Patent Publication Number: US-2021193803-A1

Title: Semiconductor module and inverter device

Description:
TECHNICAL FIELD 
     The present invention relates to a semiconductor module and an inverter device. 
     BACKGROUND ART 
     Patent document 1 describes an example of a known semiconductor module including a plurality of switching elements in which a second switching element is laminated on a first switching element with a bus bar located in between. The bus bar includes a two-dimensionally constricted region that is not connected to the two switching elements, and a gate pad exists in the constricted region. The gate pad is electrically connected to a wire. Patent document further describes that silicon carbide (SiC) is used as the switching elements. 
     PRIOR ART DOCUMENTS 
     Patent Document 
     
         
         Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-140068 
       
    
     SUMMARY OF THE PRESENT INVENTION 
     Problems that are to be Solved by the Present Invention 
     Here, the inventors of the present invention have found that in the semiconductor module including the laminated first and second switching elements, heat dissipation decreases when the bus bar includes the constricted region. This may lower the heat resistance of the semiconductor module. In detail, for example, in a configuration in which the second switching element is laminated on the first switching element that has a first element upper surface on which a gate electrode is formed, when the bus bar includes the constricted region to expose the gate electrode of the first switching element, the bus bar does not cover part of a lower surface of the second switching element, or the second element lower surface. In the portion that is not covered with the bus bar, heat is not transferred to the bus bar. This hinders heat dissipation. Therefore, heat may accumulate in the constricted region and lower the heat resistance of the semiconductor module. 
     It is an object of the present invention to provide a semiconductor module and an inverter device that increase heat dissipation in a configuration in which switching elements are laminated. 
     Means for Solving the Problem 
     A semiconductor module that solves the above problem includes a first conductive plate, a first switching element that is placed on the first conductive plate and formed from silicon carbide, a second conductive plate arranged on the first switching element, a second switching element laminated on the second conductive plate and formed from silicon carbide, a third conductive plate arranged on the second switching element, and first and second control terminals. The first switching element includes a first element upper surface, on which a first upper electrode and a first gate electrode with which the first control terminal is joined are formed, and a first element lower surface located at a side opposite to the first element upper surface and on which a first lower electrode joined with the first conductive plate is formed. The second switching element includes a second element upper surface, on which a second upper electrode joined with the third conductive plate and a second gate electrode with which the second control terminal is joined are formed, and a second element lower surface located at a side opposite to the second element upper surface. A second lower electrode is formed on the second element lower surface. The second conductive plate includes a second upper conductive plate surface, on which the second switching element is placed and which is joined with the second lower electrode and covers the entire second element lower surface, and a second lower conductive plate surface, located at a side opposite to the second upper conductive plate surface and facing the first element upper surface. The second lower conductive plate surface includes a projection projecting from the second lower conductive plate surface toward the first element upper surface and joined with the first upper electrode. The projection is located at a position that does not overlap the first gate electrode as viewed in a lamination direction of the first and second switching elements. Part of the first control terminal is located between the first gate electrode and the second lower conductive plate surface. 
     An inverter device that solves the above problem includes the semiconductor module and is configured to drive an electric motor that is arranged in a motor-driven compressor for a vehicle. The inverter device includes a transformer that transforms DC power and an LC filter circuit to which the DC power transformed by the transformer is input. The semiconductor module is configured to convert the DC power output from the LC filter circuit into drive power that allows the electric motor to be driven. 
     A semiconductor module that solves the above problem includes a first conductive plate, a switching element that is placed on the first conductive plate and formed from silicon carbide, a second conductive plate arranged on the switching element, an SiC element that is laminated on the second conductive plate and formed from silicon carbide, and a control terminal. The switching element includes a first element upper surface, on which a first upper electrode and a gate electrode with which the control terminal is joined are formed, and a first element lower surface, located at a side opposite to the first element upper surface and on which a first lower electrode joined with the first conductive plate is formed. The SiC element includes a second element upper surface, on which a second upper electrode is formed, and a second element lower surface, located at a side opposite to the second element upper surface. A second lower electrode is formed on the second element lower surface. The second conductive plate includes a second upper conductive plate surface, on which the SiC element is placed and which is joined with the second lower electrode and covers the entire second element lower surface, and a second lower conductive plate surface, located at a side opposite to the second upper conductive plate surface and facing the first element upper surface. The second lower conductive plate surface includes a projection projecting from the second lower conductive plate surface toward the first element upper surface and joined with the first upper electrode. The projection is located at a position that does not overlap the gate electrode as viewed from a lamination direction of the switching element and the SiC element. Part of the control terminal is located between the gate electrode and the second lower conductive plate surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partially cutaway schematic cross-sectional view showing an inverter module, an inverter device, a motor-driven compressor, and a vehicle air conditioner. 
         FIG. 2  is a circuit diagram illustrating the electric configuration of the motor-driven compressor in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line  3 - 3  in  FIG. 1 . 
         FIG. 4  is a front view of the inverter module shown in  FIG. 1 . 
         FIG. 5  is an exploded perspective view of the inverter module shown in  FIG. 4 . 
         FIG. 6  is an exploded perspective view of the inverter module shown in  FIG. 4 . 
         FIG. 7  is a cross-sectional view taken along line  7 - 7  in  FIG. 4 . 
         FIG. 8  is a cross-sectional view taken along line  8 - 8  in  FIG. 4 . 
         FIG. 9  is a schematic cross-sectional view illustrating an inverter module of another example. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     One embodiment of a semiconductor module, an inverter device including the semiconductor module, and a motor-driven compressor including the inverter device will now be described. The motor-driven compressor of the present embodiment is installed in a vehicle and used in a vehicle air conditioner. 
     As illustrated in  FIG. 1 , a vehicle air conditioner  100  includes a motor-driven compressor  10 , and an external refrigerant circuit  101  that supplies refrigerant serving as a fluid to the motor-driven compressor  10 . For example, the external refrigerant circuit  101  includes a heat exchanger, an expansion valve, and the like. In the vehicle air conditioner  100 , the motor-driven compressor  10  compresses the refrigerant and the external refrigerant circuit  101  exchanges heat with and expands the refrigerant to heat and cool that passenger compartment. 
     The vehicle air conditioner  100  includes an air conditioning ECU  102  that entirely controls the vehicle air conditioner  100 . The air conditioning ECU  102  is configured to recognize the passenger compartment temperature, a set temperature (target temperature) set by a user. Based on these parameters, the air conditioning ECU  102  transmits various commands, such as ON/OFF commands, to the motor-driven compressor  10 . 
     The motor-driven compressor  10  includes a housing  11 , a compression unit  12 , and an electric motor  13 . The housing  11  includes a suction port  11   a  through which a refrigerant is drawn from the external refrigerant circuit  101 . The compression unit  12  and the electric motor  13  are accommodated in the housing  11 . 
     The housing  11  is substantially cylindrical as a whole and formed from a heat conductive material (for example, a metal such as aluminum). The housing  11  includes discharge port  11   b  through which the refrigerant is discharged. 
     When a rotation shaft  21 , which will be described later rotates, the compression unit  12  compresses the refrigerant drawn through the suction port  11   a  into the housing  11  and discharges the compressed refrigerant from the discharge port  11   b . Furthermore, the specific configuration of the compression unit  12  may be of any type, such as a scroll type, a piston type, or a vane type. 
     The electric motor  13  drives the compression unit  12 . The electric motor  13  includes, for example, the rod-shaped rotation shaft  21  that is supported in a rotatable manner by the housing  11 , a cylindrical rotor  22  that is fixed to the rotation shaft  21 , and a stator  23  that is fixed to the housing  11 . An axial direction of the rotation shaft  21  coincides with an axial direction of the cylindrical housing  11 . The stator  23  includes a cylindrical stator core  24  and coils  25  that are wound around teeth of the stator core  24 . The rotor  22  is opposed to the stator  23  in a radial direction of the rotation shaft  21 . When the coils  25  are energized, the rotor  22  and the rotation shaft  21  rotate, and the compression unit  12  compresses the refrigerant. 
     As illustrated in  FIG. 2 , the coils  25  have a three-phase construction that includes a U-phase coil  25   u , a V-phase coil  25   v , and a W-phase coil  25   w . For example, the coils  25   u  to  25   w  form a Y-connection. 
     As illustrated in  FIG. 1 , the motor-driven compressor  10  includes an inverter device  30  that drives the electric motor  13 , and an inverter case  31  in which the inverter device  30  is accommodated. 
     The inverter case  31  is formed from a heat conductive material (for example, a metal such as aluminum). The inverter case  31  includes a plate-shaped base member  32  and a tubular cover member  33 . Among the two axial walls of the housing  11 , the inverter case  31  is in contact with the wall  11   c  located at the side opposite to the discharge port lib. The cover member  33  is coupled to the base member  32 . The base member  32  and the cover member  33  are fixed to the housing  11  by bolt  34  serving as fasteners. Thus, the inverter case  31  and the inverter device  30 , which is accommodated in the inverter case  31 , are coupled to the housing  11 . That is, the inverter device  30  of the present embodiment is integrated with the motor-driven compressor  10 . 
     The inverter case  31  and the housing  11  are in contact and thus thermally coupled to each other. In addition, the inverter device  30  is thermally coupled to the housing  11  through the inverter case  31 . 
     A connector  35  is provided on the inverter case  31  (specifically, the cover member  33 ). The connector  35  supplies the inverter device  30  with DC power from a DC power supply E, which is installed in a vehicle, and electrically connects the air conditioning ECU  102  and the inverter device  30 . The DC power supply E is, for example, an electricity storage device such as a rechargeable battery or an electric double-layer capacitor that are installed in the vehicle. 
     As illustrated in  FIG. 2  and  FIG. 3 , the inverter device  30  includes a transformer  41  and a filter circuit  42 . The transformer  41  transforms the DC power supplied from the DC power supply E. The DC power transformed by the transformer  41  is input to the filter circuit  42 . In addition, the inverter device  30  includes an inverter module  43  and a controller  44 . The inverter module  43  converts the DC power output from the filter circuit  42  into AC power that can drive the electric motor  13  as a semiconductor module. The controller  44  that controls the inverter module  43 . The inverter module  43  is electrically connected to the coils  25  of the electric motor  13  by hermetic terminals (not illustrated) extending through both of the wall  11   c  of the housing  11  and the base member  32 . 
     The electric configuration of the inverter device  30  will now be described. 
     As illustrated in  FIG. 2 , in the transformer  41 , a primary coil is connected to the DC power supply E, and a secondary coil is connected to the filter circuit  42 . A transformation ratio of the transformer  41  is set in correspondence with the voltage at the DC power supply E so that the voltage of DC power output from the transformer  41  is a value suitable for driving the electric motor  13 . 
     The filter circuit  42  is an LC filter circuit configured by a filter coil  42   a  and a filter capacitor  42   b . The filter circuit  42  is a low-pass filter circuit that reduces noise at frequencies higher than a threshold frequency (for example, a cut-off frequency) that is determined in advance. The filter circuit  42  reduces high-frequency noise of the DC power output from the transformer  41  and transfers the DC power. The filter circuit  42  also restricts the emission of high-frequency noise, which is generated from the inverter module  43 , to the outside of the inverter device  30 . 
     In addition, the cut-off frequency of the filter circuit  42  is based on the inductance of the filter coil  42   a  and the capacitance of the filter capacitor  42   b.    
     Furthermore, the filter capacitor  42   b  of the present embodiment is a film capacitor. However, the filter capacitor  42   b  is not limited to a film capacitor and may be an electrolytic capacitor or the like. 
     The inverter module  43  includes two input terminals  43   a  and  43   b  and three output terminals  43   u  to  43   w . Both of the input terminals  43   a  and  43   b  are electrically connected to the filter circuit  42 . The three output terminals  43   u  to  43   w  are electrically connected to the electric motor  13 . 
     The inverter module  43  includes U-phase switching elements  51   u  and  52   u  corresponding to the U-phase coil  25   u , V-phase switching elements  51   v  and  52   v  corresponding to the V-phase coil  25   v , and W-phase switching elements  51   w  and  52   w  corresponding to the W-phase coil  25   w.    
     For example, the switching elements  51   u  to  52   w  are power switching elements such as IGBTs. The switching elements  51   u  to  52   w  are constructed by using silicon carbide (SiC). For example, the switching elements  51   u  to  52   w  are configured by a silicon carbide substrate including a drift region and a body region. 
     The U-phase switching elements  51   u  and  52   u  are connected to each other in series by a connection line, and the connection line is connected to the U-phase coil  25   u  via the U-phase output terminal  43   u . In addition, DC power from the filter circuit  42  is input to a series-connected body of the U-phase switching elements  51   u  and  52   u . Specifically, the collector of the U-phase upper arm switching element  51   u  is connected to the first input terminal  43   a . The emitter of the U-phase lower arm switching element  52   u  is connected to the second input terminal  43   b.    
     Furthermore, the other switching elements  51   v ,  52   v ,  51   w , and  52   w  are connected in the same manner as the U-phase switching elements  51   u  and  52   u  except in that the corresponding output terminals and coil are different. Thus, such connection will not be described. 
     As illustrated in  FIG. 2 , the inverter module  43  includes freewheeling diodes  53   u  to  54   w  (body diodes) which are connected in inverse-parallel to the switching elements  51   u  to  52   w . Specifically, the anodes of the freewheeling diodes  53   u  to  54   w  are respectively connected to the emitters of the switching elements  51   u  to  52   w , and the cathodes of the freewheeling diodes  53   u  to  54   w  are respectively connected to the collectors of the switching elements  51   u  to  52   w.    
     Furthermore, to simplify the description, the switching elements  51   u ,  51   v , and  51   w  of the upper arm will hereafter simply referred to as upper arm switching elements  51   u  to  51   w , and the switching elements  52   u ,  52   v , and  52   w  of the lower arm will hereafter simply be referred to as the lower arm switching elements  52   u  to  52   w . In the same manner, the freewheeling diodes  53   u ,  53   v , and  53   w , which are connected in inverse-parallel, to the upper arm switching elements  51   u  to  51   w  will hereafter simply be referred to as the upper arm freewheeling diodes  53   u  to  53   w , and the freewheeling diodes  54   u ,  54   v , and  54   w , which are connected in inverse-parallel, to the lower arm switching elements  52   u  to  52   w , will simply be referred to as the lower arm freewheeling diodes  54   u  to  54   w.    
     In the present embodiment, the upper arm switching elements  51   u  to  51   w  each correspond to “a first switching element,” and the lower arm switching elements  52   u  to  52   w  correspond to “a second switching element.” 
     The controller  44  is connected to the gates of the switching elements  51   u  to  52   w  and controls switching operations of the switching elements  51   u  to  52   w . The controller  44  is electrically connected to the air conditioning ECU  102  via the connector  35  and cyclically turns the switching elements  51   u  to  52   w  on and off based on commands from the air conditioning ECU  102 . For example, the controller  44  performs pulse width modulation (PWM) control on the inverter module  43 . However, the specific control mode of the controller  44  is not limited to PWM control, and any control may be performed instead. 
     As illustrated in  FIG. 3 , the transformer  41 , the filter coil  42   a , the filter capacitor  42   b , and the inverter module  43  are attached to the base member  32  of the inverter case  31 . The base member  32  has a circular shape as viewed in an axial direction of the rotation shaft  21 . The filter coil  42   a  and the filter capacitor  42   b  are arranged next to each other in one direction near the center of the base member  32 . The inverter module  43  and the transformer  41  are arranged at the two sides of the base member  32  in a direction perpendicular to the layout direction of the filter coil  42   a  and the filter capacitor  42   b . In other words, the inverter module  43  is located at the side of the filter coil  42   a  and the filter capacitor  42   b  opposite to the transformer  41 . Furthermore, in the present embodiment, the controller  44  is provided separately from the inverter module  43  but instead may be incorporated in the inverter module  43 . 
     The structure of the inverter module  43  will now be described. 
     As illustrated in  FIGS. 4 and 5 , the inverter module  43  includes an insulation substrate  60  and a first conductive plate  61  that is mounted on the insulation substrate  60 . The upper arm switching elements  51   u  to  51   w  and the upper arm freewheeling diodes  53   u  to  53   w  are placed on the first conductive plate  61 . 
     The inverter module  43  includes second conductive plates  62   u  to  62   w  which are provided on the upper arm switching elements  51   u  to  51   w  and the upper arm freewheeling diodes  53   u  to  53   w . The lower arm switching elements  52   u  to  52   w  are laminated on the upper arm switching elements  51   u  to  51   w  with the second conductive plates  62   u  to  62   w  located in between. The lower arm freewheeling diodes  54   u  to  54   w  are laminated on the upper arm freewheeling diodes  53   u  to  53   w  with the second conductive plates  62   u  to  62   w  located in between. In addition, the inverter module  43  includes a third conductive plate  63  that is provided on the lower arm switching elements  52   u  to  52   w  and the lower arm freewheeling diodes  54   u  to  54   w.    
     The inverter module  43  has a structure in which the order of lamination from the insulation substrate  60  is the first conductive plate  61 , the upper arm switching elements  51   u  to  51   w  and the upper arm freewheeling diodes  53   u  to  53   w , the second conductive plates  62   u  to  62   w , the lower arm switching elements  52   u  to  52   w  and the lower arm freewheeling diodes  54   u  to  54   w , and the third conductive plate  63 . 
     Here, a unit including both of the U-phase switching elements  51   u  and  52   u , both of the U-phase freewheeling diodes  53   u  and  54   u , the U-phase second conductive plate  62   u , and the like is set as a U-phase unit  64   u . In the same manner, a unit including both of the V-phase switching elements  51   v  and  52   v , both of the V-phase freewheeling diodes  53   v  and  54   v , the V-phase second conductive plate  62   v , and the like is set as a V-phase unit  64   v , and a unit including both of the W-phase switching elements  51   w  and  52   w , both of the W-phase freewheeling diodes  53   w  and  54   w , the W-phase second conductive plate  62   w  is seL as a W-phase unit  64   w . The units  64   u  to  64   w  have the same construction. 
     In addition to the first conductive plate  61 , the insulation substrate  60  includes a plurality of control pads  71   u  to  72   w  that electrically connect the switching elements  51   u  to  52   w  and the controller  44 . The inverter module  43  includes control terminals  73   u  to  74   w  that electrically connect the switching elements  51   u  to  52   w  and the control pads  71   u  to  72   w . Specifically, the U-phase unit  64   u  includes the U-phase upper arm control terminal  73   u , which electrically connects the U-phase upper arm switching element  51   u  and the U-phase upper arm control pad  71   u , and the U-phase lower arm control terminal  74   u , which electrically connects the U-phase lower arm switching element  52   u  and the U-phase lower arm control pad  72   u . The V-phase unit  64   v  includes a V-phase upper arm control terminal  73   v , which electrically connects the V-phase upper arm switching element  51   v  and a V-phase upper arm control pad  71   v , and a V-phase lower arm control terminal  74   v , which electrically connects the V-phase lower arm switching element  52   v  and a V-phase lower arm control pad  72   v . The W-phase unit  64   w  includes a W-phase upper arm control terminal  73   w , which electrically connects the W-phase upper arm switching element  51   w  and a W-phase upper arm control pad  71   w , and a W-phase lower arm control terminal  74   w , which electrically connects the W-phase lower arm switching element  52   w  and a W-phase lower arm control pad  72   w . The upper arm control terminals  73   u  to  73   w  each correspond to “a first control terminal” and the lower arm control terminals  74   u  to  74   w  each correspond to “a second control terminal.” 
     Each element of the inverter module  43  will now be described in detail. 
     As illustrated in  FIGS. 5 and 6 , the switching elements  51   u  to  52   w  each have a generally rectangular parallelepiped form as a whole. The switching elements  51   u  to  52   w  include element lower surfaces  51   au  to  52   aw  and element upper surfaces  51   bu  to  52   bw . As illustrated in  FIG. 6 , collector electrodes  51   cu  and  52   cw  are formed on the element lower surfaces  51   au  to  52   aw . The collector electrodes  51   cu  to  52   cw  are formed entirely by the element lower surfaces  51   au  to  52   aw.    
     As illustrated in  FIG. 5 , emitter electrodes  51   eu  to  52   ew  and gate electrodes  51   gu  to  52   gw  are formed on the element upper surfaces  51   bu  to  52   bw  of the switching elements  51   u  to  52   w . The emitter electrodes  51   eu  to  52   ew  are formed to be larger than the gate electrodes  51   gu  to  52   gw . Each of the emitter electrodes  51   eu  to  52   ew  and each of the gate electrodes  51   gu  to  52   gw  are spaced apart from each other in an X direction on the element upper surfaces  51   bu  to  52   bw . Furthermore, an insulation layer is formed at portion other than the emitter electrodes  51   eu  to  52   ew  and the gate electrodes  51   gu  and  52   gw  on the element upper surfaces  51   bu  to  52   bw.    
     The upper arm emitter electrodes  51   eu  to  51   ew  each correspond to “a first upper electrode,” the upper arm gate electrodes  51   gu  to  51   gw  each correspond to “a first gate electrode,” and the upper arm element upper surfaces  51   bu  to  51   bw  each correspond to “a first element upper surface.” In addition, the upper arm collector electrodes  51   cu  to  51   cw  each correspond to “a first lower electrode,” and the upper arm element lower surfaces  51   au  to  51   aw  each correspond to “a first element lower surface.” 
     In addition, the lower arm emitter electrodes  52   eu  to  52   ew  each correspond to “a second upper electrode,” the lower arm gate electrodes  52   gu  to  52   gw  each correspond to “a second gate electrode,” and the lower arm element upper surfaces  52   bw  to  52   bw  each correspond to “a second element upper surface.” In addition, the lower arm collector electrodes  52   cu  to  52   cw  each correspond to “a second lower electrode,” and the lower arm element lower surfaces  52   au  to  52   aw  each correspond to “second element lower surface.” 
     The freewheeling diodes  53   u  to  54   w  each have a generally rectangular parallelepiped form as a whole. The freewheeling diodes  53   u  to  54   w  include a diode lower surface on which cathode electrodes  53   cu  to  54   cw  are formed, and a diode upper surface on which anode electrodes  53   au  to  54   aw  are formed. The cathode electrodes  53   cu  to  54   cw  are formed entirely by the diode lower surface. The anode electrodes  53   au  to  54   aw  are formed to be slightly smaller than the diode upper surface. Furthermore, an insulation layer is formed at portions other than the anode electrodes  53   au  to  54   aw  in the diode upper surface. 
     As illustrated in  FIG. 5 , the insulation substrate  60  has a rectangular plate shape with rounded corners. Coupling holes  60   a  are formed in the two longitudinal ends of the insulation substrate  60 . Fasteners such as screws are inserted through the coupling holes  60   a  and engaged with the base member  32  to fix the insulation substrate  60  to the base member  32  in a state in which a thickness direction of the insulation substrate  60  coincides with the axial direction of the rotation shaft  21 . This fixes the inverter module  43  to the base member  32 . In this case, the insulation substrate  60  can exchange heat with the refrigerant through the base member  32  and the housing  11 . 
     To simplify description, the longitudinal direction of the insulation substrate  60  will hereafter be referred to as the X direction, and the transverse direction of the insulation substrate  60  will hereafter be referred to as the Y direction. In addition, the lamination direction of the upper arm switching elements  51   u  to  51   w  and the lower arm switching elements  52   u  to  52   w  will hereafter be referred to as the Z direction. In addition, in the Z direction, a direction from the insulation substrate  60  toward the third conductive plate  63  will hereafter be referred to as the upper direction, and a direction from the third conductive plate  63  toward the insulation substrate  60  will hereafter be referred to as the lower direction. The Z direction may also be referred to as the thickness direction of the insulation substrate  60 . 
     The Z direction that is the lamination direction of the upper arm switching elements  51   u  to  51   w  and the lower arm switching elements  52   u  to  52   w  is not limited to the vertical direction or the horizontal direction and may be any direction such as a direction that intersects both of the vertical direction and the horizontal direction. In the present embodiment, the Z direction coincides with the axial direction of the rotation shaft  21 . In the same manner, to simplify description, the upper direction and the lower direction are used to illustrate the positional relationship of the switching elements  51   u  to  52   w  and are not limited to the vertical direction (gravity direction). 
     As illustrated in  FIGS. 4 and 5 , the first conductive plate  61  has a plate shape and extends in the X direction that is the layout direction of the units  64   u  to  64   w . Further, the first conductive plate  61  is provided between the two coupling holes  60   a  of the insulation substrate  60 . The first conductive plate  61  includes a first base portion  61   a  having a rectangular plate shape in which the X direction is the longitudinal direction, and a first input terminal  43   a  that projects from one longitudinal end surface of the first base portion  61   a  in the X direction. In addition, the control pads  71   u  to  72   w  are provided at positions spaced apart from the first conductive plate  61  in the Y direction and are spaced apart from one another in the X direction. 
     The units  64   u  to  64   w  are provided on the first conductive plate  61  in a state aligned in the X direction that is the longitudinal direction of the insulation substrate  60 . Specifically, the upper arm switching elements  51   u  to  51   w  are spaced apart from one another by a predetermined gap and aligned in the X direction on the first conductive plate  61 . The upper arm freewheeling diodes  53   u  to  53   w  are arranged on the first conductive plate  61  at positions spaced apart from the upper arm switching elements  51   u  to  51   w  in a direction (specifically, the Y direction) that is perpendicular to the layout direction of the upper arm switching elements  51   u  to  51   w . In this case, in the same manner as the upper arm switching elements  51   u  to  51   w , the upper arm freewheeling diodes  53   u  to  53   w  are spaced apart from one another by a predetermined gap and aligned in the X direction. 
     The upper arm collector electrodes  51   cu  to  51   cw  are joined with the first conductive plate  61  by a conductive joining material J such as solder or a silver paste. In addition, the upper arm cathode electrodes  53   cu  to  53   cw  are joined with the first conductive plate  61  by the joining material J. Consequently, the same phases in the upper arm collector electrodes  51   cu  to  51   cw  and the upper arm cathode electrodes  53   cu  to  53   cw  are electrically connected with one another, and the upper arm collector electrodes  51   cu  to  51   cw  are electrically connected to one another. 
     When describing the configuration of the U-phase unit  64   u  in detail, as illustrated in  FIGS. 5 and 6 , the U-phase second conductive plate  62   u  of the U-phase unit  64   u  has a rectangular plate shape in which the Y direction that is the layout direction of the U-phase upper arm switching element  51   u  and the U-phase upper arm freewheeling diode  53   u  is set as the longitudinal direction. The U-phase second conductive plate  62   u  is sized to cover both of the U-phase upper arm switching element  51   u  and the U-phase upper arm freewheeling diode  53   u  from the upper side. The U-phase second conductive plate  62   u  includes a U-phase output terminal  43   u  projecting from one longitudinal end surface in a direction (specifically, the Y direction) that is perpendicular to the one longitudinal end surface. 
     The U-phase second conductive plate  62   u  includes a U-phase second lower conductive plate surface  62   au  and a U-phase second upper conductive plate surface  62   bu . The U-phase second lower conductive plate surface  62   au , which is a surface opposite to the U-phase second upper conductive plate surface  62   bu , faces the U-phase upper arm element upper surface  51   bu  in the Z direction. 
     As illustrated in  FIGS. 6 to 8 , a U-phase first projection  81   u  and a U-phase second projection  82   u , which project from the U-phase second lower conductive plate surface  62   au  toward the U-phase upper arm element upper surface  51   bu  (specifically, toward a lower side), are provided on the U-phase second lower conductive plate surface  62   au . In the present embodiment, both of the projections  81   u  and  82   u  are formed from the same material as the U-phase second conductive plate  62   u  and are formed integrally with the U-phase second conductive plate  62   u . Accordingly, the projections  81   u  and  82   u  are electrically connected to the U-phase second conductive plate  62   u . Both of the projections  81   u  and  82   u  on the U-phase second lower conductive plate surface  62   au  are set to have the same projecting dimension. 
     As illustrated in  FIGS. 6 and 7 , the U-phase first projection  81   u  is provided at a position that does not overlap the U-phase upper arm gate electrode  51   gu  and overlaps the U-phase upper arm emitter electrode  51   eu  as viewed in the Z direction. The U-phase first projection  81   u  is shaped to be located in a projection range of the U-phase upper arm emitter electrode  51   eu  as viewed from the Z direction. Specifically, the U-phase first projection  81   u  has the same shape as the U-phase upper arm emitter electrode  51   eu  as viewed in the Z direction. As illustrated in  FIGS. 7 and 8 , the U-phase first projection  81   u  is joined with the U-phase upper arm emitter electrode  51   eu  by the joining material J. In this case, the U-phase first projection  81   u  is in contact with the entire U-phase upper arm emitter electrode  51   eu  through the joining material J. 
     The U-phase second projection  82   u  is provided at a position that does not overlap the U-phase upper arm gate electrode  51   gu  and overlaps the U-phase upper arm anode electrode  53   au  as viewed in the Z direction. The U-phase second projection  82   u  is shaped to be located in a projection range of the U-phase upper arm anode electrode  53   au  as viewed in the Z direction. Specifically, the U-phase second projection  82   u  has the same shape as the U-phase upper arm anode electrode  53   au  as viewed in the Z direction. As illustrated in  FIG. 8 , the U-phase second projection  82   u  is joined with the U-phase upper arm anode electrode  53   au  through the joining material J. Thus, the U-phase upper arm anode electrode  53   au  and the U-phase upper arm emitter electrode  51   eu  are electrically connected to each other by the U-phase second conductive plate  62   u . That is, the first conductive plate  61  and the U-phase second conductive plate  62   u  function to connect the U-phase upper arm freewheeling diode  53   u  to the U-phase upper arm switching element  51   u  in an inverse-parallel manner. 
     Here, both of the projections  81   u  and  82   u  are arranged not to overlap the U-phase upper arm gate electrode  51   gu . Accordingly, as illustrated in  FIG. 7 , a U-phase terminal region A, which is a gap corresponding to the projecting dimensions of both of the projections  81   u  and  82   u , is formed between the U-phase upper arm gate electrode  51   gu  and the U-phase second lower conductive plate surface  62   au.    
     As illustrated in  FIGS. 7 and 8 , the U-phase upper arm control terminal  73   u  is joined with both of the U-phase upper arm gate electrode  51   gu  and the U-phase upper arm control pad  71   u  in a state in which part of the U-phase upper arm control terminal  73   u  is located in the U-phase terminal region A. The U-phase upper arm control pad  71   u  is arranged at a position spaced apart from the U-phase upper arm gate electrode  51   gu  in the Y direction. As illustrated in  FIGS. 5 and 8 , the U-phase upper arm control terminal  73   u  is shaped to extend in the Y direction as viewed in the Z direction and has the form of a reversed U as viewed from the X direction. The U-phase upper arm control terminal  73   u  includes a terminal base portion  73   au  that extends in the Y direction, a terminal base end  73   bu  that downwardly extends from one end of the terminal base portion  73   au  and is joined with the U-phase upper arm control pad  71   u , and a terminal distal end  73   cu  that downwardly extends from the other end that is opposite to the one end and is joined with the U-phase upper arm gate electrode  51   gu . The terminal distal end  73   cu  has a length set to be shorter than the projecting dimensions of both of the projections  81   u  and  82   u . As illustrated in  FIG. 7 , the entire terminal distal end  73   cu  and part of the terminal base portion  73   au  are located in the U-phase terminal region A. Part of the U-phase upper arm control terminal  73   u  projects from both of the U-phase switching elements  51   u  and  52   u  in the Y direction as viewed in the Z direction and does not project in the X direction. 
     As illustrated in  FIGS. 5 and 8 , the U-phase lower arm switching element  52   u  and the U-phase lower arm freewheeling diode  54   u  are placed on the U-phase second upper conductive plate surface  62   bu . The U-phase second upper conductive plate surface  62   bu  is formed to be wider than the U-phase lower arm collector electrode  52   cu  (i.e., U-phase lower arm element lower surface  52   au ) and joined with (i.e., in contact with) the entire U-phase lower arm collector electrode  52   cu  through the joining material J. That is, the U-phase second upper conductive plate surface  62   bu  covers the entire U-phase lower arm element lower surface  52   au.    
     The U-phase lower arm cathode electrode  54   cu  is joined with the U-phase second upper conductive plate surface  62   bu  through the joining material J. Thus, the U-phase lower arm cathode electrode  54   cu  and the U-phase lower arm collector electrode  52   cu  are electrically connected to each other by the U-phase second conductive plate  62   u.    
     Here, in the present embodiment, the U-phase lower arm switching element  52   u  and the U-phase upper arm switching element  51   u  are laminated so that the entire U-phase lower arm switching element  52   u  and the entire U-phase upper arm switching element  51   u  overlap each other as viewed in the Z direction. Specifically, the U-phase lower arm switching element  52   u  and the U-phase upper arm switching element  51   u  are laminated in a state in which a peripheral edge  52   xu  of the U-phase lower arm switching element  52   u  and a peripheral edge  51   xu  of the U-phase upper arm switching element  51   u  are aligned in the Z direction. In the same manner, the U-phase lower arm freewheeling diode  54   u  and the U-phase upper arm freewheeling diode  53   u  are laminated in a state in which peripheral edges thereof are aligned in the Z direction. 
     Furthermore, the V-phase second conductive plate  62   v  and the W-phase second conductive plate  62   w  have the same shape as the U-phase second conductive plate  62   u . In addition, the lamination structure of the upper and lower arms of the V-phase and the W-phase is the same as the lamination structure of the upper and lower arms of the U-phase. 
     As illustrated in  FIGS. 5 and 6 , the V-phase second conductive plate  62   v  includes a V-phase second upper conductive plate surface  62   bv , on which the V-phase lower arm switching element  52   v  and the V-phase lower arm freewheeling diode  54   v  are placed, and a V-phase second lower conductive plate surface  62   av  that is opposite to the V-phase second upper conductive plate surface  62   bv  and faces the V-phase upper arm element upper surface  51   bv . A V-phase lower arm collector electrode  52   cv  and a V-phase lower arm cathode electrode  54   cv  are joined with the V-phase second upper conductive plate surface  62   bv . A V-phase first projection  81   v  and a V-phase second projection  82   v , which project from the V-phase second lower conductive plate surface  62   av  toward the V-phase upper arm element upper surface  51   bv  and are arranged at positions that do not overlap a V-phase upper arm gate electrode  51   gv , are provided on the V-phase second lower conductive plate surface  62   ay . The V-phase first projection  81   v  and a V-phase upper arm emitter electrode  51   ev  are joined with each other, and the V-phase second projection  82   v  and a V-phase upper arm anode electrode  53   av  are joined with each other. In addition, the V-phase upper arm control terminal  73   v  is joined with the V-phase upper arm gate electrode  51   gv  in a state in which part of the V-phase upper arm control terminal  73   v  is located between the V-phase upper arm gate electrode  51   gv  and the V-phase second lower conductive plate surface  62   ay.    
     In the same manner, the W-phase second conductive plate  62   w  includes a W-phase second upper conductive plate surface  62   bw , on which the W-phase lower arm switching element  52   w  and the W-phase lower arm freewheeling diode  54   w  are placed, and a W-phase second lower conductive plate surface  62   aw  that is opposite to the W-phase second upper conductive plate surface  62   bw  and faces the W-phase upper arm element upper surface  51   bw . The W-phase lower arm collector electrode  52   cw  and the W-phase lower arm cathode electrode  54   cw  are joined with the W-phase second upper conductive plate surface  62   bw . The W-phase first projection  81   w  and the W-phase second projection  82   w , which project from the W-phase second lower conductive plate surface  62   aw  toward the W-phase upper arm element upper surface  51   bw  and are arranged at positions that do not overlap a W-phase upper arm gate electrode  51   gw , are provided on the W-phase second lower conductive plate surface  62   aw . The W-phase first projection  81   w  and the W-phase upper arm emitter electrode  51   ew  are joined with each other, and the W-phase second projection  82   w  and a W-phase upper arm anode electrode  53   aw  are joined with each other. In addition, the W-phase upper arm control terminal  73   w  is joined with the W-phase upper arm gate electrode  51   gw  in a state in which part of the W-phase upper arm control terminal  73   w  is located between the W-phase upper arm gate electrode  51   gw  and the W-phase second lower conductive plate surface  62   aw . Furthermore, the first projections  81   u  to  81   w  each correspond to a “first switching element projection.” 
     The third conductive plate  63  is joined with the lower arm emitter electrodes  52   eu  to  52   ew  and the lower arm anode electrodes  54   au  to  54   aw . As illustrated in  FIGS. 5 and 6 , the third conductive plate  63  includes a U-phase conductive part  63   u  that is arranged on an upper side of the U-phase second conductive plate  62   u , a V-phase conductive part  63   v  that is arranged on an upper side of the V-phase second conductive plate  62   v , a W-phase conductive part  63   w  that is arranged on an upper side of the W-phase second conductive plate  62   w , and the second input terminal  43   b  that projects from the U-phase conductive part  63   u  in the X direction. 
     The conductive parts  63   u  to  63   w  have the same shape. The conductive parts  63   u  to  63   w , which are each T-shaped as viewed in the Z direction, respectively include first extension portions  63   au  to  63   aw , which extend in the X direction, and second extension portions  63   bu  to  63   bw , which extend from the first extension portions  63   au  to  63   aw  in the Y direction. The first extension portions  63   au  to  63   aw  are connected to each other. That is, the conductive parts  63   u  to  63   w  are connected to each other in a state laid out in the X direction. The third conductive plate  63  extends in the X direction as a whole. 
     Lamination structures of the conductive parts  63   u  to  63   w  and the lower arm switching elements  52   u  to  52   w  are basically the same. Thus, only the U-phase will now be described in detail. 
     The U-phase conductive part  63   u  is laid out so that the U-phase first extension portion  63   au  overlaps the U-phase lower arm freewheeling diode  54   u  and the U-phase second extension portion  63   bu  overlaps the U-phase lower arm switching element  52   u  as viewed in the Z direction. 
     As illustrated in  FIG. 7 , the U-phase lower arm gate electrode  52   gu  and the U-phase upper arm gate electrode  51   gu  are provided at positions offset from each other as viewed in the Z direction. Specifically, both of the gate electrodes  51   gu  and  52   gu  of the U-phase are arranged to be spaced apart from each other in the X-direction as viewed in the Z direction. In the present embodiment, the positional relationship between the U-phase upper arm gate electrode  51   gu  and the U-phase upper arm emitter electrode  51   eu  on the U-phase upper arm element upper surface  51   bu  is set to be reversed from the positional relationship between the U-phase lower arm gate electrode  52   gu  and the U-phase lower arm emitter electrode  52   eu  on the U-phase lower arm element lower surface  52   au.    
     The U-phase second extension portion  63   bu  covers the U-phase lower arm emitter electrode  52   eu  so as not to overlap the U-phase lower arm gate electrode  52   gu  as viewed in the Z direction. Accordingly, the U-phase lower arm gate electrode  52   gu  is open to an upper side. 
     As illustrated in  FIGS. 6 and 7 , the U-phase conductive part  63   u  includes a U-phase third lower conductive plate surface  63   cu  that faces the U-phase lower arm element upper surface  52   bu . A U-phase third projection  83   u  and a U-phase fourth projection  84   u , which project from the U-phase third lower conductive plate surface  63   cu  toward the U-phase lower arm element upper surface  52   bu , are provided on the U-phase third lower conductive plate surface  63   cu . In the present embodiment, the U-phase third projection  83   u  and the U-phase fourth projection  84   u  are formed from the same material as the U-phase conductive part  63   u  and integrally with the U-phase conductive part  63   u . Accordingly, the projections  83   u  and  84   u  are electrically connected to the U-phase conductive part  63   u.    
     The U-phase third projection  83   u  is provided at a position that overlaps the U-phase lower arm emitter electrode  52   eu  as viewed in the Z direction. Specifically, the U-phase third projection  83   u  projects toward a lower side from a portion corresponding to a distal end of the U-phase second extension portion  63   bu  in the U-phase third lower conductive plate surface  63   cu . The U-phase third projection  83   u  is shaped to be located in a projection range of the U-phase lower arm emitter electrode  52   eu  as viewed in the Z direction. Specifically, the U-phase third projection  83   u  has the same shape as the U-phase lower arm emitter electrode  52   eu  as viewed in the Z direction. As illustrated in  FIGS. 7 and 8 , the U-phase third projection  83   u  is joined with the U-phase lower arm emitter electrode  52   eu  by the joining material J. In this case, the U-phase third projection  83   u  is in contact with the entire U-phase lower arm emitter electrode  52   eu  through the joining material J. 
     As illustrated in  FIGS. 6 and 8 , the U-phase fourth projection  84   u  is provided at a position that overlaps the U-phase lower arm anode electrode  54   au  as viewed in the Z direction. Specifically, the U-phase fourth projection  84   u  projects to a lower side from a portion corresponding to the U-phase first extension portion  63   au  in the U-phase third lower conductive plate surface  63   cu . The U-phase fourth projection  84   u  is shaped to be located in a projection range of the U-phase lower arm anode electrode  54   au  as viewed in the Z direction. Specifically, the U-phase fourth projection  84   u  has the same shape as the U-phase lower arm anode electrode  54   au  as viewed in the Z direction. As illustrated in  FIG. 8 , the U-phase fourth projection  84   u  is joined with the entire U-phase lower arm anode electrode  54   au  by the joining material J. Thus, the U-phase lower arm anode electrode  54   au  and the U-phase lower arm emitter electrode  52   eu  are electrically connected to each other by the U-phase conductive part  63   u . That is, the U-phase second conductive plate  62   u  and the U-phase conductive part  63   u  function to connect the U-phase lower arm freewheeling diode  54   u  to the U-phase lower arm switching element  52   u  in inverse-parallel. 
     In addition, the U-phase third projection  83   u  and the U-phase fourth projection  84   u  are set to have the same projecting dimension. There is no limit to the projecting dimension as long as insulation can be ensured between the U-phase third lower conductive plate surface  63   cu  and the U-phase lower arm element upper surface  52   bu.    
     Both of the two control pads  71   u  and  72   u  of the U-phase are arranged at positions spaced apart from the U-phase unit  64   u  in the Y direction. The U-phase lower arm control pad  72   u  and the U-phase upper arm control pad  71   u  are arranged to be spaced apart from each other in the X direction so as not to interfere with each other. The U-phase lower arm control pad  72   u  is arranged at a position spaced apart from the U-phase lower arm gate electrode  52   gu  in the Y direction as viewed in the Z direction. The U-phase lower arm control terminal  74   u  is joined with both of the U-phase lower arm control pad  72   u  and the U-phase lower arm gate electrode  52   gu  by the joining material J. 
     Furthermore, the U-phase lower arm control terminal  74   u  has the same structure as that of the U-phase upper arm control terminal  73   u  except in that a terminal base end is longer in length than the terminal base end  73   bu  of the U-phase upper arm control terminal  73   u . That is, the U-phase lower arm control terminal  74   u  extends in the Y direction as viewed in the Z direction and has the form of a reversed U as viewed from the X direction. 
     In addition, as illustrated in  FIG. 4 , both of the control terminals  73   u  and  74   u  of the U-phase are provided at positions offset from each other as viewed in the Z direction. Specifically, both of the gate electrodes  51   gu  and  52   gu  of the U-phase are arranged to be spaced apart from each other in the X-direction, and both of the control pads  71   u  and  72   u  of the U-phase are arranged to be spaced apart from each other in the X direction. Accordingly, both of the control terminals  73   u  and  74   u  of the U-phase, which electrically connect the gate electrode  51   gu  and  52   gu  and the control pads  71   u  and  72   u , are arranged to be spaced apart from each other in the X direction without interfering each other. 
     The V-phase unit  64   v  and the W-phase unit  64   w  are constructed in the same manner as the U-phase unit  64   u . Specifically, the V-phase conductive part  63   v  includes a V-phase third lower conductive plate surface  63   cv  that faces the V-phase lower arm element upper surface  52   bv . A V-phase third projection  83   v  and a V-phase fourth projection  84   v , which project from the V-phase third lower conductive plate surface  63   cv  toward the V-phase lower arm element upper surface  52   bv , are provided on the V-phase third lower conductive plate surface  63   cv . The V-phase third projection  83   v  and the V-phase lower arm emitter electrode  52   ev  are joined with each other, and the V-phase fourth projection  84   v  and the V-phase lower arm anode electrode  54   av  are joined with each other. Both of the gate electrodes  51   gv  and  52   gv  of the V-phase are provided at positions offset from each other as viewed in the Z direction, and the control terminals  73   v  and  74   v  of the V-phase are arranged at positions offset from each other as viewed in the Z direction. 
     In the same manner, the W-phase conductive part  63   w  includes a W-phase third lower conductive plate surface  63   cw  that faces the W-phase lower arm element upper surface  52   bw . A W-phase third projection  83   w  and a W-phase fourth projection  84   w , which project from the W-phase third lower conductive plate surface  63   cw  toward the W-phase lower arm element upper surface  52   bw , are provided on the W-phase third lower conductive plate surface  63   cw . The W-phase third projection  83   w  and the W-phase lower arm emitter electrode  52   ew  are joined with each other, and the W-phase fourth projection  84   w  and the W-phase lower arm anode electrode  54   aw  are joined with each other. Both of the gate electrodes  51   gw  and  52   gw  of the W-phase are provided at positions offset from each other as viewed in the Z direction, and the control terminals  73   w  and  74   w  of the W-phase are arranged at positions offset from each other as viewed in the Z direction. The third projections  83   u  to  83   w  each correspond to a “second switching element projection.” 
     The lower arm emitter electrodes  52   eu  to  52   ew  are electrically connected to one another by the third conductive plate  63 . That is, the third conductive plate  63  functions to electrically connect the same phases of the lower arm emitter electrodes  52   eu  to  52   ew  and the lower arm anode electrodes  54   au  to  54   aw . The third conductive plate  63  also functions to electrically connect the lower arm emitter electrodes  52   eu  to  52   ew  of units  64   u  to  64   w  to one another. 
     Furthermore, although not illustrated in the drawings, the units  64   u  to  64   w  are actually sealed in a hermetic manner by an insulating resin. Accordingly, a gap portion of the U-phase terminal region A and the like is filled with the resin. In addition, in the present embodiment, the projecting direction of the output terminals  43   u  to  43   w  intersects (specifically, perpendicular to) the projecting direction of both of the input terminals  43   a  and  43   b    
     The operation of the present embodiment will now be described. 
     The first projections  81   u  to  81   w  are joined with the upper arm emitter electrodes  51   eu  to  51   ew , the upper arm emitter electrodes  51   eu  to  51   ew  and the lower arm collector electrodes  52   cu  to  52   cw  are electrically connected to each other by the second conductive plates  62   u  to  62   w . The first projections  81   u  to  81   w  are provided at positions that do not overlap the upper arm gate electrodes  51   gu  to  51   gw . Thus, the upper arm control terminals  73   u  to  73   w  may be located between the upper arm gate electrodes  51   gu  to  51   gw  and the second lower conductive plate surfaces  62   au  to  62   aw . In addition, parts of the upper arm control terminals  73   u  to  73   w  are located between the upper arm gate electrodes  51   gu  to  51   gw  and the second lower conductive plate surfaces  62   au  to  62   aw . This avoids interference between the upper arm control terminals  73   u  to  73   w  and the second conductive plates  62   u  to  62   w.    
     The present embodiment has the advantages described below. 
     (1) The inverter module  43  includes upper arm switching elements  51   u  to  51   w , which are placed on the first conductive plate  61 , and the lower arm switching elements  52   u  to  52   w , which are laminated on the upper arm switching elements  51   u  to  51   w  with the second conductive plates  62   u  to  62   w  located in between. The switching elements  51   u  to  52   w  are formed from silicon carbide. This configuration allows for reduction in the mounting area of the switching elements  51   u  to  52   w , specifically, the area occupied by the switching elements  51   u  to  52   w  in a plane perpendicular to the lamination direction (Z direction) of the switching elements  51   u  to  51   w  and the switching elements  52   u  to  52   w . That is, the mounting area can be reduced in comparison to a configuration in which the upper arm switching elements  51   u  to  51   w  and the lower arm switching elements  52   u  to  52   w  are arranged next to one another on the first conductive plate  61 . This allows the inverter module  43  to be reduced in size. 
     In a structure in which the lower arm switching elements  52   u  to  52   w  are laminated on the upper arm switching elements  51   u  to  51   w , heat has a tendency to accumulate in the switching elements  51   u  to  52   w . In this regard, in the present embodiment, the switching elements  51   u  to  52   w  are formed from silicon carbide. A switching element that uses silicon carbide generates less heat and has superior heat resistance as compared with a switching element formed from silicon. Thus, it is possible to cope with the shortcoming that occurs when the lower arm switching elements  52   u  to  52   w  are laminated on the upper arm switching elements  51   u  to  51   w.    
     In addition, in a switching element formed from silicon carbide, the on-resistance has a tendency to decrease. Thus, even when the switching elements  51   u  to  52   w  have a small size, the desired on-resistance can be obtained. This allows the switching elements  51   u  to  52   w  to be reduced in size while obtaining the desired on-resistance. Thus, the inverter module  43  may be reduced in size. 
     (2) The upper arm switching elements  51   u  to  51   w  respectively include the upper arm element upper surfaces  51   bu  to  51   bw . The upper arm emitter electrodes  51   eu  to  51   ew  and the upper arm gate electrodes  51   gu  to  51   gw , to which the upper arm control terminals  73   u  to  73   w  are joined, are formed on the upper arm element upper surfaces  51   bu  to  51   bw . The upper arm switching elements  51   u  to  51   w  respectively include the upper arm element lower surfaces  51   au  to  51   aw , which are opposite to the upper arm element upper surfaces  51   bu  to  51   bw . The upper arm collector electrodes  51   cu  to  51   cw  joined with the first conductive plate  61  are formed on the upper arm switching elements  51   u  to  51   w . The lower arm switching elements  52   u  to  52   w  respectively include the lower arm element upper surfaces  52   bu  to  52   bw , on which the lower arm emitter electrodes  52   eu  to  52   ew  and the lower arm gate electrodes  52   gu  to  52   gw  are formed. The lower arm emitter electrodes  52   eu  to  52   ew  are joined with the third conductive plate  63  provided on the lower arm switching elements  52   u  to  52   w . The lower arm gate electrodes  52   gu  to  52   gw  are joined with the lower arm control terminals  74   u  to  74   w . The lower arm switching elements  52   u  to  52   w  respectively include the lower arm element lower surfaces  52   au  to  52   aw , which are opposite to the lower arm element upper surfaces  52   bu  to  52   bw . The lower arm collector electrodes  52   cu  to  52   cw  are formed on the lower arm element lower surfaces  52   au  to  52   aw.    
     In the above-described configuration, the second conductive plates  62   u  to  62   w  respectively include the second upper conductive plate surfaces  62   bu  to  62   bw , on which the lower arm switching elements  52   u  to  52   w  are placed, and the second lower conductive plate surfaces  62   au  to  62   aw , which are opposite to the second upper conductive plate surfaces  62   bu  to  62   bw  and face the upper arm element upper surfaces  51   bu  to  51   bw  in the Z direction. The second upper conductive plate surfaces  62   bu  to  62   bw  are respectively joined with the lower arm collector electrodes  52   cu  to  52   cw  and entirely cover the lower arm element lower surfaces  52   au  to  52   aw . In addition, the first projections  81   u  to  81   w , which project from the second lower conductive plate surfaces  62   au  to  62   aw  toward the upper arm element upper surfaces  51   bu  to  51   bw  and are joined with the upper arm emitter electrodes  51   eu  to  51   ew , are respectively provided in the second lower conductive plate surfaces  62   au  to  62   aw . The first projections  81   u  to  81   w  are provided at positions that do not overlap the upper arm gate electrodes  51   gu  to  51   gw  as viewed in the Z direction. Further, parts of the upper arm control terminals  73   u  to  73   w  are located between the upper arm gate electrodes  51   gu  to  51   gw  and the second lower conductive plate surfaces  62   au  to  62   aw.    
     This configuration realizes the electrical connection of the upper arm emitter electrodes  51   eu  to  51   ew  and the lower arm collector electrodes  52   cu  to  52   cw  with the second conductive plates  62   u  to  62   w . Further, the electrical connection of the upper arm control terminals  73   u  to  73   w  and the upper arm gate electrodes  51   gu  to  51   gw  can be realized without interference with the second conductive plates  62   u  to  62   w.    
     In addition, the present embodiment increases heat dissipation of the inverter module  43 . Specifically, to realize the electrical connection described above under a situation in which the upper arm emitter electrodes  51   eu  to  51   ew  and the upper arm gate electrodes  51   gu  to  51   gw  exist on the upper arm element upper surfaces  51   bu  to  51   bw , for example, the portions corresponding to the upper arm gate electrodes  51   gu  to  51   gw  in the second conductive plates  62   u  to  62   w  can be cutaway. In this case, the lower arm element lower surfaces  52   au  to  52   aw  will include sections that are not covered by the second conductive plates  62   u  to  62   w . Such sections limit the transfer of heat to the second conductive plates  62   u  to  62   w  and hinder heat dissipation. In this manner, heat dissipation deteriorates when realizing electrical connection between the upper arm gate electrodes  51   gu  to  51   gw  and the upper arm control terminals  73   u  to  73   w . Thus, the lower arm element lower surfaces  52   au  to  52   aw  may include sections where the temperature locally rises and deteriorates the heat resistance. 
     Particularly, the first conductive plate  61  is mounted on to the insulation substrate  60  that allows for heat exchange with the refrigerant through the inverter case  31  and the housing  11 . This facilitates cooling of the upper arm switching elements  51   u  to  51   w  that are placed on the first conductive plate  61 . In contrast, it is difficult to cool the lower arm switching elements  52   u  to  52   w , which are laminated on the upper arm switching elements  51   u  to  51   w  with the second conductive plates  62   u  to  62   w  located in between. Thus, the temperature easily rises when the lower arm element lower surfaces  52   au  to  52   aw  of the lower arm switching elements  52   u  to  52   w  includes sections that are not covered by the second conductive plates  62   u  to  62   w.    
     In the present embodiment, the second upper conductive plate surfaces  62   bu  to  62   bw  cover the entire lower arm element lower surfaces  52   au  to  52   aw . This avoids the formation of sections where heat has a tendency to accumulate. In addition, parts of the upper arm control terminals  73   u  to  73   w  are located between the upper arm gate electrodes  51   gu  to  51   gw  and the second lower conductive plate surfaces  62   au  to  62   aw . This allows for electrical connection between the upper arm control terminals  73   u  to  73   w  and the upper arm gate electrodes  51   gu  to  51   gw  to be realized without interfering with the second conductive plates  62   u  to  62   w  while covering the entire lower arm element lower surfaces  52   au  to  52   aw  with the second conductive plates  62   u  to  62   w . This resolves the shortcoming described above. 
     (3) The lower arm collector electrodes  52   cu  to  52   cw  are formed by the entire lower arm element lower surfaces  52   au  to  52   aw , and the second upper conductive plate surfaces  62   bu  to  62   bw  are in contact with the entire lower arm collector electrodes  52   cu  to  52   cw . This configuration lowers the on-resistance. 
     Specifically, for example, when notches are formed in the second conductive plates  62   u  to  62   w  as described above, even when the lower arm collector electrodes  52   cu  to  52   cw  are formed by the entire lower arm element lower surfaces  52   au  to  52   aw , parts of the lower arm collector electrodes  52   cu  to  52   cw  do not contact the second conductive plates  62   u  to  62   w . Thus, parts of the lower arm collector electrodes  52   cu  to  52   cw  do not function. This increases the on-resistance. In this regard, the present configuration includes the first projections  81   u  to  81   w . This avoids interference between the upper arm control terminals  73   u  to  73   w  and the second conductive plates  62   u  to  62   w  and electrically connects the upper arm control terminals  73   u  to  73   w  to the upper arm gate electrodes  51   gu  to  51   gw  while the lower arm collector electrodes  52   cu  to  52   cw  entirely contact the second upper conductive plate surfaces  62   bu  to  62   bw . This resolves the shortcoming described above. 
     (4) The upper arm gate electrodes  51   gu  to  51   gw  are arranged at positions offset from the lower arm gate electrodes  52   gu  to  52   gw  as viewed in the Z direction, and the upper arm control terminals  73   u  to  73   w  are arranged at positions offset from the lower arm control terminals  74   u  to  74   w  as viewed in the Z direction. With this configuration, the upper arm gate electrodes  51   gu  to  51   gw  are arranged at positions offset from the lower arm gate electrodes  52   gu  to  52   gw  as viewed in the Z direction. This easily avoids interference between the upper arm control terminals  73   u  to  73   w  and the lower arm control terminals  74   u  to  74   w.    
     (5) The U-phase upper arm switching element  51   u  and the U-phase lower arm switching element  52   u  are laminated in a state in which the peripheral edge  51   xu  of the U-phase upper arm switching element  51   u  and the peripheral edge  52   xu  of the U-phase lower arm switching element  52   u  are aligned in the Z direction. With this configuration, the mounting area of both of the U-phase switching elements  51   u  and  52   u  can be reduced in comparison with a configuration in which both of the U-phase switching elements  51   u  and  52   u  are laminated in a state offset from each other as viewed in the Z direction. Thus, the inverter module  43  may be further reduced in size. The same applies to the other phases. 
     (6) The third conductive plate  63  includes the conductive parts  63   u  to  63   w  that respectively correspond to the U-phase, the V-phase, and the W-phase. The conductive parts  63   u  to  63   w  respectively include the third lower conductive plate surfaces  63   cu  to  63   cw  that face the lower arm element upper surfaces  52   bu  to  52   bw . The third projections  83   u  to  83   w , which project from the third lower conductive plate surfaces  63   cu  to  63   cw  toward the lower arm element upper surfaces  52   bu  to  52   bw  and are joined with the lower arm emitter electrodes  52   eu  to  52   ew , are respectively provided on the third lower conductive plate surfaces  63   cu  to  63   cw . With this configuration, the third lower conductive plate surfaces  63   cu  to  63   cw  and the lower arm element upper surfaces  52   bu  to  52   bw  can be arranged spaced apart from one another. This avoids unintentional contact and improves insulation. 
     (7) The units  64   u  to  64   w  respectively include the upper arm switching elements  51   u  to  51   w , the lower arm switching elements  52   u  to  52   w , the upper arm control terminals  73   u  to  73   w , the lower arm control terminals  74   u  to  74   w , and the second conductive plates  62   u  to  62   w . The units  64   u  to  64   w  are laid out on the first conductive plate  61  in one direction (specifically, the X direction). This configuration decreases the mounting area per unit and allows the units  64   u  to  64   w  to be entirely reduced in size. 
     Particularly, when laying out the units  64   u  to  64   w , it is preferable that the intervals between the units  64   u  to  64   w  be increased from the viewpoint of heat dissipation. However, a longer interval will enlarge the inverter module  43 . In contrast, in the present embodiment, as described above, the improvement of heat dissipation in each of the units  64   u  to  64   w  allows the intervals to be shortened. This allows the inverter module  43  to be further reduced in size. 
     (8) The inverter module  43  includes the insulation substrate  60 , on which the first conductive plate  61  is attached. The insulation substrate  60  includes the upper arm control pads  71   u  to  71   w , with which the upper arm control terminals  73   u  to  73   w  are joined, and the lower arm control pads  72   u  to  72   w , with which the lower arm control terminals  74   u  to  74   w  are joined. With this configuration, the controller  44 , which controls the switching elements  51   u  to  52   w , is electrically connected to the gate electrodes  51   gu  to  52   gw.    
     (9) Both of the control pads  71   u  and  72   u  of the U-phase are arranged at positions spaced apart from the U-phase unit  64   u  in the Y direction that is a direction perpendicular to the layout direction of the units  64   u  to  64   w . In addition, both of the control terminals  73   u  and  74   u  of the U-phase extend in the Y direction as viewed in the Z direction. This also applies to the other phases. With this configuration, both of the control pads  71   u  and  72   u  of the U-phase and both of the control terminals  73   u  and  74   u  of the U-phase do not interferes with the arrangement of the units  64   u  to  64   w . Specifically, to avoid interference of the V-phase unit  64   v , which is adjacent to the U-phase unit  64   u , with both of the control pads  71   u  and  72   u , for example, there is no need to widen the interval between the U-phase unit  64   u  and the V-phase unit  64   v . This allows the interval of the units  64   u  to  64   w  to be decreased. 
     (10) The units  64   u  to  64   w  respectively include the upper arm freewheeling diodes  53   u  to  53   w  and the lower arm freewheeling diodes  54   u  to  54   w . In addition, the first conductive plate  61  and the second conductive plates  62   u  to  62   w  connect the upper arm freewheeling diodes  53   u  to  53   w  to the upper arm switching elements  51   u  to  51   w  in inverse-parallel, and the second conductive plates  62   u  to  62   w  and the third conductive plate  63  connect the lower arm freewheeling diodes  54   u  to  54   w  to the lower arm switching elements  52   u  to  52   w  in inverse-parallel. With this configuration, the first conductive plate  61 , the second conductive plates  62   u  to  62   w , and the third conductive plate  63  are also used for electrical connection between the freewheeling diodes  53   u  to  54   w  and the switching elements  51   u  to  52   w . This simplifies the configuration. In addition, the freewheeling diodes  53   u  to  54   w  are combined with the switching elements  51   u  to  52   w  as units. This allows for further reduction in the size of the inverter module  43 . 
     (11) The inverter device  30  includes the inverter module  43 , the transformer  41  that transforms DC power supplied from the DC power supply E, and the filter circuit  42  that receives the DC power transformed by the transformer  41 . The inverter module  43  converts the DC power output from the filter circuit  42  into AC power for driving the electric motor  13 . This drives the electric motor  13 . 
     The switching elements  51   u  to  52   w  are formed from silicon carbide and have a small switching loss. This allows the inverter module  43  to operate at high frequencies. For example, when the controller  44  performs pulse width modulation (PWM) control on the inverter module  43 , a high carrier frequency can be set. This allows the cut-off frequency of the filter circuit  42  to be raised. The filter circuit  42  removes noise from the inverter module  43 . Accordingly, the inductance of the filter coil  42   a  and the capacitance of the filter capacitor  42   b  may be lowered. The filter coil  42   a  and the filter capacitor  42   b  are elements of the filter circuit  42 . Thus, the filter circuit  42  may be reduced in size. This, in turn, allows the entire inverter device  30  to be reduced in size. 
     The above-described embodiment may be modified as follows. 
     The switching elements  51   u  to  52   w  are not limited to IGBTs and may be MOSFETs formed from silicon carbide (SiC), and the like. For example, when the switching elements  51   u  to  52   w  are n-type MOSFETs, the switching elements  51   u  to  52   w  include a source electrode instead of the emitter electrodes  51   eu  to  52   ew  and a drain electrode instead of the collector electrodes  51   cu  to  52   cw . That is, the upper arm switching elements  51   u  to  51   w  each include an upper arm drain electrode as a first lower electrode and an upper arm source electrode as a first upper electrode. The lower arm switching elements  52   u  to  52   w  each include a lower arm drain electrode as a second lower electrode and a lower arm source electrode as a second upper electrode. 
     Furthermore, when MOSFETs are employed as the switching elements  51   u  to  52   w , a parasitic diode of the MOSFET functions as the freewheeling diodes  53   u  to  54   w . Thus, the freewheeling diodes  53   u  to  54   w  may be omitted. That is, the freewheeling diodes  53   u  to  54   w  are not essential. 
     As illustrated in  FIG. 9 , a U-phase first projection  111   u  may be configured separately from the U-phase second conductive plate  62   u . In this case, for example, the U-phase first projection  111   u  may be formed from a conductive material such as copper and molybdenum, and the U-phase first projection  111   u  and the U-phase second conductive plate  62   u  may be joined with each other by the joining material J. In this case, the U-phase first projection  111   u  functions as a heat mass. In the same manner, a U-phase third projection  112   u  and the U-phase second extension portion  63   bu  may be provided separately from each other and be joined with each other by the joining material J. 
     The upper arm switching elements  51   u  to  51   w  may be laminated on the lower arm switching elements  52   u  to  52   w . That is, the “first switching element” may be an upper arm switching element or a lower arm switching element. This also applies to the “second switching element.” 
     The inverter module  43  includes three units  64   u  and  64   w . However, there may be any number of units. For example, only one unit may be provided. 
     The inverter module  43  can be used to drive the electric motor  13  of the motor-driven compressor  10  that is installed in a vehicle. However, there is no limit to the application of the inverter module  43 . For example, when a vehicle-driving motor is installed in a vehicle, the inverter module  43  may be used to drive the vehicle-driving motor. 
     The semiconductor module is not limited to the inverter module  43 . For example, the semiconductor module may be a DC/DC converter module or a charger module. 
     The U-phase first projection  81   u  has the same shape as the U-phase upper arm emitter electrode  51   eu  as viewed in the Z direction but there is no limit to the shape. The U-phase first projection  81   u  may have any shape as long as it does not project out of the U-phase upper arm emitter electrode  51   eu  as viewed in the Z direction. In addition, the U-phase first projection  81   u  may slightly project from the U-phase upper arm emitter electrode  51   eu  as viewed in the Z direction as long as it does not interfere with the U-phase upper arm control terminal  73   u . However, it is preferable that the U-phase first projection  81   u  be in a projection range of the U-phase upper arm emitter electrode  51   eu  as viewed in the Z direction from the viewpoint of insulation properties. 
     The emitter electrodes  51   eu  to  52   ew , the collector electrodes  51   cu  to  52   cw , and the gate electrodes  51   gu  to  52   gw  may have any shape or be located at any position. For example, the upper arm gate electrodes  51   gu  to  51   gw  and the lower arm gate electrodes  52   gw  to  52   gw  may overlap each other as viewed in the Z direction. In addition, the collector electrodes  51   cu  to  52   cw  may be formed in parts of the element lower surfaces  51   au  to  52   aw.    
     The control pads  71   u  to  72   w  may be located at any position or have any shape as long as the control terminals  73   u  to  74   w  can be arranged without interfering each other. 
     Part of the U-phase upper arm control terminal  73   u  and part of the U-phase lower arm control terminal  74   u  may overlap each other in the Z direction in a state in which a height difference exists. This also applies to the other phases. 
     The third conductive plate  63  may have any shape. For example, the third projections  83   u  to  83   w  or the fourth projections  84   u  to  84   w  may be omitted. 
     The U-phase upper arm switching element  51   u  and the U-phase lower arm switching element  52   u  may be laminated in a state offset from each other as viewed in the Z direction. In other words, a non-overlapping region may exist between the U-phase upper arm switching element  51   u  and the U-phase lower arm switching element  52   u . However, it is preferable that both of the U-phase switching elements  51   u  and  52   u  be laminated in a state in which the peripheral edge  51   xu  of the U-phase upper arm switching element  51   u  and the peripheral edge  52   xu  of the U-phase lower arm switching element  52   u  are aligned to decrease the mounting area. 
     The semiconductor module may be configured as follows. That is, the semiconductor module includes a first conductive plate, a switching element placed on the first conductive plate and formed from silicon carbide, a second conductive plate arranged on the switching element, an SiC element that is laminated on the second conductive plate and formed from silicon carbide, and a control terminal. The switching element includes a first element upper surface on which a first upper electrode and a gate electrode that is joined with the control terminal is formed, and a first element lower surface located at a side opposite to the first element upper surface and on which a first lower electrode joined with the first conductive plate is formed. The SiC element includes a second element upper surface, on which a second upper electrode is formed, and a second element lower surface, which is located at a side opposite to the second element upper surface and on which a second lower electrode is formed. The second conductive plate includes a second upper conductive plate surface, on which the SiC element is placed and which is joined with the second lower electrode covering the entire second element lower surface, and a second lower conductive plate surface, which is located at a side opposite to the second upper conductive plate surface facing the first element upper surface. A projection is arranged on the second lower conductive plate surface projecting from the second lower conductive plate surface toward the first element upper surface and joined with the first upper electrode, and the projection is arranged at a position that does not overlap the gate electrode when viewed from a lamination direction of the switching element and the SiC element. Part of the control terminal is located between the gate electrode and the second lower conductive plate surface. 
     As described above, a SiC element other than the switching element may be laminated on the switching element with the second conductive plate located in between. As the SiC element other than the switching element, for example, a diode that is formed from silicon carbide or the like may be used. In this case, one of an anode electrode and a cathode electrode corresponds to the second upper electrode, and the other one corresponds to the second lower electrode. In addition, as the switching element, an emitter electrode may be formed on the element lower surface and a collector electrode may be formed on the element upper surface.