The Naked Scientists

The Naked Scientists Forum

Author Topic: What is VLSI Circuit editing?  (Read 12086 times)

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
What is VLSI Circuit editing?
« on: 10/03/2009 04:34:19 »
Does any one have idea about VLSI circuit edit.
« Last Edit: 20/03/2009 09:47:28 by chris »


 

lyner

  • Guest
Re: What is VLSI Circuit editing?
« Reply #1 on: 10/03/2009 13:00:30 »
Uh?
What's it all about chandan?
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #2 on: 10/03/2009 15:00:25 »
I think you are talking about changing a Very Large Scale Integrated Circuit - circuit diagram. It may be a change to a circuit containing a VLSI chip (or chips) or a change to the circuit within the chip itself. This is my line of business so if you explain what you want to know I should be able to answer you.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #3 on: 11/03/2009 08:14:05 »
Uh?
What's it all about chandan?

Its about changing the circuit with in the Integrated chip.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #4 on: 11/03/2009 08:17:37 »
I think you are talking about changing a Very Large Scale Integrated Circuit - circuit diagram. It may be a change to a circuit containing a VLSI chip (or chips) or a change to the circuit within the chip itself. This is my line of business so if you explain what you want to know I should be able to answer you.
Thats great, i want to know how circuit edit is done on an chip and its effect.
 

lyner

  • Guest
Re: What is VLSI Circuit editing?
« Reply #5 on: 11/03/2009 08:45:56 »
Can it be done on a chip, apart from one which is designed to be reconfigurable in some way?
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #6 on: 11/03/2009 08:57:56 »
ya its possible to do circuit edit on chip, i dont know how do they do, it seems that it is sophisticated as FAB process.
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #7 on: 11/03/2009 13:58:43 »
Chandan, a bit of background would help.

Some chips are simply not in any way configurable and it needs a new chip if you want to change the functions. But there are chips made that have memory built on to them. This memory can be Read Only Memory (ROM), Random Access Memory (RAM), or something in-between, which may be a memory that is written once only, or not written often, or erased/written in blocks (Flash). There are many methods of accessing such memories but that is not the question. These chips can use this memory to configure their specific functionality. Sometimes the bulk of this memory is not on the chip itself but external, as in the processor chip at the heart of the computer you are working on.

I can only think you are speaking about a Field Programmable Gate Array (FPGA). These can also use external or internal memory to "configure" them. These can be used to create quite complex logic structures. The design to be made is created by designers by writing a software description of the logic functions required using languages like Verilog or VHDL and thoroughly simulated to ensure the design conforms to the requirements. Careful timing constraints and assertions are added to this code to ensure the resulting design will meet its speed requirements and to aid the subsequent software processes. The design is then "Synthesised" for a particular cell library. For an FPGA this is supplied by the manufacturer and is a range of minimal logic structures that are fully characterised over process variation and temperature and for various loading states. The resulting output (which often takes a few iterations) can then be physically applied to the FPGA. Hopefully the FPGA will then work as intended. If it does not, then it can be re-programmed to iron out bugs.

FPGAs come in various sizes and with with some software free. The synthesis software (if specific to the FPGA) is heavily subsidised compared with general purpose synthesis tools. General purpose IC design tools cost a lot of money! The bigger FPGAs use quite modern fine geometry processes to pack a lot on to each chip and are very expensive. They are great for prototyping and smaller volume production but not for very high volume where a conventional dedicated chip (standard product or custom) would be more cost effective.


As far as "circuit edit" on-chip, it is sometimes possible to make small changes to a synthesised design without the need to resynthesise the whole design. For an FPGA this will still require the FPGA to be reprogrammed but it cuts out a lot of work. For full chip designs the circuit is hard wired and once the chip is made it is a lengthy and costly process to make a new one. The latest chips (in sub 45nm technology) are estimated to cost about $75m to develop and bring to production status. It is best to get them right but with 100s of millions of transistors on each device this is not a trivial exercise.

As an aside, very few large logic designs have anything resembling a circuit schematic now. All the design is defined by the HArdware Description Language (HDL) be it Verilog or VHDL. Analogue circuits are still done with schematics though.

 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #8 on: 11/03/2009 17:30:51 »
Just to add to this, chips can also be modified in a small way by using a Focussed Ion Beam to cut tracks and deposit other tracks. It is limited to very small changes and is a manual process that requires some skill. The package has to have a hole etched in it (if plastic) or the lid removed (if ceramic) so that the die can be accessed in the area requiring the modification. This is handy as a one-off test that a proposed modification works and can be valuable in reducing risk in a follow-up design.
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #9 on: 11/03/2009 20:00:50 »
We used to install EPROMs as security devices but they're the only type I know of. We put a code into the software and the same code on the EPROM. We used them as a type of security dongle in that respect.
« Last Edit: 11/03/2009 20:22:50 by DoctorBeaver »
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #10 on: 12/03/2009 03:47:13 »
I want to know how tracks are cut and deposited and how to make a hole. and which metal is used for forming the tracks.
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #11 on: 12/03/2009 13:39:32 »
It is not a DIY activity :-) You may need a plasma etcher to remove the plastic. You can also use acids in a wet etch environment - boiling sulphuric works. Both these methods can end up removing all the plastic though, which tends to result in the package pins falling off. Masking the plastic (where you don't want the etch), using a directed ion beam, or (it can be done) by dropping acid on the plastic carefully, are methods that can be employed. You then need a minimum of a focussed ion beam etcher. You, of course, need a detailed plot of the chip's structure close to where the modification is to be carried out, and a plan of what to do. The FIB is used to erode through the layers of SiO2 and metal tracking where required. Multi layer metal processes can be a problem because the track you wish to cut maybe masked by higher levels of metal which you don't want to cut. It is not always possible to do a required modification and, even if possible, can have a variable success rate. Selective etching of some materials is also possble. The FIB can also deposit material to connect nodes. But be aware that the material deposited is very thin and, unlike the metal, will have a much higher resistance.

I can recommend a UK company who do this work at a reasonable cost if you wish. They charge by the hour, but even for a simple change, it will probably cost a few thousand pounds to get a few devices done. And you need to provide all the data in some detail.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #12 on: 13/03/2009 10:11:22 »
Which Metal is used to join the nodes. What will be the approximate resistance.
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #13 on: 13/03/2009 17:14:20 »
Various metals can be used. I think it was Tungsten on the last FIB mod I had done. I don't remember the exact resistance although you have a thicker layer deposited to reduce the resistance if this is important, but don't expect to get close to the resistance of normal interconnect. I think it was in the region of a few hundred ohms/square (compared with a few tens of milli-ohms/square for normal interconnect metal.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #14 on: 16/03/2009 04:16:04 »
Hi graham,
   I googled for FIB I could find some material and was amazed, now i want to know more about that, i am still confused that how the thin metal is deposited. ???
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #15 on: 16/03/2009 14:04:41 »
I have not personally operated a FIB machine myself though I have had contract companies do such work many times. A reasonable description is on wikipedia:

http://en.wikipedia.org/wiki/Focused_ion_beam

It explains that deposition is done by "ion beam induced vapour deposition". To elaborate, the beam is controlled so as to scan the surface in the area where deposition is to be made, so it is not required to deposit over a wide area (as with normal vapour deposition) and then use any masking processes to remove the unwanted depositions. The same technique is used in ion beam lithography but on a larger scale. Basically Tungsten Hexacarbonyl vapour (for example) is present in the chamber with the sample to be worked on. The compound gets adsorbed onto the material's surface and the impacting ions (usually Gallium) causes the tungsten to be deposited.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #16 on: 17/03/2009 05:33:46 »
Ok,i think scanning is same as raster scanning in electron tube, but how does ion beam induced vapour deposition will be done.
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #17 on: 17/03/2009 14:22:08 »
Chandan, you have reached the point where I am having to do research on Google for you. I have found a very good summary of FIB techniques here:

http://www.absoluteastronomy.com/topics/Focused_ion_beam

 

Offline erickejah

  • Sr. Member
  • ****
  • Posts: 347
  • Parking? I make my own parking spot!!
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #18 on: 18/03/2009 01:55:21 »
what about using CPLDs?
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #19 on: 18/03/2009 05:39:14 »
what about using CPLDs?

Can i know what you are expecting.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #20 on: 18/03/2009 06:07:13 »
Hi Graham
     The link was useful, i need favor from you,
"A FIB can also be used to deposit material via ion beam induced deposition. FIB-assisted chemical vapor deposition occurs when a gas, such as tungsten carbonyl (W(CO)6) is introduced to the vacuum chamber and allowed to chemisorb onto the sample. "

This i found in the link you send it to me,

i want to know how ion beam induced deposition is done using (W(CO)6).., i want the chemical equation.

i thought you will be having good contacts with the person working on FIB, i thought you can get some details. i tried in net i dint get.
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #21 on: 18/03/2009 14:03:25 »
I am afraid the people I know are experts in using the equipment but only have a basic understanding of the chemistry involved. I think it is rather complex and not wholy understood. A quite good paper on the subject from 1991 is here:

http://www.iop.org/EJ/article/0953-8984/3/S/032/cm910a32.pdf?request-id=5DA8FC08-13A7-11DE-A4F5-29286948AA0C

It shows that it is not a simple effect bt that there are resulting deposits of Gallium and compounds formed with the Silicon (as you may expect), but also Carbon deposits and compounds.

There is a PhD paper from MIT which goes over a lot of the basics. If you search in Google for:

"Ndno-cellular Microstructure Evolution In Ion-Induced Chemical"

You should find the reference and download the paper. I think the "Ndno" should be "Nano" but this is exactly how they have mis-spelled it. I cut and pasted this so you should copy this phrase exactly.

I am not a chemist so my knowledge is superficial about the chemistry involved. In fact I think a lot of the chemical processes involved are not wholly understood and much of the developmental work is empirical.
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
Re: What is VLSI Circuit editing?
« Reply #22 on: 20/03/2009 07:15:38 »
The topic huge.., and an unending story...
 

Offline erickejah

  • Sr. Member
  • ****
  • Posts: 347
  • Parking? I make my own parking spot!!
    • View Profile
What is VLSI Circuit editing?
« Reply #23 on: 22/03/2009 02:36:22 »
The topic huge.., and an unending story...
that is life>>..... though isn't it?
 

Offline Dr.IC

  • Sr. Member
  • ****
  • Posts: 112
    • View Profile
What is VLSI Circuit editing?
« Reply #24 on: 24/03/2009 03:38:32 »
Any free e-book available for this topic?
 

The Naked Scientists Forum

What is VLSI Circuit editing?
« Reply #24 on: 24/03/2009 03:38:32 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length