Sorry I don't want to hijack the thread but it is somewhat relevant and I hope you find this interesting as well.
At work we use some temperature sensor diodes those are suitable measuring between 1.4K-500K temperatures, with reasonable precision (up to +/-0.25K at low temperatures). Needless to say these can be stupidly expensive, so interesting to take them apart
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
One such example is the Lakeshore DT-670 series:
https://www.lakeshore.com/products/categories/overview/temperature-products/cryogenic-temperature-sensors/dt-670-silicon-diodesOne can find these in many flavours, even in 'bare die' configuration.
![](https://www.eevblog.com/forum/projects/transistors-die-pictures/?action=dlattach;attach=1166082;image)
Here you can see this is in fact a transistor's C-B diode that is used for temperature sensing. It would be nice to find out which transistor could this be -roughly. It is possible that this is somewhat a custom part made by 3rd party vendor, but then why would they hassle with transistor structure when only a diode is needed?
Obviously the very precise pieces are heavily binned so I don't think there is a free meal here, but still it would be nice to get a rough idea on the source.
Here is a self made shot too of such die (not as nice as you are use to it, sorry):
![](https://www.eevblog.com/forum/projects/transistors-die-pictures/?action=dlattach;attach=1166078;image)