My Mater of Technology Dissertation Presentation.

1. Microelectrode Arrays for
Retinal Prosthesis
M. Tech. Project Presentation
under the guidance of
Prof. D K Sharma
By
Dilawar Singh (07307011)

2. Objectives
• Fabrication of micro-electrodes arrays
for retinal tissue characterization.
• Fabrication of micro-electrode arrays
of needle like electrodes (for
prosthesis).

3. Introduction
• Diseases like retinitis
pigmentosa and AMD destroys
the photo-receptors (rods and
cones) but leaves the ganglion
cells unharmed. These tissue
can be electronically stimulated
via microelectrodes arrays.
• Microelectrode with needle like
stuctures are needed since they
can penetrate the outer layer of
the retina to reach the ganglion
cells.
source :
internet.

4. Microelectrode arrays with
needle like electrodes
• Needle length of about 5-10 um is desired so it
can reach the randomly distribution ganglion
cells.
• Needle were grown on Si and on Si-Oxide-
polySi in HW-CVD by selective Liquid-vapor-
Solid (LVS) growth method.

5. Fabrication Steps
• RCA cleaning of the wafer.
• Wet thermal oxidation (1-2 um).
• polySi deposition after oxidation
in CVD; approximately 300 nm.
Immediately given for
lithography.
• Gold dots of 2, 4 and 10 um
were deposited by liftoff method.
DSA exposure was used.
• Needle grown in HW-CVD using
VLS.
• Grass like growth seen.

6. Results: After the Au-liftoff
Gold strip.
Peeling off of the gold dot when Gold dot 2 um after 2nd lifoff
liftoff is done just after the
deposition. done
Liffoff showed nice results when 2 days after Au-deposition.
done
after 2 days.

7. Results HW-CVD (1)
First sample : only flake were Needle grown on
seen Si.
on the poly-Si. Perhaps due to
the
porous poly-Si deposition.

8. HW-CVD results (2)
Needle on the 4 um gold
dot. No growth seen on the gold dots. Needle
Si wafer without poly on it. grown on
the gold-strip. No furthur experiment carried
out on
polySi.

9. HW-CVD results (3)
Needles grown on Gold strip.
Diameter approx is 0.25 um. Right side is the zoom in picture.

10. HW-CVD results (4)
Needles grown in 4 um Au dots arrays. Right hand side
Is the angular view of the single dot.

11. HW-CVD results (5)
Needle grown in 2 um diameter gold dot.
Right hand side shows the angular view.

12. Parameters used in various
experiments

13. Results summaried

14. MEA with needles..
proprosed fabrication plan
• Interconnects.
• Oxide deposited thermally
and n+ doped after removing
oxide from active region.
• CVD oxide layer. Etching of
this layer and subsequent W
wiring.
• Passivation oxide layer by
CVD.

15. Mircroelectrode Array on
ITO coated glass
MEA geometry (CAD file)
256 electrode with 6 um diameter.
Average separation is 25 um.

16. Process steps

17. Results
After ITO etching..

18. ITO -MEA
ITO coated MEA.
Without
electroplating.

19. Simplified Retinal Model

20. Model Equations
The basic network of the retina: (1) is receptor cell, (2) is a
bipolar cell, (3) is a horizontal cell, (4) is a amacrine cell,
(5) is a ganglion cell, and f1 is the input.