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Posted on 09 January 2019

IGBT Development - Then and Now

 

 

 

 

 

 

 

Since IGBTs were invented, their basic principles have been utilized in different concepts. IGBT chips have therefore been further developed in separate ways, pursuing the objectives and taking the directions outlined for chip technology. In order to both reduce costs by reducing (shrinking) chip area and to get even closer to the physical limits, three main paths have been followed in the further development of IGBT chips:

  • Finer cell structure / chip area reduction / increase in maximum current density
  • Reduced chip thickness
  • Increase in permissible chip temperature.

Every IGBT concept must – adapted to its main applications – achieve a balance between various conflicting component properties, e.g.

a) Between on-state voltage VCE(sat) and turn-off power loss Eoff

b) Between on-state voltage VCE(sat) and short-circuit behaviour

The limits for a) are pushed further in the latest IGBT concepts, e.g. SPT+ (ABB), IGBT4 (Infineon) and CSTBT (Mitsubishi), by increasing the concentration of free charge carriers among the n-emitter cells. One negative consequence, however, is often the very steep decline in collector current during turn-off with the resultant side-effects as regards EMC, for instance. The trade off in b) is improved by a continuous reduction in chip thickness and the introduction of weakly doped field stop layers. The IGBT cell pitch has a crucial impact on its properties. This determines, among other things, the influence the MOS channel has on conductivity modulation.

Figure 1 below shows, using the example of a 1200 V IGBT in Trench-Gate technology, how VCE(sat) or collector current density JC(sat) depend on the cell pitch (distance between adjacent gate centers) for Tj = 125°C.

Dependency of the on-state voltage and collector current density

Figure 1. a) Dependency of the on-state voltage VCE(sat) of a 1200 V IGBT on the cell pitch for Tj = 125°C; b) Dependency of the collector current density JC(sat) of a 1200 V IGBT on the cell pitch for Tj = 125°C

Figure 2 shows the development of chip size and on-state voltage for different component generations using 1200 V / 75 A IGBT chips made by Infineon as an example.

Development of chip size and on-state voltage of 1200 V / 75 A IGBT chips (Infineon)

Figure 2. Development of chip size and on-state voltage of 1200 V / 75 A IGBT chips (Infineon)

To enable system costs (cooling, chip area) to be reduced, a crucial development target is to increase the permissible chip temperature. This was achieved by Infineon, for example, for IGBTs up to 1700 V in the IGBT4 chip generation, raising the temperature from 150°C to 175°C; 200°C is planned for future IGBT generations. An increase in the IGBT operating temperature, however, means that the freewheeling diode (inverse diode), too, has to be suitable for this temperature. This increases the requirements that IGBT module packaging has to fulfill.

 

For more information, please read:

IGBT Technologies

Criteria for Successful Selection of IGBT and MOSFET Modules

Comparing the Incomparable - Understanding and Comparing IGBT Module Datasheets

Teaching Tool for IGBTs and Thyristors

 

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