Method for forming a security barrier of an electronic device under protection and security barrier of an electronic device under protection

Abstract

A method is provided for forming a security barrier for one of a protected electronic devices. The method includes depositing a variable dielectric material layer on the protected electronic device, and converting a target portion of the variable dielectric material layer into at least one electrical circuit structure having at least one measurable electrical characteristic. The method further includes depositing a thermally stable material layer onto the variable dielectric material layer.

Description

Expandable Method for a Security Barrier Expandable Method for a Security Barrier The present disclosure relates to anti-tampering technology, and more particularly, to a protective physical barrier having measurable electrical properties that can indicate unauthorized access to a protected device for inspection and / or modification. Inspection can include, for example, imaging for the purpose of forging a protected device. Modification can include, for example, replacing components with counterfeit components that may have inferior performance and quality. Modification can also include instrumentation for the purpose of recording intellectual property embodied as software, firmware, or data residing in a protected device. For example, a counterfeit device may be installed with malware that collects information unknown to the product owner. An indication of unauthorized access can be used, for example, to assess system integrity, as evidence of intellectual property theft; or to signal a gap in the device's origin. According to a non-limiting embodiment, a method of forming a security barrier for a protected electronic device is provided. The method includes depositing a transformable dielectric material layer on the protected electronic device, and converting a target portion of the transformable dielectric material layer into at least one electrical circuit structure having at least one measurable electrical property. The method further includes depositing a thermally stable material layer on the transformable dielectric material layer. According to any previous embodiment, forming the security barrier includes establishing a blending ratio of conductive nanoparticles and electrically insulating nanoparticles in the transformable dielectric material layer. According to any previous embodiment, the conductive nanoparticles include silver (Ag) nanoparticles and the electrically insulating nanoparticles include barium strontium titanate (BST) nanoparticles. According to any previous embodiment, the transformable dielectric material layer is cured at 80 degrees Celsius for 15 minutes. According to any previous embodiment, converting the target portion of the transformable dielectric material layer includes performing a selective laser sintering (SLS) process such that laser energy impinges on the transformable dielectric material layer to convert the target portion into the at least one electrical circuit structure. According to any previous embodiment, the laser energy causes the conductive nanoparticles to melt together to form a conductive path defining the at least one electrical circuit structure. According to any previous embodiment, the electrically insulating nanoparticles electrically isolate the at least one electrical circuit structure from the remainder of the transformable dielectric material layer. According to any previous embodiment, the thermally stable material layer includes nanoparticles that impede the formation of additional conduction paths within the transformable dielectric material layer. According to any previous embodiment, the nanoparticles include boron nitride (BN) nanoparticles. According to any previous embodiment, the thermally stable material layer reduces at least one of an amount and a size of air voids present in the transformable dielectric material layer. According to any previous embodiment, reducing the amount of air voids includes filling the air voids with polymerized ethoxylated trimethylolpropane triacrylate. According to any previous embodiment, the thermally stable layer is cured via ultraviolet (UV) exposure to inhibit further change of the security barrier layer at temperatures below 250 degrees Celsius. According to a non-limiting embodiment, a security barrier for a protected electronic device is provided. The security barrier includes a transformable dielectric material layer on the protected electronic device. The transformable dielectric material layer includes a plurality of conductive nanoparticles and a plurality of insulating nanoparticles. The security barrier further includes at least one electrical circuit structure and a thermally stable material layer. The at least one electrical circuit structure includes a portion of the conductive nanoparticles and has at least one measurable electrical property. The thermally stable material layer covers the transformable dielectric material layer including the at least one electrical circuit structure. According to any previous embodiment, the at least one measurable electrical property changes in response to changing the electrical circuit structure. According to any previous embodiment, the at least one measurable electrical property includes at least one of resistance, capacitance, and inductance. According to any previous embodiment, the at least one electrical circuit structure is at a target portion of the transformable dielectric material layer, and the insulating nanoparticles electrically isolate the at least one electrical circuit structure from the remainder of the transformable dielectric material layer. According to any previous embodiment, the transformable dielectric material layer includes other electrical circuit structures. According to any previous embodiment, the conductive nanoparticles include silver (Ag) nanoparticles, and the insulating nanoparticles include barium strontium titanate (BST) nanoparticles. According to any previous embodiment, the thermally stable material layer includes a boron nitride (BN) material and a polymerized ethoxylated trimethylolpropane triacrylate material. According to any previous embodiment, the transformable dielectric material layer and the thermally stable layer are combined to form a composite substrate that includes a combination of Ag particles, BST particles, and BN particles. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects are described in detail herein and are considered a part of the claimed disclosure. To better understand the disclosure with these advantages and features, refer to the description and the drawings. Previous solutions for creating a safety barrier with measurable electrical characteristics fall into two categories: (1) attaching a prefabricated safety barrier to an electronic assembly containing a protected device; or (2) depositing one or more material layers that combine to form a safety barrier covering the protected device. Solutions in the first category typically prefabricate a physical structure containing electrical circuit elements (and possibly other features) separately and attach the prefabricated structure (mechanically and electrically) to a circuit card assembly (CCA) to cover or enclose the target device and interconnects. First-category methods typically also require design customization of the electronic assembly containing the protected device to incorporate electrical and mechanical interfaces into the prefabricated cover. The practical application of first-category methods is currently limited to CCA-level barrier structures; however, the application can be extended to include barrier structures attached via 3D heterogeneous integration (3DHI) manufacturing methods. Size, weight, power, and cost (SWaP-C) considerations may limit the utility of this first-category solution. Solutions in the second category typically utilize material layers (possibly containing electrical circuit elements and other features) that are deposited via a fabrication or manufacturing process to cover or enclose the target device and interconnects. The combined one or more layers exhibit measurable electrical / mechanical characteristics that are used to form a protective barrier for the protected device. The deposition methods utilized by second-category solutions vary widely and include, for example, 3D printing of conductive or resistive inks for forming circuit structures and photolithography for depositing metal layers in integrated circuit fabrication processes. Various non-limiting embodiments of the present disclosure provide a protective physical barrier with measurable electrical characteristics and a method of manufacturing the same, the measurable electrical characteristics being capable of indicating unauthorized access to inspect and / or modify a protected device. The safety barrier includes a transformable or convertible dielectric material, such as, for example, silver-barium strontium titanate (Ag-BST) ink. A sintering process is then applied to the convertible dielectric material to transform selected portions from the dielectric material into one or more conductive structures having measurable electrical properties (such as resistance, capacitance, or inductance) that can be incorporated into an electrical circuit. The sintering process can be achieved, for example, using laser energy. The sintering process is designed to form the (one or more) conductive structures such that tampering or other unauthorized efforts to physically access the protected device will change or damage the structure(s), thereby changing the electrical properties of the structure(s) in a measurable manner. The electrical properties of the structures formed by the foregoing process can be measured in various ways, for example, by incorporating the structure into an electrical circuit and comparing the electrical response of the circuit to its expected electrical response (established at initial fabrication). In this way, the present disclosure provides a method for forming a safety barrier by selectively transforming portions of a dielectric material layer into conductive structures having measurable electrical properties that change when a bad actor attempts to access the protected device. The security barrier methods described herein are extended to individually address a broader range of problems than can be individually addressed by previously known methods. In terms of size, for example, the material properties of the aforementioned dielectric ink layer allow sintering into a conductive structure to form a security barrier for a small device (such as a security barrier covering the back of a semiconductor die) and a larger assembly (such as a single-board computer or CCA). One or more of the methods described herein can be applied to various electrical devices and components, including but not limited to microelectronic fabrication wafers, die attached to a substrate, printed circuit board (PCB) layers, packaged (capped) components, and CCAs, and can be used to form security barriers for commercial off-the-shelf (COTS) devices or assemblies as well as custom microelectronic devices or assemblies. In terms of the product life cycle, for example, the method can be applied during microelectronic wafer processing, during PCB fabrication steps (to form a security barrier under the device), or to a fabricated microelectronic assembly. Additionally, for a single microelectronic assembly or device, the method is extended to allow the formation of a single security barrier or multiple spatially distributed security barriers of different sizes. Furthermore, since the transformed circuit variations can be controlled via the sintering process (e.g., the software used by the sintering tool), the variations between components can be achieved at the inter-component level of wafer fabrication and at the inter-CCA level. Turning now to FIGS. 1A and 1B, an electronic device 100 is illustrated in accordance with a non-limiting embodiment of the present disclosure after a transformable dielectric material 102 has been deposited onto a surface 104. As described herein, the processed electronic device 100 can include but is not limited to a microelectronic fabrication wafer, a die attached to a substrate, a PCB layer, a packaged and / or capped component, an integrated circuit (IC) chip, and a circuit card assembly. In FIGS. 1A and 1B, the transformable dielectric material 102 is shown in an "insulating phase" that exists prior to applying a sintering process described in more detail below. Various deposition methods can be used to deposit the transformable dielectric material onto the electronic device surface 104, including but not limited to direct write printing, spin coating, or spraying. Although a single layer of transformable dielectric material 102 is shown, it should be understood that additional layers of transformable dielectric material can be deposited on the device 100 without departing from the scope of the present invention. Continuing to refer to FIG. 1B, the transformable dielectric material is also referred to as “transformable ink” or “composite functional ink”. In one or more non-limiting embodiments, the transformable dielectric material is a silver-barium strontium titanate (Ag-BST) composite ink that includes a blending ratio of conductive silver (Ag) nanoparticles 200 and electrically insulating barium strontium titanate (BST) nanoparticles 202. According to one non-limiting embodiment, the Ag nanoparticles 200 can have a size in the range of, for example, about 75 nanometers (nm) to about 85 nm, and the BST nanoparticles 202 can have a size in the range of, for example, about 80 nm to about 100 nm. In one or more non-limiting embodiments, the blending ratio of the Ag nanoparticles 200 and the BST nanoparticles 202 can be optimized to obtain an insulating phase when initially deposited on the surface 104 and having undergone a curing process (e.g., cured at 80 degrees Celsius for about 15 minutes) to stabilize the arrangement of the Ag nanoparticles 200 and the BST nanoparticles 202. Turning to FIG. 2A, it shows that the transformable dielectric material 102 undergoes a sintering process, after which the sintered material reaches a “highly conductive phase”. The sintering process can include a selective laser sintering (SLS) process, and the SLS process causes laser energy 106 output from the laser sintering tool 108 to impinge on a selected or target portion of the transformable dielectric material 102. The laser energy 106 generates a temperature above 150 degrees Celsius (about 300 degrees Fahrenheit) at the target point on the transformable dielectric material 102, causing the Ag nanoparticles 200 to melt and coalesce, thereby transforming the heated portion from the electrically insulating phase to the conductive phase, as shown in FIG. 2B. Thus, the selectively transformed portion of the transformable dielectric material 102 forms conductive traces 110 having various measurable electrical properties (such as, for example, resistance, capacitance, or inductance), and these conductive traces can be incorporated into an electrical circuit. FIG. 2C illustrates the transformable dielectric material 102 after the laser sintering process. As shown, the target portion of the transformable dielectric material is transformed to form a meandering-profile conductive trace 110 that forms a resistor. As discussed herein, the measurable electrical properties of the conductive trace 110 are derived from the physical characteristics of the trace (e.g., line width, line thickness), such that if the conductive trace 110 is altered due to tampering or other sources of damage, a measurable change in the electrical properties of the conductive trace 110 will occur. In this way, when a sintering process is used to convert portions of the convertible dielectric material 102 into the conductive traces 110, a security barrier is formed that covers the protected device such that unauthorized physical access to the protected device changes the physical characteristics of the traces 110, thereby measurably changing the electrical properties of the traces. Although a single conductive trace 110 is shown, it should be understood that additional conductive traces may be formed from the convertible dielectric material 102 without departing from the scope of the invention. In addition to the conductive traces, one or more conductive pads 111 may be formed, as appropriate, using the methods described herein for forming the conductive traces. The conductive pads 111 may provide access for using an electrical measurement tool (e.g., an ohmmeter) to facilitate measuring the electrical properties of a given trace 110. The conductive pads 111 depicted herein represent one example of using the methods described herein for forming the conductive traces to electrically connect the conductive traces to other electrical or electronic devices. In one or more non-limiting embodiments, the SLS process described herein may be used to form conductive traces that are electrically connected to pre-existing pads on the underlying device 104. In one or more non-limiting embodiments, the laser sintering tool 108 may store a design layout that controls the operation of the laser sintering tool 108. Additionally, the operating parameters of the laser sintering tool 108, such as laser energy power, laser wavelength, grating speed, may be adjusted, for example, when forming the electrical circuit structure. In this way, the electrical properties of the conductive trace 110 may be tuned to achieve target electrical properties. Additionally, the target areas and / or designs of the conductive traces 110 may be selected and formed accordingly. Thus, different types of conductive traces having different types of shapes and profiles may be formed. In one or more non-limiting embodiments, adjusting the sintering tool operating parameters allows for wider and / or thicker portions of the conductive traces. The traces may be designed to produce complex impedance and / or may be connected to discrete electronic components as part of an assembly. The operating parameters may also be adjusted to allow for configurability of line width, spacing, trace thickness, thereby creating any unique barrier structure that may be utilized in authentication (integrity) and / or confidentiality strategies. The sintering tool 108 may also be programmed (e.g., using software) to perform patterned laser scans that may be dynamically changed and quickly modified for component-to-component variations. Now turn to FIGS. 3A and 3B, which illustrate the security barrier of FIG. 2 after the thermally stable ink 112 is deposited on the switchable dielectric material 102 and the conductive traces 110. The thermally stable ink 112 is formed of various non-conductive heat-resistant materials such as, for example, boron nitride (BN), which materials include nanoparticles that fill most of the air voids in the barrier layer containing the switchable dielectric material 102 and the conductive traces 110. The thermally stable ink 112 can be deposited using various deposition techniques such as, for example, direct write printing, spin coating, or spray coating. Once deposited, the thermally stable ink 112 undergoes a curing process to cure the thermally stable ink 112. The curing process of the thermally stable ink 112 can be achieved by exposing the thermally stable ink 112 to ultraviolet (UV) energy. Curing the thermally stable ink 112 prevents the switchable dielectric material 102 and the conductive traces 110 from changing due to subsequent exposure to high temperatures (e.g., solder reflow). Referring to FIG. 3B, the cured thermally stable ink 112 is shown in more detail. In this example, the thermally stable ink 112 introduces larger BN particles 206 into the air voids in the switchable dielectric material 102 having the conductive traces 110. Once cured, the BN nanoparticles prevent further melting and coalescence of the Ag nanoparticles, thereby hindering the formation of additional conductive paths at locations that were not initially the target of the SLS process (e.g., non-SLS processed regions of the switchable dielectric material 102), which locations may be caused, for example, by subsequent thermal exposure. Thus, the combination of the thermally stable ink 112 and the switchable dielectric material 102 creates a composite substrate that includes a combination of Ag particles 200, BST particles 202, and BN particles 206. The UV-cured thermally stable ink reduces the amount of air voids present in the switchable dielectric material layer 102 by filling the air voids with polymerized ethoxylated trimethylolpropane triacrylate, thereby minimizing the likelihood of an increase in the particle size of the AG nanoparticles 200 when the thermal insulation film 112 is exposed to a subsequent heat source. As described herein, the electrical circuit structure 110 formed by selectively transforming the switchable dielectric material layer has measurable electrical properties (e.g., resistance, capacitance, current output, voltage output, etc.), which change when the electrical circuit structure having the barrier layer 110 is damaged, tampered with, and / or destroyed. In this way, the properties of the measurable electrical circuit structure 110 can be measured and compared with the expected electrical properties of the electrical circuit structures (e.g., measured at the initial manufacture of the electrical device) to detect tampering of the electrical device 100. In one or more non-limiting embodiments, the electrical characteristics or properties of the conductive traces 110 can be measured by connecting the traces and possibly other circuit elements to a logic device (not shown), which is programmed to excite the resulting electrical circuit and measure the electrical response of the electrical circuit. Thus, the resulting subsystem can be used to compare the responses measured at a point during the system life cycle with the measured responses recorded during manufacturing. According to another embodiment, the conductive traces 110 can be designed such that electrical instruments (e.g., probes, ohmmeters, voltmeters, etc.) can be used to detect open circuits or short circuits that did not exist during the initial manufacture of the electronic device 100. FIG. 4A, for example, depicts an ohmmeter measurement of a complete conductive trace 110 present in the untampered barrier layer 102. In this example, the complete conductive trace 110 provides a finite resistance measurement of Ω. However, FIG. 4B depicts an ohmmeter measurement of the conductive trace 110 that has been damaged by a tampering event 150. In this example, the ohmmeter signals the damaged conductive trace as an open circuit (OC). Thus, it can be determined that unauthorized tampering and / or damage has occurred to the electrical device 100. It should be understood that the damage caused by the tampering event may have caused the measured resistance to change from its original value to a different finite value, or that different electrical measurement methods will result in a similar change in the measured value caused by the tampering event 150. Turning now to FIG. 5, there is shown a method of fabricating a security barrier according to one non-limiting embodiment of the present disclosure. The method begins at operation 500, and at operation 502, a convertible dielectric material layer is deposited onto the protected device. As described herein, the layer is formed from a convertible Ag-BST composite ink that is cured at 80 degrees Celsius for approximately 15 minutes. At operation 504, one or more target portions of the barrier layer are converted from a dielectric insulating phase to a conductive phase via a sintering process, thereby forming conductive traces that can be incorporated into an electrical circuit. As described herein, a SLS process can be performed to precisely form the conductive traces using laser energy. At operation 506, a thermally stable ink is deposited into the convertible dielectric material and the conductive traces. In one or more non-limiting embodiments, the thermally stable ink is formed from a material containing polymerized ethoxylated trimethylolpropane triacrylate and BN particles. At operation 508, the thermally stable ink is cured (e.g., using UV energy) to fix the conductive traces and prevent further conversion of the convertible dielectric material to a conductive phase. The method ends at operation 510, at which time an electrical structure forms a security barrier over the protected device. All means or steps and corresponding structures, materials, acts, and equivalents of the function-plus-element in the following claims are intended to include any structure, material, or act for performing a function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the embodiments as disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated. Although the preferred embodiments of the present disclosure have been described, it will be understood that various improvements and enhancements may now and in the future be made by those of ordinary skill in the art that fall within the scope of the appended claims. These technical solutions should be interpreted as maintaining appropriate protection for the disclosure first described. 100: Electronic device / Device 102: Transformable dielectric material / Transformable dielectric layer / Unauthorized tampering barrier layer 104: Surface / Electronic device surface 106: Laser energy 108: Laser sintering tool / Sintering tool 110: Conductive trace / Zigzag conductive trace / Electrical circuit structure / Barrier layer 111: Conductive pad 112: Thermally stable ink / Thermal insulation film 150: Tampering event 200: Conductive silver (Ag) nanoparticles / Ag particles / AG nanoparticles 202: Electrically insulating barium strontium titanate (BST) nanoparticles / BST particles 206: BN particles 500: Operation 502: Operation 504: Operation 506: Operation 508: Operation 510: Operation To more fully understand the present disclosure, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, in which like reference numerals represent like components: [FIG. 1A] depicts an electronic device after depositing a convertible dielectric material layer according to a non-limiting embodiment of the present disclosure; [FIG. 1B] depicts a convertible dielectric material layer formed on the surface of an electrical device according to a non-limiting embodiment of the present disclosure; [FIG. 2A] depicts the convertible dielectric material of FIG. 1 undergoing a laser sintering process, the laser sintering process being applied to the convertible dielectric material layer to convert a portion of the convertible dielectric material layer into an electrical circuit structure; [FIG. 2B] depicts the convertible dielectric material layer after the laser sintering process, the laser sintering process converting a portion of the convertible dielectric material layer into an electrical circuit structure; [FIG. 2C] depicts an example of an electrical circuit structure as the converted portion of the convertible dielectric material layer according to a non-limiting embodiment corresponding to the present disclosure; [FIG. 3A] depicts the electrical circuit structure of FIG. 2 after thermally stable ink is deposited on the convertible dielectric material layer having the electrical circuit structure according to a non-limiting embodiment of the present disclosure; [FIG. 3B] depicts the thermally stable ink deposited on the convertible dielectric material layer having the electrical circuit structure and after a curing process; and [FIG. 4A] depicts the measurement of the converted electrical circuit structure present in the non-tampered barrier layer according to a non-limiting embodiment of the present disclosure; [FIG. 4B] depicts the measurement of the converted electrical circuit structure present in the tampered barrier layer according to a non-limiting embodiment of the present disclosure; and [FIG. 5] is a flowchart illustrating a method of manufacturing a security barrier layer according to a non-limiting embodiment of the present disclosure. 100: Electronic device / device 102: Convertible dielectric material / convertible dielectric material layer / non-tampered barrier layer 104: Surface / electronic device surface 110: Conductive trace / zigzag conductive trace / electrical circuit structure / barrier layer 111: Conductive pad 112: Thermally stable ink / heat insulating film

Claims

1. A method for forming a security barrier for a protected electronic device, the method comprising: depositing a variable dielectric material layer on the protected electronic device, the variable dielectric material layer comprising a plurality of conductive nanoparticles and a plurality of insulating nanoparticles; performing a selective laser sintering (SLS) process to bombard the variable dielectric material layer with laser energy, transforming a target portion of the variable dielectric material layer into at least one electrical circuit structure having at least one measurable electrical characteristic, the at least one electrical circuit structure comprising a portion of the conductive nanoparticles; and depositing a thermally stable material layer onto the variable dielectric material layer; wherein, The electrically insulating nanoparticles electrically isolate at least one electrical circuit structure from the remainder of the transformable dielectric material layer.

2. The method of claim 1, wherein forming the security barrier includes setting a mixing ratio of the conductive nanoparticles and the electrically insulating nanoparticles in the variable dielectric material layer.

3. The method of claim 2, wherein the conductive nanoparticles include silver (Ag) nanoparticles and the electrically insulating nanoparticles include barium strontium titanate (BST) nanoparticles.

4. The method of claim 2, wherein the transformable dielectric material layer is cured at 80 degrees Celsius for 15 minutes.

5. The method of claim 1, wherein the laser is capable of melting the conductive nanoparticles together to form a conductive path defining one of the at least one electrical circuit structure.

6. The method of claim 1, wherein the thermally stable material layer includes nanoparticles that prevent the formation of additional conductive paths within the transformable dielectric material layer.

7. The method of claim 6, wherein the nanoparticles include boron nitride (BN) nanoparticles.

8. The method of claim 1, wherein the thermally stable material layer reduces at least one of the amount and size of air gaps present in the transformable dielectric material layer.

9. The method of claim 8, wherein reducing the amount of air gaps includes filling the air gaps with polymerized ethoxylated trimethylolpropane triacrylate.

10. The method of claim 9, wherein the thermally stable material layer is cured by ultraviolet (UV) exposure to inhibit further alteration of the safety barrier at temperatures below 250 degrees Celsius.

11. A security barrier for a protected electronic device, formed by the method described in claim 1, comprising: a variable dielectric layer on the protected electronic device, the variable dielectric layer including a plurality of conductive nanoparticles and a plurality of insulating nanoparticles; at least one electrical circuit structure including a portion of the conductive nanoparticles, the at least one electrical circuit structure having at least one measurable electrical characteristic, the at least one electrical circuit structure being formed by performing a selective laser sintering (SLS) process; and a thermally stable material layer covering the variable dielectric layer including the at least one electrical circuit structure; wherein the at least one electrical circuit structure is located at a target portion of the variable dielectric layer, and the insulating nanoparticles electrically isolate the at least one electrical circuit structure from the remainder of the variable dielectric layer.

12. The safety barrier of claim 11, wherein the at least one measurable electrical characteristic changes in response to a change in the electrical circuit configuration.

13. The safety barrier of claim 12, wherein the at least one measurable electrical characteristic includes at least one of resistance, capacitance and inductance.

14. The safety barrier of claim 11, wherein the changeable dielectric material layer includes other electrical circuit structures.

15. The safety barrier of claim 11, wherein the conductive nanoparticles include silver (Ag) nanoparticles and the insulating nanoparticles include barium strontium titanate (BST) nanoparticles.

16. The safety barrier of claim 15, wherein the thermally stable material layer comprises a boron nitride (BN) material and a polymerized ethoxylated trimethylolpropane triacrylate material.

17. The safety barrier of claim 16, wherein the variable dielectric material layer and the thermally stable material layer are combined to form a composite substrate, the composite substrate comprising a combination of Ag particles, BST particles and BN particles.

Images