HK1165450A - Dielectric composition - Google Patents

Description

Dielectric composition

RELATED APPLICATIONS

This application claims priority to U.S. provisional patent application No.61/147,055; the entire contents of the above-mentioned prior application are incorporated by reference into this specification.

Technical Field

Embodiments described herein pertain generally to Voltage Switchable Dielectric (VSD) materials and, more particularly, to VSD materials that use binders having enhanced electron mobility at high electric fields.

Background

Voltage Switchable Dielectric (VSD) material is material that is insulating at low voltages and conducting at high voltages. These materials are typically composites containing conductive, semiconductive, and insulating particles in a polymer matrix. These materials are used for transient protection of electronic devices, most notably for electrostatic discharge protection (ESD) and Electrical Overstress (EOS). Generally, VSD material behaves as a dielectric unless a characteristic voltage or range of voltages is applied, in which case it will behave as a conductor. There are a variety of VSD materials. Examples of voltage switchable dielectric materials are given in documents such as U.S. patent No.4,977,357, U.S. patent No.5,068,634, U.S. patent No.5,099,380, U.S. patent No.5,142,263, U.S. patent No.5,189,387, U.S. patent No.5,248,517, U.S. patent No.5,807,509, WO 96/02924, and WO 97/26665.

VSD material can be formed in a variety of ways. One conventional technique proposes to fill the polymer layer with high levels of metal particles to very close to the percolation threshold, typically in excess of 25% by volume. Semiconductor and/or insulator materials are then added to the mixture.

Another conventional technique proposes mixing doped metal oxide powders and then sintering the powders to produce grain boundary-carrying particles, which are then added to a polymer matrix above the percolation threshold to form the VSD material.

U.S. patent application No.11/829,946 entitled VOLTAGE SWITCH DIELECTRIC MATERIALHAVING CONDUCTIVE OR SEMI-CONDUCTIVE ORGANICMATERIAL; and U.S. patent application No.11/829,948, entitled vstageswitch DIELECTRIC MATERIALHAVING HIGH ASPECTRATIO PARTICLES, describes other techniques for forming VSD material.

Drawings

Figure 1 is a schematic (non-to-scale) cross-sectional view of a layer or thickness of VSD material showing the composition of the VSD material of various embodiments.

Fig.2A and 2B show the electrical conductivity of an epoxy (Epon) -based polymer adhesive used in VSD material compositions with respect to an electric field as a basis for comparison of adhesive compositions that enhance electron mobility in the presence of high electric fields.

Fig.3A shows measured conductivity versus electric field for an HFC polymer, according to one embodiment.

Fig.3B and 3C show measured conductivity versus electric field for suitable alternative polymeric materials that exhibit improved electron mobility under high electric fields, according to other embodiments or variations.

Fig.4 shows measured values of electrical conductivity versus electric field for a polymer-based matrix including a plurality of fillers, according to various embodiments.

Figure 5A illustrates a substrate device configured with VSD material containing, for example, a composition as described in any of the embodiments provided herein.

Fig.5B shows a configuration in which a conductive layer is embedded in a substrate.

Figure 5C shows a vertical switching arrangement incorporating VSD material into the substrate.

Figure 6 is a simplified diagram of an electronic device upon which VSD material according to the described embodiments of the present invention may be provided.

Detailed Description

According to various embodiments, the binder of a VSD composition is selected to have enhanced electron mobility in the presence of high electric fields (e.g., generated by an applied voltage measuring hundreds or thousands of volts). In some embodiments, the polymeric binder material is selected to exhibit greater electron mobility characteristics in the presence of high electric fields. Additionally or alternatively, some embodiments provide that the polymeric binder is reinforced with a semiconductive filler to form a binder having improved electron mobility in the presence of high electric fields.

According to an embodiment, the binder or matrix of the VSD material is formed of a polymeric material having the property of exhibiting a relatively high electron mobility or conductivity in the presence of a high electric field. Such polymeric materials are also known as high field conductivity ("HFC") polymers. The HFC polymer matrix or binder enables the VSD material to be formulated to have improved electrical characteristics, including reduced clamping and trigger voltages, compared to the non-conductive polymers typically used in VSD compositions, such as Epon 828.

Additionally, according to some embodiments, the VSD material composition includes a polymer matrix containing fillers that are intimately mixed into the polymer resin to form the binder of the VSD material. As illustrated in the embodiment of fig.4, the presence of the filler enhances the overall electron mobility of the VSD material, thereby reducing the clamping and trigger voltages of the VSD composition formed from the binder. Other particles, such as conductive materials (e.g., metal particles), may also be added to the binder. The total particle concentration of the resulting VSD material may be below the percolation threshold.

With respect to the polymer composition in VSD material, it is believed that when a sufficiently high electric field (e.g., an electric field that exceeds a characteristic threshold) is present, the internal field between conductive particles can become sufficiently high to allow conduction of electrons from one conductive particle to an adjacent conductive polymer via the polymer. As mentioned elsewhere, the internal field of the VSD material is one or more orders of magnitude greater than the electric field applied to the VSD material, and therefore, the applied external field is amplified by the conductive particles in the VSD composition. In VSD materials, the polymer (or binder) acts as a "semiconductor" with an effective "bandgap". It is recognized by embodiments that the polymer used as the binder may be selected based on the assumption that if the high field electron mobility of the polymer matrix is enhanced, the characteristic "turn on" voltage will drop. In other words, if the polymer binder is selected or designed to have high field electron mobility, it is expected that the corresponding VSD material composition will have lower trigger and clamp voltage thresholds.

It is also recognized by embodiments that conventional undoped "conductive polymers" do not necessarily belong to the class of polymers that can be considered to have high field conductivity. In fact, as a matter of conventional consideration, undoped polymers, which are considered to be conductive polymers, are not necessarily more conductive at high fields than other polymers, such as epoxies (e.g., Epon). In addition, conventional conductive polymers are typically "conductive" at low fields (i.e., have lower impedance than other polymers) and thus do not facilitate the characteristic "off-state" that is essential for use in VSD compositions. In contrast, HFC polymers are relatively non-conductive at low voltages and are considered "conductive" when higher fields are applied. It should be understood that in the context of describing the resistive properties of polymers, the term "conductive" is a relative term for materials such as polymers. "conductive polymers" are non-conductive materials, but are conductive relative to polymers and the like.

According to one embodiment, the HFC polymer has the following properties: such polymers can carry an electrical current of at least 1 nanoamp in the presence of an electric field equal to or greater than 400 volts/mil. For reference, some examples are provided with figures showing the magnitude of current versus electric field when a voltage is applied across a 2.5 mil gap. Some embodiments described herein incorporate an HFC polymer, while others incorporate polymeric materials having enhanced electron mobility at high fields. Thus, it is recognized by embodiments that even modest improvements in the high field electron mobility of the binder can benefit the electrical properties of the resulting VSD material.

Overview of VSD Material

As used herein, a "voltage switchable material" or "VSD material" is any composition or combination of compositions having dielectric or non-conductive properties, unless an electric field or voltage is applied to the material that exceeds the level characteristic of the material, in which case the material becomes conductive. VSD material is therefore dielectric unless a voltage (or electric field) is applied to the material that exceeds a characteristic level (e.g., caused by an ESD event), in which case the VSD material switches to a conductive state. VSD material can also be characterized as a non-linear resistive material. For one embodiment such as that described, the characteristic voltage may vary over a range of values that exceeds the operating voltage level of the circuit or device by a factor of several. Such voltage levels may be on the order of transient conditions (e.g., caused by electrostatic discharge), but embodiments may also include the use of planned electrical events. Further, one or more embodiments provide that the material behaves similarly to an adhesive when there is no voltage exceeding a characteristic voltage.

Additionally, one embodiment provides that the VSD material can be characterized as a material that includes a binder that is partially mixed with conductive or semiconductive particles. The material as a whole conforms to the dielectric properties of the adhesive in the absence of a voltage exceeding the characteristic voltage level. When a voltage exceeding a characteristic level is applied, the material as a whole conforms to the conductive property.

Many VSD material compositions can provide desirable "voltage switchable" electrical characteristics by dispersing an amount of conductive material in a polymer matrix to just below the percolation threshold, which is statistically defined as the threshold at which a conductive path through the thickness of the material is likely to form. Other materials, such as insulators or semiconductors, are dispersed in the matrix to better control the percolation threshold. In addition, other VSD material compositions, including those containing particulate components (e.g., core shell particles or other particles), can be loaded with these selected particles (particulate compositions) above the percolation threshold.

As described in some embodiments, VSD material can be disposed on an electronic device to protect the circuitry or electrical elements of the device (or particular sub-regions of the device) from some electrical event, such as ESD or EOS. Accordingly, one or more embodiments provide that the characteristic voltage level of the VSD material is higher than the characteristic voltage level of the operating circuits or elements of the device.

According to embodiments described herein, the ingredients of the VSD material may be homogeneously mixed into the binder or polymer matrix. In one embodiment, the mixture is dispersed on a nanoscale, which means that the particles comprising the organic conductive/semiconductive material are nanoscale in at least one dimension (e.g., cross-section), and that a substantial majority of the particles in the volume, including the full partial dispersion, are separated from each other (so as not to aggregate or pack together).

Additionally, an electronic device having VSD material of one of the embodiments described herein can also be provided. Such electronic devices may include substrate devices such as printed circuit boards, semiconductor packages, discrete devices, Light Emitting Diodes (LEDs), and Radio Frequency (RF) components.

Figure 1 is a schematic (non-to-scale) cross-sectional view of a layer or thickness of VSD material showing the composition of the VSD material of various embodiments. As shown, the VSD material 100 includes a binder 105 and a plurality of particulate components dispersed in the binder at different concentrations. The particle composition of the VSD material may include a combination of conductive particles 110, semiconductor particles 120, nano-sized particles 130, and/or other particles 140, such as core shell particles or varistor particles.

In some embodiments, the use of conductive particles 110, semiconductive particles 120, or nano-sized particles 130 is omitted from the VSD composition. For example, semiconductive particles 120 may be omitted from selected particles of VSD material. Thus, the type of particulate component included in the VSD composition can vary depending on the electrical and physical properties of the VSD material desired.

According to embodiments described herein, the matrix binder 105 is formulated from a polymeric material having enhanced electron mobility at high electric fields. In some embodiments, the polymeric material used for the adhesive 105 includes an HFC polymer, such as a polyacrylate (e.g., hexanediol diacrylate). Additionally or alternatively, the polymeric material comprises a blend or mixture of polymers (monomers) having high electron mobility and polymers (monomers) having low electron mobility. Such polymers (or blends) with enhanced electron mobility are capable of carrying 1.0 x 10 at about 400 volts/mil^-9Current (extrapolated from empirical data at 1000 volts and across a 2.5 mil gap). According to a variant, the polymeric binder 105 may also comprise a mixture of standard polymers (for example Epon or GP611) with HFC polymers or polymers with enhanced electron mobility at high fields. The polymeric binder 105 may be reinforced using nano-sized particles 130 that are mixed into the binder to form a doped variant of the binder 105.

Examples of the conductive material 110 include metals such as copper, aluminum, nickel, silver, gold, titanium, stainless steel, nickel phosphorous (nickel phosphorous), niobium, tungsten, chromium, other metal alloys, or conductive ceramics such as titanium diboride or titanium nitride. Examples of semiconductive material 120 include organic and inorganic semiconductors. Some inorganic semiconductors include silicon carbide, boron nitride, aluminum nitride, nickel oxide, zinc sulfide, bismuth oxide, titanium dioxide, cerium oxide, bismuth oxide, tin oxide, indium tin oxide, antimony tin oxide, and iron oxide, praseodymium oxide. The specific formulation and composition can be selected to provide mechanical and electrical properties that are most suitable for the particular application of the VSD material.

The nano-sized particles 130 may have one or more types. Depending on the implementation, at least one component comprising a portion of the nano-sized particles 130 is (i) organic particles (e.g., Carbon Nanotubes (CNTs), graphene, C60 fullerene); or (ii) inorganic particles (metal), metal oxide, nanorods or nanowires). The nano-sized particles may have a High Aspect Ratio (HAR) such that the aspect ratio is at least over 10: 1 (and may be over 1000: 1 or higher). Specific examples of such particles include: copper, nickel, gold, silver, cobalt, zinc oxide, tin oxide, silicon carbide, gallium arsenide, aluminum oxide, aluminum nitride, titanium dioxide, antimony, boron nitride, antimony tin oxide, indium zinc oxide, bismuth oxide, cerium oxide, and antimony zinc oxide. In at least some embodiments, the nano-sized particles correspond to a semiconductive filler that constitutes part of the binder. Such fillers may be uniformly dispersed in the polymer matrix or binder at various concentrations. As mentioned in the embodiment of FIG.4, some nano-sized particles (e.g., Antimony Tin Oxide (ATO), CNT, zinc oxide, bismuth oxide (Bi)₂O₃) May enhance electron mobility of the adhesive 105 under high electric fields.

The dispersion of the plurality of particles in the matrix 105 allows the VSD material 100 to be non-delaminated and have a uniform composition while exhibiting the electrical properties of a voltage switchable dielectric material. Typically, the characteristic voltage of VSD material is measured in volts/length (e.g., every 5 mils), but other field measurements may be used instead of voltage. Thus, a voltage 108 applied across the VSD material layer boundary 102 can switch the VSD material 100 to a conductive state if the characteristic voltage of the gap distance L is exceeded.

As shown in sub-region 104 (intended to be representative of VSD material 100), when a voltage or field is applied to the VSD composition, the VSD material 100 contains a respective charged particle component. If the field/voltage is above the trigger threshold, at least some of the particles carry sufficient charge to switch at least a portion of the composition 100 to a conductive state. More specifically, as shown in representative sub-region 104, when a voltage or field is present, each particle (such as a class of particles such as conductor particles, core shell particles, or other semiconducting or compound particles) forms a conductive region 122 in the polymer binder 105. The voltage or field level of the conductive region 122 can be made to be sufficient in magnitude and number to cause current to pass through the thickness of the VSD material 100 (e.g., between the boundaries 102), consistent with the characteristic trigger voltage of the composition. It is believed that the presence of the conductive particles amplifies the applied voltage 108 within the thickness of the composition, thereby causing the electric field of each conductive region 122 to be more than an order of magnitude higher than the electric field of the applied voltage 108.

Fig.1 illustrates the presence of a conductive region 122 in a portion of the total thickness. The portion or thickness of VSD material 100 provided between boundaries 102 represents the spacing between electrodes that are moved laterally or vertically. Some or all of the portion of VSD material is affected when a voltage is present, thereby increasing the size and number of conductive regions within that region. When a voltage is applied, the presence of the conductive region varies along the thickness (vertical or lateral thickness) of the VSD composition depending, for example, on the location and intensity of the voltage at the event. For example, only a portion of the VSD material may be pulsed, depending on the voltage and power level of the electrical event.

Accordingly, figure 1 illustrates that the electrical characteristics of the VSD composition, such as conductivity or trigger voltage, are affected in part by: (i) a concentration of particles, such as conductive particles, semiconductive particles, or other particles (e.g., core shell particles); (ii) electrical and physical properties of the particles, including impedance properties (which are affected by the type of particle, e.g., whether the particle is a core shell particle or a conductor); and (iii) the electrical properties of the binder 105 (including the electron mobility of the polymeric material used for the binder).

U.S. patent application No.11/829,946 entitled VOLTAGE SWITCH DIELECTRIC MATERIALHAVING CONDUCTIVE OR SEMI-CONDUCTIVE ORGANICMATERIAL; and U.S. patent application No.11/829,948, entitled voltageswitchele DIELECTRIC MATERIAL HAVING HIGH ASPECTRATIO PARTICLES, describes specific compositions and techniques for incorporating organic and/or HAR PARTICLES into VSD material compositions; the entire contents of each of the two aforementioned patent applications are incorporated by reference into this application.

In addition, one embodiment contemplates VSD material that includes varistor particles as part of its particle composition. Thus, one embodiment incorporates a concentration of particles each exhibiting nonlinear impedance properties, and thus is considered an active varistor particle. Such particles typically comprise zinc oxide, titanium dioxide, bismuth oxide, indium oxide, tin oxide, nickel oxide, copper oxide, silver oxide, praseodymium oxide, tungsten oxide, and/or antimony oxide. The concentration of varistor particles may be formed by sintering the varistor particles (e.g., zinc oxide) and then mixing the sintered particles into the VSD composition. In some applications, the varistor particle compound is formed by combining a primary component, which is zinc oxide or titanium dioxide, with a secondary component, or other metal oxide (as listed above), which melts or diffuses into the grain boundaries of the primary component, such as by sintering.

Particles having a high band gap (e.g., using an insulating shell layer (s)) may also be used. Thus, in some embodiments, the total particle concentration of the VSD material, including the concentration of core shell particles (as described herein), is sufficient in number such that the particle concentration exceeds the percolation threshold of the composition.

In some conventional methods, the VSD material composition includes metal or conductive particles dispersed in a binder of the VSD material. The range of sizes and numbers of metal particles may, in some cases, depend on the desired electrical characteristics of the VSD material. In particular, the metal particles may be selected to have properties that affect specific electrical characteristics. For example, to obtain a lower clamping value (e.g., the amount of voltage applied needed to render the VSD material conductive), the VSD material composition may include a higher volume fraction of metal particles. As a result, it becomes difficult to maintain a low initial leakage current (or high impedance) at a low bias voltage because the metal particles form a conductive path (short circuit). As described below, the polymer material can be selected and/or doped to facilitate the clamp/trigger voltage reduction and to minimize the negative impact on the off-state electrical characteristics required for the VSD material.

Polymeric binders with enhanced high field electron mobility

Fig.2A to 4 graphically show experimental results in which the electrical conductivity of various polymer resins with respect to an electric field is measured. Measurements were made at a 2.5 mil gap, 45 mil inner pad diameter (inner gauge). The measurements are used to determine polymers that exhibit high field electron mobility (e.g., HFC polymers).

Referring to the figures, fig.2A and 2B show the electrical conductivity with respect to an electric field of a standard epoxy (Epon828) based polymer adhesive, including pure Epon (fig. 2A) and a mixture of Epon and an epoxidized silicone resin (GP 611). The designer of VSD material can purposefully select a mixture of Epon and GP611 in combination with an HFC material as shown in figure 3, taking into account the high field electron mobility of the adhesive. Thus, figure 2B illustrates a polymer binder for an improved VSD material when taking into account the electron mobility parameters.

In comparison to fig.2A and 2B, fig.3A illustrates the measured value of conductivity versus electric field for the HFC polymer. In the illustrated embodiment, the HFC polymer is a polyacrylate, more specifically, hexanediol diacrylate (HDDA). As shown in FIG.3A, the high field conductivity of the HFC polymer is greater than that of pure Epon, since the current that HDDA can carry is measured at about 1.5X 10^-9(about 400 volts) to 4.0X 10^-9In the ampere (at about 1000 volts). In contrast, pure Epon carries 5.0X 10^-11(about 400V) to 1.5X 10^-10Amperes (about 1000 volts).

Fig.3B and 3C depict measurements of conductivity versus electric field for suitable alternative polymer materials that exhibit improved electron mobility at high electric fields. Surprisingly, FIG.3C shows that 1: 1 polyaniline (Polyaninlne)/epoxy carries a current of about 1.8 to 2.0X 10 at 1000 volts^-10Much less current than HFC polymers, such as HDDA. Embodiments described herein contemplate that carbonyl-bearing polymers, such as hexanediol diacrylate, have improved high field conductivity.

With respect to the depicted measurements of conductivity versus electric field for the various polymeric materials, it should be noted that in VSD applications, the actual amount of electric field present is significantly higher than that provided by the applied voltage. As previously mentioned, the conductive particles in the VSD composition amplify the applied electric field. For example, an electronic event measuring about 1000 volts can produce an internal electric field in the range of tens of thousands of volts within the material.

Fig.4 illustrates measurements of conductivity versus electric field for a polymer-based matrix comprising a plurality of fillers. The examples provided use the following nano-sized particles: carbon Nanotubes (CNT), Antimony Tin Oxide (ATO), zinc oxide (ZnO), and bismuth oxide (Bi)₂O₃). In each embodiment, the particles are thoroughly mixed into a polymer resin (e.g., Epon) before accepting metal particles or other particles and compounds that cause the compounds to have their switchable electrical properties&GP 611). The results show that the polymer-based matrix has improved electron mobility at high electric fields. The polymeric matrix containing ATO and CNT exhibits higher conductivity than the pure polymeric resin and polymeric matrix containing other semiconducting fillers. It is expected that a polymer matrix with higher conductivity at high electric fields will result in a reduction in the clamping and trigger voltages of the resulting VSD material.

Table 1 lists experimental values for VSD composites containing multiple classes of polymeric binders. Each VSD composite listed in table 1 contained the same total concentration of conductive and semiconductive particles (see table 2 for the exact concentration). The main difference between each composition is that the polymer-based binder is altered. All described voltages were measured across a 2.5 mil gap.

Table 1 shows that the electrical properties of VSD material change when different polymer based binders are used. Table 1 shows that VSD compositions generally exhibit lower clamping and trigger voltages relative to polymer-based adhesives with enhanced high field electron mobility. VSD compositions comprising HFC polymer hexanediol diacrylate (HDDA) in their adhesive, e.g., (i) HDDA with polyBD, (ii) HDDA with EPON, or (iii) both HDDA with polyBD and GP611, exhibit trigger values of 80-100V (3 mil gap), lower than when a standard adhesive system (EPON & GP611) is used in the polymer composite. Hexanediol diacrylate (HDDA) also switches faster when combined with other resins and used as a binder for polymer composites than the standard binder system for VSD materials.

According to one or more embodiments, a VSD composition incorporating an HFC polymer (e.g., HDDA) may include 25% metal particle filler, 25% semiconductor filler (micron-sized or nano-sized), and optionally may contain 1% nanoparticles (e.g., nanorods, nanowires, or carbon nanotubes). A wider range of particles may also be used. For example, the VSD material may comprise 10-40% metal particle filler, 10-45% semiconductor particles, and 0.1-15% nanoparticles. In this embodiment, the polymer matrix may correspond to a mixture of hexanediol diacrylate and epoxy resin. The measured electrical properties of the samples, such as trigger and clamp voltages, were about 100-200V lower than the sample material using pure epoxy as the polymer resin. More specific compositions are also provided in table 2.

One method of formulating the VSD composition using the HDDA polymer blend is given below (see table 1, line 4).In a clean 1000ml plastic beaker, 4.74g of short graphitized (d > 50nm, l ═ 0.2-1um) carbon nanotubes (CNTs, manufactured by CHEAP TUBES inc.) were mixed with 65.9g of epoxy resin (EPON828) and 65.9g of hdda added in the form of liquid resin. Next, 160g N-methyl-2-pyrrolidone was added as a solvent to the above mixture. Then, 20.1g of dicyandiamide and 0.75g of 1-methylimidazole were added as a curing agent and a catalyst. The beaker was placed in a cold water bath to control the temperature during the pre-mixing process. The mixture is mixed to make the solution a homogeneous mixture of CNTs, resin and solvent. The mixture was further mixed. Then, 70.5g P25 (TiO) was weighed out₂) And 2.37g KR44 (isopropyl tris (N-ethylenediamino) ethyltitanate) was added to the powder to disperse the particles. The P25 powder was slowly added to the mixture in the beaker while mixing using a blade. And adding a filler: 564.4g of wet-chemically treated nickel oxide, 76.4g of TiO were weighed out₂And 127.5g of bismuth oxide (Bi)₂O₃) And then slowly added to the mixture containing the CNTs and resin. 0.66g of benzoyl peroxide was then dissolved in 5g of NMP and then added to the mixture to initiate free radical polymerization of HDDA. Then, the mixture was mixed again.

Table 2 lists the composition of each VSD composition identified in table 1 in more detail.

While there are some differences in the concentrations of the particulate components in the VSD compositions listed, the differences in the electrical characteristics of the various compositions (see table 1 for clamp and trigger voltage values) are apparently due to differences in the polymer component(s) in the binder of the various compositions.

Applications of VSD materials

The VSD material compositions according to any of the described embodiments of the invention have a wide variety of applications. In particular, embodiments provide that VSD material can be provided on substrate devices, such as printed circuit boards, semiconductor packages, discrete devices, thin film electronics, and more specialized applications such as LEDs and radio frequency devices (e.g., RFID tags). In addition, other applications may also be provided using VSD material, such as liquid crystal displays, organic light emitting displays, electrochromic displays, electrophoretic displays, or backplane drivers for these devices, as described herein. The purpose of including VSD material can be to improve control of transient and overvoltage conditions such as may occur in an ESD event. Another application for VSD material includes metal deposition, such as L. As described in U.S. patent No.6,797,125 to Kosowsky (which patent is incorporated by reference herein in its entirety).

Figure 5A depicts a substrate device constructed with VSD material containing compositions such as those described in any of the embodiments provided herein. As shown in fig.5A, the substrate arrangement 500 corresponds to, for example, a printed circuit board. A conductive layer 510, which includes electrodes 512 and other tracking elements or interconnects (interconnects), is formed on the surface of a substrate 500 of one thickness. In the illustrated construction, VSD material 520 (including, for example, a composition according to any aspect of the invention) can be provided on the substrate 500 (e.g., as part of a core structure) to provide a lateral switch (lateral switch) between the electrodes 512 overlying the VSD layer 520 when a suitable electronic event (e.g., ESD) occurs. The gap 518 between the electrodes 512 may function as a lateral or horizontal switch that is triggered to turn "on" when a sufficient transient electrical event occurs. In one application, one of the electrodes 512 is a ground element that extends to a ground plane or device. As the material in the VSD layer 520 is switched to a conductive state (due to a transient electrical event), the ground electrode 512 is interconnected to ground with other conductive elements 512 separated by gaps 518.

In one implementation, one via 535 extends from the ground electrode 512 into the thickness of the substrate 500. The vias provide electrical connections to complete the ground path extending from ground electrode 512. The portion of the VSD layer located below gap 518 bridges conductive element 512, thereby grounding the transient electrical event, thereby protecting the components and devices interconnected with conductive element 512 including conductive layer 510.

Fig.5B illustrates a structure in which a conductive layer is embedded in a substrate. In the illustrated structure, the conductive layer 560 includes electrodes 562, the electrodes 562 being distributed through the thickness of the substrate 550. A layer of VSD material 570 and a dielectric material 574, such as a B-stage material, may overlie the embedded conductive layer. An additional layer 577 of dielectric material may also be included, such as just below or in contact with the VSD layer 570. The surface electrodes 582, 582 comprise a conductive layer 580 provided on the surface of the substrate 550. The surface electrodes 582, 582 may also overlie the layer 571 of VSD material. One or more vias 575 may electrically interconnect the electrodes/conductive elements of the conductive layers 560, 580. The layers of VSD material 570, 571 are arranged so that when a transient electrical event of sufficient strength reaches the VSD material, adjacent electrodes are switched and bridged horizontally across the gap 568 of each conductive layer 560, 580.

Alternatively or in variation, fig.5C shows a vertical switching arrangement incorporating VSD material into the substrate. The substrate 586 incorporates a layer of VSD material 590 separating two layers of conductive material 588, 598. In one implementation, one of the conductive layers 598 is embedded. When the transient electrical event reaches the layer of VSD material 590, it switches to a conductive state and bridges the conductive layers 588, 598. The vertical switching structure may also be used to interconnect conductive elements to ground. For example, embedded conductive layer 598 may provide a ground plane.

Figure 6 is a simplified diagram of an electronic device on which VSD material of the described embodiments of the present invention can be provided. Fig.6 shows that device 600 includes a substrate 610, a component 640, and optionally a housing or casing 650. VSD material 605 (in accordance with any of the schemes) can be incorporated into any one or more of a number of locations, including one location on surface 602, below surface 602 (e.g., below its tracking elements or below component 640), or in the thickness of substrate 610. Alternatively, the VSD material may be incorporated into the housing 650. In each case, VSD material 605 may be incorporated to engage conductive elements such as trace leads when a voltage exceeding a characteristic voltage is present. Thus, under particular voltage conditions, the VSD material 605 is a conductive element.

For any of the applications described herein, device 600 may be a display device. For example, the component 640 may correspond to an LED that emits light from the substrate 610. The arrangement and configuration of VSD material 605 on substrate 610 can be selected to accommodate electrical leads, terminals (i.e., input or output terminals), and other conductive elements provided, used, or incorporated for the light emitting device. Alternatively, the VSD material can be bonded between the positive and negative leads of the LED device, separate from the substrate. Additionally, one or more embodiments also provide for the use of organic LEDs, in which case the VSD material can be provided, for example, below an Organic Light Emitting Diode (OLED).

With respect to LEDs and other light emitting devices, any of the embodiments described in U.S. patent application No.11/562,289 (incorporated herein by reference) can be implemented using VSD materials as described in other embodiments herein.

Alternatively, the device 600 may correspond to a wireless communication device, such as a radio frequency identification device. For wireless communication devices, such as Radio Frequency Identification Devices (RFID) and wireless communication elements, the VSD material may protect the component 640 from, for example, overcharging or ESD events. In this case, the component 640 may correspond to a chip or a wireless communication element of the device. Alternatively, VSD material 605 may be used to protect other elements from the charge generated by component 640. For example, the component 640 can correspond to a block of cells and the VSD material 605 can be provided as a tracking element on the surface of the substrate 610 to protect it from voltage conditions caused by cell events. Any of the compositions of VSD material according to the embodiments of the present invention may be used as VSD material in the devices and device structures described in U.S. patent application No.11/562,222 (incorporated herein by reference), which describes the implementation of a number of wireless communication devices that incorporate VSD material.

Alternatively or in variation, the component 640 may correspond to, for example, a discrete semiconductor device. The VSD material 605 may be integrated with the component or arranged to engage the component in the presence of a voltage that causes it to switch on.

Alternatively, the device 600 may correspond to a packaging device or a semiconductor package for receiving a substrate assembly. The VSD material 605 may be combined with the housing 650 prior to including the substrate 610 or the component 640 in the device.

Although exemplary embodiments have been described in detail herein with reference to the accompanying drawings, variations in specific embodiments and details are also included herein. It is intended that the scope of the invention be defined by the following claims and their equivalents. Furthermore, it is to be understood that the specific features described, either individually or as part of an embodiment, may be combined with other individually described features, or as part of other embodiments. Accordingly, the failure to describe combinations does not preclude the inventors from claiming rights to such combinations.

Claims (20)

1. A composition of Voltage Switchable Dielectric (VSD) material comprising:

an adhesive comprising a polymeric material having an ability to carry at least 1.0 x 10 in the presence of an electric field equal to 400 volts per mil^-9A characteristic of ampere; and

one or more types of particles dispersed in the binder;

wherein the particles and the binder form a composition that is non-conductive in the absence of an electric field exceeding a threshold value and conductive in the presence of an electric field exceeding a threshold value.

2. The composition of claim 1, wherein the adhesive has a capability of carrying at least 2.0 x 10 in the presence of an electric field equal to 400 volts per mil^-9Characteristic of amperes.

3. The composition of claim 2, wherein the binder comprises a polyacrylate.

4. The composition of claim 3, wherein the binder comprises hexanediol diacrylate.

5. The composition of claim 1, wherein the binder comprises one or more binders selected from (i) polyaniline, (ii) polybutadiene, or (iii) hexanediol diacrylate.

6. The composition of claim 5, wherein the adhesive further comprises an epoxy resin.

7. The composition of claim 1, wherein the overall concentration level of particles dispersed in the binder is below the percolation threshold of the binder.

8. The composition of claim 1, wherein the one or more types of particles comprise a concentration of metal particles.

9. The composition of claim 1, wherein the one or more types of particles comprise a concentration of the semiconductive filler dispersed in the binder prior to the concentration of the metal particles.

10. The composition of claim 1, wherein the concentration of the semiconductive filler comprises carbon nanotubes.

11. The composition of claim 1, wherein the concentration of semiconductive filler comprises Antimony Tin Oxide (ATO).

12. The composition of claim 1, wherein the concentration of semiconductive filler comprises zinc oxide.

13. An adhesive for use in VSD compositions, the adhesive comprising:

a polymeric material;

one or more concentrations of nano-sized semi-conductive particles mixed with the polymeric material prior to conductive particles and other particle constituents used to make the VSD composition;

wherein the adhesive is formulated to conduct at least 1.0 x 10 in the presence of an electric field equal to 400 volts per mil^-9In amperes.

14. The binder of claim 13, wherein the one or more concentrations of nanometer-sized semiconducting particles comprise carbon nanotubes.

15. The binder of claim 13, wherein the one or more concentrations of nano-sized semi-conductive particles comprise Antimony Tin Oxide (ATO).

16. The binder of claim 13, wherein the one or more concentrations of nanometer sized semi-conductive particles include Antimony Tin Oxide (ATO) and carbon nanotubes.

17. The adhesive of claim 13 wherein the polymeric material comprises hexanediol diacrylate.

18. The adhesive of claim 13, wherein the adhesive is formulated to conduct at least 1.0 x 10 in the presence of an electric field equal to 1000 volts per mil^-6In amperes.

19. The binder of claim 13, wherein the one or more concentrations of the nanosized semiconducting particles comprise zinc oxide.

20. The binder of claim 13, wherein the one or more concentrations of nano-sized semi-conductive particles comprise bismuth oxide (Bi)₂O₃)。