Control device for double gate semiconductor device

Abstract: A control device (20) includes a first gate control circuit (21) for supplying a control signal from a control signal inputted to an input terminal P1 to a gate G1, and a second gate control circuit (22) for supplying a control signal from a control signal inputted to the same input terminal P1 to a gate G2. The first gate control circuit (21) is provided with a delay circuit (31), and after a turn-off signal is supplied to the gate G2 for the transition from a thyristor condition to a transistor condition, a turn-off signal is supplied to the gate G1, thereby positively stopping operation of the double gate semiconductor device.

Description: The present invention relates to a structure of a control device for semiconductor power devices, selectable for thyristor operation or transistor operation as IGBT, specifically to a structure of a control device which makes a semiconductor power device having two gate electrodes operable by a single signal. Fig. 1A and Fig. 1B show a structure of a connection circuit of conventional art MOSFET and IGBT. Such MOSFET and IGBT are an insulated gate type semiconductor device, which has a gate electrode formed through a gate oxide film on a semiconductor substrate provided with a drain, a source, an emitter, a collector, or the like, and controlled by a gate potential applied thereto. Fig. 2 shows a timing chart of such an insulated gate type semiconductor device. First, when an input signal I is at a low level, a potential Vg of the gate electrode applied with the input signal I also increases. As a result, the MOSFET or IGBT becomes conductive. Therefore, an operating voltage Vce applied to between the emitter and collector or the like of the insulated gate type semiconductor device decreases, and a passing current Ic flowing between the emitter and collector or the like increases. Off course, there are some types of insulated gate semiconductor devices which make the reverse operation against the level of the input signal I. As such an insulated gate type semiconductor device, a double gate semiconductor device having two gate electrodes as a device which has a low ON voltage to enable high-speed operation and reduce power loss and a short turn-on time is disclosed in detail in Japanese Patent Application No. 17575/1992 applied for by the same Applicant on February 3, 1992. A brief structure of the double gate semiconductor device is shown in Fig. 3. The double gate semiconductor device comprises a p + type substrate as a collector layer 2 provided on its backside with a collector electrode 1, and an n-type base layer 3 formed on the collector layer 2 by an epitaxial technique or the like. Corresponding European and United State Patent Applications based on the foregoing Japanese Patent Application had been filed on February 2nd, 1993, and these European and United State Patent Applications numbers are 93300748.6 and 014,454. A p - type base layer 4 as a well-formed p + type diffusion layer is formed on the surface of the n - type base layer 3, and further n - type emitter layers 5a and 5b are formed on the inside surface of the p - type base layer 4 by two n - type wells. In addition, two p + type emitter layers 6a and 6b are formed on the inside surface of each of the n - type emitter layers 5a and 5b. These two p + type emitter layers 6a and 6b and the n - type emitter layers 5a and 5b are connected with an emitter electrode 7. From the p + type emitter layer 6a, a first gate electrode 11 (hereinafter referred to as gate G1) constituting a first MOS 13 is provided over the surfaces of the n - type emitter layer 5a or 5b, the p - type base layer 4, and the n - type base layer 3 through the gate oxide film 8. On the other hand, from the p + type emitter layer 6b, a second gate electrode 12 (hereinafter referred to as gate G2) constituting a second MOS 14 is provided over the surfaces of the n - type emitter layer 5a or 5b, and the p - type base layer 4 through the gate oxide film 8. In such a double gate semiconductor device, an npn type transistor Qnpn is formed of the n - type emitter layer 5a, the p - type base layer 4, and the n - type base layer 3. Further, a pnp type transistor Qpnp is formed of the p - type base layer 4, the n - type base layer 3, and the p + type collector layer 2. Therefore, when the MOS 13 comprising the gate G1 is turned on, the transistor Qpnp is turned on, and the device becomes conductive in an IGBT mode. Furthermore, when the MOS 14 comprising the gate G2 is turned on, the transistor Qnpn becomes an ON state. As a result, a thyristor 15 comprising the p + type collector layer 2, the n - type base layer 3, the p - type base layer 4, and the n - type emitter layer 5a becomes an ON state, a high density of carriers exist in the device, and the device has a low resistance. Thus, in the present device, a thyristor condition can be achieved by setting the gate G1 and the gate G2 to a high potential, thereby achieving a power device with a low ON voltage. From the ON state, a gate 12 of the second MOS 14 comprising the gate G2 is set to a negative potential. As a result, the thyristor operation disappears since the transistor Qnpn is turned off, and a transistor state is achieved in which solely the transistor Qpnp comprising the p - type base layer 4, the n - type base layer 3, and the p + type collector 2 operates. This condition is the same as the operating condition of IGBT, where the carrier density in the device is decreased. As a result, a carrier sweeping time can be reduced when the gate G1 is turned off, and the turn-off time can be reduced. Fig. 4 shows potentials of the gate G1 and the gate G2 for controlling the double gate semiconductor device. First, when the gates G1 and G2 are set to high potentials, the device becomes an ON state, and exhibits a low ON voltage under the thyristor condition. When a negative potential is applied to the gate G2, the device transfers to the transistor condition. Under this condition, when a negative potential is further applied to the gate G1, the device is turned off in a short turn-off time. The transition from the thyristor condition to the transistor condition can be completed in 0.5 microseconds or less. Thus, with the double gate semiconductor device, it becomes an ON state at a low voltage as used in MCT and the like, and also in high-frequency applications where the device becomes an OFF state in a short turn-off time as in IGBT, a power device with a reduced switching loss can be achieved. A problem with the double gate semiconductor device when used in inverters or the like is that the control terminals have to be individually driven. That is, whereas a prior art power device has only a single control terminal connecting the gate electrode, and the power device can be controlled only by supplying a signal to drive the control terminal, in the double gate semiconductor device, two signals meeting the two control terminals connecting to the two gate electrodes have to be prepared. Furthermore, unless the two control signals are appropriately controlled, since the device does not positively transfer from the thyristor condition to the transistor condition, nor can be turned off, for inverters and the like, this tends to cause generation of an arm short-circuit, leading to a major accident. Furthermore, since the double gate semiconductor device cannot be turned off unless it is transferred from the thyristor condition to the transistor condition, even when a trouble occurs at the initial state where the device becomes conductive, it is necessary to first transfer the device to the thyristor condition, and there is a possibility of occurrence of an unrestorable damage during the transition. Furthermore, since, even if a trouble occurs during operation, immediate shut down is difficult, it is necessary to find a trouble during operation as early as possible and take a measure to transfer to the transistor condition. In view of the above problems, it is a primary object of the present invention to provide a control device applied to a double gate semiconductor device having advantageous characteristics such as high speed and reduced power, which is possible to be handled as conventional power devices, The control device of the present invention is of the kind, such as described in European Patent Application EP-A-0463325, for controlling a double gate semiconductor device operable in one mode as a transistor and in another mode as a thyristor and having a collector electrode, an emitter electrode, a first gate electrode for controlling ON/OFF operation of the semiconductor device in the transistor mode and a second gate electrode for controlling transition from the thyristor mode to the transistor mode, and for controlling a passing current from the collector electrode to the emitter electrode, the control device comprising: first and second gate control means for receiving a common input signal and outputting transition signals to the first gate and the second gate of the double gate semiconductor device respectively, the first gate control means being for delaying a turn-off signal to said first gate electrode of said double gate semiconductor device relative to the turn-off signal to said second gate electrode. The control device in accordance with the present invention, and as set forth in claim 1 hereinafter, is characterised in that: said first gate control means comprises a comparator circuit for determining an operating voltage applied to the collector electrode of the double gate semiconductor device for determining when the double gate semiconductor device has made a transition from the thyristor mode to the transistor mode; the first gate control means applying the delayed turn-off signal to said first gate electrode when the comparator circuit detects that the double gate semiconductor device has made a transition from the thyristor mode to the transistor mode. It is also desirable to provide rectification means allowing current to pass only in a direction from the second gate electrode to the first gate electrode and, in this case, it is effective that the first gate electrode, the second gate electrode, and the rectification means are formed of polycrystalline silicon formed on the surface of the double gate semiconductor device. When the first gate electrode is of an n - type and the second gate electrode is of a p - type, the n - type portion of the rectification means having a pn junction may be connected to the first gate electrode, and the p - type portion may be connected to the second gate electrode. Also, it is effective to connect the n - type portion of the rectification means to the first gate electrode by aluminum deposition wiring, and the p - type portion to the second gate electrode by aluminum deposition wiring. In the control device of the above arrangement, when a turn-off signal to the double gate semiconductor device is delayed by the first gate control means capable delaying a turn-off signal and applied to the first gate electrode, after the double gate semiconductor device is transferred to the transistor condition by a turn-off signal applied to the second gate electrode, the first gate electrode can be applied with a turn-off signal, and it is possible to positively turn off the double gate semiconductor device. Therefore, it is possible to control the double gate semiconductor device by a single turn-off signal, and it is sufficient that an external device using the double gate semiconductor device may have a single control signal as in the prior art. Furthermore, when the rectification means is provided, occurrence of an inhibited mode such that the potential of the second gate electrode is higher than the first gate electrode can be prevented in any cases. Therefore, the double gate semiconductor device can be prevented from being latched up uncontrollably. Other effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof and comparative examples taken in conjunction with the accompanying drawings. Fig. 1A is a circuit diagram showing an example of control method for a prior art insulated gate type semiconductor device; Fig. 1B is a circuit diagram showing another example of control method for a prior art insulated gate type semiconductor device; Fig. 2 is a timing chart showing the operation of the semiconductor device by the control methods shown in Figs. 1A and 1B; Fig. 3 is a schematic cross sectional illustration showing the structure of double gate semiconductor device; Fig. 4 is a timing chart showing the operation of the double gate semiconductor device shown in Fig. 3; Fig. 5 is a circuit diagram showing the structure of a control device according to a first example (Example 1) given as background to the present invention; Fig. 6 is a timing chart showing the operation of the control device shown in Fig. 5; Fig. 7 is a circuit diagram showing the structure of a control device according to a first embodiment of the present invention; Fig. 8 is a circuit diagram showing the structure of a control device according to a second example (Example 2); Fig. 9 is a timing chart showing the operation of the control device shown in Fig. 8 in a normal condition of the double gate semiconductor device; Fig. 10 is a timing chart showing the operation of the control device shown in Fig. 8 in an abnormal condition of the double gate semiconductor device; Fig. 11 is a circuit diagram showing a control device of a different structure according to a second example, which with modification can provide the embodiment 2 of the present invention; Fig. 12 is a circuit diagram showing a control device of a different structure according to the second example; Fig. 13 is a circuit diagram showing the structure of a control device according to a third example (Example 3), which with modification can provide embodiment 3 of the present invention; Fig. 14 is a timing chart showing the operation of the control device shown in Fig. 13; Fig. 15 is a circuit diagram showing the structure of a control device according to a fourth example (Example 4); Fig. 16 is a timing chart showing the operation of the control device shown in Fig. 15 in a normal condition of the double gate semiconductor device; Fig. 17 is a timing chart showing the operation of the control device shown in Fig. 15 when an abnormality occurs at turning on the double gate semiconductor device; Fig. 18 is a timing chart showing the operation of the control device shown in Fig. 15 when an abnormality occurs in the thyristor condition of the double gate semiconductor devices; Fig. 19 is a circuit diagram showing the structure of a control device according to a fifth example (Example 5); Fig. 20 is a perspective illustration showing a condition of a diode formed on the surface of a double gate MOS power device of the control device shown in Fig. 19; Fig. 21 is a perspective illustration showing a condition of a diode formed as in Fig. 20 where the diode and a gate electrode is connected by aluminum deposition wiring; and Fig. 22 is a circuit diagram showing another example of the structure of the control device according to example 5. Example 1 Fig. 5 shows the structure of a control device as a first example by way of background to the present invention. A control device 20 of the present example is a control device for driving a double gate semiconductor device 15 having a first gate G1 and a second gate G2, the structure and function of the double gate semiconductor device are as described previously with reference to Fig. 3 end Fig. 4, and description thereof is omitted here. The device 20 comprises a first gate control circuit 21 for applying a control signal inputted to an input terminal P1 to the gate G1, and a second gate control circuit 22 for applying a control signal inputted to the same input terminal P1 to the gate G2. First, in the second gate control circuit 22, four inverters 23.1 - 23.4 are connected in series, and an input signal is inverted, shaped, and then applied to the gate G2 of the double gate semiconductor device 15. Therefore, an intermediate potential time where the gate potential is unstable is reduced, thereby preventing a mis-operation. On the other hand, the first gate control circuit 21 comprises two paths, that is, an ON path 24 and an OFF delay path 25. The ON path 24 comprises an inverter 26 used in combination with the OFF delay path 25, an inverter 27 connected in series with the inverter 26, a NOR gate 28 inputted with a signal from the inverter 27 and a signal from a delay circuit 31 of the OFF delay path 25, and an inverter 29 used in combination with the OFF delay path 25. The OFF delay path 25 comprises the inverter 26, an inverter 30 connected in series with the inverter 26, the delay circuit 31 including a resistor 32 and a capacitor 33, the NOR gate 28, and the inverter 29. Therefore, when a high-level turn-on signal is inputted to the input terminal P1, the turn-on signal, after delaying by the inverters 26, 27, and 28, and the NOR gate 28, is applied to the gate G1. On the other hand, when a low-level turn-off signal is inputted, in addition to the above delay, the turn-off signal, after charging the delay circuit 31, is applied to the gate G1. Therefore, the first gate control circuit 21 is a control circuit in which only the turn-off signal is delayed by the time of the timer circuit 31 and applied to the gate G1. The inverters 26 and 30 also have a function for shaping the waveform of the input signal to suppress errors in delay time of the timer circuit 31. Fig. 6 shows the operation for controlling the double gate semiconductor device 15 using the control circuit 20. First, when an input signal I varies from a low level to a high level at a time t1, the signal is applied to the gate G1 and the gate G2. Therefore, the double gate semiconductor device 15 becomes a thyristor condition where it is conductive under a low-on resistance, and an operating voltage Vce between an emitter E and a collector C decreases to Vce1. On the other hand, a passing current Vc passing through the emitter E and the collector C increases. Then, when the input signal I varies from a high level to a low level at a time t2, the gate G2 is applied with the low-level signal, as is, and the gate G1 is continuously applied with a high-level signal by the delay circuit 31 of the first gate control circuit 21. Therefore, the double gate semiconductor device 15 transfers from the thyristor condition to a transistor condition which is the same condition as IGBT. At this moment, the turn-on resistor increases due to the transition from the thyristor condition to the transistor condition, and the operating voltage Vce increases from Vce1 to Vce2. Then, since a low-level signal is applied to the gate G1 at a time t3 which is later by a delay time T than the time t2 due to the delay circuit 31, the double gate semiconductor device 15 is turned off. Therefore, the operating voltage Vce increases, and the passing current Ic decreases. Thus, by providing the delay circuit 31 capable of delaying the signal for a predetermined time in the first gate control circuit 21, it is possible to control the double gate semiconductor device 15 by the single input signal I. Furthermore, by adjusting the delay time T, it is possible to apply a turn-off signal to the gate G1 after the completion of the transition from the thyristor condition to the transistor condition, thereby positively turning off the double gate semiconductor device. Embodiment 1 Fig. 7 shows the structure of the control device according to a first embodiment. The control device 20 in the present embodiment, as in example 1, is a control device for driving the double gate semiconductor device 15 having the first gate G1 and the second gate G2, similar components are indicated by similar symbols and description thereof is omitted. The control device 20 of the present embodiment, as in example 1, comprises the first gate control circuit 21 for applying a control signal inputted to the input terminal P1 to the gate G1, and the second gate control circuit 22 for applying a control signal inputted to the same input terminal P1 to the gate G2. A point to be noted in the control device 20 in the present embodiment is that in the first gate control circuit 21, a comparator circuit 41 is provided in place of the delay circuit. First, in the second gate control circuit 22, as in the example 1, four inverters 23.1 - 23.4 are connected in series, and an input signal is inverted, shaped, and then applied to the gate G2 of the double gate semiconductor device 15. Similarly, the first gate control circuit 21 comprises the ON path 24 and the OFF delay path 25. The ON path 24 comprises inverters 26 and 27, the NOR gate 28 inputted with a signal from the inverter 27 and a signal from the comparator circuit 41 of the OFF delay path 25, and an inverter 29 commonly used with the turn-off delay circuit 25. On the other hand, the OFF delay path 25 of the present device is provided with the comparator circuit 41 applied with the operating voltage Vce appearing as a collector voltage of the double gate semiconductor device 15, and its output is inputted to the NOR gate 28. The comparator circuit 41 comprises a comparator 42 applied with the operating voltage Vce to an inverted input, and a reference power supply 43 for generating a reference voltage applied to a non-inverted input of the comparator 42. Therefore, referring to the timing chart shown in Fig. 6, a turn-off signal is applied to the gate G2 at the time t2, when the double gate semiconductor device 15 transfers to the transistor condition, and the operating voltage Vce increases to Vce2. Since a reference voltage V0 inputted to the comparator 42 is set to a value lower than Vce2, when the operating voltage Vce exceeds the reference voltage V0, the output of the comparator 42 is inverted. As a result, signals from the ON path 24 and the OFF path 25 coincide in the NOR gate 28, and a turn-off signal is supplied from the first gate control circuit 21 to the gate G1. This stops operation of the double gate semiconductor device 15. As described above, in the control device of the present embodiment, after the transition from the thyristor condition to the transistor condition is confirmed using the comparator circuit 41, a turn-off signal is applied to the gate G1. Therefore, as in example 1, the double gate semiconductor device 15 can be controlled by a single input signal, and the double gate semiconductor device 15 can be positively turned off. Example 2 Fig. 8 shows the structure of the control device according to a second example. The control device 20 of the present example, as in the example 1, is a control device for driving the double gate semiconductor device 15 having the first gate G1 and the second gate G2, similar components are indicated by similar symbols and description thereof is omitted. The control device 20 of the present example is provided with the first gate control circuit 21 of the same structure as in example 1 or, to provide a second embodiment, as in embodiment 1. And, the control device 20 of the present example is provided with the second gate control circuit 22 which is capable of delaying a turn-on signal to the gate G2. That is, the second gate control circuit 22 of this device comprises a delay circuit 51 for delaying the input signal I inputted from the input terminal P1, a determination circuit 52 capable of detecting and determining the passing current Ic of the double gate semiconductor device 15, and a turn-off signal transmission circuit 53 capable of converting a turn-on signal applied to the gate G1 to a turn-off signal according to the determination result of the determination circuit 52. Furthermore, the determination result of the determination circuit 52 is reflected to the delay circuit 51 so that a turn-on signal from the delay circuit 51 is applied to the gate G2 according to the determination result of the determination circuit 52. First, the delay circuit 51 for delaying the input signal I from the timing applied to the gate G1 comprises two inverters 23.1 and 23.2 connected in series, a delay circuit 45 for delaying signals from the inverters 23.1 and 23.2 for a predetermined time, and an AND gate 46 inputted with a signal from the delay circuit 45 and a signal from the determination circuit 52. Therefore, the turn-on signal inputted to the input terminal P1 is first applied to the gate G1 by the first gate control circuit 21, and delayed and applied to the gate G2. Therefore, by the control device 20 of the present example, first the double gate semiconductor device 15 is started from the transistor condition. The determination circuit 52 for inputting the determination result to the delay circuit 51 comprises a detection resistor 56 through which the passing current Ic of the double gate semiconductor device 15 passes, a comparator 54 supplied to its inverted input with a voltage drop in the detection resistor 56, and a reference power supply 55 for generating a reference voltage V1 supplied to a non-inverted input of the comparator 54. Therefore, when a turn-on signal is supplied to the gate G1 and the double gate semiconductor device 15 is in the transistor condition, the current Ic flows through the detection resistor 56, and a voltage drop proportional to the current Ic is compared with the reference voltage V1 by the comparator 54. Therefore, when a high passing current Ic exceeding a predetermined value flows under the transistor condition, a signal from the comparator 54 is inverted, and it can be determined whether or not the double gate semiconductor device 15 is started under an overcurrent condition. When it is an overcurrent condition, the turn-on signal delayed by the delay circuit 45 can be canceled by inputting the output from the comparator 54 of the determination circuit 52 to the AND gate 46 of the delay circuit 51. The output of the determination circuit 52 is connected to the output of the first gate control circuit 21 through the turn-off signal transmission circuit 53. The turn-off signal transmission circuit 53 comprises a diode 57 of which a current flow from the output side of the first gate control circuit 21 to the determination circuit 52 side is the forward direction. When an overcurrent is detected by the determination circuit 52 and the output of the comparator 54 is inverted, the turn-on signal applied from the first gate control circuit 21 to the gate G1 is inverted, and the turn-off signal is supplied to the gate G1. Therefore, when an overcurrent condition is detected by the determination circuit 52, the turn-on signal to the gate G2 is canceled by the delay circuit 51, whereas, a turn-off signal is supplied to the gate G1. Therefore, the double gate semiconductor device 15 is turned off. The operation of the control device 20 of the present example will be described with reference to the timing charts shown in Fig. 9 and Fig. 10. Fig. 9 shows a normal start operation. First, when an input signal goes from a low level to a high level at a time t11, a high-level signal is supplied, as is, to the gate G1 by the first gate control circuit 21. On the other hand, a low-level signal is continued to be supplied to the gate G2 by the delay circuit 51 of the second gate control circuit 22. Therefore, the double gate semiconductor device 15 is not in the thyristor condition, but is conductive in the transistor condition. As a result, the conductive current Ic flows through the detection resistor 56, and a voltage drop in the detection resistor 56 is determined by the comparator 54. When the conductive current Ic is smaller than the normal Ic level, the output of the comparator 54 is not inverted, and at the time t2 after a predetermined time, a high-level turn-on signal is supplied from the delay circuit 51 to the gate G2. The double gate semiconductor device 15 transfers to the thyristor condition with a low-on resistance. On the other hand, as shown in Fig. 10, when the device starts at a time 15 under the transistor condition, and when the conductive current Ic exceeds the normal Ic level, the output of the comparator 54 is inverted. Therefore, the turn-on signal is canceled in the second gate control circuit 22. Further, a turn-off signal is supplied by the turn-off signal transmission circuit 53 to the gate G1 at a time t16, and the double gate semiconductor device 15 is turned off. Thus, with the control device of the present example, the double gate semiconductor device 15 is started in the transistor condition by the gate G1. Therefore, when an abnormality is detected by the , determination circuit 52, the double gate semiconductor device 15 can be immediately turned off by supplying a turn-off signal to the gate G1. In the prior art control device, the double gate semiconductor device 15 is started in the thyristor condition, and even if an abnormality occurs, it is necessary to stop operation of the device after transition to the transistor condition, and the device may be unrestorably damaged during the transition. However, with the present control device, when an abnormality is detected, the device can be immediately stopped,.. thereby minimizing possible damages. In the control device 20 shown in Fig. 8, the passing current Ic is determined using the detection resistor 56 connected to the emitter E side of the double gate semiconductor device 15. However, alternatively, it is of course possible to use a sense MOS 16 provided with a sense terminal E1 as shown in Fig. 11 to detect an overcurrent from a sense current Is flowing through the sense terminal E1. This is because the sensor current Is has a relation to the passing current Ic as Is = Ic/(sense ratio), and it is possible to determine the passing current Ic. Furthermore, since it is possible to suppress a detection current flowing through the detection resistor 56 to a low value, a power generated for the detection can be suppressed. Furthermore, as shown in Fig. 12, since the operating voltage Vce increases when an abnormal Ic flows, an overcurrent condition can also be determined by supplying the operating voltage Vce to the inverted input of the comparator 54. Especially, in cases such as a low short-circuit, an arm short-circuit, and the like, Vce is almost the power supply rectification voltage, and it is sufficient to detect an overcurrent. Also with the present example, a power required for the detection an be suppressed. Example 3 Fig. 13 shows the structure of the control device according to a third example. The control device 20 of the present example, as in the above examples and embodiments, is a control device for driving the double gate semiconductor device 15 having the first gate G1 and the second gate G2, similar components are indicated by similar symbols and description thereof is omitted. The control device 20 of the present example is provided with the first gate control circuit 21 having the delay circuit 31 capable of delaying only a turn-off signal as in example 1, and the second gate control circuit 22 having no delay circuit. Since the circuit arrangement of these components is the same as described in example 1, description thereof is omitted. A point to be noted in the present control device 20 is that an abnormality detection circuit 60 is provided in addition to the first gate control circuit 21 and the second gate control circuit 22. The abnormality detection circuit 60 comprises a determination circuit 61 capable of determining the passing current Ic of the double gate semiconductor device 15, and a turn-off signal output circuit 62 capable of supplying a turn-off signal to the first gate control circuit 21 and the second gate control circuit 22 according to the determination result of the determination circuit 61. Therefore, when an overcurrent flows during the operation of the double gate semiconductor device 15, the overcurrent is determined by the determination circuit 61, when it is determined to be a current value exceeding a specified value, a turn-off signal can be supplied from the turn-off signal output circuit 62 to the first and second gate control circuits 21 and 22 to turn off the double gate semiconductor device 15. In such a determination circuit 61 of the abnormality detection circuit 60, as nearly the same as described in embodiment 1, the passing current Ic is detected as a voltage drop by a detection resistor 64 connected to the emitter side of the double gate semiconductor device 15. The voltage drop value is supplied to the inverted input of the comparator 63, and a reference voltage V2 from a reference power supply 65 is supplied to the non-inverted input of the comparator 63. Furthermore, the turn-off signal output circuit 62 comprises a diode 66 of which a current flow from the input terminal P1 to the determination circuit 61 is the forward direction. Therefore, when the passing current Ic is over a reference value, and the voltage drop in the detection resistor 64 exceeds the reference voltage V2, the output of the comparator 63 is inverted, and a low-level turn-off signal is supplied to the first and second gate control circuits 21 and 22 through the diode 62. Therefore, the double gate semiconductor device 15 transfers from the thyristor condition to the transistor condition, and further to be turned off. The operation of the present device will be described with reference to the timing chart shown in Fig. 14. First, the input signal I goes to a high level at a time t21, turn-on signals are individually supplied from the first and second gate control circuits 21 and 22 to the gate G1 and G2, and the double gate semiconductor device 15 is started in the thyristor condition. After that, when a load short-circuit, an arm short-circuit, or the like occurs at a time t22, and the passing current Ic exceeds a normal level, an overcurrent condition is determined by the determination circuit 61. As a result, a turn-off signal is outputted from the turn-off signal output circuit 62 at a time t23, and inputted to the first gate control circuit 21 and the second gate control circuit 22. Therefore, the turn-off signal is applied, as is, from the second gate control circuit 22 to the gate G2, and the double gate semiconductor device 15 transfers from the thyristor condition to the transistor condition at the time t23. And, the turn-off signal is supplied from the first gate control circuit 21 to the gate G1 at a time t24 after a predetermined delay time, and the double gate semiconductor device 15 is turned off. As described above, the control device 20 of the present example is provided with the abnormality detection circuit 60, and is thus possible to detect an abnormality such as an overcurrent even in the normal operation under the thyristor condition. When an abnormality is detected, a turn-off signal is automatically outputted, and the double gate semiconductor device 15 can be stopped from the thyristor condition via the transistor condition. In the prior art control device, when such a double gate semiconductor device 15 is controlled, when an abnormality is detected by an external device, it is necessary to supply first a signal to turn off the gate G2, and then a signal to turn off the gate G1. Therefore, there has been a problem in that the double gate semiconductor device 15 may be damaged during the time from the detection of the abnormality to the outputting the two signals. However, with the present device, an abnormal condition can be immediately detected by always determining the passing current, and a turn-off signal can be outputted within the control device. And, the double gate semiconductor device 15 can be positively turned off by the first gate control circuit 21 using the delay circuit, thereby preventing the occurrence of possible damages. The control device of the present example uses the same circuit as in the example 1 as the first gate control circuit, alternatively, however, as a third embodiment, it is also possible to use a control circuit in which is confirmed the transition to the transistor condition of the semiconductor device as in embodiment 1, and then output a turn-off signal to the gate G1. Furthermore, as a determination circuit for detecting an overcurrent, the present example uses a detection resistor disposed at the downstream of the emitter E, however, as described in example 2, it is of course possible to detect the sense current in a double gate semiconductor device provided with the sense terminal E1. Furthermore, as described in example 2, an abnormal condition can be determined from the operating voltage Vce. Example 4 Fig. 15 shows the structure of the control device according to a fourth example. The control device 20 of the present example as in the above example 2, is a control device for driving a double gate semiconductor device 16 with a sense MOS provided with the first gate G1, the second gate G2, and the sense terminal E1, nearly the same as the control device shown in Fig. 11. The control device 20 of the present example is provided with the first gate control circuit 21 of the same structure as example 1 described with reference to Fig. 5. Furthermore, it has. the second gate control circuit 22 capable of delaying a turn-on signal to the gate G2 as in the embodiment 3. Also similarly, the second gate control circuit 22 comprises the delay circuit 51 for delaying the input signal I inputted from the input terminal P1, the determination circuit 52 capable of detecting and determining the passing current Ic of the double gate semiconductor device 16, and the turn-off signal transmission circuit 53 for converting the turn-on signal applied to the gate G1 to the turn-off signal according to the determination result of the determination circuit 52. Therefore, similar components are indicated by similar symbols, and description thereof is omitted. A point to be noted in the present example is that a turn-off signal from the turn-off signal transmission circuit 53 is not applied directly to the gate G1, but turns off an input signal from the first gate control circuit 21. Therefore, the operation of the double gate semiconductor device 16 with sense MOS can be assured even if a condition to transmit a turn-off signal is established momentarily due to a mis-operation or the like in the determination circuit 52. In the present example, the AND gate 46 comprises two inverters 46b and 46c, and the NOR gate 46a, but the operation is the same as for the above examples and embodiments. The operation of the control device 20 of the present example will be described with reference to the timing charts shown in Fig. 14 to Fig. 18. The control device is provided with the delay circuit 31 in the first gate control circuit 21 to turn off the double gate semiconductor device 16 after the transition from the thyristor condition to the transistor condition. A delay time (off-delay time) Td1 of the delay circuit 31 depends upon the product of a resistor 32 and a capacitor 33 forming the delay circuit 31, that is, upon a time constant R1·C1. On the other hand, the second gate control circuit 22 is provided with the delay circuit 45 so that the device can transfer to the thyristor operation after the operation is confirmed in the transistor operation at turning on. A delay time (on-delay time) Td2 of the delay circuit 45 depends upon the product of a resistor 47 and a capacitor 48 forming the delay circuit 45, that is, upon a time constant R2·C2. Since, not only the turn-off signal but also the turn-on signal is applied to the double gate semiconductor device 16 past the second gate control circuit 22, the on-delay time Td2 is also the off-delay time of the second gate control circuit 22. Therefore, to turn off the double gate semiconductor device 16 after positive transition from the thyristor operation to the transistor operation using the first gate control circuit 21, it is necessary to satisfy R1·C1 > R2·C2. For this purpose, the delay circuits 31 and 45 of the control device 20 are designed so that the values of the resistors 32 and 47 and the capacitors 33 and 48 satisfy this relation. Fig. 16 shows signals applied to the gate G1 and the gate G2 in the normal ON/OFF operation. When a turn-on signal is inputted at a time t30, after an operation delay time of the ON path 24 of the first gate control circuit 21, the signal at the gate G1 goes to a high level, and the double gate semiconductor device 16 goes to the transistor condition. And, at a time t31 after a turn-on delay time Ta of the second gate control circuit 22, the device transfers to the thyristor operation. On the other hand, when a turn-off signal is inputted at a time t32, the device transfers to the transistor operation at a time t33 after a turn-off delay time Tb of the second gate control circuit 22, and the double gate semiconductor device 16 is turned off at a time t34 after a turn-off delay time Tc of the first gate control circuit 21 from the time t32. The above-described turn-on or turn-off delay time Td2 is the times Ta and Tb, and the turn-off delay time Td1 is the time Tc. Therefore, since the time Tc is longer than the time Tb if the relation R1·C1 > R2·C2 is satisfied, after necessary transition to the transistor operation, the gate G1 is turned off, and the double gate semiconductor device 16 can be turned off. Fig. 17 shows the operation when an abnormality is detected during the transistor operation at turning on. When a turn-on signal is inputted at the time t30, after an operation delay time as in Fig. 16, a high-level signal is applied to the gate G1, and the double gate semiconductor device is turned on in the transistor condition. When an abnormality is detected at a time t35 before the turn-on signal is applied to the gate G2, the device is turned off at a time t36 after the turn-off delay time Tc. Fig. 18 shows a case where an abnormality is detected during the thyristor operation of the double gate semiconductor device 16. The turn-on signal is inputted at the time t30, the gate G1 and the gate G2 go to a high level, when an abnormality is detected at a time t37 after the transition to the thyristor condition, the gate G2 goes to a low level after an operation delay of the determination circuit 52 including an abnormality detection comparator and the like, and the device goes to the transistor condition. And, also the gate G1 goes to a low level at a time t38 after the turn-off delay time Tc from the time t37, and the double gate semiconductor device 16 is turned off. As described above, since the control device of the present example goes off necessarily after the transition to the transistor condition even in an abnormal operation, it is possible to positively turn off the double gate semiconductor device. Furthermore, since the turning off is achieved under the condition where the gate G1 is at a high level and the gate G2 is at a low level, there is no danger of the generation of latching up. Example 5 Fig. 19 shows the structure of the control device according to a fifth example. The control device 20 of the present example, as in example 4, is a control device for driving the double gate semiconductor device 16 with a sense MOS provided with the first gate G1, the second gate G2, and the sense terminal E1, and is provided with the first gate control circuit 21 and the second gate control circuit 22. Therefore, similar components are indicated by similar symbols, and description thereof is omitted. A point to be noted in the present example is that in the first gate control circuit 21, a delay circuit 31a is used as a circuit for setting the turn-off delay time, and the delay circuit 31a comprises two resistors 32a and 32b connected in series, and the capacitor 33. Also, the second gate control circuit 22 is provided with a turn-off signal transmission circuit 53a as a turn-off signal transmission circuit for abnormal condition use for supplying a turn-off signal to the delay circuit 31a, in addition to the turn-off signal transmission circuit 53 for supplying a turn-off signal to the input of the first gate control circuit 21. The turn-off signal transmission, circuit 53a for abnormality use, as the turn-off signal transmission circuit 53, comprises a diode 57a, and the anode side of the diode 57a is connected to the upstream of the resistor 32b forming the delay circuit 31a, that is, the connection point of the resistors 32a and 32b. Furthermore, a rectification circuit 67 for connecting the gate G1 and the gate G2 of the double gate semiconductor device 16 is used, and the rectification circuit 67 also comprises a diode 68 with the anode side being the gate G2 side. The control device 20 of the present example is a control device intended to reduce the turn-off delay time Tc of the control device shown in example 4. Specifically, in the control device of example 4 described with reference to Fig. 15, the turn-off delay time Tc for applying a low-level signal to the gate G1 is set to a sufficiently large value compared to the time Tb or Td2 for applying a low-level signal to the gate G1, whereby the transition from the thyristor condition to the transistor condition is positively achieved, and then the double gate semiconductor device is turned off. Therefore, it is a device that can assure the positive ON/OFF driving. On the other hand, even when an abnormality is detected, the device can be turned off only after the turn-off delay time Tc, which may be long for the double gate semiconductor device to be driven. In this case, if the cause of the abnormality is an overcurrent generated due to an arm short-circuit during bridging operation, the double gate semiconductor device 16 evolves heat during the turn-off delay time Tc and increases in temperature, which may exceed the heat resistance limit leading to a breakdown. Thus, in the control device 20 of the present example, to allow a reduction in the turn-off delay time in an abnormal condition, the delay circuit 31a capable of varying the time constant which determines the delay time is used. In the delay circuit 31a of the present device, the time constant in a normal condition, that is, the time constant when a turn-off signal is inputted from the input terminal P1 is (R11 + R12)·C1. Therefore, the delay time Tc is determined by (R11 + R12)·C1. On the other hand, in an abnormal condition where an overcurrent flows, the abnormality is detected in the determination circuit 52, and the output of the comparator 54 goes to a low potential. And, a low-potential turn-off signal is supplied by the turn-off signal transmission circuits 53 and 53a to the input of the first gate control circuit 21 and the upstream of the resistor 32b of the delay circuit 31a. Therefore, in the delay circuit 31a, the capacitor 33 is discharged only through the resistor 32b. Therefore, after a delay time Tc' determined by the time constant R12·C1, a turn-off signal is supplied to the NOR gate 28. Thus, in the present control device, the delay time in an abnormal condition can be reduced to R12/(R11 + R12), and temperature increase in the abnormal condition is suppressed to prevent the double gate semiconductor device 16 from breakdown. In the normal condition, a delay time Tc is applied which has a sufficient allowance for the transition from the thyristor operation to the transistor operation. Furthermore, in the control device 20 of the present example, the rectification circuit 67 to connect the gate G1 and the gate G2 is provided. As described in Fig. 16 to Fig. 18, it is necessary that the gate G1 goes to a high potential prior to the gate G2, and the gate G2 goes to a low potential prior to the gate G1. On the contrary, if the gate G2 goes to a higher potential than the gate G1, the double gate semiconductor device 16 will be in a latch-up condition to become uncontrollable. Therefore, the mode where the gate G2 is at a high potential and the gate G1 is at a low potential is an inhibited mode. However, it is considered that the gate G2 may go to a high potential by chance due to generation of a spark voltage or the like. Furthermore, until the double gate semiconductor device 16 is combined with the control device, or if any one of the gate G1 and the gate G2 is in an open condition even after being combined, such an inhibited mode may be achieved due to static charges or the like. Therefore, it is desirable that the inhibited mode will never be generated, and the control device of the present example uses the rectification circuit 60 to prevent generation of the inhibited mode. The rectification circuit 67 used in the control device 20 of the present example comprises a diode 68. Even when a condition occurs where the potential of the gate G2 is higher than the potential of the gate G1 due to an external disturbance, clamping is established by a forward voltage of the diode 68, and generation of the above inhibited mode is prevented. Since the latch-up condition is not generated unless the potential of the gate G2 is to the extent, for example at least 3V, that the gate can sufficiently operate as a gate, it is sufficient to use the diode 68 having a forward voltage falling in this range. As the rectification circuit 67, it is possible to use an element of a totem pole type, or an open collector type by a pull-up resistor. Although being not shown, when the gate G1 or the gate G2 is connected through a gate resistor to prevent oscillation, the rectification circuit 67 may be disposed at the upstream of the gate resistor or, of course, at the downstream. Fig. 20 shows an example in which the diode 68 is formed at the double gate semiconductor device side. The double gate semiconductor device shown in Fig. 20 is a double gate MOS power device 70, and polysilicon-based gate electrodes G1 and G2 are formed on a surface 71 of the device. All components are shown except the emitter electrode. The gate electrode G1 is adjusted to an n + type by introducing a dopant such as phosphorus, and the gate electrode G2 is adjusted to a p + type by introducing a dopant such as boron. A polysilicon layer 72 is formed on an area between the gate electrodes G1 and G2 except for an area of the emitter electrode (not shown), and a pn junction 73 is formed by introducing a dopant. Therefore, the diode 68 can be formed by the polysilicon layer 72, and it is possible to provide the rectification circuit 67. The individual gate electrodes and the emitter electrode (not shown) are insulated by silicon oxide films. It is of course possible to form a pn junction by directly connecting the high-concentration polysilicon layers forming the gate electrodes G1 and G2, but since the diode formed tends to have a low dielectric resistance and to be difficult to maintain reliability, in the present control device, a pn junction is separately formed using the polysilicon layer 72. Fig. 21 shows an example in which a diode is formed on the surface 71 of the double gate MOS power device 70 as in Fig. 20. In the double gate MOS power device 70 shown in Fig. 21, both the gate electrodes G1 and G2 are formed of the n + type, and it is superior to the double gate MOS power device shown in Fig. 20 in view of a reduction of the polysilicon resistance. However, it cannot be connected directly to the diode 61 formed between the gate electrodes G1 and G2 also using the polysilicon layer 72. Then, in the double gate MOS power device, a window is formed in an insulating layer (not shown) on the polysilicon layer, and the n + type gate electrode G2 and a p - type portion of the diode 68 are connected with an aluminum deposition wiring 74. As shown above, the control device 20 of the present example reduces the turn-off delay time in an abnormal condition to prevent the double gate semiconductor device from being damaged, generation of an inhibited mode is suppressed in all cases by introducing the rectification circuit, thereby achieving the safe and positive driving of the double gate semiconductor device. The present example is described for an example where a resistor for determining the time constant of the delay circuit 31a is divided. Alternatively, however, as shown in Fig. 22, it is also possible to divide the capacitance and vary the time constant by using two capacitors 33a and 33b connected in series. The examples 4 and 5 are described for the double gate semiconductor device having a sense MOS, however, it is of course possible to determine a main current flowing between the collector - emitter of the double gate semiconductor device. As described above, in the control device for the double gate semiconductor device according to the present invention, first a turn-off signal to the double gate semiconductor device is delayed by the first gate control means capable of delaying a turn-off signal and applied to the first gate electrode, thereby stopping and controlling the double gate semiconductor device by a single control signal. Furthermore, using the second gate control means capable of delaying a turn-on signal, it is possible to immediately turn off the double gate semiconductor device even when an abnormality occurs at turning on, thereby preventing generation of unrestorable damages. Furthermore, when the passing current of the double gate semiconductor device is monitored by the passing current determination means and a turn-off signal is outputted according to the value of the passing current, the double gate semiconductor device can be protected earlier than other protective circuits. Thus, the control device according to the present invention makes it possible to incorporate the advantageous double gate semiconductor device that can be turned on with a low turn-on resistance as with MCT and turned off in a short time as with IGBT in power converter apparatus and the like as prior art IGBT. And, it is a control device that can prevent the double gate semiconductor device from being damaged. Therefore, with the present control device, it is possible to widely apply double gate semiconductor devices which are power devices with reduced switching loss also in high-frequency applications. By forming the timer delay means of the first gate control means using the first and second time constant determination units, it is possible to vary the turn-off delay time in abnormal and normal operation conditions. Therefore, in the abnormal operation condition, the turn-off delay time can be reduced to prevent the double gate semiconductor device from exceeding the heat resistance limit and leading to breakdown, thereby achieving a reliable control device. Furthermore, by providing the rectification means, the generation of an inhibited mode where the potential of the second gate electrode is higher than the first gate electrode can be prevented in all cases, thereby preventing an uncontrollable malfunction and improving the reliability. In particular, using the polysilicon-based diode, rectification means can be provided in the double gate semiconductor device itself. This prevents the generation of dangers such as latch-up due to unforeseeable causes such as static charges even when the double gate semiconductor device is handled alone, and the control device can be formed compact.

Claims: A control device (20) for controlling a double gate semiconductor device (15) operable in one mode as a transistor and in another mode as a thyristor and having a collector electrode (C), an emitter electrode (E), a first gate electrode (G1) for controlling ON/OFF operation of the semiconductor device (15) in the transistor mode and a second gate electrode (G2) for controlling transition from the thyristor mode to the transistor mode, and for controlling a passing current from the collector electrode (C) to the emitter electrode (E), the control device comprising: first (21) and second (22) gate control means for receiving a common input signal (P1) and outputting transition signals to the first gate (G1) and the second gate (G2) of the double gate semiconductor device (15) respectively, the first gate control means (21) being for delaying a turn-off signal to said first gate electrode (G1) of said double gate semiconductor device (15) relative to the turn-off signal to said second gate electrode (G2); characterised in that : said first gate control means (21) comprises a comparator circuit (41) for determining an operating voltage applied to the collector electrode (C) of the double gate semiconductor device (15) for determining when the double gate semiconductor device (15) has made a transition from the thyristor mode to the transistor mode; the first gate control means (21) applying the delayed turn-off signal to said first gate electrode (G1) when the comparator circuit (41) detects that the double gate semiconductor device (15) has made a transition from the thyristor mode to the transistor mode. A control device (20) according to claim 1, in combination with the double gate semiconductor device (15) specified therein. A control device according to claim 1 or claim 2, wherein the comparator circuit (41) has a comparator (42) having said operating voltage applied to one input and a reference voltage (43) applied to another input thereof. A control device according to any one of the preceding claims comprising: rectification means (67) capable of passing a current only in a direction from said second gate electrode (G2) to said first gate electrode (G1). A control device according to claim 4 depending directly or indirectly from claim 2, wherein said first gate electrode (G1), said second electrode (G2), and said rectification means (67) comprise polycrystalline silicon on the surface of said double gate semiconductor device. A control device according to claim 5, wherein: said first gate electrode (G1) is of n-type, said second gate electrode (G2) is of p-type, said rectification means (67) has a pn junction, the n-type pole of said rectification means (67) is connected to said first gate electrode (G1), and the p-type pole of said rectification means (67) is connected to said second gate electrode (G2). A control device according to claim 6, wherein: the n-type pole of said rectification means (67) is connected to said first gate electrode (G1) with an aluminium deposition wiring, and the p-type pole of said rectification means (67) is connected to said second gate electrode (G2) with an aluminium deposition wiring. A double gate semiconductor device (15) operable in one mode as a transistor and in another mode as a thyristor and having a collector electrode (C), an emitter electrode (E), a first gate electrode (G1) for controlling ON/OFF operation of the semiconductor device (15) in the transistor mode and a second gate electrode (G2) for controlling transition from the thyristor mode to the transistor mode, and for controlling a passing current from the collector electrode (C) to the emitter electrode (E) and a control device comprising: first (21) and second (22) gate control means for receiving a common input signal (P1) and outputting transition signals to the first gate (G1) and the second gate (G2) of the double gate semiconductor device (15) respectively, the first gate control means (21) being for delaying a turn-off signal to said first gate electrode (G1) of said double gate semiconductor device (15) relative to the turn-off signal to said second gate electrode (G2); characterised in that : said first gate control means (21) comprises a comparator circuit (41) for determining an operating voltage applied to the collector electrode (C) of the double gate semiconductor device (15) for determining when the double gate semiconductor device (15) has made a transition from the thyristor mode to the transistor mode; the first gate control means (21) applying the delayed turn-off signal to said first gate electrode (G1) when the comparator circuit (41) detects that the double gate semiconductor device (15) has made a transition from the thyristor mode to the transistor mode.

Inventors: MASAHITO OTSUKI, MIYASAKA TADASHI, NISHIURA AKIRA, NISHIURA MASAHARU, SAKURAI KENYA, TERASAWA NORIHO, MASAHITO, OTSUKI, MIYASAKA, TADASHI, NISHIURA, AKIRA, NISHIURA, MASAHARU, SAKURAI, KENYA, TERASAWA, NORIHO, Masahito, Otsuki c/o Fuji Electric Co., Ltd, MIYASAKA, TADASHI, C/O FUJI ELECTRIC CO., LTD., NISHIURA, AKIRA, C/O FUJI ELECTRIC CO., LTD., Nishiura, Masaharu c/o Fuji Electric Co., Ltd, Sakurai, Kenya c/o Fuji Electric Co.,Ltd, TERASAWA, NORIHO, C/O FUJI ELECTRIC CO., LTD.
Applicants: FUJI ELECTRIC CO LTD, FUJI ELECTRIC CO., LTD.
Application year: 1993
Main classification: H03K17
IPC codes: H03K17