Array of cross point memory cells

Abstract

An array of cross point memory cells comprises spaced first lines which cross spaced second lines. Two memory cells are individually between one of two immediately adjacent of the second lines and a same single one of the first lines.

Description

TECHNICAL FIELD

Embodiments disclosed herein pertain to arrays of cross point memory cells.

BACKGROUND

Memory is one type of integrated circuitry, and is used in computer systems for storing data. Memory may be fabricated in one or more arrays of individual memory cells. Memory cells may be written to, or read from, using digit lines (which may also be referred to as bit lines, data lines, sense lines, or data/sense lines) and access lines (which may also be referred to as word lines). The digit lines may conductively interconnect memory cells along columns of the array, and the access lines may conductively interconnect memory cells along rows of the array. Each memory cell may be uniquely addressed through the combination of a digit line and an access line.

Memory cells may be volatile or non-volatile. Non-volatile memory cells can store data for extended periods of time including when the computer is turned off. Volatile memory dissipates and therefore requires being refreshed/rewritten, in many instances multiple times per second. Regardless, memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.

A capacitor is one type of electronic component that may be used in a memory cell. A capacitor has two electrical conductors separated by electrically insulating material. Energy as an electric field may be electrostatically stored within such material. One type of capacitor is a ferroelectric capacitor which has ferroelectric material as at least part of the insulating material. Ferroelectric materials are characterized by having two stable polarized states and thereby can comprise programmable material of a memory cell. The polarization state of the ferroelectric material can be changed by application of suitable programming voltages, and remains after removal of the programming voltage (at least for a time). Each polarization state has a different charge-stored capacitance from the other, and which ideally can be used to write (i.e., store) and read a memory state without reversing the polarization state until such is desired to be reversed. Less desirable, in some memory having ferroelectric capacitors the act of reading the memory state can reverse the polarization. Accordingly, upon determining the polarization state, a re-write of the memory cell is conducted to put the memory cell into the pre-read state immediately after its determination. Regardless, a memory cell incorporating a ferroelectric capacitor ideally is non-volatile due to the bi-stable characteristics of the ferroelectric material that forms a part of the capacitor. One type of memory cell has a select device electrically coupled in series with a ferroelectric capacitor.

Another type of non-volatile memory is phase change memory. Such memory uses a reversibly programmable material that has the property of switching between two different phases, for example between an amorphous disorderly phase and a crystalline or polycrystalline orderly phase. The two phases may be associated with resistivities of significantly different values. Presently, typical phase change materials are chalcogenides, although other materials may be developed. With chalcogenides, the resistivity may vary by two or more orders of magnitude when the material passes between the amorphous (more resistive) phase and the crystalline (more conductive) phase. Phase change can be obtained by locally increasing the temperature of the chalcogenide. Below 150° C., both phases are stable. Starting from an amorphous state and rising to temperature above about 400° C., a rapid nucleation of crystallites may occur and, if the material is kept at the crystallization temperature for a sufficiently long time, it undergoes a phase change to become crystalline. Reversion to the amorphous state can result by raising the temperature above the melting temperature (about 600° C.) followed by cooling.

Other reversibly programmable materials for memory cells exist and undoubtedly will be developed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic isometric view of a substrate fragment comprising a portion of an array of cross point memory cells in accordance with an embodiment of the invention.

FIG. 2 is an enlarged side-elevational view of the FIG. 1 substrate.

FIG. 3 is an enlarged diagrammatic top view the FIG. 1 substrate at the same scale as that of FIG. 2.

FIG. 4 is an enlarged side-elevational view like FIG. 2 and emphasizes an example outline of a single memory cell.

FIG. 5 is an enlarged side-elevational view like FIG. 2 and emphasizes an example outline of a single memory cell.

FIG. 6 is an enlarged side-elevational view like FIG. 2 and emphasizes an example outline of a single memory cell.

FIG. 7 is an enlarged side-elevational view like FIG. 2 and emphasizes an example outline of a single memory cell.

FIG. 8 is an enlarged side-elevation view like FIG. 2 and emphasizes example outlines of four memory cells in combination.

FIG. 9 is an enlarged side-elevational view like FIG. 2 and emphasizes current flow paths of seven memory cells.

FIG. 10 is a diagrammatic isometric view of a substrate fragment comprising a portion of an array of cross point memory cells in accordance with an embodiment of the invention.

FIG. 11 is an enlarged top view of the FIG. 10 substrate.

FIG. 12 is a diagrammatic isometric view of a substrate fragment comprising a portion of an array of cross point memory cells in accordance with an embodiment of the invention.

FIG. 13 is a diagrammatic schematic diagram of two memory cells in accordance with an embodiment of the invention.

FIG. 14 is a diagrammatic schematic diagram of two memory cells in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the invention encompass an array of cross point memory cells. FIGS. 1-9 show a small portion of a substrate construction 8 comprising an array 10 of individual cross point memory cells that has been fabricated relative to a base substrate 11. Substrate 11 may comprise any one or more of conductive (i.e., electrically herein), semiconductive, or insulative/insulator (i.e., electrically herein) materials. Various materials have been formed elevationally over base substrate 11. In this document, “elevational”, “upper”, “lower”, “top”, “bottom”, and “beneath” are generally with reference to the vertical direction. “Horizontal” refers to a general direction along a primary surface relative to which the substrate is processed during fabrication, and vertical is a direction generally orthogonal thereto. Further, “vertical” and “horizontal” as used herein are generally perpendicular directions relative one another and independent of orientation of the substrate in three-dimensional space.

Materials may be aside, elevationally inward, or elevationally outward of the FIG. 1-depicted materials. For example, other partially or wholly fabricated components of integrated circuitry may be provided somewhere above, about, or within fragment 11. Control and/or other peripheral circuitry for operating components within the memory array may also be fabricated, and may or may not wholly or partially be within a memory array or sub-array. Further, multiple sub-arrays may also be fabricated and operated independently, in tandem, or otherwise relative one another. As used in this document, a “sub-array” may also be considered as an array. Regardless, any of the materials, regions, and structures described herein may be homogenous or non-homogenous, and regardless may be continuous or discontinuous over any material which such overlie. Further, unless otherwise stated, each material may be formed using any suitable or yet-to-be-developed technique, with atomic layer deposition, chemical vapor deposition, physical vapor deposition, epitaxial growth, diffusion doping, and ion implanting being examples.

In one embodiment, array 10 comprises spaced lower first lines 14A, 14B, and 14C (also referred to as first lines 14 collectively and as individual first line[s] 14) and spaced upper second lines 16A, 16B, 16C, 16D, 16E, and 16F (also referred to as second lines 16 collectively and as individual second line[s] 16) which cross first lines 14. Reference to “first” and “second” with respect to different components herein is only for convenience in description in referring to different components. Accordingly, “first” and “second” may be interchanged independent of relative position within the finished circuit construction and independent of sequence in fabrication. Lines 14 and 16 comprise conductive material, with examples being elemental metals, a mixture or alloy of two or more elemental metals, conductive metal compounds, and conductively-doped semiconductive materials. Lines 14 and 16 may be of the same composition or of different compositions relative one another. In one embodiment, first lines 14 and second lines 16 angle other than orthogonally relative one another, and in one embodiment at an angle of about 45°. In one embodiment, the first and second lines are straight linear within the array. In one embodiment, lines 14 are access or word lines and lines 16 are sense or bit lines. Dielectric material 15 is between individual first lines 14. Analogously, dielectric material would be between immediately adjacent second lines 16 but is not shown for clarity.

Two memory cells are individually elevationally between one of two immediately adjacent of the second lines and a same single one of the first lines. The two memory cells overlap and/or share some component(s), for example a same first line, and are accordingly difficult to show and perceive when example outlines of numerous memory cells of the array are shown and designated with numerals in a single figure. Accordingly, example outlines of individual memory cells are not shown or designated with numerals in FIGS. 1-3 and other figures are provided showing example individual memory cells to assist the reader. Specifically, FIGS. 4-8 collectively show four example memory cell outlines 12A, 12B, 12C, and 12D (also referred to as memory cells 12 collectively and as individual memory cell[s] 12). FIGS. 4-8 are the same essential FIG. 2-side elevational views of the FIG. 1 substrate yet designate only one or four memory cells 12A, 12B, 12C, and/or 12D. Specifically, FIG. 4 shows an example thick solid-line outline of only memory cell 12A. FIG. 5 shows an example thick solid-line outline of only memory cell 12B. FIG. 6 shows an example thick solid-line outline of only memory cell 12C. FIG. 7 shows an example thick solid-line outline of only memory cell 12D. FIG. 8 shows the outlines of memory cells 12A, 12B, 12C, and 12D taken together, and using two different style thick dashed-lines. Example outlines of immediately adjacent individual memory cells (e.g., 12A/12B, 12B/12C, 12C/12D) are shown as being elevationally staggered for ease of depiction in FIGS. 4-8.

Referring primarily to FIGS. 4, 5, and 8, the two memory cells 12A and 12B are individually elevationally between one of two immediately adjacent of the second lines (12A with 16D, and 12B with 16E) and a same single one 14B of first lines 14. Referring primarily to FIGS. 6-8, the two memory cells 12C and 12D are individually elevationally between one of two immediately adjacent of the second lines (12C with 16E, and 12D with 16F) and a same single one 14C of first lines 14.

Individual memory cells 12 comprise a select device 18 (the three on the front right face of construction 8 being labeled 18A, 18B, and 18C) and a programmable device 20 in series (i.e., electrical) with each other. Select device 18 is proximate (e.g., more so than is the programmable device) and electrically coupled to one of first lines 14 or one of second lines 16. Programmable device 20 is proximate (e.g., more so than is the select device) and electrically coupled to one of the other of a first line 14 or a second line 16. In one embodiment, select device 18 is directly electrically coupled to the one first or second line and in one embodiment programmable device 20 is directly electrically coupled to the one of the other first or second line. In this document, two electronic devices or components are “electrically coupled” to one another if in normal operation electric current is capable of continuously flowing from one to the other, and does so predominately by movement of subatomic positive and/or negative charges when such are sufficiently generated. Another electronic component may be between and electrically coupled to the two electrically coupled electronic components or devices. In contrast, when two electronic components or devices are referred to as being “directly electrically coupled”, no intervening electronic component is between the two directly electrically coupled components or devices. In the example FIGS. 1-9 embodiments, select device 18 is proximate and directly electrically coupled to one of first lines 14 and programmable device 20 is proximate and directly electrically coupled to one of second lines 16. Any existing or yet-to-be developed select devices may be used, for example a junction device or a diode. Example diodes include PN diodes, PIN diodes, Schottky diodes, Zener diodes, avalanche diodes, tunnel diodes, diodes having more than three materials, etc. As an additional example, select device 18 may be a junction bipolar transistor. Select device 18 may include an elevationally outer and/or elevationally inner conductive material as a part thereof (not specifically shown).

Individual programmable devices 20 comprise a first electrode 22 (the front three being labeled 22A, 22B, and 22C) in the form of a conductive pillar elevationally over one of first lines 14. In this document, a “pillar electrode” and a “conductive pillar” is a conductive structure that is of radially continuous conductive material(s) longitudinally along at least a majority of its length. First pillar electrodes 22 individually comprise a top 24 and sidewalls 26 and 27 (FIGS. 2 and 4-7). Any suitable conductive material(s) may be used for first pillar electrodes 22, with TiN being one example. Individual first pillar electrodes 22 are shared by the two memory cells. For example as shown, first pillar electrode 22B is shared by memory cells 12A and 12B (FIGS. 4, 5, and 8), and first pillar electrode 22C is shared by memory cells 12C and 12D (FIGS. 6-8).

For an individual memory cell 12, programmable device 20 comprises programmable material 28 laterally outward of one of opposing sidewalls 26, 27 of an individual first pillar electrode 22. For example in memory cell 12A, programmable material 28 is at least laterally outward of sidewall 26 of first pillar electrode 22B (FIG. 4). For example in memory cell 12B, programmable material 28 is at least laterally outward of sidewall 27 of first pillar electrode 22B (FIG. 5). For example in memory cell 12C, programmable material 28 is at least laterally outward of sidewall 26 of first pillar electrode 22C (FIG. 6). For example in memory cell 12D, programmable material 28 is at least laterally outward of sidewall 27 of first pillar electrode 22C (FIG. 7). In one embodiment and as shown, programmable material 28 is elevationally over pillar top 24, and in one embodiment comprises a continuous layer extending over opposing sidewalls 26, 27 and top 24 of individual first pillar electrodes 22. Any existing or yet-to-be-developed programmable material may be used, for example those described in the “Background” section above.

Programmable device 20 includes a second electrode 30 (the three on the front right face of construction 8 being labeled 30A, 30B, and 30C) outward of the programmable material 28 that is laterally over the one opposing sidewall 26 or 27 of first pillar electrode 22. In one embodiment and as shown, individual second electrodes 30 are in the form of a conductive pillar. Second electrode 30 may be of the same or different composition from that of first pillar electrode 22, and may be of the same or different composition from second lines 16. In the depicted example, second electrode 30 is shown to be of different conductive composition than second lines 16. Regardless, second electrodes 30 may be considered as part of or an elevational extension of a conductive line 16. In one embodiment, programmable material 28 is beneath second electrode 30 between two immediately adjacent first lines 14. Further in one embodiment, programmable material 28 is continuous over multiple tops 24 and sidewalls 26, 27 of multiple first pillar electrodes 22, and beneath multiple second electrodes 30 between immediately adjacent first lines 14. In one embodiment, first pillar electrode 22 has a maximum conductive material width that is greater than that of second electrode 30 laterally proximate the programmable material that is laterally outward of the one opposing sidewall 26 or 27 of first pillar electrode 22. In one embodiment, first pillar electrode 22 has a maximum conductive material volume that is greater than that of second electrode 30. Regardless, in one embodiment programmable device 20 is a ferroelectric capacitor with programmable material 28 thereby comprising ferroelectric material.

The first pillar electrode or the second electrode is electrically coupled to the select device (in one embodiment directly electrically coupled) and the other of the first pillar electrode or the second electrode is electrically coupled (in one embodiment directly electrically coupled) to one of the first or second lines. In the depicted embodiment where select device 18 is proximate and electrically coupled to a first line 14, first pillar electrode 22 is elevationally over and electrically coupled to select device 18. Second electrode 30 is electrically coupled to one of second lines 16, and again may be considered as comprising a part thereof.

FIG. 9 is provided to further assist the reader in perceiving the individual memory cells. FIG. 9 is essentially a repeat of FIG. 2 and wherein most of the numeral designations are removed for clarity. FIG. 9 shows in respective solid lines example current paths for memory cells 12A, 12B, 12C, and 12D. A solid-line current path 12X and a solid-line current path 12Y are shown for the two memory cells that would be to the immediate left of memory cell 12A. A solid-line current path 12Z is shown for the memory cell that would be to the immediate right of memory cell 12D.

FIG. 13 is a diagrammatic schematic showing two immediately adjacent memory cells of the FIGS. 1-9 construction, specifically showing memory cells 12A and 12B comprising second lines 16D and 16E, individual programmable devices 20, shared select device 18B, and single first line 14B.

In one embodiment, the second electrodes individually comprise a non-shared conductive pillar comprising a pair of laterally outermost corner edges and the second lines having laterally outermost longitudinal sidewalls. For example, as designated in FIG. 3, second electrodes 30 are non-shared with respect to any other second pillar electrode 30 for immediately adjacent memory cells and may be considered as having respective pairs of laterally outermost corner edges 31. Second lines 16 have laterally outermost sidewalls 33. In one embodiment and as shown, sidewalls 33 laterally align elevationally over the pairs of laterally outermost corner edges 31 of the non-shared conductive pillars along second lines 16. FIGS. 10 and 11 show an alternate example embodiment construction 8a to that shown in FIGS. 1-9 wherein no laterally outermost longitudinal sidewall of the second lines laterally aligns with any laterally outermost corner edge of the non-shared conductive pillars. Like numerals from the above-described embodiments have been used where appropriate, with some construction differences being indicated with the suffix “a”. In array 10a, laterally outermost longitudinal sidewalls 33 do not align with any laterally outermost corner edge 31 of non-shared conductive pillars 30. Any other attribute(s) or aspect(s) as described above and/or shown generally in FIGS. 1-9 may be used in the FIGS. 10 and 11 embodiments.

FIG. 12 shows an alternate embodiment construction 8b to that shown in FIG. 1. Like numerals from the above-described embodiments have been used where appropriate, with some construction differences being indicated with the suffix “b”. In array 10b, individual memory cells have select device 18 proximate (e.g., more so than the programmable device) and electrically coupled to one of second lines 16. Programmable device 20 is proximate (e.g., more so than the select device) and electrically coupled to one of first lines 14. Accordingly, individual first pillar electrodes 22 are elevationally over, proximate, and electrically coupled to one first line 14 and individual second electrodes 30 are electrically coupled to one select device 18. Thereby, each memory cell has its own non-shared select device.

FIG. 14 is a diagrammatic schematic showing two immediately adjacent memory cells of the FIG. 12 construction, specifically showing two immediately adjacent memory cells individually comprising a second line 16D or 16E, individual programmable devices 20, non-shared select devices 18, and single first line 14B.

Other attribute(s) or aspect(s) as described above and/or shown generally in FIGS. 1-11 may be used in the FIGS. 12 and 14 embodiments.

Embodiments of the invention encompass an array of cross point memory cells (e.g., 12) comprising spaced first lines (e.g., 14) which cross spaced second lines (e.g., 16, and independent of any elevational arrangement of the first lines relative to the second lines). Two memory cells are individually between one of the two immediately adjacent of the second lines and a same single one of the first lines (independent of presence of a select device, programmable material, and/or a shared pillar electrode). In one embodiment, the memory cells comprise select devices (e.g., 18), and in one embodiment comprise one select device for every memory cell (e.g., FIG. 14) and in another embodiment comprise one select device for every two memory cells (e.g., FIG. 13). In one embodiment, the two memory cells each comprise programmable material (e.g., 28) and a single shared select device electrically coupled to the one first line and electrically coupled to the programmable material of each of the two memory cells. In one embodiment, the two memory cells each comprise programmable material and two non-shared select devices individually electrically coupled to a respective one of the two immediately adjacent second lines and electrically coupled to the programmable material of a different one of the two memory cells.

In one embodiment, the first and second lines angle relative one another other than orthogonally, and in one such embodiment at about 45°. In one embodiment, the second lines are elevationally outward of the first lines. In one embodiment, the first and second lines are individually straight linear within the array. In one embodiment, the two memory cells are individually elevationally elongated and share an elevationally elongated conductive pillar, and in one embodiment which is elevationally over the one first line. In one embodiment, the two memory cells are individually elevationally elongated and collectively comprise a shared elevationally elongated conductive pillar (e.g., 22) and two non-shared elevationally elongated conductive pillars (e.g., 30). In one such embodiment, the two non-shared conductive pillars are individually of lower conductive material volume than that of the shared conductive pillar.

CONCLUSION

In some embodiments, an array of cross point memory cells comprises spaced first lines which cross spaced second lines. Two memory cells are individually between one of two immediately adjacent of the second lines and a same single one of the first lines.

In some embodiments, an array of cross point memory cells comprises spaced lower first lines, spaced upper second lines which cross the first lines, and two memory cells individually elevationally between one of two immediately adjacent of the second lines and a same single one of the first lines. The individual memory cells comprise a select device and a programmable device in series with each other. The select device is proximate and electrically coupled to one of the first or second lines. The programmable device is proximate and electrically coupled to one of the other of the first or second lines. The programmable device comprises a first pillar electrode elevationally over the one first line. The first pillar electrode comprises a top and opposing sidewalls. The first pillar electrode is shared by the two memory cells. Programmable material is laterally outward of one of the opposing sidewalls of the first pillar electrode. A second electrode is outward of the programmable material that is laterally outward of the one opposing sidewall of the first pillar electrode. One of the first pillar electrode or the second electrode is electrically coupled to the select device. The other of the first pillar electrode or the second electrode is electrically coupled to the one of the other of the first or second lines.

In some embodiments, an array of cross point memory cells comprises spaced lower first lines, spaced upper second lines which cross the first lines, and two memory cells individually elevationally between one of two immediately adjacent of the second lines and a same single one of the first lines. The individual memory cells comprise a select device and a programmable device in series with each other. The select device is proximate and directly electrically coupled to one of the first lines. The programmable device is proximate and directly electrically coupled to one of the second lines. The programmable device comprises a first pillar electrode elevationally over and directly electrically coupled to the select device. The first pillar electrode comprises a top and opposing sidewalls. The first pillar electrode and the select device are shared by the two memory cells. Programmable material is laterally outward of one of the opposing sidewalls of the first pillar electrode. A second pillar electrode is outward of the programmable material that is laterally outward of the one opposing sidewall of the first pillar electrode. The second pillar electrode is directly electrically coupled to the one second line.

In some embodiments, an array of cross point memory cells comprises spaced lower first lines, spaced upper second lines which cross the first lines, and two memory cells individually elevationally between one of two immediately adjacent of the second lines and a same single one of the first lines. The individual memory cells comprise a select device and a programmable device in series with each other. The select device is proximate and directly electrically coupled to one of the second lines. The programmable device is proximate and directly electrically coupled to one of the first lines. The programmable device comprises a first pillar electrode elevationally over and directly electrically coupled to the one first line. The first pillar electrode comprises a top and opposing sidewalls. The first pillar electrode is shared by the two memory cells. Programmable material is laterally outward of one of the opposing sidewalls of the first pillar electrode. A second pillar electrode is outward of the programmable material that is laterally outward of the one opposing sidewall of the first pillar electrode. The second pillar electrode is directly electrically coupled to the select device. Each of the two memory cells comprises its own non-shared select device.

In compliance with the statute, the subject matter disclosed herein has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the claims are not limited to the specific features shown and described, since the means herein disclosed comprise example embodiments. The claims are thus to be afforded full scope as literally worded, and to be appropriately interpreted in accordance with the doctrine of equivalents.

Claims

1. An array of cross point memory cells comprising: spaced first lines which cross spaced second lines;two memory cells individually between one of two immediately adjacent of the second lines and a same single one of the first lines, the two memory cells sharing a single first electrode and having non-shared second electrodes, the first electrode being a conductive pillar electrode; andone select device for every memory cell.

2. The array of claim 1 wherein the first and second lines angle relative one another other than orthogonally.

3. The array of claim 2 wherein the first and second lines angle relative one another at about 45°.

4. An array of cross point memory cells comprising: spaced first lines which cross spaced second lines;two memory cells individually between one of two immediately adjacent of the second lines and a same single one of the first lines, the two memory cells sharing a single first electrode and having non-shared second electrodes, the first electrode being a conductive pillar electrode, and each comprising a programmable material, and comprising two non-shared select devices individually electrically coupled to a respective one of the two immediately adjacent second lines and electrically coupled to the programmable material of a different one of the two memory cells.

5. The array of claim 4 wherein the second lines are elevationally outward of the first lines.

6. The array of claim 4 wherein the first and second lines are individually straight linear within the array.

7. The array of claim 4 wherein the two memory cells are individually elevationally elongated and share an elevationally elongated conductive pillar.

8. The array of claim 7 wherein the shared conductive pillar is elevationally over the one first line.

9. The array of claim 4 wherein the two memory cells are individually elevationally elongated, the two memory cells collectively comprising a shared elevationally elongated conductive pillar and two non-shared elevationally elongated conductive pillars.

10. The array of claim 9 wherein the two non-shared conductive pillars are individually of lower conductive material volume than the shared conductive pillar.

11. An array of cross point memory cells comprising: spaced lower first lines, spaced upper second lines which cross the first lines, and two memory cells individually elevationally between one of two immediately adjacent of the second lines and a same single one of the first lines, the individual memory cells comprising: a select device and a programmable device in series with each other, the select device being proximate and directly electrically coupled to one of the second lines, the programmable device being proximate and directly electrically coupled to one of the first lines; andthe programmable device comprising: a first pillar electrode elevationally over and directly electrically coupled to the one first line, the first pillar electrode comprising a top and opposing sidewalls, the first pillar electrode being shared by the two memory cells;programmable material laterally outward of one of the opposing sidewalls of the first pillar electrode; anda second pillar electrode outward of the programmable material that is laterally outward of the one opposing sidewall of the first pillar electrode, the second pillar electrode being directly electrically coupled to the select device, each of the two memory cells comprising its own non-shared select device.

12. The array of claim 11 wherein the programmable material is over the top of the first pillar electrode.

13. The array of claim 12 wherein the programmable material is beneath the second pillar electrode between two immediately adjacent of the first lines.

14. The array of claim 13 wherein the first pillar electrode has a maximum conductive material volume that is greater than that of the second pillar electrode.