JPH02244752A - Static electricity protection circuit of semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To achieve a high withstand voltage regardless of the polarity of static electricity by providing a break-down element and resistor inserted in the opposite direction toward a base between the base and input/output terminal of a bipolar transistor. CONSTITUTION:A collector of a bipolar transistor Q is connected io an input/ output terminal T10, an emitter is connected to a grounding terminal TVS, a break-down element D for enabling current to flow when a voltage exceeding the rated voltage is applied between the input/output terminal T10 and the base of the bipolar transistor Q is connected in the opposite direction toward the base, a resistor RB is connected between the base of the bipolar transistor Q and the grounding terminal TVS, in this circuit configuration, collector potential is always higher than base potential by BV and each bias voltage turns on the transistor Q. Namely, since the transistor Q can be in its original current drive state, static electricity applied to a terminal A can be largely discharged to the grounding terminal B side in a short time, thus allowing a semiconductor integrated circuit with this static electricity protection circuit to have an increased withstand voltage against static electricity.

Description

[Detailed Description of the Invention] [Summary] Regarding an electrostatic protection circuit for a semiconductor integrated circuit that has been improved to increase the effect of discharging static electricity generated in a semiconductor integrated circuit, the polarity of static electricity applied to a terminal in a semiconductor integrated circuit is In order to obtain a semiconductor integrated circuit protection element that exhibits high withstand voltage, regardless of the
a breakdown element inserted between the base of the bipolar transistor and the input/output terminal in an opposite direction toward the base; and a breakdown element inserted between the base of the bipolar transistor and the ground terminal. or a bipolar transistor whose collector is connected to a power supply terminal and whose emitter is connected to an input/output terminal, and the base is connected between the base of the bipolar transistor and the power supply terminal. and a break down element inserted in a direction opposite to the direction shown in FIG.

[Industrial Field of Application] The present invention relates to an electrostatic protection circuit for semiconductor integrated circuits that is improved so as to be more effective in discharging static electricity generated in semiconductor integrated circuits.

Currently, the use of semiconductor integrated circuits in industrial equipment and consumer equipment is rapidly increasing, and this trend is expected to continue in the future.

As a result, the environment in which semiconductor integrated circuits are used is expected to deteriorate further, and signs of this are already beginning to appear.

One of the problems caused by the usage environment is electrostatic damage.
Various countermeasures have been considered and implemented for this purpose. For example, a protection element is formed at the input/output part of a semiconductor integrated circuit, and static electricity is discharged through the protection element.
Efforts have been made to prevent the internal elements from being affected, but their effectiveness is still far from satisfactory.

[Conventional technology]

FIG. 7 shows an explanatory diagram of a main circuit for explaining a conventional example of a semiconductor integrated circuit incorporating a protection element.

In the figure, TVD is a power supply terminal, TIO is an input/output terminal,
'Tvs is the ground terminal, Ql and Q2 are protection elements, Qr,
o indicates each protected element.

In the illustrated example, protection elements Q1 and Q2, which are bipolar transistors, are inserted between the protected element (QGI), which is an internal element of the semiconductor integrated circuit, and the input/output terminal TIO, and the static electricity that enters from the input/output terminal TIo is removed from the power source. The protected element QG5 is prevented from being destroyed by discharging it into the wiring or the ground wiring.

Normally, it is completely unpredictable to which of the many terminals of a semiconductor integrated circuit static electricity will be applied, so it is practically impossible to discharge the applied static electricity by selecting an appropriate discharge path each time. Therefore, generally, a power supply wiring or a ground wiring is used as the discharge light. Since this rewiring has a relatively large capacitance inside the semiconductor integrated circuit, it can act as a reservoir. Therefore, by discharging this rewiring, the voltage at the input/output terminal is significantly reduced, and destruction of the protected element due to static electricity is avoided.

In general, the protection elements Q1 and Q2 are bipolar transistors, which are connected to an input/output terminal TIO and a ground terminal', for example.
rvs (in the illustrated example, the protective element Q2
), the collector is connected to the input/output terminal TIG, the base is connected to the ground terminal T"vs via a resistor R2, and the emitter is directly connected to the ground terminal 'r"vs. Here, the conductivity type of the bipolar transistor is npn, but p
The same can be considered for np.

Input/output terminals T in the circuit having the above configuration. and ground terminal T
v! The analysis of the operation when high voltage static electricity with positive polarity is applied between the two is as follows. cough high voltage
Applied to the collector-base junction of the protection element Q2,
The electric field within the depletion layer is strengthened. When the electric field within the depletion layer is greater than the level at which the electric field is generated, carriers, that is, electrons and genuine tags are generated due to impact ionization within the depletion layer. Among these, the holes flow into the base and then pass through the resistor R2 to the ground terminal 1. At the same time, the base potential increases. Therefore, the emitter-base junction is forward biased and electrons are injected from the emitter. Most of the injected electrons go to the collector
It flows into the base junction and acts as a trigger to generate new impact ionization. This is a type of positive feedback, and the current flowing through the protection element Q2 continues to increase until the number of newly generated electrons is balanced with the number of electrons flowing through the resistor R2 plus the injected electrons. This mechanism lowers the breakdown voltage of the collector-base junction, allowing static electricity to be discharged in a shorter time than with a simple diode.

Further, in the above-mentioned circuit, for example, a resistor R inserted between the base of the protection element Q2 and the ground terminal T''vs
2 and grounding the base directly has also been done. In this case, the internal resistance of the base itself plays the role of resistor R2, and although the effect is not sufficient, a discharge operation based on the same mechanism as described above can be expected.

[Problem to be solved by the invention]

The operating mechanism of the protection element described above is not the original operating mechanism of a bipolar transistor, and therefore does not fully utilize the current driving ability of the bipolar transistor. Therefore, with the above-mentioned operating mechanism, there is a possibility that the discharge capacity will be insufficient.

By the way, in recent years, Bi-0MO3 (bipo 1a
r complementary metalox
IDE semiconductors are likely to be widely used as semiconductor integrated circuits in the future. The present inventor measured the strength against static electricity (withstand voltage) of a Bi-0MO3 in which a bipolar transistor insertion type static electricity protection circuit as explained in FIG. 7 was provided between the output terminal and the ground terminal. However, the withstand voltage was significantly lower when the output terminal side had positive polarity than when it had negative polarity.

The reason for this is, of course, the insufficient ability of the protection circuit described above, and this will be described in more detail.

FIG. 8 is an explanatory diagram of the main part of the test circuit used for measurement.

In the figure, VP is a DC power source with variable output voltage, C is a capacitor with a capacity of 10 (pF), S is a switch, ■ and ■ are terminals, and TP is a semiconductor integrated circuit as a sample.

To perform measurements with this test circuit, first, the terminal (2) side of the switch S is closed, and a voltage from the DC power supply VP is applied to the capacitor C of 10 (pF) to accumulate charge. Then,
The terminal (2) side of the switch S is closed to allow the charge stored in the capacitor C to flow into the semiconductor integrated circuit TP. Then, this operation is repeated by increasing the voltage output from the DC power supply ■, and each time, the semiconductor integrated circuit T
Check whether P is destroyed or not, and determine its strength against static electricity.

As a result of measuring in this way, it was possible to withstand a voltage of 2300 (V) when a negative polarity voltage was applied to the output terminal side, but on the contrary, when a positive polarity voltage was applied. When becomes 1700 (V), the semiconductor integrated circuit TP
was destroyed.

The present invention aims to provide an electrostatic protection circuit for a semiconductor integrated circuit that exhibits a high withstand voltage regardless of the polarity of electrostatic electricity applied to terminals in the semiconductor integrated circuit.

[Means to solve the problem]

In order to solve the above-mentioned problems, it is necessary to make sure that the transistors prepared for discharging abnormal charges operate normally when a voltage higher than the rated voltage is applied to the input/output terminals of the semiconductor integrated circuit. All you have to do is set the potential of each part appropriately.

Figures 1 and 2 are circuit explanatory diagrams of main parts for explaining the principle of the electrostatic protection circuit according to the present invention, and the same symbols as those used in Figure 7 represent the same parts or are the same. It shall have meaning.

In the figure, Q represents a bipolar transistor which is a protection element, D represents a breakdown element, and RB represents a resistor.

The difference between FIG. 1 and FIG. 2 is that an electrostatic protection circuit is inserted between the input/output terminal Tl (l and the grounding terminal Tvs), or between the power supply terminal Tvo and the input/output terminal T10. The only point is whether or not it was inserted.

In the electrostatic protection circuit shown in Figure 1, the collector of the bipolar transistor Q is connected to the input/output terminal TIO.
Then, connect the emitter to the ground terminal Tv! and input/output terminals T, respectively. A breakdown element through which a current flows when a voltage higher than the rated voltage is applied is connected between the base of the bipolar transistor Q and the base of the bipolar transistor base and ground terminal T1. A resistor RB is connected between the two.

In the electrostatic protection circuit shown in FIG. 2, the collector of the bipolar transistor Q is connected to the power supply terminal TvI,
The emitters are connected to the input/output terminal T1o, and a break-down element similar to the above is connected between the power supply terminal 'T'vn and the base of the bipolar transistor Q in the opposite direction toward the base. Furthermore, a resistor RB is connected between the base of the bipolar transistor Q and the input/output terminal Tlo.

The electrostatic protection circuit shown in FIGS. 1 and 2 is combined, that is, the input/output terminal T. and the ground terminal T'vs,
Of course, it is also possible to insert an electrostatic protection circuit between the power supply terminal T%l+1 and the input/output terminal TIO, and also to appropriately select the number of breakdown elements. The voltage can be controlled to a desired value.

For this reason, in the electrostatic protection circuit for a semiconductor integrated circuit according to the present invention, the collector is connected to the input/output terminal (for example, the input/output terminal T + o), and the emitter is connected to the ground terminal (for example, the ground terminal Tvs). bipolar·
A transistor (e.g. bipolar transistor Q) and a break down element (e.g. a break down element) inserted between the base of the bipolar transistor and the input/output terminal in the opposite direction towards the acid base. D) and a resistor inserted between the base of the bipolar transistor and the ground terminal (for example, a resistor R
B), or a bipolar transistor whose collector is connected to a power supply terminal (for example, power supply terminal TvD) and whose emitter is connected to an input/output terminal, and between the base of the bipolar transistor and the power supply terminal. a breakdown element inserted in a direction opposite to the base; and a resistor inserted between the base of the bipolar transistor and the input/output terminal; or Configure to have everything.

[Effect]

By taking the above measures, the bipolar transistor Q can perform a good protection operation, which will be explained in more detail.

Figure 3 is an explanatory diagram of the main part of the electrostatic protection circuit shown in Figures 1 and 2 to facilitate operational analysis, and the same symbols as those used in Figures 1 and 2 are used. Symbols shall represent the same part or have the same meaning.

In the figure, A and B indicate the terminals, and R3 indicates the DC resistance component of the wiring.

In the illustrated electrostatic protection circuit, it is assumed that a voltage VA due to static electricity is applied to terminal A while terminal B is grounded.

When the voltage applied to the break-down element becomes higher than its break-down voltage BV, current flows through the resistor RB, the base potential rises, and the base-emitter junction becomes forward biased. In this circuit configuration, the collector potential is always higher than the base potential by BV, and each bias voltage turns on the transistor Q. That is, since the transistor Q is in its original current drive state, most of the static electricity applied to the terminal A can be discharged to the ground terminal B side in a short time. Therefore, a semiconductor integrated circuit having this static electricity protection circuit has a high It has static electricity resistance.

Figure 4 shows a diagram to explain how much current can flow through the electrostatic protection circuit shown in Figure 3, with voltage V on the horizontal axis and current I on the vertical axis. The same symbols as those used in FIGS. 1 to 3 indicate the same parts or have the same meaning.

In the figure, the thin solid line Q' is the characteristic line showing the 1-V characteristic of transistor Q, the broken line R3' is the characteristic line showing the IV characteristic regulated by resistor R3, and K is the characteristic line Q'. The operating point is the intersection with the characteristic line R3', VK is the voltage corresponding to the intersection K, BVI and BV2 are the break down voltages of the break down elements, and K1 is the breakdown voltage BV.
The operating points on the characteristic line R5' corresponding to I are shown.

As is clear from the figure, the breakdown voltage BV of the breakdown element is higher than the voltage VK.
'1, the operating point is Kl, and although the transistor Q still has some remaining current drive capacity, the discharge current is first regulated by the resistor R3.

Voltage B whose breakdown voltage BV is lower than voltage VK
The discharge current when the voltage is V2 is first regulated by the transistor Q, but ultimately it is determined by the resistor R3, and the operating point settles at K. Therefore, the operating point K
It is not possible to flow a discharge current higher than the current value corresponding to . The operating point K can be raised by increasing the resistance RB and deepening the base potential. However, the breakdown voltage BV must be higher than (power supply voltage + margin), so even if you increase the resistance RB arbitrarily, the operating point will be determined by the breakdown voltage BV, as in 1. It becomes fixed depending on the situation. Moreover, the resistor R3 also has regulations as described below. That is, when negative static electricity is applied to terminal A, the collector-base junction of transistor Q becomes a forward state and discharges. At this time, resistor RB acts as a series resistor in the discharge path. Therefore, in order to ensure a high discharge capacity, it is desirable that the value of the resistor RB be small. Therefore, in order to maximize the effects of the present invention, the breakdown voltage BV of the breakdown element should be set to (power supply voltage + margin), and the resistance RB
It is important to set the value to a low enough value to prevent the break-down element from being destroyed by excessive current flowing through it.

〔Example〕

FIG. 5 shows an explanatory diagram of the main part circuit of one embodiment of the present invention.
The same symbols as those used in FIGS. 4, 7, and 8 indicate the same parts or have the same meanings.

In the figure, DI and D2 are break down elements, C
I each indicate an internal circuit of the B1-CMOS configuration to be protected.

Breakdown elements DI and D2 in this embodiment
has two Zener diodes connected in series with the same structure as the emitter-base of the bipolar transistor in the internal circuit CI, the breakdown voltage BV of which is 14 (V), and the resistor RBO value is approximately 1
(KΩ).

FIG. 6 shows a cutaway side view of essential parts for explaining the specific structure of the embodiment shown in FIG.
The same symbols as those used in the figures and FIG. 8 indicate the same parts or have the same meanings.

In the figure, 1 is a p-type silicon semiconductor substrate, 2 is an n-type impurity region, 3 is a p-type impurity region, 4 is an n-type impurity region,
5 is an n-type impurity region, 6 is a p-type impurity region, 7 is an n-type collector region, 8 is a p-type large region, 9 is an n-type emitter i
The iI region is shown respectively.

In contrast to the embodiment described in FIGS. 5 and 6, FIG.
When the withstand voltage was measured using the test circuit described in the figure, it was found that it could withstand voltages of about 2100 (V). In the conventional example shown in Figure 7, approximately 1700
(V), this means that the voltage resistance has improved by about 400 [V].

In addition, in the conventional example, 25 (V) is applied to the input/output terminal TIO.
When a voltage higher than the voltage applied, the bipolar transistor Q2
In contrast, in the embodiment described above, when the voltage exceeds 14 (V), discharge to the ground terminal TVS is started via the bipolar transistor Q. This indicates that the electrostatic protection circuit according to the present invention can operate more effectively than the conventional one.

〔Effect of the invention〕

In the semiconductor integrated circuit protection device according to the present invention, there is provided a bipolar transistor whose collector is connected to an input/output terminal and whose emitter is connected to a ground terminal, and between the base of the bipolar transistor and the input/output terminal. A breakdown element inserted in a direction opposite to the base, and a resistor inserted between the base of the bipolar transistor and the ground terminal, or a collector connected to the power supply terminal. and a bipolar transistor whose emitters are respectively connected to input and output terminals, and a break down element inserted between the base of the bipolar transistor and the power supply terminal in a direction opposite to the base. The device may include a resistor inserted between the base of the bipolar transistor and the input/output terminal, or may include all of the above configurations.

By adopting the above configuration, static electricity applied to the terminals of the semiconductor integrated circuit can be discharged in a short time through the bipolar transistor that operates in its original standard manner, thereby effectively preventing destruction of the semiconductor integrated circuit. It is possible,
It is possible to expand the environment in which it can be used.

[Brief explanation of drawings]

Figures 1 and 2 are main circuit explanatory diagrams for explaining the principle of the electrostatic protection circuit according to the present invention, and Figure 3 is an illustration for easy operation analysis of the electrostatic protection circuit shown in Figures 1 and 2. FIG. 4 is a diagram for explaining the current that can flow through the electrostatic protection circuit shown in FIG. 3, and FIG. 5 is an explanation of the main circuit according to an embodiment of the present invention. 6 is a cutaway side view of the main part for explaining the specific structure of the embodiment shown in FIG. 5, FIG. 7 is an explanatory diagram of the main part circuit of the conventional example, and FIG.
The figures each show an explanatory diagram of the main parts of the test circuit used to measure the electrostatic protection circuit. In the figure, Tvo is the power supply terminal, TIO is the input/output terminal,
Tvs is a ground terminal, Ql and Q2 are protection elements, QGD is a protected element r, Q is a bipolar transistor which is a protection element t, D is a breakdown element, and RB is a resistor. Patent Applicant Fujitsu Co., Ltd. Representative Patent Attorney Shoji Aitani

Claims (2)

[Claims] (1) A bipolar transistor whose collector is connected to an input/output terminal and whose emitter is connected to a ground terminal, and a bipolar transistor whose collector is connected to an input/output terminal and whose emitter is connected to a ground terminal; An electrostatic protection circuit for a semiconductor integrated circuit, comprising: a break down element inserted; and a resistor inserted between the base of the bipolar transistor and the ground terminal. (2) A bipolar transistor whose collector is connected to a power supply terminal and whose emitter is connected to an input/output terminal, and inserted between the base of the bipolar transistor and the power supply terminal in the opposite direction toward the base. 1. An electrostatic protection circuit for a semiconductor integrated circuit, characterized in that the electrostatic protection circuit comprises: a break-down element having a conductive structure, and a resistor inserted between the base of the bipolar transistor and the input/output terminal.