J. Im

Studies of hydrogen-induced degradation processes in SrBi2Ta2O9 ferroelectric film-based capacitors

It is known that the forming gas (N2–H2 mixture) annealing process required for microcircuit fabrication results in an unacceptable electrical degradation of SrBi2Ta2O9 (SBT) ferroelectric capacitors due mainly to the interaction of H2 with the ferroelectric layer of the capacitor. We have found a strong relationship between changes in the surface composition of the ferroelectric layer and the electrical properties of SBT capacitors as a result of hydrogen annealing. Mass spectroscopy of recoiled ions (MSRI) analysis revealed a strong reduction in the Bi signal as a function of exposure to hydrogen at high temperatures (∼500 °C). The Bi signal reduction correlates with Bi depletion in the SBT surface region. Subsequent annealing in oxygen at temperatures in the range of 700–800 °C resulted in the recovery of the MSRI Bi signal, corresponding to the replenishment of Bi in the previously Bi-depleted surface region. X-ray diffraction (XRD) analysis (probing the whole SBT film thickness) showed little differe...

Influence of Pt heterostructure bottom electrodes on SrBi2Ta2O9 thin film properties

The properties of SrBi2Ta2O9 (SBT) films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films grown on stable Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibit high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films synthesized on Pt/Ti/SiO2/Si. It is shown that severe diffusion of Ti from the Ti interlayer onto the surface of the Pt bottom electrode and the increased surface roughness of this electrode stack play key roles in degradation of SBT properties.

Studies of metallic species and oxygen incorporation during sputter-deposition of SrBi2Ta2O9 films, using mass spectroscopy of recoiled ions

We have recently developed a mass spectroscopy of recoiled ions technique which is suitable for monolayer-specific surface analysis of thin films during growth. We present initial results using this technique to study the effect of different bottom electrode layers on metallic species and oxygen incorporation in the early stages of SrBi2Ta2O3 (SBT) film growth via ion beam-sputter deposition. The work discussed here has been focused on studying the incorporation of Sr, Bi, and Ta during growth of SBT on Pt/Ti/SiO2/Si, Pt/MgO, Ti, and Si substrates. We found that the incorporation of Bi in sputter-deposited SBT films depends critically on the bottom electrode surface composition and the growth temperature.

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

Abstract We have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+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.

Impact of changes in the Pt heterostructure bottom electrodes on the ferroelectric properties of SBT thin films

Abstract The crystallinity and the microstructure of Sr0.8Bi2.3Ta2O9 (SBT) thin films improved with increasing annealing temperature, and strongly influenced the ferroelectric properties. In addition, the properties of SBT films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films on Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibited high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films on Pt/Ti/SiO2/Si substrates. This is deduced to be related to differences in film orientation, electrode roughness, and out-diffusion of Ti onto the surface of the bottom electrode.

Studies of hydrogen-induced degradation processes in Pb(Zr1-xTix)O3 (PZT) and SrBi2Ta2O9 (SBT) ferroelectric film-based capacitors

Abstract The integration of PZT and SBT film-based capacitors with Si integrated circuit technology requires the use of processing steps that may degrade the performance of individual device components. Hydrogen annealing to remove damage in the Si FET adversely affects both PZT and SBT, although the mechanisms of degradation are different. We have used Mass spectroscopy of recoiled ions (MSRI), X-ray diffraction (XRD), Raman spectroscopy and electrical characterization to study the mechanisms of hydrogen-induced degradation in these two materials. The mechanism responsible for degradation in SBT during hydrogen annealing appears to be hydrogen-induced volatilization of Bi from the near-surface region during film growth. Although there is a similar, but smaller, loss of Pb in PZT, the resulting change in stoichiometry is not responsible for the degradation of the ferroelectric properties. Raman spectroscopy reveals that PZT films exposed to hydrogen exhibit evidence for the formation of polar hydroxyl [OH...

Submicron Ferroelectric Elements Fabricated by Direct Electron Beam Lithography

To realize Gigabit density ferroelectric memory devices, downscaling issues involving processing, materials, and fundamental ferroelectric behavior must be resolved. To address patterning and characterizing ferroelectric films at the nanoscale, we have prepared different lateral sizes of ferroelectric PZT capacitors down to 120 nm, using direct-write electron beam lithography. Characterization of the piezoelectric activity of the patterned elements was performed by means of piezoelectric-sensitive scanning probe microscope in the contact mode. Switching of single 120 nm cells was achieved.

Studies of ferroelectric heterostructure thin films, interfaces, and device-related processes via in situ analytical techniques

Abstract The science and technology of ferroelectric thin films has experienced an explosive development during the last ten years. Low-density non-volatile ferroelectric random access memories (NVFRAMs) are now incorporated in commercial products such as “smart cards”, while high permittivity capacitors are incorporated in cellular phones. However, substantial work is still needed to develop materials integration strategies for high-density memories. We have demonstrated that the implementation of complementary in situ characterization techniques is critical to understand film growth and device processes relevant to device development. We are using uniquely integrated time of flight ion scattering and recoil spectroscopy (TOF-ISARS) and spectroscopic ellipsometry (SE) techniques to perform in situ, real-time studies of film growth processes in the high background gas pressure required to growth ferroelectric thin films. TOF-ISARS provides information on surface processes, while SE permits the investigati...