Bryan C. Hendrix

Effect of applied mechanical strain on the ferroelectric and dielectric properties of Pb(Zr0.35Ti0.65)O3 thin films

A wafer bending method has been devised to impose biaxial strains on Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 A grown by metal-organic chemical vapor deposition. The ferroelectric and dielectric properties of PZT capacitors were investigated while the film was placed under biaxial tension. It was observed that biaxial strains as small as 0.08% can reversibly reduce the remanent polarization of PZT films by 12 to 14% for all film thicknesses. The small-signal capacitance measured at voltages significantly larger than the switching voltage increased with increasing biaxial tension. These observations present clear evidence of room temperature strain accommodation in PZT thin films by reversible 90° domain wall motion that changes the volume fraction of the film that switches during electrical testing.

Thickness-dependent phase evolution of polycrystalline Pb(Zr0.35Ti0.65)O3 thin films

The structural and electrical properties of metalorganic chemical vapor deposition-grown Pb(Zr0.35Ti0.65)O3 thin films ranging in thickness from 700 to 4000 A have been investigated. Cross-sectional scanning electron microscopy showed that these films are columnar, with grains extending through the thickness of the film. High-resolution x-ray diffraction showed that while the thickest films are tetragonal, with reflections corresponding to a-type and c-type domains, films thinner than 1500 A are not. Electron backscatter diffraction and hysteresis loop measurements showed that the thinnest films are ferroelectric and have a rhombohedral crystal structure.

Common and unique aspects of perovskite thin film CVD processes

Abstract In the past 5 years there has been a large amount of work to develop CVD technology for the deposition of the predominant perovskite oxide thin films, (Ba, Sr)TiO3, SrBi2Ta2O9 and Pb(Zr, Ti)O3. For each of these families of materials, CVD processes have matured such that state-of-the-art film properties may be achieved with this technique. Much of the progress is attributed to the use of the liquid delivery technique to transfer relatively involatile metalorganic precursors to the reactor. This paper will discuss common attributes of these thermal CVD processes, particularly the precursors, delivery methodology and reactor hardware. The paper will also highlight unique aspects that differentiate the processes, including the CVD decomposition regime, strategies for film composition control and approaches for forming the crystalline perovskite phase. Representative film properties are presented, demonstrating that these processes are becoming increasingly mature.

Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr0.35Ti0.65)O3 thin films

The structural and electrical properties of Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 A have been investigated. These (001)/(100)-textured films were grown by metalorganic chemical vapor deposition on (111)-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high tempe...

Oxygen tracer studies of ferroelectric fatigue in Pb(Zr, Ti)O3 thin films

Long-range oxygen motion has been observed in Pt/Pb(Zr,Ti)O3/Ir thin-film structures after electrical fatigue cycling at room temperature. Through an exchange anneal, isotopic 18O was incorporated as a tracer into bare Pb(Zr,Ti)O3 (PZT) films, allowing secondary ion mass spectrometry measurements of the tracer profile evolution as a function of the number of polarization reversals. Observation of 18O tracer redistribution during voltage cycling, which is presumably mediated by oxygen vacancy motion, was found to be strongly dependent upon the thermal history of the film. However, there was no strong correlation between the extent of 18O tracer redistribution and the extent of polarization suppression induced by voltage cycling. Our results suggest that oxygen vacancy motion plays, at most, a secondary role in ferroelectric fatigue of PZT thin films.

Structural analysis of coexisting tetragonal and rhombohedral phases in polycrystalline Pb(Zr 0.35 Ti 0.65 )O 3 thin films

Structural properties of polycrystalline Pb(Zr 0 . 3 5 Ti 0 . 6 5 )O 3 (PZT) thin films grown by metalorganic chemical vapor deposition on Ir bottom electrodes were investigated. Symmetric x-ray diffraction measurements showed that as-deposited 1500 A-thick PZT films are partially tetragonal and partially rhombohedral. Cross-section scanning electron microscopy showed that these films have a polycrystalline columnar microstructure with grains extending through the thickness of the film. X-ray depth profiling using the grazing-incidence asymmetric Bragg scattering geometry suggests that each grain has a bilayer structure consisting of a near-surface region in the tetragonal phase and the region at the bottom electrode interface in the rhombohedral phase. The required compatibility between the tetragonal and rhombohedral phases in the proposed layered structure of the 1500 A PZT can explain the peak shifts observed in the symmetric x-ray diffraction results of thicker PZT films.

MOCVD of SrBi 2 Ta 2 O 9 for Integrated Ferroelectric Capacitors

SrBi 2 Ta 2 O 9 (SBT) is a promising material for ferroelectric random access memories (FERAMs) 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 (e) of 200 and remanent polarization (2P r )up to 16 μC/cm 2 have been achieved on 150 mm wafers.

Metalorganic Chemical Vapor Deposition of Thin Film ZrO2 and Pb(Zr,Ti)O3: Precursor Chemistry and Process Characteristics.

Metalorganic chemical vapor deposition (MOCVD) process characteristics of several zirconium source reagents were investigated. These source reagents included metal β-diketonates [e.g., Zr(thd)4 where thd=(2,2,6,6-tetramethyl-3,5-heptanedionate)] and metal alkoxide/β-diketonates [e.g., Zr(OiPr)2(thd)2 and Zr(OtBu)2(thd)2]. Thermal properties and transport behaviors of these precursors were examined by thermogravimetric analysis. Zirconium oxide films were deposited on silicon substrates at reduced pressure. Under the process conditions examined, the deposition behavior was mass-transport controlled, and Zr(OiPr)2(thd)2 and Zr(OtBu)2(thd)2 behaved similarly. The films exhibited low carbon content. Pb(Zr, Ti)O3 (PZT) films were deposited on iridium-coated silicon substrates under reduced pressure. Zirconium incorporation efficiency was significantly improved for Zr(OiPr)2(thd)2 when compared to Zr(thd)4. Use of M(OtBu)2(thd)2 (where M=Zr or Ti) as source reagents for MOCVD of PZT was examined and compared to M(OiPr)2(thd)2 analogues. In this case, higher process pressures were needed to improve the incorporation efficiencies of M(OtBu)2(thd)2 precursors.