CA1303245C - Semiconductor switching device - Google Patents
Semiconductor switching deviceInfo
- Publication number
- CA1303245C CA1303245C CA000606343A CA606343A CA1303245C CA 1303245 C CA1303245 C CA 1303245C CA 000606343 A CA000606343 A CA 000606343A CA 606343 A CA606343 A CA 606343A CA 1303245 C CA1303245 C CA 1303245C
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- CA
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- Prior art keywords
- type
- region
- semiconductor switching
- switching device
- island
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- 239000012535 impurity Substances 0.000 claims description 11
- 230000004044 response Effects 0.000 claims description 6
- 230000006872 improvement Effects 0.000 claims description 3
- 238000012360 testing method Methods 0.000 abstract description 7
- 238000012423 maintenance Methods 0.000 abstract description 6
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000009977 dual effect Effects 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/22—Arrangements for supervision, monitoring or testing
- H04M3/26—Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
- H04M3/28—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
- H04M3/30—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop
- H04M3/301—Circuit arrangements at the subscriber's side of the line
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
- H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body
- H01L27/06—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including a plurality of individual components in a non-repetitive configuration
- H01L27/0611—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including a plurality of individual components in a non-repetitive configuration integrated circuits having a two-dimensional layout of components without a common active region
- H01L27/0641—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including a plurality of individual components in a non-repetitive configuration integrated circuits having a two-dimensional layout of components without a common active region without components of the field effect type
- H01L27/0647—Bipolar transistors in combination with diodes, or capacitors, or resistors, e.g. vertical bipolar transistor and bipolar lateral transistor and resistor
- H01L27/0652—Vertical bipolar transistor in combination with diodes, or capacitors, or resistors
- H01L27/0664—Vertical bipolar transistor in combination with diodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/74—Thyristor-type devices, e.g. having four-zone regenerative action
- H01L29/7404—Thyristor-type devices, e.g. having four-zone regenerative action structurally associated with at least one other device
- H01L29/7408—Thyristor-type devices, e.g. having four-zone regenerative action structurally associated with at least one other device the device being a capacitor or a resistor
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/74—Thyristor-type devices, e.g. having four-zone regenerative action
- H01L29/7404—Thyristor-type devices, e.g. having four-zone regenerative action structurally associated with at least one other device
- H01L29/7412—Thyristor-type devices, e.g. having four-zone regenerative action structurally associated with at least one other device the device being a diode
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/861—Diodes
- H01L29/87—Thyristor diodes, e.g. Shockley diodes, break-over diodes
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/30—Modifications for providing a predetermined threshold before switching
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Ceramic Engineering (AREA)
- Signal Processing (AREA)
- Bipolar Integrated Circuits (AREA)
Abstract
TEXAS INSTRUMENTS LIMITED
ABSTRACT
A Semiconductor Switching Device A semiconductor switching device that is suitable for use as a remote isolation device (RID) in telephone networks. The semiconductor switching device is a two-terminal voltage sensitive device that switches from an open-circuit condition to a short-circuit condition at a fixed breakover voltage, appears as an open-circuit below the breakover voltage, and appears as a short-circuit above the breakover voltage. When semiconductor switching devices are installed in a telephone network, they are held in their short-circuit condition by the network voltage supply and do not affect the normal operation of the network but will switch to their open-circuit condition if the network voltage supply is reduced to below the breakover voltage, and therefore, parts of the network may be isolated from each other by reducing the voltage supply. Isolation of the parts of the network from each other facilitates testing for maintenance purposes.
ABSTRACT
A Semiconductor Switching Device A semiconductor switching device that is suitable for use as a remote isolation device (RID) in telephone networks. The semiconductor switching device is a two-terminal voltage sensitive device that switches from an open-circuit condition to a short-circuit condition at a fixed breakover voltage, appears as an open-circuit below the breakover voltage, and appears as a short-circuit above the breakover voltage. When semiconductor switching devices are installed in a telephone network, they are held in their short-circuit condition by the network voltage supply and do not affect the normal operation of the network but will switch to their open-circuit condition if the network voltage supply is reduced to below the breakover voltage, and therefore, parts of the network may be isolated from each other by reducing the voltage supply. Isolation of the parts of the network from each other facilitates testing for maintenance purposes.
Description
``` ~3~3~
The present invention relates to a semiconductor switching device that has a particular application in telephone networks.
The invention is used in a circuit system having a supply line to an apparatus and having a remote isolation device to disconnect the apparatus in response to a remote command, the improvement in which the remote isolation device comprises a semiconductor switching device comprising a PNP
transistor having a P-type emitter region, an N-type base region, and P-type collector region, an NPN transistor having an N-type emitter region, a P-type base region, and an N-type collector region and a reverse breakdown PN diode having a P-type region and an N-type region, wherein the respective emitter regions of the transistors are connected in series in the supply line to serve as terminals of the semiconductor switching device, the collector region of the NPN transistor is connected to the base region of the PNP transistor and to the N-type region of the reverse breakdown PN diode, and the collec~or region of the PNP transistor is connected to the base region of the NPN transistor and to the P-type region of the reverse breakdown PN diode.
The semiconductor switching device behaves as a voltage sensitive switch that appears as a high impedance to voltages applied at the emitter regions of the transistors, (the emitter region of the PNP transistor being positive relative to the emitter region of the NPN transistor) up to voltag~s slightly in excess of the reverse breakdown voltage of the PN diode, that changes to a low impedance once the applied voltage is large enough to cause reverse conduction, through the PN diode, the transition from the high to the low impedance state being by way of a negative ~d rn/
imped~nce sta~e, and reverts to the high impedance state, by way of the negative impedance state, on the removal of the applied voltage.
The semiconductor switching devi.ce, i~ capable of operating as a remote isolation device (RIDl when ins~alled in the supply lines to a subscriber's apparatus, in a telephone networ~, since the line supply voltage may be used to make it switch between its high and low impedance status and thereby act as a voltage controlled switch that will disconnect the subscriber's apparatus in response to a remote command, the re~ote command being effected by a reduction in the line supply voltage. The semiconductor switching device is designed to go to its low impedance state when subjected to the normal line supply voltage an~, therefore, it does not interfere with the use of the subscriber's apparatus. - .
The reverse breakdown PN diode is, preferably, formed at the collector-base junction of one of ~he transistor~ and may be formed either at the collector-ba~e junction of the NPN transistor or the collector-base junction of the P~P transi~tor.
Thus the NPN transistor may include an additio~al N-type regisn, that e~tends across the collector-base junction of the tran~istor ~ of higher impurity concen-tration than the collector re~ion of the transistor, which additional N-type }egion provides a part of the reverse breakdown P~ diode.
-3~
Alternatively, the P~P transi~tor may include an additional ~-type region, that extends across the collector-base junction of the transistor, of higher impurity concentration than the base re~ion of the S transistor, which additional N-type region provides a part of the reverse breakdown PN diode.
In either arrangement, the impurity concentration of the additional N-type region ~ay be of the order of 102 to 1021 atoms per cubic centimetre~
There may be a resistive element connected between the base and the emitter regions of the NPN transistor.
Preferably, the semicondu~tor switching device has the form of a monolithic integrated circuit, in order to minimise the cost per device and the space occupied by the device when installed in, say, a telephone networkl ~n integrated circuit se~iconductor swit~hing device may comprise an N-type semicondu~tor body that is both the base region of the PNP transistor and the collector region of the NPN transistor, a firs~ P-type i~land, at a surface of the N-type body, that is bo~h the ba3e region of the NPN transistor and the collec~or ~1 reqion of the PNP tran~istor, a se~ond P-type island, ;¦
at the surface of the semiconductor body, that is the e~itter region of the P~P transistor, an N-type island, ln the first P-type island, that is the emitter region of the NP~ transi~tor, and conductive contact region~
providing re~pective ter~in~ls for the se~ond P-~ype t ~4~ ~L3~,1'3~'~S
island and the N-type island.
An impurity concentration of bet~een 10l4 and 1016 atoms per cubic centimetre is suitable for the N-type semiconductor body, and, an impurity concentration of S b~tween 1017 and 1019 atoms per cubic centimetre is suitable for the first and second P-type islands.
Alternatively, the integrated circuit semiconductor switching device may comprise a P-type semiconductor body that is both the base region of the NPN transistor and the collector region of the PNP
transistor, an N-type island, at a surface of the P-type body, that is both the base region of the PNP
transistor and the collector region of the NPN
transistor, a P-type island, in the N-type island, that is the emitter region of the PNP transistor, an N -type island, at the surface of the P-type body~ that is the emitter region of the NPN transistor, and conductive contact regions providing respective terminals for the P-type island and the N+-type island.
An impurity concentration of bet~een 1014 and 10l6 atoms per cubic centimetre is suitable for the N-type island, and, an i~purity concnetration of between 1017 and 1019 atoms per cubic centi~etre, is suitable for the P-type semiconductor body and the P-type island.
The integrated~circuit semiconductor switehinq device ba~ed on an N-type body may include a ~3~3~f~
semiconductor re~istor connected between the conductive contact region with the N type island and the first P-type island, providing a resistive element connected between the base and emitter reqions of the NPN
S transistor.
The integrated circuit semiconductor switching device based on a P-type body may include a semi-conductor resistor connected between the conductive contact region with the N -type island and the P-type body, providing a re~istive element between the base and emitter reqions of the NPN transistor.
An alternative arrangement to that of providing a resistive element between the base and emitter regions of the NPN transistor is that of providing an NPN
transistor with low emitter efficiency, ~his being achieved by partly short-circuiting the base-emitter junction of the PNP transistor, either by laying out the conductive contact re~ion with the N~-type island to contact the first P-type island, when the integrated circuit semiconductor switching device is based on an N-type body, or laying out the conductive contact region with the N -type island to contact the P-type body, when the inte~rated circuit semiconductor switching device is based on the P-type body.
The present invention relates to a semiconductor switching device that has a particular application in telephone networks.
The invention is used in a circuit system having a supply line to an apparatus and having a remote isolation device to disconnect the apparatus in response to a remote command, the improvement in which the remote isolation device comprises a semiconductor switching device comprising a PNP
transistor having a P-type emitter region, an N-type base region, and P-type collector region, an NPN transistor having an N-type emitter region, a P-type base region, and an N-type collector region and a reverse breakdown PN diode having a P-type region and an N-type region, wherein the respective emitter regions of the transistors are connected in series in the supply line to serve as terminals of the semiconductor switching device, the collector region of the NPN transistor is connected to the base region of the PNP transistor and to the N-type region of the reverse breakdown PN diode, and the collec~or region of the PNP transistor is connected to the base region of the NPN transistor and to the P-type region of the reverse breakdown PN diode.
The semiconductor switching device behaves as a voltage sensitive switch that appears as a high impedance to voltages applied at the emitter regions of the transistors, (the emitter region of the PNP transistor being positive relative to the emitter region of the NPN transistor) up to voltag~s slightly in excess of the reverse breakdown voltage of the PN diode, that changes to a low impedance once the applied voltage is large enough to cause reverse conduction, through the PN diode, the transition from the high to the low impedance state being by way of a negative ~d rn/
imped~nce sta~e, and reverts to the high impedance state, by way of the negative impedance state, on the removal of the applied voltage.
The semiconductor switching devi.ce, i~ capable of operating as a remote isolation device (RIDl when ins~alled in the supply lines to a subscriber's apparatus, in a telephone networ~, since the line supply voltage may be used to make it switch between its high and low impedance status and thereby act as a voltage controlled switch that will disconnect the subscriber's apparatus in response to a remote command, the re~ote command being effected by a reduction in the line supply voltage. The semiconductor switching device is designed to go to its low impedance state when subjected to the normal line supply voltage an~, therefore, it does not interfere with the use of the subscriber's apparatus. - .
The reverse breakdown PN diode is, preferably, formed at the collector-base junction of one of ~he transistor~ and may be formed either at the collector-ba~e junction of the NPN transistor or the collector-base junction of the P~P transi~tor.
Thus the NPN transistor may include an additio~al N-type regisn, that e~tends across the collector-base junction of the tran~istor ~ of higher impurity concen-tration than the collector re~ion of the transistor, which additional N-type }egion provides a part of the reverse breakdown P~ diode.
-3~
Alternatively, the P~P transi~tor may include an additional ~-type region, that extends across the collector-base junction of the transistor, of higher impurity concentration than the base re~ion of the S transistor, which additional N-type region provides a part of the reverse breakdown PN diode.
In either arrangement, the impurity concentration of the additional N-type region ~ay be of the order of 102 to 1021 atoms per cubic centimetre~
There may be a resistive element connected between the base and the emitter regions of the NPN transistor.
Preferably, the semicondu~tor switching device has the form of a monolithic integrated circuit, in order to minimise the cost per device and the space occupied by the device when installed in, say, a telephone networkl ~n integrated circuit se~iconductor swit~hing device may comprise an N-type semicondu~tor body that is both the base region of the PNP transistor and the collector region of the NPN transistor, a firs~ P-type i~land, at a surface of the N-type body, that is bo~h the ba3e region of the NPN transistor and the collec~or ~1 reqion of the PNP tran~istor, a se~ond P-type island, ;¦
at the surface of the semiconductor body, that is the e~itter region of the P~P transistor, an N-type island, ln the first P-type island, that is the emitter region of the NP~ transi~tor, and conductive contact region~
providing re~pective ter~in~ls for the se~ond P-~ype t ~4~ ~L3~,1'3~'~S
island and the N-type island.
An impurity concentration of bet~een 10l4 and 1016 atoms per cubic centimetre is suitable for the N-type semiconductor body, and, an impurity concentration of S b~tween 1017 and 1019 atoms per cubic centimetre is suitable for the first and second P-type islands.
Alternatively, the integrated circuit semiconductor switching device may comprise a P-type semiconductor body that is both the base region of the NPN transistor and the collector region of the PNP
transistor, an N-type island, at a surface of the P-type body, that is both the base region of the PNP
transistor and the collector region of the NPN
transistor, a P-type island, in the N-type island, that is the emitter region of the PNP transistor, an N -type island, at the surface of the P-type body~ that is the emitter region of the NPN transistor, and conductive contact regions providing respective terminals for the P-type island and the N+-type island.
An impurity concentration of bet~een 1014 and 10l6 atoms per cubic centimetre is suitable for the N-type island, and, an i~purity concnetration of between 1017 and 1019 atoms per cubic centi~etre, is suitable for the P-type semiconductor body and the P-type island.
The integrated~circuit semiconductor switehinq device ba~ed on an N-type body may include a ~3~3~f~
semiconductor re~istor connected between the conductive contact region with the N type island and the first P-type island, providing a resistive element connected between the base and emitter reqions of the NPN
S transistor.
The integrated circuit semiconductor switching device based on a P-type body may include a semi-conductor resistor connected between the conductive contact region with the N -type island and the P-type body, providing a re~istive element between the base and emitter reqions of the NPN transistor.
An alternative arrangement to that of providing a resistive element between the base and emitter regions of the NPN transistor is that of providing an NPN
transistor with low emitter efficiency, ~his being achieved by partly short-circuiting the base-emitter junction of the PNP transistor, either by laying out the conductive contact re~ion with the N~-type island to contact the first P-type island, when the integrated circuit semiconductor switching device is based on an N-type body, or laying out the conductive contact region with the N -type island to contact the P-type body, when the inte~rated circuit semiconductor switching device is based on the P-type body.
2~ The integrated circuit semiconductor switching device ba~ed on an N-type ~ody may in~lude a further N -type island that extends across the junction beeween the firs~ P-type island and the M type body, and the :
i' -6- ~3~ S
first P type island may include a P-type re~ion immediately adjacent to the further N -type island.
The alternative integrated circuit semiconductor switchinq device based on a P-type body may include a S further N -type island that extends across the junction between the N-type island and the P-type body, and the P-type body may include a P -type region immediately adjacent to the further N -type island. In either arrangement, the further N -type island provides a part of the reverse breakdown diode and the P -type region allows adjustment of the breakdown voltage.
An impurity concentration of between 102 and 10 atoms per cubic centimetre i5 suitable for the further N -type lsland, and, an impurity concentration of between 1015 and 1017 atoms per cu~ic centimetre is sui~able for the P -type region.
The semiconductor switching device requires connection in a specific sense, relative to the supply voltage in a telephone network, say, in order to function as a remote isclation device or a voltage sensitive switch, and for such an application it is desirable to provide a compound semiconductor switching device comprising first and second semiconductor switching devices connected in parallel with each o~her and in opposite senses one relative to the other, which compound switching device behaves as a voltage f sensitiYe switch to an applied voltage of either polarity. ¦.
~ ' ~;
-7- ~3~3z~S
The first and second semiconductor switchin~
devices may be formed in a common semi~onductor body and be interconnected by means of conductive contact regions laid on a surface of the se~iconductor body.
The semiconductor body may be either ~-type or P-type material.
A first and a second form of the semiconductor switching device, and integrated circuit arrangments of the first and second forms of the semiconductor switching device, in accordance with the present invention, will now be described by way of example only and with reference to the accompanying drawings, in which:-Fig~ 1 is a circuit diagram representing the first lS form of the semiconductor switching device;
Fig. 2 is a circuit diagram representing the second orm of the semiconductor switching device;
Fi~. 3 is a circuit diagram representing dual semiconductor switching devices of the second form:
Fig. 4 is a plan view of an integrated circuit arrangement of the second form of the semiconductor switching device:
Fig. 5 is a sectional view through the integrated circuit arrangement of Pig. 4 taken along the line X-X;
Fig. 6 is a sectional view through the integrated circuit arrangement of Fig. 4 taken along the line Y-Y;
:~ Fig, 7 is a part plan view of an inte~rated circuit arrangement of the first form of the semiconductor switching device;
~ig. 8 is a sectional view throu~h the integrated circuit arrangement of Fig. 7 taken along the line Y-Y;
S Fig. 9 is a sectional view through an integrated circuit arrangement, with a modification, of the second form of the inteqrated circuit arrangement.
Fig. 10 is a sectional view through an integrated circuit arrangement comprisins two devices of either the first or the second form, and;
~ig. 11 represents semiconductor switching devices of the first form installed in a telep~one system.
Referring to Fig. 1 of the accompanying drawings, the first form of the semiconductor switching device comprises a PNP bipolar transistor 1, an NPN bipolar transistor 2, .
and a reverse bre~kdown diode 3 that is generally known as a zener diode. The collector electrode of the PNP
transistor 1 ls connected to the base electrode of the NPN transistor 2, the base electrode of the PNP transis-tor 1 is connected to the collector electrode of the NPN
transistor 2, and the reverse breakdown diode 3 has its a~ode and cathode electrodes connected respectively to the collector electrode and the base electrode of the NPN
transistor 2. The emitter electrodes of the PNP tran-sistor 1 and the NPN transistor 2 provide respective terminals 4 and 5 for the semiconductor switching device.
The breakdown diode 3 is effectively connected in parallel with the collector-base junctions of the PNP
-9~ 3Z~l~
tranSistor 1 and the NPN transistor 2 and has a lower reverse breakdown voltage than either of those junctions.
The semiconductor switching device is responsive to the magnltude cf a voltaqe applied to the terminals ~ and 5 and is intended for operation with an applied voltage in the sense that makes the terminal 4 positive with respect to the ~erminal 5. On the application to the terminals 4 and 5 of a voltage less than the breakdown voltage of the diode 3 in the sense indicated, the revese brea~down diode 3 and the collector-base junction of tAe NPN transistor 2 both act to block current flow that would occur through the emittex electrodes of the PNP transistor 1 and the NPN transistor 2. On the application to the t~-~inals 4 and S of a voltage, in the same sense, that exceeds the lS reverse breakdown voltage of the diode 3 (and which need not exceed the breakdown voltage for the NPN transistor 2), the diode 3 penmits current flow. If the a2plied voltage is increased gradually, current flowing into the emikter electrode of the PNP transistor 1 and out of the emitter electrode of the NPN transistor 2 will first increase gradually as the applied voltage increases and there will be corresponding current flows in the collector electrodes of the transistors 1 and 2. The transistor cuxrents will continue to increase with increasing applied voltage up to a current (the ~reakover current) beyond which the two transistors act together as a negative impedance, each of the transistors then ~ 1o~ 3~
driving the other into its fully sa.urated state and they then present, together, a high negative dynamic impedance for a range of currents slightly in excess of the breakover current. The negative dynamic impedance region extends from the breakover current to a current known as the holding current. For a range of currents in excess of the holding current, the saturated transistors present a low positive dynamic impedance to current flow. When the transistors are in thelr low positive dynamic impedance state, alteration of the eonditions at the terminals ~
and 5 to cause the current flow through the transistors 1 and 2 to move into the negative impedance region of their combined current/ voltage relationship will result in a rapid decrease of the current drawn through the terminals ~ and 5 and the turning off of both the transistors 1 and 2. The applied voltaqe at which the breakover current is reached is ~nown as the breakover voltage. Reversal of the applied voltage, that is, the application of an increasing voltage that makes the terminal S positive with respect to the terminal 4 results in substantially no current flow through the transistors 1 and 2 since their respective base-emitter junctions are reverse biassed by such an applied voltage. There will eventually be breakdown of both base-emittex junctions ln response to the applied voltage and there will be current flbw through the transistor but there is no negative lmpedance region in the current/voltage relationship for applied voltages .
!
, 3~3Z~
that make the terminal S positive with respect to the terminal ~.
Referring to Fig. 1, the PNP transistor 1 and the NPN translstor 2 may, in practice, be provided by, respectively, the P1N1P2 and N1P2N2 g region (P1N1P2N2) device in which the N1 re~ion acts both as the base region of the PNP transistor 1 and the collector region of the NPN txansistor 2, and the P2 region acts both as the collector region of the PNP
transistor 1 and the ~ase re~ion of the NPN transistor 2.
Referrlng to Fig. 1, the breakover voltage for the semiconductor switching device is determined by the reverse breakdown voltage of the diode 3 and is, as a result, set by the choice of the doping levels of the semiconduc~or regions that make up the reverse breakdown diode 3. The breakover current fo.r the semiconductor switching device is determined by the ~mitter efficiencies of the transistors 1 and 2 and is, as a result, set by the design of the emitters of the transistors 1 and 2.
Referring to Fig. 2 of the accompanying drawings,~ ~.
the second form of the semiconductor switching device i includes a PNP transistor 1, an NPN transistor 2, a reverse breakdown diode 3, and a resistor 6. The PNP
transistor 1, the NPN transistor 2, and the reverse 25 breakdown diode 3 are connected to each other in the same,i manner as are the transistors and diode in Fig. 1 and the I
emitter electrodes of the transistors 1 and 2, as in I
-12- ~3~.~3~
Fig. 1, are connected to the respec~ive terminals 4 and 5.
The resistor 6 is connected between the base and the emitter electrodes of the NPN transistor 2. The resistor 6 acts as a current snunt to the base electrode of the NPN transistor 2 and, as a result of its shunting action, the resistor 6 affec~s the breakover current for the semiconductor switching device. The breakover current of the semiconductor switching device is thexefore set by the device designer by means of the resist3r 6.
~he operation of the semlconductor switching device represented by Fi~. 2, is essentially the same as that of the semiconductor switching device represented by Fi~. 1, the effect of the resistor 6 that is included in Fig. 2 and not in Fig. 1 being that the breakover current of lS the device represented by Fig. 2 is dependent on the magnitude of the resistox 6.
The current/voltage relationship of the semiconductor switching device that is represented by Fig. 2, as is that for the device represented by F.ig. 1, is asymmetrical in that it includes a range o~ currents over which the impedance of the device is negative when the applied voltage is in the sense that makes the terminal 4 positive with respect to the terminal 5, and includes no negative résistance portion for situations where the terminal 4 is negative with respect to the termlnal 5.
A symmetrical current/~olta~e relationship is obtained by the connection of two semiconductor switching devices ~ 3~3~,f~s, between the te~inals 4 and 5, where the two d~vice~ are connect~d in oppo~ite ~ense~ bet~een the termin~ls 4 and S
~nd opera~ion changes from one de~ice to the other ~hen the sense oE ~he volt~ge applled ~o the terminals 4 and 5 S is ch~nged.
Fi~. 3 of the accompanying draw~ngs represents a c~mpoun~ seml¢~ductor swl~ching device comprisin~ two of the de~ioes repre~ented by ~iq. 2 ~Qhne~te~ in opposite sense~ one ta the o~her b~twe~n ~wo terminals l~ and 19.
One device cQ~prise~ a PNP tran~istor 10, a~ NPW
translstor 11, a reverse b~eakdo~n ~iod~ 12, an~ a resistor 13, conne~ed toge~her ~s ar~ th~ corresponding componen~s of the device represe~t~d by Fiy. 2, ~nd wi~h the emi~er ~le~trod~s of the PNP tran~istor 10 and ~he NPN tran~istor ll ¢onnected r~pe~ively to th~ terminals 18 ~nd 1~. The othe~ devl~e compri~es a P~P transisto~
14, an NPN t~ansistor lS, a rever~ b~eakdown ~iode 16, and a resi~t~r 17, agaitl~ ~onne~t~d ~o~ether as ar~ ~h~
correspon~ng c~mponent~ o~ the de~ic~ repre~en~d by 2Q Fig. ~, ~ut wl~h the ~mitter alectrodes of the PNP
tr~n~ or 14 ~nd ~he NPN transis~or 15 connec~ed respectl~ly to ~h~ termin~I6 19 and 1~
When ~h~ comp~und semicondu~tor swl~chlng d~viee ~h~t is ~epresented ~y ~ 3 i~ xub~ected ~o ~n increasing ~xt~rn~lly appli~d vol~ge t~at make~ the t~minals 1a more positive ~han the ~ermln~ the ~ ter-base junctlon Qf the NPN ~r~nsi~tnx 15 ~lo~ks cu~r~n~ flow.
-14- ~3~2-f~S
The applied voltage is of the sense to forward bi,as the base-collector junction of the ~PN transistor 15 and the diode 16 by way of the resistor 17, but current flow through these routes is blocked by the collector base and base-emitter diodes of the PNP transistor 14. A continued increase in the applied voltage without change in its sense would eventually force the reverse breakdown of one of the blocking junctions, but before that occurs, the reverse breakdown diode 12 wi11 permit current flow through the transistors 10 and 11, and the semiconductor switching device that includes the reverse breakdown diode 12 will change to its low impedance conductive state. The reversal oî the sense of the applied voltage will result in the changeover of the devices as regards which one remains in its non-conductive state and which one changes to its conductive state.
In Fig. 3, the first form of the semiconductor switching device, as represented by Fig. 1, may be substituted for each os the second fo.rm of the device, as represented by Fig~ 2.
Referring to Fig. 4 of the accompanying drawings, the integrated circuit arrangement of the second form of the semiconductor switching deYice comprises a body 45 of N-type silicon into a surface of which are diffused P-type regions 41, 4 2, and 4 3 . The P-type regions 41, 42, and 43 are situated alongside each other with the region 43 occupying a position between the regions 41 and 42. A first N -type region 44 is diffused into the P-type region 43 and a further N+-type region 47 is diffused into the same surface of the N-type ~ody 45 as is diffused the P-type region 43, the further N -type region 47 being positioned to overlie a part of the junction between the N-type body 45 and the P-type region ; 43. A further P-type region 48, diffused into the surface of the N-type body 45, connects to the P-type region 43 and extends in a part loop into the N-type body ~5. The surface of the N-type body 45 into which the regions are diffused is covered by a layer 46 of silicon dioxide except for windows provided in the silicon dioxide permitting electrical contact to be made with the P-type regions 41, 42 and 48 and the N+-type region 44.
Electrical contact with the P-type regions 41 and 42 is provided by a first metallic layer 40 and electrical ..
contact with the N+-type reqion 44 and the P-type region 48 is provided by a second metallic layer 50, both of which layers overlie the silicon dioxide layer 46 which separates the metallic layers 40 and 50 from the surface of the N-type body 45 where there are no windows in the ,¦
silicon dioxide layer 46. ~1 Figs. 5 and 6 of the accompanying drawings, ¦
representing respectively a part view along a transverse ' cross-section through the P~type regions 41, 42, and 43, : and a part view along a 1Ongitudinal cross-section through the P-type region 43, assist in clarifyinq Fig~ 4. In ::: : i, ¦ !
.
i ' ..
-16- ~3V3z~
Figs. 4, 5, and 6, the regions 41, 42, 43, and 45 provide a PNP transistor structure (the regions 41 and 42 are connected together by the metallic layer 40) that is the PNP transistor 1 of Fig. 2, the regions 43, 44, and 45 S provide an NPN translstor structure that is the NPN
transistor 2 of Fig. 2, the regions 47 and 43 provide a reverse breakdown diode that is the diode 3 of Fig. 2, and the region 48 provides a resistor that is the resistor 6 of Fig. 2. The regions 43 and 45 are 5hared by the PNP
and the NPN transistors eff~ctively making the base electrode of the PNP transistor the same as the collector electrode of the NPN transistor, and vice-versa. The metallic layers 40 and S0 provide the terminals ~ and 5 of Fig. 2.
Referrin~ to Figs. 2, 4, 5, and 6, the range of reverse breakdown voltages fox the diode 3 may lie in the range ~ volts to 20 volts, corresponding to impurity concentrations ~or the P~type region ~3 of between 1017 and 101~ atoms per cubic centimetre. Reverse breakdown voltages exceeding 20 volts but less than the reverse breakdown voltage for the junction between the P-type ,l region 43 and the N-type region 45 are achieved by the 'I
modified a.rrangement represented by Fig. 9 which shows an i~
additional regio~ 51 that is a P-type region positioned in ¦~
the P-type region 43 immediately next to the N+-type region 47. In the modified arrangement represented by Flg. 9, the P-type region 43 aCts as a co~mon regioD of -17- ~3Q3~5 the PNP and NPN translstors while the N -t~pe region 47 and the P -type region 51 act as the reverse breakdown diode. ~his arrangement avoids any conflicting doping level requirements for the P -type and P-type regions 51 and 43, when a reverse breakdown diode Wl th a breakdown vol~age in excess of 20 volts is required (limited, of course, to the reverse breakdown voltage f~r the junction between the N-type region 45 and the P-type region 43).
An integrated circuit arrangement of '~.e first form of the semiconductor switching device may ~e substantially the same as that shown in Fig. ~ for the second form of the device, except that the resistive regi_r. 48, shown in Fig. 4, is omitted. In an integrated circ~ t arrangement of the first form of the semiconductor swit-hing device, the characteristics obtained by including the resistive reqion 4a, shown in Fig. 4, may be provided by modifica-tion of the structure of one of the active ~evices.
Figs. 7 and 8 of the accompanying drawlngs show one modification that may be used in an integrated circuit arrangement of the first form of the semiconductor switching device to compensate for the absence of the resistive region 48 that is shown in Fig. 4. Figs. 7 and 8 show that part of the integrated circuit arrangement of the first form of the semiconductor switchin~ device 25 corresponding to the P-type region 43 of Fig. 4 and its immediately adjacent regions.
Referring to Fiqs. 7 and 8 of the accompanying i I
-l8~ 3~
drawings, an integrated circuit arrangement of the ~irst form of the semiconductor switching device includes a window in the silicon dioxide layer 46. The window extends through one end of the N -type region 44 and over S the P-type region 43, permitting the metallic layer 50 to lie in electrical contact with both the N type region 44 and the P-type region 43. This arrangement represents a conductive bridge between the base and the emitter regions of the ~PN transistor 2 of Fig. 1, resulting in a transistor of low emitter injection efficiency and an increase in the breakover current for the semiconductor switching device of Fi~. 1. It will be understood, therefore, t.~at the inclusion of the partly short-circuited base-emitter junction in the NPN transistor ~
of Fig. 1 removes the need for the resistor 6 included in the second form of the semiconductor switching device, represented by Fig. 2.
Referring to Figs. ~1 to 9 of the accompanying drawings, a doping level in the range lOl4 to lOl6 atoms per cubic centimetre is suitable for the N-type region 45;
a doping level in the range 1017 to 1019 atoms per cubic centimetre is suitable for each of the P-type regions 4l, 42, and 43; a doping level in the range 10~ to 1021 -atoms per cubic centimetre is suitable for each of the P-type regions 44 and 47; and a dopiny level in the range 1015 to 1017 atoms per cubic centimetre is suitable for the P-type reqion Sl. A depth in the range 2 to 20 -1 9- 3~3~Z~S
microns is suitable for each of the P-type reqions 41, ~2, and 43 and a depth of about half that of the P-type region 43 is suitable for each of the N-type regions 44 and 47.
Both limits are included in each of the ranges given above.
Referring to Fig. 10 of the accompanying drawings, an integrated circuit arrangement comprising two of the semiconductor switching devices of either the first or the second form includes an N-type silicon body 1~5 at one surface of which are formed a first set of regions 1~1, 142, ;43, and 144 and a second set or similar regions 241, 242, 243, and 244. The regions 141, 142, 143, 241, 242, and 243 are P-type and t.~e regions 144 and 2~4 are N -type. The regions 141, 142, and 244 are connected together by a metallised layer 140 and the regions 144, 241, and 242 are connected together by a metallised layer 150. The metallised layers perform the function of connection terminals 18 and 19 to the dual device structure. A silicon dioxide layer 146 is included.
The breakover voltage of the switching device shown in Fig. 1 is determined by the breakdown characteristics of the PN junction breakover diode that is connected in parallel with the base-collector junctions of the transistors, and it is possible to obtain relia~le .
switching of the device in response to the supply voltages normally used for telephone systems. Telephone system supply voltages are normally of the order of 50 volts or ' ',:
-20- ~3~3Z~
below. The same situation of clean and reliable switching is obtained for the switching devices shown in Figs. 2 and 3.
The switching device shown in Fig. 2 provides, in addition to a clean and reliable switching characteristic, a well defined swi~ching current that depends on the value of the resistor connected in par~llel with the base-emitter junction of the NPN transistor.
It will be understood by those skilled in the electrical art that the device resulting from the ~tructure re~resented by Fi~s. ~ ~nd 6, say, may be provided by a structure based on a P-type semiconductor body rather than on an N-type semiconductor body as has been described. In a structure based on a P-type body, the P-type body would perform the function of the regions 43 of Figs. 5 and 6, iIl which case the N-type body 45 is reduced to two N-type islands that accommodate the P-t~pe islands 41 and 42, respectively, and the N -type region 44 becomes an island in the P-type body. The N+-type island 47 would be positioned along a part of the junction between the P-type body and one of the N-type islands. In a structure based on a P-typ~ body, the P-type loop 48 may be provided by the presence of an additional contact between the P-type body and the meta1 contact S0 at a position removed from the N -type island ; by a~out the length of the P-type loop 48. In a structure based on a P-type body, the arrangement ~.
-21- ~3~3Z~
represented by ~igs. 7 and a is provided by allowing the metal contact to the N -type island to make contact with the surface of the P-type body over a part of the junction between the N -island and the P-type body.
S Similarly, in a structure based on a P-type ~ody, the arrangement represented by Fig. 9 is pro~ided by means of a P -type region adjacent to the N+-type island corresponding to the N+-type island 47 of Fig. 6. A
compound device, corresponding to that represented by Fig. 10, may also be provided in an arrangement based on a P-type semiconductor body.
Fig. 11 of the accompanying drawings represents a part of a tele?hone system including an incoming line 100, an outgoing line 101, a subscriber's telephone apparatus 102, and semiconductor switching devices 103 and 1a4 of the first form as represented by Fig. 1 of the accompanying .. ...
drawings. A network consisting of a diode 105 in series with a resistor 106 is connected in parallel with the telephone apparatus 102. The semiconductor switching device 103 is connected in series with the incoming line 100 with such polarity as to permit current flow along the incoming line 100 towards the telephone apparatus 102 and the semiconductor switching device is conected in series with the outgoing line 101 with such polarity as to permit current flow along the outgoing line 101 away from the telephone apparatus 102. The semiconductor switching devices 103 and 104 are located at the -22- ~3~f~
telephone apparatus 102 effectively at the respective ends of the incoming and outgoing lines 100 and 101.
The incoming and outgoing lines 100 and 101 connect the telephone apparatus 102 to some form of central or control office~
Referring to Fiy. 11, the inclusion of the semi-conductor switching devices 103 and 104 in the respective incoming and outgoing lines 100 and 101 permits the perfonmance of tests on the telephone apparatus 102 from the central office by way of the lines 100 and 101, and permits the performance of tests on the lines 100 and 101, themselves. The testing of parts or the telephone system is made possible because the semiconduct^r switching devices 103 and 104 behave as voltage sensitive switches that are controllable from the central office by means of the voltages applied to the lines 100 and 101. The reverse breakdown voltage of the reverse break-down diodes included in the semiconductor switching devices is set at a value that causes the semlconductor 20 switching devices 103 and 104 to be conductive when the telephone apparatus 102 is "off-hoo~", in which case the semiconductor switching devices 1~3 and 104 are electri-cally "transparent", that is, they have no effect on normal system operation and are maintained in their low-impedance conductive states by the current flow through the lines 100 and 101 under the influence of the ~: normal supply voltage from the central office. ~oweverp I
-23- ~3~Z~
the semiconductor switching devices 103 and 104 may be switched off by reducing the central office supply voltage and will then isolate the telephone apparatus 102 from the lines 100 and 101. With the semiconductor S switching devices 103 and 104 in the switched off condi-tion, the parameters of the lines 100 and 101 may be checked with the knowledge that the telephone apparatus 102 is effectively disconnected form these lines. The semiconductor switching devices 103 and 134 also permit checks to be made to the telephone apparat~s 102 which should appear as a high impedance, when "on-hook", ~o the normal voltage supply from the central office. Also ~ith the telephone apparatus 102 "on-hook", the diode 105 and the resistor 106 permit checks to determine whether or not there are semiconductor switching devices connected in the lines 100 and 101 (conduction occurs only when the voltage applied to the outgoing line 101 is positive relative to that applied to the incoming line 100 and exceeds the combined breakdown voltages of the breakdown diodes in the semicondcutor switching devices 103 and 104) and to identify the incoming line relative to the outgoing line.
Referring to Fig. 11, it will be noted that the ,~
semiconductor switching device 103 connected in the ¦~
. 25 incoming line 100 is connected in the opposite sense to the semiconductor switch device 104 connected in the outgoing line 101. The need for the installer to pay attention to .
-2~- ~3~3Z~5 the polar1ty of each semiconductor switching device when installiny it may be avoided by providing two semiconduc-tor switching devices, such as the devices 103 and 104, iA a single four-terminal package in which the terminals 107 and 108 are identified as a first port, the terminals 108 and 109 are identified as a second port and the package has clearly marked top and bottom surfaces. It w1ll be evident that, as re~ards the pac~age with a pair of semiconductor switching devices, it is immaterial whether the first port is connected to the lines 100 and 101 of the telephone apparatus 102, and sim1larly for the second port, provided that the top surface of the package is always kept "above" the bottom surface. The need for an installex to pay attentino to either the polarities of the semiconductor switching devices or the attitude of the package, when installing the devices, is avoided by .. . .
providing compound semiconductor switching devices, as representeA by Fig. 3, or as represented by Fig. 10, for example, in which case each of the devices 103 and 104 is replaced by a compound device.
For a telephone system in which the line supply voltage is 48 volts, suitable brea~over voltages i-or the semiconduetor switchin~ devices lie in the range 10 to 20 volts, both limits included, that is to say, the range of breakover voltages extends slightly beyond the range lying between one quarter and one third of the line supply voltage.
-2~- ~3~32~S
When semiconductor switchlng devices as herein described are included in telephone systems for the purposes explained with reference to Fig. 11, they are qenerally known as remote isolation devices (RIDS).
S The remote isolation function performed by semiconductor switching devices as herein described may be carried cut by electrical networks that include many more circuit elements than the semiconductor switching devices, but such electrical networks are costlier to manufacture~, and are bulkier and less convenient to handle and install than the sem1conductor switching devices descrlbed.
Semiconductor switching devices, as described herein, may be employed, at minimal cost for installation, as remote isolation devices or maintenance termination units (MTUs) in a variety or ways. The installation of RIDs at demarcation points in a telephone network will permit the telephone operating company to divide up the network for testing purposes by variation of the network supply voltages. Thus a telephone maintenance centre or repair service centre may determine the condition of virtually any selected part of the network (as regards the existence of resistive faults or open-circuit conditions) without the need for personnel to leave the maintenance or repair centre for the purpose of testing the network equipment.
The semiconductor switching devices, when specifically intended for use as telephone network RIDs, may be provided in enclosures appropriate to the intended use -26- ~3~3Z~
ranging from single-line units to plug-in modules for multi-line applications such as PABX trunk llnes.
In all cases where the semiconductor switching devices are used as RIDs they will, at low cost, effect S maintenance cost reduction, avoid revenue lcsses by facilitating the quick repair and return to service of high-revenue lines, prevent difficulties associated with disagreements as to who is responsible for repair when a line is faulty, permit a 2~-hour test facili-y without the need to send repair personnel out to investigate customer complaints of faults and generally provide an environment leading to the maintenance of high quality transmissions.
i ~.
i' -6- ~3~ S
first P type island may include a P-type re~ion immediately adjacent to the further N -type island.
The alternative integrated circuit semiconductor switchinq device based on a P-type body may include a S further N -type island that extends across the junction between the N-type island and the P-type body, and the P-type body may include a P -type region immediately adjacent to the further N -type island. In either arrangement, the further N -type island provides a part of the reverse breakdown diode and the P -type region allows adjustment of the breakdown voltage.
An impurity concentration of between 102 and 10 atoms per cubic centimetre i5 suitable for the further N -type lsland, and, an impurity concentration of between 1015 and 1017 atoms per cu~ic centimetre is sui~able for the P -type region.
The semiconductor switching device requires connection in a specific sense, relative to the supply voltage in a telephone network, say, in order to function as a remote isclation device or a voltage sensitive switch, and for such an application it is desirable to provide a compound semiconductor switching device comprising first and second semiconductor switching devices connected in parallel with each o~her and in opposite senses one relative to the other, which compound switching device behaves as a voltage f sensitiYe switch to an applied voltage of either polarity. ¦.
~ ' ~;
-7- ~3~3z~S
The first and second semiconductor switchin~
devices may be formed in a common semi~onductor body and be interconnected by means of conductive contact regions laid on a surface of the se~iconductor body.
The semiconductor body may be either ~-type or P-type material.
A first and a second form of the semiconductor switching device, and integrated circuit arrangments of the first and second forms of the semiconductor switching device, in accordance with the present invention, will now be described by way of example only and with reference to the accompanying drawings, in which:-Fig~ 1 is a circuit diagram representing the first lS form of the semiconductor switching device;
Fig. 2 is a circuit diagram representing the second orm of the semiconductor switching device;
Fi~. 3 is a circuit diagram representing dual semiconductor switching devices of the second form:
Fig. 4 is a plan view of an integrated circuit arrangement of the second form of the semiconductor switching device:
Fig. 5 is a sectional view through the integrated circuit arrangement of Pig. 4 taken along the line X-X;
Fig. 6 is a sectional view through the integrated circuit arrangement of Fig. 4 taken along the line Y-Y;
:~ Fig, 7 is a part plan view of an inte~rated circuit arrangement of the first form of the semiconductor switching device;
~ig. 8 is a sectional view throu~h the integrated circuit arrangement of Fig. 7 taken along the line Y-Y;
S Fig. 9 is a sectional view through an integrated circuit arrangement, with a modification, of the second form of the inteqrated circuit arrangement.
Fig. 10 is a sectional view through an integrated circuit arrangement comprisins two devices of either the first or the second form, and;
~ig. 11 represents semiconductor switching devices of the first form installed in a telep~one system.
Referring to Fig. 1 of the accompanying drawings, the first form of the semiconductor switching device comprises a PNP bipolar transistor 1, an NPN bipolar transistor 2, .
and a reverse bre~kdown diode 3 that is generally known as a zener diode. The collector electrode of the PNP
transistor 1 ls connected to the base electrode of the NPN transistor 2, the base electrode of the PNP transis-tor 1 is connected to the collector electrode of the NPN
transistor 2, and the reverse breakdown diode 3 has its a~ode and cathode electrodes connected respectively to the collector electrode and the base electrode of the NPN
transistor 2. The emitter electrodes of the PNP tran-sistor 1 and the NPN transistor 2 provide respective terminals 4 and 5 for the semiconductor switching device.
The breakdown diode 3 is effectively connected in parallel with the collector-base junctions of the PNP
-9~ 3Z~l~
tranSistor 1 and the NPN transistor 2 and has a lower reverse breakdown voltage than either of those junctions.
The semiconductor switching device is responsive to the magnltude cf a voltaqe applied to the terminals ~ and 5 and is intended for operation with an applied voltage in the sense that makes the terminal 4 positive with respect to the ~erminal 5. On the application to the terminals 4 and 5 of a voltage less than the breakdown voltage of the diode 3 in the sense indicated, the revese brea~down diode 3 and the collector-base junction of tAe NPN transistor 2 both act to block current flow that would occur through the emittex electrodes of the PNP transistor 1 and the NPN transistor 2. On the application to the t~-~inals 4 and S of a voltage, in the same sense, that exceeds the lS reverse breakdown voltage of the diode 3 (and which need not exceed the breakdown voltage for the NPN transistor 2), the diode 3 penmits current flow. If the a2plied voltage is increased gradually, current flowing into the emikter electrode of the PNP transistor 1 and out of the emitter electrode of the NPN transistor 2 will first increase gradually as the applied voltage increases and there will be corresponding current flows in the collector electrodes of the transistors 1 and 2. The transistor cuxrents will continue to increase with increasing applied voltage up to a current (the ~reakover current) beyond which the two transistors act together as a negative impedance, each of the transistors then ~ 1o~ 3~
driving the other into its fully sa.urated state and they then present, together, a high negative dynamic impedance for a range of currents slightly in excess of the breakover current. The negative dynamic impedance region extends from the breakover current to a current known as the holding current. For a range of currents in excess of the holding current, the saturated transistors present a low positive dynamic impedance to current flow. When the transistors are in thelr low positive dynamic impedance state, alteration of the eonditions at the terminals ~
and 5 to cause the current flow through the transistors 1 and 2 to move into the negative impedance region of their combined current/ voltage relationship will result in a rapid decrease of the current drawn through the terminals ~ and 5 and the turning off of both the transistors 1 and 2. The applied voltaqe at which the breakover current is reached is ~nown as the breakover voltage. Reversal of the applied voltage, that is, the application of an increasing voltage that makes the terminal S positive with respect to the terminal 4 results in substantially no current flow through the transistors 1 and 2 since their respective base-emitter junctions are reverse biassed by such an applied voltage. There will eventually be breakdown of both base-emittex junctions ln response to the applied voltage and there will be current flbw through the transistor but there is no negative lmpedance region in the current/voltage relationship for applied voltages .
!
, 3~3Z~
that make the terminal S positive with respect to the terminal ~.
Referring to Fig. 1, the PNP transistor 1 and the NPN translstor 2 may, in practice, be provided by, respectively, the P1N1P2 and N1P2N2 g region (P1N1P2N2) device in which the N1 re~ion acts both as the base region of the PNP transistor 1 and the collector region of the NPN txansistor 2, and the P2 region acts both as the collector region of the PNP
transistor 1 and the ~ase re~ion of the NPN transistor 2.
Referrlng to Fig. 1, the breakover voltage for the semiconductor switching device is determined by the reverse breakdown voltage of the diode 3 and is, as a result, set by the choice of the doping levels of the semiconduc~or regions that make up the reverse breakdown diode 3. The breakover current fo.r the semiconductor switching device is determined by the ~mitter efficiencies of the transistors 1 and 2 and is, as a result, set by the design of the emitters of the transistors 1 and 2.
Referring to Fig. 2 of the accompanying drawings,~ ~.
the second form of the semiconductor switching device i includes a PNP transistor 1, an NPN transistor 2, a reverse breakdown diode 3, and a resistor 6. The PNP
transistor 1, the NPN transistor 2, and the reverse 25 breakdown diode 3 are connected to each other in the same,i manner as are the transistors and diode in Fig. 1 and the I
emitter electrodes of the transistors 1 and 2, as in I
-12- ~3~.~3~
Fig. 1, are connected to the respec~ive terminals 4 and 5.
The resistor 6 is connected between the base and the emitter electrodes of the NPN transistor 2. The resistor 6 acts as a current snunt to the base electrode of the NPN transistor 2 and, as a result of its shunting action, the resistor 6 affec~s the breakover current for the semiconductor switching device. The breakover current of the semiconductor switching device is thexefore set by the device designer by means of the resist3r 6.
~he operation of the semlconductor switching device represented by Fi~. 2, is essentially the same as that of the semiconductor switching device represented by Fi~. 1, the effect of the resistor 6 that is included in Fig. 2 and not in Fig. 1 being that the breakover current of lS the device represented by Fig. 2 is dependent on the magnitude of the resistox 6.
The current/voltage relationship of the semiconductor switching device that is represented by Fig. 2, as is that for the device represented by F.ig. 1, is asymmetrical in that it includes a range o~ currents over which the impedance of the device is negative when the applied voltage is in the sense that makes the terminal 4 positive with respect to the terminal 5, and includes no negative résistance portion for situations where the terminal 4 is negative with respect to the termlnal 5.
A symmetrical current/~olta~e relationship is obtained by the connection of two semiconductor switching devices ~ 3~3~,f~s, between the te~inals 4 and 5, where the two d~vice~ are connect~d in oppo~ite ~ense~ bet~een the termin~ls 4 and S
~nd opera~ion changes from one de~ice to the other ~hen the sense oE ~he volt~ge applled ~o the terminals 4 and 5 S is ch~nged.
Fi~. 3 of the accompanying draw~ngs represents a c~mpoun~ seml¢~ductor swl~ching device comprisin~ two of the de~ioes repre~ented by ~iq. 2 ~Qhne~te~ in opposite sense~ one ta the o~her b~twe~n ~wo terminals l~ and 19.
One device cQ~prise~ a PNP tran~istor 10, a~ NPW
translstor 11, a reverse b~eakdo~n ~iod~ 12, an~ a resistor 13, conne~ed toge~her ~s ar~ th~ corresponding componen~s of the device represe~t~d by Fiy. 2, ~nd wi~h the emi~er ~le~trod~s of the PNP tran~istor 10 and ~he NPN tran~istor ll ¢onnected r~pe~ively to th~ terminals 18 ~nd 1~. The othe~ devl~e compri~es a P~P transisto~
14, an NPN t~ansistor lS, a rever~ b~eakdown ~iode 16, and a resi~t~r 17, agaitl~ ~onne~t~d ~o~ether as ar~ ~h~
correspon~ng c~mponent~ o~ the de~ic~ repre~en~d by 2Q Fig. ~, ~ut wl~h the ~mitter alectrodes of the PNP
tr~n~ or 14 ~nd ~he NPN transis~or 15 connec~ed respectl~ly to ~h~ termin~I6 19 and 1~
When ~h~ comp~und semicondu~tor swl~chlng d~viee ~h~t is ~epresented ~y ~ 3 i~ xub~ected ~o ~n increasing ~xt~rn~lly appli~d vol~ge t~at make~ the t~minals 1a more positive ~han the ~ermln~ the ~ ter-base junctlon Qf the NPN ~r~nsi~tnx 15 ~lo~ks cu~r~n~ flow.
-14- ~3~2-f~S
The applied voltage is of the sense to forward bi,as the base-collector junction of the ~PN transistor 15 and the diode 16 by way of the resistor 17, but current flow through these routes is blocked by the collector base and base-emitter diodes of the PNP transistor 14. A continued increase in the applied voltage without change in its sense would eventually force the reverse breakdown of one of the blocking junctions, but before that occurs, the reverse breakdown diode 12 wi11 permit current flow through the transistors 10 and 11, and the semiconductor switching device that includes the reverse breakdown diode 12 will change to its low impedance conductive state. The reversal oî the sense of the applied voltage will result in the changeover of the devices as regards which one remains in its non-conductive state and which one changes to its conductive state.
In Fig. 3, the first form of the semiconductor switching device, as represented by Fig. 1, may be substituted for each os the second fo.rm of the device, as represented by Fig~ 2.
Referring to Fig. 4 of the accompanying drawings, the integrated circuit arrangement of the second form of the semiconductor switching deYice comprises a body 45 of N-type silicon into a surface of which are diffused P-type regions 41, 4 2, and 4 3 . The P-type regions 41, 42, and 43 are situated alongside each other with the region 43 occupying a position between the regions 41 and 42. A first N -type region 44 is diffused into the P-type region 43 and a further N+-type region 47 is diffused into the same surface of the N-type ~ody 45 as is diffused the P-type region 43, the further N -type region 47 being positioned to overlie a part of the junction between the N-type body 45 and the P-type region ; 43. A further P-type region 48, diffused into the surface of the N-type body 45, connects to the P-type region 43 and extends in a part loop into the N-type body ~5. The surface of the N-type body 45 into which the regions are diffused is covered by a layer 46 of silicon dioxide except for windows provided in the silicon dioxide permitting electrical contact to be made with the P-type regions 41, 42 and 48 and the N+-type region 44.
Electrical contact with the P-type regions 41 and 42 is provided by a first metallic layer 40 and electrical ..
contact with the N+-type reqion 44 and the P-type region 48 is provided by a second metallic layer 50, both of which layers overlie the silicon dioxide layer 46 which separates the metallic layers 40 and 50 from the surface of the N-type body 45 where there are no windows in the ,¦
silicon dioxide layer 46. ~1 Figs. 5 and 6 of the accompanying drawings, ¦
representing respectively a part view along a transverse ' cross-section through the P~type regions 41, 42, and 43, : and a part view along a 1Ongitudinal cross-section through the P-type region 43, assist in clarifyinq Fig~ 4. In ::: : i, ¦ !
.
i ' ..
-16- ~3V3z~
Figs. 4, 5, and 6, the regions 41, 42, 43, and 45 provide a PNP transistor structure (the regions 41 and 42 are connected together by the metallic layer 40) that is the PNP transistor 1 of Fig. 2, the regions 43, 44, and 45 S provide an NPN translstor structure that is the NPN
transistor 2 of Fig. 2, the regions 47 and 43 provide a reverse breakdown diode that is the diode 3 of Fig. 2, and the region 48 provides a resistor that is the resistor 6 of Fig. 2. The regions 43 and 45 are 5hared by the PNP
and the NPN transistors eff~ctively making the base electrode of the PNP transistor the same as the collector electrode of the NPN transistor, and vice-versa. The metallic layers 40 and S0 provide the terminals ~ and 5 of Fig. 2.
Referrin~ to Figs. 2, 4, 5, and 6, the range of reverse breakdown voltages fox the diode 3 may lie in the range ~ volts to 20 volts, corresponding to impurity concentrations ~or the P~type region ~3 of between 1017 and 101~ atoms per cubic centimetre. Reverse breakdown voltages exceeding 20 volts but less than the reverse breakdown voltage for the junction between the P-type ,l region 43 and the N-type region 45 are achieved by the 'I
modified a.rrangement represented by Fig. 9 which shows an i~
additional regio~ 51 that is a P-type region positioned in ¦~
the P-type region 43 immediately next to the N+-type region 47. In the modified arrangement represented by Flg. 9, the P-type region 43 aCts as a co~mon regioD of -17- ~3Q3~5 the PNP and NPN translstors while the N -t~pe region 47 and the P -type region 51 act as the reverse breakdown diode. ~his arrangement avoids any conflicting doping level requirements for the P -type and P-type regions 51 and 43, when a reverse breakdown diode Wl th a breakdown vol~age in excess of 20 volts is required (limited, of course, to the reverse breakdown voltage f~r the junction between the N-type region 45 and the P-type region 43).
An integrated circuit arrangement of '~.e first form of the semiconductor switching device may ~e substantially the same as that shown in Fig. ~ for the second form of the device, except that the resistive regi_r. 48, shown in Fig. 4, is omitted. In an integrated circ~ t arrangement of the first form of the semiconductor swit-hing device, the characteristics obtained by including the resistive reqion 4a, shown in Fig. 4, may be provided by modifica-tion of the structure of one of the active ~evices.
Figs. 7 and 8 of the accompanying drawlngs show one modification that may be used in an integrated circuit arrangement of the first form of the semiconductor switching device to compensate for the absence of the resistive region 48 that is shown in Fig. 4. Figs. 7 and 8 show that part of the integrated circuit arrangement of the first form of the semiconductor switchin~ device 25 corresponding to the P-type region 43 of Fig. 4 and its immediately adjacent regions.
Referring to Fiqs. 7 and 8 of the accompanying i I
-l8~ 3~
drawings, an integrated circuit arrangement of the ~irst form of the semiconductor switching device includes a window in the silicon dioxide layer 46. The window extends through one end of the N -type region 44 and over S the P-type region 43, permitting the metallic layer 50 to lie in electrical contact with both the N type region 44 and the P-type region 43. This arrangement represents a conductive bridge between the base and the emitter regions of the ~PN transistor 2 of Fig. 1, resulting in a transistor of low emitter injection efficiency and an increase in the breakover current for the semiconductor switching device of Fi~. 1. It will be understood, therefore, t.~at the inclusion of the partly short-circuited base-emitter junction in the NPN transistor ~
of Fig. 1 removes the need for the resistor 6 included in the second form of the semiconductor switching device, represented by Fig. 2.
Referring to Figs. ~1 to 9 of the accompanying drawings, a doping level in the range lOl4 to lOl6 atoms per cubic centimetre is suitable for the N-type region 45;
a doping level in the range 1017 to 1019 atoms per cubic centimetre is suitable for each of the P-type regions 4l, 42, and 43; a doping level in the range 10~ to 1021 -atoms per cubic centimetre is suitable for each of the P-type regions 44 and 47; and a dopiny level in the range 1015 to 1017 atoms per cubic centimetre is suitable for the P-type reqion Sl. A depth in the range 2 to 20 -1 9- 3~3~Z~S
microns is suitable for each of the P-type reqions 41, ~2, and 43 and a depth of about half that of the P-type region 43 is suitable for each of the N-type regions 44 and 47.
Both limits are included in each of the ranges given above.
Referring to Fig. 10 of the accompanying drawings, an integrated circuit arrangement comprising two of the semiconductor switching devices of either the first or the second form includes an N-type silicon body 1~5 at one surface of which are formed a first set of regions 1~1, 142, ;43, and 144 and a second set or similar regions 241, 242, 243, and 244. The regions 141, 142, 143, 241, 242, and 243 are P-type and t.~e regions 144 and 2~4 are N -type. The regions 141, 142, and 244 are connected together by a metallised layer 140 and the regions 144, 241, and 242 are connected together by a metallised layer 150. The metallised layers perform the function of connection terminals 18 and 19 to the dual device structure. A silicon dioxide layer 146 is included.
The breakover voltage of the switching device shown in Fig. 1 is determined by the breakdown characteristics of the PN junction breakover diode that is connected in parallel with the base-collector junctions of the transistors, and it is possible to obtain relia~le .
switching of the device in response to the supply voltages normally used for telephone systems. Telephone system supply voltages are normally of the order of 50 volts or ' ',:
-20- ~3~3Z~
below. The same situation of clean and reliable switching is obtained for the switching devices shown in Figs. 2 and 3.
The switching device shown in Fig. 2 provides, in addition to a clean and reliable switching characteristic, a well defined swi~ching current that depends on the value of the resistor connected in par~llel with the base-emitter junction of the NPN transistor.
It will be understood by those skilled in the electrical art that the device resulting from the ~tructure re~resented by Fi~s. ~ ~nd 6, say, may be provided by a structure based on a P-type semiconductor body rather than on an N-type semiconductor body as has been described. In a structure based on a P-type body, the P-type body would perform the function of the regions 43 of Figs. 5 and 6, iIl which case the N-type body 45 is reduced to two N-type islands that accommodate the P-t~pe islands 41 and 42, respectively, and the N -type region 44 becomes an island in the P-type body. The N+-type island 47 would be positioned along a part of the junction between the P-type body and one of the N-type islands. In a structure based on a P-typ~ body, the P-type loop 48 may be provided by the presence of an additional contact between the P-type body and the meta1 contact S0 at a position removed from the N -type island ; by a~out the length of the P-type loop 48. In a structure based on a P-type body, the arrangement ~.
-21- ~3~3Z~
represented by ~igs. 7 and a is provided by allowing the metal contact to the N -type island to make contact with the surface of the P-type body over a part of the junction between the N -island and the P-type body.
S Similarly, in a structure based on a P-type ~ody, the arrangement represented by Fig. 9 is pro~ided by means of a P -type region adjacent to the N+-type island corresponding to the N+-type island 47 of Fig. 6. A
compound device, corresponding to that represented by Fig. 10, may also be provided in an arrangement based on a P-type semiconductor body.
Fig. 11 of the accompanying drawings represents a part of a tele?hone system including an incoming line 100, an outgoing line 101, a subscriber's telephone apparatus 102, and semiconductor switching devices 103 and 1a4 of the first form as represented by Fig. 1 of the accompanying .. ...
drawings. A network consisting of a diode 105 in series with a resistor 106 is connected in parallel with the telephone apparatus 102. The semiconductor switching device 103 is connected in series with the incoming line 100 with such polarity as to permit current flow along the incoming line 100 towards the telephone apparatus 102 and the semiconductor switching device is conected in series with the outgoing line 101 with such polarity as to permit current flow along the outgoing line 101 away from the telephone apparatus 102. The semiconductor switching devices 103 and 104 are located at the -22- ~3~f~
telephone apparatus 102 effectively at the respective ends of the incoming and outgoing lines 100 and 101.
The incoming and outgoing lines 100 and 101 connect the telephone apparatus 102 to some form of central or control office~
Referring to Fiy. 11, the inclusion of the semi-conductor switching devices 103 and 104 in the respective incoming and outgoing lines 100 and 101 permits the perfonmance of tests on the telephone apparatus 102 from the central office by way of the lines 100 and 101, and permits the performance of tests on the lines 100 and 101, themselves. The testing of parts or the telephone system is made possible because the semiconduct^r switching devices 103 and 104 behave as voltage sensitive switches that are controllable from the central office by means of the voltages applied to the lines 100 and 101. The reverse breakdown voltage of the reverse break-down diodes included in the semiconductor switching devices is set at a value that causes the semlconductor 20 switching devices 103 and 104 to be conductive when the telephone apparatus 102 is "off-hoo~", in which case the semiconductor switching devices 1~3 and 104 are electri-cally "transparent", that is, they have no effect on normal system operation and are maintained in their low-impedance conductive states by the current flow through the lines 100 and 101 under the influence of the ~: normal supply voltage from the central office. ~oweverp I
-23- ~3~Z~
the semiconductor switching devices 103 and 104 may be switched off by reducing the central office supply voltage and will then isolate the telephone apparatus 102 from the lines 100 and 101. With the semiconductor S switching devices 103 and 104 in the switched off condi-tion, the parameters of the lines 100 and 101 may be checked with the knowledge that the telephone apparatus 102 is effectively disconnected form these lines. The semiconductor switching devices 103 and 134 also permit checks to be made to the telephone apparat~s 102 which should appear as a high impedance, when "on-hook", ~o the normal voltage supply from the central office. Also ~ith the telephone apparatus 102 "on-hook", the diode 105 and the resistor 106 permit checks to determine whether or not there are semiconductor switching devices connected in the lines 100 and 101 (conduction occurs only when the voltage applied to the outgoing line 101 is positive relative to that applied to the incoming line 100 and exceeds the combined breakdown voltages of the breakdown diodes in the semicondcutor switching devices 103 and 104) and to identify the incoming line relative to the outgoing line.
Referring to Fig. 11, it will be noted that the ,~
semiconductor switching device 103 connected in the ¦~
. 25 incoming line 100 is connected in the opposite sense to the semiconductor switch device 104 connected in the outgoing line 101. The need for the installer to pay attention to .
-2~- ~3~3Z~5 the polar1ty of each semiconductor switching device when installiny it may be avoided by providing two semiconduc-tor switching devices, such as the devices 103 and 104, iA a single four-terminal package in which the terminals 107 and 108 are identified as a first port, the terminals 108 and 109 are identified as a second port and the package has clearly marked top and bottom surfaces. It w1ll be evident that, as re~ards the pac~age with a pair of semiconductor switching devices, it is immaterial whether the first port is connected to the lines 100 and 101 of the telephone apparatus 102, and sim1larly for the second port, provided that the top surface of the package is always kept "above" the bottom surface. The need for an installex to pay attentino to either the polarities of the semiconductor switching devices or the attitude of the package, when installing the devices, is avoided by .. . .
providing compound semiconductor switching devices, as representeA by Fig. 3, or as represented by Fig. 10, for example, in which case each of the devices 103 and 104 is replaced by a compound device.
For a telephone system in which the line supply voltage is 48 volts, suitable brea~over voltages i-or the semiconduetor switchin~ devices lie in the range 10 to 20 volts, both limits included, that is to say, the range of breakover voltages extends slightly beyond the range lying between one quarter and one third of the line supply voltage.
-2~- ~3~32~S
When semiconductor switchlng devices as herein described are included in telephone systems for the purposes explained with reference to Fig. 11, they are qenerally known as remote isolation devices (RIDS).
S The remote isolation function performed by semiconductor switching devices as herein described may be carried cut by electrical networks that include many more circuit elements than the semiconductor switching devices, but such electrical networks are costlier to manufacture~, and are bulkier and less convenient to handle and install than the sem1conductor switching devices descrlbed.
Semiconductor switching devices, as described herein, may be employed, at minimal cost for installation, as remote isolation devices or maintenance termination units (MTUs) in a variety or ways. The installation of RIDs at demarcation points in a telephone network will permit the telephone operating company to divide up the network for testing purposes by variation of the network supply voltages. Thus a telephone maintenance centre or repair service centre may determine the condition of virtually any selected part of the network (as regards the existence of resistive faults or open-circuit conditions) without the need for personnel to leave the maintenance or repair centre for the purpose of testing the network equipment.
The semiconductor switching devices, when specifically intended for use as telephone network RIDs, may be provided in enclosures appropriate to the intended use -26- ~3~3Z~
ranging from single-line units to plug-in modules for multi-line applications such as PABX trunk llnes.
In all cases where the semiconductor switching devices are used as RIDs they will, at low cost, effect S maintenance cost reduction, avoid revenue lcsses by facilitating the quick repair and return to service of high-revenue lines, prevent difficulties associated with disagreements as to who is responsible for repair when a line is faulty, permit a 2~-hour test facili-y without the need to send repair personnel out to investigate customer complaints of faults and generally provide an environment leading to the maintenance of high quality transmissions.
i ~.
Claims (7)
1. In a circuit system having a supply line to an apparatus and having a remote isolation device to disconnect the apparatus in response to a remote command, the improvement in which the remote isolation device comprises a semiconductor switching device comprising a PNP transistor having a P-type emitter region, an N-type base region, and P-type collector region, an NPN transistor having an N-type emitter region, a P-type base region, and an N-type collector region and a reverse breakdown PN diode having a P-type region and an N-type region, wherein the respective emitter regions of the transistors are connected in series in the supply line to serve as terminals of the semiconductor switching device, the collector region of the NPN transistor is connected to the base region of the PNP transistor and to the N-type region of the reverse breakdown PN diode, and the collector region of the PNP transistor is connected to the base region of the NPN transistor and to the P-type region of the reverse breakdown PN diode.
2. A system having a semiconductor switching device as claimed in claim 1, including a further N+-type island that extends across the junction between the N-type island and the P-type body, which further N+-type island provides a part of the reverse breakdown diode.
3. A system having a semiconductor switching device as claimed in claim 2, wherein the P-type body includes a P--type region immediately adjacent to the further N+-type island.
4. A system for a telephone network having a semiconductor switching device as claimed in claim 3, wherein the impurity concentration of the P--type region is of the order 1015 to 1017 atoms per cubic centimeter.
5. In a circuit system having a supply line to an apparatus and having a remote isolation device to disconnect the apparatus in response to a remote command, the improvement in which the remote isolation device comprises a semiconductor switching device comprising a PNP transistor having a P-type emitter region, an N-type base region, and a P-type collector region, an NPN transistor having an N-type emitter region, a P-type base region, and an N-type collector region, and a reverse breakdown PN diode having a P-type region and an N-type region, wherein the respective emitter regions of the transistors are connected in series in the supply line to serve as terminals of the semiconductor switching device, the collector region of the NPN transistor is connected to the base region of the PNP transistor and to the N-type region of the reverse breakdown PN diode, and the collector region of the PNP transistor is connected to the base region of the NPN transistor and to the P-type region of the reverse breakdown PN diode, the reverse breakdown PN diode being formed at a junction of the collector and base region in one of the transistors, the semiconductor switching device comprising a P-type semi conductor body that is both the base region of the NPN
transistor and the collector region of the PNP transistor, an N-type island, at a surface of the P-type body, that is both the base region of the PNP transistor and the collector region of the NPN transistor, a P-type island, in the N-type island, that is the emitter region of the PNP transistor, and N+-type island, at the surface of the P-type body, that is the emitter region of the NPN transistor, and conductive contact regions providing respective terminals for the P-type island and the N+-type island, the semiconductor switching device including a further N+-type island that extends across the junction between the N-type island and the P-type body, which further N+-type island provides a part of the reverse breakdown diode.
transistor and the collector region of the PNP transistor, an N-type island, at a surface of the P-type body, that is both the base region of the PNP transistor and the collector region of the NPN transistor, a P-type island, in the N-type island, that is the emitter region of the PNP transistor, and N+-type island, at the surface of the P-type body, that is the emitter region of the NPN transistor, and conductive contact regions providing respective terminals for the P-type island and the N+-type island, the semiconductor switching device including a further N+-type island that extends across the junction between the N-type island and the P-type body, which further N+-type island provides a part of the reverse breakdown diode.
6. A system having a semiconductor switching device as claimed in claim 5, wherein the P-type body includes a P--type region immediately adjacent to the further N+-type island.
7. A system for a telephone network having a semiconductor switching device as claimed in claim 6, wherein the impurity concentration of the P--type region is of the order 1015 to 1017 atoms per cubic centimeter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB88.17574 | 1988-07-22 | ||
| GB8817574A GB2221088B (en) | 1988-07-22 | 1988-07-22 | A semiconductor switching device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1303245C true CA1303245C (en) | 1992-06-09 |
Family
ID=10640980
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000606343A Expired - Lifetime CA1303245C (en) | 1988-07-22 | 1989-07-21 | Semiconductor switching device |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1303245C (en) |
| GB (1) | GB2221088B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9223143D0 (en) * | 1992-11-05 | 1992-12-16 | Texas Instruments Ltd | Improvements relating to maintenance termination units |
| US5602404A (en) * | 1995-01-18 | 1997-02-11 | National Semiconductor Corporation | Low voltage triggering silicon controlled rectifier structures for ESD protection |
| US11575379B2 (en) | 2021-03-23 | 2023-02-07 | Delphi Technologies Ip Limited | Switch with hysteresis |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1212767B (en) * | 1983-07-29 | 1989-11-30 | Ates Componenti Elettron | SEMICONDUCTOR OVERVOLTAGE SUPPRESSOR WITH PREDETINABLE IGNITION VOLTAGE WITH PRECISION. |
-
1988
- 1988-07-22 GB GB8817574A patent/GB2221088B/en not_active Expired - Fee Related
-
1989
- 1989-07-21 CA CA000606343A patent/CA1303245C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| GB2221088A (en) | 1990-01-24 |
| GB2221088B (en) | 1992-02-26 |
| GB8817574D0 (en) | 1988-08-24 |
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