Switch module

Abstract

The present invention relates to a switching module in which a MOSFET and a drive circuit for applying a drive voltage to a gate electrode of the MOSFET are mounted on a substrate. In the switching module of the present invention, the drive circuit is electrically connected to the MOSFET via a damping adjustment element and a bonding wire between the drive circuit and the gate electrode.

Description

Technical Field

[0001] The present invention relates to a switching module applicable to a class-D amplifier or the like, and particularly to a switching module including a MOSFET applicable to a high-frequency power supply amplifier and a drive circuit for applying a drive voltage to the gate electrode of the MOSFET. Background Art

[0002] A high-frequency power supply is used as a power supply for ultrasonic oscillation, induction power generation, or plasma generation, and has a function of converting direct current into high-frequency alternating current through the switching operation of a class-D amplifier. The class-D amplifier performing such a switching operation is characterized by high power efficiency and low heat generation. As a module performing such a switching operation, a module using a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transmitter) is known.

[0003] As a switching module using such a MOSFET, for example, the following switching modules are disclosed in Patent Document 1 and Patent Document 2: a switching module in which a MOSFET and a drive circuit for applying a gate drive voltage to the gate electrode of the MOSFET are mounted on a substrate. According to these switching modules, they are suitable for a high-frequency power supply and can further improve the power conversion efficiency. Also, in these switching modules, a structure in which the output terminal of the driver is directly connected to the gate electrode of the MOSFET through a bonding wire is adopted.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-25567

[0007] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2008-228304 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] The switching operation of the MOSFET is performed by turning on and off the application of the gate drive voltage to the gate electrode. In the on-control, if the gate / source voltage of the gate drive voltage applied from the drive circuit to the gate electrode of the MOSFET exceeds a predetermined value, the MOSFET becomes an on-state. On the other hand, in the off-control, by stopping the application of the gate drive voltage and setting the gate / source voltage to a voltage lower than the predetermined value, the MOSFET becomes an off-state.

[0010] In this turn-off control, a resonance phenomenon occurs in a resonance circuit formed by a drive circuit and a MOSFET. The resonance voltage vibrates due to internal components while its amplitude decays with a predetermined time constant. Hereinafter, this voltage will be described as a damped voltage.

[0011] In the turn-off control, the gate-source voltage of the MOSFET vibrates due to the damped voltage. At this time, when the gate-source voltage exceeds the threshold value that turns the MOSFET on due to the vibration of the damped voltage, the MOSFET is regarded as having received a turn-on command signal and turns on, resulting in a problem of malfunction (false triggering) where it turns on when it should be in the off state.

[0012] In addition, in a conventional switching module as shown in Patent Document 1 or Patent Document 2, a structure is adopted in which the output terminal of the driver is directly connected to the gate electrode of the MOSFET by a bonding wire. In this structure, an RLC series resonance circuit is formed between the drive circuit and the MOSFET by the stray inductance, internal resistance of the bonding wire, and the gate-source capacitance of the MOSFET. The decay rate (damping constant) of the damped voltage generated in the series resonance of the RLC series resonance circuit varies depending on the electrical characteristics and the length of the bonding wire.

[0013] However, in order to prevent malfunction caused by the damped voltage when the MOSFET mounted on the switching module is replaced, it is necessary to change the wire length of the bonding wire, the internal resistance of the internal output stage of the drive IC of the drive circuit, etc., which takes a lot of effort. In addition, when the MOSFET chip is replaced, the parasitic capacitance Ciss of the MOSFET in the frequency band of several MHz to several tens of MHz differs by about 10 times, so abnormal oscillation may occur due to frequency resonance. Also, when the patterns of the drive circuit and the MOSFET mounted on the switching module are made common, the wire length of the bonding wire becomes a fixed length, so the wire length and resistance component of the bonding wire also become fixed values.

[0014] The present invention has been completed to solve the above-mentioned conventional problems, and its object is to provide a switching module that can suppress malfunction caused by the damped voltage in the connection circuit between the MOSFET and the drive circuit even when the MOSFET is replaced or the frequency used is changed.

[0015] Means for Solving the Problem

[0016] In order to solve the above problems, one of the representative embodiments of the present invention is a switching module in which a MOSFET and a drive circuit for applying a gate drive voltage to the gate electrode of the MOSFET are mounted on a substrate, and the drive circuit is electrically connected to the MOSFET via a damping adjustment element and a bonding wire between the drive circuit and the gate electrode.

[0017] According to the present invention having such a structure, a damping adjustment element capable of adjusting the attenuation rate (damping constant) of the damping voltage of the gate / source voltage is disposed between the drive circuit and the MOSFET, and the drive circuit is electrically connected to the MOSFET via the damping adjustment element, thereby being able to suppress the occurrence of malfunction caused by the damping voltage due to specification changes of the switching module such as replacement of the MOSFET or change in the usage frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a side view showing an outline of a switching module according to a representative example, i.e., Embodiment 1 of the present invention.

[0019] Figure 2 It is a circuit diagram showing an equivalent connection circuit near the module when the switching module of Embodiment 1 is applied to an amplifier of a high-frequency power supply device.

[0020] Figure 3 It shows Figure 1 A perspective view showing a typical example of the damping adjustment element shown and a modified example thereof.

[0021] Figure 4 It is a graph showing the time change of the voltage when a gate pulse is applied to the gate electrode using the switching module of Embodiment 1.

[0022] Figure 5 It is a circuit diagram showing an equivalent connection circuit near the module when the switching module of Embodiment 2 is applied to an amplifier of a high-frequency power supply device.

[0023] Figure 6 It is a circuit diagram showing an equivalent connection circuit near the module when the switching module of a modified example of Embodiment 2 is applied to an amplifier of a high-frequency power supply device. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, representative specific examples of the switching module of the present invention will be described using Figures 1 to 6 to illustrate.

[0025] <Example 1>

[0026] Figure 1It is a side view showing the outline of a switching module which is a representative example of the present invention, namely, Example 1. Here, the switching module shown in the specification of this application can be applied to high-frequency power supplies for semiconductor manufacturing apparatuses and the like. At this time, an amplifier with an output of 1 kW or more and an output frequency of 0.3 MHz or more can be exemplified.

[0027] As Figure 1 shown, the switching module 100 of Example 1 includes a substrate 110, a MOSFET 120 mounted on the substrate 110, a drive circuit 130, a damping adjustment element 140, and bonding wires 150, 152 for electrically connecting these elements. In addition, Figure 1 only the path connected to the gate electrode G of the MOSFET 120 is shown, and the paths connected to the drain electrode D and the source electrode S for forming a part of the amplifier are omitted from the illustration.

[0028] As an example thereof, the substrate 110 is formed as a flat plate-shaped member on which the MOSFET 120, the drive circuit 130, and the damping adjustment element 140 are mounted. The substrate 110 is formed of a material with good thermal conductivity such as beryllium oxide (BeO) or aluminum nitride (AlN). Thereby, heat generated when driving the module can be effectively dissipated or discharged.

[0029] The MOSFET 120 is a type of field effect transistor, and is configured as a semiconductor element in which, for example, an oxide film as an insulating layer and a gate electrode G are laminated on a substrate such as silicon, and a drain electrode D and a source electrode S are formed by ion implanting high-concentration impurities. In the present invention, any MOSFET element generally referred to as a p-type or n-type can be applied.

[0030] The drive circuit 130 is a structure including a drive power supply and a switching mechanism not shown, and applies a predetermined gate drive voltage to the gate electrode G of the MOSFET 120 through the on / off operation of the switching mechanism. As the drive circuit 130, an IC chip having a push-pull circuit composed of transistors and MOSFETs at the output stage can be exemplified.

[0031] The damping adjustment element 140 is disposed between the MOSFET 120 and the drive circuit 130 on the substrate 110, and is electrically connected to the MOSFET 120 and the drive circuit 130 via the bonding wires 150, 152, respectively. In Example 1, the damping adjustment element 140 is configured as a gate resistor Rg, for example.

[0032] Such a damping adjustment element 140 selects the resistance value of the gate resistor Rg included in the damping adjustment element 140 according to the parasitic capacitance of the MOSFET 120 as described later, thereby setting the damping voltage (return voltage) Vgs1 of the gate / source voltage Vgs applied from the gate electrode G to a value not exceeding a predetermined threshold. That is, by appropriately adjusting the resistance value of the gate resistor Rg of the damping adjustment element 140, the attenuation rate of the damping voltage (return voltage) Vgs1 with respect to the output voltage of the drive circuit 130 is controlled.

[0033] The bonding wires 150 and 152 are, for example, wires made of gold, copper, or aluminum. Here, Figure 1 The illustrated bonding wires 150 and 152 are bonded to the respective elements by a known method such as ball bonding or wedge bonding. In addition, the damping adjustment element 140 is assembled interchangeably according to the type of the MOSFET 120 and the output frequency used.

[0034] Figure 2 is a circuit diagram showing an equivalent connection circuit near the module when the switching module of Embodiment 1 is applied to an amplifier of a high-frequency power supply device. Here, Figure 2 The case where the voltage input Vin and the ground GND are connected to the MOSFET 120 is illustrated, however, the equivalent connection circuits of other configurations of the high-frequency power supply device are omitted from the illustration and description.

[0035] As Figure 2 shown, the MOSFET 120 and the drive circuit 130 are mounted on the substrate 110, and the damping adjustment element 140 and the bonding wires 150 and 152 are electrically connected and arranged therebetween to form a connection circuit from the drive circuit 130 to the MOSFET 120. Here, as described above, Figure 1 the described damping adjustment element 140 is simulated as a gate resistor Rg, and the bonding wires 150 and 152 are simulated as a structure that is integrated and internally includes a stray inductance Ls and a resistance component Rs.

[0036] The drive circuit 130 includes a driver Dr, which is connected to the bonding wires 150 and 152 and is also connected to the ground GND. Then, a gate / source voltage Vgs corresponding to the operation of the above-described switching mechanism is applied between the gate electrode G and the source electrode S of the MOSFET 120 by the output voltage from the drive circuit 130.

[0037] Figure 3 is a perspective view showing Figure 1 a typical example of the illustrated damping adjustment element and its modified example. As Figure 3As shown in (a) of FIG. , as an example, the damping adjustment element 140 is formed of a metal member 142 having a thickness H1, a length L1 in the arrangement direction of the elements, and a width W1. At this time, by fixing the length L1 and changing the thickness H1 and width W1 of the metal member 142, the gate resistance Rg of the damping adjustment element 140 can be adjusted while keeping the intervals between the respective elements and the lengths of the bonding wires 150 and 152 fixed. In addition, instead of the metal member 142, a commercially available resistor may be used.

[0038] In addition, as shown in Figure 3 As a modified example of the damping adjustment element 140, as shown in (b) of FIG. , a resistor body 146 having a thickness H2, a length L2 in the arrangement direction of the elements, and a width W2 is laminated on one surface of the base member 144, and a high-power chip resistor, a thin-film printed resistor, etc. in which these are integrated with a protective body 148 may be applied. In these configurations, by fixing the length L2 and changing the thickness H2 and width W2 of the resistor body 146, the gate resistance Rg of the damping adjustment element 140 can be adjusted while keeping the intervals between the respective elements and the lengths of the bonding wires 150 and 152 fixed.

[0039] In the switching module 100 having the configuration shown in Figure 1 and Figure 2 as an example, the resistance value of the gate resistance Rg of the damping adjustment element 140 is determined in the following order according to the parasitic capacitance of the MOSFET 120.

[0040] As described above, there is a parasitic capacitance in the MOSFET 120. And in this parasitic capacitance, the gate / source capacitance Cgs and the gate / drain capacitance Cgd are used, and the input capacitance Ciss is defined as in the following formula 1.

[0041] Ciss = Cgs + Cgd... Formula 1

[0042] In addition, as described above, in the Figure 2 equivalent circuit described above, when forming a connection circuit from the drive circuit 130 via the bonding wires 150 and 152 and the damping adjustment element 140 to the MOSFET 120, the stray inductance Ls, the resistance component Rs of the bonding wires 150 and 152, the gate resistance Rg of the damping adjustment element 140, and the gate / source capacitance Cgs of the MOSFET 120 constitute a series resonance circuit. It is well known that when series resonance occurs in this series resonance circuit, the amplitude of the gate / source voltage Vgs decays according to the damping constant ζ expressed by the following formula 2.

[0043]

[0044] On the other hand, when a gate / source voltage Vgs is applied to the MOSFET 120 and its voltage value exceeds a predetermined value, the MOSFET 120 enters the on state. However, even when the switching control of the drive circuit 130 turns off, the gate / source voltage Vgs does not instantaneously switch, generating a so-called damping voltage (return voltage). At this time, when the output voltage of the drive circuit 130 is set to Vdr, the gate / source voltage Vgs1 after one cycle from the disconnection of the gate / source voltage Vgs from the drive circuit 130 can be calculated according to Equation 3 below.

[0045]

[0046] Then, when the above Vgs1 exceeds a predetermined threshold value (threshold) Vth for turning on the MOSFET 120, the MOSFET 120 enters the on state as a signal with an on command input, resulting in a malfunction (false triggering) where it turns on when it should be off. Therefore, in order to prevent such false triggering of the MOSFET 120, it is required that the gate / source voltage Vgs1 after one cycle be smaller than the above-mentioned predetermined threshold value (threshold voltage for turning on the MOSFET 120) Vth. That is, the resistance value of the gate resistor Rg can be determined such that the damping constant ζ is such that Vgs1 shown in Equation 3 is smaller than the threshold value Vth.

[0047] Figure 4 is a graph showing the time variation of the voltage when a gate pulse is applied to the gate electrode using the switching module of Embodiment 1. As Figure 4 shown, when the horizontal axis represents time and the vertical axis represents the gate / source voltage, the output voltage Vdr based on the gate pulse in the drive circuit 130 is represented by a dashed line, and the actual gate / source voltage Vgs applied to the gate electrode G is represented by a solid line.

[0048] At this time, due to the vibration after the pulse disconnection, the gate / source voltage after one cycle, i.e., the damping voltage (return voltage) Vgs1, occurs at time t1. Here, as described above, the resistance value of the gate resistor Rg is set such that the gate / source voltage Vgs1 at time t1 does not exceed the predetermined threshold value Vth, thereby suppressing false triggering of the MOSFET 120. That is, by adjusting the resistance value of the gate resistor Rg, the damping constant ζ is adjusted, and as a result, the attenuation rate of the damping voltage (return voltage) Vgs1 can be controlled.

[0049] With the above-described configuration, in the switching module 100 of the first embodiment, in addition to the bonding wires 150 and 152, the drive circuit 130 is electrically connected to the MOSFET 120 via the damping adjustment element 140. Therefore, when replacing the MOSFET 120 or changing the operating frequency, the damping voltage (return voltage) Vgs1 of the gate / source voltage can be adjusted by the gate resistance Rg of the damping adjustment element 140. As a result, malfunction due to the damping voltage in the connection circuit between the MOSFET and the drive circuit can be suppressed.

[0050] <Embodiment 2>

[0051] Generally, in a MOSFET, the gate electrode G is insulated from other electrodes (drain electrode D and source electrode S) by an oxide film. It is well known that there is a parasitic capacitance due to the capacitance of this oxide film. There is an inverse relationship between this parasitic capacitance and the frequency of the MOSFET used (i.e., as the frequency of the MOSFET increases, a smaller parasitic capacitance is desired). Therefore, in the design of an amplifier, a MOSFET corresponding to the output frequency is selected.

[0052] At this time, in the equivalent connection circuit of the switching module equipped with the MOSFET, the bonding wire connecting the driver and the MOSFET has a stray inductance Ls and a resistance component Rs. These stray inductance Ls and resistance component Rs form an RLC series circuit with the gate / source capacitance Cgs in the above-mentioned parasitic capacitance, and sometimes series resonance occurs, resulting in a problem of excessive current flowing through the circuit.

[0053] Figure 5 FIG. is a circuit diagram showing the equivalent connection circuit near the module when the switching module of the second embodiment is applied to the amplifier of a high-frequency power supply device. Here, in the switching module 200 of the second embodiment, components having the same or similar structure as those of the first embodiment are given the same reference numerals as in the first embodiment, and repeated description thereof is omitted.

[0054] As Figure 5 shown, in the switching module 200 of the second embodiment, the MOSFET 120 and the drive circuit 130 are mounted on the substrate 110, and the damping adjustment element 240 and the bonding wires 150 and 152 are electrically connected and arranged therebetween to form a connection circuit from the drive circuit 130 to the MOSFET 120. In addition, in Figure 5 , as in the case of the first embodiment, the case where the voltage input Vin and the ground GND are connected to the MOSFET 120 is illustrated, and the equivalent connection circuits based on other structures of the high-frequency power supply device are omitted from the drawings and the description.

[0055] In Figure 5In the switch module 100 shown, the damping adjustment element 240 is configured as a vibration suppression circuit formed by an RL parallel circuit in which a gate resistor Rg and a gate inductor Lg are connected in parallel. Here, Figure 5 The gate resistor Rg shown is applied with the same structure as that used in the first embodiment. In addition to the function of controlling the damping voltage based on the gate resistor Rg, the damping adjustment element 240 having such a structure also allows a current of a low-frequency component (DC component) lower than the resonance frequency ω0 (ω0 = Rg / Lg) of the RL parallel circuit to flow through the subsequent MOSFET 120 via the gate inductor Lg, and allows a high-frequency component higher than the resonance frequency ω0 of the RL parallel circuit to flow through the MOSFET 120 via the gate resistor Rg.

[0056] That is, in Figure 5 In the damping adjustment element 240 shown, for example, by changing the number of turns of the gate inductor Lg, its inductance value is changed. At this time, since the resonance frequency of the connection circuit from the drive circuit 130 to the MOSFET 120 is expressed as a function of the gate resistor Rg and the gate inductor Lg as described above, if the inductance value of the gate inductor Lg changes, the resonance frequency of the connection circuit also changes. Thereby, the resonance frequency of the connection circuit can be freely adjusted, and thus the series resonance of the RLC series circuit formed by the connection circuit from the drive circuit 130 to the MOSFET 120 can be suppressed.

[0057] Figure 6 FIG. is a circuit diagram showing an equivalent connection circuit near the module when the switch module of the modified example of the second embodiment is applied to an amplifier of a high-frequency power supply device. Here, similar to Figure 5 the case of, in Figure 6 In the switch module 200 shown, those having the same or similar structure as in the first embodiment are given the same reference numerals as in the first embodiment, and repeated description is omitted.

[0058] In Figure 6 In the shown modified example, the damping adjustment element 240' is configured as a vibration suppression circuit formed by an RC series circuit in which a gate resistor Rg and a gate capacitor Cg are connected in series. Such an RC series circuit together with the stray inductance Ls included in the bonding wires 150 and 152 forms a vibration absorption circuit. Here, for Figure 6 the gate resistor Rg shown, the same structure as that used in the first embodiment is also applied. In addition to the function of controlling the damping voltage based on the gate resistor Rg, the damping adjustment element 240' having such a structure also has a function in which the voltage applied to both ends of each element changes according to the resistance value of the gate resistor Rg and the capacitance value of the gate capacitor Cg.

[0059] That is, in Figure 6In the damping adjustment element 240 shown, for example, by changing the area and spacing of the electrode plates of the gate capacitance Cg, the capacitance value changes. At this time, since the resonance frequency of the connection circuit from the drive circuit 130 to the MOSFET 120 is expressed as a function of the stray inductance Ls and the gate capacitance Cg, if the capacitance value of the gate capacitance Cg changes, the resonance frequency of the connection circuit also changes. Thus, similar to the Figure 5 case shown, the resonance frequency in the connection circuit can be freely adjusted, so that the series resonance of the RLC series circuit in the connection circuit from the drive circuit 130 to the MOSFET 120 can be suppressed.

[0060] By having the structure as described above, in the switching module 200 of the second embodiment, by configuring the damping adjustment elements 240, 240' to include a vibration suppression circuit containing the gate resistance Rg inside, and changing the value of the gate inductance Lg or the gate capacitance Cg arranged in parallel or in series with the gate resistance Rg, the damping adjustment elements 240, 240' are made to have the function of a damping resistance based on the gate resistance Rg, and also have the function of freely adjusting the resonance frequency in the connection circuit from the drive circuit 130 to the MOSFET 120.

[0061] In addition, the descriptions of the above embodiments and their modification examples are examples of the switching module of the present invention, and the present invention is not limited to each embodiment. In addition, those skilled in the art can make various changes without departing from the gist of the present invention, and these modes are not excluded from the scope of the present invention.

[0062] Symbol Description

[0063] 100 Switching module

[0064] 110 Substrate

[0065] 120 MOSFET

[0066] 130 Drive circuit

[0067] 140 Damping adjustment element

[0068] 142 Metal component

[0069] 144 Base component

[0070] 146 Resistor body

[0071] 148 Protective body

[0072] 150, 152 Bonding wire

[0073] 200 Switching module

[0074] 240, 240' damping adjustment element

[0075] G gate electrode

[0076] D drain electrode

[0077] S source electrode

[0078] Dr driver

[0079] Rg gate resistance

[0080] Lg gate inductance

[0081] Cg gate capacitance

[0082] Vgs: gate / source voltage

[0083] Vgs1 damping voltage (return voltage).

Claims

1. A switching module, which mounts a MOSFET and a drive circuit for applying a gate drive voltage to the gate electrode of the MOSFET on a substrate, characterized in that, the drive circuit is electrically connected to the MOSFET via a damping adjustment element and a bonding wire between the drive circuit and the gate electrode, the damping adjustment element at least includes a gate resistor, and the gate resistor is used to control the attenuation rate of the return voltage after the application of the gate drive voltage from the drive circuit ends, the damping constant ζ of the amplitude attenuation of the gate / source voltage Vgs is defined by the following formula: where Ciss is the input capacitance, defined as Ciss = Cgs + Cgd, where Cgs and Cgd are the gate / source capacitance and gate / drain capacitance of the MOSFET, Ls and Rs are the stray inductance and resistance components of the bonding wire, and Rg is the gate resistor of the damping adjustment element, the resistance value of the gate resistor Rg is set so that the gate / source voltage Vgs1 after one cycle after the disconnection of the gate / source voltage Vgs from the drive circuit does not exceed the threshold voltage Vth at which the MOSFET becomes in the on state, the gate / source voltage Vgs1 is defined by the following formula: where Vdr is the output voltage of the drive circuit.

2. The switching module according to claim 1, characterized in that, the gate resistor is a high-power chip resistor or a thin-film resistor.

3. The switching module according to claim 1, characterized in that, the substrate is formed of beryllium oxide or aluminum nitride.

Images