DESC:TECHNICAL FIELD
The present disclosure relates generally to wireless communication systems. The disclosure, more particularly, relates to tunable dielectric capacitors.
BACKGROUND
Recently, the wireless communication system demands Radio frequency (RF) based high tunable and switchable components with a high dielectric constant value, which pave a path for further miniaturization of the present P-N diode-based varactor devices. The tunable capacitors based on P-N diodes suffer from drawbacks such as low Q-factor, high insertion loss, particularly at high frequencies, and limited power handling capability. However, ferroelectric-based devices are gaining prominence in today’s technology due to their unique properties, such as spontaneous polarization. This polarization can be easily switched reversibly by applying an external electric field, resulting in a non-linear dielectric response to a Direct Current (DC) electric field. These properties make them suitable for applications such as voltage-controlled oscillators, tunable filters, switching networks, and matching networks. Amidst, carrying out various studies on perovskite materials such as Barium Strontium Titanate (BST), having a chemical formula (BaxSr1-x)TiO3, and Lead Zirconate Titanate, also called Lead Zirconium Titanate and commonly abbreviated as PZT, is an inorganic compound with the chemical formula Pb[Zr xTi 1-x]O 3 and so on. These studies involved variations in electrode materials, growth parameters, growth methods, and ion doping to achieve high dielectric tunability, low dielectric loss tangent, increased breakdown electric field, thermal stability and reduced device dimensions.
BST is one of the most studied materials due to its unique properties such as high dielectric constant, high Curie temperature, voltage tunable permittivity and a small loss tangent, making it attractive in applications of tunable RF devices. These properties entertain the usage of BST thin film in the dielectric state to the ferroelectric state by altering the Strontium (Sr) composition. The extension of Sr concentration into BaTiO3 changes the Curie point, transforming BST into a paraelectric material at room temperature, offering a high dielectric constant and low leakage current. In the present application, we utilized a conductive oxide layer of SrRuO3 (SRO), acting as a source and sink for oxygen vacancies. This approach helps reduce dielectric loss and improve the dielectric constant and tunability compared to prior studies that used metal electrodes, which result in higher leakage value due to free electrons in metals. Moreover, the ferroelectric to paraelectric transition can be broadened based on the Ba/Sr ratio, providing large thermal stability of tunability and frequency-based stability due to the high quality of the SRO/BST interface, resulting in a small response time.
The property addressed in the following is tunability in ferroelectrics, which is defined as,
Tunability(%)=(?_max- ?_min)/?_max ×100 (1)
Where ?max and ?min are the maximum and minimum values of the dielectric constant in the dielectric constant v/s voltage curve, respectively.
However, for the microwave circuit design, there should be an optimal trade-off between tunability and dielectric loss tangent (tan d) to achieve the best device performance.
There have been several endeavours to develop BST-based tunable capacitors. For example, US2010/0096678A1 titled “Nanostructured barium strontium titanate thin-film varactors on sapphire” discloses a varactor shunt switch based on nanostructured BST thin-film for microwave application. The nanostructured BST thin films were grown on a sapphire substrate, featuring a metal layer stack serving as both top and bottom electrodes. The varactor demonstrated a substantial tunability of 77% with exceptionally low loss tangents below 0.025 at zero bias and 20 GHz.
The US Patent Application US6212059 titled “Capacitor including barium strontium titanate film” discloses a BST-based capacitor for dielectric memory and dielectric filter applications. In the invention, the BST thin film was grown using a chemical vapour deposition (CVD) technique, in which respective organometallic compounds of barium, strontium, and titanium are dissolved in tetrahydrofuran.
The US Patent Application US0116796 A1 titled “Electronically tunable combine filters tuned by tunable dielectric capacitors” discloses a tunable dielectric capacitor, based on a BST thin film. The capacitor demonstrated a Cmax/Cmin is about 2, i.e. a tunability of 50% with a Q factor of about 200-500 at 1 GHz.
In the literature published by A.Tombak, J. P. Maria, F. Ayguavives, Z. Jin, G. T. Stauf, A. I. Kingon, and A. Mortazawi, IEEE Microwave and Wireless Components Letters, vol. 12, no. 1, page. 2-5(2002) demonstrated an out-of-plane tunable capacitor based on Ba0.7Sr0.3TiO3 (BST-30) thin film. The capacitor exhibited a tunability of 71 % at an operating voltage of 9 V and a dielectric loss tangent ranging from 0.003 to 0.009 at VHF. The BST-30 thin films were grown on silicon dioxide (SiO2) coated silicon (Si) substrate using the metalorganic chemical vapour deposition (MOCVD) technique.
In the literature published by J. C. Meyers, C. R. Freeze, S. Stemmer, and R. A. York, Applied Physics Letters, vol. 111, page. 262903 (2017), an in-plane tunable capacitor was fabricated on Ba0.29Sr0.71TiO3 (BST-71) thin film. The BST-71 thin film was grown on a LaAlO3 (LAO) substrate using a molecular beam epitaxy (MBE) system. The capacitors demonstrated a tunability of 56% with a Q-factor of 200 at 1GHz.
In the literature published by R. Li, S. Jiang, L. Gao, L. Wang, and Y. Li, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 58, no. 6, page. 1140-1144 (2011) reported the fabrication of tunable parallel plate capacitors utilizing the bilayers of Bi1.5Zn1.0Nb1.5O7 (BZN) and Ba0.5Sr0.5TiO3 (BST) for RF applications. The capacitors achieved a tunability of 39% at an operating voltage of 40 V, along with a high Q-factor of 300 at 1 MHz.
In brief, various efforts have been undertaken to develop highly tunable capacitors using Strontium, (Sr) doped BaTiO3 (BST)-based thin films. Despite numerous attempts, the achieved tunability in the above capacitors disclosed in the state of art above is relatively modest. Hence, there is still a need for an invention which solves the dire need for capacitors exhibiting significantly enhanced tunability, low dielectric loss, low leakage current and high breakdown voltage.
Therefore, in view of the above-mentioned problems, it is advantageous to provide an improved system and method that can overcome the above-mentioned problems and limitations associated with the existing tuning techniques.
SUMMARY
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention nor is it intended for determining the scope of the invention.
According to an embodiment of the present disclosure, disclosed herein is a tunable capacitor that includes a dielectric material deposited on a substrate, where the substrate is SrTiO3 and the dielectric material is 20% Sr doped Ba0.8Sr0.2TiO3 (BST-20). In one example, the dielectric material is forming an epitaxial layer on the substrate using pulsed laser deposition (PLD) technique.
To further clarify the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawing. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.
Brief Description of Accompanying Drawings
The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference features and modules.
Figure 1 illustrates a flow chart, depicting the deposition of BST and SRO thin films on Strontium Titanate, SrTiO3, (STO) substrate using pulsed laser deposition (PLD) technique, as well as the fabrication of the capacitor device through photolithography and wet etching, according to an exemplary implementation of the present disclosure.
Figure 2a illustrates the x-ray diffraction ?-2? scan of the SRO/BST-20/SRO heterostructure with various thicknesses of BST-20, according to an exemplary implementation of the present disclosure.
Figure 2b illustrates the x-ray diffraction rocking scan of the BST film compared with Strontium Titanate, SrTiO3, (STO) substrate, according to an exemplary implementation of the present disclosure.
Figure 2c illustrates displays the atomic force microscopy (AFM) surface morphological images of the heterostructure, according to an exemplary implementation of the present disclosure.
Figure 2d illustrates a demonstration the asymmetric reciprocal space mapping (RSM) of SRO/BST/SRO heterostructure along off axis of Strontium Titanate, SrTiO3, (STO), according to an exemplary implementation of the present disclosure.
Figure 3a illustrates a demonstration a schematic diagram of the device, showing different layers of tunable capacitor according to an embodiment of the present invention (top row); and an optical view of the real devices ranging from 25µm-200µm size after photolithography and wet etching of top SRO electrode (bottom row), according to an exemplary implementation of the present disclosure.
Figure 3b illustrates the frequency-dependent dielectric constant and dielectric loss (tan d) of the BST -20-based capacitor devices, according to an exemplary implementation of the present disclosure.
Figure 3c illustrates the DC bias voltage-dependent of the dielectric constant of the BST-20-based capacitor devices at various frequency values, according to an exemplary implementation of the present disclosure.
Figure 3d illustrates the DC bias voltage-dependent of the dielectric loss (tan d) of the BST-20-based capacitor devices at various frequency values, according to an exemplary implementation of the present disclosure.
Figure 4a illustrates the frequency-dependent dielectric constant of BST-20 capacitors with various thicknesses of BST-20 film ranging from 60 nm –180 nm keeping bottom and top SRO thickness constant, according to an exemplary implementation of the present disclosure.
Figure 4b illustrates the DC bias voltage-dependent dielectric constant of BST-20 capacitors with various thicknesses of BST-20 film ranging from 60 nm – 180 nm keeping bottom and top SRO thickness constant, according to an exemplary implementation of the present disclosure.
Figure 4c illustrates the dependence of tunability on frequency for different thicknesses of BST-20 film, according to an exemplary implementation of the present disclosure.
Figure 5a illustrates the temperature stability of the devices, showing the DC bias voltage-dependent dielectric constant of the BST -20-based capacitor devices at different temperature values, according to an exemplary implementation of the present disclosure.
Figure 5b illustrates the temperature-dependent dielectric constant of the BST -20-based capacitor devices at different frequency ranges from 1kHz to 1000kHz, according to an exemplary implementation of the present disclosure.
Figure 5c illustrates the frequency stability (red) and temperature stability (blue) of the tunability of BST-20-based capacitor devices, according to an exemplary implementation of the present disclosure.
Figure 5d illustrates a comparative analysis between our current work and prior studies, highlighting differences in tunability and breakdown electric field, according to an exemplary implementation of the present disclosure.
Figure 6a illustrates the ferroelectric loop depicting polarization versus electric field for BST-20-based capacitor devices at various frequency values, according to an exemplary implementation of the present disclosure.
Figure 6b illustrates a demonstration the leakage current density across the device as a function of the applied DC electric field, according to an exemplary implementation of the present disclosure.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present disclosure. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the various embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the present disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof.
Whether or not a certain feature or element was limited to being used only once, it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element do not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, “there needs to be one or more…” or “one or more elements is required.”
Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements of the present disclosure. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and/or elements of the proposed disclosure fulfil the requirements of uniqueness, utility, and non-obviousness.
Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.
Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed disclosure.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by “comprises... a” does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.
The various embodiments of the present disclosure describe a fabrication of a Barium Strontium Titanate tunable capacitor device for microwave devices utilizing a ferroelectric Ba0.8Sr0.2TiO3 (BST-20) thin film.
An objective of the present invention is to develop a tunable capacitor based on ferroelectric thin films, which provides high tunability, low dielectric loss, low leakage current and high breakdown voltage. Further, the pulsed laser deposition (PLD) technique is utilized to grow high-quality BaxSr1-xTiO3 (BST-x) thin film on SRO-coated (001)-oriented SrTiO3 (STO) substrate.
Another objective of the present invention is to grow a high-quality SRO layer as bottom and top electrodes for the BST capacitor.
An additional objective of the present invention is to fabricate out-of-plane capacitors using standard device fabrication techniques such as photolithography and wet chemical etching processes.
An additional objective of the present invention is to fabricate a compact tunable capacitor, characterized by a very small circular out-of-plane device with diameters ranging from 25 to 200 µm.
The present disclosure provides tunable capacitors utilizing a ferroelectric Ba0.8Sr0.2TiO3 (BST-20) thin film. These capacitors exhibit notable characteristics, including high tunability, compact dimensions, minimal dielectric loss, low leakage current, and a high breakdown voltage. To achieve significant tunability with minimal leakage current, the key lies in introducing the Sr composition in the BaxSr1-xTiO3 thin film, as the Ba/Sr composition can trap the charge to reduce the leakage current in the system and change ferroelectric phase transition temperature, bringing it near room temperature at a certain Sr composition value. However, it is crucial to emphasize that there exists an optimal range of Sr composition and film thickness where both high tunability and low leakage current can be achieved near room temperature. Additionally, the choice of substrates and the quality and thickness of the electrode also affect certain aspects of the properties of the fabricated capacitors. Therefore, finely tuning the Sr composition, film thickness, substrate type, electrode type, and film growth method is highly essential to achieve exceptional tunability with a substantially low leakage current.
In an embodiment of the present disclosure, a tunable capacitor fabricated for microwave devices in accordance with the present disclosure comprises: a dielectric material of composition Ba0.8Sr0.2TiO3 is deposited on a Strontium Titanate, SrTiO3, (STO) substrate and the said dielectric material form an epitaxial layer on the STO substrate using the pulsed laser deposition (PLD) technique. The dielectric material composition Ba0.8Sr0.2TiO3 is also referred to as BST-20. The dielectric material layer has a thickness in the range of 60-200 nm. Most preferably, the dielectric material layer has a thickness of 180nm. Further, the dielectric layer is sandwiched between two electrodes, a bottom electrode measuring the thickness of 60 nm and a top electrode measuring the thickness of 80nm. The top electrode and bottom electrodes are made up of Strontium Ruthenate, and SrRuO3 (SRO) layers. The top electrode has a diameter in the range of 20-30 µm. The tunable capacitor, having the above composition, exhibits a tunability of 91% at an operating DC voltage of 15 V, also demonstrates a breakdown electric field of 800 kV/cm, and displays thermal stability up to 473 K and frequency stability ranging from 10 to 1000 kHz.
The highly tunable capacitors fabricated for microwave devices are doped using 20% Sr concentration in barium strontium titanate (BaxSr1-xTiO3) as the ferroelectric material to achieve the maximum tunability of ~91%. By this precise modulation of the Sr concentration in BaxSr1-xTiO3 on STO substrate and optimizing film thickness to minimize the leakage current while withstanding a breakdown electric field of ~ 800 kV/cm.
Referring to Figure 1, the flow chart 100 illustrates the deposition process of dielectric material layer BST-20 and SRO thin films on STO substrate using pulsed laser deposition (PLD) technique with a krypton fluoride (KrF) excimer laser (?=248 nm) source. Here, the tunable capacitor containing the SrRuO3 (SRO) (60nm)/ Ba0.8Sr0.2TiO3 (BST-20) (180nm)/ SrRuO3 (SRO) (60nm) heterostructure was epitaxially grown on Strontium Titanate, SrTiO3, (STO) substrate. Initially, at step 102, the termination of the Titanium Oxide (TiO2) on the substrate using Hydrogen Floride (HF) etching followed by the annealing in an Oxygen atmosphere. As part of step 102, the deposition of a bottom electrode layer, SrRuO3 (SRO) having a thickness of 60 nm may be carried out on Strontium Titanate, SrTiO3, (STO) substrate at a temperature of 700 ºC, oxygen pressure of 100 m Torr, laser fluence of 1.34 J/cm2, and laser repetition rate of 10 Hz. Subsequently, at step 104, a stack of material may be deposited over the STO substrate-SRO bottom, the ferromagnetic material (BST-20), SRO top electrode. Specifically, the dielectric material layer Ba0.8Sr0.2TiO3 (BST-20) having a thickness of 180nm and the top electrode SrRuO3 (SRO) layer having a thickness of 80 nm may be deposited at a growth temperature of 600 ºC under an oxygen pressure of 50 m torr with same laser fluency as a top electrode with a laser repetition rate of 2 Hz for BST-20 and 10 Hz for top SRO electrode. The target substrate distance was maintained at 4.5 cm during the whole process. After the growth, the sample was cooled down at a rate of 5°C/min under atmospheric pressure. Thereafter, at step 106, pattering of the out-of-plane circular device (25 to 200 µm) using photolithography is performed. Finally, at step 108, the chemical etching of the top SRO using NaIO4 solution is performed.
Referring to Figure 2a, a graphical representation of the (001) and (002)-reflection ?-2? high-resolution X-ray diffraction (HRXRD) scan of the as-deposited SRO(60nm)/BST-20(60-180nm)/SRO(60nm) heterostructure is presented. The measurement is performed using the Bruker D8 Discover triple-axis high-resolution diffractometer with Cu-Ka radiation (?=1.5405 Å). The scan reveals that both BST-20 and SRO are high-quality single-crystalline phases, and epitaxially grown on the STO substrate. The peaks along the (001) and (002)-reflection of BST-20 and SRO are clearly visible, aligning with the STO peak, indicating the good quality of each individual layer. The calculated out-of-plane lattice parameters (c) of BST, SRO, and STO are 4.015 Å, 3.953 Å, and 3.905 Å, respectively, resulting in compressive strains of 1.568% and 1.23 % for the BST and SRO layer on the STO substrate.
Referring to Figure 2b, the x-ray diffraction of omega (?)-scan (rocking curve) along the (002)-reflection for both STO (black) and BST film (red) is presented. The full-width-at-half-maximum (FWHM) values of the STO and BST film are 0.026 deg., and 0.151 deg., respectively. This low FWHM indicates good film quality, with all grains aligned in one direction.
Referring to Figure 2c, the Atomic Force Microscopy (AFM) study of the morphology using tapping mode reveals that the surface of the SRO (60 nm)/BST(180 nm)/SRO(60nm) heterostructure is epitaxially grown, exhibiting a root mean square roughness value of 233.57 pm across a scanned area of 3.3 µm × 3.3 µm, providing a crystalline surface suitable for capacitor fabrication.
Referring to Figure 2d, the XRD reciprocal space mapping along the (103) off-axis of STO reveals that the film is coherently strained by the substrate. The in-plane lattice parameters were calculated for the BST-20 film as 3.945 Å, resulting in in-plane lattice compression of -1.335% when compared to the bulk in-plane lattice parameters (a = 3.998 Å). Additionally, the out-of-plane lattice parameter is elongated with c = 4.015 Å > a = 3.945 Å, yielding a c/a ratio of 1.0177, which confirms the tetragonal phase of the grown film.
Referring to Figure 3a, the illustration presents a pictorial representation (top) and an optical microscopic view (bottom) of the SRO (60nm)/BST-20(180nm)/SRO (60nm) capacitor device on the STO substrate. In this depiction, the top SRO layer was etched using standard photolithography, followed by chemical etching to define the top circular electrode. The wet chemical etching of SRO was carried out in a solution consisting of 0.4 gm of NaIO4 and 20 ml of DI water. Circular out-of-plane devices with diameters ranging from 25 to 200 µm were fabricated. Subsequently, the devices were tested with one contact taken from the bottom SRO and another contact from the top SRO.
Referring to Figure 3b, the frequency dependent-dielectric constant, ranging from 10 KHz to 1 MHz, exhibits a linear decrease from 1355 KHz to 951 KHz. As the frequency increases, the time for the switching of dipoles decreases. At higher frequencies, dipoles lag behind the electric field response, resulting in a lower dielectric constant value, dependent on the relaxation time of the dipoles.
In the frequency-dependent dielectric loss, the device demonstrates significantly low loss, revealing the high quality of the devices. More interestingly, it can be observed that up to 200 kHz, the dielectric constant and dielectric loss exhibit the same behaviour. However, at frequencies beyond 200 KHz, an increase in the tan d value is observed due to the piling up of space charges at the interface, resulting in interfacial polarization.
Referring to Figures 3c and 3d illustrate a change in capacitance with respect to DC bias was measured for both directions of voltage sweep (up and down) at different frequencies for 25 µm diameter devices. The dielectric constant value was calculated using the equation,
e=Cd/(e_0 pr^2 );
,where C is the capacitance value of the BST-20 layer,
d is the thickness of the BST-20 layer (180 nm),
r is the radius of the device (12.5 µm), and
e0 is the dielectric constant in free space. Simultaneously, dielectric loss (tan d) measurements were performed by varying DC bias. All measurements were conducted with a constant AC-biased voltage of 50 mV.
It was observed that there is a non-linear change in the dielectric constant with DC bias. Moreover, the up and down bias sweep shows a very weak hysteresis, as expected in ferroelectrics materials, with the maximum dielectric constant ~ 1330 observed at 0 V bias. Here, a small AC signal is superimposed on a DC signal, causing an increase in domain wall motion and partial switching of domains with a small coercive field, resulting in an increase in dielectric constant. With a further increase in DC voltage, all domains align along the same direction due to elastic constraints, leading to a reduction in dielectric response with voltage. The dielectric loss (tan d) is significantly low under DC bias voltage for the fabricated device.
Referring to Figures 4a and 4b, the frequency-dependent and DC bias-dependent dielectric constant for various thicknesses of BST-20 (60-200nm), respectively. Notably, a discernible trend emerges as the dielectric constant values consistently increase with the thickness of BST-20. This observed pattern holds true for both frequency-dependent and DC bias-dependent dielectric constants under different thicknesses of BST-20.
Referring to Figure 4c which illustrates the frequency-dependent tunability with various thicknesses of BST-20. It is observed that as the thickness increases, the tunability also increases, as tunability is directly dependent on the dielectric constant. Additionally, consistent frequency stability in tunability is observed across all thickness values of BST-20.
Referring to Figures 5a, 5b and 5c, illustrate the DC voltage-dependent dielectric constant, frequency-dependent dielectric constant changes from room temperature to 453 K, and temperature, frequency-dependent tunability, respectively. It is evident that with an increase in temperature, the emax (Cmax) values decrease. The calculated tunability of the devices, utilizing Equation 1, underscores both thermal and frequency stability, with our device achieving a remarkable maximum tunability of approximately 91%, in comparison to existing records. Additionally, a discernible dispersion in dielectric constant versus temperature curves at various frequency values suggests a relaxed or-like behaviour for the grown film, attributed to the formation of polar nano regions in the BST-20 layer.
Referring to Figure 5d, illustrates a comparison of tunability and breakdown electric field for different materials reported to date, demonstrating that the current work exhibits the maximum tunability and breakdown electric field values.
Referring to Figure 6a, the demonstration of electric field-dependent polarization at various frequencies reveals a noteworthy trend. It is observed that with an increase in frequency, the saturation polarization increases, reaching 20.44 µC/cm2 at 50 kHz. In accordance with the anticipated behaviour in relax or ferroelectrics, the remnant polarization stands at 4.67 µC/cm2, accompanied by a switching coercive voltage of approximately 578 mV at 2 kHz, a value that exhibits an increasing trend with the rise in frequency.
Referring to Figure 6b, the electric field-dependent leakage current density is presented. The minimum leakage current at zero applied voltage is approximately ~5 × 10?5 A/cm². The leakage current can arise with electric field mainly due to two mechanisms: one being space charge current generation at low electric fields due to the presence of free charges, and Schottky emission current as the electric field value increases due to thermally excited electrons at the film-electrode interface. The minimum leakage current at zero applied voltage is approximately ~5 × 10?5 A/cm².
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:1. A tunable capacitor comprising:
a dielectric material deposited on a substrate, where the substrate is SrTiO3 and the dielectric material is 20% Sr doped Ba0.8Sr0.2TiO3 (BST-20).
2. The device of claim 1, wherein the dielectric material is forming an epitaxial layer on the substrate using pulsed laser deposition (PLD) technique.
3. The device of claim 2, wherein the thickness of the dielectric layer is ranging from 60 to 200 nm.
4. The device of claim 3, wherein the dielectric layer is being sandwiched between two electrodes.
5. The device of claim 4, wherein the two electrodes are being composed of top and bottom SrRuO3 (SRO) layers.
6. The device of claim 5, wherein the thickness of the top electrode is 80 nm, whereas, the thickness of the bottom electrode is 50 nm.
7. The device of claim 5, wherein the top electrodes having a diameter ranging from 20 to 30 µm.
8. The device of claim 1, wherein the said device demonstrates a tunability of 91% at an operating DC voltage of 15 V.
9. The device of claim 1, wherein the said device exhibits a breakdown electric field of 800 kV/cm.
10. The device of claim 1, wherein the said device showcases thermal stability up to 473 K and frequency stability ranging from 10 to 1000 kHz.