摘要:

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 complementaryin situcharacterization techniques is critical to understand film growth and device processes relevant to device development.

ISSN:1058-4587    

DOI:10.1080/10584589908228460

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The Laser Intensity Modulation Method (LIMM) is used to determine the spatial distribution of polarization in the direction of the polar axis of a ferroelectric sample. It is based upon measurement of the pyroelectric current generated by the material when it is heated with a laser beam which is intensity-modulated over a range of frequencies. A modification of this technique has been developed which will permit detailed profiling of the polarization distribution in a thin-film electroded ferroelectric layer on a substrate, such as a ferroelectric memory. The theory of the technique is discussed and it is shown that the determination of the polarization distributions requires the solution of a Fredholm integral equation of the 1st kind using experimental data. A novel method of solution of this problem using neural networks is described.

ISSN:1058-4587    

DOI:10.1080/10584589908228461

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this work, the laser-intensity-modulation method (LIMM), e.g. the determination of the spatial polarization profile from the pyroelectric current spectrum caused by the interaction of thermal waves generated by an intensity modulated laser and the unknown polarization distribution, is applied for investigation of sputtered PZT thin films on a thermally coupled bulk silicon substrate or a thermally isolating membrane, respectively. To investigate thin films with a thickness of about 1 μm the modulation frequency of the laser was extended up to 2 MHz. The reconstruction of the spatial polarization distribution requires to solve a Fredholm's integral equation of the first kind which is a so called “ill-posed” problem. For deconvolution of the inverse LIMM problem several approaches like power series trial functions and Lagrange polynomials are used and compared with the original Fourier series approach for LIMM introduced by S.B. Lang. To obtain a non-oscillating solution of the inverse LIMM-problem the Tikhonov regularization method is used.

ISSN:1058-4587    

DOI:10.1080/10584589908228462

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We present real-time studies of nucleation and growth of 180° ferroelectric domains in congruent LiTaO3under an external electric field using optical microscopy. The measured wall velocities are an order of magnitude higher than those reported before using ex-situ techniques. Merger of growing domains form serrated fronts which show a futher order of magnitude increase in wall velocity. A time dependent velocity is required in the Avrami theory to explain the change in domain area versus time at a constant electric field. We believe that these features of domain switching must be considered when studying ferroelectrics in general.

ISSN:1058-4587    

DOI:10.1080/10584589908228463

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

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−] bonds, which can block the movement of ions in the lattice and inhibit polarization. The possible sites for the incorporation of hydrogen are discussed in terms of ionic radii, and crystal structure.

ISSN:1058-4587    

DOI:10.1080/10584589908228464

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Scanning force microscopy (SFM) has been used for comparative studies of domain structures in SrBi2Ta2O9(SBT) thin films grown by sol-gel, Flash MOCVD and pulsed laser deposition (PLD) techniques. Investigation has been focused on establishing microscopic correlation between crystallinity, domain arrangements and switching behavior of the films. It has been shown that the domain contrast of an individual grain and its switchability are strongly dependent on the grain orientation. The remnant polarization value was found to decrease with decrease in the fraction ofa-oriented grains which exhibit sharp domain contrast.

ISSN:1058-4587    

DOI:10.1080/10584589908228465

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Switching and imprint effects as a function of fatigue in Pt-PZT-Pt ferroelectric capacitors (FeCap) were studied by means of Atomic Force Microscopy (AFM). This approach enable the local characterisation of the ferroelectric properties. It is found that although fatigue appears to occur, as expected, “region by region” and shows a preferential direction for the polarisation, the dead areas can consist of an unequal quantity of very small frozen regions oriented in both directions. This coexistence gives rise to regions with different piezoelectric activity and degree of fatigue. The surviving areas also contain a minority of small frozen regions which manifest itself by shifting the piezoelectric loops along the y-axis. In addition it was shown that although fatigue onset can influence the imprinted state by centring the typical field offset, imprint treatment in opposite directions cannot influence the completed fatigued state (size, shape and preferred orientation of the frozen regions).

ISSN:1058-4587    

DOI:10.1080/10584589908228466

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We demonstrate how the mathematical treatment of the switching current data allows to characterize the variation of the domain structure during fatigue. Investigating PZT/YBCO heterostructures on SrTiO3and NdGaO3substrates we propose two different scenarios of fatigue-induced evolution of the domain structure. The essential role of as-grown domain structure is pointed out. It is shown that for higha-domain concentration the growth of the area occupied bya-domains prevails. For low “a-cratio” we obtain the competition between rejuvenation process and growth of the “frozen”c-domain area at the grain boundaries.

ISSN:1058-4587    

DOI:10.1080/10584589908228467

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Ferroelectric properties of metal/ferroelectric/metal capacitors can be severely degraded during FRAM® integration in a hydrogen containing ambient. To understand the mechanism of hydrogen damage we characterized ferroelectric capacitors with the configuration of Pt/PLZT/Pt and Pt/SBTN/Pt annealed in the temperature range of 50°C to 200°C using hysteresis and DC pulsing. The capacitors were stored in specific remanent states (negative, positive, and zero) by poling prior to annealing. The annealing was carried out in a forming gas ambient, containing 1% hydrogen and 99% nitrogen. The degradation is strongly dependent on the polarity of the remanent polarization. From the results, we propose an empirical model of the formation of a fixed dipole layer at the top electrode-ferroelectric interface and we confirm that the polarity of this charge is positive.

ISSN:1058-4587    

DOI:10.1080/10584589908228468

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A novel fabrication process of ferroelectric-semiconductor heterostructures based ondirect wafer bonding(DWB) andlayer transferis proposed. Metal-ferroelectric-silicon (MFS) structures were fabricated by both layer transfer process and direct deposition of ferroelectric films onto Si. Detailed transmission electron microscope (TEM) investigations revealed that a direct wafer bonding and layer transfer process yields good quality ferroelectric/Si interfaces. Interface trap measurements show a large difference for MFS structures fabricated by bonding or by direct deposition, respectively. The trap density values were ranging from 2×1012cm−2eV−1for SBT/Si directly deposited to 4×1011cm−2eV−1for SBT/Si bonded interfaces.

ISSN:1058-4587    

DOI:10.1080/10584589908228469

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor