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.

/pdf/ferroelectric-thin-films-review-of-materials-properties-and-rc7umdkxk5.pdf

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

J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons

/pdf/ultrawide-bandgap-semiconductors-research-opportunities-and-49ev1zu2ym.pdf

Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.

Tuning in to RF MEMS

The influence of film thickness on the material properties of aluminum nitride (AlN) thin films deposited on Pt(111) electrodes has been investigated experimentally by means of x-ray diffraction, dielectric response, atomic force microscopy, interferometry measurement of effective d33, and residual stress measurement. The thickness was varied between 35 nm and 2 μm. Full width at mid-height of the rocking curve decreased from 2.60 to 1.14°, rms roughness increased from 3.8 to 18.6 A, the effective d33, namely d33,f, from 2.75 to 5.15 pm/V. The permittivity eAlN was stable at 10.2, whereas the dielectric losses decreased from 1% to 0.1%. The breakdown electric field under dc voltages varied between 4.0 and 5.5 MV/cm.

Thickness dependence of the properties of highly c-axis textured AlN thin films

Thin film bulk acoustic wave (BAW) resonators and filters are well suited for mobile communication systems operating at high frequencies between 0.5 and 10 GHz. Piezoelectric thin film materials investigated for BAW devices within Philips include AlN thin films. The relationship between sputter deposition conditions, AlN film structure, electromechanical coupling factor kt, and relevant electrical parameters of BAW devices are discussed.

Piezoelectric thin AlN films for bulk acoustic wave (BAW) resonators

Thin film bulk acoustic wave (BAW) resonators and filters are appropriate for mobile communication systems operating at high frequencies between 0.5 and 10 GHz. c-axis orientated AlN films are used for medium bandwidth applications. Electromechanical coupling factors k/sub t/ of 0.25/spl plusmn/0.03, which are close to the bulk data, have been found in AlN thin films using optimum sputter conditions. The correlation between k/sub t/ and AlN film orientation is discussed. Resonator Q values of approx. 450 are reported at 2.6 GHz and a Q of 250 was realized at 9.2 GHz. A physical model is shown to accurately predict the frequency responses of BAW resonators and band-pass filters. For wide bandwidth applications PbZr/sub x/Ti/sub 1-x/O/sub 3/ (PZT) films are investigated. They exhibit large coupling coefficients.

Piezoelectric materials for BAW resonators and filters

Small sized, highly selective solidly mounted bulk acoustic wave (BAW) band pass filters are of great interest for mobile and wireless systems operating in the frequency range of 0.8 GHz up to more than 10 GHz. They can be fabricated on silicon or glass wafers using standard semiconductor integration techniques. These filters are based on electro-acoustic high Q resonators, which exploit the thickness extensional mode of a thin piezoelectric AlN or ZnO film. This film has to be grown with its polar axis, oriented perpendicular to the substrate. Both the deposition process and using a textured electrode support excellent c-axis oriented growth and thus high electromechanical coupling coefficient kt and filter bandwidth. Modelling of the filter and resonator response is performed by means of a combination of a 1D electro-acoustic model together with an electromagnetic model. The paper shows examples of filters operating in the range between 2 and 8 GHz.

RF Bulk Acoustic Wave Resonators and Filters

To preserve the link quality, in fluctuating operating environments, an adaptive antenna matching module is presented that consists of a 5-bit RF-MEMS switched capacitor array, a bipolar 60/30 V MEMS-biasing voltage generator for improved reliability, and an impedance phase detector that provides information on mismatch. It uses an iterative up-down counting algorithm for robust control. Measurements show proper correction of the antenna reactance, even for a VSWR of 10. The switched capacitor array exhibits a large tuning range from 1 to 15 pF and an insertion loss of 0.4 dB. The detector dynamic range equals 35 dB with an accuracy of 8 degrees from 0.8 to 2 GHz. Adaptive matching will make isolators redundant.

/pdf/rf-mems-based-adaptive-antenna-matching-module-458f7ca7xc.pdf

RF-MEMS based adaptive antenna matching module

Small sized, highly selective solidly mounted bulk acoustic wave (BAW) band pass filters are suitable for mobile and wireless systems operating in the frequency range 0.8 and 10 GHz. Both lattice and ladder BAW resonator filters have been designed and fabricated on 6" wafers using multilayer Bragg type acoustic reflectors. For the piezoelectric film highly oriented AlN has been deposited using an optimised sputter process. Resonators and filters were made and measured both on glass and silicon wafers. Resonators on glass and Si show different substrate loss. Dielectric loss in the AlN piezo-layer is small. The acoustic loss is found to be small in all the materials. The properties of the acoustic reflector can be monitored by a thorough examination of small details of the resonator's frequency response. Resonator and filter examples are shown for 2 GHz, 2.8 GHz, and 8 GHz.

P. Lok

Papers

Piezoelectric thin AlN films for bulk acoustic wave (BAW) resonators

Piezoelectric materials for BAW resonators and filters

RF Bulk Acoustic Wave Resonators and Filters

RF-MEMS based adaptive antenna matching module

Solidly mounted bulk acoustic wave filters for the GHz frequency range