Patent Application
20200321397
The invention relates to the technical field of recurrent-neural-network computers. Recurrent neural networks are networks of artificial neurons in which the connections between the units form at least one cycle in the sense of graph theory. More precisely, the technical domain relates to recurrent neural networks trained using the reservoir-computing paradigm. This paradigm is a highly nonlinear dynamic system, comprising:
The principle of this paradigm is to project the input layer onto the reservoir, then to modify the connections between the reservoir and the output layer via supervised learning.
In other words, the invention relates to a computer that is a physical or hardware implementation of the reservoir-computing paradigm.
The invention is notably applicable to classifying tasks, extracting features, tracking objects, predicting movements in robotics, voice recognition and sound recognition.
One process for fabricating a recurrent-neural-network computer that is known in the prior art, notably from the document “Atomic switch networks—nanoarchitectonic design of a complex system for natural computing”, E. C. Demis et al., Nanotechnology, 26, 204003, 2015, comprises a step of randomly growing silver nanowires on a structured platinum electrode. The random character is obtained via a prior step of forming copper microspheres on the structured electrode. The copper microspheres form a seed layer for the silver nanowires. The process comprises a step of sulfurizing the silver nanowires so as to obtain Ag/Ag2S/Ag structures. Such structures form resistive atomic-switch memory cells.
Such a prior-art process allows a computer that is a physical implementation of the reservoir-computing paradigm to be fabricated. However; such a prior-art process is not entirely satisfactory insofar as the choice of materials from which the resistive memory may be made is restricted. Specifically, it is necessary to choose a compatible pair of materials, i.e. a compatible electrical conductor/dielectric, in the present case Ag/Ag2S, to form the nanowires and the resistive memory cells.
The invention aims to remedy all or some of the aforementioned drawbacks. To this end, one subject of the invention is a process for fabricating a recurrent-neural-network computer, comprising the successive steps of:
Thus, such a process according to the invention allows the physical implementation of a recurrent-neural-network computer able to be trained using the reservoir-computing paradigm. Specifically, the block copolymers possess the property of self-assembling into dense networks of nanoscale objects with the capacity to form a lithography mask.
This self-assembly introduces the random character required in the reservoir-computing paradigm, i.e., for example:
Furthermore, the lithography mask thus formed by the first and second block-copolymer layers allows the first and second electrodes to be structured in steps c) and h).
Lastly, such a process according to the invention permits freedom in the choice of the material of the memory layer insofar as the memory layer is formed independently of the first and second block-copolymer layers.
Definitions
The process according to the invention may comprise one or more of the following features.
According to one feature of the invention, step b) comprises the successive steps of:
By “random polymer” what is meant is a polymer possessing a random coil.
Thus, the random-polymer layer is a functionalization layer allowing the surface energies of the first electrode to be controlled. One procured advantage is accentuation of the random character and improvement of the quality of the formation of the first block-copolymer layer.
According to one feature of the invention, step g) comprises the successive steps of:
Thus, the random-polymer layer is a functionalization layer allowing the surface energies of the second electrode to be controlled. One procured advantage is accentuation of the random character and improvement of the quality of the formation of the second block-copolymer layer.
According to one feature of the invention, the random polymer is selected from the group containing a statistical copolymer, a homopolymer, a self-assembled monolayer.
According to one feature of the invention, the block copolymers of the first layer and second layer are selected from the group containing;
According to one feature of the invention, the memory layer is made from at least one material selected from the group containing HfO2, Al2O3, SiO2, ZrO, a titanium oxide, a chalcogenide, Ta2O5.
According to one feature of the invention, the first and second electrodes are made from at least one material selected from the group containing Ti, TiN, Pt, Zr, Al, Hf, Ta, TaN, C, Cu, Ag.
According to one feature of the invention, the first block-copolymer layer and the second block-copolymer layer formed in steps b) and g) have a thickness comprised between 30 nm and 50 nm, respectively.
Thus, one procured advantage is to obtain a lithography mask of good quality for structuring the first and second electrodes.
According to one feature of the invention, the process comprises a step j) consisting in forming an encapsulation layer on the second electrode structured in step h), step j) being executed after step i).
Thus, one procured advantage is to protect the computer from air and moisture,
According to one feature of the invention, the first electrode structured in step c) has a pitch, denoted p, and step e) is executed so that the memory layer has a thickness, denoted E, respecting:
p/2≤E≤p.
Thus, such a thickness E of the memory layer allows an almost planar surface topology to be obtained so as to facilitate the formation of the second electrode in step f), while avoiding the need for a step of chemical-mechanical polishing.
Another subject of the invention is a recurrent-neural-network computer obtained using a process according to the invention.
Other features and advantages will become apparent from the detailed description of various embodiments of the invention, the description being coupled with examples and references to the appended drawings.
It will be noted that the drawings described above are schematic and not to scale for the sake of legibility.
In the various embodiments, elements that are identical or that perform the same function have been designated with the same references for the sake of simplicity.
One subject of the invention is a process for fabricating a recurrent-neural-network computer 1 comprising the successive steps of:
The first electrode 20 is advantageously made from at least one material selected from the group containing Ti, TIN, Pt, Zr, Al, Hf, Ta, TaN, C, Cu, Ag. The first electrode 20 may be made from an alloy of these materials. The first electrode 20 preferably has a thickness comprised between 3 nm and 100 nm. By way of nonlimiting example, the first electrode 20 may be formed on the substrate 2 by physical vapor deposition (PVD), chemical vapor deposition (CVD), or even atomic layer deposition (ALD).
The substrate 2 preferably comprises a metallization layer 22 (for contact redistribution) and a layer of an oxide 23 such as SiO2 or SiN. By way of nonlimiting example, the metallization layer 22 may be a Ti (10 nm)/AlCu (440 nm)/Ti (10 nm)/TiN (100 nm) structure.
Step b) advantageously comprises the successive steps of:
The random polymer of the layer formed in step b1) is advantageously selected from the group containing a statistical copolymer, a homopolymer, a self-assembled monolayer. The random polymer is advantageously chosen in step b1) so that the force of attraction between each of the monomer blocks of the block copolymer and the random-polymer layer (i.e. the functionalization layer) are equivalent.
Step b2) may be executed using a heat treatment, such as a thermal anneal, or by light-induced cross-linking. The random-polymer layer that was not grafted in step b2) is preferably removed using a wet process.
The first block-copolymer layer 3 formed in step b3) is preferably structured using a thermal anneal.
By way of example, step b4) may be a selective removal when the random polymer and the block copolymer of the first layer 3 possess two phases. Step b4) may be executed using a UV treatment followed by a wet development process. Step b4) may also be executed using a plasma etch.
The block copolymers of the first layer 3 are advantageously selected from the group containing:
By way of example, when the block copolymers of the first layer 3 are polystyrene-b-poly(methyl methacrylate), denoted PS-b-PMMA, of lamellar form, the random polymer of the functionalization layer is advantageously polystyrene-r-poly(methyl methacrylate), denoted PS-r-PMMA, preferably containing 50% by weight of PS and 50% by weight of PMMA. The step b1) is preferably executed by spin coating. The spin coating may be executed by diluting the random polymer in an organic solvent. When the random polymer is PS-r-PMMA, the organic solvent may be propylene glycol methyl ether acetate (PGMEA). The solution of the random polymer diluted in the organic solvent may have a concentration by weight of about 1.5%. Step b2) may be executed using a thermal anneal at a temperature of about 250° C. for a time of about 10 minutes. The thermal anneal may be executed on a hot plate or in a furnace. When the random polymer is able to be cross-linked, such a thermal anneal allows the random polymer to be cross-linked. Step b2) may comprise a rinsing step in which the surplus of random polymer is removed using a solvent. When the random polymer is PS-r-PMMA, the solvent is preferably PGMEA. Step b3) is preferably executed by spin coating. The spin coating may be executed by diluting the block copolymer in an organic solvent. When the block copolymer is PS-b-PMMA, the organic inorganic solvent may be PGMEA. The solution of block copolymer diluted in the organic solvent may have a concentration by weight of about 1.5%. Step b3) is advantageously followed by a thermal anneal allowing self-assembly of the PS-b-PMMA block copolymer and the selective removal of the PS-r-PMMA. The thermal anneal is preferably executed at a temperature of about 250° C. for a time of about 10 minutes.
The first block-copolymer layer 3 formed in step b) advantageously has a thickness comprised between 30 nm and 50 nm.
Step c) is preferably executed using a plasma etch. By way of nonlimiting examples, it is possible to use as gas O2, Ar, COH2, N2H2. Step c) may also be executed using a UV treatment followed by a wet development process (e.g. in acetic acid).
Step d) is preferably executed using a UV treatment followed by a wet development process. Step d) may also be executed using a plasma etch.
the memory layer 4 is advantageously made from at least one material selected from the group containing HfO2, Al2O3, SiO2, ZrO, a titanium oxide, a chalcogenide, Ta2O5. The memory layer 4 may be formed from a plurality of sub-layers made from these materials. By way of nonlimiting examples, the chalcogenide may be GeSe or GeSbTe.
The memory layer 4 advantageously has a thickness smaller than or equal to 10 nm.
the second electrode 21 is advantageously made from at least one material selected from the group containing Ti, TiN, Pt, Zr, Al, Hf, Ta, TaN, C, Cu, Ag. The second electrode 21 may be made from an alloy of these materials. The second electrode 21 preferably has a thickness comprised between 3 nm and 100 nm. By way of nonlimiting examples, the second electrode 21 may be formed on the memory layer 4 by physical vapor deposition (PVD), chemical vapor deposition (CVD), or even by atomic layer deposition (ALD).
Step g) advantageously comprises the successive steps of:
The random polymer of the layer formed in step g1) is advantageously selected from the group containing a statistical copolymer, a homopolymer, a self-assembled monolayer. The random polymer is advantageously chosen in step g1) so that the force of attraction between each of the monomer blocks of the block copolymer and the random-polymer layer (i.e. the functionalization layer) are equivalent.
Step g2) may be executed using a heat treatment, such as a thermal anneal, or by light-induced cross-linking. The random-polymer layer that was not grafted in step b2) is preferably removed using a wet process.
The second block-copolymer layer 5 formed in step g3) is preferably structured using a thermal anneal.
By way of example, step g4) may be a selective removal when the random polymer and the block copolymer of the second layer 5 possess two phases. Step g4) may be executed using a UV treatment followed by a wet development process. Step g4) may also be executed using a plasma etch.
The block copolymers of the second layer 5 are advantageously selected from the group containing:
By way of example, when the block copolymers of the second layer 5 are polystyrene-b-poly(methyl methacrylate), denoted PS-b-PMMA, of lamellar form, the random polymer of the functionalization layer is advantageously polystyrene-r-poly(methyl methacrylate), denoted PS-r-PMMA, preferably containing 50% by weight of PS and 50% by weight of PMMA. The step g1) is preferably executed by spin coating. The spin coating may be executed by diluting the random polymer in an organic solvent. When the random polymer is PS-r-PMMA, the organic solvent may be propylene glycol methyl ether acetate (PGMEA). The solution of the random polymer diluted in the organic solvent may have a concentration by weight of about 1.5%. Step g2) may be executed using a thermal anneal at a temperature of about 250° C. for a time of about 10 minutes. The thermal anneal may be executed on a hot plate or in a furnace. When the random polymer is able to be cross-linked, such a thermal anneal allows the random polymer to be cross-linked. Step g2) may comprise a rinsing step in which the surplus of random polymer is removed using a solvent. When the random polymer is PS-r-PMMA, the solvent is preferably PGMEA. Step g3) is preferably executed by spin coating. The spin coating may be executed by diluting the block copolymer in an organic solvent. When the block copolymer is PS-b-PMMA, the organic solvent may be PGMEA. The solution of block copolymer diluted in the organic solvent may have a concentration by weight of about 1.5%. Step g3) is advantageously followed by a thermal anneal allowing self-assembly of the PS-b-PMMA block copolymer and the selective removal of the PS-r-PMMA. The thermal anneal is preferably executed at a temperature of about 250° C. for a time of about 10 minutes.
The second block-copolymer layer 5 formed in step g) advantageously has a thickness comprised between 30 nm and 50 nm.
Step h) is preferably executed using a plasma etch. By way of nonlimiting examples, it is possible to use as gas O2, Ar, COH2, N2H2. Step h) may also be executed using a UV treatment followed by a wet development process (e.g, in acetic acid).
Step i) is preferably executed using a UV treatment followed by a wet development process. Step i) may also be executed using a plasma etch.
As illustrated in
Moreover, as illustrated in figure id, the process advantageously comprises a step d1) consisting in forming an encapsulation layer 7 on the structured first electrode 200. Step d1) is executed after step d) before step e). The encapsulation layer 7 is preferably a layer of an oxide such as SiOx or SiN. Step d1) is advantageously followed by a step d2) of planarizing the encapsulation layer 7, which may be executed by chemical-mechanical polishing (CMP). In the absence of steps d1) and d2), the memory layer 4 formed in step e) follows the topology of the structured first electrode 200.
More precisely, as illustrated in
In the absence of steps d1) and d2), the memory layer 4 formed in step d) advantageously has a thickness, denoted E, respecting:
p/2≤E≤p
where p is the pitch of the structured first electrode 200 forming a periodic structure. Such a thickness E of the memory layer 4 allows an almost planar surface topology to be obtained so as to facilitate the formation of the second electrode 21 in step f) (illustrated in
The pitch p of the structured first electrode 200 corresponds to the pitch of the first block-copolymer layer 3 formed in step b). By way of nonlimiting example, when the first block-copolymer layer 3 formed in step b) is made of PS-PMMA, the pitch of said first layer 3 is defined by the molar mass of the block copolymer, as mentioned in the document by Kim et al, “Directed assembly of high molecular weight block polymers: highly ordered line patterns of perpendicularly oriented lamellae with large periods:”, ACS Nano, 7 (3), pp. 1952-60, 2013. The molar mass of the first block-copolymer layer 3 formed in step b) will therefore possibly be chosen so as to control the pitch p of the structured first electrode 200. By way of nonlimiting example, the pitch p of the structured first electrode 200 may be about 20 nm.
In the absence of steps d1) and d2), the memory layer 4 is advantageously made from at least one material selected from the group containing:
Such materials are sub-stoichiometric oxides allowing an electrically conductive filament to be created when they are subjected to a high potential difference. Such materials may thus form, with the first and second structured electrodes 200, 210, a resistive random-access memory.
As illustrated in
The invention is not limited to the described embodiments. Those skilled in the art will be able to consider technically functional combinations thereof, and to substitute equivalents therefor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1758900 | Sep 2017 | FR | national |
| 1851910 | Mar 2018 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/052348 | 9/25/2018 | WO | 00 |
