PZT capacitor with Ir/IrO2/Ir electrode fabricated by RTA

Abstract

PZT capacitor with direct contact between Si substrate and bottom electrode of the capacitor was obtained with Ir/IrO₂/Ir/Ti electrode, by crystallizing sol-gel PZT thin film using RTA (650°CC 30 sec.). Contact resistance for hole diameter of 0.72 μm was 19 Ω. It was observed by cross-sectional TEM that Ti silicide was formed at the interface, but there was not oxygen diffusion from PZT thin film. Fatigue property of the PZT thin film was improved by RTA compared with furnace annealed film (600°CC 60 min.). The absolute value of the remnant polarization was 13 μC/cm² for both films, but it did not degrade until 10⁸ cycles of switching for the film by RTA, while it degraded before 10⁵ cycles for furnace annealed film.     

Influence of Post-Annealing on the Characteristics of Pb(Zr,Ti)O3 Thin Films Deposited by Liquid Delivery MOCVD Using a Cocktail Solution

Ferroelectric PZT thin films were deposited by liquid delivery MOCVD using a cocktail solution. The cocktail solution consisted of Pb(METHD)₂, Zr(METHD)₄ and Ti(MPD)(METHD)₂ diluted with ethylcyclohexane. The films deposited on Pt/Ti/SiO₂/Si at a substrate temperature of 500°C consisted of PZT, PbO and PbPt_x, and showed poor properties. However, after annealing at 450°C in air for thirty minutes, the PbPt_x phase disappeared while the volume of the PbO phase increased. The hysteresis properties were also improved by annealing at 450°C. After annealing at 600°C in air for thirty minutes, the PbPt_x and the PbO phases disappeared perfectly and the PZT thin films showed good hysteresis properties with the remanent polarization of 30 μC/cm² and the coercive field of 88 kV/cm.     

PZT capacitors using IrO2 electrode by RF magnetron sputtering

Abstract

RF magnetron sputtered Pb(Zr_x, Ti_1-x)O₃ [PZT] films were prepared on IrO₂/SiO₂/Si and Pt/IrO₂/SiO₂/Si substrates using the ceramic PZT target with Pb_1.1(Zr_0.52Ti_0.48)O₃ composition. In order to obtain single perovskite phase, PZT film was sputtered at room temperature under Ar plasma and followed by high temperature annealing under oxygen atmosphere. In case of Pt/PZT/IrO₂ capacitor, Δ P (=P*-P∧) was decreased with oxygen annealing temperature. However, it was increased in Pt/PZT/Pt/IrO₂ capacitor. Leakage current density of Pt/PZT/Pt/IrO₂ capacitor, which was used for improving leakage characteristics, was about 10^-2A/cm^?2 order lower than that of Pt/PZT/IrO₂ capacitor. Leakage current density of Pt/PZT/Pt/IrO₂ capacitor annealed at 700°C was 6.6x10^-6A/cm². From the fatigue test, Pt/PZT/IrO₂ capacitor annealed at 650°C and Pt/PZT/Pt/IrO₂ capacitor annealed at 700°C showed 3% and 12% degradation of Δ P after 5×10¹⁰ fatigue cycles, respectively.     

Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

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.     

Preparation and electrochemical properties of La<Subscript>1.0</Subscript>Sr<Subscript>1.0</Subscript>FeO<Subscript>4+δ</Subscript> as cathode material for intermediate temperature solid oxide fuel cells

Cathodic material La_1.0Sr_1.0FeO_4+δ for an intermediate temperature solid oxide fuel cell (IT-SOFC) was prepared via the glycine-nitrate process and characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM). XRD results showed that no reaction occurred between the La_1.0Sr_1.0FeO_4+δ electrode and Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte at 1000 °C. SEM results showed that the electrode formed good contact with the SDC electrolyte after sintering at 1000 °C for 2 h. The electrochemical properties of La_1.0Sr_1.0FeO_4+δ were measured using electrochemical impedance spectroscopy (EIS) and steady state polarization measurement. At 700 °C, the polarization resistance was about 3.90 Ωcm², and the lowest polarization overpotential was 57 mV at a current density of 55 mA cm⁻².     

Investigation on various insulator layers for MFIS capacitors

Abstract

Effects of insulator layers of Metal(Au)/Ferroelectrics(PZT)/Insulator/Si (MFIS) structure capacitors are investigated for non-destructive type non-volatile memory device applications. Various high dielectric oxide layers such as Al₂O₃, Ta₂O₅, TiO₂ and ZrO₂ were fabricated by reactive sputtering as insulating layers. The oxide insulators give significant impacts on the morphologies of PZT layer and the properties of capacitors. It is noted that the oxide layers with small thermal expansions (<6x10^–6/°C) coefficient caused cracks on PZT films during PZT crystallization annealing. The effects of insulators as a diffusion barrier are also comparatively studied using Auger electron spectroscopy. In addition, the characteristics of high dielectric solid solution, such as titanium oxide-zirconium oxide, are also studied.     

Improvement on ferroelectric properties of metal-organic decomposited PZT thin film prepared by using prenucleation layer

Abstract

Perovskite SrRuO₃ (SRO) layer was, for the first time, been successfully synthesized by using metal-organic decomposition (MOD) process. The presence of SRO buffer layer on Pt(Si) substrates has significantly enhanced the crystallization and densification behavior of the subsequently deposited Pb(Zr_0.52Ti_0.48)O₃ films. The pyrochlore free perovskite phase can be obtained by post-annealing the PZT/SRO/Pt(Si) films at 500°C, which is 50°C lower than that needed in PZT/Pt(Si) films. The fine grain (～0.3 μm) microstructure can be attained by post-annealing at 650°C for PZT/SRO/Pt(Si) films and 700°C for PZT/Pt(Si) films. The ferroelectric hysteresis properties of the two PZT films are comparable to each other. The leakage current properties of PZT/SRO/Pt(Si) films increased pronouncedly with post-annealing temperature, resulting in inferriar leakage behavior to PZT/Pt(Si) films.     

High temperature electrical characterization of nano-crystalline BaTiO3 synthesized using Ba(NO3)2 and TiO2

The reaction of Ba(NO₃)₂ with TiO₂ was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO₃ takes place above 600°C. BaTiO₃ powder was prepared by calcination of Ba(NO₃)₂ and TiO₂ precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO₃ confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (V_O^??).     

Degradation mechanisms of SrBi2Ta2O9 ferroelectric thin film capacitors during forming gas annealing

Abstract

The effects of annealing in forming gas (5% hydrogen, 95% nitrogen; FGA) are studied on spin coated SrBi₂Ta₂O₉ (SBT) thin films. SBT films on platinum bottom electrode are characterized with and without platinum top electrode by Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), High Temperature X-Ray Diffraction (HT-XRD) and Secondary Ion Mass Spectrometry (SIMS).

High Temperature X-Ray Diffraction (HT-XRD) of blanket Ti/Pt/SBT films in forming gas revealed that the bismuth layered perovskite structure of the SBT is stable up to approx. 500°C. SIMS analysis of Pt/SBT/Pt samples annealed in deuterated forming gas (5% D₂, 95% N₂) showed that the hydrogen accumulates in the SBT layer and at the platinum interfaces next to the SBT. After FGA of blanket SBT films, tall platinum-bismuth whiskers are seen on the SBT surface.

Performing the FGA of the whole Pt/SBT/Pt/Ti stack, two different results are found. For the samples with a high temperature annealing (HTA) step in oxygen after top electrode patterning, top electrode peeling is observed after FGA. For the samples without a HTA step after top electrode patterning, no peeling is observed after FGA.     

Low temperature preparation of ferroelectric SrBi2Ta2O9 thin films by a modified RF magnetron sputtering technique

Abstract

Bi–layered ferroelectric SrBi₂Ta₂O₉ (SBT) films were successfully prepared on Pt/Ti/SiO₂/Si substrates at 650°C by a modified rf magnetron sputtering technique. The SBT films annealed for 1 h in O₂ (760 torr) and again for 30 min in O₂ (5 torr) at 650°C show a average grain size of about 49 nm. The SBT films annealed at 65 0°C have a remanent polarization (P_r) of 6.0 μC/cm² and coercive field (E_c) of 36 kV/cm at an excitation voltage of 5 V. The films showed fatigue–free characteristics up to 4.0 × 10¹⁰ switching cycles under 5 V bipolar pulse. The retention characteristics of SBT films looked very promosing up to 1.0 × 10⁵ s.     

Low Temperature Process for Synthesis of (100) Textured Pb(Zr0.48Ti0.52)O3 Thin Films on Si Substrate by Laser Lift-Off Transferring Technique

(100) textured Pb(Zr_0.48Ti_0.52)O₃ (PZT) films were prepared on silicon substrates by MOD process and laser lift-off technique. Textured PZT films were first grown on (001) Sapphire substrate, using Ba(Mg_1/3Ta_2/3)O₃ (BMT) materials as buffer layer. The (100) textured PZT/BMT/Sapphire films were attached to Si substrate using a transient-liquid-phase Pd-In bonding process, and then were separated from Sapphire substrates by a laser lift-off process, in which, a 38 ns pulse from excimer laser (248 nm) at 600 mJ/cm² fluence melted BMT buffer layer, expelling the Sapphire. The crystallinity of the surface of films was further improved by laser annealing. X-ray diffraction analysis of the PZT films showed that the crystallographic structure of films is maintained during laser lift-off process. Electrical testing of the films after laser lift-off process followed by laser annealing demonstrated that the ferroelectric properties are retained for the transferred films (P_r = 9μ C/cm² and E_c = 74 kV/cm).     

Recent progress in sputtering PZT thin films for ferroelectric memories

Abstract

This paper describes amorphous Pb(Zr, Ti)O₃ (PZT) thin films deposited by cosputtering Pb(Zr_0.5 Ti_0.5)O₃ and PbO targets. By optimizing the amount of the excess Pb and the deposition temperature, PZT thin films with a single perovskite phase were obtained successfully on Ir substrates and Pt substrates at 520°C. 250-nm-thick PZT films crystallized by rapid thermal annealing (RTA) at 600°C for 20 s exhibited excellent ferroelectric properties: a coercive voltage of 1.0 V, a remanent polarization density of about 40 μC/cm², and a polarization switching endurance over 1x109 cycles. Although a heat treatment in a reductive ambient causes degradation of ferroelectric properties of PZT thin films, their degraded ferroelectric properties can be easily recovered from by a 1-min RTA in an oxygen at 400°C.     

MOCVD of Pb(Zr x Ti1-x )O3 thin films on MgTiO3/Si substrates and their electrical properties

Abstract

Pb(Zh _x , Ti_1-x )O₃(PZT) thin films were deposited on Si substrates using MgTiO₃ as the buffer layer and the electrical properties of those MFIS structures were investigated. PZT and MgTiO₃ films were made by MOCVD using ultrasonic spraying technique. Perovskite PZT films have been succesfully made at the substrate temperature of 550 to 600°C only when using MgTiO₃ buffer layer. AES depth profile analysis and RBS analysis revealed that there is no remarkable interdiffusion and no formation of reaction layer between PZT and MgTiO₃ and/or between MgTiO₃ and Si substrate. The capacitance-voltage (C-V) curves of the MFIS structure which were made with PZT and MgTiO₃buffer layer have shown the hysteresis resulted from the ferroelectric switching of the PZT films.     

Low temperature sintering of screen-printed Pb(ZrTi)O3 thick films

Abstract

There has been increasing interest in ferroelectric lead zirconate titanate (PZT) films for the applications in piezoelectric and pyroelectric devices. Many potential applications require a film thickness of above 10 μm for higher force, better sensitivity and stability. But it is very difficult to fabricate the PZT thick film on the silicon substrate because of the volatility of PbO and the interdiffusion of the Pb and Si through the bottom electrode during the sintering at normal temperatures (such as above 1200°C). We speculated densification and reaction mechanism of the PZT thick films fabricated at relatively low temperature (under 1000°C) without sintering aids. The PZT thick films were screen-printed on Pt / Al₂O₃ substrate using a paste of PbO, ZrO₂ and TiO₂ powder mixture. Highly densified PZT thick films could be fabricated on Pt / Al₂O₃ substrate at 1000°C, and we achieved the density, remanent polarization, coercive field, dielectric permittivity, dissipation factor and breakdown field of 98%, 10 μC/cm² and 20 kV/cm, 540, 0.009 and 15 MV/m, respectively. The results show the possibility of densification of the PZT thick film at relatively low temperature without sintering aids, and the results are promising for the use of PZT thick films in various applications.     

Sol-gel PZT thin films on nickel alloy electrodes

Abstract

The Ni alloy electrode was used for a bottom electrode of PZT thin films prepared by sol-gel process. Although PZT films were crystallized on soda–lime glass substrates with the alloy electrodes at a relatively low temperature of 500°C, second phases of Pb₃O₄ and ZrTiO₄ were produced on the electrode in addition to the perovskite PZT phase. In order to prevent the second phases forming, the heat treatment time of the electrode was increased to obtain the thicker Al₂O₃ layer on the alloy electrode. The second phases decreased with increasing the heat treatment time; however, the phases did not disappear. When BaTiO₃ films were inserted between the electrodes and PZT films, the PZT single phase was obtained. The tan δ of the films decreased with decreasing the amount of the second phases, finally it became 3.9%, the film of which possessed a remanent polarization of 20 μC/cm².     

PZT Capacitors on Top of CrTiN/TiN Double Barrier Layers

In this paper we investigated the thermal stability of a novel CrTiN/TiN double barrier, compared to those of TiN and CrTiN single layer barriers. The CrTiN/TiN double layer was stable against heat treatments at higher than 700°C in oxygen ambient for 30 min. However, the double layer showed a severe Pt and Cr interdiffusion issue after crystallization annealing for PZT. We found that pre-annealing treatments prior to deposition of Pt significantly reduced the interdiffusion. In addition, we also demonstrated ferroelectric characteristics of PZT capacitors on top of Pt/CrTiN/TiO₂/Si bottom electrode system for ultra-high density memory applications.     

Electro-Optic Properties of Heteroepitaxial Pb(Zr,Ti)O3/La0.5Sr0.5CoO3 Film Structures

Vertical ferroelectric Pb(Zr,Ti)O₃ (PZT) 1 μm thick film capacitor was fabricated by pulsed laser deposition technique (PLD) onto conducting La_0.5Sr_0.5CoO₃(LSCO) 100 nm thick bottom electrode on both side polished YAlO₃ + 1% Nd₂O₃ (Nd:YAlO₃) single crystal substrate to operate as a Pockels cell optical modulator. On top of the PZT film, semitransparent 30 nm thick Au electrode was deposited by thermal evaporation. Intensity of the chopped 670 nm polarized laser radiation transmitted through the Au/PZT/LSCO/Nd:YAlO₃ cell was measured at various temperatures and bias voltage applied. Applying 20 V (200 kV/cm) across the capacitive cell, modulation of the transmitted light as high as 3% was achieved while the voltage tunability measured at 1 kHz from C-V characteristics was about 70%. Thermo-optical measurements performed for PZT/Nd:YAlO₃ sample in the range up to 400°C showed the phenomenon of critical opalescence in the vicinity of Curie temperature at 208°C. Optical transmission through the PZT film biased with electric field was studied in the range 400 to 1000 nm. Film thickness, refraction index and absorption coefficient have been determined from the interference pattern observed in the PZT transmission spectrum. A simple model yields the dispersion relation for the electro-optic coefficient.     

MOCVD preparation of SBTN thin films from two organometallic sources bottles

Abstract

SrBi₂(Ta_0.7Nb_0.3)₂O₉ (SBTN) films were first prepared on (111)Pt/Ti/SiO₂/Si substrates by MOCVD from only two organometallic source bottles. Bi(CH₃)₃ and the mixture of Sr[Ta(O°C₂H₅)₆]₂ and Sr[Nb(O°C₂H₅)₆]₂ were used as source materials. High compositional reproducibility was obtained; the Nb/(Ta+Nb) ratio was the same as the mixing ratio of the source. Sr/(Ta+Nb) and Bi/(Ta+Nb) ratios can be controlled by the reactor pressure and the input gas flow rate ratio of the source gases. Almost single phase of SBTN was obtained for the film deposited at 500°C and the following heat-treated at 800°C in O₂ atmosphere. Pr and Ec values of 330 nm-thick SBTN film were 8.5 μC/cm² and 91 kV/cm, respectively and were larger than those of SrBi₂Ta₂O₉ film. There was no degradation after 5x10¹⁰ cycles polarization switching.