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发表于 2012-6-25 09:26:23
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Depends on process technology
Beta of vertical / substrate PNP is a strong function of base thickness and doping concentration.
In the substrate PNP BJT structure, N-well is the base terminal.
The thinner base (i.e. the depth of N-well), the higher number for beta. <- minority carrier transmission efficiency will be higher with thinner base.
The higher doping concentration of N-well, the lower beta.
Unfortunately both N-well depth and N-well doping concentration will NOT be optimized for PNP beta.
0.5 um and less advanced technologies: greater than 5
0.18 um: around 3
more advanced: < 1
In general, the more advanced process technology, the lower forward current gain (i.e., beta) of the substrate PNP. |
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