US3546540A

US3546540A - Control system

Info

Publication number: US3546540A
Application number: US794283*A
Authority: US
Inventors: Siri R Bhola
Original assignee: Conductron Corp
Current assignee: Conductron Corp
Priority date: 1969-01-27
Filing date: 1969-01-27
Publication date: 1970-12-08
Anticipated expiration: 1987-12-08

Description

DEQ# `8,1970 s, R, BHQLA 3,546,540

' CONTROL SYSTEM Filed Jan. 27, 1969 "IIN F/G 4. Je 22 f3 32 2 lll,...` 1 60/^ faf I if, Mx V/// /l///f/f .ff f

United States Patent O 3,546,540 CONTROL SYSTEM Siri R. Bhola, St. Louis, Mo., assignor to Conductron Corporation, St. Charles, Mo., a corporation of Dela- Ware Filed Jan. 27, 1969, Ser. No. 794,283 Int. Cl. H03k 17/30 U.S. Cl. 317-101 14 Claims ABSTRACT OF THE DISCLOSURE A voltage actuated switch comprises a conductor, an essentially defect-free layer of insulating material which has a portion thereof that overlies and engages at least a part of a surface of that conductor and that has a predetermined thickness and resistivity to enable it to have a relatively high breakdown voltage, a tiny area of that layer of insulating material which has a thickness and resistivity that enable it to have a predetermined lower breakdown voltage, and an electrode which overlies and engages said tiny area of said layer of insulating material. The tiny area of the layer of insulating material will normally insulate the electrode from the conductor; but it will respond to a voltage, which is higher than the predetermined breakdown voltage of that tiny area but which is lower than said relatively high breakdown voltage, and which is applied across that electrode and that conductor, to break down and permit an irreversible, low-resistance connection to form that'electrode and that conductor.

This invention relates to improvements in Control Systems. More particularly, this invention relates to improvements in voltage actuated switches for control systems.

It is, therefore, an object of the present invention to provide an improved voltage actuated switch for control syste-ms.

Some control systems, such as the Control System for sequentially Actuating A Plurality of Loads disclosed in co-pending patent application Ser. No. 589,560 now U.S. Pat. No. 3,417,259 of Nozawa and Nasser which was led Oct. 26, 1966, utilize voltage actuated switches; and one commonly-used type of voltage actuated switch is generally similar to an electrolytic capacitor. Specifically, that type of voltage actuated switch usually consists of a foil of aluminum which has an anodized insulating lm on one surface thereof, of a metal screen which is formed on that anodized insulating iilm, and of an electrode which is bonded to that metal screen. While voltage actuated switches of that type are usable, the voltages at which those voltages actuated switches change from their initial high-resistance states to their low-resistance states cannot be predicted with a sufficiently close degree of accuracy. Moreover, voltage actuated switches of that type can sometimes respond to current or voltage surges to change back from their low-resistance states to their initial highresistance states. It would be desirable to provide a voltage actuated switch which would change from its initial high-resistance state to a low-resistance state whenever a closely-predictable breakdown voltage was applied to it, and which would thereafter remain in its low-resistant state even though it was subjected to voltage or current surges. The present invention provides such a voltage actuated switch; and it is, therefore, an object of the present invention to provide a voltage actuated switch which will change from its initial high-resistance state to a low-resistance state whenever a closely-predictable breakdown voltage is applied to it, and which will thereafter remain in its low-resistance state even though it is subjected to current or voltage surges.

The voltage actuated switch provided by the present invention comprises a conductor, an essentially defect-free layer of insulating material which has a portion that overlies and engages at least a part of a surface of that conductor and that has a predetermined thickness and resistivity to enable it to have a relatively high breakdown voltage, a tiny area of that layer of insulating material which has a thickness and resistivity that enable it to have a predetermined lower breakdown voltage, and an electrode which overlies and engages said tiny area of said layer of insulating material. The tiny area of the layer of insulating material will normally insulate the electrode from the conductor; but it will respond to a voltage, which is higher than said predetermined breakdown voltage of that tiny area but which is lower than said relatively high breakdown voltage, and which is applied across that electrode and that conductor, to break down and permit an irreversible, low-resistance connection to form between the electrode and that conductor. The essentially defectfree nature of the layer of insulating material will obviate any premature breakdowns of the voltage actuated switch; and hence that voltage actuated switch can have a closely-predictable breakdown voltage. The thickness and resistivity of the tiny area will make the predetermined breakdown voltage for that tiny area high enough so a suiliciently-large portion of that tiny area will be broken down to enable an irreversible, lowresistance connection to form between the conductor and the electrode. It is, therefore, an object of the present invention to provide an improved voltage actuated switch which comprises a conductor, an essentially defect-free layer of insulating material which has a portion that overlies and engages at least a part of a surface of that conductor and that has a predetermined thickness and resistivity to enable it to have a relatively high breakdown voltage, a tiny area of that layer of insulating material which has a thickness and resistivity that enable it to have a predetermined lower breakdown voltage, and an electrode which overlies and engages said tiny area of said layer of insulating material.

One preferred embodiment of the voltage actuated switch provided by the present invention comprises a wafer of silicon, a layer of silicon dioxide on one surface of that wafer, a tiny opening in that layer of silicon dioxide, a reduced-thickness layer of silicon dioxide within that tiny opening, and an electrode in engagement with that reduced-thickness layer of silicon dioxide. That reduced-thickness layer of silicon dioxide normally isolates the electrode from the silicon wafer, but it will respond to a predetermined breakdown voltage to break down and permit a low-resistance connection to form between that electrode and that silicon wafer. The voltage which is required to convert the voltage actuated switch from its initial high-resistance state to its low-resistance state can be closely controlled by closely controlling the thickness of the reduced-thickness layer of silicon dioxide; and that voltage will be high enough lso a sufficiently large portion of that reduced-thickness layer will be broken down to enable an irreversible, low-resistance connection to form between the conductor and the electrode. If a current or voltage surge were to be applied to the said preferred embodiment of the voltage actuated switch, after that voltage actuated switch had changed from its initial high-resistance state to its low-resistance state, that voltage or current surge could not cause that voltage actuated switch to revert to its initial high-resistance state. If such a voltage or current surge were to have any effect upon the voltage actuated switch, it would merely cause more of the reduced-thickness, silicon dioxide layer to break down-thereby making even more certain that the voltage actuated switch would not revert to its initial high-resistance state. It is, therefore, an object of the present invention to provide an improved voltage actuated switch which comprises a wafer of silicon, a layer of silicon dioxide on one surface of that wafer, a tiny opening in that layer of silicon dioxide, a reduced-thickness layer of silicon dioxide within that tiny opening, and an electrode in engagement with that reduced-thickness layer of silicon dioxide.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description two preferred embodiments of the present invention are shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. 1 is a side elevational View of a conductor and of a layer of insulating material on the upper surface of that conductor,

FIG. 2 is a vertical section through the conductor and layer of insulating material shown in FIG. l after tiny openings have been formed in that layer of insulating material,

FIG. 3 s a plan view of the conductor and layer of insulating material shown in FIG. 2, and it is taken along the plane indicated by the line 3 3 in FIG. 2,

FIG. 4 is a vertical section through the conductor and l layer of insulating material shown in FIG. 2 after further FIG. 5 is a sectional view through a voltage actuated switch which is made from the conductor and the layers of insulating material of FIG. 4,

FIG. 6 is a sectional view through a second conductor and a layer of insulating material thereon,

FIG. 7 is a sectional view through the conductor and layer of insulating material of FIG. 6 after a second insulating layer has been formed within a small opening in the layer of insulating material shown in FIG. 6,

FIG. 8 is a sectional view through the conductor and the layers of insulating material shown in FIG. 7 after a tiny opening has been formed in the second layer of insulating material,

FIG. 9 is a sectional view through the conductor and layers of insulating material of FIG. 8 after a third layer of insulating material has been formed within the tiny opening in the second layer of insulating material,

FIG. lO is a plan View, on a smaller scale, of the conductor and layers of insulating material shown in FIG. 9 after two spaced electrodes are formed on that conductor and on those layers of insulating material, and

FIG. 1l is a sectional view, on the scale of FIG. 6, through the conductor and layers of insulating material shown in FIG. l0 after leads have been attached to the spaced electrodes formed on that conductor and on those layers of insulating material.

Referring to the drawing in detail, the numeral denotes a conductor which has a smooth upper surface, and which will be incorporated into one preferred embodiment of voltage actuated switch that is made in accordance with the principles and teachings of the present invention. A layer 22 of insulating material overlies the upper surface of the conductor 20, and that layer is an essentially defect-free layer of insulating material; and that layer will have a thickness and a resistivity which will enable that layer to have a relatively high breakdown voltage. In the said one preferred embodiment of voltage actuated switch provided by the present invention, the conductor 20 is a single crystal wafer of silicon, and the layer 22 of insulating material is a layer of silicon dioxide which is thermally grown on the upper surface of that silicon wafer. The wafer of silicon is square in plan, each side is eighteen thousandths of an inch long, and it is one one one-half thousandths of an inch thick. The layer 22 `of silicon dioxide is about seventy-live hundred angstroms thick.

Tiny openings

24, 26, 28 and 30 are formed in the layer 22 of insulating material; and those tiny openings will preferably be formed in that insulating layer by an etching process. For example, a layer which is resistant to an etching agent can be formed on the upper surface of the layer 22 of insulating material by a photolithographic process, and that resistant layer will have four openings therein in the positions occupied by the

tiny openings

24, 26, 28 and 30 in FIG. 3. Thereafter, a suitable etching agent will be applied to the resistant layer; and that etching agent will flow through the four openings in that resistant layer and form the

tiny openings

24, 26, 28 and 30 in the layer 22 of insulating material. In the said one preferred embodiment of voltage actuated switch provided by the present invention, the bottom of each of the openings 24, 2'6, 28 and 30 is square, and it is one thousandths of an inch on each side.

Once the

tiny openings

24, 26, 28 and 30 have been formed, the etching agent and the resistant layer atop the layer 22 of insulating material will be removed; and then reduced-thickness layers 3-2 of insulating material will be thermally grown within those tiny openings. The thicknesses of all of the reduced-thickness layers 32 of insulating material within the

tiny openings

24, 26, 28 and 30 will be as close to being the same as it is possible to make them; and those reduced-thickness layers of insulating material will be essentially defectfree-having essentially the same breakdown voltage that a theoretically-perfect layer of the same insulating material of the same thickness would have. The thickness of each of the reduced-thickness layers 32 of insulating material within the

tiny openings

24, 26, 28 and 30 will be very much smaller than the thickness of the layer 22 of insulating material and hence the breakdown voltage of each of the reduced-thickness layers 32 of insulating material will be substantially smaller than the break- .down voltage of the layer 22 of insulating material.

The numeral 36 denotes an electrode which overlies the reduced thickness layers 32 of insulating material within the

openings

24, 26, 28 and 30; and that electrode also overlies the layer 22 of insulating material. That electrode will preferably be made of aluminum; and it will preferably be applied by an evaporation process. A lead 38 is secured to the upper surface of the electrode 36, and a lead 40` is secured to the bottom of the conductor 20; and those leads will permit the voltage actuated switch of FIG. 5 to be incorporated into an appropriate control system.

In the said one preferred embodiment of voltage actuated switch provided by the present invention, each of the reduced-thickness 'insulating layers 32 is about six hundred angstroms thick, and the electrode 36 is about twenty thousand angstroms thick. Each of the reducedthickness layers 32 of insulating material within the

openings

24, 26, 28 and 30I will have a breakdown voltage of twenty-two volts plus or minus two volts. To make sure that all of the reduced-thickness layers 32 of insulating material within the

openings

24, 26, 28 and 30 have breakdown voltages close to or above the lower limit of twenty volts, the voltage actuated switch will be tested by applying a D.C. voltage of nineteen and one-half volts to the

leads

38 and 40. If any of the reduced-thickness layers 32 of insulating material within the

openings

24, 26, 28 and 30 is not essentially defectfree or does not have the prescribed thickness, and thus break downs when the nineteen and one-half volts are applied to the leads 38 and 30, the voltage actuated switch will be considered a reject and will be discarded. Only those voltage actuated switches which do not experience a breakdown when nineteen and one-half volts are applied to the

leads

38 and 40 will be accepted; and hence full assurance can be given that those voltage actuated switches will not break down under D.C. voltages less than nineteen and one-half volts.

When the voltage actuated switch of FIG. 5 is incorporated into a control system which utilizes one or more voltage actuated switches, the reduced thickness layers 32 of insulating material within the

openings

24, 26, 28 and 30 will insulate the electrode 36 from the conductor 20, as long as the voltage applied to the

leads

38 and 40 does not exceed nineteen and one-half volts. However, when a voltage in the range of twenty-two volts, plus or minus two volts, is applied to the

leads

38 and 40, that voltage will exceed the breakdown voltage of one 0f the reduced-thickness layers 32 of insulating material within the

openings

24, 26, 2'8 and 30; and an appreciable portion of that reduced-thickness layer will be converted from its initial high-resistance state to a lowresistance state. The conversion of the appreciable portion of the reduced-thickness layer from its initial highresistance state to a low-resistance state will be very rapid-occurring in less than twenty-five microseconds; and the ohmic resistance of that reduced-thickness layer, after an appreciable portion thereof has been changed to a low-resistance state will be quite low-being no greater than one and one-half ohms.

Where the reduced-thickness layer 32 that breaks down is square and is one thousandth of an inch on each side, from fty percent to eighty percent of the area of that reduced-thickness layer of insulating material will be converted from its initial high-resistance state to its loW- resistance state as that reduced-thickness layer breaks down. The conversion of such a substantial area of the` reduced-thickness layer from its initial high-resistance state to its low-resistance state is desirable; because it will keep a voltage or current surge from causing that area, of that reduced-thickness layer, to revert back to its initial high-resistance state. Consequently, once a voltage actuated switch provided by the present invention changes from its initial high-resistance state to its lowresistance state, that voltage actuated switch will not revert back to its initial high-resistance state.

The present invention makes certain that an appreciable percentage of the area of the reduced-thickness layer of insulating material will be converted to its low-resistance state, by making the upper surface of the conductor as smooth as possible, by making the reduced-thickness layer essentially defect-free, and by giving the reduced-tthickness layer a uniform thickness. A smooth upper surface on the conductor 20 will coact with an essentially defect-free, uniform thickness layer 32 of insulating material to require a breakdown voltage which is high enough to cause suicient energy to be released, as the reduced-thickness layer 32 breaks down, to effect the conversion of an appreciable portion of the area of that reduced-thickness layer from its initial high-resistance state to its low-resistance state. If the upper surface of the conductor 20 was not smooth, or if the reduced-thickness layers 32 were not essentially defectfree or were not of uniform thickness, it would be possible for a voltage, appreciably lower that the desired breakdown voltage, to cause that reduced-thickness layer to break down; and the amount of energy which was released when that lower voltage caused that reduced-thickness layer to breakdown could be insuicient to convert an appreciable portion of the area of that reduced-thickness layers 32 were not essentially defectto its low-resistance state. In that event, a voltage or current surge might be able to cause that reduced-thickness layer to revert back to its initial high-resistance state. For example, the type of voltage actuated switch that consists of a foil of aluminum which has an anodized insulating lm on one surface thereof, of a metal screen which is formed on that anodized insulating film, and of an electrode which is bonded to that metal screen has been known to revert from its low-resistance state to its high-resistance state when subjected to a current surge of eight amperes for twenty milliseconds or to a voltage surge in the range of twelve and one-half volts to forty: two volts; and any such reversion is very objectionable. Any such reversion is obviated by the present invention;

terial-which is located in and hence any voltage actuated switch provided by the present invention, that has been converted to its low-resistaiice state, will remain in that low-resistance statedespite the application of anticipatable voltage or current pulses to that voltage actuated switch.

The numeral 44 in FIGS. 6-11 denotes a conductor; and that conductor has a layer 46 of insulating material on the upper surface thereof. The layer 46 of insulating material is appreciably thicker than the layer 22 of insulating material on the upper surface of the conductor 20 1n FIGS. 1-5. A very small opening 48 is formed in the layer y46 of insulating material, and that opening extends to the upper surface of the conductor 44. The numeral 50 denotes a second layer of insulating material which is thinner than the layer 46 of insulating material; and that second layer fills the lower part of the very small opening 48 in the layer 46 of insulating material. :The numeral 52 denotes a tiny opening which is formed in the second layer 50 of insulating material; and the numeral 54 denotes a third layer of insulating materialappreciably thinner than the layer 50 of insulating maa the bottom of the tiny opening 52 in the layer 50 of insulating material. The bottom of the tiny opening 52 can have the same configuration and dimensions as the bottom of any of the

tiny openings

24, 26, 28 and 30 in the layer 22 of insulating material shown in FIG. 3; and the layer 54 of insulating material will directly engage the upper surface of the conductor 44. Where the conductor 44 is a silicon wafer and the layer l46 of insulating material is silicon dioxide, the very small opening 48 can be formed by an etching operation; the second layer 50 of insulating material can be thermally grown on the upper surface of the conductor 44, the tiny opening 52 can be etched in the second layer 50 of insulating material, and the layer 54 can be thermally grown on the upper surface of the conductor 44. As indicated particularly by FIG. l0, the layer 46 of insulating material has four openings 48 therein, each of the four layers 50 has a tiny opening 52 therein, and each of the openings 52 has a reduced-thickness layer 54 therein.

The layer 46 of insulating material has a generally U- shaped recess 60 therein; and an electrodeV 62 is formed in that recess and extends upwardly above the upper surface of the layer 46. A lead 64 is suitably connected to that electrode; and that lead will serve as one lead of a Voltage actuated switch 58 which includes the conductor 44, the

layers

46, 50, and 54 of insulating material, the electrode 62, and an electrode 66. The electrode 66 overlies the four reduced-thickness layers 54, and a lead 68 is connected to that electrode. The fact that the layer 46 of insulating material is thicker than the layer 22 of insulating material in FIGS. 1-5 makes it possible for very heavy pressures to be applied to the conductor 44 and to the electrode 66 when the lead 68 is aixed to that electrode. Heavy pressures are required with some electrodes and with some leads, and injury to the layer 46 of insulating material can be avoided by making that layer thick, in the manner shown by FIGS. 6-11.

The conductor 20 and the conductor `44 are preferably made from a material, such as silicon, which can have an insulating layer readily formed thereon. However, those conductors can be made from different materials such as aluminum, germanium and gallium. Aluminum oxide, germanium oxide, gallium arsenide, glass, silicon carbide, zirconium oxide, and many other insulating materials could be used as the

layers

22, 32, 46, 50 and 54 The

electrodes

36, 62 and 66 can be made from many different metals, and they can be made of any desired thickness.

The forming of

tiny openings

24, 26, 28, 30 and 52 in the

layers

22 and 50 of insulating material, and the forming of reduced-thickness layers 32 and S4 in those tiny holes, limit the areas where voltage-induced breakdowns can occur to specific areas, and thus do not permit breakdowns to occur in randomly-located areas. By restricting voltage-induced breakdowns to a small number of tiny areas, the present invention avoids the highly objectionable premature breakdowns which have been experienced with the voltage actuated switches that generally resemble electrolytic capacitors. A voltage actuated switch of that type can break down prematurely at any point on the overall surface thereof where the aluminum oxide coating contains a defect or is not of full thickness; and each of those voltage actuated switches inherently contains a considerable number of points where the aluminum oxide coating contains a defect or is not of full thickness. As a result, it has been exceedingly diflicult to obtain comercial quantities of voltage actuated switches, that generally resemble electrolytic capacitors, with closely-predictable breakdown voltages. Moreover, because such voltage actuated switches can frequently be broken down by voltages smaller than the desired breakdown voltages, the energy released during the breaking down of those voltage actuated switches can be too small t form an irreversible, low-resistance connection between the conductor and the electrode; and hence subsequentlyapplied voltage or current surges have been known to cause those voltage actuated switches to revert from their low-resistance states to their initial high-resistance states.

In the two preferred embodiments of the present invention shown by the drawing, the conductors and 44 are single crystal silicon wafers, and the upper surfaces of those conductors are substantially perfectly smooth. Where such conductors are used, the thicknesses of the

layers

22 and 46, and the thicknesses of the

layers

32, 50 and 54 can be controlled with a high degree of precision. Furthermore, those layers can be made so they are essentially defect-free; and hence the voltage actuated switches made 4by the present invention can have closely-predictable breakdown voltages. Where the

layers

32 and 54 are made of silicon dioxide and are about six hundred angstroms thick, those layers have initial ohmic resistances in excess of one megohm; and they have low-resistance ohmic values of about three tenths of an ohm after they have broken down and permitted the voltage actuated switches to become actuated.

In the preferred embodiment of voltage actuated switch shown by FIG. l0, the conductor 44 is square, is three hundredths of an inch on each side; and is two thousandths of an inch thick. That conductor will initially be formed as part of a larger conductor, and then will be suitably separated from the rest of that larger conductor by scoring and cutting or breaking that larger conductor into small pieces.

The

layers

22, 32, 46, 50 and 54 of insulating material can be formed in different ways. Where the

conductors

20 and 44 are made from materials which can have oxides or other salts with dielectric properties formed on the surfaces thereof, those layers of insulating material can be formed in the manner in which oxides or other salts with dielectric properties are formed on conductors. Where the

conductors

20 and 44 are not made from materials which can have oxides or other salts with dielectric properties formed on the surfaces thereof, the

layers

22, 32, 46, 5t) and 54 of insulating material can be formed by a depositing or coating process. The primary requirements of the

layers

32 and 54 of insulating material are that they are essentially defect-free and are of uniform thickness.

As indicated by FIG. 5, the leads for a voltage actuated switch can be attached to the opposite faces of that voltage actuated switch; and, as indicated by FIG. 11, the leads for a voltage actuated switch can be attached to the same face of that voltage actuated switch. As a result, voltage actuated switches which are made in accordance with the principles and teachings of the present invention can be made to have almost any configuration and geometry that is desired.

In the drawing, the various layers of insulating material which are intended to break downA are shown as being thinner than the surrounding layers of insulating material; and such an arrangement is very useful and desirable. However, if desired, the layers of insulating material wherein the breakdowns are to occur could be made so the thicknesses thereof are the same as the thicknesses of the surrounding layers of insulation but could be made so the dielectric values thereof are lower than the dielectric values of the surrounding layers of insulation. In either event, the layers of insulating material which are intended to break down will have breakdown voltages lower than the breakdown voltages of the surrounding layers of insulation.

Voltage actuated switches that are made in accordance with the principles and teachings of the present invention can be made to respond to breakdown voltages of different values. For example, those voltage actuated switches could be made to respond to breakdown voltages as low as five volts, and they could be made to respond to almost any desired voltage above five volts. The particular voltage at which a voltage actuated switch of the present invention will fbreak down will be a function of the thickness and of the dielectric strength of the layers 32 and S4 of insulating material. Almost any desired dielectric strength can be attained, by selecting an appropriate material for the

layers

32 and 54; and, if desired, suitable dopants can be used to modify the inherent dielectric characteristics of a material to give that material the desired dielectric strength. As a result, the voltage actuated switches of thepresent invention can be made to respond to almost any desired breakdown voltage; and those voltage actuated switches will promptly and irreversibly change from their high-resistance states to their low-resistance states when subjected to those breakdown voltages.

The shapes and sizes of the openings in which the breakdowns are to occur can vary; but those openings should be tiny. Openings wherein the longest dimensions are less than three thousandths of an inch are preferred; and the smallest dimension of any opening in which a breakdown is to occur should not exceed one hundredth of an inch.

Only one tiny opening is actually needed in a voltage actuated switch; because only one breakdown ordinarily occurs when a voltage actuated switch changes from its initial high-resistance state to its low-resistance state. However, two, three or four tiny openings will usually be provided to make certain that the breakdown voltage is not higher than desired, as would be the case if just one tiny opening was provided and the layer of insulating ymaterial within that opening was inadvertantly made thicker than desired. While the provision of two, three, or four tiny openings increases the possibility that the voltage actuated switch might have a reduced-thickness layer of insulating material which was undesirably thin, the testing of the voltage actuated switches at voltage values just a fraction of a volt below the lower limit of the desired range of breakdown voltages makes it possible to reject any voltage actuated switch which might tend to breakdown prematurely because one of its reduced-thickness layers of insulating material was too thin. In actual practice, where the conductors are silicon wafers and the layers of insulating material are silicon dioxide, the provsion of four tiny openings in each voltage actuated switch has not signicantly increased the likelihood of premature voltage-induced breakdowns. Also, where the conductors are silicon wafers and the layers of insulating material are of silicon dioxide, the voltage actuated switches can be made at less cost than can voltage actuated switches which are similar to electrolytic capacitors.

It thus should be apparent that the present invention makes it possible to provide voltage actuated switches which become actuated at closely-predictable voltages. Further, it should be apparent that once those voltage actuated switches have been actuated, they will not revert to their initial high-resistance states even if they are exposed to predictable voltage or current surges. In addition,

it should be apparent that those voltage actuated switches can be made at moderate cost.

Whereas the drawing and accompanying description have shown and described two preferred embodiments of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is: 1. A voltage actuated switch which comprises: a substrate of conductive material, an insulating layer which overlies and engages at least a part of said substrate,

said insulating layer having a portion of predetermined thickness and predetermined resistivity to enable said portion of said insulating layer to have a predetermined breakdown voltage,

said insulating layer having a tiny area of predetermined size which overlies and engages said part of said surface of said substrate, and

an electrode overlying and engaging said tiny area of said insulating layer,

said tiny area of said insulating layer having an essentially uniform thickness,

said tiny area of said insulating layer having a thickness and a resistivity which enable said tiny layer to have a breakdown Voltage substantially lower than said predetermined breakdown voltage,

said tiny area of said insulating layer responding to the application of a voltage across said substrate and said electrode, which is greater than said breakdown voltage of said tiny area of said insulating layer but which is less than said predetermined breakdown voltage, to break down and thereby permit an irreversible, low-resistance connection to form between said electrode and said substrate.

2. A voltage actuated switch as claimed in claim 1 wherein said substrate is silicon and wherein said insulating layer is silicon dioxide.

3. A voltage actuated switch as claimed in claim 1 wherein the longest dimension of said tiny area of said insulating layer is one hundredth of an inch.

4. A voltage actuated switch as claimed in claim 1 wherein said insulating layer has a second tiny area which is substantially identical to but is spaced from the rst said tiny area, and wherein either of said tiny areas is capable of responding to the application of a voltage across said substrate and said electrode, which is greater than said breakdown voltage of said tiny area of said insulating layer but which is less than said predetermined breakdown voltageyto break down and thereby permit an irreversible, low-resistance connection to form between said electrode and said substrate.

5. A voltage actuated switch as claimed in claim 1 wherein said substrate is silicon and wherein said insulating layer is silicon dioxide and wherein said tiny area is silicon dioxide but has a thickness substantially smaller than the thickness of said portion of said insulating layer.

6. A voltage actuated switch as claimed in claim 1 wherein said substrate is metallic, wherein said insulating layer is a salt, and wherein said tiny layer is the same salt, said tiny area having a thickness substantially smaller than the thickness of said portion of said insulating layer.

7. A voltage actuated switch as claimed in claim 1 wherein said electrode extends to and directly engages said substrate, and wherein leads connected to said electrode and said substrate are at the same side of said voltage actuated switch.

8. A voltage actuated switch as claimed in claim 1 wherein said tiny area has a thickness less than one thousand angstroms.

9. A voltage actuated switch as claimed in claim 1 wherein said tiny area has a length less than one hundredth of an inch and has a width less than one hundredth of an inch.

10. A voltage actuated switch which comprises:

a substrate of conductive material,

an insulating layer which overlies and engages at least a part of said substrate,

an electrode overlying and engaging said tiny area of said insulating layer,

said tiny area of said insulating layer having an essenitally uniform thickness,

said tiny area of said insulating layer responding to the application of a voltage across said substrate and said electrode, which is greater than said breakdown voltage of said tiny area of said insulating layer but which is less than said predetermined breakdown voltage, to breakdown and thereby permit an irreversible, low-resistance connection to form between said electrode and said substrate,

the thickness of said tiny area of said insulating layer being substantially smaller than the thickness of said portion of said insulating layer.

11. A voltage actuated switch which comprises:

a substrate of conductive material,

an electrode overlying and engaging said tiny area of said insulating layer,

said tiny area of said insulating layer responding to the application of a voltage across said substrate and said electrode, which is greater than said breakdown voltage of said tiny area of said insulating layer but which is less than said predetermined breakdown voltage, to breakdown and thereby permit an irreversible, low-resistance connection to form between said electrode and said substrate.

said substrate having a smooth, ilat surface in register with said tiny area of said insulating layer, and

each of said substrate and said electrode being many times thicker than said tiny area.

12. A voltage actuated switch which comprises:

a substrate of conductive material,

said insulating layer having a portion of predetermined thickness and predetermined resisitivity to enable said portion of said insulating layer to have a predetermined breakdown voltage,

an electrode overlying and engaging said tiny area of said insulating layer,

said tiny area of said insulating layer having a thickness and a resistivity which enable said tiny layer tov have a breakdown voltage substantially lower than said predetermined breakdown voltage,

the thickness of said tiny area of said insulating layer being substantially smaller than the thickness of said portion of said insulating area, and

said insulating layer having a second portion with a thickness intermediate the thicknesses of said tiny area and of the rst said portion of said insulating area,

said second portion of said insulating area surrounding said tiny area,

the thickness of the first said portion of said insulating area being great enough to enable pressure to be used in connecting a lead to said electrode without injuring said rst said portion of said insulating area.

f 13. A voltage actuated switch which comprises:

a substrate of conductive material,

an electrode overlying an engaging said tiny area of said insulating layer,

said tiny area of said insulating layer responding to the application of a voltage across said substrate and said electrode, which is greater than said breakdown voltage of said tiny area of said insulating layer but which is less than said predetermined breakdown voltage, to break down and thereby permit an irreversible, low-resistance connection to form between said electrode and said substrate,

said substrate being metallic, said insulating layer being a salt, and said tiny layer being the same salt. 14. A voltage actuated switch which comprises: a substrate of conductive material, an insulating layer which overlies and engages at least a part of said substrate, said insulating layer having a portion of predetermined thickness and predetermined resistivity to enable said portion of said insulating layer to have a predetermined breakdown voltage, said insulating layer having a tiny area of predetermined size which overlies and engages said part of said surface of said substrate, and an electrode overlying and engaging said tiny area of said insulating layer, said tiny area of said insulating layer having an essentially uniform thickness, said tiny area of said insulating layer having a thickness and aI resistivity which enable said tiny layer to have a breakdown voltage substantially lower than said predetermined breakdown voltage, said tiny area of said insulating layer responding to the application of a voltage across said substrate and said electrode, which is greater than said breakdown voltage of said tiny area of said insulating layer but which is less than said predetermined breakdown voltage, to breakdown and thereby permit an irreversible, low-resistance connection to form between said electrode and said substrate, said tiny area being dimensioned so the major portion thereof will be converted from an initial high-resistance state to a low-resistance state as said tiny area responds to said voltage across said substrate and said electrode to break down.

- References Cited UNITED STATES PATENTS 2,909,122 10/1959 Shoemaker et al. 102-70.2 2,986,660 5/ 1961 Franklin et al. 307--108 3,378,116 4/1968 Hennig 18S-250 3,417,259 12/1968 Nozawa et al. 307-108 ROBERT K. SCHAEFER, Primary Examiner J. R. SCOTT, Assistant Examiner U.S. Cl. X.R.