CH659152A5 - SOLID BODY SWITCHING DEVICE AND CIRCUIT ARRANGEMENT WITH AT LEAST TWO SUCH A SOLID BODY SWITCHING DEVICE. - Google Patents

Description

The invention relates to a solid-state switching device according to the preamble of claim 1, in particular to high-voltage solid-state switching devices which can be used in telephone switching systems, and a circuit arrangement according to the preamble of claim 7.

An article entitled "A Field Terminated Diode" by Douglas E. Houston et al., Published in "IEEE Transactions on Electron Devices", Vol. ED-23, No. 8, August 1976 describes a discrete solid-state high-voltage switch that has a vertical geometry and contains a zone that can be pinched off to create an “OFF” state, or that can be made highly conductive by double-carrier injection to create an “ON” state. "Double carrier injection" refers to the injection of both holes and electrons to form a conductive plasma in the semiconductor. A problem with this switch is that it is not easy to manufacture on a common substrate with other similar switching devices.

Another problem is that the distance between the control electrodes and the cathode should be small to limit the strength of the control electrode voltage; however, this limits the useful voltage range because it lowers the control electrode-cathode breakdown voltage. This limitation in turn limits the use of two devices connected in anti-parallel, that is to say devices whose cathode is respectively coupled to the anode of the other device, to relatively low operating voltages. Solid-state switches of this type are described, for example, in US Pat. Nos. 3,722,079, 3,657,616 and 3,911,463. In such known solid-state switches with high doping of the base zone, however, this leads to a low dielectric strength between anode and cathode. The breakthrough effect can be limited by widening the base zone, but this also increases the resistance of the switch when it is in the "ON" state.

It is desirable to have a solid-state switching device that is easy to integrate so that two or more switching devices can be manufactured simultaneously on a common substrate, and each switching device is capable of blocking relatively high voltages on both sides.

The solid-state switching device according to the invention is characterized by the features stated in the characterizing part of patent claim 1.

The circuit arrangement according to the invention is characterized by the features stated in the characterizing part of patent claim 7.

The structure is designed in such a way that a double carrier injection takes place during operation. The body is in contact with the substrate and the substrate can be designed to facilitate the attachment of an electrode thereon that serves as the gate of the structure.

This structure, if suitably designed, can be operated as a switch which is characterized in the ON (conductive) state by a low impedance path between the anode and cathode and in the OFF (blocking) state is characterized by a high path Impedance between anode and cathode. The potential applied to the gate determines the state of the switch. During the on-state there is a double carrier injection which reduces the resistance between anode and cathode.

In another embodiment of the invention, a semiconductor body, as described above, and which has the first and second zones, with the exception of its main surface portion, is opposed to a semiconductor zone

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surrounded conductivity type. A plurality of semiconductor bodies, each of which has a surrounding, separate semiconductor zone, are formed on a common semiconductor wafer of one conductivity type, parts of the semiconductor wafer separating all the semiconductor bodies.

These structures, referred to as gated diode switches (GDSs), if properly designed, can block relatively large potential differences between the anode and cathode in the OFF state regardless of polarity, and they are in able to conduct relatively high currents in the ON state, there being a relatively low voltage drop between the anode and cathode.

The double-sided blocking properties of these GDS structures make them particularly useful for many applications. Two of the GDSs described above can be coupled together, the gates being common and the cathode of each GDS coupled to the anode of the other. This combination forms a bidirectional high voltage switch. Fields of GDSs can be fabricated on a common semiconductor wafer to form cross points, or two GDSs can be fabricated with a common gate to create a bidirectional switch.

1 shows a structure according to an embodiment of the invention;

Fig. 2 shows a proposed electrical symbol for the structure of Fig. 1;

3 shows a top view of a structure according to another embodiment of the invention;

4 shows a structure according to a further embodiment of the invention;

5 shows a structure according to yet another embodiment of the invention;

6 shows a structure in accordance with yet another embodiment of the invention; and

Fig. 7 shows a structure according to still another switching device of the invention.

Reference is now made to FIG. 1, which shows a semiconductor structure 10 that has two substantially identical gated diode switches GDS1 and GDS2, shown within dashed lines and both in a semiconductor wafer or substrate 12 are formed. The semiconductor structure 10 has a main surface 11. The substrate 12 is of the one conductivity type and serves as a common gate and carrier for GDS1 and GDS2.

An epitaxial layer of the conductivity type opposite to the conductivity type of the substrate 12 is separated by semiconductor zones 20 in semiconductor bodies 16 and 16a. In addition to the two bodies shown, many bodies 16, 16a can be formed on the substrate 12. The zones 20 are of the same conductivity type as the substrate 12, but have a higher impurity concentration (hereinafter called impurity concentration) and extend from the main surface 11 down to the substrate 12. Also within the body 16 is a semiconductor anode zone 18 of the same conductivity type as that Body 16, but with a higher impurity concentration. A semiconductor zone 22 is of the same conductivity type as the body 16, but has a lower resistivity than the body 16. A semiconductor cathode zone 24 is contained in a portion of the zone 22 and has a portion that extends toward the main surface 11 . Zone 24 is of the same conductivity type as zone 20 and has substantially the same impurity concentration. Electrodes 28, 30 and 32 make low resistance contact with zones 18, 24 and 20, respectively. Zone 20 makes low resistance contact with substrate 20. Thus, the electrode 30 is in contact with the substrate 12 with low resistance and serves as a common gate electrode for GDS1 and GDS2. An optional electrode 38, which can be made of metal or semiconductor material, is arranged between the anode electrode 28 and the cathode electrode 32. The electrode 38 is electrically coupled to the substrate by means of an electrical connection on the electrode 30.

The semiconductor regions 18a, 22a and 24a are contained in the body 16a. Electrodes 28a, 32a and 30 are connected to zones 18a, 22a and 24a. These zones are substantially the same as the corresponding zones of the body 16. An insulating layer 26 electrically isolates all of the electrodes described above from portions of the structure 10, except for those portions which are intended to be electrically contacted.

In an exemplary embodiment, substrate 12 is n-type, zones 20 and 24 (24a) are n + -type, body 16 (16a) is p-type, zone 18 (18a) is p + - Conductivity type, zone 22 (22a) is of the p-conductivity type and has a smaller resistivity than body 16 (16a), and electrodes 28 (28a) 32 (32a) and 30 are made of aluminum. In this embodiment, the anode electrode 28 is electrically coupled to the cathode electrode 32a and the cathode electrode 32 is coupled to the anode electrode 28a.

Proposed electrical symbols for GDS1 and GDS2 are shown in FIG. 2. The anode, cathode, and gate electrode connections of GDS1 are 28, 32 and 30, respectively. The corresponding connections of GDS2 are 28a, 32a and 30. This combination of GDS1 and GDS2 works as a bidirectional switch that is capable of mutual potentials block, regardless of whether the anode or cathode of one of the gate-controlled diode switches is at a more positive potential.

GDS1 and GDS2 are both essentially identical and operate in essentially the same way. Thus, the description of GDS1 below is equally applicable to GDS2. GDS1 is characterized by a relatively low resistance path between anode zone 18 and cathode zone 24 when it is in the ON (conducting) state and is characterized by a significantly higher impedance when it is in the OFF (blocking) state . In the ON state, the potential of the gate electrode 30 is typically at or below the potential of the anode 28. Holes are injected into the body 16 from the anode zone 18 and electrons are injected into the body 16 from the cathode zone 24. These holes and electrons can be present in sufficient numbers to form a plasma, the conductivity of which modulates the body 16. This effectively reduces the resistance of the body 16 so that the resistance between the anode zone 18 and the cathode zone 24 is relatively small when GDS1 is operating in the ON state. This mode of operation, in which both holes and electrons serve as current carriers, is referred to as double carrier injection. The type of structure described here is referred to as a gated diode switch (GDS).

Zone 22 helps limit the penetration of an operational depletion layer that is formed between zone 20 and substrate 12 and cathode zone 24 during operation. Zone 22 also helps prevent the formation of a surface inversion layer between zones 24 and 20. In addition, it allows the anode zone 18 and the cathode zone 24 to be spaced relatively closely. This results in a relatively low resistance between the anode zone 18 and the cathode zone 24 in the ON state.

The line between the anode zone 18 and the cathode

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The zone 24 is prevented or blocked if the potential of the gate electrode 30 is sufficiently more positive than that of the anode electrode 28 and the cathode electrode 32. The amount by which the positive potential must be greater in order to prevent or block the line is one Function of geometry and impurity concentration levels of structure 10. This positive gate potential causes the portion of body 16 between gate region 12 and a portion of oxide layer 26 to become depleted, so the potential of that portion of body 16 is more positive than that of the anode zone 18 and the cathode zone 24. This positive potential barrier prevents the conduction of holes from the anode zone 18 to the cathode zone 24. It also serves to collect electrons which are emitted at the cathode zone 24 before they can reach the anode zone 18. This essentially clamps the body 16 against the dielectric layer 26 in the main part of the body that lies between the anode and cathode zones 18, 24 and extends from the zone 12 to the dielectric layer 26.

The use of the electrode 38 reduces the potential strength necessary to prevent or block the line. In the OFF state, GDS1 is able to block relatively high potentials between the anode and cathode zones, regardless of which zone has the more positive potential.

During the ON state of GDS1, the pn junction diode consisting of the body 16 and the zone 20 is biased in the forward direction. Current limiting devices (not shown) can be used to limit the conduction through the forward biased diode.

GDS1 and GDS2 need not be connected together with the anodes and cathodes. GDS1 or GDS2 can be used individually, but the gates are common.

Reference is now made to FIG. 3, which illustrates a top view of a preferred embodiment of a dual GDS semiconductor structure 100 that has been fabricated. Structure 100 is similar to structure 10 except that

that the anode and cathode zones are curved. This geometry tends to limit a localized voltage field concentration that causes a voltage breakdown, and additionally adds a common perimeter for the anode and cathode zones to facilitate the low ON resistance and thereby simplify high current operation . The structure 100 was produced on an n-substrate with a thickness of 457 to 559 micrometers and a conductivity of 1015 to 1016 impurities / cm 3. The bodies 160 and 160a are of the p-conductivity type and have a thickness of 30 to 40 micrometers, a width of 720 micrometers, a length of 910 micrometers and an impurity concentration in the range of 5-9 X 1013 impurities / cm 3. The curved anode zones 180 and 180a are of the p + conductivity type and have a thickness of 2 to 4 micrometers and an impurity concentration of 1019 impurities / cm3. The curved cathode zones 240 and 240a are of the n + conductivity type and have a thickness of 2 to 4 micrometers and an impurity concentration of 1019 impurities / cm 3. The total length and width of the circuit produced is 1910 microns by 1300 microns. The distance between the anode and cathode is typically 120 micrometers.

Some of the structures fabricated contained conductor zones 380, 380a that were 60 microns wide, and other structures did not contain these zones. The structures fabricated without zones 380 and 380a required a potential of 22 volts more at the gate than at the anode in order to prevent or block the line between the anode and cathode. With

Structures made of conductor zones 380 and 380a required that the gate potential was only 7.5 V above the anode potential in order to achieve a shutdown. The fabricated structure was able to block 300 V and conduct 500 milliamps with an anode-cathode voltage drop of 2.2 volts. This structure was able to operate at a current of 10 amps with a duration of one millisecond.

Referring now to FIG. 4, a structure 1,000 is shown that is very similar to structure 10, and all parts of the structure that are substantially identical or similar to the elements of structure 10 are identified by the same reference number , with two "Oen" added at the end. The basic difference between the structures 1000 and 100 is that in the structure 1000 the semiconductor zones 22 and 22a of the structure 10 according to FIG. 1 are omitted. Appropriate spacing of zones 2400, 2400a from zone 2000 provides adequate protection against depletion layer access to zones 2400, 2400a and enables structure 1000 to operate as a high voltage switch.

Reference is now made to FIG. 5, which shows a structure 10,000 that is very similar to the solid structure 10 and all elements of this structure that are essentially identical to the elements of the structure 10,

are identified by the same reference number, with three "oen" added. The basic difference between structures 10,000 and 10 is the use of semiconductor guard ring zones 40 and 40a which circularly surround zones 24,000 and 24,000a and which are separated from them by sections of bodies 16,000 and 16,000a. Guard ring zones 40 and 40a provide the same type of protection against surface layer inversion as zones 22, 22a of structure 10. Protection is in some cases considered adequate for the creation of a high voltage solid state switch. Guard rings 40 and 40a are of the same conductivity type as bodies 16,000 and 16,000a, but have a smaller resistivity. The guard rings 40 and 40a can be expanded (as shown by the dashed lines) to contact the cathode zones 24,000 and 24,000a.

Reference is now made to FIG. 6, where a structure 100,000 that is similar to structure 10 is shown. All parts of structure 100,000 that are similar or substantially identical to corresponding parts of structure 10 are identified by the same reference numeral, with four "oes" added at the end. A difference between structure 100,000 and structure 10 is the use of semiconductor guard ring zones 400 and 400a which circularly surround the cathode zones 240,000 and 240,000a. Guard rings 400 and 400a are similar to semiconductor guard ring zones 40 and 40a of structure 10,000. The dashed line portion of guard rings 400 and 400a illustrates that the rings can be expanded to contact cathodes 240,000 and 240,000a. The combination of zones 220,000, 220,000a and guard rings 400, 400a provides protection against inversion of bodies 160,000, 160,000a, particularly between gate zone 200,000 and cathode zone 240,000, 140,000a, and provides protection against depletion layer penetration of the cathode zone 240,000, 240,000a. This type of double protection around the cathode zone 240,000, 240,000a is the preferred protective structure. Zones 220,000, 220,000a and 400, 400a are all of the same conductivity type as bodies 160,000, 160,000a, but have a lower resistivity. Zones 400, 400a have a lower specific resistance than zones 220,000, 220,000a. Another difference between structure 100,000 and structure 10 is in the semiconductor zones 70, 70a, which are the same

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Conductivity type are like the cathode zones 240,000,

240,000a. Zones 70, 70a are in electrical contact with electrodes 380,000, 380,000a and serve as upper gates. The use of the gate zones 70, 70a leads to a reduction in the size of the potential which is necessary in order to block or prevent the conduction between the anode zones 180,000 and 180,000a and the cathode zones 240,000 and 240,000a.

Reference is now made to FIG. 7, where a semiconductor structure 42 is shown which has a plurality of essentially identically gated diode switches (GDSs), of which only two, GDS3 and GDS4 (shown in dashed rectangles) are shown. The semiconductor structure 42 includes a semiconductor support piece (substrate) 44, which is of a first conductivity type and has a main surface 46. Separate zones 48 and 48a, which are of the opposite conductivity type to the substrate, are disposed within 15 of a portion of the substrate 44. 44, and which are separated from one another by sections of the substrate 44 and by zones 50, which are of the same conductivity type as the substrate 44, but have a 20 higher impurity concentration. Zones 50 are optional. Essentially identical semiconductor bodies 52 and 52a are contained within the zones 48 and 48a.

The bodies 52 and 52a are of the same conductivity type as the substrate 44. Within the body 42 there is an anode zone 54, which is of the same conductivity type as the body 52, but has a higher impurity concentration. There is also a zone 56 in the body 52 which is of the same conductivity type as the body 52 but has a higher impurity concentration and is separated from the zone 54 30 by portions of the body 52. Within a portion of zone 56 is a cathode zone 58 which is of the same conductivity type as zone 48. Electrodes 60, 62, 64 and 66 make low resistance contact with zones 48, 54, 58 and 50, respectively. If zones 50 are left out, electrode 66 contacts zone 44 directly or through a low resistance semiconductor zone (not shown) similar to zone 54 but contained in a portion of substrate 44. An insulating layer 68, typically silicon dioxide, electrically isolates all of the electrodes of the structure 42 from the major surface 46 except for the areas that are desired to have low resistance contact with them.

The body 52a, the zones 54a, 56a and 58a and the electrodes 60a, 62a and 64a of the GDS4 are essentially identical to the corresponding zones of the GDS3.

The substrate 44 is typically kept at the most negative available potential. This serves to ensure that the pn- formed by the zones 48, 48a and the substrate 44

Bias transitions in the reverse direction so that all GDSs in the substrate 44 are isolated from each other.

GDS3 and GDS4 operate in essentially the same manner as was described for the operation of GDS1 and GDS2 according to FIG. 1. Zone 48 serves as the gate, with zones 54 and 58 serving as the anode and cathode, respectively. It should be noted that gate zones 48 and 48a are physically and electrically separate, and consequently GDS3 and GDS4 can operate essentially completely independently of one another since the respective gates, anodes and cathodes are electrically separated. Structure 42 thus facilitates the creation of a field consisting of GDSs, each GDS being able to operate independently of all other GDSs in the field.

The embodiments described herein are intended to illustrate the basic principles of the invention. For example, the degree of impurity concentration, the distances between the zones and other sizes of the zones can be set so that noticeably higher operating voltages and currents are possible than was described. A dielectric layer may be interposed between zones 48 and 48a and zone 44, or the dielectric layer may replace zones 44 and 50. Furthermore, other types of dielectric materials, e.g. Silicon nitride takes the place of silicon dioxide. 3, 4, 5, 6 and 7, conductor zones such as zone 38 according to FIG. 1 can be included. Zones 56 and 56a can be omitted. This reduces the resilience of the resulting GDS structures; however, the distance between the anode and cathode and between adjacent GDS structures can be increased to increase the useful voltage ranges. Furthermore, the zones 56 and 56a can be replaced by protective rings of the type, for example, as shown in FIG. 5 around the cathode 24,000. Furthermore, for example, a zone such as zone 220,000 and a guard ring similar to guard ring 400 according to FIG. 6 can take the place of zones 56, 56a according to FIG. 7. The electrodes can be doped polysilicon, gold, titanium or other types of conductors. The conductivity of all semiconductor substrates and zones can be reversed, provided that the voltage polarities are changed accordingly in a manner known from the prior art. In such a case, zones 18, 18a, 180, 180a, 1800, 1800a, 18,000, 18,000a, 54, 54a, 180,000 and 180,000a become cathodes, and zones 24, 24a, 240, 240a, 2400, 2400a, 24,000 , 24,000a, 58, 58a, 240,000 and 240,000a become anodes. It can be seen that the structures according to the present invention enable AC or DC operation.

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Claims (8)

659 152 2nd PATENT CLAIMS Solid-state switching device, having a semiconductor body (16), the main part of which is of a first conductivity type, a first zone (18) of the first conductivity type, a second zone (24) of a second conductivity type, which is opposite to the first conductivity type, a gate zone (12) of the second conductivity type, wherein the first, second and gate regions have a smaller resistivity than the main part and are separated from each other by portions of the semiconductor body main part, and the parameters of the device are such that when on the gate zone is set with a first voltage, in the semiconductor body forms a depletion zone which prevents current flow between the first and second zones, and that when a second voltage is applied to the gate zone and suitable voltages are applied to the first and second zones, between the first and second zones by double-carrier injection a current path with a smaller resistance and than in the de-energized state, characterized in that the first and second zones (18, 24) each have a surface contained in a first main surface of the semiconductor body (16), and in that the gate zone is a semiconductor piece (12) which forms the semiconductor body contacted along a second surface opposite the first surface. 2. Device according to claim 1, characterized in that the semiconductor body (16) has a localized third zone (22) of the first conductivity type, the specific resistance of which lies between that of the main part of the semiconductor body (16) and that of the first zone (18), and that the third zone (22) is arranged such that it surrounds the second zone (24). 3. The device according to claim 1, characterized in that the gate zone (48) between the semiconductor body main part (52) and a wafer substrate portion (44) of the first conductivity type is arranged (Fig. 7). 4. The device according to claim 2, characterized in that the conductivities of the semiconductor body (16), the first zone (18), the second zone (24) and the third zone (22) from (P -) -. (P + K (n +) - or (p) -type are. 5. The device according to claim 1, characterized in that the semiconductor body (16,000) has a localized fourth zone (40) which surrounds but does not contact the second zone, and that the fourth zone is of the first conductivity type and has a lower resistivity than the main body (16,000). 6. The device according to claim 2, characterized in that the semiconductor body has a fourth zone (400) contained in the third zone (220,000), which surrounds the second zone (240,000) but does not contact, and that the fourth zone of the first conductivity type and has a lower specific resistance than the third zone. 7. Circuit arrangement with at least two solid-state switching devices according to claim 1, characterized in that the gate zone is common to the two solid-state switching devices, the first zone (18) of one device being connected to the second zone (24a) of the other device and the second zone (24) of the first device is connected to the first zone (18a) of the second device. 8. The circuit arrangement according to claim 7, characterized in that a plurality of solid-state switching devices are arranged on a wafer substrate (44), and in that the wafer substrate has a plurality of zones (50) of the first conductivity type, but with a lower resistivity than the wafer Substrate.