JPS62249403A - Limit switching device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to circuit protection devices, particularly for protecting circuits against voltage transients caused by electromagnetic pulses, such as lightning strikes, and current transients caused by electrostatic discharges. Regarding devices for.

BACKGROUND OF THE INVENTION One type of material that has been proposed for use in the manufacture of circuit protection devices is generally chalcogenide glass.

What is chalcogenide glass?
Group VIB elements (revised in 1965) and other elements, especially I
Glasses made by combining VB and elements of group VB, such as those described in Ovshinsky, US Pat. No. 3,271,591, are meant. Some of these glasses are
A high voltage (the lowest of such voltages is called the "threshold voltage") changes from a high resistance state to a low resistance state when j = , only as long as a small "holding" current is maintained. can be used to create a "marginal" device, meaning a device that remains in a low resistance state. Other chalcogenide glasses change from a high resistance state to a low resistance state when a high voltage is applied, and remain in the low resistance state even when no voltage is applied until a suitable different voltage pulse is applied. Can be used to create "memory" devices.

It will be appreciated that only marginal devices are suitable for circuit protection devices.

Chalcogenide glass materials typically have very short switching times between high and low resistance states when the voltage transient that causes the switching is significantly above the threshold voltage (e.g., about 50 V or more). It has the advantage of being less than 1 nanosecond, fast enough to protect the circuit from transients.

British Patent Application No. 8508304 describes circuit protection devices made from certain germanium/selenium/superium amorphous compositions. The device described in that application is a surprisingly large "latch".
atch) energy.

That is, the device can withstand surprisingly large amounts of electrical energy due to voltage transients before permanently latching into a low resistance state.

One factor that determines the performance of a switch is the contact resistance between the chalcogenide glass material and the electrode, and the reduction in contact resistance reduces the latching energy of the switch to the latching energy produced by the substantial reduction in electrode contact resistance. It is believed that the improvement can be increased to the extent that the composition effectively changes from exhibiting memory properties to exhibiting marginal properties. It is therefore speculated that the memory properties previously observed by Pinto and Opsinski et al. could in fact be caused by high electrode contact resistance.

SUMMARY OF THE INVENTION The present invention provides a limit switching device comprising a switching element made from an amorphous chalcogenide composition and a pair of electrodes in contact with the composition.
by using an indium or indiwindium-containing layer in contact with the composition to reduce electrical contact resistance between the composition and at least one electrode;
In many cases, it is possible to increase the false-chip energy of a device to the extent that devices using chalcogenide glasses that previously exhibited only memory properties can be observed to exhibit marginal properties. Other compositions can be used in conjunction to increase the latch energy to allow optimization of other properties of the material. The device preferably exhibits a latching energy of at least 40 mJ, more preferably at least 60 mJ, especially at least 100 mJ.

The electrode contact resistance is preferably low enough such that the overall electrode-to-electrode resistance of the device (in the low resistance state) does not exceed 10 ohms, especially 1 ohm, and the most preferred resistance is 0.1 ohm or less.

The present invention relates generally to chalcogenide glass compositions, particularly oxygen-free glasses, and particularly optionally and preferably to rVB and VB group elements such as germanium, silicon, phosphorus, arsenic and antimony. Preferred glasses are those containing germanium, selenium and arsenic, such as those described in the above-mentioned British patent application, containing at least 15 atom % selenium;
Preferably it contains not more than 75 atomic percent selenium. The arsenic content is preferably at least at % IO and preferably does not exceed 65 at %. Additionally or alternatively, the composition comprises at least 5 atomic % and 4 atomic %
Preferably, it contains no more than 2 atomic percent germanium.

The most preferred compositions contain no more than 35 atom % germanium, more preferably no more than 30 atom % germanium, especially no more than 25 atom % germanium. The composition also preferably contains at least 20 atom % selenium, especially at least 30 atom % selenium,
Preferably not more than 70 atom % selenium, especially 60/i
Contains not more than % selenium. The composition preferably contains at least 20 atomic % arsenic, especially at least 25 atomic % arsenic, preferably not more than 60 atomic % arsenic, especially 55 atomic % arsenic.

Other materials may be present in the compositions used in the devices of the invention, e.g. in amounts of up to 10%, or sometimes greater, e.g. the presence of such materials may improve the latch energy and/or off resistance. Elements such as antimony, bismuth, silicon, tin, lead, halogens and transition metals may be present in small amounts as long as they do not significantly adversely affect properties such as yield. However, the presence of tellurium
Preferably, the composition is substantially free of tellurium, as it has been found to strongly reduce the off-resistivity of the material, although in some circumstances it may contain small amounts, such as up to 1 atomic %, preferably up to 5 atomic %. tellurium is acceptable.

Glass and metal films can be processed by vacuum evaporation or direct current (
Deposition is preferably carried out by vacuum methods such as by magnetron sputtering (for metals) or by radio frequency (for chalcogenide glasses) magnetron sputtering.

Steam may be generated by heating a suitable mixture of components (not necessarily of the same composition as the target glass) or by heating separate components simultaneously.

One preferred method of making the device involves using a substrate masked in the desired pattern with a suitable electrode structure.
By evaporating the coating material from a separate resistance-heated boat in a vacuum chamber at a pressure of 10-3 to 'Pa, indium (to a thickness of about 0°1 micrometer) was then coated with about IO micrometers. Continuously coated with chalcogenide glass to a thickness of meter. A second indium interlayer and top electrode are deposited on the glass in a similar manner, but using an electron beam heating source rather than a resistive heated boat to deposit a thick metal electrode film in a reasonable amount of time. With this, higher evaporation rates can be achieved. In order to achieve good adhesion and low constant resistance, the layers should be removed unless the mask needs to be changed or realigned and to reduce the possibility of surface oxidation or contamination when the substrate is cold. , it is necessary to attach it without releasing the vacuum.

In another method, a thickness of 0.1
A ~0.5 micrometer indium-containing chalcogenide glass interlayer is formed between the chalcogenide glass switching element and the electrode. Preferably, the indium-containing glass has the same composition (other than indium) as the switching element, preferably the indium content is (
at least 1 based on the total weight of the glass (including indium)
%, preferably at least 5%, preferably 20
%, especially 15%.

In a modification of this method, a layer of indium (e.g. 0.1 micrometer thick) may be provided at each electrode;
An indium-containing glass interlayer (about 0.5 micrometers thick) may also be provided between the glass forming the switching element and the indium layer. This modification ranges from approximately 1°0% indium adjacent to the electrode to 0.0% in-glass depth.
Figure 2 is an example of a method of forming a device in which there is a concentration gradient of indium across the thickness of the glass, varying from about 0% indium at 3 to 1 micrometers.

This is accomplished by the most preferred method among various methods.
% indium) ranges of indium layers m may be deposited successively on the electrodes and, after deposition of the switching material, in the reverse order. Alternatively, the indium and switching element glass compositions may be deposited simultaneously from different boats at the beginning and end of the deposition process. In this case, the power supplied to heat the two boats was varied continuously so that a large deposition rate of indium and a small deposition rate of glass were achieved near the electrodes and at a large distance from the electrodes. As the temperature increases, the indium deposition rate decreases and the glass deposition rate increases.

It is possible to include indium throughout the switching element. However, in this case the device must comprise a layer between the switching element and the at least one electrode with a substantially higher indium content (for example at least 10%, in particular at least 20 atomic % higher). In some cases, indium can evaporate at a faster rate than other components, so the element has a higher indium content adjacent to one of the electrodes, in which case a portion of the glass layer has no indium. Since it probably won't be included, the second one? It is suitable to deposit an indium layer on the glass immediately before depositing the lX pole.

The dimensions of the switching element used in the device of the invention will depend on the particular chalcogenide glass composition forming the element, but the thickness of the switching element will typically not exceed 40 micrometers, preferably exceed 20 micrometers. No, but usually at least 5 micrometers, preferably at least 10 micrometers.

The cross-sectional area of the switching element in the plane perpendicular to the direction of current flow depends on the maximum current. Preferably at least 0.5
π shoulder 2, and the preferred dimensions are about 1 +u'' for stand-alone devices and at least 2ix'' for maximum pulse levels.

The device may be incorporated at any suitable location in an electrical circuit, usually with a conductive wire and a ground (the term "ground" herein refers to a conductive wire with a suitable shape and/or (including connections to chassis and connections in vehicles such as aircraft), where two or more such devices are used in an electrical circuit. Of course it is okay to do so. The device is conveniently incorporated into another electrical element, e.g. an electrical connector, in which case the device is usually connected between a conductive element of the device and a terminal or other part of the device to be earthed, e.g. a conductive housing. Connected.

In most cases, the device will return to the high resistance state as soon as the voltage transient drops, but if, for example, the voltage transient is unreasonably large, or if many rapid transients are encountered, the device may be forced to a permanently low resistance state. It is possible to make the state. As mentioned above, it depends on the amount of energy that Debye absorbs from the transient. For some applications, such as some grounding installations, it is preferable for the protection device to fail such that the device is still protected against transients, but is non-functional until the protection device is replaced or reset. In other applications, it is preferable for the device to fail in a high resistance (open circuit) state so that the device is not protected from later transients but continues to function. Thus, in some cases the device may be connected in series with means that exhibit a high resistance to the intended electrical circuit current, at least when the switching element becomes permanently conductive. Thus, for example, a switching element can be connected to a current line or May be connected to ground.

Alternatively or additionally, the device uses a capacitor in series with a high switching element for all frequencies below the cut-off limit of the capacitor. ", filed March 29, 1985). That is, since most of the energy of the transient current occurs at frequencies above l0k)rz, it is possible to transfer the transient current to ground by using a capacitor of appropriate size, e.g. 10 pF to 2 μF, in series with the switching element. is possible, but has a fairly low frequency or presents a high impedance to the intended current of the circuit, which is direct current. The use of a capacitor also eliminates or significantly reduces the possibility that the switching element will remain latched in a low resistance state after a transient has occurred. Such latching occurs in the absence of a capacitor due to the current passing through the switching element latching it into a low resistance state. If a capacitor is used, it is often possible to use only one capacitor to protect many lines if the capacitor is connected on the ground side of the switching element, thereby providing a significant Saves space.

In addition to improving the latching energy of the device, the use of indium as described above improves the electrode/glass adhesion considerably, to the extent that it is reliably possible to make electrical connections to the electrodes by wire bonding methods. Ru.

A device of the invention and an article incorporating the device will now be described by way of example with reference to the accompanying drawings.

FIG. 1 schematically shows a circuit protection device of the invention.

The device is deposited on a copper electrode 202 to a thickness of 0 using a vacuum evaporation method.
．． A 1 micrometer thick layer of indium 201 is deposited, followed by a 10 micrometer thick germanium/propylene/selenium glass layer 210 and an additional indium layer 203.
was formed by further supplying a copper electrode 204.

All additional layers other than the copper electrode 204, which was formed by electron beam evaporation, were formed by vacuum evaporation. indium 52
Adjacent to 01,203 there are two additional layers 205,206 comprising germanium/propylene/selenium glass and a small amount of indium.

Layers 205 and 206 are formed from layers 201 and 203 to glass layer 2.
formed by diffusion of a portion of indium into 10 or
Alternatively, it may be formed as a separate layer by any of the methods described above.

In FIG. 2, a connecting part for connecting two coaxial cables comprises a connector shell 1 and a male connector 2. Male connector 2 is pin.

3, comprising a central part and a rear part which is hollow for receiving the central conductor of a coaxial cable (not shown) to be connected. The pin has a molten solder ring 4 and a number of openings (not shown) below the solder ring communicating between the solder ring 4 and the hollow inside of the pin 3. The rear end 1o of the pin is precisely positioned within the connector housing 5 by means of an electrically insulating plastic spacer 6. The housing 5, which provides the electrical connection between the shields of the cables to be connected, has a solder-impregnated brake KR
It has a termination part 7 with a nodal ring 9 attached thereto.

The rear end of the pin IO is provided with an electrode on its outer surface, for example a molybdenum or copper electrode, on which a switching element of a thickness IO micrometer has an indium/chalcogenide glass/indium structure formed by vapor deposition. is formed thereon, and on the outer surface of the glass element 11 there is an additional thin (approximately 5 micrometers thick) formed from molybdenum or copper, for example by electron beam evaporation.
Electrodes are supplied. The electrodes are electrically connected to the housing 5 by columns or wires 12 of solder or other conductive material.

To connect a coaxial cable to a connector, the outer jacket, shield and dielectric material are cut back by the appropriate amount, the cable is inserted into the connector, and the resulting
The exposed end of the inner conductor is placed within the hollow interior of the pin 3, the dielectric material abuts the rear end of the spacer 6, and the exposed shield is
It is placed within the solder-impregnated blade 8. The connector is then briefly heated, for example by a pot air gun, to melt the solder rings 4 and 9 and form solder connections between the pin 3 and the center conductor and between the blade 8 and the coaxial cable shield.

The connector remains closed until the connected cable encounters an excess e':TS pressure when the potential difference across the thickness of the glass layer 11 makes the glass conductive and forms a closed circuit between the central conductor and the shield. , functions exactly as a standard coaxial cable.

In Figures 3 and 4, British Patent No. 1゜522
．． 485 schematically shows a mass termination connector as described in No. 485;

The connector comprises a connector housing 21 and a pair of connector wafers 22 and 23 that can be inserted into the housing. Each wafer 22.23 has pin 2
5 or a complementary "turning fork" female contact and at the other end in the form of a contact 26 for connection to a flat cable or many thin single conductors. , has a number (usually 20 or 40) of metal electrical conductors 24 extending through the wafer. The specific means used to connect conductor 24 to the wire or flat cable are not shown;
Typically, for example, U.S. Patent No. 3,852,517
and one or more soldering devices as described in the above.

Each wafer 22 and 23 has a stepped recess 27 extending across the width of the wafer to expose each conductor.
is formed. In one aspect of this connector,
molybdenum or copper electrodes are attached to the individual conductors 24;
Then a layer of indium 0.1 micrometers thick, then a layer 28 of the above-mentioned selenium-germanium-arsenic glass 10 micrometers thick, then a layer of indium 0.1 micrometers thick and an intermediate layer. Thin electrode 2 made of e.g. molybdenum, copper, gold or aluminum
9 is attached. An additional conductive layer 30 or gold or aluminum "ground plane" is deposited on the wafer material within the stepped recess 27, the ground plane being electrically grounded to, for example, the metal housing of the connector or a ground bin. Each electrode 29 is connected to a ground plane by a wire 31 made of gold or aluminum, for example, and bonded to the electrode 29 and ground plane 30 by conventional wire bonding methods.

Alternatively, a single layer of glass indium 28 and electrode 2
9 is deposited across the entire width of the wafer, in which case only a single wire is needed for connection to the ground plane, or if one of the conductors 24 is grounded, the ground plane and the wire can be omitted.

In an alternative construction, after depositing the selenium/germanium/epithelium glass layer, the indium layer and the electrodes on a common ground plane, and after appropriate surface treatment if necessary, the wire 31 is
A conductor 24 is connected to the electrode of the glass layer.

FIG. 5 schematically shows an example of modification of the wafer shown in FIGS. 3 and 4. FIG. In this wafer form, a glass layer 28, an indium layer and an electrode 29 are deposited on the conductor 24 described above and connected to a ground plane 30 through three wires. Additionally, a 100 nP capacitor 40 is placed in the recess 27 and connected between the ground plane and the connector housing or ground terminal. In this form of the device, the capacitor stops the direct current or the alternating current at a frequency considerably lower than about IMHz, and the
Transient currents with a frequency spectrum above MHz are conducted directly to earth. This example of a modification of the device shows that the direct current in the electrical system after the transient has been transferred to earth
Advantageously, it eliminates or reduces the possibility that glass switching layer 28 will become latched into a low resistance state.

Examples I-3 Ge+aASs4Sest glasses were prepared by mixing the components that were at least 99.99% pure and melting the mixture in a silica ampoule under vacuum or reduced pressure of argon. During the melting, which was carried out at a temperature of 1000° C. for 48 hours, the ampoule was shaken to ensure a homogeneous melt.

Decoys IO micrometers thick were prepared from the glass thus prepared using a resistive heating source at pressures of 10-3 to
It was formed by vapor deposition using IO'Pa.

A deposition rate of 0.03 to 1.0 micrometers/min was employed. A number of electrodes with varying electrode contact resistances were provided in the layer, and the latching energy of the switch device so formed was measured as described below.

In Example 1, one gold spring probe with a diameter of L mm was used.
A force of g-force was applied to the upper surface of the glass layer and a copper film electrode was applied to the opposite surface.

In Example 2, copper electrodes were provided on both sides of the glass layer by vacuum evaporation. However, while the electrode was hot, reinserting air into the vacuum chamber partially oxidized the electrode.

In Example 3, a 0.5 micrometer thick layer of the same glass composition but containing 15% indium was provided on each surface of the glass layer, and a layer of indium 011 micrometer thick was applied to each indium containing layer. Glass and (non-oxidized)
It was supplied between vacuum-attached copper electrodes. The results are shown in Table 1.

11. The latching energy of the device and therefore of the glass material was measured by the circuit shown in FIG.

The single shot pulses generated by the pulse generator I are sent to a switching element 2 connected in series with a current limiting resistor 3 having a resistance R, of 40 to +00 Ω, and the voltage across the switching element is observed by an oscilloscope 4. did. The voltage generated by the pulse generator l was gradually increased (approximately 5 to IO pulses for each voltage level of the pulse generator) until the switching element was in a low resistance state (determined by continuous measurements of resistance). passed)
.

The latch energy EL of the device is calculated by the following formula: V''R.

(+000) (R, +R2) [where J: Energy supplied from the pulse generator V: Peak voltage from the pulse generator when retention occurs R5: Internal output impedance of the pulse generator R3: Current limit It is the resistance of the resistor. ] This equation gives very good agreement with the values obtained by integrating the current and voltage of the pulse.

The resistance across the device was measured by replacing the device with a standard resistance and comparing the voltage/time curve to that of the device when subjected to a standard pulse. The peak current through the device was observed to be approximately IA for all cases, so that the resistance across the device (Ω) was numerically equal to the voltage across the electrodes (V).

[Brief explanation of drawings]

1 is a cross-sectional view of a device of the present invention with the thickness enlarged for clarity; FIG. 2 is a side view and partial cross-section of a BNC coaxial connector incorporating a circuit protection device of the present invention; FIG. 4 is a partially enlarged sectional view of the connector shown in FIG. 3; FIG. 5 is a partially enlarged sectional view of the connector shown in FIG. FIG. 3 is a perspective view of the wafer modification example, and FIG. 6 is a circuit diagram for measuring the latch energy of the device. 201... Indium layer, 202... Copper electrode, 20
3... Indium layer, 204... Copper electrode, 205.
206...Additional layer, 210...Glass layer. l...Connector shell, 2...Male connector, 3
... Pin, 4... Soldering, End... Housing, 6... Spacer, 7... Termination part, 8... Blade, 9... Soldering, IO...
- Rear end, 11... Glass element, 12... Column, 2
1... Connector housing, 22. 23... Connector wafer, 24... Conductor, 25 - Pin, 26 Contact, 27... Recess,
28 - Glass layer, 29... Electrode, 30... Ground plane, 31... Wire, 40... Capacitor. Figure 6 I...Pulse generator, 2...Switching element, 3.
- Current limiting resistor, 4... Onroscope. Patent applicant: Raychem Limited, patent attorney: Seibai, Seiba, and two others Engraving of the drawings (
No change in content) h6 Procedural amendment (Dear Commissioner of the Self-Responsive Patent Office May 13, 1988 1 Indication of the case Patent application No. 75757 of 1988 2 Name of the invention Limitation switching device 3 Make amendments Relationship with the Patent Case Patent Applicant Address London, England, United Kingdom 4
・1 N.L., Fetter Lane, Rolls Buildings No. 7, Rolls House Name: Raychem Limited 4 Agent address: 2-1-61 Mi, Higashi-ku, Osaka City, Osaka Prefecture, 540
Item 6 Subject of amendment 2 Drawings

Claims (1)

[Claims] 1. A limit switching device comprising a switching element made of an amorphous chalcogenide composition and a pair of electrodes in contact with the composition, wherein a switching element is provided between the composition and the electrodes. A device having an indium or indium-containing layer between the composition and at least one electrode to reduce the electrical contact resistance of the composition. 2. A device according to claim 1 having an electrode-to-electrode resistance of not more than 10 ohms in the low resistance state. 3. A device according to claim 2 having an electrode-to-electrode resistance of not more than 1 ohm in the low resistance state. 4. The device of claim 3 having an electrode-to-electrode resistance of not more than 0.1 Ω in the low resistance state. 5. Claims 1 to 5, wherein the amorphous chalcogenide glass composition comprises germanium, selenium, and arsenic.
4. The device according to any one of Item 4. 6. A device according to any one of claims 1 to 5, wherein the concentration of indium in the indium-containing layer increases towards the electrode. 7. The at least one indium or indium-containing layer comprises an indium-containing chalcogenide layer in contact with the switching element and a layer consisting essentially entirely of indium between the indium-containing chalcogenide layer and the electrode. A device according to any one of ranges 1 to 6. 8. Claim 1 between the conductive wire of the circuit and the ground
An electrical element comprising a limit switching device according to any of clauses . 9. The element of claim 8 which is an electrical connector.