DIRECT MEASUREMENT OF BASE DRIFT FIELD IN BIPOLAR-TRANSISTORS

We have developed a new method to measure an effective base drift field and the base transit-time reduction factor of bipolar transistors, by measuring the excess phase of the base transport factor. This technique relies on measuring small-signal characteristics of the transistor at low frequency and following the phase of the transconductance at the frequency approaching and exceeding the unity current gain frequency (f(T)). With this technique, we verify that the effective drift field inside the base of Si bipolar transistors decreases with increased base implantation energy and thermal treatment. Such directly measured drift-dependent base transport provides additional insight for optimizing processing used in bipolar technology development.