Multilayer phase-change memory devices

Abstract

A phase change memory (PCM) cell comprises a first electrode comprised of a first conductive material, a second electrode comprised of a second conductive material, a first phase change layer positioned between the first and second electrodes and comprised of the first phase change material, and a second phase change layer positioned between the first and second electrodes and comprised of the second phase change material, where the first phase change material has a first resistivity and the second phase change material has a second resistivity, where the first resistivity is at least twice the second resistivity.

Description

Technical Field

[0001] The present invention relates to computer memory, and more particularly to a phase change material memory device having multiple layers.

Background Art

[0002] Phase change memory (PCM) can be used for both training and inference in analog computing for artificial intelligence. A phase change memory structure can include a phase change memory resistive device having an adjustable conductivity for each device and an overall high device resistance with a high holding power to minimize energy consumption. Mixing (also known as doping) a PCM material with a dielectric and a low-conductive material such as silicon dioxide (SiO2), silicon monoxide (SiO), silicon oxynitride (SiON), silicon oxycarbide (SiOC), and aluminum nitride (AlN) can increase both the crystallization temperature and the resistivity, improve the resistance state retention, and reduce the programming power.

Summary of the Invention

[0003] According to an embodiment of the present disclosure, a phase change memory (PCM) cell includes a first electrode made of a first conductive material, a second electrode made of a second conductive material, a first phase change layer positioned between the first electrode and the second electrode and made of a first phase change material, and a second phase change layer positioned between the first electrode and the second electrode and made of a second phase change material. The first phase change material has a first resistivity, the second phase change material has a second resistivity, and the first resistivity is at least twice the second resistivity.

[0004] According to embodiments of the present disclosure, a PCM cell comprises a first electrode made of a first conductive material, a second electrode made of a second conductive material, and a first phase change layer positioned between the first electrode and the second electrode, having a first thickness and made of the first phase change material. The PCM cell further comprises a second phase change layer positioned between the first electrode and the second electrode, having a second thickness and made of the second phase change material, wherein the second thickness is less than one-quarter of the first thickness.

[0005] Embodiments of the present disclosure disclose a method using a PCM cell comprising: a first electrode; a second electrode; a doped phase transition layer positioned between the first electrode and the second electrode; and a first undoped phase transition layer in contact with the doped phase transition layer and one of the first electrode and the second electrode. The method includes: passing a first current from the first electrode to the second electrode through the first undoped phase transition layer to create a first amorphous zone having an amorphous structure in the doped phase transition layer; measuring a first electrical resistance between the first electrode and the second electrode through the first amorphous zone; and passing a second current from the first electrode to the second electrode through the undoped phase transition layer to anneal the first amorphous zone to have a polycrystalline structure.

[0006] According to embodiments of the present disclosure, a PCM cell comprises a first electrode made of a first conductive material, a second electrode made of a second conductive material, and an insulator made of an electrically insulating material positioned between the first electrode and the second electrode. The PCM cell also comprises a first phase change layer positioned along the first electrode and the second electrode and the insulator, the first phase change layer comprising a mixture of a first phase change material and a dopant material and having a first thickness, and a second phase change layer in contact with the first phase change layer and located in an electrical circuit between the first electrode and the second electrode, comprising essentially a second phase change material and having a second thickness. The second thickness is less than half the first thickness.

[0007] According to embodiments of the present disclosure, a PCM cell comprises a first electrode, a second electrode, and a pillar having a first height, which is composed of a mixture of a first phase change material and a dopant material. The PCM cell also comprises an insulator surrounding the pillar, which comprises an electrically insulating material, and a layer essentially made of a second phase change material, which is in contact with the pillar, extends along the entire side of the pillar, is in contact with at least one of the first electrode and the second electrode, and has a second height, the second height being less than half of the first height. [Brief explanation of the drawing]

[0008] [Figure 1A] This is a cross-sectional view of a mushroom PCM cell having a polycrystalline doped layer according to an embodiment of the present disclosure. [Figure 1B] This is a cross-sectional view of a mushroom PCM cell having a doped phase change material layer including an amorphous portion of the doped phase change layer, according to an embodiment of the present disclosure. [Figure 1C] This is a cross-sectional view of a mushroom PCM cell according to an embodiment of the present disclosure, having a doped phase change material layer including an amorphous portion of a doped phase change layer and an undoped phase change material layer including an amorphous portion of an undoped phase change layer. [Figure 2A] This is a cross-sectional view of a mushroom PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 2B] This is a cross-sectional view of a mushroom PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 2C] This is a cross-sectional view of a mushroom PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 2D] This is a cross-sectional view of a mushroom PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 2E] This is a cross-sectional view of a mushroom PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 2F] This is a cross-sectional view of a mushroom PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 3A] This is a cross-sectional view of a bridge PCM cell of an alternative embodiment according to the embodiments of this disclosure. [Figure 3B] This is a cross-sectional view of a bridge PCM cell of an alternative embodiment according to the embodiments of this disclosure. [Figure 3C] This is a cross-sectional view of a bridge PCM cell of an alternative embodiment according to the embodiments of this disclosure. [Figure 4] This is a cross-sectional view of a pillar PCM cell of an alternative embodiment according to the embodiments of this disclosure. [Figure 5A] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 5B] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 5C] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 5D] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 5E] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 5F] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Figure 5G] This is a cross-sectional view of a confined PCM cell of an alternative embodiment according to the embodiments of the present disclosure. [Modes for carrying out the invention]

[0009] Various embodiments of the present disclosure are described herein with reference to the relevant drawings. Alternative embodiments can be devised without departing from the scope of the present disclosure. Note that various connections and positional relationships (e.g., above, below, adjacent, etc.) are shown between elements in the following description and drawings. These relationships or positional relationships, or both, may be direct or indirect unless otherwise specified, and the present disclosure is not intended to be limiting in this respect. Thus, the joining of entities may refer to either direct or indirect joining, and the positional relationships between entities may be direct or indirect positional relationships. As an example of an indirect positional relationship, the reference in this description to forming layer "A" on layer "B" includes a situation in which one or more intermediate layers (e.g., layers "C" and "D") are between layer "A" and layer "B" insofar as the properties and functions related to layer "A" and layer "B" are not substantially altered by the intermediate layers.

[0010] The following definitions and abbreviations are for use in interpreting the claims and specification. Where used herein, the terms “equipped,” “possessing,” “included,” “contained,” “having,” “having,” “containing,” or “containing,” or any other variation thereof, are intended to be non-exclusive inclusions. For example, a composition, mixture, process, method, article, or apparatus containing a list of elements is not necessarily limited to those elements alone and may include other elements not expressly listed or specific to that composition, mixture, process, method, article, or apparatus. Furthermore, any numerical ranges included herein, unless otherwise specified, include their boundaries.

[0011] For the following description, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", and derivatives thereof are related to the structures and methods described as oriented in the drawing figures. The terms "overlap", "atop", "on", "positioned on", or "positioned atop" mean that a first element, such as a first structure, is present over a second element, such as a second structure, and intervening elements, such as a bonding structure, may be present between the first and second elements. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected at the junction of the two elements without any intermediate conductive, insulating, or semiconductor layer. Note, for example, that the term "selective to", such as "a first element selective to a second element", means that the first element is etchable and the second element can function as an etch stop.

[0012] In this specification, for the sake of brevity, there may or may not be a detailed description of the prior art related to semiconductor device and integrated circuit (IC) manufacturing. Further, the various tasks and process steps described in this specification can be incorporated into more comprehensive procedures or processes having additional steps or functions not detailed herein. In particular, since the various steps in the manufacture of semiconductor devices and semiconductor-based ICs are well known, from the perspective of brevity, in this specification, many of the conventional steps are only briefly touched upon or completely omitted without providing details of well-known processes.

[0013] Generally, the various processes used to form microchips packaged in ICs are classified into four general categories: namely, film deposition, removal / etching, semiconductor doping, and patterning / lithography.

[0014] Film formation can be any process of growing, coating, or otherwise transferring a material onto a wafer. Among the available techniques are, among others, physical vapor deposition (PVD), chemical vapor deposition (CVD), electrolytic plating (ECD), molecular beam epitaxy (MBE), and, more recently, atomic layer deposition (ALD). Another film formation technique is plasma CVD (PECVD), which is a process that uses energy in a plasma to cause reactions on the wafer surface. This eliminates the need for the high temperatures typically associated with conventional CVD. The energy-ion bombardment during PECVD film formation can also improve the electrical and mechanical properties of the film.

[0015] Removal / etching can be any process of removing a material from a wafer. Examples of etching processes (either wet or dry) include chemical mechanical planarization (CMP). An example of a removal process is ion beam etching (IBE). Generally, IBE (or milling) refers to a dry plasma etching method that uses a remote broad beam ion / plasma source to remove substrate material by means of a physical inert gas means or a chemically reactive gas means or both. Like other dry plasma etching techniques, IBE has advantages such as etching rate, anisotropy, selectivity, uniformity, aspect ratio, and minimization of substrate damage. Another example of a dry removal process is reactive ion etching (RIE). Generally, RIE uses a chemically reactive plasma to remove a material deposited on a wafer. In RIE, the plasma is generated under low pressure (vacuum) by an electromagnetic field. High energy ions from the RIE plasma attack the wafer surface and react with it to remove the material.

[0016] Semiconductor doping can involve altering the electrical properties of a transistor, for example, by doping the source or drain, generally through diffusion, ion implantation, or both. These doping processes are followed by furnace annealing or rapid thermal annealing ("RTA"). Annealing activates the implanted dopants. Both conductive (e.g., polysilicon, aluminum, copper, etc.) and insulating (e.g., various forms of silicon dioxide, silicon nitride, etc.) films are used to connect or isolate transistors and their components. By selectively doping different areas of a semiconductor substrate, the conductivity of the substrate can be altered by applying a voltage. By creating structures of these various components, millions of transistors can be assembled and wired to form the complex circuits of modern microelectronic devices.

[0017] Semiconductor lithography can be the process of forming a three-dimensional relief image or pattern on a semiconductor substrate for subsequent transfer of the pattern to the substrate. In semiconductor lithography, the pattern is formed by a photosensitive polymer called photoresist. The lithography and etching / pattern transfer steps are repeated multiple times to build the complex structures that make up the transistors and the many wires that connect the millions of transistors in the circuit. Each pattern printed on the wafer is aligned with previously formed patterns, and conductors, insulators, and selectively doped regions are gradually built up to form the final device.

[0018] Figure 1A is a cross-sectional view of a PCM cell 100 having a polycrystalline doped layer 102. Figure 1B is a cross-sectional view of a PCM cell 100 having a doped layer 102 including an amorphous zone 116. Figure 1C is a cross-sectional view of a PCM cell 100 having a doped layer 102 including an amorphous zone 116 and an undoped layer 108-1 including an amorphous zone 118. Figures 1A to 1C will be explained in relation to each other.

[0019] In the illustrated embodiment, the PCM cell 100 includes a heater 106, an undoped layer 108-1 in contact with the bottom electrode heater 106, Non The PCM cell 100 comprises a doped layer 102 in contact with a doped layer 108-1, an undoped layer 108-2 in contact with the doped layer 102, and an electrode 110 in contact with the undoped layer 108-2. The widths of the undoped layer 108-1, the doped layer 102, the undoped layer 108-2, and the electrode 110 are the same, but the width of the heater 106 is reduced relatively significantly. As a result, the PCM cell 100 can be said to have a mushroom structure through which current can flow from the heater 106 to the electrode 110 through the undoped layer 108-1, the doped layer 102, and the undoped layer 108-2.

[0020] The heater 106 and electrode 110 can be made of a conductive material such as a metal, for example, titanium nitride (TiN). The heater 106 is an electrode with a relatively small cross-sectional area that focuses the current flowing through the PCM cell 100. This allows the heater 106 to generate heat by resistive heating, and this heat can be used to raise the temperature of the PCM cell 100 (e.g., the undoped layer 108-1 and the doped layer 102) above, for example, the crystallization temperature or the melting temperature of the doped layer 102. Furthermore, the heater 106 can be made of multiple different conductive materials that can be arranged in multiple layers.

[0021] The undoped layers 108-1 and 108-2 (collectively referred to as undoped layer 108) may be essentially made of a phase-change material such as germanium-antimony-tellurium (GST), gallium-antimony-tellurium (GaST), or silver-iridium-antimony-telluride (AIST) material, but other materials may be used as needed. Furthermore, the phase-change materials of undoped layers 108-1 and 108-2 are the same in some embodiments and different in other embodiments. The terms “essentially made of” and “essentially consisting of” as used herein with respect to the materials of different layers indicate that other materials, if present, do not substantially alter the fundamental properties of the cited material. For example, a layer consisting essentially of GST material does not contain other materials that substantially alter the fundamental properties of the GST material. Thus, layers 108-1 and 108-2 are also called undoped layers. On the other hand, doped layer 102 may be a mixture of phase-change material 112 and phase-separation dopant material 114. The doped layer 102 may also be a substitutional or interstitial doped phase-change material, such as titanium-GST (TiGST), gallium-GST (GaGST), silicon-GST (SiGST), or bismuth-GST (BiGST). This is because these atoms can substitute / sit in the gaps to dissolve into the GST. The phase-change material 112 may be a GST material (however, other materials may be used, which may be the same as or different from the undoped layer 108, if necessary). The phase-separation dopant material 114 may be one or more dielectric materials, or low-conductivity metals such as SiO2, SiO, SiON, SiOC, carbon (C), tantalum nitride (Ta3N5), aluminum nitride (AlN), and titanium nitride (TiN), but other materials may be used, if necessary. The particles of the phase-separating dopant material 114 can limit the particle size of the phase-change material 112 and provide "nano-open" regions (i.e., localized areas with relatively high electrical resistance) to increase the resistance of the doped layer 102. In some embodiments, the amount of the phase-separating dopant material 114 in the doped layer 102 is at least 10% by volume.

[0022] In the illustrated embodiments, the undoped layer 108 is substantially thinner (in height) than the doped layer 102. Furthermore, the thicknesses of the undoped layers 108-1 and 108-2 are the same in some embodiments and different in others. In some embodiments, the thickness of the undoped layer 108 is less than half the thickness of the doped layer 102. In some embodiments, the thickness of the undoped layer 108 is less than one-eighth the thickness of the doped layer 102. In some embodiments, the thickness of the undoped layer 108 is less than one-sixteenth the thickness of the doped layer 102. In some embodiments, the thickness of the undoped layer 108 is less than one-eighth the thickness of the doped layer 102. In some embodiments, the thickness of the undoped layer 108 is between 0.2 nanometers (nm) and 10 nm, and the thickness of the doped layer 102 is between 20 nm and 100 nm. In some embodiments, the thickness of the undoped layer 108 is 0.5 nm to 5 nm, and the thickness of the doped layer 102 is 40 nm to 80 nm.

[0023] In some embodiments, the cross-section of the PCM cell 100 (towards the back of the page in Figures 1A and 1B) can be square, while in other embodiments, it can be rectangular or circular. In some embodiments, the width or diameter of the heater 106 may be 20 nm to 60 nm. In some embodiments, the width or diameter of the heater 106 may be about 40 nm. In some embodiments, the width or diameter of the doped layer 102, the undoped layer 108, and the electrode 110 may be 100 nm to 300 nm. In some embodiments, the width or diameter of the doped layer 102, the undoped layer 108, and the electrode 110 may be about 200 nm. In some embodiments, the width or diameter of the doped layer 102, the undoped layer 108, and the electrode 110 may be greater than 200 nm.

[0024] In the illustrated embodiment, the PCM cell 100 can be operated as a memory cell by passing current from the heater 106 to the electrode 110. This can be done at various voltages to read and write values ​​to the PCM cell 100. For example, high voltage (e.g., 1 volt (V) to 4 V) can be used for a short time for writing. This allows the heater 106 to heat the doped layer 102 above its melting point. When the current flow stops, the doped layer 102 can cool rapidly, forming a zone 116 in a process called "reset". Zone 116 is a dome-shaped region of the doped layer 102, where the phase change material 112 inside zone 116 has an amorphous structure, while the phase change material 112 outside zone 116 still has a polycrystalline structure. Furthermore, a similar "reset" zone 118 can be formed in the undoped layer 108-1 depending on the voltage, current, duration, or combination thereof of the reset electrical pulse. Furthermore, the diameter of zone 118 can be larger than, the same as, or smaller than zone 116 (although it is shown as larger in Figure 1C). Generally, this amorphous configuration does not have a distinct structure. However, locally non-bonded crystal nuclei (i.e., small crystallized regions of the phase-change material 112) may exist in zone 116 or zone 118 or both.

[0025] In some embodiments, zone 116 may have a height of 40 nm and a diameter of 40 nm. By creating zone 116, the overall electrical resistance of the PCM cell 100 can be increased compared to the polycrystalline structure of the doped layer 102 alone (see Figure 1A). This new resistance value can be read using a low voltage (e.g., 0.2 V) current without changing the resistance value.

[0026] Furthermore, the phase change material 112 can be returned to a polycrystalline structure alone by "setting" the PCM cell 100 in order to rewrite it. A high voltage (e.g., 1V to 4V) can be used for a short time (e.g., 10 nanoseconds (ns)). This allows the heater 106 to heat the doped layer 102 above its crystallization point but not to its melting point. Since the crystallization temperature is lower than the melting point, the doped layer 102 can anneal and form crystals once the current flow stops. This reduces the overall electrical resistance of the PCM cell 100 compared to having an amorphous zone 116 (see Figure 1B) or zone 118 (see Figure 1C) or both. This new resistance value can be read using a low voltage (e.g., 0.2V) current without changing the resistance value.

[0027] In some embodiments, the melting temperatures of the undoped layer 108 and the doped layer 102 (i.e., the melting temperatures of the phase change material 112 and the phase change material 112 having the phase separation dopant material 114) can be about 600°C. In some embodiments, if the phase separation dopant material 114 is, for example, SiO2, the crystallization temperature of the doped layer 102 can be about 220°C. In some embodiments, the crystallization temperature of the undoped layer 108 can be about 180°C. Furthermore, the process of setting and resetting the PCM cell 100 can be repeated. In some embodiments, different zones 116 with different resistances can be created in the doped layer 102 (for example, by different sizes and amounts of crystallization nuclei in zone 116). This allows the PCM cell 100 to be non-binary, as different resistances can be created by changing the reset parameters.

[0028] The function of setting and resetting the doped layer 102 can be facilitated by including an undoped layer 108 between the doped layer 102 and the heater 106 / electrode 110. More specifically, the phase-separating dopant material 114 in the doped layer 102 can minimize the time and voltage conditions under which the phase-change material 112 can be electrically crystallized. This allows the undoped layer 108 to function as a transition between the low resistance of the heater 106 / electrode 110 and the high resistance of the doped layer 102, allowing the current to diffuse over a wider area than the top surface of the heater 106. The undoped layer 108 may have better ohmic contact with the heater 106 / electrode 110 than the doped layer 102, and homogeneous contact with the heater 106 reduces variability in the low-resistance state of the undoped layer 108-1. Furthermore, the undoped layer 108 can homogenize the ohmic contact region with the doped layer 102 and the heater 106 / electrode 110, thereby reducing low-resistance state dispersion.

[0029] The components and structure of the PCM cell 100 provide analog computing capabilities. For example, the variable resistors of the PCM cell 100 can be set to correspond to analog weight values. These weights, not only 1 and 0 associated with high and low resistance states suitable for binary computing, exist on a continuum of analog resistance values ​​and can be used as artificial synaptic weights in neural networks for artificial intelligence computation and machine learning. A relatively thin undoped layer 108 positioned between the heater 106 / electrode 110 and the doped layer 102 broadens the voltage range that can be used to set and reset the PCM cell 100. This is important when the doping amount of the doped layer 102 is high, as otherwise the PCM cell 100 may not be able to set after its initial reset. Furthermore, the wide voltage range expands the operating range of the memory programming function of the PCM cell 100, allowing for a narrower distribution of resistance states and enabling more reliable operation of the PCM cell 100.

[0030] Figures 1A to 1C illustrate one embodiment of the present disclosure in which alternatives exist. For example, the doped layer 102 can be replaced with another undoped layer of the same thickness as the doped layer 102. In such embodiments, the thicker undoped layer may be made of a different material than the thin undoped layer 108, which has substantially higher electrical resistivity. In some embodiments, if the undoped layer 108 is essentially made of antimony telluride (Sb2Te3), the thicker undoped layer may be essentially made of GST225 (i.e., Ge2Sb2Te5). In the crystalline structure, Sb2Te3 has a resistivity of about 0.0005 ohms*cm, and GST225 has a resistivity of about 0.003 ohms*cm. This is in contrast to the doped layer 102, which can have a resistivity of about 1 ohm*cm in the crystalline structure and can be used together with the undoped layer 108, which is essentially made of GST225. The resistivity of the doped layer 102 / thick undoped layer and undoped layer 108 can change with changes in the crystalline or amorphous structure, but generally, the resistivity of the thick undoped layer can be 2 to 1000 times greater than that of the undoped layer 108. In some embodiments, the resistivity of the thick undoped layer can be 8 to 750 times greater than that of the undoped layer 108. In some embodiments, the resistivity of the thick undoped layer can be 10 to 500 times greater than that of the undoped layer 108.

[0031] In another example, one or both of the undoped layers 108 can be replaced with another doped layer that is as thin as the undoped layer 108. In such embodiments, the thin doped layer may be made of a different material from the thick doped layer 102, which has substantially low electrical resistivity. Examples of dopants that result in low resistivity include titanium (Ti), bismuth (Bi), indium (In), and silver (Ag). These dopants are in contrast to dopants that result in high resistivity, such as SiO2, SiO, SiON, SiOC, C, Ta3N5, AlN, and TiN. Thus, in some embodiments, if the doped layer 102 contains SiO2:GST, the thin doped layer may contain TiGST.

[0032] Figures 2A to 2F are cross-sectional views of alternative embodiments of PCM cells 200A to 200E (collectively referred to as PCM cells 200), respectively. In certain embodiments, PCM cells 200 may be similar to or identical to PCM cell 100 (shown in Figure 1). Therefore, some of these embodiments may have reference numbers 100 greater than those of PCM cell 100.

[0033] In the embodiment shown in Figure 2A, PCM cell 200-1 includes a single thin undoped layer 208-1 positioned between the heater 206 and the doped layer 202. In the embodiment shown in Figure 2B, PCM cell 200-2 includes a single thin undoped layer 208-2 positioned between the doped layer 202 and the electrode 210. PCM cells 200-1 and 200-2 have fewer undoped layers than PCM cell 100, but the function and purpose of the undoped layers 208-1 and 208-2 may be the same as that of the undoped layer 108.

[0034] In the embodiment shown in Figure 2C, the PCM cell 200-3 includes a projection liner 218-1 positioned between the heater 206 and the undoped layer 208-3, with the undoped layer 208-3 also in contact with the doped layer 202. In the embodiment shown in Figure 2D, the PCM cell 200-4 includes a projection liner 218-2 positioned between the heater 206 and the doped layer 202, with the undoped layer 208-4 positioned between the doped layer 202 and the electrode 210. In the embodiment shown in Figure 2E, the PCM cell 200-5 includes a projection liner 218-3 positioned between the heater 206 and the undoped layer 208-5, with the undoped layer 208-5 also in contact with the doped layer 202. Furthermore, the PCM cell 200-5 includes a second undoped layer 208-6 positioned between the doped layer 202 and the electrode 210. In the embodiment shown in Figure 2F, the PCM cell 200-6 includes an undoped layer 208-7 positioned between the heater 206 and the projection liner 218-4, the projection liner 218-4 also in contact with the doped layer 202.

[0035] Projection liners 218-1, 218-2, and 218-3 (collectively referred to as projection liners 218) can extend across the entire width of the undoped layer 208-3, the doped layer 202, and the undoped layer 208-5, respectively. The projection liners 218 can be made of metallic material, semiconductor material, or both. This allows the projection liners 218 to provide a certain amount of electrical resistance when the PCM cells 200-3, 200-4, and 200-5 are reset, creating a parallel current path around zone 116 (shown in Figure 1).

[0036] Figures 3A to 3C are cross-sectional views of alternative embodiments of PCM cells 300-1, 300-2, and 300-3 (collectively referred to as PCM cell 300), respectively. In certain embodiments, PCM cell 300 may be similar to or identical to PCM cell 100 (shown in Figures 1A and 1B) or 200 (shown in Figures 2A to 2E). Therefore, some of these embodiments may have reference numbers that are 200 greater than those of PCM cell 100, or 100 greater than those of PCM cell 200.

[0037] In the embodiment shown in Figure 3A, the PCM cell 300-1 includes electrodes 306 and 310, with an insulator 320 positioned between and coplanar with the electrodes 306 and 310. The insulator 320 can be made of an electrically insulating material such as a low dielectric constant material, SiO2, silicon nitride (SiN), and fluorinated tetraethyl orthosilicate (FTEOS). Furthermore, an undoped layer 308-1 extends across the entire width of the upper part of electrode 306, and an undoped layer 308-2 extends across the entire width of the upper part of electrode 310. A doped layer 302 extends along the entire length of the undoped layers 308-1 and 308-2 (collectively, the undoped layer 308) and the insulator 320.

[0038] When current flows through PCM cell 300-1, it travels from electrode 306 to electrode 310, through the undoped layer 308-1, the doped layer 302, and the undoped layer 308-2. Thus, PCM cell 300-1 has a bridge structure. Similar to PCM cell 100 (shown in Figures 1A and 1B), the undoped layer 308 is thin compared to the thickness of the doped layer 302, which can have the same proportions or dimensions as PCM cell 100, or both. In some embodiments, the height of the doped layer 302 is 5 nm to 30 nm. In some embodiments, the depth of PCM cell 300-1 (i.e., the dimension to the back of the page in Figure 2A) is 100 nm to 800 nm. However, in some embodiments, the doped layer 302 has a dogbone or bowtie shape, which is shallower in the middle, with a depth of 10 nm to 50 nm. Although PCM cell 300-1 has a different undoped layer structure from PCM cell 100, the function and purpose of the undoped layer 308 may be the same as those of the undoped layer 108.

[0039] In the embodiment shown in Figure 3B, the PCM cell 300-2 includes a single thin undoped layer 308-3 that extends over the entire length of electrodes 306 and 310 and the insulator 320. Thus, the doped layer 302 extends along the entire length of the undoped layer 308-3. When current flows through the PCM cell 300-2, it travels from electrode 306 to electrode 310, through the undoped layer 308-3 and the doped layer 302 (in this way, the current traveling through the doped layer 302 crosses the undoped layer 308-3 twice).

[0040] In the embodiment shown in Figure 3C, the PCM cell 300-3 includes a projection liner 318 that extends over the entire length of electrodes 306 and 310 and the insulator 320. As a result, the undoped layer 308-4 extends along the entire length of the projection liner 318, and the doped layer 302 extends along the entire length of the undoped layer 308-4. When current is passed through the PCM cell 300-2, it travels from electrode 306 to electrode 310, through the projection liner 318, the undoped layer 308-4, and the doped layer 302 (in this way, the current traveling through the undoped layer 308-4 crosses the projection liner 318 twice, and the current traveling through the doped layer 302 crosses the doped layer 308-4 and the projection liner 318 twice). Although PCM cell 300-3 has a different projection liner structure from PCM cells 200-3, 200-4, and 200-5, the function and purpose of projection liner 318 may be the same as that of projection liner 218.

[0041] Figure 4 is a cross-sectional view of PCM cell 400 in an alternative embodiment. In certain embodiments, PCM cell 400 may be similar to or identical to PCM cell 100 (shown in Figures 1A and 1B), PCM cell 200 (shown in Figures 2A to 2E), or PCM cell 300 (shown in Figures 3A to 3C). Therefore, some of these embodiments may have a reference number that is 300 greater than that of PCM cell 100, 200 greater than that of PCM cell 200, and 100 greater than that of PCM cell 300.

[0042] In the illustrated embodiment, the diameters of electrode 406, undoped layer 408-1, doped layer 402, undoped layer 408-2, and electrode 410 are all the same (e.g., about 40 nm). Thus, the PCM cell 400 has a pillar structure. The PCM cell 400 can be made by forming (e.g., depositing) each layer (i.e., electrode 406, undoped layer 408-1, doped layer 402, undoped layer 408-2, and electrode 410) and etching them to form pillars.

[0043] Furthermore, the PCM cell 400 includes a selector 422 beneath the electrode 406. The selector 422 comprises a carbon layer 424-1, an ovonic threshold switch layer 426 in contact with the carbon layer 424-1, and a carbon layer 424-2 in contact with the ovonic threshold switch layer 426 and the electrode 406. However, those skilled in the art will recognize that there are other selectors besides the selector 422 that could be used in the PCM cell 400.

[0044] Figures 5A to 5G are cross-sectional views of alternative embodiments of PCM cells 500-1, 500-2, 500-3, 500-4, 500-5, 500-6, and 500-7 (collectively referred to as PCM cells 500). In certain embodiments, PCM cells 500 may be similar to or identical to PCM cell 100 (shown in Figures 1A and 1B), PCM cell 200 (shown in Figures 2A to 2E), PCM cell 300 (shown in Figures 3A to 3C), or PCM cell 400 (shown in Figure 4). Thus, some of these embodiments may have reference numbers that are 400 greater than those of PCM cell 100, 3000 greater than those of PCM cell 200, 200 greater than those of PCM cell 300, or 100 greater than those of PCM cell 400.

[0045] In the embodiment shown in Figure 5A, the PCM cell 500-1 comprises an electrode 506, a doped layer 502-1, an undoped layer 508-1, an electrode 510, and an insulator 520. Since the doped layer 502-1 is substantially narrower than the electrode 506 and the undoped layer 508-1, the insulator 520 is positioned to occupy the space around the doped layer 502-1 within the projection of the electrode 506 and the undoped layer 508-1. Thus, the PCM cell 500-1 has a confined pillar structure.

[0046] Unlike the PCM cell 400 (shown in Figure 4), the PCM cell 500-1 can be made by forming (e.g., depositing) electrodes 506 and an insulator 520. Next, holes or via channels (i.e., blind holes) can be formed (e.g., etching) in the insulator 520, and a doped layer 502-1 can be formed therein (e.g., depositing and polishing). Next, an undoped layer 508-1 can be formed (e.g., depositing) on ​​the doped layer 502-1 and the insulator 520. Next, electrodes 510 can be formed (e.g., depositing) on ​​the undoped layer 508-1.

[0047] In the embodiment shown in Figure 5B, the PCM cell 500-2 includes an undoped layer 508-2 that is shorter than the undoped layer 508-1. However, given that the undoped layer 508-2 extends over the entire top of the doped layer 502-2, the function and purpose of the undoped layer 508-2 may be the same. Since the doped layer 502-2 is surrounded by the insulator 520, the current flowing from electrode 506 to electrode 510 still passes through the undoped layer 508-2.

[0048] In the embodiment shown in Figure 5C, the PCM cell 500-3 includes a short undoped layer 508-3 at the bottom of the doped layer 502-3. Thus, the PCM cell 500-3 can be made by forming (e.g., depositing) electrodes 506 and an insulator 520. Next, holes or via channels can be formed (e.g., etching) in the insulator 520 and an undoped layer 508-3 can be formed (e.g., depositing) therein. Next, a doped layer 502-3 can be formed (e.g., depositing and polishing) on ​​top of the undoped layer 508-3. Next, electrodes 510 can be formed (e.g., depositing) on ​​top of the doped layer 502-3 and the insulator 520.

[0049] In the embodiment shown in Figure 5D, the PCM cell 500-4 includes a full-width undoped layer 508-4 beneath a doped layer 502-4. Thus, the PCM cell 500-4 can be made by forming (e.g., depositing) an electrode 506, an undoped layer 508-4, and an insulator 520. Next, holes or via channels extending down to the undoped layer 508-4 can be formed (e.g., etching) within the insulator 520. Next, a doped layer 502-4 can be formed (e.g., depositing and polishing) on ​​top of the undoped layer 508-4. Next, an electrode 510 can be formed (e.g., depositing) on ​​top of the doped layer 502-4 and the insulator 520.

[0050] In the embodiment shown in Figure 5E, the PCM cell 500-5 includes two undoped layers 508-5 and 508-6 at both ends of the doped layer 502-5. The undoped layer 508-5 is only the width of the doped layer 502-5, while the undoped layer 508-6 is the full width of the electrode 510. In the embodiment shown in Figure 5F, the PCM cell 500-6 includes two undoped layers 508-7 and 508-8 at both ends of the doped layer 502-6. The undoped layer 508-7 is the full width of the electrode 506, while the undoped layer 508-8 is only the width of the doped layer 502-6. In the embodiment shown in Figure 5G, the PCM cell 500-7 includes an undoped layer 508-9 extending along the sides and bottom of the doped layer 502-6.

[0051] Further discussion of several exemplary embodiments The following non-exclusively describes some exemplary embodiments of the present disclosure.

[0052] A PCM cell according to an exemplary embodiment of the present disclosure includes, among many others, a first electrode made of a first conductive material, a second electrode made of a second conductive material, a first phase change layer positioned between the first electrode and the second electrode and made of a first phase change material, and a second phase change layer positioned between the first electrode and the second electrode and made of a second phase change material, wherein the first phase change material has a first resistivity, the second phase change material has a second resistivity, and the first resistivity is at least twice the second resistivity.

[0053] The PCM cells described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0054] A further embodiment of the PCM cell described above, comprising a third phase change layer in contact with a first phase change layer and a second electrode, the third phase change layer being composed of a third phase change material, wherein the third phase change material has a third resistivity, and the first resistivity is at least twice that of the third resistivity.

[0055] A further embodiment of any of the above PCM cells, wherein the third phase change layer further comprises a dopant material.

[0056] A further embodiment of any of the above PCM cells, wherein the first phase change layer further comprises a dopant material.

[0057] A further embodiment of any of the above PCM cells, wherein the second phase change layer is made of a second phase change material.

[0058] In any further embodiment of the PCM cell described above, the second phase change layer is in contact with the first electrode and the second electrode.

[0059] A further embodiment of any of the above-described PCM cells further comprises a projection liner positioned between a first electrode and a second electrode and made of a semiconductor material.

[0060] In any further embodiment of the PCM cell described above, the projection liner is in contact with the first electrode and the second phase change layer.

[0061] A PCM cell according to an exemplary embodiment of the present disclosure includes, among many others, a first electrode made of a first conductive material, a second electrode made of a second conductive material, a first phase change layer positioned between the first electrode and the second electrode, having a first thickness and made of the first phase change material, and a second phase change layer positioned between the first electrode and the second electrode, having a second thickness and made of the second phase change material, wherein the second thickness is less than one-quarter of the first thickness.

[0062] The PCM cells described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0063] A further embodiment of the PCM cell described above, comprising a third phase change layer in contact with a first phase change layer and a second electrode, the third phase change layer having a third thickness and being composed of a third phase change material, wherein the third thickness is less than one-quarter of the first thickness.

[0064] A further embodiment of any of the above PCM cells, wherein the third phase change layer further comprises a dopant material.

[0065] A further embodiment of any of the above PCM cells, wherein the first phase change layer further comprises a dopant material.

[0066] A further embodiment of any of the above PCM cells, wherein the second phase change layer is essentially made of an undoped second phase change material.

[0067] A further embodiment of any of the above-described PCM cells, wherein the first phase change layer has a first resistivity, the second phase change layer has a second resistivity, and the first resistivity is at least twice that of the second resistivity.

[0068] In any further embodiment of the PCM cell described above, the second phase change layer is in contact with the first electrode and the second electrode.

[0069] A further embodiment of any of the above-described PCM cells further comprises a projection liner positioned between a first electrode and a second electrode and made of a semiconductor material.

[0070] In any further embodiment of the PCM cell described above, the projection liner is in contact with the first electrode and the second phase change layer.

[0071] A PCM cell according to an exemplary embodiment of the present disclosure includes, among many others, a first electrode made of a first conductive material, a second electrode made of a second conductive material, a first phase change layer made of a mixture of a first phase change material and a dopant material having a first thickness, and a second phase change layer in contact with only one of the first electrode and the second electrode, having a second thickness and essentially made of an undoped second phase change material, wherein the second thickness is less than half the thickness of the first thickness.

[0072] The PCM cells described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0073] A further embodiment of the PCM cell described above, wherein a second phase change layer is in contact with the first phase change layer and the first electrode. The PCM cell further comprises a third phase change layer in contact with the first phase change layer and the second electrode, the third phase change layer having a third thickness and being composed of an undoped third phase change material, wherein the third thickness is less than half the thickness of the first.

[0074] A further embodiment of any of the above PCM cells, wherein the dopant material is a dielectric material.

[0075] A further embodiment of any of the above PCM cells, wherein the dopant material is selected from the group consisting of titanium, gallium, silicon, and nitrogen.

[0076] A further embodiment of any of the above-described PCM cells, wherein the second phase change material essentially consists of germanium, antimony, and tellurium.

[0077] A further embodiment of any of the above-described PCM cells, wherein the first electrode, the second electrode, the first phase change layer, and the second phase change layer form a column having a constant cross-sectional area.

[0078] A further embodiment of any of the above-described PCM cells further comprises a selector connected to a first electrode, the selector including an obonic threshold switch.

[0079] Among many, a method using a PCM cell according to an exemplary embodiment of the present disclosure, comprising a first electrode, a second electrode, a doped phase transition layer positioned between the first electrode and the second electrode, and a first undoped phase transition layer in contact with the doped phase transition layer and one of the first electrode and the second electrode, the method according to an exemplary embodiment of the present disclosure comprising, among many, passing a first current from the first electrode to the second electrode through the first undoped phase transition layer to create a first amorphous zone having an amorphous structure in the doped phase transition layer, measuring a first electrical resistance between the first electrode and the second electrode through the first amorphous zone, and passing a second current from the first electrode to the second electrode through the undoped phase transition layer to anneal the first amorphous zone to have a polycrystalline structure.

[0080] The methods described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0081] A further embodiment of the above method further includes measuring a second electrical resistance between a first electrode and a second electrode after annealing of a first amorphous zone, wherein the second electrical resistance is less than the first electrical resistance.

[0082] A further embodiment of any of the above methods further includes passing a third current from the first electrode through the first undoped phase transition layer to the second electrode in order to create a second amorphous zone having an amorphous structure in the doped phase transition layer.

[0083] A further embodiment of any of the above methods, wherein the first current first passes through the first undoped phase-change layer and then through the doped phase-change layer.

[0084] A further embodiment of any of the above methods, wherein the PCM cell further comprises a second undoped phase-change layer in contact with a doped phase-change layer, and the first current passes first through the first undoped phase-change layer, then through the doped phase-change layer, and then through the second undoped phase-change layer.

[0085] A PCM cell according to an exemplary embodiment of the present disclosure includes, among many others, a first electrode made of a first conductive material and having a first width, a second electrode made of a second conductive material and having a second width, a first phase change layer made of a mixture of a first phase change material and a dopant material and having a first thickness, and a second phase change layer positioned between the first phase change layer and one of the first electrode and the second electrode, the second phase change layer being essentially made of the second phase change material and having a second thickness, wherein the first electrode is configured to heat the first phase change layer to a temperature at least above the crystallization temperature of the first phase change material.

[0086] The PCM cells described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0087] A further embodiment of the PCM cell described above, wherein the first width is less than half of the second width, and the second thickness is less than half of the first thickness.

[0088] A further embodiment of any of the above PCM cells, wherein the first thickness is 20 nanometers (nm) to 100 nm and the second thickness is 0.2 nm to 10 nm.

[0089] A further embodiment of any of the above PCM cells, wherein the first width is 20 nm to 60 nm and the second width is 100 nm to 300 nm.

[0090] A further embodiment of any of the above-described PCM cells, wherein a second phase change layer is in contact with the first electrode, and the first and second phase change materials are the same and essentially consist of germanium, antimony, and tellurium.

[0091] A PCM cell according to an exemplary embodiment of the present disclosure includes, among many others, a first electrode made of a first conductive material, a second electrode made of a second conductive material, an insulator made of an electrically insulating material positioned between the first electrode and the second electrode, a first phase change layer positioned along the first electrode and the second electrode and the insulator, the first phase change layer being made of a mixture of the first phase change material and a dopant material and having a first thickness, and a second phase change layer in contact with the first phase change layer and located in an electrical circuit between the first electrode and the second electrode, the second phase change layer being essentially made of the second phase change material and having a second thickness, wherein the second thickness is less than half the first thickness.

[0092] The PCM cells described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0093] A further embodiment of the above PCM cell, wherein the first thickness is 20 nanometers (nm) to 100 nm, and the second thickness is 0.2 nm to 10 nm.

[0094] A further embodiment of any of the above PCM cells, wherein the first thickness is 40 nm to 80 nm and the second thickness is 0.5 nm to 5 nm.

[0095] A further embodiment of any of the above-described PCM cells, wherein the second phase change layer includes a first portion separated from the second portion, the first portion being in contact with and extending along the first electrode, the second portion being in contact with and extending along the second electrode, and the first phase change layer being in contact with and extending along the first portion, the insulator, and the second portion.

[0096] A further embodiment of any of the above-described PCM cells, comprising a projection liner in contact with a first electrode, an insulator, and a second electrode, and extending along the first electrode, the insulator, and the second electrode, the projection liner being made of a material selected from the group consisting of metallic materials and semiconductor materials, wherein the projection liner further comprises a second phase change layer in contact with and extending along the entire projection liner, and the first phase change layer in contact with and extending along the entire second phase change layer.

[0097] A PCM cell according to an exemplary embodiment of the present disclosure includes, among many others, a first electrode, a second electrode, a pillar comprising a mixture of a first phase change material and a dopant material having a first height, an insulator surrounding the pillar comprising an electrically insulating material, and a layer essentially made of a second phase change material, in contact with the pillar, extending along the entire side of the pillar, in contact with at least one of the first electrode and the second electrode, and having a second height, wherein the second thickness is less than half of the first thickness.

[0098] The PCM cells described in the preceding paragraph may optionally include, additionally, or alternatively, or both, one or more of the following features, structures, or additional components or combinations thereof:

[0099] A further embodiment of the above PCM cell, wherein the first height is 20 nanometers (nm) to 100 nm and the second height is 0.2 nm to 10 nm.

[0100] A further embodiment of any of the above-described PCM cells, wherein the layer is in contact with a first electrode and a second electrode.

[0101] A further embodiment of any of the above-described PCM cells further comprises a selector connected to a first electrode, the selector including an obonic threshold switch.

[0102] The descriptions of various embodiments of the present invention are presented for illustrative purposes only and are not intended to be exhaustive or limitful to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope of the described embodiments. The terms used herein have been selected to best describe the principles of the embodiments, their practical applications to the art found in the market or technical improvements, or to enable those skilled in the art to understand the embodiments disclosed herein.

Claims

1. A phase-change memory (PCM) cell, A first electrode made of a first conductive material, A second electrode made of a second conductive material, A first phase change layer, which is positioned between the first electrode and the second electrode and is made of a first phase change material, A second phase change layer is positioned between the first electrode and the second electrode and is made of a second phase change material, wherein the second phase change layer is in contact with the first electrode and the second electrode. Equipped with, The first phase change layer is in contact with the first electrode and the second phase change layer. The first phase change material has a first resistivity, The second phase change material has a second resistivity, The first resistivity is at least twice the second resistivity. Phase-change memory (PCM) cell.

2. The PCM cell according to claim 1, wherein the first phase change layer further comprises a dopant material.

3. A phase-change memory (PCM) cell, A first electrode made of a first conductive material, A second electrode made of a second conductive material, A first phase change layer positioned between the first electrode and the second electrode, having a first thickness and composed of a first phase change material, A second phase change layer positioned between the first electrode and the second electrode, having a second thickness and composed of a second phase change material, the second phase change layer is in contact with the first electrode and the second electrode, and the second phase change layer and Equipped with, The first phase change layer is in contact with the first electrode and the second phase change layer. The second thickness is less than one-quarter of the first thickness. Phase-change memory (PCM) cell.

4. The PCM cell according to claim 3, wherein the first phase change layer further comprises a dopant material.

5. The PCM cell according to claim 3 or 4, wherein the second phase change layer is essentially made of the undoped second phase change material.

6. The first phase change layer has a first resistivity, The second phase change layer has a second resistivity, The PCM cell according to claim 3, wherein the first resistivity is at least twice the second resistivity.

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