Use of TFT technology for retinal vision.

1. ARTIFICIAL RETINA USING THIN
FILM TRANSISTOR

2. 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. Moreover,
since the human eyeballs are curved, the flexible
substrate is also preferable.
• Wireless power supply is used

3. 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.

4. 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 photosensitivity of the reverse-biased p/i/n poly-Si
phototransistor is 150 pA at 1000 lx for white light.
• The retina pix-els irradiated with bright light output a
higher Vout, whereas the retina pixels irradiated with
darker light output a lower Vout.

5. 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.
• Ion implantation is one of the key factors in fabricating

6. ION DOPING TECHNIC
• 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
13.56MHz.
Main features of this system are:
1) A large beam area (over 300 mm square)
2)A high accelerating voltage (maximum: 110 KeV)

7. 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.
• The new I/D technique was used to achieve a self-
aligned structure.
• In these experiments, it is found that the
characteristics of S/A and non-S/A TFTs are similar.
• No degradation can be observed as a result of using
the new I/D technique.

8. 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.
• An SiO2 buffer layer is deposited on the glass
substrate to protect TFTs from contamination from
components of the glass.

9. Electro optical Measurement
• The p/i/n TFPT is located on a rubber spacer in a shield
chamber and connected via a manual prober to a voltage
source and ampere meter.

10. WIRELESS POWER SUPPLY USING
INDUCTIVE COUPLING
• Many implanted electrical power to function; be it in
the form of an im-planted battery or via wireless
power transmission.
• which requires additional surgery is undesirable.
• An example of this is a retinal prosthesis.
• continuous power transmission
• Efficient transmission of power is a performance
limiting factor
• High density electrode array with more than 1000
electrodes will consume about 45 mW of power.

11. • Chip-25mw
• Neuronal stimulation-20mw(3.3vth)
• Based on 64 simultaneously operating electrodes
each requiring a maximum of 0.3 mW at 60 Hz image
refresh rate.

12. 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.

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

14. PIN
• A PIN diode is a diode with a wide, undoped intrinsic
semiconductor region between a p-type
semiconductor and an n-type semiconductor region.
The p-type and n-type regions are typically heavily
doped because they are used for ohmic contacts. The
wide intrinsic region is in contrast to an ordinary
PNdiode.

15. CONCLUSIONS
•The articial retina using poly-Si TFTs and
wireless power supply using inductive
couplinare located in a light-shield chamber
•Vout in each retina pixel is probed by a
manual prober and voltage meter.
•it is driven using unstable power source
generated by induc-tive coupling, Diode
Bridge, and Zener diodes.

16. THANK YOU