Silicon vs. Silicon Carbide: Schottky Barrier Diode Edition
How does a silicon carbide Schottky barrier diode compare to its silicon counterparts? Let's look to a few examples.
Microchips’ Microsemi division has announced a series of SiC Schottky diodes available in module form. Composed of SiC Schottky Barrier Diode (SBD) operating at 700 V, 1200 V, and 1700 V, the modules encompass such technologies as dual diode, full-bridge, dual common cathode as well as a 3-phase bridge.
Microchip's new SiC SBD modules. Image used courtesy of Microchip
These devices are also offered in different current and package options. Offering SiC SBDs in module form saves space, and Microsemi offers the opportunity to “mix and match” baseplate and substrate material in the same module.
In recent years, silicon-carbide based Schottky diodes have become more commonplace as an alternative to their silicon-based counterparts. While we've discussed the benefits of SiC extensively in the past (for instance, in Majeed Ahmad's article about silicon carbide's footprint growing in power electronics), it may be useful to delve into a discussion of how this wide band-gap (WBG) semiconductor comes in handy for Schottky diodes, specifically.
Silicon vs. Silicon Carbide Schottky Diodes
Classical silicon diodes are based on a P-N junction. In Schottky diodes, metal is substituted for the p-type semiconductor, creating what’s known as a metal-semiconductor (m-s) junction, or Schottky barrier.
M–S junction. Image used courtesy of the University of Colorado
When they conduct, there is a very low voltage drop. Other benefits include high switching speed and low noise.
Using silicon carbide (SiC) in place of silicon bestows the diode with a higher breakdown voltage and greater current carrying capacity. These power components serve in applications such as EVs and their charging stations, the smart power grid, and in power systems for industrial and aircraft applications.
Other Suppliers Dipping Into SiC Schottky Diodes
Microchip isn't the only manufacturer providing SiC Schottky diodes. Several others are taking advantage of SiC's power efficiency with this particular device.
ROHM Semiconductor points out that the small capacitance charge of SiC Schottky barrier diodes (SBDs) enables high switching speeds. ROHM offers a range of 650 V and 1200 V devices, some AEC-Q101 qualified.
Mitsubishi also offers another option, the BD20060T, which is a 600 V, 20 A SiC SBD. As Mitsubishi points out, their SiC SBDs take it a step further, employing the Junction Barrier (JBS) Schottky structure illustrated below.
Diagram of a JBS structure. Image used courtesy of Mitsubishi
Littelfuse's series of SiC SBDs, LSIC2SD0, are 650 V devices that carry as much as 20 A continuously. Many come in TO-220 packages, typical for this class of product.
Global Power’s GP2D0 series are available in bare die format. They are available in 500 V, 550 V, 1200 V, and 1700 V versions, and can carry as much as 30 A.
Another player in this space is UnitedSiC, which specializes in all-things-SiC. Its UJ3D series are 650 V and 1200 V devices that come in both single and dual diode versions.
With so many burgeoning options for SiC SBDs on the market, including the new modules from Microchip, it's clear that the performance of SiC in Schottky diodes may be worth the additional price.
High Avalanche Performance and Snubber Circuits
In Microchip’s announcement, the company asserts that their new devices feature a “high avalanche performance [that] allows system designers to reduce the need for snubber circuits.” Those concepts require a bit of explanation.
High Avalanche Performance
Avalanche noise is generated in a semiconductor when it is operated at a reverse bias at or near its avalanche breakdown point. At this point, electrons may break loose and naturally head to the anode.
The effect can cascade, with one electron blasting others out of their place, creating an “avalanche” effect. One result of the phenomena is electronic noise. SiC SBDs can be especially useful to designers because they resist this effect.
Snubber circuits are energy-absorbing circuits designed to suppress voltage spikes the can occur when any switch, like a diode, is turned on or off. Sometimes designers can achieve this suppression by combining a resistor and capacitor in series across an output, but this will nonetheless increase the BOM count and take up board space.
So, since Microchip claims the new SiC SBDs have high avalanche performance, it makes sense that snubber circuits can be avoided altogether. For more information on this topic in a more specific sense, check out Anup Bhalla's (from UnitedSiC) article on using small snubbers to fix fast switching issues.
How Does SiC Make a Difference in Other Components?
In the past, we've discussed a number of ways that SiC has improved or even revolutionized the performance of any given component, from plummeting the RDS(on) of UnitedSiC's new SiC FETs to amping up inverters in solar technology. Judging by the industry representation of SiC SBDs alone, it seems that the benefits of SiC will affect components specifically just as much as they will affect the electronics industry generally.
What's your experience with Schottky barrier diodes? Do you feel that some of its disadvantages could be ameliorated turning to SiC? Share your thoughts in the comments below.