Improving the Short-Circuit Reliability in IGBTs: How to Mitigate Oscillations

Abstract

Abstract-In this paper, the oscillation mechanism limiting the ruggedness of IGBTs is investigated through both circuit and device analysis. The work presented here is based on a timedomain approach for two different IGBT cell structures (i.e., trench-gate and planar), illustrating the 2-D effects during one oscillation cycle. It has been found that the gate capacitance varies according with the strength of the electric field near the emitter, which in turn leads to charge-storage effects associated with low carrier velocity. For the first time, it has been discovered that a parametric oscillation takes place during the short-circuit in IGBTs, whose time-varying element is the Miller capacitance, which is involved in the amplification mechanism. This hypothesis has been validated through simulations and its mitigation is possible by increasing the electric field at the emitter of the IGBT with the purpose of counteracting the Kirk Effect.

Modeling of IGBT With High Bipolar Gain for Mitigating Gate Voltage Oscillations During Short Circuit

“…Many experimental works show that under adverse combinations (i.e., large circuit stray inductance and low gate resistance) and under certain operating conditions (i.e., low DC-link voltage), IGBTs exhibit high-frequency oscillations as it has been found in [3], [5], [6] for planar IGBTs and, recently, for trench-gate, field-stop IGBTs [4], [7]- [10]. This instability may cause the destruction of the gate-oxide, in the case that the oscillation amplitude runs out of control, as reported in [3], [11] for planar IGBTs and in [9] for trench IGBTs.…”

“…Although several measures have been implemented, short circuit failures as a consequence of high-frequency oscillations are still observed in practical applications. The problem was not fully understood until recently, where the complex behavior of the IGBT with both circuit and device analysis has been investigated in [6]. It has been proposed that the root cause of such oscillatory behaviour is a parametric oscillation involving the IGBT and the gate circuit.…”

“…The aim is to increase the electric field at the IGBT's surface and counteract the weak electric field. A sensitivity study has been performed in [6], [11], [15] and later in [10], varying different parameters and investigating its influence on the short-circuit oscillation behavior. Those studies have proven that the IGBT oscillations are more likely to be observed when the device is operated at low DC-link voltages, high positive gate voltages and low case temperatures, because the electric field becomes weaker at the emitter.…”

Reliability Enhancement of Power IGBTs under Short-Circuit Fault Condition Using Short-Circuit Current Limiting-Based Technique

“…There are several further factors that may break the device in particular cases; however, IGBT can withstand the SCF condition for a limited time, e.g., IGBTs can survive 10 µs of SCF condition until it reaches thermal runaway [14,15]. Among serious failure modes during SCF condition, we can name latch-up [16], gate oscillation [17,18], self-turn off [19], thermal run away during the turn-off state [20,21], Negative Differential Resistance (NDR) [22,23], and Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) mode [24]. Toward enhancing the reliability of IGBT devices, there have been several attempts in the literature.…”

A self-adaptive blanking time circuit for fast IGBT de-saturation short-circuit protection

“…Therefore, monitoring and predicting failure are always carried out to effectively improve reliability and prolong the life span of IGBTs [3]. Short-circuit protection is one of the most concerns in IGBT applications where IGBTs withstand high current, high voltage and overheat [4]. In previous works, numerous short-circuit detection methods have been reported, such as gate voltage pattern, di/dt detection, collector current detection and de-saturation detection.…”