Abstract:
A compression bonded type semiconductor device including a semiconductor substrate having a gate electrode and a cathode electrode formed on a first surface and an anode electrode formed on a second surface opposite to the first surface, an external cathode electrode disposed so as to be compression bondable to the cathode electrode, and an external anode electrode disposed so as to be compression bondable the anode electrode. Also included is an insulating cylinder containing the semiconductor substrate, an external gate terminal having an outer peripheral portion protruding to an outside of the insulating cylinder and having a protrusion at an inner peripheral portion configured to about said gate electrode, and an elastic body configured to press the protrusion of the external gate terminal to the gate electrode.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     This application is a continuation of international application PCT/JP99/00119, filed on Jan. 18,1999, the entire contents of which are incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     The present invention relates to a compression bonded type semiconductor device, such as GCT (Gate Commutated Turn-off) thyristor. 
     2. Description of the Background 
     Although a GTO (Gate Turn-OFF) thyristor has been widely used as a device for large capacity power electronics, the GTO requires a snubber circuit. Further, it is difficult to suppress an increase of snubber loss due to an increase in an operating voltage of the GTO. However, a GCT (Gate Commutated Turn-off) thyristor does not require such a snubber circuit and realizes a performance of 6000 A for a maximum breaking current and less than or equal to 3 μs for a turn-off storage time. The GCT also has an increased capacity and speed. 
     FIG. 3 is a cross-sectional view illustrating a background compression bonded type semiconductor device (e.g., a GCT) described in Japanese Patent Laid-Open No. Hei. 8-330572 (1996). In the figure, reference numeral  1  denotes a semiconductor substrate. An aluminum gate electrode  2   a  is formed at an outer peripheral portion on a surface of the semiconductor substrate  2 , a cathode electrode  2   b  is formed at an inside of the gate electrode  2   a , and an anode electrode  2   c  is formed on a back surface of the substrate  2 . Also shown are a cathode distortion buffer disk  3  and an external cathode electrode  4  mounted one after another on a side of the cathode electrode  2   b , and an anode distortion buffer disk  5  and an external anode electrode  6  mounted one after another on a side of the anode electrode  2   c . A ring gate electrode  7  made of iron or nickel alloy contacts the gate electrode  2   a , and a ring-shaped external gate terminal  8  made of iron or nickel alloy is electrically connected with the ring gate electrode  7 , though it is not fixed thereto. In addition, an elastic body  9  (such as a disk spring) presses the ring gate electrode  7  to the gate electrode  2   a  together with the external gate terminal  8  via an annular insulator  10 . 
     Further shown is an insulator  11  for insulating the ring gate electrode  7  from the cathode distortion buffer disk  3  and the external cathode electrode  4 , a first flange  12  secured to the external cathode electrode  4 , a second flange  13  secured to the external anode electrode  6 , and an insulating cylinder  14  made of ceramics or the like and which is divided into upper and lower parts. An outer periphery of the external gate terminal  8  protrudes out of a side of the insulating cylinder  14  and is hermetically secured to a divisional portion  14 a by soldering. In addition, an end portion  15  secured to the insulating cylinder  14  by soldering is hermetically secured to the first and second flanges  12  and  13  by arc welding. Thus, the GCT  1  has a closed structure and the inside is filled with an inert gas. 
     Next, the operation of the GCT  1  will be explained. Current flows toward the external cathode electrode  4  from the external gate terminal  8  when the GCT  1  is turned on. A gradient of rise of the gate current at this time is generally set at 1000 A/μs or more in operating the GCT  1  without a current limiting reactor and the turn-on spreading speed of the GCT  1  must be increased. While current flows toward the external gate terminal  8  from the external cathode electrode  4  when the GCT  1  is turned off, the current must be fed with the gradient of several thousands A/μs to commutate a current equivalent to the main current of the GCT  1  to the gate in about 1 μs to operate it without a snubber circuit. A contact resistance of a current feeding path from the external gate terminal  8  to the external cathode electrode  4  must be minimized to feed such a large current instantly. 
     While the cathode electrode  2   b ,the cathode distortion buffer disk  3  and the external cathode electrode  4  are pressed by a large force of several hundreds kg/cm 2  from outside of the GCT  1 , the gate electrode  2   a , the ring gate electrode  7 , and the external gate terminal  8  are pressed only by the elastic body  9 . This is because the elastic body  9  is disposed at a peripheral part of the external cathode electrode  4 . Thus, the pressure at a portion A, where the external gate terminal  8  contacts the ring gate electrode  7 , is several kg/cm 2  and a contact resistance sufficient to feed the above-discussed instantaneous large power cannot be obtained. 
     The above-constructed background GCT  1  also has the following problems. 
     First, there is a case in which the external gate terminal  8  causes a waviness in a circumferential direction at the contact portion A between an inner peripheral portion of the external gate terminal  8  and the ring gate electrode  7  due to a strain caused by a thermal residual stress from soldering the external gate terminal  8  and the divisional portion  14   a  of the insulating cylinder  14 . In addition, because the external gate terminal  8  is only pressed by the elastic body  9 , the pressure at the contact portion A is several kg/cm 2  and the waviness can not be corrected. Therefore, the contact resistance of the contact portion A is greater than a desired contact resistance. That is, the contact resistance of the feeding path from the external gate terminal  8  to the external cathode electrode  4  is too large. Thus, the power feeding capability of the gate is inhibited, because the gradient of the inverse direction gate current is insufficient when the GCT  1  is turned off, for example. 
     Secondly, the abnormality of the contact caused by the waviness also results in a contact resistance which fluctuates within the plane of the ring-shaped external gate terminal  8 . Thus, the power feeding capability of the gate partially drops, which causes an extreme drop in the turn-off capability of the GTC  1 . 
     Thirdly, the GTC  1  abnormally generates heat by locally receiving electromagnetic induction from the magnetic field of an external circuit when operating at high frequencies, because iron or nickel alloy is used for the external gate terminal  8  to thereby solder with ceramics (which is the material of the insulating cylinder  14 ). This problem influences the characteristics of the semiconductor substrate  2 . 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to solve the above-noted and other problems. 
     Another object of the present invention is to provide a novel compression bonded type semiconductor device which decreases a contact resistance of a current feeding path from an external gate terminal to an external cathode electrode. 
     Yet another object of the present invention is to provide a novel compression bonded type semiconductor device which can suppress a fluctuation of contact resistance within the plane of the external gate terminal caused by waviness produced in the circumferential direction of the external gate terminal from occurring at a portion where the inner peripheral part of the external gate terminal contacts a ring gate electrode. 
     Still another object of the present invention is to provide a novel compression bonded type semiconductor device which prevents the external gate terminal from abnormally generating heat by locally receiving electromagnetic induction by the magnetic field of the external circuit when operating at a high frequency. 
     To achieve these and other objects, the present invention provides a novel gate electrode and a cathode electrode formed on a top surface of a semiconductor substrate, and an anode electrode formed on a back surface of the substrate. An external cathode electrode is disposed to be compression bondable to the cathode electrode and an external anode electrode is disposed to be compression bondable to the anode electrode. Also included is an insulating cylinder containing the semiconductor substrate, and an external gate terminal whose outer peripheral portion protrudes out of the side of the insulating cylinder and which is fixed to the insulating cylinder. The external gate terminal also has a protrusion formed at an inner peripheral portion and which abuts the gate electrode. In addition, the external gate terminal is pressed to the gate electrode by an elastic body. Thus, the external gate terminal directly contacts the gate electrode and a contact resistance which otherwise exists in the background art between the external gate terminal and the ring gate electrode is eliminated. Accordingly, it is possible to decrease the contact resistance of the feeding path from the external gate terminal to the external cathode electrode, and to improve the power feeding capability of the gate. 
     Further, a ring-shaped press-contact auxiliary block may also be provided between the protrusion of the external gate terminal and the elastic body. Thus, it is possible to reduce the fluctuation of a press-contact force at the portion where the external gate terminal contacts the gate electrode. This suppresses the fluctuation of the contact resistance within the plane of the external gate terminal from occurring, due to the waviness at the inner peripheral part of the external gate terminal by the strain caused by thermal residual stress in soldering the external gate terminal with the insulating cylinder. 
     Furthermore, the external gate terminal may include a first ring-shaped portion and the protrusion may include a second ring-shaped portion formed at an inner peripheral portion of the first ring-shaped portion. Thus, the external gate terminal directly contacts the gate electrode and a contact resistance is decreased. 
     In addition, the protrusion abutting the gate electrode may have a ring-shape. Thus, the press-contact force at the portion where the external gate terminal contacts the gate electrode may be increased by about several tens of times compared. with the background art. Thus, it is possible to obtain a contact resistance sufficient to feed a large power instantly, by correcting the waviness which otherwise occurs at the inner peripheral part of the external gate terminal due to the strain caused by the thermal residual stress in soldering the external gate terminal with the insulating cylinder. 
     Further, the external gate terminal may include a non-magnetic material, which suppresses the external gate terminal from abnormally generating heat by locally receiving electromagnetic induction by the magnetic field of an external circuit when operating at a high frequency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional view of a compression bonded type semiconductor device according to a first embodiment of the invention; 
     FIG. 2 is a cross-sectional view of a compression bonded type semiconductor device according to a second embodiment of the invention; and 
     FIG. 3 is a cross-sectional view of a background compression bonded type semiconductor device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the first and second embodiments of the present invention will be discussed. 
     First Embodiment 
     FIG. 1 is a cross-sectional view of a compression bonded type semiconductor device (e.g., a GCT) according to a first embodiment of the present invention. In FIG. 1, reference numeral  21  denotes the GCT, and reference numeral  22  denotes a disk-like semiconductor substrate, in which an aluminum gate electrode  22   a  is formed at a peripheral surface portion of the substrate  22 , a cathode electrode  22   b  is formed at an inside of the gate electrode  22   a , and an anode electrode  22   c  is formed on a back surface of the substrate  22 . As shown, a cathode distortion buffer disk  23  made of molybdenum and an external cathode electrode  24  made of copper are mounted one after another on a side of the cathode electrode  22   b , and an anode distortion buffer disk  25  made of molybdenum and an external anode electrode  26  made of copper are mounted one after another on a side of the anode electrode  22   c . Also shown is a first flange  27  made of iron, nickel or the like and which is secured to the external cathode electrode  24 , a second flange  28  made of iron, nickel or the like and which is secured to the external anode electrode  26 , and an insulating cylinder  29  made of ceramics or the like and which is divided into upper and lower parts at a divisional portion  29   a.    
     Further illustrated is a ring-shaped external gate terminal  30  made of a non-magnetic ring shaped plate including a material which does not receive electromagnetic induction (such as copper, molybdenum, tungsten or their alloy, e.g., phosphor bronze) as a main component. An outer periphery of the external gate terminal  30  protrudes out of a side of the insulating cylinder  29  and is hermetically secured to the divisional portion  29   a  by soldering. A ringshaped protrusion  30   a  is formed at an inner peripheral section of the external gate terminal  30  and an edge portion of the protrusion  30   a  abutting the gate electrode  22   a  has a ring-shaped flat portion of about 0.5 mm. An elastic body  31  (such as a disk spring or a wave spring) presses the external gate terminal  30  to the gate electrode  22   a  via a press-contact auxiliary block  32 . The press-contact auxiliary block  32  comprises a ring-shape and is made of a rigid material such as molybdenum. The thermal expansion ratio of the auxiliary block  32  is close to that of silicon. Further, the auxiliary block  32  is disposed between the elastic body  31  and the protrusion  30   a  of the external gate terminal  30 , and a ring-shaped insulator  33  electrically insulates the elastic body  31  and the press-contact auxiliary block  32 . 
     In addition, an insulator  35  made of an insulating sheet such as Teflon or polyimide is provided between the inner peripheral part of the external gate terminal  30  and the external cathode electrode  24  to electrically insulate the inner peripheral part of the external gate terminal  30  from the external cathode electrode  24 . A first edge portion  36  made of iron, nickel or the like has one end hermetically secured to the insulating cylinder  29  and the other end hermetically secured to the first flange  27 . A second edge portion  36  is similarly secured to the second flange  28  and the insulating cylinder  29 . Thus, the GCT  21  has a closed structure and the inside thereof is replaced by inert gas. 
     Next, an operation of the GCT  21  will be explained. Current flows toward the external cathode electrode  24  from the external gate terminal  30  when the GCT  21  is turned on. A gradient of rise of the gate current at this time is set at about 1000 A/μs or more in operating the GCT  21  without a current limiting reactor, for example, and the turn-on spreading speed of the GCT  21  must be increased. While current flows toward the external gate terminal  30  from the external cathode electrode  24  when the GCT  21  is turned off, the current must be fed with the gradient of several thousands A/μs to commutate a current equivalent to the main current of the GCT  21  to the gate in about 1 μs to operate it without a snubber circuit, which aids the turn-off of the GCT  21 . A contact resistance of a current feeding path from the external gate terminal  30  to the external cathode electrode  24  must be minimized to instantly feed such a large current. 
     According to the first embodiment of the present invention, the external gate terminal  30  has a protrusion  30   a  which abuts the gate electrode  22   a . This configuration allows the external gate terminal  30  to directly contact the gate electrode  22   a . Thus, a contact resistance interposed between the external gate terminal  8  and the ring gate electrode  7  shown in the background art in FIG. 3 is eliminated. Therefore, it is possible to decrease the contact resistance of the feeding path from the external gate terminal  30  to the external cathode electrode  24  and to improve the power feeding capability of the gate. 
     Further, the ring-shaped press-contact auxiliary block  32  is provided between the protrusion  30   a  and the elastic body  31 . This configuration lessens the fluctuation of presscontact forces at the portion where the external gate terminal  30  (made of a thin plate) contacts the gate electrode  22   a . Thus, it is possible to. suppress the fluctuation of the contact resistance within the plane of the external gate terminal  30  from occurring due to waviness at the inner peripheral part of the external gate terminal  30 . As previously discussed, the waviness is due to the strain caused by thermal residual stress in soldering the external gate terminal  30  with the insulating cylinder  29 . 
     Further, the protrusion  30   a  comprises a ring-shape and an edge portion of the protrusion  30   a  contacting the gate electrode  22   a  is a ring-shaped flat portion of about 0.5 mm. Thus, the press-contact force at the portion where the external gate terminal  30  contacts the gate electrode  22   a  is increased by about several tens of times as compared to the background art. Thus, it is possible to obtain a contact resistance sufficient to feed a large power instantly by correcting the waviness, which otherwise occurs at the inner peripheral part of the external gate terminal  30  due to the strain caused by the thermal residual stress in soldering the external gate terminal  30  with the insulating cylinder  29 . 
     In addition, the external gate terminal  30  is a non-magnetic member. Thus, the external gate terminal  30  is suppressed from abnormally generating heat by locally receiving electromagnetic induction by the magnetic field of an external circuit operating at a high frequency. 
     Further, the GCT  21  shown in the first embodiment is made by assembling the insulator  35 , the elastic body  31 , the ring-shaped insulator  33  and the press-contact auxiliary block  32 , while placing at the lower side the external cathode electrode  24  (to which the first flange  27  is secured), resulting in a semi-finished item in which the external gate terminal  30  and the edge portion  36  are secured to the insulating cylinder  29 . Then the first flange  27  is secured to the edge portion  36  at a desired position. This allows the external cathode electrode  24  and the external gate terminal  30  to be positioned. Therefore, it is possible to position the gate electrode  22 , the external gate terminal  30  and the external cathode electrode  24  accurately from each other because a mold portion  22   d  provided at the outer peripheral portion of the gate electrode  22  engages with the external gate terminal  30 . 
     Second Embodiment 
     Next, a compression bonded type semiconductor device according to the second embodiment of the present invention will be explained. 
     FIG. 2 is a cross-sectional view of a GCT according to the second embodiment of the present invention. The same reference numerals as those used in FIG. 1 denote the same or corresponding components. The difference between FIGS. 1 and 2 is that the press-contact auxiliary block  32  is eliminated and the structure of the external gate terminal  30  is changed. In more detail, reference numeral  41  denotes the GTC, and reference numeral  42  denotes a ring-shaped external gate terminal formed of a non-magnetic ring-shaped plate having a main material which does not receive electromagnetic induction, such as copper, molybdenum, tungsten or their alloy, e.g., phosphor bronze. An outer periphery  42   a  of the external gate terminal  42  protrudes out of a side of the insulating cylinder  29  and is hermetically secured to a divisional part  29   a  by soldering. In addition, a ring-shaped protrusion  42   c , which abuts the gate electrode  22   a , is formed at an inner periphery part of a ring-shaped gate portion  42   b . The ring-shaped gate portion  42   b  includes a nonmagnetic ring-shaped plate made of a material which does not receive electromagnetic induction such as copper, molybdenum, tungsten or their alloy, e.g., phosphor bronze, as the main material. The ring-shaped gate portion  42   b  is soldered to an inner periphery of the external terminal  42 . An edge portion of the protrusion  42   c  abutting the gate electrode  22   a  has a ring-shaped flat portion of about 0.5 mm. 
     According to the second embodiment, the ring-shaped protrusion  42   c  (which abuts the gate electrode  22   a ) is formed in a body with the ring-shaped gate portion  42   b  soldered to the inner peripheral part of the external gate terminal  42 . Such a configuration allows the external gate terminal  42  to directly contact the gate electrode  22   a  and a contact resistance which otherwise exists between the external gate terminal  8  and the ring gate electrode  7  in the background art is eliminated. Therefore, it is possible to decrease the contact resistance of the power feeding path from the external gate terminal  42  to the external cathode electrode  24 , and to improve the power feeding capability of the gate. 
     In addition, the gate electrode may be formed at an intermediate portion of the surface of the semiconductor substrate, rather than at the outer peripheral portion as discussed in the first and second embodiments. 
     Further, the present invention is also applicable to a compression bonded type semiconductor device having a main electrode and a control electrode such as a compression bonded type GTO or compression bonded type IGBT. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.