Device and method for MOV with improved edges

Abstract

An electrical device and a method for manufacturing the same that suppress damage to the edge regions of electrodes are provided. In an electrical device configured as an improved edge metal oxide varistor (MOV), the MOV has metal oxide layers (412, 420) having first and second surfaces, and a first electrode (414) and a second electrode (418) mounted on the first and second surfaces of the metal oxide layers, respectively, each electrode including a laterally inner portion (510a, 512a) and an edge portion. At least the edge portion of the first electrode has a flared shape. Two such MOVs are joined to form a sealed chamber (416) defined by the shape of the first surface of each metal oxide layer and containing a gas therein, such that the sealed chamber with the gas and the first electrodes of the two MOVs form a gas discharge tube (GDT).

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0002] This application claims priority to U.S. Provisional Application No. 62 / 982,220, filed February 27, 2020, entitled "MOV WITH MODIFIED EDGE CONFIGURATION," and U.S. Provisional Application No. 62 / 982,542, filed February 27, 2020, entitled "INTEGRATED DEVICE HAVING GDT AND MOV WITH MODIFIED EDGE," the disclosures of which are expressly incorporated herein by reference in their entireties.

[0003] The present disclosure relates to devices and methods relating to metal oxide varistors (MOVs) with improved edges. [Background technology]

[0004] A metal oxide varistor (MOV) typically comprises a layer of a metal oxide material, such as zinc oxide, mounted between two electrodes. Under normal conditions (e.g., up to the rated voltage between the electrodes), the MOV is non-conductive, but becomes conductive when the voltage exceeds the rated voltage.

[0005] In electrical applications, the aforementioned MOVs can be implemented in a circuit alone or in combination with other electrical devices, such as gas discharge tubes (GDTs), which are devices that have a gas between two electrodes in a sealed chamber. When a triggering condition, such as a high-voltage spike, occurs between the electrodes, the gas ionizes and conducts electricity between the electrodes. Summary of the Invention [Means for solving the problem]

[0006] In some embodiments, the present disclosure relates to an electrical device comprising a metal oxide layer having first and second surfaces, and first and second electrodes mounted on the first and second surfaces, respectively, of the metal oxide layer, each electrode including a lateral inner portion and an edge portion, the edge portion of the first electrode having a flared shape.

[0007] In some embodiments, the electrical device may be configured as a metal oxide varistor (MOV).

[0008] In some embodiments, the flared shape can be configured to provide a desired edge effect at least at or near the edge of the first electrode when a potential difference exists between the first electrode and the second electrode. The desired edge effect can include reduced edge effects. The edge effect can include temperature, electric field strength, or surface charge density.

[0009] In some embodiments, the edge portion of the second electrode may also include a flared shape. In some embodiments, the first electrode may be a near mirror image of the second electrode with respect to a midplane between the first and second electrodes.

[0010] In some embodiments, the edge portion of each of the first and second electrodes may include a straight portion extending from the respective inner portion at an angle that forms a flared shape when viewed in side cross section. The straight portion of the edge portion of each electrode may be sized and oriented to extend laterally outward relative to the inner portion by an amount a3 and extend away from the other electrode by an amount a2.

[0011] In some embodiments, the quantity a3 can have a value in the range between 0.02×D and 0.3×D, or in the range between 0.02×D and 0.03×D, where D is the overall dimension of the MOV. In some embodiments, the quantity a3 can have a value of about 0.025×D. In some embodiments, the quantity a3 can have a value in the range between 0.02×D and 0.4×D, or in the range between 0.05×D and 0.20×D, where D is the overall dimension of the MOV. In some embodiments, the quantity a3 can have a value of about 0.14×D, about 0.10×D, or about 0.08×D. In some embodiments, the MOV can have a disk shape with an overall diameter, and the overall dimension D is approximately equal to the overall diameter.

[0012] In some embodiments, the quantity a2 can have a value in the range between 0.05 x a1 and 0.25 x a1, or in the range between 0.08 x a1 and 0.21 x a1, where a1 is the central separation distance between the laterally inner portions of the first and second electrodes. In some embodiments, the quantity a2 can have a value of about 0.2 x a1.

[0013] In some embodiments, the edge portion of each of the first and second electrodes may further include another straight portion extending from the straight portion at another angle different from the angle.

[0014] In some embodiments, the edge portions of each of the first and second electrodes may include curved portions extending from their respective inner portions to form a flared shape when viewed in side cross section. The curved portions may include, for example, portions of conic sections or exponential curves. In some embodiments, the curved portions may include portions of circles such that the curved portions have a radius of curvature of R. For example, the quantity R may have a value ranging from 0.5×a1 to 0.8×a1, where a1 is the median separation distance between the laterally inner portions of the first and second electrodes.

[0015] In some embodiments, the second electrode may be substantially planar such that an edge portion of the second electrode is flush with the interior portion.

[0016] In some embodiments, the first surface of the metal oxide layer may be sized to accommodate a first electrode, and the second surface of the metal oxide layer may be sized to accommodate a second electrode. The first surface of the metal oxide layer may define a recess shaped to accommodate the flared shape of the edge portion of the first electrode.

[0017] In some embodiments, the metal oxide layer may have a circular shape when viewed from either the first side or the second side of the metal oxide layer, and in some embodiments, each of the first and second electrodes may have a circular shape when viewed from either the first side or the second side of the metal oxide layer.

[0018] In some embodiments, the metal oxide layer may have a rectangular shape when viewed from either the first or second side of the metal oxide layer, and in some embodiments, each of the first and second electrodes may have a circular or rectangular shape when viewed from either the first or second side of the metal oxide layer.

[0019] In some embodiments, the metal oxide layer with the first and second electrodes can form a first metal oxide varistor (MOV). In some embodiments, the electrical device can further include a second MOV coupled to the first MOV by an electrically insulating seal. The second MOV can include a metal oxide layer having first and second surfaces and first and second electrodes mounted on the first and second surfaces of the metal oxide layer, respectively. Each electrode can include a lateral inner portion and an edge portion, and the edge portion of the first electrode has a flared shape. The first and second MOVs can include the electrically insulating seal and be oriented such that the first surfaces of the first and second MOVs face each other to define a sealed chamber containing a gas, the sealed chamber containing the gas and the first electrodes of the first and second MOVs forming a gas discharge tube (GDT).

[0020] In some embodiments, the electrical device can form an electrical series arrangement of a first MOV, a GDT, and a second MOV, where the first electrode of the first MOV is also one of the two electrodes of the GDT, the first electrode of the second MOV is also the other of the two electrodes of the GDT, and the second electrodes of the first and second MOVs are external electrodes of the electrical device. In some embodiments, the electrically insulating seal can include a glass seal.

[0021] In some embodiments, the electrically insulating seal can be sized to extend laterally inward and cover some or all of the edge portions of the first electrodes of each of the first and second MOVs, thereby increasing the leak path length between the first electrodes.

[0022] In some embodiments, the metal oxide layer of each of the first and second MOVs can include a sidewall and an outer edge joining the sidewall and the first surface of each MOV. The outer edge can include an edge feature dimensioned to form a space for accommodating at least a portion of excess material associated with the electrically insulating seal. The edge feature can be dimensioned so that excess material associated with the electrically insulating seal does not extend outward beyond the sidewall of each metal oxide layer.

[0023] In some embodiments, the present disclosure relates to a method of fabricating a metal oxide varistor device, the method comprising forming or providing a metal oxide layer having first and second surfaces, and mounting first and second electrodes on the first and second surfaces of the metal oxide layer, respectively, each electrode comprising a lateral inner portion and an edge portion, the edge portion of the first electrode having a flared shape.

[0024] In some embodiments, the second electrode can be implemented to be substantially planar, such that the edge portion of the second electrode is flush with the inner portion, hi some embodiments, the second electrode can be implemented to form a flared shape at the edge portion of the second electrode.

[0025] In some embodiments, the metal oxide layer may be a unit of a plurality of similar units joined together in an array, hi some embodiments, the method may further include separating the plurality of units into a plurality of separate units.

[0026] According to some embodiments, the present disclosure relates to an electrical device including a first metal oxide varistor (MOV) including a first metal oxide layer having an outer surface and an inner surface having a first shaped depression, a first external electrode on the outer surface of the first metal oxide layer, and a first internal electrode covering some or all of the first shaped depression, the first internal electrode having an edge portion that flares away from the first external electrode. The electrical device further includes a second MOV including a second metal oxide layer having an outer surface and an inner surface having a second shaped depression, a second external electrode on the outer surface of the second metal oxide layer, and the second internal electrode covering some or all of the second shaped depression, the second internal electrode having an edge portion that flares away from the second external electrode. The electrical device further includes a seal defined by the first and second shaped recesses and mounted between the inner surface of the first metal oxide layer and the inner surface of the second metal oxide layer to form a sealed chamber that encloses a gas therein, the sealed chamber with the gas and the first and second internal electrodes forming a gas discharge tube (GDT).

[0027] In some embodiments, the seal may be formed of an electrically insulating material such as glass. In some embodiments, the electrically insulating seal may be sized to be between at least the outer edge of the edge portion of the first internal electrode and the outer edge of the edge portion of the second internal electrode. In some embodiments, the electrically insulating material may have a dielectric strength greater than the dielectric strength of the gas present in the sealed chamber to reduce the possibility of dielectric breakdown between the ends of the edge portions. In some embodiments, the electrically insulating seal may be further sized to extend laterally inward and cover some or all of the edge portions of each of the first and second internal electrodes, thereby increasing the leak path length between the first and second internal electrodes.

[0028] In some embodiments, the seal may include a spacer, a first layer of electrically insulating material bonding one side of the spacer to the inner surface of the first metal oxide layer, and a second layer of electrically insulating material bonding the other side of the spacer to the inner surface of the second metal oxide layer. The electrically insulating material may include glass. The spacer may have a washer shape with outer lateral dimensions similar to the outer lateral dimensions of each metal oxide layer. The spacer may be formed of an electrically conductive material or an electrically insulating material.

[0029] In some embodiments, the first MOV may be a substantial mirror image of the second MOV with respect to a midplane between the first and second MOVs. In some embodiments, the edge portion of each internal electrode may include one or more straight segments, each extending laterally outward at an angle to form a flared shape when viewed in cross-sectional side view. In some embodiments, the edge portion of each internal electrode may include a curved segment extending laterally outward to form a flared shape when viewed in cross-sectional side view. In some embodiments, the curved segment may include a portion of a conic section or an exponential curve. For example, the curved segment may include a portion of a circle, such that the curved segment has a radius of curvature R.

[0030] In some embodiments, the electrical device may further include an emissive coating formed on each of the internal electrodes.

[0031] In some embodiments, each of the first and second metal oxide layers may include a sidewall, the sidewalls of the first and second metal oxide layers defining a sidewall of the electrical device, and in some embodiments, the first and second metal oxide layers may have substantially the same lateral dimension such that the sidewalls of the first and second metal oxide layers are substantially collinear.

[0032] In some embodiments, the device may further comprise a passivation coating mounted on a sidewall of each of the first and second metal oxide layers, the passivation coating configured to prevent or reduce the possibility of external arcing.

[0033] In some embodiments, each of the first and second metal oxide layers may include an outer edge on a respective inner surface, and in some embodiments, the outer edge of each of the first and second metal oxide layers may have a generally right-angled shape.

[0034] In some embodiments, the respective outer edges of either or both of the first and second metal oxide layers may include edge features dimensioned to form spaces to accommodate at least a portion of excess material associated with the seal, ie, the respective edge features of either or both of the first and second metal oxide layers may be dimensioned such that excess material associated with the seal does not extend outward beyond the sidewalls of the respective metal oxide layers.

[0035] In some aspects, the edge shape may include a chamfered edge shape or a beveled edge shape. For example, the beveled edge shape may include a curved bevel edge or a bevel edge having multiple straight segments.

[0036] In some embodiments, the outer edge of only one of the first and second metal oxide layers may include the respective edge features, hi some embodiments, the outer edge of each of both the first and second metal oxide layers may include the respective edge features.

[0037] In some embodiments, the edge shape of the first metal oxide layer may be a substantial mirror image of the edge shape of the second metal oxide layer relative to the midplane between the first and second metal oxide layers, hi some embodiments, the edge shape of the first metal oxide layer may differ in size and / or shape from the edge shape of the second metal oxide layer.

[0038] According to some embodiments, the present disclosure relates to a method for manufacturing an electrical device. The method includes forming or providing first and second metal oxide layers, each having an outer surface and an inner surface with a shaped depression. The method further includes forming an internal electrode covering some or all of the shaped depression in each of the first and second metal oxide layers, the internal electrode having an edge portion that flares away from the respective outer surfaces. The method further includes bonding the internal surfaces of the first metal oxide layer and the second metal oxide layer to form a sealed chamber defined by the first and second shaped depressions and containing a gas therein, the sealed chamber containing the gas and the first and second internal electrodes forming a gas discharge tube (GDT).

[0039] The method further includes forming an external electrode on an outer surface of each of the first and second metal oxide layers, wherein the first metal oxide layer and each of the external and internal electrodes form a first metal oxide varistor (MOV) on a first side of the GDT, and the second metal oxide layer and each of the external and internal electrodes form a second MOV on a second side of the GDT.

[0040] In some embodiments, the joining can include forming a seal with an electrically insulating material, such as glass, hi some embodiments, forming the seal can result in an electrically insulating material extending laterally inward to cover some or all of the edge portions of each of the internal electrodes.

[0041] In some embodiments, the method may further include forming an emissive coating over each inner electrode.

[0042] In some embodiments, forming or providing the first and second metal oxide layers may include forming or providing a sidewall on each of the first and second metal oxide layers, where the sidewall and an inner surface of each metal oxide layer form an outer edge. In some embodiments, the method may further include forming a passivation coating on the sidewall of each of the first and second metal oxide layers.

[0043] In some embodiments, forming or providing the sidewalls may include forming or providing a shape that is substantially perpendicular to each outer edge, hi some embodiments, forming or providing the sidewalls may include forming or providing an edge shape for each outer edge, the edge shape being dimensioned to form a space that accommodates at least a portion of excess material resulting from joining the inner surfaces of the first metal oxide layer and the second metal oxide layer.

[0044] In some embodiments, the assembly of the first MOV, GDT, and second MOV may be a unit of a plurality of similar units joined together in an array. In some embodiments, the method may further include separating the plurality of units into a plurality of separate units.

[0045] In some embodiments, the present disclosure relates to a metal oxide varistor (MOV) comprising a metal oxide layer having a first surface and a second surface, and first and second electrodes mounted on the first and second surfaces of the metal oxide layer, each electrode including a laterally inner portion and an edge portion, and at least one of the first and second electrodes configured such that a parameter associated with the MOV at an edge of the edge portion of each electrode has a magnitude that is within a selected range of the magnitude of the parameter at a center of the electrode.

[0046] In some embodiments, the parameter may include temperature, electric field strength, or surface charge density. In some embodiments, the selected range includes ±50%, ±40%, ±30%, ±20%, or ±10% of the magnitude of the parameter at the center of the electrode.

[0047] For purposes of summarizing the disclosure, certain aspects, advantages, and novel features of the present invention are described herein. It is to be understood that not all such advantages need be achieved in accordance with any particular embodiment of the invention. Thus, the present invention may be embodied or practiced to achieve or optimize one advantage or group of advantages as taught herein, without necessarily achieving other advantages as may be taught or suggested herein. [Brief explanation of the drawings]

[0048] [Figure 1] 1 is a cross-sectional side view of a conventional metal oxide varistor (MOV) having a metal oxide layer with first and second electrodes mounted on first and second sides of the metal oxide layer. [Figure 2] 2A-2C illustrate examples of electric fields that may be established at the edge of the MOV of FIG. 1. [Figure 3] FIG. 3 shows an example of a MOV having similar edge portions to the example of FIG. 2, but with one of the two electrodes having a larger lateral dimension than the other electrode. [Figure 4] 2 is a perspective view of the MOV of FIG. 1 implemented in the form of a circular disk. [Figure 5] FIG. 5 shows a temperature plot of the edge portion of the MOV of FIG. 4. [Figure 6] FIG. 10 shows an example of a MOV with improved edge configuration. [Figure 7] FIG. 7 is a diagram showing an enlarged view of an edge portion of the MOV in FIG. 6. [Figure 8] FIG. 10 shows another example of a MOV with improved edge configuration. [Figure 9] FIG. 9 is a diagram showing an enlarged view of an edge portion of the MOV in FIG. 8. [Figure 10] FIG. 10 illustrates that in some embodiments, a MOV having one or more features as described herein can be implemented in a symmetrical shape with respect to the first and second electrodes. [Figure 11] FIG. 10 illustrates that in some embodiments, a MOV having one or more features as described herein can be implemented to have an asymmetric shape relative to the first and second electrodes. [Figure 12] FIG. 1 illustrates that in some embodiments, a MOV having one or more features as described herein may be implemented in a disc-shaped format. [Figure 13A] FIG. 1 illustrates an example of a process that can be used to fabricate a MOV having one or more features as described herein. [Figure 13B] FIG. 1 illustrates an example of a process that can be used to fabricate a MOV having one or more features as described herein. [Figure 13C] FIG. 1 illustrates an example of a process that can be used to fabricate a MOV having one or more features as described herein. [Figure 13D] FIG. 1 illustrates an example of a process that can be used to fabricate a MOV having one or more features as described herein. [Figure 14A]FIG. 1 illustrates an example of a process that can be used to fabricate multiple MOVs, where at least some of the process steps are performed while multiple units are mounted in an array. [Figure 14B] FIG. 1 illustrates an example of a process that can be used to fabricate multiple MOVs, where at least some of the process steps are performed while multiple units are mounted in an array. [Figure 14C] FIG. 1 illustrates an example of a process that can be used to fabricate multiple MOVs, where at least some of the process steps are performed while multiple units are mounted in an array. [Figure 14D] FIG. 1 illustrates an example of a process that can be used to fabricate multiple MOVs, where at least some of the process steps are performed while multiple units are mounted in an array. [Figure 14E] FIG. 1 illustrates an example of a process that can be used to fabricate multiple MOVs, where at least some of the process steps are performed while multiple units are mounted in an array. [Figure 14F] FIG. 1 illustrates an example of a process that can be used to fabricate multiple MOVs, where at least some of the process steps are performed while multiple units are mounted in an array. [Figure 15] FIG. 10 shows a comparison between a conventional MOV without improved edge configuration and a MOV with improved edge configuration. [Figure 16A] FIG. 10 illustrates an example of variations in edge effects that may depend on variations in edge shapes of MOVs. [Figure 16B] FIG. 10 illustrates an example of variations in edge effects that may depend on variations in edge shapes of MOVs. [Figure 17] FIG. 10 illustrates that in some embodiments, edge portions of the electrodes of a MOV can be configured such that the edge parameters of the MOV are within a selected range relative to the center parameters of the MOV. [Figure 18A]FIG. 1 illustrates that a MOV having one or more features as described herein can be implemented in a variety of form factors. [Figure 18B] FIG. 1 illustrates that a MOV having one or more features as described herein can be implemented in a variety of form factors. [Figure 18C] FIG. 1 illustrates that a MOV having one or more features as described herein can be implemented in a variety of form factors. [Figure 19] FIG. 10 illustrates that in some embodiments, an MOV having one or more features as described herein can include more than one set of electrodes implemented for a given metal oxide layer, with at least some of such sets of electrodes having an improved edge configuration. [Figure 20] 20A-20C show examples of how the multi-electrode MOV of FIG. 19 can be configured as an electrical device. [Figure 21] FIG. 10 illustrates that in some embodiments, a MOV having one or more features as described herein can be combined with one or more other electrical devices to provide a combined device. [Figure 22] FIG. 22 shows that in some embodiments, the one or more other electrical devices of FIG. 21 can be one or more gas discharge tubes (GDTs). [Figure 23] FIG. 1 is a circuit representation of a GDT / MOV device comprising a series arrangement of a first MOV, a GDT, and a second MOV, where the first MOV has one of its electrodes also functioning as one of the electrodes of the GDT, and the second MOV has one of its electrodes also functioning as the other of the electrodes of the GDT. [Figure 24] FIG. 1 is a perspective cutaway view of a GDT / MOV device having one or more features as described herein. [Figure 25A] FIG. 25 is a side cross-sectional view of the GDT / MOV device of FIG. 24. [Figure 25B] FIG. 25B is an enlarged view of one side of the cross-sectional side view of FIG. 25A. [Figure 26A] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 26B] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 26C] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 26D] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 26E] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 26F] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 26G] FIG. 26 illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 24 and 25. [Figure 27A] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27B] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27C] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27D] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27E] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27F] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27G] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 27H] FIG. 1 illustrates an example of a process that may be implemented to fabricate a plurality of MOVs, where at least some of the process steps are performed while the plurality of units are mounted in an array format. [Figure 28] FIG. 1 is a cross-sectional side view of a GDT / MOV device having one or more features as described herein, where first and second metal oxide layers are joined with a seal to define an outer wall. [Figure 29] 29 illustrates that in some cases, material associated with the seal of the GDT / MOV device of FIG. 28 may protrude outward from the outer wall. [Figure 30A] FIG. 1 is a perspective cutaway view of a GDT / MOV device having an edge configuration that can eliminate or reduce outward protrusion of the sealing material. [Figure 30B] FIG. 30B is a side cross-sectional view of the GDT / MOV device of FIG. 30A. [Figure 31A] FIG. 30C is a close-up view of an example of an outer edge portion of the GDT / MOV device of FIG. 30B. [Figure 31B] FIG. 31B shows an example of the outer edge portion of FIG. 31A with the sealing material omitted. [Figure 32A] 1A-1C illustrate non-limiting examples of edge configurations of GDT / MOV devices that can eliminate or reduce outward protrusion of sealing material. [Figure 32B]1A-1C illustrate non-limiting examples of edge configurations of GDT / MOV devices that can eliminate or reduce outward protrusion of sealing material. [Figure 32C] 1A-1C illustrate non-limiting examples of edge configurations of GDT / MOV devices that can eliminate or reduce outward protrusion of sealing material. [Figure 32D] 1A-1C illustrate non-limiting examples of edge configurations of GDT / MOV devices that can eliminate or reduce outward protrusion of sealing material. [Figure 32E] 1A-1C illustrate non-limiting examples of edge configurations of GDT / MOV devices that can eliminate or reduce outward protrusion of sealing material. [Figure 32F] 1A-1C illustrate non-limiting examples of edge configurations of GDT / MOV devices that can eliminate or reduce outward protrusion of sealing material. [Figure 33A] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. [Figure 33B] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. [Figure 33C] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. [Figure 33D] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. [Figure 33E] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. [Figure 33F] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. [Figure 33G] FIG. 3C illustrates an example of a process that can be implemented to fabricate the GDT / MOV device of FIGS. 30A and 30B. DETAILED DESCRIPTION OF THE INVENTION

[0049] Headings, if any, herein are for convenience only and do not necessarily affect the scope or intent of the claimed invention.

[0050] Disclosed herein are various examples of devices and methods related to metal oxide varistors (MOVs). MOV devices are known to be popular overvoltage protection devices. Distinguishing features of such MOVs include operating voltage ratings and surge current ratings. In many implementations, MOVs are configured as disk-shaped devices with radial leads. The thickness of such disks typically corresponds to the voltage rating of the MOV device, and the diameter of the disk is roughly proportional to the surge current rating.

[0051] 1 is a cross-sectional side view of a conventional MOV 10 having a metal oxide layer 14 (e.g., disk-shaped) with first and second electrodes 12, 16 mounted on first and second sides of the metal oxide layer 14. When the potential difference between the two electrodes (12, 16) is less than the rated voltage of the MOV, the metal oxide layer 14 remains electrically non-conductive. However, if, during an event (e.g., an overvoltage event, a surge current event, etc.), the potential difference between the two electrodes (12, 16) exceeds the rated voltage of the MOV, the metal oxide layer 14 becomes electrically conductive, thereby diverting current associated with the event through the MOV 14 and away from the electrical components it is protecting.

[0052] In the example of Figure 1, the two electrodes 12, 16 are mounted to form an essentially parallel configuration. In such a configuration, an electric field is established between the two electrodes 12, 16 when a potential difference exists between them. Such an electric field typically has a substantially uniform field strength near the lateral center of the metal oxide layer 14. However, at or near the edge regions (shown as 20 in Figure 1), the charge density on each electrode, i.e., the field strength near the electrode, increases.

[0053] FIG. 2 illustrates an example of an electric field 24 that may be established at an edge portion 20 of the MOV 10 of FIG. 1. In FIG. 2, the first electrode 12 is shown as having an edge 22, and the second electrode 16 is shown as having a corresponding edge 26. Note that in the example of FIG. 2, the electric field 24 is shown as originating from the first electrode 12 to the second electrode 16 (e.g., with the first electrode 12 having a net positive charge and the second electrode 16 having a net negative charge). However, it will be understood that the electric field 24 may also be oriented in other directions, such as originating from the second electrode 16 to the first electrode 12. In situations where the MOV 10 is subjected to alternating current (AC), the electric field that is established between the first and second electrodes 12, 16 may alternate in direction.

[0054] 1 and 2, the electric field strength at or near the lateral center of the metal oxide layer 14 can be approximated as E=-ΔV / a, where the quantity ΔV is the potential difference and the quantity a is the separation distance between the two parallel electrodes 12, 16. In the edge regions near the ends of each electrode (32 for the first electrode 12 and 36 for the second electrode 16), the magnitude of the electric field is generally greater than the magnitude of the uniform field strength discussed above. Therefore, such edge regions are more prone to failure.

[0055] For example, a high density of charge at the edge of the electrode (and therefore a high electric field strength in the metal oxide near the edge of the electrode) can cause current to concentrate near the edge of the electrode, resulting in overheating and damage to the MOV. Often, such overheating and damage to the MOV can result in the formation of holes that partially or completely burn through the metal oxide material. More specifically, the edge region 32 associated with the first electrode edge 22 can be damaged by the holes, and similarly, the edge region 36 associated with the second electrode edge 26 can be damaged by the holes.

[0056] 2, the first and second electrodes 12, 16 are assumed to have the same shape and lateral dimensions, and therefore the electric field pattern may be approximately symmetrical about the mid-plane between the two electrodes, and each of the edge regions 32, 36 may be susceptible to the aforementioned damage.

[0057] FIG. 3 illustrates an example of an MOV having an edge portion 20, similar to the example of FIG. 2, except that in FIG. 3, one of the two electrodes 12, 16 has a larger lateral dimension than the other electrode. For example, the second electrode 16 is shown to have a larger lateral dimension than the lateral dimension of the first electrode 12. Thus, an electric field established between the two electrodes 12, 16 may cause an electric field at the edge region 32 (associated with the first electrode edge 22) to be stronger than the edge region associated with the second electrode 16. In such a configuration, the edge region 32 associated with the first electrode 12 may be more susceptible to damage than the edge region associated with the second electrode 16.

[0058] Figure 4 is a perspective view of the MOV 10 of Figure 1 implemented in the form of a circular disk. An edge portion of such a MOV is designated 20, and Figure 5 shows a temperature plot of such an edge portion obtained during modeling of surge current conduction. Hot spots are seen to exist near the edge of each electrode (e.g., hot spot 40a associated with first electrode 12 and hot spot 40b associated with second electrode 16). As described herein, such hot spots having temperatures at or near the value designated as 41 (e.g., about 1350°C) can potentially damage the MOV.

[0059] In some embodiments, a metal oxide varistor (MOV) can include first and second electrodes mounted on first and second sides of a metal oxide layer, and either or both of such electrodes can be configured to cause the MOV to have different (e.g., smaller) electrode edge effects than those in similarly sized MOVs having substantially planar electrodes arranged substantially parallel.

[0060] For ease of explanation, the MOVs of Figures 2 and 3 can be considered examples of MOVs having substantially planar electrodes arranged substantially parallel.

[0061] For convenience of explanation, electrode edge effects may include, for example, the magnitude of the electric field strength, the magnitude of the charge density, the magnitude of the temperature at or near the edge of the electrode, etc. Such electrode edge effects may be obtained by simulation, modeling, measurement, extrapolation, interpolation, or a combination thereof.

[0062] In some embodiments, the aforementioned MOV with reduced electrode edge effects can include first and second electrodes configured such that the edge of the first electrode is separated from the second electrode by an edge separation distance that is greater than the center separation distance at the lateral center of the first electrode. For ease of explanation, it will be understood that each of such edge and center separation distances is along a direction perpendicular to the midplane between the two electrodes. Thus, in each of the exemplary MOVs of Figures 2 and 3, the center separation distance is the same as the edge separation distance (a) for the first electrode 12.

[0063] Figure 6 shows that in some embodiments, MOV 100 can include a metal oxide layer 104 having a first and second side. A first electrode 102 can be implemented on the first side of metal oxide layer 104, and a second electrode 106 can be implemented on the second side of metal oxide layer 104. Figure 7 is an enlarged view of an edge portion 110 of MOV 100 of Figure 6. In the enlarged view of Figure 7, metal oxide layer 104 is shown to have an edge shape similar to the edge shape in the side view of Figure 6.

[0064] 6 and 7, each of the first and second electrodes 102, 106 can include a laterally inner portion (also referred to as an inner portion) and a laterally outer portion (also referred to as an outer portion or edge portion). The inner portions of the first and second electrodes 102, 106 can include respective planar surfaces that are substantially parallel and opposed to each other. The outer portions of the first and second electrodes 102, 106 can be joined to the respective inner portions and configured to flare away from each other at an angle.

[0065] 6 and the close-up view of edge portion 110 of MOV 100 in FIG. 7, it can be seen that portions 112a and 112b represent the inner and outer portions, respectively, of first electrode 102. Similarly, portions 116a and 116b represent the inner and outer portions, respectively, of second electrode 106.

[0066] 7, portion 112b is shown extending outward from portion 112a of the first electrode 102 by an amount a3 and away from the second electrode 106 (from portion 112a) by an amount a2, forming an angle θ with respect to portion 112a. In some embodiments, the second electrode 106 may be dimensioned to be a substantial mirror image of the first electrode 102 with respect to the midplane between the two electrodes. Configured in the foregoing manner, the center separation distance between the two electrodes 102, 106 is designated as a1, and the edge separation distance between the two electrodes 102, 106 is designated as a4, where a4 is greater than a1.

[0067] 6 and 7, the aforementioned shapes of electrodes 102, 106 can be achieved by forming appropriately shaped depressions on each side of a planar layer of metal oxide. Examples relating to processes involving the formation of such shaped depressions are described in more detail herein.

[0068] Note that in the examples of Figures 6 and 7, the aforementioned shapes of electrodes 102, 106 refer to the shape of the electrode surface facing the other electrode. Thus, in such exemplary configurations, the material forming the electrode (102 or 106) can be dispensed into the shaped depressions on each side of metal oxide layer 104 to form a layer that conformally covers some or all of the surface of the shaped depressions and partially or completely fills the shaped depressions, for example. In the example configurations of Figures 6 and 7, each electrode is depicted as having a generally uniform thickness that substantially conformally covers the entire surface of the respective shaped depressions and the electrode material partially fills the shaped depressions. In other examples, the electrodes can have a thickness profile (e.g., the electrode thickness at the center is greater than the electrode thickness at the edges) that substantially covers the entire surface of the respective shaped depressions and leads to the electrode material filling the shaped depressions more (e.g., completely filling the shaped depressions).

[0069] In the examples of Figures 6 and 7, edge portion 110 of MOV 100 includes straight portions 112b, 116b (as viewed in side cross-section) of respective electrodes 102, 106 that extend in a flared manner. It will be understood that in some embodiments, such flared edges of electrodes 102, 106 can also be implemented using two or more straight portions for each electrode. For example, portion 112b of Figure 7 can be replaced with two portions, having a first portion extending from portion 112a at a first angle (relative to portion 112a), followed by a second portion extending from the first portion at a second angle (relative to portion 112a) that is different from the first angle. In some embodiments, the second angle can be greater than the first angle to continue the flared pattern.

[0070] In the examples described above with reference to Figures 6 and 7, the flared edges of the electrodes 102, 106 are implemented using one or more straight segments (when viewed in a cross-sectional side view). Figures 8 and 9 show that in some embodiments, the edge portion 110 of the MOV 100 can be implemented using a curved shape. More specifically, the MOV 100 can include a metal oxide layer 104 having first and second sides, and a first electrode 102 having a curved edge shape (when viewed in a cross-sectional side view) can be implemented on the first side of the metal oxide layer 104, and a second electrode 106 having a curved edge shape can be implemented on the second side of the metal oxide layer 104.

[0071] 8 and 9, each of the first and second electrodes 102, 106 can include a lateral inner portion (also referred to as an inner portion) and a lateral outer portion (also referred to as an outer portion or edge portion). The inner portions of the first and second electrodes 102, 106 can include respective planar surfaces that are substantially parallel and opposed to each other. The outer portions of the first and second electrodes 102, 106 can be joined to the respective inner portions and configured to curvedly flare away from each other.

[0072] 8 and the close-up view of edge portion 110 of MOV 100 in FIG. 9, it can be seen that the portions generally designated as 117 and 118 may represent outer portions of first and second electrodes 102, 106, respectively.

[0073] In some embodiments, each of the outer portions 117, 118 of the first and second electrodes 102, 106 can have a shape based on a conic section (when viewed in cross-sectional side view), including a hyperbola, a parabola, or an ellipse. For example, in FIG. 9, the shape of the outer portion 117 can be based on a portion of a circle 119, which is a type of ellipse, for purposes of explanation herein. Such a circle can have a radius R that can be selected to create a desired amount of flare in the corresponding electrode 102.

[0074] 9, the second electrode 106 may be sized to be a substantial mirror image of the first electrode 102 with respect to the midplane between the two electrodes. Configured in the manner described above, the center separation distance is designated as a1 and the edge separation distance is designated as a4, with a4 being greater than a1.

[0075] 8 and 9, the aforementioned shapes of electrodes 102, 106 can be obtained by forming appropriately shaped depressions on each side of a planar layer of metal oxide. Examples relating to processes involving the formation of such shaped depressions are described in more detail herein.

[0076] Note that in the examples of Figures 8 and 9, the aforementioned shapes of electrodes 102, 106 refer to the shape of the electrode surface facing the other electrode. Thus, in such an exemplary configuration, the material forming the electrode (102 or 106) can be dispensed into the shaped depressions on each side of metal oxide layer 104 to form a layer that conformally covers some or all of the surface of the shaped depression and partially or completely fills the shaped depressions, for example. In the example configurations of Figures 8 and 9, each electrode is depicted as having a generally uniform thickness that substantially conformally covers the entire surface of the respective shaped depression and the electrode material partially fills the shaped depressions. In other examples, the electrodes can have a thickness profile (e.g., the electrode thickness at the center is greater than the electrode thickness at the edges) that substantially covers the entire surface of the respective shaped depression and leads to the electrode material filling the shaped depressions more (e.g., completely filling the shaped depressions).

[0077] In the examples of Figures 6 and 7, the edge shape of each electrode is depicted as including one or more straight segments. In the examples of Figures 8 and 9, the edge shape of each electrode is depicted as including curved segments. It will be understood that in some embodiments, the edge shape can include straight segments, curved segments, or any combination thereof.

[0078] In each of the two examples of Figures 6 and 7 (electrode edge shapes with straight portions) and Figures 8 and 9 (curved electrode edge shapes), the electrodes of corresponding pairs are assumed to be substantial mirror images of each other with respect to the midplane between the two electrodes. It will be understood that in some embodiments, such symmetry may or may not exist while still providing a desired edge configuration of the electrodes.

[0079] For example, Figure 10 shows a symmetrical configuration of MOV 100, which may represent the embodiments of Figures 6 and 7 and Figures 8 and 9. In such a symmetrical configuration, the overall dimension d1 of the electrodes may be, for example, the overall diameter (e.g., in a plan view of MOV 100) of either electrode.

[0080] In another example, Figure 11 illustrates that in some embodiments, the first and second electrodes 102, 106 of the MOV need not be symmetrical about the midplane between the two electrodes. In the example of Figure 11, the first electrode 102 can be configured to form a flared edge similar to the examples of Figures 6-9, while the second electrode 106 has a substantially flat configuration similar to the second electrode (16) in the example of Figure 3. Thus, the first electrode 102 can have an overall dimension of d1, and the second electrode 106 can have an overall dimension of d2 that is different from d1 (e.g., d2 > d1). As with the previous configurations of electrodes, the center separation distance is indicated as a1 and the edge separation distance is indicated as a4, where a4 is greater than a1.

[0081] 12 illustrates that, in some embodiments, a MOV 100 having one or more features as described herein can be implemented in a disk-shaped format. For example, a disk-shaped metal oxide layer 104 can include first and second shaped depressions formed on first and second sides of the metal oxide layer 104, and such shaped depressions can be partially or completely covered by the respective electrodes 102, 106. The resulting first and second electrodes 102, 106 can thus have respective surfaces that face each other and form flared edge profiles as described herein.

[0082] In the example of Figure 12, the shaped depressions and corresponding electrodes 102, 106 are depicted as being similar to the straight electrode edge shape examples of Figures 6 and 7. However, it will be understood that the disk-shaped example of Figure 12 can also use the curved electrode edge shape configurations of Figures 8 and 9 and / or the asymmetric configuration of Figure 11.

[0083] 12, Figures 13A-13D illustrate an exemplary process that can be used to fabricate an MOV having one or more features as described herein. In some embodiments, such a process can include providing or forming a flat, disk-shaped metal oxide 130, as shown in Figure 13A.

[0084] 13B, a first shaped depression 131 can be formed on a first side of metal oxide 130, and a second shaped depression 132 can be formed on a second side of metal oxide 130 to form assembly 133. In some embodiments, each such shaped depression can be formed by, for example, applying pressure with a shaped tool, removing material, or some combination thereof.

[0085] 13A and 13B, it is envisioned that shaped depressions (131, 132) are formed from an already formed flat metal oxide disk 130. In some embodiments, the shape of FIG. 13B can be formed directly without first forming a flat disk.

[0086] For example, the shape of FIG. 13B (with shaped depressions 131 and 132) can be pressed directly from powder under high pressure. In some embodiments, such powder can include materials that create metal oxide functionality (e.g., ZnO and dopants) and one or more binder materials (e.g., organic binder materials). Following such pressing, a process step can be performed in which the binder material is burned off by heating the pressed assembly above its ignition temperature, thereby leaving only the ceramic material and traces of the binder material. This ceramic state is sometimes referred to as the green state. The green state ceramic assembly is then sintered at a sufficiently high temperature to a hardened state. Such a sintering process can reduce the size of the ceramic assembly (e.g., by about 20%). Thus, in some embodiments, assembly 133 of FIG. 13B can be such a sintered ceramic assembly.

[0087] 13C, a first electrode 134 can be formed on a first surface of the metal oxide 130 to partially or completely cover the first shaped depression (131 in FIG. 13B), and a second electrode 135 can be formed on a second surface of the metal oxide 130 to partially or completely cover the second shaped depression (132 in FIG. 13B) to form an assembly 136. In some embodiments, each such electrode can be formed of, for example, silver, copper, tungsten, nickel, or silver overplated with tin. Formation of such electrodes can be achieved by, for example, screen printing, pad printing, or evaporation / photoetching techniques.

[0088] In the process stage of Figure 13D, the assembly 136 of Figure 13C is subjected to one or more curing processes (e.g., oven bake processes) to bond the electrode metal to the metal oxide, thereby obtaining a MOV 100 having one or more characteristics as described herein.

[0089] The exemplary process of Figures 13A-13D depicts the fabrication of a single MOV. In some embodiments, multiple MOVs can be fabricated in an array format, and such MOVs can be separated into multiple individual MOVs. Figures 14A-14F show an example of such a fabrication process in which multiple units are attached in an array format, but at least some of the process steps are performed.

[0090] For example, Figure 14A illustrates a process stage where a metal oxide plate may be provided or formed. Such a plate is shown to include multiple units 150, each unit ultimately becoming a MOV.

[0091] 14B, a first shaped depression 151 may be formed on a first side of the metal oxide for each unit 150, and a second shaped depression 152 may be formed on a second side of the metal oxide for each unit 150 to form an assembly 154. In some embodiments, each such shaped depression may be formed as described herein with reference to FIG.

[0092] 14C, a first electrode 155 can be formed on the metal oxide first surface of each unit 150 to partially or completely cover each first shaped depression, and a second electrode 156 can be formed on the metal oxide second surface of each unit 150 to partially or completely cover each second shaped depression, to form assembly 158. In some embodiments, each such electrode can be formed as described herein with reference to FIG.

[0093] 14D, the assembly 158 of FIG. 14C can undergo one or more processes to separate each unit 150 from the array 162. For example, a separation process, such as stamping, cutting, etc., can be performed along the unit boundaries 160 to remove the units 150 from the array 162.

[0094] At the process stage of Figure 14E, the separated units from the process stage of Figure 14D are shown as 166, each having first and second electrodes 155, 156 formed over first and second shaped depressions in metal oxide layer 157. Such metal oxide layer is also shown to include sidewalls 164 resulting from the separation process.

[0095] In the process stage of FIG. 14F, the separated units 166 of FIG. 14E can be subjected to one or more hardening processes (e.g., sintering processes) to harden the electrodes and / or metal oxides, thereby obtaining multiple MOVs 100 having one or more characteristics as described herein.

[0096] As described herein with reference to FIGS. 1-5, conventional MOVs can suffer from one or more hot spots at or near the edges of their electrodes. FIG. 15 shows a side-by-side comparison of such a conventional MOV 10 (similar to the example of FIG. 4) with an MOV 100 having flared edge electrodes described herein (e.g., similar to the examples of FIGS. 8 and 9). Beneath the conventional MOV 10 is a temperature plot of the edge of such an MOV obtained during surge current conduction modeling. Hot spots can be seen near the edges of each electrode. Such hot spots are shown as 200a for the upper electrode and 200b for the lower electrode, and each hot spot is shown to have a relatively high temperature value (e.g., approximately 1350°C), indicated as 202, significantly higher than the average temperature of the interior volume of the metal oxide between the electrodes.

[0097] 15, below MOV 100 is a temperature plot of a portion of such an MOV obtained during surge conduction modeling. It can be seen that there are desirably no hot spots at or near the edges of each electrode. More specifically, the regions near the edges of each electrode are shown to have temperature values, designated as 206, that are no higher than the average temperature of the volume 204 of metal oxide between the electrodes.

[0098] In the example of FIG. 15 , the flared edge configuration of the MOV 100 is achieved by a curved edge shape with a finite radius of curvature R. In that context, a non-flared configuration of the MOV 10 with a straight edge shape can be considered to have an infinite radius of curvature. Therefore, when the radius of curvature of the curved electrode edge shape is large, edge effects such as hot spots can be expected to be more pronounced compared to curved edge shapes with smaller radii of curvature. Figures 16A and 16B, which show temperature plots obtained during modeling of surge current conduction, clearly demonstrate such effects.

[0099] In the example of FIG. 16A, the curved edge shape of each electrode has a radius of curvature R of approximately 1 mm, and in the example of FIG. 16B, the curved edge shape of each electrode has a radius of curvature R of approximately 3 mm. When R=1 mm (FIG. 16A), there are no observable hot spots at the edges of the electrodes. When R=3 mm (FIG. 16B), there are regions 210a, 210b of elevated temperature near the electrodes. Such elevated temperature spots may or may not be within certain design limits, but they are at a lower temperature than hot spots 200a, 200b of the MOV 10 in the example of FIG. 15.

[0100] Based on the examples of FIGS. 16A and 16B, it can be seen that there may be one or more preferred geometric shapes that can bring one or more desired characteristics of the MOV. For example, referring to the configuration of the edge portion in FIG. 7, the dimension a2 can be a ratio to the central separation distance a1 such that a2 = f × a1 (f is a ratio). In some embodiments, the ratio f can have a value within the range of 0.01 < f < 0.40, 0.05 < f < 0.25, or 0.08 < f < 0.21. In some embodiments, the ratio f can have a value of about 0.2. It will be understood that other values or ranges of f can also be used.

[0101] In other examples, referring to the configuration of the edge portion in FIG. 7, the dimension a3 can be a ratio to the overall diameter D of the MOV such that a3 = f × D (f is a ratio). In some embodiments, the ratio f can have a value within the range of 0.001 < f < 0.05, 0.005 < f < 0.045, 0.015 < f < 0.035, or 0.02 < f < 0.03. In some embodiments, the ratio f can have a value of about 0.025. In some embodiments, the ratio f can have a value within the range of 0.02 < f < 0.40, or 0.05 < f < 0.20. In some embodiments, the ratio f can have a value of about 0.14, about 0.10, or about 0.08. It will be understood that other values or ranges of f can also be used.

[0102] Table 1 lists the various dimensions of a number of exemplary MOV devices implemented in a disk form having electrodes with a flared edge portion similar to the configurations of FIGS. 6 and 7. In Table 1, such MOV devices are also referred to as 10 mm, 14 mm, and 20 mm devices, and the listed dimensions are approximate values in millimeters. The quantity D refers to the overall diameter of the corresponding MOV device (100 in FIG. 6), the electrode diameter refers to the overall diameter of each electrode of the MOV device (102 or 106 in FIG. 6), the flat portion diameter refers to the diameter of the parallel portion of the corresponding electrode (112a or 116a in FIG. 7), and the quantities a3, a2, and a1 are as shown in FIG. 7.

[0103]

Table 1

[0104] In still other examples, referring to the configuration of the edge portion in FIG. 9, the radius of curvature R can be such that R = m × a1 (where m is a real number in the range of 0.1 < m < 2.0, 0.2 < m < 1.5, 0.3 < m < 1.0, 0.4 < m < 0.9, or 0.5 < m < 0.8) based on the central separation distance a1. In some embodiments, for the example where the central separation distance a1 is about 1.6 mm, the value of R can be within the range of 0.5 < m < 0.8 so that R can be in the range of 0.8 mm < R < 1.2 mm. It will be understood that other values or ranges of m and / or R can also be used.

[0105] In the foregoing examples of dimensional ranges, the edge configuration (e.g., a2, a3, or R) can depend on other dimensions associated with the corresponding MOV. It will be understood that in some embodiments, the dimensions of one or more edge configurations can be based on the operating parameters or operating conditions of the MOV rather than directly depending on other dimensions.

[0106] For example, FIG. 17 shows a MOV100 similar to the MOV in FIG. 8. Such a MOV can have parameters such as temperature, electric field strength, surface charge density, etc. in or near the electrode. Thus, the parameter at or near the center of the electrode 102 is shown as 212 (also referred to herein as the central parameter), and the parameter at or near the edge of the electrode 102 is shown as 214 (also referred to herein as the edge parameter).

[0107] In some embodiments, referring to FIG. 17, the edge portion of the electrode can be configured such that the magnitude of the edge parameter is within a selected range with respect to the magnitude of the central parameter (e.g., the radius of curvature of the curved end shape or the angle and length of the straight portion of the end shape).

[0108] Thus, in some embodiments, the edge parameters of the MOV may have a magnitude that is, for example, within ±50% of the magnitude of the central parameter, within ±40% of the magnitude of the central parameter, within ±30% of the magnitude of the central parameter, within ±20% of the magnitude of the central parameter, or within ±10% of the magnitude of the central parameter.

[0109] If the parameter of the MOV is temperature, the edge temperature of the MOV can have a magnitude within ±50% of the magnitude of the center temperature, within ±40% of the magnitude of the center temperature, within ±30% of the magnitude of the center temperature, within ±20% of the magnitude of the center temperature, or within ±10% of the magnitude of the center temperature, for example.

[0110] When the parameter of the MOV is electric field strength, the edge electric field strength of the MOV may have a magnitude, for example, within ±50% of the magnitude of the center electric field strength, within ±40% of the magnitude of the center electric field strength, within ±30% of the magnitude of the center electric field strength, within ±20% of the magnitude of the center electric field strength, or within ±10% of the magnitude of the center electric field strength.

[0111] When the parameter of the MOV is surface charge density, the edge charge density of the MOV can have a magnitude that is, for example, within ±50% of the magnitude of the central surface charge density, within ±40% of the magnitude of the central surface charge density, within ±30% of the magnitude of the central surface charge density, within ±20% of the magnitude of the central surface charge density, or within ±10% of the magnitude of the central surface charge density.

[0112] It will be appreciated that other values ​​or ranges for the aforementioned parameters may also be used, as may other parameters related to MOV.

[0113] 18A-18C illustrate that MOVs having one or more features as described herein can be implemented in various form factors. For example, FIG. 18A illustrates an MOV 100 having a disk-shaped metal oxide layer 104 and circular-shaped electrodes (first electrode 102 is shown, second electrode 106 is hidden).

[0114] In another example, the MOV 100 may have a rectangular metal oxide layer 104 and a circular electrode, as shown in Figure 18B. As in the example of Figure 18A, the first electrode 102 is shown and the second electrode 106 is hidden.

[0115] In yet another example, as shown in Figure 18C, the MOV 100 can have a rectangular metal oxide layer 104 and a rectangular electrode. As in the example of Figure 18A, the first electrode 102 is shown, and the second electrode 106 is hidden. In the example of Figure 18C, each corner of the rectangular electrode 102 (and similarly of the electrode 106) may be rounded to reduce the effect of sharp corners (e.g., right-angled corners).

[0116] 18A-18C, a cross-sectional side view of such a device (e.g., along a midline through the center of each device) may include any of the exemplary edge configurations described with reference to Figures 6-11, 13, and 14. It will therefore be understood that MOVs having edge configurations as described herein may be implemented in devices having a variety of side shapes, including the examples of Figures 18A-18C.

[0117] It should also be noted that various examples are described herein in the context of the edge of an electrode being an edge of the outer periphery. However, there may be electrode configurations in which the edge is laterally inward of the outer periphery. For example, consider an electrode having an annular shape when viewed from the electrode side of a corresponding MOV device (e.g., a plan view such as FIGS. 18A-18C). Such an annular-shaped electrode includes an outer edge at the outer periphery and an inner edge at the inner ring. Thus, it will be understood that one or more features of the present disclosure can be implemented with respect to any edge, including an outer edge, an inner edge, or any combination thereof.

[0118] In various examples described herein with reference to Figures 1-18, the MOVs are depicted as having one set of electrodes implemented on a given layer of metal oxide. It will be understood that in some embodiments, a given layer of metal oxide can include multiple sets of electrodes.

[0119] For example, FIG. 19 illustrates an MOV 100 having a metal oxide layer 104 and multiple sets of electrodes mounted to the metal oxide layer 104. A first set of electrodes can include a first electrode 102a and a second electrode 106a (hidden), a second set of electrodes can include a first electrode 102b and a second electrode 106b (hidden), a third set of electrodes can include a first electrode 102c and a second electrode 106c (hidden), and a fourth set of electrodes can include a first electrode 102d and a second electrode 106d (hidden). In some embodiments, some or all of such sets of electrodes can include edge configurations as described herein. It will be understood that an MOV can include more or fewer sets of electrodes than the four example sets of FIG. 19.

[0120] Figure 20 shows an example of how the multiple-set electrode MOV 100 of Figure 19 can be configured as an electrical device 300. For example, four sets of first electrodes 102 can be electrically connected via conductive features 304, and such connected first electrodes can be electrically connected to a first terminal 306. Similarly, four sets of second electrodes (106) can be electrically connected via conductive features, and such connected second electrodes can be electrically connected to a second terminal 308. Figure 20 also shows that the MOV 100 can include a filler material 302, for example, to protect the electrodes.

[0121] 21 illustrates that, in some embodiments, a MOV 100 having one or more features as described herein can be combined with one or more other electrical devices 402 to provide an integrated device 400. In some embodiments, such a combination of a MOV with another electrical device can include an electrode of the MOV 100 electrically connected to an electrode of the other electrical device 402. In some embodiments, such a combination of a MOV with another electrical device can include an electrode of the MOV being shared as an electrode of the other electrical device.

[0122] Figure 22 illustrates that in some embodiments, one or more other electrical devices of Figure 21 can be one or more gas discharge tubes (GDTs). For example, integrated device 400 can include MOVs mounted on both sides of a GDT. Thus, in some embodiments, integrated device 400 can include a first MOV 100a, a GDT 402, and a second MOV 100b arranged in series. Examples related to such integrated devices are described in more detail herein.

[0123] Among others, International Publication No. WO 2020 / 047381 (International Application No. PCT / 2019 / 049008), entitled "INTEGRATED DEVICE HAVING GDT AND MOV FUNCTIONALITIES," the disclosure of which is expressly incorporated by reference in its entirety and is incorporated herein by reference, discloses various aspects of an electrical device having the functionality of a gas discharge tube (GDT) and a metal oxide varistor (MOV). In some embodiments, referring to the example of FIG. 22, such an electrical device may include a series arrangement of a first MOV 100a, a GDT 402, and a second MOV 100b. In such a configuration, the first MOV 100a may have one of its electrodes also function as an electrode for the GDT 402. Such an electrode may be referred to as a first shared electrode. Similarly, the second MOV 100b may have one of its electrodes also function as an electrode for the GDT 402. Accordingly, such an electrode may be referred to as a second shared electrode.

[0124] 23 shows a circuit representation 400′ of the aforementioned electrical device using shared electrodes. Thus, in circuit representation 400′, each electrode of GDT portion 402 is shown overlapping a respective MOV portion (100a or 100b).

[0125] Figure 24 illustrates that in some embodiments, an electrical device can be implemented according to the examples of Figures 22 and 23 such that at least one MOV is configured to provide reduced electrode edge effects as described herein. For example, Figure 24 illustrates that in some embodiments, a GDT / MOV device 400 can include an enclosed chamber 416 having opposing sides. A first electrode 414 can be mounted on one of the opposing sides, and a second electrode 418 can be mounted on the other side, thereby providing a GDT configuration 402 (also referred to herein as a GDT).

[0126] 24, the first electrode 414 of the GDT 402 is also shown to function as one of two electrodes of the first MOV configuration 100a (also referred to herein as an MOV). More specifically, a metal oxide layer 412 is shown implemented between the first electrode 414 of the GDT 402 and the first outer electrode 410, thereby providing the functionality of the first MOV.

[0127] Similarly, the second electrode 418 of the GDT 402 is also shown functioning as one of two electrodes of a second MOV configuration 100b (also referred to herein as an MOV). More particularly, a metal oxide layer 420 is shown implemented between the second electrode 418 of the GDT 402 and a second outer electrode 422, thereby providing the functionality of the second MOV.

[0128] As described with reference to FIG. 23 , the circuit representation 400′ of the GDT / MOV device 400 is depicted as including a series arrangement of a first MOV 100a, a GDT 402, and a second MOV 100b. In such a circuit representation, the first MOV 100a is depicted with one of its electrodes also functioning as one of the electrodes of the GDT 402. Thus, in the structure shown in FIG. 24 , the electrode 414 can be referred to as a first shared electrode. Similarly, the second MOV 100b is depicted with one of its electrodes also functioning as the other of the electrodes of the GDT 402. Thus, in the structure shown in FIG. 24 , the electrode 418 can be referred to as a second shared electrode.

[0129] FIG. 24 is a perspective cutaway view of a GDT / MOV device 400. In the example of FIG. 24, the GDT / MOV device 400 is shown to include optional passivation coatings 504, 506 to prevent or reduce the possibility of external arcing. FIG. 25A shows a cross-sectional side view of the GDT / MOV device 400 of FIG. 24, but without the passivation coatings (504, 506 in FIG. 24). FIG. 25B is an enlarged view of one lateral side of the cross-sectional side view of FIG. 25A.

[0130] 24 and 25, as described above, a GDT / MOV device 400 is shown to include an enclosed chamber 416 having opposing sides. A first electrode 414 can be mounted on one of the opposing sides and a second electrode 418 can be mounted on the other side, thereby providing a GDT configuration 402 (also referred to herein as a GDT).

[0131] In some embodiments, an emissive coating (432 or 434) may be provided on each of the electrodes 414, 418. Such an emissive coating may be utilized in the operation of the GDT portion of the GDT / MOV device 400. It will be understood that a GDT / MOV device having one or more features as described herein may or may not include an emissive coating on the electrodes.

[0132] 24 and 25 illustrate that in some embodiments, the GDT / MOV device 400 can include edge configurations for some or all of its electrodes (410, 414, 418, 422). As described herein, such edge configurations can include flared edges of electrodes associated with the MOV that are implemented to reduce damage to the MOV at or near the edges of the electrodes.

[0133] 24 and 25A, the aforementioned edge configuration is generally designated as 502, and FIG. 25B shows an expanded view of a portion of FIG. 25A including various components associated with edge configuration 502. Referring to FIGS. 25A and 25B, the first shared electrode 414 is shown to include an inner portion 510a and an outer portion 510b that flare away from the first outer electrode 410. Accordingly, it can be seen that the separation distance between the inner portion 510a of the first shared electrode 414 and the first outer electrode 410 has a dimension a1 (FIG. 25B), and the separation distance between the outer edge of the outer portion 510b of the first shared electrode 414 and the first outer electrode 410 has a dimension a4 (FIG. 25B), where a4 is greater than a1. Similarly, assuming the second MOV 100b is a substantial mirror image of the first MOV 100a, the separation distance between the inner portion 512a of the second electrode 418 and the outer electrode 422 has a dimension a1 (FIG. 25B), and the separation distance between the outer edge of the outer portion 512b of the second shared electrode 418 and the second outer electrode 422 has a dimension a4 (FIG. 25B), where a4 is greater than a1.

[0134] As described herein, the aforementioned edge configurations of the electrodes desirably reduce the likelihood of damage to the MOVs at or near the electrode edges. For example, the first MOV 100a can benefit from reduced likelihood of damage at or near the edge of the first shared electrode 414. Similarly, the second MOV 100b can benefit from reduced likelihood of damage at or near the edge of the second shared electrode 418.

[0135] Stated another way, suppose a shared electrode of a MOV (such as a MOV / GDT / MOV configuration similar to FIG. 25A ) does not have a flared edge configuration for its corresponding outer electrode. Such a configuration is associated with a failure current threshold that leads to an edge failure mode. By providing a flared edge configuration as described herein, such an edge failure mode can be substantially eliminated or reduced, and the failure current threshold can be raised to another failure mode (which may or may not involve edge failure).

[0136] 24 and 25, the outer portion of each of the first and second shared electrodes 414, 418 is depicted as having the shape of a straight segment when viewed in a side cross-sectional view, such as in Figures 25A and 25B. It will be understood that in some embodiments, as described herein, the outer portion of each of the first and second shared electrodes 414, 418 can have a variety of shape profiles, including curved shapes.

[0137] 24 and 25, each of the first and second MOVs 100a, 100b is configured such that the respective shared electrode (414 or 418) forms a flared edge configuration, while the respective outer electrode (410 or 422) has a flat configuration without a flared edge portion. It will be appreciated that in some embodiments, each of the first and second MOVs 100a, 100b can have their respective electrodes configured differently to form a desired edge configuration.

[0138] For example, each of the first and second outer electrodes 410, 422 may have a flared edge portion, such that both electrodes of each MOV have a flared edge portion. In another example, each of the first and second outer electrodes 410, 422 can have a flared edge portion, and each of the first and second shared electrodes 414, 418 can have a flat configuration without a flared edge portion.

[0139] 24 and 25 illustrate that in some embodiments, GDT / MOV device 400 can include edge regions generally designated as 500 or 415. Such edge regions of GDT / MOV device 400 can include shaped edge portions of each of metal oxide layers 412, 420 that are sized to accommodate the flared edge configuration of the respective shared electrode (414 or 418). Examples of how such shaped edge portions can be formed are described in more detail herein.

[0140] 24 and 25, the edge region 500 of the GDT / MOV device 400 can further include a seal 513 implemented to join peripheral portions of the first and second metal oxide layers 412, 420. In some embodiments, such a seal can be an electrically insulating seal, such as a glass seal.

[0141] In some embodiments, the edge region 500 of the GDT / MOV device 400 can further include a seal assembly including a spacer (e.g., a washer-shaped spacer) having a glass seal that bonds each side of the spacer to a peripheral portion of the respective metal oxide layer (412 or 420). Further details regarding such spacers are disclosed in the above-referenced WO 2020 / 047381.

[0142] In some embodiments, the seal 513 (e.g., a glass seal) can be configured to extend inward from the outer edge of the GDT / MOV device 400 to a location between the edges of at least the outer portions 510b, 512b of the first and second shared electrodes 414, 418. A seal 513 configured in such a manner forms a seal portion 514 that provides a sealing function for the GDT chamber 416 and can provide desired dielectric properties between the edges of the outer portions 510b, 512b of the first and second shared electrodes 414, 418.

[0143] Regarding the seal portion 514 providing the desired dielectric properties described above, note that in the example of FIGS. 24 and 25 , the flared edge configuration of each of the first and second shared electrodes 414, 418 results in the edge of one shared electrode being closer to the edge of the other shared electrode compared to the separation distance between the inner portions 510 a, 512 a of the shared electrodes 414, 418. In FIG. 25B , this closer distance between the edges is depicted by arrow 515. While such closer distance (515) may increase the likelihood of an electrical breakdown event between the edges of the outer portions 510 b, 512 b of the shared electrodes 414, 418, the presence of the seal portion 514 can provide a higher dielectric strength (e.g., higher than the dielectric strength of the gas in the GDT chamber 416) to reduce the likelihood of such a breakdown event. For example, if glass is used as the seal portion 514, such a glass material can produce a dielectric strength value greater than 10 MV / m, whereas gases generally have lower dielectric strength values.

[0144] 24 and 25, the seal 513 can be configured to extend inwardly beyond a location between the edges of the outer portions 510b, 512b of the first and second shared electrodes 414, 418. In the example shown in Figures 24 and 25, such extension of the seal 513 is shown as 516 on the side of the first shared electrode 414 and as 518 on the side of the second shared electrode 418. Each such seal extension 516, 518 may also be referred to herein as an inward insulating wing.

[0145] In some embodiments, each of the seal extensions 516, 518 may extend inward to cover part or all of the respective outer portion (510b or 512b). In some embodiments, each of the seal extensions 516, 518 may extend inward to cover substantially all of the respective outer portion (510b or 512b) and part of the respective inner portion (510a or 512a) of the respective shared electrode (414 or 418).

[0146] In some embodiments, the seal extensions (or inward insulating wings) 516, 518 can be sized to create an extended leakage path between the first and second shared electrodes 414, 418. Note that in a GDT, leakage currents can exist between the electrodes. Such leakage currents typically follow leakage paths from one electrode to the other along various surfaces of the sealed chamber. In many GDT applications, it is desirable to reduce such leakage currents. To achieve such a reduction in leakage current, the corresponding leakage path can be increased.

[0147] 25B, the leak path between the first and second shared electrodes 414, 418 is depicted as 517. In the illustrated example, such leak path includes the sum of the surface-path length of the first inwardly facing insulating wing 516 and the surface-path length of the second inwardly facing insulating wing 518. Note that in the absence of the first and second inwardly facing insulating wings 516, 518 (such as when the seal 513 terminates at or near the edges of the outer portions 510b, 512b of the electrodes 414, 418), the corresponding leak path would be similar in dimension to the edge gap distance 515. It can thus be seen that the first and second inwardly facing insulating wings 516, 518 can provide a significant increase in leak path length for a given separation arrangement of the first and second shared electrodes 414, 418.

[0148] Further details regarding the aforementioned feature of increased leak path length are disclosed in, among others, International Publication No. WO 2020 / 257532 (International Application No. PCT / US2020 / 038552), entitled "GAS DISCHARGE TUBE HAVING ENHANCED RATIO OF LEAKAGE PATH LENGTH TO GAP DIMENSION," the disclosure of which is expressly incorporated by reference in its entirety and is hereby incorporated by reference.

[0149] 26A-26G illustrate an exemplary process that can be performed to fabricate the GDT / MOV device 400 of FIGS. 24 and 25. FIG. 26A illustrates that in some embodiments, a metal oxide layer 520 can be provided or formed. In some embodiments, such a metal oxide layer can be used as the first metal oxide layer 412 or the second metal oxide layer 420 of FIGS. 24 and 25.

[0150] 26B, a shaped depression 522 can be formed on one side of metal oxide layer 520 to create assembly 524. Examples of how such a shaped depression can be formed are described herein with reference to FIGS.

[0151] 26C, an electrode 526 can be formed on the metal oxide 520 to partially or completely cover the molded depression (522 in FIG. 26B) to create an assembly 534. In some embodiments, such an assembly can further include an emissive coating 532 formed on a laterally inner portion of the electrode 526. It will be understood that in some embodiments, the emissive coating 532 may or may not be used. Note that the electrode 526 includes an inner portion 528 and an outer portion 530 implemented as described herein.

[0152] In some embodiments, the electrode 526 of Figure 26C can be formed of, for example, silver, copper, tungsten, silver overplated with nickel or tin, etc. Formation of such an electrode can be performed by, for example, screen printing, pad printing, or evaporation / photoetching techniques, etc.

[0153] 26D, a layer of sealing material 536 can be formed around the periphery of assembly 534 to form assembly 538. In some embodiments, such sealing material can be an electrically insulating material, such as insulating sealing glass or other high-temperature insulating sealing material. In some embodiments, sealing material layer 536 can be dimensioned to provide one or more of the functions described herein with reference to FIGS. 24 and 25 when assembly 538 is assembled with other similar assemblies.

[0154] At the process stage of Figure 26E, the two assemblies 538 of Figure 26D can be stacked to allow for joining of the inner facing portions of the two assemblies (538, 538'). More specifically, a first assembly 538 (similar to assembly 538 of Figure 26D) can be inverted and placed on top of a second assembly 538' (also similar to assembly 538 of Figure 26D).

[0155] At the process stage of Figure 26F, the assembly (538 and 538') of Figure 26E can be further processed to form seal 540 and corresponding sealed chamber 542 to form assembly 544. By way of example, such further processing can include supplying a desired gas (e.g., an inert gas, an active gas, or some combination thereof) so that the unsealed chamber is filled with gas. The assembly (538 and 538') can then be heated such that the seal layer (536 in Figure 26D) melts to form seal 540 and sealed chamber 542 with the desired gas therein.

[0156] At the process stage of Figure 26G, first and second external electrodes 410, 422 can be formed on the assembly 544 of Figure 26F to form an assembly 400 similar to the GDT / MOV device 400 of Figures 24 and 25. More specifically, the first external electrode 410 can be formed on the outwardly facing surface of the first metal oxide layer 412, and the second external electrode 422 can be formed on the outwardly facing surface of the second metal oxide layer 420.

[0157] It will be appreciated that in some embodiments, the order of the exemplary process steps depicted in Figures 26A-26G can be changed. For example, outer electrodes 410 and 422 (formed in the process step of Figure 26G) may be formed before the encapsulation process step (e.g., in the same or additional process step of Figure 26C in which electrodes 526 (414 and 418 in Figure 26G) are formed).

[0158] The exemplary process of Figures 26A-26G depicts the fabrication of a single GDT / MOV device. In some embodiments, multiple GDT / MOV devices can be fabricated in an array format, and such devices can be separated into multiple individual devices. Figures 27A-27H show an example of such a fabrication process in which at least some of the process steps are performed while multiple units are attached in an array format.

[0159] For example, Figure 27A illustrates a process stage where a plate of metal oxide 552 may be provided or formed. Such a plate is shown to include multiple units 550, each unit ultimately becoming a GDT / MOV device.

[0160] 27B, a shaped depression 554 can be formed on one side of the metal oxide 552 of each unit 550 to form an assembly 556. In some embodiments, each such shaped depression can be formed as described herein with reference to FIG.

[0161] At the process stage of FIG. 27C , electrodes 558 can be formed on the metal oxide 552 to partially or completely cover the shaped recesses (554 in FIG. 27B ) of each unit 550 to form an assembly 562. In some embodiments, each such electrode can be formed as described herein with reference to FIG. 26C . In some embodiments, such an assembly can further include an emissive coating 560 formed on a laterally inner portion of the corresponding electrode 558. It will be understood that in some embodiments, the emissive coating 560 may or may not be used. Note that the electrode 558 includes inner and outer portions implemented as described herein.

[0162] 27D, a layer 564 of sealing material may be formed over a peripheral portion of each unit 550 of assembly 562 to form assembly 566. In some embodiments, each such sealing layer 564 may be formed as described herein with reference to FIG.

[0163] At the process stage of Figure 27E, two assemblies 566 of Figure 27D can be assembled to allow for joining of inner facing portions of the two assemblies (566, 566'). More specifically, a first assembly 566 (similar to assembly 566 of Figure 27D) can be inverted and placed over a second assembly 566' (also similar to assembly 566 of Figure 27D).

[0164] At the process stage of Figure 27F, the assembly of Figure 27E (566 and 566') can be further processed to form seals 568 and corresponding sealed chambers 570 for each unit to form assembly 572. In some embodiments, such further processing can be performed as described herein with reference to Figure 26F.

[0165] At the process stage of Figure 27G, first and second external electrodes 574, 576 can be formed for each unit on assembly 572 of Figure 27F to form assembly 580. In some embodiments, such external electrodes can be laterally dimensioned to allow separation of the units along separation line 578.

[0166] At the process stage of Figure 27H, the units of assembly 580 of Figure 27G can be separated to create a plurality of individual GDT / MOV devices 400, each similar to GDT / MOV device 400 of Figures 24 and 25. As described herein, each such GDT / MOV device 400 can include an electrode edge configuration 502 as described herein and / or an edge configuration 500 as described herein.

[0167] It will be appreciated that in some embodiments, the order of the exemplary process steps depicted in Figures 27A-27H can be changed. For example, outer electrodes 574 and 576 (formed in the process step of Figure 27G) can be formed before the encapsulation process step (e.g., in the same or additional process step of Figure 27C in which electrodes 558 (414 and 418 in Figure 26G) are formed).

[0168] Figure 28 illustrates a GDT / MOV device 600 similar to GDT / MOV device 400 of Figures 24 and 25. In the example of Figure 28, GDT / MOV device 600 is shown to include a sidewall 606 defined by the sidewalls of two metal oxide layers (412, 420 in Figures 24 and 25) and a lateral profile 604 of sealing portion 602 (514 in Figures 24 and 25). In some embodiments, lateral profile 604 of sealing portion 602 preferably does not protrude outwardly beyond sidewall 606. In such configurations, GDT / MOV device 600 is shown having a lateral profile 608 in which lateral profile 604 of sealing portion 602 does not protrude outwardly beyond sidewall 606.

[0169] 29 illustrates that in some cases, the side profile of the sealing portion 602 may protrude outwardly beyond the sidewall 606. For example, excess sealing material, such as glass, may form a bead 610 that protrudes outwardly beyond the sidewall 606. Such bead formation may occur, for example, during the sealing process (e.g., during one or more of the process steps of FIGS. 26E-26G).

[0170] In some cases, such protruding beads may cause undesirable problems during one or more process steps. For example, the protruding beads may unnecessarily cause the corresponding assembly to stick to an alignment fixture during process steps subsequent to the bead-forming process step. In other instances, the protruding beads may unnecessarily transmit external forces to the corresponding assembly during process steps subsequent to the bead-forming process step, thereby making the corresponding GDT / MOV device 600 of FIG. 29 more fragile during manufacturing.

[0171] 30A and 30B illustrate that in some embodiments, a GDT / MOV device 700 can include an edge portion 705 configured to form a volume that allows excess sealing material to collect in the sealing portion 702. FIG. 31A shows a close-up of the edge portion 705, and FIG. 31B shows the same close-up of the edge portion (705′) without the sealing portion (702 in FIG. 31A).

[0172] 30A, 30B, 31A, and 31B, exemplary GDT / MOV device 700 is shown to be similar to exemplary GDT / MOV devices 400, 600 of Figures 24, 25, and 28, except that GDT / MOV device 700 (of Figures 30A, 30B, 31A, and 31B) is shown to include edge features (750a, 750b) for each of first and second metal oxide layers 712, 720. In some embodiments, such edge features of first and second metal oxide layers 712, 720 can be sized to accommodate any excess seal material that may be present when seal portion 702 is formed to join first and second metal oxide layers 712, 720.

[0173] In some embodiments, the edge features 750a, 750b that accommodate excess sealing material can form a side profile 704 of the sealing portion 702 that does not protrude outwardly beyond the sidewall 708 of the GDT / MOV device 700 defined by the sidewalls 706a, 706b of the first and second metal oxide layers 712, 720. For example, in Figures 30A, 30B, and 31A, the side profile 704 of the sealing portion 702 is depicted as having a concave shape that does not protrude outwardly beyond the sidewall 708. In other examples, the side profile (704) of the sealing portion 702 can be substantially flush with the sidewalls 706a, 706b of the first and second metal oxide layers 712, 720.

[0174] It should be noted that other portions of GDT / MOV device 700 (of Figures 30A, 30B, 31A and 31B), such as electrodes 710, 714, 718, 722, emissive coatings 732, 734 and sealed chamber 716, may be similar to their corresponding portions in GDT / MOV devices 400, 600 of Figures 24, 25 and 28.

[0175] In some embodiments, the edge shape of the metal oxide layer that forms a volume for at least a portion of the excess sealing material in the sealing portion can be implemented as a chamfered edge, a beveled edge, etc. For example, referring to FIG. 31B, each of the first and second metal oxide layers 712, 720 is shown having an edge shape (750a or 750b) implemented as a beveled edge formed with two straight segments. Such a beveled edge having two straight segments is also shown in FIG. 32A, where the edge shape 750a of the first metal oxide layer 712 is shown to include first and second straight segments 752a, 754a that form the beveled edge, and the edge shape 750b of the second metal oxide layer 720 is shown to include first and second straight segments 752b, 754b that form the beveled edge.

[0176] 32B illustrates an example in which the first and second metal oxide layers 712, 720 each have an edge feature (750a or 750b) implemented as a chamfered edge. More specifically, a straight portion 756a is shown forming the chamfered edge of edge feature 750a, and a straight portion 756b is shown forming the chamfered edge of edge feature 750b.

[0177] 32C illustrates an example in which the first and second metal oxide layers 712, 720 each have an edge feature (750a or 750b) implemented as a curved bevel edge. More specifically, curve 758a is shown forming the bevel edge of edge feature 750a, and curve 758b is shown forming the bevel edge of edge feature 750b.

[0178] Figures 32A-32C show non-limiting examples of edge geometries 750a, 750b that are mirror images of one another and are therefore symmetrical with respect to the midplane between the first and second metal oxide layers 712, 720. It will be understood that a GDT / MOV device having one or more features as described herein may include edge geometries (of the first and second metal oxide layers) that are not symmetrical. Figures 32D-32F show non-limiting examples of such edge geometries that are not symmetrical.

[0179] For example, Figure 32D illustrates a configuration in which the first and second edge shapes 750a, 750b are implemented as similar types of edge shapes (e.g., a first bevel edge formed of two straight portions 760a, 762a and a second bevel edge formed of two straight portions 760b, 762b), but the two edge shapes 750a, 750b are sized differently, thereby resulting in asymmetric edge shapes.

[0180] 32E illustrates a configuration in which the first and second edge features 750a, 750b are implemented with different types of edge features (e.g., a beveled edge having two straight portions for the first metal oxide layer 712 and a curved beveled edge for the second metal oxide layer 720). Thus, the two edge features 750a, 750b are not symmetrical to each other.

[0181] In yet another example, Figure 32F illustrates a configuration in which the first and second edge features 750a, 750b are implemented with different types of edge features (e.g., a square edge on the first metal oxide layer 712 and a beveled edge on the second metal oxide layer 720), and therefore the two edge features 750a, 750b are not symmetrical to each other.

[0182] Figures 32A-32F also illustrate that, in some embodiments, an edge portion (e.g., 750 in Figures 30A, 30B, and 31A) of the GDT / MOV device 700 can include volume-forming features (e.g., chamfered edges, beveled edges, etc.) implemented in either or both of the first and second metal oxide layers 712, 720. More specifically, Figures 32A-32E illustrate an example in which volume-forming features are implemented in both the first and second metal oxide layers 712, 720, while Figure 32F illustrates an example in which volume-forming features are implemented in only one of the first and second metal oxide layers 712, 720.

[0183] 33A-33G illustrate an exemplary process that can be performed to fabricate the GDT / MOV device 700 of FIGS. 30A and 30B. FIG. 33A illustrates that, in some embodiments, a metal oxide layer 770 can be provided or formed. In some embodiments, such a metal oxide layer can be used as the first metal oxide layer 712 or the second metal oxide layer 720 of FIGS. 30A and 30B.

[0184] 33B, a shaped depression 772 and a volume-forming edge feature 773 can be formed on one side of metal oxide layer 770 to form assembly 774. In some embodiments, volume-forming edge feature 773 can be implemented as, for example, a chamfered edge, a beveled edge, or the like.

[0185] At the process stage of FIG. 33C , an electrode 776 can be formed on the metal oxide 770 to partially or completely cover the molded depression (772 in FIG. 33B ) to form an assembly 784. In some embodiments, such an assembly can further include an emissive coating 782 formed on a laterally inner portion of the electrode 776. It will be understood that in some embodiments, the emissive coating 782 may or may not be used. In some embodiments, the electrode 776 can include an inner portion 778 and an outer portion 780 implemented as described herein. In some embodiments, the electrode 776 of FIG. 33C can be formed of, for example, silver, copper, tungsten, silver overplated with nickel, or tin. Formation of such an electrode can be achieved by, for example, screen printing, pad printing, or evaporation / photoetching techniques.

[0186] 33D , a layer of sealing material 786 can be formed over a peripheral portion of assembly 784 to form assembly 788. In some embodiments, such sealing material can be an electrically insulating material, such as insulating sealing glass or other high-temperature insulating sealing material. In some embodiments, sealing material layer 786 can be dimensioned to provide one or more functions described herein with reference to FIGS. 30A and 30B when assembly 788 is assembled with other similar assemblies. In some embodiments, sealing material layer 786 can be implemented such that its outer edge is at or near an inner portion of volume-forming edge feature 773.

[0187] At the process stage of Figure 33E, two assemblies 788 of Figure 33D can be assembled to allow for joining of inner facing portions of the two assemblies (788, 788'). More specifically, a first assembly 788 (similar to assembly 788 of Figure 33D) can be inverted and positioned over a second assembly 788' (also similar to assembly 788 of Figure 33D).

[0188] In the process step of FIG. 33F, the assembly (788 and 788′) of FIG. 33E can be further processed to form a seal 790 and a corresponding sealed chamber 792 to form assembly 794. By way of example, such further processing may include supplying a desired gas (e.g., an inert gas, an active gas, or some combination thereof) so that the unsealed chamber is filled with the gas. The assembly (788 and 788′) can then be heated to melt the sealing layer (786 in FIG. 33D) and form the seal 790 and the sealed chamber 792 with the desired gas therein. As described herein, the volume-forming edge feature (773 in FIG. 33D) exists as a space to accommodate any excess sealing material of the seal 790 formed by the sealing process step of FIG. 33F. Thus, the resulting seal 790 has an outer edge shape 791 that does not protrude beyond the outer wall of the assembly 794 defined by the walls of the first and second metal oxide layers.

[0189] At the process stage of Figure 33G, first and second outer electrodes 710, 722 can be formed on the assembly 794 of Figure 33F to form an assembly 700 similar to the GDT / MOV device 700 of Figures 30A and 30B. As described herein, such a GDT / MOV device 700 includes an edge portion 705 where the sealing material of the seal (790 of Figure 33E) does not protrude outwardly beyond the outer wall of the GDT / MOV device 700.

[0190] It will be appreciated that in some embodiments, the order of the exemplary process steps depicted in Figures 33A-33G can be varied. For example, outer electrodes 710 and 722 (formed in the process step of Figure 33G) may be formed prior to the encapsulation process step (e.g., in the same or additional process step of Figure 33C in which electrodes 776 (714 and 718 in Figure 30B) are formed).

[0191] The exemplary process of Figures 33A-33G depicts the fabrication of a single GDT / MOV device. In some embodiments, multiple GDT / MOV devices can be fabricated in an array format, and such devices can be separated into multiple individual devices. For example, Figures 27A-27H show an example of such a fabrication process in which at least some of the process steps are performed while multiple units are attached in an array format.

[0192] 27A-27H is appropriately modified to incorporate volume-forming edge features (e.g., 773 in FIGS. 33B and 33D) in each unit, so that it can benefit from that functionality when the sealing process step is performed. In some embodiments, a separation process step, such as the process step in FIG. 27H, can be performed such that separation occurs along a line or region between the volume-forming edge features of adjacent units.

[0193] 30-33, the sealing material of the seal may be glass, and the presence of volume-forming edge features of the GDT / MOV device may accommodate excess glass formed during the sealing process to prevent the excess glass from protruding beyond the walls of the GDT / MOV device (e.g., as the bead structure of FIG. 29). As described herein, such volume-forming edge features may be beneficial when protrusion of the sealing material is to be avoided.

[0194] It will therefore be appreciated that in some embodiments, GDT / MOV devices using any sealing material (including glass and non-glass materials that can be extruded or flowed out during the sealing process) can benefit from the presence of volume-forming edge features as described herein.

[0195] In various examples described herein, MOV devices in which either or both electrodes have flared edge portions can reduce edge failures. Examples of various types of flared edges are provided herein, including the straight flare of Figures 6 and 7 and the curved flare of Figures 8 and 9. Numerous more specific examples are provided for the straight flare and curved flare configurations, with dimensions that can be used to achieve desired performance results.

[0196] Additionally, as described herein with reference to Figures 15-17, MOVs can be configured with flared edge configurations to provide edge values ​​of MOV parameters having magnitudes less than a range of magnitudes relative to the median value of the MOV parameter. Such MOV parameters can be, for example, temperature, electric field strength, or surface charge density. It will be understood that such flared edge configurations can be applied to the exemplary edge shapes described herein (e.g., straight-section flares and curved flares), but are not necessarily limited to such specific example shapes.

[0197] It will therefore be understood that an MOV device having one or more features as described herein can have a flared edge electrode configuration based on a selected flared edge shape, based on selected ranges or values ​​of edge and center MOV parameters (regardless of the type and / or dimensions of the corresponding edge shape), or some combination thereof, taking into account design considerations such as device rating, materials, size, and application specifications.

[0198] Furthermore, GDT / MOV devices having one or more features as described herein can be configured based on design considerations related to GDT performance, MOV performance, or some combination thereof. For example, with reference to the exemplary GDT / MOV devices of FIGS. 25A and 30B, note that the amount of flare of the internal electrodes (e.g., 414 or 417 in FIG. 25A) can affect the edge performance of the corresponding MOV. The flare of the edges of the internal electrodes (414 and 417 in FIG. 25A) can also affect, for example, the breakdown voltage of the GDT because the flared edges of the electrodes are closer than the center gap dimension.

[0199] In the previous example, assume that a particular edge flare configuration is desired to obtain the desired MOV performance. In such a situation, the GDT configuration can be adapted to accommodate the edge flare configuration while remaining within the desired GDT performance range. For example, the thickness of the seal (e.g., 513 in FIG. 25A) can be appropriately adjusted to obtain the desired minimum gap between the edges of the electrodes to provide the corresponding breakdown voltage.

[0200] In other examples, the amount of flare of the internal electrodes of a GDT / MOV device can be based on the desired GDT performance. In such situations, each MOV section can be configured to accommodate such edge flare configurations while remaining within the desired MOV performance range. For example, MOV design considerations such as metal oxide material and / or metal oxide layer thickness can be appropriately tailored to the MOV section.

[0201] Unless the context clearly requires otherwise, throughout the specification and claims, words like "comprises," "comprising," and the like should be interpreted in an inclusive sense, i.e., a sense of "including" rather than being limited thereto, as opposed to an exclusive or exhaustive sense. Generally, as used herein, the term "coupled" means that two or more elements are directly connected or connected via one or more intermediate elements. Also, the words "herein," "above," "below," and similar phrases, when used in this application, refer to this application as a whole and not to any particular portions thereof. Where the context permits, words in the singular or plural form in the specification can include the plural or singular, respectively. The word "or" referring to a list of two or more items includes all of the following interpretations: any of the items in the list, all of the items in the list, and any combination within the list.

[0202] The above detailed description of embodiments of the present invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the present invention have been described above for illustrative purposes, various equivalent modifications are possible within the scope of the present invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are shown in a certain order, alternative embodiments may perform routines having steps or use systems having blocks in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks may be shown as being performed in serial, these processes or blocks may instead be performed in parallel or at different times.

[0203] The teachings of the invention provided herein may be applied to other systems, not necessarily limited to the systems described above. Elements and acts of the various embodiments described above may be combined to provide further embodiments.

[0204] While several embodiments of the present invention have been described, these embodiments are presented for illustrative purposes only and are not intended to limit the scope of the present disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms, and various omissions, substitutions, and modifications of the forms of the methods and systems described herein may be made without departing from the spirit of the present disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the present disclosure.

Claims

1. a metal oxide layer having a first and a second surface; first and second electrodes mounted on the first and second surfaces of the metal oxide layer, respectively, each electrode including a lateral inner portion and an edge portion, the edge portion of the first electrode having a flared shape; An electrical device having:

2. The electrical device of claim 1 , wherein the electrical device is configured as a metal oxide varistor (MOV).

3. 3. The electrical device of claim 2, wherein the flared shape is configured to provide a desired edge effect at least at or near an edge of the first electrode when a potential difference exists between the first electrode and the second electrode.

4. The electrical device of claim 3 , wherein the desired end effect comprises a reduction in the end effect.

5. The electrical device of claim 4 , wherein the edge effect comprises temperature, electric field strength, or surface charge density.

6. The electrical device of claim 2 , wherein the edge portion of the second electrode also includes a flared shape.

7. 7. The electrical device of claim 6, wherein the first electrode is a substantial mirror image of the second electrode with respect to a midplane between the first and second electrodes.

8. 7. The electrical device of claim 6, wherein the edge portion of each of the first and second electrodes includes a straight portion extending from the respective inner portion at an angle that forms the flared shape when viewed in side cross section.

9. 9. The electrical device of claim 8, wherein the straight portion of the edge portion of each electrode is sized and oriented to extend laterally outwardly relative to the inner portion an amount a3 and away from the other electrode an amount a2.

10. 10. The electrical device of claim 9, wherein the MOV has a disk shape with an overall diameter, and an overall dimension D is approximately equal to the overall diameter.

11. The electrical device of claim 8 , wherein the edge portions of each of the first and second electrodes further include another straight portion extending from the straight portion at another angle different from the angle.

12. 7. The electrical device of claim 6, wherein the edge portion of each of the first and second electrodes includes a curved portion extending from the respective inner portion to form the flared shape when viewed in side cross section.

13. The electrical device of claim 12 , wherein the curved portion comprises a portion of a conic section or an exponential curve.

14. 14. The electrical device of claim 13, wherein the curved portion comprises a portion of a circle such that the curved portion has a radius of curvature of R.

15. The electrical device of claim 2 , wherein the second electrode is substantially planar such that an edge portion of the second electrode is flush with the inner portion.

16. 3. The electrical device of claim 2, wherein the first surface of the metal oxide layer is sized to accommodate the first electrode and the second surface of the metal oxide layer is sized to accommodate the second electrode.

17. 17. The electrical device of claim 16, wherein the first surface of the metal oxide layer defines a recess shaped to accommodate the flared shape of the edge portion of the first electrode.

18. The electrical device of claim 2 , wherein the metal oxide layer has a circular shape when viewed from either the first side or the second side of the metal oxide layer.

19. 20. The electrical device of claim 18, wherein each of the first and second electrodes has a circular shape when viewed from either the first or second side of the metal oxide layer.

20. The electrical device of claim 2 , wherein the metal oxide layer has a rectangular shape when viewed from either the first surface or the second surface of the metal oxide layer.

21. 21. The electrical device of claim 20, wherein each of the first and second electrodes has a circular or rectangular shape when viewed from one of the first and second sides of the metal oxide layer.

22. 10. The electrical device of claim 1, wherein the metal oxide layer with the first and second electrodes forms a first metal oxide varistor (MOV).

23. 23. The electrical device of claim 22, further comprising a second MOV coupled to the first MOV by an electrically insulating seal, the second MOV including a metal oxide layer having first and second surfaces, and first and second electrodes mounted on the first and second surfaces, respectively, each electrode including a lateral inner portion and an edge portion, the edge portion of the first electrode having a flared shape, the first and second MOVs including the electrically insulating seal and oriented such that first surfaces of the first and second MOVs face each other to define a sealed chamber containing a gas, the sealed chamber containing the gas and the first electrodes of the first and second MOVs forming a gas discharge tube (GDT).

24. 24. The electrical device of claim 23, wherein the electrical device forms an electrical series arrangement of the first MOV, the GDT, and the second MOV, the first electrode of the first MOV is also one of the two electrodes of the GDT, the first electrode of the second MOV is also the other of the two electrodes of the GDT, and the second electrodes of the first and second MOVs are external electrodes of the electrical device.

25. 25. The electrical device of claim 24, wherein the electrically insulating seal comprises a glass seal.

26. 25. The electrical device of claim 24, wherein the electrically insulating seal is dimensioned to extend laterally inward and cover some or all of the edge portions of the first electrodes of each of the first and second MOVs, thereby increasing a leakage path length between the first electrodes.

27. 25. The electrical device of claim 24, wherein the metal oxide layer of each of the first and second MOVs includes a sidewall and an outer edge joining the sidewall and the first face of each of the MOVs, the outer edge including an edge feature dimensioned to form a space to accommodate at least a portion of excess material associated with the electrically insulating seal.

28. 28. The electrical device of claim 27, wherein the edge features are dimensioned such that the excess material associated with the electrically insulating seal does not extend outwardly beyond the sidewall of each of the metal oxide layers.

29. 1. A method of manufacturing a metal oxide varistor device, comprising: forming or providing a metal oxide layer having a first and a second surface; mounting first and second electrodes on the first and second surfaces of the metal oxide layer, respectively, each electrode including a lateral inner portion and an edge portion, the edge portion of the first electrode having a flared shape; A method comprising:

30. 30. The method of claim 29, wherein mounting the second electrode causes the second electrode to be substantially planar such that an edge portion of the second electrode is flush with the interior portion.

31. 30. The method of claim 29, wherein mounting the second electrode forms a flared shape at the edge portion of the second electrode.

32. 30. The method of claim 29, wherein the metal oxide layer is a unit of a plurality of similar units joined together in an array.

33. 33. The method of claim 32, further comprising separating the plurality of units into a plurality of separate units.

34. a first metal oxide varistor (MOV) including a first metal oxide layer having an outer surface and an inner surface with a first shaped depression, a first external electrode on the outer surface of the first metal oxide layer, and a first internal electrode covering some or all of the first shaped depression, the first internal electrode having an edge portion that extends away from the first external electrode; a second MOV including a second metal oxide layer having an outer surface and an inner surface with a second shaped depression, a second external electrode on the outer surface of the second metal oxide layer, and a second internal electrode covering some or all of the second shaped depression, the second internal electrode having an edge portion that extends away from the second external electrode; a seal mounted between the inner surface of the first metal oxide layer and the inner surface of the second metal oxide layer to form a sealed chamber defined by the first and second shaped depressions and enclosing a gas therein, the sealed chamber with the gas and the first and second inner electrodes forming a gas discharge tube (GDT); An electrical device having:

35. 35. The electrical device of claim 34, wherein the seal is formed from an electrically insulating material.

36. 36. The electrical device of claim 35, wherein the electrically insulating material comprises glass.

37. 36. The electrical device of claim 35, wherein the electrically insulating seal is sized to be between at least an outer end of the edge portion of the first internal electrode and an outer end of the edge portion of the second internal electrode.

38. 38. The electrical device of claim 37, wherein the electrically insulating material has a dielectric strength greater than a dielectric strength of the gas present in the sealed chamber to reduce the likelihood of dielectric breakdown between the ends of the edge portions.

39. 38. The electrical device of claim 37, wherein the electrically insulating seal is further dimensioned to extend laterally inward and cover some or all of the edge portions of each of the first and second internal electrodes, thereby increasing a leakage path length between the first and second internal electrodes.

40. 35. The electrical device of claim 34, wherein the seal includes a spacer, a first layer of electrically insulating material joining one side of the spacer to the inner surface of the first metal oxide layer, and a second layer of electrically insulating material joining the other side of the spacer to the inner surface of the second metal oxide layer.

41. 41. The electrical device of claim 40, wherein the electrically insulating material comprises glass.

42. 41. The electrical device of claim 40, wherein the spacers have a washer shape with outer lateral dimensions similar to the outer lateral dimensions of each metal oxide layer.

43. 43. The electrical device of claim 42, wherein the spacer is formed from an electrically conductive or electrically insulating material.

44. 35. The electrical device of claim 34, wherein the first MOV is a substantial mirror image of the second MOV with respect to a midplane between the first and second MOVs.

45. 35. The electrical device of claim 34, wherein the edge portion of each internal electrode includes one or more straight portions, each straight portion extending laterally outward at an angle that forms a flared shape when viewed in side cross section.

46. 35. The electrical device of claim 34, wherein the edge portion of each inner electrode includes a curved portion that extends laterally outward to form a flared shape when viewed in side cross section.

47. 47. The electrical device of claim 46, wherein the curved portion comprises a portion of a conic or exponential curve.

48. 48. The electrical device of claim 47, wherein the curved portion comprises a portion of a circle such that the curved portion has a radius of curvature of R.

49. 35. The electrical device of claim 34, further comprising an emissive coating formed on each internal electrode.

50. 35. The electrical device of claim 34, wherein each of the first and second metal oxide layers includes a sidewall, the sidewalls of the first and second metal oxide layers defining a sidewall of the electrical device.

51. 51. The electrical device of claim 50, wherein the first and second metal oxide layers have substantially the same lateral dimensions such that the sidewalls of the first and second metal oxide layers are substantially collinear.

52. 51. The electrical device of claim 50, further comprising a passivation coating mounted on the sidewalls of each of the first and second metal oxide layers, the passivation coating configured to prevent or reduce the possibility of external arcing.

53. 51. The electrical device of claim 50, wherein each of the first and second metal oxide layers includes an outer edge on a respective inner surface.

54. 54. The electrical device of claim 53, wherein the outer edge of each of the first and second metal oxide layers has a generally right-angled shape.

55. 54. The electrical device of claim 53, wherein the outer edge of each of either or both of the first and second metal oxide layers includes an edge feature dimensioned to form a space to accommodate at least a portion of excess material associated with the seal.

56. 56. The electrical device of claim 55, wherein the edge shape of each of either or both of the first and second metal oxide layers is dimensioned so that the excess material associated with the seal does not extend outward beyond the sidewall of each of the metal oxide layers.

57. 56. The electrical device of claim 55, wherein the edge shape comprises a chamfered edge shape or a beveled edge shape.

58. 58. The electrical device of claim 57, wherein the bevel edge shape comprises a curved bevel edge or a bevel edge having multiple straight segments.

59. 56. The electrical device of claim 55, wherein the outer edge of only one of the first and second metal oxide layers includes the respective edge feature.

60. 56. The electrical device of claim 55, wherein the outer edge of each of both the first and second metal oxide layers includes a respective edge feature.

61. 61. The electrical device of claim 60, wherein the edge shape of the first metal oxide layer is a substantial mirror image of the edge shape of the second metal oxide layer relative to a midplane between the first and second metal oxide layers.

62. 61. The electrical device of claim 60, wherein the edge features of the first metal oxide layer differ in size and / or shape from the edge features of the second metal oxide layer.

63. 1. A method of manufacturing an electrical device, comprising: forming or providing first and second metal oxide layers each having an outer surface and an inner surface with a shaped depression; forming an internal electrode covering part or all of the shaped depression in each of the first and second metal oxide layers, the internal electrodes having edge portions that extend away from the outer surface of each internal electrode; bonding the inner surface of the first metal oxide layer to the inner surface of the second metal oxide layer to form a sealed chamber defined by the first and second shaped depressions and containing a gas therein, the sealed chamber with the gas and the first and second inner electrodes forming a gas discharge tube (GDT); forming an external electrode on the outer surface of each of the first and second metal oxide layers, the first metal oxide layer and each of the external and internal electrodes forming a first metal oxide varistor (MOV) on a first side of the GDT, and the second metal oxide layer and each of the external and internal electrodes forming a second MOV on a second side of the GDT; A method comprising:

64. 64. The method of claim 63, wherein the joining comprises forming a seal with an electrically insulating material.

65. 65. The method of claim 64, wherein the electrically insulating material comprises glass.

66. 65. The method of claim 64, wherein forming the seal causes the electrically insulating material to extend laterally inward to cover some or all of the edge portion of each of the internal electrodes.

67. 64. The method of claim 63, further comprising forming an emissive coating over each inner electrode.

68. 64. The method of claim 63, wherein forming or providing the first and second metal oxide layers comprises forming or providing a sidewall on each of the first and second metal oxide layers, wherein the sidewall and the inner surface of each of the metal oxide layers form an outer edge.

69. 69. The method of claim 68, further comprising forming a passivation coating on the sidewalls of each of the first and second metal oxide layers.

70. 69. The method of claim 68, wherein forming or providing the sidewalls comprises forming or providing a shape that is substantially perpendicular to each of the outer edges.

71. 69. The method of claim 68, wherein forming or providing the sidewalls comprises forming or providing an edge shape for each of the outer edges, the edge shape being dimensioned to form a space to accommodate at least a portion of excess material resulting from joining the inner surface of the first metal oxide layer and the inner surface of the second metal oxide layer.

72. 64. The method of claim 63, wherein the assembly of the first MOV, the GDT, and the second MOV is a unit of a plurality of similar units joined together in an array.

73. 73. The method of claim 72, further comprising separating the plurality of units into a plurality of separate units.

74. A metal oxide varistor (MOV), a metal oxide layer having a first surface and a second surface; first and second electrodes mounted on the first and second surfaces of the metal oxide layer, respectively, each electrode including a laterally inner portion and an edge portion, and at least one of the first and second electrodes configured such that a parameter associated with the MOV at an edge of the edge portion of each of the electrodes has a magnitude that is within a selected range of the magnitude of the parameter at a center of the electrode; MOV having

75. 75. The MOV of claim 74, wherein the parameter comprises temperature, electric field strength, or surface charge density.

76. 75. The MOV of claim 74, wherein the selected range comprises ±10% of the magnitude of the parameter at the center of the electrode.

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