ARTIFICIAL RETINA USING

THIN FILM TRANSISTOR

Submitted By : BRIJITH P P

RETINA STRUCTURE

INTRODUCTION• The Artificial Retina made using Thin-Film Transistors, which can

be fabricated on transparent and flexible substrates.

• Electronic photo devices and circuits are integrated on the artificial retina.

• Implanted on the inside surface of the living retina at the back part of the human eyeballs. Wireless power supply is used

Major Diseases of Eye Retinitis Pigmentosa• Hereditary genetic disease.• Degeneration of the retina• Gradually progress towards center of eye.• Tunnel vision results

Macular Degeneration

• Genetically related.• Cones in macula region degenerate. • Loss or damage of central vision• Common among aged people.

Age Related Macular Degeneration

RETINAL IMPLANTATION• A retinal implant is a biomedical implant technology

• The first application of an implantable stimulator for vision restoration was developed by Drs. Brindley and Lewin in 1968.

• There are two types of retinal implants namely epiretinal implant and subretinal implant.

EPIRETINAL IMPLANT

EPIRETINAL IMPLANT• Advantages:-

Minimizes the amount of microelectronics implanted and upgrades are easy to do on the wearable portion thus avoiding future surgery

Heat can be dissipated into the vitreous humor External control over image processing allowing for

customizability, possible better clarity

• Disadvantages:-

Difficulty attaching the implant to the fragile inner retina Complicated processing.

SUBRETINAL IMPLANT

CIRCUIT OPERATION• It uses the same fabrication processes as conventional poly-Si TFTs

and encapsulated using SiO2• The retina array includes matrix-like multiple retina pixels• The retina pixel consists of a photo transistor, current mirror, and load

resistance.• The retina pix-els irradiated with bright light output a higher Vout,

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

SUBRETINAL IMPLANT• Advantages

Utilizes the surviving bipolar cells – the next step in the pathway –Retinal processing can take place

Placing the micro photodiodes between layers on the retina will allow for it to be held in position next to functioning cells

• Disadvantages:Limited spaceAmbient light may not be adequate to generate current in

this array Additional power supplies can be used to improve the

light intensity.

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 necessary.

• Ion implantation is one of the key factors in fabricating

ION DOPING TECHNIQUE• The new I/D system which is one of the non mass separated

implanters. 5 percent Phosphane (PH3) or 5 percent Diborane (B2H6) diluted by hydrogen is used for the doping gas

• Main features of this system are:1) A large beam area (over 300 mm square)

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

WIRELESS POWER SUPPLY USING INDUCTIVE COUPLING

• For implanted electrical power to function, either an im-planted battery or via wireless power transmission used.

• For proper retinal functioning, continuous power transmission is required.

• Inefficient transmission of power is a performance limiting factor.

• High density electrode array with more than 1000 electrodes will consume about 45 mW of power.

• Chip-25mw

• Neuronal stimulation-20mw

• Based on 64 simultaneously operating electrodes each requiring a maximum of 0.3 mW at 60 Hz image refresh rate.

Disadvantages of power transmission• Difficulty in placing a large receive coil inside the eye.• We face are large separation between the coils• Reduction in power transfer to the device.

Overcome problems:• Intermediate link between the primary and secondary coil• Which are embedded under the wall of the eye.

WORKING

• The power transmitter consists of an ac voltage source(10V,34khz) and induction coil.

CONCLUSIONS

People suffering from low vision to, people who are completely blind will benefit from this project.This technology used by US and economic Europe countries.

Hope in INDIA also will acquire this technology soon….Hope in INDIA also will acquire this technology soon….

REFERENCES

www.researchgate.com www.onlinelibrary.wiley.com www.electrochem.org en.m.wikipedia.org www.nano-retina.com