[SOLVED] Is this an unusual pinch or pinch-like resistor or something else?

[Mszlazak]

Attached is an image of a standard bipolar process IC that seems to have a dog-bone resistor with an emitter-type diffusion (n+ layer) like a pinch resistor (circled in blue).

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However, it differs from a standard layout/design that you find in textbooks where the n+ layer spans across the entire body of the resistor, completely overlapping it, and going beyond it (see attached image of Pinch Resistor).

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First, am i interpreting the image of that resistor correctly. If not then what is going on?
Second, why didn't the designers span the entire body of the dog-bone and beyond?
If this is a pinch-resistor then how is this partial overlap affecting the "squeezing" effect to increase resistance value of the resistor? Why would designers do this?

 

[dick_freebird]

If you can zoom in a lot more I might be able to dope it out.

If N+ doesn't fully cross and extend past Pbase then it's not a pinched resistor or PJFET.

One common "cheat" that puts N+ as a one-sided "stick-in" is on NPN "C-B transdiodes" where the N+ collector plug will be tucked into a notch in the Pbase and share a stretched contact to make the connection.

 

[Mszlazak]

If you can zoom in a lot more I might be able to dope it out.

If N+ doesn't fully cross and extend past Pbase then it's not a pinched resistor or PJFET.

One common "cheat" that puts N+ as a one-sided "stick-in" is on NPN "C-B transdiodes" where the N+ collector plug will be tucked into a notch in the Pbase and share a stretched contact to make the connection.

I'm not sure because of the following i got off Richi Lab webpage on the LM306. He identifies as a resistor but he maybe wrong.

 

[Mszlazak]

If you can zoom in a lot more I might be able to dope it out.

If N+ doesn't fully cross and extend past Pbase then it's not a pinched resistor or PJFET.

One common "cheat" that puts N+ as a one-sided "stick-in" is on NPN "C-B transdiodes" where the N+ collector plug will be tucked into a notch in the Pbase and share a stretched contact to make the connection.

I got a large image and cropped out the R6 resistor in question. Hope that helps.

 

[dick_freebird]

OK. Looks like "R6" has multiple diffusions, the green appears
to be N+ and maybe they "replaced" 150-ohm Pbase R6 with
a lower valued N+ "bridge" to let them not-change Pbase and
Metal (needing the space to run that cross-through trace, so
can't go much shorter on contact-contact). So the resistor may
really be N+ in parallel with the remaining Pbase that's not
"stepped on", and a pinched Pbase that probably can be
ignored underneath that "add-on" N+ plug.

I'd guess that the net resistance is now something like 10-15
ohms, a slightly oversquare N+ (usually about 10 ohms/sq)
with maybe 200 ohms Pbase in parallel.

They probably left the marketing schematic as-original, just
to mess with anyone looking to copy.

Output stages and their short circuit protection seem to be
one place where different vendors of "standard" parts seem
to be prone to diverge in topology & values. Been looking at
some op amps where no two "old time vendors" agreed on
the network, component types or values. And agreement in
published datasheet schematics? Forget it, fiction galore.

 

[Mszlazak]

OK. Looks like "R6" has multiple diffusions, the green appears
to be N+ and maybe they "replaced" 150-ohm Pbase R6 with
a lower valued N+ "bridge" to let them not-change Pbase and
Metal (needing the space to run that cross-through trace, so
can't go much shorter on contact-contact). So the resistor may
really be N+ in parallel with the remaining Pbase that's not
"stepped on", and a pinched Pbase that probably can be
ignored underneath that "add-on" N+ plug.

I'd guess that the net resistance is now something like 10-15
ohms, a slightly oversquare N+ (usually about 10 ohms/sq)
with maybe 200 ohms Pbase in parallel.

They probably left the marketing schematic as-original, just
to mess with anyone looking to copy.

Output stages and their short circuit protection seem to be
one place where different vendors of "standard" parts seem
to be prone to diverge in topology & values. Been looking at
some op amps where no two "old time vendors" agreed on
the network, component types or values. And agreement in
published datasheet schematics? Forget it, fiction galore.

Well that may make more sense that modifications were added on after the layout was mostly set-up ... for some reason(s). This schematic I initially provided was from National Semiconductor and it's their second version of this chip.

I don't know if this means anything but when Texas Instruments bought National, they also gave a slightly different schematic for the LM306 where R6 changed it's value to 70-ohm and also it's position. See attached schematic from TI.

 

[andre_luis]

A guessing from someone not experienced on this:
Isn't this a poly resistor using silicide block, as stated on section 18.7.2 of Razavi textbook?

 

[dick_freebird]

This is old-timey "standard linear" bipolar with vertical NPN
and lateral PNP (though this part appears NPN-only), some
flow variants might have offered PJFET, high-sheet P resistor,
super-beta NPN, MOS-on-N+ capacitor etc. All made off as
few masks / implants as possible.

 

[Mszlazak]

This is old-timey "standard linear" bipolar with vertical NPN
and lateral PNP (though this part appears NPN-only), some
flow variants might have offered PJFET, high-sheet P resistor,
super-beta NPN, MOS-on-N+ capacitor etc. All made off as
few masks / implants as possible.

Yeah it's all standard bipolar process. Your answer seems best to me. Thanks to everyone for contributing. I will mark it as solved.