JPH07163148A - Three-phase full-wave rectifier of ac generator for vehicle - Google Patents

Abstract

PURPOSE:To decrease the parasitic resistance of source and the channel resistance significantly by constituting a three-phase full-wave rectifier of an MOS power transistor using a single crystal SiC as a material. CONSTITUTION:An N-type voltage withstand layer 105 is formed on an N<+>-type substrate 106 of SiC, a P-type well region 103 is formed on the surface part of the N-type voltage withstand layer 105, and an N<+>-type region 104 is formed on the surface part of the P-type well region 103. Only the trench forming region is opened on the wafer surface to make a trench 108 and a gate insulation film 109 is formed on the surface of the trench 108 before a gate electrode 110 is formed. A metal electrode 111 is then brought into contact with the surface of the N<+> region 104 and the P-well region 103 whereas a metal electrode 112 is brought into contact with the surface of the N<+> type substrate 106 thus completing an element. A low loss three-phase full-wave rectifier can be obtained by employing single crystal SiC as a material thereby decreasing the parasitic resistance of source and the channel resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase full-wave rectifier for a vehicle AC generator using a MOS power transistor. INDUSTRIAL APPLICABILITY The three-phase full-wave rectifier of the vehicle alternator of the present invention can be applied not only to an engine-driven alternator, but also to an alternator capable of generating and electric power that regenerates kinetic energy during vehicle braking as electric power and a traveling motor for electric vehicles.

[0002]

2. Description of the Related Art Three-phase having a high-side semiconductor power element and a low-side semiconductor power element for individually connecting each end of a three-phase armature winding of an automotive alternator and a high end and a low end of a battery, respectively. A full-wave rectifier and a controller for synchronously connecting and disconnecting each semiconductor power element are provided, and the three-phase full-wave rectifier converts a generated voltage of a three-phase armature winding into a DC voltage and supplies AC power to a battery. Machine is known, and for example, Japanese Patent Laid-Open No. 138030/1992 discloses the use of a MOS power transistor as the semiconductor power element.

In this type of MOS power transistor, an N-type silicon substrate is used as one of the main electrodes of the MOS power transistor to secure the breakdown voltage and reduce the on-resistance, and the surface of the P-type well region formed on the surface of the chip is used. Vertical MO that forms an N ⁺ type region that forms the other main electrode
The S power transistor structure is usually adopted.

[0004]

A three-phase full-wave rectifier using this MOS power transistor has a configuration in which a parasitic diode which functions as a PN junction diode of a conventional three-phase full-wave rectifier and a MOS power transistor are connected in parallel. Therefore, as compared with the conventional three-phase full-wave rectifier using the silicon diode, there is a possibility that the power loss can be reduced by the amount that there is no forward voltage drop of the junction diode.

However, according to the analysis by the present inventors,
It has been found that the above MOS power transistor type three-phase full-wave rectifier has the following problems. In vehicle alternators, the amount of stored magnetic energy in the three-phase armature windings and field coils is large. It is necessary to set the breakdown voltage to 20 times or more of the battery voltage, that is, the output rectified voltage of the three-phase full-wave rectifier, for example, about 300V.

Further, an output current of 100 A or more is demanded due to the recent increase in vehicle-mounted electric load (for example, a heater for defrost). The power loss of the MOS power transistor having such a high breakdown voltage and large current structure is equal to that of the diode. This is about the same, and it becomes meaningless to use a MOS power transistor having a complicated structure instead of the diode.

The problems of the above MOS power transistor type three-phase full-wave rectifier will be analyzed in more detail below with reference to FIGS. However, FIGS. 3 (a) and 3 (b) show MOS
It is an inverter circuit showing a one-phase portion of a power transistor type three-phase full-wave rectifier.
(B) shows the case of P channel. Further, FIGS. 4 and 5 show examples of typical cross-sectional structures of MOS power transistors.

In the inverter circuit of the N-channel MOS power transistor of FIG. 3A, the drain electrode D of the high-side MOS power transistor 101 and the source electrode S of the low-side MOS power transistor 102 are three-phase AC generators (see FIG. (Not shown) connected to one-phase output terminal,
The drain electrode D of the low-side MOS power transistor 102 is connected to the low end of a battery (not shown),
The source electrode S of the high-side MOS power transistor 101 is connected to the high end of the battery. By the way, the direction of charging current and the moving direction of electrons at the time of charging are opposite.

Further, the MOS power transistor 10 described above.
In Nos. 1 and 102, in principle, a parasitic diode Ds on the source connection side and a parasitic diode Dd on the drain connection side occur between the P-type well region and the source electrode S or the drain electrode D as illustrated. Since it is necessary to apply a potential to the P-type well region, the P-type well region and the source electrode S or the drain electrode D
However, when this inverter circuit is used as a one-phase circuit of the three-phase full-wave rectifier, as shown in FIG. 3A, a P-type well region (for example, FIG. It is necessary to connect the drain electrode D (for example, 104 in FIGS. 4 and 5) to 103) in FIG. 5, that is, to short-circuit the parasitic diode Dd on the drain connection side.

That is, in a three-phase full-wave rectifier for a vehicle AC generator, a P-type well region (for example, 10 in FIGS. 4 and 5) is used.
3) is connected to the source electrode S (for example, 106 in FIGS. 4 and 5) and the parasitic diode Ds on the source connection side is short-circuited, the generated voltage connected to the drain electrode D of the high-side MOS power transistor is the battery. If the voltage is lower than the voltage, a reverse current will flow through the parasitic diode Dd on the drain connection side. Similarly, if the generated voltage connected to the source electrode S of the low-side MOS power transistor rises higher than the potential (ground potential) voltage at the low potential end of the battery, a reverse current flows through the parasitic diode Dd on the drain connection side. Therefore, in order to prevent such a reverse current flow through the parasitic diode Dd, it is necessary to connect the P-type well region 103 to the drain electrode and prevent the reverse current by the parasitic diode Ds on the source connection side.

After all, it is necessary to connect the P-type well region (eg 103 in FIGS. 4 and 5) of the MOS power transistor used in the three-phase full-wave rectifier of the vehicle AC generator to the drain electrode D. This also applies to the P-channel MOS power transistor shown in FIG. 3 (b). However, in the conventional MOS power transistor structure shown in FIGS. 4 and 5, the P-type well region 103 and the N of the surface portion thereof are formed.
^{The +} type region 104 is short-circuited, and the P type well region 103 and N
The depletion layer 107 of the PN junction between the epitaxial epitaxial breakdown layer 105 and the epitaxial epitaxial breakdown layer 105 must be extended to the N-type epitaxial breakdown layer side to increase the breakdown voltage.

That is, when the three-phase full-wave rectifier of the vehicle alternator is constructed with the conventional MOS power transistor structure shown in FIGS. 4 and 5, the N ⁺ type substrate 106 is used.
Must be the source region and the N ⁺ type region 104 must be the drain region. However, in this case, the N-type breakdown voltage layer 10
The large source parasitic resistance Rs of 5 is substantially the source end S '.
And the source electrode are connected in series.

Drain saturation current I of MOS transistor
dsat ignores the threshold voltage Vt for simplification, K is a proportional constant, ΔVgs is a gate-source voltage (Vg−Vs), Vg is a gate voltage, and Vs ′ = Vs + I.
If dsat · Rs is substantially the potential of the source end S ′, Idsat = K (Vg−Vs ′) ² = K (ΔVgs−Idsat · Rs) ^2, that is, the drain saturation current (maximum when a predetermined gate voltage is applied). The current) Idsat is equal to the gate voltage Vg being lowered by the amount of Idsat · Rs. The change in the threshold voltage Vt due to the substrate effect is also ignored.

For example, if the gate voltage is +20 V, the source (battery) potential is +12 V, the current is 100 A, and the source parasitic resistance Rs is 0.05 ohm, the actual source potential Vs' is 17 V and the channel current Rs is 0. It will be reduced to 9/64 compared to the case of. That is, it can be seen that the channel current is extremely reduced by a slight increase in the source parasitic resistance Rs. Hereinafter, this current reducing action, in other words, the channel resistance increasing action is referred to as a source resistance feedback effect.

The above equation is for the drain current saturation region, but similarly in the non-saturation region, the drain non-saturation current similarly decreases due to the increase of Rs. Such a decrease in drain current means an increase in channel resistance,
It is understood that the increase of the source parasitic resistance Rs causes the power loss by itself and the power loss due to the increase of the channel resistance, so that the power loss and the heat generation are large as a whole.

Of course, in the MOS power transistor structure of FIGS. 4 and 5, it is possible to make the N-type breakdown voltage layer 105 thin in order to reduce the source parasitic resistance Rs, but as described above, in the vehicle alternator. Since a high breakdown voltage of 300 V is required, it is difficult to thin the N-type breakdown layer 105. That is, in a normal silicon MOS power transistor, the breakdown field strength of silicon is about 30 V / μm, and if the breakdown voltage of 300 V is to be earned only by the N-type breakdown layer 105, the field strength in the N-type breakdown layer 105 will be. Even if it is assumed to be constant, a thickness of 10 μm is required.
The electric field strength in the N-type breakdown voltage layer 105 is set to about 30 V / μm,
In order for the N-type breakdown voltage layer 105 to bear 300 V, its thickness must actually be about 20 μm or more, and its impurity concentration must be about 1 × 10 ¹⁵ atoms / cm ³ or less.

Forming the N-type withstand voltage layer 105 having such a thickness and impurity concentration in order to secure the withstand voltage increases the source parasitic resistance Rs described above and the resistance loss thereby, and also reduces the drain current ( (Significant increase in channel resistance), and as a result, M
It is theoretically impossible for the OS power transistor type three-phase full-wave rectifier to surpass the PN junction diode type three-phase full-wave rectifier in the vehicle AC generator application (that is, in the field of reactance load), and the structure and control are complicated. However, there is no merit of practical application because only the drawback remains.

On the other hand, in the MOS power transistor structure shown in FIGS. 4 and 5, the N ⁺ type region 104 serves as a source electrode and the N ⁺ type substrate 106 serves as a drain electrode.
It is also conceivable to short-circuit the P-type well region 103 and the N ⁺ -type drain region 106 as in (a). However, in this method, the N ⁺ type region (source electrode) 104 and P
The above breakdown voltage of 300 V is secured between the well region 103 and the gate electrode, and the P well region 107 and the N ⁺
It is extremely difficult to secure the breakdown voltage between the mold region 104 and the mold region 104.

For the reasons described above, the present inventors have found that it is difficult to implement the MOS power transistor used in the three-phase full-wave rectifier of the vehicle AC generator with the current silicon MOS power transistor. In order to realize a full-wave rectifier, it is essential to significantly reduce the withstand voltage layer resistance, and for that purpose, it is indispensable to significantly reduce the thickness of the withstand voltage layer and significantly increase the impurity concentration. Based on the analysis result, it is possible to significantly reduce the thickness of the breakdown voltage layer and increase the impurity concentration only after realizing the significant improvement of the breakdown field strength of the breakdown voltage layer.
It is based on the discovery that loss and heat generation of a three-phase full-wave rectifier of a vehicle AC generator can be significantly reduced if the breakdown field strength of the breakdown layer can be improved.

Therefore, an object of the present invention is to provide a MOS power transistor type three-phase full-wave rectifier for a vehicle AC generator, which is capable of significantly reducing loss as compared with a conventional three-phase full-wave rectifier and which can be cooled easily. To do.

[0021]

A three-phase full-wave rectifier for a vehicular alternator according to the present invention has three ends of a three-phase armature winding of an alternator for a vehicle and a high end and a low end of a battery. A three-phase full-wave rectifier for a vehicle AC generator, which has a high-side MOS power transistor and a low-side MOS power transistor to be connected, converts a generated voltage of a three-phase armature winding into a DC voltage, and supplies the DC power to the battery. In the MO
The S power transistor is characterized by being made of SiC.

In a preferred mode, the three-phase full-wave rectifier has both high-side and low-side MOS power transistors. In a preferred aspect, the three-phase full-wave rectifier is composed of either a high-side or low-side MOS power transistor, and the remaining PN junction diode forming a semiconductor power element.

In a preferred aspect, the MOS power transistor comprises an N ⁺ type substrate which constitutes a source electrode,
An N-type breakdown voltage layer formed on the substrate, a P-type well region formed on the surface of the breakdown voltage layer, and an N ⁺ forming a drain electrode on the surface of the P-type well region.
Type drain region and a gate electrode disposed on the surface of the P type well region via an insulating film and forming an N type channel for electrically connecting the drain region and the breakdown voltage layer.

In a preferred embodiment, the N ⁺ type drain region and the P type well region are short-circuited. In a preferred aspect, the substrate constitutes a common source region of each of the high-side MOS power transistors, the P-type well regions of each phase are individually formed on the substrate, and each P-type well region is formed. The N ⁺ -type drain regions are individually formed on the surface of each of the P + -type well regions, and channels are formed on the surface of each of the P-type well regions to individually conduct the drain regions and the breakdown voltage layers via an insulating film. Each gate electrode to be formed is individually arranged.

In a preferred mode, the three-phase full-wave rectifier is mounted on the same substrate as a voltage adjusting unit that controls switching of the MOS power transistor. In a preferred aspect, the breakdown voltage between the source and drain and between the drain and gate of the MOS power transistor is set to 50 V or more. In a preferred mode, the breakdown voltage between the source and drain and between the drain and gate of the MOS power transistor is set to 100 V or more.

[0026]

The three-phase full-wave rectifier of the vehicle alternator of the present invention is formed by connecting a MOS power transistor made of SiC. As described above, in the vehicle alternator, since the stored magnetic energy amount of the three-phase armature winding and the field coil is large, as a countermeasure against the accidental release of it, the three-phase full-wave rectifier It is necessary to set the breakdown voltage of each semiconductor power element to 20 times or more of the battery voltage, that is, the output rectified voltage of the three-phase full-wave rectifier, for example, about 300V.

In addition, from the recent increase in vehicle-mounted electric load, 10
A large output current of 0 A or more is required. SiC here
The breakdown electric field strength of Si is about 400 V / μm, which is about 1% that of Si.
It has tripled. In this way, the breakdown field strength of SiC is significantly higher than that of SiC, which means that when it is used as a constituent element of a three-phase full-wave rectifier of a vehicle AC generator, the power loss of a MOS power transistor is markedly increased. The effect that it can reduce is produced. Hereinafter, the power loss reduction effect based on the difference in the breakdown electric field strength will be described in more detail.

As an example, let us consider a case where a withstand voltage of 300 V is secured by using a SiC MOS power transistor in the three-phase full-wave rectifier of the vehicle AC generator shown in FIG. 3A. For simplicity, it is considered that the N-type breakdown voltage layer 107 (see, for example, FIG. 4 or FIG. 5) bears all 300V. Assuming that this breakdown voltage of 300 V is simply borne by the N-type breakdown voltage layer 107, the breakdown field strength of SiC is 400 V / c.
m, the required thickness of the N-type breakdown voltage layer 105 is about 4 μm,
The impurity concentration is 2 × 10 ¹⁶ atoms / cm ³ , and the resistivity is about 1.25 Ω · cm. On the other hand, the M of Si described above
The required thickness of the 300V breakdown voltage layer of the OS power transistor is about 20 μm, and its impurity concentration is 1 × 10 ¹⁵ atoms / c.
m ³ , and the resistivity is about 5 Ω · cm. Therefore, Si
The resistance of the N type withstand voltage layer 107 of the C MOS power transistor is the N type withstand layer 10 of the Si MOS power transistor.
The resistance can be reduced to 1/20 as compared with the resistance of 7. However, it is needless to say that the impurity concentration of the N-type breakdown voltage layer 107 can be set to be lower than the above value in relation to the impurity concentration of the P-type well region 103.

As a result, the three-phase full-wave rectifier of the vehicle AC generator using the SiC MOS power transistor of the present invention can significantly reduce the resistance power loss itself of the withstand voltage layer, that is, the source parasitic resistance Rs. A significant reduction in channel resistance can also be realized by reducing the source resistance feedback effect.
Due to their synergistic effect, the loss is significantly lower than that of a three-phase full-wave rectifier of a vehicle AC generator using a Si MOS power transistor and a diode-type three-phase full-wave rectifier having the same power loss. There is an excellent effect that the cooling is also extremely simple.

[0030]

(Embodiment 1) The overall structure of a vehicle alternator of the present embodiment driven by a vehicle engine, a so-called alternator, will be described with reference to FIG. The outer shell of the generator is composed of a pair of drive frame 1 and rear frame 2,
It is directly connected by a plurality of stud bolts 15 and the like.

A stator core 3 is fixed to the inner circumferences of the frames 1 and 2, and a three-phase armature winding 5 is wound around the stator core 3. Bearings 13 and 14 fixed to the frames 1 and 2 rotatably support the shaft 9, and a rotor core 6 is fixed to the shaft 9 at the inner circumference of the stator core 3. A field coil 10 is wound around the rotor core 6, and cooling fans 11 and 12 are arranged on both end faces of the pole cores 7 and 8. A voltage regulator 18 with a built-in three-phase full-wave rectifier 19 is attached to the outside of the rear frame 2.

Next, the circuit configuration of the vehicle alternator of this embodiment will be described with reference to FIG. Voltage regulator 18
Is composed of a three-phase full-wave rectifier 19 and a voltage adjusting unit 20. The rectifier unit 19 is a three-phase full-wave rectifier composed of N-channel enhancement type MOS power transistors 19a to 19f made of single crystal SiC.
The high-side transistors 19a to 19c connect each phase output terminal of the three-phase armature winding 5 to the high-level end of the battery 21, and the low-side transistors 19d to 19f each phase of the three-phase armature winding 5. The output end and the low end of the battery 21 are connected.

The voltage adjusting unit 20 is connected to the field winding 10 via the brush 16 and the slip ring 17, and is mounted on the same substrate (not shown) as the three-phase full-wave rectifier 19. The three-phase full-wave rectifier 19 and the voltage adjusting unit 2
Mounting 0 and 0 on the same substrate makes it possible to shorten the wiring. Further, the voltage adjusting section 20 inputs the generated voltage of each phase from the output terminal of each phase of the three-phase armature winding 5, and based on these input signals, the MOS power transistors 19a to 19f.
The gate voltage applied to each gate electrode is controlled.

The voltage control operation will be briefly described. The engine (not shown) rotates the rotor core 6 so that the voltage adjuster 20 of the voltage adjuster 18 reads the voltage of the battery 21 so that it becomes constant. Field coil 10
When the N, OFF control is performed, a three-phase AC voltage is induced in the three-phase armature winding 5, whereby the DC current full-wave rectified by the three-phase full-wave rectifier 19 charges the battery 21, and
It is consumed by the vehicle electronic load. The cooling fans 11 and 12 rotate to cool the field coil 10, the three-phase armature winding 5, the voltage regulator 18, and the like.

Next, the open / close control of the MOS power transistors 19a to 19f of the three-phase full-wave rectifier 19 by the voltage adjusting section 20 will be described. The voltage adjusting unit 20 determines the generated voltage V for each phase, which is the potential at the output end of the three-phase armature winding 5 for each phase.
u, Vv, Vw are read, and the interphase power generation voltage Vu-V
v, Vu-Vw, Vv-Vu, Vv-Vw, Vw-V
Among u, Vw-Vv, the interphase power generation voltage having the largest positive value and larger than the terminal voltage of the battery 21 is selected, and the high-side MOS power is applied so that the selected interphase power generation voltage is applied to the battery 21. Transistor 19a-
One MOS power transistor in 19c and one MOS power transistor in the low side MOS power transistors 19d to 19f are turned on. As a result, the battery 21 is removed from the selected three-phase armature winding.
The charging current is supplied to.

The voltage adjusting section 20 detects the terminal voltage of the battery 21, compares the detected voltage with a preset reference voltage, and interrupts the exciting current based on the magnitude of the detected voltage, as in a normal regulator. Controlling and maintaining the terminal voltage of the battery 21 at the target level is the same as before. The details of the MOS power transistor type three-phase full-wave rectifier using SiC described above will be described below with reference to FIGS.
Further description will be made. However, FIG. 3A shows the MO of this embodiment.
FIG. 5 is an inverter circuit showing one phase portion of the S power transistor type three-phase full-wave rectifier, and FIG. 5 shows a part of the cross-sectional structure of the MOS power transistors 19a to 19f.

In the inverter circuit of the N-channel MOS power transistor of FIG. 3A, the drain electrode D of the high-side MOS power transistor 101 and the source electrode S of the low-side MOS power transistor 102 are three-phase armature windings 5. Is connected to the one-phase output terminal, the drain electrode D of the low-side MOS power transistor 102 is connected to the low-level terminal of the battery 21, and the high-side MOS is connected.
The source electrode S of the power transistor 101 is the battery 2
Connected to the high end of 1. Note that the direction of the charging current and the moving direction of electrons at the time of charging the battery are opposite to each other, and the source electrode S is an electrode on the side of injecting carrier charges into the channel at the time of charging.

MOS power transistors 101, 102
Then, a P-type well region 103 (that is, a region immediately below the gate electrode 101) and a source electrode S or a drain electrode D which will be described later
A parasitic diode Ds on the source connection side and a parasitic diode Dd on the drain connection side are generated between the P-type well region 103 and the drain electrode D because of the necessity of applying a potential to the P-type well region 103. Short circuited. The reason is as described above. As a result, the parasitic diode Ds on the source connection side blocks the reverse flow from the battery 21.

Next, a part of the sectional structure of the MOS power transistor of this embodiment will be described with reference to FIG. Si
An N-type withstand voltage layer 105 is formed by epitaxial growth on a C N ⁺ -type substrate 106, and a P-type well region 103 is formed on the surface of the N-type withstand voltage layer 105 by ion implantation of aluminum. An N ⁺ type region 104 is formed on the surface of 103 by implanting nitrogen ions. Then, a well-known R.I. i. Trench 10 by dry etching
8, a gate insulating film 109 made of a silicon oxide film is formed on the surface of the trench 108 by a thermal oxidation method, and then a gate electrode 110 made of doped polysilicon is formed in the trench 108. After that, the metal electrode 111 is brought into contact with the surface 104 of the N ⁺ type region (drain electrode) and the P type well region, and the metal electrode 112 is brought into contact with the surface of the N ⁺ type substrate (source electrode) 106 to complete the device.

Therefore, in this embodiment, when the MOS power transistor is off, a high voltage (eg +3) is applied.
(00 V) is applied between the source electrode 106 and the drain electrode 111, a depletion layer is mainly projected on the N-type breakdown voltage layer 105 to withstand this high voltage. As a result, the N-type breakdown voltage layer 105 becomes the source feedback resistance Rs, and as described above, power loss occurs due to both its own resistance and the channel resistance increasing effect.

However, since the single crystal SiC is used as the material in this embodiment, the thickness and the impurity concentration of the N-type breakdown voltage layer 105 can be greatly improved as compared with the conventional Si.
The design conditions of the N-type breakdown voltage layer 105 when the breakdown voltage of the N-type breakdown voltage layer 105 is 300 V will be considered below. In the case of Si, the breakdown electric field strength is about 30 V / μm, and considering that the breakdown voltage of 300 V is simply borne by the N-type breakdown layer 107,
The required thickness of the breakdown voltage layer is about 20 μm, and its impurity concentration is 1 ×
It is 10 ¹⁵ atoms / cm ³ , and the resistivity is about 5 Ω · cm.

On the other hand, the breakdown electric field strength of SiC is 400 V /
cm, the required thickness of the N-type breakdown voltage layer 105 is about 4 μm.
m, the impurity concentration is 2 × 10 ¹⁶ atoms / cm ³ , and the resistivity is about 1.25 Ω · cm. Therefore, M of SiC
The resistance of the N-type withstand voltage layer 107 of the OS power transistor is S
The resistance can be reduced to 1/20 as compared with the resistance of the N-type breakdown voltage layer 107 of the MOS power transistor of i.

After all, the source parasitic resistance Rs in the SiC MOS power transistor of the present embodiment can be reduced to 1/20 as compared with that of Si, and accordingly, the channel resistance is significantly increased as described above. It is possible to realize a three-phase full-wave rectifier for an automotive alternator with extremely low loss due to their synergistic effect.

That is, N due to the adoption of SiC
By improving the breakdown electric field strength of the die breakdown voltage layer 105,
It has been found that the three-phase full-wave rectifier 19 having excellent efficiency which cannot be predicted from the conventional one can be realized. As a matter of course, the above relationship is the same when a high voltage other than 300 V is applied to the N-type breakdown voltage layer 105. Next, Si diode manufactured with the same chip size and design rule and Si M
Voltage-current characteristics of the OS power transistor and the SiC MOS power transistor are shown in FIGS. However, their breakdown voltage is set to 250V. 6 shows the characteristics of the Si diode, FIG. 7 shows the characteristics of the Si MOS power transistor, and FIG. 8 shows the test characteristics of the SiC MOS power transistor. As can be seen from FIGS. 6 to 8,
Under the condition of an output current of 75 A, the three-phase full-wave rectifier 19 of this embodiment has a power loss of 9 compared to the conventional three-phase full-wave rectifier.
It has become possible to reduce by 0% or more.

FIG. 9 shows an example of the calculation result of the on-resistivity when the required breakdown voltage of the MOS power transistor is changed. Note that this on-resistivity depends on the channel resistance and N
Although it is the sum of the resistance of the N-type breakdown voltage layer 105, the channel resistance fluctuates due to various factors, but as shown in FIG. 9, the resistance of the N-type breakdown voltage layer 105 is dominant in the high breakdown voltage region.

That is, even if the breakdown voltage increases, the channel resistance itself hardly changes (when the increase in the channel resistance due to the feedback effect due to the increase in the source parasitic resistance Rs is ignored), but the resistance of the N-type breakdown voltage layer 105 is a breakdown voltage. Increase while maintaining a positive correlation with. Therefore, in Si, the on-resistance ratio increases proportionally with increasing breakdown voltage from around 25V, but in SiC, the increase in resistance of the N-type breakdown layer 105 is almost negligible up to a breakdown voltage of 250V.
It can be seen that the on-state resistivity slowly increases only when the voltage exceeds 0V.

Next, SiC MOS of the same chip size
10 and 11 show the characteristics of the vehicular AC generator of this embodiment that employs a three-phase full-wave rectifier 19 incorporating a power transistor and a Si MOS power transistor (comparative example).
Shown in. Output current is about 10% (12 poles, 5000 rpm
In addition, since the rectification loss can be almost ignored, the rectification efficiency can be improved by about 3 to 5%.

Further, since the heat generation of the three-phase full-wave rectifier 19 is greatly reduced, the heat radiation fin can be downsized, and the three-phase full-wave rectifier 19 and the voltage adjusting unit 20 can be integrated. Furthermore, the three-phase full-wave rectifier 19 and the voltage adjusting unit 2
By integrating 0 and 0, the wiring connecting them can be omitted, and the electromagnetic noise radiated from this wiring can also be reduced. As shown in FIG. Can be exposed without being directly covered with a cover, and as a result, the space for mounting the three-phase full-wave rectifier 19 on the vehicle alternator can be reduced, and ventilation resistance and ventilation power can be reduced accordingly.

Further, according to this embodiment, as shown in FIG. 11, a 12 pole, 100 A specification generator is operated at 10,000 rpm.
3 phase full wave rectifier of SiC when rotated at
It was found that in No. 9, the noise voltage contained in the rectified output voltage can be reduced by about 20% as compared with the conventional Si three-phase full-wave rectifier. This is a MOS power transistor 1
This is because the resistances of 9a to 19f are small, so that the potential change across the three-phase armature winding 5 due to the opening and closing of the MOS power transistors 19a to 19f is suppressed.

Further, in the above-described embodiment, the voltage regulator 18 with the built-in three-phase full-wave rectifier 19 is housed inside the generator, but the voltage regulator 18 can be arranged outside the generator, and the three-phase generator is provided. The full-wave rectifier 19 and the voltage adjusting unit 20 may be separately configured. 12 is an axial view of the voltage regulator 18 with the built-in three-phase full-wave rectifier 19, and FIG. 13 shows the inside of the voltage regulator 18 with the built-in three-phase full-wave rectifier 19 shown in FIG. It is a perspective enlarged view. (Embodiment 2) Another embodiment of the present invention will be described with reference to FIG.

In this embodiment, only the high-side MOS power transistor of the three-phase full-wave rectifier 19 is made of SiC, and the low-side semiconductor power element is made of a conventional PN diode made of Si. Even in this case, although the effect is reduced as compared with the first embodiment, the effect of loss reduction and simplification of cooling can be achieved. Of course, only the low-side MOS power transistor is Si
Alternatively, the high-side semiconductor power element may be formed of C and may be formed of a conventional PN diode made of Si. Alternatively, a MOS power transistor made of Si may be used instead of the diode. (Embodiment 3) Another embodiment of the present invention will be described with reference to FIG.

In this embodiment, the N ⁺ type substrate 106 constitutes the common source electrode S (see FIG. 1) of each of the high-side MOS power transistors 19a to 19c, and the substrate 106
Individually formed apart enough of each phase P-type well region 103a to 103c only punch-through non distance from each other in the upper, respectively on the surface portion of the P-type well region 103a to 103c N ⁺ -type drain region 104a To 104c are individually formed, and the gate electrodes 110a to 110c are formed on the surface portions of the P-type well regions 103a to 103c via the insulating film 109.
110c is provided and each drain region 104a-104 is provided.
c is the breakdown voltage layer 105 due to the gate electrodes 110a to 110c.
Are individually conducted.

By doing so, there is an excellent effect that a half bridge composed of three high-side MOS power transistors can be integrated on one chip without increasing the number of steps. Further, since the power loss of each of the MOS power transistors 19a to 19c is small, it is possible to avoid the temperature rise of each element due to the integration. (Si-
Analysis of Relationship Between Breakdown Voltage and Resistance Value of MOS Power Transistor and SiC-MOS Power Transistor) The MOS power transistor 1 of each of the above-described embodiments
9a to 19f are made of 6H-SiC as a material and withstand voltage 250V
The 6-phase full-wave rectifier 19 for a vehicle AC generator using the 6H-SiC MOS power transistors 19a to 19f and the vehicle AC generator using a Si MOS power transistor. The theoretical analysis result of the resistance value of the three-phase full-wave rectifier 19 (see FIG. 9) will be described below. However, here, the effect of increasing the channel resistance due to the feedback effect of the source parasitic resistance Rs is ignored.
The circuit structure is the vertical structure shown in FIG. 5, and the chip areas are the same.

[0054] the resistance R of the transistor is the sum of the resistance rb of the channel resistance rc and the N ⁺ -type withstand voltage layer 105, rc = L / W · (1 / μs · εs · εo) -1 · (Tox / ( Vg-Vt)) rb = 4Vb ² · (1 / μ · εs · εo · Ec · A), the resistance value of the SiC MOS power transistor is about 1/15 compared to that of the Si MOS power transistor. It was

However, the breakdown electric field strength Ec is 3 × 1 for Si.
0^Five, SiC is 3 × 10⁶V / cm, relative permittivity εs is S
i is 11.8, SiC is 10.0, and area A is 1 for both.
mm ², Vb is a breakdown voltage (withstand voltage). Change
In addition, μ is the bulk mobility of electrons, and Si is 110
0, SiC is 370 cm²/ (V / S), channel length
L is 1 μm for both, and channel width W is 222 for both
μm and μs are channel mobilities of electrons, and Si is
500, SiC is 100 cm²/ (V · S).

From the above equation, it was found that SiC has a smaller resistance value at a withstand voltage of 50 V or more. Since the substrate is used as the drain in the above calculation, when the substrate is used as the source, the resistance of Si should be remarkably increased due to the increase of the channel resistance due to the feedback effect of the source parasitic resistance Rs described above. Therefore, even if the design rule is changed to some extent, it can be estimated that the SiC MOS power transistor has a low resistance at a withstand voltage of 100 V or more.

In each of the embodiments described above, the P-type well region 103 was formed by ion implantation, but in the structure of FIG. 5, it may be formed by epitaxial growth.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a vehicle AC generator according to an embodiment.

FIG. 2 is a cross-sectional view of the vehicle AC generator of FIG.

FIG. 3 is an equivalent circuit diagram of an inverter circuit showing one phase of the three-phase full-wave rectifier shown in FIG.

FIG. 4 is a partially enlarged cross-sectional view showing an example of a MOS power transistor forming the three-phase full-wave rectifier shown in FIG.

5 is a partially enlarged cross-sectional view showing an example of a MOS power transistor forming the three-phase full-wave rectifier shown in FIG.

FIG. 6 is a voltage-current characteristic diagram of a conventional PN diode made of Si.

FIG. 7 is a voltage-current characteristic diagram of a conventional MOS power transistor made of Si as a material.

FIG. 8 is a voltage-current characteristic diagram of a MOS power transistor made of SiC as a material of the present embodiment.

9 is a diagram showing the relationship between the breakdown voltage and the channel resistance of the MOS power transistors of FIGS. 7 and 8. FIG.

FIG. 10 shows the relationship between the output current and efficiency of the vehicle alternator and the number of revolutions when the Si-MOS power transistor type three-phase full-wave rectifier and the SiC-MOS power transistor type three-phase full-wave rectifier are used. It is a figure.

FIG. 11 is a diagram showing the relationship between the noise voltage and the rotation speed of the vehicle alternator when the Si-MOS power transistor type three-phase full-wave rectifier and the SiC-MOS power transistor type three-phase full-wave rectifier are used. is there.

FIG. 12 is a side view of the rear side of the vehicle alternator seen through the three-phase full-wave rectifier of FIG. 2.

FIG. 13 is an internal perspective plan view of the three-phase full-wave rectifier of FIG.

FIG. 14 is an equivalent circuit diagram showing a second embodiment.

FIG. 15 is a cross-sectional view showing a third embodiment.

[Explanation of symbols]

5 is a three-phase armature winding, 21 is a battery, 19a to 19c
Is a high-side MOS power transistor, 19d-1
9f is a low-side MOS power transistor, 19 is a three-phase full-wave rectifier, 20 is a voltage regulator, and 18 is a voltage regulator.

Claims (9)

[Claims] 1. A high-side MOS power transistor or a low-side MOS power transistor for connecting each end of a three-phase armature winding of an automotive alternator to a high end and a low end of a battery, and a three-phase In a three-phase full-wave rectifier of a vehicle AC generator that converts a generated voltage of an armature winding into a DC voltage to supply power to a battery, the MOS power transistor is formed of SiC as a material. AC generator three-phase full-wave rectifier. 2. A three-phase full-wave rectifier for a vehicle alternator according to claim 1, wherein the three-phase full-wave rectifier has both high-side and low-side MOS power transistors. 3. The on-vehicle AC power generator according to claim 1, wherein the three-phase full-wave rectifier comprises a high-side or low-side MOS power transistor and a PN junction diode forming the remaining semiconductor power element. Machine three-phase full-wave rectifier. 4. The MOS power transistor comprises an N ⁺ type substrate forming a source electrode, an N type withstand voltage layer formed on the substrate, and a P formed on a surface portion of the withstand voltage layer.
A well region, and an N ⁺ -type drain region formed on the surface of the P-type well region to form a drain electrode,
The vehicle AC generator according to claim 1, further comprising: a gate electrode that is provided on a surface portion of the P-type well region via an insulating film and forms an N-type channel that electrically connects the drain region and the breakdown voltage layer. Three-phase full-wave rectifier. 5. The three-phase full-wave rectifier for a vehicle AC generator according to claim 4, wherein the N ⁺ type drain region and the P type well region are short-circuited. 6. The substrate constitutes a common source region of each of the high-side MOS power transistors, the P-type well regions of each phase are individually formed on the substrate, and each P-type well region is formed. The N ⁺ -type drain regions are individually formed on the surface of each of the P + -type well regions, and channels are formed on the surface of each of the P-type well regions to individually conduct the drain regions and the breakdown voltage layers via an insulating film. The three-phase full-wave rectifier for a vehicle AC generator according to claim 5, wherein each gate electrode to be formed is individually arranged. 7. The three-phase full-wave rectifier for a vehicle alternator according to claim 1, wherein the three-phase full-wave rectifier is mounted on the same substrate as a voltage adjusting unit that controls switching of the MOS power transistor. 8. The source of the MOS power transistor
The three-phase full-wave rectifier for a vehicle AC generator according to any one of claims 1 to 7, wherein the breakdown voltage between the drain and the drain-gate is set to 50 V or more. 9. The source of the MOS power transistor
The three-phase full-wave rectifier for a vehicle AC generator according to any one of claims 1 to 7, wherein the breakdown voltage between the drain and the drain-gate is set to 100 V or more.