Layered solid-state device including a ferroelectric layer and its manufacturing method

Abstract

The layered solid-state component (100) is made of a crystalline material Li that has an X or 33° Y orientation relative to the substrate (10) of the layered solid-state component. 1-x (Nb 1-y Ta y ) 1+x O 3+2x-z The ferroelectric layer (2) has the chemical formula L k Ni r O 1.5·(k+r)+w or L n+1 Ni n O 3n+1+δ (L is a lanthanide element) are epitaxially grown from a buffer layer (1). Such layered solid-state components can form thin-film bulk acoustic resonators, which may be useful in integrated electronic circuits such as RF filters, or in inductive optical devices such as integrated optical modulators.

Description

[Technical Field]

[0001] The present invention relates to a layered solid-state device including a ferroelectric layer and to a method for manufacturing such a device. [Background technology]

[0002] The chemical formula Li, often written in simplified form as LiNbO3 or LiTaO3, respectively. 1-x Nb 1+x O 3+2x and Li 1-x Ta 1+x O 3+2x Lithium niobate and lithium tantalate, which have the following structure, are ferroelectric materials useful for many applications in microelectronics, microacoustics, pyroelectric devices, and guided photonics. In particular, they are used to fabricate RF filters, such as those implemented in communication terminals. However, LiNbO3 or LiTaO3 layers have mainly been fabricated on dielectric sapphire substrates, making them usable only for surface acoustic wave (SAW) implementation. There is a challenge in fabricating LiNbO3 or LiTaO3 films at low cost on bottom electrodes and / or on structures based on silicon (Si) substrates, particularly those that include sacrificial layers or acoustic mirrors, so that these films can be used for bulk acoustic wave (BAW) implementation. In fact, RF filters based on BAW have a better ability to withstand high power densities. Therefore, they are more suitable for high-frequency operation than SAW filters. BAW filters using such LiNbO3 or LiTaO3 films offer high electromechanical coupling and can operate at higher frequencies than filters based on standard aluminum nitride (AlN) films, or can form wideband or frequency-tunable filters.

[0003] Fabrication of LiNbO3-based resonators has been reported by cutting slices from LiNbO3 single crystal wafers and bonding such slices to appropriate circuit structures. The slice thickness can be thinned sufficiently using such a method to obtain resonators based on bulk acoustic waves generated within the LiNbO3 slices. However, realizing RF filters operating at approximately 6 GHz (gigahertz) requires very thin films with thicknesses of approximately 200 nm (nanometers), which are difficult to fabricate by this wafer cutting method. Furthermore, such a method involves additional slice transfer, which makes it costly and unfeasible to implement low-cost mass production. Summary of the Invention [Problem to be solved by the invention]

[0004] Starting from this situation, one object of the present invention is to provide a low-cost, highly coupled ferroelectric film suitable for implementing bulk acoustic waves.

[0005] Another object of the present invention is to produce ferroelectric films that have well-controlled thickness values and / or are free of defects such as cracks and delamination.

[0006] Another object of the present invention is to produce a ferroelectric film having a well-controlled chemical composition with an accuracy of 0.2 mol % or better.

[0007] It is yet another object of the present invention to provide a ferroelectric film in a form that can be integrated with electronic circuits, acoustic devices, electro-optical devices, pyroelectric devices, or inductive photonic devices. [Means for solving the problem]

[0008] To meet at least one of these or other objectives, a first aspect of the present invention proposes a layered solid-state device comprising a substrate and a stack supported by a surface of the substrate, the stack comprising a buffer layer of a first crystalline material and a ferroelectric layer of a second crystalline material in direct contact with each other along an epitaxial interface, the buffer layer being closer to the substrate than the ferroelectric layer.

[0009] The first crystalline material has the chemical formula L k Ni r O 1.5·(k+r)+w where L is a lanthanide element or elements substituted for one another in the first crystalline material, Ni is nickel, and O is oxygen. k is a first coefficient comprised between 0.7 and 1.3, r is a second coefficient comprised between 0.7 and 1.3, and w is a third coefficient quantifying the amount of missing or excess (interstitial) oxygen atoms comprised between -0.5 and +0.5. The values k=1, r=1, and w=0 correspond to the stoichiometric nickelate of the lanthanides, i.e., LNiO3.

[0010] chemical formula L k Ni r O 1.5·(k+r)-w The first crystalline material having the formula (I) is a trigonal crystalline system.

[0011] Alternatively, and still within the scope of the present invention, the first crystalline material may be a compound of formula L n+1 Ni n O 3n+1+δ where n is a non-zero integer and δ is a coefficient comprised between −0.5 and +0.5, where L is again the lanthanide element or elements substituted for one another in the so-called further first crystalline material, Ni is nickel and O is oxygen.

[0012] chemical formula L n+1 Ni n O 3n+1+δ Another first crystalline material having a tetragonal or orthorhombic crystal system has lattice dimensions of trigonal L k Nir O 1.5·(k+r)+w The lattice dimensions are similar to those of the hexagonal cell of such a crystal. n+1 Ni n O 3n+1+δ The material is in the Ruddlesden-Popper phase.

[0013] The second crystalline material may be lithium niobate, lithium tantalate, or a compound of the formula Li 1-x (Nb 1-y Ta y ) 1+x O 3+2x-z where Li is lithium, Nb is niobium, Ta is tantalum, x is another first coefficient comprised between 0 and 0.08, y is another second coefficient comprised between 0 and 1, and z is another third coefficient comprised between 0 and +0.5. The values x=0, y=0 and z=0 correspond to stoichiometric lithium niobate LiNbO3, the values x=0, y=1 and z=0 correspond to stoichiometric lithium tantalate LiTaO3, and more generally, y denotes the ratio of niobium cations substituted for tantalum cations with respect to lithium niobate LiNbO3. x is the ratio of niobium cations substituted for tantalum cations with respect to the composition LiNbO3. 1-y Ta y Quantify the amount of lithium oxide Li2O that is deficient with respect to O3, while the crystal structure of this latter remains almost identical. + ions to Nb 5+ or Ta 5+ quantifies the supplementary oxygen atoms used to compensate for the positive charge of the defects caused by substitution with ions, and z quantifies the amount of missing oxygen atoms.

[0014] Additionally, the first crystalline material, the further first crystalline material, and the second crystalline material may contain doping amounts of other chemical elements from the above formula, again without significantly altering the crystal structure.

[0015] Thanks to the elemental layered structure of the present invention, the material can be deposited on a substrate using deposition processes available to industrial manufacturers, particularly integrated circuit manufacturers working in microelectronics, microacoustics, or guided photonics. Such processes allow for good or very good control of film thickness and material composition and quality, so that films obtained using these processes can be well crystallized, largely defect-free, and have good adhesion throughout the stack. In particular, the low thickness values achievable using these processes allow the use of ferroelectric layers to implement high-frequency bulk acoustic waves, particularly above 5 GHz.

[0016] The layered solid-state components of the present invention can form part of integrated electronic circuits such as RF filters, or integrated acoustic devices, or integrated inductive photonic devices, or pyroelectric devices. The resulting RF filters can have higher resonant frequencies and wider bandwidths than standard filters. They can be manufactured industrially and can be based on surface acoustic waves or bulk acoustic waves. They can also be broadband or tunable filters, useful for new generation communication terminals.

[0017] Additionally, having an epitaxial interface between the buffer layer and the ferroelectric layer allows for the selection of a desired crystal orientation for the ferroelectric layer relative to the substrate, thereby improving or maximizing ferroelectric coupling efficiency. k Ni r O 1.5·(k+r)+w The compound having the formula L has a crystal structure in the R-3c space group and is suitable for producing a material with controlled crystal orientation. n+1 Ni n O 3n+1+δCompounds having the formula (I) are suitable for preparation with a Ruddlesden-Popper phase crystalline structure, i.e., a tetragonal (I4 / mmm or F4 / mmm space group) or orthorhombic (Bmab or F / mmm space group) structure and controlled crystalline orientation, depending on the synthesis conditions and the oxygen content of the material. In the literature, there is no general agreement regarding the phase diagram of this material and the phases present, and L n+1 Ni n O 3n+1+δ It should be noted that even monoclinic structures of the compounds have been reported, and such crystalline orientation of the buffer layer causes the material of the ferroelectric layer to be crystalline as deposited, with the desired crystalline orientation of the ferroelectric layer set by the crystalline orientation of the buffer layer.

[0018] The second crystalline material of the ferroelectric layer may be an ilmenite material having a trigonal crystal structure. k Ni r O 1.5·(k+r)+w The buffer layer of the first crystalline material may have a crystal plane (0,1,-1,2) in a hexagonal setting parallel to the epitaxial interface, and the second crystalline material in the ferroelectric layer may be oriented (0,1,-1,2) relative to the epitaxial interface. As known to those skilled in the art of solid state materials, crystalline L k Ni r O 1.5·(k+r)+w The crystal plane (0,1,-1,2) in the hexagonal setting for ferroelectric layer (R) corresponds to the 36°±5° Y orientation in the IEEE convention. Similarly, the epitaxial interface being parallel to the (0,1,-1,2)R plane of the ferroelectric layer in the hexagonal setting means that the ferroelectric layer is oriented at 33°±5° Y in the IEEE convention.

[0019] In addition, when the second crystalline material of the ferroelectric layer has an ilmenite structure having a trigonal crystal structure, the buffer layer of the first crystalline material is an L crystalline material having a trigonal crystal structure. k Ni r O 1.5·(k+r)+wBased on the above, the second crystalline material in the ferroelectric layer may have a crystallographic plane (1,1,-2,0) in a hexagonal setting parallel to the epitaxial interface, and the second crystalline material in the ferroelectric layer may have a crystallographic X-axis oriented perpendicular to the epitaxial interface in accordance with the IEEE rules. The crystallographic plane (1,1,-2,0) in a hexagonal setting is perpendicular to the X-axis in accordance with the IEEE rules. Similarly, a second crystalline material in a ferroelectric layer whose crystallographic X-axis is oriented perpendicular to the epitaxial interface in accordance with the IEEE rules means that the epitaxial interface is parallel to the (2,-1,-1,0)A-plane in the hexagonal setting.

[0020] In addition, when the second crystalline material of the ferroelectric layer has an ilmenite structure having a trigonal crystal structure, L having a tetragonal or orthorhombic crystal structure n+1 Ni n O 3n+1+δ The buffer layer of the first crystalline material in the case based on this may have a crystal plane (0,0,1) parallel to the epitaxial interface, and the second crystalline material in the ferroelectric layer may be oriented at (0,1,-1,2) with respect to the epitaxial interface, i.e., oriented at 33°±5°Y with respect to the epitaxial interface according to the IEEE rule.

[0021] Alternatively, when the second crystalline material of the ferroelectric layer has an ilmenite structure having a trigonal crystal structure, L having a tetragonal or orthorhombic crystal structure n+1 Ni n O 3n+1+δ When based on this, the buffer layer of the first crystalline material may have a crystallographic plane (1,1,0) parallel to the epitaxial interface, and the second crystalline material in the ferroelectric layer may have a crystallographic X-axis oriented perpendicular to the epitaxial interface per IEEE rules.

[0022] In various embodiments of the present invention, for further advantages such as better quality or reliability of the element of the present invention or for the intended use of this element, one or more of the following additional features may additionally be reproduced:

[0023] The buffer layer may have a first thickness of between 1 nm (nanometer) and 1000 nm, when this first thickness is measured perpendicular to the epitaxial interface.

[0024] The ferroelectric layer may have a second thickness of between 10 nm and 2000 nm, when the second thickness is also measured perpendicular to the epitaxial interface.

[0025] The substrate may be a silicon-based substrate or a substrate designed for integrated optical or acoustic devices. In particular, the substrate may be monocrystalline silicon with a (100) orientation.

[0026] The stack may further comprise, between the substrate and the buffer layer, at least one of a silica layer, a titanium layer, a titania layer, a tantalum layer, a tantalum oxide layer, a chromium layer, a chromium oxide layer, an electrode layer, a sacrificial layer adapted to be selectively etched, for example, by wet or dry etching, and a Bragg mirror. If the electrode layer is a lower electrode layer, the material of such a lower electrode layer may be selected from platinum, iridium, ruthenium, or a conductive oxide. If the electrode layer is an upper electrode layer, the material of such an upper electrode layer may be any metal.

[0027] a cavity may be disposed between a first portion of the layered solid-state component comprising the substrate and a second portion of the layered solid-state component comprising the buffer layer and the ferroelectric layer; The ferroelectric layer may be arranged between two electrode layers in the stack along a direction perpendicular to the layers, such that the layered solid-state element is adapted to implement bulk acoustic waves or optical changes generated in the ferroelectric layer by a time-varying voltage applied between these electrode layers.

[0028] In general, layered solid state elements may be adapted to form high harmonic bulk acoustic resonators, commonly designated HBARs.

[0029] Alternatively, the layered solid state components may be adapted to form free-standing thin film bulk acoustic resonators, commonly referred to as TFBARs.

[0030] Alternatively, the layered solid state component may be of the solid state mounted resonator type known as SMR.

[0031] A second aspect of the present invention proposes a method for manufacturing a layered solid-state device according to the first aspect of the invention, according to which a second crystalline material is epitaxially grown from a buffer layer of a first crystalline material or a so-called second crystalline material to form a ferroelectric layer.

[0032] The first crystalline material may be deposited using any known deposition process, including chemical processes, sol-gel processes, pulsed laser deposition, or physical deposition processes such as atomic layer deposition. However, it may be advantageous to use an RF sputtering deposition process or chemical vapor deposition to form the buffer layer. In particular, RF sputtering produces a L crystalline material with a (0,1,-1,2) crystal plane parallel to the substrate surface. k Ni r O 1.5·(k+r)+w directly based on L or with a crystal plane (0,0,1) parallel to the substrate plane n+1 Ni n O 3n+1+δ This allows for the formation of a first crystalline material, the first crystalline material of the buffer layer. Next, a second crystalline material, the second crystalline material of the ferroelectric layer, is epitaxially grown on the buffer layer with a 33° Y-orientation. Alternatively, a buffer layer can be formed using chemical vapor deposition to obtain a L-type ferroelectric layer with a crystal plane (1,1,-2,0) parallel to the substrate surface. k Ni r O 1.5·(k+r)+w or L having a crystal plane (1,1,0) parallel to the substrate plane n+1 Ni n O 3n+1+δ A second crystalline material, the second crystalline material of the ferroelectric layer, is then epitaxially grown on the buffer layer with its crystallographic X-axis perpendicular to the epitaxial interface.

[0033] The second crystalline material may also be deposited using any of the known deposition processes listed above, however, it may be advantageous to use chemical vapor deposition, particularly direct liquid injection chemical vapor deposition or pulsed injection chemical vapor deposition, to form the ferroelectric layer.

[0034] In some cases, the process of the present invention may further comprise applying an electric field to the second crystalline material as it is being deposited to form the ferroelectric layer, or after it has been deposited, such an electric field may be suitable for aligning ferroelectric orientation present in domains within the ferroelectric layer.

[0035] A third aspect of the present invention proposes an integrated circuit comprising a layered solid-state component according to the first aspect of the invention. The integrated circuit may form at least part of an electronic device or at least part of an acoustic device, in particular at least part of a microacoustic device, at least part of an electro-optical device, at least part of a pyroelectric device or at least part of an inductive photonic device. In particular, it may form an RF filter, a waveguide or an optical modulator. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a cross section of a layered solid-state device according to the present invention. [Figure 2] 2 is a schematic representation of a material deposition assembly that can be used to deposit the ferroelectric layer of the layered solid-state device of FIG. 1; [Figure 3a] 1A-1C are cross-sectional views of two layered solid-state devices according to the present invention, each having an SMR and a TFBAR structure. [Figure 3b] 1A-1C are cross-sectional views of two layered solid-state devices according to the present invention, each having an SMR and a TFBAR structure. [Figure 4] 1 shows the crystal structure of a compound that can be used in the buffer layer of the layered solid-state device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] For clarity, element sizes shown in these figures do not correspond to actual dimensions or to scale, and like reference numerals shown in these figures refer to like elements having like functions.

[0038] 1, the layered solid-state component 100 comprises a substrate 10 having an upper surface S, and a stack of layers disposed on the upper surface S. Thus, the stacking direction D of the stack of layers is perpendicular to the upper substrate surface S. For example, the substrate 10 may be a portion of a (100) single crystal silicon wafer.

[0039] The stack includes a buffer layer 1 and a ferroelectric layer 2 in direct contact with each other along an intermediate epitaxial interface ES. The orientation of layer 2 is defined by the orientation of layer 1. Both layers 1 and 2 are crystalline with crystal structures of the R-3c and R3c space groups, respectively. Layer 1 may be a Ruddlesden-Popper phase with a tetragonal or orthorhombic crystal structure. The epitaxial interface ES is perpendicular to the stacking direction D and parallel to the upper substrate surface S. For example, the thickness of buffer layer 1 may be 15 nm, and the thickness of ferroelectric layer 2 may be 250 nm, measured parallel to the stacking direction D. Buffer layer 1 may be crystalline lanthanum nickelate with the chemical formula LaNiO3, and ferroelectric layer 2 may be lithium niobate with the chemical formula LiNbO3 or lithium tantalate with the chemical formula LiTaO3. However, the Li content of the ferroelectric layer 2 may vary to some extent, and the material of the ferroelectric layer 2 may be LiNbO3 in which some of the niobium cations are substituted with tantalum cations without disturbing the crystal structure. The amount of oxygen in the buffer layer 1 and the ferroelectric layer 2 may also vary to some extent.

[0040] The stack may further comprise a lower stack portion 11 located between the upper substrate surface S and the buffer layer 1, and an upper stack portion 12 located on the opposite side of the ferroelectric layer 2 from the substrate .

[0041] The first layer 3 of the bottom stack 11 may be, for example, a silica (SiO2) layer formed by thermal oxidation when the substrate 10 is silicon. The bottom stack 11 may further include a number of individual layers, including, for example, an oxide layer of a platinum-, iridium-, or ruthenium-based material, such as ruthenia (RuO2) or cerium oxide (CeO2), a bottom electrode layer 4 of indium tin oxide (ITO), and a layer subset 5 suitable for forming an acoustic or optical Bragg mirror. In a known manner, such a Bragg mirror is designed to reflect bulk acoustic or optical waves generated in the ferroelectric layer 2. In some cases, the bottom stack 11 may also include a sacrificial layer, which is intended to be etched later in the manufacturing process to form a thin film bulk acoustic resonator (TFBAR). Such structures compatible with the layered solid-state device of the present invention are further described below, particularly with reference to FIGS. 3a and 3b. The bottom stack 11 may further include one or more adhesion layers, which may be based on chromium, chromium oxide, titanium, titanium oxide, tantalum, tantalum oxide, metal alloys, etc. The implementation of such adhesion layers is known in the art, so there is no need to further describe them here. In FIG. 1, two adhesion layers 6a and 6b are shown on either side of the bottom electrode layer 4, although typically only layer 6a is sufficient. Layer 6b may be used to prevent diffusion from the buffer layer 1 or the ferroelectric layer 2, specifically lithium oxide, into the electrode layer 4, or generally into the layer subset 5.

[0042] Top stack 12 may also include one or more individual layers, including top electrode layer 7, other adhesion layers 8a and 8b, and protective or temperature compensating layer 9. Top electrode 7 may be the same material as bottom electrode layer 4, or may be an aluminum, tungsten, molybdenum, or gold-based material, or may be based on other metals. Layer 9 may be, for example, silicon oxide, aluminum oxide, or other dielectric material.

[0043] Layers other than the buffer layer 1 and the ferroelectric layer 2 are not directly related to the present invention and will not be further described here. The actual composition of the layered solid-state device 100 may differ from the compositions listed above depending on its application. In particular, for applications other than RF filters and optical modulators, such as energy harvesting, conductive oxides, including doped oxides, can be used as electrode layer materials.

[0044] The layered solid state component 100 may be part of an integrated circuit such as an integrated electronic device, an integrated acoustic device, or an integrated inductive photonic device. In the case of an integrated electronic device, the substrate 10 may incorporate or support electrical components and connections in a known manner, and the layered solid state component 100 having a configuration such as that shown in FIG. 1 may constitute a solid-state mounted resonator, commonly designated an SMR. Alternatively, for an integrated inductive photonic device, the substrate 10 may incorporate or support waveguide segments (not shown) arranged in a manner suitable for injecting radiation into the ferroelectric layer 2 and collecting radiation exiting therefrom. For example, for such optical applications, the layered solid state component 100 may constitute an optical modulator.

[0045] Referring now to FIG. 2 , a CVD reactor suitable for depositing at least a ferroelectric layer 2, or a buffer layer 1 and a ferroelectric layer 2 sequentially, is illustrated. The CVD reactor is of a type commonly known as DLI-CVD for direct liquid injection chemical vapor deposition, although other types, such as PI-CVD for pulsed injection chemical vapor deposition, can alternatively be used. The DLI-CVD reactor comprises a low-pressure, temperature-controlled vessel 20, which includes two chambers 20 a and 20 b with a gas passage 20 c therebetween. Chamber 20 a is designed to vaporize chemical precursors, and chamber 20 b is designed to chemically react these precursors on substrate 10 to form the desired layer. When depositing the ferroelectric layer 2, two double injectors 21a and 21b can be provided to supply the following mixtures to the chamber 20a: a liquid organic solution containing a first metal organic compound as a lithium (Li) precursor and a gas mixture of oxygen (O), nitrogen (N), or argon (Ar) for injector 21a, and another liquid organic solution containing another metal organic compound as a niobium (Nb) or tantalum (Ta) precursor for injector 21b with the same gas mixture as injector 21a. In the case of liquid organic solutions containing mixtures of all metal organic compounds forming lithium (Li), niobium (Nb), or tantalum (Ta) precursors and a gas mixture of oxygen (O), nitrogen (N), or argon (Ar), a single injector can be used instead. Reference numeral 23a denotes a sealed tank containing a Li precursor, for example (2,2,6,6-tetramethyl-3,5-heptanedione)Li, dissolved in 3,3,5-trimethylbenzene, also known as mesitylene, and N,N,N',N'-tetramethylethylenediamine (TMEDA), pressurized with argon or nitrogen gas through pipe 24. Double injector 21a is connected to tank 23a through pipe 25a and is supplied with an oxygen-nitrogen-argon mixture through pipe 26a.Similarly, reference numeral 23b denotes another sealed tank containing a Nb- or Ta-precursor, e.g., (2,2,6,6-tetramethyl-3,5-heptanedione)4Nb or (2,2,6,6-tetramethyl-3,5-heptanedione)4Ta, dissolved in mesitylene and TMEDA. The double injector 21b is then connected via pipe 25b to an Ar pressurized tank 23b, which is supplied with an oxygen-nitrogen-argon mixture via pipe 26b. Suitable heating modules (not shown) are integrated into the walls of chambers 20a and 20b and inside the substrate support 22 to generate the desired temperature values, and the exhaust 27 of chamber 20b is connected to a pumping system (not shown).

[0046] Chamber 20b encloses a substrate support 22 to which substrate 10 is secured. Support 22 may optionally be equipped with a spin mechanism to produce a deposition layer with improved thickness uniformity over a large useful deposition area. In particular, this method allows for processing large area substrates that are intended to be subsequently cut into separate integrated circuits.

[0047] According to a first embodiment of the present invention, the substrate 10 is already provided with the lower stack 11, if any, and the buffer layer 1 before being subjected to CVD processing. The buffer layer 1 of crystalline LaNiO3 may be deposited using known RF sputtering processes, resulting in a crystallographic orientation with the crystallographic R-plane (0,1,-1,2) in a hexagonal setting parallel to the upper substrate surface S, also referred to as a 36°Y crystallographic orientation in IEEE regulations. Suitable sputtering conditions for the deposition of such a buffer layer 1 are: LaNiO3 as the sintered target material, a deposition temperature between 350°C (Celsius) and 600°C, a target power between 50W (Watts) and 200W, and a 3·10 -3 Torr and 6·10 -3 Torr, and an oxygen / argon ratio of less than 50%. n+1 Ni n O 3n+1+δ Using the same deposition conditions, a La SiO2 target with a crystal plane (0,0,1) parallel to the upper substrate plane S was deposited. n+1 Ni nO 3n+1+δ This will allow for the growth of layers.

[0048] For these first embodiments, the ferroelectric layer 2 can be deposited directly on the buffer layer 1 using the DLI-CVD reactor of FIG. 2, with deposition parameters of a temperature in the evaporation chamber 20a between 250°C and 270°C, a temperature in the deposition chamber 20b between 600°C and 700°C, a pressure in the deposition chamber 20b between 2 Torr and 10 Torr, and an O / (O + N + Ar) ratio between 30% and 50%. These deposition parameters produce a growth rate for the ferroelectric layer 2 parallel to the deposition direction D between 0.5 nm / min (nanometers per minute) and 2 nm / min. The LiNbO material thus deposited to form the ferroelectric layer 2 is crystalline, and the 36°Y orientation of the LaNiO material in the buffer layer 1 induces a 33°Y orientation by epitaxy.

[0049] If tantalum is used to replace some or all of the niobium in the ferroelectric layer 2, the tantalum precursor should be combined with the niobium precursor or the tantalum precursor should replace the niobium precursor when supplying the chemical compounds to the CVD chamber. The deposition parameters described above for the LiNbO3 composition also apply to the LiTaO3 composition, and such adaptations can be readily made by one skilled in materials deposition.

[0050] According to a second embodiment of the present invention, both the buffer layer 1 and the ferroelectric layer 2 can be deposited consecutively using a DLI-CVD reactor, as shown in Figure 2. The deposition conditions used for the LaNiO3 material of the buffer layer 1 in the CVD reactor dedicated to the buffer layer 1 can be as follows: (2,2,6,6-tetramethyl-3,5-heptanedione)3La is dissolved in tank 21a with mesitylene-TMEDA as the lanthanum precursor, and (2,2,6,6-tetramethyl-3,5-heptanedione)2Ni is dissolved in tank 21b with mesitylene-TMEDA as the nickel precursor; the temperature inside evaporation chamber 20a is between 185°C and 215°C; the temperature inside deposition chamber 20b is between 650°C and 775°C; the ratio of the oxygen, nitrogen, and argon gas mixture, O2 / (O2 + N2 + Ar), is between 30% and 50%; and the pressure inside deposition chamber 20b is between 2 Torr and 10 Torr. By adjusting the La and Ni precursor ratio in the solution under the same deposition conditions, La with a crystal plane (1,1,0) parallel to the upper substrate surface S was deposited. n+1 Ni n O 3n+1+δ These deposition conditions produce a growth rate for the buffer layer 1 between 0.5 nm / min and 1 nm / min. The LaNiO3 material thus deposited to form the buffer layer 1 is crystalline and has an X-orientation, and the LaNiO3 n+1 Ni n O 3n+1+δ The layer has a (1,1,0) orientation, which means that the X axis of the LaNiO3 crystal structure is perpendicular to the substrate plane S.

[0051] For this second embodiment, the ferroelectric layer 2 is directly CVD deposited on the thus obtained buffer layer 1. The CVD deposition parameters described above for the LiNbO3 material in the first embodiment can be used again for the second embodiment. However, now, due to the X orientation of the LaNiO3 material of the buffer layer 1, the LiNbO3 material of the ferroelectric layer 2 is obtained by epitaxy with a crystal orientation X, where the X axis of the LiNbO3 crystal structure is perpendicular to the epitaxy interface ES, and the (2,-1,-1,0)A plane of the LiNbO3 is parallel to the epitaxial interface ES.

[0052] Alternatively, if the substrate 10 or the lower stack 11 is epitaxially grown with the (0,1,-1,2) plane of LaNiO parallel to the epitaxial interface, the LaNiO material deposited to form the buffer layer 1 may be crystalline with a 36° Y orientation.

[0053] In some cases, if the substrate 10 or the lower stack 11 epitaxially grows the (2,-1,-1,0) plane of LaNiO parallel to the epitaxial interface, the LaNiO material deposited to form the buffer layer 1 may be crystalline with an X orientation.

[0054] To form the buffer layer 1, n+1 Ni n O 3n+1+δ When depositing the material, the substrate 10 or the lower stack 11 is n+1 Ni n O 3n+1+δ The L deposited to form the buffer layer 1 may be a crystalline material with a (0,0,1) orientation, provided that the (0,0,1) plane of the L is epitaxially grown parallel to the epitaxial interface. n+1 Ni n O 3n+1+δ The material is a substrate 10 or a lower laminate 11 with an L parallel to the epitaxial interface. n+1 Ni n O 3n+1+δ When these planes are epitaxially grown, they may be crystalline with a (1,1,0) orientation.

[0055] The ferroelectric layers 2 obtained in the first and second embodiments exhibit high piezoelectric and electro-optical efficiencies due to their 33° Y-orientation or X-orientation. Thanks to such piezoelectric and electro-optical efficiencies, integrated devices incorporating the layered solid-state component 100 can enable improved operation and / or a larger frequency operating band regardless of the application of the device, particularly RF filtering and optical modulation.

[0056] For all embodiments of the present invention, an electrical poling step may be necessary to align various polarizations that may exist within the domains in the as-deposited ferroelectric layer 2. Such poling can be achieved by applying an electric field to layer 2 that is higher than the coercive field. Such an electric field can be applied to ferroelectric layer 2 during this latter deposition, so that the as-deposited ferroelectric material has one single polarization throughout layer 2. Alternatively, electrical poling may be performed after ferroelectric layer 2 or the entire layered solid-state device 100 is completed. To perform such poling, one or both of electrode layers 4 and 7 may be used for electrical connection to an external voltage source. For example, if the coercive field of the ferroelectric material in layer 2 is equal to 85 kV / cm (kilovolts per centimeter), the poling field used may be greater than 85 kV / cm.

[0057] The layered solid state device 100 of the present invention can be combined with a variety of device configurations, including high-harmonic bulk acoustic resonators, or HBARs, bulk acoustic wave solid-state mounted resonators, or SMRs, or free-standing thin film bulk acoustic resonators, designated TFBARs.

[0058] For the HBAR structure, the bottom stack 11 is free of the acoustic Bragg mirror 5 and the substrate 10 forms the propagation medium for the acoustic waves.

[0059] For the SMR structure shown in [Figure 3a], the bottom stack 11 includes the acoustic Bragg mirror 5, so that the propagation medium for the acoustic waves is limited to the stack located above the Bragg mirror 5 opposite the substrate 10. This propagation medium is thus constituted by the bottom electrode 4, buffer layer 1, ferroelectric layer 2 and top electrode 7, which is separated from the substrate 10 by the acoustic Bragg mirror 5. [Figure 3a] also shows electrode connections 4e and 7e, which are intended to be connected to an electrical signal source, such as an RF source.

[0060] For the TFBAR structure shown in FIG. 3b, the bottom stack 11 initially includes a layer of sacrificial material. This sacrificial material is then etched through the opening O after the bottom electrode 4, buffer layer 1, ferroelectric layer 2, and top electrode 7 are deposited. Reference numeral 10′ denotes the surrounding material, which may be silica. A dry or wet etching process can be performed to selectively extract the sacrificial material relative to the other materials. This creates a cavity 13 between the bottom electrode 4 and the substrate 10. The acoustic propagation medium is again formed by the bottom electrode 4, buffer layer 1, ferroelectric layer 2, and top electrode 7, but is separated from the substrate 10 by the cavity 13 instead of the acoustic Bragg mirror 5.

[0061] If the layered solid state component 100 of the present invention is intended to form an inductive photonic device, it may lack the layer subset 5 or the layer subset 5 may be an optical Bragg mirror.

[0062] The buffer layer 1 has a chemical composition L k Ni r O 1.5·(k+r)+w where L is a lanthanide element or several lanthanide elements substituted for each other, and 0.7≦k≦1.3, 0.7≦r≦1.3, and −0.5≦w≦+0.5. However, alternatively, other chemical compositions L n+1 Ni n O 3n+1+δwhere n is a non-zero integer and -0.5≦δ≦+0.5. For n=1, the compound is La2NiO4 with the K2NiF4 structure, and for very large n, it is close to LaNiO3 with the perovskite structure. Such other compositions are known as Ruddlesden-Popper phases, and the L2NiO4 crystal structure can be induced by alternating 45° rotated LNiO3 perovskite blocks and LaO layers along the 001 crystallographic direction at the base of a tetragonal cell. [Figure 4] shows the LaNiO4 from La2NiO4. n+1 Ni n O 3n+1+δ Such a derivation of composition is shown. k Ni r O 1.5·(k+r)+w and L n+1 Ni n O 3n+1+δ In each of the formulas, L may represent a mixture of several lanthanide elements, provided that the composition thus obtained for the buffer layer can be deposited in a crystalline form that allows the subsequent deposition of a ferroelectric material with an X or ≈33° Y orientation by epitaxy from the buffer layer.

[0063] It should also be noted that the chemical composition of the ferroelectric material can be varied significantly while maintaining both its ferroelectric efficiency and its ability to grow epitaxially from a buffer layer. Thus, a typical composition for the ferroelectric layer 2 implemented in accordance with the present invention is Li 1-x (Nb 1-y Ta y ) 1+x O 3+2x-z where 0≦x≦0.08, 0≦y≦1, and 0≦z≦0.5.

[0064] Finally, all details in the CVD reactor design provided and all quoted numerical values are for illustrative purposes only and may be adapted depending on the actual reactor used, the exact chemical composition implemented, and the desired growth rate and layer thickness.

Claims

1. A layered solid-state component (100) comprising a substrate (10) and a stack supported on a surface (S) of the substrate, the stack comprising a buffer layer (1) of a first crystalline material and a ferroelectric layer (2) of a second crystalline material in direct contact with each other along an epitaxial interface (ES), the buffer layer being closer to the substrate than the ferroelectric layer; The first crystalline material has the formula L k Ni r O 1.5・(k+r)+w where L is a lanthanide element or several lanthanide elements substituted for one another in said first crystalline material, Ni is nickel, O is oxygen, k is a first coefficient comprised between 0.7 and 1.3, r is a second coefficient comprised between 0.7 and 1.3, and w is a third coefficient comprised between -0.5 and +0.5, Alternatively, the first crystalline material may have the formula L n+1 Ni n O 3n+1+δ wherein n is an integer other than 0 and δ is a coefficient between −0.5 and +0.5; The second crystalline material may be lithium niobate, lithium tantalate, or a material having the chemical formula Li 1-x (Nb 1-y Ta y ) 1+x O 3+2x-z wherein Li is lithium, Nb is niobium, Ta is tantalum, x is another first coefficient comprised between 0 and 0.08, y is another second coefficient comprised between 0 and 1, and z is another third coefficient comprised between 0 and +0.5, the second crystalline material has an ilmenite structure having a trigonal crystal structure, the buffer layer (1) of the first crystalline material is based on LkNirO1.5.(k+r)+w with a trigonal crystal structure and has a crystal plane (0,1,-1,2) in a hexagonal setting parallel to the epitaxial interface (ES), and the second crystalline material in the ferroelectric layer (2) is oriented at 33°±5° Y relative to the epitaxial interface according to the IEEE rules, or the buffer layer (1) of the first crystalline material is based on LkNirO1.5.(k+r)+w with a trigonal crystal structure and has a crystallographic plane (1,1,-2,0) in a hexagonal setting parallel to the epitaxial interface (ES), and the second crystalline material in the ferroelectric layer (2) has a crystallographic X-axis oriented perpendicular to the epitaxial interface in accordance with IEEE rules, or the buffer layer (1) of the first crystalline material is based on Ln+1Ni nO3n+1+δ with a tetragonal or orthorhombic structure and has a crystal plane (0,0,1) parallel to the epitaxial interface (ES), and the second crystalline material in the ferroelectric layer (2) is oriented at 33°±5°Y relative to the epitaxial interface according to the IEEE rules, or A layered solid-state device (100), wherein the buffer layer (1) of the first crystalline material is based on Ln+1NinO3n+1+δ having a tetragonal or orthorhombic crystal structure and has a crystallographic plane (1,1,0) parallel to the epitaxial interface (ES), and the second crystalline material in the ferroelectric layer (2) has a crystallographic X-axis oriented perpendicular to the epitaxial interface in accordance with IEEE rules.

2. 2. The layered solid-state component (100) of claim 1, wherein the buffer layer (1) has a first thickness of 1 nm to 1000 nm and the ferroelectric layer (2) has a second thickness of 10 nm to 2000 nm, the first and second thicknesses being measured perpendicular to the epitaxial interface (ES).

3. 3. A layered solid-state component (100) according to claim 1 or 2, wherein the substrate (10) is a silicon-based substrate or a substrate designed for integrated optical or acoustic devices.

4. 4. The layered solid-state component (100) of claim 1, wherein the stack further comprises at least one of a silica layer (3), a titanium layer, a titania layer, a tantalum layer, a tantalum oxide layer, a chromium layer, a chromium oxide layer, an electrode layer (4), a selectively etched sacrificial layer, and a Bragg mirror (5) between the substrate (10) and the buffer layer (1).

5. 5. The layered solid-state component (100) according to claim 1, wherein a cavity (13) is disposed between a first portion of the layered solid-state component comprising the substrate (10) and a second portion of the layered solid-state component comprising the buffer layer (1) and the ferroelectric layer (2).

6. 6. A layered solid-state component (100) according to any one of claims 1 to 5, wherein the ferroelectric layer (2) is arranged between two electrode layers (4, 7) in the stack along a direction perpendicular to the ferroelectric layer and the electrode layers, and the layered solid-state component is adapted to implement bulk acoustic waves or optical changes generated in the ferroelectric layer by a time-varying voltage applied between the electrode layers.

7. A layered solid state component (100) according to any one of claims 1 to 6, forming part of an integrated electronic circuit, an integrated acoustic device, an integrated inductive photonic device or a pyroelectric device.

8. 8. A method for manufacturing a layered solid-state component (100) according to any one of claims 1 to 7, wherein the second crystalline material is epitaxially grown from the first crystalline material or a buffer layer (1) of another first crystalline material to form the ferroelectric layer (2).

9. 9. The method of claim 8, wherein the first crystalline material is deposited using RF sputtering deposition or chemical vapor deposition to form the buffer layer (1).

10. 10. The method according to claim 8 or 9, wherein the second crystalline material is deposited using chemical vapor deposition to form the ferroelectric layer (2).

11. The method of claim 10, wherein the second crystalline material is deposited using direct liquid injection chemical vapor deposition or pulsed injection chemical vapor deposition to form the ferroelectric layer (2).

12. 12. The method of any one of claims 8 to 11, further comprising applying an electric field to the second crystalline material as it is being deposited to form the ferroelectric layer (2) or after it has been deposited, the electric field being suitable to align ferroelectric orientation present in domains within the ferroelectric layer.

13. 8. An integrated circuit comprising a layered solid state component (100) according to any one of claims 1 to 7, said integrated circuit forming at least part of an electronic device, at least part of an acoustic device, in particular at least part of a microacoustic device, at least part of an electro-optical device, at least part of a pyroelectric device or at least part of an inductive photonic device.

14. 14. The integrated circuit of claim 13, forming an RF filter, a waveguide, or an optical modulator.

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