Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Emitter region feature
Patent
1996-07-26
1998-03-24
Fahmy, Wael
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Emitter region feature
257165, 257133, H01L 2974, H01L 31111
Patent
active
057316058
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a power semiconductor component which can be turned off by gate control and whose semiconductor body has a plurality of unit cells arranged side by side which are comprised of a p-emitter region adjacent to the anode, an adjoining lightly doped n-base region, followed by a p-base region and an n-emitter region embedded therein and which unit cells form a thyristor structure. Such a component is known, for example, from DE 38 02 050 A1.
In the off-state voltage range above 600 V, power semiconductor components of the above-mentioned type are characterized by a lower on-state voltage at a defined current and thus by lower on-state power dissipation and a higher permissible current density than other power semiconductor components which can be turned off such as the MOSFET, the insulated gate bipolar transistor (IGBT) and the (normal) bipolar transistor. In contrast to the latter, they are also suitable up to very high off-state voltages. In practical applications, the gate current-controlled GTO thyristors are widely used. A problem of high-power GTO thyristors is that they tend to form filaments of high current density during turn-off, whereby the current that can be turned off is significantly reduced.
A drawback of the GTO thyristors compared to power semiconductor components controlled by voltage at an MOS gate such as the MOSFET and IGBT is that they require a much higher control and wiring complexity. In order to combine the advantages of a good transmission characteristic on the one hand and of low drive power on the other, MOS-controlled thyristors or MCT's (MOS controlled thyristors) were developed. Like the other power semiconductor components that can be turned off, the MCT comprises a plurality of unit cells which are connected in parallel and disposed side by side. The thyristor of these unit cells of the MCT comprises a MOSFET integrated into the n-emitter region, which MOSFET opens a current bypass from the p-base to the n-emitter during turn-on and thus turns off the power semiconductor component.
The current filamenting, which already is a drawback in the GTO, even results in considerably greater impairment of the turn-off capacity in the MCT. This is the case because the charge carriers are only removed from the control base by way of a voltage which, including the channel voltage of the turned-on MOSFET, is equal to the forward voltage of the emitter base junction and which further decreases by heating. Thus, in MCT's having a larger surface, the current that can be turned off without the risk of destruction is very considerably reduced due to the filamenting.
The transmission characteristics of the GTO and MCT are similar to that of a conventional thyristor, i.e., different from the MOSFET, IGBT and bipolar transistor, the current does not tend toward a saturation value as the voltage increases. This means that, in the event of a short circuit of the load, the current is not limited by the component itself so that fuses must be connected upstream to prevent destruction in the event of a short circuit. In other words, the GTO and MCT are not "short-circuit-proof", which is considered a serious drawback compared to, for example, the IGBT.
In order to prevent current filamenting in these components it is known from DE 38 02 050 A1 to insert a ballast resistor into the connection between the n-emitter region of the unit cells and the outer cathode, namely in the form of a resistive film. Since, in this manner, it is problematic to set the resistor to be sufficiently accurate and homogeneous, it is known from EP 0 433 825 A1 to integrate the ballast resistor in lateral form and to select it as non-linear resistor to increase the effect, with the resistor increasing as the current increases. The resistor was embodied by an n-channel MOSFET of the depletion type. Here, the n-emitter is directly connected to the cathode contact via the more lightly doped n-channel region. But the components cited in this reference have the drawback that under
Schlangenotto Heinrich
Serafin Josef
Daimler-Benz Aktiengesellschaft
Fahmy Wael
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