Structure and dielectric properties of Ca-doped (Ba0.7Sr0.3) TiO3 thin films fabricated by sol–gel method

A wide range of Ca-doped (Ba_0.7Sr_0.3)TiO₃ (BST) thin films (from 0 to 20 mol%) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by sol–gel technique. The structural and dielectric properties of BST thin films were investigated as a function of Ca dopant concentration. The results showed that the microstructure and dielectric properties of the BST films were strongly dependent on the Ca contents. With the Ca dopant concentration increasing, the grain size, dielectric constant and dielectric loss of the BST thin films decreased. As the content of Ca dopant reaches 10 mol%, the dielectric constant, dielectric loss, tunability, the value of FOM and the leakage current density are 281, 0.0136, 16.7%, 12.3 and 5.5?×?10^?6 A/cm², respectively.     

Thick electrodes for high frequency high Q tunable ferroelectric thin film varactors

Abstract

Thin film barium strontium titanate (BST) shows great promise for voltage tunable dielectric devices for use at RF and microwave frequencies. An MOCVD process has been developed for production of BST, resulting in films with very low losses (as low as 0.002–0.004) and tunabilities over 50% at low operation voltages. With these values of BST loss, overall device quality factors at RF (100 MHz+) frequencies are primarily limited by losses in the thin metal electrodes, such as Pt, normally used for ferroelectric thin films. The bottom electrode in parallel plate capacitor structures is particularly challenging, since it must provide a good growth surface for BST and be stable at high (>600 °C) growth temperatures in an oxidizing atmosphere yet have high conductivity and compatibility with Si or SiO₂/Si substrates. These challenges have previously prevented use of Pt thicknesses over 0.1–0.2 urn. Our solution to this problem, involves combinations of adhesion layers at the Pt/SiO₂ interface and embedded stabilization layers to make functioning Pt bottom electrodes as thick as 2 μm. Devices with dielectric Q factors over 150 at 100 MHz (tan δ ～ 0.006 as measured and modeled by S-parameters) and overall device Q factors over 50 at 30 MHz are described. We have also inserted these devices into tunable filters, achieving tunabilities of 50% and low insertion losses (0.3 dB) at RF frequencies.     

Preparation of BST thin films on Pt electrode on Si wafer with down-flow LSMCVD reactor

Abstract

A novel type of down-flow LSMCVD (Liquid Source Mist CVD) reactor was developed to prepare a high dielectric BST thin film on Pt electrode on Si wafer. Barium acetate [Ba (OOCCH₃)₂], strontium acetate [Sr (OOCCH₃)₂], and titanium isoproxide [Ti (OC₃H₇ ⁱ )₄] were used as metal sources. Metal sources were dissolved in acetic acid, 1-butanol, or 2-methoxyethanol. BST [Ba/(Ba + Sr) = 0.7] film annealed on Pt/Ti/SiO₂/Si above 650°C was polycrystalline. BST film has a (110) preferred orientation with increasing temperature. Surface roughness of BST film and grain size increased with increasing temperature. The metal-oxygen bond was formed at 650°C as shown in the spectra of FTIR. The depth profiles of elements of BST thin films indicated a uniform composition throughout the film. BST films annealed at 750°C showed a dielectric constant and a tanδ of 390 (thickness: 150 nm) and 0.06 at a frequency of 100 kHz, respectively. The behavior of capacitance of the BST film with bias voltage showed paraelectric property. BST film annealed at 750°C had the leakage current density of 3.2 (μA/cm²) at a bias voltage of 2V.     

The influence of microstructure on the electronic properties of thin films of barium strontium titanium oxide composites

Abstract

Microstructural and electrical properties were investigated for barium strontium titanium oxide (BSTO) magnesium oxide doped (0 to 10 wt.%) thin films deposited by the pulsed laser deposition (PLD) method on Pt/TiO_x/SiO₂/Si substrates. The dielectric properties were found to be strongly dependent on composition and microstructure. In cross-section, all films exhibited a columnar polycrystalline microstructure with vertical orientation deviations dictated by the surface roughness of the Pt electrode. A uniform granular microstructure was observed for all films in plan view. The dielectric constant, loss tangent and grain size decreased with increasing MgO concentration.     

MOCVD (BaxSr1−x)Ti1+yO3+z (BST) thin films for high frequency tunable devices

Abstract

We have investigated the structural and electrical characteristics of (Ba_xSr_1?x)Ti_1+yO_3+z (BST) thin films synthesized at 650°C on Pt/SiO₂/Si substrates using a large area, vertical metalorganic chemical vapor deposition (MOCVD) reactor equipped with a liquid delivery system. Films with a Ba/Sr ratio of 70/30 were studied, as determined using X-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). A substantial reduction of the dielectric loss was achieved when annealing the entire capacitor structure in air at 700°C. Dielectric tunability as high as 2.3:1 was measured for BST capacitors with the currently optimized processing conditions.     

Characterization of MOCVD Pt electrode for ferroelectric thin films

Abstract

Platinum thin films were deposited by low pressure chemical vapor deposition (LPMOCVD) on SiO₂/Si and (Ba, Sr)TiO₃/Pt/SiO₂/Si substrates using Pt-hexafluoroacetylacetonate at various deposition temperatures. The shiny mirror-like Pt thin films of a high electrical conductivity were obtained, when the deposition temperature is between 325°C and 350°C, whereas above 375°C Pt thin films showed rough surface as well as poor adhesion property to oxide substrate. Pt thin films had a good step coverage of 90%. The results indicate that LPMOCVD Pt thin films can be applied for the top electrode of high dielectric thin film, which is thought to be one of the best candidate materials for a capacitor of ULSI DRAM.     

Preparation of PZT Thin Films by Liquid-Source MOCVD Using of Cyclohexane Solvent

Pb(Zr, Ti)O₃ thin films were grown on 8-inch Ir(111)/SiO₂/Si substrate by a MOCVD system aiming at application utilizing high-density ferroelectric memory (FRAM). Two types of solvents, THF and cyclohexane were used for liquid source delivery. It was found that the ferroelectric properties of the MOCVD-PZT films using cyclohexane solvent were better than them using THF solvent. By choosing cyclohexane as solvent, the MOCVD-PZT thin films showed strong ?111? preferred orientation and the Pt/PZT/Ir capacitors exhibited promising ferroelectric performances, for instance, large switching charge (Qsw) of 56.4 uC/cm².     

Characterization of Ni/Ce Co-Doped BST Thin Film Grown on LSCO/Pt Electrodes Prepared by Pulsed Laser Deposition

Perovskite (Ba_0.6Sr_0.4)TiO₃ (BST) thin films doped with Ni, Ce and Ni/Ce codopants were prepared on LSCO/Pt/SiO₂/Si substrates by pulsed laser deposition method. In this study, La_0.5Sr_0.5CoO₃ (LSCO) bottom electrodes were used to improve the crystallinity and dielectric properties of BST films. Single ion doped(1 mol%Ni doped,1 mol%Ce doped) BST films showed more improved crystallinity, smoother surface, and smaller grain size than that with 1 mol%Ni/1 mol%Ce. The dielectric constant and loss of Ni/Ce co-doped BST films were about 298 and 1.8%, respectively. In addition, tunability and figure of merit of co-doped BST films showed minimum values of approximately 9.3% and 5, respectively. With 1% Ni-doped BST thin films, results gave a tunability of 54.2% and a loss tangent of 1.8% while a figure of merit was 30. Correlation of the material properties with dielectric and tunable properties suggests the 1 mol%Ni-doped BST films are effective potential candidate for tunable device applications.     

INTEGRATED INFRARED DETECTORS BASED ON (Ba0.65Sr0.35)TiO3 THIN FILMS

ABSTRACT

The integrated single element infrared detectors were developed for high-loading smart munition application using (Ba_0.65Sr_0.35)TiO₃ (BST) pyroelectric films and SiO₂ thermal insulating layer. (Ba,Sr)RuO₃ (BSR) seeding-layer was deposited on the Pt/Ti/SiO₂/Si to induce BST films c-axis preferred orientation growth. The capacitance dependant with temperature of BST films were measured at the temperature ranging from 230 K to 340 K, releasing that the temperature coefficient of capacitance was 1.6%/K. The pyroelectric coefficient of BST films was 7.45 × 10^{? 7} C/K cm² measured by dynamic method. Infrared response evaluation of the fabricated sensor has been carried out with D* of 6.34 × 10⁷ cm Hz^1/2/W indicating that the integrated infrared detectors have potential application as gun-launched smart munition seeker.     

Influence of Y and Mn alternately doped order on the microstructures and dielectric properties of Ba0.6Sr0.4TiO3 films

ABSTRACT

The influences of Y and Mn alternately doped order on the microstructures and dielectric properties of the Ba_0.6Sr_0.4TiO₃ (BST) films were reported in this paper. The Y and Mn alternately doped BST films were designed as YBST/MnBST/… and MnBST/YBST…multilayer films orderly expressed as (Y/Mn)_M and (Mn/Y)_M for short, and prepared on Pt/Ti/SiO₂/Si wafers by an improved sol-gel method, where Y and Mn represent yttrium doped BST layer and manganese doped BST layer, and M is cycle unit, respectively. The microstructures of the alternately doped BST films were observed by SEM and the capacitance-voltage curves at 100 kHz or 1 MHz were measured by a HP4284A LCR meter and the dielectric properties in the range of 1GHz were measured by an E4991A impedance analyzer. Compared to Y or Mn doped multilayer BST film, (Y/Mn)_M and (Mn/Y)_M show higher dielectric tunability and lower dielectric loss with higher dielectric constant. Moreover, (Y/Mn)_M show better dielectric properties than (Mn/Y)_M because (Y/Mn)_M show granular microstructures independent of M, while the (Mn/Y)_M show granular microstructures when M is 2 and add to a surface layer of columnar microstructures on the granular microstructures when M is 4. The related mechanisms were obtained in terms of the XRD phase structures, the cross-sectional SEM microstructures and the AFM morphologies.     

Preparation of Zr-rich PZT and La-doped PbTiO3 thin films by RF magnetron sputtering and their properties for pyroelectric applications

Abstract

Zr-rich PZT and La-doped PT films were fabricated on a PLT/Pt/Ti/SiO₂/Si or Pt/Ti/SiO₂/Si substrate by an RF planar magnetron sputtering equipment using powder targets with compositions of PbZr_{0 94}Ti_0.06O₃, PbZr_0.92Ti_0.08O₃ and Pb_0.85La_0.15 Ti_0.96O₃ with excess PbO of 20 mol%. The dielectric constants of PZT and PLT films showed anomalies at the transition temperatures of around 246 and 300°C, and their dielectric constants at room temperature were 350 and 1070, respectively. Significant pytroelectric currents were observed in both as-grown PZT and PLT films even without a poling treatment. The pyroelectric coefficients of those films were 10 and 30 nC/cm²K, respectively. Therefore, Zr-rich PZT and [111]-oriented PLT films sputtered on Pt/Ti/SiO₂/Si substrates possess desirable properties for potential applications to pyroelectric devices.     

EFFECTS OF PZT BUFFER LAYERS ON PZFNT FERROELECTRIC THIN FILMS

ABSTRACT

PZFNT thin films were fabricated on 5-inch Pt/Ti/SiO₂/Si and PZT/Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering method and rapid thermal annealing process. By investigating the two thin films at various annealing temperatures, the results show that the annealing temperature of PZFNT thin films without PZT buffer layers is about 730°C, which is higher than that of PZFNT films with PZT buffer layers. By use of PZT buffer layers, the annealing temperature of PZFNT films is decreased greatly, and the dielectric and ferroelectric properties are improved. In the optimum process, the thin films with PZT buffer layers have a dielectric constant of 1199 and dielectric loss of 3.0% at 1 KHz. The remanent polarization and coercive field of the thin films are 21.1 μC/cm² and 53.5 KV/cm respectively. The films have the significant potential for FRAM and pyroelectric infrared detectors.     

The effects of forming gas anneal on the electrical characteristics of ir-electroded BST thin film capacitors

Abstract

The effect of various temperature nitrogen anneals prior to top electrode deposition on the ability of Ba_0.7Sr_0.3TiO₃ (BST) thin-film capacitors with both Ir and Pt top electrodes to withstand hydrogen damage was investigated. Experimental results show that samples that underwent a 750 °C N₂ pre-top electrode anneal exhibited the lowest leakage current density at positive bias for both Ir- and Pt-electroded devices after forming gas anneal. It was also found that DRAM polarization values decreased slightly after forming gas anneal. Also, a post-top electrode deposition 550°C O₂ anneal improved both electrical characteristics (lowered leakage and increased DRAM polarization) of these devices. Complete recovery of the leakage level prior to hydrogen damage was obtained after a 550°C N₂ recovery anneal for some devices independent of the pre-top electrode anneal. Ir- and Pt-electroded BST (40nm) capacitors have been shown to meet the 1 giga-bit DRAM leakage current requirement of 10^?8 A/cm² at 1.7 V. These Ir- and Pt-electroded BST devices achieved capacitance density levels of approximately 50 fF/μm².     

Ferroelectric properties and reliability of La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O heterostructures on si for non-volatile memory applications

Abstract

Highly oriented La-Sr-Co-O(LSCO)/Pb-La-Zr-Ti-O(PLZT)/La-Sr-Co-O heterostructures have been successfully grown on a highly oriented Pt film which was grown on a thermally oxidized Si (SiO₂/Si) substrate. The growth of oriented Pt film on the SiO₂/Si substrate was made possible through the use of a thin bismuth titanate template layer which is c-axis oriented on the SiO₂/Si substrate. The hybrid LSCO/Pt structure effectively reduced the sheet resistance of the electrodes by at least 3–5 times compared with a single LSCO electrode. These ferroelectric PLZT capacitors on Si exhibited symmetric hysteresis loops with very desirable ferroelectric properties. The test capacitors showed reliable performance at both room and high (100°C) temperatures with respect to fatigue, retention, aging, and imprint, suggesting that they can be used as reliable, nonvolatile memory elements.     

Structure and dielectric properties of Ba(Sn0.2Ti0.8)O3 thin films grown on different substrates by a sol-gel process

Ba(Sn_0.2Ti_0.8)O₃ (BTS) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃/Pt/Ti/SiO₂/Si substrates by a sol-gel processing technique, respectively. The influences of substrates on the phase and microstructure of the thin films were examined. Dielectric properties of the thin films were investigated as a function of frequency and direct current electric field. The results showed that the substrates strongly influenced the microstructure and the dielectric properties of the films. The properties of BTS thin films on LaNiO₃/Pt/Ti/SiO₂/Si substrates were superior to that of the films grown on Pt/Ti/SiO₂/Si substrates.     

Fatigue and retention of Pb(Zr0.53Ti0.47)O3 thin film capacitors with Pt and RuO2 electrodes

Abstract

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were deposited on Pt and RuO₂ coated Si and MgO substrates using the sol-gel process. Fatigue and retention tests were performed on these samples. The films grown on RuO₂ electrodes are fatigue-free up to nearly 10¹¹ cycles. Their retention life-time extrapolates to more than 10¹⁰ seconds. The fatigue behavior of films grown on Pt electrodes depends on the PZT film orientation. Highly oriented (001) PZT films maintain 50% of their initial P?r-P?r value after 10¹¹ cycles. The randomly oriented films maintain less than 3% of the initial P?r-P?r value after 10¹¹ cycles. However, the retention life-time of both highly oriented and randomly oriented PZT films grown on Pt electrodes extrapolates to higher than 10¹¹ seconds. It appears that fatigue of films grown on RuO₂ is mainly controlled by the film/electrode interface. On the other hand, fatigue of films grown on Pt appears to depend on both the film/electrode interface as well as on bulk effects.     

CHARACTERISTIC OF (100)-TEXTURED (PbxSr1 −x)TiO3 THIN FILMS USED FOR DRAM AND TUNABLE DEVICE APPLICATION

ABSTRACT

The (Pb_xSr_1-x)TiO₃ (PST) thin films were deposited on LaNiO₃ (LNO(1 0 0))/ Pt/Ti/SiO₂/Si substrates electrode by RF-magnetron sputtering using three different Pb target composition ranging from 32.5%～37.5% and different process condition. Structural and dielectric properties of the PST thin films for tunable microwave and DRAM application were investigated. The PST thin films deposited at 400°C show higher dielectric constant than those post-annealed at 600°C because of better crystallization. The former also have lower leakage current around 10^?8 A/cm² up to applied field of 350 kv/cm, which is suitable for DRAM application. On the other hand, the post-annealed PST thin films have satisfactory tunability around 58% and figure of merit around 30, which are more suitable for microwave device application.     

Glycolate tantalum based solutions for the sol-gel spin-coating deposition of SrBi2Ta2O9 thin films

Abstract

The reaction of tantalum ethoxide with a glycol solvent produces the interchange of the ethoxide groups with the glycol. As a result, a polymeric derivative is formed with a high resistance towards hydrolysis. Compounds of Sr(II) and Bi(II) can be added to this Ta-glycol sol, leading to strontium bismuth tantalate (SBT) precursor solutions stable in air. These solutions were spin-coated onto two substrates: Pt/TiO₂/SiO₂/(100)Si and Ti/Pt/Ti/SiO₂/(100)Si. Crystallisation of the SBT phase was carried out by a first formation of a fluorite phase that evolves to the layered perovskite at temperatures over 600°C. During crystallisation, a larger tendency to the formation of a substrate/film interface was observed in the films deposited onto Ti/Pt/Ti/SiO₂/(100)Si than onto Pt/TiO₂/SiO₂/(100)Si. A remanent polarisation of P_r5 μC/cm² and a coercive field of E_c <100 kV/cm were measured in the films on Pt/TiO₂/SiO₂/(100)Si. These films retain its remanent polarisation, P_r, up to 10⁵seconds and are fatigue-free up to 10⁹ cycles.     

Structure and electrical properties of Ba0.67 Sr0.33TiO3 thin film fabricated by sol-gel based composite technique

A sol-gel based novel technique is used to fabricate Ba_0.67Sr_0.33TiO₃ (BST) thin films with thickness up to several microns. In this technique, surface-modified fine BST particles are dispersed in a sol-gel precursor solution. The pH value of the precursor solution is modified to achieve high zeta potential for the dispersed powder, hence a very stable and uniform slurry can be produced. The slurry is then spin-coated onto Pt/Ti/SiO₂/Si substrate, pre-heated and annealed as in conventional sol-gel process. The resulting films show well-developed dense polycrystalline structure with uniform grain distribution. The metal-BST-metal structure of the films displays good dielectric properties.     

Ferroelectric Properties of (Bi, Sm)4Ti3O12 (BST) Thin Films Fabricated by a Metalorganic Solution Deposition Method

Ferroelectric properties of samarium substituted Bi₄Ti₃O₁₂ films, Bi_3.15Sm_0.85Ti₃O₁₂ (BST), were evaluated for use as lead-free thin film ferroelectrics for FeRAM applications. The BST films were fabricated on the Pt/Ti/SiO₂/Si(100) substrates by a metalorganic solution deposition method. The measured XRD patterns revealed that the BST films showed only a Bi₄Ti₃O₁₂-type phase with a random orientation. The BST film capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700C, 2P_r of 64.2 C/cm² and 2E_c of 101.7 kV/cm at applied electric field of 150 kV/cm were observed. The capacitor did not show any significant fatigue up to 1.5 × 10⁸ read/write switching cycles at a frequency of 1 MHz, which suggests that the samarium should be considered for a promising lanthanide elements to make a good thin ferroelectric film for memory applications.