AND USES THEREOF

Technical Field

The present invention relates, in general terms, to dysprosium scandate films and their methods of fabrication thereof. The present invention also relates to uses of dysprosium scandate film as a crystal growth platform on silicon. Background

Most oxides used in photonics/electronics consist of two classes, amorphous layers on silicon or single crystal oxides with surface processing to delineate the device structures. The single crystal oxide layers have the advantage of increased functionality such as ferroelectricity, piezoelectricity and possibly ferromagnetism (for active devices). However, the growth of such layers on silicon is non-trivial.

Dysprosium scandate (DSO) single crystal has a good lattice mismatch with the multifunctional perovskite oxides. It is an excellent substrate for growing high- quality thin films. However, there are still several challenges in integrating DSO films on silicon. Firstly, the surface of the silicon wafer gets oxidized very fast, which would severely affect subsequent epitaxial film growth. Secondly, a high- quality single crystallinity of DSO is required for the DSO film to act as a buffer layer.

It would be desirable to overcome or ameliorate at least one of the above- described problems. Summary

The present invention is predicated on the understanding that the growth and/or

1 deposition of high-quality single-crystal DSO, CeC>2 (Cerium Oxide) and YSZ (yttria-stabilized zirconia) thin films on a substrate is dependent on the structural and chemical properties of the substrate. Accordingly, by carefully controlling the chemical state of the substrate, physical properties of the single crystal thin films can be altered.

Accordingly, the present invention provides a method of fabricating a dysprosium scandate film on an etched surface of a silicon wafer immersed in an etchant, comprising: a) contacting the etched surface of the silicon wafer with an alcohol for at least 1 h in order to allow alkoxy moieties to be chemisorbed on the etched surface of the silicon wafer; b) depositing a Yttria-stabilized zirconia (YSZ) layer on the etched surface; c) depositing a CeC>2 layer on the YSZ layer; and d) depositing a dysprosium scandate (DSO) layer on the Ce02 layer.

Advantageously, it was found that the reaction of alcohol with silicon can yield chemisorbed alkoxy species, which can help avoid the oxidation of the silicon wafer. Additionally, by keeping the surface of the wafers in contact with alcohol, the surface can be kept clean and unoxidized until its usage.

Advantageously, the dysprosium scandate (DSO, DyScC ) layer can act as a platform for growing high-quality single-crystal thin films on silicon (including both p-type or n-type silicon).

In some embodiments, the etched surface is contacted with the alcohol within less than about 10 s after removal of the silicon wafer from the etchant.

In some embodiments, the alcohol is selected from methanol, ethanol, isopropanol and/or n-propanol.

In some embodiments, the alcohol has a purity of more than about 90%.

2 In some embodiments, the alcohol has a water content of less than about 1%. In some embodiments, the alcohol is purged with an inert gas.

In some embodiments, the alcohol is de-gassed.

In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol under oxygen free conditions.

In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol for about 1 h to about 24 h.

In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol at a temperature of about 5 °C to about 50 °C.

In some embodiments, the method further comprises a step of cleaning the etched surface of the silicon wafer in order for the etched surface to be free of the etchant.

In some embodiments, the etchant is selected from Piranha solution, hydrofluoric acid, ammonia water, hydrogen peroxide and/or hydrochloric acid.

In some embodiments, the YSZ layer is deposited via pulsed laser deposition (PLD).

In some embodiments, the YSZ layer is deposited at a temperature of about 700 °C to about 800 °C.

In some embodiments, the YSZ layer is deposited at a pressure of about 10 ⁶ Torr to about 10 ⁵ Torr.

3 In some embodiments, the CeC>2 layer is deposited via pulsed laser deposition (PLD).

In some embodiments, the CeC>2 layer is deposited at a temperature of about 700 °C to about 800 °C.

In some embodiments, the CeC>2 layer is deposited at a pressure of about 10 ⁶ Torr to about 10 ⁵ Torr.

In some embodiments, the DSO layer is deposited via pulsed laser deposition (PLD).

In some embodiments, the DSO layer is deposited at a temperature of about 700 °C to about 800 °C.

In some embodiments, the DSO layer is deposited at a pressure of about 80 mTorr to about 150 mTorr.

In some embodiments, the DSO layer is characterised by a X-ray diffraction peak with a full width of half maximum (FWHM) value of about 0.22° to about 0.3°.

The present invention also provides a dysprosium scandate film, comprising: a) a silicon wafer; b) a Yttria-stabilized zirconia (YSZ) layer on the silicon wafer; c) a Ce02 layer on the YSZ layer; and d) a dysprosium scandate (DSO) layer on the Ce02 layer; wherein the DSO layer is characterised by a X-ray diffraction peak with a full width of half maximum (FWHM) value of about 0.220° to about 0.300°.

In some embodiments, the DSO layer has an X-ray diffraction peak at about 22° to about 23°.

4 In some embodiments, the YSZ layer has a thickness of about 15 nm to about 40 nm.

In some embodiments, the CeC>2 layer has a thickness of about 30 nm to about 60 nm.

In some embodiments, the DSO layer has a thickness of about 15 nm to about 40 nm.

In some embodiments, the YSZ layer is a YSZ epitaxial layer.

In some embodiments, the CeC>2 layer is a CeC>2 epitaxial layer.

In some embodiments, the DSO layer is a DSO epitaxial layer.

Brief description of the drawings

Embodiments of the present invention will now be described, by way of nonlimiting example, with reference to the drawings in which:

Figure 1 is a X-ray diffraction spectrum of Q-2Q scan of DSO based platform on silicon;

Figure 2 is a X-ray diffraction spectrum of the rocking curve of DSO based platform on silicon; and

Figure 3 is an atom-resolution scanning transmission electron microscopy images of DSO based platform on silicon.

Detailed description

The present invention is predicated on the understanding that avoiding or at least reducing the oxidation of silicon wafer before the pulsed laser deposition

5 can be advantageous for epitaxial growth of crystalline layers on the silicon wafer. This method can be beneficial for obtaining a clean surface of silicon, for example, to achieve a better crystallinity of the grown film.

Although the amorphous native silicon dioxide layer can be removed by buffered hydrofluoric acid, this amorphous oxidized layer will be formed again very soon if exposed to air even if only for a short duration. This re-oxidized layer is amorphous and not suitable for crystal film growth. It was found that after etching with hydrofluoric acid, the silicon wafers can be soaked immediately and immersed in methanol for several hours in order to maintain its pristine nature. Before deposition, the silicon wafer should not be exposed to the air and/or oxygen as much as possible.

Accordingly, the present invention provides a method of preventing or reducing oxidation of an etched surface of a silicon wafer removed from an etchant, comprising: contacting the etched surface of the silicon wafer with an alcohol for at least 1 h in order to allow alkoxy moieties to be chemisorbed on the etched surface of the silicon wafer.

The silicon wafer can have a (100) crystal plane or any other orientations.

Advantageously, it was found that the reaction of alcohol with silicon can yield chemisorbed alkoxy species, which can help avoid the oxidation of silicon wafer. Additionally, by keeping the wafers in alcohol, the surface can be kept clean and unoxidized until its usage. Further, as the surface is saturated or at least covered with alkoxy moieties, the duration for handling the silicon wafer in an exposed environment can be increased without the adverse effect of oxidation.

Without wanting to be bound by theory, it is believed that soaking the silicon wafer in alcohol can play a role of anti-oxidation in that the silicon will react with methanol at room temperature, and this yields a chemisorbed alkoxy species

6 with negligible oxidation occurring. The alkoxy species will disappear or be removed when exposed to a high temperature and thus will not affect film deposition. This anti-oxidation technique of silicon wafer is advantageously low- cost and highly efficient.

In some embodiments, the etched surface is immersed in the alcohol. In other embodiments, the etched surface is completely immersed in the alcohol. In this regard, the etched surface and/or the silicon wafer can be submerged in the alcohol such that it is completely covered.

In some embodiments, the etched surface of the silicon wafer is contacted with an alcohol within less than about 10 s after removal of the silicon wafer from the etchant. In other embodiments, the etched surface on the silicon wafer is contacted with the alcohol within less than about 20 s after removal from the etchant. In other embodiments, the timing is less than about 18 s, about 16 s, about 14 s, about 12 s, about 8 s, about 6 s, about 5 s, about 4 s, about 3 s, about 2 s, or about 1 s.

It was found that the re-oxidized layer will form immediately after the exposure of Si to the air. Thus, growth of films on Si can be improved by reducing the time of exposure to air. Advantageously, by quickly transferring the etched surface of the silicon wafer from the etchant to the alcohol, the exposure to air and hence oxygen is minimised.

In some embodiments, the alcohol is selected from methanol, ethanol, iso propanol and/or n-propanol. In other embodiments, the alcohol is methanol.

In some embodiments, the alcohol has a purity of more than about 90%. In other embodiments, the purity is more than about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 99.2%, about 99.4%, about 99.6%, or about 99.8%.

7 In some embodiments, the alcohol has a water content of less than about 1%. In other embodiments, the water content is less than about 0.9%, about 0.8%, about 0.7%, about 0.6%, about 0.5%, about 0.4%, about 0.3%, or about 0.2%.

In some embodiments, the alcohol is diluted with a solvent. In some embodiments, the solvent is an aqueous medium. The term 'aqueous medium' used herein refers to a water based solvent or solvent system, and which comprises of mainly water. Such solvents can be either polar or non-polar, and/or either protic or aprotic. Solvent systems refer to combinations of solvents which resulting in a final single phase. Both 'solvents' and 'solvent systems' can include, and is not limited to, pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, dioxane, chloroform, diethylether, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, formic acid, butanol, isopropanol, propanol, ethanol, methanol, acetic acid, ethylene glycol, diethylene glycol or water. Water based solvent or solvent systems can also include dissolved ions and salts.

In other embodiments, the solvent is an organic based solvent. Organic based solvents can be any carbon based solvents. Such solvents can be either polar or non-polar, and/or either protic or aprotic. Solvent systems refer to combinations of solvents which resulting in a final single phase. Both 'solvents' and 'solvent systems' can include, and is not limited to, pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, dioxane, chloroform, diethylether, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, formic acid, butanol, isopropanol, propanol, ethanol, methanol, acetic acid, ethylene glycol, diethylene glycol or water. Organic based solvents or solvent systems can include, but not limited to, any non-polar liquid which can be hydrophobic and/or lipophilic. As such, oils such as animal oil, vegetable oil, petrochemical oil, and other synthetic oils are also included within this definition.

8 In some embodiments, the alcohol is diluted with a solvent such that its concentration is at least 50% of the solution.

In some embodiments, the alcohol is purged with an inert gas. An inert gas is a gas that does not undergo chemical reactions under a set of given conditions. For example, noble gases such as He, Ne, Ar, Kr or Xe can be used. Inert gases can be used to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. By purging with an inert gas, oxygen can be displaced out from the alcohol.

In some embodiments, the alcohol is de-gassed. For example, sonication can be used to de-gas the alcohol. Alternatively, a vacuum can be used to remove air and/or oxygen from the alcohol.

Additionally, purging the Si surface or maintaining the Si wafer in an inert environment further reduce the re-oxidation of the Si layer. In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol under oxygen free conditions. For example, the contact step can be performed in a glove box. Alternatively, the contact step can be conducted under a curtain or flow of nitrogen gas. In such cases, the oxygen content in the environment is maintained at a minimum.

In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol for at least about 1 h. In other embodiments, the timing is at least about 2 h, about 3 h, about 4 h, about 5 h, about 6 h, about 7 h, about 8 h, about 10 h, about 12 h, about 14 h, about 16 h, about 18 h, about 20 h, about 22 h, or about 24 h.

In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol for about 1 h to about 24 h. In other embodiments, the timing is about 1 h to about 22 h, about 1 h to about 20 h, about 1 h to about 18 h, about

9 1 h to about 16 h, about 1 h to about 14 h, about 1 h to about 12 h, about 1 h to about 10 h, about 1 h to about 8 h, about 1 h to about 6 h, about 1 h to about 5 h, about 1 h to about 4 h, about 1 h to about 3 h, or about 1 h to about

2 h.

In some embodiments, the etched surface on the silicon wafer is contacted with the alcohol at a temperature of about 5 °C to about 50 °C. In other embodiments, the temperature is about 5 °C to about 45 °C, about 5 °C to about 40 °C, about 5 °C to about 35 °C, about 5 °C to about 30 °C, or about 5 °C to about 25 °C.

In some embodiments, the method further comprises a step of cleaning the etched surface of the silicon wafer in order for the etched surface to be free of the etchant. This can for example be performed using a blow gun or wiping the etched surface using an appropriate cleaning agent.

In some embodiments, the etchant is selected from Piranha solution, hydrofluoric acid ammonia water, hydrogen peroxide and/or hydrochloric acid.

For example, RCA clean can be used, which is a standard set of wafer cleaning steps which need to be performed before high-temperature processing steps (oxidation, diffusion, CVD) of silicon wafers in semiconductor manufacturing. It involves the following chemical processes performed in sequence: i) Removal of the organic contaminants (SC-1; organic clean + particle clean)

The first step is performed with a solution of (ratios may vary):

5 parts of deionized water

1 part of ammonia water, (29% by weight of Nhb)

1 part of aqueous H2O2 (hydrogen peroxide, 30%) at 75 or 80 °C typically for 10 minutes. This base-peroxide mixture removes organic residues. Particles are also very effectively removed, even insoluble particles, since SC-1 modifies the surface and particle zeta potentials and causes

10 them to repel. This treatment results in the formation of a thin silicon dioxide layer (about 10 Angstrom) on the silicon surface, along with a certain degree of metallic contamination (notably iron) that will be removed in subsequent steps. ii) Removal of thin oxide layer (oxide strip, optional)

The optional second step (for bare silicon wafers) is a short immersion in a 1: 100 or 1:50 solution of aqueous HF (hydrofluoric acid) at 25 °C for about fifteen seconds, in order to remove the thin oxide layer and some fraction of ionic contaminants. If this step is performed without ultra high purity materials and ultra clean containers, it can lead to recontamination since the bare silicon surface is very reactive. In any case, the subsequent step (SC-2) dissolves and regrows the oxide layer. iii) Removal of ionic contamination (SC-2; ionic clean)

The third and last step (called SC-2) is performed with a solution of (ratios may vary):

6 parts of deionized water

1 part of aqueous HCI (hydrochloric acid, 37% by weight)

1 part of aqueous H2O2 (hydrogen peroxide, 30%) at 75 or 80 °C, typically for 10 minutes. This treatment effectively removes the remaining traces of metallic (ionic) contaminants, some of which were introduced in the SC-1 cleaning step. It also leaves a thin passivating layer on the wafer surface, which protects the surface from subsequent contamination (bare exposed silicon is contaminated immediately).

The Si substrate as treated herein can be exposed to air for at least about 10 min. In comparison, the etched Si without alcohol treatment cannot be used because of the re-oxidized layer.

By maintaining the non-oxidised state of the etched surface of the silicon wafer, the etched surface can be used for epitaxial growth of single crystals whenever it is required. As the etched surface can be stored for a greater period of time using this method, greater flexibility in the production of semiconductors can be expected.

11 Single crystal oxide layers can have the advantages of increased functionality such as ferroelectricity, piezoelectricity, and possibly ferromagnetism (for active devices). However, the growth of such layers on silicon is non-trivial.

In another aspect, the present invention also relates to single crystal oxide layers formed on the etched surface on the silicon wafer and methods of fabrication thereof. The single crystal films provide a platform for integrating multifunctional oxide materials onto silicon platform used in the semiconductor industry useful for designing various high-performance devices.

This is predicated on the understanding that current single crystal oxides and/or its production thereof cannot meet the requirements in a commercial setting. For example, complex oxides such as Lao.67Sro.33MnC>3 can be grown on silicon using CeC>2 and Yttria-stabilized zirconia (YSZ) as buffer layers. However, this is insufficient as there can be a large lattice mismatch between CeC>2 and the perovskite oxides. Epitaxial growth will be poor and the crystallinity of the thin film is not good. A prior solution involves using SrRuC as an additional buffer layer and epitaxial template to deposit Lao.67Sro.33MnC>3. However, there are two issues of using SrRuC buffer layer. Firstly, SrRuC is not an insulator, which will severely affect the electrical property and applications of the film deposited on it. Secondly, SrRuC is not a widely used substrate for oxide thin film as surface treatment procedures to accomplish atomically flat surfaces with single terminating layer for various metal oxide substrates is not straightforward.

Accordingly, the present invention provides a method of fabricating a dysprosium scandate film on an etched surface of a silicon wafer immersed in an etchant, comprising: a) contacting the etched surface of the silicon wafer with an alcohol for at least 1 h in order to allow alkoxy moieties to be chemisorbed on the etched surface of the silicon wafer; b) depositing a Yttria-stabilized zirconia (YSZ) layer on the etched surface;

12 c) depositing a CeC>2 layer on the YSZ layer; and d) depositing a dysprosium scandate (DSO) layer on the CeC>2 layer.

Advantageously, as the etched surface of the silicon wafer is protected by alkoxy, single crystals films with low defects can be formed on the silicon wafer. By protecting the etched surface with chemisorbed alkoxy moieties, the handling time of the silicon wafer can be increased. The dysprosium scandate (DSO, DyScOs) layer can act as a platform for growing high-quality singlecrystal thin films on silicon (including both p-type or n-type silicon).

In contrast, single crystal DSO film cannot be grown directly on Si; only amorphous or polycrystal DSO film can grow on Si substrate due to the lattice mismatch. When determined using X-ray diffraction, amorphous or polycrystal films have peaks with a full width of half maximum (FWHM) much larger than 1°, or in other cases the FWHM value is unobtainable as the peak is too broad. In this regard, the inventors have found that by gradually and specifically tuning the crystal lattice, a DSO platform with a suitable crystallinity can be formed.

It would be clear to the skilled person that the method of fabricating a dysprosium scandate film is on an etched surface of a silicon wafer, the silicon wafer having been previously immersed in an etchant and is removed from the etchant in order for the dysprosium scandate film to form on the etched surface. Accordingly, the method is a method of fabricating a dysprosium scandate film on an etched surface of a silicon wafer (removed from an etchant).

In some embodiments, the method of fabricating a dysprosium scandate film on an etched surface of a silicon wafer comprises a step before step a) of providing a silicon wafer which has been etched by an etchant. The etchant can be selected from Piranha solution, hydrofluoric acid ammonia water, hydrogen peroxide and/or hydrochloric acid.

13 In some embodiments, the YSZ layer is deposited via pulsed laser deposition (PLD). Pulsed laser deposition (PLD) is a physical vapor deposition (PVD) technique where a high-power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited. This material is vaporized from the target (in a plasma plume) which deposits it as a thin film on a substrate (such as a silicon wafer facing the target). This process can occur in ultra high vacuum or in the presence of a background gas, such as oxygen which is commonly used when depositing oxides to fully oxygenate the deposited films.

In some embodiments, the YSZ layer is deposited at a temperature of about 700 °C to about 800 °C. In other embodiments, the temperature is about 700 °C to about 780 °C, about 700 °C to about 760 °C, about 700 °C to about 740 °C, or about 700 °C to about 720 °C.

In some embodiments, the YSZ layer is deposited at a pressure of about 10 ⁷ Torr to about 10 ⁴ Torr, or about 10 ⁶ Torr to about 10 ⁵ Torr.

In some embodiments, the CeC>2 layer is deposited via pulsed laser deposition (PLD).

In some embodiments, the CeC>2 layer is deposited at a temperature of about 700 °C to about 800 °C. In other embodiments, the temperature is about 700 °C to about 780 °C, about 700 °C to about 760 °C, about 700 °C to about 740 °C, or about 700 °C to about 720 °C.

In some embodiments, the CeC>2 layer is deposited at a pressure of about 10 ⁷ Torr to about 10 ⁴ Torr, or about 10 ⁶ Torr to about 10 ⁵ Torr.

In some embodiments, the DSO layer is deposited via pulsed laser deposition (PLD).

14 In some embodiments, the DSO layer is deposited at a temperature of about 700 °C to about 800 °C. In other embodiments, the temperature is about 700 °C to about 780 °C, about 700 °C to about 760 °C, about 700 °C to about 740 °C, or about 700 °C to about 720 °C.

In some embodiments, the DSO layer is deposited at a pressure of about 80 mTorr to about 150 mTorr. In other embodiments, the pressure is about 80 mTorr to about 140 mTorr, about 80 mTorr to about 130 mTorr, about 80 mTorr to about 120 mTorr, about 80 mTorr to about 110 mTorr, or about 80 mTorr to about 100 mTorr.

For example, Yttria-stabilized zirconia (YSZ) layer can be first deposited on silicon at high vacuum and 720 °C by pulsed laser deposition (PLD). This approach is very effective in removing any extra silicon dioxide. Subsequently, CeC>2 can be deposited on YSZ under the same vacuum condition and temperature to provide a beneficial chemical buffer layer between YSZ and oxide thin film (like DSO) and also to overcome the lattice mismatch between them. Finally, DSO can be deposited on the YSZ/Ce02 layer at 100 mTorr and 720 °C. The X-ray diffraction (XRD) spectra confirmed the epitaxial growth of DySc03, as shown in Figure 1.

The present invention also provides a dysprosium scandate film, comprising: a) a silicon wafer; b) a Yttria-stabilized zirconia (YSZ) layer on the silicon wafer; c) a Ce02 layer on the YSZ layer; and d) a dysprosium scandate (DSO) layer on the Ce02 layer; wherein the DSO layer has an X-ray diffraction peak with a full width of half maximum (FWHM) value of about 0.220° to about 0.300°.

As the silicon wafer is treated with alcohol as disclosed herein, single crystals with low defects can be grown or deposited on its etched surface.

15 In some embodiments, the DSO layer has an X-ray diffraction peak at about 22° to about 23°. In other embodiments, the X-ray diffraction peak at about 22° to about 22.9°, about 22° to about 22.8°, about 22° to about 22.7°, about 22° to about 22.6°, about 22° to about 22.5°, about 22° to about 22.4°, about 22° to about 22.3°, about 22° to about 22.2°, or about 22.1° to about 22.2°.

In some embodiments, the DSO layer has an X-ray diffraction peak with a full width of half maximum (FWHM) value of about 0.230° to about 0.300°, about 0.240° to about 0.300°, about 0.250° to about 0.300°, about 0.260° to about 0.300°, about 0.270° to about 0.300°, or about 0.280° to about 0.300°. In other embodiments, the FWHM is about 0.230° to about 0.290°, about 0.240° to about 0.290°, or about 0.240° to about 0.280°.

In some embodiments, the YSZ layer has a thickness of about 15 nm to about 40 nm. In other embodiments, the thickness is about 15 nm to about 38 nm, about 15 nm to about 36 nm, about 15 nm to about 34 nm, about 15 nm to about 32 nm, about 15 nm to about 30 nm, about 16 nm to about 30 nm, about 18 nm to about 30 nm, about 20 nm to about 30 nm, about 22 nm to about 30 nm, about 24 nm to about 30 nm, or about 26 nm to about 30 nm.

In some embodiments, the CeC>2 layer has a thickness of about 30 nm to about 60 nm. In other embodiments, the thickness is about 30 nm to about 58 nm, about 30 nm to about 56 nm, about 30 nm to about 54 nm, about 30 nm to about 52 nm, about 30 nm to about 50 nm, about 32 nm to about 50 nm, about 34 nm to about 50 nm, about 36 nm to about 50 nm, about 38 nm to about 50 nm, about 40 nm to about 50 nm, about 40 nm to about 48 nm, about 40 nm to about 46 nm, or about 40 nm to about 44 nm.

In some embodiments, the DSO layer has a thickness of about 15 nm to about 40 nm. In other embodiments, the thickness is about 15 nm to about 38 nm, about 15 nm to about 36 nm, about 15 nm to about 34 nm, about 15 nm to about 32 nm, about 15 nm to about 30 nm, about 16 nm to about 30 nm, about

16 18 nm to about 30 nm, about 20 nm to about 30 nm, about 20 nm to about 28 nm, about 20 nm to about 26 nm, about 20 nm to about 24 nm, or about 20 nm to about 22 nm.

In some embodiments, the YSZ layer is a YSZ epitaxial layer. Epitaxy refers to a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline substrate. The deposited crystalline film is called an epitaxial film or epitaxial layer. The relative orientation(s) of the epitaxial layer to the crystalline substrate is defined in terms of the orientation of the crystal lattice of each material. For epitaxial growth, the new layer must be crystalline and each crystallographic domain of the overlayer must have a well-defined orientation relative to the substrate crystal structure. Amorphous growth or multicrystalline growth with random crystal orientation does not meet this criterion.

In some embodiments, the crystal orientation of YSZ layer is [001].

In some embodiments, the CeC>2 layer is a CeC>2 epitaxial layer. In some embodiments, the crystal orientation of CeC>2 layer is [001].

In some embodiments, the DSO layer is a DSO epitaxial layer. In some embodiments, the crystal orientation of DSO layer is [001].

The X-ray diffraction rocking curve of DySc03 has a full width of half maximum (FWHM) value of 0.285°, as shown in Figure 2, which shows an excellent crystallinity. With this high-quality single-crystal thin films (Si/YSZ/Ce02/DSO), multiple oxide thin films can be deposited on it.

The atom-resolution scanning transmission electron microscopy (STEM) images of DSO buffer layers show a distinct contrast among different buffer layers of DSO/Ce0 ₂ /YSZ. The epitaxy relationship is well maintained in the Ce0 ₂ /YSZ buffered layer case, but there is a small off tilt between DSO and Ce02,

17 originated from the symmetry mismatch between DSO and CeC>2. The DSO crystal structure and atoms can be observed in the zoom image of the DSO layer, which confirms the high-quality crystallinity of the DSO.

The high-quality single-crystal DSO thin film grown on silicon was achieved. The FWHM value of the DSO is about 0.285° (fitting using Matlab), which is very good as a buffer layer. The high-resolution STEM images also confirmed the epitaxial growth mode and good crystallinity of DSO film. The DSO layer will provide a platform for depositing functional materials and further the device design. This platform allows for integration of innumerable multifunctional oxide materials into a silicon platform used in the semiconductor industry for designing various high-performance devices, such as an ultrahigh-speed optical modulator.

In some embodiments, the DSO layer is characterised by a X-ray diffraction peak with a FWHM value of about 0.2° to about 0.4°, about 0.2° to about 0.3.8°, about 0.2° to about 0.36°, about 0.2° to about 0.34°, about 0.2° to about 0.32°, about 0.2° to about 0.3°, about 0.22° to about 0.3°, about 0.24° to about 0.3°, about 0.26° to about 0.3°, or about 0.28° to about 0.3°.

The FWHM (full width half maximum) value of rocking curve obtained from an x-ray diffraction analysis of the DSO film on silicon is about 0.242°, indicating a high degree of crystal quality. This result can be obtained by fitting using the SPEC software which is a control software of the x-ray diffraction instrument.

Accordingly, in some embodiments, the method of fabricating a dysprosium scandate film on an etched surface of a silicon wafer removed from an etchant, comprises: a) contacting the etched surface of the silicon wafer with an alcohol for at least 1 h in order to allow alkoxy moieties to be chemisorbed on the etched surface of the silicon wafer; b) depositing a Yttria-stabilized zirconia (YSZ) layer on the etched surface;

18 c) depositing a CeC>2 layer on the YSZ layer; and d) depositing a dysprosium scandate (DSO) layer on the CeC>2 layer; wherein the DSO layer is characterised by a X-ray diffraction peak with a FWHM value of about 0.2° to about 0.4°.

In summary, the integration of DSO onto a silicon wafer provides a platform for depositing innumerable multifunctional oxide materials on silicon wafers for designing various high-performance devices because a DSO single crystal can be a good substrate for epitaxial films. Additionally, because of the low oxidation state of the etched surface of the silicon wafer, a high quality of the buffer layers can be obtained. It is thus much easier to deposit high-quality epitaxial films when the quality of the buffer layers is high. The method preventing and/or reducing oxidation of silicon wafer provides an epitaxial growth template for the growth of oxide thin films using a physical deposition technique, which is crucial for growing high-quality DSO films.

It will be appreciated that many further modifications and permutations of various aspects of the described embodiments are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Throughout this specification and the claims which follow, unless the context requires otherwise, the phrase "consisting essentially of", and variations such as "consists essentially of" will be understood to indicate that the recited element(s) is/are essential i.e. necessary elements of the invention. The phrase allows for the presence of other non-recited elements which do not materially

19 affect the characteristics of the invention but excludes additional unspecified elements which would affect the basic and novel characteristics of the method defined. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

20