PHASE CHANGE MATERIAL AND CORRESPONDING RESISTIVE PHASE CHANGE MEMORY

Description

DOMAINE TECHNIQUE DE L'INVENTION

[0001] The technical field of the invention is that of phase change memory materials and more particularly that of materials intended to change phase which can be used as active materials for resistive phase change memories.

[0002] The present invention relates to a material for phase change. The present invention also relates to a resistive phase change memory and associated manufacturing methods. ARRIERE-PLAN TECHNOLOGIQUE DE L'INVENTION

[0003] Phase-change resistive memories or PCM memories (for "Phase-Change Memory") are resistive memories comprising an active zone based on a chalcogenide material located between two electrodes. The operation of PCM memories is based on the phase transition of the chalcogenide material, induced by the heating of this material under the effect of specific electrical pulses applied via its two electrodes. This transition takes place between a crystalline phase, of low resistance and thermodynamically stable, called LRS state (for "Low-Resistive State" otherwise known as "SET") and an amorphous, disordered phase, of high resistance and thermodynamically unstable, called HRS state (for "High-Resistive State" otherwise known as "RESET").

[0004] In automotive applications, PCM memories are subjected to temperatures of around 250°C for a few minutes and temperatures above 150°C for years. To preserve the information stored in PCM memories during their manufacture and during their use, they must not crystallize when subjected to such temperatures: their active material must therefore have a crystallization temperature above 250°C.

[0005] However, the materials constituting the active layer of PCM memories, such as the Ge 2 Sb 2 Te 5 material, are subject to the "drift" phenomenon for the LRS or SET state. This "drift" phenomenon corresponds to an evolution over time and under the effect of temperature, of the electrical resistance of the material in the crystalline phase towards increasingly higher values, which can approach the electrical resistance of the material in the HRS or RESET state, i.e. in the amorphous phase. The two resistive states LRS and HRS of the PCM memory may then no longer be sufficiently distinct for the PCM memory to operate nominally.

[0006] There is therefore a need to provide a PCM memory having a high crystallization temperature, and in particular greater than 250°C, not subject to the “drift” phenomenon for the LRS or SET state.

[0007] Document US 2013 / 187111 A1 entitled "Memory cells" is known from the state of the art. The chalcogenide composition GeSbTe of the active layer of the PCM memory may contain (Fig. 7) from 52 to 80% Ge atoms, from 2 to 28% Te atoms and from 10 to 34% Sb atoms, preferably Ge 61 Sb 22 Te 17 or Ge 63 Sb 25 Te 12 . RESUME DE L'INVENTION

[0008] The invention offers a solution to the problems mentioned above, by making it possible to obtain a PCM memory crystallizing at a temperature particularly compatible with an automotive or on-board application, i.e. above 250°C, with an LRS or SET state having a resistance that changes little over time.

[0009] A first aspect of the invention relates to a material intended to change phase comprising germanium Ge, tellurium Te and antimony Sb, comprising at least 37% of germanium Ge, the ratio between the quantity of antimony Sb and the quantity of tellurium Te being between 2.3 and 2.5.

[0010] Thanks to the invention, under the effect of a strong electrical impulse, in particular in the initialization step, otherwise called the forming step, the material will reorganize to create a first zone and a second zone having different compositions. Indeed, during initialization, a part of the germanium Ge located in the first zone Z1 is expelled towards the second zone Z2, so as to deplete the first zone Z1 in germanium Ge, the Sb / Te ratio remaining substantially identical in the first zone Z1 and the second zone Z2. After initialization, the first zone Z1 comprises a material called Delta material, consisting of 10.7% germanium Ge, 62.7% antimony Sb and 26.6% tellurium Te and excess germanium Ge.Since the Delta material has a trigonal or even hexagonal phase, it has a faster crystal growth than a classic ternary mixture, such as Ge 2 Sb 2 Te 5 , which crystallizes in the cubic phase and generates a very significant "drift" phenomenon on the SET state, and is therefore not itself subject to the "drift" phenomenon for the LRS or SET state. In addition, the Delta material has a crystallization temperature above 250°C.

[0011] Thus, a PCM memory having the material according to the invention as active material has a crystallization temperature greater than 250°C and is not subject to the “drift” phenomenon for its LRS or SET state.

[0012] In addition to the characteristics which have just been mentioned in the preceding paragraph, the material according to the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations.

[0013] According to an embodiment variant compatible with the previous embodiment variant, the ratio between the quantity of antimony Sb and the quantity of tellurium Te is approximately 2.4.

[0014] According to an embodiment variant compatible with the previous embodiment variants, the material comprises between 37% and 90% of germanium Ge, preferably it comprises substantially 76% of germanium Ge.

[0015] According to an embodiment variant compatible with the previous embodiment variants, the material comprises between 65% and 80% germanium Ge, between 15% and 25% antimony Sb and between 5% and 11% tellurium Te.

[0016] According to an embodiment variant compatible with the previous embodiment variants, the material comprises 76% germanium Ge, 17% antimony Sb and 7% tellurium Te.

[0017] According to an embodiment variant compatible with the previous embodiment variants, the material consists of germanium Ge, tellurium Te and antimony Sb, with optionally at least one dopant.

[0018] According to an embodiment variant compatible with the preceding embodiment variants, the material comprises at least one dopant chosen from the following group: carbon C, titanium Ti, oxygen O, phosphorus P, arsenic As, boron B, gallium Ga or silicon Si.

[0019] Thus, crystal growth is further slowed down.

[0020] According to an embodiment variant compatible with the previous embodiment variants, the material comprises at least one dopant, the dopant being nitrogen N.

[0021] Thus, the crystallization temperature is increased and the LRS or SET state is improved. Indeed, the nitrogen N will bind to the germanium Ge and thus reduce the growth of germanium Ge aggregates in the active zone. Since germanium Ge is a very resistive material indifferently in the LRS or HRS phase of the memory 100, preventing the formation of germanium Ge aggregates will favor the growth of the Delta material which is on the contrary responsible for the switch between the LRS or SET state and the HRS or RESET state.

[0022] According to a first alternative embodiment compatible with the previous embodiment variants, the material is in the form of a stack of layers, with each of the layers having a thickness less than or equal to 10 nm, preferably less than or equal to 5 nm.

[0023] According to a first example of embodiment of the first alternative, the stack comprises a first layer of Ge 2 Sb 2 Te 5 , a second layer of antimony Sb and a third layer of germanium Ge doped with nitrogen N.

[0024] Thus, the materials used in the layer stack are available from the catalog, so its manufacturing cost is lower.

[0025] According to an alternative embodiment of the first exemplary embodiment, the first layer has a thickness of substantially 2.5 nm, the second layer has a thickness of substantially 2.5 nm and the third layer has a thickness of substantially 10 nm.

[0026] According to a second exemplary embodiment, the stack of layers comprises a first layer of material comprising germanium Ge, antimony Sb and tellurium Te, and a second layer of germanium Ge doped with nitrogen N.

[0027] Thus, doping with nitrogen N makes it possible to control the crystal growth of germanium Ge and thus increases the stability of the layers, to avoid degeneration of the morphology of the stack during fusion.

[0028] According to an alternative embodiment of the second exemplary embodiment, the first layer of material comprises between 0% and 20% of germanium Ge, between 50% and 70% of antimony Sb and between 15% and 35% of tellurium Te.

[0029] According to a second alternative embodiment compatible with the previous embodiment variants, the material is in the form of a single layer.

[0030] A second aspect of the invention relates to a resistive phase change memory comprising: an upper electrode; a lower electrode; at least one active layer made from the material according to the invention; the memory being intended to pass from a first resistive state to a second resistive state by applying a voltage or a current between the upper electrode and the lower electrode.

[0031] According to an alternative embodiment, the active layer, arranged between the upper electrode and the lower electrode, has a first zone defined around an axis connecting the center of the lower electrode and the center of the upper electrode comprising at least one part made of a material consisting of 10.7% germanium Ge, 62.7% antimony Sb and 26.6% tellurium Te, and a second zone located around and outside the first zone.

[0032] A third aspect of the invention relates to a method of manufacturing the memory according to the invention, comprising the steps carried out in the following order: a step of forming the lower electrode; a step of forming the active layer of the memory; a step of forming the upper electrode.

[0033] According to an alternative embodiment, the step of forming the active layer comprises a deposition of a single layer made from the material according to the invention or comprises the formation of a stack of layers intended to form at least in part the material according to the invention.

[0034] According to an embodiment variant compatible with the previous embodiment variant, the method comprises a step of applying an electrical pulse between the upper electrode and the lower electrode, the step of applying the electrical pulse being implemented after the steps of forming the lower electrode, forming the active layer, and forming the upper electrode.

[0035] According to an alternative embodiment compatible with the previous alternative embodiment, the step of forming the active layer comprises at least one cathode sputtering sub-step using at least one sputtering target.

[0036] According to a sub-variant embodiment of the previous variant embodiment, the cathode sputtering sub-step uses at least one sputtering target composed of a molecule chemically stable at room temperature, such as for example a molecule of chemical formula Ge 2 Sb 2 Te 5 .

[0037] The target, composed of the molecule with the chemical formula Ge 2 Sb 2 Te 5, is stable and therefore prevents the formation of aggregates. Furthermore, since this target is available from a catalog, its cost is lower.

[0038] According to an exemplary embodiment, the sputtering sub-step comprises at least one sputtering target of chemical formula Ge 2 Sb 2 Te 5 . According to an exemplary embodiment, the sputtering sub-step comprises at least one sputtering target consisting of antimony Sb. According to an exemplary embodiment, the sputtering sub-step comprises at least one sputtering target consisting of germanium Ge. According to one embodiment, the sputtering sub-step consists of sputtering a target consisting of Ge 2 Sb 2 Te 5 , a target consisting of antimony Sb, and a target consisting of germanium Ge.

[0039] According to a sub-variant embodiment of the previous variant embodiment, the cathode sputtering sub-step uses at least one sputtering target composed of a molecule chemically stable at room temperature, such as for example a molecule consisting of 10.7% germanium Ge, 62.7% antimony Sb and 26.6% tellurium Te.

[0040] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BREVE DESCRIPTION DES FIGURES

[0041] The figures are presented for information purposes only and in no way limit the invention. There figure 1 is a Ge-Sb-Te ternary diagram on which the area close to the possible compositions for a material according to the invention is hatched (line L2). figure 2 shows a schematic representation of a first embodiment of a memory according to the invention. The figure 3 shows a schematic representation of a second embodiment of a memory according to the invention. The figure 4 is a block diagram illustrating the sequence of steps in a method of manufacturing a device according to the invention. figure 5 represents the resistivity as a function of temperature for a Delta material enriched with 11% germanium, for the Delta material enriched with 35% germanium, for the Delta material enriched with 49% germanium, for the Delta material enriched with 64% germanium and for the Delta material enriched with 70% germanium. The figure 6 shows an X-ray diffractometry of a material according to the invention comprising 35% germanium at 320°C, of ​​the material according to the invention comprising 35% germanium at 450°C, of ​​the material according to the invention comprising 50% germanium at 450°C, of ​​the material according to the invention comprising 64% germanium at 450°C and of the material according to the invention comprising 70% germanium at 450°C. DESCRIPTION DETAILLEE

[0042] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0043] A first aspect of the invention relates to a phase-changing material which can be used as an active material of a resistive phase-change memory or PCM for "Phase-Change Memory".

[0044] A second aspect of the invention relates to a resistive phase change memory having as active material the material according to the invention, i.e. comprising an active zone based on the material according to the invention.

[0045] The material according to the invention comprises germanium Ge, tellurium Te and antimony Sb.

[0046] [ Fig. 1 ] There figure 1 is a Ge-Sb-Te ternary diagram on which is hatched a REF zone close to the possible compositions for the material according to the invention.

[0047] The percentage used throughout the description is a molar percentage, that is to say that by "the material contains at least X% of an element", we mean that the quantity of matter of the element in the material corresponds to X% of the total quantity of matter of the material, whether before or after initialization.

[0048] In the following description, all percentages used are molar percentages.

[0049] The material according to the invention comprises at least 37% germanium Ge.

[0050] When there is sufficient germanium Ge in the active area of ​​a PCM memory, it acts as a retarder for the nucleation and crystal growth of the active area material, which has the effect of increasing the crystallization temperature of the active area.

[0051] The PCM memory according to the invention having the material according to the invention comprising at least 37% of germanium Ge in its active zone therefore necessarily has a crystallization temperature of its active zone greater than 250°C. Thus, for automotive applications, or for embedded applications, preservation of the information stored in the PCM memory according to the invention is ensured.

[0052] The material according to the invention comprises, for example, between 37% and 90% germanium Ge.

[0053] On the figure 1 , line L4 represents 37% germanium Ge, line L5 represents 90% germanium Ge and the hatched area REF is bounded by lines L4 and L5.

[0054] Preferably, the material according to the invention comprises 76% germanium Ge.

[0055] The ratio between the quantity of antimony Sb and the quantity of tellurium Te in the material according to the invention is such that: 1.5 ≤ Sb Te ≤ 4

[0056] On the figure 1 , line L1 represents: Sb Te = 1.5

[0057] On the figure 1 , line L3 represents: Sb Te = 4

[0058] The ratio between the amount of antimony Sb and the amount of tellurium Te in the material can be such that: 2 ≤ Sb Te ≤ 2.8

[0059] The ratio between the quantity of antimony Sb and the quantity of tellurium Te in the material according to the invention is such that: 2.3 ≤ Sb Te ≤ 2.5

[0060] In other words, the ratio between the quantity of antimony Sb and the quantity of tellurium Te in the material according to the invention is approximately 2.4.

[0061] According to one embodiment, the ratio between the quantity of antimony Sb and the quantity of tellurium Te in the material according to the invention is strictly equal to 2.4.

[0062] On the figure 1 , line L2 represents: Sb Te = 2.4

[0063] The material according to the invention is, for example, a composition comprising between 65% and 80% germanium Ge, between 15% and 25% antimony Sb and between 5% and 11% tellurium Te.

[0064] Preferably, the material according to the invention comprises 76% germanium Ge, 17% antimony Sb and 7% tellurium Te, which corresponds to the Delta-G point on the figure 1 .

[0065] According to a particular embodiment, the material according to the invention may additionally comprise at least one doping species.

[0066] The term "doping species or dopant of a system" means a chemical element that does not generate covalent bonds with the system, when the latter is in crystalline phase. Preferably, the proportion of dopant within the system is less than 15%, and even more preferably between 1% and 10% or between 1% and 5%.

[0067] The doping species is for example carbon C, titanium Ti, oxygen O, phosphorus P, arsenic As, boron B, nitrogen N, gallium Ga and / or silicon Si.

[0068] [ Fig. 2 ] There figure 2 shows a schematic representation of a first embodiment of the memory 100 according to the invention.

[0069] [ Fig. 3 ] There figure 3 shows a schematic representation of a first embodiment of the memory 100 according to the invention.

[0070] Whatever the embodiment, the memory 100 comprises: a lower electrode 101; at least one layer made from the material according to the invention, called active layer 102; and an upper electrode 103.

[0071] An upper electrode of a device is defined as the electrode located above this device and the lower electrode of a device as the electrode located below this device, the electrodes being located on either side of the device. Of course, the adjectives "upper" and "lower" here relate to the orientation of the assembly including the upper electrode, the device and the lower electrode so that by turning this assembly over, the electrode previously described as upper becomes the lower electrode and the electrode previously described as lower becomes the upper electrode. However, the adjectives "upper" and "lower" do not limit the invention to the arrangement of the electrodes, the device being able, of course, to be rotated by 90° so as to be arranged vertically.

[0072] The lower electrode 101 and the upper electrode 103 may be planar or in the form of an L or an I.

[0073] On the figures 2 And 3 , the lower electrode 101 has an L-shape and the upper electrode 103 is planar. In particular, the lower electrode 101 has an L-shape with a larger vertical portion than its horizontal portion.

[0074] The term "vertical electrode" means an electrode whose maximum dimension is in the vertical direction.

[0075] The lower 101 and upper 103 electrodes are each made of a conductive material which may be different or the same for the two electrodes 101, 103. Such a conductive material is for example TiN, TaN, W, TiWN, TiSiN or even WN.

[0076] In the first embodiment of the memory 100, the active layer 102 comprises a stack 301 of layers, before initialization.

[0077] Each layer of the stack 301 of layers has a thickness less than or equal to 10 nm, for example less than or equal to 5 nm.

[0078] The term "thickness of a layer" refers to the dimension of the layer along an axis perpendicular to a layer plane, corresponding to the plane formed by the layer. Here, the axis in question is associated with the vertical direction.

[0079] In a first exemplary embodiment, the stack 301 of layers comprises, for example, at least two layers each made of a different material, for example a first layer of Ge 2 Sb 2 Te 5 , a second layer of antimony Sb and a third layer of germanium Ge doped with nitrogen N.

[0080] For example, the first layer is 2.5 nm thick, the second layer is 2.5 nm thick, and the third layer is 10 nm thick.

[0081] According to a second exemplary embodiment, the stack 301 of layers comprises a first layer comprising between 0% and 20% of germanium Ge, between 50% and 70% of antimony Sb and between 15% and 35% of tellurium Te, and a second layer of germanium Ge doped with nitrogen N.

[0082] For example, the stack 301 of layers comprises a first layer of Delta material, i.e. comprising 10.7% of germanium Ge, 62.7% of antimony Sb and 26.6% of tellurium Te, having a thickness of 1 nm, and a second layer of germanium Ge doped with nitrogen N having a thickness of 2.7 nm.

[0083] Whatever the embodiment, the overall composition of the stack 301 of layers corresponds to one of the compositions described previously for the material according to the invention.

[0084] On the figure 2 , the stack 301 of layers comprises a repetition of seven sub-stacks 3011 each comprising a first layer shown in white made from a first material and a second layer shown in hatching made from a second material.

[0085] According to the second embodiment, the active layer 102 is formed by a single layer composed of the material according to the invention.

[0086] The single layer has for example a thickness between 1 nm and 100 nm, preferably a thickness greater than or equal to 10 nm.

[0087] On the figure 2 , the memory 100 according to the first embodiment is represented before initialization, that is to say before having been subjected to a strong electrical pulse.

[0088] On the figure 3 , the memory 100 according to the second embodiment is represented after initialization, that is to say after having been subjected to a strong electrical pulse.

[0089] During the initialization step of the memory 100 according to the invention, a reorganization of the active zone is implemented. This reorganization, induced under the effect of a strong electrical pulse, has the effect of creating two zones within the active layer 102, a first zone Z1 defined around an axis connecting the center of the lower electrode 101 and the upper electrode 103 and a second zone Z2 located around and outside the first zone Z1. The first zone Z1 and the second zone Z2 are visible on the figure 3 .

[0090] Under the effect of the initialization electrical pulse, part of the germanium Ge located in the first zone Z1 is expelled towards the second zone Z2, so as to deplete the first zone Z1 in germanium Ge. However, the Sb / Te ratio remains substantially identical in the first zone Z1 and the second zone Z2.

[0091] After initialization, the first zone Z1 includes a material called Delta, shown in the figure 1 , and excess germanium Ge.

[0092] The Delta material consists of 10.7% germanium Ge, 62.7% antimony Sb and 26.6% tellurium Te. The Delta material is interesting in that it has a trigonal, even hexagonal, crystalline phase with a very high crystal growth rate ensuring high crystalline uniformity, low resistivity, few grain boundaries and no drift.

[0093] The remaining germanium Ge in the first Z1 zone helps to delay the nucleation and crystal growth of the first Z1 zone, which has the effect of increasing the crystallization temperature of the first Z1 zone. However, the Delta material alone crystallizes at a temperature below 250°C.

[0094] It should be noted that overall, the material of the active layer 102 has the proportions stated above before and after initialization of the memory 100.

[0095] Thus, the initialization step induces a reorganization of the material but does not modify its composition. In the first zone Z1 and the second zone Z2, the ratio between Sb and Te remains substantially identical; only the germanium Ge is mobile at the time of initialization.

[0096] The various ratios previously cited between Sb and Te make it possible to ensure that after initialization, it is certain to find, in the first zone Z1, at least a part in Delta material, which has the effect of inducing a crystallinity of the first zone Z1 and at least in part in trigonal phase, more particularly in hexagonal phase, which has the advantage of having a favored crystalline growth compared to a cubic phase.

[0097] Following the initialization step, the material of the invention having antimony Sb and tellurium Te in the proportions previously described interacts with germanium Ge to give rise to nucleation allowing crystallization of the active zone in a rhombohedral phase having very significant crystal growth. The size and homogeneity of such a crystalline phase makes it possible to reduce the phenomenon of "drift" of the LRS or SET state.

[0098] On the figure 3 , the memory 100 is shown after initialization, that is to say after having been subjected to a strong electrical pulse, which has caused a reorganization of the material, by dividing it into a first zone Z1 and a second zone Z2. It should be noted that the same division takes place for the first embodiment. The fusion of a part of the active layer 102 therefore makes it possible to define the first zone Z1. The fusion takes place around an axis connecting the center of the lower electrode 101 and the upper electrode 103. According to the example illustrated, the lower electrode 101 and the upper electrode 103 are each positioned opposite each other. According to an alternative embodiment, the lower electrode 101 and the upper electrode 103 could not be arranged opposite each other, but offset. In this case, the first zone Z1 would be in the form of a diagonal.In any case, the second zone Z2 is located around this central axis, outside the first zone Z1.

[0099] Nitrogen N doping makes it possible to increase the crystallization temperature of the active zone of the memory 100 according to the invention and to improve its LRS or SET state. Indeed, the nitrogen N will bind to the germanium Ge and thus reduce the growth of germanium Ge aggregates in the active zone. Given that germanium Ge is a very resistive material indifferently in the LRS or HRS phase of the memory 100, preventing the formation of germanium Ge aggregates will favor the growth of the Delta phase which is on the contrary responsible for the switching between the LRS or SET state and the HRS or RESET state.

[0100] A third aspect of the invention relates to a method of manufacturing the memory 100 according to the invention.

[0101] [ Fig. 4 ] There figure 4 is a block diagram illustrating the sequence of steps of the method 200 according to the third aspect of the invention.

[0102] A first step 201 consists of forming the lower electrode 101 of the memory 100. For example, to obtain a planar lower electrode 101, the first step 201 consists of carrying out a conformal deposition of a layer of lower electrode conductive material 101 on a substrate.

[0103] "Conformal deposition of a layer of material on a substrate" means that the material is deposited uniformly over the entire surface of the substrate.

[0104] The substrate may comprise one or more layers: for example, it comprises a layer with exposed copper lines enabling metallic contacts to be made to a top metal layer and thus includes all the logic necessary to enable connection to the lines of the top layers.

[0105] A second step 202 of the method 200 consists of forming the active layer 102.

[0106] In the first embodiment of the memory 100, the second step 202 consists of forming the stack 301 of layers.

[0107] In the second embodiment, the second step 202 consists of forming the single layer constituting the active layer 102.

[0108] Whatever the embodiment, the second step 202 comprises for example at least one deposition, for example a physical vapor deposition or PVD deposition (for “Physical Vapor Deposition”), or at least one cathodic sputtering using at least one sputtering target composed of a molecule chemically stable at room temperature.

[0109] The second step 202 uses for example at least one sputtering target composed of the molecule of chemical formula Ge 2 Sb 2 Te 5 .

[0110] The second step 202 uses for example at least one sputtering target composed of the molecule of chemical formula Ge 2 Sb 2 Te 5 and a sputtering target composed of antimony Sb or germanium Ge.

[0111] The second step 202 uses for example at least one sputtering target composed of the Delta molecule.

[0112] Other intermediate steps may be carried out between the second step 202 and the third step 203 of the method 200, for example the formation of a selector device between the lower electrode 101 and the active layer 102 or between the active layer 102 and the upper electrode 103.

[0113] A third step 203 of the method 200 consists of forming the upper electrode 103 of the memory 100.

[0114] The third step 103 consists, for example, of carrying out a conformal deposition of a layer of upper electrode conductive material 103, for example on the active layer 102.

[0115] The method 200 according to the invention may also comprise an optional fourth step 204 of applying an electrical pulse between the upper electrode 103 and the lower electrode 101, corresponding to the initialization of the memory 100.

[0116] [ Fig. 5 ] There figure 5 represents the resistivity as a function of temperature for the Delta material enriched with 11% germanium, for the Delta material enriched with 35% germanium, for the Delta material enriched with 49% germanium, for the Delta material enriched with 64% germanium and for the Delta material enriched with 70% germanium.

[0117] We see on the figure 5 that the greater the quantity of germanium, the more on the one hand, the crystallization of the Delta material is carried out at a high temperature and on the other hand, the crystallization of the Delta material is done abruptly, that is to say, the more the curve becomes vertical in an abrupt manner, the abrupt nature of the crystallization being synonymous with a very rapid crystallization, due to the very high growth rate, typical of the "Delta" phase.

[0118] [ Fig. 6 ] There figure 6 shows an X-ray diffractometry of a material according to the invention comprising 35% germanium at 320°C, of ​​the material according to the invention comprising 35% germanium at 450°C, of ​​the material according to the invention comprising 50% germanium at 450°C, of ​​the material according to the invention comprising 64% germanium at 450°C and of the material according to the invention comprising 70% germanium at 450°C, in which the values ​​of 2θ corresponding to germanium crystallized in cubic phase and to Delta material crystallized in hexagonal phase are identified.

[0119] We see on the figure 6 that regardless of the percentage of germanium, the material always comprises cubic-phase crystallized germanium and hexagonal-phase crystallized Delta material at 450°, while at 320°C the material comprises only hexagonal-phase crystallized Delta material.

[0120] Thus, at 450°C we find a first part in Delta material crystallized in hexagonal phase and a second part in germanium crystallized in cubic phase.

Claims

1. Phase-change material comprising germanium Ge, tellurium Te and antimony Sb, characterised in that it comprises at least 37% germanium Ge and in that the ratio between the quantity of antimony Sb and the quantity of tellurium Te is comprised between 2.3 and 2.5.

2. Material according to claim 1, characterised in that it comprises between 37% and 90% germanium Ge, preferably it comprises substantially 76% germanium Ge.

3. Material according to any preceding claim, characterised in that it comprises between 65% and 80% germanium Ge, between 15% and 25% antimony Sb and between 5% and 11% tellurium Te, preferably it comprises 76% germanium Ge, 17% antimony Sb and 7% tellurium Te.

4. Material according to any preceding claim, characterised in that it consists of germanium Ge, tellurium Te, and antimony Sb, with optionally at least one dopant.

5. Material according to any preceding claim, characterised in that it comprises at least one dopant chosen from the following group: nitrogen N, carbon C, titanium Ti, oxygen O, phosphorus P, arsenic As, boron B, gallium Ga or silicon Si.

6. Material according to any preceding claim, characterised in that it has the form of a stack (301) of layers, with each one of the layers having a thickness less than or equal to 10 nm, preferably less than or equal to 5 nm.

7. Material according to claim 6, characterised in that the stack (301) comprises a first layer of Ge2Sb2Te5, a second layer of antimony Sb and a third layer of germanium Ge doped with nitrogen N.

8. Material according to claim 6, characterised in that the stack (301) of layers comprises a first layer of material comprising germanium Ge, antimony Sb and tellurium Te, and a second layer of germanium Ge doped with nitrogen N.

9. Material according to any of claims 1 to 5, characterised in that it has the form of a single layer.

10. Resistive phase-change memory (100) comprising: - an upper electrode (103); - a lower electrode (101); - at least one active layer (102) made from a material defined according to any preceding claim; the memory (100) being intended to pass from a first resistive state to a second resistive state by application of a voltage or of a current between the upper electrode (103) and the lower electrode (101).

11. Memory (100) according to the preceding claim, characterised in that the active layer (102), disposed between the upper electrode (103) and the lower electrode (101), has a first zone (Z1) defined about an axis connecting the centre of the lower electrode (101) and the centre of the upper electrode (103) comprising at least one portion made from a material consisting of 10.7% germanium Ge, 62.7% antimony Sb and 26.6% tellurium Te, and a second zone (Z2) located around and outside of the first zone (Z1).

12. Method (200) for manufacturing memory (100) defined according to any of claims 10 or 11, characterised in that it comprises the steps carried out in the following order: - a step (201) of forming the lower electrode (101); - a step (202) of forming the active layer (102); - a step (203) of forming the upper electrode (103).

13. Method (200) according to claim 12, characterised in that the step (202) of forming the active layer (102) comprises a deposition of a single layer made from a material defined according to claim 9 or comprises the formation of a stack of layers intended to form at least partially the material defined according to any of claims 6 to 8.

14. Method of manufacturing (200) according to claim 12 or 13, characterised in that it comprises a step (204) of applying an electrical pulse between the upper electrode (103) and the lower electrode (101), the step of applying an electrical pulse being implemented after the steps (201, 202, 203) of forming the lower electrode (101), of forming the active layer (102), and of forming the upper electrode (103).