Solid State Physics (condensed matter): FERROELECTRICS

Transcription

1 Solid State Physics (condensed matter): FERROELECTRICS Prof. Igor Ostrovskii The University of Mississippi Department of Physics and Astronomy Oxford, UM: May,

2 People:

3 Solid State Physics Condensed Matter Physics Understanding of the macroscopic and microscopic properties of matter. Interactions: Solid / Liquid + Phonons + Electrons + Photons + Crystal Lattice + Electromagnetic Field + PARTICLES + Gravitation. Directions of Research 1. Nano Acoustics: interaction of the acoustic waves with nano-scale substructures. 2. Acousto-Electric phenomena in 2-D ferroelectrics (wafers & films). 3. Applications of multidomain ferroelectrics (cantilevers, transducers, actuators, etc.) 4. Acoustic waves in multidomain ferroelectrics: excitation and propagation. 5. Optical and Acousto-optical properties of crystals.

4 Ferroelectric ceramic: PZT PZT (Pb (ZrTi)O3) is a typical ferroelectric material. An electric polarization of PZT (shift up/down of Zr/Ti atom) remains after applying and removing an external electric field, from which a nonvolatile property results: As a result of this, the power consumption required for data storage is very low. FRAM (ferroelectric random access memory) is one of a growing number of alternative non-volatile random-access memory technologies that offer the same functionality as flash memory. E 2 PROM = Electrically Erasable Programmable Read-Only Memory. Compared with E 2 PROM, Fujitsu's FRAM has the following features: 1. 1/30,000 high-speed write time 2. 1/400 or less power consumption ,000 times or more rewrite count capability.

5 Ferroelectric crystal: Lithium Niobate (LiNbO3) Lithium niobate single crystals are an important material for: 1) optical waveguides, 2) mobile phones, 3) optical modulators, 4) ultrasonic transducers and oscillators, 5) very high frequency filters (next gen.), 6) surface acoustic wave devices, 7) various other linear and non-linear applications such as SHG. O - PPLN is a domain-engineered lithium niobate crystal. The ferroelectric domains point alternatively to the +c and the -c direction.

6 Ferroelectric domains and domain walls + side Li + O - Li + O - - side O - Li + O - Li + δ Domain wall O - With the help of applying electric field we can switch domain direction P P

7 Periodically poled lithium niobate (PPLN): rf Admittance YR42-cut LTYR42B5a, 50 domains λ = 100 µm Admittance (Ω 1 ) LTYR42B5a Z-cut LTZA17, 85 domains λ = 98 µm Admittance (Ω -1 ) LTZA17 Frequency (MHz) Domain resonances Plot 1 LTZA17a Plot 2 LTZA17b Plot 3 - Theory Frequency (MHz) 7

8 Theory: Equations of Motion and Electrodynamics ρ D x i u t i 2 i 2 = x i = T x ij j = x j ( c uk S ( ei kl + ε ik Ek ) = x l E ijkl 0 u x k l e Piezoelectric properties are given by: E kij i E k ) = h i kl u x k l + β S ij D j Where: ρ - density, u K - acoustic displacement, E i D i - stress tensor -piezoelectric field, - electric displacement, - elastic modules T ij E c ijkl e kij, h- piezoelectric coefficients, - dielectric impermeabilities Boundary conditions:1. Loaded surface: S β ij Z L - acoustic impedance of Load T xx Crystal = U Z 2.Free: L Load T ij n j = 0 + Internal Boundary Conditions: continuity of the displacements and piezoelectric fields at all interdomain walls inside the multidomain transducer. 8

9 F G P C 4 Ch1 V(ω) -Nd Acousto-electric properties of LiNbO3 2 2t 1 k -d Z +Z -Z Digital storage oscilloscope a 0 +e b d a -e +e Ch2 +Nd X 3 PAW: Plate Acoustic Waves Allowed modes (real k) Phase velocity dispersion Group velocity dispersion Attenuation Interaction with nano-size interdomain walls Electromechanical coupling Acousto-electric interaction AG V(ω) 2 1 k Z +Z -Z -e +e +e 3 2t a b a X Acoustic Stop-Bands at Brillouin Zone Boundary λ = 2d. Double Domain Resonance. FG PC -Nd -d 0 d Spectrum Analyzer +Nd

10 Resonances at Acoustic Brillouin Zone (ABZ) Boundary 2 nd st ABZ 1 st ABZ Stop-band Frequency (MHz)

11 Results & Applications: Nano-cantilever Measured masses, ng : ; 0.1 ; 0.24 ; 1; 2; 5 18,000. Laser Electric voltage U = V Frequency F = khz Metal electrode Vibrations Photo-detector Small mass Digital Oscilloscope A Generator Computer A vibration amplitude F frequency F

12 Nanoscience: Multidomain Ferroelectric Cantilever for Pico-gram mass Detection. Applications: Detection and Identification of Protein Molecules (including those in air or water).

13 Results & Applications: MUT MUT: Multidomain Ultrasonic Transducer Amplitude (arb. units) free n1 n2 n10 n200 free n = 200 n = 10 n = 2 n = 1 z y x ~V 2 1E Frequency (arb. units) 1 +e A e B +e A e B Acoustic wave

14 New Effect: Acoustical Memory in LiNbO 3 14

15 Physics Today Jobs: Apr 30, 2012 ALL = 129 Total Result(s)