vivkr
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Hi Berti,
If you look at the link I sent in the earlier post, you will see the reason.
In short, the counter doping which leads to formation of buried channels was an extra step which was necessary in the older technologies to achieve a reasonable (small) level of threshold voltage. This was due to the flatband voltage which results when using an n+ poly-Si gate for a PMOS.
In the new processes where it is possible to have a p+ gate for PMOS, the flatband voltage is much better and there is no need for the extra step which was responsible for buried channel formation in PMOS. In fact, I doubt if you could actually achieve anything with counter doping anymore. It was the large amount of counterdoping required in older processes which led to formation of buried channels.
So, it is not that the modern processes avoid buried channels per se, but more that the older processes could produce nothing but buried channels due to the use of an n+ gate for both PMOS and NMOS.
Regards,
Vivek
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