| 摘要 |
A mixed-signal CMOS integrated semiconductor device exhibits reduced substrate noise coupling between digital and analog circuit functions using selectively formed isolated, high-impurity buried regions (46, 48) between substrate and epitaxial layers. The impedance within the high-impurity regions (46, 48) is relatively lower than the impedance between high-impurity regions, thereby reducing noise-induced potentials, and latchup, within high-impurity regions and noise-induced currents between high-impurity regions. An attenuation network is effectively formed in the semiconductor device layers to reduce noise coupling, the impedance within the high-impurity region acting as the pi attenuation network shunt path. High-impurity regions (46, 48) are formed by selectively diffusing or implanting impurities into bulk lightly-doped, silicon substrate layer (40) prior to growing an epitaxial layer (50). The high-impurity regions, substrate and epitaxial layers are all of the same conductivity type.
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