# 3D Circuitry

Discussion in 'Electronic Design' started by Jon Slaughter, Oct 9, 2009.

1. ### Jon SlaughterGuest

Why are circuits not layed in 3D to produce fast amounts of gates? If you
take your average memory circuit such as SRAM and "layer" it as high as it
is wide then you'll get a huge increase.

What is the difficulties in doing such things? I imagine heat dissipation
would be a big problem but maybe one can add in "heat pipes" to carry the
heat from the inner layers. If one has a matrix of 1000x1000 cells for a 1Mb
memory then repeating that in the "z" dimension would give a 1Gb
memory.(sure it would be square and bulky but thats not the point)

Now maybe they already do this to some degree but I've never seen it
mentioned. Maybe it's difficult to layer the substraits together?

I was thinking that a true 3D method would be optimial for density reasons.
If a potential solid substance could be created where one could apply a
laser of difficult wave lengths to get different properties such as a
conductor or semi-conductor then one might be able to make truely 3D
circuits. Similar to 3D printing. The laser heats the material in such a way
as to turn it into a conductor or semiconductor. It is built up in a
continuous manner. Anyways... just an idea. Not saying it is practical but
just the abstract idea would work.

But I don't even see devices that use true "layering" techniques. I do
realize that in some sense standard semiconductor fabrication uses
"layering" but they only have one substrate layer? If one could layer, say,
fpga cores then they would become vastly more powerful.

Anyways, just something I was wondering about...

2. ### GMGuest

http://en.wikipedia.org/wiki/Three-dimensional_integrated_circuit

5. ### krwGuest

The last IC I worked on had ten levels of metal and a set of masks was
north of 2\$M. That was in 90nM and they're down to 40nM now (two full
generations later). My last (and most likely next) product was on six
layer FR4. ;-)

6. ### krwGuest

Cooling is the #1 reason. Memory could be stacked but the cost is
against you there. Memory has to be *cheap*, even in expensive
applications.

7. ### krwGuest

Gene Amdahl started Trilogy, which was supposed to build a WS system
many moons ago. There was also WSI. ;-)
Couple of years (mid '80s). He folded shop on WSI and started
building VAX clones. Some come down form building very successful IBM
clones.

8. ### Paul KeinanenGuest

Memory stacking should not be too hard, say with one layer for each
bit plane. The address, Chip select, R/W and power lines are in
parallel, so arranging the vias or edge connectors should be easy. The
only signals needing special handling is the data in/out pins.

Some hobbyists used to piggyback RAM memories in DIP packages, solder
address etc. lines together and only wire wrap the data lines . I
guess it had been easier to bend the DIP pins horizontally and then
use some small vertical Vero-board strips to connect the address lines
and then only wire wrap the data lines separately.

Paul

9. ### Dirk Bruere at NeoPaxGuest

IIRC he spent some \$300m on the failed process, and that was a lot of
money back then

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party

10. ### krwGuest

Leaky, for sure. Particularly the 0Vt transistors. It is a bit
mind-bending to realize that one can make precision voltage dividers
out of gate tunneling currents. ;-)

11. ### krwGuest

IT's not hard, just expensive. Expensive isn't done much, which makes
it much more expensive.
It wasn't just hobbyists. Stacked memory was a standard product in
the '80s. The two chips had /CS bonded out to different pins (the
adjacent pin was a NC on the standard part). It can be and was done,
it's just expensive (so it's not done much, making it...).

12. ### Charlie E.Guest

There is also package scale integration, where multiple chips are
wired together inside the package, often involving stacking one on top
of the other and wirebonding in three dimensions. Was working with
that tool at Cadence before the axe...

Charlie

13. ### krwGuest

It was only driven to church on Sunday by a little old lady, huh? ;-)