Ultra-thin phase-change storage device with side electrode configuration

Abstract

The invention relates to a phase-change memory device (PCM device). The device comprises an electrically insulating material and a PCM cell embedded in the electrically insulating material. The PCM cell comprises a phase-change material layer (or PCM layer for short), for example, a layer comprising a germanium-antimony-tellurium alloy. The PCM layer has a top surface, a bottom surface, and a side surface connecting the top and bottom surfaces. The PCM cell further comprises an external electrode that contacts the side surface of the PCM layer. That is, the external electrode covers the PCM layer laterally. The PCM cell also comprises a heater that extends at least partially through the PCM layer, transversely to the top and bottom surfaces of the PCM layer, in order to contact the PCM layer.

Description

TECHNICAL AREA

[0001] The invention relates generally to the field of phase-change material (PCM) devices and systems comprising such PCM devices, methods for operating such a PCM device, and methods for manufacturing PCM devices. In particular, it relates to a PCM device comprising a phase-change material layer, an external electrode, and a heater in a "punch-through" configuration: the phase-change material layer is laterally covered by the external electrode, resulting in a donut-shaped phase-change material layer. BACKGROUND

[0002] Resistive memory devices are gaining increasing attention, particularly for multi-tiered data storage and in-memory computing hardware applications. Resistive memory devices specifically include PCM devices that can be reverse-switched between multiple conductivity states.

[0003] PCM devices can be used, for example, for inference purposes in analog computing for artificial intelligence using in-memory computing hardware. The memory elements can include phase-change memristor devices with tunable conductivities, high device resistance, and high retention to minimize power consumption. Tuning can be achieved by forming different structural states with varying proportions of crystalline and amorphous phases of the phase-change material.

[0004] PCM cells can have various configurations. A common PCM cell structure is the so-called "mushroom" cell. This is because a phase-change material is enclosed between an upper electrode and an insulating layer, which is itself bounded by a lower electrode. The latter contacts a heater that extends through the insulating layer. The standard mushroom cell includes a large-area electrode on top of the phase-change material and a much smaller heater on the bottom. Heating the phase-change material layer causes the amorphous phase to expand over the insulating layer in the shape of a spherical cap, thus resembling a mushroom (along with the heater). Other designs incorporate a line cell in a side-mounted configuration.Another PCM cell design has been proposed, in which the cell has a “pancake” configuration: The upper electrode only touches a circumferential area of ​​the upper surface of a thin phase-change layer.

[0005] In general, PCM devices require high-current reset operation to switch the device from a low-resistance (crystalline) state to a high-resistance (amorphous) state. High currents now hinder the scaling of the technology. There is a need for low reset currents, if only for power efficiency. Lower reset currents are also required to achieve smaller devices, improve PCM cell density, and for back-end-of-line (BEOL) integration. SUMMARY

[0006] According to a first aspect, the invention is designed as a phase-change material (PCM) device. The device comprises an electrically insulating material and a PCM cell embedded in the electrically insulating material. The PCM cell comprises a phase-change material layer (or PCM layer for short), for example, a layer comprising a germanium-antimony-tellurium alloy. The PCM layer has a top surface, a bottom surface, and a side surface connecting the top and bottom surfaces. The PCM cell further comprises an external electrode that contacts the side surface of the PCM layer. That is, the external electrode covers the PCM layer laterally. The PCM cell also comprises a heater that extends at least partially through the PCM layer, transversely to the top and bottom surfaces of the PCM layer, in order to contact the PCM layer.

[0007] By definition, the heating element is located within the PCM cell, i.e., within the outer electrode. As with pancake-type cells, the present PCM cell design allows for lower RESET currents than mushroom-type cells. However, here the phase change is triggered radially from within the PCM layer (e.g., from the center) because the heating element extends at least partially through the PCM layer. Furthermore, the outer electrode covers the PCM layer laterally (i.e., it touches the lateral side of the PCM layer) instead of extending around the perimeter of the top surface of the PCM layer. This saves considerable vertical space and consequently results in flatter PCM devices, which is advantageous for back-end-of-line integration. The advantages of the present approach are even more pronounced compared to a mushroom-type cell, whether in terms of dimensions (and thus integration) or RESET currents.

[0008] The heating element may only partially extend through the PCM layer to minimize the contact area. This design option requires more precise control of the heating element's manufacturing process. In other variations, the heating element extends completely through the PCM layer, requiring less control over the heating element's manufacturing process. Nevertheless, the PCM layer can still be made sufficiently thin to limit the contact area with the heating element.

[0009] In principle, the outer electrode only partially covers the side surface of the PCM layer. In some embodiments, however, the outer electrode completely covers the side surface of the PCM layer. This promotes electrical contact and improves performance, as electrical currents applied to the heater can be conducted more homogeneously through the outer electrode. Additionally, such an electrode configuration is easier to manufacture and reduces the risk of oxidation of the PCM side walls.

[0010] In some embodiments, the heating element extends essentially perpendicular to each of the upper and lower surfaces of the PCM layer. The longitudinal axis of the heating element can even pass essentially through the center of the PCM layer. This results in a symmetrical arrangement that allows for a better distribution of the area of ​​the PCM layer that changes phases when the heating element is energized.

[0011] In embodiments, the average thickness of the PCM layer is less than the average diameter of a section of the heater extending through the PCM layer. In embodiments, the average diameter of the heater section is between 5 nm and 100 nm, and preferably between 5 nm and 40 nm. For example, in embodiments, the average diameter of the heater section is between 30 nm and 40 nm, while the average thickness of the PCM layer is between 1 nm and 20 nm. The average thickness of the PCM layer is preferably less than 10 nm. The average diameter of the upper and lower surfaces of the PCM layer is typically between 45 nm and 500 nm.

[0012] In embodiments, the PCM cell further includes a resistive projection liner to reduce resistive drift and conductivity variations. The resistive projection liner contacts the PCM layer on its upper or lower surface. The external electrode completely covers the side face of the PCM layer and one side face of the resistive projection liner laterally. The heating element extends through and contacts each of the PCM layer and the resistive projection liner. The resistive projection liner can, for example, comprise one of carbon (C), titanium nitride (TiN), or tantalum (TaN). More generally, the resistive projection liner can comprise a metal nitride, a metal oxide, polysilicon, or a silicon-doped metal.

[0013] In embodiments, the PCM cell further comprises an electrically insulating layer and a protective layer on the insulating layer, the latter sandwiched between the protective layer and the upper surface of the PCM layer. The outer electrode completely covers the side surface of the PCM layer as well as the side surfaces of the protective layer and the insulating layer. The heating element extends through and makes contact with each of the protective layer, the insulating layer, and the PCM layer. The thickness of the complete layer stack (i.e., including the protective layer, the insulating layer, the PCM layer, and any resistive lining) will not exceed 70 nm in embodiments.

[0014] In some embodiments, the outer electrode is structured to cover only a peripheral area of ​​the upper surface of the protective layer. This creates a safety margin that ensures the outer electrode laterally covers the entire side surface of the protective layer as well as all layers below it in the layer stack that forms part of the PCM cell. The protective layer can, for example, comprise hydrogen silsesquioxane.

[0015] In embodiments, the PCM device further comprises a heating electrode that contacts the heater and a circuit component that also contacts the heating electrode. This circuit component can be, for example, a resistor, a selector, or a component thereof. The heating electrode and this circuit component extend along one side of the PCM layer and are embedded in the electrically insulating material.

[0016] In embodiments, the PCM device further comprises two electrical contact surfaces, each filling two vias extending through the electrically insulating material to contact the circuit component and the outer electrode, respectively.

[0017] According to another aspect, the invention is designed as a data processing system. The data processing system comprises a control system and one or more PCM devices, as described above. That is, the data processing system comprises a PCM cell embedded in an electrically insulating material, the PCM cell comprising a PCM layer, an outer electrode contacting the side surface of the PCM layer, and a heater extending at least partially through the PCM layer, transverse to the top and bottom surfaces of the PCM layer, in order to contact the PCM layer. Each PCM device is connected to the control system.

[0018] In some embodiments, the data processing system includes an in-memory computing (IMC) device having a crossbar array structure. The crossbar array structure includes N input lines and M output lines connected at intersection points to define N × M cells, where N ≥ 2 and M ≥ 2. The intersection points contain respective memory systems, each containing a group of K memory elements, where K ≥ 1. That is, each of the N × M cells contains K memory elements, each of which contains one of the PCM devices. The control system includes a programming unit connected to the crossbar array structure. The programming unit is configured to program each cell according to a given target conductance value, corresponding to a target weight value to be stored in each cell.

[0019] According to another aspect, the invention is designed as a method for operating a PCM device. The method initially involves providing a PCM device as described above, i.e., a device comprising a PCM cell with a PCM layer embedded in an electrically insulating material, wherein a heater extends at least partially transversely through the PCM layer, while an external electrode contacts the side surface of the PCM layer laterally. The method essentially revolves around repeatedly applying a RESET current pulse and a SET current pulse through the heater. The RESET current pulse causes an annular amorphous region to grow in the PCM layer from the heater, bringing the PCM layer into a high-resistance state.Conversely, the SET current pulse causes the annular amorphous region in the PCM layer to decrease, thus bringing the PCM layer into a low-resistance state. In typical applications, multiple PCM devices are operated simultaneously, for example, in a data processing system, as described above.

[0020] According to a final aspect, the invention is designed as a method for manufacturing a PCM device as described above. The method essentially involves manufacturing a PCM cell by obtaining a stack of layers. The stack comprises a PCM layer with a top face and a bottom face connected by a side face. An outer electrode layer is deposited on the stack such that the outer electrode layer contacts the side face of the PCM layer and a top face of the stack. A via is opened from the top face of the stack. The resulting via extends at least partially through the PCM layer, transversely to the top and bottom faces of the PCM layer. The via is then filled to create a heater that contacts the PCM layer.The PCM cell is then covered with an electrically insulating material to embed it. It should be noted that the outer electrode layer may be deposited after the via is opened to retain the heating element.

[0021] In embodiments, the resulting layer stack further includes a resistive projection liner that contacts the PCM layer on its upper or lower surface. In this case, the via is opened to extend at least partially through each of the PCM layer and the resistive projection liner. That is, the heating, as obtained by subsequent filling of the via, contacts each of the resistive projection liner and the PCM layer.

[0022] In embodiments, the resulting layer stack further comprises an electrically insulating material layer and a protective layer on the electrically insulating material layer. The latter is arranged in a sandwich-like manner between the protective layer and the upper surface of the PCM layer.

[0023] In embodiments, the method further includes, after filling the via and before covering the PCM cell, depositing a layer on the filled heater and structuring the deposited layer to obtain an electrode and a circuit component, which may be a resistor or a selector or an element thereof.

[0024] In embodiments, the method further includes, after covering the PCM cell, etching further vias through the electrically insulating material and filling the further vias to obtain two electrical contact surfaces, each touching the outer electrode and the circuit component. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] These and other problems, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which should be read in conjunction with the accompanying drawings. The illustrations serve to clarify the invention and facilitate its understanding by a person skilled in the art in conjunction with the detailed description. The drawings show: Fig. 1 A 2D cross-sectional view of a phase change storage device (PCM device) according to embodiments. The plane on which the cross-sectional view is taken includes the longitudinal axis of the heater; Fig. 2 another cross-sectional view of the device of Fig. 1, recorded in the mid-plane of the phase-change material layer. In the example of Fig. 1 and Fig. 2 the phase-change material layer is essentially cylindrical, and the layer stack exhibits roughly rotational symmetry, as in embodiments; Fig. 3 and Fig. 4 are cross-sectional views, showing the variants to Fig. 1 and Fig. 2 illustrate, in which the layer stack has a tetragonal or pyramidal shape extending from a phase-change material layer that forms a rectangular ( Fig. 3) or square ( Fig. 4) has the form shown in embodiments; Fig. 5A, Fig. 5B, Fig. 5C, Fig. 5D, Fig. 5E, Fig. 5F, Fig. 5G, Fig. 5H and Fig. 5I are a sequence of cross-sectional views (in the plane containing the longitudinal axis of the heater, as in Fig. 1) the manufacturing steps at a higher level of a PCM device similar to that of Fig. 1 illustrate, with the exception that the resistive projection lining is now located above the phase-change material layer and the heating element only partially extends through the phase-change material layer, according to embodiments; Fig. Figure 6 is a diagram of a data processing system that includes an in-memory computing unit whose memory elements include PCM devices, as shown in Fig. 1, Fig. 2 and Fig. 5I shown, according to embodiments; and Fig. Figure 7 is a flowchart illustrating higher-level steps of a method for operating a PCM device according to embodiments.

[0026] The accompanying drawings show simplified representations of devices or parts thereof as involved in embodiments. Technical features shown in the drawings are not necessarily to scale. Similar or functionally similar elements in the figures have been designated with the same reference numerals unless otherwise indicated.

[0027] Devices, systems and methods embodying the present invention are now described as non-limiting examples. DETAILED DESCRIPTION OF FORMATIONS OF THE INVENTION

[0028] A first aspect of the invention will now be described in detail, usually with reference to the Fig. 1 to Fig. 4. This aspect relates to a phase change memory (PCM) device 10 comprising an electrically insulating material 11 and a PCM cell 12-16, wherein the PCM cell is embedded in the electrically insulating material 11.

[0029] The PCM cell comprises an outer electrode 12, a phase-change material layer 14, and a heater 15. For the sake of simplicity, the term "PCM layer" will be used hereafter to refer to the phase-change material layer 14. The PCM layer 14 has a top surface (on top of layer 14 in Fig. 1) a bottom surface and a side surface connecting the top and bottom surfaces. The PCM layer 14, for example, can have a cylindrical shape, i.e., be roughly formed as a right circular cylinder, as in the Fig. 1 and Fig. 2. In this case, the top surface and the bottom surface correspond to the top base and the bottom base of the cylinder, respectively, and the side surface is the curved surface connecting the top and bottom bases of the cylinder.

[0030] The heater 15 extends at least partially through the PCM layer 14, transversely to the PCM layer 14, i.e., transversely to the upper and lower surfaces of the PCM layer 14. That is, the heater has a "punch-through" configuration. The heater 15 is a heating element that is normally connected by an electrode 17, e.g., on top of the heater 15 in Fig. 1. The heater mechanically contacts the PCM layer 14, ensuring close thermal communication between the heater 15 and the PCM layer 14. The heater can be considered an internal electrode that, in this context, extends at least partially through the PCM layer 14 and therefore contacts the inner boundary surface of the PCM ring 14.

[0031] Conversely, the outer electrode 12 is an edge electrode that laterally contacts the outer side surface (i.e., the outer edge surface) of the PCM layer 14. Preferably, the outer electrode 12 completely covers the outer side surface of the PCM layer 14 laterally as shown in the Fig. 1-4 assumed. The outer electrode 12 is used to dissipate currents that are applied during operation by the heater 15.

[0032] The proposed design results in a lateral PCM configuration, which allows for flatter PCM cells. This configuration leads to phase changes triggered laterally by the heater 15. That is, the phase region that changes phases (from crystalline to amorphous) grows radially from the heater 15 and typically forms a ring shape (or donut shape). This is in the Fig. 1 and Fig. 2 illustrates; the plane on which the cross-sectional view of Fig. 2 is taken, is shown by the dashed line CSP in Fig. 1 is displayed. This level corresponds to the middle level of PCM layer 14. As shown in the Fig. 1 and Fig. As can be seen in Figure 2, an amorphous phase region AP grows radially from the heater 15 when it is energized (i.e., when a RESET current pulse is applied), which causes the crystalline phase region CP to decrease. The resulting configuration of the amorphous phase can thus be described as a "donut" configuration.

[0033] As with pancake-type cells, the present PCM cell design allows for lower RESET currents than mushroom-type cells. This is because the phase change is triggered laterally from an inner region of the PCM layer (e.g., from the center). Consequently, the annular section of the material that changes phases is more homogeneous during operation. The proposed design is indeed similar to that of the so-called pancake-type cell and, moreover, results in similar SET / RESET resistances. However, there are two major differences compared to the pancake-type cell. First, in this case, the outer electrode 12 covers the PCM layer laterally (i.e., it touches the lateral side of the PCM layer) instead of extending around the perimeter of the upper surface of the PCM layer. This saves considerable vertical space and consequently results in flatter PCM devices, which has advantages for back-end-of-line (BEOL) integration.Secondly, the phase change is triggered radially from within the PCM layer (e.g. from the center), since the heating extends at least partially through the PCM layer.

[0034] The advantages of the present approach are even more pronounced with respect to a mushroom-type cell, whether in terms of dimensions (and thus integration) or RESET currents. One reason for the lower RESET current is that the outer electrode 12 and the heater 15 contact the PCM layer at its lateral edges. This effectively reduces the contact (or interface) areas between the heater and the PCM layers to 2π r1 h (for the heater 15) and 2π r2 h (for the outer electrode 12) instead of π ρ1. 2 (lower heating) and π ρ2 2(upper electrode) in the mushroom cell. The dimensions r1 and r2 correspond to the average inner hole radius (through which the heater 15 extends in this case) and the average radius of the PCM layer 14, while ρ1 and ρ2 correspond to the average radii of the interfaces with the lower heater and the upper electrode in the mushroom-type cell. Furthermore, in this context, the contact area 2π r1 h between the heater 15 and the PCM layer can be further reduced if the heater does not extend completely through the PCM layer 14, as in other embodiments.

[0035] Furthermore, the production of the PCM cells presented here is simpler than the production of fungal cells. In particular, the PCM layer can be refined by chemical-mechanical polishing / planarizing (CMP). The production of the heating element is also quite simple and can benefit from a self-alignment process, as will be discussed later with reference to another aspect of the invention.

[0036] All of this will now be described in detail, with reference to specific embodiments of the invention. To begin, the heating element 15 can extend completely through the PCM layer 14, as shown in Fig. Figure 1 illustrates this. That is, the heating element 15 penetrates the PCM layer 14 from one side (e.g., from the top surface of the PCM layer 14). Fig. 1) and extends to the other side (the lower surface of layer 14). It may even protrude slightly from the lower side, i.e., pass through the PCM layer, as in Fig. Assuming 1. In this case, the PCM layer has a ring-like or donut-like shape. Such a design requires less control over the etch stop, insofar as the heater via can be completely etched through the PCM layer 14.

[0037] In variations, see e.g. Fig. In Figure 5I, the heater 15a extends only partially through the PCM layer 14. This design option requires more precise control of the etch stop. However, it also allows for a further minimization of the electrical contact area between the heater 15 and the PCM layer 14. The PCM layer 14 can, in turn, be made slightly thicker. That is, a more precise manufacturing process for the heater allows for a relaxation of the limitations regarding the PCM layer thickness. This means that even if the heater 15 extends completely through the PCM layer 14 (as in Figure 5I), the electrical contact area between the heater 15 and the PCM layer 14 can be further reduced. Fig. 1) The latter can still be made sufficiently thin to limit the electrical interface area.

[0038] In principle, the outer electrode 12 only partially covers the outer side surface of the PCM layer 14 laterally. In embodiments, however, the outer electrode 12 completely covers the side surface of the PCM layer 14 laterally, as shown in the Fig. 1-3 assumed. This promotes electrical contacts and improves performance, insofar as electrical currents applied to the heater 15 can be conducted more homogeneously through the outer electrode 12. Additionally, such an electrode configuration reduces the risk of PCM sidewall oxidation and is easier to manufacture, as it results in a more symmetrical arrangement.

[0039] While the longitudinal axis of the heater 15 generally extends in a direction transverse to the PCM layer 14, in embodiments this direction is perpendicular (or substantially perpendicular) to the PCM layer. In particular, the heater 15 may be roughly symmetrical about its longitudinal axis (it exhibits rotational symmetry), and this axis may ideally pass through the center of the PCM layer. Thus, in embodiments, the heater 15 extends substantially perpendicular to each of the upper and lower faces of the PCM layer 14, and the longitudinal axis of the heater 15 passes substantially through the center of the PCM layer 14. For example, the PCM layer 14 may have a shape that is substantially cylindrical, and the longitudinal axis of the heater 15 may substantially coincide with the cylindrical axis of the PCM layer. In this example, the PCM layer 14 can be considered a flattened, straight cylinder.In variants, the PCM layer 34, 44 can, for example, have a square or rectangular shape (and likewise the outer electrode 32, 42), as in the . Fig. 3 and Fig. 4 illustrates.

[0040] The fact that the heating element passes through the center of the PCM layer 14 results in a more symmetrical arrangement, which makes it possible to better distribute the area of ​​the PCM layer 14 that changes phases when the heating element 15 is energized. Fairly symmetrical arrangements, as disclosed above, can be achieved in particular by using a self-aligning manufacturing process for the heating element, as will be discussed later with reference to another aspect of the invention.

[0041] If a different, more conventional manufacturing process is used, the heater 15 may be slightly off-center. For example, for a disk size of 200 nm outer diameter, a misalignment of between 10 and 20 nm is expected for the heater 15. This can affect the variability between devices with respect to the resistance value of the full RESET state and the threshold voltage. For the shorter leg, the full RESET state effectively provides a parallel path for current flow. This means that the resistance value is covered and does not change even if larger amorphous volumes are formed on the longer leg. However, this is not necessarily a problem. In fact, it is not always necessary to utilize full RESET states, as they can be very resistive and thus produce very weak currents.Furthermore, if the device is projected with a lining 13 as in embodiments, the achievable resistance value is covered anyway. Moreover, the threshold voltages on the smaller leg would decrease because they scale linearly with the amorphous volume size. For the sake of completeness, the electric field (and current profile) may increase towards the side with the smaller distance due to the misalignment, but the heat flux should remain relatively stable since the heater 15 is the main heat sink.

[0042] In embodiments, the average thickness of the PCM layer 14 is smaller than the average diameter of a section of the heater 15 extending through the PCM layer 14. Reducing the thickness of the PCM layer and the heater size both lead to a reduction in the device reset current. The heater may be slightly tapered, as shown in Fig. Figure 1 illustrates this. The average diameter of the heating section penetrating the PCM layer is between 5 nm and 100 nm in embodiments y. For example, this average diameter may be between 30 nm and 40 nm, while the average thickness of the PCM layer 14 is between 1 nm and 20 nm. It should be noted that a very thin (e.g., 1 nm) PCM layer can be achieved using atomic layer deposition (ALD), while layers of 2 nm or more can be obtained by physical vapor deposition (PVD), as in some embodiments. In comparison, the average diameter of the PCM layer (and thus the average diameter of the upper and lower surfaces of the PCM layer) is typically between 45 nm and 400 or even 500 nm. For example, the one in Fig. The assumed average PCM wafer diameters are approximately equal, though slightly smaller than 200 nm, while the average thickness of the PCM layer is less than 10 nm. The average diameter of the PCM layer 14 is measured in the plane, e.g., at the top or bottom surface of the PCM layer 14, while the thickness is measured perpendicular to the mean plane of the PCM layer, i.e., along the stacking direction.

[0043] In embodiments, the PCM cell 12-16 further includes a resistive projection lining 13 (also referred to in this document as the "lining") to reduce resistive drift and conductivity variations. In principle, the lining 13 can contact the PCM layer 14 on its upper or lower surface. For example, in Fig. 1 the lining under PCM layer 14, while it is in the Fig. The layer stack shown in Figures 5A-5I extends over the PCM layer 14. The thickness of the liner 13 is typically between 1 and 20 nm; in embodiments, it is slightly thicker than the PCM layer 14, notwithstanding the apparent proportions in the accompanying drawings. It should be noted that when a liner 13 is present, the outer electrode 12 laterally covers the side faces of both the PCM layer 14 and the liner 13, since the outer electrode laterally covers the entire layer stack. Additionally, the heater 15 extends through (and thus contacts) each of the PCM layer 14 and the liner 13. More precisely, the heater 15 contacts each of the PCM layer 14 and the liner 13 along a via that is open in the thicknesses of the PCM layer 14 and the liner 13.

[0044] The liner 13 is subject to certain design rules to enable the projection mechanism to function. These rules exploit the highly nonlinear, field-dependent electrical transport properties of phase-change materials. At a minimum, the resistance of the projection component must satisfy the following conditions: (i) The resistance of the amorphous part (in the ON state) of the PCM layer 14 must be (much) higher than the resistance of the projection component of the liner 13; (ii) The resistance of the crystalline part of the PCM layer 14 must be much lower than that of the liner 13; and (iii) The resistance of the amorphous part must be much lower than that of the liner 13.

[0045] As further in Fig. As can be seen in Figure 1, the PCM cell 12-16 typically includes an electrically insulating material layer 11a and a protective layer 16 on top of the electrically insulating material layer 11a. The layer 11a is thus sandwiched between the protective layer 16 and the upper surface of the PCM layer 14. Again, the outer electrode 12 completely covers the side faces of the entire stack, i.e., the lining 13 (if present), the PCM layer 14, the electrically insulating material layer 11a, and the protective layer 16.

[0046] Interestingly, the outer electrode 12 can be structured to cover only a circumferential area of ​​the upper surface of the protective layer 16, as shown in the Fig. 1 and Fig. 5A-5I illustrates this. That is, the outer electrode 12 forms a safety edge on the protective layer 16. Such a structural feature results from the structuring of the outer electrode 12, see Fig. 5G, to provide a passage for electrode 17, which contacts the heater 15. This safety margin is maintained to ensure that the outer electrode 12 laterally covers the entire side surface of the protective layer 16. For completeness, the heater 15 extends through (and thus contacts) each layer 13, 14, 11a, 16 of the PCM cell stack.

[0047] As mentioned above, the PCM device 10 can further comprise a heating electrode 17 that contacts the heater 15, as well as a circuit component 18 that contacts the heating electrode 17. The circuit component 18 can be, for example, a resistor (as assumed in the accompanying drawings) or a selector. The component 18 may, in fact, be only a part of the selector or the resistor. The heating electrode 17 and this circuit component 18 extend on one side of the PCM layer 14 (i.e., on the PCM layer 14 in the accompanying drawings) and are embedded in the electrically insulating material 11.

[0048] For the sake of completeness, the PCM device 10 can further comprise two electrical contact surfaces 19, each contacting the circuit component 18 and the outer electrode 12. As in Fig. As can be seen in Figure 1, the two electrical contact surfaces 19 each fill two vias extending through the electrically insulating material 11 to the respective elements, i.e., the outer electrode 12 and the component 18. As further shown in Figure 1, the two electrical contact surfaces 19 each fill two vias extending through the electrically insulating material 11 to the respective elements, i.e., the outer electrode 12 and the component 18. Fig. As can be seen in Figure 1, the outer electrode 12 can, for example, include a neck flange, i.e., a protruding edge that can be touched by the right-hand contact surface 19.

[0049] The PCM layer 14 can comprise or even consist entirely of a germanium-antimony-tellurium alloy (GeSbTe, or GST for short), doped in some embodiments. In other variants, the PCM layer 14 comprises or consists of an alloy containing Ge, Sb, and Te, as well as one or more additional elements, such as Se. Other dopants can be used, including SiO2, O2, Ti, and Cu. The PCM layer can, for example, comprise Ge2Sb2Te5 or Ge2Sb2Se4Te. Other potentially suitable PCM materials include, for example, VOx, NbOx, GeTe, GeSb, GaSb, AglnSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe, and AlSb.

[0050] Suitable materials for the resistive projection lining 13 include carbon (C), a metal nitride such as titanium nitride (TiN) and tantalum nitride (TaN). Other materials may be considered, such as metal oxides, polysilicon, or silicon-doped metals. The electrically insulating material layer 11a will typically be of the same material as the insulating matrix 11, although this is not a strict requirement. In principle, such electrically insulating materials 11, 11a can be electrical insulators or dielectric materials. Suitable materials include SiO2 and Si3N4, although other oxides or nitrides may be considered, such as Al2O3 or HfO. xThe protective layer 16 typically comprises hydrogen silsesquioxane (HSQ). An HSQ film can typically be produced with a thickness between 0.01 and 2 µm. In some variants, the protective layer can be a spacer material, as will be discussed in detail later.

[0051] The Fig. 1 and Fig. Figure 5I shows two embodiments of a PCM device 10, 10a. In each case, the device 10, 10a comprises a PCM cell embedded in a dielectric material 11, 11s, 11c. The PCM cell comprises a layer stack consisting of a PCM layer 14, a resistive projection lining 13, 13a coating the PCM layer 14 on its upper or lower surface, a dielectric layer 11a on the PCM layer 14, and a protective layer 16 on the dielectric layer 11a. The outer electrode 12 laterally covers the side surface of the PCM layer stack (14) and forms a circumferential edge on the protective layer 16. The heater 15 extends through the protective layer 16, the dielectric layer 11a, the resistive projection lining 13, 13a and at least partially through the PCM layer 14. The heater extends perpendicular to the layers of the stack, i.e., along the stack direction.If the resistive projection lining 13 is located beneath the PCM layer 14 (as in . Fig. 1) the heating element 15 extends completely through the PCM layer 14, whereas it can only partially extend through the PCM layer 14 if the lining 13a is located on it ( Fig. 5I). Contact surfaces are formed by the embedding material 11, 11c to touch the outer electrode 12 and the heater 15.

[0052] With reference to Fig. Section 6 relates to another aspect of the invention: a data processing system 1 (or simply "system") comprising one or more PCM devices 10, as described above. The system 1 typically comprises several PCM devices 10, as assumed below. The system 1 further comprises a control system 26-29 to which the PCM devices 10 are connected. The data processing system 1 can, in particular, be an information processing system or a storage system.

[0053] In some embodiments, the data processing system 1 includes an in-memory computing (IMC) device 25-29, which can be used in particular to perform matrix operations such as matrix-vector multiplications (MVM). Such operations are especially useful for performing inferences based on artificial neural networks (ANNs) and decision trees. In this context, MVM operations present several challenges due to their repetitive nature and their computational and memory requirements. Conventional computer architectures are based on the von Neumann computing concept, according to which processing capability and data storage are separated into distinct physical units. This architectural concept suffers from overload and high power consumption because data must be continuously transferred from the storage units to the control and computing units through interfaces that are physically limited and costly.

[0054] One way to accelerate MVM is to use dedicated hardware acceleration devices, such as IMC devices with a crossbar array structure. Such an architecture can implement MVM simply and efficiently: vectors are encoded in signals applied to the crossbar array's input lines to perform the MVM as multiply-accumulate (MAC) operations. The weights can be updated as needed by reprogramming the memory elements to perform successive MVMs. Such in-memory computing devices break the "memory wall" by merging the computing and storage units into a single in-memory computing (IMC) unit. Furthermore, using analog storage devices within an IMC unit enables efficient execution of MVM operations by leveraging the IMC device's analog storage capabilities and Kirchhoff's circuit laws.Another advantage of crossbar array structures is their support for transposed matrix operations, which can be used to train ANNs. More generally, the key computational primitive enabled by such devices can also be used for other applications, such as solvers for systems of linear equations.

[0055] As in Fig. As can be seen in Figure 6, the IMC device has a crossbar array structure 25. That is, the IMC device 15 includes N input lines 251 and M output lines 252, which are connected to each other at crossing points (i.e., connection points). The crossing points accordingly define N × M cells 254, which are also called unit cells. The input and output lines are connected to each other by memory systems 256. In principle, at least two input lines and two output lines are required to define an array (i.e., N ≥ 2² and M ≥ 2). In practice, however, the number of input lines 251 and output lines 252 is typically on the order of several hundred to thousands of lines. For example, arrays of 256 × 256, 512 × 512, or 1024 × 1024 can be considered, although N does not necessarily have to be equal to M.The IMC device 15 can, for example, be used as a neural processing device designed to implement M neurons simultaneously. The number of neurons can thus be, for example, 256, 512, or 1024. Vectors are encoded in signals that are applied to the input lines of the crossbar array via the input unit 27.

[0056] As in Fig. As shown schematically in Figure 6, the intersection points contain respective memory systems 256. Each memory system 256 contains a group of K memory elements 257, where K ≥ 1. That is, each cell 254 contains K memory elements. In variants, each cell contains K ≥ 2 memory elements, which can be arranged in parallel in each group. In particular, each cell can contain two groups of K memory elements 257. Various connection schemes can be considered. In embodiments, each input (or output) line is typically subdivided into K or 2K conductors to establish an adequate connection to (or from) the respective memory elements of each cell. Thus, each input (or output) line typically contains several parallel electrical conductors.

[0057] Each of the K storage elements includes a PCM device 10, as described herein. In addition, the control system 26-29 includes a programming unit 29, see Fig. 6, which is connected to the crossbar array structure 25. The programming unit 29 is configured to program each cell 254 according to a given target conductance value, i.e., a value corresponding to a target weight value to be stored in each cell. Programming a cell means storing a target weight value in that cell. The target weight value can be converted into an electrical conductance value. Thus, the goal is to program the storage elements of this cell so that they produce a summed conductance value that matches a target conductance value corresponding to the target weight value to be stored in that cell.

[0058] During operation, the programming unit 29 is used to set the conductivity values ​​of the memory elements 257 by applying suitable voltage signals via the input or output lines of the IMC device 15. In some variants, the programming unit 29 can be connected to the memory elements via independent connectors. Additionally, the processing system 1 typically includes a readout circuit 26, which is connected to the output of the output lines 252. The programming unit 29 can thus be connected to the output of the readout circuit 26 to set the conductivity values ​​of the memory elements 257, for example, according to a single-device programming procedure. Furthermore, the system 1 can also include a processing unit 28, which is connected to the output of the crossbar array 25 (i.e., to the output of the readout circuit 26).This processing unit 28 can be arranged as a storage-adjacent processing unit, as in . Fig. 6. In this case, the programming unit 29 can advantageously be connected to the output of the memory-related processing unit 28 to enable control of the programming of the crossbar array structure 25. In variants, the processing unit 28 and the programming unit 29 are implemented as one and the same unit. The programming unit 29 can further include an input / output (I / O) controller and be configured to communicate with external devices or computers, as in Fig. 6 proposed.

[0059] Next, the invention can be embodied, according to a further aspect, as a method for operating one or more PCM devices 10, as disclosed herein. Such PCM devices can, in particular, form part of a data processing system 1, as described above. As in Fig. As shown in Figure 7, the procedure involves repeatedly applying (steps S30 and S50) current pulses through the heater 15 of each PCM device to bring each PCM device into a high- or low-resistance state. That is, a RESET current pulse is applied to the heater 15 of a given device 10 (S30) to grow an annular amorphous region in the corresponding PCM layer 14 from the heater 15. This brings the PCM layer 14 into a high-resistance state. A SET current pulse (S50) can then be applied to decrease the annular amorphous region in the PCM layer 14 and, accordingly, bring the PCM layer 14 into a low-resistance state.

[0060] In practice, steps S30 and S50 can typically be nested with other steps, such as by Fig. 7 is proposed. Such operations can, for example, aim to program memory elements of an IMC device 25 as described above. PCM devices 10 are first provided as part of the IMC device at step S10. Next, preliminary steps S20 are performed, e.g., to appropriately initialize or prepare the PCM devices. An iterative process then begins at step S25, selecting the next IMC cell 254. At step S30, a RESET signal is applied to all memory elements of the currently selected cell. Next, at step S40, a subset of memory elements of this cell is selected according to the target weight value to be stored in this cell. A SET signal is then applied to all selected memory elements at S50, before conductivity values ​​of the cell's memory elements are read at step S60. The process then proceeds to the next cell S25.This process is repeated until all cells are appropriately programmed.

[0061] One final aspect of the invention will now be discussed with reference to the Fig. 5A to Fig. 5I described. This aspect concerns a method for manufacturing a PCM device 10a, as previously described. Essentially, the manufacturing method aims to produce a PCM cell 12-16 and to embed the resulting PCM cell in an electrically insulating material 11c.

[0062] To produce the PCM cell 12-16, a stack of layers is first obtained using a suitable layer deposition process, see Fig. 5A. However, in embodiments, a PVD process is used that is compatible with the layer thicknesses considered here. The material layers in the stack depend on the chosen PCM cell design option and may also depend on the fabrication process used. In all cases, the stack includes a PCM layer 14, e.g., a 2–4 ​​nm thick layer of GST. Additionally, the layer stack can typically include additional layers, such as an electrically insulating material layer 11s (e.g., a dielectric layer containing SiO2 and serving as a substrate for growing or depositing additional layers) and another insulating layer 11a (e.g., an 8 nm thick dielectric layer of SiO2) on the PCM layer 14. Furthermore, the layer stack may also include a resistive projection liner 13a, e.g., a 2–5 nm thick layer of TiN, as in certain embodiments. The liner 13a coats (i.e.,touches) the PCM layer 14 on its upper surface in the example of the . Fig. 5A-5I, in contrast to the example of Fig. 1. The upper surface and the lower surface of the PCM layer 14 are connected by their side surface; the PCM layer can roughly have a cylindrical or rhombohedral shape, as mentioned previously.

[0063] The layer stack can then be subjected to various processing steps, for example to form a side wall spacer 16 using a mask 16m, as in Fig. 5B is shown. A via is then opened from the top surface of the stack perpendicular to the average plane of PCM layer 14. In the example of the Fig. 5B and Fig. 5C, the 15V through-hole connection is made by the spacer 16 ( Fig. 5B) and then etched through the lining 13a to partially penetrate the dielectric layer ( Fig. 5C). That is, in this example, the 15V via does not extend completely through the PCM layer. In some variations, the via can extend completely through the PCM layer and even protrude from it, as previously described with reference to Fig. 1 mentioned.

[0064] The 15V via is then filled with a heating material ( Fig. 5D), such as tungsten, TiN, or another metal nitride, to obtain a heating element 15. By design, the heating element 15 contacts the PCM layer 14 as well as all other layers of the stack. The mask 16m can then be removed. The structure transfer can result in a tapered or pyramidal shape of the layer stack, see Fig. 5E, which improves the adhesion of the outer electrode to be deposited next.

[0065] As in Fig. As can be seen in Figure 5F, the outer electrode layer 12a is deposited onto the layer stack to contact the side face of the layer stack (including the side face of the PCM layer 14) and the top face of the layer stack. A via is then opened at the top, see Figure 5F. Fig. 5G, which results in an outer electrode 12 with a circumferential edge on the spacer layer, before the layer stack 12, 13a, 11a, 14-16 is covered by an electrically insulating material 11c to embed the PCM cell, see Fig. 5H. Another via can then be opened at the top to deposit and structure another layer to form an upper electrode 17 and another element 18, e.g. an electrical conductor (as part of a selector) or a resistor, see Fig. 5I. Another via can then be etched and filled with the electrically insulating embedding material to create an electrical contact surface (in Fig. 5I not shown, see Fig. 1) to obtain that touches the outer electrode 12.

[0066] The in Fig. The manufacturing process shown in Figures 5A-5I incorporates a self-aligning deposition method, allowing the heater to self-align with the layer stack. In previous approaches, due to unavoidable superposition errors or misalignment between the structured heater and the phase-change material layer, the heater is not always located in the center of the PCM cell. For example, the heater and the PCM cell may not be perfectly concentric. This misalignment can lead to an uneven distribution of the programming current, resulting in degraded (and sometimes unpredictable) performance of the PCM device. Furthermore, this conventional integration process introduces cell-to-cell variability into the PCM device.

[0067] Therefore, a self-alignment process is advantageously used, in which a hard mask is formed 16m on the layer stack ( Fig. 5B). The hard mask 16m has an opening that exposes a section of the upper dielectric layer 11a (not shown); the inner spacer 16 is formed in this opening before the via 15v is opened, see Fig. 5B. The via 15V then extends downwards to the PCM layer 14 (see Fig. 5C), before the expanded via is filled with a heating element. By forming the heating element 15 in the expanded via, which is maintained by the inner spacer 16, the heating element 15 is located at a substantially identical distance to the outer edge or sidewall of the layer stack. The spacer 16 then serves as a protective layer.

[0068] The in Fig. The manufacturing process shown in Figures 5A-5I requires first etching the via 15v (to obtain the heater 15) and then depositing the outer electrode layer 12a. However, in variations, the outer electrode layer can be deposited before opening the via and filling it with a heating material. Once the layer stack has been structured, it can, for example, be covered with a layer forming an outer electrode before a via is opened from the top surface of a protective layer (e.g., HSQ) of the stack and the via is filled to form the heater (not shown). Prior to depositing the outer electrode, the sidewalls of the PCM layer can advantageously be cleaned using a reverse sputter etching process to ensure ohmic contact between the outer electrode and the PCM layer.Thus, as can be understood, the outer electrode layer can be deposited before or after receiving the heating element.

[0069] As illustrated above, various fabrication processes can be considered that make it possible to obtain flat structures. The PCM layer 14 can be fabricated to be ultrathin (e.g., less than 10 nm). Similarly, other layers 13, 11a, 16 can be fabricated to be thin or ultrathin. Furthermore, the external electrode configuration allows the thickness of the entire layer stack to be reduced, which in some embodiments is less than, for example, 70 nm (as in Fig.(assumed to be 1) or even smaller than 40 nm. In principle, however, the entire layer stack can reach 100 nm or more. The various layers can be deposited using a PVD process. Thus, there is no need to rely on complex deposition processes such as ALD or chemical vapor deposition (CVD) processes, at least not for forming the layer stack of the PCM cell. However, it should be noted that an ALD process can still be considered where very small PCM layer thicknesses are desired, e.g., less than 2 nm, as mentioned previously.

[0070] Furthermore, the proposed lateral design is compatible with ultrathin heaters 15. That is, ultrathin vias with radii down to 5 nm can be etched using a reactive ion etching (RIE) process or wet chemistry. The heater 15 is then obtained by filling the via, e.g., using ALD (for diameters below 10 nm) or CVD if the via diameters exceed 20 nm. It should be noted that slight RIE damage may occur to the PCM 14. However, this does not significantly affect the performance of the device, as the present inventors have verified.

[0071] Although the present invention has been described with reference to a limited number of embodiments, variants, and the accompanying drawings, those skilled in the art will understand that various modifications can be made and equivalents substituted without departing from the scope of the present invention. In particular, a feature (device-like or process-like) shown in a particular embodiment, variant, or drawing can be combined with or replaced by another feature in a different embodiment, variant, or drawing without departing from the scope of the present invention. Accordingly, various combinations of the features described with respect to one of the above embodiments or variants can be considered that remain within the scope of the accompanying claims.In addition, many minor modifications can be made to adapt a particular situation or material to the teachings of the present invention without deviating from its scope. Therefore, it is intended that the present invention is not limited to the specific embodiments disclosed, but rather encompasses all embodiments that fall within the scope of the appended claims. Furthermore, many other variants besides those explicitly mentioned above can be considered.

Claims

[1] Phase change memory (PCM) device, comprising: an electrically insulating material; and a PCM cell embedded in the electrically insulating material, wherein the PCM cell comprises: a phase change material layer with a top surface, a bottom surface and a side surface connecting the top surface and the bottom surface, an external electrode that touches the side surface of the phase-change material layer, and a heater that extends at least partially through the phase change material layer, perpendicular to the upper surface and the lower surface of the phase change material layer, and touches the phase change material layer. [2] PCM device according to claim 1, wherein the heating extends completely through the phase change material layer. [3] PCM device according to claim 1, wherein the heating extends only partially through the phase change material layer. [4] PCM device according to claim 1, wherein the outer electrode completely covers the side surface of the phase change material layer laterally. [5] PCM device according to claim 2, wherein the heating element extends perpendicularly to each of the upper and lower surfaces of the phase change material layer, and a longitudinal axis of the heating element passes through the center of the phase change material layer. [6] PCM device according to claim 1, wherein an average thickness of the phase change material layer is less than an average diameter of a section of the heater extending through the phase change material layer. [7] PCM device according to claim 6, wherein the average diameter of the section is between 5 nm and 100 nm. [8] PCM device according to claim 7, wherein the average diameter of the section is between 30 nm and 40 nm, while the average thickness of the phase change material layer is between 1 nm and 20 nm. [9] PCM device according to claim 1, wherein the average diameter of the upper surface and the lower surface is between 45 nm and 500 nm. [10] PCM device according to claim 1, wherein the PCM cell further comprises a resistive projection lining that touches the phase change material layer on one of the upper and lower surfaces; the outer electrode completely, laterally covers the side surface of the phase-change material layer and one side surface of the resistance projection lining; and The heating element extends through and touches each of the phase change material layers and the resistance projection lining. [11] PCM device according to claim 1, wherein the resistance projection lining comprises one of C, TiN and TaN. [12] PCM device according to claim 1, wherein The PCM cell further comprises an electrically insulating material layer and a protective layer on the electrically insulating material layer, wherein the electrically insulating material layer is arranged sandwich-like between the protective layer and the upper surface of the phase change material layer. the outer electrode completely covers the side surface of the phase change material layer as well as the side surfaces of the protective layer and the electrically insulating material layer laterally, and The heating element extends through and touches each of the protective layer, the electrically insulating material layer, and the phase-change material layer. [13] PCM device according to claim 12, wherein the outer electrode is structured to cover only a circumferential area of ​​the upper surface of the protective layer. [14] PCM device according to claim 12, wherein the protective layer comprises hydrogen silsesquioxane. [15] PCM device according to claim 1, wherein the phase change material layer comprises a germanium-antimony-tellurium alloy. [16] PCM device according to claim 1, wherein The PCM device further comprises a heating electrode that contacts the heater and a circuit component that contacts the heating electrode, wherein the circuit component is a resistor and a selector, and The heating electrode and the circuit component extend on one side of the phase change material layer and are embedded in the electrically insulating material. [17] PCM device according to claim 16, wherein the PCM device further comprises two electrical contact surfaces, each filling two vias extending through the electrically insulating material to contact the circuit component and the outer electrode respectively. [18] Data processing system, comprising: a tax system; and one or more PCM devices, each device of the one or more PCM devices being connected to the control system and comprising a PCM cell embedded in an electrically insulating material, the PCM cell comprising: a phase change material layer with a top surface, a bottom surface and a side surface connecting the top surface and the bottom surface; an external electrode that touches the side surface of the phase change material layer; and a heater that extends at least partially through the phase change material layer, transverse to the upper surface and the lower surface of the phase change material layer, and thereby touches the phase change material layer. [19] Data processing system according to claim 18, wherein The data processing system comprises an in-memory computing device having a crossbar array structure containing N input lines and M output lines connected at intersection points defining N × M cells, where N ≥ 2 and 2, where the intersection points contain respective memory systems, each containing a group of K memory elements, where K > 1, where each cell of the N × M cells contains K memory elements, where each of the K memory elements contains one of the PCM devices, and The control system includes a programming unit connected to the crossbar array structure, the programming unit being configured to program each cell according to a given target conductivity value corresponding to a target weight value to be stored in each cell. [20] Method for operating a PCM device, the method comprising: Providing a PCM device comprising a PCM cell embedded in an electrically insulating material, wherein the PCM cell comprises: a phase change material layer with a top surface, a bottom surface and a side surface connecting the top surface and the bottom surface; an external electrode that touches the side surface of the phase-change material layer; and a heater that extends at least partially through the phase change material layer, perpendicular to the upper and lower surfaces of the phase change material layer, in order to touch the phase change material layer, and repeated application, due to the heating, a RESET current pulse to form a ring-shaped amorphous region in the phase-change material layer from the heater and accordingly bring the phase-change material layer into a high-resistance state, and a SET current pulse to reduce the annular amorphous region in the phase change material layer and accordingly bring the phase change material layer into a low-resistance state. [21] Method for manufacturing a PCM device, the method comprising: Creating a PCM cell by: Obtaining a layer stack comprising a phase change material layer with a top surface and a bottom surface connected by a side surface of the phase change material layer; Deposition of an outer electrode layer on the stack so that the outer electrode layer touches the side surface of the phase change material layer and an upper surface of the stack, Opening a via from the top face of the stack, wherein the via extends at least partially through the phase-change material layer, transverse to the top face and the bottom face of the phase-change material layer; and Filling the via to obtain a heater that touches the phase-change material layer, and Covering the PCM cell with an electrically insulating material to embed the PCM cell in the electrically insulating material. [22] Method according to claim 21, wherein the obtained layer stack further comprises a resistive projection lining that contacts the phase change material layer on one of the upper and lower surfaces of the phase change material layer, and the via is opened to extend at least partially through each of the phase-change material layer and the resistance projection layer, so that the received heating touches each of the resistance projection lining and the phase-change material layer. [23] Method according to claim 21, wherein the obtained layer stack further comprises an electrically insulating material layer and a protective layer on the electrically insulating material layer, the latter being arranged sandwich-like between the protective layer and the upper surface of the phase change material layer. [24] Method according to claim 21, wherein The process further comprises, after filling the via and before covering the PCM cell, depositing a layer on the filled heater; and Structuring the deposited layer to obtain an electrode and a resistor and a selector. [25] Method according to claim 24, wherein The process further comprises, after covering the PCM cell, etching additional vias through the electrically insulating material; and Filling the remaining vias to obtain two electrical contact surfaces, each touching the outer electrode and the circuit component.

Images