Charge Sheet Super Junction in 4H-Silicon Carbide: Practicability, Modeling and Design

Abstract

We discuss details of the Charge Sheet SuperJunction (CSSJ) in 4H-Silicon Carbide (SiC). This device was earlier proposed in Si material. A CSSJ is obtained by replacing the p-pillar of a SJ by a bilayer insulator, e.g. Al2O3 / SiO2; the inter-layer interface of this insulator has a negative charge-sheet, whose magnitude is easily controlled via the insulator deposition temperature. This charge-sheet depletes the n-pillar. Two potential advantages of this structural modification are brought out. First, it can avoid the problems related to SiC SJ's p-pillar fabrication. Second, it can lower the specific-on resistance, RONSP, below that of SJ by 5−45 %, since SiC technology allows the insulator to be thinner than the p-pillar. The critical field, EC, in SiC is > 10 times higher than that in Si. We give an analytical breakdown voltage, VBR, model, which shows that the VBR sensitivity to charge imbalance due to inevitable process variations is inversely proportional to EC; hence, this sensitivity of CSSJ in SiC is > 10 times lower than that in Si. On the other hand, we give numerical simulations to establish that, in spite of EC differences, the SiC CSSJ inherits the advantage of upto 15% higher VBR compared to SiC SJ, from its Si counterparts. We show how our prior analytical procedure of designing a SJ can be adapted to design a CSSJ having a lower RONSP than the SJ, at a specified VBR in 1-10 kV range and charge imbalance  20 %. Our work should strengthen the motivation for fabricating the CSSJ in SiC.

Note Clarifying the Paper, “Charge Sheet Super Junction in 4H-Silicon Carbide: Practicability, Modeling and Design”

“…3(c) of [1] which is reproduced here as breaks down, and confirmed that this ER,SiO2 remains well below 5 MV/cm. It is the purpose of the present note to clarify an important approximation employed in [1] to simulate ER,SiO2.…”

“…We have clarified an elegant approximation employed in [1] to numerically simulate the field in the SiO2 layer of the Charge-Sheet Superjunction overcoming the interface charge placement limitation of the device simulator. Our present approximation was shown to be a case of transfer of an existing approach to new surroundings.…”

“…2(b) from Fig. 3(a) of [1], we obtained the fields Ey,SiC and Ex,SiC in SiC that are parallel and normal to the vertical Al2O3 / SiC interface (see Fig. 2(a)).…”

“…his note is related to an accompanying paper [1] which discussed the practicability, modeling and design of a variation of the Superjunction (SJ) called the Charge Sheet SJ (CSSJ) in 4H-Silicon Carbide (SiC) material (see Fig. 1(a)).…”

“…(a) Cross-section of the unit cell of the proposed Charge-Sheet SuperJunction[1]. Diagram not to scale; the actual SO2 liner is much thinner than shown.…”