Semiconductor device

Abstract

To provide a semiconductor device capable of reducing switching losses without complicating the control circuit and control method.SOLUTION: A semiconductor device of the present disclosure is configured to have a first gate electrode, a second gate electrode connected in parallel with the first gate electrode, a control circuit connected to the first and second gate electrodes to control the gate voltage, and a coil connected between the second gate electrode and the control circuit.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a semiconductor device.

Background Art

[0002] For energy saving of power electronics devices such as inverters, it is necessary to reduce the losses of semiconductor switching elements. Examples of semiconductor switching elements include insulated gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field effect transistors (MOSFETs). Since the losses are determined by the conduction loss and the switching loss of the element, development aimed at further reducing the losses of the switching element has been promoted by reducing these losses.

[0003] Particularly in bipolar transistor elements such as IGBTs, by adjusting the amount of minority carriers during conduction, it is possible to control the values of turn-off loss, which is part of the switching loss, and conduction loss. However, in semiconductor devices, since there is a trade-off relationship between switching loss and conduction loss, there has been a problem that it is difficult to achieve both reduction of these losses.

[0004] To solve this problem, Patent Document 1 discloses a semiconductor device that improves the switching loss by improving the turn-off loss. This semiconductor device controls two gate electrodes in the same chip with different gate control signal circuits. Then, by shifting the timing of turning off each gate during turn-off, the discharge of minority carriers is partially advanced from the gate that turned off first. As a result, the turn-off loss is improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the above-described method, there is a problem that the control circuit and the control method become complicated when individually controlling two gate electrodes.

[0007] In order to solve the above problems, an object of the present disclosure is to provide a semiconductor device capable of reducing switching loss without complicating the control circuit and the control method by connecting a coil to only one of two gate electrodes.

Means for Solving the Problems

[0008] An aspect of the present disclosure includes a first gate electrode, a second gate electrode connected in parallel with the first gate electrode, a control circuit connected to the first gate electrode and the second gate electrode to control a gate voltage, and a coil connected between the second gate electrode and the control circuit. A first diode that is connected in parallel to the coil, with the side of the second gate electrode being the cathode and the side of the control circuit being the anode Preferably, it is a semiconductor device.

Effects of the Invention

[0009] According to an aspect of the present disclosure, it is possible to provide a semiconductor device capable of reducing switching loss without complicating the control circuit and the control method.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Embodiment 1 Prior to the description of Embodiment 1, the effects and problems of the conventional example will be described. FIG. 1 is a graph showing the relationship between switching loss and conduction loss. It can be seen that the switching loss and the conduction loss are in a trade-off relationship.

[0012] The semiconductor device of Patent Document 1 includes a normal gate electrode and a control gate electrode. Since this semiconductor device is an n-channel type IGBT, holes are accumulated in the drift layer at turn-off. After turn-off, it is necessary to discharge these holes, resulting in switching loss.

[0013] This semiconductor device controls these two gate electrodes individually and shifts the turn-off timing, thereby discharging some holes in advance. Then, when all the gate electrodes are turned off, the number of holes that need to be discharged decreases, so that the switching loss can be reduced.

[0014] In the semiconductor device of the conventional example, in this way, by controlling a plurality of gate electrodes individually, holes at turn-off are controlled to improve the switching loss. However, there is a problem that the control circuit and the control method become complicated by controlling a plurality of gate electrodes individually. To solve this, the present disclosure provides a semiconductor device that controls a plurality of gate electrodes with a simple control circuit and a control method.

[0015] FIG. 2 is a cross-sectional view of a semiconductor device according to Embodiment 1 of the present disclosure and a diagram showing its control circuit. This semiconductor device 101 is specifically an n-channel type IGBT.

[0016] The semiconductor device 101 includes an n-type drift layer 11. A p-type base layer 12 is formed on the drift layer 11. A plurality of n-type emitter layers 14 are formed on the surface layer of the base layer 12.

[0017] The semiconductor device 101 also includes a trench 15. The trench 15 is formed to penetrate the base layer 12 and reach the drift layer 11. Inside the trench 15, a first gate electrode 21 and a second gate electrode 22 are formed via a gate insulating film 16. An interlayer insulating film 17 for separating the gate and the emitter is formed on the first gate electrode 21 and the second gate electrode 22. An emitter electrode 32 is formed on the interlayer insulating film 17. The emitter electrode 32 is in contact with the base layer 12 and the emitter layer 14.

[0018] The semiconductor device 101 includes a p-type collector layer 13. The collector layer 13 is formed below the drift layer 11, and a collector electrode 31 is further formed below it.

[0019] Furthermore, the semiconductor device 101 includes a control circuit 41. The control circuit 41 is connected to the first and second gate electrodes in order to control the gate voltage of the IGBT. A coil 51 is connected between the second gate electrode 22 and the control circuit 41.

[0020] FIG. 3 is a diagram showing an equivalent circuit of the semiconductor device according to Embodiment 1 of the present disclosure. As described above, in the semiconductor device 101, a coil 51 is connected between the second gate electrode 22 and the control circuit 41. No coil is connected between the first gate electrode 21 and the control circuit 41.

[0021] FIG. 4 is a graph showing the voltage applied to the gate electrode of the semiconductor device according to Embodiment 1 of the present disclosure. The switching operation of this semiconductor device 101 will be described with reference to FIG. 4.

[0022] In the graph, VG1 represents the voltage applied to the first gate electrode, and VG2 represents the voltage applied to the second gate electrode. The vertical axis represents the voltage value. VG1on and VG2on represent the voltage values when the gate is on, and VG1off and VG2off represent the voltage values when the gate is off. The values of VG1on and VG2on are, for example, 15 V, and the values of VG1off and VG2off are, for example, 0 V. The horizontal axis represents time. t1 and t2 represent the times when VG1 and VG2 turn on, respectively, and t3 and t4 represent the times when VG1 and VG2 turn off, respectively. The operation of transitioning from VG1off to VG1on and from VG2off to VG2on is called turn-on, and conversely, the operation of transitioning from VG1on to VG1off and from VG2on to VG2off is called turn-off.

[0023] When power is supplied from the control circuit 41 to the first and second gate electrodes, the gate turns on, and the voltages of VG1 and VG2 rise to VG1on and VG2on. On the other hand, when the power supply is stopped, the gate turns off, and the voltages of VG1 and VG2 drop to VG1off and VGoff.

[0024] Here, since the coil 51 is connected to the second gate electrode, a delay occurs in the gate signal. Therefore, a delay time of t4 - t3 occurs in the time from VG1off to VG2off. By this operation, without using a plurality of control circuits, the timing to turn off the gate can be individually controlled, so that the turn-off loss can be improved.

[0025] Note that the voltages at the on and off states of VG1 and VG2 are shown as rectangular waves for convenience, but may have distorted waveforms due to the capacitance characteristics of the semiconductor device, the inductance of the coil, and other parasitic impedances. However, these waveforms can be appropriately adjusted according to the design of the semiconductor device and the circuit.

[0026] Embodiment 2 FIG. 5 is a diagram showing an equivalent circuit of a semiconductor device according to Embodiment 2 of the present disclosure. The semiconductor device 102 according to Embodiment 2 is different from Embodiment 1 in that a gate control diode 52 is connected in parallel with the coil 51. The diode 52 has its anode side connected to the control circuit 41 and its cathode side connected to the second gate electrode 22.

[0027] FIG. 6 is a graph showing the voltage applied to the gate electrode of the semiconductor device according to Embodiment 2 of the present disclosure. The switching operation of this semiconductor device 102 will be described with reference to FIG. 6.

[0028] In Embodiment 1, due to the influence of the coil 51, a delay time occurred not only during turn-off but also during turn-on. However, in Embodiment 2, during turn-on, power is supplied to the second gate electrode through the diode 52. Therefore, the influence of the coil is reduced, and the delay time during turn-on can be eliminated. As a result, the turn-off loss is improved without affecting the turn-on loss, so that the switching loss can be improved.

[0029] FIG. 7 is a diagram showing an equivalent circuit of a semiconductor device according to a first modification of Embodiment 2 of the present disclosure. The semiconductor device 102a is the same as the semiconductor device 102 in that the diode 53 is connected in parallel with the coil 51, but is different in that the diode 54 is connected in series with the coil 51. The anode side of the diode 54 is connected to the second gate electrode 22, and the cathode side is connected to the control circuit 41.

[0030] When power is applied to the gate of the semiconductor device 102, the operation is strictly the operation of the parallel circuit of the coil 51 and the diode 52. Therefore, the coil 51 affects the rise of VG2 at turn-on.

[0031] On the other hand, when power is applied to the semiconductor device 102a, the diode 54 can suppress the power supply from the coil side to the second gate electrode 22. Therefore, the influence of the coil 51 on the rise of VG2 at turn-on can be reduced.

[0032] FIG. 8 is a diagram showing an equivalent circuit of a semiconductor device according to a second modification of Embodiment 2 of the present disclosure. The semiconductor device 102b is different from the semiconductor device 102a in that the positions of the coil 51 and the diode 54 are interchanged. Also in this case, in order to exhibit the same effect as the semiconductor device 102a, the influence on the rise of VG2 at turn-on can be reduced.

[0033] Note that any one or all of the diodes 52, 53, and 54 may be built-in diodes. Thereby, since there is no need to externally attach a diode, the semiconductor device can be miniaturized.

[0034] Embodiment 3 FIG. 9 is a diagram showing the IGBT characteristics of the gate electrode according to Embodiment 3 of the present disclosure. Embodiment 3 is different from Embodiments 1 and 2 in that the semiconductor element regions controlled by the two gate electrodes are IGBTs having different characteristics in order to effectively improve the loss of the semiconductor device.

[0035] In the semiconductor device according to Embodiment 3, the characteristics of the IGBT operating with the first gate electrode are designed such that the conduction loss is relatively low and the switching loss is relatively high. On the other hand, the characteristics of the IGBT operating with the second gate electrode are designed such that the conduction loss is relatively high and the switching loss is relatively low.

[0036] In an IGBT, the conduction loss is reduced by increasing the accumulation amount of minority carriers. Then, since the number of minority carriers released at turn-off increases, the switching loss increases. This is the reason why the conduction loss and the switching loss are in a trade-off relationship.

[0037] In Embodiment 3, the IGBT characteristics of the first gate electrode are set to have a relatively low conduction loss, and by actively utilizing this during conduction, the conduction loss is reduced. Subsequently, by turning off the first gate electrode first, the loss related to carrier discharge is suppressed. At this time, due to the IGBT characteristics of the second gate electrode having a relatively low conduction loss, the conduction loss temporarily increases. However, since this is for a short period, the impact is small.

[0038] Subsequently, the second gate electrode is turned off. At this time, since the first gate electrode, which has a relatively high switching loss, has already been turned off, carrier discharge has advanced first. Therefore, the impact on the overall switching loss is greater for the second gate electrode. Since the second gate electrode has a relatively low switching loss, the overall switching loss is reduced. As described above, according to the aspect of Embodiment 3, it is possible to achieve both reduction of the conduction loss and the switching loss of the IGBT.

[0039] As a method of changing the IGBT characteristics for each region, for example, the following four methods can be considered. First, it is to change the concentration of the collector layer 13. Specifically, for the collector layer of the IGBT region operating with the first gate electrode, the impurity concentration is relatively decreased to reduce the conduction loss.

[0040] Second, a carrier accumulation layer is partially formed below the base layer by a known technique. Specifically, a partially n-type carrier accumulation layer is formed in the IGBT region operating with the first gate electrode to reduce conduction loss. Alternatively, after forming a carrier accumulation layer in all regions, the conduction loss is reduced by relatively increasing the impurity concentration of the carrier accumulation layer in the IGBT region operating with the first gate electrode.

[0041] Third, for the IGBT region operating with the second gate electrode, the lifetime of minority carriers is locally decreased. Specifically, a lifetime killer such as an electron beam is selectively implanted into the IGBT region operating with the second gate electrode to locally decrease the lifetime of minority carriers.

[0042] Fourth, the interval between trenches in the IGBT region operating with the second gate electrode is made relatively large.

[0043] Embodiment 4 FIG. 10 is a top view of an IGBT included in the semiconductor device according to Embodiment 4 of the present disclosure. Embodiment 4 is different from Embodiment 1 in that a built-in coil 63 is used instead of the coil 51.

[0044] The semiconductor device 103 includes an emitter electrode 33. The emitter electrode 33 corresponds to the emitter electrode 32 of the semiconductor device 101. The semiconductor device 103 also includes a gate wiring 61. The gate wiring 61 is electrically connected to the first gate electrode in a form that penetrates the emitter electrode and the interlayer insulating film. The semiconductor device 103 also includes a built-in coil 63. The built-in coil 63 is electrically connected to the second gate electrode and corresponds to the coil 51 of the semiconductor device 101.

[0045] Furthermore, the semiconductor device 103 includes a gate pad 62. The gate pad 62 is electrically connected to the gate wiring 61 and the built-in coil 63 and is connected to the control circuit 41 in the semiconductor device 101. With such a configuration, the same configuration as in Embodiment 1 can be realized without using an external coil.

[0046] Also, as shown in the semiconductor device 102a and the semiconductor device 102b, a diode may be built in on the chip and connected to the built-in coil, the gate electrode, and the gate pad. The built-in diode can be formed, for example, by doping polycrystalline silicon with n-type or p-type impurities. Thereby, the system can be miniaturized without attaching an external diode.

[0047] FIG. 11 is a graph showing the voltage applied to the gate electrode of the semiconductor device according to Embodiment 4 of the present disclosure. t3, t4, and t5 indicate the times when VG1, VG2 during low-temperature operation, and VG2 during high-temperature operation are turned off, respectively. Since t5 is later than t4, it can be seen that t5 - t3 is longer than t4 - t3.

[0048] Generally, the switching loss during high-temperature operation of an IGBT is larger than that during low-temperature operation. Therefore, in the switching operation of Embodiment 4, the delay time from VG1off to VG2off during high-temperature operation is designed to be longer than that during low-temperature operation. By realizing such an operation, it is possible to reduce the loss that increases during high-temperature operation.

[0049] The above-described effect can be realized by using a coil having a positive temperature dependence of inductance. This can be achieved, for example, by using metals such as Al, Cu, Ti, Ni, Mo, W, Ta and their nitrides. Alternatively, it can also be achieved by using a laminated film composed of them or an alloy layer thereof. In particular, in the structure in which a coil is built in on the same chip as in Embodiment 4, when the semiconductor device becomes high temperature, the coil also becomes high temperature at the same time, so such an operation is possible.

[0050] Embodiment 5 FIG. 12 is a diagram showing an equivalent circuit of the semiconductor device according to Embodiment 5 of the present disclosure. The semiconductor device 104 according to Embodiment 5 is different from Embodiment 1 in that a protection element 55 is connected between the first gate electrode 21 and the second gate electrode 22.

[0051] When an accident such as a short circuit occurs in a switching element such as an IGBT, the gate is cut off by the operation of the protection circuit. At this time, in the semiconductor device according to Embodiment 1, a delay occurs on the second gate electrode side due to the influence of the coil. Therefore, in the semiconductor device according to Embodiment 5, a protection element is connected to the second gate electrode side. As a result, during the cutoff operation, since the first gate electrode 21 and the second gate electrode 22 are electrically connected, an effect of preventing a delay from occurring can be obtained.

[0052] Embodiment 6 FIG. 13 is a cross-sectional view of a semiconductor device according to Embodiment 6 of the present disclosure and a diagram showing its control circuit. The semiconductor device 105 is a semiconductor element called an RC-IGBT in which an IGBT region 71 and a diode region 72 are formed in parallel in the same element. In the diode region 72, a cathode layer 18 formed below the drift layer 11 functions as a cathode, and the upper base layer 12 functions as an anode.

[0053] On the other hand, the cathode layer 18 is also formed in a part of the IGBT region related to the second gate electrode 22. The cathode layer is generally formed by known photolithography technology and ion implantation technology. However, by forming the cathode layer also in a part of the IGBT region 71 related to the second gate electrode 22 at this time, the substantial collector concentration can be reduced. Thereby, adjustment of IGBT characteristics as shown in Embodiment 3 can be realized without an additional process.

[0054] In the present disclosure, although Embodiments 1 to 6 have been described for IGBTs and RC-IGBTs having first and second gate electrodes, embodiments having third and subsequent gate electrodes may also be used, or a mode in which coils having a plurality of different inductances are connected may be used. Furthermore, the same control is possible for known multi-gate IGBTs having third and subsequent gate electrodes.

[0055] Further, according to desired characteristics, other semiconductor elements may be connected between the control circuit and the gate electrode. Examples of the other semiconductor elements include a gate resistor, a capacitor, etc. They may be connected in parallel or in series, or may be incorporated on the same element or connected as separate elements.

[0056] Note that the semiconductor device of the present disclosure may be formed of a wide bandgap semiconductor. Examples of the wide bandgap semiconductor include silicon carbide, gallium nitride-based materials, or diamond.

Description of Reference Numerals

[0057] 11 Drift layer 12 Base layer 13 Collector layer 14 Emitter layer 15 Trench 16 Gate insulating film 18 Cathode layer 21 First gate electrode 22 Second gate electrode 31 Collector electrode 32 Emitter electrode 33 Emitter electrode 41 Control circuit 51 Coil 52 Diode 53 Diode 54 Diode 55 Protection element 63 Built-in coil 72 Diode region 101 Semiconductor device 102 Semiconductor device 102a Semiconductor device 102b Semiconductor device 103 Semiconductor device 104 Semiconductor device 105 Semiconductor device

Claims

1. A first gate electrode, a second gate electrode connected in parallel with the first gate electrode, a control circuit connected to the first gate electrode and the second gate electrode for controlling a gate voltage, and a coil connected between the second gate electrode and the control circuit are provided, a first diode is connected in parallel with the coil, wherein the cathode side is the second gate electrode and the anode side is the control circuit is provided. A semiconductor device.

2. The semiconductor device according to claim 1, wherein the first diode is built-in.

3. A second diode is connected in series with the coil, wherein the anode side is the second gate electrode and the cathode side is the control circuit is provided in the semiconductor device according to claim 1.

4. The semiconductor device according to claim 3, wherein the second diode is built-in.

5. A first gate electrode, a second gate electrode connected in parallel with the first gate electrode, a control circuit connected to the first gate electrode and the second gate electrode for controlling a gate voltage, and a coil connected between the second gate electrode and the control circuit are provided, and a protection element for connecting the first gate electrode and the second gate electrode is provided in a semiconductor device.

6. A drift layer of a first conductivity type, a base layer of a second conductivity type formed on a first main surface of the drift layer, a collector layer of a second conductivity type formed on a second main surface of the drift layer, an emitter layer of a first conductivity type formed on a surface layer portion of the base layer, a plurality of trenches penetrating the base layer and the emitter layer and reaching the drift layer, a gate insulating film formed on a wall surface of the plurality of trenches, a collector electrode electrically connected to the collector layer, and an emitter electrode electrically connected to the emitter layer are provided in a transistor region, wherein the first gate electrode and the second gate electrode are formed on the gate insulating film in the semiconductor device according to claim 1.

7. A semiconductor element region controlled by the first gate electrode exhibits characteristics of relatively low conduction loss and high switching loss, and a semiconductor element region controlled by the second gate electrode exhibits characteristics of relatively high conduction loss and low switching loss in the semiconductor device according to claim 1.

8. The semiconductor device according to claim 1, wherein the coil is a built-in coil.

9. The semiconductor device according to claim 1, wherein the coil exhibits inductance characteristics having a positive temperature dependence.

10. The semiconductor device according to claim 6, further comprising a diode region formed in parallel with the transistor region within the same element.

11. The semiconductor device according to claim 10, wherein a cathode layer of the diode region is formed in the collector layer.

12. The semiconductor device according to any one of claims 1 to 11, formed from a wide bandgap semiconductor.

13. The semiconductor device according to claim 12, wherein the wide bandgap semiconductor is silicon carbide, a gallium nitride-based material, or diamond.

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