JPH11307786A - Semiconductor diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prohibit operations of vertical type bipolar transistors by a method wherein a gate of a first MOS transistor is connected to a drain to be connected to a resistor element, to be connected to a bulk to be connected to a second MOS transistor, to be connected to sources of the first and second MOS transistors. SOLUTION: A gate and a drain of a first MOS transistor 101 are connected to an anode electrode 104, to be connected to one of resistor elements 103. The other one of the resistor elements 103 is connected to a bulk of the first MOS transistor 101, to be connected to a drain, a gate and a bulk of a second MOS transistor 102 having the same polarity as the first MOS transistor 101. A source of the first MOS transistor 101 and a source of the second MOS transistor 102 are connected to a cathode electrode 105. Thus, it is possible to prohibit operations of vertical type bipolar transistors and realize a diode applicable to a circuit having a low power consumption as MOS transistors on a semiconductor integrated circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor diode formed on a MOS type semiconductor integrated circuit.

[0002]

2. Description of the Related Art On a MOS type semiconductor integrated circuit,
By connecting MOS transistors, a rectifying action can be realized without using a junction diode. However, there is a problem that it can be realized only under limited conditions.

A rectifying function is realized by using FIGS. 2 and 3.
A description will be given of a conventional MOS transistor connection method and its problems.

FIG. 2A shows connection of a conventional MOS transistor. The drain and gate of the MOS transistor 201 are connected to form an anode electrode 202, and the source and bulk are connected to form a cathode electrode 203.

The anode electrode 202 has a positive electrode and the cathode electrode 2 has a positive electrode.
When a negative voltage is applied to the 03, the voltage difference between both electrodes becomes MOS
Current starts to flow from a value exceeding the threshold voltage of the transistor. That is, since the voltage between the gate and the source of the MOS transistor 201 exceeds the threshold voltage of the MOS transistor 201, a current flows between the drain and the source. When a voltage difference is further applied to both electrodes, the current becomes approximately the square of the applied voltage. Increase in proportion.

The threshold voltage of a MOS transistor is generally used. By setting this voltage to be equal to or lower than the built-in potential of a junction diode, the voltage at which current flows (hereinafter referred to as VF) can be made lower than that of the junction diode. it can.

Conversely, when a negative voltage is applied to the anode electrode 202 and a positive voltage is applied to the cathode electrode 203, the voltage between the drain and the source does not flow. This is because the voltage difference between the gate and the source in this case is zero due to the connection of the MOS transistor.

From this, it is understood that the rectifying action of the diode in which the current flows only in one direction can be realized by connecting the MOS transistors.

[0009] However, this rectifying function is different from the case of the junction diode and can be realized only under limited conditions. The conditions will be described with reference to FIG.

FIG. 2B shows a cross-sectional structure when the MOS transistor 201 is realized in a semiconductor integrated circuit. Although this example shows an N-channel MOS transistor, the present invention can be easily applied to a P-channel MOS transistor by reversing the PN of the semiconductor and reversing the relationship of the applied voltage.

The MOS transistor 201 is an N-type substrate 21
The N-type diffusion layer 213 formed in the P-type well 210 formed in
12 and an N-type diffusion layer 21 connected to the cathode electrode 203
4 and a P-type diffusion layer 215.

The problem of the MOS transistor connection method shown in FIG. 2A occurs when a negative voltage is applied to the anode electrode 202 and a positive voltage is applied to the cathode electrode 203.

In this case, the drain-source current does not flow because the gate electrode 212 and the N-type diffusion 213 serving as the source are connected to the same potential. However, when the voltage difference between the two electrodes is further increased, the P-type well 210 is connected to the P-type diffusion layer 215 which becomes a bulk, so that the junction diode between the P-type well 210 and the N-type diffusion layer 213 as a source is formed. Is biased in the forward direction, and a current starts to flow.

The voltage difference flowing out is equal to the built-in potential of the junction diode and is approximately 0.6V.

In other words, in the MOS transistor connection method shown in FIG. 2A, when a negative voltage is applied to the anode electrode 202 and a positive voltage is applied to the cathode electrode 203, if the voltage difference exceeds 0.6 V, the current is increased. It will flow out and the rectification action will not be established.

Next, referring to FIG. 3, description will be given of connection of a conventional MOS transistor which has solved the problem of the connection method of FIG.

FIG. 3A shows the connection of the improved MOS transistor, in which the gate, drain and bulk of the MOS transistor 301 are connected to the anode electrode 302 and the source is connected to the cathode electrode 303, respectively.

The anode 302 has a positive electrode and the cathode 3
03, when a negative voltage is applied, the voltage difference
A current between the source and the drain flows from a value exceeding the threshold voltage of the transistor 302.

The anode electrode 302 has a negative and the cathode electrode 3
When a positive voltage is applied to 03, since the source and the gate are connected to the anode electrode 302, there is no voltage difference between the source and the gate, and no current flows between the drain and the source.

Further, even if the voltage difference between the anode electrode 302 and the cathode electrode 303 increases beyond 0.6 V, no current flows between the anode electrode 302 and the cathode electrode 303. Because the P-type diffusion layer 315 existing in the P-type well 310 and serving as a bulk is connected to the anode electrode 302, the N-type diffusion 314 serving as the drain and the P-type well 310 are biased in opposite directions, and the current is Is because it does not flow.

If the MOS transistor connection method shown in FIG. 3A is used, a correct rectifying operation can be obtained regardless of the direction of the potential difference between the anode electrode and the cathode electrode.

Next, the problem of the improved connection method of the MOS transistor will be described with reference to FIG. FIG.
(B) shows a cross-sectional structure when the MOS transistor 301 is realized in a semiconductor integrated circuit. This example is Nch
Although a MOS transistor is shown, the PN of the semiconductor is reversed, and the P-type MOS transistor can be easily formed by reversing the relation of the applied voltage.
Applicable to S transistors.

The MOS transistor 301 is an N-type substrate 31
N-type diffusion layer 313 and gate electrode 3 formed in P-type well 310 formed on
12, a P-type diffusion layer 315, and an N-type diffusion layer 314 connected to the cathode electrode 303.

When a positive voltage is applied to the anode electrode 302 and a negative voltage is applied to the cathode electrode 303, a current flows between the source and the drain if the potential difference exceeds the threshold voltage of the MOS transistor 301. When the voltage difference is further increased, the current flowing between the source and the drain increases, but at the same time, the same-polarity P-type well 3 connected to the bulk-type P-type diffusion 315 is formed.
Since the junction between the transistor 10 and the N-type diffusion 314 serving as the source diffusion is biased in the forward direction, a current flows.

That is, when a voltage difference of at least about 0.6 V or more than the built-in potential between the P-type well 310 and the N-type diffusion 314 serving as a source is applied, a current other than the current between the source and the drain is applied to the anode electrode 302 and the cathode electrode 3.
It flows between 03.

As can be seen from FIG. 3B, the MOS transistor 301 is formed in the P-type well 310 on the N-substrate 311. Therefore, a vertical bipolar transistor 318 having the P-type well 310 as a base, the N-type diffusion 314 as a source as an emitter, and the N-type substrate 311 as a collector is formed in a parasitic manner.

The flow of a current between the P-type well 310 and the N-type diffusion 314 serving as a source is equivalent to the flow of a base-emitter current (IBE) through the vertical bipolar transistor 318. According to the operation principle of the bipolar transistor, when a current between the base and the emitter flows, a current multiplied by a current amplification factor of this current value is applied to a current between the emitter and the collector (IE
Flow to the collector as C). This current is equivalent to the current flowing between the P-type well 310 and the N-type substrate 311.

That is, in the connection method of the MOS transistor shown in FIG. 3A, when a positive voltage is applied to the anode electrode 302 and a negative voltage is applied to the cathode electrode 303, the potential difference becomes equal to 0.
When the voltage exceeds 6 V, the N-type substrate 311
Current leaks out.

In general, the substrate is often fixed at the ground potential, so that the cathode electrode 303 is short-circuited to the ground potential, which causes inconvenience in circuit operation. At the same time, unnecessary current flows, and the purpose of the circuit for low power consumption is not fulfilled.

As described above, even with the improved MOS transistor connection method, only a limited rectifying action can be obtained due to the existence of the parasitic vertical bipolar transistor.

Next, the problem of the improved connection method of the MOS transistor will be described, and a further improved conventional connection method of the MOS transistor will be described.

FIG. 4 shows a further improved MOS transistor connection method. The gate and the drain of the MOS transistor 401 are connected to the anode electrode 402 and to one end of the resistance element 404. The other end of the resistor is connected to the bulk, and the source is connected to the cathode electrode 403.

The operating principle of the further improved MOS transistor connection method shown in FIG. 4 is substantially the same as the improved MOS transistor connection method shown in FIG.

When a negative voltage is applied to the anode electrode 402 and a positive voltage difference is applied to the cathode electrode 403, the current does not flow as described with reference to FIG.

Conversely, when a positive voltage difference is applied to the anode electrode 402 and a negative voltage difference is applied to the cathode electrode 403, the current between the drain and the source is changed from the value where the voltage difference between the gate and the source exceeds the threshold value of the MOS transistor 401. Flow out.

As described in detail with reference to FIG. 3B, when the voltage difference between the source and the bulk exceeds the built-in potential of about 0.6 V, a current starts to flow. This current flows from the anode electrode 402 to the cathode electrode 403 via the resistance element 404.

The parasitic vertical bipolar transistor described with reference to FIG. 3B still exists in a further improved MOS transistor connection method.

However, since the current between the bulk and the source, which becomes the current between the base and the emitter of the vertical bipolar transistor, flows through the resistance element 404, most of the voltage difference is generated at both ends of the resistance element 404 when the current flows. However, it does not occur between the bulk and the source. Anode electrode 4
The voltage between the bulk and the source is almost fixed at about 0.6 V regardless of the voltage difference between the cathode 02 and the cathode electrode 403.

As a result, the current between the base and the emitter of the vertical bipolar transistor is greatly limited, and the current between the emitter and the collector is also greatly reduced. The occurrence can be greatly improved.

However, even with this further improved MOS transistor connection method, a slight current flows between the bulk and the source, the vertical bipolar transistor operates, and an unnecessary current also slightly flows. Therefore, it cannot be applied to a circuit in which low power consumption is particularly important, such as a clock integrated circuit.

[0041]

As described above, the conventional method of connecting a MOS transistor used as a diode cannot be realized due to the presence of a vertical bipolar transistor due to the configuration of a semiconductor integrated circuit.

An object of the present invention is to inhibit the operation of the above-mentioned vertical bipolar transistor, to have a rectifying effect which is effective even in a circuit requiring low power consumption, and to have a lower VF than a junction diode.
The object of the present invention is to provide a semiconductor diode circuit having the following.

[0043]

In order to achieve the above object, in the method of connecting a MOS transistor according to the present invention, a first M transistor is connected.
A gate and a drain of the OS transistor are connected to one of the resistance elements, and the other of the resistance elements is connected to the first MOS transistor.
Connected to the bulk of the transistor, and connected to the drain and gate of the second MOS transistor having the same polarity as the first MOS transistor, to the bulk, and connected to the source of the first MOS transistor and the source of the second MOS transistor It is characterized by becoming.

In the circuit configuration of the MOS transistor according to the present invention, the vertical bipolar transistor does not operate due to the configuration of the semiconductor integrated circuit, so that the cathode electrode is not short-circuited to the substrate and unnecessary current does not flow.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The MOS transistor connection method according to the present invention can realize a diode on a semiconductor integrated circuit without using a junction diode. Hereinafter, the structure and the operating principle will be described using an N-type MOS transistor as an example. However, the same can be realized with a P-type MOS transistor by reversing the P-type and N-type of the potential relationship and diffusion.

FIG. 1 shows a connection method of a MOS transistor according to the present invention. The gate and the drain of the first MOS transistor 101 are connected to the anode electrode 104 and connected to one of the resistance elements 103, the other of the resistance elements 103 is connected to the bulk of the first MOS transistor 101, and the first Second M of the same polarity as MOS transistor 101
The drain, gate, and bulk of the OS transistor 102 are connected to the bulk, and the source of the first MOS transistor 101 and the source of the second MOS transistor 102 are connected to the cathode electrode 105.

First, a case where a voltage difference between a negative voltage is applied to the anode electrode 104 and a positive voltage is applied to the cathode electrode 105 will be described. In this case, since the voltage difference between the gate and the drain of the second MOS transistor 102 is zero, the second MOS transistor 102 is in the OFF state and no current flows through the resistance element 103. Therefore, there is no voltage difference between both ends of the resistance element 103, and no current flows at the same voltage between the gate, the drain and the bulk of the first MOS transistor.

In each of the first MOS transistor 101 and the second MOS transistor 102, the junction between the bulk and the source is biased in the opposite direction, and there is no other path through which current flows. Therefore, no current flows between the anode electrode 104 and the cathode electrode 105.

Next, a case where a voltage difference between a positive voltage is applied to the anode electrode 104 and a negative voltage is applied to the cathode electrode 105 will be described. Since the bulk of the second MOS transistor 102 is connected to the drain, the threshold voltage is lower than that of the first MOS transistor formed on the same semiconductor substrate due to the substrate bias effect. Therefore, at the applied voltage in this case, first, the second MOS transistor 102 is turned on.

If the threshold voltage of the second MOS transistor 102 is set to be equal to or lower than the built-in potential of the junction diode, the voltage difference between the source and the bulk of any MOS transistor does not exceed the built-in potential of the junction diode. No current flows between the base and the emitter of the illustrated vertical bipolar transistor.

Therefore, the parasitic vertical bipolar transistor does not turn on, and the cathode electrode 105 does not short-circuit to the substrate.

The setting of the threshold voltage of the MOS transistor is as follows.
It is generally done and can be done easily. Even when the original threshold voltage is higher than the built-in voltage, the drain and the bulk are connected to each other, so that the substrate bias effect lowers the voltage and the purpose can be achieved.

When the voltage difference between the positive voltage on the anode electrode 104 and the negative voltage on the cathode electrode 105 is further expanded, the current flows through the resistor 103, and most of the applied voltage difference is generated at both ends of the resistance element 103. The voltage between the drain and the source of the second MOS transistor 102 remains below the built-in potential between the source and the bulk.

Therefore, even at the applied voltage in this case, the vertical bipolar transistor does not turn on, and the cathode electrode 105 does not short-circuit to the substrate or an unnecessary current does not flow. For example, low power consumption of a clock integrated circuit or the like can be reduced. It can also be applied to particularly important circuits.

The resistance element 103 is constituted by a resistor or a diffusion resistor such as polysilicon or metal.

Generally, the resistance element formed on a semiconductor integrated circuit has a large area and affects the area of the semiconductor integrated circuit itself. Therefore, it is better that the resistance value per unit area is as large as possible, and no leakage current occurs on the semiconductor integrated circuit substrate. Therefore, it is desirable to form the resistance element 103 with polysilicon.

[0057]

According to the MOS transistor connection method of the present invention, the operation of the vertical bipolar transistor due to the structure of the semiconductor integrated circuit is inhibited, and a diode which can be applied to a low power consumption circuit is provided on the semiconductor integrated circuit. MOS transistors can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a connection method of a MOS transistor in an embodiment of the present invention.

FIG. 2 is a diagram showing a connection method of a conventional MOS transistor.

FIG. 3 is a diagram showing an improved conventional MOS transistor connection method.

FIG. 4 is a diagram showing a further improved conventional MOS transistor connection method.

[Explanation of symbols]

 Reference Signs List 101 first MOS transistor 102 second MOS transistor 103 resistive element 104 anode electrode 105 cathode electrode 201 MOS transistor 202 anode electrode 203 cathode electrode 210 p-type well 211 n-type substrate 212 gate electrode 213 n-type diffusion layer 214 serving as drain N-type diffusion layer 215 serving as a source P-type diffusion layer 301 serving as a bulk MOS transistor 302 Anode electrode 303 Cathode electrode 310 P-type well 311 N-type substrate 312 Gate electrode 313 N-type diffusion layer 314 serving as a drain N-type diffusion serving as a source Layer 315 Bulk P-type diffusion layer 316 N-type diffusion layer connected to substrate electrode 317 Substrate electrode 401 MOS transistor 402 Anode electrode 403 Cathode electrode 404 Resistance element

Claims (2)

[Claims] 1. A semiconductor diode formed on a MOS integrated circuit, wherein a gate and a drain of a first MOS transistor are connected, and one of the resistance elements is connected, and the other of the resistance elements is connected to a first MOS transistor. A second MOS transistor having the same polarity as the first MOS transistor, connected to a drain, a gate, and a bulk; a source of the first MOS transistor and a second MOS transistor;
A semiconductor diode characterized by being connected to a source of a transistor. 2. The semiconductor diode according to claim 1, wherein said resistance element is a polysilicon resistance, a metal resistance, or a diffusion resistance.