Examination of Horizontal Current Bipolar Transistor (HCBT) with double and single polysilicon region

Horizontal Current Bipolar Transistor (HCBT) with implanted n
⁺
collector (single-poly HCBT) has a higher f
T
and f
max
by 50 % and 36 %, respectively, comparing to HCBT with polysilicon n
⁺
collector (double-poly HCBT). The physical mechanisms responsible for the improvement of f
T
and f
max
of single-poly HCBT are examined by the measurements of transistors, test structures and by simulations. Besides the current crowding effect, it is shown that R
C
dominantly limits f
T
in double-poly HCBT. The dominant component of R
C
is identified to be the resistance of the interface oxide between the n
⁺
polysilicon and the n-hill collector regions.