JPH06291337A - Voltage regulation - Google Patents

Abstract

PURPOSE:To provide a voltage regulation diode for a MOSFET type not exceeding 6V, where a backward direction characteristic and a forward direction characteristic are improved up to a stage of the practical use. CONSTITUTION:The P-type base region 2 and drain region 3 are formed on the surface side of a semiconductor substrate being an n-type collector region 1 while an n-type emitter region 4 is formed in the central part of the base region 2 and an anode electrode 7 formed on the emitter region 4 is extended on an insulating film 6 on a channel part 5 between the base region 2 and the drain region so as to form a p-channel type MOSFET 11 of the drain region 3, the base region 2 and the emitter region 4. Then, a p-type by-pass region 10 partially contacting the anode electrode 7 and the base region 2 with the emitter region 4 in a MOSFET type voltage regulation type where an NPN transistor is formed of the collector region 1, the base region 2 and the emitter region 4 in the vertical direction is formed, in order to improve a breakdown waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MOSFET type constant voltage diode for 6V or less, which controls the Zener breakdown voltage by the gate voltage of the MOSFET.

[0002]

2. Description of the Related Art A PN junction type diode is generally used as a constant voltage diode which causes a breakdown at a voltage of 6 V or less. The breakdown waveform of the reverse characteristic of this PN junction type constant voltage diode is the zener voltage V _Z of the threshold value at which the reverse voltage V _R applied causes breakdown as shown in the waveform (f) of FIG. The reverse current I _R flows in a gentle curve before and after, and after the breakdown, the reverse current I _R flows in almost proportion to the reverse voltage V _R. In such a PN junction type constant voltage diode, the breakdown waveform in the vicinity of the Zener voltage V _Z is a waveform of a gentle curve with a poor rise, and the waveform after breakdown is an inclined waveform with a small inclination angle θ. It is often unsuitable for millimeter current control.

Therefore, as a constant voltage diode for 6 V or less in which the above-mentioned breakdown waveform is improved to a sharp one, for example, a MOSFET type constant voltage diode as shown in FIG. 4 is known. The constant voltage diode of FIG. 4 will be described with reference to the equivalent circuit of FIG.

P-type impurities are selectively diffused on the surface of an N-type semiconductor substrate (1) to form a base [source] region (2) and a drain region (3) in the vicinity thereof. Base area (2)
N type impurities are selectively diffused in the central portion of the N to form an N ⁺ type emitter [gate] region (4). A portion of the insulating film (6) formed on the surface of the semiconductor substrate (1) on the emitter region (4) and the drain region (3) is selectively removed, and the anode is formed on the exposed emitter region (4). A [gate] electrode (7) is formed, and a short electrode (8) is formed on the drain region (3). The anode electrode (7) extends onto the insulating film (6) on the channel portion (5) between the base region (2) and the drain electrode (3). A cathode electrode (9) is formed on the back surface of the semiconductor substrate (1). The semiconductor substrate (1) is, for example, N ⁻ -type substrate (1 ′) and N ⁻
A type epitaxial layer (1 '') is laminated to form a collector region (1) on a semiconductor substrate (1).

A drain region (3), a base region (2), and an emitter region (4) arranged side by side are P-channel MOSFETs.
(11) is formed, and an N ⁺ PN ⁺ type transistor (12) is formed by the vertical collector region (1), base region (2) and emitter region (4). The base region (2) of the transistor (12) becomes the source region of the MOSFET (11),
The emitter region (4) of the transistor (12) is MOSFE
In the gate region of T (11), the zener voltage V _Z of the constant voltage diode is controlled by the gate voltage V _T of the MOSFET (11).

That is, when a reverse bias voltage is applied to the constant voltage diode shown in FIG. 4, when the negative gate voltage V _T applied to the anode electrode (7) reaches a predetermined value, the channel portion of the MOS structure ( 5) becomes conductive and MOSF
The ET (11) is turned on, and the channel current flowing through the channel portion (5) at this time becomes the base current of the transistor (12), and the transistor (12) is turned on. When the transistor (12) is turned on, the constant voltage diode breaks down, and the breakdown waveform shown in the waveform (c) of FIG. 6A is obtained.

Gate voltage for turning on the MOSFET (11)
Pressure V_TBy controlling the
Zener voltage V_ZThe breakdown waveform in the vicinity rises
It is possible to make a sharp waveform. Also, Tran
Current gain h of transistor (12) _FEAnd after the breakdown
It is possible to cause the waveform inclination to approach 90 °. This
A constant voltage diode with a breakdown waveform
This is advantageous for controlling a small amount of current.

[0008]

By the way, the MO of FIG.
The SFET type constant voltage diode has N ⁺ PNP in the area of the emitter region (4), the base region (2), the channel portion (5), and the drain region (3) which are arranged side by side when the MOSFET (11) is turned on. Thyristor occurs parasitically. This parasitic thyristor is turned on immediately when the constant voltage diode breaks down, and as shown in FIG. 6A, the Zener saturation current I _BO is limited to a small value so that the Zener saturation current I _BO becomes practical. There was a problem that the required value could not be set too high.

The forward characteristic of the constant voltage diode of FIG. 4 is as shown in the waveform (d) of FIG. 6 (b). That is,
When a positive forward voltage V _F is applied to the anode electrode (7), since the base region (2) of the transistor (12) is in an electrically floating state, the breakdown voltage of the emitter region (4) is in the reverse direction. appear in the outside becomes the breakdown voltage, the waveform of the forward characteristic of the forward voltage V _F and the forward current I _F, V _F waveform and reverse (e) LV in chain line in FIG conventional Zener diode 6 (b)
It becomes the _CEO waveform (d). Therefore, the constant voltage diode of FIG. 4 has a narrow range of applications where the field of application of the forward characteristic is extremely limited.

Actually, the constant voltage diode of FIG. 4 is based on the literature, and since both the reverse characteristic and the forward characteristic have narrow fields of use, they are not yet in practical use.

It is an object of the present invention to provide a MOSFET type constant voltage diode for 6 V or less in which the reverse characteristic and the forward characteristic are improved to a practical level.

[0012]

SUMMARY OF THE INVENTION According to the present invention, a base region and a drain region formed by selectively diffusing impurities of another conductivity type in two regions of a surface of a one conductivity type semiconductor substrate, which are collector regions, are separated from each other, and a base. An emitter region formed by selectively diffusing another conductivity type impurity into the region, an insulating film formed on the channel region between the base region and the drain region and on the base region, and on the emitter region and the insulating film. In the MOSFET constant voltage diode having the formed anode electrode and the cathode electrode formed on the back surface of the semiconductor substrate, the anode electrode and the base region are partially formed in the same emitter type as the base region. By forming the bypass region for conduction, the above object is achieved.

[0013]

By contacting the base region [source region] and the anode electrode [gate electrode] of the MOSFET type constant voltage diode in the bypass region, the channel current flowing when the MOSFET is turned on is suppressed, and the emitter region, the base region and the connector region are suppressed. The current amplification factor h _{FE of the} transistor formed in 1 is decreased, and the timing at which the thyristor parasitically generated in the lateral direction of the emitter region, the base region, the channel portion, and the drain region is turned on is delayed, which causes Zener saturation of the reverse characteristic. The current I _BO increases.

When the base region [source region] and the anode electrode [gate electrode] are brought into contact with each other in the bypass region, the forward characteristic is the same as that of a normal PN junction type constant voltage diode in the forward direction.

[0015]

FIG. 1 shows an embodiment of the present invention applied to the constant voltage diode of FIG. 4 and its equivalent circuit is shown in FIG. Note that FIG.
2 and FIG. 2 that are the same as or equivalent to those in FIG. 4 and FIG.

In the MOSFET type constant voltage diode for 6 V or less of FIG. 1, a bypass region (10) of the same conductivity type as the base region (2) is formed up to the base region (2) in the center of the emitter region (4). The base region (2) and the anode electrode (7) are in contact with each other in the bypass region (10). This constant voltage diode is equivalent to that shown in FIG.
As shown in, between the source and the base of the P-channel MOSFET (11) or the N ⁺ PN ⁺ type transistor (12)
A resistor (13) is connected between the base and the emitter of. This resistor (13) is a P-channel MOSFET
It corresponds to the resistance component in the base region (2) when the channel current that turns on (11) flows in the base region (2). The additional connection of the resistor (13) between the base and the emitter of the transistor (12) reduces the current amplification factor h _FE of the transistor (12).

In the constant voltage diode of FIG. 1, the zener voltage V _Z of the constant voltage diode is controlled by the gate voltage V _T of the MOSFET (11) as in the constant voltage diode of FIG. That is, when the negative gate voltage V _T applied to the anode electrode (7) reaches a predetermined value, the channel part (5) is turned on and the MOSFET (11) is turned on. The transistor (12) is turned on by the channel current flowing in (5), and the voltage regulator diode flakes down.

In the case of the constant voltage diode shown in FIG.
When the FET (11) is turned on, N ⁺ PNP thyristors are parasitically generated in the areas of the emitter region (4), the base region (2), the channel part (5), and the drain region (3) that are arranged side by side. To do. This parasitic thyristor turns on by the breakdown current of the constant voltage diode, but the bypass area (1
Transistor (12) by adding resistor (13) by (0)
Due to the decrease of the current amplification factor h _FE of, the timing of turning on the parasitic thyristor is delayed. As a result, the reverse characteristic of the constant voltage diode in FIG. 1 becomes as shown in the breakdown waveform (a) in FIG. 3 (a), and the Zener saturation current is increased by the time extension from the breakdown until the parasitic thyristor turns on. I _BO gets bigger. Growth rate of the Zener saturation current I _BO is the area of the bypass area (10), can be easily adjusted by such an impurity concentration, it becomes possible to the value required for practical use zener saturation current I _BO.

The forward characteristic of the constant voltage diode shown in FIG. 1 has a V _F waveform similar to the forward characteristic of a normal Zener diode, as shown in the waveform (b) of FIG. That is, when a positive forward voltage V _F is applied to the anode electrode (7), the base region (2) of the transistor (12) is
Is in contact with the anode electrode (7) in the bypass region (10), the forward breakdown voltage is the breakdown voltage of the PN junction between the collector region (1) and the base region (2), and the forward characteristics are as shown in FIG. The waveform (b) in (b) is obtained.

Although the constant voltage diode of FIG. 1 has been described as a P-channel type, the present invention can be similarly applied to an N-channel type constant voltage diode.

[0021]

According to the present invention, the bypass region for contacting the base region [source region] and the anode electrode [gate electrode] of the MOSFET type constant voltage diode,
The channel current that flows when the MOSFET is turned on is suppressed, and the current amplification factor h _{FE of the} transistor formed in the emitter region, the base region, and the connector region is lowered, and the parasitic current is parasitic in the lateral direction of the emitter region, the base region, the channel portion, and the drain region. When the thyristor generated at 1 is turned on, the Zener saturation current I _BO having the reverse characteristic can be increased, and a constant voltage diode having a sharp breakdown waveform and high practical value can be provided.

Further, by forming the bypass region, the forward characteristic similar to that of the normal PN junction type constant voltage diode is obtained, and the MOSFET type constant voltage diode which can be applied to a wide range of applications like the normal PN junction type constant voltage diode is obtained. A voltage diode can be provided.

[Brief description of drawings]

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

FIG. 2 is an equivalent circuit diagram of the constant voltage diode shown in FIG.

3A is a reverse characteristic diagram of the constant voltage diode of FIG. 1, and FIG. 3B is a forward characteristic diagram of the constant voltage diode of FIG.

FIG. 4 is a sectional view of a MOSFET type constant voltage diode for 6 V or less, which is a premise of the present invention.

5 is an equivalent circuit diagram of the constant voltage diode of FIG.

6A is a reverse characteristic diagram of the constant voltage diode of FIG. 4, and FIG. 6B is a forward characteristic diagram of the constant voltage diode of FIG.

FIG. 7 is a reverse characteristic diagram of a general PN junction type constant voltage diode.

[Explanation of symbols]

 1 Semiconductor substrate [collector region] 2 Base region 3 Drain region 4 Emitter region 5 Channel part 6 Insulating layer 7 Anode electrode 9 Cathode electrode 10 Bypass region 11 MOSFET 12 Transistor

Claims (2)

[Claims] 1. A base region and a drain region formed by selectively diffusing another conductivity type impurity in two regions of a surface of a one conductivity type semiconductor substrate, which are collector regions, separated from each other, and another conductivity type impurity is selected in the base region. A diffused emitter region, an insulating film formed on the channel region between the base region and the drain region and on the base region, an anode electrode formed on the emitter region and the insulating film, and a semiconductor substrate Having a cathode electrode formed on the back surface of the
1. A constant voltage diode of the type: wherein a bypass region, which has the same conductivity type as that of the base region and is electrically connected to the anode electrode and the base region, is formed in the emitter region. 2. A constant voltage diode according to claim 1, wherein the drain region, the collector region and the base region are P-channel type MOSFETs, and the collector region, the base region and the emitter region are NPN type transistors.