Cascode device with one or more self-conducting gates

Abstract

A switching device comprises at least two bidirectional switches electrically interconnected in a cascode configuration. A first bidirectional switch and a second bidirectional switch of the at least two bidirectional switches each have a conducting gate and a blocking gate. Each remaining bidirectional switch of the at least two bidirectional switches, cascoded between the first and second bidirectional switches, has a first conducting gate and a second conducting gate. The switching device is actively controlled by the blocking gate of the first bidirectional switch and the blocking gate of the second bidirectional switch.Each self-conducting gate of the at least two bidirectional switches is electrically connected to a source of another of the at least two bidirectional switches via a voltage-blocking device configured to block a portion of the voltage across the switching device when the switching device is off. Embodiments for additional switching devices are described.

Description

BACKGROUND

[0001] GaN (gallium nitride) technology requires many buffer layers to withstand at least 1.2 kV, making it difficult to realize a single discrete or bidirectional switching device with a breakdown voltage of at least 1.2 kV in GaN. Accordingly, higher voltage rated applications, such as 3-phase matrix converters and 3-phase current source inverters, are currently difficult to achieve with GaN technology. For discrete devices, a 1.2 kV switch can be realized by stacking two (2) 650 V rated devices. This approach has two active gates, which requires both gates to be driven at exactly the same time. Otherwise, one 650 V device may be more stressed than the other 650 V device.For bidirectional blocking devices, two (2) discrete bidirectional switches can be placed back-to-back to block in either direction, while both gates are driven either by the same driver or by two individual drivers but powered by the same auxiliary supply. However, to realize a 1.2 kV bidirectional blocking device, two (2) discrete 1.2 kV devices must be placed back-to-back. This results in inefficient use of the two devices, with only one device blocking in one voltage direction, but current flowing through the semiconductor material of both devices. Furthermore, this approach is expensive compared to a discrete component of the same RDSon (on-resistance) class, as the required chip size is now approximately four (4) times larger.

[0002] Therefore, there is a need for an improved 1.2 kV or higher discrete or bidirectional switch using GaN technology. SUMMARY

[0003] According to one embodiment of a switching device, the switching device comprises: a first power transistor die comprising a normally-on transistor with at most half a maximum rated drain-source voltage of the switching device; a second power transistor die comprising a normally-off transistor with at most half the maximum rated drain-source voltage of the switching device, wherein a drain of the normally-off transistor is electrically connected to a source of the normally-on transistor to form a cascode device; a voltage blocking device electrically connected between a gate of the normally-on transistor and a source of the normally-off transistor and configured to block a portion of the voltage across the switching device when the cascode device is off;and an overvoltage protection device configured to turn off the normally-on transistor when the normally-off transistor turns off, such that the cascode device is actively controlled only by a gate of the normally-off transistor.;

[0004] According to another embodiment of a switching device, the switching device comprises: a first bidirectional switch comprising a first source, a second source, a normally-off gate, and a normally-on gate; a second bidirectional switch comprising a first source electrically connected to the second source of the first bidirectional switch to form a cascode device, a second source, a normally-off gate, and a normally-on gate; a first voltage blocking device electrically connected between the first source of the first bidirectional switch and the normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is off;a first overvoltage protection device configured to turn off the normally-on gate of the first bidirectional switch when the normally-off gate of the second bidirectional switch is turned off, such that the normally-on gate of the first bidirectional switch is passively controlled by the normally-off gate of the second bidirectional switch; a second voltage blocking device electrically connected between the second source of the second bidirectional switch and the normally-on gate of the first bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off;and a second overvoltage protection device configured to turn off the normally-on gate of the second bidirectional switch when the normally-off gate of the first bidirectional switch is turned off, such that the normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the first bidirectional switch;

[0005] According to another embodiment of a switching device, the switching device comprises: a first bidirectional switch comprising a first source, a second source, a normally-off gate, and a normally-on gate; a second bidirectional switch comprising a first source electrically connected to the second source of the first bidirectional switch to form a first part of a cascode device, a second source, a first normally-on gate, and a second normally-on gate; a third bidirectional switch comprising a first source electrically connected to the second source of the second bidirectional switch to form a second part of the cascode device, a second source, a normally-on gate, and a normally-off gate;a first voltage blocking device electrically connected between the first source of the first bidirectional switch and the first normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a first overvoltage protection device configured to turn off the first normally-on gate of the second bidirectional switch when the normally-off gate of the first bidirectional switch is turned off, such that the first normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the first bidirectional switch;a second voltage blocking device electrically connected between the first source of the third bidirectional switch and the normally-on gate of the first bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a second overvoltage protection device configured to turn off the normally-on gate of the first bidirectional switch when the first normally-on gate of the second bidirectional switch is turned off; a third voltage blocking device electrically connected between the second source of the third bidirectional switch and the second normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off;a third overvoltage protection device configured to turn off the second normally-on gate of the second bidirectional switch when the normally-off gate of the third bidirectional switch is turned off, such that the second normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the third bidirectional switch; a fourth voltage blocking device electrically connected between the normally-on gate of the third bidirectional switch and the first source of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off;and a fourth overvoltage protection device configured to turn off the normally-on gate of the third bidirectional switch when the second normally-on gate of the second bidirectional switch is turned off, such that the normally-on gate of the third bidirectional switch is passively controlled by the second normally-on gate of the second bidirectional switch;

[0006] According to another embodiment of a switching device, the switching device comprises: a first normally-off switch; a second normally-off switch; at least two bidirectional switches electrically connected in a cascode configuration between the first normally-off switch and the second normally-off switch, each bidirectional switch comprising a first normally-on gate and a second normally-on gate; a voltage blocking device electrically connected to one of the normally-on gates of each bidirectional switch and configured to block a portion of the voltage across the switching device when the switching device is off;a first overvoltage protection device configured to turn off the first normally-on gate of each bidirectional switch when the first normally-off switch is turned off, such that the first normally-on gate of each bidirectional switch is passively controlled by the first normally-off switch; and a second overvoltage protection device configured to turn off the second normally-on gate of each bidirectional switch when the second normally-off switch is turned off, such that the second normally-on gate of each bidirectional switch is passively controlled by the second normally-off switch.

[0007] According to a further embodiment of a switching device, the switching device comprises at least two bidirectional switches that are electrically connected in a cascode configuration, wherein a first bidirectional switch and a second bidirectional switch of the at least two bidirectional switches each have a normally-on gate and a normally-off gate, wherein each remaining bidirectional switch of the at least two bidirectional switches that is cascoded between the first bidirectional switch and the second bidirectional switch has a first normally-on gate and a second normally-on gate, wherein the switching device is actively controlled by the normally-off gate of the first bidirectional switch and the normally-off gate of the second bidirectional switch, wherein each normally-on gate of the at least two bidirectional switches is controlled by a voltage blocking device,which is designed to block a portion of the voltage across the switching device when the switching device is switched off, is electrically connected to a source of another of the at least two bidirectional switches.,

[0008] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description and examining the accompanying drawings. SHORT DESCRIPTION OF THE CHARACTERS

[0009] The elements of the drawings are not necessarily to scale. Like reference numerals indicate corresponding similar parts. The features of the various illustrated embodiments may be combined, provided they are not mutually exclusive. Embodiments are illustrated in the drawings and described in detail in the following description. Fig. 1A illustrates a circuit schematic of one embodiment of a unidirectional cascode switching device. Fig. Figure 1B illustrates the circuit diagram of Fig. 1 with superimposed voltages at different nodes of the circuit. Fig. 2A and Fig. 2B illustrate the respective courses of the Fig. 1 shown voltages and load current during operation of the switching device of Fig. 1. Fig. Figure 3 illustrates the unidirectional cascode switching device of Fig. 1 with a stray inductance. Fig. Figure 4 illustrates a circuit diagram of an embodiment of a circuit that implements the Fig. 3 shows the leakage inductance. Fig. Figure 5 illustrates a circuit diagram of another embodiment of a circuit that incorporates the Fig. 3 shows the leakage inductance. Fig. 6 illustrates a circuit diagram of another embodiment of a unidirectional cascode switching device. Fig. Figure 7 illustrates a waveform of voltages and load current during operation of the switching device of Fig. 6. Fig. 8 illustrates a circuit diagram of an embodiment of a bidirectional cascode switching device based on asymmetric bidirectional switches. Fig. 9 illustrates a circuit diagram of an embodiment of a bidirectional cascode switching device based on a pair of asymmetric bidirectional switches and at least one symmetric bidirectional switch. Fig. 10 illustrates a circuit schematic of an embodiment of a bidirectional cascode switching device based on symmetrical bidirectional switches stacked between low-voltage MOS switching devices in a cascode configuration. DETAILED DESCRIPTION

[0010] The embodiments described herein provide a 1.2 kV or higher rated switching device implemented using discrete and / or bidirectional switching devices with a lower (<1.2 kV) breakdown voltage, while maintaining the same number of active gates as a single high-voltage device and utilizing the entire device for blocking voltage and conducting current. In the case of a 1.2 kV rated switching device, the discrete and / or bidirectional switching devices used to implement the switching device have a breakdown voltage of 650 V. However, the embodiments described herein may be applied to voltage classes other than 650 V, and the resulting switching device may have a blocking voltage greater than 1.2 kV.More generally, the switching devices disclosed herein may have a breakdown voltage of at least 1.2 kV and, depending on the number of devices arranged in a cascode configuration, may be implemented using discrete and / or bidirectional switching devices with a breakdown voltage of at most half the breakdown voltage of the switching device.

[0011] Next, exemplary embodiments of switching devices will be described with reference to the figures.

[0012] Fig. 1A illustrates one embodiment of a switching device 100. According to this embodiment, the switching device 100 is a discrete unidirectional cascode device based on a first power transistor die (chip) 102 having a normally-on transistor (i.e., depletion-mode transistor) Q1 and a second power transistor die 104 having a normally-off transistor (i.e., enhancement-mode transistor) Q2. Both the normally-on transistor Q1 and the normally-off transistor Q2 have at most half the maximum rated drain-to-source (D-to-S) voltage of the switching device 100.

[0013] For the normally-on transistor Q1, a current conduction channel exists between the drain and source terminals D1, S1 of the normally-on transistor Q1 without a voltage being applied to the gate terminal G1 of the normally-on transistor Q1. For the normally-off transistor Q2, a current conduction channel does not exist between the drain and source terminals D2, S2 of the normally-off transistor Q2 without a suitable voltage being applied to the gate terminal G2 of the normally-off transistor Q2.

[0014] In one embodiment, normally-on transistor Q1 is a normally-on GaN transistor, normally-off transistor Q2 is a normally-off GaN transistor, and the maximum rated drain-source voltage of switching device 100 is 1.2 kV. In GaN technology, a polarization difference between the GaN channel layer and the AlGaN barrier layer results in a 2-dimensional (2D) "sheet" of uncompensated charge. The 2D charge sheet is typically positive and causes a 2D electron gas to be formed, even in the absence of doping. Accordingly, GaN devices tend to be normally-on devices unless an additional device construction technique, such as doping the barrier with acceptors, gate construction, etc., is applied to render the device normally off.

[0015] The drain D2 of the normally-off transistor Q2 is electrically connected to the source S1 of the normally-on transistor Q1 to form a cascode device. According to this configuration, the drain D1 of the normally-on transistor Q1 forms the drain D of the cascoded switching device 100, and the source S2 of the normally-off transistor Q2 forms the source S of the cascoded switching device 100. The cascoded switching device 100 has a single actively controlled (driven) gate G formed by the gate G2 of the normally-off transistor Q2.

[0016] To maximize the use of both transistor devices Q1, Q2, the switching device 100 in Fig. 1A also includes a voltage blocking device 106 electrically connected between the gate G1 of the normally-on transistor Q1 and the source S2 of the normally-off transistor Q2. The voltage blocking device 106 blocks a portion of the drain-source voltage 'VDS' across the switching device 100 when the cascode device formed by Q1 and Q2 is off. In one embodiment, the voltage blocking device 106 is a capacitor C1 having a first terminal 108 electrically connected to the gate G1 of the normally-on transistor Q1 and a second terminal 110 electrically connected to the source S2 of the normally-off transistor Q2. The voltage blocking capacitor C1 may be in the pF range if the transistors Q1 and Q2 are rated for 650 V.

[0017] The switching device 100 in Fig. 1A further includes an overvoltage protection device 112 that protects the gate G1 of the normally-on transistor Q1 from overvoltage conditions in the negative direction when the normally-off transistor Q2 is off. The overvoltage protection device 112 turns off the normally-on transistor Q1 when the normally-off transistor Q2 is off, so that the cascode device formed by Q1 and Q2 is actively controlled only by the gate G2 of the normally-off transistor Q2. Accordingly, only the normally-off gate G2 is actively controlled (driven) to control the cascode structure, and no synchronous driving of the normally-on gate G1 is required.

[0018] In one embodiment, the overvoltage protection device 112 comprises one or more diodes connected in series between the gate G1 of the normally-on transistor Q1 and the source S1 of the normally-on transistor Q1. The number of diodes depends on the total forward voltage of the overvoltage protection device 112, which in an absolute sense should be greater than the negative threshold voltage of the normally-on transistor Q1 in order to turn off the normally-on transistor Q1. Accordingly, the overvoltage protection device 112 may comprise a single diode, with the anode AN1 electrically connected to the source S1 of the normally-on transistor Q1 and the cathode CTN electrically connected to the gate G1 of the normally-on transistor Q1. In the case of multiple diodes connected in series, e.g., as in Fig. As shown in Figure 1A, the anode AN1 of the first diode in the series chain is electrically connected to the source S1 of the normally-on transistor Q1, and the cathode CTN of the last diode in the series chain is electrically connected to the gate G1 of the normally-on transistor Q1. The diode(s), e.g., ESD (electrostatic discharge) structure(s), may, for example, be monolithically integrated into the same die 102 as the normally-on transistor Q1.

[0019] Fig. Figure 1B illustrates the drain-source voltage 'VDS' of the switching device 100, the voltage 'VM' across the normally-off transistor Q2, and the gate-source voltage 'NONVGS' of the normally-on transistor Q1. Fig. Figure 2A is a graph of these voltages and the load current IL during operation of the switching device 100. In this example, VDS is 1.2 kV when the switching device 100 is off (blocking).

[0020] As in Fig. As shown in Figure 2A, the voltage 'VM' across the normally-off transistor Q2 and the drain-source voltage 'VDS' of the switching device 100 both begin to rise when the normally-off transistor Q2 turns off by actively reducing the gate-source voltage applied to the gate G2 below the threshold voltage of Q2. As the voltage 'VM' across the normally-off transistor Q2 increases, the voltage across the overvoltage protection device 112 also increases. Eventually, the voltage across the overvoltage protection device 112 rises high enough that the gate-source voltage 'NONVGS' of the normally-on transistor Q1 reaches a negative threshold voltage (-6 V in this example), and the normally-on transistor Q1 safely turns off before being subjected to an overvoltage condition.

[0021] The distribution of the drain-source voltage 'VDS' of the switching device 100 is controlled by the value of the voltage blocking device 106. How quickly the voltage across the overvoltage protection device 112 rises determines when the normally-on transistor Q1 turns off. This speed depends on the size of the capacitor C1. As shown in Fig. As shown in Figure 2B, the choice of capacitor size also affects the voltage 'VM' across the normally-off transistor Q2. In Fig. 2B, C1 = 14 pF to VM1 of about 560 V, C2 = 17 pF to VM2 of about 610 V, and C3 = 20 pF to VM3 of about 670 V. In each case, the gate-source voltage 'NONVGS' of the normally-on transistor Q1 becomes negative and turns off the normally-on transistor Q1 when the normally-off transistor Q2 turns off.

[0022] Although the voltage distribution across the cascode structure formed by transistors Q1 and Q2 can be modified based on a single parameter, the value of C1, the stability of this value must be carefully considered to enable stable performance. Since the Fig. 1A uses two individual (discrete) dies 102, 104, additional parasitic effects are also present due to the inter-die connections required to form the switching device 100.

[0023] As in Fig. 3. One parasitic effect affecting switching performance is the leakage inductance 'Lp' between the gate G1 of the normally-on transistor Q1 and the capacitor C1 of the voltage blocking device 106. This leakage inductance 'Lp' could generate oscillations that might require further protection for the gate G1 of the normally-on transistor Q1.

[0024] Fig. 4 illustrates an embodiment according to which an additional diode D_AP, such as an anti-parallel ESD diode, is electrically connected between the gate G1 of the normally-on transistor Q1 and the source S1 of the normally-on transistor Q1 and anti-parallel to the diode(s) of the overvoltage protection device 112. The cathode CD2 of the additional diode D_AP is electrically connected to the anode AN1 of the first diode of the overvoltage protection device 112, and the anode AD2 of the additional diode D_AP is electrically connected to the cathode CTN of the last diode of the overvoltage protection device 112.

[0025] Fig. 5 illustrates an embodiment according to which the capacitor C1 of the voltage blocking device 106 is replaced by another component with a capacitive behavior. The component should block 650 V for the 1.2 kV example and have sufficient capacitance for this function. For example, the component with the capacitive behavior can be a gate diode device MGD1, such as a MOS gate diode. The gate diode device MGD1 has a drain D3 electrically connected to the gate G1 of the normally-on transistor Q1. Both the gate G3 and the source S3 of the gate diode device MGD1 are electrically connected to the source S2 of the normally-off transistor Q2. The gate diode device MGD1 can be integrated into the same die 104 as the normally-off transistor Q2, thereby providing the corresponding Fig. 3 is reduced. This is likely due to the nonlinearity of the output capacitance of the gate diode device MGD1.

[0026] Fig. 6 illustrates another embodiment of the discrete unidirectional cascode switching device 100. In Fig. 6, the cascode configuration is extended to include a third power transistor die 114, which includes an additional normally-on transistor Q3. The source S3 of the additional normally-on transistor Q3 is electrically connected to the drain D1 of the first normally-on transistor Q1.

[0027] An additional voltage blocking device 116 is electrically connected between the gate G3 of the additional normally-on transistor Q3 and the source S1 of the first normally-on transistor Q1 to block a portion of the voltage across the switching device 100 when the cascode device is off. In one embodiment, the additional voltage blocking device 116 is a capacitor C2 having a first terminal 118 electrically connected to the gate G3 of the additional normally-on transistor Q3 and a second terminal 120 electrically connected to the source S1 of the first normally-on transistor Q1. The drain-source voltage distribution of the switching device 100 is controlled by the respective values ​​of the voltage blocking devices 106, 116, as described hereinbefore, and may be in the pF range for transistors Q1, Q2, Q3 rated at 650 V.In another embodiment, the additional voltage blocking device 116 is a gate diode device, such as shown in FIG. Fig. 5. In this case, the drain of the gate diode device is electrically connected to the gate G3 of the additional normally-on transistor Q3, and both the gate and source of the gate diode device are electrically connected to the source S1 of the first normally-on transistor Q1.

[0028] To ensure that the additional normally-on transistor Q3 is protected from overvoltage conditions in the negative direction when the first normally-on transistor Q1 turns off, an additional overvoltage protection device 118 is provided. The additional overvoltage protection device 118 turns off the additional normally-on transistor Q3 when the first normally-on transistor Q1 turns off, so that the cascode device formed by transistors Q1, Q2, and Q3 is actively controlled only by the gate G2 of the normally-off transistor Q2. In one embodiment, the additional overvoltage protection device 118 comprises one or more diodes connected in series between the gate G3 of the additional normally-on transistor Q3 and the source S3 of the additional normally-on transistor Q3.The number of diodes depends, as explained above, on the total forward voltage of the additional overvoltage protection device 118.

[0029] The anode AN1_b of the first diode of the additional overvoltage protection device 122 is electrically connected to the source S3 of the additional normally-on transistor Q3. The cathode CTN_b of the last diode of the additional overvoltage protection device 122 is electrically connected to the gate G3 of the additional normally-on transistor Q3. The first diode and the last diode may be the same diode if a single diode provides the desired total forward voltage of the additional overvoltage protection device 122, or may instead be different diodes electrically connected in series.

[0030] An additional diode may be electrically connected between the gate G3 of the additional normally-on transistor Q3 and the source S3 of the additional normally-on transistor Q3 and antiparallel to the diode(s) of the additional overvoltage protection device 122, e.g., as shown in Fig. 4 for the first normally-on transistor Q1 to protect against stray inductance that could otherwise generate oscillations at the gate G3 of the additional normally-on transistor Q3.

[0031] Fig. Figure 7 illustrates simulated curves for the Fig. 6 shown discrete unidirectional cascode switching device 100. In Fig. 7, 'VDS3' is the full blocking voltage of the switching device 100, which switches at 1.8 kV under a basic chopper cell structure, 'VDS2' is the voltage across the first normally-on transistor Q1, which blocks at about 1.2 kV, and 'VDS1' is the voltage across the normally-off transistor Q2. As in Fig. 7, the gate-source voltage 'NONVGS2' of the first normally-on transistor Q1 and the gate-source voltage 'NONVGS3' of the additional normally-on transistor Q3 are almost perfectly synchronized to turn off the entire cascode chain. The voltage supplied by the switching device 100 of Fig. 6 supplied load current 'IL' is also in Fig. 7 shown.

[0032] In the case of Fig. 3, forming the cascode structure, each transistor Q1, Q2, Q3 can have a maximum of one-third (1 / 3) of the maximum rated drain-source voltage of the switching device 100. For example, if each transistor Q1, Q2, Q3 has a drain-source breakdown voltage of 650 V, the switching device 100 has a drain-source breakdown voltage of 1.95 kV. Fig. 1 and Fig. The embodiments of the discrete unidirectional cascode switching device shown in Figure 6 can be generalized to a normally-off transistor cascoded with N normally-on transistors, where N is a positive integer ≥ 1, and with a voltage blocking device and an overvoltage protection device for each normally-on transistor. The breakdown voltage X_Q of each transistor forming the cascode switching device is given by X_Q = X_SW / (N+1), where X_SW is the breakdown voltage of the entire cascode switching device. For a single normally-on transistor cascoded with a normally-off transistor, as shown in Fig. 1, X_Q = 1 / 2 * X_SW. For two normally-on transistors cascoded with a normally-off transistor, as in Fig. 6, X_Q = 1 / 3 * X_SW, etc.

[0033] Next, embodiments of a bidirectional cascode switching device based on symmetric and / or asymmetric bidirectional switches are described. A bidirectional solid-state switch comprises a first source terminal, a second source terminal, a compound semiconductor substrate, such as a GaN substrate, a common drift region in the compound semiconductor substrate and in series between the two source terminals, a first gate and a second gate in series between the two source terminals. In the case of a symmetric bidirectional switch, both gates are normally-on gates. In the case of an asymmetric bidirectional switch, one gate is normally-on (i.e., depletion mode) and the other gate is normally-off (i.e., enhancement mode). For a normally-on gate, a current conduction channel is present adjacent to the gate without any voltage applied to the gate.For a normally-off gate, a current conduction channel adjacent to the gate is not present without an appropriate voltage being applied to the gate.

[0034] Fig. Figure 8 illustrates an embodiment of a bidirectional cascode switching device 200 based on asymmetric bidirectional switches BDSA, BDSB. The first asymmetric bidirectional switch BDSA includes a first source S1A, a second source S2A, a normally-off gate G1A, and a normally-on gate G2A. The second asymmetric bidirectional switch BDSB includes a first source S1B electrically connected to the second source S2A of the first asymmetric bidirectional switch BDSA to form a cascode device, a second source S2B, a normally-off gate G2B, and a normally-on gate G1B.

[0035] The asymmetric bidirectional switches BDSA, BDSB can be provided as discrete dies 202, 204. For example, the first asymmetric bidirectional switch BDSA can be included in a first GaN die 202 and have at most half (1 / 2) of the maximum rated source-to-source voltage (S2B-S1A) of the bidirectional cascode switching device 200. The second asymmetric bidirectional switch BDSB can be included in a second GaN die 204 and have at most half (1 / 2) of the maximum rated source-to-source voltage of the bidirectional cascode switching device 200. The maximum rated source-to-source voltage of the bidirectional cascode switching device 200 can, for example, be 1.2 kV or higher. The asymmetric bidirectional switches BDSA, BDSB can instead be monolithically integrated into the same die.In any case, the common drift region / compound semiconductor substrate SUB1, SUB2 of the asymmetric bidirectional switches BDSA, BDSB are electrically isolated from each other to ensure that each asymmetric bidirectional switch BDSA, BDSB can safely block its own individual voltage.

[0036] The bidirectional cascode switching device 200 also includes a first voltage blocking device 206 electrically connected between the first source S1A of the first asymmetric bidirectional switch BDSA and the normally-on gate G1B of the second asymmetric bidirectional switch BDSB. The first voltage blocking device 206 blocks a portion of the voltage across the bidirectional cascode switching device 200 when the cascode device is off. A first overvoltage protection device DA turns off the normally-on gate G2A of the first asymmetric bidirectional switch BDSA when the normally-off gate G2B of the second asymmetric bidirectional switch BDSB turns off, so that the normally-on gate G2A of the first asymmetric bidirectional switch BDSA is passively controlled by the normally-off gate G2B of the second asymmetric bidirectional switch BDSB.

[0037] The bidirectional cascode switching device 200 also includes a second voltage blocking device 208 electrically connected between the second source S2B of the second asymmetric bidirectional switch BDSB and the normally-on gate G2A of the first asymmetric bidirectional switch BDSA. The second voltage blocking device 208 blocks a portion of the voltage across the bidirectional cascode switching device 200 when the cascode device is off. A second overvoltage protection device DB turns off the normally-on gate G1B of the second asymmetric bidirectional switch BDSB when the normally-off gate G1A of the first asymmetric bidirectional switch BDSA turns off, so that the normally-on gate G1B of the second asymmetric bidirectional switch BDSB is passively controlled by the normally-off gate G1A of the first asymmetric bidirectional switch BDSA.Accordingly, only the normally-off gates G1A, G2B of the asymmetric bidirectional switches BDSA, BDSB are actively controlled (driven) to operate the bidirectional cascode switching device 200.

[0038] In one embodiment, the first voltage blocking device 206 is a first capacitor CA having a first terminal 210 electrically connected to the first source S1A of the first asymmetric bidirectional switch BDSA and a second terminal 212 electrically connected to the normally-on gate G1B of the second asymmetric bidirectional switch BDSB. Similarly, the second voltage blocking device 208 may be a second capacitor CB having a first terminal 214 electrically connected to the second source S2B of the second asymmetric bidirectional switch BDSB and a second terminal 216 electrically connected to the normally-on gate G2A of the first asymmetric bidirectional switch BDSA.

[0039] In one embodiment, the first overvoltage protection device DA comprises one or more first diodes connected in series between the normally-on gate G2A of the first asymmetric bidirectional switch BDSA and the second source S2A of the first asymmetric bidirectional switch BDSA. The anode AN1_DA of the first diode of the first overvoltage protection device DA is electrically connected to the second source S2A of the first asymmetric bidirectional switch BDSA, and the cathode CTN_DA of the last diode of the first overvoltage protection device DA is electrically connected to the normally-on gate G2A of the first asymmetric bidirectional switch BDSA.Likewise, the second overvoltage protection device DB may include one or more second diodes connected in series between the normally-on gate G1B of the second asymmetric bidirectional switch BDSB and the first source S1B of the second asymmetric bidirectional switch BDSB. The anode AN2_DA of the first diode of the second overvoltage protection device DB is electrically connected to the first source S1B of the second asymmetric bidirectional switch BDSB, and the cathode of the last diode of the second overvoltage protection device DB is electrically connected to the normally-on gate G1B of the second asymmetric bidirectional switch BDSB. The number of diodes included in each overvoltage protection device DA, DB depends, as explained above, on the desired total forward voltage.

[0040] Both stacked asymmetric bidirectional switches BDSA, BDSB in Fig. 8 are used to block the entire (e.g., 1.2 kV) source-to-source voltage of the bidirectional cascode switching device 200, with both devices BDSA, BDSB being utilized at 100% at all times. Furthermore, only two active gates G1A, G2B are required to fully operate the bidirectional cascode switching device 200. The bidirectional cascode switching device approach can also be extended to provide higher blocking voltage capability, as described in more detail next.

[0041] Fig. Figure 9 illustrates an embodiment of a bidirectional cascode switching device 300 based on a pair of asymmetric bidirectional switches BDSA, BDSB and at least one symmetric bidirectional switch BDSC. The asymmetric bidirectional switches BDSA, BDSB in Fig. 9 have the same source and gate construction as described above in connection with Fig. 8. At least one symmetrical bidirectional switch BDSC is electrically connected between the pair of asymmetrical bidirectional switches BDSA, BDSB in a cascode configuration.

[0042] In particular, the symmetrical bidirectional switch BDSC includes a first source S1C electrically connected to the second source S2A of the first asymmetrical bidirectional switch BDSA to form a first part of the cascode device, and a second source S2C electrically connected to the first source S1B of the second asymmetrical bidirectional switch BDSB to form a second part of the cascode device. The symmetrical bidirectional switch BDSC also includes a first normally-on gate G1C and a second normally-on gate G2C, both of which are not actively controlled.

[0043] A first voltage blocking device 302 is electrically connected between the first source S1A of the first asymmetric bidirectional switch BDSA and the first normally-on gate G1C of the symmetric bidirectional switch BDSC. The first voltage blocking device 302 blocks a portion of the source-to-source voltage (S2B-S1A) across the switching device 300 when the cascode device is turned off. A first overvoltage protection device DC1 turns off the first normally-on gate G1C of the symmetric bidirectional switch BDSC when the normally-off gate G1A of the first asymmetric bidirectional switch BDSA turns off, so that the first normally-on gate G1C of the symmetric bidirectional switch BDSC is passively controlled by the normally-off gate G1A of the first asymmetric bidirectional switch BDSA.

[0044] A second voltage blocking device 304 is electrically connected between the first source S1B of the second asymmetric bidirectional switch BDSB and the normally-on gate G2A of the first asymmetric bidirectional switch BDSA. The second voltage blocking device 304 blocks a portion of the source-to-source voltage (S2B-S1A) across the switching device 300 when the cascode device is turned off. A second overvoltage protection device DA turns off the normally-on gate G2A of the first asymmetric bidirectional switch BDSA when the first normally-on gate G1C of the symmetric bidirectional switch BDSC turns off.

[0045] A third voltage blocking device 306 is electrically connected between the second source S2B of the second asymmetric bidirectional switch BDSB and the second normally-on gate G2C of the symmetric bidirectional switch BDSC. The third voltage blocking device 306 blocks a portion of the source-to-source voltage (S2B-S1A) across the switching device 300 when the cascode device is turned off. A third overvoltage protection device DC2 turns off the second normally-on gate G2C of the symmetric bidirectional switch BDSC when the normally-off gate G2B of the second asymmetric bidirectional switch BDSB turns off, so that the second normally-on gate G2C of the symmetric bidirectional switch BDSC is passively controlled by the normally-off gate G2B of the second asymmetric bidirectional switch BDSB.

[0046] A fourth voltage blocking device 308 is electrically connected between the normally-on gate G1B of the second asymmetric bidirectional switch BDSB and the first source S1C of the symmetric bidirectional switch BDSC. The fourth voltage blocking device 308 blocks a portion of the source-to-source voltage (S2B-S1A) across the switching device 300 when the cascode device is turned off. A fourth overvoltage protection device DB turns off the normally-on gate G1B of the second asymmetric bidirectional switch BDSB when the second normally-on gate G2C of the symmetric bidirectional switch BDSC turns off, so that the normally-on gate G1B of the second asymmetric bidirectional switch BDSB is passively controlled by the second normally-on gate G2C of the symmetric bidirectional switch BDSC.

[0047] According to one embodiment, each voltage blocking device 302, 304, 306, 308 is implemented as a capacitor. For example, the first voltage blocking device 302 may be a first capacitor CA having a first terminal 310 electrically connected to the first source S1A of the first asymmetric bidirectional switch BDSA and a second terminal 312 electrically connected to the first normally-on gate G1C of the symmetric bidirectional switch BDSC. The second voltage blocking device 304 may be a second capacitor CB having a first terminal 314 electrically connected to the first source S1B of the second asymmetric bidirectional switch BDSB and a second terminal 316 electrically connected to the normally-on gate G2A of the first asymmetric bidirectional switch BDSA.The third voltage blocking device 306 may be a third capacitor CC having a first terminal 318 electrically connected to the second source S2B of the second asymmetric bidirectional switch BDSB and a second terminal 320 electrically connected to the second normally-on gate G2C of the symmetric bidirectional switch BDSC. The fourth voltage blocking device 308 may be a fourth capacitor CD having a first terminal 322 electrically connected to the normally-on gate G1B of the second asymmetric bidirectional switch BDSB and a second terminal 324 electrically connected to the second source S2A of the first asymmetric bidirectional switch BDSA.

[0048] According to one embodiment, each overvoltage protection device DA, DB, DC1, DC2 is implemented as a chain of diodes. For example, the first overvoltage protection device DA may comprise first diodes connected in series between the normally-on gate G2A of the first asymmetric bidirectional switch BDSA and the second source S2A of the first asymmetric bidirectional switch BDSA. The anode AN1_DA of the first diode of the first overvoltage protection device DA is electrically connected to the second source S2A of the first asymmetric bidirectional switch BDSA, and the cathode CTN_DA of the last diode of the first overvoltage protection device DA is electrically connected to the normally-on gate G2A of the first asymmetric bidirectional switch BDSA.

[0049] The second overvoltage protection device DC1 may include second diodes connected in series between the first normally-on gate G1C of the symmetrical bidirectional switch BDSC and the first source S1C of the symmetrical bidirectional switch BDSC. The anode AN1_DC1 of the first diode of the second overvoltage protection device DC1 is electrically connected to the first source S1C of the symmetrical bidirectional switch BDSC, and the cathode CTN_DC1 of the last diode of the second overvoltage protection device DC1 is electrically connected to the first normally-on gate G1C of the symmetrical bidirectional switch BDSC.

[0050] The third overvoltage protection device DC2 may include third diodes connected in series between the second normally-on gate G2C of the symmetrical bidirectional switch BDSC and the second source S2C of the symmetrical bidirectional switch BDSC. The anode AN1_DC2 of the first diode of the third overvoltage protection device DC2 is electrically connected to the second source S2C of the symmetrical bidirectional switch BDSC, and the cathode CTN_DC2 of the last diode of the third overvoltage protection device DC2 is electrically connected to the second normally-on gate G2C of the symmetrical bidirectional switch BDSC.

[0051] The fourth overvoltage protection device DB may include fourth diodes connected in series between the normally-on gate G1B of the second asymmetric bidirectional switch BDSB and the first source S1B of the second asymmetric bidirectional switch BDSB. The anode AN1_DB of the first diode of the fourth overvoltage protection device DB is electrically connected to the first source S1B of the second asymmetric bidirectional switch BDSB, and the cathode CTN_DB of the last diode of the fourth overvoltage protection device DB is electrically connected to the normally-on gate G1B of the second asymmetric bidirectional switch BDSB. More generally, as explained above, the number of diodes included in each overvoltage protection device DA, DB, DC1, DC2 depends on the desired total forward voltage.

[0052] The bidirectional switches BDSA, BDSB, BDSC, which are used in Fig. The bidirectional switches BDSA, BDSB, BDSC forming the cascode switching device 300 shown in Figure 9 may be provided as discrete dies 326, 328, 330. For example, each bidirectional switch BDSA, BDSB, BDSC may be contained in a separate GaN die 326, 328, 330 and may have a maximum of one-third (1 / 3) of the maximum rated source-to-source voltage (S2B-S1A) of the switching device 300. The maximum rated source-to-source voltage (S2B-S1A) of the switching device 300 may be, for example, 1.8 kV or higher.

[0053] More generally, the bidirectional cascode switching device approach uses at least two bidirectional switches electrically connected in a cascode configuration, where a first bidirectional switch (e.g., BDSA in Fig. 8 and Fig. 9) and a second bidirectional switch (e.g. BDSB in Fig. 8 and Fig. 9) the at least two bidirectional switches each have a normally-on gate and a normally-off gate. Each remaining bidirectional switch (for example, BDSC in Fig. 8 and Fig. 9) of the at least two bidirectional switches, which is cascoded between the first bidirectional switch and the second bidirectional switch, has a first normally-on gate and a second normally-on gate. The switching device is controlled by the normally-off gate (for example, G1A in Fig. 8 and Fig. 9) of the first bidirectional switch and the self-locking gate (for example G2B in Fig. 8 and Fig. 9) of the second bidirectional switch is actively controlled. Each normally-on gate (for example, G2A, G1B, G1C and G2C in Fig. 8 and Fig. 9) the at least two bidirectional switches is protected by a voltage blocking device (for example CA, CB, CC and CD in Fig. 8 and Fig. 9), which is a part of the source-source voltage (for example S2B-S1A in Fig. 8 and Fig. 9) across the switching device blocks when the switching device is off, electrically connected to a source of another of the at least two bidirectional switches.

[0054] Next, an embodiment of a bidirectional cascode switching device based on symmetric bidirectional switches and low-voltage MOS devices (e.g., 20 V) is described.

[0055] Fig. Figure 10 illustrates an embodiment of a bidirectional cascode switching device 400 based on symmetrical bidirectional switches BDSX, BDSY stacked between low-voltage MOS switching devices LV1, LV2 in a cascode configuration. The low-voltage MOS switching devices LV1, LV2 are normally off switches, since both low-voltage MOS switching devices LV1, LV2 are enhancement-mode devices. The normally off MOS switching devices LV1, LV2 in Fig. 10 are referred to as “low voltage” because the normally-off MOS switching devices LV1, LV2 have a lower breakdown voltage (e.g., 20 V) compared to the symmetrical bidirectional switches BDSX, BDSY, which may be, for example, 650 V GaN devices.

[0056] The at least two bidirectional switches BDSX, BDSY are electrically connected in a cascode configuration between the first normally-off MOS switching device LV1 and the second normally-off MOS switching device LV2. Each bidirectional switch BDSX, BDSY has a first normally-on gate G1X, G1Y and a second normally-on gate G2X, G2Y. A first voltage blocking device 402, such as a capacitor, is electrically connected to the second normally-on gate G2X of the first bidirectional switch BDSX and blocks a portion of the drain-source voltage (DLV2-SLV1) across the switching device 400 when the switching device 400 is off.A second voltage blocking device 404, such as a capacitor, is electrically connected to the first normally-on gate G1Y of the second bidirectional switch BDSY and blocks a portion of the drain-source voltage (DLV2-SLV1) across the switching device 400 when the switching device 400 is off.

[0057] A first overvoltage protection device DX1, such as a single diode or diode chain, turns off the first normally-on gate G1X of the first bidirectional switch BDSX when the first (lower) normally-off MOS switching device LV1 is turned off, so that the first normally-on gate G1X of the first bidirectional switch BDSX is passively controlled by the first normally-off MOS switching device LV1.

[0058] A second overvoltage protection device DY1, such as a single diode or diode chain, turns off the first normally-on gate G1Y of the second bidirectional switch BDSY when the first (lower) normally-off MOS switching device LV1 turns off, so that the first normally-on gate G1Y of the second bidirectional switch BDSY is passively controlled by the first normally-off MOS switching device LV1.

[0059] A third overvoltage protection device DX2, such as a single diode or diode chain, turns off the second normally-on gate G2X of the first bidirectional switch BDSX when the second (upper) normally-off MOS switching device LV2 turns off, so that the second normally-on gate G2X of the first bidirectional switch BDSX is passively controlled by the second normally-off MOS switching device LV2.

[0060] A fourth overvoltage protection device DY2, such as a single diode or diode chain, turns off the second normally-on gate G2Y of the second bidirectional switch BDSY when the second (upper) normally-off MOS switching device LV2 turns off, so that the second normally-on gate G2Y of the second bidirectional switch BDSY is passively controlled by the second normally-off MOS switching device LV2.

[0061] The Fig.The bidirectional cascode switching device approach illustrated in Figure 10 can be extended to provide a higher blocking voltage capability for the switching device 400 by cascading one or more additional bidirectional switches between the first (lower) and second (upper) low-voltage MOS switching devices LV1, LV2. An additional voltage blocking device, such as a capacitor, is provided for each additional bidirectional switch to block a portion of the switching device drain-source voltage (DLV2-SLV1) when the switching device 400 is off.A first additional overvoltage protection device, such as a single diode or diode chain, is provided to turn off the lower normally-on gate of each additional bidirectional switch when the first (lower) normally-off MOS switching device LV1 turns off, such that the lower normally-on gate of each additional bidirectional switch is passively controlled by the first normally-off MOS switching device LV1. A second additional overvoltage protection device, such as a single diode or diode chain, is provided to turn off the upper normally-on gate of each additional bidirectional switch when the second (upper) normally-off MOS switching device LV2 turns off, such that the upper normally-on gate of each additional bidirectional switch is passively controlled by the second normally-off MOS switching device LV2.

[0062] Although the present disclosure is not so limited, the following numbered examples illustrate one or more aspects of the disclosure.

[0063] Example 1. A switching device comprising: a first power transistor die comprising a normally-on transistor having at most half a maximum rated drain-source voltage of the switching device; a second power transistor die comprising a normally-off transistor having at most half the maximum rated drain-source voltage of the switching device, wherein a drain of the normally-off transistor is electrically connected to a source of the normally-on transistor to form a cascode device; a voltage blocking device electrically connected between a gate of the normally-on transistor and a source of the normally-off transistor and configured to block a portion of the voltage across the switching device when the cascode device is off;and an overvoltage protection device configured to turn off the normally-on transistor when the normally-off transistor turns off, such that the cascode device is actively controlled only by a gate of the normally-off transistor.;

[0064] Example 2. The switching device of Example 1, wherein the normally-on transistor is a normally-on GaN transistor, wherein the normally-off transistor is a normally-off GaN transistor, and wherein the maximum rated drain-source voltage of the switching device is 1.2 kV or higher.

[0065] Example 3. The switching device according to example 1 or 2, wherein the voltage blocking device is a capacitor having a first terminal electrically connected to the gate of the normally-on transistor and a second terminal electrically connected to the source of the normally-off transistor.

[0066] Example 4. The switching device according to example 1 or 2, wherein the voltage blocking device is a gate diode device having a drain electrically connected to the gate of the normally-on transistor and both a gate and a source electrically connected to the source of the normally-off transistor.

[0067] Example 5. The switching device of any one of examples 1 to 4, wherein the overvoltage protection device comprises one or more diodes connected in series between the gate of the normally-on transistor and the source of the normally-on transistor, wherein an anode of a first of the one or more diodes is electrically connected to the source of the normally-on transistor, and wherein a cathode of a last of the one or more diodes is electrically connected to the gate of the normally-on transistor.

[0068] Example 6. The switching device of Example 5, further comprising: an additional diode electrically connected between the gate of the normally-on transistor and the source of the normally-on transistor and anti-parallel to the one or more diodes such that a cathode of the additional diode is electrically connected to the anode of the first of the one or more diodes and an anode of the additional diode is electrically connected to the cathode of the last of the one or more diodes.

[0069] Example 7. The switching device of any one of examples 1 to 6, further comprising: a third power transistor die comprising an additional normally-on transistor having at most one-third of the maximum rated drain-source voltage of the switching device, wherein a source of the additional normally-on transistor is electrically connected to a drain of the normally-on transistor; an additional voltage blocking device electrically connected between a gate of the additional normally-on transistor and the source of the normally-on transistor and configured to block a portion of the voltage across the switching device when the cascode device is off;and an additional overvoltage protection device configured to turn off the additional normally-on transistor when the normally-on transistor turns off, such that the cascode device is actively controlled only by the gate of the normally-off transistor.;

[0070] Example 8. The switching device of Example 7, wherein the voltage blocking device is a capacitor having a first terminal electrically connected to the gate of the normally-on transistor and a second terminal electrically connected to the source of the normally-off transistor, and wherein the additional voltage blocking device is a capacitor having a first terminal electrically connected to the gate of the additional normally-on transistor and a second terminal electrically connected to the source of the normally-on transistor.

[0071] Example 9. The switching device of Example 7, wherein the voltage blocking device is a gate diode device having a drain electrically connected to the gate of the normally-on transistor and both a gate and a source electrically connected to the source of the normally-off transistor, and wherein the additional voltage blocking device is a gate diode device having a drain electrically connected to the gate of the additional normally-on transistor and both a gate and a source electrically connected to the source of the normally-on transistor.

[0072] Example 10. The switching device of any one of Examples 7 to 9, wherein the overvoltage protection device comprises a first or more diodes connected in series between the gate of the normally-on transistor and the source of the normally-on transistor, wherein an anode of a first of the first or more diodes is electrically connected to the source of the normally-on transistor, wherein a cathode of a last of the first or more diodes is electrically connected to the gate of the normally-on transistor, wherein the additional overvoltage protection device comprises a second or more diodes connected in series between the gate of the additional normally-on transistor and the source of the additional normally-on transistor,wherein an anode of a first of the second or more diodes is electrically connected to the source of the additional normally-on transistor, and wherein a cathode of a last of the second or more diodes is electrically connected to the gate of the additional normally-on transistor.

[0073] Example 11. The switching device of Example 10, further comprising: a first additional diode electrically connected between the gate of the normally-on transistor and the source of the normally-on transistor and anti-parallel to the one or more diodes such that a cathode of the first additional diode is electrically connected to the anode of the first of the one or more diodes and an anode of the first additional diode is electrically connected to the cathode of the last of the one or more diodes;and a second additional diode electrically connected between the gate of the additional normally-on transistor and the source of the additional normally-on transistor and anti-parallel to the one or more diodes such that a cathode of the second additional diode is electrically connected to the anode of the first of the one or more diodes and an anode of the second additional diode is electrically connected to the cathode of the last of the one or more diodes.;

[0074] Example 12. A switching device comprising: a first bidirectional switch comprising a first source, a second source, a normally-off gate, and a normally-on gate; a second bidirectional switch comprising a first source electrically connected to the second source of the first bidirectional switch to form a cascode device, a second source, a normally-off gate, and a normally-on gate; a first voltage blocking device electrically connected between the first source of the first bidirectional switch and the normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is off;a first overvoltage protection device configured to turn off the normally-on gate of the first bidirectional switch when the normally-off gate of the second bidirectional switch turns off, such that the normally-on gate of the first bidirectional switch is passively controlled by the normally-off gate of the second bidirectional switch; a second voltage blocking device electrically connected between the second source of the second bidirectional switch and the normally-on gate of the first bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off;and a second overvoltage protection device configured to turn off the normally-on gate of the second bidirectional switch when the normally-off gate of the first bidirectional switch turns off, such that the normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the first bidirectional switch;

[0075] Example 13. The switching device of Example 12, wherein the first bidirectional switch is arranged in a first GaN die and has at most half of a maximum rated source-source voltage of the switching device, wherein the second bidirectional switch is arranged in a second GaN die and has at most half of the maximum rated source-source voltage of the switching device, and wherein the maximum rated source-source voltage of the switching device is 1.2 kV or higher.

[0076] Example 14. The switching device of example 12 or 13, wherein: the first voltage blocking device is a first capacitor having a first terminal electrically connected to the first source of the first bidirectional switch and a second terminal electrically connected to the normally-on gate of the second bidirectional switch; and the second voltage blocking device is a second capacitor having a first terminal electrically connected to the second source of the second bidirectional switch and a second terminal electrically connected to the normally-on gate of the first bidirectional switch.

[0077] Example 15. The switching device of any one of examples 12 to 14, wherein: the first overvoltage protection device comprises a first or more diodes connected in series between the normally-on gate of the first bidirectional switch and the second source of the first bidirectional switch, wherein an anode of a first of the first or more diodes is electrically connected to the second source of the first bidirectional switch, and wherein a cathode of a last of the first or more diodes is electrically connected to the normally-on gate of the first bidirectional switch;and the second overvoltage protection device comprises a second or more diodes connected in series between the normally-on gate of the second bidirectional switch and the first source of the second bidirectional switch, wherein an anode of a first of the second or more diodes is electrically connected to the first source of the second bidirectional switch and wherein a cathode of a last of the second or more diodes is electrically connected to the normally-on gate of the second bidirectional switch;

[0078] Example 16. A switching device comprising: a first bidirectional switch comprising a first source, a second source, a normally-off gate, and a normally-on gate; a second bidirectional switch comprising a first source electrically connected to the second source of the first bidirectional switch to form a first part of a cascode device, a second source, a first normally-on gate, and a second normally-on gate; a third bidirectional switch comprising a first source electrically connected to the second source of the second bidirectional switch to form a second part of the cascode device, a second source, a normally-on gate, and a normally-off gate;a first voltage blocking device electrically connected between the first source of the first bidirectional switch and the first normally-on gate of the second bidirectional switch, and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a first overvoltage protection device configured to turn off the first normally-on gate of the second bidirectional switch when the normally-off gate of the first bidirectional switch turns off, such that the first normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the first bidirectional switch;a second voltage blocking device electrically connected between the first source of the third bidirectional switch and the normally-on gate of the first bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a second overvoltage protection device configured to turn off the normally-on gate of the first bidirectional switch when the first normally-on gate of the second bidirectional switch is turned off; a third voltage blocking device electrically connected between the second source of the third bidirectional switch and the second normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off;a third overvoltage protection device configured to turn off the second normally-on gate of the second bidirectional switch when the normally-off gate of the third bidirectional switch turns off, such that the second normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the third bidirectional switch; a fourth voltage blocking device electrically connected between the normally-on gate of the third bidirectional switch and the first source of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off;and a fourth overvoltage protection device configured to turn off the normally-on gate of the third bidirectional switch when the second normally-on gate of the second bidirectional switch turns off, such that the normally-on gate of the third bidirectional switch is passively controlled by the second normally-on gate of the second bidirectional switch;

[0079] Example 17. The switching device of Example 16, wherein the first bidirectional switch is arranged in a first GaN die and has at most one-third of a maximum rated source-source voltage of the switching device, wherein the second bidirectional switch is arranged in a second GaN die and has at most one-third of the maximum rated source-source voltage of the switching device, wherein the third bidirectional switch is arranged in a third GaN die and has at most one-third of the maximum rated source-source voltage of the switching device, and wherein the maximum rated source-source voltage of the switching device is 1.8 kV or higher.

[0080] Example 18. The switching device of example 16 or 17, wherein: the first voltage blocking device is a first capacitor having a first terminal electrically connected to the first source of the first bidirectional switch and a second terminal electrically connected to the first normally-on gate of the second bidirectional switch; the second voltage blocking device is a second capacitor having a first terminal electrically connected to the first source of the third bidirectional switch and a second terminal electrically connected to the normally-on gate of the first bidirectional switch;the third voltage blocking device is a third capacitor having a first terminal electrically connected to the second source of the third bidirectional switch and a second terminal electrically connected to the second normally-on gate of the second bidirectional switch; and the fourth voltage blocking device is a fourth capacitor having a first terminal electrically connected to the normally-on gate of the third bidirectional switch and a second terminal electrically connected to the second source of the first bidirectional switch.

[0081] Example 19. The switching device of any one of examples 16 to 18, wherein: the first overvoltage protection device comprises a first or more diodes connected in series between the normally-on gate of the first bidirectional switch and the second source of the first bidirectional switch, wherein an anode of a first of the first or more diodes is electrically connected to the second source of the first bidirectional switch, and wherein a cathode of a last of the first or more diodes is electrically connected to the normally-on gate of the first bidirectional switch;the second overvoltage protection device comprises a second or more diodes connected in series between the normally-on gate of the second bidirectional switch and the first source of the second bidirectional switch, wherein an anode of a first of the second or more diodes is electrically connected to the first source of the second bidirectional switch and wherein a cathode of a last of the second or more diodes is electrically connected to the normally-on gate of the second bidirectional switch;the third overvoltage protection device comprises a third or more diodes connected in series between the normally-on gate of the second bidirectional switch and the second source of the second bidirectional switch, wherein an anode of a first of the third or more diodes is electrically connected to the second source of the second bidirectional switch and wherein a cathode of a last of the third or more diodes is electrically connected to the normally-on gate of the second bidirectional switch;and the fourth overvoltage protection device comprises a fourth or more diodes connected in series between the normally-on gate of the third bidirectional switch and the first source of the third bidirectional switch, wherein an anode of a first of the fourth or more diodes is electrically connected to the first source of the third bidirectional switch and wherein a cathode of a last of the fourth or more diodes is electrically connected to the normally-on gate of the third bidirectional switch;

[0082] Example 20. A switching device comprising: a first normally-off switch; a second normally-off switch; at least two bidirectional switches electrically connected in a cascode configuration between the first normally-off switch and the second normally-off switch, each bidirectional switch having a first normally-on gate and a second normally-on gate; a voltage blocking device electrically connected to one of the normally-on gates of each bidirectional switch and configured to block a portion of the voltage across the switching device when the switching device is off;a first overvoltage protection device configured to turn off the first normally-on gate of each bidirectional switch when the first normally-off switch turns off, such that the first normally-on gate of each bidirectional switch is passively controlled by the first normally-off switch; and a second overvoltage protection device configured to turn off the second normally-on gate of each bidirectional switch when the second normally-off switch turns off, such that the second normally-on gate of each bidirectional switch is passively controlled by the second normally-off switch.

[0083] Example 21. A switching device comprising: at least two bidirectional switches electrically connected in a cascode configuration, wherein a first bidirectional switch and a second bidirectional switch of the at least two bidirectional switches each have a normally-on gate and a normally-off gate, wherein each remaining bidirectional switch of the at least two bidirectional switches cascoded between the first bidirectional switch and the second bidirectional switch has a first normally-on gate and a second normally-on gate, wherein the switching device is actively controlled by the normally-off gate of the first bidirectional switch and the normally-off gate of the second bidirectional switch, wherein each normally-on gate of the at least two bidirectional switches is controlled by a voltage blocking device configured toto block a portion of the voltage across the switching device when the switching device is switched off, is electrically connected to a source of another of the at least two bidirectional switches.,

[0084] As used herein, the terms "comprise," "include," "have," "comprising," and the like are open-ended terms that indicate the presence of the specified elements or features but do not preclude additional elements or features. The articles "a," "an," and "the" are intended to include both the plural and singular unless the context clearly indicates otherwise.

[0085] It is understood that the features of the various embodiments described herein may be combined with one another unless expressly stated otherwise.

[0086] Although specific embodiments have been illustrated and described herein, it will be understood by one of ordinary skill in the art that a variety of alternative and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and their equivalents.

Claims

[1] Switching device comprising: a first power transistor die comprising a normally-on transistor having at most half a maximum rated drain-source voltage of the switching device; a second power transistor die comprising a normally-off transistor having at most half the maximum rated drain-source voltage of the switching device, wherein a drain of the normally-off transistor is electrically connected to a source of the normally-on transistor to form a cascode device; a voltage blocking device electrically connected between a gate of the normally-on transistor and a source of the normally-off transistor and configured to block a portion of the voltage across the switching device when the cascode device is turned off; and an overvoltage protection device configured to turn off the normally-on transistor when the normally-off transistor is turned off, so that the cascode device is actively controlled only by a gate of the normally-off transistor. [2] The switching device according to claim 1, wherein the normally-on transistor is a normally-on GaN transistor, wherein the normally-off transistor is a normally-off GaN transistor, and wherein the maximum rated drain-source voltage of the switching device is 1.2 kV or higher. [3] The switching device according to claim 1, wherein the voltage blocking device is a capacitor having a first terminal electrically connected to the gate of the normally-on transistor and a second terminal electrically connected to the source of the normally-off transistor. [4] The switching device of claim 1, wherein the voltage blocking device is a gate diode device having a drain electrically connected to the gate of the normally-on transistor and both a gate and a source electrically connected to the source of the normally-off transistor. [5] The switching device of claim 1, wherein the overvoltage protection device comprises one or more diodes connected in series between the gate of the normally-on transistor and the source of the normally-on transistor, an anode of a first of the one or more diodes being electrically connected to the source of the normally-on transistor, and a cathode of a last of the one or more diodes being electrically connected to the gate of the normally-on transistor. [6] Switching device according to claim 5, further comprising: an additional diode electrically connected between the gate of the normally-on transistor and the source of the normally-on transistor and anti-parallel to the one or more diodes such that a cathode of the additional diode is electrically connected to the anode of the first of the one or more diodes and an anode of the additional diode is electrically connected to the cathode of the last of the one or more diodes. [7] Switching device according to claim 1, further comprising: a third power transistor die comprising an additional normally-on transistor having at most one-third of the maximum rated drain-source voltage of the switching device, wherein a source of the additional normally-on transistor is electrically connected to a drain of the normally-on transistor; an additional voltage blocking device electrically connected between a gate of the additional normally-on transistor and the source of the normally-on transistor and configured to block a portion of the voltage across the switching device when the cascode device is turned off; and an additional overvoltage protection device configured to turn off the additional normally-on transistor when the normally-on transistor is off, so that the cascode device is actively controlled only by the gate of the normally-off transistor. [8] The switching device of claim 7, wherein the voltage blocking device is a capacitor having a first terminal electrically connected to the gate of the normally-on transistor and a second terminal electrically connected to the source of the normally-off transistor, and wherein the additional voltage blocking device is a capacitor having a first terminal electrically connected to the gate of the additional normally-on transistor and a second terminal electrically connected to the source of the normally-on transistor. [9] The switching device of claim 7, wherein the voltage blocking device is a gate diode device having a drain electrically connected to the gate of the normally-on transistor and both a gate and a source electrically connected to the source of the normally-off transistor, and wherein the additional voltage blocking device is a gate diode device having a drain electrically connected to the gate of the additional normally-on transistor and both a gate and a source electrically connected to the source of the normally-on transistor. [10] The switching device of claim 7, wherein the overvoltage protection device comprises a first or more diodes connected in series between the gate of the normally-on transistor and the source of the normally-on transistor, wherein an anode of a first of the first or more diodes is electrically connected to the source of the normally-on transistor, wherein a cathode of a last of the first or more diodes is electrically connected to the gate of the normally-on transistor, wherein the additional overvoltage protection device comprises a second or more diodes connected in series between the gate of the additional normally-on transistor and the source of the additional normally-on transistor,wherein an anode of a first of the second or more diodes is electrically connected to the source of the additional normally-on transistor, and wherein a cathode of a last of the second or more diodes is electrically connected to the gate of the additional normally-on transistor. [11] Switching device according to claim 10, further comprising: a first additional diode electrically connected between the gate of the normally-on transistor and the source of the normally-on transistor and anti-parallel to the one or more diodes, such that a cathode of the first additional diode is electrically connected to the anode of the first of the one or more diodes and an anode of the first additional diode is electrically connected to the cathode of the last of the one or more diodes; and a second additional diode electrically connected between the gate of the additional normally-on transistor and the source of the additional normally-on transistor and anti-parallel to the one or more diodes such that a cathode of the second additional diode is electrically connected to the anode of the first of the second or more diodes and an anode of the second additional diode is electrically connected to the cathode of the last of the one or more diodes. [12] Switching device comprising: a first bidirectional switch having a first source, a second source, a normally-off gate, and a normally-on gate; a second bidirectional switch having a first source electrically connected to the second source of the first bidirectional switch to form a cascode device, a second source, a normally-off gate, and a normally-on gate; a first voltage blocking device electrically connected between the first source of the first bidirectional switch and the normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a first overvoltage protection device configured to turn off the normally-on gate of the first bidirectional switch when the normally-off gate of the second bidirectional switch is turned off, such that the normally-on gate of the first bidirectional switch is passively controlled by the normally-off gate of the second bidirectional switch; a second voltage blocking device electrically connected between the second source of the second bidirectional switch and the normally-on gate of the first bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; and a second overvoltage protection device configured to turn off the normally-on gate of the second bidirectional switch when the normally-off gate of the first bidirectional switch is turned off, such that the normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the first bidirectional switch. [13] The switching device of claim 12, wherein the first bidirectional switch is included in a first GaN die and has at most half of a maximum rated source-source voltage of the switching device, wherein the second bidirectional switch is included in a second GaN die and has at most half of the maximum rated source-source voltage of the switching device, and wherein the maximum rated source-source voltage of the switching device is 1.2 kV or higher. [14] Switching device according to claim 12, wherein: the first voltage blocking device is a first capacitor having a first terminal electrically connected to the first source of the first bidirectional switch and a second terminal electrically connected to the normally-on gate of the second bidirectional switch; and the second voltage blocking device is a second capacitor having a first terminal electrically connected to the second source of the second bidirectional switch and a second terminal electrically connected to the normally-on gate of the first bidirectional switch. [15] Switching device according to claim 12, wherein: the first overvoltage protection device comprises a first or more diodes connected in series between the normally-on gate of the first bidirectional switch and the second source of the first bidirectional switch, wherein an anode of a first of the first or more diodes is electrically connected to the second source of the first bidirectional switch, and wherein a cathode of a last of the first or more diodes is electrically connected to the normally-on gate of the first bidirectional switch; and the second overvoltage protection device comprises a second or more diodes connected in series between the normally-on gate of the second bidirectional switch and the first source of the second bidirectional switch, wherein an anode of a first of the second or more diodes is electrically connected to the first source of the second bidirectional switch, and wherein a cathode of a last of the second or more diodes is electrically connected to the normally-on gate of the second bidirectional switch. [16] Switching device comprising: a first bidirectional switch having a first source, a second source, a normally-off gate, and a normally-on gate; a second bidirectional switch having a first source electrically connected to the second source of the first bidirectional switch to form a first part of a cascode device, a second source, a first normally-on gate, and a second normally-on gate; a third bidirectional switch having a first source electrically connected to the second source of the second bidirectional switch to form a second part of the cascode device, a second source, a normally-on gate, and a normally-off gate; a first voltage blocking device electrically connected between the first source of the first bidirectional switch and the first normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a first overvoltage protection device configured to turn off the first normally-on gate of the second bidirectional switch when the normally-off gate of the first bidirectional switch turns off, such that the first normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the first bidirectional switch; a second voltage blocking device electrically connected between the first source of the third bidirectional switch and the normally-on gate of the first bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a second overvoltage protection device configured to turn off the normally-on gate of the first bidirectional switch when the first normally-on gate of the second bidirectional switch turns off; a third voltage blocking device electrically connected between the second source of the third bidirectional switch and the second normally-on gate of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; a third overvoltage protection device configured to turn off the second normally-on gate of the second bidirectional switch when the normally-off gate of the third bidirectional switch turns off, such that the second normally-on gate of the second bidirectional switch is passively controlled by the normally-off gate of the third bidirectional switch; a fourth voltage blocking device electrically connected between the normally-on gate of the third bidirectional switch and the first source of the second bidirectional switch and configured to block a portion of the voltage across the switching device when the cascode device is turned off; and a fourth overvoltage protection device configured to turn off the normally-on gate of the third bidirectional switch when the second normally-on gate of the second bidirectional switch is turned off, such that the normally-on gate of the third bidirectional switch is passively controlled by the second normally-on gate of the second bidirectional switch. [17] The switching device of claim 16, wherein the first bidirectional switch is arranged in a first GaN die and has at most one-third of a maximum rated source-source voltage of the switching device, wherein the second bidirectional switch is arranged in a second GaN die and has at most one-third of the maximum rated source-source voltage of the switching device, wherein the third bidirectional switch is arranged in a third GaN die and has at most one-third of the maximum rated source-source voltage of the switching device, and wherein the maximum rated source-source voltage of the switching device is 1.8 kV or higher. [18] Switching device according to claim 16, wherein: the first voltage blocking device is a first capacitor having a first terminal electrically connected to the first source of the first bidirectional switch and a second terminal electrically connected to the first normally-on gate of the second bidirectional switch; the second voltage blocking device is a second capacitor having a first terminal electrically connected to the first source of the third bidirectional switch and a second terminal electrically connected to the normally-on gate of the first bidirectional switch; the third voltage blocking device is a third capacitor having a first terminal electrically connected to the second source of the third bidirectional switch and a second terminal electrically connected to the second normally-on gate of the second bidirectional switch; and the fourth voltage blocking device is a fourth capacitor having a first terminal electrically connected to the normally-on gate of the third bidirectional switch and a second terminal electrically connected to the second source of the first bidirectional switch. [19] Switching device according to claim 16, wherein: the first overvoltage protection device comprises a first or more diodes connected in series between the normally-on gate of the first bidirectional switch and the second source of the first bidirectional switch, wherein an anode of a first of the first or more diodes is electrically connected to the second source of the first bidirectional switch and wherein a cathode of a last of the first or more diodes is electrically connected to the normally-on gate of the first bidirectional switch; the second overvoltage protection device comprises a second or more diodes connected in series between the normally-on gate of the second bidirectional switch and the first source of the second bidirectional switch, wherein an anode of a first of the second or more diodes is electrically connected to the first source of the second bidirectional switch and wherein a cathode of a last of the second or more diodes is electrically connected to the normally-on gate of the second bidirectional switch; the third overvoltage protection device comprises a third or more diodes connected in series between the normally-on gate of the second bidirectional switch and the second source of the second bidirectional switch, wherein an anode of a first of the third or more diodes is electrically connected to the second source of the second bidirectional switch, and wherein a cathode of a last of the third or more diodes is electrically connected to the normally-on gate of the second bidirectional switch; and the fourth overvoltage protection device comprises a fourth or more diodes connected in series between the normally-on gate of the third bidirectional switch and the first source of the third bidirectional switch, wherein an anode of a first of the fourth or more diodes is electrically connected to the first source of the third bidirectional switch, and wherein a cathode of a last of the fourth or more diodes is electrically connected to the normally-on gate of the third bidirectional switch. [20] Switching device comprising: a first self-locking switch; a second self-locking switch; at least two bidirectional switches electrically connected in a cascode configuration between the first normally-off switch and the second normally-off switch, each bidirectional switch having a first normally-on gate and a second normally-on gate; a voltage blocking device electrically connected to one of the normally-on gates of each bidirectional switch and configured to block a portion of the voltage across the switching device when the switching device is turned off; a first overvoltage protection device configured to turn off the first normally-on gate of each bidirectional switch when the first normally-off switch turns off, such that the first normally-on gate of each bidirectional switch is passively controlled by the first normally-off switch; and a second overvoltage protection device configured to turn off the second normally-on gate of each bidirectional switch when the second normally-off switch turns off, such that the second normally-on gate of each bidirectional switch is passively controlled by the second normally-off switch. [21] Switching device comprising: at least two bidirectional switches electrically connected in a cascode configuration, wherein a first bidirectional switch and a second bidirectional switch of the at least two bidirectional switches each have a normally-on gate and a normally-off gate, wherein each remaining bidirectional switch of the at least two bidirectional switches cascoded between the first bidirectional switch and the second bidirectional switch has a first normally-on gate and a second normally-on gate, wherein the switching device is actively controlled by the self-locking gate of the first bidirectional switch and the self-locking gate of the second bidirectional switch, wherein each normally-on gate of the at least two bidirectional switches is electrically connected to a source of another of the at least two bidirectional switches through a voltage blocking device configured to block a portion of the voltage across the switching device when the switching device is turned off.

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