Optimum Aspect Ratio of Superjunction Pillars Considering Charge Imbalance

K Akshay,Shreepad Karmalkar

doi:10.1109/ted.2021.3060684

Abstract

Development of Superjunction (SJ) technology has striven to raise the pillar aspect ratio, r, believing that this is the key to progressively reduce the specific ON-resistance, R ONSP , for a target breakdown voltage ( V BR ). We study the variation of R ONSP with r and show the following analytically. The minimum R ONSP of practical Si and 4H-SiC SJs is attained at an optimum r = r 0 which is as low as 8-15 for V BR = 0.1-10 kV and charge imbalance, k = 5%-20%. Moreover, an advantage is that the r 0 is not sharply defined, as even ±30% change in r around r 0 raises R ONSP by <; 10% above the minimum, the raise being lower for lower k and higher V BR . In general, for k ≥ 2.5/r 2 , the r 0 increases logarithmically with ( V BR /Bandgap). In contrast, the r 0 of a balanced SJ increases super-linearly with ( V BR /Bandgap) and is several times higher, calling for caution while using balanced SJ theory to design practical SJs. We give a generic closed-form solution valid across materials for designing SJs based on these insights. We verify our results by technology computer-aided design (TCAD) simulation and compare them with prior experimental and theoretical data.

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