Patent Description:
A power module is used to selectively deliver power to and from a load. The primary function of a power module is provided by a number of power semiconductor devices, (e.g., transistors, diodes, etc.) within the power module. These power semiconductor devices are provided as one or more semiconductor die mounted on a power substrate. When provided in a power system with one or more other power modules and/or one or more other components, the power semiconductor devices of a power module may form part of a power converter such as a half-bridge converter, a full-bridge converter, a buck converter, a boost converter, and the like. Power systems often deal with high voltages and currents, and thus the power semiconductor devices of a power module must similarly be capable of reliably switching said high voltages and currents. In recent years, reduced power consumption has become a primary concern in power applications and thus it is desirable for a power module to provide low losses and thus high efficiency. As always, it is desirable to do so at a low cost.

Generally, the one or more power semiconductor devices in a power module form at least one switch position. A typical configuration of a power module allows current to be passed in both a forward direction (<NUM>st quadrant conduction) and a reverse direction (<NUM>rd quadrant conduction) through the at least one switch position. Conventionally, the power semiconductor devices of a power module have been silicon devices due to well-known processes for producing silicon power semiconductor devices capable of reliably switching high voltages and currents. However, in recent years silicon carbide power semiconductor devices have become popularized due to significant increases in switching speed and efficiency provided thereby. While power modules with silicon carbide power semiconductor devices provide several performance benefits over their silicon counterparts, using silicon carbide power semiconductor devices in a power module presents several challenges in the design thereof such that the design principles applied to power modules including silicon power semiconductor devices do not equally apply to power modules including silicon carbide power semiconductor devices. In short, including silicon carbide power semiconductor devices in a power module is not a matter of simply swapping them for their silicon counterparts in an existing power module. <CIT> discloses transistor devices that include a first transistor and a second transistor coupled in parallel between a first terminal and a second terminal. The second transistor is based on a wide bandgap semiconductor material. The second transistor has a breakthrough voltage lower than a breakthrough voltage of the first transistor over a predetermined operating range. <CIT> discloses a method to improve accuracy of manufacturing steps of a wide bandgap semiconductor device and to shorten a time needed to perform the manufacturing steps. <CIT> discloses a semiconductor module comprising at least one silicon device in form of a reverse conducting insulated gate bipolar transistor and at least one wide band-gap voltage controlled reverse conducting unipolar switch
<CIT> discloses a semiconductor device which can equalize magnitudes of current flowing in respective fly-wheel diodes at the time of commutation. <CIT> discloses a semiconductor module comprising an insulated gate bipolar transistor and a wide band-gap switch.

There remains a present need for power modules including silicon carbide power semiconductor devices that are capable of handling high voltages and currents while maintaining high efficiency, a small footprint, and low cost.

According to the present invention, there is provided a power module according to claim <NUM>.

<FIG> illustrates a power module <NUM> according to one embodiment of the present disclosure. The power module <NUM> includes a housing <NUM>, a power substrate <NUM> in the housing <NUM>, and a number of power semiconductor die <NUM> on the power substrate <NUM>. While not shown, the housing <NUM> may cover the power substrate <NUM> such that the power substrate <NUM> is partially or completely enclosed by the housing <NUM>. Further, a number of signal paths formed by traces on the power substrate <NUM>, wirebonds, and contact terminals may connect the power semiconductor die <NUM> to one another to form a desired topology for the power module <NUM> as discussed below. Finally, the power substrate <NUM> may be provided on a baseplate, which is exposed through a bottom of the housing <NUM>. While twelve power semiconductor die <NUM> are shown in <FIG>, any number of power semiconductor die <NUM> may be provided in the power module <NUM> without departing from the principles of the present disclosure. However, as discussed below, the footprint of the power module <NUM> is generally limited by standards and practicality, and thus the total number of power semiconductor die <NUM> that can be provided in the power module <NUM> may be limited. In various embodiments, the power module <NUM> may include four power semiconductor die <NUM>, eight power semiconductor die <NUM>, or any other number of power semiconductor die <NUM>.

<FIG> is a functional schematic illustrating a switch position SW in the power module <NUM> useful for understanding the invention. The switch position SW may include all or a portion of the power semiconductor die <NUM>, which may be coupled together to form a number of power semiconductor devices as shown. In particular, the power semiconductor die <NUM> may be coupled together to provide an insulated gate bipolar transistor (IGBT) <NUM> coupled in anti-parallel with a diode <NUM>. The IGBT <NUM> includes a base contact (B) coupled to a control terminal <NUM>, a collector contact (C) coupled to a first power switching terminal <NUM>, and an emitter contact (E) coupled to a second power switching terminal <NUM>. The diode <NUM> includes an anode coupled to the second power switching terminal <NUM> and a cathode coupled to the first power switching terminal <NUM>.

The IGBT <NUM> is provided by a number of the power semiconductor die <NUM>, each of which are IGBT semiconductor die, coupled in parallel. Similarly, the diode <NUM> may be provided by a number of the power semiconductor die <NUM>, each of which are diode semiconductor die, coupled in parallel. The number of semiconductor die <NUM> used for the IGBT <NUM> may be different from the number of semiconductor die <NUM> used for the diode <NUM> (e.g., depending on the current carrying capacity of each device). Each one of the power semiconductor die <NUM> may be rated for a certain blocking voltage and a certain forward conduction current. Providing multiple power semiconductor die <NUM> for each one of the IGBT <NUM> and the diode <NUM> increases the forward conduction current thereof (by an integer multiple for each additional power semiconductor die <NUM>). Accordingly, the switch position SW may be capable of blocking high voltages and conducting high currents, both in the forward direction (from the first power switching terminal <NUM> to the second power switching terminal <NUM>) through the IGBT <NUM> and the reverse direction (from the second power switching terminal <NUM> to the first power switching terminal <NUM>) through the diode <NUM>.

In some embodiments, the power module <NUM> may include multiple switch positions SW. The switch positions SW may be coupled together in series or parallel between the first power switching terminal <NUM> and the second power switching terminal <NUM>, depending on the application of the power module <NUM>. In some embodiments, the switch positions SW may not be coupled together at all. For example, <FIG> shows two switch positions SW coupled in series, which may be used to form the switching portion of a half-bridge power converter. <FIG> shows four switch positions SW, wherein two pairs of the four switch positions SW are coupled in series. The two pairs of series coupled switch positions SW may be coupled in parallel to form the switching portion of a full-bridge power converter, or may be left uncoupled. Notably, the power module <NUM> may provide any number of switch positions SW arranged in any desired manner.

In one embodiment, the IGBT <NUM> and the diode <NUM> are silicon carbide semiconductor devices. Providing the IGBT <NUM> and the diode <NUM> as silicon carbide devices may provide several performance benefits to the power module <NUM>, such as increased blocking voltage, forward conduction current, and reverse conduction current, as well as decreased switching and conduction losses as compared to a conventional power module of the same size. For example, the power module <NUM> may be capable of blocking voltages greater than 1kV between the first power switching terminal <NUM> and the second power switching terminal <NUM> in a blocking mode of operation. In various embodiments, the power module <NUM> may be capable of blocking voltages greater than 2kV, greater than 3kV, greater than 4kV, greater than 5kV, greater than 6kV, greater than 7kV, greater than 8kV, greater than 9kV, greater than 10kV, greater than 11kV, greater than 12kV, greater than 13kV, greater than 14kV, greater than 15kV, greater than 16kV, greater than 17kV, greater than 18kV, greater than 19kV, greater than 20kV, greater than 21kV, greater than 22kV, greater than 23kV, greater than 24kV, greater than 25kV, and up to 26kV. The blocking voltage of the power module <NUM> may further be expressed as a range with any of the above blocking voltages as a starting point and end point. For example, the power module <NUM> may be capable of blocking voltages between 2kV and 26kV, between 10kV and 26kV, between 20kV and 26kV, between 2kV and 12kV, between 10kV and 15kV, between 11kV and 26kV, and the like. For the above blocking voltages, a forward conduction current (between the first power switching terminal <NUM> and the second power switching terminal <NUM>) and a reverse conduction current (between the second power switching terminal <NUM> and the first power switching terminal <NUM>) depends on the area of the semiconductor die, and thus the number of power semiconductor die <NUM>, devoted to each one of the IGBT <NUM> and the diode <NUM>, respectively.

<FIG> is a graph illustrating the forward conduction current and reverse conduction current for the power module <NUM> based on the number of power semiconductor die <NUM> utilized for the IGBT <NUM> versus the number of power semiconductor die <NUM> utilized for the diode <NUM>. As shown, a maximum reverse conduction current occurs when all twelve of the power semiconductor die <NUM> are used for the diode <NUM>. However, the power module <NUM> is not capable of providing a forward conduction current in this scenario. As the number of power semiconductor die <NUM> used for the IGBT <NUM> increases, the forward conduction current of the power module <NUM> similarly increases, and the reverse conduction current of the power module <NUM> decreases. The power module <NUM> is capable of blocking the voltages discussed above in any of the scenarios illustrated in <FIG> and thus is capable of both forward and reverse conduction currents greater than 200A as well as the other illustrated scenarios. In various embodiments, the power module is capable of providing forward and reverse conduction currents in the range of 100A to 6kA, 150A to 6kA, 200A to 6kA, 250A to 6kA, 300A to 6kA, 500A to 6kA, 1kA to 6000kA, and any subranges formed by any of the above ranges. In the exemplary situation described by the graph in <FIG>, the forward conduction current and the reverse conduction current of the power module <NUM> are relatively equal when three of the twelve power semiconductor die <NUM> are used for the IGBT <NUM> and the remaining nine of the twelve power semiconductor die <NUM> are used for the diode <NUM>.

As discussed above, the footprint of the power module <NUM> is limited both by standards and practicality. For the same footprint, the power module <NUM> can achieve far greater blocking voltages with the above forward conduction currents and reverse conduction currents than a power module wherein the power semiconductor devices are silicon.

As illustrated above, a tradeoff exists between forward conduction current and reverse conduction current in the power module <NUM>. Because the footprint of the power module <NUM> is limited, the achievable forward and reverse conduction currents of the power module <NUM> are similarly limited by the space available for the power semiconductor die <NUM>. This is because the amount of current that can be passed by the IGBT <NUM> (forward conduction current) is a function of the area of semiconductor die devoted to the IGBT <NUM> and, similarly, the amount of current that can be passed by the diode <NUM> (reverse conduction current) is a function of the area of semiconductor die devoted to the diode <NUM>. In some embodiments, the diode <NUM> may be a junction barrier Schottky (JBS) diode. Accordingly, for a given area of semiconductor die the diode <NUM> may conduct far less current than the IGBT <NUM>, thereby requiring far more area of semiconductor die (and thus number of the power semiconductor die <NUM>) to be devoted to the diode <NUM> than to the IGBT <NUM> to achieve a desired reverse conduction current. Since to total number of power semiconductor die <NUM> is limited by the footprint of the power module <NUM>, the forward conduction current and reverse conduction current of the power module <NUM> are also limited. While the power module <NUM> described above is capable of achieving higher blocking voltages, forward conduction currents, and reverse conduction currents than previously attainable, it is always desirable to further increase the forward conduction current and reverse conduction current of the power module <NUM>.

<FIG> is a functional schematic illustrating a switch position SW in the power module <NUM> according to an embodiment of the present disclosure. The switch position SW may include all or a portion of the power semiconductor die <NUM>, which may be coupled together to form a number of power semiconductor devices as shown. In particular, the power semiconductor die <NUM> are coupled together to provide an IGBT <NUM> and a metal-oxide-semiconductor field-effect transistor (MOSFET) <NUM>. The IGBT <NUM> includes a gate contact (G) coupled to a first control terminal <NUM>, a collector contact (C) coupled to a first power switching terminal <NUM>, and an emitter contact (E) coupled to a second power switching terminal <NUM>. The MOSFET <NUM> includes a gate contact (G) coupled to a second control terminal <NUM>, a drain contact (D) coupled to the first power switching terminal <NUM>, and a source contact (S) coupled to the second power switching terminal <NUM>.

The IGBT <NUM> is provided by a number of the power semiconductor die <NUM>, each of which are IGBT semiconductor die, coupled in parallel. Similarly, the MOSFET <NUM> is provided by a number of the power semiconductor die <NUM>, each of which are MOSFET semiconductor die, coupled in parallel. In one embodiment, one or more of the semiconductor die <NUM> provide both IGBT and MOSFET devices on the same die, either discretely (i.e., not electrically coupled on the die itself), or integrated with one another in any desired manner. Each one of the power semiconductor die <NUM> may be rated for a certain blocking voltage and a certain forward conduction current. Providing multiple power semiconductor die for each one of the IGBT <NUM> and the MOSFET <NUM> increases the forward conduction current thereof (by an integer multiple for each additional power semiconductor die <NUM>). Accordingly, the switch position SW may be capable of blocking high voltages and conducting high currents, both in the forward direction (from the first power switching terminal <NUM> to the second power switching terminal <NUM>) and the reverse direction (from the second power switching terminal <NUM> to the first power switching terminal <NUM>).

As discussed above, in some embodiments the power module <NUM> may include multiple switch positions SW. The switch positions SW may be coupled in series or parallel between the first power switching terminal <NUM> and the second power switching terminal <NUM>, depending on the application of the power module <NUM>. In some embodiments, the switch positions SW may not be coupled together at all.

The IGBT <NUM> and the MOSFET <NUM> are silicon carbide semiconductor devices. Providing the IGBT <NUM> and the MOSFET <NUM> as silicon carbide devices may provide several performance benefits to the power module <NUM>, such as increased blocking voltage, forward conduction current, and reverse conduction current, as well as decreased switching and conduction losses as compared to a conventional power module. For example, the power module <NUM> may be capable of blocking voltages greater than 1kV between the first power switching terminal <NUM> and the second power switching terminal <NUM>. In various embodiments, the power module <NUM> may be capable of blocking voltages greater than 2kV, greater than 3kV, greater than 4kV, greater than 5kV, greater than 6kV, greater than 7kV, greater than 8kV, greater than 9kV, greater than 10kV, greater than 11kV, greater than 12kV, greater than 13kV, greater than 14kV, greater than 15kV, greater than 16kV, greater than 17kV, greater than 18kV, greater than 19kV, greater than 20kV, greater than 21kV, greater than 22kV, greater than 23kV, greater than 24kV, greater than 25kV, and up to 26kV. The blocking voltage of the power module <NUM> may further be expressed as a range with any of the above blocking voltages as a starting point and end point. For example, the power module <NUM> may be capable of blocking voltages between 2kV and 26kV, between 10kV and 26kV, between 20kV and 26kV, between 2kV and 12kV, between 10kV and 15kV, between 11kV and 26kV, and the like. For the above blocking voltages, a forward conduction current (between the first power switching terminal <NUM> and the second power switching terminal <NUM>) and a reverse conduction current (between the second power switching terminal <NUM> and the first power switching terminal <NUM>) depends on the area of semiconductor die, and thus the number of power semiconductor die <NUM>, devoted to each one of the IGBT <NUM> and the MOSFET <NUM>.

<FIG> is a graph illustrating the forward conduction current and reverse conduction current for the power module <NUM> based on the number of power semiconductor die <NUM> utilized for the IGBT <NUM> versus the number of power semiconductor die <NUM> utilized for the MOSFET <NUM>. In the exemplary situation illustrated by the graph in <FIG>, a maximum reverse conduction current occurs when all twelve of the power semiconductor die <NUM> are used for the MOSFET <NUM>. While the power module <NUM> is still capable of a forward conduction current in this scenario, the tradeoff between reverse conduction current and forward conduction current can be improved by introducing one or more IGBTs. As the number of power semiconductor die <NUM> used for the IGBT <NUM> increases, the forward conduction current of the power module <NUM> similarly increases, and the reverse conduction current of the power module <NUM> decreases. The power module <NUM> is capable of blocking the voltages discussed above in any of the scenarios illustrated in <FIG> and thus is capable of forward and reverse conduction currents greater than 250A as well as the other illustrated scenarios. In various embodiments, the power module is capable of providing forward and reverse conduction currents in the range of 100A to 6kA, 150A to 6kA, 200A to 6kA, 250A to 6kA, 300A to 6kA, 500A to 6kA, 1kA to 6kA, and any subranges formed by any of the above ranges. The forward conduction current and the reverse conduction current of the power module <NUM> are relatively equal when three of the twelve power semiconductor die <NUM> are used for the IGBT <NUM> and the remaining nine of the twelve power semiconductor die <NUM> are used for the MOSFET <NUM>.

As discussed above, the footprint of the power module <NUM> is limited. For the same footprint, the power module <NUM> can achieve far greater blocking voltages with the above forward conduction currents and reverse conduction currents than a power module wherein the devices are silicon. Further, the power module <NUM> discussed with respect to <FIG> and <FIG> can achieve a higher forward conduction current for the same reverse conduction current than the power module <NUM> discussed with respect to <FIG> and <FIG>.

As discussed above, a tradeoff exists between forward conduction current and reverse conduction current in the power module <NUM>. Because the footprint of the power module <NUM> is limited by standards and practicality, the achievable forward and reverse conduction currents of the power module are similarly limited by the space available for the power semiconductor die <NUM>. This is because the amount of current that can be passed by the IGBT <NUM> (forward conduction current) is a function of the area of semiconductor die devoted to the IGBT <NUM> and, similarly, the amount of current that can be passed by the MOSFET <NUM> (both forward conduction current and reverse conduction current) is a function of the area of semiconductor die devoted to the MOSFET <NUM>. MOSFETs pass more current in the reverse direction (source to drain) than JBS diodes (anode to cathode) for the same area of semiconductor die. Further, MOSFETs are capable of passing current bidirectionally (source to drain and drain to source) due to an internal body diode thereof. IGBTs pass more current in the forward direction (collector to emitter) than MOSFETs (drain to source) for the same area of semiconductor die. Accordingly, using the IGBT <NUM> and the MOSFET <NUM> in the switch position SW of the power module <NUM> allows for a better tradeoff between forward conduction current and reverse conduction current than was previously achievable. In one embodiment, the power module <NUM> provides a specific current rating as measured in Amperes per square centimeter (A/cm2) of greater than <MAT>, where Vb(r) is the rated blocking voltage of the power module. In one embodiment, the specific current rating applies both in the forward and reverse directions.

In addition to a better tradeoff between forward conduction current and reverse conduction current, using the IGBT <NUM> and the MOSFET <NUM> in the switch position SW of the power module <NUM> increases an efficiency of the power module <NUM> as illustrated by <FIG>. As shown, the power module <NUM> including the IGBT <NUM> and the MOSFET <NUM> provides significantly higher DC efficiency than its counterpart power module <NUM> including the IGBT <NUM> and the diode <NUM> discussed above, especially in light-load conditions. While not shown, the power module <NUM> discussed above significantly outperforms power modules including only MOSFETs as well as conventional power modules utilizing silicon devices in their efficiency.

As shown in <FIG>, the switch position SW has the first control terminal <NUM> and the second control terminal <NUM>. Providing separate control terminals for the IGBT <NUM> and the MOSFET <NUM> may allow for several performance benefits to be realized by the power module <NUM>. In particular, the IGBT <NUM> and the MOSFET <NUM> may be individually controlled (e.g., by switching control signals from switching control circuitry, which is not shown) such that switching control schemes may be used that minimize switching losses in the power module <NUM>.

<FIG> is a flow diagram illustrating a method for controlling the IGBT <NUM> and the MOSFET <NUM> in the power module <NUM> to minimize switching losses according to one embodiment of the present disclosure. First, the power module <NUM> may be switched from a forward conduction mode in which current is conducted between the first power switching terminal <NUM> and the second power switching terminal <NUM> to a blocking mode in which current is not conducted between the first power switching terminal <NUM> and the second power switching terminal <NUM> by placing the IGBT <NUM> in a blocking mode before placing the MOSFET <NUM> in a blocking mode (step <NUM>). Placing the IGBT <NUM> in a blocking mode before the MOSFET <NUM> reduces switching losses in the power module <NUM>, since the IGBT <NUM> generally takes much longer to transition from a forward conduction mode to a blocking mode due to the recombination time of minority carriers in the device.

Second, the power module <NUM> may be switched from the blocking mode to the forward conduction mode by placing the MOSFET <NUM> in a reverse conduction mode prior to placing the IGBT <NUM> in a forward conduction mode (step <NUM>). Placing the MOSFET <NUM> in a reverse conduction mode before placing the IGBT <NUM> in a forward conduction mode mitigates reverse recovery loss by allowing charge to recombine rather than being swept out of the drift region by the reverse recovery process, thereby reducing switching losses in the power module <NUM>.

In some embodiments, it may be desirable to also include a diode in the switch position SW discussed above with respect to <FIG>. Accordingly, <FIG> is a functional schematic illustrating the switch position SW according to an alternative embodiment in which a diode <NUM> is provided in parallel with the IGBT <NUM> and the MOSFET <NUM>. In particular, the diode <NUM> includes an anode contact coupled to the second power switching terminal <NUM> and a cathode coupled to the first power switching terminal <NUM>. The diode <NUM> may be provided by any number of the power semiconductor die <NUM> coupled in parallel as discussed above.

<FIG> is a graph illustrating a normalized output power vs. normalized power loss for a conventional power module wherein the switch positions are formed by a number of silicon IGBTs and silicon PiN diodes (solid line), a power module wherein the switch positions are formed by a number of silicon carbide MOSFETs using the internal body diodes thereof for reverse current conduction (wide dashed line), a power module <NUM> wherein the switch positions are formed by a number of silicon carbide IGBTs and silicon carbide JBS diodes (narrow dashed line), and a power module <NUM> according to one embodiment of the present disclosure wherein the switch positions are formed by a number of silicon carbide IGBTs and a number of silicon carbide MOSFETs (dashed and dotted line). As shown, all of the power modules utilizing silicon carbide provide far less loss than the power module utilizing silicon. Further, the power module using silicon carbide IGBTs and JBS diodes provides much lower losses at low output power than the power module using only silicon carbide MOSFETs. The lowest overall losses are provided by the power module using IGBTs and MOSFETs as discussed herein.

Claim 1:
A power module (<NUM>) comprising:
a power substrate (<NUM>);
a first power switching terminal (<NUM>) and a second power switching terminal (<NUM>); and
a plurality of power semiconductor devices (<NUM>; <NUM>, <NUM>) on the power substrate (<NUM>), the plurality of power semiconductor devices (<NUM>; <NUM>, <NUM>) comprising:
• at least one insulated gate bipolar junction transistor, IGBT (<NUM>); and
• at least one metal-oxide-semiconductor field-effect transistor, MOSFET (<NUM>), wherein:
• the at least one IGBT comprises a number of IGBT semiconductor die coupled in parallel;
• the at least one MOSFET comprises a number of MOSFET semiconductor die coupled in parallel, wherein the number of MOSFET semiconductor die is greater than the number of IGBT semiconductor die;
• the at least one IGBT and the at least one MOSFET are coupled in parallel between the first power switching terminal (<NUM>) and the second power switching terminal (<NUM>); and
• the at least one IGBT and the at least one MOSFET are silicon carbide semiconductor devices.