Summary
Article highlights:
-
IGBTs are available in PT, NPT, and FS variations in single or module form.
-
Power electronics lie on a continuum. To the right of the IGBTs we find the highest power SCRs and GTOs. To the left we find MOSFETs. There is fluctuation in this arena with IGBTs expanding into the highest power areas and MOSFETs, enabled by SiC technology, expanding into IGBT territory.
-
Type FS IGBTs have largely replaced the earlier PT and NPT types. From the public DigiKey catalog, FS modules have nearly a 10 to 1 availability when compared to the earlier technology.
-
IGBTs are incredibly powerful devices but are susceptible to ESD, which can damage the MOS gate.
Figure 1: Image of the Infineon FZ2400R17HP4B2BOSA2 which is among the largest IGBT modules offered by DigiKey. This IGBT module is rated for 1700 V at 2400 A.
Insulated Gate Bipolar Transistors (IGBTs) come in several different flavors including Punch Through (PT), Non-Punch Through (NPT), and Field Stop (trench) FS. This engineering brief provides a brief introduction to the IGBT families with a focus on current and emerging trends.
Let’s start by recognizing that the IGBTs are a relatively new invention, with roots dating back to the late 1960s. The technology blossomed in the 1990s and came to dominate high-power applications by the turn of the century, edging out thyristors in all but the highest power levels.
Chances are high that motor drives ranging from your new washing machine all the way to 1000 hp industrial drives are using IGBTs. Manufacturers are continually pushing the power limits of the technology leading to devices such as the powerhouse Infineon FZ2400R17HP4B2BOSA2 shown in Figure 1. This device has design maximum ratings of 1700 V, 2400 A, with a 13 kW power dissipation. Yet, it has a tiny +/- 20 V gate rating.
Tech Tip: Handle IGBTs with extreme care, as even the most powerful device can be destroyed by a static discharge to the gate terminals. This is counterintuitive, as some IGBT modules are huge, yet they all have the metal oxide gate structure common to all MOSFETS. Exceed the +/- 20 V and the dielectric will fail. This failure may not be immediately apparent, but the device will certainly have a short life.
Always follow electrostatic discharge (ESD) procedure for storage and handling of IGBTs and MOSFETs.
Requirements of power electronics
Power electronics requirements are typically determined in terms of:
-
foundational voltage and current characteristics
-
efficiency
-
speed including turn on and turn off times
-
survivability of short circuits, voltage transients, and thermal events
At the same time, we need to recognize that there are horses for courses. A device optimized for a residential induction burner will not have the same electrical and mechanical requirements as a small motor drive, or a welder. Consequently, semiconductor designers will favor certain device attributes to optimize performance for a given application. The result is a wide variety of IGBTs each with their niche applications.
Over the years the IGBT technology has improved with a clear focus on these niche opportunities. Designers started with PT devices, added NPT, followed by FS with a variety of devices for niche applications. This upward trend is likely to continue with availability of new technologies such as SiC (Silicon Carbide) and GaN (Gallium Nitride). We should also mention the blurred line between MOSFET and IGBT applications. While IGBT still dominates in high voltage and high current applications, the MOSFET isn’t far behind.
IGBT physics
We could explore the underlying physical structures for the PT, NPT, and FS IGBTs. We would find that PT and NPT are similar with differences in the N and P layers including thickness and doping. As implied by the name, the FS includes a trench-like structure to change the field properties. These internal physics and semiconductor theory discussions are beyond the scope of this article. Please see the related links for a few tutorials.
DigiKey offerings
To better understand the difference between the PT, NPT, and FS IGBTs, I conducted an informal review of DigiKey’s offerings. When I initially started, I assumed we could identify clear data trends in terms of switching speed (t-on and t-off), saturation voltage, and design maximum current.
I started with a focus on devices with VCE in the 1000 V range and a 100 A current rating. Unfortunately, this was a poor approach as there was considerable overlap between the various families. Stated another way, there is no value in looking at the “average” IGBT.
IGBT trends
Instead, we need to look at the edges to see the patterns:
-
Popularity: When viewed from an active product perspective, FS devices dominate in for both discrete and modular IGBTs. This is especially true for IGBT modules, where the FS devices outnumber other technologies nearly 10 to 1.
-
Voltage: The FS devices appear to be middle-of-the-road in terms of VCE (max). The best available is about 1800 V while the PT and NPT are available in 4500 and 3000 V respectively.
-
Switch time: There is considerable overlap in each category. However, the FS devices tend to have a slower on time. The PT tend to have fast off times. The NPT and FS devices turn off with half the speed of the PT.
-
MOSFETS: Continuing with our exploration of niche applications, the line between IGBT and MOSFET application is blurred. For example, the Wolfspeed CAB400M12XM3 as pictured in Figure 2, isn’t that far removed from the IGBT. The SiC MOSFET module has a design maximum of 1200 V with a 400 A drain current.
Figure 2: Image of the Wolfspeed CAB400M12XM3 MOSFET module. This SiC module is rated for 1200 V and 400 A.
Parting thoughts
This article seemed simple when I started. All I wanted to do was show the differences between the PT, NPT and FS types from a DigiKey logistics perspective. Several hours later things were not so clear, as we find significant overlap between the characteristics of the “average” 1000 V 100 A IGBT. This forced us to find meaningful differences in terms of popularity and the design maximum extremes.
PT is fast while FS is popular.
In a surprising twist we see that MOSFETS and IGBTs are closely related, especially as new SiC and Ga semiconductor technologies mature. We will need to check back in 10 years to see the exciting landscape changes.
Is there anything missing from this brief?
Let’s talk in the comments section.
Best wishes,
APDahlen
Related information
Please follow these links to related and useful information:
About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.