MATRIX CONTAINING A MULTIPLE NUMBER OF NON-VOLATILE MEMORY CELLS

Abstract

The invention relates to a memory matrix comprising a plurality of memory cells (1) having a first electrode (2), a second electrode (3), and a layer (4) of crystalline active material disposed between the first electrode (2) and the second electrode and having a thickness between 2 nm and 20 nm, the active material being either hafnium dioxide doped with a dopant element selected from one of the following: Si, Al, Zr, Gd, Ge, Y, or N, or an undoped HfxZr1-xO2 alloy or one doped with a dopant element selected from one of the following: Si, Al, Gd, Ge, Y, or N, with 0

Description

Title of the invention: MATRIX COMPRISING A PLURALITY OF NON-VOLATILE MEMORY CELLS TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a matrix comprising a plurality of non-volatile memory cells of the OxRAM and FeRAM type. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] For applications that require information storage even when the power is off, non-volatile memories of the EEPROM or FLASH type are conventionally used.

[0003] Other types of emerging non-volatile memories based on active materials such as ferroelectric materials (FeRAM memories) or materials such as oxides (OxRAM memories) constitute a promising alternative to FLASH or EEPROM type memories. These memories are generally assembled in the form of an array integrating a plurality of memory cells, for example defined by a 1T1R architecture (a selector transistor in series with a memory).

[0004] OxRAM, short for "Oxide Resistive RAM," is a non-volatile resistive memory. This memory can exhibit at least two resistive states, corresponding to a high resistance state (HRS, or "High Resistance State") and a low resistance state (LRS, or "Low Resistance State"), under the application of a voltage. OxRAM has a MIM (Metal-Insulator-Metal) structure comprising an active material with variable electrical resistance, generally a transition metal oxide (e.g., WO3, HfO2, Ta2O5, TiO2...), arranged between two metallic electrodes. One of the two electrodes often has a layer, for example in Ti, which has the particularity of being an "Oxygen scavening layer", that is to say a layer to create oxygen vacancies in the hafnium dioxide-based active layer of the OxRAM when this conductive layer is in contact with the active layer of the OxRAM.The transition from the "HRS" state to the "LRS" state is indeed governed by the formation and breaking of a conductive filament between the two electrodes. This conductive filament is created thanks to the presence of oxygen vacancies in the active layer of the memory. By modifying the potentials applied to the electrodes, it is possible to change the distribution of the filament, and thus modify the electrical conduction between the two electrodes. In the active layer, the electrically conductive filament is either broken or, conversely, reformed to vary the resistance level of the memory cell during write and reset cycles of this cell (reset operations). SET occurs when the filament is reformed, resulting in the LRS state, and RESET occurs when the filament is broken again by applying a voltage of SET (VSEt) or RESET (Vreset) to the electrode terminals, respectively. The fabrication of a filamentary memory includes a "forming" step, during which the filament is formed for the first time in the active layer, which is initially filamentless. The active layer is initially completely electrically insulating. During the initial "forming" step, an electrically conductive filament is formed within the active layer by performing a controlled breakdown of this layer. The filament thus formed then extends completely through the active layer, electrically connecting the lower and upper electrodes.To perform this forming step, an electrical voltage can be applied between the lower and upper electrodes of the memory cell in question, and the value of this voltage can then be progressively increased up to a threshold voltage, called the forming voltage (Vforming), beyond which breakdown of the active layer occurs. After this "forming" step, the memory cell is ready for use. The conductive filament can then be broken, then reformed, then broken again, and so on, at a voltage value lower than the forming voltage (Vforming).

[0005] OxRAM memories have the main qualities of being non-volatile, that is to say, of retaining the stored information even when the voltage is cut off, of having low write and read times compared to other types of non-volatile memories such as FLASH memories, of being able to be integrated on chips in a massive way due to the reduced spatial dimensions and the thinness of the active layers and of allowing a "back end" integration compatible with CMOS technology.

[0006] However, OxRAM resistive memories still have certain properties that need improvement.

[0007] It would therefore be particularly desirable to increase the memory window of OxRAM memories. The memory window of an OxRAM memory is defined as a range of resistance values ​​between two limits. The lower limit is the highest resistance value among the resistances of the conducting states (LRS). The upper limit is the lowest resistance value among the resistances of the insulating states (HRS). A narrow memory window is thus associated with insulating and conducting states with closely spaced resistance values, which leads to reliability problems in the OxRAM resistive memory cell.

[0008] In addition, the write and erase endurance of OxRAM memories is quite limited (on the order of 104-105 cycles).

[0009] OxRAM memories also exhibit relatively high forming voltages as well as a relatively high variability within the resistance values ​​in the LRS state and in the HRS state.

[0010] Finally, it would also be desirable to reduce the compliance current of the OxRAM memories. As a reminder, the compliance current is the current intensity value set by a selection transistor in series with the OxRAM memory. This current limits the maximum current allowed to flow through the memory to prevent damage. To use the lowest possible resistance value, a sufficient compliance current is required to achieve a sufficiently low on-state resistance. A high compliance current level necessitates the use of bulky selection transistors, which limits the integration density and, moreover, reduces the lifetime of the memory points. Thus, reducing the compliance current makes it possible to reduce the footprint of the selection transistor and, consequently, that of the complete 1T-1R cell.

[0011] It is known that the variability of OxRAM memories can be improved by the use of an active material of variable electrical resistance which is rather amorphous than crystalline, for example amorphous HfO2.

[0012] It is also known that reducing the forming voltage of OxRAM memories can be achieved by a silicon ion implantation step in the active layer, for example with HfO2, in order to obtain a doped active layer. The implantation doses are on the order of 3 to 4 x 10¹⁵ cm² with an implantation energy between 2 keV and 4 keV in order to have a silicon content of 4 to 5% in the active layer, which has a thickness between 5 and 1 µm.

[0013] It is understood from the above that a person skilled in the art wishing to produce an OxRAM memory exhibiting good properties will use an active layer of amorphous HfO2 implanted with silicon at high doses (i.e. greater than or equal to 3.1015cm2).

[0014] Ferroelectric memories or FeRAM memories have the main qualities of being non-volatile, that is to say retaining the stored information even when the voltage is cut off, of consuming little energy, of having low write and read times compared to other types of non-volatile memories such as FLASH memories, of having excellent temperature resistance and of allowing a "back end" integration compatible with CMOS technology.

[0015] Like OxRAM memories, FeRAM memories have a MIM (Metal-Insulator-Metal) structure comprising an active material of variable electrical resistance, for example HfO2, arranged between two metallic electrodes, for example TiN. Hafnium dioxide is used here in its orthorhombic phase. conferring ferroelectric properties: it is known that this crystallization in the orthorhombic phase is obtained by an implantation, for example of Si, in the active layer, with a dose of the order of 3.101 4cm2 with an implantation energy of the order of 4keV, i.e. typically 10 times less silicon dopants than what is used in an OxRAM type memory.

[0016] Ferroelectric memories are capacitive type memories exhibiting two remanent polarization states, +Pr and -Pr. Figure 1 illustrates the operation of ferroelectric memories. This operation is based on the ferroelectric properties of their active material placed between two electrodes. By applying a potential difference between the two electrodes, creating an electric field with a value greater than the positive coercive field +Ec, the ferroelectric memory is placed in a high remanent polarization state +Pr, and by applying a potential difference creating an electric field with a value less than the negative coercive field -Ec, the ferroelectric memory is placed in a low remanent polarization state -Pr. The high remanent polarization state +Pr then corresponds to the binary logic state '0' and the low remanent polarization state -Pr to the binary logic state '1', which allows the storage of information.It should be noted that when the application of the potential difference is stopped, the remanent polarization state remains: this explains the non-volatile nature of ferroelectric memories. When reading a ferroelectric memory, its polarization state is unknown a priori. Therefore, for reading, we assume it is in a given state and apply a voltage, for example, a positive one, beyond the voltage that creates an electric field with a value greater than the positive coercive field +Ec. If the memory was already in the high remanent polarization state +Pr, this polarization state remains unchanged, and no current peak will be observed (or a very small current peak will be observed). Conversely, if the memory was in the low remanent polarization state -Pr, a much larger current peak will be observed. The consequence of this reading operation is that it destroys the polarization state.

[0017] It may also prove useful to have on the same matrix a cointegration of OxRAM memories and FeRAM memories due to the limitation either in reading for FeRAM or in writing for OxRAM. Summary of the invention

[0018] The invention offers a solution to the problems mentioned above by proposing a memory cell matrix, said cells having an improved OxRAM type operation, in particular in terms of increased memory window and lower compliance current.

[0019] To this end, the invention relates in particular to a memory matrix comprising a plurality of memory cells of a first type, said matrix not comprising any other memory cells of a type other than the first type, each of said memory cells of the first type comprising a first electrode, a second electrode and a layer of crystalline active material disposed between the first electrode and the second electrode, the layer of active material having a thickness of between 2nm and 20nm, the active material being: • either hafnium dioxide doped with a dopant element chosen from one of the following: Si, Al, Zr, Gd, Ge, Y or N; • either an undoped HfxZri XO2 alloy or one doped with a doping element chosen from one of the following: Si, Al, Gd, Ge, Y or N, with 0 <x<l ; at least one of the said first or second electrode being formed of at least two layers comprising: • a first conductive layer in contact with the active material layer and chosen to create oxygen vacancies in the active material layer; • a second conductive layer placed on top of the first conductive layer.

[0020] Memory cells of a first type are understood to be a set of cells identical in terms of the layers forming their stack, the materials of these layers and the thicknesses of these layers measured along the axis perpendicular to the plane of the layers; cells of a first type may, however, have different lateral dimensions, or even different shapes.

[0021] Thanks to the invention, the particular structure of the memory cells makes it possible to obtain a matrix of cells functioning both as FeRAM and as OxRAM, despite an identical structure.

[0022] In other words, each memory cell of the matrix operates simultaneously: • as a filamentary resistive memory (OxRAM) via SET operations, when the filament is formed resulting in an LRS state, and RESET operations resulting in the HRS state, when the filament is broken, by respective application of a SET voltage, VSet or RESET voltage, VRESet to the terminals of the electrodes; • such as a capacitive memory (FeRAM) via the application of a potential difference between the two electrodes creating an electric field with a value greater than the positive coercive field +Ec, the ferroelectric memory being placed in a state of high remanent polarization +Pr and by the application of a potential difference creating an electric field with a value less than the negative coercive field -Ec, the ferroelectric memory being placed in a state of low remanent polarization -Pr. The presence of The first conductive layer chosen to create oxygen gaps in the active material layer might lead a person skilled in the art to believe that the cells operate almost exclusively in a filamentary mode; surprisingly, the inventors realized that the cells could also exhibit ferroelectric operation.

[0023] Surprisingly, the inventors discovered that an identical active layer for memory cells made it possible to obtain both the ferroelectric effect of FeRAM and the resistive memory effect of OxRAM. Thus, the doping of the active layer with hafnium dioxide, necessary for FeRAM, also ensures the resistive operation of OxRAM. The same reasoning applies to an active layer formed by an HfZrO2 alloy: in the case of HfZrO2, the ternary HfZrO2 alloy does not necessarily require doping of the active layer.

[0024] Furthermore, each memory cell in the matrix according to the invention has improved OxRAM functionality compared to known OxRAM cells. The combination of a relatively thin active layer (i.e., between 2 and 1 µm) and an oxygen scavenging layer in contact with the active layer promotes the crystallization of the active layer in its orthorhombic or tetragonal phase. Surprisingly, this crystallization does not impair the functionality of the OxRAM memory, for which amorphous or monoclinic HfO2 is typically used by those skilled in the art.On the contrary, the configuration of each cell according to the invention makes it possible to obtain memory windows which increase with memory cycling, in particular compared to an amorphous material of the active layer as well as an operation at a lower compliance current (again compared to an active layer in amorphous material): this lower compliance current allows for lower consumption and thus a smaller 1T-1R cell size.

[0025] Finally, each memory cell of the matrix according to the invention has improved FeRAM operation. The addition of an "Oxygen scavenging layer" (first conductive electrode layer) between the active layer and the second conductive electrode layer increases the remanent polarization value of the ferroelectric active layer (orthorhombic crystallization) in its blank state, as well as the maximum polarization during cell cycling. Similarly, the addition of this layer significantly increases the FeRAM memory window and reduces the programming / reading voltages.

[0026] In addition to the characteristics mentioned in the preceding paragraph, the matrix according to the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • In the case of hafnium dioxide active material doped with a dopant element chosen from one of the following: Si, Al, Zr, Gd, Ge, Y or N, the dopant element is present at a percentage less than or equal to 2% in the active material relative to the total number of atoms in the active material. • The crystalline active material layer is crystallized in an orthorhombic or tetragonal phase. • The matrix according to the invention comprises a plurality of first access lines and a plurality of second access lines, each memory cell being located at an intersection between a first access line and a second access line allowing its individual addressing. • The thickness of the active material layer is between 2 and 1 nm and preferably between 4 and 6 nm. • The thickness of the active material layer is approximately 5nm. • The doping element is Silicon implanted in the active material layer and the dose of Si implantation in the active material layer is between 2.1014cm2 and 5.1014cm2. • The conductive material of the second conductive layer is chosen from the following materials: TiN, TaN or W. • The conductive material of the first conductive layer is Ti or Hf when the material of the second conductive layer is TiN or Ta or Hf when the material of the second conductive layer is TaN or Ti, Hf or Ta when the material of the second layer of the W. • The thickness of the first conductive layer is less than or equal to the thickness of the active material layer. • Each memory cell is connected in series with a selection transistor. • The said selection transistor is chosen to deliver a current of compliance crossing the memory cell having an intensity less than or equal to 150pA. • The second conductive layer has a thickness between 10 nm and 200 nm. • The first type of memory cells corresponds to the same nature and thickness of the active material layer.

[0027] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0028] The figures are presented for illustrative purposes only and are in no way limiting of the invention. • Fig. 1 illustrates the operation of a ferroelectric memory FeRAM. • Fig. 2 represents a memory cell used in the matrix according to the invention. • Fig. 3 represents a matrix according to the invention comprising a plurality of memory cells as illustrated in Fig. 2. • Fig. 4 represents an enlargement of part of the matrix of Fig. 3. • Fig. 5 shows the empirical cumulative distribution function measured as a function of the resistance value for different matrices, including one according to the invention, and for different cyclings. • Fig. 6 shows a TEM image of a memory cell of a matrix according to the invention. • Fig. 7 shows an X-ray diffraction intensity measurement at grazing incidence in 2 thetas on the memory cell imaged in Fig. 6. • Fig. 8 shows a grazing incidence X-ray diffraction intensity measurement at 2 thetas on two memory cells, one of which is used in the matrix according to the invention. • Fig. 9 shows a grazing incidence X-ray diffraction intensity measurement at 2 thetas on two memory cells, one of which is used in the matrix according to the invention with a lower active layer thickness than in the case of the cells in Fig. 8. • Fig. 10 shows an X-ray diffraction intensity measurement at grazing incidence in 2 thetas on two memory cells, one of which has a highly doped active layer and the other an undoped active layer. • Fig. 11 shows the remanent polarization values ​​as a function of cycling for a memory cell operating in FeRAM mode of a matrix according to the invention and a state-of-the-art FeRAM cell; • Fig. 12 shows the evolution of the memory window measured on a matrix according to the invention of 16384 FeRAM memory cells. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

[0029] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0030] The invention relates to an array of identical memory cells; in other words, the array according to the invention comprises a plurality of memory cells identical without including another type of memory cell. An example of a memory cell 1 included in the matrix according to the invention is illustrated in [Fig.2].

[0031] The memory cell 1 comprises a first electrode 2 (called lower electrode), a second electrode (called upper electrode) 3 and a layer of active material 4 in hafnium dioxide HfO2 disposed between the first electrode 2 and the second electrode 3.

[0032] The active material layer 4 made of hafnium dioxide (HfO2) is here made of an active material HfO2 doped with silicon and crystallized in its orthorhombic or tetragonal phase. The thickness of the active material layer 4 is between 2 and 1 nm and preferably between 4 and 6 nm (typically on the order of 5 nm).

[0033] The active material is made in an orthorhombic or tetragonal crystallization state. To achieve this, the HfO2 material is doped with a dopant element, preferably silicon (Si). However, other dopant elements such as aluminum (Al), zirconium (Zr), germanium (Ge), gadolinium (Gd), yttrium (Y), or nitrogen (N) could also be used. The active material layer 4 is, for example, exposed to a dopant dose of between 2 x 10¹⁴ ions / cm² and 5 x 10¹⁴ ions / cm², corresponding to a dopant element presence of 2% or less in the active material relative to the total number of atoms in the active material. It is also possible to use a ternary alloy HfZrO2 (for example, Hfo.5Zro.5O2) as the active material, the latter being doped (for example, with silicon) or undoped.

[0034] The conductive material of the lower electrode 2 is, for example, titanium nitride (TiN). TiN is a non-limiting example, but other conductive materials such as TaN or W could also be used. The thickness of the lower electrode is, for example, between 10 nm and 200 nm.

[0035] The upper electrode 3 is formed by a bilayer comprising a first conductive layer 5 and a second conductive layer 6.

[0036] The conductive material of the second conductive layer 6 is also, for example, titanium nitride (TiN). TiN is a non-limiting example, but other conductive materials such as TaN or W could also be used. The thickness of the second conductive layer 6 is, for example, between 10 nm and 200 nm.

[0037] The first conductive layer 5 is in direct contact with the active layer 4 and has the particularity of being an "Oxygen scavenging layer," that is to say, a layer designed to create oxygen vacancies in the active layer when this second conductive layer is in contact with the active layer. The material of the first conductive layer 5 is, for example, titanium (Ti) or hafnium when The material of the second conductive layer 6 is TiN. It can also be Tantalum (Ta) or Hafnium when the material of the second conductive layer 6 is TaN. Note that Ti (respectively Ta) is a good bonding material for the top TiN (respectively TaN) layer.

[0038] The thickness of the first conductive layer 5 is strictly positive and preferably less than or equal to the thickness of the active layer 4. The thickness of the first conductive layer 5 is, for example, substantially equal to the thickness of the active layer 4. The first conductive layer 5 has the advantage of promoting the crystallization of the active layer 4 in its orthorhombic or tetragonal phase, particularly with fairly small active layer thicknesses (i.e., on the order of 5 nm).

[0039] As explained previously, cell 1 of [Fig.2] can function as both a filamentary OxRAM type memory and a capacitive FeRAM type memory (ferroelectric if the active layer is crystallized in an orthorhombic state or antiferroelectric if the active layer is crystallized in a tetragonal state).

[0040] Figure 3 represents a matrix 100 according to the invention comprising a plurality of cells 1 as shown in Figure 2. The architecture of the matrix 100 is a 1T1R type architecture (one selection transistor 101 in series with a memory cell 1). Figure 4 is a magnification of the matrix 100 on a 1T1R assembly. Here, the upper electrode 3 of cell 1 is connected to the drain of transistor 101.

[0041] The matrix 100 thus comprises a plurality of sets 1T1R arranged respectively in row and in column.

[0042] The matrix 100 comprises a plurality of word lines 102, shown here vertically. Each word line 102 is connected to each gate of a plurality of selection transistors 101 arranged in the same column.

[0043] The matrix 100 also comprises a plurality of source lines 103, shown here horizontally. Each source line 103 is connected to each source of the plurality of selection transistors 101 arranged on the same line.

[0044] The matrix 100 also comprises a plurality of bit lines (or "bit lines" in English terminology) 104, shown here horizontally. Each bit line 104 is connected to the lower electrode 2 of the plurality of cells 1 arranged on the same line.

[0045] The matrix 100 thus comprises a plurality of first access lines 103 (source lines) and a plurality of second access lines 104 (bit lines), each memory cell 1 in series with a transistor 101 being located at an intersection between a first access line and a second access line allowing its individual addressing, the matrix also comprising a plurality of word lines 102 connected to the gates of the transistors 101.

[0046] The selection of memory cell 1 to be programmed is done by activating transistor 101 by applying a voltage to its gate via the word line and by injecting a desired programming voltage (SET or RESET) via the bit line.

[0047] The matrix 100 of [Fig. 3] is shown for illustrative purposes only, it being understood that other types of matrix architecture can be considered for the invention. In particular, in [Fig. 3], the bit lines and source lines are parallel to each other, but they can also be perpendicular to each other. In this case, the word lines can be parallel to the bit lines. Thus, the matrix according to the invention could also be a matrix comprising a plurality of cells 1 in series with a selector such as a PN diode or an OTS (Ovonic Threshold Switching) selector. Similarly, the matrix according to the invention can be a two-dimensional matrix or a three-dimensional matrix.

[0048] In order to illustrate the advantages of the matrix according to the invention in OxRAM operation, the applicant has produced three different 1T1R matrices of 16kb (i.e. approximately 16384 cells per matrix): • A first Ml matrix comprising OxRAM cells having an active layer of undoped amorphous HfO2 with a thickness of 5nm and a first conductive layer of Ti with a thickness of 5nm in contact with the active layer; • A second matrix M2 according to the invention with both OxRAM and FeRAM cells comprising an active layer of crystallized HfO2 (orthorhombic or tetragonal) doped with 1% Si (i.e. dopant dose of 2.1014 ions / cm2 with an implantation energy of 2keV) with a thickness of 5nm with a first conductive layer of Ti with a thickness of 5nm in contact with the active layer; • A third M3 matrix with OxRAM cells comprising an active layer of amorphous HfO2 doped with 10% Si (i.e., dopant dose of 2 x 10¹⁵ ions / cm² with an implantation energy of 2 keV) with a thickness of 5 nm and a first conductive Ti layer with a thickness of 5 nm in contact with the active layer

[0049] It should be noted that the other elements of the cells are identical from one matrix to another and are formed by: • A first TiN electrode of the same thickness • A second conductive layer of the second electrode made of TiN of the same thickness.

[0050] The applicant performed several cycles (a first type of cycle corresponding to a series of SET operations and a second type of cycle corresponding to a series of RESET operations) under the same conditions on each of the matrices M1, M2, and M3. The series correspond respectively to 10, 100, 1000, and 105 cycles (i.e., writing SET or RESET depending on the first or second type of cycle) and were performed so as to have a compliance current on the order of 105 pA when the cells are in a low-resistance state (LRS). More generally, the selection device (here, the transistor) is sized to provide a compliance current less than or equal to 150 pA.

[0051] Fig. 5 shows respectively the empirical cumulative distribution function ECDF (“Empirical Cumulative Distribution Function” according to English terminology) as a function of the resistance value for the matrices M1, M2 and M3 and for the different SET and RESET cycles.

[0052] Two important observations emerge from these curves.

[0053] First, it should be noted that the M2 matrix according to the invention has far fewer memory points where the LRS state can no longer be distinguished from the HRS state (the case of intersecting curves) than in the case of the M1 and M3 matrices. Thus, for low compliance currents (i.e., advantageously less than 150 pA), the performance of the M2 matrix is ​​much better than that of the M1 and M3 matrices. Such a result is particularly advantageous when seeking to use smaller selection transistors and therefore, overall, smaller 1T1R cell sizes, resulting in lower energy consumption.

[0054] Furthermore, advantageously and unexpectedly, it is observed that the highly resistive HRS state drifts towards higher resistance values ​​as the number of cycles increases. Thus, the memory window of the M2 matrix according to the invention increases with cycling, unlike the other matrices M1 and M3.

[0055] Figure 6 shows a transmission electron microscopy (TEM) image of a memory cell used in a matrix according to the invention. This image shows an 8.9 nm active layer of Si-doped HfO2 (with less than 2%) in contact with a Ti layer. The active zone exhibits crystallites in orthorhombic or tetragonal form. This latter result is confirmed by the curve shown in Figure 7, which displays 200 μm X-ray diffraction intensity measurements at grazing incidence in 2θ. The curve shows a diffraction peak at 30.5° corresponding to the respective theoretical O and T positions of a crystallized structure in orthorhombic or tetragonal form. It is not possible to distinguish from the curve whether it is an orthorhombic or tetragonal crystallization insofar as the experimental diffraction peak is too broad and may correspond to one or the other of the theoretical peaks; on the other hand, it is clear from the curve that the active layer is indeed crystallized in orthorhombic (ferroelectric) or tetragonal (antiferroelectric) form.

[0056] Figure 8 shows a grazing incidence X-ray diffraction intensity measurement at 2-theta on two memory cells: • A first P08 intended to be used in a matrix according to the invention and comprising 10 nm of Si-doped HfO2 (less than 2%) in contact with a Ti layer; • A second P04 containing 10 nm of Si-doped HfO2 (less than 2%) in contact with a TiN layer (and therefore without a Ti layer).

[0057] It can be seen on this curve that the presence of the Ti layer creating oxygen vacancies in contact with the active layer promotes the crystallization of the active layer, the absorption peak at 30.5° characteristic of orthorhombic or tetragonal crystallization being significantly more important in the case of the P08 cell than in that of the P04 cell.

[0058] The first conductive layer of material creates oxygen vacancies that promote orthorhombic or tetragonal crystallization of the active layer, thus allowing the use of thinner active layer thicknesses. This is illustrated by [Fig. 9], which shows a grazing incidence surface diffraction intensity measurement at 2θ on two memory cells: • A first P10 intended for use in a matrix according to the invention and comprising 5 nm of Si-doped HfO2 (less than 2%) in contact with a Ti layer; • A second P09 containing 5 nm of Si-doped HfO2 (less than 2%) in contact with a TiN layer (and therefore without a Ti layer).

[0059] It can be seen on this curve that the presence of the Ti layer creating oxygen vacancies in contact with the active layer allows to obtain a crystallization of the active layer of the P10 cell with the presence of the absorption peak at 30.5° characteristic of orthorhombic or tetragonal crystallization, this peak being absent in the case of the P09 cell.

[0060] Figure 10 illustrates the importance of low doping of the active layer (i.e., less than 2%). In other words, to obtain orthorhombic or tetragonal crystallization, the doping must be neither too high nor absent. This phenomenon is illustrated by Figure 10, which shows a grazing incidence X-ray diffraction intensity measurement at 2-theta on two memory cells: • A first P21 containing 10 nm of HfO2 without doping and in contact with a layer of Ti; • A second P22 containing 10 nm of 10% Si-doped HfO2 in contact with a Ti layer.

[0061] It can be seen here that neither of the two curves exhibits the characteristic peak of orthorhombic or tetragonal crystallization. Thus, it is indeed the combination of the presence of the first conducting layer in a material creating oxygen vacancies (in Ti, for example) with the low doping of less than 2% of the active layer doped with less than 2% (for example, Si-doped) that makes it possible to obtain the effect of the ad hoc crystallization. In the case of an undoped HfxZrl xO2 alloy, it can be considered that the Zr replaces the Si doping so that crystallization is also obtained.

[0062] As mentioned above, the matrix according to the invention comprises cells capable of functioning both as OxRAM and as FeRAM. We have shown that the performance of the cells operating as OxRAM is improved. We will show below that the same is true when these cells operate as FeRAM (i.e., in a capacitive mode).

[0063] Fig. 11 shows that, all other things being equal, the addition of a first conductive layer of Ti between the second conductive layer of TiN of the upper electrode and the ferroelectric layer of HfO2:Si (here with lOnm thickness) makes it possible to increase the value of the remanent polarization of the ferroelectric layer in the virgin state, and the maximum polarization during cycling.

[0064] The measurements are performed on a 200mm wafer, using ferroelectric capacitor cells (FeRAM) integrated in the backend. The addition of Ti also helps to reduce the dispersion of electrical properties across the wafer.

[0065] Figure 12 shows the memory window (MW) measured on a 16kbit matrix according to the invention, consisting of 16,384 FeRAM cells with a diameter of 600 nm, each in series with a selection transistor. The memory window is defined in volts and corresponds here to the median memory window (i.e., the median of the distribution of state 1 minus the median of the distribution of state 0). These measurements are therefore statistically significant.

[0066] Adding a Ti layer between the second conductive TiN layer of the upper electrode and the ferroelectric HfO2:Si layer (here 1 µm thick) significantly increases the memory window (by programming / reading at a voltage of 3V or 4V, for example) and reduces the programming / reading voltages, particularly compared to a conventional OxRAM memory cell. Thus, the present invention provides a memory OxRAM resistive technology with improved performance and the possibility of operating like FeRAM.

Claims

Demands

1. A memory matrix (100) comprising a plurality of memory cells (1) of a first type, said matrix (100) not comprising any other memory cells of a type other than the first type, each of said memory cells (1) of the first type comprising a first electrode (2), a second electrode (3) and a layer (4) of crystalline active material disposed between the first electrode (2) and the second electrode (3), the layer of active material (4) having a thickness between 2 nm and 20 nm, the active material being: - either hafnium dioxide doped with a dopant element selected from one of the following: Si, Al, Zr, Gd, Ge, Y or N; - or an undoped HfxZri XO2 alloy or one doped with a dopant element selected from one of the following: Si, Al, Gd, Ge, Y or N, with 0 <x<l;at least one of said first or second electrode (3) being formed of at least two layers comprising: - a first conductive layer (5) in contact with the active material layer and chosen to create oxygen vacancies in the active material layer (4); - a second conductive layer (6) disposed on the first conductive layer; the conductive material of the second conductive layer being chosen from the following materials: TiN, TaN or W.;

2. Matrix according to the preceding claim characterized in that, in the case of the hafnium dioxide active material doped with a dopant element selected from one of the following elements: Si, Al, Zr, Gd, Ge, Y or N, the dopant element is present at a percentage less than or equal to 2% in the active material relative to the total number of atoms in the active material.

3. Matrix according to any one of the preceding claims characterized in that the layer (4) of crystalline active material is crystallized in an orthorhombic or tetragonal phase.

4. Matrix according to any one of the preceding claims characterized in that it comprises a plurality of first access lines and a plurality of second access lines, each memory cell being located at an intersection between a first access line and a second access line allowing its individual addressing.

5. Matrix according to any one of the preceding claims characterized in that the thickness of the active material layer is between 2 and 1 nm and preferably between 4 and 6 nm.

6. Matrix according to the preceding claim characterized in that the thickness of the active material layer is substantially equal to 5nm.

7. Matrix according to any one of the preceding claims characterized in that the doping element is Silicon implanted in the active material layer and the implantation dose of Si in the active material layer is between 2.10 cm and 5.10 cm.

8. Matrix according to the preceding claim characterized in that the conductive material of the first conductive layer is Ti or Hf when the material of the second conductive layer is TiN or Ta or Hf when the material of the second conductive layer is TaN or Ti, Hf or Ta when the material of the second layer of the W.

9. Matrix according to any one of the preceding claims characterized in that the thickness of the first conductive layer is less than or equal to the thickness of the active material layer.

10. Matrix according to any one of the preceding claims characterized in that each memory cell is mounted in series with a selection transistor.

11. Matrix according to the preceding claim characterized in that said selection transistor is chosen to deliver a compliance current through the memory cell having an intensity less than or equal to 150pA.

12. Matrix according to any one of the preceding claims characterized in that the second conductive layer has a thickness between 10 nm and 200 nm.

13. Matrix according to any one of the preceding claims characterized in that the first type of memory cells (1) corresponds to the same nature and the same thickness of the active material layer (4).