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Artificial retinas have been desired to recover the sight sense for sight handicapped people. Electronic Photo devices and circuits substitutes deteriorated photoreceptor cells implanted inside the eyes.
Third year (ece),
JIET School of Engineering
and Technology for Girls ,
Normal vision is where light enters the eye and falls on
photosensitive cells that lie on the surface of the retina.
The "circuits" in the retina convert the light into a series of
coded electrical signals or neural pulses, and pass them onto
output cells called ganglion cells that transmit the coded
pulses to the brain via the optic nerve at the back of the eye.
The brain understands the stream of coded neural pulses and
translates it into meaningful images.
A common cause of blindness is when the retina is damaged
by diseases that kill the photoreceptors, and/or destroy the
circuits that create the coded neural pulses.
Blindness is caused by damage to clear structures in the eye that
allow the light to pass through, the nerves within the eye, the Optic
nerve and brain.
Various diseases of eye blindness are-
1. Retinitis Pigmentosa: It is a medical condition which may result in
blured or no vision in the center of the vision field. Macular
degeneration typically occur in older people. Genetic factors and
smoking also play a role.
2. Macular Degeneration: This is also genetically related. Cones in
macula region degenerate. Loss or damage of central vision. Common
among aged people. People with RP experience a gradual decline in
their vision because photoreceptor cells (rods and cones) die.
Artificial Thin-Film Transistor Retina recovers the sight sense for sight-
Electronic Photo devices and circuits substitutes deteriorated
photoreceptor cells implanted inside the eyes.
We develop electronic artificial retina for restoration of sight to patients
suffering from degenerative retinal diseases such as Retinitis Pigmentosa
and Age-Related Muscular Degeneration.
• A retinal implant is a biomedical implant technology.
• The first application of an implantable stimulator for vision restoration was
developed by Drs. Brindley and Lewis in 1968.
• There are two types of retinal implants :
- Epiretinal Implant
- Sub retinal Implant
Fig. Retinal Implantation
1. Epiretinal implant:
The epiretinal implants typically work in a two component system that consists of
an extraocular and intraocular part.
The extraocular part contains-
• Image sensor: It is responsible for catching visual images,
• Artificial neural net: It can imitate the functions of different layers of the retina
The neural net transform the visual images control signals that the electrodes pick
up and become stimulated.
The signal is passed on to the internal eye and then is picked up by the intraocular
part of the implant.
The intraocular component consists of a receiver for the relayed signals and also
power for the implant.
Radiofrequency links are being used currently and optical links may be used in the
There is an integrated circuitry component that decodes the signals for the
electrodes and controls the stimulation array to produce action potentials in the
upper ganglion cell layers to cause visual sensations.
2. Sub retinal implant
Sub retinal implants sit on the outer surface of the retina.
Directly stimulates the retinal cells.
Replace damaged rods and cones by Silicon plate carrying 1000’s 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.
Fig. 2 Subretinal implant
1. New masking technology
2. Electro optical Measurement
SiO2 buffer layer is deposited on the glass substrate. Then, poly-Si
patterns are formed for source and drain regions.
A 25 nm channel poly-Si layer is deposited by low pressure chemical
vapor deposition (LPCVD) at 600 Degree Celsius.
A 150 nm SiO2 gate insulator is deposited by electron cyclotron
resonance chemical vapor deposition (ECR-CVD) at 100 Degree Celsius
in a vacuum.
Then, a Cr film is deposited at 180 Degree Celsius. 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 of
80 keV. N-channel gate electrodes are also formed and phosphorus
ions are implanted with a dose of 110 keV by the new I/D technique.
Impurities are activated by a XeCl exciter laser.
White light from a halogen lamp is reflected by a triangular prism and
irradiated through the glass substrates to the back surfaces of the 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.
Fig. 3 Setup of electro optical measurement
• It uses the same fabrication processes as conventional poly-Si TFTs and
encapsulated using SiO2, in order to perform in corrosive environment.
• The retina array includes matrix-like multiple retina pixels.
• 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 photo transistors perceive the irradiated light (Photo) and induce the
photo-induced current (IPhoto).
• Next, the current mirror ampliﬁes IPhoto to the mirror current ( I mirror).
• Finally, the load resistance converts I mirror to the output voltage (V out).
Consequently, the retina pixels irradiated with bright light output a
higher V out , whereas the retina pixels irradiated with darker light output
a lower V out.
• 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
• Self-aligned TFTs are also required because of their small parasitic
capacitance which can realize high speed operation.
• Ion implantation is one of the key factors in fabricating such as TFTs
and CMOS conﬁgurations, several non-mass separated I/D techniques
• These techniques, however, are not suitable for conventional poly-Si
TFT processes and cannot be applied to large glass substrates.
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)
• 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 the process sequence for the CMOS conﬁguration, An SiO2 buﬀer layer is
deposited on the glass substrate to protect TFTs from contamination from
components of the glass. Then, 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-Thinner
poly-Si ﬁlm gives better electrical characteristics such as high ON current, low OFF
current and low photo-current.
• Inductive coupling of magnetic field. Electrical energy can be easily
converted to magnetic energy and back using conductive coil.
• Traditionally, a pair of inductive coils are used. The secondary coil can be
located within the eye and the primary coil external to the eye.
• 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. The transmit coil is placed at the
back of the ear.
Fig. Wireless power supply using inductive coupling
• Wireless power supply using inductive coupling system includes a
power transmitter, power receiver, Diode Bridge, and Zener diodes.
• The power transmitter consists of an AC voltage source and induction
• 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 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.
Fig. Working of retinal implantation having wireless power supply
• 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
• White light from a metal halide lamp is diaphragm med 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 shows the detected result of irradiated light.
• The artificial retina is perfected using a wireless supply from the
• There are just two main units needed for the wire supply which are power
system and power transmitter.
• The units are made bio-compatible, so that they can be placed inside
• When the retina is implanted inside the eyeballs then the power generator
is not stable during that period, the reason behind that is probably the
fabrication, presence of parasite or the noise that is caused during the
• Hence, while operating the retina the surgeon should ensure that the
retina can be placed under unstable power supply or not.
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Yamashita, and T.Shima, Device characterization of p/i/n thin ﬁlm
phototransistor for photosensor applications, IEEE Electron
Device Lett., vol. 31, no. 9, pp. 984986,
IV. David C. Ng, Chris E. Williams, Penny J. Allen, Shun Bai, Clive S.
Boyd, Hamish Meﬃn, Mark E. Halpern, and Efstratios Skaﬁdas
wireless power delivery for retinal prosthesis , 33rd Annual
International Conference of the IEEE EMBS Boston, Massachusetts
USA, August 30 - September 3
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Takashi Nakazawa, and Hiroyuki Ohshima, LOW TEMPERATURE CMOS SELF-
ALIQNED POLY-Si TFTS AND CIRCUIT SCHEMEUTILIZING NEW ION DOPING
AND MASKING TECHNIQUE www.ieeexplore.ieee.org, 2011 2010. T.
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networked ﬂexible retinal stimulator designed for image-based retinal
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