LTZ1000 - nice die pictures

[Noopy]

Hi all,


today I have some nice LTZ1000 die pictures for you.




The package...




You know the structure but the picture is very nice, isn´t it?




Zoom in...




More zoom...




Does anybody know what kind of logo that is?


Some more pictures here:

https://www.richis-lab.de/REF03.htm


Greetings,


Richard

[doktor pyta]

Regarding logo: Super Zener

[TiN]

Very nice. This should be in metrology

[Noopy]

Regarding logo: Super Zener

Aha! 

Very nice. This should be in metrology

I thought about it... But since I have only pictures and less technical information I decided to put it here.
If a moderator thinks it should be in metrology please shift it! 

[iMo]

Nice!
There are 4 heaters left unconnected. Interesting..

[Noopy]

Nice!
There are 4 heaters left unconnected. Interesting..

A few minutes ago I learned that the other heaters are used in the RMS-converter LT1088.

Because of the use in the LT1088 the heaters are connected different so that the current is flowing in the one direction in the one heater and in the other direction in the other heater. Low inductance is important for the LT1088.

...I think I have to check a LT1088 in detail... 

[iMo]

The round structure is the Q1, the zener is inside the Q1 - almost perfect thermal coupling.
The Q2 (the sensor) is made of 4 transistors in parallel - in form of X around the Q1.

[magic]

Hi Noopy, I don't think I agree with your comments about substrate grounding

The substrate has to be the lowest potential in the circuit, with few exceptions*. Otherwise unlimited current would flow from the P type substrate to any of the random N type things (like NPN collectors) made in the N type epitaxial layer.

I think the brown areas are plain, unmodifed N epitaxial layer. So the "thing" connected to pin 1 is simply the whole reminder of the epitaxial layer which hasn't been separated into transistor tubs by the violet isolation diffusions.

Isolation diffusions are P type and they go all the way down to the P substrate, so we see at once that the substrate is electrically connected to pin 4 by the ring of isolation diffusion separating Q1 from Q2 clones. There appears to be yet another parasitic diode not included on the schematic, from pin 4 (substrate/isolation) to pin 8 (Q2 collector). You could detect it with a DMM.

Nominally, pin 4 is Q1 base. Of course the substrate can't be the base, the base has to be located under the emitter. There are actually two concentric "emitters", the outer one is the zener cathode. Interestingly, the base has no metal connection on the surface. Instead, it appears that there is a hidden column of P type material extending from the base all the way down to the substrate. This is the reason why pin 4 is connected to the substrate. Not sure what's the point of that, perhaps voltage at the bottom of the base was more stable than at the top

Q1 collector tub is another part of the circuit with no surface connection. Instead, it's connected from the bottom with four deep "jumper links", which might be made in the N+ burried layer, embedded in the substrate below the reach of the isolation ring. It seems somebody worked very hard to make Q1 collector current flow "upwards" through the base and stay away from the surface for some reason.

*exceptions: some emitters are one diode drop lower potential than the substrate, because they are located on bases whose potential is equal to the substrate.

edit
Now is time to power that puppy up and see if it still works
(BTW, if anyone actually wants to try that, cover the IC from light. Light will cause unwanted conduction through reverse biased junctions, perhaps even damage).

[iMo]

They do test the 4 unconnected heaters (see the pads) - why?
Perhaps quick thermal cycling before the actual selection process?

[Andreas]

Nominally, pin 4 is Q1 base. Of course the substrate can't be the base, the base has to be located under the emitter.

Pin 4 has high ohmic connection to the package.
I measured 65 Ohms on a non-A Version.

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2848044/#msg2848044

with best regards

Andreas

[magic]

Found this
https://www.electronicdesign.com/technologies/analog/article/21804689/whats-all-this-ltz1000-stuff-anyway

One useful thing to understand (it took me 15 years) about the LTZ1000 is that pin 4 is the p-substrate. All the other pins operate above that (which is why you want the heater a diode-drop up) ... except for the mysterious case of pins 6 and 7, which operate 0.6V below the substrate.” Carl Nelson, the LTZ1000 designer, notes he did this to allow for a true subsurface Kelvin connection to the bottom of the Zener, reducing its resistance.

Those mysterious pins are the trap
There are other ICs with below-the-substrate emitters, like LM317.

[Dr. Frank]

Btw: Carl Nelson designed this part, therefore CN are his initials, obviously.
MG I don't know.

SZKP could also mean Super Zener , KP maybe Kelvin Probing.
Frank

[Noopy]

Thanks for all your input!
You are right regarding the substrate! 
I did also some measurements: I could meassure something a little above 100 package to pin 4.
That´s much more consistent! 


I´m pretty sure the LTZ1000 would still work. Bonds are ok. I thought about searching for glowing in the zenerregion. 
Worked good with a 2N3055:



https://www.richis-lab.de/2N3055.htm

But I don´t think that´s possible with a small buried zener.


Why testing the heater?
A good question! The dies for the LT1088 have a different metal layer, so you don´t really have to check the heaters.* Perhaps they can check some quality points. Or they do some early aging?


Well out of the schematic pins 6 and 7 have to be 0,6V below the substrate because of the base-emitter of the connected transistors.


Thanks for the hint to Carl Nelson!


*Not sure about that. I will have to check that! 

[SilverSolder]

Fantastic pictures (love the light emitting 2N3055).   

[Noopy]

I thought about searching for glowing in the zenerregion. 
Worked good with a 2N3055:



https://www.richis-lab.de/2N3055.htm

But I don´t think that´s possible with a small buried zener.

Is it possible to put a light in the LTZ1000?
Well yes! 

I proudly present a glowing LTZ1000-Zener:



You can see that the pn-junction is in the middle of the cathode-ring of the zener. That means the junction is under the cathode-ring. That was to be expected. Nevertheless nice to see.


I can also put a light in the pn-junction of the transistor Q1. 

Whole story here:

https://www.richis-lab.de/REF03.htm#Breakdown

 

[magic]

Kinda surprised by the Q1 result. Why isn't it glowing all around the emitter?


BTW, look for "noise reduction" in the camera's settings
If you are lucky it may enable fully automatic dark frame subtraction, I know that Canon has it on their compact cameras.

[Noopy]

Kinda surprised by the Q1 result. Why isn't it glowing all around the emitter?

It seems that the luminescence of such a second breakdown is not always perfectly uniform.
I have seen such effects in the older 2N3055.

I asume that there are areas where the pn-structure breaches and then these areas emit light. When there is a breached area the current has a path to flow through and there doesn´t have to be a second breach or uniform breach over the whole pn-structure.
My assumption would match with the noise effects you have with z-diodes conducting only very little current. Literature tells us that there are different areas conducting or not.

In the LTZ1000 it´s perhaps sufficient for the current to flow only the shortest way under the metal conducts through the pn-structure. Pherhaps for the other half of the pn-circle the resistance is already too high to breach.


I have seen that the glowing points of the z-diode are always at the same locations.
It seems that there are impurities or imperfect structures that cause breach at special points.
Other explanation: In this special points there is more ionisation leading to visible light.

BTW, look for "noise reduction" in the camera's settings
If you are lucky it may enable fully automatic dark frame subtraction, I know that Canon has it on their compact cameras.

You are right. My 60D has such a setting too. But you have to wait twice the time and it takes some time to take a picture of this small glimpse of light. Even at high ISO. 
But I will try it next time. 

[Noopy]

Nice!
There are 4 heaters left unconnected. Interesting..

A few minutes ago I learned that the other heaters are used in the RMS-converter LT1088.

Because of the use in the LT1088 the heaters are connected different so that the current is flowing in the one direction in the one heater and in the other direction in the other heater. Low inductance is important for the LT1088.

...I think I have to check a LT1088 in detail... 

Of course I had to check what´s inside the LT1088:

https://www.richis-lab.de/LT1088.htm





Surprise:
The LT1088 doesn´t use the LTZ1000-die!
It´s a similar die but they changed more than only the metal layer.

So again the question is why the LTZ1000-heater was built this way.
- special testing after die production?
- (quick) aging after die production?
- a version with a more powerful heater?
Probably we will never know...


Edit: Adding teaser-picture... 

[iMo]

They bond the 1st two rings for Civilian apps, then they add - the 3rd ring for Navy, the 4th ring for Arctic Forces, 5th ring for Air Force, and the 6th for Space Defense

[Noopy]

They bond the 1st two rings for Civilian apps, then they add - the 3rd ring for Navy, the 4th ring for Arctic Forces, 5th ring for Air Force, and the 6th for Space Defense

Well at least possible... 

[aheid]

 Works of art, dies and photos both. Thanks again!

[magic]

Why does the artwork in the center remind me of a competitor's logo?

[macboy]

I believe that the die itself (the doped silicon) is probably identical between the two. Clearly, the polysilicon layer (resistive elements) is different in addition to the metal layer(s). There is no reason to believe that the die itself is not common, especially with so many small details being identical between them.

[Ranayna]

These pictures, and the others you are posting here, are absolutely amazing 
The first picture in this thread reminds me of my own curiosity causing me to file open various metal canned components when I was young

Back then I was mostly disappointed about how empty they were...

[Noopy]

Thanks for everybody giving me positive feedback! 
I think I have to go on with decapping! 

Why does the artwork in the center remind me of a competitor's logo?

Analog Devices? It´s similar but not the same...
Today NS and Analog are merged. Perhaps there was some collaboration before...

I believe that the die itself (the doped silicon) is probably identical between the two. Clearly, the polysilicon layer (resistive elements) is different in addition to the metal layer(s). There is no reason to believe that the die itself is not common, especially with so many small details being identical between them.

There is some similarity between LTZ1000 and LT1088. The isolations in the middle are the same, also the bondpads, the four transistors to measure the temperature and some metal structures. But the heaters are different, the buried zener and it´s transistor are missing completely...
It´s not completely different but they changed more than only the metal layer.