JPH0750385A - Power transistor - Google Patents

Abstract

PURPOSE:To miniaturize a circuit and to reduce power loss without using an overcurrent detecting resistor. CONSTITUTION:A collector layer is provided, a base layer 7 is formed on the collector layer 6, emitter layers 8 are provided onto the base layer 7, an emitter electrode 2 is formed on each emitter layer 8 in one piece, an emitter bonding pad is provided onto the prescribed part of the emitter electrode 2, and an overcurrent detecting electrode 5 is provided to the emitter electrode 2 apart from the emitter bonding pad by a prescribed distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transistor, and more particularly to a power transistor for medium current and large current, which is used for a switching, a series type regulator and a special circuit where surge occurs.

[0002]

2. Description of the Related Art FIG. 7 is a schematic plan view of a conventional power transistor. Although not shown, this transistor has a base layer formed on the collector layer and a plurality of emitter layers formed on the base layer to form a plurality of unit transistors. An emitter electrode 72 and a base electrode 74 are formed in a comb shape on the emitter layer and the base layer, respectively, and the unit transistors are connected to each other. Further, an emitter bonding pad portion 71 and a base bonding pad portion 73 are provided on the side of the emitter electrode 72 and the base electrode 74, respectively.

In the prior art, in order to prevent an increase in the current capacity of the power transistor and destruction of the element due to current concentration, the surface electrode has a mesh emitter structure, and the base ballast resistor and the emitter ballast resistor are used. It is performed to have a structure provided with the like.

However, even with such a structure,
If a current higher than the rating flows through the device, the device may be destroyed. In addition, with respect to a medium current or a large current transistor, a surge current of several times to several tens of times instantaneously flows as compared with a normal operating current in many cases.

For example, as shown in FIG. 8, when this power transistor is used for a regulator, it is necessary to detect such an overcurrent, and therefore an overcurrent detection resistor 85 is provided. Regulator element 8 incorporating a voltage control IC 81 incorporating this overcurrent protection circuit
In 0, the emitter wiring resistor 83 is inserted in series with the transistor to reduce the local concentration of current, and
The overcurrent detecting resistor 85 is provided in series with the emitter wiring resistor 83. This overcurrent detection resistor 85
Must be able to withstand more than the current flowing through the power transistor, and therefore has a large volume, and since it also requires heat dissipation, it is externally attached separately from the element. The overcurrent is detected by the voltage drop across the overcurrent detection resistor 85, and the protection circuit limits the base current to prevent the transistor from being destroyed.

When a power transistor is used for the purpose of switching, since the transistor is in a saturated state during operation, it is possible to detect the current by the voltage between the collector and the emitter. When operating the transistor in the active region like the above-mentioned regulator, the above-described overcurrent detection resistor 85 is indispensable.

That is, in the power transistor having such a structure, since the current flowing through the emitter electrode is larger than that of the other electrodes, the wiring resistance and the contact resistance cannot be ignored in the circuit, and the surge current is particularly large. When applied, the voltage drop generated by these resistances becomes large, and the current is evenly concentrated in a large number of unit transistors, causing problems such as breakdown. Will be needed.

[0008]

By the way, in the above-mentioned conventional technique, as described above, a resistor for detecting an overcurrent is required, and this resistor cannot withstand more than the current flowing through the power transistor. Since it must not be provided, the volume is increased and heat dissipation is also required. Therefore, it is generally externally attached in addition to the element. Therefore, there is a problem that the entire circuit has to be large.

Further, in the case of a low loss regulator or the like which requires the potential difference between the input and the output to be as small as possible, there is also a problem that the voltage drop of the overcurrent detection resistor increases the loss of the entire circuit. there were.

The present invention has been made in view of the above points, and an object of the present invention is to provide a power transistor capable of reducing the circuit size and loss without using an overcurrent detection resistor. To do.

[0011]

In order to achieve the above object, a power transistor of the present invention comprises a collector layer,
A base layer formed on the collector layer, a plurality of emitter layers formed on the base layer, an emitter electrode integrally formed on each emitter layer, and an emitter electrode In a power transistor in which a predetermined portion is provided with an emitter bonding pad portion for electrically connecting to a frame, a voltage for the predetermined distance is applied to the emitter electrode portion located at a predetermined distance from the emitter bonding pad portion. Is characterized by being provided with an electrode for detecting an overcurrent.

Here, the predetermined distance is preferably the maximum distance from the emitter bonding pad portion because the detection accuracy can be improved as the emitter electrode wiring resistance value increases.

[0013]

Function: A voltage proportional to the applied current is generated between the emitter bonding pad portion and the electrode for detecting an overcurrent provided on the emitter electrode which is separated from the emitter bonding pad portion by a predetermined distance. The applied current can be known by effectively using the wiring resistance of the emitter electrode and detecting the voltage by the electrode for detecting the overcurrent. Further, since the emitter electrode has a larger current flowing than the other electrodes, the maximum current flowing through the power transistor can be recognized by detecting the current between them.

Further, since the electrode for detecting this overcurrent is provided in the power transistor, the circuit can be simplified.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a schematic plan view of a power transistor chip according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA in FIG.

A base layer 7 is formed on the collector layer 6, and an emitter layer 8 having a lattice pattern is formed on the base layer 7.
Are formed in plural. Further, a plurality of unit transistors composed of the collector layer 6, the base layer 7, and the emitter layer 8 are connected by a comb-shaped base electrode 4 and an emitter electrode 2, respectively. In the emitter electrode portion where the comb-shaped emitter electrodes 2 are gathered, an emitter bonding pad portion 1 for electrically connecting to a frame by a wire or the like is provided, and an emitter bonding pad portion 1 is provided at a position apart from the emitter bonding pad portion 1 by a predetermined position. A current detection electrode 5 is provided. An emitter electrode wiring resistor 13 is interposed between the unit transistors, and an emitter electrode contact resistor 14 is interposed between the emitter contact portion and the emitter electrode connecting portion in each unit transistor.
Furthermore, a collector electrode 11 made of a solder electrode or the like is formed on the entire back surface of the chip.

In the power transistor of this structure, the emitter region wiring resistor 13 is effectively used to detect the voltage across it. That is, the resistance value of the overcurrent detection electrode 5 increases in proportion to the distance from the emitter bonding pad portion 1, which is effective.

FIG. 3 shows an equivalent circuit of the power transistor of this embodiment of the present invention. Multiple unit transistors Tr
₁ , Tr ₂ , ... Tr ₉ are provided. These units transistors Tr _1, Tr _2, is between · · Tr _9, emitter electrode wiring resistance
Rh ₁ , Rh ₂ , ... Rh ₉ are connected. Further, the emitter contact portion of each unit transistor, the emitter electrode connecting portion, the emitter electrode contact resistance _{Rc 1, Rc 2, ·· Rc} 9
Are connected. Further, the emitter electrode wiring resistance Rh ₁ ,
An overcurrent detection electrode 5 for detecting the voltage across Rh ₂ , ..., Rh ₉ is provided. In power transistors, in order the current flowing through the emitter electrode is larger than the other electrodes, the emitter electrode wiring resistance _{Rh 1, Rh 2, ·· Rh} 9 and the emitter electrode contact resistance _{Rc 1, Rc 2, ·· Rc} 9 Effectively acts on the circuit, and particularly when a surge current is applied, the voltage drop generated by these resistors is large. Therefore, the current is not evenly distributed to a large number of unit transistors Tr ₁ , Tr ₂ , ..., Tr ₉ and the current concentrates near the bonding pad, which causes problems such as destruction, but to prevent this. In addition, the above-mentioned overcurrent detection electrode 5 is provided.

In the manufacturing method of this embodiment, since the collector layer 6, the base layer 7, and the emitter layer are formed by known steps and then formed into a mesh structure, the base layer is formed into an island shape. Further, on the emitter layer, a hole is formed in the oxide film 9 at a portion which comes into contact with each electrode in an island shape or a comb shape, and a metal film such as aluminum serving as an electrode is formed by a vapor deposition method or the like. Then, after separating the base electrode 4 and the emitter electrode 2, the metal film is formed so that the wires for electrically connecting to the frame are concentrated on the emitter bonding pad 1 and the base bonding pad 3, respectively. By selectively removing, the base electrode 4 and the emitter electrode 2 are formed into comb-shaped electrodes that are intermeshing with each other. In this way, a power transistor in which a plurality of unit transistors are connected in parallel is completed. As described above, in the embodiment of the present invention, in the step of removing the surface electrode, as described above, the overcurrent detection electrode 5 has an electrode shape that can be provided at a position separated from the emitter bonding pad 1 by a predetermined distance. A mask pattern for selective removal of the surface electrodes may be set.

FIG. 4 is a schematic plan view of a power transistor chip according to another embodiment of the present invention. This structure has a structure in which, among the comb-shaped emitter electrodes 2, the emitter wiring provided with the electrode 5 for detecting an overcurrent is made longer than the other emitter wiring or the emitter bonding pad 1. With this structure, the resistance value of the emitter wiring resistance can be increased, and the detection accuracy can be further improved.

FIG. 5 is a schematic plan view of a power transistor chip according to another embodiment of the present invention.
This structure has a structure in which, in addition to the emitter electrode structure of the previous embodiment, a plurality of selectively narrow portions and a plurality of emitter electrode narrowing portions 10 are provided. The narrowed portion 10 can increase the resistance value of the emitter wiring resistance,
The detection accuracy can be further improved.

As described above, all the embodiments of the present invention relate to the pattern shape of the surface electrode of the power transistor chip, but the present invention is not limited to these shapes, and the resistance value of the emitter wiring resistance is increased. As long as it has a structure and an electrode for overcurrent detection is formed on the emitter electrode, other shapes can be applied.

In addition, pattern formation of these surface electrodes can be easily realized by changing a mask pattern such as a glass mask of photolithography, which has been conventionally used when forming the surface electrodes.

[0024]

As described above, according to the present invention,
Since an electrode for overcurrent detection is provided in the emitter electrode portion that is a predetermined distance away from the emitter bonding pad, the external overcurrent detection resistor that was required in the past is no longer necessary, It is possible to achieve miniaturization and simplification. Further, the voltage drop at the overcurrent detection resistor is eliminated, and the loss can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA in FIG. 1 of the embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of an embodiment of the present invention.

FIG. 4 is a schematic plan view of another embodiment of the present invention.

FIG. 5 is a schematic plan view of another embodiment of the present invention.

FIG. 6 is a circuit diagram of a regulator element incorporating an embodiment of the present invention.

FIG. 7 is a schematic plan view of a conventional example.

FIG. 8 is a circuit diagram of a regulator element incorporating a conventional example.

[Explanation of symbols]

 1 ... Emitter bonding pad 2 ... Emitter electrode 3 ... Base bonding pad 4 ... Base electrode 5 ... Overcurrent detection electrode 6 ...・ Collector layer 7 ・ ・ ・ ・ Base layer 8 ・ ・ ・ ・ ・ ・ Emitter layer 13 ・ ・ ・ ・ Emitter electrode wiring resistance 14 ・ ・ ・ ・ Emitter electrode contact resistance

Claims (1)

[Claims] 1. A collector layer, a base layer formed on the collector layer, a plurality of emitter layers formed on the base layer, and integrally formed on each emitter layer. In a power transistor having an emitter electrode and an emitter bonding pad portion for electrically connecting to a frame at a predetermined portion of the emitter electrode, the emitter electrode at a position separated from the emitter bonding pad portion by a predetermined distance. A power transistor, wherein an electrode for detecting an overcurrent for detecting a voltage for a predetermined distance is provided in a portion.