The present invention relates to a monolithic semiconductor component which is suitable for limiting transient voltages on signal lines such as telephone lines.

The occurrence of natural electrical disturbances such as lightning gives rise to transient induced voltages on signal lines, such as telephone lines, and those transient voltages are capable of damaging semicon¬ ductor devices belonging to signal-processing equipment connected to those signal lines.

A solution to the problem of transient voltages which could damage equipment connected to signal lines is to attach, to the signal lines, components capable of limiting transient voltages on the signal lines.

The present invention provides a monolithic semicon¬ ductor component which can be attached to signal lines such as telephone lines as a means of limiting transient voltages on those signal lines.

The present invention provides a monolithic semicon¬ ductor component comprising a P-type body and an N-type body having an interface with each other, in which a part of the N-type body and a part of the P-type body are the

inner P and N regions of a PNPN device, another part of the N-type body and another part of the P-type body are the P and N regions of a PN diode, and the part of the N- type body in the PNPN device is thicker than the part of that body in the PN diode, where thickness is measured in the direction of current flow through the N-type body.

Preferably, a P-type region and a first N ⁺ -type region have respective interfaces with the N-type body opposite its interface with the P-type body and have an interface with each other, a second N ⁺ -type region has an interface with the P-type body opposite the interface between the N-type body and the P-type region offset from the interface between the N-type body and the first N ⁺ -type region, the PNPN device is formed by the second N ⁺ -type region, the part of the P-type body opposite the P-type region, the P-type region, and the part of the N- type body lying between the P-type body and the P-type region, and the PN diode is formed by the part of the P- type body opposite the first N ⁺ -type region, the first IT^-type region and the part of the N-type body lying between the P-type body and the first N ⁺ -type region. In one form of the monolithic semiconductor com¬ ponent, the part of the N-type body belonging to the PN diode is not as thick as the first N ⁺ -type region.

In another form of the monolithic semiconductor component, the part of the N-type body belonging to the PN diode is not as thick as the part of the P-type body

belonging to the PN diode.

In either form of the monolithic semiconductor component, the part of the P-type body belonging to the PN diode can be thicker than the part of the P-type body belonging to the PNPN device.

In either form of the monolithic semiconductor component, in addition to the part of the P-type body belonging to the PN diode being thicker than the part of the P-type body belonging to the PNPN device, the first N ⁺ -type region can be thicker than the P-type region.

Any one of the above forms of the monolithic semiconductor component can include, in the part of the N-type body belonging to the PNPN device and adjacent to the interface between the P-type and N-type bodies, a further N-type region of higher conductivity than the N- type body.

A plurality of the monolithic semiconductor com¬ ponents can have a plurality of pairs of PNPN/PN devices fabricated on a P-type body and an N-type body having an interface with each other, respective terminals connected to the outer region of the PNPN device and to the P region of the diode of each pair of devices, and a common terminal connected to the outer P region of the PNPN device and the N region of the diode of each pair of devices.

Monolithic semiconductor components in accordance with the present invention will now be described, by way

of example only, with reference to the accompanying drawings in which:

Fig. 1 is a diagrammatic sectional representation of a first form of the monolithic semiconductor component.

Fig. 2 is a diagrammatic sectional representation of a second form of the monolithic semiconductor component. Fig. 3 is a diagrammatic sectional representation of a third form of the monolithic semiconductor component and

Fig. 4 is a diagrammatic sectional representation of a fourth form of the monolithic semiconductor component.

Referring to Fig. 1 of the accompanying drawings, as viewed, the first form of the monolithic semiconductor component includes an N-type body having a left portion 1 wider than its right portion 10, a P-type body above the N-type body, the P-type body having a left portion 2 narrower than its right portion 11 and a plane interface with the N-type body, a P-type region 4 below the left portion 1 of the N-type body having a plane interface with the left portion 1 of the N-type body, a first N ⁺ - type region 3 below the right portion 10 and alongside the left portion 1 of the N-type body and having inter¬ faces with those two portions and with the P-type region 4, and a second N ⁺ -type region 5 above the left portion 2 of the P-type body having interfaces with both the portions 2 and 20 of the P-type body. The lower surface of the P-type region 4 is level with the lower surface of

the first N ⁺ -type region 3 and he upper surface of the second N ⁺ -type region 5 is level with the upper surface of the portion 11 of the P-type body. The portion 1 of the N-type body is thicker than the portion 10 of that body.

Referring to Fig. 1, the P-type region 4, the left portion 1 of the N-type body, the left portion 2 of the P-type body, and the second P-type region 5 form the PNPN device, while the first N ⁺ -type region 3, the right portion 10 of the N-type body, and the right portion 11 of the P-type body form the PN diode. Because the N-type and P-type bodies are common to the PNPN device and the PN diode, the PNPN device and the PN diode are connected in parallel with each other with opposite polarities. Although not shown in Fig. 1, electrical contacts are provided on the upper and lower surfaces (as viewed in Fig. 1) of the monolithic semiconductor component.

Referring to Fig. 1, the fabrication of the monolithic semiconductor component includes the deep diffusion of the first N ⁺ -type region 3 into the N-type region which has an initially uniform thickness, before the diffusing of the P-type region 4 and the second N ⁺ - type region 5.

Referring to Fig. 1, in the operation of the monolithic semiconductor component, the PNPN device alone is forward biassed by a voltage which makes the P-type region 4 and the first N ⁺ -type region 3 positive with

respect to the second IT^-type region 5 and the portion 11 of the P-type body, while the PN diode alone is forward biassed when the applied voltage polarity is reversed. In the use of the monolithic semiconductor component for protection against transient voltages in a telephone system, the second N ⁺ -type region 5 and the portion 11 of the P-type body are connected to a signal line and the P- type region 4 and the first N ⁺ -type region 3 are con¬ nected to the earth line.

Referring to Fig. 1, in the situation where the PN diode has applied to it a rapidly increasing voltage which biasses the P-type portion 11 positive with respect to the N ⁺ -type region 3, the bulk resistance of the N-type portion 10 supports a sharp rise in the voltage across the diode; that rise ends when charge carriers injected from the P-type portion 11 fill the N- type portion 10 and the conductivity of the N-type portion 10 is determined mainly by those charge carriers. As an example of the required performance of the com¬ ponent, should it take O.lμS for the N-type portion 10 to be saturated by charges injected into it from the P-type portion 11, a 140V/μS transient forward voltage applied to the diode would result in the diode sustaining about a 14V transient voltage before it becomes fully conductive. That is,the transient voltage sustained by the PN diode before it conducts fully is dependent on the thickness of the N-type portion 10 of the diode.

Referring to Fig. 2, the second form of the semi¬ conductor component includes a PNPN device and a PN diode which share adjacent N-type and P-type bodies, as is the case in the first form of the component. As is the case in the first form of the component, the portion of the N-type body belonging to the PN diode is not as thick as the portion of the N-type body belonging to the PNPN device. In the second form of the component, as represen¬ ted by Fig. 2, a portion 21 of the N-type body, a portion

22 of the P-type body, a P-type region 24, an N ⁺ -type region 25, an N ⁺ -type region 23, a portion 210 of the N- type body and a portion 211 of the P-type body correspond respectively to the parts 1, 2, 4, 5, 3, 10 and 11 of Fig. 1. The portion 211 of the P-type body belonging to the PN diode is thicker than the portion 22 of the P-type body belonging to the PNPN device. The portion 211 of the P-type body is also thicker than the first N ⁺ -type region

23 corresponding to the region 3 of Fig. 1. The structure of the PNPN device is substantially the same as that represented in Fig. 1. The portion 210 of the N-type body in the component represented by Fig. 2 is substantially the same thickess as the portion 10 of the N-type body in the device represented by Fig. 1, and the device represented by Fig. 2 limits a transient overshoot to a voltage comparable with that for the device represented by Fig. 1.

Referring to Fig. 2, the component is fabricated by

a deep P-type diffusion to provide the portion 211 before the diffusing of the regions 23, 24 and 25.

Referring to Fig. 3, the third form of the semiconductor component includes a PNPN device and a PN diode which share adjacent N-type and P-type bodies, as is the case with the first form of the component. As is the case with the first form of the component, the portion of the N-type body belonging to the PN diode is not as thick as the portion of the N-type body belonging to the PNPN device. In the third form of the device as represented by Fig. 3, a portion 31 of the N-type body, a portion 32 of the P-type body, a P-type region 34, an N ⁺ - type region 35, an N ⁺ -type region 33, a portion 310 of the N-type body, and a portion 311 of the P-type body correspond respectively to the parts 1, 2, 4, 5, 3, 10 and 11 of Fig. 1. The portion 311 of the P-type body belonging to the PN diode is thicker than the portion 32 belonging to the -PNPN device and the N ⁺ -type region 33 belonging to the PN diode is thicker than the portion 311 of the P-type body.

Referring to Fig. 4 of the accompanying drawings, a fourth form of the semiconductor component includes an N~ -type body and a P-type body corresponding respectively to the N-type and P-type bodies of Fig. 1, a P-type region 44 corresponding to the P-type region 4 of Fig. 1, and first and second N^-type regions 43 and 45 cor¬ responding respectively to the N ⁺ -type regions 3 and 5 of

Fig. 1. The left portion 41 of the N~-type body is thicker than its right portion 410 and the right portion 411 of the P-type body is thicker than its left portion 42, in the figure as viewed. An N-type region 46 is accommodated in the N~-type portion 41 at its interface with the portion 42 of the P-type body, the N-type region 46 being of higher conductivity than the N~-type portion 41. The first N ⁺ -type region 43 is thicker than the portion 411 of the P-type body.

Referring to Fig. 4, as viewed, the left portion of the component represents a PNPN device with an additional N-type region 46 and a PN diode which is the right portion of the component. The PNPN device and the PN diode are connected in parallel with opposed polarities by virtue of their sharing the N"-type and P-type bodies. The PNPN device is known as a bulk breakdown diode.

As will be evident from the description of various forms of the semiconductor component, it is capable of providing protection from both positive and negative transient voltages, protection against negative transient voltages being provided by a PNPN device and protection against positive transient voltages being provided by a PN diode. The PNPN device and the PN diode are connected electrically, in shunt, in opposite senses and the PN diode has a structure which results in its permitting only a low overshoot voltage under positive (for the diode) transient voltages. The PNPN device and the PN

diode are fabricated with shared P and N bodies, a result of the sharing of P and N bodies being that the PNPN device and the PN junction diode are fabricated in shunt and in opposite senses in a "vertical" structure.

A plurality of the components can be fabricated together on common N-type and P-type bodies with each component having its own terminal for connection to respective signal lines and a common terminal for earth connection.