Electronics > Beginners
Chip making process
TheUnnamedNewbie:
--- Quote from: ZeroResistance on October 21, 2018, 08:33:56 am ---
--- Quote from: TheUnnamedNewbie on October 21, 2018, 06:15:49 am ---The purpose for building a transistor out of several transistors in parallel is for matching. If you, for example, want to build a current mirror with a 2:1 ratio of currents, you build the 2x transistor out of two parallel versions of the 1x transistor. This achieves better matching than simply building the 2x transistor 2x wider.
--- End quote ---
So the width of a transistor is the length between Drain and Source or the Drain Source channel? Correct?
That means the gate would also be porportionately longer?
--- End quote ---
The origin of 'width' and 'length' comes from considering the charge carriers that move. They go from source to drain. The 'length' is the distance they have to travel from one to the other. The width is how 'wide' (from the charge carriers view as it is traveling from source to drain) the channel is.
--- Quote from: ZeroResistance on October 21, 2018, 08:33:56 am ---
--- Quote from: TheUnnamedNewbie on October 21, 2018, 06:15:49 am ---EDIT: in case it is not clear what you are looking at: this is a '3D' view of the network to go from the top, ultra thick metal (neon green, top left of each image) to the gate/drain fingers of a transistor (teal-blue thing, bottom right). This is from a process that has, iirc, 9 metal layers + 1 UTM layer.
--- End quote ---
Yes its still not clear each layer seems to have finger shaped projections, so its not clear what is drain, gate or source.
I guess the solid block at the bottom is the substrate?
--- End quote ---
The network you can see is only for the gate or the drain (source would be connected to the substrate, the solid block). You would have two of these, coming in from both sides (so one would look like the one in the picture, the other would be mirrored) to connect both.
ZeroResistance:
So, how many layers would a typical chip have, what defines the number of layers?
Do more layers cause any side effects on the design, like increased capacitance etc.
TheUnnamedNewbie:
In terms of metalization layers, I believe 8-12 is common now in chips, depending on what size and technology. For a long time they were limited to two, until chemical-mechanical polishing was perfected and allowed them to go for more metal layers. More metal layers don't really have negatives, except for the cost (more layers = more masks and more steps = more expensive). You don't have to use them, so they just open up more options. Ofcourse for micro/millimeter wave designers like me it does mean that we need more vias (and vias = resistance) to go from the thick top metals to the transistors. An advantage of more metal layers is that your capacitors get smaller (more capacitance/unit area since there are more metals to make plates with)
ZeroResistance:
--- Quote from: TheUnnamedNewbie on October 27, 2018, 06:20:34 pm ---In terms of metalization layers, I believe 8-12 is common now in chips, depending on what size and technology. For a long time they were limited to two, until chemical-mechanical polishing was perfected and allowed them to go for more metal layers. More metal layers don't really have negatives, except for the cost (more layers = more masks and more steps = more expensive). You don't have to use them, so they just open up more options. Ofcourse for micro/millimeter wave designers like me it does mean that we need more vias (and vias = resistance) to go from the thick top metals to the transistors. An advantage of more metal layers is that your capacitors get smaller (more capacitance/unit area since there are more metals to make plates with)
--- End quote ---
Would that mean that the transistors are formed on the bottom 3 - 4 layers and then above that would be additional metal layers. I mean out of the 12 layers you mentioned.
Wimberleytech:
--- Quote ---
Would that mean that the transistors are formed on the bottom 3 - 4 layers and then above that would be additional metal layers. I mean out of the 12 layers you mentioned.
--- End quote ---
Transistors are always the bottom layers. You need at least one layer of metal for ohmic contact to transistor terminals.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version