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SiC JBS diodes with optimized p+ pilot regions for surge capability

IP.com Disclosure Number: IPCOM000249547D
Publication Date: 2017-Mar-03
Document File: 4 page(s) / 213K

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The IP.com Prior Art Database

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ABB Schweiz AG: OWNER

Abstract

This document concerns power electronics and in particular SiC Schottky diodes. In summary, designs comprising p+ wells with S short enough can offers both, unipolar and bipolar operation. For the new devices, state-of-the-art p+ regions dedicated to surge capability in the AA of SiC JBS diodes by fragmented p+ regions are substituted with S short enough that these regions enable also forward electron conduction. In such way, the p+ pilot regions also contribute to the unipolar conduction, thereby improving on-state loses, while still offering capability during surge current event.

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SiC JBS diodes with optimized p+ pilot regions for surge capability Renato Minamisawa, Andrei Mihaila, Lars Knoll, Munaf Rahimo

Background SiC Schottky diodes are commercially available since 2001 owning the challenges to fabricate Si

PiN diodes in applications from 300V to 3.3kV. Depending on the application, SiC rectifiers may be required to handle various levels of surge currents, sometimes as high as 10 times the value of the nominal current rating.

The Junction Barrier Schottky (JBS) diode is a Schottky device which features a grid of p+ rings at the surface. A schematic cross section of a typical JBS diode is shown in figure 1(b). The introduction of p+ regions just below the Schottky contact serves mainly for two purposes:

1. Protect the Schottky interface from high electric fields, which can lead to premature breakdown due to increased leakage current values.

2. Offer enhanced surge current capability when the p+ rings start injecting holes into the drift layer (please refer to figure 1(b)).

(a)

(b)

Figure 1 Schematic cross-sections of (a) SiC JBS diode (b) zoomed-in SiC JBS diodes showing the area through which current flows during normal and surge conditions operation

Surge current capability is an important event feature of SiC JBS diodes. However, when high current pulses occur, it is typically the large p+ transition area (which sits at the edges of the diode, between active and termination areas) which starts to inject holes into the drift region [1, 2]. This, in turn, can induce temperatures high enough at the diode edge to melt the top contact metallization, resulting in anode short circuit and/or premature breakdown due to electrostatic potential crowding at the edge of the termination [3].

Figure 2: Schematic cross-sections of SiC JBS diode showing the p+ transition area which typically is the first to inject holes into the drift region when a surge current condition occurs

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ABB Switzerland Ltd.

TABLE I LAYOUT PARAMETERS

Design w (m) S

(m) AS/AT (%)

Layout ID

Stripe 1.2 1.8 60 S60

Stripe1.2 4.8 80 S80

Basic device concept As aforementioned, a disadvantage of pilot regions comprising large p+ areas is the loss of Schottky

area, which strongly reduces current rating.

Recently, a new 3.3kV SiC JBS diodes have been fabricated with fixed p+ stripes width w of 1.2 m in the active area (AA) and variable distance S between them as shown in Table 1. As represents the Schottky area and AT the overall p+ covered area.

Figure 3 shows the forward characteristics of the 3.3kV JBS diodes, showing that when the distance between the cells is strongly reduced S=1.8m, the device exhibits later opening voltage (Vop=1.4 V) of the Schottky contact because the depletion region of the p+ wells overlaps underneath the Schottky con...