Resistive shield for electronic circuits and manufacturing process

Abstract

Resistive shield for electronic circuits and manufacturing method. The invention relates to a protective shield for an electronic device comprising: a resistive circuit (C3) of metallic lines, said circuit being associated with at least one resistivity signature of the circuit which constitutes a reference value for certifying the integrity of the circuit; means for monitoring the resistivity of the circuit, connected to said circuit, said monitoring means being capable of measuring at least one resistivity value of the circuit and comparing this value to said resistivity signature to certify the integrity of the circuit, characterized in that the resistive circuit comprises at least one phase-change resistive cell whose resistivity contributes to establishing said resistivity signature of the circuit. Figure for the abstract: Fig. 3

Description

Title of the invention: Resistive shield for electronic circuits and manufacturing process. Technical field

[0001] The present invention relates generally to the protection against physical attacks of electronic devices. These devices may be, for example, components, chips, electronic circuits, or devices incorporating such circuits or components.

[0002] Physical attacks on electronic devices can be carried out, for example, by drilling, grinding, or engraving. These attacks may aim, in particular, to access the data on the devices.

[0003] The invention relates to a protective shield for an electronic device comprising: • a resistive circuit of metallic lines, said circuit being associated with at least one resistivity signature of the circuit which constitutes a reference value enabling certification of the integrity of the circuit, • and means for controlling the resistivity of the circuit, connected to said circuit, said means of control being capable of measuring at least one resistivity value of the circuit and comparing this value to said resistivity signature to certify the integrity of the circuit. STATE OF THE ART

[0004] Electronic device protection shields are already known, allowing the detection of an attempt at physical access to the device.

[0005] It is known to protect the sensitive components of an electronic device by means of a shield formed by a resistive metal mesh that covers the device. The mesh is connected to a power supply and to a detector that can be located with the device inside the mesh. The mesh is fitted around the device so that any attempt to physically access the device's components risks damaging the mesh to the point of causing an open circuit or a change in electrical resistance within the mesh. The detector is capable of detecting this open circuit or this change in resistance, which signals damage to the mesh, and can trigger an appropriate countermeasure in response.

[0006] An example of such a protective shield can be found in document US20150097572 AL

[0007] This document discloses a shield made in the form of a resistive mesh of metallic lines placed in a housing intended to surround the electronic device to protect. The metallic lines of this resistive mesh can be arranged on several levels.

[0008] The resistance control of the mesh allows its integrity to be verified.

[0009] The shield disclosed in this document therefore provides a certain degree of protection.

[0010] But a limitation of this shield is that the resistance of the mesh, once known by a third party, can be simulated by this third party by connecting to the terminals of the mesh a resistance of the same value to counteract the electrical effect of the shield and thus deceive the measurement of the integrity detection of the shield.

[0011] Furthermore, if one wishes to manufacture a series of such shields, a lithography mask is typically used to create the resistive mesh of each shield, and the same mask is then used to manufacture the series of shields. Therefore, a third party only needs to know the resistance of one of these shields—the resistance being identical for all the shields—to counteract the electrical effect of each of these shields and thus circumvent the protection of the entire series of shields.

[0012] An object of the present invention is to overcome these limitations of known solutions. SUMMARY

[0013] To achieve this objective, according to one embodiment, a protective shield for the electronic device is provided, comprising: • a resistive circuit of metallic lines, said circuit being associated with at least one resistivity signature of the circuit which constitutes a reference value enabling certification of the integrity of the circuit, • means for controlling the resistivity of the circuit, connected to said circuit, said control means being capable of measuring at least one resistivity value of the circuit and comparing this value to said resistivity signature to certify the integrity of the circuit, characterized in that the resistive circuit includes at least one phase-change resistive cell whose resistivity contributes to establishing said resistivity signature of the circuit.

[0014] Preferred, but not limiting, aspects of this shield are as follows: • The resistivity of the phase-change resistive cell was established by an energy activation that allowed for the random modification of the resistivity of said phase-change resistive cell, thus constituting an individual random resistivity signature of the phase-change resistive cell to constitute a resistivity signature of said circuit, • said energy activation was achieved by applying an electrical activation voltage, • said resistivity control means are capable of applying a reading electrical voltage to the terminals of the circuit in order to measure at least one resistivity value of the circuit, • The circuit includes several phase-change resistive cells, • at least one phase-change resistive cell is of the configuration linear, • at least one phase-change resistive cell has a circular configuration, • the control means are capable of applying a voltage across the terminals of at least two parts of the circuit, and of measuring the resistivity of said parts of the circuit.

[0015] Furthermore, the invention proposes a method for manufacturing a shield according to one of the aspects mentioned above, comprising the steps of: • To create, on at least part of the area to be protected of the electronic device, a phase-change resistive cell, by constructing a region of phase-change material, • Define a resistive circuit path around the area to be protected, said path being in contact via two terminals with said region of phase-change material at each location of a phase-change resistive cell, • Deposit a conductive material at the level of said path, so as to constitute the resistive circuit, and to constitute at each location of a phase-change resistive cell two electrodes adjacent to the region of phase-change material and surrounding this region to constitute a phase-change resistive cell, • For each phase change resistive cell: apply an energy activation to the phase change resistive cell, in particular by applying an activation voltage to the phase change material region or by exposing the phase change material region to energetic radiation, the energy level supplied to the phase change material region being chosen close to the energy level allowing partial crystallization of said phase change material so that the crystalline structure of a part of said phase change material region is modified.

[0016] A preferred but not limiting aspect of this process is the following: • To deposit a conductive material at the level of said path so as to constitute the resistive circuit, a mask is applied to the area to be protected, the openings of which define the path of the resistive circuit on the area to be protected, and to deposit a conductive material at the level of said path so as to constitute the resistive circuit, a conductive material is deposited through the mask on the area to be protected, so as to constitute the resistive circuit.

[0017] Finally, the invention relates to the application of a process such as the one mentioned above to the manufacture of a plurality of shields, an application in which: • The same mask is used to deposit a conductive material through the mask onto the area to be protected by each shield, and • For each shield, an energy activation is applied to at least one phase-change resistive cell of the shield to establish an individual resistive signature of the shield. BRIEF DESCRIPTION OF THE FIGURES

[0018] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0019] [Fig. 1] Fig. 1 represents a first embodiment of the invention in which a shield comprises a phase-change resistive cell of generally rectilinear shape,

[0020] [Fig.2] Fig.2 represents a second embodiment of the invention in which a shield comprises a phase-change resistive cell, generally circular in shape,

[0021] [Fig.3] Fig.3 represents a third embodiment of the invention in which a shield comprises a mesh with several phase-change resistive cells,

[0022] [Fig.4] Figure [Fig.4] represents a fourth embodiment of the invention in which a shield comprises a mesh with several phase-change resistive cells,

[0023] [Fig. 5] Figures 5 to 10 illustrate different ways of implementing the invention, to protect a chip comprising a silicon substrate, one or more active layers comprising transistors, and one or more back-end layers,

[0024] [Fig.6]

[0025] [Fig.7]

[0026] [Fig.8]

[0027] [Fig.9]

[0028] [Fig. 10]

[0029] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the Understanding of the invention and are not necessarily at the scale of practical applications. In particular, on the schematic diagrams, the thicknesses of the various layers, vias, patterns and reliefs are not representative of reality. DETAILED DESCRIPTION

[0030] The invention uses, as will be described, at least one phase-change resistive cell to constitute a resistive signature specific to each shield.

[0031] A phase change resistive cell – or PCM cell – is a resistive transition cell using phase change materials (PCM stands for Phase Change Material, and in this text, "phase change resistive cell" and "PCM cell" are synonymous). This type of non-volatile resistive transition cell uses the phase transition of the phase change material(s) it is made of for information storage.

[0032] Fig. 1 schematically represents a shield according to a first embodiment of the invention.

[0033] This shield has the following characteristics which are common to all embodiments described in this text.

[0034] The shield comprises a resistive circuit (circuit Cl in [Fig. 1], which represents a particularly simple form of circuit), typically a metallic circuit. In practice, this circuit can be shaped in two- or three-dimensional space (for example, to be applied to the inner wall of a housing that covers the electronic device to be protected from attempts at physical access - this electronic device is not shown in [Fig. 1], nor in Figures 2, 3 and 4 which schematically show the structure of different shields).

[0035] In all cases, this resistive circuit covers and / or surrounds the electronic device to be protected. The device to be protected may consist, for example, of one or more components, a chip, an electronic circuit, or a device integrating such circuits, chips, or components.

[0036] The resistive circuit is connected to control means (represented as the controller 100 in [Fig. 1]) which include an electrical voltage source and a detector. The control means are electrically connected to the terminals of the resistive circuit. The detector is not shown in the figures.

[0037] The control means are located in the space also occupied by the device to be protected, and which is covered and / or surrounded by the resistive circuit.

[0038] Since the circuit is shaped to fit around the device to be protected, any attempt to physically access the device risks damaging the circuit to the point of causing an open circuit state or a variation in the electrical resistance in the circuit.

[0039] The detector of the control means is capable of detecting this state (for example by measuring the resistance of the circuit) and of triggering an appropriate countermeasure in response.

[0040] More specifically, the control means also include a memory in which the nominal resistance of the resistive circuit is stored. During operation, if the resistance value measured by the control means across the circuit differs from this stored nominal value, the detector triggers an appropriate countermeasure.

[0041] The control means also include a voltage source capable of applying a voltage, for example in the form of a voltage pulse, to terminals C11 and C12 of the circuit. This voltage source is programmed to apply such a pulse repeatedly—for example, regularly at a given frequency. Thus, the control means regularly measure the resistance of the energized circuit when the voltage from the source is applied to the circuit terminals.

[0042] The resistance control can also be done with a direct voltage applied to the terminals of the circuit by the source, which is then a direct voltage source.

[0043] The resistive circuit comprises a phase-change resistive cell (cell PI in [Fig. 1]). This cell comprises two electrodes (electrodes E1 and E12 in [Fig. 1]), separated by a region of phase-change material (region A1 in [Fig. 1]) which is in contact with these two electrodes. This phase-change material is typically a material that may have an amorphous phase and / or one or more crystalline phases whose resistivity varies with the phase.

[0044] This phase-change material may, for example, have the chemical formula GeTe or GeSbTe. It is also possible to use a 2D material such as a TMD (Transition Metal Dichalcogenide), for example, a material with the formula MoS2, MoSe2, MoTe2, HfS2, or HfSe2. Hexagonal boron nitride (h-BN) may also be used.

[0045] This material can also be replaced by one of the materials used for resistive memories (OxRAM, which is the acronym for the widespread Anglo-Saxon expression "Oxide-based Resistive Random Access Memories" or "oxide-based resistive RAM", CBRAM, which is the acronym for the widespread Anglo-Saxon expression "Conductive Bridge Random Access Memory" or "Conductor Bridge RAM", ...) such as NiOx, TiOx, CuOx, ZrOx, ZnOx, HfOx, TaOx, AlOx, Ag2-Os, Cu2-Os, Cu2-OO, Ag-AsSx, Ag-GeSex, Cu-GeSex, Ag-GeSx, Cu-GeSx, Cu-GeTe,... with one of the electrodes being made of an electrochemically active metal (such as Silver or Copper) if one retains a material from the CBRAM (Conductor Bridge Random Access Memory) family.

[0046] In [Fig. 1], the two electrodes of the phase-change resistive cell and the phase-change material region are rectangular regions of equal length, placed adjacent and parallel to each other, with the phase-change material region located between the two electrodes. The phase-change resistive cell thus generally has a rectilinear shape.

[0047] The voltage source of the control means, connected to the terminals of the circuit, is, as stated, capable of applying a voltage to these terminals. The terminals to which this voltage is applied surround the phase-change resistive cell, which is therefore subjected to the voltage applied by the voltage source.

[0048] When the voltage source applies a voltage pulse, this voltage is thus transmitted to the electrodes of the phase-change resistive cell, and therefore to the phase-change material region.

[0049] To construct the shield and before putting this shield into service, a circuit is thus manufactured comprising at least one phase-change resistive cell. As will be seen, the resistivity of the phase-change cell(s) contributes to establishing a resistivity signature of the circuit.

[0050] The circuit is thus manufactured, and if the phase change material region of at least one phase change resistive cell is not in the most resistive state of the cell, a reset is first carried out to bring the phase change material region into its most resistive state.

[0051] A voltage is then applied for the first time across the terminals of the circuit – and therefore across the terminals of the phase-change resistive cell. This first voltage applied to activate the phase-change resistive cell – and consequently to create its resistive signature – will be called the activation voltage.

[0052] It is also possible to apply this activation voltage directly to the terminals of the phase-change resistive cell if the terminals of the circuit are different (in the case of a more complex circuit than that shown in [Fig.1]).

[0053] This activation voltage causes localized heating in the phase-change material region. The resulting temperature rise, in turn, causes the localized phase change. During this localized phase change, a portion of the material in this region changes phase (becoming crystalline or polycrystalline). The state of the phase-change resistive cell is then fixed and requires no further energy to maintain.

[0054] The energy supplied by the application of this activation voltage is chosen to generate a localized and partial phase change in the phase-change material region. The corresponding voltage value is determined during circuit design based on the geometry of the phase-change resistive cell and the material from which this cell is made.

[0055] Applying an activation voltage thus causes a localized phase change in the phase-change material region. This localized change is represented in [Fig. 1] by the filament Ail, whose resistivity differs from the resistivity of the rest of the phase-change material region. This results in a modified resistance of this region, and consequently a modified resistance of the phase-change resistive cell.

[0056] This modified resistance following the application of the activation voltage constitutes a resistivity signature of the phase-change resistive cell.

[0057] This change in resistance is random because it is not possible to predict which part of this region will change phase under the application of the activation voltage, nor the extent of this phase change.

[0058] The parallelism of the electrodes, and the fact that the distance between these two electrodes is constant, promotes the variety of filaments that can be established during an activation, and consequently promotes the random nature of the change in resistance.

[0059] Applying an activation voltage to such a resistive circuit including a phase-change resistive cell therefore makes it possible to generate a resistivity signature which is unique and individual for the phase-change resistive cell, and therefore for the circuit which includes it.

[0060] Once this resistivity signature has been generated in an initial phase preceding the commissioning of the circuit, this signature is stored in the memory of the control means.

[0061] The so-called reading voltage, which will subsequently be applied across the circuit terminals by the voltage source to allow the control means to measure the circuit's resistivity and compare it with the stored resistive signature, has a value lower than the activation voltage. Indeed, this subsequently applied reading voltage, which aims to allow the control means to verify that the circuit's resistivity matches the signature value, is not intended to induce a phase change in the phase-change material region.

[0062] As an alternative to applying a voltage from a voltage source to activate the phase-change resistive cell and create its resistivity signature, it is possible to activate the phase-change resistive cell by generating a localized phase change through the application of energy not derived from an electrical voltage. Thus, it is possible to activate the phase-change resistive cell by applying activation light radiation.

[0063] This possibility is also schematically illustrated in Figures 1 and 2 by the application to the phase-change resistive cell, as an alternative to an activation voltage, of radiation which can be laser radiation 200.

[0064] The application of the activation voltage - or in general of an activation energy - thus allows the creation and storage in the memory of the control means of a resistivity signature of the circuit.

[0065] To store the resistive signature in the memory of the control means, the resistivity of the phase-change resistive cell is measured by applying a reading voltage to its terminals for the first time, and by measuring the resistivity of the cell.

[0066] This resistivity signature is unique and individually associated with the circuit, because it is generated in a non-deterministic way (i.e. random in the sense of this text).

[0067] This signature is “analog”, in the sense that it is expressed by a resistivity value that can take any value in a continuous space of resistivity values.

[0068] The use of phase-change resistive cells is therefore quite different here from a known use of phase-change memory cells in which one seeks to "encode" with one or more phase-change resistive cells a characteristic, assimilating each phase-change resistive cell to a bit assigned to the value 0 or 1, depending on the resistivity of the phase-change resistive cell.

[0069] And the application of a reading voltage, with the measurement of resistivity and the comparison with the stored signature, makes it possible to effectively control the integrity of the resistive circuit.

[0070] The signature is random, because the phase change which is caused by the supply of energy during activation is not determinable before this activation.

[0071] This "analog" signature can take any value in a continuous space. Each phase-change resistive cell is thus associated with a signature that is random, and which, moreover, can have any value within a continuous space of resistance values.

[0072] The features described above concerning the invention are common to all embodiments.

[0073] Figure 2 presents a variant of the invention, in which the phase-change resistive cell P2 of a resistive circuit C2 has a generally circular geometry.

[0074] In this figure, the phase-change resistive cell comprises two electrodes E21 and E22, which are round and concentric. The first electrode is located in the center and is disc-shaped, and is connected to the rest of the resistive circuit by a conductor.

[0075] The second electrode has the general shape of a ring which is concentric with the first electrode and surrounds it over a large part of its circumference, leaving free passage around the first electrode only a space E220 allowing the connection of the first electrode with a first terminal C21 of the resistive circuit.

[0076] The second electrode is connected to a second terminal C22 of the resistive circuit.

[0077] An annular region A2 of phase-change material is located between the first and second electrodes and is in contact with these electrodes. This annular region A2 has the general shape of a ring that is concentric with the two electrodes E21 and E22, and surrounds the first electrode E21.

[0078] In this embodiment, the phase-change resistive cell generally has a circular shape, which increases its isotropy and further promotes the random nature of the phase change when the cell is activated by energy input.

[0079] When this cell is activated by supplying energy (by the voltage source 100, or by a light source 200) the phase change material region A2 undergoes a localized and partial phase change, illustrated by the creation of a filament A21.

[0080] The phase-change resistive cells described above, and more generally the phase-change resistive cells implemented in the invention, can be manufactured in a plane—in which case the extended portions of the cell electrodes extend in the same plane and they can be manufactured with at least one metal deposit. Naturally, in this case, the electrodes, and the phase-change material region, do have a thickness, but this thickness is negligible.

[0081] It is also possible to manufacture all or part of these cells in three dimensions - in this case the electrodes are manufactured one on top of the other, or even one around the other in a spherical configuration for example - with the phase change material layer intercalated between the two electrodes.

[0082] Fig. 3 represents an embodiment in which the C3 circuit of the resistive shield comprises several phase-change resistive cells mounted in series.

[0083] In [Fig.3], as well as in [Fig.4], each phase change resistive cell is represented by a “PCM” cell.

[0084] In the configuration of [Fig.3] (and also of [Fig.4]), it is possible to activate all the phase-change resistive cells (by applying an activation voltage to terminals C31 and C32 of the resistive circuit, or by exposing all the phase-change resistive cells to an activation light).

[0085] Alternatively, it is also possible to activate each phase-change resistive cell separately by applying a voltage across the cell terminals (or exposure of the cell to light). It is also possible to activate phase-change resistive cells in groups of cells.

[0086] In all cases, each phase-change resistive cell can, in particular, have the geometry of the cell shown in [Fig. 1], or the geometry of the cell shown in [Fig. 2]. It is possible to construct a circuit with one or more phase-change resistive cells having the geometry shown in [Fig. 1], and one or more phase-change resistive cells having the geometry shown in [Fig. 2].

[0087] In all cases, one or more resistive signatures of the C3 circuit are measured and then stored in the memory of the control means, which again include a voltage source 100.

[0088] It is thus possible to store only the resistive signature of the entire C3 circuit.

[0089] Alternatively or in addition, it is also possible to store one or more resistive signatures of certain phase-change resistive cells, and / or of certain groups of phase-change resistive cells. In this case, a reading voltage is applied across all the entities whose resistivity signature is to be measured and stored, and the resistivity of the entity is measured. An entity is a part of the C3 circuit that includes at least one phase-change resistive cell.

[0090] Once the resistive signature(s) have been memorized, the integrity of the shield can be checked by applying a reading voltage to the terminals of the entire circuit, and / or of the entities that one wishes to check, the resistivity of the circuit or of the entity is measured, and it is compared to the value memorized for the circuit or for the entity concerned.

[0091] According to one embodiment, it is possible to provide several resistivity measurement points at different locations in the circuit. This embodiment facilitates the localization of a potential attack on the circuit.

[0092] The dashed connections illustrate other variants, in which the voltage source is connected to the terminals of each phase-change resistive cell. In this case, the reading voltage is applied by the voltage source to the terminals of each phase-change resistive cell, and the resistivity of each cell is measured and compared to an individual resistive signature of the cell, which is stored in the controller.

[0093] Fig. 4 illustrates a variant in which a large number of phase-change resistive cells are mounted in series in the resistive circuit.

[0094] In all embodiments, it is possible to foresee that the resistive circuit extends in three-dimensional space along two generally parallel levels. In this case, checking the mesh capabilities allows us to verify its integrity, as well as the proximity of a possible measurement probe intended to capture signals from the electronic device, by proximity.

[0095] In all embodiments of the invention, it is also possible to reset the shield according to the invention by subjecting the shield circuit to a treatment that returns the material regions to a most resistive state of the phase-change resistive cell(s), and then subjecting this cell(s) to an activation energy again. New resistivity signature values ​​can thus be stored.

[0096] Figures 5 to 10 illustrate different possible positions for a shield according to the invention. These possibilities all apply to the different embodiments and circuit variants mentioned above. These possibilities can be combined with each other in all possible combinations.

[0097] Each of these figures 5 to 10 shows in cross-section a structure such as a chip. This structure includes a substrate S (for example of silicon), an active layer A which covers the substrate and which typically includes transistors, and one or more BE layers of interconnection levels (also called back-end layers according to the widespread Anglo-Saxon terminology) which cover(s) the active layer.

[0098] Fig. 7 also shows a hood C which covers the interconnection level layers of the structure.

[0099] The shield B according to the invention can be implanted with great flexibility – in particular, it is possible to position it overlapping the outer layer, and possibly also the inner layer (which faces the active layer) of the BE layer assembly. This is illustrated in Figures 5 (which shows one shield B) and 6 (which shows two shields B61 and B62).

[0100] Fig. 7 shows another example in which shield B is placed inside hood C.

[0101] It is also possible to position the shield B overlapping the outer face of the substrate layer S. This is illustrated in [Fig.8].

[0102] Fig. 9 illustrates an example in which a B91 shield is placed over the outer face of the substrate S layer, and another B92 shield is placed over the outer layer of the BE layer assembly.

[0103] Figure 10, like Figure 9, illustrates an example in which a shield B101 is placed over the outer face of the substrate layer S, and another shield B102 is placed over the outer layer of the BE layer assembly. In the example of Figure 10, a metallic via (or hole) V passing through the structure allows the shields B101 and B102, placed on the front and back faces, to be interconnected. rear, of the structure, and thus constitute a single shield with the B101 and B102 shields.

[0104] The shield can indeed be arranged on several levels of the structure, which can be interconnected by metallized vias (or holes). A shield can be made with several meshes arranged on several levels of the structure, and which are interconnected by metallized vias (or holes).

[0105] In general, the shield according to the invention can thus be integrated in particular in the one or more BE layers of interconnection levels, on a thin film packaging, on a silicon packaging in FOWLP (Fan Out Wafer Level Packaging, which is a silicon wafer-scale packaging technique that consists of expanding or enlarging the connectivity levels of a chip outside its dimensions by using epoxy molding), and on the back side of silicon chips.

Claims

Demands

1. Electronic device protection shield comprising: • a resistive circuit (Cl, C2, C3) of metallic lines, said circuit being associated with at least one resistivity signature of the circuit which constitutes a reference value enabling the certification of the integrity of the circuit, • means for controlling the resistivity of the circuit, connected to said circuit, said means for controlling being capable of measuring at least one resistivity value of the circuit and comparing this value to said resistivity signature to certify the integrity of the circuit, characterized in that the resistive circuit comprises at least one phase-change resistive cell (PI, P2) whose resistivity contributes to establishing said resistivity signature of the circuit.

2. Shield according to the preceding claim, characterized in that the resistivity of the phase-change resistive cell was established by an energy activation which made it possible to randomly modify the resistivity of said phase-change resistive cell, thus constituting an individual random resistivity signature of the phase-change resistive cell to constitute a resistivity signature of said circuit.

3. Shield according to the preceding claim, characterized in that said energy activation was achieved by application of an electrical activation voltage.

4. Shield according to the preceding claim, characterized in that said resistivity control means are capable of applying to terminals (C11, C12, C21, C22, C31, C32) of the circuit an electrical reading voltage to measure at least one resistivity value of the circuit.

5. Shield according to any one of the preceding claims, characterized in that the circuit comprises several phase-change resistive cells.

6. Shield according to any one of the preceding claims, characterized in that at least one phase-change resistive cell is of linear configuration.

7. Shield according to any one of the preceding claims, characterized in that at least one phase-change resistive cell is of circular configuration.

8. Shield according to one of the three preceding claims, characterized in that the control means are capable of applying a voltage across the terminals of at least two parts of the circuit, and of measuring the resistivity of said parts of the circuit.

9. A method for manufacturing a shield according to any one of the preceding claims, comprising the steps of: • Forming, on at least a portion of the area to be protected of the electronic device, the location of a phase-change resistive cell, by forming a region of phase-change material, • Defining a resistive circuit path around the area to be protected, said path being in contact by two terminals with said region of phase-change material at each location of a phase-change resistive cell, • Depositing a conductive material at said path, so as to form the resistive circuit, and forming, at each location of a phase-change resistive cell, two electrodes adjacent to and surrounding the region of phase-change material to form a phase-change resistive cell,• For each phase-change resistive cell: apply energetic activation to the phase-change resistive cell, in particular by applying an activation voltage to the phase-change material region or by exposing the phase-change material region to energetic radiation, the energy level applied to the phase-change material region being chosen close to the energy level allowing partial crystallization of said phase-change material so that the crystalline structure of a part of said phase-change material region is modified.

10. A method according to the preceding claim, characterized in that for depositing a conductive material at said path in a manner

11. To create the resistive circuit, a mask is applied to the area to be protected, the openings of which define the path of the resistive circuit on the area to be protected, and to deposit a conductive material at the level of said path in order to create the resistive circuit, a conductive material is deposited through the mask onto the area to be protected, in order to create the resistive circuit. Application of the shield manufacturing process according to the preceding claim to the manufacture of a plurality of shields, application wherein: • The same mask is used to deposit a conductive material through the mask onto the area to be protected by each shield, and • For each shield, an energy activation is applied to at least one phase-change resistive cell of the shield to establish an individual resistive signature of the shield.