JPH0346507Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a structure of an embedded Zener diode suitable for incorporating a constant voltage reference voltage circuit into a semiconductor integrated circuit (hereinafter referred to as an IC).

[Background of the idea]

One way to obtain a reference voltage by incorporating a constant voltage circuit into an IC is to use an emitter-base junction of a transistor. When this method is adopted, it has the drawbacks that avalanche breakdown occurs on the silicon surface, resulting in large noise and lack of long-term stability.

Therefore, a buried type Zener diode is known as a Zener diode that eliminates these drawbacks (``National Semiconductor Appli
−cation Note 161” Robert Dobkin, June
1977, p. 173, "Transistor Technology" October 1977 issue (pp. 183-184), November issue (pp. 174-178)).
A buried Zener diode allows avalanche breakdown not on the surface of the semiconductor, but on its subsurface (Subsurface).
In other words, it is generated inside the semiconductor substrate.

FIG. 1 shows the cross-sectional structure of a buried Zener diode. Note that this Zener diode is
Compatible with NSC product LM199. In FIG. 1, a base diffusion region (hereinafter referred to as base region) 2 made of a first conductivity type semiconductor (P ^- ) with a low concentration of impurities is diffused and formed on the surface side of a semiconductor substrate (N ^- ) 1. A deep region 3 made of a first conductivity type semiconductor (P ⁺ ) with a high concentration of impurities is formed by penetrating this base region 2 and diffusing into the interior of the semiconductor substrate, and furthermore, the upper part of this deep region 3 is completely covered. An emitter diffusion region (hereinafter referred to as an emitter region) 4 made of a second conductivity type semiconductor (N ⁺ ) with high impurity concentration is formed in the base region 2 covering the base region 2 .

In this way, in the buried Zener diode, the deep region (P ⁺ ) 3 where the cathode electrode K is provided is completely covered by the emitter region (N ⁺ ) 4 where the anode A is provided and is buried inside. , avalanche breakdown occurs between the N ⁺ region 4 and the P ⁺ region 3, where the impurity concentration is maximum, and also inside the semiconductor substrate 1. Therefore, noise generated during avalanche breakdown is reduced, and changes in Zener voltage over time are suppressed. Furthermore, by adopting a planar structure, productivity and reliability can be improved. Note that 5 indicates a buried layer (N ⁺ ), and 6 indicates a separation layer.

Now, when configuring a reference voltage source using the above-mentioned embedded Zener diode, it is necessary to perform temperature compensation. Figure 2 shows an example of a reference voltage generation circuit incorporating a circuit for temperature compensation. Shown below. In FIG. 2, when the voltage at the cathode K tries to rise for some reason, this movement is transmitted to the base of the temperature compensation transistor _Q1 through the embedded Zener diode D and tries to increase its base current. increases the collector current of transistor _Q1 , and attempts to similarly increase the collector current of transistor _Q2 . In this way, the rise in the potential of the cathode K is suppressed in the form of an increase in current, and in the reverse case, a constant voltage is generated by the operation opposite to the above (Transistor Technology 1977 November issue, pages 177-178).

By the way, as mentioned above, when trying to obtain a breakdown voltage by causing Zener breakdown inside the semiconductor, the pinch resistance (parasitic resistance) Rp under the emitter diffusion region 4 is caused to rise from the base diffusion region 3 to the cathode K.
Therefore, the obtained reference voltage V _REF includes a voltage represented by the product (Rp·Iz) of the pinch resistance Rp and the current Iz.

Here, in order to simplify the explanation, FIG. 3 shows a simplified circuit of the reference voltage generation circuit of FIG. 2.
The reference voltage V _REF obtained by this circuit is expressed as V _REF = V _BE + Iz·Rp + Vz. Here, V _BE is the emitter-base voltage of transistor _Q1 .

In this way, the reference voltage V _REF includes the term Iz·Rp. Therefore, temperature compensation to thermally stabilize this Zener diode must be performed including the voltage due to the pinch resistor Rp, which complicates the temperature compensation circuit and makes it difficult to considerably reduce the variation between each element when mass-producing it. There is a problem that needs to be suppressed.

[Purpose of invention]

The purpose of the present invention is to prevent the voltage caused by the pinch resistor from being included in the output constant voltage characteristics.

[Summary of the idea]

In order to achieve the above object, the Zener diode according to the present invention has two anode electrodes in the base diffusion region in the above-mentioned buried Zener diode, one anode electrode is used as a current terminal, and the other anode electrode is used as a voltage terminal. It is characterized by the following points.

[Example of idea]

Next, an embodiment of the embedded Zener diode according to the present invention will be described based on the drawings.

4 to 6 show embodiments of the embedded Zener diode according to the present invention. In addition, in FIGS. 4 to 6, parts that overlap with those in FIGS. 1 to 3 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 4 (cross-sectional view), two anode electrodes (hereinafter referred to as a first electrode A ₁ and a second electrode A ₂ ) that are substantially electrically insulated from each other are provided on the surface of the base region. There is. The contact is an ohmic contact, and Al electrodes or the like are used as the first and second electrodes A ₁ and A ₂ . Further, although there is no particular restriction on the shape thereof, for example, as shown in FIG. 5 (plan view), it may be provided separately in an arc shape along the shape of the emitter region 4.

FIG. 6 shows an equivalent circuit of the embedded Zener diode constructed as described above. FIG. 7 shows an example of a circuit configured similarly to FIG. 3 for obtaining a constant voltage using this embedded Zener diode.

In FIG. 7, the obtained reference voltage V _REF becomes V _REF ≈V _BE +Vz, Iz ₁ Rp0, and there is no term related to the pinch resistance Rp.
This connects the first electrode via a Zener diode.
Current Iz ₁ flowing to A ₁ (voltage terminal) side and second electrode A ₂
This is because when compared with the current Iz ₂ flowing to the (current terminal) side, Iz ₁ << Iz ₂ and it can be seen that Iz ₁ is substantially 0. In other words, the reason why Iz ₁ can be considered to be substantially 0 is that Iz ₁ = Ic ₂ /h _FE2 Ic ₂ : Collector current of Q ₂ h _FE2 : DC current amplification factor of Q ₂ and h _FE2 > 200 is selected. If Ic ₂ Iz ₂ , then Iz ₁ = Iz ₂ /h _FE2 = 0.05・_Iz 2Comparing to Figure 3, Rp has become 1/h _FE .

When manufacturing the above-mentioned embedded Zener diode, the Zener voltage Vz is the first adjustment item during manufacturing, and the rest is based on the base-emitter voltage V _BE
By changing the collector current that generates ∂V _BE / ∂T + ∂Vz / ∂T = 0, the reference voltage source can be made extremely stable against changes over time after the power is turned on at a specified temperature. I'm struggling.

[Effect of idea]

As mentioned above, by providing two electrodes in the base region, the pinch resistance can be reduced to 0 [Ω] in terms of the circuit.
Therefore, the voltage drop can be ignored by using a pinch resistor for temperature compensation, and a stable constant pressure source can be created.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional perspective view of a conventional embedded diode, Fig. 2 is a circuit diagram showing an example of a conventional temperature compensated constant voltage circuit, Fig. 3 is a circuit diagram of a constant voltage circuit (omitted), and Fig. 2 is a circuit diagram showing an example of a conventional temperature compensated constant voltage circuit. 4 is a cross-sectional perspective view of an embedded Zener diode according to the present invention, FIG. 5 is a plan view of the embedded Zener diode according to the present invention, and FIG. 6 is a circuit diagram showing an equivalent circuit of the embedded Zener diode according to the present invention. FIG. 7 is a circuit diagram showing a constant voltage circuit. 1...Semiconductor substrate ^{(N-), 2...Base region (P-), 3...Deep layer (P+ ) ,} 4...Emitter region (N ⁺ ), 5...Buried layer (N ⁺ ), 6...Separation layer,
_A1 ...first electrode, _A2 ...second electrode, K...cathode.

Claims (1)

[Scope of utility model registration request] A base diffusion region of a first conductivity type containing a low concentration impurity is formed on one surface side of the semiconductor substrate, and a deep diffusion region of a first conductivity type containing a high concentration impurity is formed inside the semiconductor substrate passing through the base diffusion region. formed,
In a buried Zener diode in which a second conductivity type emitter diffusion region of high concentration impurity is formed in the base diffusion region so as to cover the upper part of the deep diffusion region, two anode electrodes are provided in the base diffusion region; A buried Zener diode characterized in that one anode electrode serves as a current terminal and the other anode electrode serves as a voltage terminal.