Breakdown voltage in LDMOS transistors using internal field rings

Increasing breakdown voltage of LDMOST using buried layer

“…The parameters are as following: the substrate is P-type with doping level of 6x1014cm -3, the length of the drift region is 50#m, the dose of phosphor in Ndrift region is 1.75x1012 cm -2, and its depth is 6#m. Both of the two LDMOST's drift regions have been optimized [4]. The dose of the buried layer is 1.6x1012cm -2, the implant window width is 2/~m, the distance between tile buried layer and drain electrode is 22#m.…”

“…And its technology is compatible with other LDMOST process. The N-LDMOST can be any kinds of structures reported before, so for a given Ron, the maximal breakdown voltage can be fabricated if the buried layer technique combined with lateral optimization techniques mentioned above [2][3][4] are adopted. This is a good way to relieve the conflict between breakdown voltage and on-resistance.…”

“…The thin epitaxial of the B-LDMOST adopts an internal field limiting ring in drift region [4]. It is worthwhile mentioning that, in lateral devices, the applied voltage must be sustained in both the vertical and lateral directions.…”

“…It is worthwhile mentioning that, in lateral devices, the applied voltage must be sustained in both the vertical and lateral directions. The lateral field distribution will be optimized by the internal field ring [4] and OPVLD(OPtimized Variational Lateral Doping) [5], and the breakdown caused by high electric fields will occur at the epitaxial-substrate junction as shown in point A [6] in Fig.1 rather than silicon surface. In this case, the vertical field limits the avalanche breakdown of N-LDMOST, which is still a triangular distribution.…”

“…However, these two electrical parameters tend to have conflict requirements. In order to increase the breakdown voltage of LDMOST, several techniques have been proposed, which include the use of a multiple-resistivity drift region [ 2] , the use of resistive layer on the oxide over the drift region (SIPOS) [3], the use of a floating P-type region as an internal field rings in drift region [4]. The first technique requires the drift region to have the optimum dose of impurities to satisfy the RESURF condition that is difficult to be accurately controlled.…”