Transistorbauelement

Abstract

Transistor device comprising: a unipolar transistor (11; 21; 71) coupled between a first terminal (12; 22; 73) and a second terminal (13; 23; 74), a bipolar transistor (10; 20; 70) coupled in parallel to the unipolar transistor (11; 21; 71) between the first (12; 22; 73) and second terminal (13; 23; 74), wherein the bipolar transistor (10; 20; 70) is designed to conduct a large part of a current flowing through the transistor component when the current and / or a control voltage controlling the unipolar transistor (11; 21; 71) and the bipolar transistor (10; 20; 70) exceed a predetermined threshold value, wherein the bipolar transistor (10; 20; 70) is designed to have a higher threshold voltage than the unipolar transistor (11; 21; 71) due to a dopant concentration in a body region of the bipolar transistor, wherein a difference between the threshold voltage of the bipolar transistor (10; 20; 70) and the threshold voltage of the unipolar transistor (11; 21; 71) is at least 1 V, further comprising a gate driver circuit (75;77), wherein the gate driver circuit is configured to increase a control voltage at least for the bipolar transistor (10; 20; 70) in the event of an overcurrent event, and ; a further gate driver circuit (78) configured to control the unipolar transistor.

Description

Technical field

[0001] The present application relates to transistor devices. background

[0002] Transistor devices are used in many applications. For example, transistor devices can be used as switches in electronic power applications. Various transistor types have been used as switches, for example, bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), or unipolar transistors such as metal oxide semiconductor field-effect transistors (MOSFETs). Such transistors and corresponding transistor devices, including one or more transistors and possibly additional circuitry, are available in various designs to support different voltages and / or currents.

[0003] Many electronic power applications operate at part load most of the time and require operation at a maximum load (e.g., maximum current or maximum power) only part of the time. One example of such an application is switched-mode power supplies (SMPS), which typically require no more than 20% of their maximum power for about 80% of their operating time. Nevertheless, such components must be designed to tolerate the highest possible power to prevent failures. In addition, for higher voltage ranges, for example voltages above 1700 V, there are many applications that switch between full load and part load, such as converters for solar or wind power systems or an application in vehicle powertrains where full load is required to start an engine, whereas only a portion of the full power is needed during normal driving.

[0004] Different transistor types can have different disadvantages and advantages when used in such applications. For example, IGBTs are advantageous for high currents, but often suffer from comparatively low efficiency under partial load. On the other hand, some unipolar transistor switches, such as MOSFETs, may have lower efficiency under full load and / or may require large die areas. Bipolar transistors, especially IGBTs, have better capabilities than MOSFETs, particularly in the case of overcurrents.

[0005] US 2017 / 0 047 320 A1 discloses a parallel circuit of an IGBT and a MOSFET. At least in the case of a short circuit, the IGBT carries more current than the MOSFET. By using a gate resistor, the IGBT can have a higher threshold voltage than the MOSFET.

[0006] EP 3 240 177 A1 also discloses a parallel connection of an IGBT with a MOSFET, which may be a silicon carbide-based MOSFET.

[0007] US 2017 / 0 019 097 A1 discloses another parallel connection of an IGBT and a MOSFET, where the IGBT has a higher transconductance than the MOSFET. Here, too, the threshold voltages of the IGBT and MOSFET can be different.

[0008] DE 10 2014 226 475 B3 comprises a DC switching device with two semiconductor switching elements arranged in parallel, in particular transistors, which can be switched one after the other when switching off and on.

[0009] DE 10 2014 119 544 A1 discloses an integrated transistor circuit having a plurality of IGBT cells, wherein a portion of the IGBT cells has a higher threshold voltage than the remaining IGBT cells.

[0010] FD Bauer, “Conceptual Study of Sub-600V IGBTs,” discloses an integrated parallel circuit consisting of an IGBT and a MOSFET.

[0011] US 4 941 030 A discloses an integrated circuit with a MOSFET and a bipolar transistor.

[0012] One challenge is therefore to provide transistor devices with improved overcurrent handling while still providing good capabilities under partial load, for example, low currents. Brief description

[0013] Transistor devices as defined in claim 1 are provided. The subclaims define further embodiments.

[0014] According to one embodiment, a transistor device is provided comprising: a unipolar transistor coupled between a first terminal and a second terminal, a bipolar transistor coupled in parallel to the unipolar transistor between the first and second terminals, wherein the bipolar transistor is configured to conduct a majority of a current flowing through the transistor device when the current and / or a control voltage controlling the unipolar transistor and the bipolar transistor exceed a predetermined threshold value, wherein the bipolar transistor is configured to have a higher threshold voltage than the unipolar transistor due to a dopant concentration in a body region of the bipolar transistor, wherein a difference between the threshold voltage of the bipolar transistor and the threshold voltage of the unipolar transistor is at least 1 V. The transistor device further comprises a gate driver circuit, wherein the gate driver circuit is configured to increase a control voltage at least for the bipolar transistor in the event of an overcurrent event, and another gate driver circuit configured to control the unipolar transistor.

[0015] The above summary is intended to provide only a brief overview of some features of some embodiments and is not to be construed as limiting. Short description of the drawings Fig. 1 is a block diagram of a transistor device according to one embodiment. Fig. 2A to 2C are circuit diagrams illustrating transistor devices according to various embodiments. Fig. 3 is a diagram illustrating example characteristics of transistors included in transistor devices according to some embodiments. Fig. 4 is a diagram that further illustrates exemplary characteristic curves. Fig. Figure 5 is a diagram illustrating a surge current event. Fig. 6A and Fig. 6B are diagrams illustrating the control of transistor devices according to a comparative example ( Fig. 6A) or embodiments ( Fig. 6B). Fig. 7 illustrates an example of controlling transistor devices according to one embodiment. Fig. 8A and Fig. 8B are circuit diagrams showing transistor devices according to some embodiments. Fig. 9 is a diagram illustrating a threshold voltage of an IGBT usable in some embodiments. Fig. 10A to 10D illustrate switchable cells of an IGBT according to some embodiments. Fig. 11A and Fig. 11B illustrate top views of an IGBT usable in some embodiments. Detailed description

[0016] Various embodiments are described below with reference to the accompanying drawings. It should be noted that these embodiments are presented only as examples and are not to be construed as limiting. While embodiments may be described as including numerous features or elements, in other embodiments some of these features or elements may be omitted and / or replaced with alternative features or elements. Furthermore, in addition to the features and elements explicitly shown and described, other features or elements as known to those skilled in the art may be provided.

[0017] Features or elements of different embodiments may be combined to form further embodiments. Variations or modifications described with respect to one embodiment may also be applied to other embodiments.

[0018] In the embodiments discussed and described, any direct electrical connection or coupling between elements, i.e. connection or coupling without additional intervening elements, may also be implemented by an indirect connection or coupling, i.e. a connection or coupling comprising one or more additional intervening elements, and vice versa, as long as the general purpose and general functioning of the connection or coupling, for example for transmitting some type of signal or information or for providing some type of control, is substantially maintained.

[0019] Transistor devices are described below. Transistor devices as used herein include one or more transistors. A transistor may be a bipolar transistor (e.g., using n-doped or p-doped active regions for implementation) or a unipolar transistor (using substantially only n-type or only p-type active regions for implementation). Examples of bipolar transistors include IGBTs (Insulated Gate Bipolar Transistors) with a gate terminal as a control terminal and collector and emitter terminals, or a BJT (Bipolar Junction Transistor) with a base terminal as a control terminal and also emitter and collector terminals.Examples of unipolar transistors include metal-oxide-semiconductor field-effect transistors (MOSFETs) or JFETs (junction field-effect transistors), which contain a gate terminal as a control terminal and source and drain terminals.

[0020] In some embodiments, a transistor device comprises a parallel circuit of a unipolar transistor and a bipolar transistor. The bipolar transistor in the embodiment is designed to have a higher threshold voltage than the unipolar transistor, a threshold voltage that is at least 1 V higher, for example, at least 2 V higher, at least 3 V higher, at least 4 V higher, or at least 5 V higher. Furthermore, the bipolar transistor may be designed to have a higher transconductance than the unipolar transistor. In this way, in some embodiments, the bipolar transistor may be used to support high currents, particularly surge currents or other overcurrent, whereas at lower currents, in some embodiments, only the bipolar transistor may be active. An overcurrent in this regard is a current that exceeds a threshold above normal operating currents.A surge current is an overcurrent that occurs on a comparatively short time scale, e.g., on the order of 10 ms.

[0021] Now with reference to the figures Fig. 1 illustrates a schematic block diagram of a transistor device according to an embodiment.

[0022] The transistor component of Fig. 1 includes a bipolar transistor 10 and a unipolar transistor 11 coupled in parallel between a first node 12 and a second node 13. "Coupled in parallel" in this case means that one of the emitter or collector terminals of the bipolar transistor 10 is coupled to node 12 and the other of the collector or emitter terminals of the bipolar transistor 10 is coupled to node 13. Likewise, one of the source or drain terminals of the unipolar transistor 11 is coupled to node 12 and the other of the source or drain terminals of the unipolar transistor 11 is coupled to the second node 13. In some implementations, the bipolar transistor 10 may be an IGBT. In some implementations, the unipolar transistor 11 may be a metal-oxide-semiconductor field-effect transistor (MOSFET). In some embodiments, the unipolar transistor 11 may be a silicon carbide (SiC) based transistor.

[0023] In the embodiment of Fig. 1, the bipolar transistor 10 has a higher threshold voltage than the unipolar transistor 11, for example, 1 V higher, at least 2 V higher, at least 3 V higher, at least 4 V higher, or at least 5 V higher. Furthermore, in some embodiments, the bipolar transistor 10 may have a higher transconductance than the unipolar transistor 11.

[0024] In this respect, the threshold voltage corresponds to a minimum voltage at the control terminal (e.g. gate terminal) with respect to another terminal (source terminal or emitter terminal) that is required to establish a conductive path between the source and drain terminal or collector and emitter terminal.

[0025] The bipolar transistor 10 and the unipolar transistor 11 may have the same voltage class, i.e. they may be designed to operate in the same anode-cathode voltage range or up to the same voltage limit (for example, up to 100 V, up to 500 V, up to 1400 V, up to 2000 V, up to 3.5 kV, up to 5 kV, up to 6.5 kV or even up to 7 kV, to give just a few examples).

[0026] In such an embodiment, the bipolar transistor 10 can be used to carry high currents, for example surge currents, while for lower currents essentially only the unipolar transistor is used. This allows the use of favorable properties of the bipolar transistor for higher currents compared to the unipolar transistor. This will be explained with reference to the Fig. 3 to 5 will be explained in more detail later.

[0027] Before these explanations, with reference to the Fig. 2A to 2C discuss some implementation examples for transistor devices according to embodiments. In the Fig. 2A to 2C, the same or similar elements have the same reference numerals and are not described repeatedly in detail.

[0028] The components of the Fig. 2A to 2C each include an IGBT 20 and a metal-oxide-semiconductor field-effect transistor 21 coupled in parallel between a first node 22 and a second node 23. In embodiments, the MOSFET 21 may be a SiC MOSFET, and the IGBT 20 may be a silicon (Si)-based IGBT. A MOSFET 21 is equipped with an integrated body diode 24.

[0029] In Fig. 2B, only the IGBT 20 and the MOSFET 21 are shown together with the integrated body diode 24. In the embodiment of Fig. 2A, a silicon freewheeling diode 25 is additionally provided coupled between the nodes 22 and 23, and in the embodiment of Fig. 2C, a silicon carbide (SiC) Schottky diode 26 is additionally provided between nodes 22 and 23. Therefore, as can be seen, freewheeling diodes or other circuit elements such as Schottky diodes may be provided in addition to the IGBT 20 and the MOSFET 21.

[0030] It should be noted that the embodiments of the Fig. 2A and Fig. 2C, i.e., a silicon freewheeling diode and a silicon carbide Schottky diode may both be provided. Such diodes may serve to reduce oscillations during switching of the transistor device in some embodiments.

[0031] In some embodiments, for a high-voltage application, peripheral regions of the bipolar transistor (e.g., IGBT) may be designed to be protected during current commutation processes. In particular, reduced emitter efficiency in a peripheral region of an IGBT chip may be provided by reduced emitter doping or increased field stop doping compared to a central region.

[0032] It should be noted that the IGBT can also be a SiC-based IGBT.

[0033] In some embodiments, the IGBT may be a reverse-conducting IGBT, i.e., may include an integrated freewheeling diode, in particular a so-called RCDC (reverse conducting diode controlled) IGBT. In such RCDC IGBTs, characteristics can be controlled via the gate terminal of the RCDC IGBT even when the RCDC IGBT is in diode mode (i.e., conducting a current substantially via the diode). In some embodiments, such a reverse-conducting (RC) IGBT may not be controllable. In such a case, the RC IGBT may be operated in both forward-bias mode and freewheeling diode mode as a bipolar device, and the unipolar transistor may be operated as a unipolar device in both modes. In such embodiments, control of the transistor device may be simplified.

[0034] In some embodiments, the bipolar transistor (e.g., IGBT) and / or the unipolar transistor (e.g., MOSFET) may be compensation devices, i.e., they may include regions where, for example, n-type doping is compensated by regions with (e.g., columns of) p-type doping, or vice versa. As an example, the unipolar transistor may be a superjunction MOSFET.

[0035] Next, characteristics of unipolar and bipolar transistors in embodiments are described with reference to the Fig. 3 to 5 are described using a silicon carbide MOSFET as an example of a unipolar transistor and an IGBT as an example of a bipolar transistor. The explanation is based on exemplary characteristic curves, which are for illustrative purposes only and should not be construed as limiting.

[0036] In Fig. 3 shows a curve 40 an example current I (drain-source current) for a SiC MOSFET over a gate voltage V G , and a curve 41 illustrates an example current (collector-emitter current) for an IGBT versus the gate voltage V GAs can be seen, the SiC MOSFET in the illustrated embodiment has a lower threshold voltage than the IGBT. For example, the threshold voltage of the unipolar transistor may be about 6 V below the threshold voltage of the bipolar transistor in the example shown. Furthermore, the slopes of the curves, i.e., the transconductances, vary between curve 40 and curve 41. For example, the slope may be about 15 to 20 S (Siemens) for the SiC MOSFET (curve 40) and about 50 S for the IGBT (curve 41), so that the current for the IGBT increases more quickly with increasing gate voltage after the threshold voltage has been reached. This means that high currents at high gate voltages are mostly supported by the IGBT, while lower currents are supported by the SiC MOSFET.Since IGBTs are generally more efficient at higher currents than at lower currents, this can increase the overall efficiency of the transistor device and prevent the problems initially described for SiC MOSFETs at high currents in some embodiments.

[0037] In other words, the IGBT is used as a kind of “amplifier” at high gate voltages, while at lower gate voltages (below the threshold voltage of the IGBT) the unipolar transistor is primarily used.

[0038] As mentioned, while both unipolar and bipolar transistors possess the properties discussed above, they may have approximately the same voltage rating (voltage class), which allows for a small die size in some embodiments. The voltage rating may correspond to a voltage that the transistors are actually intended to use or are approved for.

[0039] Since the temperature dependence of the reverse voltage of IGBTs and in some transistor implementations may differ, in some embodiments the IGBT has a higher reverse voltage at room temperature, which may, for example, be more than 50 V or even more than 100 V higher than the breakdown voltage of the MOSFET at room temperature. In such embodiments, the reverse voltage of the IGBT and the breakdown voltage of the MOSFET may be approximately the same at an operating temperature of the transistor device, which may, for example, be 120 °C or even 150 °C or more depending on the application. In this respect, the reverse voltage is a voltage below (avalanche) breakdown. A nominal reverse voltage of a device such as a transistor indicates a maximum voltage for which no breakdown occurs, as specified and / or guaranteed by a manufacturer.The breakdown voltage is the voltage where the actual breakdown occurs, usually specified at some predetermined breakdown current such as 1 mA.

[0040] This will now be discussed with reference to Fig. 4 is explained in more detail. Fig. 4 illustrates, similarly Fig. 3, an example current I (drain-source current) versus the gate voltage for a silicon carbide MOSFET (curve 50) and an IGBT (curve 51), where the IGBT has a higher threshold voltage (e.g., about 10 V) than the SiC MOSFET (e.g., about 4 V) and the IGBT has a higher transconductance than the SiC MOSFET. This means that at lower gate voltages below 10 V in a region 52 in the example of Fig. 4 the IGBT is essentially non-conductive and the silicon carbide MOSFET takes over the current. In this range, short-circuit robustness of the IGBT is not necessary, although the IGBT can be designed to withstand such short-circuit currents of, for example, between 12 V and 10 V in the example of Fig. 4 to ensure short circuit robustness up to 12 V in the example of Fig. 4 to provide.

[0041] On the other hand, the IGBT can be designed to withstand typical surge currents, especially surge currents with smaller time transients of, for example, about 100 µs or more, 1 ms or more, or 10 ms or more (but still significantly higher time constants than in the case of short circuits, where time constants of a few µs may occur), which may occur in some applications. This results in a capability to withstand surge currents, especially in a Fig. 4, where the IGBT takes over most or almost all of the current. Based on the time constants mentioned above, a component such as a driver that controls the IGBT and MOSFET can be designed to distinguish between surge currents and short circuits, e.g., by measuring the current slope, and activates the IGBT only in the event of a surge current.

[0042] Since typical silicon carbide MOSFETs have comparatively low voltage thresholds and IGBTs can be designed to have higher voltage thresholds, a threshold relationship as in Fig. 4 can be obtained by a corresponding device design. Examples of the design of IGBTs with high threshold voltages will be described later with reference to the Fig. 9 to 11 explained.

[0043] Such an IGBT may have a high transconductance, which in embodiments may be adjusted by a high channel width and / or a short channel length, resulting in the comparatively high transconductance of the IGBT compared to the silicon carbide MOSFET in the example of Fig. 3 and Fig. 4. In particular, the IGBT can be designed for a wide dynamic range (i.e., a wide range of currents), as in Fig. 4 shown.

[0044] In some implementations, the IGBT may be implemented with locally heavily p-doped regions at a rear side thereof to implement a strong p-emitter, particularly at higher currents. Depending on the lateral dimensions of these heavily p-doped regions, this may lead to improved turn-off softness or improved short-circuit robustness in some embodiments. In other embodiments, doping at peripheral regions at the rear side may be reduced, which may contribute to improving surge current performance. Furthermore, in some embodiments, heavily p-doped stripes may be provided at the rear side, also to improve surge current performance in some embodiments.

[0045] It should be noted that in addition to controlling the IGBT via the threshold voltage to turn on later than the SiC MOSFET (at higher voltages and for higher currents), other embodiments may also provide an active gate control that controls the IGBT to be in an on-state only when higher currents are required, as explained further below.

[0046] Fig. 5 illustrates a surge current behavior of transistor devices according to some embodiments, showing a current I versus time. A curve 60 schematically illustrates a surge current event, wherein a current reaches a peak current I max,surgereached. A line 62 shows a critical current for a unipolar transistor such as a SiC-MOS, i.e., a current where adverse effects in the unipolar transistor, as already discussed, can occur, e.g., the destruction of the transistor. As indicated by a dashed line 63, the bipolar transistor, e.g., the IGBT, is turned on, for example, by appropriately increasing the gate voltage, as soon as the surge current reaches the critical limit (or earlier), so that the bipolar transistor then carries the most current, e.g., up to 80% of the maximum current I max,surge After the surge current event, the gate voltage can be lowered again, as indicated by a dashed line 64 and an arrow 61, thereby turning off the bipolar transistor.

[0047] Shock events such as the one in Fig. 5 have typical durations, for example, about 10 ms (or 1 ms or 100 ms), and can be detected based on this temporal behavior and the associated current slopes. In some embodiments, the bipolar transistor is turned on by a dedicated gate driver. Various control options will now be described with reference to Fig. 6A and Fig. 6B. In the Fig. 6A and Fig. 6B, similar elements bear the same reference numbers and are not discussed twice to avoid repetition.

[0048] The Fig. 6A and Fig. 6B each comprise an IGBT 70 as an example of a bipolar transistor and a MOSFET 71 with a diode 72 as an example of a unipolar transistor, which are coupled in parallel between the nodes 73, 74. In a comparative example of Fig. 6A, a single gate driver 75 is provided to control both the IGBT 70 and the MOSFET 71. The gate driver 75, as indicated by an arrow 76, may include a boost stage for providing a high gate voltage to also turn on the IGBT 70. This boost stage can be implemented in a comparatively simple manner, as it is only needed for surge events. The gate driver 75 can then turn on the IGBT 70 by increasing ("boosting") the gate voltage upon detection of an overcurrent event, such as a surge current event.

[0049] Fig. 6B illustrates an implementation with separate drivers according to one embodiment, where an IGBT gate driver 77 controls the IGBT 70 and a MOSFET gate driver 78 controls the MOSFET 71. In this implementation, the IGBT gate driver 77 turns on the IGBT 70 in the event that an overcurrent event, such as a surge current event, is detected. The IGBT gate driver 77 can be implemented using a comparatively simple design, as it only needs to be able to turn on the IGBT 70 in the event of surge current events. In other words, the gate driver 77 does not need to be optimized to be able to turn the IGBT on or off during fast periodic switching or similar applications.

[0050] The Fig. 6A and Fig. 6B can also be configured to turn off the IGBT 70 and the MOSFET 71 in stages by first turning off the IGBT 70 and then the MOSFET 71. Using the characteristics of Fig. 4 as an example, when both transistors 70, 71 are turned on using a gate voltage of, for example, 15 V, the gate voltage may first be reduced to about 10 V to turn off the IGBT 70, then remain at 10 V for a certain predetermined time, and then reduced to, for example, 0 V or below to also turn off the MOSFET 71.

[0051] The embodiments discussed above can be used for any application where an overcurrent / surge current must be managed, such as an inrush current that occurs when certain light bulbs, motor drivers, or transformers are turned on. Such high-current conditions may occur particularly in applications where high load variations exist. In some implementations, the described embodiments can enhance surge current protection.

[0052] Fig. 7 illustrates an example of controlling transistor devices according to embodiments. In Fig. 7, a first transistor device comprising an RC-IGBT 82 and a MOSFET 83 is coupled between a first terminal 86, for example, a terminal for receiving a positive supply voltage, and a node 88. A second transistor device comprising an RC-IGBT 84 and a MOSFET 85 is coupled between the node 88 and a second terminal 87, which may be configured, for example, to receive a negative supply voltage or to couple to ground. The first and second transistor devices may be implemented as previously discussed. In this way, in the example of Fig. 7, the first transistor device acts as a high-voltage switch, and the second transistor device acts as a low-voltage switch. The RC-IGBT 82 and the MOSFET 83 are controlled, for example, by a signal 80, and an RC-IGBT 84 and a MOSFET 85 are controlled by a signal 81 to alternately open and close the first transistor device and the second transistor device to alternately couple a load 89 and a node 88 to the terminal 86 or the terminal 87. In the exemplary control signals 80, 81 shown, there is a time t d1 , t d3 , where both transistor components are open (switched off) to prevent a short circuit between terminals 86, 87 during switching. The Fig. The control scheme shown in Figure 8 and the signals 80, 81 serve only as examples.

[0053] The Fig. 8A and Fig. 8B illustrate transistor devices according to further embodiments, including an additional inductive ( Fig. 8A) or resistive (8B) gate coupling in a transistor device. The embodiments of the Fig. 8A and Fig. 8B each comprise a bipolar transistor 91, for example an IGBT, and a unipolar transistor 92, for example a MOSFET (e.g., SiC MOSFET), coupled between a first terminal 90 and a second terminal 95. A control voltage (gate-emitter / gate-source voltage) Vge generated by a driver 93 controls the transistors 91, 92. In Fig. 8A, an additional coupling is provided via a SiC diode 94 (e.g., a merged-pin Schottky (MPS) SiC diode) and an inductance 96 (which can be realized, for example, by bond wires), and in Fig. 8B, additional coupling is realized via a SiC diode 94 and a resistor and / or inductor 96. In the event of an overvoltage event, the diode 94 undergoes an avalanche breakdown. Therefore, during such an event, a current flows through the resistor / inductor 96. Through appropriate dimensioning, the bipolar transistor 91 can at least partially close in this case to conduct part of the current. Appropriate dimensioning in this case may include designing the diode 94 with a lower breakdown voltage than the bipolar transistor 91 and the unipolar transistor 92. Otherwise, the considerations for the design of transistors 91, 92 can be explained, for example, with reference to Fig. 1-7 discussed threshold voltages also apply to the Fig. 8A and Fig. Apply 8B.

[0054] Next, an exemplary implementation of an IGBT usable in some embodiments will be described with reference to the Fig. 9 to 11. In particular, with reference to the Fig. 9 to 11 discuss an IGBT that can be designed for a high threshold voltage, so that the threshold voltage of the IGBT can be made larger than the threshold voltage of a unipolar transistor such as a SiC MOSFET, as previously discussed.

[0055] In some embodiments, a threshold voltage may be influenced by a dopant concentration in a body region of the IGBT or a thickness of a gate insulation layer (e.g., oxide layer). Fig. 9 shows an exemplary threshold voltage Vth across a p-type body doping of a body region for varying oxide thicknesses of a gate oxide, where the different curves refer to different thicknesses. The curves of Fig. 9 may be applicable, for example, to an IGBT for voltages of about 4.5 kV.

[0056] As from Fig. As can be seen in Figure 9, the threshold voltage may be varied by varying the dopant concentration of a body region, as will be explained later for body region 312, and / or by varying a gate oxide thickness. In some embodiments, cells with different threshold voltages may be provided.

[0057] The Fig. 10A to 10D illustrate cells of an exemplary IGBT, wherein the IGBT includes multiple cells. In the example of Fig. 10, cells 101a, 101b are provided, each of which can be designed for a desired threshold voltage, for example, using the information from the curves of Fig. 9. The cells 101a, 101b are trench-type cells. The exemplary IGBT of Fig. 10A to 10B further includes inactive cells 101c. Inactive cells 101c may be provided between cell 101a and cell 101b. Cells 101a, 101b may have the same threshold voltage or different threshold voltages. In particular, cell 101b may have a higher threshold voltage than cell 101a.

[0058] When implementing Fig. 10A, the body region 312 of the cell 101b comprises a p-doped body region 313 having a higher doping concentration than the remaining body region 312. In other embodiments, the body region of the cell 101a may also include such a p-doped body region 313. In this case, parts of the p-type body region 313 associated with the cell 101b may have the same doping concentration as or a different doping concentration than the corresponding p-type body region 313 associated with the cell 101a. As described with reference to Fig. As explained in Figure 9, a threshold voltage can be adjusted by adjusting the dopant concentration. In some embodiments, a p-type body region 313 may be provided between the remaining body region 312 and a drift region.

[0059] In the implementation of Fig. 10B, each body region comprises a channel region 317, wherein channel regions 317 associated with cell 101b may have a same or different dopant concentration than the channel regions associated with cell 101a. In some embodiments, as in Fig. 10C, a thickness of a gate insulation layer 315C may be adjusted to provide a threshold voltage. In some embodiments, as shown in Fig. 10D, potential-free gate structures can be used. In Fig. 10D, inactive cells 101c may have a high-resistance connection, e.g., > 1000 ohms, to a source terminal, while in the embodiments of Fig. 10A-10C inactive cells can have a low-resistance connection, e.g., < 100 Ohm, to the source terminal. Fig. The variations shown in Figures 10A to 10D may be combined with each other or used separately to adjust a threshold voltage as desired.

[0060] The Fig. 11A and Fig. 11B illustrate exemplary top views of IGBTs 100 according to some embodiments. The device 100 of Fig. 11A and Fig. 11B has a peripheral edge 610. Furthermore, the embodiment of Fig. 11A cells 101a, 101b, as described with reference to Fig. 10A to 10D, such that more cells 101b are located near the peripheral edge 610. In such an embodiment, the cells 101b may have a higher threshold voltage than the cells 101a. A reduced carrier density during normal operation may be provided at or near the peripheral edge 610. Fig. Figure 11B illustrates a variation of Fig. 11A, where additional inactive cells 101c are provided.

[0061] In different areas that are closer to the peripheral edge 610 or are further away from it, different unit cells 620 for forming the device 100 of Fig. 11B can be used. The Fig. Figures 9 to 11 only illustrate examples of how high threshold voltage IGBTs can be implemented and are not to be construed as limiting.

[0062] It should be noted that in a similar way as in Fig. 11A and Fig. As shown in Figure 11B, the IGBT and MOSFET can be integrated into a single device, with Si IGBT cells arranged corresponding to cells 101a and Si MOSFET cells corresponding to cells 101b. In such an implementation, the Si MOSFET cells in a drift region can have a higher n-type dopant concentration. Alternatively, unipolar and bipolar transistors such as Si IGBTs and SiC MOSFETs can be bonded on a same substrate.

[0063] Furthermore, in some embodiments, the bipolar transistor (e.g., IGBT) and / or the unipolar transistor (e.g., MOSFET) may be implemented as compensation devices, i.e., they may include regions where, for example, n-type doping is compensated by regions with (e.g., columns of) p-type doping, or vice versa. As an example, the unipolar transistor may be a superjunction MOSFET.

[0064] The following embodiments are exemplary embodiments.

[0065] Example 1. A transistor device comprising: a unipolar transistor coupled between a first terminal and a second terminal, a bipolar transistor coupled in parallel to the unipolar transistor between the first and second terminals, the bipolar transistor being configured to conduct a majority of a current flowing through the transistor device when the current and / or a control voltage controlling the unipolar transistor and the bipolar transistor exceed a predetermined threshold.

[0066] Example 2. The transistor device of example 1, wherein the bipolar transistor is configured to have a higher threshold voltage than the unipolar transistor, wherein a difference between the threshold voltage of the bipolar transistor and the threshold voltage of the unipolar transistor is at least 1 V.

[0067] Example 3. Device of Example 2, wherein the difference is at least 3 V.

[0068] Example 4. The device of Example 3, wherein the difference is at least 5 V.

[0069] Example 5. The device of Example 1, wherein the unipolar transistor has the same voltage rating as the bipolar transistor.

[0070] Example 6. The device of Example 1, wherein the bipolar transistor has a higher transconductance than the unipolar transistor.

[0071] Example 7. The device of example 1, wherein the bipolar transistor comprises an insulated gate bipolar transistor.

[0072] Example 8. The device of Example 1, wherein the unipolar transistor comprises a metal oxide semiconductor field effect transistor.

[0073] Example 9. The device of example 1, wherein the unipolar transistor comprises a silicon carbide-based transistor.

[0074] Example 10. The device of example 1, further comprising a driver circuit, wherein the driver circuit is configured to increase a control voltage for at least the bipolar transistor in the event of an overcurrent event.

[0075] Example 11. The device of example 10, wherein the gate driver circuit is configured to control both the unipolar transistor and the bipolar transistor.

[0076] Example 12. The device of Example 10, comprising a further gate driver circuit configured to control the unipolar transistor.

[0077] Example 13. The device of example 10, wherein the driver circuit for turning off the transistor device is configured to turn off the unipolar transistor after turning off the bipolar transistor.

[0078] Example 14. The device of Example 1, wherein the bipolar transistor has a higher blocking voltage at 20 °C than the unipolar transistor.

[0079] Example 15. A transistor device comprising: a unipolar transistor coupled between a first terminal and a second terminal, a bipolar transistor coupled in parallel to the unipolar transistor between the first and second terminals and a gate control circuit, wherein the control circuit is configured to turn on the bipolar transistor only upon detection of an overcurrent event.

[0080] Example 16. The device of Example 15, wherein the bipolar transistor has a higher threshold voltage than the unipolar transistor.

[0081] Example 17. The device of example 16, wherein the gate driver circuit comprises a common control driver for the bipolar transistor and the unipolar transistor.

[0082] Example 18. The device of example 15, wherein the control circuit comprises separate control drivers for the bipolar transistor and the unipolar transistor.

[0083] Example 19. The device of example 15, wherein the control circuit is configured to distinguish between a short circuit event and a surge current event and to turn on the bipolar transistor only if the overcurrent event is a surge current event.

[0084] Example 20. The device of example 1, further comprising at least one of a freewheeling diode coupled between the first and second terminals or a silicon carbide diode coupled between the first and second terminals.

[0085] In view of the many variations and alternatives described above, it is to be understood that the above embodiments are intended as illustrative examples only and are not to be construed as limiting.

Claims

[1] Transistor device comprising: a unipolar transistor (11; 21; 71) coupled between a first terminal (12; 22; 73) and a second terminal (13; 23; 74), a bipolar transistor (10; 20; 70) coupled in parallel to the unipolar transistor (11; 21; 71) between the first (12; 22; 73) and second terminal (13; 23; 74), wherein the bipolar transistor (10; 20; 70) is designed to conduct a large part of a current flowing through the transistor component when the current and / or a control voltage controlling the unipolar transistor (11; 21; 71) and the bipolar transistor (10; 20; 70) exceed a predetermined threshold value, wherein the bipolar transistor (10; 20; 70) is designed to have a higher threshold voltage than the unipolar transistor (11; 21; 71) due to a dopant concentration in a body region of the bipolar transistor, wherein a difference between the threshold voltage of the bipolar transistor (10; 20; 70) and the threshold voltage of the unipolar transistor (11; 21; 71) is at least 1 V, further comprising a gate driver circuit (75;77), wherein the gate driver circuit is configured to increase a control voltage at least for the bipolar transistor (10; 20; 70) in the event of an overcurrent event, and; a further gate driver circuit (78) configured to control the unipolar transistor. [2] The transistor device of claim 1, wherein the difference is at least 3 V. [3] A transistor device according to claim 2, wherein the difference is at least 5 V. [4] Transistor component according to one of claims 1-3, wherein the unipolar transistor (11; 21; 71) has a same nominal voltage as the bipolar transistor (10; 20; 70). [5] Transistor component according to one of claims 1-4, wherein the bipolar transistor (10; 20; 70) has a higher transconductance than the unipolar transistor (11; 21; 71). [6] A transistor device according to any one of claims 1-5, wherein the bipolar transistor (10; 20; 70) comprises an insulated gate bipolar transistor. [7] Transistor device according to one of claims 1-6, wherein the unipolar transistor (11; 21; 71) comprises a metal oxide semiconductor field effect transistor. [8] Transistor device according to one of claims 1-7, wherein the unipolar transistor (11; 21; 71) comprises a silicon carbide-based transistor. [9] Transistor device according to one of claims 1-8, wherein the gate driver circuit (75; 77) and the further gate driver circuit (78) are configured to turn off the unipolar transistor (11; 21; 71) after the bipolar transistor to turn off the transistor device. [10] Transistor component according to one of claims 1-9, wherein the bipolar transistor (10; 20; 70) has a higher blocking voltage at 20 °C than the unipolar transistor (11; 21; 71). [11] Transistor device comprising: a unipolar transistor (71) coupled between a first terminal (73) and a second terminal (74), a bipolar transistor (70) coupled in parallel to the unipolar transistor (71) between the first (73) and second (74) terminals and a gate control circuit (75; 77; 78), wherein the gate control circuit (75; 77; 78) is configured to turn on the bipolar transistor (70) only upon detection of an overcurrent event, wherein the bipolar transistor (70) has a higher threshold voltage than the unipolar transistor (71) due to a dopant concentration in a body region of the bipolar transistor, wherein a difference between the threshold voltage of the bipolar transistor (10; 20; 70) and the threshold voltage of the unipolar transistor (11; 21; 71) is at least 1 V, wherein the gate control circuit (77; 78) comprises separate control drivers for the bipolar transistor (70) and the unipolar transistor (71). [12] The transistor device of claim 11, wherein the gate control circuit (75; 77; 78) is configured to distinguish between a short-circuit event and a surge current event and to turn on the bipolar transistor (76) only if the overcurrent event is a surge current event. [13] Transistor device according to one of claims 1-12, further comprising at least one of a freewheeling diode (24; 72) coupled between the first and second terminals or a silicon carbide diode coupled between the first and second terminals.

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