Timeline for Why are drain and source not actually perfectly symmetric?
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Jan 14 at 23:05 | comment | added | EE18 | Got it. Thank you again! | |
| Jan 14 at 21:21 | comment | added | jp314 | No - the drain-body depletion region extends from the drain towards the source as the drain-body (reverse) bias voltage increases. | |
| Jan 14 at 20:01 | comment | added | EE18 | Understood, thank you! In your last sentence did you mean "drain" rather than "source" by the way? | |
| Jan 14 at 18:02 | comment | added | jp314 | This could be accommodated partially by having a lighter-doped body, but HV MOSFETs also require a means of protecting the Gate-Drain overlap oxide from breaking down (this oxide can only withstand a few V). By making the drain lightly doped, when HV is applied, the (reversed biased) depletion region extends towards the source, thus 'shielding' the gate oxide from the high voltage. | |
| Jan 14 at 17:59 | comment | added | jp314 | In general PN junctions with a higher breakdown voltage require lighter doping. This comes from the fact that the depletion region width depends (inversely) on the doping, and the peak electric field (which limits the breakdown) depends on the applied voltage across this depletion region. | |
| Jan 14 at 14:49 | comment | added | EE18 | Beautiful, thanks so much for this very nice answer! A quick question though I've accepted. You say "...therefore it needs a lighter doping than the source". Why does this follow from needing to withstand higher voltages? Do avalanche or band-to-band tunneling effects at the drain-body pn junction worsen with drain doping? I would have thought that the lower-doped body would have been much more relevant than the drain doping. | |
| Jan 14 at 14:47 | vote | accept | EE18 | ||
| Jan 14 at 1:58 | history | answered | jp314 | CC BY-SA 4.0 |