Ferroelectric materials are well‐suited for a variety of applications because they can offer a combination of high performance and scaled integration. Examples of note include piezoelectrics to transform between electrical and mechanical energies, capacitors used to store charge, electro‐optic devices, and nonvolatile memory storage. Accordingly, they are widely used as sensors, actuators, energy storage, and memory components, ultrasonic devices, and in consumer electronics products. Because these functional properties arise from a noncentrosymmetric crystal structure with spontaneous strain and a permanent electric dipole, the properties depend upon physical and electrical boundary conditions, and consequently, physical dimension. The change in properties with decreasing physical dimension is commonly referred to as a size effect. In thin films, size effects are widely observed, whereas in bulk ceramics, changes in properties from the values of large‐grained specimens is most notable in samples with grain sizes below several micrometers. It is important to note that ferroelectricity typically persists to length scales of about 10 nm, but below this point is often absent. Despite the stability of ferroelectricity for dimensions greater than ~10 nm, the dielectric and piezoelectric coefficients of scaled ferroelectrics are suppressed relative to their bulk counterparts, in some cases by changes up to 80%. The loss of extrinsic contributions (domain and phase boundary motion) to the electromechanical response accounts for much of this suppression. In this article, the current understanding of the underlying mechanisms for this behavior in perovskite ferroelectrics is reviewed. We focus on the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing. In many cases, multiple mechanisms combine to produce the observed scaling effects.

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The dielectric and piezoelectric behavior of 70Pb(Mg1/3Nb2/3)O-3-30PbTiO(3) (70PMN-30PT) thin films was studied as a function of lateral scaling. Dense PMN-PT films 300-360 nm in thickness were prepared by chemical solution deposition using a 2-methoxyethanol solvent. These phase pure and strongly {001} oriented films exhibited dielectric constants exceeding 1400 and loss tangents of approximately 0.01. The films showed slim hysteresis loops with remanent polarizations of about 8 mu C/cm(2) and breakdown fields over 1500 kV/cm. Fully clamped films exhibited large signal strains of 1%, with a d(33,f) coefficient of 90 pm/V. PMN-PT films were patterned down to 200 nm in spatial scale with nearly vertical sidewalls via reactive ion etching. Upon lateral scaling, which produced partially declamped films, there was an increase in both small and large signal dielectric properties, including a doubling of the relative permittivity in structures with width-to-thickness aspect ratios of 0.7. In addition, declamping resulted in a counterclockwise rotation of the hysteresis loops, increasing the remanent polarization to 13.5 mu C/cm(2). Rayleigh analysis, Preisach modeling, and the relative permittivity as a function of temperature were also measured and further indicated changes in the domain wall mobility and intrinsic response of the laterally scaled PMN-PT.

TEXT: The information age challenges computer technology to process an exponentially increasing computational load on a limited energy budget 1-3 -a requirement that demands an exponential reduction in energy per operation. In digital logic circuits, the switching energy of present FET devices is intimately connected with the switching voltage [3][4][5] , and can no longer be lowered sufficiently, limiting the ability of current technology to address the challenge. Quantum computing offers a leap forward in capability 6 , but a clear advantage requires algorithms presently developed for only a small set of applications. Therefore, a new, general purpose, 2 classical technology based on a different paradigm is needed to meet the ever increasing demand for data processing.A promising pathway to fast, low voltage classical devices is transduction which is widely used in nature to propagate signals in bioorganisms 7 . When propagating digital logic, we require the input and output signal to be electronic -however, this still allows for an intermediate form In this work we present two physical realizations of the PET concept on an early developmental pathway leading to the fully integrated PET of Fig. 1. The two devices are evolved to generate stress and accomplish an IMT in the PR channel -key for demonstrating the viability of the PET concept. The first approach, Gen-0, uses a millimeter-scale piezoelectric 4 actuator to compress a 50 nm thick PR film, metallize the channel and cycle the transition at kHz frequencies. The second, Gen-1, uses a micron scale, lithographed, piezoelectric pillar to compress a nanoscale, e-beam patterned PR element, enabling cycling at 100-kHz frequencies.The Gen-0 PET generates the stress required to drive an insulator-metal transition in a 50 nm SmSe 18 film where the conducting area is defined by a hole in a silicon nitride layer, as shown in Fig. 2a. A microindenter is utilized as a yoke to provide the counter force against which a commercial piezoelectric actuator compresses and activates conductivity in the SmSe. In operation, a 1 kHz sine wave applied to the actuator with a 20 Vp-p (peak-to-peak) amplitude generates a displacement, resulting in a force on the SmSe element. An On/Off modulation of over three orders of magnitude in PR resistance is generated as illustrated in Fig. 2b Fig. 2b). The Gen-0 PET frequency response is bounded by actuator resonance to 1 kHz (note the small phase shift, due to the mechanical delay, between the applied actuator voltage and the PR response), a limitation removed in the Gen-1 device which employs an integrated micro-actuator.Demonstrating a device with a micro-actuator providing only nanometer sized displacement is key for establishing the viability of the PET concept. The Gen-1 PET, illustrated in Fig. 3a-b, addresses this important challenge. The micro-actuators, fabricated on an 8" silicon wafer, are PE pillars (approximately 2×2×1 µm 3 ), contacted by long leads running on top of patterned PE.Each micro-actuator is flanked by a PE mesh us...

Lateral subdivision of blanket piezoelectric thin films increases the functional properties through both increased domain wall mobility and declamping of the intrinsic response. This work presents the local effects of substrate declamping on the piezoelectric coefficient d 33,f of 300 nm thick, rhombohedral, {001}-oriented lead magnesium niobate-lead titanate thin films at the 70/30 composition (70PMN-30PT). Films grown by chemical solution deposition on platinized Si substrates are patterned into strip structures ranging from 0.75 to 9 µm in width. The longitudinal piezoelectric coefficient, d 33,f , is interrogated as a function of position across the patterned structures by three approaches: finite element modeling, piezoresponse force microscopy, and nanoprobe synchrotron X-ray diffraction. It is found that d 33,f increases from the clamped value of 40-50 to ≈160 pm V −1 at the free sidewall under 200 kV cm −1 excitation. The sidewalls partially declamp the piezoelectric response 500-600 nm into the patterned structure, raising the piezoelectric response at the center of features with lateral dimensions less than 1 µm (3:1 width to thickness aspect ratio). The normalized data from all three methods are in excellent agreement, with quantitative differences providing insight to the field dependence of the piezoelectric coefficient and its declamping behavior.