JPH0587150B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device such as a monolithic IC that is prevented from malfunctioning due to leakage current at high temperatures.

[Conventional technology]

In monolithic ICs, in addition to the leakage current caused by crystal defects, it is known that leakage current due to the steady PN reverse junction increases as the temperature rises. In particular, in bipolar ICs, the operating temperature of monolithic ICs is limited by the increase in leakage current between the semiconductor substrate and the epitaxial layer formed on its surface layer. In other words, leakage current from the collector of the NPN transistor and the base of the PNP transistor to the substrate at high temperatures changes the characteristics of the IC, causing malfunction and making it impossible to obtain the desired operation.

By the way, when configuring a basic amplifier circuit in a monolithic IC, as shown in FIG. 3, a PNP type transistor 2 is installed as a circuit element. This transistor 2 has a power supply voltage Vcc applied to its emitter from a terminal 4 through a resistor 5, its collector grounded through a resistor 6, and a specific bias voltage applied to its base through resistors 8 and 10. The switch 12 is inserted to switch the operation of the transistor 2. When this switch 12 is made conductive as shown by the broken line, a normal amplification operation is performed between the base and collector of the transistor 2, and the input terminal 13 is connected to the transistor 2.
The amplified output V _p corresponding to the input signal V _i applied to the base of the amplifier is taken out from the output terminal 14 .

For example, as shown in FIG. 4, the PNP transistor 2 in such a monolithic IC is constructed by forming a highly doped N-type buried layer 16 in a P-type semiconductor substrate 15, and then depositing N-type epitaxy on the surface layer. epitaxial layer 18 is formed, and this epitaxial layer 1
8 is separated from other adjacent conductive regions by separation regions 20 to form a base B, and a P-type conductive region 2 is formed inside the epitaxial layer 18.
2 and 24 to form emitter E and collector C.
That is. In addition, the epitaxial layer 18
A highly doped N-type conductive region 26 is formed as a base electrode. Then, an insulating layer 28 is provided on the surface of the epitaxial layer 18 and the isolation region 20, and each conductive region 22, 24, 26 is provided with an insulating layer 28.
Openings are formed in the base, emitter, and collector for electrical connection by installing wiring conductors, and the wiring conductors are installed.

In such a transistor 2, as shown in FIG. 3, when the switch 12 is opened, the bias voltage V _i
is released and the operation is stopped, but switch 12
Even when opened, the semiconductor substrate 1 may be separated from the epitaxial layer 18 forming the base B at a high temperature of 200°C.
5, a leakage current I _L flows, and this leakage current
Since the value of I _L increases at an accelerated rate as the temperature rises, transistor 2 becomes abnormally conductive.
In particular, in the PNP transistor 2 in such a monolithic IC, the base B is composed of the epitaxial layer 18, so when a leakage current I _L occurs, this leakage current I _L is converted into a current by the transistor 2. It is multiplied by the amplification factor β and appears at the output V _p .

For this reason, various protection circuits (thermal shutdown) have conventionally been devised to prevent such malfunctions at high temperatures.

[Problem that the invention seeks to solve]

By the way, malfunctions at high temperatures have a greater effect on semiconductor devices that operate with a smaller current, which is inconsistent with the goal of preventing the operating current from becoming smaller and reducing the power consumption of the semiconductor device. Furthermore, even if a thermal shutdown is performed by adding a protection circuit, the temperature range in which normal operation occurs is narrow, and the usable temperature is up to about +150°C.

Therefore, the present invention compensates for leakage current in a semiconductor device, increases the upper limit operating temperature at which normal operation can be performed, and expands the usable temperature range.

[Means for solving problems]

As illustrated in FIG. 1, the semiconductor device of the present invention includes a first transistor (transistor 2) formed on a semiconductor substrate 15, through which a leakage current flows from the base to the semiconductor substrate side at high temperatures; A second transistor (transistor 30, 32) is formed to be separated from the first transistor, and when the leakage current occurs in the first transistor, a second transistor (transistor 30, 32) that similarly generates a leakage current from the base to the semiconductor substrate side is installed. and a current mirror circuit 34 which obtains a current corresponding to the leakage current by amplifying the leakage current, and supplies the current obtained by the current mirror circuit to the base of the first transistor. It is characterized by

[Effect]

At high temperatures, a leakage current flows from the base of the first transistor to the semiconductor substrate, and at this time, a similar leakage current also flows from the base of the second transistor on the current mirror circuit side to the semiconductor substrate. In the current mirror circuit, the leakage current becomes the base input, a current corresponding to the current amplification factor of the second transistor is taken out, and this current is supplied to the base of the first transistor. Therefore, the leakage current flowing through the first transistor is compensated by the current of the current mirror circuit, thereby preventing malfunctions due to leakage current at high temperatures and improving the upper limit operating temperature of the semiconductor device.

〔Example〕

FIG. 1 shows an embodiment of a semiconductor device of the present invention.

This semiconductor device forms an amplifier circuit by installing resistors 5, 6, 8, and 10 for a transistor 2 as a first transistor, and transistors 30 and 30 as second transistors equivalent to the transistor 2. 32 is installed, and the leakage current I _L flowing from the transistor 2 to the semiconductor substrate 15 is offset by using currents corresponding to the leakage currents I _L1 and I _L2 flowing from each transistor 30 and 32 to the semiconductor substrate 15 as compensation currents. It is something that

In this semiconductor device, for example, after forming buried layers 16a, 16b, 16c of opposite conductivity type for transistors 2, 30, 32 on a P-type semiconductor substrate 15, epitaxial layers 18a, 18b,
18c will be installed. Each epitaxial layer 18a
~18c, the transistors 2, 30,
It is divided into a base B as a conductive region forming a part of 32.

Each epitaxial layer 18a-18c is provided with an emitter E consisting of conductive regions 22a, 22b, 22c of the opposite conductivity type to that of the epitaxial layers 18a-18c, and a collector C consisting of conductive regions 24a, 24b, 24c. , highly concentrated conductive regions 26a, 26b, 26 of the same conductivity type as the epitaxial layers 18a to 18c as individual base electrodes.
c is installed. Then, on the surfaces of the epitaxial layers 18a to 18c and the isolation region 20,
An insulating layer 28 is provided and each conductive region 22a-22
c, 24a to 24c, and 26a to 26c are opened to install wiring conductors to the base, emitter, and collector for electrical connection, and necessary wiring conductors are installed.

By the way, in this semiconductor device, as shown in FIG. 2, the transistors 30 and 32 installed for the PNP transistor 2 generate a compensation current that cancels out the leakage current I _L flowing from the transistor 2 to the semiconductor substrate 15. It constitutes a current source 34 that supplies the base of the transistor 2. That is, the transistors 30 and 32 form a current mirror circuit by diode-connecting the transistor 30 and commonly connecting the base and collector of the transistor 30 to the base of the transistor 32, with the collector of the transistor 32 forming a part of the transistor 2. It is bonded to epitaxial layer 18a.

In such a semiconductor device, the switch 12
When closed, the supply voltage is applied to the base of transistor 2.
Since a predetermined bias voltage V _i is applied by dividing Vcc by the resistors 8 and 10, normal amplification operation can be obtained, and when the switch 12 is opened, the bias voltage V _i is released and the amplification Operation is stopped. Therefore, at room temperature, by closing the switch 12, the transistor 2 can be caused to perform an appropriate amplification operation.

At this time, even if the switch 12 is opened to stop the operation of the transistor 2, a leakage current I _L flows from the base of the transistor 2 to the semiconductor substrate 15 under high temperature, and the transistor 2 exhibits an abnormal conduction state.

By the way, in terms of area ratio with respect to the epitaxial area of transistor 2, transistors 30 and 32
Assuming that the epitaxiality of is set to 1/2,
The leakage current I _L flowing from the epitaxial layer 18a of the transistor 2 to the semiconductor substrate 15 and the epitaxial layer 18b, 1 of each transistor 30, 32
Leakage current I _L1 flowing from 8c to semiconductor substrate 15,
The sum of I _L2 (I _L1 + I _L2 ) becomes equal (I _L1 + I _L2 =
_IL ).

Since the transistors 30 and 32 form a current mirror circuit, the emitter current I _E of the transistor 30 is equal to the leakage current I _L of the transistor 2, and the emitter current I _E of the transistor 32 is also equal to the leakage current I L of the transistor 2. It becomes equal to the leakage current I _L of .

That is, when leakage current I _L occurs in transistor 2, transistors 30 and 32 under similar conditions
At the same time, leakage currents I _L1 and I _L2 occur, and an emitter current I _E equal to the leakage current I _L flows through the transistor 3.
It flows to 0,32. This emitter current I _E flows into the base B of transistor 2, and
This cancels out the leakage current _IL of the epitaxial layer 18a. Furthermore, even when the switch 12 is closed and the amplification operation is performed, the operation is as described above, and during the high temperature amplification operation, for example,
Even if a leakage current I _L occurs in the transistor 2, the leakage current I _L can be canceled out in the same way, so stable high temperature operation is possible.

In other words, when performing amplification operations at high temperatures,
When a leakage current I _L occurs in the transistor 2, a compensation current due to the leakage currents I _L1 and I _L2 generated from the transistors 30 and 32 is caused to flow to the base B of the transistor 2, thereby preventing malfunction due to the leakage current I _L of the transistor 2. can be prevented,
This makes it possible to improve the reliability of operation at high temperatures.

Although the embodiments have been described using a lateral PNP transistor as an example of a PNP transistor, the present invention can be similarly applied to various transistors such as those having a semiconductor substrate as a collector.

〔Effect of the invention〕

According to this invention, by offsetting the leakage current that occurs under high temperatures with the compensation current obtained from other leakage currents that occur under the same conditions, the influence of the leakage current can be avoided, and malfunctions due to transistor leakage current can be prevented. This can be reliably prevented, increasing the reliability of operation under high temperatures and expanding the usable temperature range.
For example, monolithic ICs can operate stably at temperatures above 200°C, and power amplification ICs have structural advantages such as smaller heat dissipation fins, and are also economically effective.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the semiconductor device of the present invention, FIG. 2 is a circuit diagram showing the semiconductor device shown in FIG. 1, and FIG. 3 is a circuit diagram showing a conventional semiconductor device.
FIG. 4 is a diagram showing a specific structure of a transistor in the semiconductor device shown in FIG. 3. 2...transistor (first transistor),
15... Semiconductor substrate, 30, 32... Transistor (second transistor), 34... Current mirror circuit.

Claims (1)

[Scope of Claims] 1. A first transistor formed on a semiconductor substrate, through which a leak current flows from the base to the semiconductor substrate side at high temperatures; A first transistor formed on the semiconductor substrate and separated from the first transistor, and When the leakage current occurs in the first transistor, a second transistor that similarly generates leakage current from the base to the semiconductor substrate side is installed, and by amplifying the leakage current, a current corresponding to the leakage current is obtained. A semiconductor device comprising: a current mirror circuit; and supplying the current obtained by the current mirror circuit to the base of the first transistor.