阅读说明：本技术 具有改进的能量处理能力的级联变阻器 (Cascaded varistor with improved energy handling capability ) 是由 M.柯克 M.贝罗里尼 P.拉文德拉纳坦 于 2019-03-04 设计创作，主要内容包括：提供了一种变阻器,该变阻器具有限定沿长度方向偏移的第一和第二相对端面的矩形构造。变阻器可以包括邻近第一相对端面的第一端子和邻近第二相对端面的第二端子。变阻器可以包括有源电极层,该有源电极层包括与第一端子电连接的第一电极和与第二端子电连接的第二电极。第一电极可以在长度方向上与第二电极间隔开,以形成有源电极端部间隙。变阻器可以包括具有浮动电极的浮动电极层。浮动电极层可以在高度方向上与有源电极层间隔开,以形成浮动电极间隙。有源电极端部间隙与浮动电极间隙的比可以大于约2。(A varistor is provided having a rectangular configuration defining first and second opposed end faces offset along a length direction. The varistor may include a first terminal adjacent the first opposing end face and a second terminal adjacent the second opposing end face. The varistor may include an active electrode layer including a first electrode electrically connected to the first terminal and a second electrode electrically connected to the second terminal. The first electrode may be spaced apart from the second electrode in a length direction to form an active electrode end gap. The varistor may include a floating electrode layer having a floating electrode. The floating electrode layer may be spaced apart from the active electrode layer in a height direction to form a floating electrode gap. The ratio of the active electrode tip gap to the floating electrode gap may be greater than about 2.)

1. A varistor having a rectangular configuration defining first and second opposed end faces offset along a length, the varistor comprising:

a first terminal adjacent the first opposing end face;

a second terminal adjacent the second opposing end face;

an active electrode layer including a first electrode electrically connected to the first terminal and a second electrode electrically connected to the second terminal, the first electrode being spaced apart from the second electrode in a length direction to form an active electrode end gap; and

a floating electrode layer including a floating electrode, the floating electrode layer being spaced apart from the active electrode layer in a height direction to form a floating electrode gap;

wherein the ratio of the active electrode tip gap to the floating electrode gap is greater than about 2.

2. The varistor of claim 1, wherein:

the first electrode overlaps the floating electrode in the longitudinal direction along an overlap distance;

the active electrode layer has a length between the first terminal and the second terminal in a length direction; and is

The overlap ratio is greater than about 5.

3. The varistor of claim 1, wherein said floating electrode is approximately an equal distance in a length direction from each of said first and second terminals.

4. The varistor of claim 1, wherein the breakdown voltage of the varistor is greater than about 0.9 times the initial breakdown voltage of the varistor after 5000 or more electrostatic discharges at about 8000 volts.

5. The varistor of claim 1, wherein the varistor has a capacitance of less than about 100 pF.

6. The varistor of claim 1, wherein the varistor has a leakage current of less than about μ 10 amps at about 30 volts.

7. The varistor of claim 1, wherein the varistor has an instantaneous energy capacity of greater than about 0.01 joules.

8. The varistor of claim 1, wherein said varistor has a specific instantaneous energy capacity greater than about 1 x 10⁷Joules per cubic meter.

9. A varistor, comprising:

a first terminal;

a second terminal;

a plurality of active electrode layers, each of the plurality of active electrode layers being electrically connected to at least one of the first terminal or the second terminal; and

a plurality of floating electrode layers interleaved with the plurality of active electrode layers in a cascade configuration;

wherein the varistor has a capacitance of less than about 100 pF.

10. The varistor of claim 9, wherein the breakdown voltage of the varistor is greater than about 0.9 times the initial breakdown voltage of the varistor after 5000 or more electrostatic discharges at about 8000 volts.

11. The varistor of claim 9, wherein the varistor has an instantaneous energy capacity of greater than about 0.01 joules.

12. The varistor of claim 9, wherein said varistor has a specific instantaneous energy capacity greater than about 1 x 10⁷Joules per cubic meter.

13. A varistor, comprising:

a first terminal;

a second terminal;

a plurality of active electrode layers, each of the plurality of active electrode layers being electrically connected to at least one of the first terminal or the second terminal; and

a plurality of floating electrode layers interleaved with the plurality of active electrode layers in a cascade configuration;

wherein the specific instantaneous energy capability of the varistor is greater than about 1 x 10⁷Joules per cubic meter.

14. The varistor of claim 13, wherein the varistor has a breakdown voltage greater than about 0.9 times the varistor's initial breakdown voltage after 5000 or more electrostatic discharges at about 8000 volts.

15. The varistor of claim 13, wherein the varistor has an instantaneous energy capacity of greater than about 0.01 joules.

Technical Field

The present subject matter relates generally to electronic components adapted to be mounted on a circuit board, and more particularly to varistors and varistor arrays.

Background

Multilayer ceramic devices, such as multilayer ceramic capacitors or varistors, are usually composed of a plurality of stacked dielectric-electrode layers. During fabrication, these layers may typically be pressed and formed into a vertically stacked structure. The multilayer ceramic device may include a single electrode or a plurality of electrodes in an array.

Varistors are voltage dependent nonlinear resistors that have been used as surge absorbing electrodes, lightning arresters and voltage stabilizers. For example, a varistor may be connected in parallel with a sensitive electronic component. The nonlinear resistance response of a varistor is generally characterized by a parameter known as the clamping voltage. For applied voltages less than the varistor clamping voltage, a varistor typically has a very high resistance and therefore acts like an open circuit. However, when a varistor is exposed to a voltage greater than its clamping voltage, its resistance decreases, making the varistor act more like a short circuit and allowing more current to flow. Such a non-linear response may be used to divert current surges and/or prevent voltage spikes from damaging sensitive electronic components.

Over time, the design of various electronic components has been driven by the industry's general trend to miniaturization. Miniaturization of electronic components results in lower operating currents and reduced durability. The current and energy handling capabilities of the varistor are generally limited by the heat generated by the current. If too much current flows through the varistor, the varistor will overheat, causing damage such as melting, burning, etc.

Therefore, a compact varistor with improved energy handling capability would be desirable.

Disclosure of Invention

According to one embodiment of the present disclosure, the varistor may have a rectangular configuration defining first and second opposing end faces offset along a length direction. The varistor may include a first terminal adjacent the first opposing end face and a second terminal adjacent the second opposing end face. The varistor may include an active electrode layer including a first electrode electrically connected to the first terminal and a second electrode electrically connected to the second terminal. The first electrode may be spaced apart from the second electrode in a length direction to form an active electrode end gap. The varistor may include a floating electrode layer having a floating electrode. The floating electrode layer may be spaced apart from the active electrode layer in a height direction to form a floating electrode gap. The ratio of the active electrode tip gap to the floating electrode gap may be greater than about 2.

According to another embodiment of the present disclosure, a varistor may include a first terminal, a second terminal, and a plurality of active electrode layers. Each of the plurality of active electrode layers may be electrically connected to at least one of the first terminal or the second terminal. The varistor may include a plurality of floating electrode layers interleaved with a plurality of active electrode layers in a cascade (cascade) configuration. The capacitance of the varistor may be less than about 100 pF.

According to another embodiment of the present disclosure, a varistor may include a first terminal, a second terminal, and a plurality of active electrode layers. Each of the plurality of active electrode layers may be electrically connected to at least one of the first terminal or the second terminal. The varistor may include a plurality of floating electrode layers interleaved with a plurality of active electrode layers in a cascade configuration. The specific instantaneous energy capability of the varistor may be greater than about 1 x 10⁷Joules per cubic meter.

Drawings

A full and enabling disclosure of the present subject matter, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

1A-1C illustrate various views of one embodiment of a varistor according to aspects of the present disclosure;

FIG. 2 illustrates an example current pulse for testing various characteristics of a varistor in accordance with aspects of the present disclosure; and

fig. 3 illustrates current and voltage during an exemplary test of a varistor according to aspects of the present disclosure.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features, electrodes, or steps of the present subject matter.

Detailed Description

It is to be understood by one of ordinary skill in the art that the present disclosure is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present subject matter, which broader aspects are embodied in the exemplary constructions.

Generally, the present disclosure is directed to a cascaded varistor. The varistor may have excellent energy dissipation characteristics. For example, the instantaneous energy capacity of a varistor may be represented by an electrostatic discharge (ESD) repetitive shock handling capacity, an instantaneous energy capacity, and/or a specific instantaneous energy capacity (energy per unit volume). Furthermore, according to aspects of the present disclosure, the varistor may also exhibit several other desirable characteristics, including low capacitance (making the varistor particularly suitable for use in capacitance sensitive circuits) and low leakage current at varistor operating voltages.

The varistor may comprise a rectangular structure defining first and second opposed end faces offset along the length. The varistor may include a first terminal adjacent the first opposing end face and a second terminal adjacent the second opposing end face. The varistor may further include an active electrode layer including a first electrode electrically connected to the first terminal and a second electrode electrically connected to the second terminal. The first electrode may be spaced apart from the second electrode in a length direction to form an active electrode end gap. The varistor may include a floating electrode layer having a floating electrode. The floating electrode layer may be spaced apart from the active electrode layer in a height direction to form a floating electrode gap. The ratio of the active electrode tip gap to the floating electrode gap may be greater than about 2.

Without being limited by theory, the cascade configuration described above may help increase energy handling capacity. For example, at voltages greater than the varistor breakdown voltage, the floating electrode(s) may improve conduction between the terminals. However, for voltages below the breakdown voltage, the floating electrode(s) may not compromise the performance of the varistor. In addition, the floating electrode can improve heat conduction in about the length direction, thereby improving heat dissipation. During a large current/energy surge, heat is generated as current flows through the dielectric layer. The floating electrode layer(s) may help to improve heat flow outward from the middle of the dielectric layer to the terminals where it may be more easily dissipated. As a result, the varistor is able to handle larger energy surges without overheating. Thus, the floating electrode layer(s) may improve the energy handling capability of the varistor.

The dielectric layers may be pressed together and sintered to form a unitary structure. The dielectric layer may comprise any suitable dielectric material, such as barium titanate, zinc oxide, or any other suitable dielectric material. Various additives may be included in the dielectric material, for example, additives that create or enhance the voltage dependent resistance of the dielectric material. For example, in some embodiments, the additive may include an oxide of cobalt, bismuth, manganese, or a combination thereof. In some embodiments, the additive may include an oxide of gallium, aluminum, antimony, chromium, titanium, lead, barium, nickel, vanadium, tin, or a combination thereof. The dielectric material may be doped with the additive(s) in a range from about 0.5 mole percent to about 3 mole percent, and in some embodiments, from about 1 mole percent to about 2 mole percent. The average grain size of the dielectric material may contribute to the non-linear properties of the dielectric material. In some embodiments, the average particle size may be in the range of about 10 to 100 microns, and in some embodiments, in the range of about 20 to 80 microns.

The terminals and electrodes of the varistor may be formed of various conductive materials. Examples of the conductive material include palladium, silver, platinum, and copper. Any other suitable conductor that can be printed on the dielectric layer can be used to form the electrodes and/or terminals.

Regardless of the particular configuration employed, the inventors have discovered that a varistor exhibiting excellent energy handling capability can be achieved through selective control of the configuration of the electrodes and the ratio of the active electrode end gap to the floating electrode gap. In some embodiments, the ratio of the active electrode tip gap to the floating electrode gap may be greater than about 2. For example, in some embodiments, the ratio may range from about 2 to about 50, in some embodiments from about 2 to about 30, and in some embodiments, from about 3 to about 25.

The active electrode tip gap may range from about 100 microns to about 1000 microns, and in some embodiments, from about 200 microns to about 800 microns. The floating electrode gap may range from about 15 microns to about 300 microns, and in some embodiments, from about 25 microns to about 150 microns.

As described above, the varistor may exhibit excellent energy handling capability. For example, the varistor may have an instantaneous energy capacity determined by a 10 x 1000 microsecond pulse of greater than about 0.01 joules, in some embodiments greater than about 0.03 joules, and in some embodiments greater than about 0.04 joules. For example, in some embodiments, the instantaneous energy capacity may be in the range of about 0.02 to about 0.04 joules.

Furthermore, the varistor may be compact, resulting in excellent specific instantaneous energy capability. For example, the specific instantaneous energy capability of the varistor may be greater than 6 x 10⁷Joule per cubic meter (J/m)³). In some embodiments, the specific transient energy capability may be from about 1 x 10⁷J/m³To about 20X 10⁷J/m³In some embodiments from about 1.5 x 10⁷J/m³To about 10X 10⁷J/m³And in some embodiments from about 2 x 10⁷J/m³To about 7X 10⁷J/m³。

In some embodiments, varistors according to some aspects of the present disclosure are capable of withstanding repeated electrostatic discharge shock without a significant degradation in performance. For example, after 5000 or more electrostatic discharges of about 8000 volts, the breakdown voltage of the varistor may be greater than about 0.9 times, in some embodiments greater than about 0.95 times, and in some embodiments greater than about 0.98 times the initial breakdown voltage of the varistor.

In some embodiments, a varistor according to aspects of the present disclosure may also exhibit low capacitance. For example, a varistor may have a capacitance of less than about 100 picofarads ("pF"). For example, in some embodiments, the varistor may have a capacitance of less than about 50pF, in some embodiments less than about 20pF, and in some embodiments less than about 10 pF. For example, in some embodiments, the varistor may have a capacitance ranging from about 0.1pF to about 20pF, in some embodiments from about 0.1pF to about 10pF, in some embodiments from about 0.7pF to about 5pF, and in some embodiments, from about 0.1pF to about 1 pF.

In some embodiments, the varistor may exhibit low leakage current. For example, the leakage current at an operating voltage of about 30 volts may be less than about 10 microamperes (μ A). For example, in some embodiments, the leakage current at an operating voltage of about 30 volts may range from 0.01 μ A to about 5 μ A, in some embodiments from about 0.005 μ A to about 1 μ A, in some embodiments, from about 0.05 μ A to about 0.15 μ A, such as 0.1 μ A.

Referring now to the drawings, exemplary embodiments of the disclosure will now be discussed in detail. Fig. 1A-1C illustrate one embodiment of a varistor 10 in accordance with aspects of the present disclosure. Fig. 1A is a schematic cross-sectional view illustrating various layers of one embodiment of a varistor 10. In one embodiment, the varistor 10 may comprise a plurality of substantially planar dielectric layers made of, for example, a ceramic dielectric material, as described above.

Referring to fig. 1A, the varistor 10 may include a plurality of active electrode layers 12 stacked in a Z-direction 13. Each active electrode layer 12 may include a first electrode 14 electrically connected to a first terminal 16 and a second electrode 18 electrically connected to a second terminal 20. Each first electrode 14 may be spaced apart in a length direction 22 from a corresponding second electrode 18 within the same active electrode layer 12 to form an active electrode end gap 24. The length direction 22 may be generally perpendicular to the height direction 13.

The varistor 10 may also include a plurality of floating electrode layers 26. The plurality of floating electrode layers 26 may be alternately arranged (e.g., staggered) between the respective pairs of active electrode layers 12. Each floating electrode layer 26 may include a floating electrode 28. In some embodiments, the floating electrode 28 may not be in direct electrical connection with any external structure. For example, the floating electrode 28 may be electrically disconnected from the terminals 16, 20. In some embodiments, the floating electrode 28 may be disposed generally in the middle of the floating electrode layer 26, relative to about the length direction 22. For example, the floating electrode layer 26 may be disposed at approximately equal distances from each of the first terminal 16 and the second terminal 20 in the length direction 22.

In some embodiments, the varistor 10 may also include a plurality of dielectric layers 40. For example, the dielectric layers 40 may be disposed between the active electrode layer 12 and the floating electrode layer 26 in an alternating manner. Although illustrated as being disposed between each active electrode layer 12 and an adjacent floating electrode layer 26, in some embodiments, the dielectric layer 40 may be disposed between less than all of the active electrode layers 12 and adjacent floating electrode layers 26. Additionally, in some embodiments, each dielectric layer 40 may have approximately the same thickness. However, in other embodiments, the dielectric layer 40 may have a varying thickness such that the distance between the floating electrode 28 and the adjacent active electrodes 16, 18 may vary within the varistor 10.

The floating electrode layer 26 may be spaced apart from the adjacent active electrode layer 12 in the height direction 13 to form a floating electrode gap 42. As described above, in some embodiments, the ratio of the active electrode end gap 24 to the floating electrode gap 42 may be greater than about 2.

Additionally, in some embodiments, the first electrode 14 and/or the second electrode 18 may overlap the floating electrode 28 along the overlap distance 44 in about the length direction 22. The active electrode layer 12 may have a length 46 in the length direction 22 between the first terminal 16 and the second terminal 20. The overlap ratio may be defined as the length 46 of the active electrode layer 12 divided by the overlap distance 44. As described above, in some embodiments, the overlap ratio may be greater than about 5. A capacitance may be formed along the overlap distance 44 between the first and second electrodes 14, 18 and the floating electrode 28. Thus, having an overlap ratio greater than about 5 can reduce this capacitance without significantly reducing the energy dissipation capability of the varistor 10. However, in other embodiments, the first and second electrodes 14, 18 may not overlap the floating electrode layer 28. In other embodiments, the overlap ratio may be less than about 5.

It should also be understood that the present disclosure is not limited to any particular number of dielectric electrode layers. For example, in some embodiments, varistor 10 may include 2 or more dielectric electrode layers, 4 or more dielectric electrode layers, 8 or more dielectric electrode layers, 10 or more dielectric electrode layers, 20 or more dielectric electrode layers, 30 or more dielectric electrode layers, or any suitable number of dielectric electrode layers.

Referring to fig. 1B and 1C, the varistor 10 may have a first end surface 30. Although not shown from the perspective of fig. 1B and 1C, it should be understood that the varistor 10 may include a second end surface 32 opposite the first end surface 30 and offset in the length direction 22. The varistor 10 may also have a first side surface 34, and although not shown from the perspective of fig. 1B and 1C, it should be understood that the varistor may include a second side surface 36 opposite the first side surface 34 and offset in a width direction 38 perpendicular to the length direction 22.

Fig. 1B shows the varistor 10 without terminals (e.g., before terminals are formed on the varistor 10). In some embodiments, the top layer of the varistor 10 may include exposed active first and second electrodes 14, 18. The edge of the first electrode 14 may extend to the first end face 30 and the edge of the second electrode 18 may extend to the second end face 32 for connection with the terminals 16, 20. Additionally, in other embodiments, the first and second electrodes 16, 18 may also extend to the side surfaces 34, 36 to provide improved connection to the terminals, which in such embodiments may be configured to bend around the side surfaces.

Referring to fig. 1C, the varistor 10 may include a termination structure for electrically connecting the active electrodes 14, 18 of the varistor 10 to a circuit (e.g., on a printed circuit board). The termination structure may include a first terminal 16 and a second terminal 20. The first and second terminations 16, 20 may include metallized layers of platinum, copper, palladium silver, or other suitable conductor materials. A layer of chromium/nickel, followed by a layer of silver/lead, applied by typical processing techniques such as sputtering, may be used as the outer conductive layer of the termination structure.

As shown in fig. 1C, the first terminal 16 may be disposed on the first end surface 30 of the varistor 10 such that it is electrically connected with the first electrode 14. In other words, the first electrode 14 may be electrically connected with the first terminal 16 at the first end surface 30. The second terminal 20 may be electrically connected with the second terminal 20 at the second end face 32.

In some embodiments, the top and/or bottom dielectric layers of the varistor 10 may include dummy electrodes (dummy electrodes). The dummy electrodes may improve the mechanical adhesion of the terminals 16, 20 to the varistor 10 without substantially contributing to the electrical characteristics of the varistor 10. For example, the dummy electrodes may be shorter than the active electrodes 14, 18 in the length direction 22. Dummy electrodes may be formed in any of the dielectric layers 40 to improve electrical connection to the terminals 14, 18 and/or to improve formation of the terminals 14, 18 (e.g., by electroless and/or electrolytic plating, such as by using a fine copper termination process).

Applications of

The varistors disclosed herein may find application in a wide variety of devices. For example, a varistor may be used in a radio frequency antenna/amplifier circuit. Varistors may also be applied to a variety of technologies including laser drivers, sensors, radar, radio frequency identification chips, near field communication, data lines, bluetooth, optical, ethernet, and any suitable circuitry.

The varistors disclosed herein may also find particular application in the automotive industry. For example, a varistor may be used in any of the above circuits in an automotive application. For such applications, passive electronic components may be required to meet stringent durability and/or performance requirements. For example, the AEC-Q200 standard specifies certain automotive applications. Varistors according to aspects of the present disclosure are capable of satisfying one or more AEX-Q200 tests, including, for example, an AEX-Q200-002 pulse test.

Ultra-low capacitance varistors may find particular application in data processing and transmission technology. For example, aspects of the present disclosure are directed to varistors exhibiting a capacitance of less than about 1 pF. Such varistors may, for example, minimize signal distortion in high frequency data transmission circuits.

The disclosure may be better understood with reference to the following examples.

Examples of the invention

As is known in the art, the housing dimensions of an electronic device may be expressed as a four digit code (e.g., XXYY), where the first two digits (XX) are the length of the device in millimeters (or thousandths of an inch) and the second two digits (YY) are the width of the device in millimeters (or thousandths of an inch). For example, common standard housing sizes may include 2012, 1608, and 0603.

An exemplary 0402 case size varistor may exhibit a capacitance of 0.8 picofarads at 1 MHz. A 0402 case size varistor may have an operating DC voltage of 15 volts, a breakdown voltage of 125 volts, and a leakage current at an operating DC voltage of 100 nanoamps.

According to aspects of the present disclosure, the varistor may have a high specific energy capability. The following table lists exemplary high specific energy capacity varistors:

TABLE 1 high specific energy Capacity rheostat

The listed DC operating voltages and AC operating voltages are not intended to limit the application of these exemplary resistors. Rather, they are merely indicative of the ideal operating voltage. As shown in the table, the operating voltages listed are well below the breakdown voltage, such that a varistor can generally provide a high resistance (e.g., effectively operate as an open circuit) at its operating voltage to prevent unwanted current flow. For example, each of the aforementioned varistors has a leakage current of about 0.1 μ A or less at a DC operating voltage.

The 0402 varistors listed above may have an active electrode tip gap ranging from about 15 mils to about 20 mils and a floating electrode gap ranging from about 1 mil to about 5 mils. As such, the ratio of the active electrode end gap to the floating electrode gap of these example 0402 varistors may be in the range of about 3 to about 18.

The 0603 varistors listed above may have an active electrode tip gap ranging from about 22 mils to about 28 mils and a floating electrode gap ranging from about 1 mil to about 5 mils. Thus, the ratio of the active electrode end gap to the floating electrode gap of these example 0603 varistors may be in the range of about 4 to about 23.

The following table provides information regarding exemplary ultra-low capacitance varistors according to aspects of the present disclosure:

TABLE 2 ultra-low capacitance rheostat

The capacitance values listed were measured at the test frequency described above. These exemplary ultra-low capacitance varistors may find particular application in data transmission and/or processing techniques.

Test method

The following section provides an example method of testing varistors to determine various varistor characteristics.

Instantaneous energy capacity

The instantaneous energy capability of a varistor may be measured using a Keithley 2400 series Source Measurement Unit (SMU), such as Keithley 2410-C SMU. The varistor is subjected to a 10 x 1000 mus current wave. The peak current value may be selected empirically to determine the maximum energy that the varistor is able to dissipate without failing (e.g., due to overheating). Fig. 2 shows an exemplary current wave. The current (vertical axis 202) is plotted against time (horizontal axis 204). The current increases to a peak current value 206 and then decays. The "up" period (shown by the vertical dashed line 206) is from the start of the current pulse (at t ═ 0) to when the current reaches 90% of the peak current value 206 (shown by the horizontal dashed line 208). The "decay time" (shown by the vertical dashed line 210) is the time from the start of the current pulse (at t ═ 0) to the current returning to 50% of the peak current value 206 (shown by the horizontal dashed line 212). For a pulse of 10 × 1000 μ s, the "rise" time is 10 μ s, and the decay time is 1000 μ s.

During the pulse through the varistor, the voltage across the varistor may be measured. Fig. 3 shows an exemplary graph of voltage across a varistor (horizontal axis 302) versus current through the varistor (vertical axis 304). As shown in fig. 3, once the voltage exceeds the breakdown voltage 306, the additional current flowing through the varistor does not significantly increase the voltage. In other words, the varistor "clamps" the voltage approximately equal to the clamping voltage 308.

The instantaneous energy handling capability of the varistor 10 can be determined by calculating the energy that has passed through the varistor 10. More specifically, the nominal transient energy may be calculated by integrating the product of the measured current and the measured voltage over time during the pulse:

E＝∫IVdt

where E is the total energy consumed by the varistor; i is the instantaneous current through the varistor; v is the instantaneous voltage across the varistor; t represents time.

In addition, to determine the electrostatic discharge capability of the varistor, a series of repeated electrostatic discharge strikes may be performed. For example, an electrostatic discharge shock of 5000 volts or more and 8000 volts may be applied to the varistor. The breakdown voltage of the varistor may be measured periodically during this series of impacts (as described below). The breakdown voltage of the varistor after an electrostatic discharge strike may be measured and compared to the initial breakdown voltage before the strike.

Clamping and breakdown voltage

The clamping voltage of the varistor may be measured using a Keithley 2400 series Source Measurement Unit (SMU), such as Keithley 2410-C SMU. Referring again to fig. 3, the clamping voltage 308 can be accurately measured as the maximum voltage measured across the varistor during a current pulse of 8 x 20 μ s, with a rise time of 8 μ s and a decay time of 20 μ s. This is true as long as the peak current value 310 is not so large as to damage the varistor.

The breakdown voltage 306 may be detected as an inflection point in the current versus voltage relationship of the varistor. Referring to fig. 3, for voltages greater than breakdown voltage 306, as the voltage increases, the current may increase faster than for voltages less than breakdown voltage 306. For example, FIG. 3 shows a log-log plot of current versus voltage. For voltages less than the breakdown voltage 306, an ideal varistor may generally exhibit a voltage according to approximately the following relationship:

V＝CIβ

wherein V represents a voltage; i represents current; and β is a constant that depends on the varistor characteristics (e.g., material characteristics). For a varistor, the constant β is usually less than 1, so according to ohm's law, in this region the voltage increases slower than an ideal resistor.

However, for voltages greater than the breakdown voltage 306, the current versus voltage relationship can generally be approximated by ohm's law, where current is linearly related to voltage:

V＝IR

wherein V represents a voltage; i represents current; and R is a large constant resistance value. The current versus voltage relationship may be measured as described above, and the inflection point of the empirically collected current versus voltage data set may be determined using any suitable algorithm.

Peak current value

The peak current value that the varistor can handle without damage can be measured using a Keithley 2400 series Source Measurement Unit (SMU) in a manner similar to the instantaneous energy capability described above. The varistor may be subjected to successive 8 x 20 mus current pulses at increasing current levels. The peak current value may be empirically determined as the maximum current value that can be pulsed through the varistor using an 8 x 20 μ s current wave without damaging the varistor, e.g., by overheating.

Capacitor with a capacitor element

The capacitance of the supercapacitor can be measured using a Keithley 3330Precision LCZ meter with a DC bias of 0.0 volts, 1.1 volts, or 2.1 volts (0.5 volts root mean square sinusoidal). Unless otherwise specified in Table 2 above, the operating frequency was 1000 Hz. The temperature was room temperature (. about.23 ℃ C.) and the relative humidity was 25%.

These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention. Further, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.