JPH07263459A - Transistor - Google Patents

Abstract

PURPOSE:To enable protection from breakdown by thermal runaway without using a temperature detection element or a control circuit. CONSTITUTION:A thermistor thin film 10 having negative temperature characteristics is formed, so as to electrically connect the part between a base electrode 8 and an emitter electrode 10 which are formed on the upper surface of a transistor chip 1. When a current flows in the chip 1, a collector current increases to increase heating value, the resistance value of the thermistor thin film decreases, a bias voltage between a base and an emitter lowers, and a base current is decreased. Thereby an excessive current can be automatically prevented from flowing, so that protection from thermal breakdown is enabled without using independently a temperature detection element, a control circuit, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar type transistor having a base electrode and an emitter electrode formed on the surface of a chip, and more particularly to a transistor which is protected from thermal breakdown due to overcurrent.

[0002]

2. Description of the Related Art In a circuit that uses a bipolar power transistor to supply power to a load such as a motor, if an overcurrent flows through the load for some reason, the internal loss of the power transistor increases and the amount of heat radiation is insufficient. Then, the transistor is overheated, and when the current further increases or the current partially concentrates inside the transistor, the transistor may be thermally destroyed. Therefore, conventionally, the internal temperature of the transistor is detected, and when the temperature exceeds the rated temperature, the base current is cut off to turn off the transistor to prevent thermal destruction due to overcurrent.

In this case, in the transistor, when a constant bias voltage VBE is applied between the base and the emitter, the forward rising voltage of the base-emitter junction decreases as the temperature inside the chip increases. The base current increases, and the collector current increases accordingly. Then, the collector loss, which is determined by the collector saturation voltage and the collector current, increases more and more, and the heat generation inside the transistor increases, causing thermal destruction.

Therefore, as a structure for detecting the temperature of the transistor, for example, a structure in which a temperature detecting element such as a thermistor is separately provided from the outside to the transistor for detection, or a temperature detecting element is integrally provided in the chip of the transistor. There are configurations etc. Then, a control circuit is provided to control the base current based on the detected temperature signal from those temperature detecting elements to suppress the collector current and reduce the amount of heat generation, thereby protecting from thermal destruction. There is something.

[0005]

However, in the conventional device as described above, there is a problem that the number of circuit components increases because the temperature detecting element is separately provided, and such a problem is solved. Even if the temperature detection element is provided integrally with the transistor chip, a control circuit for controlling the base current based on the temperature detection signal is required, and the number of circuit components for that purpose increases. there were.

The present invention has been made in view of the above circumstances, and an object thereof is to automatically suppress the flow of an overcurrent as a function of the transistor chip itself without using a separate component or providing a circuit. Another object of the present invention is to provide a transistor capable of preventing the element from being thermally destroyed.

[0007]

The present invention is directed to a bipolar transistor having a base electrode and an emitter electrode formed on the surface of a chip, and has a negative resistance characteristic with respect to temperature. Is provided on the surface of the chip to electrically connect the base electrode and the emitter electrode.

It is preferable that the thin film resistor is formed in a portion between the base electrode and the emitter electrode formed on the surface of the chip where heat is easily generated.

The thin film resistor may be formed over the entire surface of a portion between the base electrode and the emitter electrode formed on the chip surface.

[0010]

According to the transistor of the first aspect, when the temperature of the chip rises due to heat generation due to an increase in collector loss or the like, the resistance value of the thin film resistor connected between the base and the emitter decreases, and the thin film resistor connected between the terminals increases. The voltage applied to the base of the transistor is reduced, which lowers the applied voltage between the base and emitter of the transistor. As a result, the base current is suppressed, so that the collector current is automatically reduced or cut off, the collector loss is reduced or eliminated, heat generation is suppressed, and the chip temperature is reduced. Become. Therefore, the transistor chip is prevented from being destroyed by heat.

According to the transistor of the second aspect, the thin film resistor is partially provided at a place where heat is likely to occur, so that the heat generated due to the increase of the collector current can be quickly sensed. Be able to protect from destruction.

According to the third aspect of the present invention, by providing the thin film resistor over the entire area between the base electrode and the emitter electrode, the base bias corresponding to the area where heat is generated due to overcurrent or the like. Since it is possible to prevent the concentration of the collector current by lowering the temperature, it is possible to suppress heat generation in a well-balanced manner over the entire formation region of the emitter, and it is possible to prevent thermal breakdown due to current concentration. become.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a PNP type transistor will be described below with reference to FIGS. FIG. 1 is a schematic diagram schematically showing a cross section of a transistor, and a transistor chip 1 is configured as follows. A collector region 4 is formed by a high-concentration p-type silicon substrate 2 and a low-concentration p-type epitaxial layer 3 formed on the silicon substrate 2, and a base region is formed in the p-type epitaxial layer 3 by n-type impurity diffusion. A region 5 is formed, and an emitter region 6 is further formed in the base region 5 by high-concentration p-type impurity diffusion.

An insulating film 7 such as a silicon oxide film is formed on the surface on the upper surface side where the base region 5 and the emitter region 6 are formed, and the base region 5 and the emitter region 6 exposed on the upper surface portion are formed. The insulating film 7 has windows 7a and 7b.
Are formed. A base electrode 8 and an emitter electrode 9 made of aluminum or the like are formed on the window portions 7a and 7b, respectively. A thermistor thin film 10 is formed between the base electrode 8 and the emitter electrode 9 so as to electrically connect them. This thermistor thin film 10 has a function as a thin film resistor,
As will be described later, it has a negative resistance characteristic with respect to temperature.

FIG. 2 is a view of the transistor chip 1 seen from the upper surface side, and the above-mentioned emitter region 6 is actually formed in the base region 5 having a substantially rectangular shape by diffusion in a comb-teeth shape. Correspondingly, base electrode 8 and emitter electrode 9
Are formed in a comb-teeth shape so as to be intricate with each other. Further, pad portions 8a and 9a for bonding are provided on the base electrode 8 and the emitter electrode 9, respectively. Further, the thermistor thin film 10 has a base electrode 8
And the emitter electrode 9 are formed in the central portion of the corresponding region.

The transistor chip 1 having the above structure
Is incorporated into a package (not shown) to form a PNP type transistor 11, and the collector region 4 of the chip 1 has a collector terminal C via an electrode (not shown).
The base electrode 8 is electrically connected to the base terminal B, and the emitter electrode 9 is electrically connected to the emitter terminal E by a bonding wire or the like. The transistor 11 has an electrical equivalent circuit as shown in FIG. That is, the thermistor thin film 10 for temperature detection is in a state of being connected between the base terminal B and the emitter terminal E of the PNP transistor 11.

FIG. 4 shows an electrical configuration when a drive circuit for a DC motor 12 as a load is constructed using the transistor 11 formed as described above. The emitter terminal E of the transistor 11 is connected to the DC power supply terminal VB, the collector terminal C is grounded via the DC motor 12, and the base terminal B is the input resistor 13 and the driving NP.
The N-type transistor 14 is grounded through its collector and emitter.

Next, the operation of this embodiment will be described with reference to FIG. First, the basic operation of the thermistor thin film 10 of the transistor 11 will be described. That is, the characteristic of the resistance value Rs that changes with respect to the temperature of the thermistor thin film 10 is, for example, as shown by the solid line in FIG.
The resistance value is very large at a temperature near room temperature, and the resistance value Rs greatly decreases by about two digits as the temperature rises.

In the transistor 11, the thermistor thin film 10 is connected between the emitter terminal E and the base terminal B, but its resistance value is set to be extremely high in a normal operating temperature state. When a predetermined base bias voltage VEB is applied between the base terminal B and the emitter terminal E, a base current flows to turn on and a collector current flows. And transistor 1
In No. 1, when the junction temperature rises and the forward-direction rising voltage of the emitter-base junction decreases due to an increase in collector current, etc., the base current increases and the collector current starts to increase. .

However, when the temperature of the transistor 11 rises in this way, the resistance value Rs of the thermistor thin film 10 connected between the emitter and the base of the transistor 11 sharply drops, and accordingly, the bias between the base and the emitter is correspondingly increased. The voltage VBE comes to decrease. Then, when the forward-direction rising voltage VBE between the emitter and the base at the temperature becomes equal to or lower than VBE, the base current sharply decreases, so that the collector current IC of the transistor 11 rapidly decreases.
Eventually it will be cut off. That is, the transistor 11 is automatically turned off in accordance with the heat generation of the chip 1 and the collector current IC is cut off, so that heat generation due to overcurrent is suppressed and thermal destruction can be prevented. Of.

Next, in the drive circuit of the DC motor 12 shown in FIG. 4, the drive transistor 14 is turned on when the drive signal of the "H" level is given to the base terminal b, and the collector potential becomes "L". I will change to the level. As a result, the bias voltage VBE obtained by dividing the DC power supply voltage VCC by the resistor 13 is applied between the base and the emitter of the transistor 11. At this time, since the resistance value Rs of the thermistor thin film 10 is very high when the chip temperature of the transistor 11 is low, the bias voltage VBE becomes equal to or higher than the on-voltage VBEon which is the forward rising voltage between the emitter and the base, and the transistor 11 is turned on. To do. As a result, the DC motor 12 is driven so that the DC power supply voltage VCC is applied via the transistor 11.

In such a driving state of the DC motor 12, if the current supplied to the DC motor 12 increases for some reason, the collector loss of the transistor 11 increases and the temperature inside the chip 1 rises. Along with this, the temperature of the thermistor thin film 10 rises, and as described above, the resistance value Rs decreases due to the negative resistance characteristic. At this time, if the value of the terminal voltage VBEs of the thermistor thin film 10 becomes smaller than the bias voltage VBEon required to turn on the transistor 11, (V
BEs <VBEon) The transistor 11 is turned off.

Further, the terminal voltage VB of the thermistor thin film 10
Using the resistance value Rs and the resistance value Ri of the input resistor 13, Es can be expressed by the following equation with respect to the DC power supply voltage VCC. VBEs = VCC × (Rs / (Rs + Ri)) Therefore, when the temperature of the transistor chip 1 reaches a predetermined temperature (for example, 150 ° C.), the transistor 11 is turned off, that is, the terminal voltage VBEs of the thermistor thin film 10 is turned on in that state. It is only necessary to set the film thickness and the width dimension that determine the resistance value Rs of the thermistor thin film 10 so that the voltage becomes VBEon.

According to this embodiment, since the thermistor thin film 10 is formed on the surface of the transistor chip 1 so as to electrically connect the base electrode 8 and the emitter electrode 9, the current flowing through the transistor 11 increases. When the heat is generated, the heat causes the resistance value of the thermistor thin film 10 to decrease and the base current to decrease. Therefore, it is possible to automatically prevent the heat destruction due to the heat generation due to the overcurrent. Will be able to.

Further, since the thermistor thin film 10 is provided in a portion where current concentration is likely to occur, it is possible to quickly detect a temperature rise of the transistor chip 1 due to heat generation and protect it from thermal destruction. .

FIGS. 6 and 7 show a second embodiment of the present invention. The difference from the first embodiment is that the thermistor thin film 10 is replaced by a space between the base electrode 8 and the emitter electrode 9. Thermistor thin film 15 as a thin film resistor entirely
Has been installed. That is, in FIG. 6, the thermistor thin film 15 is entirely formed in a portion where the base electrode 8 and the emitter electrode 9 face each other, which is shown in FIG.
As shown in the schematic cross section, the thermistor thin film 15 is formed by a method such as vapor deposition.

According to this structure, even when the collector current is locally concentrated in the emitter region 6 while the collector current is flowing in the same manner as described above, it is possible to deal with the local heat generation in that portion. The resistance value of the thermistor thin film 15 in the portion to be operated is reduced, and the collector current is suppressed or cut off. As a result, even when the collector currents are unevenly distributed, local heat generation can be suppressed in response to partial current concentration in the emitter region 6, and currents can flow in good balance as a whole. It becomes possible to prevent partial thermal destruction due to current imbalance.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. NPN
Shape transistor is also applicable. It can also be applied to a transistor that does not use an epitaxial layer. The thermistor thin film as a thin film resistor may be formed by being divided into a plurality of parts on the surface of the transistor.

[0029]

As is apparent from the above description, according to the transistor of the present invention, the following effects can be obtained.
That is, according to the transistor of the first aspect, since the base electrode and the emitter electrode are electrically connected by the thin film resistor having the negative resistance characteristic with respect to temperature, the collector loss is increased. When the temperature rises due to heat generation, etc., the resistance value of the thin film resistor is reduced, the applied voltage between the base and emitter of the transistor is reduced and the base current can be limited, and the collector current can be reduced or cut off. Therefore, there is an excellent effect that it is possible to automatically protect from destruction due to heat without separately providing a temperature detecting element or a control circuit.

According to the second aspect of the present invention, by providing the thin film resistor partly at a place where heat is likely to occur, it is possible to quickly detect the heat generated by the increase in the collector current. It has an excellent effect that it can be protected from destruction.

According to the third aspect of the present invention, the thin film resistor is provided on the entire surface between the base electrode and the emitter electrode, so that the base bias is provided corresponding to the portion where heat is generated due to overcurrent or the like. Since it is possible to prevent the concentration of the collector current by reducing the heat dissipation, it becomes possible to suppress the heat generation in a good balance over the entire region where the emitter is formed, and it is possible to prevent the thermal breakdown due to the current concentration. It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention.

FIG. 2 Top view

FIG. 3 is an equivalent circuit diagram of a transistor.

FIG. 4 is an electrical configuration diagram of a motor drive circuit.

FIG. 5 is a characteristic diagram of the resistance value of the thermistor thin film with respect to temperature and the base current.

FIG. 6 is a view corresponding to FIG. 2 showing a second embodiment of the present invention.

FIG. 7 is a schematic sectional view.

[Description of Reference Signs] 1 is a transistor chip, 2 is a silicon substrate, 3 is an epitaxial layer, 4 is a collector region, 5 is a base region, 6
Is an emitter region, 7 is an insulating film, 8 is a base electrode, 9 is an emitter electrode, 10 is a thermistor thin film (thin film resistor), 1
Reference numeral 1 is a transistor, 12 is a DC motor, 13 is an input resistor, 14 is a driving transistor, and 15 is a thermistor thin film (thin film resistor).

Claims (3)

[Claims] 1. A bipolar transistor in which a base electrode and an emitter electrode are formed on a chip surface, a thin film resistor having a negative resistance characteristic with respect to temperature is provided on the chip surface to form the base electrode and the emitter electrode. A transistor characterized by being configured so as to electrically connect the two. 2. The transistor according to claim 1, wherein the thin film resistor is formed in a portion between the base electrode and the emitter electrode formed on the surface of the chip where heat is likely to occur. 3. The transistor according to claim 1, wherein the thin film resistor is formed over the entire surface of a portion between the base electrode and the emitter electrode formed on the chip surface.