PST Thin Films Research Articles

MICROWAVE DIELECTRIC PROPERTIES OF Mn:BST AND PST THIN-FILMS

ABSTRACT In this study, we characterized nano-structured Mn doped BST thin-films fabricated using a pulsed laser deposition process at the University of Houston, and PST thin-films fabricated using MOCVD at the Arizona State University. Coplanar waveguide test structures were used for experimental evaluation of the dielectric properties of the BST and PST thin-films fabricated on MgO and saphire substrates respectively. The test structures were fabricated on bare substrates as well as on the thin-film test samples for determination of attenuation and phase constants with and without the ferroelectric thin-films. The ϵfilm for the Mn:BST film was approximately 1200 over the frequency range of 15–30 GHz with the loss-tangent averaging to 0.033. The PST thin-film on sapphire substrate had a zero-bias relative dielectric constant of 200 and the loss-tangent was estimated to be 0.05 over the measured frequency range of 10 to 18 GHz.

Enhancement of ferroelectricity in the compositionally graded (Pb,Sr)TiO 3 thin films derived by a sol–gel process

The compositionally graded Pb 1− x Sr x TiO 3 (PST) films with a fine compositional gradient from Pb 0.6Sr 0.4TiO 3 to Pb 0.3Sr 0.7TiO 3 were fabricated on LNO-buffered Pt/Ti/SiO 2/Si substrates by a sol–gel deposition method. The graded films crystallized into a pure perovskite structure and exhibited highly (1 0 0) preferred orientation after post-deposition annealing. Dielectric and ferroelectric properties were investigated as a function of temperature, frequency and direct current bias field. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range of 25–250 °C within which the dielectric constant showed weak temperature dependence. This compositionally graded thin film can result in a dielectric constant more than double and a remanent polarization at least two and a half times larger than conventional PST thin films.

Effects of composition and stacking sequence on dielectric properties of the multilayered (Pb,Sr)TiO 3 thin films for tunable device application

Multilayered (Pb 1− x Sr x )TiO 3 (PST( x)) thin films consisted of uniform, PST( x) and heterostructure, PST( x)–PST80 were synthesized by coating the solutions with different Sr contents (50 ≤ x, Sr(mol%) ≤80), respectively. Their structural and dielectric properties were investigated in terms of composition and stacking sequence of each film. Among uniform PST( x) thin films, the PST60 films showed the highest dielectric constant and tunability, while so lower figure of merit which is an important parameter for microwave tunable device application was obtained due to relatively higher dielectric loss. In an effort to bring down the dielectric loss, the PST( x) thin films were alternately coated with PST80 thin layer. Dielectric properties of the heterostructured PST( x)–PST80 films were found to be dependent on the intrinsic dielectric values of each film composition and corresponding phase transition temperature shift effect. Furthermore, surface roughness became smoother by inserting PST80 thin layer, resulting in decrease in dielectric loss. In case of the PST60–PST80 heterostructured film, despite of slight decrease in tunability, the figure of merit on account of lowered dielectric loss was effectively improved (>40%), compared to that of the uniform PST60 film.

Effect of La doping on tunable behavior of sol–gel-derived PST thin film

Pb x Sr 1− x TiO 3 and (Pb 0.4Sr 0.6) 1− x La 2 x/3 TiO 3 thin films were prepared on ITO/glass substrate by sol–gel technique. The crystalline phase structures of thin films were investigated by XRD. The dielectric properties were measured by LCZ meter. Results show that the perovskite phase was stable in Pb x Sr 1− x TiO 3 thin film. Its lattice constant was found to increase with the increase of x. When Pb/Sr ratio was about 50/50, the transformation of the perovskite phase between cubic and tetragonal took place at room temperature. To ensure better tunability, Pb 0.4Sr 0.6TiO 3 thin film was selected in both paraelectric state (cubic structure) and near the phase transformation point between cubic and tetragonal. The tunability of more than 80% and figure of merit (FOM) of 14.17 were obtained. (Pb 0.4Sr 0.6) 1− x La 2 x/3 TiO 3 was also prepared as La-doped thin film. Its dielectric constant was decreased below x = 0.4 and then increased above x = 0.4 with the increase in x. The inharmonic coefficient depicting ability of tunability of (Pb 0.4Sr 0.6) 1− x La 2 x/3 TiO 3 thin film kept constant due to the changeable shape of the crystal cell under electric field at a fixed temperature below x = 0.4, which is in good agreement with Johnson's theory. And the coefficient reveals a distinctive variable because of easily changeable shape under different bias above x = 0.4. The tunability of about 70% and FOM of about 7 were obtained in the (Pb 0.4Sr 0.6) 1− x La 2 x/3 TiO 3 thin film.

Structural and ferroelectric properties of Pb1-xSrxTiO3 thin films

Strontium-modified lead titanate (PST) thin films with composition Pb1-xSrxTiO3 (0.10<x≤0.60) were grown on Pt/Ti/SiO2/Si substrates using a soft chemical process. The crystallization of the PST thin films was achieved by heat treatment at 600 °C. The structural and microstructural modifications in the films were studied using X-ray diffraction (XRD) and atomic force microscopy, respectively. The XRD study shows that the lattice parameters of polycrystalline PST thin films calculated from X-ray data indicate a decrease in lattice tetragonality with the increase in strontium content in these films. This indicates a gradual change from tetragonal to cubic structure. By atomic force microscopy analysis, the average grain size of the thin films was systematically reduced with the increase in Sr content. The dielectric property of the thin films was found to be strongly dependent on the Sr concentration. With 60 at. % Sr content, a ferroelectric to paraelectric phase transition was observed at room temperature.

Preparation and phase formation of sol-gel derived PST thin film doped with Mg

PST thin film doped with Mg was successfully prepared using sol-gel process. The phase structure of the thin film was measured by XRD and the morphology of microstructure of the thin film was observed by SEM. Results showed that the cubic perovskite phase is formed in Mg-doped Pb0.4Sr0.6MgxTi1-xO3-x thin film prepared by sol gel process. The clustered crystallites are distributed and embedded in the base matrix of thin f ilm. However, the contents of the perovskite phase was controlled by both Mg dop ing and heat treatment condition due to formation of intrinsic oxygen vacancy in the perovskite phase. The charge balance between the positive from the intrinsi c oxygen vacancy and the negative from Mg substitution for Ti occurs when small amount of Mg is doped in the perovskite phase. The stable perovskite phase forms easily, and the crystallization of the perovskite phase is hence increased with increasing Mg doping up to x=0.01. The distortion of the perovskite phase struc ture would increase with farther increase of Mg doping in the crystallites above about x=0.01 due to the generation of a lot of oxygen vacancies. Henceforth uns table perovskite phase is formed and the crystallization of the film decreases w ith increasing Mg. Thus highest content of the perovskite phase is reached and t he charge balance between positive and negative occurs in the film when Mg dopin g is x=0.01. Furthermore, the formed crystalline phase may decompose with increa sing Mg content and time of heat treatment. So in the case of high Mg doping the higher the content of Mg and the longer the time of heat treatment, the lower t he content of perovskite phase is contained in the film.

Dielectric properties of highly (100) oriented (Pb0.5,Sr0.5)TiO3 thin films grown on Si with MgO buffer layer

Pb 0.5 , Sr 0.5 Ti O 3 (PST) thin films were deposited on Si with MgO (100) buffer layer by the alkoxide-based sol-gel method. Structural and dielectric properties of PST thin films for the tunable microwave device applications were investigated. For the MgO∕Si buffer layer, the PST thin films exhibited highly (100) orientation. The MgO buffer layer affects the stress state of the (100)-oriented PST thin films. The dielectric constant, tunability, and figure of merit of the highly (100)-oriented PST thin film increased with increasing annealing temperature due to the decrease in lattice distortion. The differences in dielectric properties may be attributed to the change in the film stress. The dielectric constants, dielectric loss and tunability of the PST thin films deposited on the MgO∕Si substrates measured at 10kHz were 822, 0.025, and 80.1%, respectively.

Correlation between dielectric properties and strain in Pb 0.5 Sr 0.5TiO 3 thin films prepared by using the sol–gel method

Pb 0.5Sr 0.5TiO 3 (PST) thin films were fabricated by the alkoxide-based sol–gel process using spin-coating method on Pt/Ti/SiO 2/Si substrate. The PST films annealed from 500 °C to 650 °C for 1 h show a perovskite phase and dense microstructure with a smooth surface. The grain size and dielectric constant of PST films increase with the increase in annealing temperature, which reduces the SiO 2 equivalent thickness of the PST film. The crystallinity or internal strain in the PST thin films analyzed from the diffraction-peak widths correlates well with the decrease in the dielectric losses. The dielectric constants and dielectric loss (%) of the PST films annealed at 650 °C ( t eq=0.89 nm) were 549 and 0.21%, respectively.

Dielectric properties of highly (1 0 0) oriented (Pb 0.5, Sr 0.5)TiO 3 thin films grown on LaNiO 3 electrodes

Pb 0.5,Sr 0.5TiO 3 (PST) thin films were deposited on the LaNiO 3 (LNO(1 0 0))/Si and Pt/Ti/SiO 2/Si substrates by the alkoxide-based sol–gel method. Structural and dielectric properties of PST thin films for the tunable microwave device applications were investigated. The PST films, which were directly grown on the Pt/Ti/SiO 2/Si substrates, showed the random orientation. For the LNO/Si substrates, the PST thin films exhibited highly (1 0 0) orientation. Compared with randomly oriented films, the highly (1 0 0)-oriented PST thin films showed better dielectric constant, tunability and figure of merit (FOM). The dielectric constant, tunability and FOM of the highly (1 0 0)-oriented PST thin film increased with increasing annealing temperature due to the decrease in lattice distortion. The differences in dielectric properties may be attributed to the change in the film stress and the in-plane oriented polar axis depending on the substrate that was used. The dielectric constants, dielectric loss and tunability of the PST thin films deposited on the LNO/Si substrates measured at 1 MHz were 483, 0.002 and 60.1%, respectively.

유도결합 플라즈마를 이용한 PST 박막의 식각 특성

(Pb,Sr)TiO<TEX>$_3$</TEX>(PST) thin films have attracted great interest as new dielectric materials of capacitors for Gbit dynamic random access memories. In this study, inductively coupled CF<TEX>$_4$</TEX>/Ar plasma was used to etch PST thin films. The maximum etch rate of PST thin films was 740 <TEX>$\AA$</TEX>/min at a CF<TEX>$_4$</TEX>(20 %)/Ar(80 %) 9as mixing ratio, an RF power of 800 W, a DC bias voltage of -200 V, a total gas flow of 20 sccm, and a chamber pressure of 15 mTorr. To clarify the etching mechanism, the residue on the surface of the etched PST thin films was investigated by X-ray photoelectron spectroscopy. It was found that Pb was mainly removed by physically assisted chemical etching. Sputter etching was effective in the etching of Sr than the chemical reaction of F with Sr, while Ti can almost removed by chemical reaction.

Structure and dielectrical properties of (Pb,Sr)TiO 3 thin films for tunable microwave device

The object of investigation is represented by Pb x Sr 1− x TiO 3 (PST) thin films, which were fabricated by the alkoxide-based sol–gel method on Pt/Ti/SiO 2/Si substrate. We have investigated both structural and dielectric properties of PST thin films aimed to tunable microwave device applications as a function of Pb/Sr ratio. PST thin films showed typical polycrystalline structure with a dense microstructure without secondary phase formation. Dielectric properties of PST films were found as strongly dependent on Pb/Sr composition ratio. Increasing of Pb content leads to simultaneous increasing of both dielectric constant and dielectric loss characteristics of PST films. The figure of merit (FOM) parameter (FOM=(%) tunability/tan δ (%)) reached a maximal value of 27.5 corresponding to Pb/Sr ratio of 40/60. The tunability increased with increasing Pb content. The dielectric constants, dielectric loss and tunability of the PST thin films at Pb/Sr ratio of 40/60 measured at 100 kHz were 335, 0.0174 and 47.89%, respectively.

Synthesis and characterization of lead strontium titanate thin films by sol–gel technique

A series of strontium doped lead titanate (Pb x Sr 1− x TiO 3) thin films were deposited on platinized silicon substrates by sol–gel technique and were characterized for their phase purity, surface morphology, dielectric and leakage current characteristics. The grain size of lead titanate thin films was systematically reduced with the increase in strontium content. With the addition of 50 at.% strontium doping, at room temperature, cubic perovskite phase was stabilized in lead titanate thin film. The measured dielectric constant decreased with the increase of strontium content of Pb x Sr 1− x TiO 3 thin films. The leakage current densities of PT thin films were systematically reduced with the increase in strontium content. The high dielectric constant, low loss tangent and leakage current densities of cubic PST thin films could be attractive combinations for these films to be used in dynamic random access memories (DRAM).

Comparative Studies of PST Thin Films as Prepared by Sol-Gel, LDCVD and Sputtering Techniques

Lead scandium tantalate (PST) thin films for pyroelectric applications have been deposited by using liquid delivery chemical vaporise deposition (LDCVD), sputtering and sol-gel techniques. These films were annealed by using rapid thermal annealing to improve their electrical properties. Their microstructures and electrical properties such as permittivity l r , dielectric loss tan i , pyroelectric coefficient p, and thermal detection figure of merit F d were studied. It is suggested to use a combination of methods to depositing films and then use rapid thermal annealing to producing high quality PST thin films.

Electrical Properties of PbSrTiO 3 Films on Stainless Steel Substrates with LaSrMnO 3 Buffer layers

In this study, ferroelectric Pb 0.6 Sr 0.4 TiO 3 (PST) thin films have been grown on a commercial stainless steel (SS), and metallic oxide La 0.5 Sr 0.5 MnO 3 (LSMO) buffered SS substrates, using pulsed laser deposition. Ferroelectric and dielectric properties of PST thin films were evaluated, PST films exhibited much higher dielectric constants and fatigue-resistance with LSMO-buffered substrate. The ferroelectric properties of PST/LSMO/SS layers are also pronouncedly improved. The present study also indicates that dielectric constants and leakage current density of PST/LSMO/SS films is superior to those obtained from PST/SS films. Ferroelectric properties of PST/LSMO/SS films are much more fatigue-resistant than those of PST/SS films. The results indicate that the electric properties of PST films were significantly influenced by the condition of films/electrode interfaces.

Electrical Properties of PbSrTiO 3 Films on Stainless Steel Substrates with LaSrMnO 3 Buffer layers

In this study, ferroelectric Pb 0.6 Sr 0.4 TiO 3 (PST) thin films have been grown on a commercial stainless steel (SS), and metallic oxide La 0.5 Sr 0.5 MnO 3 (LSMO) buffered SS substrates, using pulsed laser deposition. Ferroelectric and dielectric properties of PST thin films were evaluated, PST films exhibited much higher dielectric constants and fatigue-resistance with LSMO-buffered substrate. The ferroelectric properties of PST/LSMO/SS layers are also pronouncedly improved. The present study also indicates that dielectric constants and leakage current density of PST/LSMO/SS films is superior to those obtained from PST/SS films. Ferroelectric properties of PST/LSMO/SS films are much more fatigue-resistant than those of PST/SS films. The results indicate that the electric properties of PST films were significantly influenced by the condition of films/electrode interfaces.

High Performance PST Thin Films on Polysilicon Sacrificial Layers for Uncooled IR Detectors

Materials merit figures nearly 4 times that of PZT have been reported for sputtered lead scandium tantalate thin films. To achieve the required PST ferroelectric crystal phase, post-deposition annealing to temperatures above that allowable for silicon readout circuit survival is required. This paper describes the deposition of thin film lead scandium tantalate (Pb 2 ScTaO 6 ) over a polysilicon sacrificial layer, compatible with high temperature annealing, for use with a 'composite' wafer approach. A Tantalum oxide barrier layer is used to prevent PbO diffusion into the polysilicon during the high temperature annealing stage. Materials are characterised by X-ray diffraction and transmission electron microscopy. Some annealed films have shown B-site ordering. Induced pyroelectric coefficients over 1.2 2 10 m 3 Cm m 2 K m 1 have been measured in the annealed films, with materials merit figure exceeding 8 2 10 m 5 Pa m 1/2 at 9.3V/ w m.

High Performance PST Thin Films on Polysilicon Sacrificial Layers for Uncooled IR Detectors

High Performance PST Thin Films on Polysilicon Sacrificial Layers for Uncooled IR Detectors

The effect of post-annealing on the electrical properties of (Pb,Sr)TiO 3 thin films prepared by liquid source misted chemical deposition for ultra large-scale integration (ULSI) dynamic random access memory (DRAM) capacitor

The beneficial effect of post-annealing on the properties of lead–strontium–titanate (PST) thin films prepared by liquid source misted chemical deposition are reported. Their composition and depth profile were uniform. The dielectric constant and dielectric loss of the 100-nm-thick Pb 0.32Sr 0.68TiO 3 film annealed at 650°C for 5 min in air and annealed further at 630°C for 30 min after top electrode deposition were 560 (equivalent oxide thickness=0.70 nm) and 0.0173, respectively. Especially, the leakage current density was greatly influenced by post-heat treatment in O 2 and N 2 ambient gas after the top Pt electrode was deposited on a PST thin film. The leakage current density of 1.85×10 −8 A/cm 2 at 1 V was obtained after the 130-nm-thick PST thin film was treated by inductively coupled plasma (ICP).

Electrical characteristics of (Pb,Sr)TiO3 thin films for ultra-large-scale-integrated dynamic random access memory capacitors prepared by liquid-source misted chemical deposition

For the first time, the physical and electrical properties of lead–strontium–titanate (PST) thin films were prepared by liquid-source misted chemical deposition, and are reported. PST thin films were deposited on a platinum-coated Si wafer. Pb acetate, Sr acetate, and Ti isoproxide were used as metallic precursors. These were dissolved in 2-methoxyethnol. A fine mist of metallic precursor solution was carried into a deposition chamber by Ar carrier gas. The crystallization of PST thin film was achieved by heat treatment above 500 °C. The composition and depth profile of PST film, measured by wavelength-dispersive spectroscopy and Auger electron spectroscopy, were uniform. The dielectric constant and dielectric loss of Pb0.36Sr0.64TiO3 films of 80 nm thickness were 376 (equivalent oxide thickness: 0.83 nm) and 0.05, respectively. The electrical properties were improved by postheat treatment under O2 ambient gas after a top electrode Pt was deposited on a PST thin film. It is concluded that PST can be used as a high-capacity material for ultra-large-scale-integrated dynamic random access capacitors.

Characteristics of (Pb 1-xSr x)TiO 3 thin film prepared by a chemical solution processing

(Pb 1-xSr x)TiO 3 (PST) (0≤x ≤0.7) thin films on Pt/Ti/SiO 2/Si(100) substrate were prepared by the modified sol-gel process and their characteristics were investigated as a function of strontium content (x). A stable PST sol was obtained by mixing lead and strontium acetates dissolved in deionized water and ethylene glycol and a titanium alkoxide modified by chelating acetylacetone in 2-methoxyethanol. The multi-layer annealing at 700 °C was adopted to prepare the 4000 °PST thin films with perovskite phase and dense microstructure. With increasing x, the tetragonality (c/a) was slightly decreased and approached to cubic phase above x ≅ 0.5 within XRD detection limit. The dielectric constant at room temperature abnormally increased and showed the maximum one (ε r = 1377, tan 8 = 0.037 at 1 kHz) for the Pb 0.5Sr 0.5TiO 3 thin film. Also strontium substitution suppressed the leakage current density of the films effectively. These properties can be explained in terms of variations of phase transition boundary (tetragonal to cubic), resulting from the substitution of nonvolatile strontium into lead site of PbTiO 3 structure.