MOCVD of SrBi2Ta2O9 for Integrated Ferroelectric Capacitors

1997 ◽  
Vol 493 ◽  
Author(s):  
Bryan C. Hendrix ◽  
Frank Hintermaier ◽  
Debra A. Desrocherst ◽  
Jeffrey F. Roedert ◽  
Gautam Bhandarit ◽  
...  
Keyword(s):  
Perovskite Phase ◽  
Random Access ◽  
Chemical Vapor ◽  
Dielectric Constants ◽  
Fluorite Phase ◽  
Layered Perovskite ◽  
Process Pressure ◽  
Precursor Decomposition ◽  
Memory Applications ◽  
Ferroelectric Capacitors

ABSTRACTSrBi2Ta2O9 (SBT) is a promising material for ferroelectric random access memories (FERAM's) because it has high resistance to fatigue and imprint combined with low coercive field. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformai SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise delivery of low vapor pressure precursors to the process. Precursor decomposition has been examined over a wide temperature range and the effects of process pressure have been examined. It is shown that Bi(thdb is superior to Bi(Ph)3 as a source of Bi, offering a wide decomposition window with compatible Sr and Ta precursors so that a simple, well-controlled, and repeatable process is achieved at low temperatures. Films with 90% conformallity have been grown on 0.6 μm structures with a 1:1 aspect ratio. The MOCVD process yields the fluorite phase, which is transformed to the ferroelectric layered perovskite phase upon annealing in oxygen. Dielectric constants (ε) of 200 and remanent polarization (2Pr)up to 16 μC/cm2 have been achieved on 150 mm wafers.

MOCVD of Nb Substituted SrBi2Ta2O9 for Integrated Ferroelectric Capacitors

1999 ◽  
Vol 596 ◽  
Author(s):  
B. C. Hendrix ◽  
T. E. Glassman ◽  
J. F. Roeder
Keyword(s):  
Random Access ◽  
Annealing Treatment ◽  
Chemical Vapor ◽  
Precursor Solution ◽  
Layered Perovskite ◽  
High Quality ◽  
Substitution Level ◽  
Perovskite Crystal ◽  
Ferroelectric Hysteresis ◽  
Memory Applications

AbstractThe Bi layered perovskites are promising materials for ferroelectric random access memories (FeRAM's) because of their inherently high resistance to fatigue. Liquid delivery, flash vaporization metalorganic chemical vapor deposition (LD-MOCVD) is an attractive process for these materials, because it offers the ability to produce high quality, conformal films of controlled composition for both high and low density memory applications. We have developed a well-controlled process to deposit Nb-substituted SrBi2Ta2O9 (SBNT) using a mixed alkoxide-β-diketonate precursor Nb(O-i-Pr)4(thd) that is compatible with a previously developed precursor suite for SBT (Sr(thd)2-pmdeta, Bi(thd)3, and Ta(O-i-Pr)4(thd)). The Nb and Ta precursors behave in the same way in the process, making the Nb substitution level in the film identical to that in the precursor solution. In this study, wavelength dispersive x-ray fluorescence has been used to characterize composition and thickness. As-deposited films are smooth, with a surface roughness of 2 nm RMS. After a post-deposition annealing treatment, a high quality layered perovskite crystal structure was obtained. The resultant ferroelectric hysteresis shows a 50% increase in coercive voltage for 28% Nb substitution at the Ta site with the same switchable polarization. In the 28% Nb containing film, imprint was significantly improved compared to SBT films without substitution.

Ferroelectric C-Axis Oriented Pb5Ge3O11 Thin Films for One Transistor Memory Application

1998 ◽  
Vol 541 ◽  
Author(s):  
Tingkai Li ◽  
Fengyan Zhang ◽  
Sheng Teng Hsu
Keyword(s):  
Thin Films ◽  
Ferroelectric Properties ◽  
Hysteresis Loops ◽  
Chemical Vapor ◽  
Dielectric Constants ◽  
Memory Devices ◽  
Leakage Currents ◽  
Fatigue Characteristics ◽  
Ferroelectric Memory ◽  
Memory Applications

AbstractOne transistor memory devices have been proposed recently. To meet the needs of one transistor memory applications, C-axis oriented Pb5Ge3O11 (PGO) thin films were prepared using metalorganic chemical vapor deposition (MOCVD) and rapid thermal processing (RTP). It was found that the nucleation of C-axis Pb5Ge3O11 phase started at a deposition temperature below 400°C and grain growth dominated at 500°C or above. With increasing annealing temperature, the remanent polarization (Pr) and coercive field (Ec) values increased, and the hysteresis loops of the Pb5Ge3O11 films were well saturated and symmetrical after the post-annealing. The C-axis PGO thin film showed good ferroelectric properties at 5V: 2Pr and 2Ec values were 2.0 - 4.0 µC/cm2 and 90 - 110 kV/cm, respectively. The films also showed excellent fatigue characteristics: no fatigue was observed up to 1 × 109 switching cycles. The retention and imprint properties have also been studied. The leakage currents of the PGO films were 2 - 5 × 10−7 A/cm2 at 100 kV/cm and dielectric constants were 40 - 70. The high quality MOCVD Pb5Ge3O11 films can be used for single transistor ferroelectric memory devices.

Structure and Device Characteristics of SrBi2Ta2O9-Based Nonvolatile Random-Access Memories

MRS Bulletin ◽  
1996 ◽  
Vol 21 (7) ◽  
pp. 33-39 ◽  
Author(s):  
J.F. Scott ◽  
F.M. Ross ◽  
C.A. Paz de Araujo ◽  
M.C. Scott ◽  
M. Huffman
Keyword(s):  
Lead Zirconate Titanate ◽  
Barium Strontium Titanate ◽  
Paradigm Shift ◽  
Random Access ◽  
Lead Zirconate ◽  
Dielectric Constants ◽  
Barium Strontium ◽  
Stored Information ◽  
Ferroelectric Random Access Memories ◽  
Ferroelectric Capacitors

Recently there has been a paradigm shift in nonvolatile computer memories from silicon-technology-based EEPROMs (electrically erasable, programmable read-only memories) to devices in which the stored information is coded into + and − polarizations in thin-film ferroelectric capacitors. Such devices have read and erase/rewrite speeds of the order of 1–35 ns, many orders of magnitude faster than the erase/rewrite speeds of the best EEPROMs (Table I). However, fundamental questions concerning their lifetimes had delayed full commercialization. Because ferroelectrics normally have extremely large dielectric constants, their use as nonswitching capacitors in dynamic random-access memories (DRAMs) is also rapidly evolving. The majority of studies to date have emphasized lead zirconate titanate (PZT)-based capacitors for nonvolatile ferroelectric random-access memories (NVFRAMs) and barium strontium titanate-based capacitor DRAMs (see Table II).

Effect of Ta Nanobarrier in Magnetron Sputtering of Nd-Doped SrBi2Ta2O9 Thin Films

2008 ◽  
Vol 8 (5) ◽  
pp. 2618-2622
Author(s):  
Yibin Li ◽  
Sam Zhang ◽  
Thirumany Sritharan ◽  
Xiaomin Li ◽  
Yang Liu ◽  
...  
Keyword(s):  
Thin Films ◽  
Remnant Polarization ◽  
Ferroelectric Properties ◽  
Random Access ◽  
Random Access Memory ◽  
Layered Perovskite ◽  
Interfacial Diffusion ◽  
Access Memory ◽  
Memory Applications ◽  
Secondary Ion

SrBi2Ta2O9 (SBT) is a bismuth layered perovskite with attractive ferroelectric properties for random access memory applications. Our previous studies showed that Nd-doped SBT (SNBT) thin films exhibited an improved remnant polarization and reduced coercivity. This paper concentrates on the effect of Ta nanobarrier in between the SNBT and the Pt layers. Without the nanobarrier, severe bismuth diffusion is revealed by the secondary ion mass spectroscopy. However, with a nano layer (up to 2 nm) of Ta metal, the interfacial diffusion is effectively suppressed even at 800 °C. Details of the composition profiling, film crystallinity and remnant polarization are discussed in view of the nanobarrier thickness.

Preparation and Characterization of Ba and Nb Substituted SrBi2Ta2O9 Compounds

2000 ◽  
Vol 655 ◽  
Author(s):  
Rasmi R. Das ◽  
P. S. Dobal ◽  
A. Dixit ◽  
W. Perez ◽  
M.S. Tomar ◽  
...  
Keyword(s):  
Raman Spectra ◽  
Phase Formation ◽  
Perovskite Phase ◽  
Growth Conditions ◽  
Layered Perovskite ◽  
Phonon Modes ◽  
Si Substrates ◽  
Non Volatile Memory ◽  
Lower Temperature ◽  
Memory Applications

AbstractBi-layered ferroelectric compounds are considered most promising for non-volatile memory applications due to their high fatigue endurance. We have prepared SrBi2Ta2O9 powders with Ba (A sites) and Nb (B sites) substitutions using a novel solution based route. The powders were pressed and sintered at 1050°C to obtain high quality targets. Thin films were prepared using these ceramic targets on Pt/TiO2/SiO2/Si substrates using pulsed laser deposition (PLD) technique. The effects of growth conditions on phase formation as well as structural and electrical properties in films are studied. Initial results on films show good hysteretic characteristics. Though phase formation begins at much lower temperature, these films crystallize in a complete layered perovskite phase when prepared at 700°C. Optical phonon modes in these materials exhibit systematic variations with changing compositions. The changes in the Raman spectra are explained in terms of Ba and Nb substitutions at A and B sites, respectively. The temperature dependence of Raman spectra exhibits the substitution induced changes in the transition temperatures of these materials.

Iridium Electrodes for Ferroelectric Capacitors Deposited by Liquid-Delivery MOCVD

2005 ◽  
Vol 902 ◽  
Author(s):  
Yves Ritterhaus ◽  
Tetyana Hur'yeva ◽  
Marco Lisker ◽  
Edmund Paul Burte
Keyword(s):  
Growth Rates ◽  
Electrode Material ◽  
Vapor Deposition ◽  
Physical Vapor Deposition ◽  
Random Access ◽  
Chemical Vapor ◽  
Oxygen Flow ◽  
Step Coverage ◽  
Ferroelectric Capacitors ◽  
Liquid Delivery

AbstractThin iridium films are required as electrode material for ferroelectric capacitors. SBT or PZT are often used as ferroelectric material in such capacitors. The PZT based non-volatile ferroelectric random access memories show better fatigue characteristics if platinum is replaced by iridium as electrode material. Metalorganic chemical vapor deposition (MOCVD) was used for the deposition because of the superior step coverage on three-dimensional structures compared to the conventional physical vapor deposition processes of metal layers. Particularly, in memory fabrication, good step coverage is essential. The iridium films were deposited on different substrates at temperatures of 300 – 500 °C by liquid-delivery MOCVD. The precursor Ir(EtCp)(1,5COD) [iridium(ethylcyclopentadienyl)(1,5-cyclooctadiene)] was diluted in toluene (0.1 M concentration) for the deposition experiments. The iridium films were deposited onto TiO2/SiO2/Si-, SiO2/Si-, and Si-substrates to compare the iridium film properties on different substrates. The growth conditions like oxygen flow, growth temperature, and reactor pressure were varied. The growth rates were in a range between 0.05 and 4.6 nm per minute. We found that the growth rates were highly influenced by the oxygen flow and the substrate material. Oxygen assisted the decomposition of the precursor, and carbon and hydrogen of the organic source were oxidized, which suppressed its incorporation into the iridium layer. Annealing in an oxidizing ambient at temperatures above 700 °C resulted in an increased oxidation of the films as proved by XRD analyses. The resistivity of the films was determined by the Van-der-Pauw method. Low resistivities of 7 – 70 µΩcm were obtained for the as-deposited iridium films.

Correlations Between Composition, Texture, and Polarization in SrxBiyTa2O5+x+3y/2 Thin Films Deposited by MOCVD

1998 ◽  
Vol 541 ◽  
Author(s):  
Bryan C. Hendrix ◽  
Frank Hintermaieri ◽  
Debra A. Desrochers ◽  
Jeffrey F. Roeder ◽  
Thomas H. Baum ◽  
...  
Keyword(s):  
Random Access ◽  
Chemical Vapor ◽  
Annealed Film ◽  
X Ray ◽  
Precise Control ◽  
Electric Field Direction ◽  
Memory Applications ◽  
Relationship Of ◽  
Ferroelectric Random Access Memories ◽  
The Relationship

AbstractSrxBiyTa2O5+x+3y/2 (SBT) is a promising material for ferroelectric random access memories (FeRAM's) because of its inherently high resistance to fatigue and imprint. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformal SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise control of film stoichiometry and thickness. In this study, wavelength dispersive x-ray fluorescence and x-ray diffractometry have been used to survey composition and preferred crystallographic orientation (texture) relationships. It is shown that as-deposited film composition can be used to influence the texture of the Aurivillius phase in the annealed film. The polarization of the films increases with increasing (115) and (200)/(020) peak intensity due to the relationship of the electric field direction with the polarization direction in the film. The highest values of polarization are found with Sr content, x<0.8 and Bi content, 2.1 <y<2.6.

200 °C Preparation of SiNx Passivation Films for PZT Ferroelectric Capacitors by Catalytic CVD

2000 ◽  
Vol 655 ◽  
Author(s):  
Toshiharu Minamikawa ◽  
Yasuto Yonezawa ◽  
Yoshikazu Fujimori ◽  
Takashi Nakamura ◽  
Atsushi Masuda ◽  
...  
Keyword(s):  
Refractive Index ◽  
Etching Rate ◽  
Random Access ◽  
Chemical Vapor ◽  
No Oxidation ◽  
Flow Rate Ratio ◽  
Air Exposure ◽  
Oxidation In Air ◽  
Substrate Temperatures ◽  
Ferroelectric Capacitors

AbstractFeasibility of SiNx passivation films at low substrate temperatures prepared by catalytic chemical vapor deposition (Cat-CVD) is studied for ferroelectric nonvolatile random access memories (FRAMs). SiNx films were prepared at low substrate temperatures of 100 °C, 175 °C and 200 °C using Cat-CVD. Adjusting on flow rate ratio of SiH4/NH3, the refractive index of SiNx film, deposited at 175 °C and 200 °C, measured by ellipsometry is controlled around 2.0. SiNx films, with the refractive index around 2.0, deposited at only 200 °C show the following properties. 1) No oxidation during air exposure for 3 months was observed for the films. 2) Etching rate of the films in buffered HF is 20 nm/min. The dense SiNx film, which is resistive for oxidation in air exposure and dissolution in buffered HF, is prepared at 200 °C and the film is suitable to the passivation of ferroelectric capacitors.

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