimulating retinal cells and relying on the normal processing

of the inner and middle retinal layers. It has a simpler design .It replace damaged rods and cones

by Silicon plate carrying 1000s of light-sensitive micro photodiodes each with a stimulation

electrode. Light from image activates the micro photodiodes, the electrodes inject currents into

the neural cells. Among the above implant methods, the epiretinal implant has features that the

image resolution can be high because the stimulus signal can be directly conducted to neuron

cells and that living retinas are not seriously damaged. Trade off for the two types is that,

Subretinal Implant uses the entire retina (except the rods/cones). Epiretinal Implant does not; it

must replace the function of entire retina and convert light to neural code. But the input to the

Epiretinal Implant is more easily controlled (external camera)

Chapter 2

ARTIFICIAL RETINA USING THIN FILM TRANSISTORS

THIN-FILM TRANSISTOR 

A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin

films of an active semiconductor layer as well as the dielectric layer and metallic contacts over a

supporting (but non-conducting) substrate

ARTIFICIAL RETINA USING THIN FILM TRANSISTORS

Artificial Retina using Thin-Film Transistors (TFTs) is fabricated on transparent and flexible

substrates; it uses the same fabrication processes as conventional poly-Si TFTs and encapsulated

using SiO2, in order to perform in corrosive environments. Although the artificial retina is

fabricated on the glass substrate here to confirm the elementary functions, it can be fabricated on

the plastic substrate. The artificial retina using TFTs is shown in Figure

fig2.1

fig2.2

The retina array includes matrix-like multiple retina pixels. Although large contact pads are

located for fundamental evaluation, a principal part is 27 300 cm2, which corresponds to 154 ppi.

The retina pixel consists of a photo transistor, current mirror, and load resistance. The photo

transistor is optimized to achieve high efficiency, and the current mirror and load resistance are

designed by considering the transistor characteristic of TFTs. The photosensitivity of the reverse-

biased p/i/n poly-Si phototransistor is 150 pA at 1000 lx for white light and proper values for all

visible color lights. The field effect mobility and the threshold voltage of the n-type and p-type

poly-Si TFT were 93 cm2 V -1s-1 , 3.6 V, 47 cm2 V -1s-1 and -2.9 V, respectively. First, the

photo transistors perceive the irradiated light (Lphoto) and induce the photo-induced current (Iphoto).

Next, the current mirror amplifies Iphoto to the mirror current (Imirror). Finally, the load resistance

converts Imirror to the output voltage (Vout). Consequently, the retina pixels irradiated with bright

light output a higher Vout, whereas the retina pixels irradiated with darker light output a lower

Vout.

fig2.3

Electronic photo devices and circuits are integrated on the artificial retina, which is implanted on

the inside surface of the living retina at the back part of the human eyeballs. Since the irradiated

light comes from one side of the artificial retina and the stimulus signal goes out of the other

side, the transparent substrate is preferable. The concept model of the artificial retina fabricated

on a transparent and flexible substrate and implanted using epiretinal implant is shown in Figure

fig2.4

FABRICATION OF THIN FILM PHOTOTRANSISTORS

Low temperature poly-Si TFTs have been developed in order to fabricate active matrix LCDs

with integrated drivers on large glass substrates. For integrated drivers, CMOS configurations are

indispensable. Self-aligned TFTs are also required because of their small parasitic capacitance

which can realize high speed operation. Since ion implantation is one of the key factors in

fabricating such as TFTs and CMOS configurations, several non-masses separated I/D

techniques are proposed. These techniques, however, are not suitable for conventional poly-Si

TFT processes and cannot be applied to large glass substrates, especially those over 300 mm

square.

ION DOPING TECHNIQUES

Figure shows a schematic diagram of the new I/D system which is one of the non-mass-separated

implanters. 5 percent PH3 or 5 percent B2H6 diluted by hydrogen is used for the doping gas and an

RF plasma is formed in the chamber by RF power with a frequency of 13.56 MHz Ions from

discharged gas are accelerated by an extraction electrode and an acceleration electrode and are

implanted into the substrate. Main features of this system are:

1) A large beam area (over 300 mm square)

2) A high accelerating voltage (maximum: 110 KeV)

With this system, impurities can be implanted over the entire 300 mm square substrate with a

maximum accelerating voltage of over 110 KeV which is sufficient for implanting impurities

through the 150nm SiO2 gate insulator. On the other hand, the conventional non-mass-separated

I/D techniques are severely limited in beam area, which is about 150 mm in diameter.

Furthermore, they are incapable of implanting impurities through the gate insulator since the

accelerating voltages are less than 10 KeV. Consequently, the gate insulator must be removed

prior to implantation, which can result in failure from surface contamination or breakdown

between gate electrodes and source and drain regions.

fig2.5

SELF ALIGNED STRUCTURE AND TFT CHARACTERISTICS

S/A TFTs and non-S/A TFTs with 25 nm thick as-deposited channel poly-Si r31 were fabricated

on the glass substrates, and the new I/D technique was used to achieve a self-aligned structure.

Schematic cross sectional views of a S/A TFT and a non-S/A TFT are illustrated in Figure 2.4(a)

and 2.4(b), respectively. Since the parasitic capacitance between the gate electrode and source

and drain regions of a S/A TFT is estimated to be only about 2 -5 percent that of a non-S/A TFT,

high speed operation can be expected.

fig2.6

fig2.6

The characteristics of S/A TFTs are compared with those of non-S/A TFTs. The comparisons in

the n-channel and the p-channel TFTs are shown in Figure and Figure, respectively. In these

experiments, it is found that the characteristics of S/A and non-S/A TFTs are similar, and

mobility of the n-channel TFTs are around 5 cm2/V-sec while those of the p-channel TFTs are

around 3 cm2/V.sec. It should be noted that no degradation can be observed as a result of using

the new I/D technique.

NEW MASKING TECHNIQUE AND CMOS PROCESS

A non-resist-masking process, however, is required when the CMOS configuration is fabricated

using the new I/D technique, since the temperature of the substrate reaches about 300oC due to

the high accelerating voltage. In order to solve this problem, a new masking technique is also

proposed. In this process, n-channel gate electrodes and p-channel gate electrodes are formed

separately in a sequential manner. In the process sequence for the CMOS configuration, An SiO 2

buffer layer is deposited on the glass substrate to protect TFTs from contamination from

components of the glass. Then, pad poly-Si patterns are formed for source and drain regions,

which are made of a 150 nm poly-Si film. A 25 nm channel poly-Si layer is deposited by low

pressure chemical vapor deposition (LPCVD) at 600oC. Thinner poly-Si film gives better

electrical characteristics such as high ON current, low OFF current and low photo-current. After

patterning of the channel poly-Si layer, a 150 nm SiO2 gate insulator is deposited by electron

cyclotron resonance chemical vapor deposition (ECRCVD) at 100oC in a vacuum. Then, a Cr

film is deposited at 180oC. First, only p-channel gate electrodes are formed. The next step is to

form source and drain regions of p-channel TFTs by the new I/D technique. Boron ions are

implanted through the gate insulator with a dose of 5 x 1015 cm-2 at energy of 80 keV. N-

channel gate electrodes are also formed and phosphorus ions are implanted with a dose of

3x1015 cm-2 at energy of 110 keV by the new I/D technique Impurities are activated by a XeCl

excimer laser.

DEVICE CHARACTERIZATION OF P/I/N THIN- FILM

PHOTOTRANSISTORS FOR PHOTO SENSOR APPLICATIONS

Thin-Film photo devices are promising for photo sensor applications, such as ambient light

sensors, image Scanners, artificial retinas etc. Here thin-film photo devices are integrated with

low-temperature poly-Si thin-film transistors. The p/i/n TFPT is shown in Figure. 2.7. The p/i/n

TFPT is fabricated on a glass substrate using the same fabrication processes as TFTs which were

discussed earlier. First, an amorphous-Si film is deposited using low-pressure chemical-vapor

deposition of Si2H6 and crystallized using XeCl excimer laser to form a poly-Si film, whose

thickness is 50 nm. Next, a SiO2 film is deposited using plasma-enhanced chemical-vapor

deposition of tetraethylorthosilicate to form a control-insulator film, whose thickness is 75 nm. A

metal film is deposited and patterned to form a control electrode. Afterward, phosphorous ions

are implanted through a photo resist mask at 55 keV with a dose of 2 1015 cm-2 to form an n-

type anode region, and boron ions are also implanted through a photo resist mask at 25 keV with

a dose of 1.5x1015 cm-2 to form a p-type cathode region. Finally, water-vapor heat treatment is

performed at 400oC for 1 h to thermally activate the dopant ions and simultaneously improve the

poly-Si film, control-insulator film, and their interfaces. The p/i/n TFPT must be illuminated

from the backside of the glass substrate because the control electrode is usually formed using an

opaque metal film. Therefore, the other LTPS TFTs are also illuminated when the p/i/n TFPT is

integrated with them. However, the photo leakage current in the LTPS TFTs can be negligible by

appropriately designing them, i.e., he gate width should be wide for the p/i/n TFT, whereas

narrow for the LTPS TFTs.

fig2.7

ELECTROOPTICAL MEASUREMENT

fig2.8

The electro optical measurement is shown in Figure.. The p/i/n TFPT is located on a rubber

pacer in a shield chamber and connected via a manual prober to a voltage source and ampere

eter. White light from a halogen lamp is formed to be parallel through a convex lens, reflected by

triangular prism and irradiated through the glass substrates to the back surfaces of the p/i/n

TFPT. Although the light from a halogen lamp includes the light from 400 to 750 nm with a peak

around 600 nm and is therefore reddish despite a built-in infrared filter, the conclusion in this

research is generally correct. The electric current between the n- and p-type regions is detected

with changing the applied voltage and irradiated illuminance. The electrooptical characteristic is

shown in Figure.2.9. First, it is found that the dark current, Idetect when Lphoto = 0, is sufficiently

small except when Vctrl and Vapply are large. The reason is because the p/i and i/n junctions

steadily endure the reverse bias. This characteristic is useful to improve the S/N ratio of the p/i/n

TFPT for photo sensor applications. Next, Idetect increases as Lphoto increases. This characteristic is

also useful to acquire fundamental detectability. Finally, Idetect becomes maximal when Vctrl Vapply.

This reason is discussed below:

When Vctrl ¡ 0, since Vctrl ¡ in the entire intrinsic region, a hole channel is induced, and a pseudo

p/n junction appears near the anode region. Since a depletion layer is narrowly formed there,

where carrier generation occurs due to light irradiation, Idetect is small. When Vctrl is approximately

equal to 0, although a hole channel is still induced, since Vctrl is approximately equal to near the

cathode region, the hole density is low there, which is similar to the pinch off phenomena in the

saturation region of MOSFETs. Since another depletion layer is widely formed there, I detect is

large. When 0 Vctrl Vapply, since Vctrl on the side of the cathode region, an electron channel is

induced there. At the same time, since Vctrl on the side of the anode region, a hole channel is still

induced there. Since the depletion layer is widely formed between the electron and hole

channels, Idetect is large. When Vctrl is approximately equal to Vapply, although an electron channel

is further induced, since Vctrl is approximately near the anode region, the electron density is low

there. Since the depletion layer is widely formed there, Idetect is large. Since generated carriers are

transported through the electron channel with high conductance instead of the hole channel, Idetect

becomes maximal. When Vapply Vctrl, since Vctrl ¿ in the entire intrinsic region, an electron

channel is further induced, and a pseudo p/n junction appears near the cathode region. Since

another depletion layer is narrowly formed there, Idetect is small. The anomalous increases of Idetec

when Vctrl and Vapply are large may be caused by the impact ionization and avalanche breakdown

in the depletion layers. The asymmetric behavior, for example, comparing Vctrl = 2 and + 5 V for

Vapply =3 V, may be occasioned by the difference of electric field because the hole density when

Vctrl = 2 V and donor density

fig2.9

Chapter 3

WIRELESS POWER SUPPLY USING INDUCTIVE COUPLING

INTRODUCTION

Many implanted electrical power to function; be it in the form of an implanted battery or via

wireless power transmission. It is often advantageous to develop methods for wireless power

transmission to an implant located deep inside the body as replacement of batteries which

requires additional surgery is undesirable. An example of this is a retinal prosthesis. A retinal

prosthesis can create a sense of vision by electrically stimulating intact neural cells in the visual

system of the blind. Such prosthesis will require continuous power transmission in order to

achieve real-time moving images. Efficient transmission of power is a performance limiting

factor for successful implementation of the prosthesis. We estimate that a high density electrode

array with more than 1000 electrodes will consume about 45 mW of power. This includes 25

mW to operate the electronics on the chip and an additional 20 mW for neuronal stimulation with

a 3.3 V stimulation threshold. The latter is calculated based on 64 simultaneously operating

electrodes each requiring a maximum of 0.3 mW at 60 Hz image refresh rate.

fig3.1

Inductive coupling of magnetic field is an efficient way for transmitting energy through tissue.

This is because electrical energy can be easily converted to magnetic energy and back using

conductive coils. Traditionally, a pair of inductive coils; a primary (transmit) and a secondary

(receive) coils, are used. The secondary coil can be located within the eye and the primary coil

external to the eye. However, several problems will arise if we implement this method. The first

problem is difficulty in placing a large receive coil inside the eye. This will require complicated

surgical procedure, often a major challenge in implementing a wireless power solution. The other

problems we face are large separation between the coils and the constant relative motion between

the primary and secondary coils. The latter problems result in reduction in power transfer to the

device. In order to overcome these problems we propose the use of an intermediate link between

the primary and secondary coil as shown in Figure 3.1. In this figure we show the possible

locations for one-pair coils and a two pair coils system which consists of an additional

intermediate link made out of a pair of serially connected coils. In this method, the secondary

coil is located under the sclera (eye wall) and is connected to the implanted device via electrical

wires which are embedded under the wall of the eye. By placing these components under the

sclera, we avoid having a permanent wire breaching through the eye wall. The transmit coil is

placed on the skin of the head at an inconspicuous location, for example at the back of the ear.

The intermediate coils are positioned with one end on the sclera over the receive coil and the

other end under the skin beneath the transmit coil. The advantage of this method is immunity to

variation in coupling due to rapid movements of the eye as relative motion between adjacent

coils is restricted. It also has the potential to increase the power transfer efficiency compared to a

one-pair coil system.

WORKING

fig3.2

The wireless power supply using inductive coupling is shown in Figure 3.2. The right graph in

Figure 3.2. is a measured stability of the supply voltage. This system includes a power

transmitter, power receiver, Diode Bridge, and Zener diodes. The power transmitter consists of

an ac voltage source and induction coil. The Vpp of the ac voltage source is 10 V, and the

frequency is 34 kHz, which is a resonance frequency of this system. The material of the

induction coil is an enameled copper wire, the diameter is 1.8 cm, and the winding number is 370

times. The power receiver also consists of an induction coil, which is the same as the power

transmitter and located face to face. The diode bridge rectifies the ac voltage to the dc voltage,

and the Zener diodes regulate the voltage value. The Diode Bridge and Zener diodes are discrete

devices and encapsulated in epoxy resin. Although the current system should be downsized and

bio-compatibility has to be inspected, the supply system is in principle very simple to implant it

into human eyeballs. As a result, the generated power is not so stable as shown in Figure 3.2.,

which may be because the artificial retina is fabricated on a insulator substrates, has little

parasitic capacitance, and is subject to the influence of noise. Therefore, it is necessary to

confirm whether the artificial retina can be correctly operated even using the unstable power

source.

Chapter 4

SUMMARY

The artificial retina using poly-Si TFTs and wireless power supply using inductive coupling are

located in a light-shield chamber, and Vout in each retina pixel is probed by a manual prober and

voltage meter. White light from a metal halide lamp is diaphragmmed by a pinhole slit, focused

through a convex lens, reflected by a triangular prism and irradiated through the glass substrate

to the back surfaces of the artificial retina on a rubber spacer. The real image of the pinhole slit is

reproduced on the back surface. Figure shows the detected result of irradiated light. It is

confirmed that the Lphoto distribution can be reproduced as the Vout distribution owing to the

parameter optimization of the wireless power supply system even if it is driven using the

unstable power source, although shape distortion is slightly observed, which is due to the

misalignment of the optical system or characteristic variation of TFTs.

fig4.1

It was found that the Lphoto profile can be correctly detected as the Vout profile even if it is driven

using unstable power source generated by inductive coupling, Diode Bridge, and Zener diodes.

In order to apply the artificial retina to an actual artificial internal organ, we should further

develop a pulse signal generator appropriate as photorecepter cells, consider the interface

between the stimulus electrodes and neuron cells, investigate the dependence of Vout on Lphoto,

which realizes grayscale sensing, etc. However, the above result observed, shows the feasibility

to implant the artificial retina into human eyeballs.

Chapter 5

CONCLUSION

With this technology there is an pulse signal generator appropriate as photoreceptor cells

for implementation.

There is feasibility to implant the artificial retina into human eyeballs and

At most the artificial retina restores sight to the blind

Chapter 6

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Thin-Film Transistors Driven by Wireless Power Supply IEEE SENSORS JOURNAL, VOL. 11,

NO. 7, JULY 2011.

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T.Shima, Device characterization of p/i/n thinfilm phototransistor for photosensor applications,

IEEE Electron Device Lett., vol. 31, no. 9, pp. 984986, 2010 • Satoshi Inoue, Minoru Matsuo,

Tsutomu Hashizume, Hideto Ishiguro, Takashi Nakazawa, and Hiroyuki Ohshima, LOW

TEMPERATURE CMOS SELF-ALIQNED POLY-Si TFTS AND CIRCUIT SCHEME

UTILIZING NEW ION DOPING AND MASKING TECHNIQUE www.ieeexplore.ieee.org.

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Mark E. Halpern, and Efstratios Skafidas wireless power delivery for retinal prosthesis , 33rd

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September 3, 2011

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Fujikado, Y. Tano, and J. Ohta, CMOS-based

multichip networked flexible retinal stimulator designed for image-based

retinal prosthesis, IEEE Trans. Electron Devices, vol. 56, no. 11,