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Artificial retina using thin film transistor technology
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Transcript of Artificial retina using thin film transistor technology
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ARTIFICIAL RETINA USING THIN FILM TRANSISTOR
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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
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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.
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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.
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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
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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)
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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.
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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.
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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.
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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.
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• 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.
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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.
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Working• The power transmitter consists of an ac voltage
source(10V,34khz) and induction coil.
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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.
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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.
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THANK YOU