JPH0687489B2 - Semiconductor device - Google Patents

Description

The present invention relates to a semiconductor device, and more particularly to a semiconductor element used as a switching element for large current and a limit for protecting this semiconductor element from overcurrent. The present invention relates to a semiconductor device having a flow element.

(Prior Art) A contact switch is widely used as a device for turning on / off an electric circuit through which a large current flows, but in recent years, a contactless semiconductor switch has advantages such as no arc, no noise, and no maintenance. Have been started to use. Such a semiconductor switch has the advantages described above, but is very weak against overcurrent (especially abnormal current such as short circuit current). For example, when a current exceeding a specified value flows through a thyristor forming a semiconductor switch, the thyristor breaks down and is always turned on.

For this reason, a fast-acting fuse is inserted in an electric circuit, and when an overcurrent flows in the electric circuit, the circuit is cut off to protect the semiconductor switch. However, when such a fast-acting fuse is used, a new quick-acting fuse must be replaced with a new one in order to restore the circuit after the fast-acting fuse is blown by an overcurrent, and there is a problem that maintenance becomes complicated. It was Further, the responsiveness is not always satisfactory, and there is a problem in terms of cost due to replacement.

On the other hand, contact breakers have been tried to protect some semiconductor elements. However, such a breaker involves a mechanical operation to open the contact, and there is a time delay from the occurrence of overcurrent to the operation of the breaker. As a result, there is a problem that the responsiveness required to protect the semiconductor element is not sufficient.

Therefore, the present applicant has proposed that V ₂ containing a small amount of Cr, etc.
We have already applied for a protection circuit consisting of O ₃ ceramics in which a current limiting element is connected in series with a semiconductor element to restrict the current due to a resistance increase due to a metal → insulator transition when an overcurrent flows.
In such a protection circuit, the current limiting element has better responsiveness than the breaker described above and has the effect of limiting the overcurrent within a few msec, so that the electric circuit can be quickly turned off to ensure the semiconductor switch. Protects and can be used repeatedly,
You can easily restore. However, the current limiting element has a problem that heat is generated when a rated current is applied, and a satisfactory current carrying capacity cannot be obtained.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and reliably protects a semiconductor element even when an overcurrent such as a short-circuit current flows, and further, restores it. It is an object of the present invention to provide a semiconductor device which can be easily carried out and can further effectively radiate heat from a current limiting element and a semiconductor element which generate heat, thereby ensuring a sufficient current carrying capacity.

[Structure of the Invention] (Means for Solving Problems) According to the present invention, a semiconductor element and a current limiting element are electrically connected in series and fixed to the same radiation fin, and the cooling fan is attached to the radiation fin. The semiconductor device is characterized by being attached.

As the current limiting element, a ceramic-based element and a metal-based element whose resistance rapidly increases with a temperature increase, which will be specifically described below, are preferable.

． As a ceramic-based current limiting element, (V _1-x A _x ) ₂ O ₃
A current limiting element having a composition represented by [wherein A represents at least one of Cr, Al, and Sc, and x represents a numerical value in the range of 0 ≦ x ≦ 0.02] is given. Such a current limiting element has a characteristic that the resistance at room temperature is as small as 10 ⁻³ Ω · cm or less, and the resistance increases by two digits at about 100 ° C., and the response is extremely high. Incidentally, as a device whose resistance increases with temperature rise, a BaTiO ₃ semiconductor device is conventionally known, but such a device has a large resistance at room temperature of 10 to 10 ² Ωcm, which is a current limiting factor of the semiconductor device of the present invention. Not suitable as a device.

Cr, Al, and Sc in the above general formula are elements necessary to exert the characteristic (PTC characteristic) of increasing resistance when the temperature rises, and the value of x should be in the range of 0 ≦ x ≦ 0.02. Is required, and a more preferable range is 0.0005 ≦ x ≦ 0.015. When the value of x exceeds 0.02, the current limiting element maintains the high resistance state and does not show the PTC characteristic.

In the current limiting element having the above composition, Fe, Cu, Ni, Co,
By including Sn, it becomes possible to enhance the sinterability of the current limiting element. At least one of these metals is 20
It is possible to improve the sinterability by adding less than or equal to wt%. That is, the addition amount of those metals is 20% by weight.
If it exceeds, the PTC ratio will decrease. The most preferable metal addition range is 2 to 15% by weight. Among the above metals, sn is particularly effective because it can improve the PTC characteristics in addition to the above-mentioned improvement in sinterability. Sn is stable as a metal in the sintering temperature of 1400 to 1600 ° C. and in a sintering atmosphere, and intervenes as a liquid phase between particles of the metal oxide represented by the above formula, and can exert an effect of promoting sintering. In addition, the sintered body after sintering is Sn
The precipitated phase has the effect of reducing the specific resistance in the low resistance region of the PTC characteristic and expanding the current capacity. Further, the current limiting element containing Sn has a feature that the transition temperature variable showing the PTC characteristic is small.

Furthermore, in the current limiting device having the above composition, Fe, Cu, Ni, Co,
By adding W or Mo separately from Sn, the crystal grains of the sintered body can be made small, and sufficient thermal shock resistance can be exhibited even when rapidly heated by an overcurrent.

． The metal-based current limiting element is composed of an insulating cylindrical container and a metal which is enclosed in the container and whose resistance rapidly increases due to a phase transformation from solid to liquid to gas. When the overcurrent disappears, the current limiting element having such a configuration can be repeatedly used because the metal gas is cooled and undergoes a phase transformation from liquid to solid to return to the original state. In such a configuration, by providing a piston inside the tubular container, it is possible to prevent an excessive increase in the pressure of the gaseous metal, and to return to the original shape smoothly by the action of the piston when returning to solid during cooling. You can It is desirable that the metal used here has a low specific resistance and a low melting point. Specifically, H
Examples thereof include g, Na, K, Cd, Zn, In, Sn, Pb and alloys thereof.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a semiconductor device according to the present invention. This semiconductor device 1 includes a radiation fin 2 made of a material having good thermal conductivity such as copper or aluminum. The semiconductor element 3 and the current limiting element 4 are fixed to the heat radiation fin 2 with a good conductive adhesive. The semiconductor element 3 and the current limiting element 4 are connected in series by a lead terminal 5. Further, a cooling fan 6 for forcibly cooling the heat radiation fin 2 is attached to one end of the heat radiation fin 2.

(Operation) The semiconductor device 1 shown in FIG. 1 is used to form the electric circuit shown in FIG. That is, 7 in FIG. 2 is a load that is turned on / off by the semiconductor element 3 of the semiconductor device 1, 8 is a breaker, and these semiconductor device 1, breaker 8 and load 7 are connected in series. In such an electric circuit, when an abnormality occurs in the load 7 and an overcurrent starts to flow in the circuit, the current limiting element 4 with a large resistance change amount incorporated in the semiconductor device 1 responds at high speed to start its operation. Limit the overcurrent to below a specified value. In the breaker 8, a short circuit current flows in the circuit, and after the current is limited by the current limiting element 4 of the semiconductor device 1,
It acts to turn the circuit completely off. Further, although the current limiting element 4 and the semiconductor element 3 generate heat during normal energization, the current limiting element 4 and the semiconductor element 3 are fixed to the same radiation fin 2, and the radiation fin 2 is a cooling fan 6. Each current limiting element 4 is forcibly cooled by
The heat generated by the semiconductor element 3 can be effectively dissipated, and a sufficient current carrying capacity can be obtained. Moreover, since the current limiting element 4 and the semiconductor element 3 are fixed to the same radiation fin 2, the semiconductor device itself can be downsized.

(Embodiment of the Invention) An embodiment of the present invention will be described below with reference to FIGS. 1 and 2 described above.

Example 1 Semiconductor switch (current carrying capacity: 40 A, permissible current time product: I ² ·
t = 3200A ² sec) 3, composition is (V _0.997 Cr _0.003 ) ₂ O ₃ + 5%
Current limiting element made of Sn (shape: 5 mm × 5 mm × 30 mm, resistance: about 1
0 mΩ) 4 as shown in FIG. 1 on a radiation fin (surface area 1200 cm ² ) made of aluminum through a good conductive adhesive, and these semiconductor switch 3 and current limiting element 4 are connected by a lead terminal 5. Connected in series, and the heat radiation fin 2
The semiconductor device 1 was assembled by attaching a cooling fan 6 to one end of the. Such a semiconductor device 1 was connected in series to a load 7 and a commercially available breaker 8 as shown in FIG. 2 to form an electric circuit.

Comparative Example 1 Example 1 except that the radiation fin and the cooling fan were not used.
A semiconductor device having the same structure as in (1) was assembled, and this semiconductor device was connected in series to a load and a breaker in the same manner as in Example 1 to form the electric circuit of FIG.

Then, a short circuit test was performed on the electric circuits of Example 1 and Comparative Example 1 described above by a short circuit current of 220 V and 5.0 kA.
As a result, in the case of the first embodiment, the short-circuit current is limited to 1.2 kA, and the current time product (I ² · t) is 1900 A ² · sec.
It was suppressed and there was a current limiting effect. On the other hand, in the case of Comparative Example 1, as in Example 1, the short-circuit current was limited to 1.2 kA, and the current-time product (I ² · t) was suppressed to 1900 A ² · sec, which had a current limiting effect. It was

Further, in order to examine the current carrying capacity of the electric circuits of Example 1 and Comparative Example 1, a current of 40 A was applied and the temperature rise of the current limiting element was examined. As a result, in the case of the present Example 1, it was confirmed that the temperature rises only to 25 ° C. in one hour of energization, and that there is a sufficient energizing capacity. On the other hand, Comparative Example 1
In the case of, the current increased to 70 ° C when the same current was applied for 20 minutes, and a satisfactory current carrying capacity was not obtained.

Example 2 An insulating cylindrical container 11 shown in FIG. 3, a convex terminal 12a and a concave terminal 12b connected to both ends of the container 11, and a predetermined space in the concave terminal 12b. Piston 13
And a current limiting element (resistance: 5 mΩ) which is enclosed in the container 11 and Hg14 which is pressed by the piston 13.
2 was constructed by assembling a semiconductor device similar to that of Example 1 and connecting this semiconductor device in series with a load and a breaker as in Example 1.

Comparative Example 2 Example 2 except that the radiation fin and the cooling fan were not used.
A semiconductor device having the same structure as in (1) was assembled, and this semiconductor device was connected in series to a load and a breaker in the same manner as in Example 1 to form the electric circuit of FIG.

Then, the same short circuit test as in Example 1 was performed on the electric circuits of Example 2 and Comparative Example 2 described above. As a result, in the case of Example 2, the short-circuit current was limited to 1 kA, and the current-time product (I ² · t) was suppressed to 1500 A ² · sec, resulting in the current limiting effect. On the other hand, in the case of Comparative Example 2, as in Example 2, the short-circuit current was limited to 1 kA, and the current-time product (I ² · t) was suppressed to 1500 A ² · sec, which had a current limiting effect. .

In addition, in order to check the current carrying capacity of the electric circuits of Example 2 and Comparative Example 2, a current of 40 A was applied and the temperature rise of the current limiting element was examined. As a result, in the case of Example 2, it was confirmed that the temperature rises only up to 20 ° C. in one hour of energization, and that there is a sufficient energizing capacity. On the other hand, Comparative Example 1
In the case of No. 3, when the same current was applied for 30 minutes, the temperature rose to 70 ° C and a satisfactory current carrying capacity was not obtained.

Although the semiconductor switch has been described as an example of the power semiconductor element in the above-described embodiment, it can be similarly applied to protection of a semiconductor rectifying element and the like.

[Effects of the Invention] As described in detail above, according to the present invention, even if an overcurrent such as a short-circuit current flows, the semiconductor element can be reliably protected, and the recovery can be easily performed. It is possible to provide a highly reliable and compact semiconductor device capable of effectively radiating heat from a current element and a semiconductor element and ensuring a sufficiently satisfactory current carrying capacity.

[Brief description of drawings]

FIG. 1 is a schematic view showing a semiconductor device of the present invention, FIG. 2 is a circuit diagram showing an electric circuit incorporating the semiconductor device of the present invention, and FIG. 3 is an example of a current limiting element used in the semiconductor device of the present invention. FIG. 1 ... Semiconductor device, 2 ... Radiating fin, 3 ... Semiconductor element (semiconductor switch), 4 ... Current limiting element, 5 ... Lead terminal, 6 ... Cooling fan, 7 ... Load, 8 ... Breaker, 11 ... Insulating cylindrical container, 14 ... Hg.

Claims (5)

[Claims] 1. A semiconductor device in which a semiconductor element and a current limiting element are electrically connected in series and fixed to the same radiation fin, and a cooling fan is attached to the radiation fin. 2. The semiconductor device according to claim 1, wherein the current limiting element is of a ceramic type whose resistance rapidly increases with a rise in temperature. 3. A current limiting element is (V _1-x A _x ) ₂ O ₃ [wherein A is at least one of Cr, Al and Sc, and x is 0 ≦ x ≦
A semiconductor device according to claim 2, wherein the semiconductor device has a composition represented by a numerical value in the range of 0.02]. 4. The current limiting element comprises an insulating container and a metal which is enclosed in the container and whose resistance rapidly increases due to a phase transformation from solid to liquid to gas. 2. A semiconductor device according to claim 1. 5. The metal is Hg, Na, K, Cd, Zn, In, Sn, Pb.
Alternatively, the semiconductor device according to claim 4, which is made of an alloy of these.