The authors consider the polarization behavior and controllability of thin ferroelectric barium strontium titanate films in a wide range of temperatures for two groups that differ by the conditions of fabrication. An indirect connection between the coefficient of film capacitor controllability and the polarization of films is noted.

Предложена и исследована конструкция микрополоскового фотонного кристалла на однородной диэлектрической подложке, которая отличается тем, что ширина токоведущего проводника микрополосковой линии остается неизменной по всей длине, в то время как сегнетоэлектрическая пленка, на которую нанесен полосковый проводник, периодически вытравлена. Для теоретического анализа исследованного фотонного кристалла использована коммерческая программа Microwave Office с добавлением разработанных дополнительных программ, позволяющих проводить электродинамический анализ многослойных диэлектрических структур. Проведен электродинамический расчет характеристик исследованного фотонного кристалла - частотных зависимостей коэффициентов передачи и отражения его матрицы рассеяния. Для решения задачи был использован электродинамический метод, известный как метод моментов. Расчет проводился при соблюдении так называемого четвертьволнового условия, которое является необходимым для получения оптимальных характеристик фотонного кристалла. Проведен анализ частотных характеристик коэффициентов матрицы рассеяния исследованного фотонного кристалла, показано наличие эквидистантно расположенных фотонных запрещенных зон в его частотном спектре. Проведено моделирование влияния параметров исследованного фотонного кристалла на появление в его частотном спектре фотонных запрещенных зон. Установлено, что основными параметрами, которые оказывают доминирующее влияние на появление фотонных запрещенных зон в частотном спектре анализируемой структуры с периодически вытравленной наноразмерной пленкой, являются толщина сегнетоэлектрической пленки, величина диэлектрической постоянной пленки, а также толщина металлизации проводников микрополосковой линии. Показаны преимущества предложенной конструкции фотонного кристалла над известными микрополосковыми аналогами. Предложенная конструкция для своей реализации требует несравненно меньших технологических усилий и затрат, нежели фотонные кристаллы на композитной подложке с аналогичными характеристиками. Указаны возможные области применения исследованной структуры с периодически вытравленной наноразмерной сегнетоэлектрической пленкой.

This study investigates the impact of narrow-band terahertz pulses on the ferroelectric order parameter in Ba0.8Sr0.2TiO3 films on various substrates. THz radiation in the range of 1-2 THz with the pulse width of about 0.15 THz was separated from a broadband pulse with the interference technique. The 375 nm thick BST film on a MgO (001) substrate exhibits enhanced THz-induced second harmonic generation when excited by THz pulses with a central frequency of 1.6 THz, due to the resonant excitation of the soft phonon mode. Conversely, the BST film on a Si (001) substrate shows no enhancement, due to its polycrystalline state. The 800 nm thick BST film on a MgO (111) substrate demonstrates the maximum of a second harmonic generation signal when excited by THz pulses at 1.8 THz, which is close to the soft mode frequency for the (111) orientation. Notably, the frequency spectrum of the BST/MgO (111) film reveals peaks at both the fundamental and doubled frequencies, and their intensities depend, respectively, linearly and quadratically on the THz pulse electric field strength.

The ultrafast ferroelectric polarization dynamics excited by intense THz pulses (with an electric field up to 23 MV/cm) in a multidomain Ba0.8Sr0.2TiO3 thin film has been experimentally demonstrated using optical second harmonic generation (SHG) probe. The obtained nonlinear dependence of the SHG intensity on the electric field of the THz pulse can be explained in terms of Landau-Khalatnikov equation by a transient ferroelectric polarization reversal. The best agreement between the experimental and simulated data was obtained when taking into account the multidomain structure of the film and carrying out convolution of the simulated polarization dynamics and the optical probe pulse.

Представлены результаты получения и исследования структуры и диэлектрических характеристик тонких пленок слоистого титаната висмута с различной ориентацией кристаллитов относительно плоскости подложки (100)Si с использованием в качестве подслоя (Ba, Sr)TiO. В зависимости от условий роста и химического состава подслоя можно получать монокристаллические или текстурированные пленки слоистого титаната висмута с различной доменной структурой. Одновременное измерение пьезоотклика и вольт-фарадных характеристик позволило сделать вывод о том, что эффект поля в МСЭП-структуре полностью определяется сегнетоэлектрической поляризацией, обусловленной перестройкой доменного строения при внешнем полевом воздействии, а влияние поверхностных состояний незначительно.

Приведены результаты междисциплинарных исследований сегнетоэлектрических гетероструктур, полученных по принципиально новой технологии, разработанной в лаборатории физики тонких сегнетоэлектрических пленок Южного научного центра Российской академии наук (ЮНЦ РАН). Получаемые по этой технологии гетероструктуры сложных оксидов по структурному совершенству и диэлектрическим свойствам значительно превосходят лучшие зарубежные образцы. Комплексное исследование гетероструктур сложных оксидов (методы рентгендифракционного анализа, исследования диэлектрических характеристик, исследования генерации второй гармоники, спектроскопия комбинационного рассеяния света, высокоразрешающая электронная микроскопия) позволило выявить основные особенности применения такой новой активной среды в микроэлектронике СВЧ, оптическом диапазоне, в устройствах на поверхностных акустических волнах, в микродатчиках, а также разработать и создать в ЮНЦ РАН опытные образцы. Установлена область оптимальных толщин пленок для применения в управляющих устройствах СВЧ-диапазона – между 25 и 50 нм. Эта область характеризуется максимальным коэффициентом управляемости и минимальными диэлектрическими потерями. Более того, методы рентгеноструктурного анализа позволяют однозначно определить механизм роста пленок и установить ожидаемый коэффициент управляемости. Разработанный в ЮНЦ РАН микродатчик на основе наноразмерных сегнетоэлектрических гетероструктур с пороговой чувствительностью l/l 10... 10, работающий в диапазоне частот 10... 10 Гц, позволит создать системы диагностики сложных механических систем в минимальные сроки. При использовании в устройстве на поверхностных акустических волнах в качестве активного элемента тонкой сегнетоэлектрической пленки можно вдвое повысить рабочую частоту преобразователя за счет формирования в пленке периодической доменной структуры, представляющей собой фотонный кристалл. Путем изменения внешнего поляризующего напряжения на электродах пленки можно создавать преобразователи с электрически регулируемым коэффициентом электромеханической связи.

Metal–ferroelectric–semiconductor Pb(ZrTi)O 3 /Ba 0.2 Sr 0.8 TiО 3 /Si(001) heterostructures have been synthesized by radiofrequency cathode sputtering. It has been established that the Pb(ZrTi)O 3 films are single-phase and textured and the degree of predominance of one crystallographic orientation over another (110 or 001) is determined by the Ba 0.2 Sr 0.8 TiO 3 sublayer thickness. It is shown that, by varying the sublayer thickness and/or the amplitude of one period of the external bipolar field effect, one can obtain different electric states of the structure, which can give rise to creating memory cells, including multilevel ones.

A study of the electrical and photoelectric properties of the heterostructure of barium strontium titanate film on a silicon substrate was performed. The conductivity of the heterostructure significantly increased and the capacitance decreased with frequency. The photoconductivity significantly increased for the sample modified by Cr+ ion implantation. The temperature dependence of the resistance under green laser irradiation demonstrated maxima at 150 K.

We investigate the properties of quasi-two-dimensional electron gas at the interface between ferroelectric oxide and insulating oxide in Ba0.8Sr0.2TiO3/LaMnO3 heterostructure after applying magnetic or electric fields. Interface conductivity was measured by a four-point probe method before and after the effect of an electric field on the Ba0.8Sr0.2TiO3 ferroelectric film. It is shown that the state with high conductivity can be turned off when a non-uniform electric field is applied to a ferroelectric film. Besides, the high conducting interface state can be turned on under the influence of a uniform electric field on the ferroelectric film.

Single-crystal Bi4Ti3O12 films deposited on a 4-nm-thick Ba0.4Sr0.6TiO3 sublayer covering an MgO(001) substrate have been investigated. It has been found that the unit cells of Bi4Ti3O12 films in the resulting heterostructures are turned by 45° relative to the cells of the MgO substrate in the interface plane. In addition, the unit cells of the films are strained, the amount of strain depending on the Bi4Ti3O12 film thickness. When the films become about 40 nm thick, strain changes sign. It has been shown that reversible spontaneous polarization in Bi4Ti3O12 films with a 180° domain structure in the interface plane arises at a thickness of 10 nm and grows with thickness to 54 μC/cm2. The anisotropy of the film’s properties in the interface plane and the influence of unit cell distortion on the properties of the heterostructures have been confirmed by studying the dielectric performance of the films.

Pb(ZrTi)O3/Ba0.2Sr0.8TiО3/Si(001) metal-ferroelectric-semiconductor hetero-structures were fabricated by radio-frequency cathodic sputtering. It was found that Pb(ZrTi)O3 films are single-phase, textured, and Ba0.2Sr0.8TiО3 sublayer thickness in-fluence on the texture preferred orientation (110 or 001). It has been shown that by varying the sublayer thickness and / or the amplitude of one period of the applied ex-ternal bipolar electric field, it is possible to create different electrophysical states of the structure. These electrophysical states can be used in creating of the memory cells and, in particular, a multi-level memory cells.

A study of epitaxial Bi4Ti3O12 thin films with a pre-deposited 4 nm Ba0.4Sr0.6TiO3 sublay-er on (001) MgO substrates has been performed. In the obtained heterostructures, the rotation of the Bi4Ti3O12 film unit cells by an angle of 45° relative to the MgO substrate unit cell in the inter-face plane has been observed. The Bi4Ti3O12 films contain unit cell deformations depending on the thickness of the film and the sign of the deformation changes at a thickness of ~40 nm. The switchable in-plane spontaneous polarization of Bi4Ti3O12 film at the 180° domain structure oc-curs at a film thickness of 10 nm and increases with a thickness up to 54 µC/cm2. The study of the dielectric characteristics of the films confirmed the existence of properties anisotropy in the interface plane and the effect of deformation of the unit cell on the properties of heterostruc-tures.

The effect of green and ultraviolet laser light on Ba_0.8Sr_0.2TiO_3/LaMnO_3 heterostructure electrical resistance was studied. In 80-200 K range illumination induces transient resistance component at 15 transient component is 12 s. The negative photoresistance effect is found under green, infrared and ultraviolet illumination.

We investigated the epitaxial Bi4Ti3O12 (BTO) thin films with different thicknesses on a (0 0 1) MgO substrate with a Ba0.4Sr0.6TiO3 buffer layer (4 nm). The crystallographic axis [1 0 0] of Bi4Ti3O12 film is rotated on degrees relative to [1 0 0] MgO axis. When the thickness of Bi4Ti3O12 film is less than 40 nm, the unit cell of the film is compressed in the normal to the interface plane direction. In cases of large film thicknesses, the sign of strain changes and correspondingly the unit cell is stretched. Switched spontaneous polarization in the interface plane with 180 degrees domain structure occurs at 10 nm film thickness and increases with a thickness up to 55 C cm (2). Changes in the Raman spectra of the Bi4Ti3O12 films indicates to increase of monoclinic distortion of the film unit cell in comparison with the bulk unit cell. The anisotropy of in-plane dielectric properties and the effect of internal strain on dielectric properties for the Bi4Ti3O12 films are confirmed by the study of the dielectric characteristics of the films.

We investigate the effect of electric field on the properties of quasi-two-dimensional electron gas at the interface between ferroelectric oxide and insulating oxide in Ba0.8Sr0.2TiO3/LaMnO3 (BSTO/LMO) heterostructure. Interface conductivity measurements were performed by a four-point probe method before and after the effect of electric field on Ba0.8Sr0.2TiO3 ferroelectric film. We have shown that when a non-uniform electric field is applied to a ferroelectric film, we can turn off the state with high conductivity. Whereas under the influence of a uniform electric field on the ferroelectric film, we can turn on the interface state of high conductivity.

The ability to switch ferroics (magnets, ferroelectrics, multiferroics) between two stable bit states is the main principle of modern data storage technology. Due to many new ideas, originating from fundamental research during the last 50 years, this technology has developed in a breath-taking fashion. Ever increasing demands for faster and more energy efficient data storage strongly motivate fundamental studies of dynamics in ferroics triggered by ultrashort stimuli. It has been recently realized that nearly single cycle intense THz pulses and the phenomenon of the second harmonic generation are appealing tools for excitation and detection of poorly understood ultrafast dynamics of electric polarization in ferroelectrics at the picosecond timescale. Here we investigate picosecond dynamics of second harmonic from near-infrared pulse in ferroelectric heterostructure Ba0.8Sr0.2TiO3/MgO triggered by the electric field of a nearly single cycle intense THz pulse. The dynamics of the nonlinear optical signal is characterized by a step and oscillations at the frequency of about 1.67 THz. Although the observations can be mistakenly interpreted as oscillations of the electric polarization at the frequency of the soft mode and switching of the order parameter to another metastable state, here we show that the THz modulation of second harmonic generation in Ba0.8Sr0.2TiO3/MgO has a purely optical origin. The observation can be explained assuming that the THz pulse is a relativistically propagating inhomogeneity which induces center of symmetry breaking and linear birefringence. Our work reveals the role of propagation effects in interpretation of time-resolved non-linear optical experiments and thus it has important implications for experimental studies of ultrafast dynamics in ferroics.

We present the results of the investigations of high conducting area and superconductivity at the interfaces between ferroelectric oxide and insulating oxide in heterostructures, isostructural to BaTiO3/La2CuO4. The performed numerical simulations of BaTiO3/La2CuO4 heterostructure show the possibility of high conductivity state at the interface. The temperature dependence of the measured electrical resistance of the Ba0.8Sr0.2TiO3/La2CuO4 heterostructure interface have been studied and the superconducting behaviour with transition temperature Tc about 30K has been found. Therefore, the transition to the state with 2DEG at the interface is demonstrated. The results offer the possibility to design novel electronic devices.

The results of the investigations of high conducting and superconducting areas at the interfaces between ferroelectric oxide and insulating oxide are presented. The numerical simulations of BaTiO3/LaMnO3 and BaTiO3/La2CuO4 heterostructures have been performed. It is found that in the samples of the Ba0.8Sr0.2TiO3/LaMnO3 heterostructure the electrical resistance decreases significantly and exhibits metallic behaviour at low temperatures for the case when the c axis of ferroelectric film is directed along the normal to the surface of the single crystal. The superconducting behaviour with transition temperature Tc about 30K has been found at the interface of the Ba0.8Sr0.2TiO3/La2CuO4 heterostructure. The proposed concept promises the ferroelectrically controlled interface conductivity and superconductivity.

Properties of the Ba0.8Sr0.2TiO3/LaMnO3 heterostructure are investigated for when LaMnO3 and Ba0.8Sr0.2TiO3 are deposited on a surface SrTiO3. No state of high conductivity is observed. The effect a magnetic field has on the temperature behavior of resistivity is determined for samples of the Ba0.8Sr0.2TiO3/LaMnO3 heterostructure in its “normal” architecture when a Ba0.8Sr0.2TiO3 film is deposited on a LaMnO3 single crystal.