Hafnium zirconium oxide ferroelectric device

Abstract

An intermediate (1, 11) forming a ferroelectric device (10, 110) comprising: a hafnium zirconium oxide layer (4), comprising a tetragonal phase, and at least one metal oxide layer (5, 51, 52) in physical contact with the hafnium zirconium oxide layer (4) wherein the metal oxide layer (5, 51, 52) comprises at least one metal cation selected from the group consisting of Cr in oxidation state of 5 or 6, W in oxidation state of 5 or 6, Mo in oxidation state of 5 or 6, Ce in oxidation state of 4, v having an oxidation state of 4 or 5, where W and / or Mo and / or V are also present if Cr is present.

Description

Technical Field

[0001] The present invention relates to the field of ferroelectric devices. In particular, the present invention relates to ferroelectric devices (and intermediates thereof) comprising hafnium zirconium oxide. Background of the Invention

[0003] The field of non-volatile memory technology is a key area of ​​research and development in the electronics industry as it plays a vital role in a wide range of applications from mobile devices to large data centers. Among the various types of non-volatile memory, ferroelectric random access memory (FeRAM or FRAM) has attracted much attention due to its potential for high-speed operation, low power consumption, and ability to retain data without continuous power supply. Ferroelectric field-effect transistor memory also has similar advantages, which uses ferroelectric field-effect transistors to provide a single-transistor non-volatile memory.

[0004] Ferroelectric materials are characterized by their ability to exhibit spontaneous electric polarization, which can be reversed by applying an external electric field. This property is exploited in FeRAM devices, where the direction of polarization corresponds to the binary data states '0' and '1'. The ability to quickly switch polarization states with minimal energy input is critical to the performance of FeRAM.

[0005] A major challenge in the field is to scale down ferroelectric films to ultra-thin layers, especially films with thicknesses below 10 nanometers. As devices become smaller and more compact, the need for thin ferroelectric films that maintain high polarization and durability is increasing. Achieving remanent polarization (2Pr) values ​​above 30 microcoulombs per square centimeter (μC / cm 2 ) and a durability of at least 1E+11, i.e. 10 11 Secondary cycling is a key goal that researchers and engineers strive to achieve.

[0006] The development of ferroelectric hafnium (HfO2) and hafnium zirconate (HfZrO2) has been the focus of recent years to improve the ferroelectric properties of thin films. These materials are compatible with current semiconductor manufacturing processes and have the potential to be integrated into silicon-based electronics, so they are promising. However, enhancing their ferroelectric properties to meet the stringent requirements of modern memory devices remains a challenge.

[0007] Despite progress in the field, further improvements are needed to address challenges associated with scaling ferroelectric materials. The pursuit of materials and structures that can deliver the desired performance at ever-smaller sizes continues to drive innovation in ferroelectric memory technology.

[0008] Therefore, there is still a need in the art for devices and methods that can at least solve some of the above problems. Summary of the invention

[0009] It is an object of the present invention to provide a good intermediate for forming a ferroelectric device. Another object of the present invention is to provide a good method for forming a ferroelectric device. Another object of the present invention is to provide a good ferroelectric device. Another object of the present invention is to provide a good non-volatile memory device.

[0010] The above object is achieved by the method and device described in the present invention.

[0011] In a first aspect, the present invention relates to an intermediate for forming a ferroelectric device, comprising:

[0012] a hafnium zirconium oxide layer comprising a tetragonal phase, and

[0013] At least one metal oxide layer in physical contact with the hafnium zirconium oxide layer, wherein the metal oxide layer comprises at least one metal cation selected from the group consisting of Cr in oxidation state 5 or 6, W in oxidation state 5 or 6, Mo in oxidation state 5 or 6, Ce in oxidation state 4, V in oxidation state 4 or 5, wherein if Cr is present, W and / or Mo and / or V are also present.

[0014] In a second aspect, the invention relates to a method of forming a ferroelectric device, the method comprising the steps of:

[0015] i) providing an intermediate according to an embodiment of the first aspect of the present invention, and then

[0016] ii) inducing reduction of one or more of the at least one metal cation of the metal oxide layer to transfer oxygen atoms from the metal oxide layer to the hafnium zirconium oxide layer, thereby converting at least a portion of the tetragonal phase to an orthorhombic phase.

[0017] In a third aspect, the present invention relates to a ferroelectric device, which can be obtained by a method according to an embodiment of the second aspect of the present invention.

[0018] In a fourth aspect, the present invention relates to a non-volatile memory device comprising a memory cell array, wherein at least one memory cell in the memory cell array comprises a ferroelectric device according to an embodiment of the third aspect of the present invention.

[0019] An advantage of embodiments of the present invention is that the tetragonal phase of the hafnium zirconium oxide layer can be directly transformed into the orthorhombic phase. An advantage of embodiments of the present invention is that the ferroelectric properties of the hafnium zirconium oxide layer can be directly improved thereby. An advantage of embodiments of the present invention is that a ferroelectric device with good remnant polarization and durability can be achieved even when the hafnium zirconium oxide layer is thin. Another advantage of embodiments of the present invention is that the gradual phase transition ensures high durability, making the device suitable for applications requiring a large number of operating cycles.

[0020] One advantage of embodiments of the present invention is that the metal oxide layer can be composed of various metal cations that can be reduced to lower oxidation states without affecting the conductivity preferred for ferroelectric device function. Another advantage of embodiments of the present invention is that the method of forming a ferroelectric device can promote the desired phase transition from tetragonal to orthorhombic in the hafnium zirconium oxide layer.

[0021] An advantage of embodiments of the present invention is that the presence of at least one metal oxide layer in a ferroelectric device can restore the ferroelectric properties of the hafnium zirconium oxide layer when the ferroelectric properties are weakened during the life of the ferroelectric device.

[0022] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims as appropriate and with features of other dependent claims and not only where explicitly set out in a claim.

[0023] While improvements, changes and developments in apparatus are ongoing in the art, the concepts of the present invention are believed to represent substantially new and novel improvements involving changes in existing practice resulting in the provision of a more efficient, more stable and more reliable apparatus of this nature.

[0024] The above and other characteristics, features and advantages of the present invention will become apparent in the following detailed description in conjunction with the accompanying drawings, which illustrate the principles of the present invention by way of example. This description is for illustrative purposes only and does not limit the scope of the present invention. The reference figures cited below refer to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic vertical cross-sectional view of an intermediate body for forming a ferroelectric device, which is a ferroelectric capacitor, according to an embodiment of the present invention.

[0027] Figure 2 is a schematic vertical cross-sectional view of a ferroelectric capacitor according to an embodiment of the present invention.

[0028] Figure 3 is a schematic vertical cross-sectional view of an intermediate body for forming a ferroelectric device, which is a ferroelectric field effect transistor, according to an embodiment of the present invention.

[0029] Figure 4 is a schematic vertical cross-sectional view of a ferroelectric field effect transistor according to an embodiment of the present invention.

[0030] Figure 5 is a perspective view schematic diagram of a nonvolatile memory device including a memory cell array according to an embodiment of the present invention.

[0031] Figure 6is a graph of the variation of polarization as a function of applied electric field to a reference ferroelectric device and a ferroelectric device according to an embodiment of the present invention.

[0032] In different drawings, the same reference signs identify the same or similar elements. DETAILED DESCRIPTION

[0033] The present invention will be described with respect to specific embodiments and with reference to certain drawings, but the invention is not limited thereto, only by the claims. The drawings described are merely schematic and non-limiting. In the drawings, the dimensions of some elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and relative dimensions do not correspond to actual reductions in the practice of the invention.

[0034] In addition, the terms first, second, third, etc. in the specification and claims are used to distinguish similar elements and are not necessarily used to describe a sequence in time, space, hierarchy, or any other manner. It should be understood that the terms used in this way are interchangeable under appropriate circumstances, and the embodiments of the invention described herein are capable of operating in other sequences than those described or illustrated herein.

[0035] In addition, in the specification and claims, the terms top, bottom, above, below, etc. are used for descriptive purposes and not necessarily for describing relative positions. It should be understood that the terms so used are interchangeable where appropriate, and the embodiments described in the present invention are capable of operating in other orientations than those described or illustrated herein.

[0036] It should be noted that the term "comprising" used in the claims should not be interpreted as being limited to the parts listed thereafter, and it does not exclude other elements or steps. Therefore, it should be understood to indicate the presence of the features, wholes, steps or components, but this does not exclude the presence or addition of one or more other features, wholes, steps or components or their combinations. Therefore, the term "comprising" covers the situation where only the features are present and the situation where these features and one or more other features are present. Therefore, the word "comprising" as an embodiment according to the present invention also includes the situation where there are no other components. Therefore, the scope of the expression "a device comprising components A and B" should not be understood to limit the device to be composed of only components A and B. It means that for the present invention, the relevant components of the device are only A and B.

[0037] Also, it is important to note that the term “ coupling" should not be interpreted as being limited to only direct connections. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression "device A is coupled to device B" should not be limited to devices or systems in which the output of device A is directly connected to the input of device B. This means that there is a path between the output of A and the input of B, which may be a path that includes other devices or apparatuses. "Coupled" may mean that two or more elements are either in direct physical contact or in electrical contact, or that two or more elements are not in direct contact with each other, but still cooperate or interact with each other.

[0038] References to "one embodiment" or "an embodiment" in the specification mean that the specific features, structures, or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing in various places in the specification do not necessarily all refer to the same embodiment, but may all refer to the same embodiment. In addition, specific features, structures, or characteristics may be combined in one or more embodiments in any suitable manner, which will be apparent to those of ordinary skill in the art.

[0039] Similarly, it should be understood that in the description of exemplary embodiments of the invention, different features of the invention are sometimes combined into a single embodiment, figure, or description thereof, in order to simplify the disclosure and aid in understanding one or more different aspects of the invention. However, the method in the present disclosure should not be interpreted as reflecting the following intention: the claimed invention requires more features than those expressly recited in the claims. And, as reflected in the appended claims, inventive aspects may include less than all the features of a single embodiment disclosed above. Therefore, the appended claims are expressly incorporated into this detailed description, and each claim itself represents a separate embodiment of the invention.

[0040] In addition, when some embodiments described herein include some but not other features included in other embodiments, the combination of features of different embodiments should be intended to be included within the scope of the present invention and form different embodiments, which should be understood by those skilled in the art. For example, in the attached claims, any embodiment claimed for protection can be used in any combination.

[0041] In addition, some embodiments are described herein as a method or a combination of method elements implemented by a processor of a computer system or by other means of implementing a function. Therefore, a processor with instructions required for implementing the method or method elements forms a device for carrying out the method or method elements. In addition, the element of the device embodiment described herein is an example of a device for performing a function, and the function is carried out by being used to implement the element for the purpose of the present invention.

[0042] Numerous specific details are set forth in the description herein. However, it should be understood that embodiments of the present invention may be implemented without these specific details. In other cases, well-known methods, structures, and techniques are not described in detail in order not to obscure the understanding of this specification.

[0043] In a first aspect, the present invention relates to an intermediate for forming a ferroelectric device, comprising:

[0044] a hafnium zirconium oxide layer comprising a tetragonal phase, and

[0045] At least one metal oxide layer in physical contact with the hafnium zirconium oxide layer, wherein the metal oxide layer comprises at least one metal cation selected from the group consisting of Cr in oxidation state 5 or 6, W in oxidation state 5 or 6, Mo in oxidation state 5 or 6, Ce in oxidation state 4, V in oxidation state 4 or 5, wherein if Cr is present, W and / or Mo and / or V are also present.

[0046] In some embodiments, at least one metal oxide layer may include at least one metal cation selected from the group consisting of Cr in oxidation state 6, W in oxidation state 6, Mo in oxidation state 6, Ce in oxidation state 4, and V in oxidation state 5. In some embodiments, the at least one metal oxide layer may include at least one metal oxide selected from the group consisting of CrO3, WO3, MoO3, CeO2, and V2O3. These embodiments provide a specific selection of metal cations with high oxidation states that facilitate the reduction process to improve ferroelectric properties. An advantage of these embodiments is that these metal cations in high oxidation states can be directly reduced, releasing oxygen atoms from the metal oxide layer and transferring to the hafnium zirconium oxide layer.

[0047] In some embodiments, the metal oxide layer may be WO3. WO3 has good compatibility with the hafnium zirconium oxide layer. In addition, WO3 has good stability, can be safely handled, is widely available, and has an oxidation state that is easily controlled or adjusted.

[0048] In embodiments, the thickness of the metal oxide layer is 0.5 to 5.0 nanometers, preferably 1.0 to 2.0 nanometers. In these embodiments, the thickness can be small enough so that the effect of the metal oxide layer on the electrical properties of the ferroelectric device is limited. In some embodiments, the thickness can be large enough so that the stability of the layer is good during and after the reduction of the metal cations.

[0049] In some embodiments, the hafnium zirconium oxide layer and at least one metal oxide layer may be disposed above a bottom electrode layer and below a top electrode layer. These embodiments provide intermediates for forming ferroelectric capacitors, which may be used, for example, in ferroelectric random access memories.

[0050] In some embodiments, the hafnium zirconium oxide layer and at least one metal oxide layer may be disposed above the semiconductor channel and below the top electrode layer. These embodiments provide intermediates for forming ferroelectric field effect transistors, which may be used, for example, in ferroelectric random access memories.

[0051] In some embodiments, the at least one metal oxide layer consists of one or two metal oxide layers. The hafnium zirconium oxide layer may be disposed above the first metal oxide layer of the at least one metal oxide layer. The first metal oxide layer of the at least one metal oxide layer may be disposed above the hafnium zirconium oxide layer. The hafnium zirconium oxide layer may be disposed above the first metal oxide layer of the at least one metal oxide layer, and the second metal oxide layer of the at least one metal oxide layer may be disposed above the hafnium zirconium oxide layer. In other words, the hafnium zirconium oxide layer may be sandwiched between two metal oxide layers of the at least one metal oxide layer.

[0052] Any feature of any embodiment of the first aspect may be independent of the corresponding description of any embodiment of any other aspect of the invention.

[0053] In a second aspect, the invention relates to a method of forming a ferroelectric device, the method comprising the steps of:

[0054] i) providing an intermediate according to an embodiment of the first aspect of the present invention, and then

[0055] ii) inducing reduction of one or more of the at least one metal cation of the metal oxide layer to transfer oxygen atoms from the metal oxide layer to the hafnium zirconium oxide layer, thereby converting at least a portion of the tetragonal phase to an orthorhombic phase.

[0056] Without being bound by theory, the (non-ferroelectric) tetragonal phase contains a higher concentration of oxygen vacancies than the (ferroelectric) orthorhombic phase. The tetragonal phase can be transformed into the orthorhombic phase by filling some of the vacancies in the tetragonal phase with said oxygen atoms.

[0057] In some embodiments, the hafnium zirconium oxide layer of the intermediate may contain an orthorhombic phase and have non-zero ferroelectricity. Therefore, the intermediate itself can be used as a ferroelectric device. In these embodiments, the method can improve or improve the ferroelectric properties of the intermediate to achieve a ferroelectric device consistent with embodiments of the present invention.

[0058] In step ii, when the metal cation is Cr, W, V and Mo, the oxidation state of the metal cation may be reduced to an oxidation state of up to 4, or when the metal cation is Ce, the oxidation state of the metal cation may be reduced to an oxidation state of up to 3. In step ii, the oxidation state of Cr is 5 or 6 before reduction, and may be reduced to an oxidation state of 3 or 4. In step ii, the oxidation state of W is 5 or 6 before reduction, and may be reduced to an oxidation state of 3 or 4. In step ii, the oxidation state of Mo is 5 or 6 before reduction, and may be reduced to an oxidation state of 3 or 4. In step ii, the oxidation state of Ce is 4 before reduction, and may be reduced to an oxidation state of 3. In step ii, the oxidation state of V is 5 before reduction, and may be reduced to an oxidation state of 4.

[0059] The transfer of oxygen atoms from the metal oxide layer to the hafnium zirconium oxide layer may deform the lattice of the tetragonal phase. This deformation may cause the tetragonal phase to transform into the orthorhombic phase. Without being bound by theory, the oxygen atoms may fill the oxygen vacancies in the tetragonal phase lattice, which may cause the bonds within the tetragonal phase lattice to stretch, thereby transforming the tetragonal phase into the orthorhombic phase.

[0060] In some embodiments, the hafnium zirconium oxide layer may be undoped. In some embodiments, the hafnium zirconium oxide layer may be doped with a lanthanide element. The lanthanide element may provide oxygen vacancies, which may cause the hafnium zirconium oxide layer to crystallize into an orthorhombic phase.

[0061] In some embodiments, the hafnium zirconium oxide layer may be doped with a redox-active dopant, wherein the dopant and at least one of the at least one metal cation form a redox pair. One advantage of these embodiments is that good control of oxygen vacancies in the hafnium zirconium oxide layer may be achieved. After the device is formed and the hafnium zirconium oxide layer comprises an orthorhombic phase, when a voltage is applied to the metal oxide layer, for example, during a voltage cycle of the device (which is inherent to the function of the device), the metal cations in the metal oxide layer may be further reduced so that more oxygen atoms can be released into the hafnium zirconium oxide layer. These oxygen atoms can fill the oxygen vacancies in the hafnium zirconium oxide layer, causing the (ferroelectric) orthorhombic phase to transform into the (non-ferroelectric) monoclinic phase (achieved when the oxygen vacancy concentration is very low). When a redox-active dopant is present, the oxygen atoms react with the redox-active dopant instead of filling the oxygen vacancies. Thus, advantageously, due to oxidation of the redox-active dopant, by accepting excess oxygen and increasing its oxidation state, in the hafnium zirconium oxide layer, an undesirable orthorhombic to monoclinic phase transition that may occur when oxygen vacancies are completely suppressed can be suppressed. Thus, the durability or service life of the device can be improved.

[0062] Redox-active dopants may hinder the transition from the orthorhombic to monoclinic phase, but the transition from tetragonal to orthorhombic phase may occur due to the very low activation energy of the transition. In fact, the concentration of oxygen vacancies in the tetragonal phase may be high, so the reaction rate between oxygen atoms and oxygen vacancies may be high enough to occur in the tetragonal phase even in the presence of redox-active dopants.

[0063] In some embodiments, the redox-active dopant may be at least one of niobium, chromium, tungsten, vanadium, and molybdenum in oxidation states up to 4, and cerium in oxidation states up to 3. These elements are easily oxidized by oxygen atoms transferred to the hafnium zirconium oxide layer. In some embodiments, the concentration of the redox-active dopant in the hafnium zirconium oxide layer may be 0.5 to 4.5 atomic percent (at.-%), preferably 1.5 to 3.5 at.-%.

[0064] In some embodiments, the hafnium zirconium oxide layer doped with a dopant may be provided by atomic layer deposition, chemical vapor deposition, or physical vapor deposition. By the deposition, a hafnium zirconium oxide layer consisting of hafnium zirconium oxide crystals or crystallites in a tetragonal phase may be formed. In some embodiments, the hafnium zirconium oxide layer doped with a dopant (e.g., a redox-active dopant or a lanthanide dopant) may be provided by alternately depositing hafnium zirconium oxide sublayers and dopant oxide sublayers. The sublayers may be deposited by atomic layer deposition, chemical vapor deposition, or physical vapor deposition.

[0065] In some embodiments, the composition comprises TiO2, MoO x(where x is 2 to 3), an interface layer of HfO2, ZrO2 or WO3 may be present between the bottom electrode layer and the hafnium zirconium oxide layer or between the top electrode layer and the hafnium zirconium oxide layer, wherein the interface layer is in physical contact with the hafnium zirconium oxide layer on the side where no metal oxide layer is present. Preferably, the intermediate includes a hafnium zirconium oxide layer located above (e.g., in physical contact with) the interface layer. In some embodiments, in step i, providing the intermediate includes providing a hafnium zirconium oxide layer located above (e.g., in physical contact with) the interface layer. The interface layer may provide the hafnium zirconium oxide layer with larger grains and favorable grain orientation. In addition, the interface layer may induce greater tensile stress into the hafnium zirconium oxide layer, which may result in greater residual polarization. In embodiments comprising an interface layer, at least one metal oxide layer is typically composed of a single metal oxide layer.

[0066] In some embodiments, step ii comprises applying a voltage to the intermediate according to the first aspect of the present invention. Applying a voltage to induce a reduction process is a direct and controllable technique for changing material properties. In some embodiments, applying a voltage comprises cycling the voltage. The cycling may be inherent to the use of a ferroelectric device. For example, the cycling may be provided by switching the ferroelectric device between different ferroelectric states. A top electrode layer or a bottom electrode layer may be in electrical contact with the metal oxide layer. A voltage may be applied to the metal oxide layer via the top or bottom electrode layer.

[0067] In some embodiments, step ii comprises applying a heat treatment to the intermediate according to any embodiment of the first aspect of the present invention. In some embodiments, applying the heat treatment may comprise heating the intermediate according to an embodiment of the present invention to a temperature of 100°C to 600°C, preferably 300°C to 400°C. The heat treatment may be provided by a crystallization anneal, which itself may be used to form an orthorhombic phase of the hafnium zirconium oxide layer. After deposition, the hafnium zirconium oxide layer may directly comprise tetragonal hafnium zirconium oxide crystallites, and may comprise amorphous hafnium zirconium oxide. In an embodiment of the present invention, the crystallization anneal may convert the tetragonal crystallites into an orthorhombic phase. The crystallization anneal may convert the amorphous oxide (typically by crystallizing the tetragonal phase) into a crystallized orthorhombic phase.

[0068] In a preferred embodiment, the metal oxide layer provided in step i is provided by atomic layer deposition. These embodiments can provide good control over the characteristics of the metal oxide layer. In some embodiments, the metal oxide layer provided in step i can be provided by physical vapor deposition depositing the metal and then applying an oxidizing plasma to oxidize the deposited metal. For example, the oxidation can be performed by applying oxygen plasma or ozone treatment.

[0069] Any feature of any embodiment of the second aspect may be independent of the corresponding description of any embodiment of any other aspect of the invention.

[0070] In a third aspect, the present invention relates to a ferroelectric device, which can be obtained by a method according to an embodiment of the second aspect of the present invention.

[0071] In some embodiments, the ferroelectric device may include a hafnium zirconium oxide layer comprising an orthorhombic phase, and at least one metal oxide layer in physical contact with the hafnium zirconium oxide layer, wherein the metal oxide layer includes at least one metal cation selected from the group consisting of Cr, W, V, and Mo with an oxidation state up to 4, or Ce with an oxidation state up to 3.

[0072] In some embodiments, the hafnium zirconium oxide layer and at least one metal oxide layer may be disposed above the bottom electrode layer and / or below the top electrode layer. In some embodiments, the bottom electrode layer and / or the top electrode layer may include titanium nitride, chromium, chromium tungsten, or ruthenium tungsten. Preferably, the at least one metal oxide layer is in electrical contact with one of the bottom electrode layer and the top electrode layer.

[0073] In some embodiments, the hafnium zirconium oxide layer and at least one metal oxide layer are located above the bottom electrode layer and below the top electrode layer.

[0074] In some embodiments, the ferroelectric device is a ferroelectric capacitor, and the hafnium zirconium oxide layer and the at least one metal oxide layer are disposed above a bottom electrode layer and below a top electrode layer.

[0075] In some embodiments, the ferroelectric device is a ferroelectric field effect transistor, and the hafnium zirconium oxide layer and at least one metal oxide layer are disposed above a semiconductor channel and below a top electrode layer. In some embodiments, the semiconductor channel may be an oxide semiconductor channel. When the ferroelectric layer is switched, the semiconductor channel may function as a bottom contact.

[0076] Any feature of any embodiment of the third aspect may be independent of the corresponding description of any embodiment of any other aspect of the invention.

[0077] In a fourth aspect, the present invention relates to a non-volatile memory device comprising a memory cell array, wherein at least one memory cell in the memory cell array comprises a ferroelectric device according to an embodiment of the third aspect of the present invention or an intermediate according to an embodiment of the first aspect. In some embodiments, the ferroelectric device may be a ferroelectric capacitor, which may be used as a ferroelectric random access memory cell. In some embodiments, the ferroelectric device may be a ferroelectric field effect transistor, which may be used as a ferroelectric field effect transistor memory cell.

[0078] Any feature of any embodiment of the fourth aspect may be independent of the corresponding description of any embodiment of any other aspect of the invention.

[0079] The present invention is now described by a detailed description of several embodiments of the present invention. It is obvious that other embodiments of the present invention can be constructed according to the knowledge of those skilled in the art without departing from the technical teachings of the present invention, and the present invention is limited only by the appended claims.

[0080] Example 1: Formation of a ferroelectric capacitor

[0081] Reference Figure 1 , Figure 1 is a schematic vertical cross-sectional view of an intermediate body 1 for forming a ferroelectric device, which is a ferroelectric capacitor, according to an embodiment of the present invention.

[0082] In the present embodiment, the intermediate body 1 forming the ferroelectric device comprises a bottom electrode layer 2. The intermediate body 1 forming the ferroelectric device comprises an interface layer 3, which is located above the bottom electrode layer 2, for example, in physical contact with the bottom electrode layer 2. The intermediate body 1 forming the ferroelectric device comprises a hafnium zirconium oxide layer 4, which is located above the interface layer 3, for example, on the interface layer 3.

[0083] In this embodiment, without being bound by theory, the hafnium zirconium oxide layer 4 may contain a high concentration of oxygen vacancies 41. In this embodiment, the hafnium zirconium oxide layer 4 mainly includes a tetragonal phase. The hafnium zirconium oxide layer 4 forming the intermediate 1 of the ferroelectric device may further include an orthorhombic phase and / or a monoclinic phase. The hafnium zirconium oxide layer 4 may further include an amorphous hafnium zirconium oxide.

[0084] The intermediate 1 for forming a ferroelectric device comprises a metal oxide layer 5 in physical contact with a hafnium zirconium oxide layer 4. In this embodiment, the metal oxide layer 5 is in physical contact with the hafnium zirconium oxide layer 4. The metal oxide layer comprises at least one metal cation selected from the group consisting of Cr in oxidation state 5 or 6, W in oxidation state 5 or 6, Mo in oxidation state 5 or 6, Ce in oxidation state 4, V in oxidation state 4 or 5, wherein if Cr is present, W and / or Mo and / or V are also present. Each of these metal cations can be reduced to a lower oxidation state, resulting in the release of oxygen atoms into the hafnium zirconium oxide layer 4.

[0085] In an exemplary embodiment, direct physical contact between the metal oxide layer 5 and the hafnium zirconium oxide layer 4 allows oxygen to be injected from the metal oxide layer 5 into the hafnium zirconium oxide layer 4. At the same time, electrons flow from the hafnium zirconium oxide layer to the metal oxide layer. This electron movement can reduce the oxidation state of the metal cations in the metal oxide layer from a higher state to a lower state. This reaction occurs because the electron affinity of the metal oxide layer 5 is lower than that of the hafnium zirconium oxide layer 4. The reaction can be very slow, and according to one embodiment, its rate can be increased by applying a heat treatment (e.g., crystallization annealing) to the intermediate 1 forming the ferroelectric device. The crystallization annealing can further convert the amorphous and / or microcrystalline hafnium zirconium oxide into crystalline hafnium zirconium oxide.

[0086] According to another embodiment, the reaction rate may be increased by applying a voltage. The voltage may be applied to the ferroelectric device during operation, ie during cycling of the ferroelectric device (see below).

[0087] In this embodiment, the thickness of the metal oxide layer 5 is 0.5 to 5.0 nm, which is determined along a direction perpendicular to the top surface of the metal oxide layer 5 .

[0088] In the present embodiment, the intermediate body 1 forming the ferroelectric device comprises a top electrode layer 6 above, for example on, the metal oxide layer 5 .

[0089] Reference Figure 2 . Oxygen atoms can be released from the metal oxide layer 5 into the hafnium zirconium oxide layer 4 by heat treatment, and can fill some oxygen vacancies 41 of the hafnium zirconium oxide layer 4. Therefore, at least part of the tetragonal phase of the hafnium zirconium oxide layer 4 is converted into an orthorhombic phase. Since the orthorhombic phase is a ferroelectric phase, the ferroelectric properties of the hafnium zirconium oxide layer 4 can be improved. A ferroelectric device 10 is thus formed. In the present embodiment, the ferroelectric device 10 is a ferroelectric capacitor 10, whose ferroelectric layer, i.e., the hafnium zirconium oxide layer 4, is located between the top electrode layer 6 and the bottom electrode layer 2 corresponding to the "plate" of the ferroelectric capacitor 10.

[0090] In this embodiment, the bottom electrode layer 2 and the top electrode layer 6 are electrically connected to the controller 7. In one embodiment, when the ferroelectric device 10 is in operation, the controller 7 is configured to apply a voltage to the top electrode layer 6 and the bottom electrode layer 2. During the cycling of the ferroelectric device 10, a reduction of one or more of the at least one metal cation of the metal oxide layer 5 may occur by alternating (positive and negative) cycles of applying a voltage, so that oxygen atoms are transferred from the metal oxide layer 5 to the hafnium zirconium oxide layer 4.

[0091] In some embodiments, the hafnium zirconium oxide layer 4 may include redox-active ions that form redox pairs with metal cations of the metal oxide layer 5. In these embodiments, the oxygen atoms transferred into the hafnium zirconium oxide layer 4 may combine with the redox-active ions (e.g., instead of filling the oxygen vacancies 41). Then, complete suppression of the oxygen vacancies 41 may be avoided by the redox-active ions in the hafnium oxide layer 4, which initially have a lower oxidation state. Thus, an undesirable transition from the orthorhombic phase to the monoclinic phase may be avoided.

[0092] Example 2: Formation of a ferroelectric field effect transistor

[0093] Reference Figure 3 , Figure 3 is a schematic vertical cross-sectional view of an intermediate body 11 for forming a ferroelectric device, which is a ferroelectric field effect transistor, according to an embodiment of the present invention.

[0094] In the present embodiment, the intermediate body 11 forming the ferroelectric device comprises a semiconductor channel 20, such as an oxide semiconductor channel. The semiconductor channel 20 separates a source 21 from a drain 22, such as laterally.

[0095] In this embodiment, the intermediate 11 in the process of forming the ferroelectric device includes a first metal oxide layer 51, which is above the semiconductor channel 20, for example, in physical contact with the semiconductor channel 20. The intermediate 11 in the process of forming the ferroelectric device includes a hafnium zirconium oxide layer 4, which is on the first metal oxide layer 51, that is, in physical contact with the first metal oxide layer 51. The hafnium zirconium oxide layer 4 includes a tetragonal phase.

[0096] In this embodiment, the intermediate 11 in the process of forming the ferroelectric device includes a second metal oxide layer 52, and the second metal oxide layer 52 is on the hafnium zirconium oxide layer 4, that is, in physical contact with the hafnium zirconium oxide layer 4. The first metal oxide layer 51 may contain at least one metal cation that is the same as the second metal oxide layer 52. For example, the first metal oxide layer 51 and the second metal oxide layer 52 may both be formed of WO3. However, this is not necessary. For example, at least one metal cation of the first metal oxide layer 51 may be different from at least one metal cation of the second metal oxide layer 52.

[0097] In the present invention, the intermediate 11 in the process of forming a ferroelectric device includes a top electrode layer 6, which is above the second metal oxide layer 52, such as in physical contact with the second metal oxide layer 52. The top electrode layer 6 can be used as a gate of a ferroelectric field effect transistor.

[0098] Heat treatment (eg, by crystallization annealing) may be applied to the intermediate 10. This may result in reduction of metal cations of the first metal oxide layer 51 and the second metal oxide layer 52, and transfer of oxygen atoms from the first metal oxide layer 51 and the second metal oxide layer 52 to the hafnium zirconium oxide layer 4.

[0099] Reference Figure 4 The oxygen atoms transferred to the hafnium zirconium oxide layer 4 may induce at least a portion of the tetragonal phase to be transformed into an orthorhombic phase. Without being bound by theory, the oxygen atoms may fill the oxygen vacancies 41 in the hafnium zirconium oxide layer 4, thereby changing the distance and angle between oxygen and the hafnium bond or zirconium bond in the hafnium zirconium oxide layer 4, thereby transforming the tetragonal phase into an orthorhombic phase. Thus, the ferroelectric field effect transistor 110 according to an embodiment of the present invention may be formed.

[0100] In this embodiment, the controller 7 is electrically coupled to the source 21, the drain 22 and the top electrode layer 6. The controller 7 is configured to apply a voltage. The voltage may be used to operate the ferroelectric field effect transistor 110, which in turn may result in a voltage cycle.

[0101] Embodiment 3: Non-volatile storage device

[0102] Reference Figure 5 , which is a nonvolatile memory device 8 including a memory cell array according to an embodiment of the present invention.

[0103] In this embodiment, each memory cell in the memory cell array includes a ferroelectric device 10, which is a ferroelectric capacitor 10 according to an embodiment of the present invention. Each ferroelectric capacitor 10 can be used as a ferroelectric random access memory cell. Each ferroelectric capacitor 10 of this embodiment can have the same features as the ferroelectric capacitor of the above-mentioned embodiment 1.

[0104] The nonvolatile memory device 8 further includes a controller 7, which may be a processor. The controller 7 may be electrically coupled to row lines 71 for addressing rows of ferroelectric capacitors 10. Herein, each row line 71 may be connected to the bottom electrode layer 2 of each ferroelectric capacitor 10 in a row of the memory cell array. The controller 7 may be electrically coupled to column lines 72 for addressing columns of ferroelectric capacitors 10. Herein, each column line 72 may be connected to the top electrode layer 6 of each ferroelectric capacitor 10 in a column of the memory cell array. Similar to the most advanced memory cells, each ferroelectric capacitor 10 may be individually read or written by providing voltages to the row lines 71 and column lines 72 electrically connected to the ferroelectric capacitor 10.

[0105] Although the nonvolatile memory device 8 further includes a memory cell that is a ferroelectric capacitor 10 in the illustrated embodiment, the memory cell may also include a ferroelectric field effect transistor.

[0106] The ferroelectric hafnium zirconium oxide layer 4 according to an embodiment of the present invention can have high polarization remanent polarization and high durability. Therefore, the ferroelectric device according to an embodiment of the present invention can provide improved characteristics for the non-volatile memory device 8 to retain binary data written to the memory cell (i.e., the ferroelectric capacitor 10) of the memory cell array.

[0107] Example 4: Experiment

[0108] The ferroelectric properties of a ferroelectric device according to an embodiment of the present invention were tested. The tested ferroelectric device included a 10 nm thick bottom electrode layer formed of TiN by atomic layer deposition at 340°C. An interface layer with a thickness of 2 nm was deposited on the bottom electrode layer by atomic layer deposition. A hafnium zirconium oxide layer doped with lanthanum with a thickness of 8 nm was deposited on the interface layer by atomic layer deposition. A metal oxide layer with a thickness of 2 nm was deposited on the hafnium zirconium oxide layer by atomic layer deposition. A top electrode layer formed of TiN with a thickness of 30 nm was deposited on the metal oxide layer by atomic layer deposition. The metal oxide layer included WO3. A crystallization annealing at 400°C was applied to the stack for 1 hour to induce the reduction of tungsten cations in WO3, followed by oxygen transfer to the hafnium zirconium oxide layer.

[0109] A reference ferroelectric device was prepared in which the metal oxide layer contained Nb2O5, had otherwise the same properties as the ferroelectric device according to the embodiment of the present invention, and was subjected to the same crystallization annealing treatment.

[0110] Reference Figure 6 , which includes two graphs of the variation of the polarization P with the applied electric field E. The left side shows the results of a reference ferroelectric device, while the right side shows the results of a ferroelectric device according to an embodiment of the present invention. The hysteresis loop is a typical feature of ferroelectric materials and can be clearly observed in both graphs.

[0111] The remanent polarization Pr is the polarization difference between two possible ferroelectric polarization states (i.e., "up" or "down") when no electric field is applied (i.e., E = 0 MV / cm). It can be observed that the remanent polarization of the ferroelectric device is large according to the embodiments of the present invention, which is attributed to the efficient release of oxygen atoms from the metal oxide layer into the hafnium zirconium oxide layer and the subsequent transformation of the tetragonal phase into the orthorhombic phase.

[0112] It should be understood that although preferred embodiments, specific constructions and configurations, and materials of the device of the present invention have been discussed herein, various changes or modifications in form and detail may be made without departing from the scope of the present invention. Steps may be added or reduced to the methods described within the scope of the present invention.

Claims

1. An intermediate (1, 11) in a process of forming a ferroelectric device (10, 110), comprising: a hafnium zirconium oxide layer (4) comprising a tetragonal phase, and At least one metal oxide layer (5, 51, 52) in physical contact with the hafnium zirconium oxide layer (4), wherein the metal oxide layer (5, 51, 52) comprises at least one metal cation selected from the group consisting of: Cr in oxidation state 5 or 6, W in oxidation state 5 or 6, Mo in oxidation state 5 or 6, Ce in oxidation state 4, V in oxidation state 4 or 5, wherein if Cr is present, W and / or Mo and / or V are also present.

2. An intermediate (1, 11) according to claim 1, wherein at least one metal oxide layer (5, 51, 52) comprises at least one metal cation selected from the group consisting of Cr in oxidation state 6, W in oxidation state 6, Mo in oxidation state 6, Ce in oxidation state 4 and V in oxidation state 5.

3. An intermediate body (1, 11) according to claim 2, wherein the metal oxide layer (5, 51, 52) is WO3.

4. The intermediate body (1, 11) according to any one of the preceding claims, wherein the metal oxide layer (5, 51, 52) has a thickness of 0.5-5.0 nm, preferably 1.0-2.0 nanometers.

5. A method of forming a ferroelectric device (10, 110), the method comprising the steps of: i) providing an intermediate (1, 11) according to any one of claims 1 to 4, then ii) inducing reduction of one or more of the at least one metal cation of the metal oxide layer (5, 51, 52) to transfer oxygen atoms from the metal oxide layer (5, 51, 52) to the hafnium zirconium oxide layer (4), thereby converting at least a portion of the tetragonal phase to an orthorhombic phase.

6. The method according to claim 5, wherein the hafnium zirconium oxide layer (4) is doped with a redox-active dopant, wherein the dopant and at least one of the at least one metal cation form a redox couple.

7. The method of claim 6, wherein the redox-active dopant is at least one of niobium, chromium, tungsten, vanadium and molybdenum in an oxidation state up to 4, and cerium in an oxidation state up to 3.

8. The method according to claims 5-7, wherein step ii. comprises applying a voltage to the intermediate (1, 11) according to any one of claims 1-4.

9. The method according to any one of claims 5-8, wherein step ii. comprises applying a heat treatment to the intermediate (1, 11) according to any one of claims 1-4.

10. The method according to any one of claims 5 to 9, wherein the metal oxide layer (5, 51, 52) provided in step i. is provided by atomic layer deposition.

11. A ferroelectric device (10, 110) obtainable by the method according to any one of claims 5 to 10.

12. The ferroelectric device (10, 110) according to claim 9, comprising: a hafnium zirconium oxide layer (4) comprising an orthorhombic phase, and At least one metal oxide layer (5, 51, 52) in physical contact with the hafnium zirconium oxide layer (4), wherein the metal oxide layer (5, 51, 52) comprises at least one metal cation selected from the group consisting of Cr, W, V and Mo in an oxidation state up to 4, or Ce in an oxidation state up to 3.

13. The ferroelectric device (10, 110) according to claim 11 or 12, wherein the ferroelectric device (10, 110) is a ferroelectric capacitor (10), wherein the hafnium zirconium oxide layer and at least one metal oxide layer (5, 51, 52) are arranged above a bottom electrode layer (2) and below a top electrode layer (6).

14. The ferroelectric device (10, 110) according to claim 11 or 12, wherein the ferroelectric device (10, 110) is a ferroelectric field effect transistor (110), wherein the hafnium zirconium oxide layer and at least one metal oxide layer (5, 51, 52) are arranged above the semiconductor channel (20) and below the top electrode layer (6).

15. A non-volatile memory device (8) comprising a memory cell array, wherein at least one memory cell in the memory cell array comprises a ferroelectric device (10, 110) according to any one of claims 11 to 14.

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