Fraunhofer Institute for Silicon Technology
Fraunhofer Institute for Silicon Technology

Automotive Power Inverters

The most compact electric drive in the world

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The development of the world's most compact electric drive faces the challenge of maximizing the efficiency of the insulated gate bipolar transistor (IGBT) in the medium power range (> 400 V). Optimizing switching and conduction behavior requires innovative approaches, especially for ultra-thin field-stop IGBTs, while at the same time taking advanced assembly techniques into account.

As part of the flagship project ATEM InMOVE, a joint project between science and industry, we are researching technologies for a drive concept with modular distributed high-speed electric drives. The project partners, including Volkswagen AG, Danfoss Silicon Power, Vishay Siliconix Itzehoe GmbH, FTCAP GmbH, Reese + Thies Industrieelektronik GmbH, Fraunhofer ISIT, and FH Kiel: Institute for Mechatronics & Electrical Energy Technology, are working together to optimize IGBTs and power modules for converters in order to make the electric drive as compact as possible.

ISIT scientists are focusing on developing the latest generation of IGBTs, which are designed for 1200 V / 200 A and can be operated at 13.5 kHz with minimal switching losses. IGBT development also includes the production of three variants in different learning cycles and the modification of the existing standard IGBT architecture (STD-IGBT). Innovative manufacturing technologies such as metallization with electroless Ni/Au and the use of special laser processes to adjust component performance are also part of the development process.

System model of the drive inverter

  • Implementation of the thermal behavior of the half-bridge module using a Foster network.
  • Permissible component temperature at maximum load: TJ,max = 175°C
  • Lifetime: driving cycle 8875 s
  • Temperature strokes: min 2°C, max 60°C
  • Service life estimation (number of cycles until defect): Driving distance of 450,000 km
  • With Danfoss Bond Buffers 10-15 times longer service life
  • Improved overall efficiency and performance thanks to IGBTs from ISIT/Vishay
  • Chip layout, mask set and special processes
  • Metallization of the chip front side with an electroless Ni/Au layer
  • Application of carrier processes for backside processing of thin silicon (50 µm to 150µm).
  • Backside processing by implantation and laser annealing (l =515 nm)
  • Metallization of the chip backside with Ti/Ni/Ag

IGBT chip development

Based on system simulations for the modular converter to be developed, the requirements for 1200 V / 200 A trench field-stop IGBTs were defined. The IGBTs should be able to operate at 13.5 kHz and with the lowest possible switching losses up to TJ,max = 175°C. Figure 3 shows the IGBT developed by Vishay and Fraunhofer ISIT with Ni/Au as the gate and emitter contact surface.

IGBT manufacture

  • Development and manufacture of three IGBT variants in three learning cycles.
  • Modification of the existing standard IGBT architecture (STD-IGBT) to implement injection enhancement devices with 5 µm (IEP5) and 4 µm (IEP4) cell pitch.
  • Iterative adjustment of component performance through special laser-assisted adjustment of the p/n-doped rear p+ emitter and field stop layer.

The ATEM InMOVE project demonstrates the application of the developed technologies in the real world by distributing the drive power of electric vehicle drives across several compact electric drive modules. This results in scalable electric drive power and a variable drive architecture that can be implemented with the same components. The project partners are taking on the challenge of making the electric drive as compact as possible, including the slim, fast-rotating electric motor with integrated converter.

The integrated electric drive systems developed as part of the project are designed to be small, cost-effective, and reliable. The use of IGBTs from ISIT and Vishay enables a significant improvement in overall efficiency and performance, resulting in a long service life for the components and reducing the development costs of the electric drive components.

IGBT: Specifications and technical details

Expand table tab on the right:

Specification of the IGBT

Parameter Target value Layout
Temperature     25°C 125°C 150°C 175°C  
Voltage
 [V] 1200          
Rated currentInom [A] 200          
Frequency f [kHz] 13,5 Module coarse specification  
VCEsat (Trade-Off Rg = 1 Ω) dependet [V]   1,95 2,2 2,24 x IE-IGBT
Series resistorRG Ω 1          
Mechanical dimensions:
Chip dimensions [mm2] 15,92 x 12,01    
Gate-Pad Position   Rim center
          
Chip-surface (without Gate) (PAD) [mm2] 153          
Chip thickness [µm] 120-140          
1) Power dissipation: from data sheet reference module, internal Rg = 4,7, RGoff = 0,91 Ω, 30 nH, 25°C)
Eon (1200 V, 200 A) [mJ]   10,5 1)
        
Eof (1200 V, 200 A) [mJ]   11 1)        
Etot = Eon + Eoff [mJ]   21,5 1)        
Short circuit time, tsc     with IE: 7,5 µs (150°C, 800V) without IE: max 7 µs (25°, 900 v)        
Metallization structure              
Front [µm] tbd. Sinterable: Ni-Au or Ni-Pd-Au elektroless        
Back [µm]   Ti 50 / Ni 100 / Ag 1000        
Technical details of the module superstructures

Technology STD IEP5 IEP5 IEP4
Module design

Lead-Frame

5 µm Pitch open module

Lead-Frame

5 µm Pitch open module

"Mold modules"

5 µm  

"Mold modules"

4 µm
1. Modul series (Mod1) 2. Modul series (Mod2)
 3. Modul series (Mod3)
 4. Modul series (Mod4)
Superstructure technology, front   Aluminum wire bond on N/Au or Al Aluminum wire bond on Ni/Au or Al DBB on Ni/Au Cu Wire bond on DBB DBB on Ni/Au Cu Wire bond on DBB
Superstructure technology, back Ti/Ni/Ag +Sintering on DCB Ti/Ni/Ag +Sintering on DCB Ti/Ni/ag + Sintering on DCB Ti/Ni/Ag + Sintering on DCB
IGBT STD 1. Generation IEPS 2. Generation IEPS 3. Generation
 IEP4 5. Generation
Rg, IGBT_intern 0,7 Ω 0,7 Ω 0,7 Ω 0,7 Ω
Metal: Emitter
 Ni/Au Ni/Au Ni/Au Ni/Au
Metal: Collector Ti/Ni/Ag
 Ti/Ni/Ag Ti/Ni/Ag Ti/Ni/Ag
Diode: Metal: Anode SMIKORN, SKCD_81_C_120_I4F
Al Al Ni/Au Ni/Au
Metal: Cathode solderable, Ni/Ag solderable, Ni/Ag solderable, Ni/Ag solderable, Ni/Ag