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, $R_{ONSP}$ , below that of SJ by 5–45 %, since SiC technology allows the insulator to be thinner than the p-pillar. The critical field, $E_{C}$ , in SiC is > 10 times higher than that in Si. We give an analytical breakdown voltage, $V_{BR}$ , model, which shows that the $V_{BR}$ sensitivity to charge imbalance due to inevitable process variations is inversely proportional to $E_{C}$ ; 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 $E_{C}$ differences, the SiC CSSJ inherits the advantage of upto 15% higher $V_{BR}$ 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 $R_{ONSP}$ than the SJ, at a specified $V_{BR}$ in 1–10 kV range and charge imbalance ≤ 20 %. Our work should strengthen the motivation for fabricating the CSSJ in SiC.
Highlights
The performance of a conventional silicon (Si) unipolar device based on the 1-Dimensional (1-D) p-n junction is limited by the so called Si limit, which is the minimum specific on-resistance, RONSP, achievable for a given breakdown voltage, VBR [1]
Based on qualitative physics and numerical simulation, we showed that the RONSP of the Charge Sheet SuperJunction (CSSJ) is even lower than that of a SJ by upto 50 %, for a given VBR
[9], we presented a preliminary account of a CSSJ in Silicon Carbide (SiC) using TCAD simulation
Summary
The performance of a conventional silicon (Si) unipolar device based on the 1-Dimensional (1-D) p-n junction is limited by the so called Si limit, which is the minimum specific on-resistance, RONSP, achievable for a given breakdown voltage, VBR [1]. The superjunction (SJ) structure (see Fig. 1(a)) was proposed [2] to lower the RONSP below this limit In this structure, p-pillars are introduced into the ntype drift layer of the 1-D junction to realize a stack of alternating p- and n-pillars. Apart from inheriting a lower RONSP for a given VBR as compared to a SJ from its Si counterparts, the CSSJ in SiC has two additional advantages: a potentially much simpler fabrication process than a SJ in SiC, and 10 times lower VBR sensitivity to charge imbalance (due to inevitable process variations) than a CSSJ in Si. In the present paper, we discuss these features further to build a strong motivation for actual device fabrication.
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