Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device
Reexamination Certificate
2000-06-26
2004-10-12
Fahmy, Wael (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Reexamination Certificate
active
06803609
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a bipolar high-voltage power component having a semiconductor body on which at least two mutually spaced apart electrodes are provided, between which a drift path is formed in a semiconductor region of a first conduction type.
In the case of bipolar semiconductor components such as, for example, diodes, bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors), their dynamic response is determined to a very great extent by the minority charge carriers present in the drift path, that is to say in the base, in the case of a bipolar transistor. That is because the smaller the base width, the higher the limiting frequency that can ultimately be achieved.
It has recently become possible to reduce the base width of bipolar transistors down to approximately 30 nm, which leads to the aforementioned reduction in stored minority charge carriers in the base, so that an increase in the limiting frequency would be possible. Thus, it has been shown that when the base width of bipolar transistors is reduced down to about 30 nm, the quantity of stored minority charge carriers in the base and/or the diffusion capacitance can be reduced, which ultimately leads to a corresponding increase in the limiting frequency up to approximately 50 GHz, but at the same time the dielectric strength is reduced to a few volts.
In the case of high-voltage power components such as IGBTs, for example, across which there may be a voltage of up to several kV, or in the case of diodes, the base width is inherently determined by the required dielectric strength and the structure of the high-voltage power components. However, it is the case quite generally that the minority charge carriers stored in the drift zone, that is to say the minority charge carriers stored in the base zone in the case of a bipolar transistor, limit the maximum operating frequency or give rise to dynamic losses when the component is switched on and off.
Although it is possible to reduce dynamic losses in bipolar high-voltage power components by reducing the quantity of stored minority charge carriers by reducing the emitter efficiency in the case of an IGBT, for example, such a procedure nonetheless inevitably leads to an increase in static losses. It is also possible to reduce the lifetime of charge carriers by doping with a corresponding lifetime killer, that is to say, for example, gold or platinum, or by electron or helium irradiation, whereby dynamic losses can be reduced.
However, such a procedure also leads to a simultaneous increase in the static losses.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a bipolar high-voltage power component, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and in which, despite a relatively large drift path, switching losses are considerably reduced and thus possible operating frequencies are considerably increased, without adversely affecting on-state properties of the bipolar high-voltage power component.
With the foregoing and other objects in view there is provided, in accordance with the invention, a bipolar high-voltage power component, comprising a semiconductor body having a semiconductor region of a first conduction type; at least two mutually spaced apart electrodes disposed on the semiconductor body and forming a drift path between the electrodes in the semiconductor region; and floating zones of a second conduction type opposite the first conduction type, the floating zones preferably disposed in the semiconductor region and extending from the vicinity of one of the at least two electrodes as far as the vicinity of another of the at least two electrodes, the floating zones respectively emitting charge carriers of the second conduction type into the semiconductor region or taking up the charge carriers of the second conduction type from the semiconductor region, when the power component is respectively switched on or switched off.
Therefore, in the case of the bipolar high-voltage power component according to the invention, a “compromise” between dynamic and static losses (with the dielectric strength unchanged) is avoided. To that end, floating zones of the second conduction type, that is to say p-conducting zones, are inserted by diffusion or implantation into the semiconductor region of the first conduction type, that is to say, for example, to an n-conducting drift path of a bipolar transistor. These floating zones, which can also be referred to as “p-type pillars” in the case of an n-conducting semiconductor region, have the task of introducing the minority charge carriers, that is to say holes in the present example, through “ohmic conduction” into the semiconductor regions situated between the floating zones, or of conducting away those minority charge carriers from the semiconductor regions.
It has been shown that this operation, namely the introduction of minority charge carriers into the semiconductor regions from the floating zones during switch-on and the removal of the minority charge carriers from the semiconductor regions into the floating zones during switch-off, can take place much more quickly than the build up and the reduction of the minority charge carrier density by diffusion.
In accordance with another feature of the invention, the floating zones are connected, through a respective MOS transistor with a channel of the second conduction type or a bipolar transistor with a base of the first conduction type, to active regions of the power component which are connected to the two electrodes. Thus, by way of example, in the case of an IGBT with an n-conducting semiconductor region as a drift path, p-conducting pillars are connected through a pnp transistor to the emitter or the anode of the IGBT and through a p-MOS transistor to the channel or body region of the IGBT. When the IGBT is switched on, the holes are then transported through the pnp transistor and the p-conducting pillars into the drift path, while in the event of switch-off, the p-MOS transistor is switched on, with the result that the minority charge carriers, that is to say the holes, can flow away from the n-conducting semiconductor region through the p-conducting pillars as majority charge carriers and the p-MOS transistor.
In accordance with a further feature of the invention, the MOS transistor is to be connected together with a further MOS transistor containing the corresponding active region. In this case, in particular, the gates of the two MOS transistors can be connected to one another. In the above example, then, the gate of the p-MOS transistor, through which the minority charge carriers flow away from the drift path, is connected to the gate of an n-MOS transistor.
In accordance with an added feature of the invention, depending on the operating frequency, it may then be expedient, in order to reduce the switch-off losses, to switch e the p-MOS transistor on first and then switch the n-MOS transistor off with a delay of 1 &mgr;s, for example. This delay can be achieved by separate driving or else by a delay element, for example a high-value resistor between the two gates. In this case, the delay element may also be integrated in the semiconductor chip of the bipolar high-voltage power component.
In accordance with an additional feature of the invention, the dopings of the semiconductor region and of the floating zones are set in such a way that the semiconductor region and the semiconductor zones “compensate” one another, in order thus to be able to achieve high reverse voltages. Dopings of between 5×10
14
and 5×10
16
charge carriers cm
−3
are preferably chosen in this case.
However, it is not essential in this case to achieve the highest possible n-type doping in, for example, an n-conducting semiconductor region as in the case of a unipolar transistor. Instead, the resistance of the floating semiconductor zones, that is to say of the p-conducting pillars in the above example, should be matched i
Pfirsch Frank
Werner Wolfgang
Fahmy Wael
Farahani Dana
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
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