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.