Ultrathin phase change memory device with lateral electrode configuration

Abstract

A phase change memory (PCM) device (10) comprises an electrically insulating material (11) and PCM cells (12-16) embedded in the electrically insulating material (11). The PCM cells (12-16) comprise a layer of phase change material (or a PCM layer for short), such as a layer comprising a germanium-antimony-tellurium alloy. The PCM layer (14) has a top surface, a bottom surface, and side surfaces connecting the top surface and the bottom surface. The PCM cells (12-16) further comprise outer electrodes (12) that contact side surfaces of the PCM layers (14). That is to say, the outer electrode (12) covers the PCM layer (14) laterally. The PCM cells (12-16) further include a heater (15) extending at least partially through the PCM layer (14) transversely to the top and bottom surfaces of the PCM layer (14) to contact the PCM layer (14).

Description

Technical Field

[0001] This invention generally relates to phase-change memory (PCM) devices and to systems, methods of operating such PCM devices, and methods of manufacturing such PCM devices. In particular, this invention relates to a PCM device comprising a phase-change material layer having a "through-hole" structure, an external electrode, and a heater, wherein the phase-change material layer is laterally covered by the external electrode in the "through-hole" structure, thereby creating a ring-shaped phase-change material layer. Background Technology

[0002] Resistive storage devices are gaining increasing attention, particularly for multi-level data storage and in-memory computing hardware applications. Resistive storage devices specifically include PCM devices, which can switch inversely between several conductance states.

[0003] PCM devices, for example, can be used in in-memory computing hardware for inference purposes in analog calculations for artificial intelligence. Memory elements can include phase-change memristors with tunable conductivity, high device resistance, and high retention force to minimize energy consumption. This tuning can be achieved by forming different structural states using varying ratios 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-shaped" cell. This is because the phase change material is confined between a top electrode and an insulating layer, which is itself defined by a lower electrode. The latter contacts a heater that passes through the insulating layer. A standard mushroom-shaped cell consists of a large surface area electrode on top of the phase change material and a much smaller heater at the bottom. Heating the phase change material layer causes the amorphous phase to expand in the form of a cap on the insulating layer, making it look (along with the heater) like a mushroom. Other designs involve line cells with a lateral configuration. Additional PCM cell designs have been proposed where the cell has a "flat" configuration: the top electrode only contacts the peripheral region of the top surface of the thin phase change layer.

[0005] Typically, PCM devices require high-current reset operations to switch the device from a low-resistance (crystalline) state to a high-resistance (amorphous) state. Currently, this high current hinders the scaling down of the technology. Low reset current is needed for power efficiency alone. Even lower reset current is required to achieve smaller devices, increase PCM cell density, and integrate into back-end processes (BEOL). Summary of the Invention

[0006] According to a first aspect, the present invention is implemented as a phase-change memory (PCM) device. The device includes an electrically insulating material and a PCM cell embedded in the electrically insulating material. The PCM cell includes a phase-change material layer (or simply a PCM layer), 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 also includes an external electrode that contacts the side surface of the PCM layer. That is, the external electrode laterally covers the PCM layer. The PCM cell also includes a heater transversely bisects the top and bottom surfaces of the PCM layer, extending at least partially through the PCM layer to contact it.

[0007] By definition, the heater extends within the PCM cell, i.e., within the outer electrode. Similar to flat cells, this PCM cell design allows for a lower reset current than mushroom-shaped cells. However, the phase transition is triggered radially from within the PCM layer (e.g., from the center) because the heater extends at least partially through the PCM layer. Furthermore, the outer electrode laterally covers the PCM layer (i.e., it contacts the lateral sides of the PCM layer) rather than protruding above the periphery of the top surface of the PCM layer. This saves considerable space in the vertical direction and thus results in a shallower PCM device, which is beneficial for back-end process integration. The benefits of this approach are even more significant than those of mushroom-shaped cells, both in terms of size (and thus integration) and reset current.

[0008] The heater can extend only partially through the PCM layer to minimize the contact area. This design choice requires more precise control over the heater manufacturing process. In a variant, the heater extends completely through the PCM layer, which requires less control over the heater manufacturing process. Furthermore, the PCM layer can be manufactured thin enough to limit the contact interface with the heater.

[0009] In principle, the external electrode may only partially cover the side surface of the PCM layer laterally. However, in this embodiment, the external electrode completely covers the side surface of the PCM layer laterally. This facilitates electrical contact and improves performance because the current applied to the heater can be dissipated more evenly through the external electrode. Furthermore, this electrode configuration is easier to manufacture and reduces the risk of PCM sidewall oxidation.

[0010] In this embodiment, the heaters are substantially perpendicular to each extension of the top and bottom surfaces of the PCM layer. The longitudinal axis of the heaters may even extend substantially through the center of the PCM layer. This results in a symmetrical arrangement, which allows for better distribution of the phase-changing regions of the PCM layer when the heaters are energized.

[0011] In embodiments, the average thickness of the PCM layer is less than the average diameter of the portion of the heater extending through the PCM layer. In embodiments, the average diameter of said portion of the heater is between 5 nm and 100 nm, more preferably between 5 nm and 40 nm. For example, in embodiments, the average diameter of said portion of the heater 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 more preferably less than 10 nm. The average diameter of the top and bottom surfaces of the PCM layer is typically between 45 nm and 500 nm.

[0012] In an embodiment, the PCM cell further includes resistive bump pads to reduce resistance drift and conductance fluctuations. The resistive bump pads contact the PCM layer on the top or bottom surface of the PCM layer. An external electrode laterally completely covers the side surfaces of the PCM layer and the resistive bump pads. A heater extends through and contacts each of the PCM layer and the resistive bump pads. The resistive bump pads may, for example, comprise one of C, TiN, and TaN. More generally, the resistive bump pads may comprise metal nitrides, metal oxides, polycrystalline silicon, or silicon-doped metals.

[0013] In one embodiment, the PCM unit further includes an electrically insulating layer and a protective layer on top of the electrically insulating layer, the electrically insulating layer sandwiched between the protective layer and the top surface of the PCM layer. An external electrode laterally completely covers the side surfaces of the PCM layer, as well as the side surfaces of the protective layer and the electrically insulating layer. A heater extends through and contacts each of the protective layer, the electrically insulating layer, and the PCM layer. In one embodiment, the thickness of the entire layer stack (i.e., including the protective layer, the electrically insulating layer, the PCM layer, and the resistive pad, if present) will not exceed 70 nm.

[0014] In this embodiment, the external electrode is configured to cover only the peripheral region of the top surface of the protective layer. This creates a safety rim that ensures the external electrode laterally covers the entire side surface of the protective layer and all layers below it in the layer stack forming the PCM cell. The protective layer may, for example, comprise a hydrogen silsesquioxane.

[0015] In an embodiment, the PCM device further includes heater electrodes that contact the heater and circuit components that contact the heater electrodes. The circuit components may be, for example, resistors or selectors or elements thereof. The heater electrodes and the circuit components extend on one side of the PCM layer and are embedded in an electrically insulating material.

[0016] In an embodiment, the PCM device further includes two electrical contact pads that respectively fill two through-holes extending through an electrically insulating material to contact the circuit assembly and the external electrode.

[0017] According to another aspect, the present invention is implemented as a data processing system. The data processing system includes a control system and one or more PCM devices as described above. Specifically, the data processing system comprises PCM units embedded in an electrically insulating material, wherein each PCM unit includes a PCM layer, an external electrode contacting a side surface of the PCM layer, and a heater. The heater is transversely cleaved across the top and bottom surfaces of the PCM layer and extends at least partially through the PCM layer to contact it. Each PCM device is connected to the control system.

[0018] In some embodiments, the data processing system includes an in-memory computing (IMC) device with a cross-switch array structure. The cross-switch array structure includes N input lines and M output lines interconnected at crossover points to define N × M cells, where N ≥ 2 and M ≥ 2. Each crossover point includes a respective memory system, each memory system comprising a set of K memory elements, where K ≥ 1, i.e., each of the N × M cells includes K memory elements, where each of the K memory elements includes one of the PCM devices. The control system includes a programming unit connected to the cross-switch 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 present invention is implemented as a method of operating a PCM device. The method first includes providing a PCM device as described above, i.e., a device comprising PCM cells having a PCM layer embedded in an electrically insulating material, wherein a heater extends at least partially transversely through the PCM layer, and an external electrode laterally contacts a side surface of the PCM layer. The method primarily revolves around repeatedly applying RESET current pulses and SET current pulses through the heater. The RESET current pulse causes the growth of a ring-shaped amorphous region in the PCM layer from the heater, which brings the PCM layer into a high-resistance state. Conversely, the SET current pulse causes the ring-shaped amorphous region in the PCM layer to decrease, and thus brings the PCM layer into a low-resistance state. In typical applications, such as in the data processing system described above, several PCM devices are operated simultaneously.

[0020] According to the last aspect, the present invention is embodied as a method of manufacturing a PCM device as described above. The method substantially includes manufacturing a PCM cell by obtaining a layer stack. The stack includes a PCM layer having a top surface and a bottom surface connected by side surfaces. An external electrode layer is deposited on the stack such that the external electrode layer contacts the side surfaces of the PCM layer and the top surface of the stack. A via is opened from the top surface of the stack. The resulting via is transverse to the top and bottom surfaces of the PCM layer, extending at least partially through the PCM layer. The via is then filled to obtain a heater in contact with the PCM layer. The PCM cell is finally covered by an electrically insulating material to embed the PCM cell within the electrically insulating material. Note that the external electrode layer can be deposited after opening the via to obtain the heater.

[0021] In one embodiment, the resulting layer stack further includes resistive bump pads that contact the PCM layers on either the top or bottom surface of the PCM layers. In this case, the via is opened to extend at least partially through each of the PCM layers and the resistive bump layers. That is, a heater contacts each of the resistive bump pads and the PCM layers, obtained by subsequently filling the via.

[0022] In one embodiment, the resulting layer stack further includes an electrically insulating material layer and a protective layer on top of the electrically insulating material layer. The electrically insulating material is sandwiched between the protective layer and the top surface of the PCM layer.

[0023] In an embodiment, the method further includes depositing a layer on top of the filled heater after filling the via and before covering the PCM unit, and patterning the deposited layer to obtain electrodes and circuit components, which may be resistors or selectors or other elements thereof.

[0024] In an embodiment, the method further includes etching additional vias through an electrically insulating material and filling the additional vias after covering the PCM unit to obtain two electrical contact pads that contact the external electrode and the circuit assembly, respectively. Attached Figure Description

[0025] These and other objects, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is taken in conjunction with the accompanying drawings. These descriptions are intended to clearly assist those skilled in the art in understanding the invention in conjunction with the detailed description. In the drawings:

[0026] Figure 1 This is a 2D cross-sectional view of a phase-change memory (PCM) device according to an embodiment. The plane on which the cross-sectional view is taken includes the longitudinal axis of the heater;

[0027] Figure 2 yes Figure 1 Another cross-sectional view of the device, taken from the mid-plane of the phase change material layer. Figure 1and Figure 2 In the example, as in the embodiment, the phase change material layer is substantially cylindrical, and the layer stack is generally rotationally symmetric.

[0028] Figure 3 and 4 It shows Figure 1 and 2 A modified cross-sectional view, wherein, as in the embodiment, the layer stack has a shape from a rectangle ( Figure 3 ) or square ( Figure 4 The phase change material layer extends in a quadrilateral or pyramidal shape;

[0029] Figure 5A , 5B 5C, 5D, 5E, 5F, 5G, 5H, and 5I are illustrations of the relationship between the embodiments and... Figure 1 A sequence of cross-sectional views of advanced manufacturing steps for similar PCM devices (in a plane containing the vertical axis of the heater, such as...) Figure 1 In the middle, except that the resistive raised pad is now above the phase change material layer and the heater only extends partially through the phase change material layer;

[0030] Figure 6 This is a diagram of a data processing system including an in-memory computing unit according to an embodiment, wherein the memory elements of the in-memory computing unit include, for example, memory elements such as memory elements of an in-memory computing unit. Figure 1 , 2 The PCM device described in 5I; and

[0031] Figure 7 This is a flowchart illustrating the advanced steps of a method for operating a PCM device according to an embodiment.

[0032] The accompanying drawings illustrate simplified representations of the devices or components thereof as described in the embodiments. Technical features depicted in the drawings are not necessarily drawn to scale. Unless otherwise indicated, similar or functionally similar elements in the figures are assigned the same reference numerals.

[0033] The apparatus, system, and method embodying the invention will now be described by way of non-limiting example. Detailed Implementation

[0034] Currently, the main reference is... Figures 1 to 4 The first aspect of the invention is described in detail below. This aspect relates to a phase-change memory (PCM) device 10, which includes an electrically insulating material 11 and PCM cells 12-16, wherein the PCM cells are embedded in the electrically insulating material 11.

[0035] The PCM unit includes an external electrode 12, a phase change material layer 14, and a heater 15. For convenience, the abbreviation "PCM layer" will be used below to refer to the phase change material layer 14. The PCM layer 14 has a top surface (in... Figure 1 The top surface of layer 14, the bottom surface, and the side surface connecting the top and bottom surfaces. PCM layer 14 may, for example, have a cylindrical shape, i.e., be roughly formed as a straight cylinder, such as... Figure 1 and 2 This is the assumption made in the text. In this case, the top surface and the bottom surface correspond to the top base and bottom base of the cylinder, respectively, and the side surface is a curved surface connecting the top base and bottom base of the cylinder.

[0036] Heater 15 is transversely oriented across PCM layer 14, specifically across the top and bottom surfaces of PCM layer 14, and extends at least partially through PCM layer 14. In other words, the heater has a "through-hole" configuration. Heater 15 is a heating element, typically connected by electrodes 17, for example in… Figure 1 The top of the heater 15. The heater mechanically contacts the PCM layer 14, which ensures a tight thermal connection between the heater 15 and the PCM layer 14. The heater can be considered as an inner electrode, which in this context extends at least partially through the PCM layer 14 and thus contacts the inner edge surface of the PCM ring 14.

[0037] Conversely, the outer electrode 12 is an edge electrode that laterally contacts the outer surface (i.e., the outer edge surface) of the PCM layer 14. Preferably, the outer electrode 12 laterally completely covers the outer surface of the PCM layer 14, such as... Figure 1-4 As assumed in the text. The external electrode 12 is used to dissipate the current applied through the heater 15 during operation.

[0038] The proposed design produces a transverse PCM structure, which allows for shallower PCM units. That is, this structure induces a phase transition triggered transversely by heater 15; specifically, the phase region of the phase transition (from crystalline to amorphous) grows radially from heater 15 and typically forms a ring (or annular ring). This is in Figure 1 and 2 As shown in the image; Figure 2 The plane taken from the cross-sectional view is by Figure 1 The dashed line CSP in the diagram represents this plane. This plane corresponds to the middle plane of PCM layer 14. (See image.) Figure 1 and 2 As shown, after the heater 15 is energized (i.e., after a RESET current pulse is applied), the amorphous phase region AP grows radially from the heater, which leads to a decrease in the crystalline phase region CP. Therefore, the resulting amorphous phase structure can be called a "ring" structure.

[0039] Similar to flat cells, this PCM cell design enables a lower reset current than mushroom-shaped cells. This is because the phase change is triggered laterally from the internal region of the PCM layer (e.g., from the center). As a result, the annular portion of the phase change in the material is more uniform during operation. The proposed design is essentially similar to the design of a so-called flat cell, and incidentally, produces a similar SET / RESET resistance. However, there are two main differences compared to flat cells. First, in this case, the outer electrode 12 laterally covers the PCM layer (i.e., it contacts the lateral sides of the PCM layer) rather than protruding above the periphery of the top surface of the PCM layer. This saves considerable space in the vertical direction and thus results in a shallower PCM device, which is beneficial for back-to-office (BEOL) integration. Second, the phase change is triggered radially from within the PCM layer (e.g., from the center) because the heater extends at least partially through the PCM layer.

[0040] The benefits of this method are even more significant compared to mushroom-shaped cells, both in terms of size (and thus integration) and RESET current. One reason for the lower RESET current is that the external electrode 12 and heater 15 contact the PCM layer at its lateral edge. This effectively reduces the contact (or interface) area between the heater and the PCM layer to [missing information]. (for heater 15) and (For external electrode 12), and not in the mushroom-shaped unit (Lower heater) and (Top electrode). Quantity and Corresponding to the average inner radius of the PCM layer 14 (in this case, the heater 15 extends through the inner radius) and the average radius, and This corresponds to the average radius of the interface region between the lower heater and the top electrode in the mushroom-shaped unit. Incidentally, in this context, as in the embodiment, if the heater does not extend completely through the PCM layer 14, then the contact area between the heater 15 and the PCM layer... It can be further reduced.

[0041] Furthermore, the PCM unit of this invention is easier to manufacture than the mushroom-shaped unit. In particular, the PCM layer can be refined by chemical mechanical polishing / planarization (CMP). The heater is also fairly simple to manufacture and can benefit from self-aligned processes, as discussed later with reference to another aspect of the invention.

[0042] All of these will now be described in detail with reference to specific embodiments of the invention. First, the heater 15 may extend completely through the PCM layer 14, as... Figure 1As explained in the text, that is, heater 15 is from one side (e.g., from...) Figure 1 The top side of the top surface of the PCM layer 14 penetrates the PCM layer 14 and reaches the other side (the bottom surface of layer 14). It can even protrude slightly from the bottom side, that is, through the PCM layer, as... Figure 1 As assumed in the design. In this case, the PCM layer has a ring-shaped or annular shape. This design requires less control over etch stopping because the heater vias can be completely etched through the PCM layer 14.

[0043] In the variant forms, see, for example, [see...] Figure 5I Heater 15a extends only partially through PCM layer 14. This design option requires more precise control over etch termination. However, it also makes it possible to further minimize the electrical contact area between heater 15 and PCM layer 14, thereby allowing PCM layer 14 to be manufactured slightly thicker. That is, a more precise manufacturing process for the heater allows for a relaxation of the constraints on PCM layer thickness. In other words, even if heater 15 completely penetrates PCM layer 14 (as... Figure 1 (In the middle), the latter can still be manufactured thin enough to mitigate the electrical interface area.

[0044] In principle, the outer electrode 12 may only partially cover the outer surface of the PCM layer 14 laterally. However, in this embodiment, the outer electrode 12 completely covers the side surface of the PCM layer 14 laterally, such as... Figure 1-3 This is assumed in the text. This facilitates electrical contact and improves performance because the current applied to the heater 15 can be dissipated more evenly through the outer electrode 12. In addition, this electrode configuration reduces the risk of PCM sidewall oxidation and is easier to manufacture due to the more symmetrical arrangement it produces.

[0045] While the longitudinal axis of heater 15 typically extends in a direction tangential to PCM layer 14, in embodiments, this direction is perpendicular (or substantially perpendicular) to the PCM layer. Specifically, heater 15 can be made substantially symmetrical about its longitudinal axis (having rotational symmetry), and this axis can ideally pass through the center of the PCM layer. Thus, in embodiments, heater 15 is substantially perpendicular to each extension of the top and bottom surfaces of PCM layer 14, and the longitudinal axis of heater 15 substantially passes through the center of PCM layer 14; for example, PCM layer 14 can have a substantially cylindrical shape, and the longitudinal axis of heater 15 can substantially coincide with the cylindrical axis of the PCM layer. In this example, PCM layer 14 can be considered a shallow right cylinder. In variations, PCM layers 34, 44 can have a square or rectangular shape (and so can the outer electrodes 32, 42), for example, as Figure 3 and 4 As explained in the text.

[0046] Having the heater pass through the center of the PCM layer 14 results in a more symmetrical arrangement, which allows for better distribution of the regions of the PCM layer 14 that change phase when the heater 15 is energized. This fairly symmetrical arrangement, as described above, can be significantly achieved using a self-aligned manufacturing process for the heater, as discussed later with respect to another aspect of the invention.

[0047] When using other, more conventional manufacturing processes, heater 15 can be slightly off-center. For example, for a disk size with an outer diameter of 200 nm, heater 15 is expected to have a misalignment of 10 to 20 nm. This can affect variability between devices, such as the resistance and threshold voltage in the fully reset state. For shorter legs, the fully reset state will effectively provide parallel paths for current flow. This means that even when a larger amorphous volume is formed in a longer leg, the resistance will be capped and will not change. However, this may not be a systemic problem. In fact, it is not necessarily necessary to utilize the fully reset state, as they may be very resistive and thus produce a very weak current. Furthermore, when the device is raised with pad 13, as in the embodiment, the achievable resistance will be capped anyway. In addition, because threshold voltages are linearly proportional to the amorphous volume size, they will decrease in smaller legs. For integrity, the electric field (and current distribution) can be increased toward the side with smaller spacing due to misalignment, but the heat flux should remain relatively stable, as heater 15 is the primary heat dissipation device.

[0048] In this embodiment, the average thickness of the PCM layer 14 is less than the average diameter of the portion of the heater 15 extending through the PCM layer 14. Reducing both the thickness of the PCM layer and the size of the heater results in a decrease in the device reset current. The heater may be slightly tapered, such as... Figure 1 As shown in the figure. The average diameter of the heater portion penetrating the PCM layer is between 5 nm and 100 nm in this embodiment. For example, this average diameter can be between 30 nm and 40 nm, while the average thickness of the PCM layer 14 is between 1 nm and 20 nm. Note that very thin (e.g., 1 nm) PCM layers can be obtained using atomic layer deposition (ALD), while in some embodiments, layers of 2 nm or thicker can be obtained by physical vapor deposition (PVD). In contrast, the average diameter of the PCM layer (and the average diameter of the top and bottom surfaces of the PCM layer) will typically be between 45 nm and 400 nm, or even 500 nm. For example, Figure 1The assumed average PCM disk diameter is approximately equal to, but slightly less 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 a plane, for example, on the top or bottom surface of the PCM layer 14, while the thickness is measured perpendicular to the middle plane of the PCM layer, i.e., along the stacking direction.

[0049] In embodiments, PCM cells 12-16 further include resistive raised pads 13 (also referred to as “pads” in this document) to reduce resistance drift and conductance fluctuations. In principle, the pads 13 may contact the PCM layer 14 on either their top or bottom surface. For example, in Figure 1 In the middle, the padding extends below the PCM layer 14, while... Figure 5A In the layer stack shown in –5I, the pad extends above the PCM layer 14. The thickness of the pad 13 is typically between 1 and 20 nm; in the embodiment, it is slightly thicker than the PCM layer 14, although the proportion is not apparent in the figures. Note that with the pad 13 present, the external electrode 12 laterally covers the side surfaces of both the PCM layer 14 and the pad 13, as the external electrode laterally covers the entire layer stack. Furthermore, the heater 15 extends through (and thus contacts) each of the PCM layer 14 and the pad 13; more precisely, the heater 15 contacts each of the PCM layer 14 and the pad 13 along through-holes opened in the thickness of the PCM layer 14 and the pad 13.

[0050] The pad 13 conforms to certain design rules to enable the protrusion mechanism to function. These rules utilize the highly nonlinear, field-dependent electrical transport characteristics of the phase change material. At minimum values, the resistance of the protrusion assembly must satisfy the following conditions: (i) the resistance of the amorphous portion (in the ON state) of the PCM layer 14 must be (significantly) higher than the resistance of the protrusion assembly of the pad 13; (ii) the resistance of the crystalline portion of the PCM layer 14 must be significantly lower than the resistance of the pad 13; and (iii) the resistance of the amorphous portion must be significantly lower than the resistance of the pad 13.

[0051] like Figure 1 As further shown, PCM cells 12-16 typically include an electrically insulating layer 11a and a protective layer 16 on top of the electrically insulating layer 11a. Layer 11a is thus sandwiched between the protective layer 16 and the top surface of the PCM layer 14. Again, the outer electrode 12 laterally completely covers the entire side surface of the stack, i.e., the pad 13 (if present), the PCM layer 14, the electrically insulating layer 11a, and the protective layer 16.

[0052] Interestingly, the outer electrode 12 can be configured to cover only the peripheral region of the top surface of the protective layer 16, such as... Figure 1 and 5A–5I is shown. That is, the outer electrode 12 extends a safety edge on top of the protective layer 16. This structural feature is generated by the patterning of the outer electrode 12, see Figure 5G This provides a channel for electrode 17 to contact heater 15. A safety margin is maintained to ensure that outer electrode 12 laterally covers the entire side surface of protective layer 16. For integrity, heater 15 extends through (and thus contacts) each layer 13, 14, 11a, 16 of the PCM cell stack.

[0053] As described above, the PCM device 10 may further include a heater electrode 17 that contacts the heater 15 and a circuit assembly 18 that contacts the heater electrode 17. The circuit assembly 18 may be, for example, a resistor (as assumed in the figures) or a selector. The assembly 18 may actually be just a part of a selector or a resistor. The heater electrode 17 and the circuit assembly 18 extend on one side of the PCM layer 14 (i.e., on top of the PCM layer 14 in the figures) and are embedded in the electrically insulating material 11.

[0054] For completeness, the PCM device 10 may further include two electrical contact pads 19, which respectively contact the circuit assembly 18 and the external electrode 12. Figure 1 As shown, two electrical contact pads 19 respectively fill two through-holes, which extend downwards through the electrical insulating material 11 to the corresponding components, namely the external electrode 12 and the assembly 18. Figure 1 As further shown, the external electrode 12 may include, for example, a neck flange, i.e., a protruding lip, which may contact the right-hand side contact pad 19.

[0055] In an embodiment, the PCM layer 14 may comprise, or even consist of, a doped germanium-antimony-tellurium alloy (denoted as GeSbTe, or simply GST). In a variation, the PCM layer 14 comprises or is composed of an alloy comprising Ge, Sb, and Te, and one or more additional elements, such as Se. Other dopants may be used, including SiO2, O2, Ti, and Cu. The PCM layer may, for example, comprise Ge2Sb2Te5 or Ge2Sb2Se4Te. Other possible suitable PCM materials may be, for example, VOx, NbOx, GeTe, GeSb, GaSb, Ag1nSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe, and AlSb.

[0056] Suitable materials for the resistive bump pad 13 include carbon (C), metal nitrides such as titanium nitride (TiN) and tantalum nitride (TaN). Other materials, such as metal oxides, polycrystalline silicon, or silicon-doped metals, may also be considered. The electrically insulating layer 11a is typically made of the same material as the insulating substrate 11, although this is not a strict requirement. In principle, this electrically insulating material 11, 11a can be either an electrical insulator or a dielectric material. Suitable materials include SiO2 and Si3N4, although other oxides or nitrides, such as Al2O3 or HfO, may also be considered. x The protective layer 16 typically comprises hydrogen silsesquioxane (HSQ). HSQ films are typically available in thicknesses between 0.01 and 2 μm. In variations, the protective layer may be a spacer material, as discussed in detail later.

[0057] Figure 1 and 5I Two embodiments of PCM devices 10, 10a are shown. In each case, devices 10, 10a include PCM cells embedded in dielectric materials 11, 11s, 11c. The PCM cell includes a layer stack comprising a PCM layer 14, resistive bump pads 13, 13a coated on the top or bottom surface of the PCM layer 14, a dielectric layer 11a on top of the PCM layer 14, and a protective layer 16 on top of the dielectric layer 11a. An external electrode 12 laterally covers the layer stack side surface of the PCM layer (14) and forms a peripheral edge on top of the protective layer 16. A heater 15 extends through the protective layer 16, the dielectric layer 11a, the resistive bump pads 13, 13a, and at least partially through the PCM layer 14. The heater extends perpendicular to the stacked layers, i.e., along the stacking direction. When the resistive bump pad 13 is below the PCM layer 14 (e.g. Figure 1 The heater 15 extends completely through the PCM layer 14, while when the pad 13a is above the PCM layer, it can only extend partially through the PCM layer 14. Figure 5I Contact pads are formed through embedded materials 11, 11c to contact the external electrode 12 and the heater 15.

[0058] refer to Figure 6 Another aspect of the present invention relates to a data processing system 1 (or simply "system") comprising one or more PCM devices 10 as described above. System 1 typically includes a plurality of PCM devices 10, as assumed below. System 1 also includes control systems 26-29 to which the PCM devices 10 are connected. Data processing system 1 may be, in particular, an information processing system or a memory system.

[0059] In some embodiments, the data processing system 1 includes in-memory computing (IMC) devices 25-29, which can be particularly used to perform matrix operations, such as matrix-vector multiplication (MVM). Such operations are particularly useful for performing inference based on artificial neural networks (ANNs) and decision trees. In this case, MVM operations present several challenges due to their reproducibility and computational and memory requirements. Traditional computer architectures are based on the von Neumann computing concept, in which processing power and data storage are divided into separate physical units. This architectural concept suffers from congestion and high power consumption because data must be continuously transferred from memory units to control and arithmetic units through physically constrained and expensive interfaces.

[0060] One possibility for accelerating MVM is the use of dedicated hardware acceleration devices, such as IMC devices with a cross-switch array structure. Such an architecture allows for simple and efficient mapping of MVM: vectors are encoded as signals that are applied to the input lines of the cross-switch array to perform MVM as a multiply-accumulate (MAC) operation. Weights can be updated as needed to perform continuous MVM. These in-memory computing devices break down the "memory wall" by fusing arithmetic and memory units into a single in-memory computing (IMC) unit. Moreover, by leveraging the analog memory capabilities of IMC devices and Kirchhoff's circuit laws, the use of analog memory devices within the IMC unit allows for efficient execution of MVM operations. Another advantage of the cross-switch array structure is its support for transpose matrix operations, which can be used to train ANNs. More generally, key computational primitives enabled by such devices can also be used in other applications, such as solvers for linear equation systems.

[0061] like Figure 6 As shown, the IMC device has a cross-switch array structure 25, that is, the IMC device 15 includes N input lines 251 and M output lines 252, which are interconnected at crossover points (i.e., nodes). The crossover points correspondingly define N × M units 254, also called unit cells. The input and output lines are interconnected via a memory system 256. In principle, at least two input lines and two output lines are required to define the array (i.e., N ≥ 2 and M ≥ 2). However, in practice, the number of input lines 251 and output lines 252 will typically be on the order of hundreds to thousands of lines. For example, arrays of 256 × 256, 512 × 512, or 1024 × 1024 can be considered, although N does not necessarily equal M. The IMC device 15 can, for example, be used as a neural processing device, designed to implement M neurons at a time. The number of neurons can therefore be equal to, for example, 256, 512, or 1024. Vectors are encoded in signals that are applied to the input lines of the cross-switch array via input units 27.

[0062] like Figure 6 As schematically shown, the intersections comprise corresponding memory systems 256. Each memory system 256 includes a set of K memory elements 257, where K ≥ 1, i.e., each cell 254 includes K memory elements. In a variant, each cell includes K ≥ 2 memory elements, which may be arranged in parallel within each set. In particular, each cell may contain two sets, each with K memory elements 257. Various connection schemes are conceivable. In embodiments, each input (and corresponding output) line is typically further divided into K or 2K conductors to adequately connect to (and from) the corresponding memory element of each cell. Thus, each input (or output) line typically includes several parallel electrical conductors.

[0063] Each of the K memory elements includes a PCM device 10 as described herein. Furthermore, the control system 26–29 includes a programming unit 29, see [link to relevant documentation]. Figure 6 It is connected to the cross switch array structure 25. The programming unit 29 is configured to program each cell 254 according to a given target conductance value, which corresponds to the target weight value to be stored in each cell. Programming a cell means storing the target weight value in that cell. The target weight value can be converted into a conductance value. Therefore, the purpose is to program the memory element of the cell to produce a total conductance value that matches the target conductance value, which corresponds to the target weight value to be stored in that cell.

[0064] In operation, programming unit 29 is used to adjust the conductance of memory element 257 by applying an appropriate voltage signal to the input or output line of IMC device 15. In a variant, programming unit 29 can be connected to the memory element via a separate connector. Additionally, processing system 1 typically includes readout circuitry 26 connected to the output of output line 252. Programming unit 29 can therefore be connected to readout circuitry 26 in its output to adjust the conductance of memory element 257, for example, according to a single-device programming method. Furthermore, system 1 may also include processing unit 28 connected to the output of crossbar switch array 25 (i.e., in the output of readout circuitry 26). This processing unit 28 can be arranged near the memory processing unit, such as... Figure 6 As assumed in the text. In this case, programming unit 29 can advantageously be connected to the output of near-memory processing unit 28 to allow closed-loop programming of crossbar switch array structure 25. In a variant, processing unit 28 and programming unit 29 are implemented as a single unit. Programming unit 29 may also include input / output (I / O) controller and is configured to communicate with external devices or computers, such as... Figure 6 As shown.

[0065] Next, according to another aspect, the present invention can be implemented as a method of operating one or more PCM devices 10 as disclosed herein. Such PCM devices can particularly be incorporated as part of the data processing system 1 as described above. Figure 7 As seen, the method revolves around 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. Specifically, a RESET current pulse S30 is applied to the heater 15 of a given device 10 to grow a ring-shaped amorphous region from the heater 15 in the corresponding PCM layer 14, which brings the PCM layer 14 into a high resistance state. A SET current pulse S50 can then be applied to reduce the ring-shaped amorphous region in the PCM layer 14 and thus bring the PCM layer 14 into a low resistance state.

[0066] In practice, steps S30 and S50 can often be interleaved with other steps, such as... Figure 7 As shown, such an operation can, for example, be intended to program the memory elements of the IMC device 25 as described above. First, in step S10, the PCM device 10 is provided as part of the IMC device. Next, in S20, preparatory steps are taken, for example, to properly initialize or prepare the PCM device. Subsequently, in step S25, an iterative process begins, thereby selecting the next IMC cell 254. In step S30, a RESET signal is applied to all memory elements of the currently selected cell. Next, in step S40, a subset of the memory cells of the cell is selected according to the target weight value to be stored in that cell. Then, in S50, a SET signal is applied to all selected memory elements, and in step S60, the conductance value of the memory elements of that cell is read. The process then continues to the next cell S25. This process is repeated until all cells are properly programmed.

[0067] Now for reference Figure 5A –5I describes the last aspect of the invention. This aspect relates to a method of manufacturing the PCM device 10a as described above. Essentially, the purpose of this manufacturing method is to manufacture PCM cells 12-16 and embed the obtained PCM cells in an electrically insulating material 11c.

[0068] To fabricate PCM cells 12–16, first obtain the layer stack using any suitable layer deposition process, see [link to relevant documentation]. Figure 5AHowever, in the embodiments, a PVD process is used, which is compatible with the layer thicknesses as anticipated herein. The material layers in the stack depend on the selected PCM cell design options and may also depend on the fabrication process used. In all cases, the stack comprises a PCM layer 14, for example, a 2–4 ​​nm thick GST layer. Additionally, the layer stack may typically include additional layers, such as electrically insulating material layers 11s (e.g., a dielectric layer comprising SiO2, which acts as a substrate for growing or depositing the additional layers) and another insulating layer 11a (e.g., an 8 nm thick dielectric layer of SiO2) on top of the PCM layer 14. Furthermore, the layer stack may further include resistive bump pads 13a, such as a 2–5 nm thick TiN layer, as in some embodiments. Figure 1 In contrast, in Figure 5A In the example of –5I, the pad 13A is coated (i.e., in contact) with the top surface of the PCM layer 14. The top and bottom surfaces of the PCM layer 14 are connected by its side surfaces; the PCM layer may have a generally cylindrical or rhomboid shape, as previously described.

[0069] Then, as Figure 5B As shown, various processing steps can be performed on the layer stack using a mask 16m, such as to form sidewall spacers 16. Subsequently, through-holes are opened by transecting the average plane of the PCM layer 14 from the top surface of the stack. Figure 5B and 5C In the example, through spacer 16 ( Figure 5B And then etch through the via 15v through the pad 13a to partially penetrate into the dielectric layer. Figure 5C That is, in this example, the via 15v does not extend completely through the PCM layer. In variations, as previously referenced... Figure 1 The vias can extend completely through the PCM layer and even protrude from the PCM layer.

[0070] The vias were then filled with a heating material (e.g., tungsten, TiN, or another metal nitride) at a temperature of 15°C. Figure 5D This is done to obtain heater 15. By design, heater 15 contacts PCM layer 14 and all other layers stacked. Mask 16M can then be removed. Pattern transfer can result in a conical or pyramidal shape for the layer stack, see [link to relevant documentation]. Figure 5E This will facilitate the adhesion of the external electrode to be deposited next.

[0071] like Figure 5F As seen, the outer electrode layer 12a is deposited on the layer stack to contact the side surfaces of the layer stack (including the side surfaces of the PCM layer 14) and the top surface of the layer stack. A via is then opened at the top, as shown. Figure 5GAn external electrode 12 with a peripheral edge is formed on top of the spacer layer, and then stacked with an electrically insulating material 11c covering layer 12, 13a, 11a, 14-16 to embed the PCM cell, see Figure 5H Then, another via can be opened on top to deposit and pattern another layer to form the top electrode 17 and another element 18, such as an electrical conductor (as part of a selector) or a resistor, see [link to relevant documentation]. Figure 5I Then, another via can be etched through the electrically insulating embedded material and filled to obtain the electrical contact pads. Figure 5I Not shown in the image, see [link / reference]. Figure 1 The electrical contact pad contacts the external electrode 12.

[0072] Figure 5A The fabrication process shown in –5I involves a self-aligned deposition method, where the heater and layer stack are self-aligned. In existing methods, the heater is not always centered on the PCM cell due to unavoidable overlap errors or misalignment between the patterned heater and the phase change material layer. For example, the heater and PCM cell may not be perfectly concentric. This misalignment can now significantly lead to uneven distribution of programming current, which can cause performance degradation (and sometimes unpredictability) in the PCM device. Furthermore, this conventional integration process introduces cell-to-cell variability in the PCM device.

[0073] Therefore, a self-aligned process is advantageously used, in which a hard mask 16m is formed on top of the layer stack. Figure 5B The hard mask 16m has an opening (not shown) that exposes a portion of the top dielectric layer 11a; see also Figure 5B An inner spacer 16 is formed in this opening, and then a through-hole 15v is opened. The through-hole 15v is then extended downwards to the PCM layer 14 (see...). Figure 5C The extended through-holes are then filled with heating elements. Heating elements 15 are formed in the extended through-holes obtained from the inner spacer 16, at substantially the same distance from the outer edge or sidewall of the layer stack. The spacer 16 ultimately serves as a protective layer.

[0074] Figure 5AThe manufacturing process shown in –5I first requires etching vias 15v (to obtain heater 15), followed by depositing an external electrode layer 12a. However, in a variation, the external electrode layer can be deposited before opening the vias and filling them with a heating material. For example, once the layer stack has been patterned, it can be covered with the layer forming the external electrode before opening and filling the vias from the top surface of the stacked protective layer (e.g., HSQ) to form the heater (not shown). Before depositing the external electrode, a backsputtering etching process can advantageously be used to clean the sidewalls of the PCM layer to ensure ohmic contact between the external electrode and the PCM layer. Therefore, it can be understood that the external electrode layer can be deposited before or after obtaining the heater.

[0075] As described above, various manufacturing processes can be considered, allowing for the attainment of shallow structures. The PCM layer 14 can be fabricated to be ultrathin (e.g., less than 10 nm). Similarly, the other layers 13, 11a, and 16 can be fabricated to be thin or ultrathin. Furthermore, the external electrode configuration allows for a reduction in the overall thickness of the layer stack, which in some embodiments can be less than, for example, 70 nm (e.g., ...). Figure 1 The thickness is assumed in the text, or even less than 40 nm. However, in principle, the entire layer stack can reach 100 nm or greater. Individual layers can be deposited using a PVD process. Therefore, it is not necessary to rely on complex deposition processes such as ALD or chemical vapor deposition (CVD) processes, or at least not on a layer stack to form PCM units. However, note that, as mentioned earlier, the ALD process can still be considered when very small PCM layer thicknesses (e.g., less than 2 nm) are required.

[0076] Furthermore, the proposed lateral design is compatible with the ultrathin heater 15, meaning that ultrathin vias with radii as low as 5 nm can be etched using reactive ion etching (RIE) or wet chemical etching. Then, if the via diameter exceeds 20 nm, the heater 15 is obtained by filling the vias, for example, using ALD (for diameters less than 10 nm) or CVD. Note that slight RIE damage may occur to the PCM 14; however, as demonstrated by the inventors, this substantially does not affect the device performance.

[0077] Although the invention has been described with reference to a limited number of embodiments, variations, and drawings, those skilled in the art will understand that various changes can be made and equivalents can be substituted without departing from the scope of the invention. In particular, features (of the apparatus or method) described in a given embodiment or variation or shown in the drawings may be combined with or substituted for another feature in another embodiment, variation, or drawing without departing from the scope of the invention. Therefore, various combinations of features described with respect to any of the foregoing embodiments or variations are contemplated, which remain within the scope of the appended claims. Furthermore, many minor modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from the scope of the invention. Therefore, the invention is not limited to the specific embodiments disclosed, but rather the invention will include all embodiments falling within the scope of the appended claims. In addition, many other variations besides those explicitly mentioned above are contemplated.

Claims

1. A phase-change memory (PCM) device, comprising: Electrically insulating materials; as well as PCM units embedded in the electrical insulating material, the PCM units comprising: A phase change material layer having a top surface, a bottom surface, and a side surface connecting the top surface and the bottom surface. The external electrode, which contacts the side surface of the phase change material layer, and A heater that cuts across the top and bottom surfaces of the phase change material layer and extends at least partially through the phase change material layer, thereby contacting the phase change material layer.

2. The PCM device according to claim 1, wherein The heater extends completely through the phase change material layer.

3. The PCM device according to claim 1, wherein The heater extends only partially through the phase change material layer.

4. The PCM device according to claim 1, wherein The external electrode completely covers the side surface of the phase change material layer laterally.

5. The PCM device according to claim 2, wherein... The heater extends perpendicularly to each of the top and bottom surfaces of the phase change material layer, and The longitudinal axis of the heater passes through the center of the phase change material layer.

6. The PCM device according to claim 1, wherein The average thickness of the phase change material layer is less than the average diameter of the portion of the heater that extends through the phase change material layer.

7. The PCM device of claim 6, wherein the average diameter of said portion is between 5 nm and 100 nm.

8. The PCM device according to claim 7, wherein The average diameter of the portion is between 30 nm and 40 nm, and the average thickness of the phase change material layer is between 1 nm and 20 nm.

9. The PCM device according to claim 1, wherein The average diameter of the top surface and the bottom surface is between 45 nm and 500 nm.

10. The PCM device according to claim 1, wherein The PCM unit further includes a resistive raised pad that contacts the phase change material layer on one of the top surface and the bottom surface; The outer electrode laterally completely covers the side surface of the phase change material layer and the side surface of the resistive protrusion pad; as well as The heater extends through and thus contacts each of the phase change material layer and the resistive raised pad.

11. The PCM device of claim 1, wherein the resistive bump pad comprises one of C, TiN, and TaN.

12. The PCM device according to claim 1, wherein The PCM unit further includes an electrically insulating material layer and a protective layer on top of the electrically insulating material layer, the electrically insulating material layer being sandwiched between the protective layer and the top surface of the phase change material layer. The external electrode laterally completely covers the side surface of the phase change material layer, as well as the side surfaces of the protective layer and the electrical insulation material layer. The heater extends through and thereby contacts each of the protective layer, the electrical insulation layer, and the phase change material layer.

13. The PCM device according to claim 12, wherein The outer electrode is configured to cover only the outer region of the top surface of the protective layer.

14. The PCM device according to claim 12, wherein The protective layer comprises hydrogen silsesquioxane.

15. The PCM device according to claim 1, wherein The phase change material layer comprises a germanium-antimony-tellurium alloy.

16. The PCM device according to claim 1, wherein... The PCM device further includes heater electrodes that contact the heater and circuit components that contact the heater electrodes, the circuit components being one of a resistor and a selector, and The heater electrode and the circuit assembly extend on one side of the phase change material layer and are embedded in the electrical insulating material.

17. The PCM device according to claim 16, wherein The PCM device also includes two electrical contact pads that respectively fill two through-holes extending through the electrical insulating material to contact the circuit assembly and the external electrode.

18. A data processing system, comprising: Control system; as well as One or more PCM devices, wherein each of the one or more PCM devices is connected to the control system and includes a PCM unit embedded in an electrically insulating material, wherein the PCM unit includes: A phase change material layer having a top surface, a bottom surface, and a side surface connecting the top surface and the bottom surface; External electrode, which contacts the side surface of the phase change material layer; and A heater that cuts across the top and bottom surfaces of the phase change material layer and extends at least partially through the phase change material layer, thereby contacting the phase change material layer.

19. The data processing system according to claim 18, wherein... The data processing system includes an in-memory computing device having a crossbar switch array structure. The crossbar switch array structure includes N input lines and M output lines interconnected at crossbars, defining N×M cells, where N≥2 and M≥2. Each crossbar includes a respective memory system, and each memory system includes a set of K memory elements, where K≥1. Thus, each of the N×M cells includes K memory elements, and each of the K memory elements includes one of the PCM devices. The control system includes a programming unit connected to the cross switch array structure, the programming unit being configured to program each cell according to a given target conductance value corresponding to a target weight value to be stored in each cell.

20. A method of operating a PCM device, the method comprising: A PCM device is provided, the PCM device comprising a PCM unit embedded in an electrically insulating material, wherein the PCM unit comprises: A phase change material layer having a top surface, a bottom surface, and a side surface connecting the top surface and the bottom surface; External electrode, which contacts the side surface of the phase change material layer; and A heater, which is transversely oriented to the top and bottom surfaces of the phase change material layer, and extends at least partially through the phase change material layer to contact it, and Repeatedly apply A RESET current pulse passes through the heater to grow annular amorphous regions from the heater in the phase change material layer, thereby bringing the phase change material layer into a high-resistivity state. A SET current pulse passes through the heater to reduce the annular amorphous region in the phase change material layer, thereby bringing the phase change material layer into a low-resistance state.

21. A method for manufacturing a PCM device, the method comprising: The PCM unit is manufactured using the following steps: A layer stack including a phase change material layer is obtained, the phase change material layer having a top surface and a bottom surface connected by the side surfaces of the phase change material layer; An outer electrode layer is deposited on the stack such that the outer electrode layer contacts the side surface of the phase change material layer and the top surface of the stack; A through-hole is opened from the top surface of the stack, the through-hole being transversely intersecting the top and bottom surfaces of the phase change material layer and extending at least partially through the phase change material layer; as well as A heater is filled in the through-hole to obtain contact with the phase change material layer, and The PCM unit is covered with an electrically insulating material to embed the PCM unit in the electrically insulating material.

22. The method of claim 21, wherein... The obtained layer stack also includes resistive protrusions on one of the top and bottom surfaces of the phase change material layer that contact the phase change material layer, and The through-hole is opened to extend at least partially through each of the phase change material layer and the resistive bump layer, thereby obtaining a heater that contacts each of the resistive bump pad and the phase change material layer.

23. The method of claim 21, wherein The resulting layer stack also includes an electrically insulating material layer and a protective layer on top of the electrically insulating material layer, the electrically insulating material layer being sandwiched between the protective layer and the top surface of the phase change material layer.

24. The method of claim 21, wherein... The method further includes depositing a layer on top of the filled heater after filling the via and before covering the PCM unit; and The deposited layer is patterned to obtain one of the electrodes, resistors, and selectors.

25. The method of claim 24, wherein... The method further includes etching additional through-holes through the electrically insulating material after covering the PCM cell; and The additional through-hole is filled to obtain two electrical contact pads that respectively contact the external electrode and the circuit assembly.

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