Switching device

Abstract

To provide a switching device having a higher breakdown voltage than a phase change switch alone using a phase change material switch.SOLUTION: A switching device 10 includes a phase change material switch 100 and a normally-on first series switch 120 connected in series to the phase change material switch 100. The phase change material switch 100 and the first series switch 120 are connected between a first terminal P1 and a second terminal P2 of the switching device 10, with the phase change material switch 100 connected to the first terminal side and the first series switch 120 connected to the second terminal side, and a control terminal G of the first series switch 100 is connected to a terminal S1 of the phase change material switch 100 on the first terminal side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a switch device. [Background technology]

[0002] Patent Document 1 states, "FIG. 2 is a circuit diagram showing the configuration of a memory cell MM included in memory array 1. In FIG. 2, this memory cell MM includes an N-channel MOS transistor 4 and a phase change element 5. A gate G of N-channel MOS transistor 4 receives a word line voltage VWL, a source S thereof receives a source line voltage VSL, a substrate SUB (well, back gate) thereof receives a well line voltage VMW, and a drain D thereof is connected to one electrode of phase change element 5. The other electrode of phase change element 5 receives a bit line voltage VBL. The word line voltage VWL and the bit line voltage VBL are controlled by a write circuit 2 and a read circuit 3. The source line voltage VSL and the well voltage VMW are both fixed to the ground voltage (0V)." (paragraph 0010)

[0003] Patent Document 2 states, "FIG. 1 shows a schematic configuration of a phase-change memory 7. A memory array (MARY) 10 is composed of word lines WL0 to WLn, bit lines BL0 to BLk, and a plurality of memory cells 11 (M00 to Mnk) arranged at each intersection of the word lines and bit lines. Various configurations of the memory cells 11 will be described in detail later, but here, as an example, a configuration is shown which includes a select transistor CT as a select element and a memory element PCR as a phase-change element using a phase-change material. The memory cell 11 is composed of a select transistor CT and a memory element PCR connected in series in the direction from the bit line to the power supply line of the ground voltage Vss." (paragraph 0049)

[0004] Patent Document 3 states, "Phase-change memory cell 104a includes phase-change element 106a and TFET 108a. One end of phase-change element 106a is electrically coupled to bit line 112a, and the other end of phase-change element 106a is electrically coupled to the drain of TFET 108a. The source of TFET 108a is electrically coupled to ground plate 114. The gate of TFET 108a is electrically coupled to word line 110a. Phase-change memory cell 104b includes phase-change element 106b and TFET 108b. One end of phase-change element 106b is electrically coupled to bit line 112a, and the other end of phase-change element 106b is electrically coupled to the drain of TFET 108b. The source of TFET 108b is electrically coupled to ground plate 114" (paragraph 0017).

[0005] Patent Document 4 states, "Referring to FIG. 1, a schematic diagram of a memory system 100 according to an embodiment of the present invention is shown. The memory system 100 includes memory cells 102 arranged in an array. Each of the memory cells 102 includes a switch element 104, such as a metal-insulator-metal (MIM) switch cell or a phase-change switch cell, and a cell transistor 106, such as a junction field-effect transistor (JFET)." (Paragraph 0019), and "The switch element 104 includes a first side 114 and a second side 116. The first side 114 is connected to one of word lines 118, such as word line 1 to word line 1024 of the memory system 100. The second side 116 is connected to a gate terminal 108 of the cell transistor 106." (Paragraph 0021). [Prior art document] [Patent documents] [Patent Document 1] JP 2009-252253 A [Patent Document 2] International Publication No. 2010 / 004652 [Patent Document 3] JP 2008-021970 A [Patent Document 4] Japanese Patent Publication No. 2009-538491 [Non-patent literature] [Non-Patent Document 1] Tejinder Singh et al., "Reconfigurable PCM GeTe-based Latching 6-bit Digital Switched Capacitor Bank", 15th European Microwave Integrated Circuits Conference (EuMIC), Utrecht, Netherlands, pp. 93-96, January 2021 [Non-Patent Document 2] Tejinder Singh et al., "Ultra-Compact Phase-Change GeTe-Based Scalable mmWave Latching Crossbar Switch Matrices," IEEE Transactions on Microwave Theory and Techniques, pp. 938-949, December 2021 Summary of the Invention

[0006] A first aspect of the present invention provides a switch device comprising a phase change material switch and a normally-on first series switch connected in series with the phase change material switch.

[0007] In the above switch device, the phase change material switch and the first series switch may be connected between a first terminal and a second terminal of the switch device, with the phase change material switch connected to the first terminal side and the first series switch connected to the second terminal side, and a control terminal of the first series switch may be connected to a terminal on the first terminal side of the phase change material switch.

[0008] Any of the above switch devices may further include a normally-on second series switch connected in series with the phase change material switch, the second series switch being connected between the first terminal and the second terminal of the switch device on the first terminal side of the phase change material switch, and a control terminal of the second series switch being connected to a terminal on the second terminal side of the phase change material switch.

[0009] In any of the switch devices described above, the first series switch may be turned off in response to a potential difference between the first terminal and the second terminal exceeding a first threshold value.

[0010] In any of the above switch devices, the first threshold value may be smaller than a breakdown voltage of the phase change material switch.

[0011] In any of the switch devices described above, the second series switch may be turned off in response to a potential difference between the first terminal and the second terminal exceeding a second threshold value.

[0012] In any of the above switch devices, the first series switch may have a higher breakdown voltage than the phase change material switch.

[0013] In any of the above switch devices, the withstand voltage of the first series switch may be ten times or more the withstand voltage of the phase change material switch.

[0014] The above summary of the invention does not list all of the features of the present invention, and subcombinations of these features may also be inventions. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows the configuration of a switch device 10 according to this embodiment. [Figure 2] 10 shows the configuration of a switch device 20 according to a modified example of the present embodiment. [Figure 3] 1 shows the configuration of a capacitor bank 30 according to this embodiment. [Figure 4] 2 shows the configuration of a switch matrix 40 according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0017] A phase-change material (PCM) is a material that can reversibly change phase between an amorphous phase with high resistance and low refractive index and a crystalline phase with low resistance and high refractive index by heating and cooling cycles. Examples of such phase-change materials are GeTe (germanium telluride) and Sb2Te3 (antimony telluride). A switch using a phase-change material (also referred to as a "phase-change material switch" or "PCM-SW") has a phase-change material placed between terminals, and the phase-change material can be switched between a high-resistance state (off state) and a low-resistance state (on state) by heating and cooling cycles. A phase-change material switch is a nonvolatile device and does not require a power supply to maintain the on and off states.

[0018] Such phase change material switches are applied to nonvolatile phase change memories (see Patent Documents 1 to 4), switched capacitor banks (see Non-Patent Document 1), switch matrices (see Non-Patent Document 2), etc. However, phase change material switches have a low breakdown voltage between terminals, for example, about 4 V, making them difficult to apply to applications requiring high breakdown voltage. In this embodiment, a phase change material switch is used to realize a switch device with a higher breakdown voltage than a phase change material switch alone.

[0019] FIG. 1 shows the configuration of a switch device 10 according to this embodiment. The switch device 10 functions as a nonvolatile switch that electrically connects or disconnects a first terminal P1 and a second terminal P2. The switch device 10 includes a phase change material switch 100, a heater 110, and a series switch 120. The phase change material switch 100 has a structure in which a channel of a phase change material is disposed between terminals S1 and S2. Here, the "channel" refers to a member that switches on and off (whether to allow or block current flow) between terminals S1 and S2.

[0020] Heater 110 is disposed near the channel of phase change material switch 100 and heats phase change material switch 100 when phase change material switch 100 is switched on and off. In this embodiment, heater 110 is made of an electrothermal material such as tungsten. Heater 110 generates more heat as the current flowing between terminals H1 and H2 increases.

[0021] The heater 110 heats the phase-change material of the phase-change material switch 100 to a high temperature above its melting point (e.g., 700°C for a GeTe film), and then stops heating and rapidly cools it, thereby changing the phase-change material from a crystalline phase to an amorphous phase. The heater 110 changes the phase-change material of the phase-change material switch 100 from an amorphous phase to a crystalline phase by thermally annealing the phase-change material of the phase-change material switch 100 at a relatively low temperature above its crystallization temperature (e.g., 200°C for a GeTe film). A control device that controls the switching of the switch device 10 may change the phase state of the phase-change material as described above by controlling the current flowing between terminals H1 and H2 of the heater 110. Note that, although the present embodiment illustrates a configuration in which an electric heater is used as the heater 110, the heater 110 may also heat the phase-change material switch 100 by other methods, such as light irradiation.

[0022] The series switch 120 is connected in series with the phase change material switch 100. The series switch 120 is a semiconductor switch element such as a MOSFET (metal oxide semiconductor field effect transistor) or an IGBT (insulated gate bipolar transistor). The series switch 120 may be a GaN-FET, a Si-MOSFET, a SiC-MOSFET, a SiC-IGBT, or the like. The series switch 120 has a first main terminal and a second main terminal, and a control terminal that controls the connection state between the first main terminal and the second main terminal. When the series switch 120 is a MOSFET or a GaN FET, the series switch 120 has a drain and a source as the first main terminal and a gate as the control terminal. When the series switch 120 is an IGBT, the series switch 120 has a collector and an emitter as the first main terminal and a second main terminal, and the gate as the control terminal. For convenience of explanation, this embodiment will be described assuming that the series switch 120 is a GaN-FET.

[0023] The series switch 120 is a normally-on switch. In this embodiment, the phase change material switch 100 and the series switch 120 are connected between a first terminal P1 and a second terminal P2 of the switch device 10, with the phase change material switch 100 connected to the first terminal P1 and the first series switch 120 connected to the second terminal P2. In the example shown in the figure, the terminal S1 of the phase change material switch 100 is directly connected to the first terminal P1, the first main terminal T1 (for example, a source) of the series switch 120 is directly connected to the terminal S2 of the phase change material switch 100, and the second main terminal T2 (for example, a drain) of the series switch 120 is directly connected to the second terminal P2. Alternatively, a passive component such as a resistor or an inductor may be provided between the first terminal P1 and the terminal S1, between the terminal S2 and the first main terminal T1, or between the second main terminal T2 and the second main terminal P2.

[0024] Control terminal G of series switch 120 is connected to terminal S1 on the first terminal P1 side of phase change material switch 100. In the example shown in the figure, control terminal G of series switch 120 is directly connected to terminal S1 of phase change material switch 100. Alternatively, a passive component such as a resistor or inductor may be provided between terminal S1 and control terminal G of series switch 120.

[0025] In this embodiment, the series switch 120 may be designed to turn off when the potential difference between the first terminal P1 and the second terminal P2 exceeds a first threshold. In this figure, the series switch 120 turns off when the potential difference between the control terminal G and the first main terminal T1, more specifically, the gate-source voltage = (voltage at the control terminal G - voltage at the first main terminal T1), is equal to or less than the threshold voltage TH of the series switch 120, and turns on when it exceeds the threshold voltage TH. Since the series switch 120 is normally on, the threshold voltage TH is less than 0.

[0026] As an example, the operation of switch device 10 will be described when first terminal P1 is 0V, threshold voltage TH of series switch 120 is -2V, and the withstand voltage of phase change material switch 100 is 4V, and the voltage at second terminal P2 rises from 0V to 4V or higher after phase change material switch 100 is turned off. When phase change material switch 100 is on, both control terminal G and first main terminal T1 of series switch 120 are 0V, and therefore the gate-source voltage of series switch 120 = 0V > threshold voltage TH (-2V), and series switch 120 is on. If phase change material switch 100 is turned off in this state, series switch 120 remains on.

[0027] When the voltage at second terminal P2 rises to nearly 2V, series switch 120 is on, so terminal T1 rises to nearly 2V. When the voltage at second terminal P2 reaches 2V, the control terminal of series switch 120 becomes 0V, terminal T1 becomes 2V, and the gate-source voltage of series switch 120 becomes −2V≦threshold voltage TH (−2V), so series switch 120 turns off. Even if the voltage at second terminal P2 subsequently rises further to 4V or higher, series switch 120 remains off, so the voltage at terminal T1 does not rise above 2V. Therefore, switch device 10 can limit the voltage applied to phase-change material switch 100 to less than the absolute value of threshold voltage TH of series switch 120 (2V in this example).

[0028] In this way, by setting the threshold voltage of series switch 120 to −2 V, it is possible to turn off the series switch 120 when the potential difference between the second terminal and the first terminal P1 exceeds the first threshold value of 2 V. Switch device 10 is designed so that the first threshold value is smaller than the withstand voltage of phase change material switch 100, thereby realizing a high-withstand-voltage switch using phase change material switch 100. Note that, to ensure a sufficient margin for withstand voltage, the first threshold value may be equal to or less than ½, ⅓, or ¼ of the withstand voltage of phase change material switch 100, for example.

[0029] The withstand voltage of series switch 120 may be greater than the withstand voltage of phase change material switch 100. This allows switch device 10 as a whole to achieve a withstand voltage more than twice that of phase change material switch 100. Series switch 120 may be a high-voltage switch having a withstand voltage that is sufficiently greater than that of phase change material switch 100. The withstand voltage of series switch 120 may be 5 times or more, 10 times or more, 20 times or more, 50 times or more, or 100 times or more the withstand voltage of phase change material switch 100.

[0030] Fig. 2 shows the configuration of a switch device 20 according to a modified example of this embodiment. The switch device 20 shown in this figure is a modified example of the switch device 10 shown in Fig. 1, so a description will be omitted below except for the differences.

[0031] Switch device 20 has a function of protecting phase change material switch 200 from overvoltage not only when the potential of second terminal P2 becomes relatively higher than the potential of first terminal P1 but also when the potential of second terminal P2 becomes relatively lower than the potential of first terminal P1. Switch device 20 includes phase change material switch 200, heater 210, and series switches 220a-b.

[0032] Phase change material switch 200 may have the same function and configuration as phase change material switch 100 shown in FIG. 1 . Heater 210 may have the same function and configuration as heater 110 shown in FIG. 1 . Series switches 220a and 220b are normally-on switches. Series switches 220a and 220b are connected in series to phase change material switch 100 between first terminal P1 and second terminal P2 of switch device 20. Series switch 220a is an example of a “first series switch” and is connected between first terminal P1 and second terminal P2 of switch device 20 closer to second terminal P2 than phase change material switch 200. In the example shown in the figure, a first main terminal T1a (e.g., a source) of series switch 220a is directly connected to terminal S2 of phase change material switch 200, and a second main terminal T2a (e.g., a drain) of series switch 220a is directly connected to second terminal P2. Instead of directly connecting these terminals, a passive component may be provided between the terminals.

[0033] Control terminal G of series switch 220a is connected to terminal S1 on the first terminal P1 side of phase change material switch 200. In the example shown in the figure, control terminal G of series switch 220a is directly connected to terminal S1 of phase change material switch 200. Control terminal G of series switch 220a may also be directly connected to first terminal P1. A passive component such as a resistor or inductor may be provided between terminal S1 or first terminal P1 and control terminal G of series switch 220a.

[0034] Series switch 220b is an example of a "second series switch" and is connected between the first and second terminals of switch device 20 and closer to first terminal P1 than phase change material switch 200. In the example shown in the figure, a first main terminal T1b (as an example, a source) of series switch 220b is directly connected to terminal S2 of phase change material switch 200, and a second main terminal T2b (as an example, a drain) of series switch 220b is directly connected to first terminal P1. Instead of directly connecting these terminals, a passive component may be provided between the terminals.

[0035] Control terminal G of series switch 220b is connected to terminal S2 on the second terminal P2 side of phase change material switch 200. In the example shown in the figure, control terminal G of series switch 220b is directly connected to terminal S2 of phase change material switch 200. Control terminal G of series switch 220b may also be directly connected to second terminal P2. A passive component such as a resistor or inductor may be provided between terminal S2 or second terminal P2 and control terminal G of series switch 220b.

[0036] The series switch 220a and the series switch 220b may have the same function and configuration as the series switch 120 shown in FIG. 1, except for the following points. Here, the series switch 220b may be designed to be turned off when the potential difference between the first terminal P1 and the second terminal P2 exceeds a first threshold, similar to the series switches 120 and 220a. Alternatively, the series switch 220b may be designed to be turned off when the potential difference between the first terminal P1 and the second terminal P2 exceeds a second threshold different from the first threshold. The second threshold may be determined to satisfy the same constraint as the first threshold described in relation to FIG. 1.

[0037] The operation of the switch device 20 shown in FIG. 2 can be explained as follows, based on the operation of the switch device 10 shown in FIG.

[0038] (1) When the potential of the second terminal P2 becomes higher than the potential of the first terminal P1 The control terminal G of the series switch 220b is connected to the second terminal P2 via the series switch 220a. Therefore, when the voltage of the first terminal P1 is less than or equal to the voltage of the second terminal P2, the voltage of the control terminal G of the series switch 220b is greater than or equal to the voltage of the first main terminal T1b of the series switch 220b. Therefore, the gate-source voltage of the series switch 220b is greater than the threshold voltage TH (a negative value such as −2 V), and the series switch 220b is turned on.

[0039] Therefore, when the potential of the second terminal P2 becomes higher than the potential of the first terminal P1, the switch device 20 can be regarded as a circuit equivalent to the switch device 10, and like the switch device 10, the voltage applied to the phase change material switch 200 can be limited to less than the absolute value of the threshold voltage TH of the series switch 220a.

[0040] (2) When the potential of the first terminal P1 becomes higher than the potential of the second terminal P2 The control terminal G of the series switch 220a is connected to the first terminal P1 via the series switch 220b. Therefore, when the voltage of the second terminal P2 is less than or equal to the voltage of the first terminal P1, the voltage of the control terminal G of the series switch 220a is greater than or equal to the voltage of the first main terminal T1a of the series switch 220a. Therefore, the gate-source voltage of the series switch 220a is greater than the threshold voltage TH (a negative value such as −2 V), and the series switch 220a is turned on.

[0041] Therefore, when the potential of the first terminal P1 becomes higher than the potential of the second terminal P2, the switch device 20 can be regarded as a circuit equivalent to the circuit in which the first terminal P1 and the second terminal P2 in the switch device 10 shown in Figure 1 are reversed, and like the switch device 10, the voltage applied to the phase change material switch 200 can be limited to less than the absolute value of the threshold voltage TH of the series switch 220b.

[0042] 3 shows the configuration of a capacitor bank 30 according to this embodiment. The capacitor bank 30 according to this embodiment receives a signal from an input terminal IN and outputs it from an output terminal OUT. The capacitor bank 30 has a variable capacitance capacitor added to a signal line between the input terminal IN and the output terminal OUT.

[0043] The capacitor bank 30 includes a plurality of switch devices 310a-h and a plurality of capacitors 320a-h. The switch device 310a and the capacitor 320a are connected between a signal line and a power supply potential VCC. The switch device 310b and the capacitor 320b, the switch device 310c and the capacitor 320c, and the switch device 310d and the capacitor 320d are also connected between the signal line and the power supply potential VCC. The switch device 310e and the capacitor 320e are connected between the signal line and the ground potential GND. The switch device 310f and the capacitor 320f, the switch device 310g and the capacitor 320g, and the switch device 310h and the capacitor 320h are also connected between the signal line and the ground potential GND. Note that the capacitor bank 30 may include a different number of capacitors and switch devices from the example shown in this figure.

[0044] Each of the switch devices 310a-h may be the switch device 10 shown in Fig. 1 or the switch device 20 shown in Fig. 2. When the switch device 10 shown in Fig. 1 is used as the switch devices 310a-d, the second terminal P2 of the switch device 10 is on the power supply potential VCC side. When the switch device 10 shown in Fig. 1 is used as the switch devices 310e-h, the second terminal P2 of the switch device 10 is on the signal line side.

[0045] The capacitors 320a-h may have the same capacitance or different capacitances. Furthermore, each pair of capacitors 320a and 320e, capacitors 320b and 320f, capacitors 320c and 320g, and capacitors 320d and 320h may have the same capacitance, and different pairs may have different capacitances.

[0046] According to capacitor bank 30 shown in the figure, the capacitance added to the signal line can be varied by changing the number or combination of switches to be turned on among switch devices 310a-h. Furthermore, by using switch device 10 or switch device 20 as switch devices 310a-h, phase change material switch 100 or phase change material switch 200 can be protected even when the amplitude of the signal flowing through the signal line is large.

[0047] 4 shows the configuration of the switch matrix 40 according to this embodiment. The switch matrix 40 according to this embodiment is capable of switching the connection between a plurality of input terminals IN0 to IN3 and a plurality of output terminals OUT0 to OUT3.

[0048] The switch matrix 40 includes a plurality of input terminals IN0-3, a plurality of output terminals OUT0-3, and a plurality of switch devices 410-00-33 (also referred to as "switch devices 410"). A plurality of switch devices 410 are provided between each of the plurality of input terminals IN0-3 and each of the plurality of output terminals OUT0-3. Each switch device 410 may be the switch device 10 shown in FIG. 1 or the switch device 20 shown in FIG. 2. Note that the switch matrix 40 may have at least one of the number of input terminals or the number of output terminals different from the example shown in this figure, and the number of switch devices 410 may also be different accordingly.

[0049] A switch device 410-00 is connected between the output terminal OUT0 and the input terminal IN0, a switch device 410-10 is connected between the output terminal OUT0 and the input terminal IN1, a switch device 410-20 is connected between the output terminal OUT0 and the input terminal IN2, and a switch device 410-30 is connected between the output terminal OUT0 and the input terminal IN3. In the switch matrix 40, the output terminal OUT0 can be electrically connected to the input terminal IN0 by turning on the switch device 410-00 and turning off the other switch devices 410, the output terminal OUT0 can be electrically connected to the input terminal IN1 by turning on the switch device 410-10 and turning off the other switch devices 410, the output terminal OUT0 can be electrically connected to the input terminal IN2 by turning on the switch device 410-20 and turning off the other switch devices 410, and the output terminal OUT0 can be electrically connected to the input terminal IN3 by turning on the switch device 410-30 and turning off the other switch devices 410. Similarly, for the other output terminals OUT1 to OUT3, the switch matrix 40 can switch which input terminal an output terminal is electrically connected to by selectively turning on the switch devices 410 connected to the output terminals. Note that, although the example in this figure shows input terminals and output terminals for the sake of convenience, the switch matrix 40 may also transmit and receive electrical signals bidirectionally between the terminals IN0 to OUT3 and the terminals OUT0 to OUT3.

[0050] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0051] It should be noted that the execution order of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before," "prior to," etc., and that the processes can be performed in any order unless the output of a previous process is used in a subsequent process. Even if the operational flow in the claims, specifications, and drawings is described using "first," "next," etc. for convenience, this does not mean that the processes must be performed in this order. [Explanation of symbols]

[0052] 10 Switching device 20 Switching device 30 Capacitor Bank 40 Switch Matrix 100 Phase change material switches 110 Heater 120 Series Switch 200 Phase change material switch 210 Heater 220 Series Switch 310a~h Switch device 320a~h capacitor 410-00~33 Switch device

Claims

1. a phase change material switch; a normally-on first series switch connected in series with the phase change material switch; A switch device comprising:

2. the phase change material switch and the first series switch are connected between a first terminal and a second terminal of the switch device, the phase change material switch being connected to the first terminal side and the first series switch being connected to the second terminal side; A control terminal of the first series switch is connected to a terminal on the first terminal side of the phase change material switch. The switch device according to claim 1 .

3. a second normally-on series switch connected in series with the phase change material switch; the second series switch is connected between the first terminal and the second terminal of the switch device and closer to the first terminal than the phase change material switch; A control terminal of the second series switch is connected to a terminal on the second terminal side of the phase change material switch. The switch device according to claim 2 .

4. 4. The switch device according to claim 2, wherein the first series switch is turned off when a potential difference between the first terminal and the second terminal exceeds a first threshold value.

5. The switch device according to claim 4 , wherein the first threshold value is smaller than a breakdown voltage of the phase change material switch.

6. The switch device according to claim 3 , wherein the second series switch is turned off when a potential difference between the first terminal and the second terminal exceeds a second threshold value.

7. The switch device according to claim 4 , wherein the withstand voltage of the first series switch is greater than the withstand voltage of the phase change material switch.

8. The switch device according to claim 5 , wherein the withstand voltage of the first series switch is 10 times or more the withstand voltage of the phase change material switch.

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