Question

The ‘buried layer’ reduces collector series resistance by providing,

(a) A low resistivity current path from n-type layer to n^+ contact layer

(b) A low resistivity current path from p-type layer to n^+ contact layer

(c) A high resistivity current path from n-type layer to n^+ contact layer

(d) A high resistivity current path from p-type layer to n^+ contact layer

The question was posed to me in unit test.

I would like to ask this question from Active and Passive Components of IC topic in chapter IC Fabrication of Linear Integrated Circuits

Answer 1

The accurate option is (a) A low resistivity current path from n-type layer to n^+ contact layer

To put it plainly: A heavily doped n^+ region is sandwiched between the n-type epitaxial collector and p-type substrate. This buried n^+ region provide a low resistivity current path from active collector region (n-type layer) to the collector contact (n^+ contact layer). In effect, the n^+ layer shunt n-layer of collector region with respect to flow of current, thus effectively reduces the collector resistance.