Influence of the collector resistance on the performance of accumulation channel driven bipolar transistor
In this paper, the physical mechanism limiting the maximum controllable current density ( Jmcc) and safe operating area (SOA) of the accumulation channel driven bipolar transistor (ACBT) is identified and analyzed for the first time. According to our analysis, the hole current flowing into the P + collector at the shallow trench creates a bias opposing the built-in potential of the P + collector/N-drift junction due to a finite resistance associated with the contact to the diffused P + collector region. This lowers the potential barrier established in the narrow mesa region (in between the self-aligned trenches) by the built-in potential of the P + collector/N-drift junction and the control gate potential and promotes electron injection from the N + emitter into the N-drift region over the potential barrier. At the onset of electron injection over the potential barrier, gate control over the base drive of the vertical wide base PNP transistor in the ACBT is lost. This hypothesis has been verified through numerical simulations and confirmed by experimental measurements which indicated an increase of over 300% in Jmcc due to a reduction in the contact resistance to the P + collector region after a post metallization anneal of the fabricated ACBT designs. Based upon these observations, a new ACBT structure with a Schottky collector junction is proposed. It is demonstrated that the proposed ACBT structure has a higher Jmcc and wider SOA in comparison to the ACBT structure with P + collector region.