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Introduction of New Generation Field-stop Shorted Anode IGBT

With the rapid progress in power electronics and semiconductors, each power electronics application has required dedicated and specialized semiconductor switching devices from a cost and performance standpoint. The field-stop (FS) IGBT provides lower saturation voltage drop and lower switching losses versus the conventional non-punch-through (NPT) IGBT. In addition, a relatively recent improvement—the integration of an anti-parallel diode on the IGBT die through use of the shorted-anode (SA) technology – makes the FS IGBT well suited for soft switching power conversion applications.

Field-stop Shorted-anode Trench IGBT vs. NPT IGBT

Although NPT (non-punch through) IGBT improves switching speed by reducing the minority carrier injection quantity and by raising the recombination rate during the turn-off transition, it is undesirable for certain high power applications due to its higher VCE(sat) because its n- substrate has to be lightly doped, and consequently the thicker substrate is needed to sustain the electric field during the off state as shown in Figure 1(a). – The thickness of the n- substrate is the major factor of the saturation voltage drop in IGBTs.

The “n” doped field stop layer between “n-” drift layer and “p+” collector of conventional NPT IGBT as shown in Figure 1(b) drastically improves the performance of IGBT. This is the field-stop IGBT concept. In the FS IGBT, the electric field rapidly decreases within the field stop layer while gradually decreases within “n-” drift layer. Therefore, the thickness of the “n-” drift layer and the saturation voltage drop can be significantly improved. The trench gate structure also improves the saturation voltage drop. Besides, the field stop layer of FS IGBT accelerates the majority carrier recombination during the turn-off instance, and thereby its tail current is much smaller than NPT or PT IGBTs. This leads lower switching losses and lower turn-off energy, Eoff.

Figure 1

NPT IGBT(Left) and Field Stop IGBT(Right)

NPT IGBT(Left) and Field Stop IGBT(Right)

Meanwhile, a new idea emerged—a shorted-anode IGBT (SA IGBT) that allows embedding of the body diode into IGBT in the same fashion as a MOSFET. Figure 2 shows the basic structure of a field stop trench shorted anode (FS T SA) IGBT concept where the “n+” collector is adjacent to the field-stop layer and acts as a cathode of a PN diode, while the “p+” collector layer acts as the general collector of the FS T IGBT.

Figure 2

Cross section of FS SA T IGBT

Cross section of FS SA T IGBT

Figure 3

Typical output characteristic comparison

Typical output characteristic comparison

Figure 3 shows the typical output characteristic comparison of the new shorted anode device (FGA20S140P), the previous generation device (FGA20S120M), and the best competitor. At the rated current, 20 A; the saturation voltage, VCE(sat) of FGA20S140P is 1.9 V, while that of FGA20S120M is 1.55 V and that of the best competitor is 1.6V respectively. Figure 4 shows the reverse recovery performance comparison results. The reverse recovery performances of SA IGBT is slightly inferior to the ultra fast recovery diode (UFRD) co-packaged with IGBT. Fortunately, higher VCE(sat) isn’t detrimental in induction heating (IH) applications.

Figure 4

Reverse recovery performance comparison

Reverse recovery performance comparison

With an advanced field-stop shorted anode technology optimized for IH, the recent Fairchild’s second generation FS T SA IGBT technology has greatly improved not only breakdown voltage but also switching performance compared to the previous version; even though, VCE(sat) is a little bit higher. The turn-off characteristic comparison using a soft switching test jig is illustrated in Figure 5. The turn-off energy of the FS T SA IGBT is 573uJ while of the previous generation FGA20S120M is 945uJ and the best competitor is 651 µJ respectively. Consequently, the new generation FS T SA IGBT device is at least 12% in this particular soft switching test that simulates and IH application!

Figure 5

Eoff comparison

Eoff comparison

The key parameters of each device are compared in Table 1.

Table 1

Key parameter comparison

Key parameter comparison

Summary

The latest-generation shorted-anode IGBT that embeds the intrinsic body diode in a fashion similar to that of a MOSFET was introduced. This device has smaller Eoff characteristics than the best competitor as well as the previous version. In summary, the new device can make the FS IGBT more useful for designs of soft-switching applications that are not requiring high performance anti-parallel diode.

For more IGBT product information, click here.

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Are all high voltage MOSFET and IGBT SPICE models created equal?. To Simulate or Not to Simulate?.

9 comments on “Introduction of New Generation Field-stop Shorted Anode IGBT

  1. samicksha
    November 30, 2014

    In summary, the new device can make the FS IGBT more useful for designs of soft-switching applications that are not requiring high performance anti-parallel diode.

    I believeboth FRD and TGBT functions are combined into single chip, still claim is that the new device performs better than the previous devices, but is it size which will increase.

  2. amrutah
    November 30, 2014

    Richard,

      Thanks for sharing a very informative post on IGBT.  The links at the bottom are very helpful.

  3. Sachin
    November 30, 2014

    The links at the bottom are very helpful.

    @amrutah, true. I really liked “The links at the bottom are very helpful” article. I would like to download those spice models not sure if its freely accessible to all.

  4. dassa.an
    November 30, 2014

    @sachinee: Even I too really want to see. Let me know how to do so on a trial run app

  5. fasmicro
    December 1, 2014

    I have always failed to see competitive position from the redesign of transistor than from the business model which drives the products. Yet, Fairchild and others still think changing transistors offer a new opportunity. They are right but Wall Street may not always care.

  6. amrutah
    December 8, 2014

    @fasmicro:  With the applications changing, raning from high voltage to high frequency, low power low leakage the challenges on the existing technology is huge.  As you pointed, changing the process tech is the way forward, but the cost of R&D is so much that it can hit a business.

  7. samicksha
    December 10, 2014

    When i see IGBT being at continious growth and improvement path, the only question i ask is can we now reliably use IGBT for electric vehicles and hybrid cars.

  8. Davidled
    December 13, 2014

    It could be expected that new generation IGBT could easily control the motor because of small EPI gap on condition of motor turn on-off transition period time, based on IGBT electric characteristics review. 

  9. amrutah
    December 16, 2014

    @Samicksha:

      You are right, the ITRS roadmap suggests that the IGBT is one of the technology that will drive us forward and new improvements will open up space for new applications.  IGBT's are in use in automotive applications already and further improving the realibility will help the cause.  I don't know to what extent the new generation IGBT will help.

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