Patent Application
20130003254
1. Field of the Invention
The present invention relates to thin film materials, suitable for ferroelectric tunable devices and/or decoupling thin film capacitors based on such materials, and methods of manufacturing thin film devices, and more particularly, to paraelectric perovskite oxynitride nanocomposite materials and methods of making such materials for use in forming varactor devices with improved voltage tunabilities and high capacitance density thin film decoupling capacitors.
2. Description of the Related Art
In order to achieve maximum tunability of a ferroelectric varactor, a maximum voltage must be applied to induce a change in the dielectric constant needed to produce the maximum possible shift in capacitance.
U.S. 2009/0069274 discloses a tunability of 2.8:1 under an electric field of 450 kV/cm to 500 kV/cm or a 70% reduction of the original capacitance under a 450 kV/cm bias field as shown in
Oxynitrides perovskites can often be described as derivatives of oxides, formed by simultaneous substitutions (charge equivalency (balance) rule) of cation and anion components. The higher anionic charge resulting from the N3−/O2− substitution can be compensated according to two different principles. In the first case, a cross-substitution is applied with trivalent RE3+ (rare earth) elements as suitable substitutes, for instance, for divalent alkaline-earth cations. For example, the oxynitride “charge balance equivalent” to BaTiO3 will be LaTiO2N1, or NdTiO2N1. Another example for charge compensation in AB(ON)3 oxynitrides perovskites, is simultaneous substitution of the Ti4+ with Me5+ and partial substitution of O2− sites with N3− so as to convert the perovskite oxide BaTiO3 into the oxynitride perovskites, such as BaTaO2N or BaNbO2N, in addition to LaTaON2.
The incorporation of N3−/N2− into oxygen anion sites of the perovskite oxides results in pronounced structural effects, such as an elongated Ti(Zr)—N bond length and the reduced electronegativity of the nitride ion N3−, with respect to the oxide ion O2−, which will tend to increase the covalence of the cation-anion bonds. The increased covalence of the bonding can in turn increase the likelihood of cation displacements through a second order Jahn-Teller-like distortion of the d0 cation and could influence the ferroelectric properties of the oxynitride perovskites by suppressing the formation of a ferroelectric phase and enhancing the paraelectric properties into a superparaelectric state. Even the oxynitride formation could be associated with a structural change from cubic symmetry (Pm3m) to non-cubic (e.g., tetragonal) or quasi-cubic with increased in the tetragonal distortion (c/a ratio). On the other hand, the mixed occupancy of the anion site in oxynitrides AB(O1-xNx)3, provides a condition similar to that found in relaxors, as the polarizing octahedral cations (Ti4+) will experience random chemical environments in the absence of complete O/N sites ordering. Anion control has previously been utilized to tune the properties of ferromagnetic and paramagnetic perovskite or double perovskite materials.
Most recently both N2 and NH3 containing plasmas have been used for the nitridation of cubic perovskite single crystals, bulk ceramic, and thin film samples, such as SrTiO3, and for PLD and RF-sputtered depositions of BaTaO2N1, as well as growth of LaTiO2N1 epitaxial thin films on SrTiO3 or MgO substrates from oxynitride targets. However, there have been no reports of deposition and characterization of oxynitride polycrystalline ABO2N1 or ABO3-γNγ thin films grown on Pt electrodes on common large size commercially available substrates nor any C-V or I-V characteristics of any ferroelectric oxynitride perovskite, except for the dielectric constants of LaTiO2N1 and BaTaO2N1 thin films at zero dc bias. In addition, even epitaxially grown BaTaO2N films at 760° C. from a oxynitride target on a SrTiO3:Nb substrate with a SrRuO3 buffer by PLD method with gas ratio of N2/O2 of 20:1 had a dielectric constant of only 220, which is about 20 less than that of BaTaO2N bulk samples. Temperature coefficient of capacitance (TCC) of BaTaO2N films from 10K to 300K is in the range of −50 ppm/K to 100 ppm/K.
For the case of RF sputter-deposited LaTiO2N1, the dielectric constant had been reported to be from 400 to 1100 without any bulk ceramic data shown for comparison and without any voltage tunability or TCC data.
It had been previously observed that that the presence of N2 in the plasma reduces the surface defects on the electrodes as well as reducing the leakage current with almost no noticeable enhancement of the dielectric constant in SrTiO3 films for low deposition temperatures (200° C.). The observed lower leakage (higher insulation resistance) in N-doped SrTiO3 films had been attributed to nitrogen substitution of the oxygen vacancies generated by the high deposition rate of the SrTiO3, and N compensation of the donor sites created by the oxygen vacancies, without any further evidence or actual mechanism causing the lower leakage.
All of the commonly known deposition methods of BST films, and particular solutions for achieving high voltage tunability and/or high capacitance density required for achieving better performance variable capacitors and/or high density decoupling thin film capacitors, typically require using very high deposition temperatures of about 800° C. or higher, very high post-deposition annealing temperatures between 800° C. and 900° C., and thicker BST dielectric layers, typically between 200 nm and 600 nm, all of which make it very difficult to simultaneously achieve large volume manufacturing reproducible quality paraelectric thin films with reasonably high tunability ratios, i.e., tunability ratios of at least 4-6:1, under applied DC biases below 6-8 Volts, low dielectric loss, i.e., of less than 1% at 1 KHz or 1 GHz, which is typically only possible at lower deposition temperatures of about 600° C. to about 650° C. The deposition of oxynitride perovskite thin films requires using epitaxially matching substrates which are not available in large manufacturing sizes and typically obtained oxynitride perovskite materials are not stable above 600° C. if annealed in oxygen atmospheres.
To overcome the problems described above, preferred embodiments of the present invention provide a novel oxynitride paraelectric nanocomposite material which exhibits no measurable ferroelectricity and has good voltage tunable properties as well as a high dielectric constant, and also provide a method of producing of oxynitride paraelectric nanocomposite material that is compatible with large volume manufacturing processes.
In accordance with a preferred embodiment of the present invention, a method of depositing oxynitride containing dielectric thin layers with perovskite structure in a radio frequency (RF) physical vapor deposition (PVD) process from insulating or semiconducting ceramic targets is provided.
According to a preferred embodiment of the present invention, an RF sputter deposition process preferably provides a dense crystalline composite paraelectric material that includes nano-regions containing rich N3− anions dispersed in a nano-grain sized matrix of crystalline oxide perovskite material, wherein (ABO3-δ)α−(ABO3-δ-γNγ)1-α (0.01<γ<1.5) or (Ba1-x,Srx)TiO3-δ)α−(Ba1-x,Srx)TiO3-δ-γNγ)1-α or BSTON-BSTO (0.5<1-x<0.8) nanocomposite films, which can be utilized as a dielectric layer, for example, in voltage tunable capacitors, high density capacitance devices, such as de-coupling thin film capacitors, or monolithically integrated with other micro-electronic or passive devices.
A method of depositing a perovskite or ceramic oxide layer according to a preferred embodiment of the present invention preferably includes placing a substrate in a PVD reactor; flowing a gaseous mixture, for example, argon, nitrogen and oxygen, through the reactor; maintaining the sputtering gas mixture under a constant pressure using an automatic pressure control (APC) valve, and applying RF power to a target or applying different RF power levels to multiple targets simultaneously; wherein each target material includes a perovskite-type multicomponent ceramic oxide material, single metal oxides, or single metal nitrides, such as BST, TiN, and GdTiOx positioned with an approximately 45 degree off-axis configuration relative to the substrate.
According to another preferred embodiment of the present invention, the deposition process preferably occurs with very little oxygen, for example, less than about <1%, present in the gas mixture (Ar+ N2+O2) flow while the N2/O2 gas flow ratio is relatively high, and preferably between 40 to 58, to provide a high insulation resistance perovskite structure nanocomposite film with nitrogen-rich nano-regions in an oxide matrix as opposed to pure oxide grown perovskite films which predominantly include columnar grains and have much lower insulation resistances and lower dielectric constants. The resulting nanocomposite oxynitride films have much higher breakdown voltages, typically greater than 32 Volts for 10 nm-150 nm thick films, with uniform dielectric constant and voltage tunability, and low temperature coefficients of capacitance and tunability.
According to various preferred embodiments of the present invention, the substrate is preferably preheated. The substrate may preferably be heated to temperatures from about 550° C. to about 700° C. for perovskite nanocomposite oxynitride film deposition on various substrates capable of withstanding such a temperature range with appropriate heating and cooling rates from/to room temperature. A perovskite nanocomposite oxynitride layer having a thickness from about 75 nm to about 1-2 microns thick may preferably be deposited.
In a preferred embodiment of the present invention, the perovskite nanocomposite oxynitride layer formed on the substrate is preferably later rapid thermally annealed (RTA). The annealing atmosphere may preferably be 100% N2 or an N2+O2 mixture having an oxygen concentration of about 1% to 2% in N2. The annealing temperature may preferably be as low as about 450° C. and as high as about 700° C. depending on the thermal stresses that are induced by the difference in coefficient of thermal expansion between the dielectric perovskite layer and the substrate during the deposition and during the post-deposition anneal to guarantee lower dielectric loss factor (tan δ). The perovskite nanocomposite oxynitride films may preferably be doped with either transition metal dopants, for example, zirconium, niobium, tantalum, scandium; lanthanides including the rare earth ions, such as gadolinium, for example; and/or other amphoteric elements, such as Ge, Sn, for example.
According to a preferred embodiment of the present invention, a parallel-plate thin-film capacitor having a stacked structure is preferably provided. The parallel-plate thin-film capacitor structure preferably includes one or more capacitor structures deposited on a substrate, wherein each capacitor structure includes a bottom electrode layer, a bottom buffer oxide perovskite layer, main oxynitride perovskite nanocomposite layer, for example, a BSTON-BSTO dielectric layer deposited over the bottom electrode layer or over the bottom buffer oxide layer, and a top electrode layer deposited over the nanocomposite BSTON-BSTO dielectric layer or over the top buffer oxide layer. An additional conducting interconnect layer may preferably be deposited over the top electrode layer of the capacitor device structure.
According to various preferred embodiment of the present invention, most of the layers of the capacitor structure may preferably be formed within the same reactor chamber of a PVD reactor.
The oxynitride perovskite nanocomposite layer may preferably be deposited on a substrate coated with platinum or other suitable conductive electrode material that is sufficiently stable at intermediate deposition temperatures of, for example, about 500° C. to about 700° C., and during the annealing that is needed for the processed capacitor structure.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
A highly tunable ferroelectric variable capacitor (varactor) structure according to a preferred embodiment of the present invention, as shown in
An optional core bottom electrode 2 is either recessed and planarized to the substrate level or conventionally deposited and patterned by ion milling, for example. The core bottom electrode 2 is preferably made of a highly conductive metal or metallic alloy including Cu, Al, W, Ag, Au, other suitable metallic material, for example, that is capped with a diffusion barrier conductive layer such, as TiN, TaN, ZrN, TaSiN, TiAlN, for example, and finally coated with an additional different type of electrode material 3 (e.g., Pt).
A high dielectric constant, preferably greater than 100, dielectric bottom buffer layer 4 is preferably arranged near the bottom electrode with a given lattice expansion ratio and deposited with controlled oxygen partial pressure of about 1% to about 5% O2 in Ar, for example, to ensure optimal oxygen stoichiometry and sufficient crystallinity. This buffer layer may be deposited using the same material as the main nonlinear dielectric layer 5, such as (Ba1-x,Srx)TiO3-δ)α—(Ba1-x,Srx)TiO3-δ-γNγ)1-α or BSTON-BSTO (0.5<1-x<0.8) or a multilayer combination of such nanocomposite oxynitride perovskites or oxide perovskite material (Ba1-x,Srx)TiO3-δ.
A thin electrode material 3 that is stable at high temperatures, such as Pt, Ru, Ir, Ni, for example, or a conductive oxide or oxynitride material, such as LaNiO3, SrRuO3, SrIrO3, LaTiO2N1, (La,Sr)TiOxNy, for example, may be used as an upper portion of the bottom electrode 2.
The main layer 5 with nonlinear dielectric dependence of the dielectric constant and high voltage tunability which is a crystalline composite paraelectric material preferably includes nano-regions containing rich N3− anions dispersed in a nano-grain sized matrix of crystalline oxide perovskite material, wherein (ABO3-δ)α-(ABO3-δ-γNγ)1-α (0.01<γ<1.5) or (Ba1-x,Srx)TiO3-δ)α—(Ba1-xSrx)TiO3-δ-γNγ)1-α or BSTON-BSTO (0.5<1-x<0.8) and/or a multilayer combination of such perovskites that is partially anion substituted (nitrogen, boron, fluorine, or their combinations) and/or includes nitrogen with deferent valence states (e.g., N3− and N2−) and/or ABO3 material with controllable modification of the lattice parameters that can be achieved by the addition of a different gas mixture including nitrogen (N2, N2O, NH3 or other N-containing gas or organic compound containing NH2— groups), Kr, Ne, He or other gases. Preferably, the main nonlinear dielectric layer 5 is RF sputtered or deposited by any other suitable PVD method at intermediate to high temperatures of about 500° C. to about 750° C., for example, with Ar/O2/N2 gas or other gases, e.g., Kr, He, Ne, N2O, for example, and their mixtures with appropriate N2/O2 ratios that are preferably between about 22 and about 58, and more preferably between about 40 and about 48, for example, which enables appropriate oxygen and nitrogen partial pressures to be obtained. The RF power densities are typically from about 4.4 W/cm2 to about 5.5 W/cm2 and sputtering pressures from about 0.3 Pa to about 1 Pa, for example.
The high dielectric constant (>100) dielectric top buffer layer 6 near the top electrode is preferably deposited with controlled oxygen partial pressure to ensure some oxygen non-stoichiometry and low surface roughness. This buffer layer may preferably be deposited as the same material as the main nonlinear dielectric layer such as (Ba1-x,Srx)TiO3-δ)α—(Ba1-x,Srx)TiO3-δ-γNγ)1-α or BSTON-BSTO (0.5<1-x<0.8) or as a multilayer combination of such nanocomposite oxynitride perovskites or oxide perovskite material (Ba1-x,Srx)TiO3-δ, and/or a multilayer combination of any suitable oxide or anion-substituted perovskites. The oxygen partial pressure used for the top buffer 6 layer deposition is preferably much lower than the one used for the bottom buffer layer 4 in order to enable formation of symmetrical Schottky barriers between the perovskite and metal electrode interface which also produces symmetrical C-V characteristics even as deposited without any post-annealing, since the deposition temperatures used for the top and bottom electrodes are very different.
A top electrode material 7, such as Pt, Ru, Ir, Ni, for example, and/or a conductive oxide or oxynitride material, such as LaNiO3, SrRuO3, SrIrO3, LaTiO2N1, (La,Sr)TiOxNy, for example, as a lower portion of the upper electrode layer 10 that can also function as a low resistivity metal interconnect layer is preferably provided. The top electrode material 7 is preferably deposited by DC sputtering at about 100° C. to about 200° C., for example, directly on the top buffer perovskite layer. Preferably using photolithography and other patterning techniques, such as ion milling, a mesa-structure is formed and high tunability of the capacitance thin film variable capacitors (varactors) can be formed as shown on
An Interlayer dielectric (ILD) 8 is preferably provided that functions as an insulation layer between top and bottom electrodes. The ILD 8 can preferably be made of Al2O3, SiO2, SiNX, or other type of low dielectric constant insulating material, for example, and can preferably be deposited by sputtering, e-beam evaporation, or plasma enhanced CVD (PECVD) or low pressure CVD (LPCVD), for example. The thickness of the Interlayer dielectric (ILD) 8 is preferably about 200 nm to about 600 nm, for example, and it is preferably deposited at low temperatures of about 100° C. to about 300° C.
Low resistivity (low loss) metal interconnect layers 9 and 10 are preferably arranged to connect the bottom and top electrodes to other integrated passive devices or to the I/O pads of the ferroelectric device. The material of the interconnect layers 9 and 10 can preferably be Al, Cu, Au, for example, with sufficient thickness of about 1 um to about 5 um, for example.
More specifically, a perovskite dielectric thin film varactor structure according to a preferred embodiment of the present invention preferably includes a deposition at medium temperature of a crystalline adhesion layer, such as TiN, TiO2, or other suitable adhesion layer, for example, deposition at medium temperatures of about 200° C. to about 450° C. and vacuum annealing or directly annealing at high temperatures of about 600° C. to about 800° C., for example, thus enabling the bottom electrode layer of conductive material to have a high crystalline quality with crystals oriented predominantly along (111) crystallographic plane of a highly conductive metal, such as Pt, Ni, Cu, Ag, Al, or other multilayers separated by appropriate barrier layer(s), for example, a perovskite buffer (seed) ABO3 layer with a controlled value of its lattice constant, typically greater than the bulk value. In the case of the BST bottom buffer, the lattice constant will preferably be about 3.997 Å to about 4.00 Å, for example, which is greater than the bulk value of a Ba0.7Sr0.3TiO3 target, that has a cubic lattice constant a of about 3.974 Å, deposited at intermediate (about 300° C. to about 400° C.) to high temperatures (about 500° C. to about 800° C.) by PVD method (RF sputtering) using an Ar/O2 atmosphere with a given range of oxygen partial pressures preferably of about PO2>10−6 atm, for example, deposited on top of the bottom electrode layer. A main crystalline composite paraelectric material includes nano-regions containing rich N3− anions dispersed in a nano-grain sized matrix of crystalline oxide perovskite material, wherein a (ABO3-δ)α-(ABO3-δ-γNγ)1-α (0.01<γ<1.5) or (Ba1-x,Srx)TiO3-δ)α—(Ba1-x,Srx)TiO3-δ-γNγ)1-α or a BSTON-BSTO (0.5<1-x<0.8) nanocomposite film is deposited at high temperatures of about 550° C. to about 700° C., for example, on top of the buffer (seed) layer preferably in a different gas mixture including nitrogen (N2), or N2O, NH3 or other N-containing gas or organic compound containing NH2— groups, for example, with an effectively non-cubically distorted lattice constant (c/a ratio) that is much greater than that of the buffer (seed) layer. Preferably, the quasicubic-lattice or the c-lattice (noncubic crystal) is increased by about 3% to about 5-7%, e.g., about 4.065 Å for BSTON-BSTO(1-x(Ba)=0.7, as compared to the bottom buffer layer. Therefore, the tetragonality ratio c/a of the BSTON-BSTO nanocomposite layer can preferably be as high as about 1.03 deposited under the typical N2/O2 ratios, followed by an additional top buffer layer deposited with very low or close to zero oxygen partial pressures, e.g., PO2<10−6 atm, and a top electrode layer of conductive electrode material 7 on top of the dielectric layer deposited at low temperatures of about 100° C. to about 300° C., for example. The lattice constant of about 4.065 Å for the BSTON-BSTO main dielectric layer (1-x(Ba)=0.7) is significantly expanded as compared to the oxide perovskite buffer layer which remains closer to the bulk BST ceramic(1-x(Ba)=0.7) cubic crystal of about 3.974 Å. Preferably, the lattice constant of the buffer layer is in the range of about 3.990 Å to about 4.00 Å, and c/a=1.005, for example. In another preferred embodiment of the present invention, the lattice constant of about 3.995 Å for the BSTON-BSTO main dielectric layer (1-x(Ba)=0.5) is significantly expanded as compared to the oxide perovskite buffer layer which remains closer to the bulk BST ceramic(1-x(Ba)=0.5) cubic crystal of about 3.9537 Å. Typically, the lattice constant of the buffer layer is in the range of about 3.973 Å to about 3.982 Å, for example.
The inventors the present invention observed that an increase in the lattice parameter or lattice volume with an N2/O2 gas flow ratio may be a result of the lattice strain due to defects in the film, bottom layer(s) misfit strain, film stress (ion bombardment or gas incorporation in to the film), and/or a change in the lattice induced by a change of the Ti—N bond length during the partial substation of O—Ti—O with O—Ti—N incorporated into the BSTON-BSTO nancomposite crystalline layer. In this regard, by using density functional theory (DFT) generalized gradient approximation (GGA), it had been estimated that the ideal tetragonal lattice volumes from which to extract the quasi-cubic lattices for Ba0.5Sr0.5TiO3, Ba0.5Sr0.5TiO2.5N0.2 and BaSrTiO2N1, as summarized in
The observed enlargement of the unit-cell volume for the BSTO films sputtered with approximately 25%-50% N2 in the plasma while maintaining the oxygen partial pressure almost constant between about 0.5% and about 0.8% showed some tendency which is very consistent in comparison to the theoretical modeling, and that alone cannot be associated with the commonly observed phenomena for conventionally sputtered BSTO films while the oxygen partial pressure is reduced by orders to be able produce such lattice expansion phenomenon. Some type of chemical interaction of N occurs within the BSTO lattice, and it is actually incorporated into the BSTO lattice or localized areas, since under the same N2/O2 ratio of about 40 to about 58 at deposition temperatures of less than about 600° C., the BSTO lattice is still somehow expanded, but the tetragonality ratio is not significantly deviated from the bulk level of about 1.006. The lower tetragonality ratio also correlates with non-enhancement of the dielectric constant of the BSTO which is the case for BSTO that is deposited at about 550° C. For temperatures greater than about 600° C., higher N2/O2 ratios lead not only to lattice volume enlargement, but also to a significant increase of the tetragonality ratio up to about 1.025.
Usually thicker (about 300 nm to about 800 nm) sputtered conventional BSTO films tend to have larger tetragonality, e.g., about 1.012, for example, but that is not the case for thinner (about 100 nm to about 150 nm) conventionally sputtered BSTO films. Therefore, the observed large tetragonality of BSTON-BSTO nancomposite films as high as about 1.030 on Pt/TiOx/sapphire substrates most definitely originates from the chemical incorporation of N into some of the Ti—O bonds of the BSTO lattice.
As shown by STEM (Scanning Transmission Electron Microscopy) cross-sectional analysis with “dark” spots of (Ba0.7Sr0.3)TiO3-δ-γN7 correlates well with EELS (Electron energy loss spectroscopy) maps for the nano-regions with higher N concentration within (Ba0.7Sr0.3)TiO3-δ.matrix.
The observed presence of bonded N—Ti—N in BSTON-BSTO nancomposite crystalline layer by the EELS is also supported by the observed strong N 1s XPS peak, as shown in
As shown in
Immediately after deposition of the top electrode layer and the formation of a shadow mask dot structure or after ion milling of the top electrode, the C-V characteristics of the BSTON-BSTO nancomposite films can be directly evaluated. This is because the top Pt electrode deposition at about 100° C. to about 300° C. does not seem to cause any observable damage near the top BST interface. There are a few factors contributing to this. First, the sputtered perovskite films are much denser than films that are deposited using chemical solution decomposition (CSD). Second, the effective use of very low O2 partial pressures to form the top BST buffer layer, the low surface roughness of the top layer of the BST film, and the use of moderate temperatures for the top Pt electrode deposition, all lead to a significantly reduced degree of damage to the BST interface with the top Pt electrode interface area. The sputtered BSTO buffer is arranged to cover the main BSTON-BSTO nancomposite layer. As-deposited BSTON-BSTO films enabled direct evaluation of insulation resistance, dielectric loss, and C-V asymmetry, while for conventionally sputtered BST samples, their C-V remained very unstable under high positive DC biases as shown in
The observed dielectric constants in the range of about 800 to about 1100 from BSTON-BSTO nancomposite films according to a preferred embodiment of the present invention as compared to about 400 to about 500 for the conventional BSTO films show a similar trend of enhancement of their voltage tunabilities from about 2.1:1 to about 5.7-6.0:1 times under the same electric fields of about 500 kV/cm as shown in
Particular attention should be paid about the synergy of co-interactions of multiple dopants applied together with the anion doping. For this particular preferred embodiment of the present invention, when the inventors of the present invention perform co-sputtering from Ba0.7Sr0.3TiO3 and Gd2Zr2O7 targets simultaneously with different RF power ratios to enable formation of BSTON-BSTO-GZO solid solution nancomposite films under Ar+O2+N2 atmospheres which induce even further additional tetragonal distortion of the BSTO lattice as compared to pure BSTON-BSTO films, the BSTON-BSTO-GZO films have higher insulation resistance than the BSTON films and also have higher voltage tunabilities of greater than about 6.5:1 at about 6.5 Volts as shown in
(Gd, Zr, N) triple doped BSTO films according to a preferred embodiment of the present invention are shown to have enhanced tetragonality ratios and lattice volumes as compared to BSTO or BSTON-BSTO films. An additional important finding is that, for the first time, there is suppression of a direct correlation dependence between the tunability and dielectric constant for (Gd, Zr) co-doped BSTON film when the N2/O2 ratio is greater than about 40 as shown in
Another important performance of the shadow mask BSTON-BSTO highly tunable thin film capacitors according to a preferred embodiment of the present invention is their polarization hysteresis loop vs. applied Electric field (P-E) characteristics. In
As shown on
The normalized 5V DC bias tunability vs. temperature curves for the BSTON-BST) film capacitor is shown in
Some benefits and advantages of the perovskite structure nonlinear dielectric thin film capacitor (varactor) having a high voltage tunability at lower DC bias voltages and the method of manufacturing the same according to preferred embodiments of the present invention include the capability to combine multiple technologies, such as physical vapor deposition, co-sputtering to form multiple cathodes ensuring a high deposition rate and a high throughput suitable for high volume manufacturing; deposition of perovskite films with very low oxygen pressures which enables the use of low cost and high conductivity electrode materials; controlling the lattice parameters of materials with the perovskite structure which enables tuning of their voltage dependences of their dielectric constant at low electric fields; maintaining low dielectric loss, low leakage currents at operation voltages, and high breakdown strengths of the N-doped or oxynitride perovskites; maintaining low temperature dependence of zero bias dielectric constant as well as low temperature dependence of voltage tunabilities; and concurrent monolithic integration with high precision capacitor, resistor, and inductor networks capable of providing low loss high performance at high frequencies in tunable circuits, such as tunable band-pass filters, antenna matching, phase shifters, and other suitable circuits, for example.
A method of fabricating a perovskite dielectric thin film capacitor (varactor) according to a preferred embodiment of the present invention preferably includes two generalized steps: (1) forming a highly tunable device structure with appropriate electrodes on top of a substrate; and (2) integrating the highly tunable device structure with other thin film devices, such as, for example, SAW duplexers, RF-MEMS based switches, piezoelectrically actuated MEMS air gap varactors, fixed (low tunability) high density thin film capacitors, TFBAR circuits, resistors, inductors, and oxide based TFT and/or sensors, for example. Other thin film devices, such as well known passive components, for example, can also be used and the above specific examples are non-limiting.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | |
|---|---|---|---|
| 61412893 | Nov 2010 | US | |
| 61328720 | Apr 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/IB2011/000905 | Apr 2011 | US |
| Child | 13616908 | US |
