Thomas Basler

Dynamic self-clamping at short-circuit turn-off of high-voltage IGBTs

Measurements show that the IGBT is able to clamp the collector-emitter voltage to a certain value at short-circuit turn-off despite a very low gate turn-off resistor in combination with a high parasitic inductance is applied. The IGBT itself reduces the turn-off diC/dt by avalanche injection. However, device destructions during fast turn-off were observed which cannot be linked with an overvoltage failure mode. Measurements and semiconductor simulations of high-voltage IGBTs explain the self-clamping mechanism in detail. Possible failures which can be connected with filamentation processes are described. Options for improving the IGBT robustness during short-circuit turn-off are discussed.

Short-circuit ruggedness of high-voltage IGBTs

The IGBT can run into different short-circuit types (SC I, SC II, SC III). Especially in SC II and III, an interaction between the gate drive unit and the IGBT takes place. A self-turn-off mechanism after short-circuit turn on can occur. Parasitic elements in the connection between the IGBT and the gate unit as well as asymmetrical wiring of devices connected in parallel are of effect to the short-circuit capability. In high-voltage IGBTs, filament formation can occur at short-circuit condition. Destructive measurements with its failure patterns and short-circuit protection methods are shown.

Mechanical analysis of press-pack IGBTs

Abstract At present two packages for IGBT devices are available for applications in the MW power range: the bonded power module and the press-pack housing. Power modules have been object of extensive research including their thermo-mechanical characterisation under variable operating conditions and the analysis of their failure mechanisms. These aspects have been critical to improve the manufacturing process, increase reliability and provide lifetime estimations. The press-pack package eliminates bonding wires and solder layers, and is claimed to offer improved power cycling lifetime. However, the knowledge on press-pack devices is much less mature with only limited data published in literature related to their thermo-mechanical behaviour. This paper presents results of FEM simulations on a full 3D model of a press pack IGBT under power-cycling conditions and during the clamping process.

Various structures of 1200V SiC MPS diode models and their simulated surge current behavior in comparison to measurement

In this work, the surge current behavior of 1200V SiC MPS diodes is analyzed using electro-thermal simulations. The results are compared to measurements for calibration. The isothermal surge current simulations are performed with a simplified model of the real diode structure with various sizes of pin-regions and various total model widths. The simulation result shows that smaller pin-regions trigger minority carrier injection at higher voltage drop and current density than the larger pinregions. The negative differential resistance (NDR) regime, seen in the measurement, is modeled successfully. Both, simulations and measurements show a similar behavior during a surge current event. Furthermore, the influence of the model geometry during the surge current event is investigated.

Performance and ruggedness of 1200V SiC — Trench — MOSFET

This paper describes a novel SiC trench MOSFET concept. The device is designed to balance low conduction losses with Si-IGBT like reliability. Basic features of the static and dynamic performance as well as short circuit capability of the 45mΩ/1200 V CoolSiC™ MOSFET are presented. The favorable temperature behavior of the on-state resistance combined with a low sensitivity of the switching energies to temperature simplify the design-in. Long-term gate oxide tests reveal a very low extrinsic failure rate well matching the requirements of industrial applications.

1200V SiC Trench-MOSFET optimized for high reliability and high performance

A detailed analysis of the typical static and dynamic performance of the new developed Infineon 1200V CoolSiCTM MOSFET is shown which is designed for an on-resistance of 45 mΩ. In order to be compatible to various standard gate drivers the gate voltage range is designed for-5 V in off-state and +15 V in on-state. Long term gate oxide life time tests reveal that the extrinsic failure evolution follows the linear E-model which allows a confident prediction of the failure rate within the life time of the device of 0.2 ppm in 20 years under specified use condition.

Optimization of the selenium field-stop profile with respect to softness and robustness

Tailoring the field-stop layer is an effective measure to increase the switching softness and to improve the avalanche robustness of high-voltage power diodes. Diodes and IGBTs with deeper field-stop layers having a superior switching behavior can be created with a relatively low temperature budget by using selenium as field-stop dopant. In this work, we show that a further improvement of the diode performance can be achieved by using a selenium double-field-stop layer. Providing a CIBH-diode with such a selenium double field-stop layer results in a very soft and robust diode. The characteristic of the selenium traps (donor levels and capture cross sections) are determined by DLTS and by frequency resolved admittance spectroscopy measurements. Simulations of the reverse recovery behavior using these trap properties show good agreement with experimental results and are essential for finding further optimized field stop profiles.

Measurement of a complete HV IGBT I-V-characteristic up to the breakdown point

This paper describes how to measure the complete output characteristic of a high-voltage IGBT non-destructively up to the breakdown point and beyond. Hereby, a deep knowledge of the IGBT behaviour at high voltages and saturation currents is gained. To construct the complete characteristic, short-circuit and curve-tracer measurements are combined. The results are compared and recapitulated with semiconductor simulations of IGBT models fitted to experimental characteristics.

Switching ruggedness and surge-current capability of diodes using the self-adjusting p emitter efficiency diode concept

The surge-current ruggedness of free-wheeling diodes can be improved by implementing the self-adjusting p emitter efficiency diode concept (SPEED). Simulations indicate that the switching ruggedness is reduced because of the occurrence of cathode-side filaments during reverse-recovery. Experiments confirm the weak switching performance of such a diode in comparison to a conventional diode. By implementing the controlled injection of backside holes concept cathode-side filaments can be suppressed. However, this measure is not sufficient to regain the switching ruggedness of a conventional diode. It is also necessary to fully embed the p + -areas of the SPEED anode in the low-doped p-type area to avoid high electrical field strengths at the p + p-junction and pinning of anode-side filaments. However, anode-side adjustments for improving the switching ruggedness can reduce the benefit of the SPEED concept regarding the surge-current capability.

Surge current capability of IGBTs

Commonly an IGBT cannot withstand a surge-current pulse (large overcurrent with a duration of some milliseconds) due to the current saturation characteristic of this device. In the case of a converters single device failure the IGBT switches are driven into pulse-blocking mode to prevent a DC-link short-circuit and subsequent IGBT failures. This strategy leads to an asymmetric short circuit of the load. The paper introduces the possibility to symmetrize the load short circuit with active turned on IGBTs and shows first measurements on high-voltage press-pack IGBT chips under heavy overcurrent condition with increased gate voltage.