An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.

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Ferroelectric thin films: Review of materials, properties, and applications

This paper reviews deposition, integration, and device fabrication of ferroelectric PbZrxTi1-xO3 (PZT) films for applications in microelectromechanical systems. As examples, a piezoelectric ultrasonic micromotor and pyroelectric infrared detector array are presented. A summary of the published data on the piezoelectric properties of PZT thin films is given. The figures of merit for various applications are discussed. Some considerations and results on operation, reliability, and depolarization of PZT thin films are presented.

http://iopscience.iop.org/article/10.1088/0960-1317/10/2/307/pdf

Ferroelectric thin films for micro-sensors and actuators: a review

The broad spectrum of electronic and optical properties exhibited by oxides offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired Here we describe the use of reactive molecular-beam epitaxy and pulsed-laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time Owing to the dependence of properties on direction, it is often optimal to grow functional oxides in particular directions to maximize their properties for a specific application But these thin film techniques offer more than orientation control; customization of the film structure down to the atomic-layer level is possible Numerous examples of the controlled epitaxial growth of oxides with perovskite and perovskite-related structures, including superlattices and metastable phases, are shown In addition to integrating functional oxides with conventional semiconductors, standard semiconductor practices involving epitaxial strain, confined thickness, and modulation doping can also be applied to oxide thin films Results of fundamental scientific importance as well as results revealing the tremendous potential of utilizing functional oxide thin films to create devices with enhanced performance are described

/pdf/a-thin-film-approach-to-engineering-functionality-into-51t9902h5j.pdf

A Thin Film Approach to Engineering Functionality into Oxides

A method of fabricating a semiconductor structure including the steps of providing a silicon substrate (10) having a surface (12), forming on the surface (12) of the silicon substrate (10), by atomic layer deposition (ALD), a seed layer (20;20') characterised by a silicate material and forming, by atomic layer deposition (ALD) one or more layers of a high dielectric constant oxide (40) on the seed layer (20;20').

Method for fabricating a semiconductor structure including a metal oxide interface with silicon

This paper reviews deposition, integration, and device fabrication of PbZr/sub x/Ti/sub 1-x/O/sub 3/ (PZT) films for applications in micro-electromechanical systems. An ultrasonic micromotor is described as an example. A summary of the published data on piezoelectric properties is given. The figures of merit for various applications are discussed. Some considerations and results on operation, reliability, and depolarization of PZT thin films are presented. The state of the art allows some preliminary conclusions.

PZT thin films for microsensors and actuators: Where do we stand?

A planar multi target sputtering technology was used to deposit highly (111) oriented Pb(Zr
 x
 Ti1−x
)O3 (PZT) thin films with x ranging from 0–0.6. The preparation of a stable Pt/ZrO2 electrode is described and analyzed in terms of stress and stress-temperature behavior. The PZT films with low Zr content are under compressive stress after deposition. The dielectric constant and loss peaks occur at a composition close to the morphotropic phase boundary. Films on the tetragonal side of the phase diagram with a Zr content up to about 25% exhibited a strong self polarization and strong voltage shifts in the C(V) curves. High pyroelectric coefficients of >2×10−4 C/(m2K) have been measured on these films without additional poling. The self polarization fades out with increasing Zr content. The low values of the pyroelectric coefficient for the PZT film with 60% Zr is discussed in terms of the possible crystallographic variants after distortion and the tensile stress state during the phase transition. Based on the systematic study of stress and electrical properties of PZT films with a wide range of composition presented in this paper, films with a Zr content up to about 25% turned out to give the best properties for the use in pyroelectric detector arrays.

Optimized PZT Thin Films for Pyroelectric IR Detector Arrays

The deposition of the bottom electrode plays a key role in the fabrication of ferroelectric capacitors. Processing at elevated temperatures of up to 800°C can give rise to diffusion processes and thereof formation of harmful dielectric layers. p]In this paper we used Rutherford backscattering spectrometry (RBS), Auger electron spectrometry (AES) and transmission electron microscopy (TEM) to study Pt/Ti/SiO2/Si substrates with various thicknesses of the Ti and Pt layers. During heating up to about 450°C in vacuum the initial layer sequence remains unchanged. However, drastic changes occur when the electrodes are exposed to Ar/O2 atmosphere during heat treatment. Oxidation induced diffusion of Ti into Pt and oxidation of Ti were observed. A Pt electrode with a 100 nm thick Ti adhesion layer proved to be suitable for the “in-situ” deposition of PZT films.

Investigation of Pt Bottom Electrodes for “In-Situ” Deposited Pb(Zr,Ti)O3 (PZT) thin Films

A planar multi target sputtering approach was used to deposit self polarized PZT films on TiO2/Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays By using elevated substrate temperatures of about 450°C “in situ” growth of tetragonal PZT could be achieved The films exhibited pyroelectric currents without poling The pyroelectric coefficient was 2×10−4 C/m2K, the dielectric constant was 300 and dielectric loss tan δ was 001 The self polarization disappears after heating the sample to 600°C Stresses were studied in the thin film processing for the bottom electrode and the PZT film The TiO2/Pt electrode is under high tensile stress of 900 MPa after preparation PZT has a small compressive stress of -60 MPa, the whole TiO2/Pt/PZT stack has a tensile stress of +80 MPa This low stress level together with the self polarization and the good electrical properties makes the films suitable for the use in pyroelectric detector arrays

Deposition of self-polarized PZT films by planar multi-target sputtering

A planar multi-target sputtering system was used to deposit ferroelectric lead zirconate titanate (PZT) films. At substrate temperatures of about 450°C “in-situ” deposition of single phase perovskite PZT was obtained. By investigation with SEM and TEM films exhibited a columnar structure with crystallites of about 200 nm in size. The permittivity of the films varied from 450-600. The films exhibited hysteresis loops, remanent polarization of 15-20 μC/cm2 and coercive field strength of 70-85 kV/cm.

Deposition of ferroelectric PZT thin films by planar multi-target sputtering

A novel pyrodetector element is produced by oriented growth, with the aid of buffer layers, above a monocrystalline silicon substrate and thus enables the fabrication of an array of pyrodetectors having read-out and amplifier circuitry integrated on the common substrate. Proposed as the buffer layers are yttrium-stabilized zirconium oxide YSZ or magnesium oxide above an interlayer made of spinel.

Rainer Bruchhaus

Papers

Optimized PZT Thin Films for Pyroelectric IR Detector Arrays

Investigation of Pt Bottom Electrodes for “In-Situ” Deposited Pb(Zr,Ti)O3 (PZT) thin Films

Deposition of self-polarized PZT films by planar multi-target sputtering

Deposition of ferroelectric PZT thin films by planar multi-target sputtering

Pyrodetector element having a pyroelectric layer produced by oriented growth, and method for the fabrication of the element