Neuromorphic Devices and Methods (Transfer-Length Phase Change Material (PCM)-Based Bridge Cells)

Abstract

To provide a technology of designing and producing an RPU in which drift is reduced.SOLUTION: There is provided a tunable nonvolatile resistive element in which a device conductance is modulated by changing the length of a contact between a phase change material and a resistive liner. By choosing the contact length to be less than the transfer length, a linear modulation of the conductance is obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to the field of phase change materials, and more specifically to an efficient and practical implementation of a phase change material bridge cell. [Background technology]

[0002] Phase change materials, or PCMs, are materials that can be switched from one phase to another. Based on the properties of their different phases, PCMs have been investigated for use as memory elements for cognitive computing as well as tunable resistors. That is, most PCMs offer a relatively high resistance when in the amorphous phase and a relatively low resistance when in the crystalline phase.

[0003] The resistance processing unit (RPU) stores information based on the resistance of the RPU. During programming, a full SET operation is used to program the RPU to a low resistance state representing a data value such as a logic "1" or logic "0". A subsequent full RESET operation is then used to return the RPU to its previous high resistance state. A partial SET or partial RESET can be used to adjust the RPU to an intermediate resistance state.

[0004] Conventional PCM RPU devices often use a PCM material as a layer placed between two electrodes. For example, the PCM material can be patterned into a bar or fin shape, with two contacts formed on either end of the bar. This configuration is referred to herein as a bridge cell design.

[0005] However, most PCM materials exhibit resistance drift, which is typically more pronounced after a RESET pulse is applied. This drift is undesirable for applications using bridge devices as RPUs.

[0006] Therefore, RPU designs and manufacturing techniques with reduced drift are desirable. Summary of the Invention [Problem to be solved by the invention]

[0007] RPU designs and manufacturing techniques with reduced drift are desirable. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is a neuromorphic device including, but not necessarily limited to, the following components: (i) a phase change material bar structured and configured to have at least two portions joined by a first narrow portion, the first narrow portion being located at a center of the phase change material bar; (ii) a resistive liner located adjacent to the phase change material bar, the resistive liner being a conduit for conducting at least a portion of a first current; (iii) an interfacial layer located between the resistive liner and the phase change material bar, the interfacial layer having a tunable contact resistance; and (iv) a set of ohmic contacts, at least one ohmic contact of the set of ohmic contacts being located at each end of the phase change material bar.

[0009] According to one aspect of the present invention, there is a method of operating a neuromorphic device, the method comprising the following acts (not necessarily in this order): (i) providing a neuromorphic device including a crystalline phase-change portion, a resistive liner, and an engineered interface layer; and (ii) applying a RESET pulse to the device to form an amorphous phase-change portion. According to one aspect of the present invention, the size of the amorphous phase-change portion sets the contact length between the crystalline phase-change portion and the resistive liner. Furthermore, according to one aspect of the present invention, a larger RESET pulse results in a shorter contact length and, correspondingly, a lower conductance.

[0010] According to one aspect of the present invention, there is a method of assembling a neuromorphic device, the method comprising the following acts (not necessarily in the following order): (i) providing a phase change material (PCM) bar including a crystalline phase portion and an amorphous phase portion; (ii) disposing a resistive liner adjacent to the PCM bar; (iii) disposing an engineered interface layer between the PCM bar and the resistive liner, such that the engineered interface layer acts as a contact buffer between the PCM bar and the resistive liner; (iv) forming a pair of ohmic contacts on each end of the PCM bar; and (v) encapsulating the PCM bar. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram of a structure of a first embodiment according to the present invention;

[0012] [Figure 2] FIG. 4 is a block diagram of a second embodiment of the structure according to the present invention.

[0013] [Figure 3] 1 is a block diagram of a cross section of a first embodiment of a structure according to the present invention;

[0014] [Figure 4] FIG. 2 is a block diagram of a cross section of a second embodiment of a structure according to the present invention.

[0015] [Figure 5] 1 is a block diagram of a top view of a first embodiment of a structure according to the present invention; FIG.

[0016] [Figure 6] FIG. 2 is a block diagram of a top view of a second embodiment of a structure according to the present invention.

[0017] [Figure 7] 1 is a graphical representation illustrating information useful in understanding embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Some embodiments of the present invention are directed to tunable nonvolatile resistive elements in which the device conductance is modulated by varying the length of contact between the phase change material and the resistive liner. By selecting the contact length to be shorter than the transfer length, linear modulation of the conductance is obtained.

[0019] Some embodiments of the present invention provide a neuromorphic device that includes at least the following components: (i) a phase change material patterned into a bar with a centrally located narrow portion, (ii) a resistive liner, (iii) an interface layer adjacent to the resistive liner and the phase change material, and (iv) ohmic contacts at each end of the phase change material bar. In some embodiments of the present invention, the phase change material bar (sometimes referred to herein as a PCM bar) is composed of an amorphous phase portion and a crystalline phase portion.

[0020] In some embodiments, the composition and thickness of the engineered interface layer is used to tailor the contact resistance between the phase change material and the resistive liner. Additionally, in some embodiments, the neuromorphic device further includes an insulator region at each end of the resistive liner, thereby effectively limiting the span of the resistive liner on each side to one transfer length measured from the end of the narrow phase change bar portion to the beginning of the insulator region.

[0021] Embodiments of the present invention are constructed from a variety of materials. This paragraph includes some non-limiting, illustrative examples of materials from which various components of a neuromorphic device (as discussed above) are constructed. The phase change material bar can be any of the following: Ge2Sb2Te5, Sb2Te3, or GeTe, or a combination thereof. The resistive liner can include any of TaN, amorphous carbon, or TiN, or a combination thereof. The interface layer can include any of Si3N4, HfO2, Al2O3, SiO2, TiO2, and TaNO.

[0022] In some embodiments of the present invention, the resistance of the neuromorphic device is modulated by varying the contact length between the crystalline portion of the PCM bar and the resistive liner. In some examples, varying the contact length between the crystalline phase change material and the resistive liner is achieved by varying the size of the amorphous phase change material. To further explain the variation in contact length in this context, the resistance of the amorphous phase change material is at least 100 times greater than the resistive liner.

[0023] Some embodiments of the present invention may include one or more of the following features, characteristics, or advantages, or combinations thereof: (i) conduction is through a resistive liner; (ii) mitigation of resistive drift can occur at any level of applied resistance; (iii) conductance is approximately linear with respect to the size of the amorphous region; (iv) contact resistance can be tuned by liner selection or by engineering the liner / crystalline phase PCM interface; (v) the range of resistance that the neuromorphic device can provide is from the liner resistance (low end) to an arbitrarily high resistance, as long as the current does not flow through the amorphous region; and (vi) the neuromorphic device can be implemented as a vertical or horizontal bridge cell. In some embodiments of the present invention, the effective contact length (L C ) is the contact length is the transfer length L T shorter than (i.e., L C < <L T), which is modulated by changing the size of the amorphous phase portion of the PCM bar.

[0024] Transfer length L T is calculated using the following formula (F1):

number

[0025] In this formula (F1), ρ C represents the contact resistance between a liner (such as liner 106 described below in connection with the description of FIG. 1 ) and a crystalline portion of the PCM bar (such as crystalline portion 104 described below). LINER ) represents the value of the sheet resistance of the liner film, and the resistance variable (R GST ) represents the value of the sheet resistance of the PCM bar material (typically referring to the crystalline phase portion). In some embodiments of the present invention, the liner resistance is selected to be approximately equal to the c-PCM resistance, but much lower than the amorphous PCM (a-PCM) resistance. The liner resistance is calculated by R LINER < <R a-PCM and the resulting current applied to the PCM bar material is R a-PCM R LINER , which is very high compared to the flow through the resistive liner (as further shown in the figure below).

[0026] The following description of the figures (FIGS. 1-6) describes various embodiments of the present invention, including the structure, manufacture, and method of operation of the PCM bar.

[0027] The diagram 100 in FIG. 1 shows the contact length (L C ) is the transfer length L T 1. Diagram 100 is a cross-sectional view of a phase change material bar larger than 102. Diagram 100 includes the following components: amorphous phase portion 102, crystalline phase portion 104, and resistive liner 106. The contact length (L C ) is significantly longer than the transport length (i.e., L C >>L T), the device resistance is mostly the resistance of the c-PCM and the resistive liner. The contribution of the contact resistance is small.

[0028] Diagram 200 of FIG. 2 shows the contact length (L C ) is the transfer length L T 2 is a cross-sectional view of a phase change material bar smaller than 100. Diagram 200 includes the following components: amorphous phase portion 202, crystalline phase portion 204, and resistive liner 206.

[0029] The contact length (L) between the liner and crystalline phase portion 204 and the resistive liner 206 C ) is less than the transport length, the device resistance becomes dominated by the contact resistance. The contributions of the c-PCM resistance and the resistive liner resistance to the total resistance are small. As the contact length decreases further, the device resistance decreases by 1 / L C or the conductance of the device is approximately proportional to L C is proportional to.

[0030] Because the PCM bar in the amorphous phase has low conductivity, the applied current typically does not flow through the amorphous phase portions 102 and 202. However, as the contact length decreases and the resistance contribution from the contact reaches the resistance of the a-PCM, the above assumption is no longer valid.

[0031] Diagram 300 in FIG. 3 is a cross-sectional view of a bridge PCM device after a "weak RESET" that forms an amorphous PCM region 306 in a narrow portion of the PCM bar. A top view of the same device is shown in diagram 500. Diagram 300 includes the following components: ohmic contact 302, ohmic contact 304, amorphous PCM portion 306, oxide layer 308, oxide layer 310, crystalline PCM portion 312, engineered tuning interface 314, and resistive liner 316. As discussed above in connection with FIG. 1, the contact length between crystalline portion 312 and resistive liner 316 is approximately one transport length. In some embodiments of the invention, the material selected to engineer tuning interface 314 is selected to provide a low contact resistance (ρ C) Determining the contact resistance ultimately determines the transfer length (as discussed above in connection with Equation F1). Thus, the overall resistance of the PCM bar can be adjusted or tuned by changing the material of the engineered interface 314. The total resistance of the device in this weak RESET case is roughly the resistance of the c-PCM portion plus the resistance of the liner under the a-PCM.

[0032] Diagram 400 in Figure 4 is a cross-sectional view of a bridge PCM device after "strong RESET," which forms an amorphous PCM region 406 in a narrow portion of the PCM bar and extends further into the wider portion of the PCM bar. A top view of the same device is shown in diagram 600. Diagram 400 includes the following components: ohmic contact 402, ohmic contact 404, amorphous PCM portion 406, oxide layer 408, oxide layer 410, crystalline PCM portion 412, engineered interface 414, and resistive liner 416. The total resistance of the device in strong RESET in this case is dominated by the contact resistance. The total resistance is determined by ρ C / (W*L C ) plus the resistance of the c-PCM section and the liner under the a-PCM. W is the width of the contact, and L C is the length of the contact area.

[0033] A distinction is made between programming and read operations. In a programming operation, a large amplitude RESET pulse is applied to the device terminals 402 and 404, causing the PCM to change phase. The RESET pulse is intended to melt and quench the PCM, leaving the solidified material in the amorphous phase. The size of the amorphous PCM 406 during a RESET operation is proportional to the electrical pulse amplitude applied to the PCM bar. Another programming operation is SET, which reduces the size of the amorphous regions and may even cause them to become completely crystalline. SET pulses usually have a smaller amplitude than RESET, and in most cases, the pulse has a longer trailing edge. The RESET and SET operations can be used to adjust the device's resistance to a desired value. When a read operation is performed, a small amplitude pulse is used to prevent the size of the amorphous PCM region from changing.

[0034] It is important to note that during a read operation, conduction of a steady current (or electrical pulse) applied to the device flows primarily through the c-PCM portion 412 to the resistive liner 416. No substantial current passes through the amorphous region 406. This has the effect of reducing resistance drift, as most of the resistance drift occurs in the amorphous phase of the PCM.

[0035] Diagram 500 in Figure 5 is a top view of the bridge PCM material during a "weak RESET" operation. Diagram 500 includes the following components: ohmic contact 502, ohmic contact 504, first crystalline phase portion 506, second crystalline phase portion 508, and amorphous phase portion 510. In some embodiments of the invention, portions 506 and 508 can be considered the same portion.

[0036] Diagram 600 in Figure 6 is a top view of the bridge PCM material during a "strong RESET" operation. Diagram 600 includes the following components: ohmic contact 602, ohmic contact 604, first crystalline phase portion 606, second crystalline phase portion 608, and amorphous phase portion 610. In some embodiments of the present invention, portions 606 and 608 can be considered the same portion.

[0037] In some embodiments of the invention, the PCM bars are encapsulated (not shown in the figures), sometimes in silicon nitride (Si3N4), HFO2, and many other materials.

[0038] Graph 700 of FIG. 7 shows the relationship between the contact resistance (ρ C ) (discussed above in connection with Equation F1), and the transfer length (L T ) and the resistance of the resistive liner (R LINER ) is a graph showing the relationship between

[0039] Graph 700 has a low resistance R LINER Selecting indicates a longer transfer length (or multiple transfer lengths).

[0040] Some embodiments of the present invention recognize that the choice of engineered interface layer material (such as engineered interface 414) is ultimately decisive in the strength and polarity of the interface dipole. Some embodiments recognize that (i) the strength and polarity of the interface dipole can be controlled by the geometric mean electronegativity, (ii) oxides with high geometric mean electronegativity create a high barrier height between the PCM and the liner material, and (iii) ρ C When ρ is high, a dielectric material with high geometric mean electronegativity (e.g., TiO2, Al2O3, SiO2) should be selected, and (iv) ρ C It is further recognized that when ρ is low, a dielectric material with low geometric mean electronegativity (such as Group 2A and Group 3B oxides) should be selected.

[0041] The following chart (Table 1) is provided as an exemplary reference for selecting materials for engineered interface layers. Additionally, the geometric mean electronegativity value is calculated using the Sanderson Criterion. The geometric mean electronegativity value is calculated using the following formula: (A X B Y ) 1 / x+y It is calculated using [Table 1] [Table 1]

[0042] The description of various embodiments of the present invention has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terms used herein have been selected to best explain the principles of the embodiments, practical applications or technical improvements to technology found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

[0043] The following paragraphs provide definitions of certain words or terms that are necessary for the understanding and / or interpretation of this document.

[0044] The present invention: The term "the present invention" should not be construed as an absolute indication that the subject matter described is encompassed by either the claims as filed or the claims that may ultimately be issued after patent prosecution. The term "the present invention" is used to help the reader get a general sense that the disclosures herein are believed to be potentially novel, but this understanding, as indicated by the use of the term "the present invention," is temporary and provisional, and is subject to change throughout the course of patent prosecution as relevant information is developed and as the claims are potentially revised.

[0045] Embodiments: See definition of "present invention" above. A similar caution applies to the term "embodiments."

[0046] Or...or both (combinations thereof): Inclusive, or for example, A, B "or" C "or combinations thereof," means that at least one of A, B, or C is true and applicable.

[0047] Including / include / includes: Unless otherwise specified, means "including but not necessarily limited to."

[0048] Receive / Provide / Send / Input / Output / Report: Unless otherwise specified, these words should not be construed to imply (i) any particular degree of directness in the relationship between object and subject, or (ii) the absence of intermediate components, actions, or things, or a combination thereof, between object and subject, or both.

[0049] Comprise / comprises / comprising: As used herein (particularly outside the claims), this term is intended to be fully synonymous with the term "include" and its various conjugations (as defined herein). The term "comprises" (and its various conjugations) as used in the claims should be interpreted in a manner consistent with the interpretation of the claims.

[0050] Without Substantial Human Intervention: A process that occurs automatically (often through the operation of machine logic such as software) with little or no human input. Some examples that involve "without substantial human intervention" include (i) a computer performing a complex process and a grid power outage causes a human to switch the computer to an alternate power source so that the process continues uninterrupted; (ii) a computer is about to perform a resource-intensive process and a human confirms that the resource-intensive process should actually be performed (in this case, the confirmation process, considered in isolation, involves substantial human intervention, but the resource-intensive process does not involve any substantial human intervention, despite a simple yes-no style confirmation that must be made by a human); and (iii) using machine logic, a computer makes an important decision (e.g., a decision to ground all planes in anticipation of bad weather), but before implementing the important decision, the computer must obtain a simple yes-no style confirmation from a human source.

[0051] Automatically: Without human intervention.

[0052] [Explanation of symbols] 102 amorphous phase portion, 104 crystalline phase portion, 106 liner, 202 amorphous phase portion, 204 crystalline phase portion, 206 resistive liner, 302 contact, 304 contact, 306 amorphous PCM portion, 308 oxide layer, 310 oxide layer, 312 crystalline PCM portion, 314 engineered interface, 316 resistive liner, 402 contact, 404 contact, 406 amorphous PCM portion, 408 oxide layer, 410 oxide layer, 412 crystalline PCM portion, 414 engineered interface, 416 resistive liner, 502 contact, 504 contact, 506 first crystalline phase portion, 508 second crystalline phase portion, 510 amorphous phase portion, 602 contact, 604 contact, 606 First crystalline phase portion, 608, second crystalline phase portion, 610, amorphous phase portion, LC, contact length, LT, transport length According to this specification, the following items are also disclosed. [Item 1] A neuromorphic device, a phase change material bar structured and configured to have at least two portions joined by a first narrow portion, the first narrow portion being located at the center of the phase change material bar; a resistive liner located adjacent the phase change material bar, the resistive liner being a conduit for conducting at least a portion of a first electrical current; an interface layer located between the resistive liner and the phase change material bar, the interface layer having a tunable contact resistance; a set of ohmic contact portions, at least one ohmic contact of the set of ohmic contact portions being located at each end of the phase change material bar; Neuromorphic devices, including: [Item 2] 2. The neuromorphic device of item 1, wherein the resistive liner includes an insulator region located at each end of the resistive liner, the insulator region comprising a material designed to limit the span of the resistive liner to one transfer length. [Item 3] 3. The neuromorphic device of claim 2, wherein the contact length is measured from an end of the amorphous phase portion of the phase change material bar to a first end of the insulator region. [Item 4] 3. The neuromorphic device of claim 1 or 2, wherein the phase change material bar comprises at least a first crystalline phase portion and at least a first amorphous phase portion. [Item 5] Item 5. The neuromorphic device of item 4, wherein at least the first crystalline phase portion is located in a first portion of the phase change material bar. [Item 6] 3. The neuromorphic device according to item 1 or 2, wherein an amorphous phase portion is initially formed in the first narrow portion of the phase change material bar. [Item 7] 3. The neuromorphic device according to item 1 or 2, wherein the contact length is adjusted by modulating the amorphous phase fraction of the phase change material bar. [Item 8] 8. The neuromorphic device of any one of items 1 to 7, wherein the tunable contact resistance of the interface layer is the product of the composition and thickness of the interface layer. [Item 9] Item 9. The neuromorphic device of item 8, wherein the tunable contact resistance of the interface layer is used to tune the contact resistance between the phase change material bar and the resistive liner. [Item 10] 3. The neuromorphic device of claim 1 or 2, wherein the resistance of the neuromorphic device is modulated by adjusting a first contact length between a first crystalline phase portion of the phase change material bar and the resistive liner. [Item 11] 3. The neuromorphic device of claim 1 or 2, wherein resistance drift is mitigated by conducting the first current from a crystalline phase portion of the phase change material bar through the resistive liner during a read operation. [Item 12] Item 11. The neuromorphic device of item 10, wherein the resistance of the neuromorphic device is increased by decreasing the first contact length between the first crystalline phase portion of the phase change material bar and the resistive liner. [Item 13] Item 11. The neuromorphic device of item 10, wherein the resistance of the neuromorphic device is decreased by increasing the first contact length between the first crystalline phase portion of the phase change material bar and the resistive liner. [Item 14] 3. The neuromorphic device of claim 1 or 2, wherein a resistance of the first amorphous phase portion of the phase change material bar allows up to one percent (1%) of the first current to flow through the first amorphous phase portion. [Item 15] 3. The neuromorphic device of claim 1 or 2, wherein when the length of contact between the crystalline phase portion and the resistive liner is shorter than one transport length, the electronic conductance between the pair of ohmic contacts is approximately linearly proportional to the length of the contact. [Item 16] 16. The neuromorphic device of any one of items 1 to 15, wherein the phase change material bar is composed of at least one of Ge2Sb2Te5, Sb2Te3, and GeTe. [Item 17] 17. The neuromorphic device of any one of items 1 to 16, wherein the resistive liner is composed of at least one of TaN, amorphous carbon, and TiN. [Item 18] 18. The neuromorphic device of any one of items 1 to 17, wherein the interface layer is composed of at least one of Si3N4, HfO2, Al2O3, SiO2, TiO2 and TaNO. [Item 19] providing a neuromorphic device comprising a crystalline phase change portion, a resistive liner, and an engineered interface layer; applying a RESET pulse to the neuromorphic device to form an amorphous phase change portion; Including, a size of the amorphous phase change portion sets a contact length between the crystalline phase change portion and the resistive liner; The larger the RESET pulse, the shorter the contact length and the correspondingly lower the conductance. method. [Item 20] 1. A method for assembling a neuromorphic device, comprising: providing a phase change material (PCM) bar comprising a crystalline phase portion and an amorphous phase portion; disposing a resistive liner adjacent to the PCM bar; disposing an engineered interface layer between the PCM bar and the resistive liner, the engineered interface layer acting as a contact buffer between the PCM bar and the resistive liner; forming a pair of ohmic contacts on each end of the PCM bar; encapsulating the PCM bar; A method comprising:

Claims

1. 1. A neuromorphic device, comprising: a phase change material bar structured and configured to have at least two portions joined by a first portion, the first portion being located at a center of the phase change material bar; a resistive liner located adjacent the phase change material bar, the resistive liner being a conduit for conducting at least a portion of a first electrical current; an interface layer located between the resistive liner and the phase change material bar, the interface layer having a tunable contact resistance; a set of ohmic contact portions, at least one ohmic contact of the set of ohmic contact portions being located at each end of the phase change material bar; Neuromorphic devices, including

2. 2. The neuromorphic device of claim 1, wherein the resistive liner includes an insulator region located at each end of the resistive liner, the insulator region comprising a material designed to limit the span of the resistive liner to one transfer length.

3. The neuromorphic device of claim 2 , wherein a contact length is measured from an end of the amorphous phase portion of the phase change material bar to a first end of the insulator region.

4. The neuromorphic device of claim 1 or 2, wherein the phase change material bar comprises at least a first crystalline phase portion and at least a first amorphous phase portion.

5. The neuromorphic device of claim 4 , wherein at least the first crystalline phase portion is located in a second portion of the phase change material bar.

6. The neuromorphic device of claim 1 or 2, wherein an amorphous phase portion is initially formed in the first portion of the phase change material bar.

7. The neuromorphic device of claim 1 or 2, wherein the contact length is adjusted by modulating the amorphous phase portion of the phase change material bar.

8. The neuromorphic device of claim 1 , wherein the tunable contact resistance of the interface layer is adjusted by the composition and thickness of the interface layer.

9. The neuromorphic device of claim 8 , wherein the tunable contact resistance of the interface layer is used to adjust the contact resistance between the phase change material bar and the resistive liner.

10. 3. The neuromorphic device of claim 1, wherein the resistance of the neuromorphic device is modulated by adjusting a first contact length between the first crystalline phase portion of the phase change material bar and the resistive liner.

11. 3. The neuromorphic device of claim 1, wherein resistance drift is mitigated by conducting the first current from a crystalline phase portion of the phase change material bar through the resistive liner during a read operation.

12. 11. The neuromorphic device of claim 10, wherein the resistance of the neuromorphic device is increased by decreasing the first contact length between the first crystalline phase portion of the phase change material bar and the resistive liner.

13. 11. The neuromorphic device of claim 10, wherein the resistance of the neuromorphic device is decreased by increasing the first contact length between the first crystalline phase portion of the phase change material bar and the resistive liner.

14. 3. The neuromorphic device of claim 1 or 2, wherein a resistance of a first amorphous phase portion of the phase change material bar allows up to one percent (1%) of the first current to flow through the first amorphous phase portion.

15. 3. The neuromorphic device of claim 1, wherein when the length of contact between the crystalline phase portion and the resistive liner is shorter than one transport length, the electronic conductance between the set of ohmic contacts is approximately linearly proportional to the length of the contact.

16. 16. The neuromorphic device of claim 1, wherein the phase change material bar is composed of at least one of Ge2Sb2Te5, Sb2Te3, and GeTe.

17. 17. The neuromorphic device of claim 1, wherein the resistive liner is composed of at least one of TaN, amorphous carbon, and TiN.

18. 18. The neuromorphic device of claim 1, wherein the interface layer is composed of at least one of Si3N4, HfO2, Al2O3, SiO2, TiO2, and TaNO.

19. providing a neuromorphic device comprising a crystalline phase change portion, a resistive liner, and an engineered interface layer, the engineered interface layer being located between the crystalline phase change portion and the resistive liner to adjust contact resistance between the crystalline phase change portion and the resistive liner, a pair of ohmic contacts being formed on each end of the crystalline phase change portion, and the resistive liner being a conduit for conducting at least a portion of an electrical current; applying a RESET pulse to the set of ohmic contacts of the neuromorphic device to change the phase of the crystalline phase change portion to form an amorphous phase change portion, the size of the amorphous phase change portion being proportional to the amplitude of the RESET pulse; Including, the size of the amorphous phase change portion sets a contact length between the crystalline phase change portion and the resistive liner; the greater the amplitude of the RESET pulse, the shorter the contact length and the correspondingly lower the conductance of the neuromorphic device. method.

20. 1. A method for assembling a neuromorphic device, comprising: providing a phase change material (PCM) bar comprising a crystalline phase portion and an amorphous phase portion; disposing a resistive liner adjacent to the PCM bar; disposing an engineered interface layer between the PCM bar and the resistive liner; forming a pair of ohmic contacts on each end of the PCM bar; encapsulating the PCM bar; A method comprising:

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