279 results about "Spontaneous polarization" patented technology

An active matrix display comprises a chiral smectic liquid crystal mixture which has the phase sequence I-N*-SmC*, a spontaneous polarization in the operating temperature range of <40 nC/cm2 and a pitch of >10 mum at at least one temperature in the nematic or cholesteric phase and comprises at least one compound each from at least two of the substance classes (A), (B) and (C) and one or more compounds from substance class (D):(A): compounds comprising two rings which are directly linked to one another and are selected from phenylene-1,4-diyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl and pyridazine-2,5-diyl with the proviso that at least one of these rings is a nitrogen heterocycle;(B): compounds comprising three rings selected from phenylene-1,4-diyl, two of the rings being directly linked to one another and the third ring being linked to one of the other two rings via an -OC(=O)- or -C(=O)-group, with the proviso that at least one of the three rings is fluorophenylene-1,4-diyl or ortho-difluorophenylene-1,4-diyl;(C): compounds comprising three rings which are directly linked to one another and are selected from phenylene-1,4-diyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl and pyridazine-2,5-diyl with the proviso that at least one of these rings is a nitrogen heterocycle;(D): compounds comprising mesogenic groups suitable as components of liquid crystal mixtures.

A liquid crystal apparatus comprises: a liquid crystal device including a liquid crystal having a spontaneous polarization and causing a state change accompanied with a polarity inversion thereof within a response time. Drive means sequentially selects scanning signal lines each in a scanning selection period and applies data signal voltages to the pixels along an associated scanning signal line, wherein the scanning selection period for a scanning signal line is shorter than the response time for the liquid crystal at a pixel on the scanning signal line thus being liable to leave a remaining portion of polarity inversion to reach a desired state change, and the data signal voltage applied to the pixel is set to include a compensation voltage for compensating for a voltage decrease caused by the remaining portion of polarity inversion.

The present invention relates to a new method and apparatus for converting heat to electric energy. The invention exploits the rapid changes in spontaneous polarization that occur in ferroelectric materials during phase change. The invention permits robust and economical generation of electric energy from thermal energy, and it can be used in many different applications. In one aspect, the present invention relates to an apparatus for converting heat to electric energy comprising a pair of electrodes; a ferroelectric layer formed there between with a ferroelectric material characterized with a Curie temperature, T_c, such that when the temperature of the ferroelectric material is lower than T_c, the ferroelectric material is in a ferroelectric phase in which very powerful polarization is established spontaneously in the unit cells of the ferroelectric material, and when the temperature of the ferroelectric material is greater than T_c, spontaneous polarization is not established in the unit cells of the ferroelectric material; and a means for alternately delivering a flow of cold fluid and a flow of hot fluid to the ferroelectric layer so as to alternately cool the ferroelectric layer at a first temperature T_L that is lower than T_c, and heat the ferroelectric layer at a second temperature T_H that is higher than T_c, thereby the ferroelectric material of the ferroelectric layer undergoes alternating phase transitions between the ferroelectric phase and the paraelectric phase with temperature cycling.

The invention discloses an apparatus for measuring the ferroelectric hysteresis of ferroelectric materials which is based on a current measurement circuit, as well as a measurement method thereof. The invention inputs a simulated output signal generated by a computer processing unit into a high voltage amplifier through a signal source and a data acquisition board, thus giving excitation voltage to a sample being tested, and then through a sampling resistance R₀, sampled current signal is input into a signal regulating module through an operational amplifier, and then the sampled current signal is transmitted back into the computer processing unit through the data acquisition board. By separating the current signal acquired from the measurement into three parts as linear polarization, non-linear polarization and electric loss, the measurement system is provided with not only the function of measuring the P-E relationship, but also the function of acquiring the relationship between the real spontaneous polarization and induced polarization of the dielectric substance being tested and the field intensity. Furthermore, by superimposing actuating signal of a small alternative electric field to a bias electric field with constant intensity and synchronously collecting the corresponding change information of the polarization intensity of the sample being tested, then the reversible permittivity can be acquired.

A voltage corresponding to desired image data is applied to a ferroelectric liquid crystal having a spontaneous polarization at a predetermined cycle to rewrite the displayed image (period A), and then, all voltages applied to the ferroelectric liquid crystal are removed (timing C) to retain the displayed image before the removal (period B). A gate selection period (voltage application period to the ferroelectric liquid crystal) t₂ before stopping the voltage application is set longer than a gate selection period (voltage application period to the ferroelectric liquid crystal) t₁ in the normal display. Increasing the voltage application period to the ferroelectric liquid crystal provides a sufficient response of the liquid crystal during the gate selection period, thereby realizing high memory ability.

An object is to improve a positive hole injection efficiency into an active layer in a nitride semiconductor light-emitting device. The nitride semiconductor light-emitting device is formed by stacking nitride semiconductor crystals each of which contains Al and has a polar or semipolar surface either serving as a growth face. The device includes an active layer (103), and first and second composition-graded layers (102, 104). The active layer (103) is interposed between the first and second composition-graded layers (102, 104). Each one of the first and second composition-graded layers is composition-graded so that an Al composition value is rendered smaller as each one of the first and second composition-graded layers (102, 104) comes close to a side where a sum of spontaneous polarization and piezoelectric polarization is negative.

On an insulating film on a surface of a substrate a lower electrode is formed, and on the lower electrode a ferroelectric film is formed at a temperature equal to or less than 450 degree centigrade, or at a temperature equal to or less than the Curie temperature of the ferroelectric film. Thereafter, on the ferroelectric film an upper electrode is formed, and after the upper electrode is formed, heat treatment is applied at a temperature higher than the deposition temperature or the Curie temperature. Thereby, a ferroelectric film having a particular crystal orientation is formed, and when heat treatment at a temperature higher than the deposition temperature or the Curie temperature is applied to transform once to a paraelectric phase, without altering a crystal structure, a ferroelectric phase can be obtained, and thereby a ferroelectric film aligned in the spontaneous polarization orientations of the respective domains can be obtained.

A normally-off type field-controlled channel GaN heterojunction diode belongs to the technical field of semiconductor devices. The invention adopts the technology of combining insulating layer-groove, modulation doping and groove-modulation doping to change the conductive channel structure of the existing GaN heterojunction diode, and convert the original normally-on spontaneously polarized GaN heterojunction The junction conductive channel is changed into a normally-off field-controlled conductive channel combining spontaneous polarization and piezoelectric polarization in the present invention, which realizes the field-controlled characteristics of the GaN heterojunction diode conductive channel and reduces the forward conduction resistance and enhanced reverse cut-off capability. The invention has lower forward conduction resistance and power consumption, stronger reverse cut-off ability, and is compatible with AlGaN/GaN HEMT power switching device technology, which is beneficial to the application of the device.

A semiconductor device has a sapphire substrate, a semiconductor layer made of GaN provided on the sapphire substrate, a multilayer film provided on the semiconductor layer, and an electrode in ohmic contact with the multilayer film. The multilayer film has been formed by alternately stacking two types of semiconductor layers having different amounts of piezopolarization or different amounts of spontaneous polarization and each containing an n-type impurity so that electrons are induced at the interface between the two types of semiconductor layers. This allows the contact resistance between the electrode and the multilayer film and a parasitic resistance in a current transmission path to be reduced to values lower than in a conventional semiconductor device.

The invention relates to a ferroelectric metal hetero-junction based memristor; wherein the memristor material-ferroelectric lithium niobate is prepared by a pulse laser deposition system; monocrystal LN target material (4) is fixed on a target platform (5) of the pulse laser deposition system, and is placed in a growth chamber (6) of a pulse laser deposition film-making system; the vacuum in the growth chamber is pumped to be below 0.8*10-4Pa, oxygen gas flows in, and the oxygen pressure is from 25 to 35Pa, the substrate temperature is heated from 600-650 DEG; a KrF excimer laser is started, and the deposition time is determined according to monopulse energy; in-situ 500-650 DEG annealing is carried out 20-90min; the film has spontaneous polarization and 180-degree domain boundary; the memristor ferroelectric lithium niobate film is clamped between two metal electrode films to form a memristor unit with a miniature sandwich structure; the device can be applied to a high-density low-energy-consumption nonvolatile resistance random access memory.

A switchable element. The element includes a source electrode, a drain electrode, a conducting channel between the source electrode and the drain electrode, and a gate with multiferroic material being switchable, by application of an electrical signal to the gate, between a first switching state with a first spontaneous polarization direction and a second switching state with a second spontaneous polarization direction. The conducting channel is magnetoresistive, and a magnetic field strength at the conducting channel in the first switching state is different than a magnetic field strength in the second switching state, whereby a current-voltage characteristic of the conducting channel is dependent on the switching state of the multiferroic material.

A projection display device includes: a light source unit including at least one light source configured to emit coherent light; an image light generation unit configured to generate an image light by modulating light emitted by the light source unit; a projection unit configured to project the image light; and a liquid crystal element, disposed in an optical path between the light source unit and the image light generation unit, configured to temporally change a phase and/or polarization of transmitted light, wherein: the liquid crystal element at least includes transparent electrodes respectively provided on opposing faces of a plurality of transparent substrates; a liquid crystal layer including smectic phase liquid crystal showing spontaneous polarization under voltage application is sandwiched between the transparent electrodes; and an AC voltage is applied to the liquid crystal layer through the transparent electrodes.

A III-nitride based field effect transistor obtains improved performance characteristics through manipulation of the relationship between the in-plane lattice constant of the interface of material layers. A high mobility two dimensional electron gas generated at the interface of the III-nitride materials permits high current conduction with low ON resistance, and is controllable through the manipulation of spontaneous polarization fields obtained according to the characteristics of the III-nitride material. The field effect transistor produced can be made to be a nominally on device where the in-plane lattice constants of the material forming the interface match. A nominally off device may be produced where one of the material layers has an in-plane lattice constant that is larger than that of the other layer material. The layer materials are preferably InAlGaN/GaN layers that are particularly tailored to the characteristics of the present invention.

The present disclosure relates to a semiconductor light-emitting device which includes: a light-emitting layer composed of an active layer and of barrier layers formed as superlattice layers and disposed on and under the active layer to relieve stresses applied to the active layer and reduce the sum of electric fields generated in the active layer by the spontaneous polarization and the piezo; an N-type contact layer injecting electrons into the light-emitting layer; and a P-type contact layer disposed opposite to the N-type contact layer with respect to the light-emitting layer and injecting holes into the light-emitting layer, wherein the active layer contains InGaN, and the barrier layers are formed by alternately stacking of an AlGaN thin film and an InGaN thin film.

A bright, and contrasty reflective display can be performed without using polarizer films, and display switching can be performed fast. A ferroelectric liquid crystal is sandwiched between substrates, and electrodes are formed face to face with each other in a direction parallel to the substrates. The ferroelectric liquid crystal, when no electric field is applied to it, goes into a planer state in which a helical axis becomes perpendicular to or almost perpendicular to the substrates, selectively reflecting light of specific wavelengths in a visible region. A driving circuit applies an electric field between the electrodes in a direction perpendicular to or almost perpendicular to the helical axis of the ferroelectric liquid crystal in the planer state. When an electric field equal to or greater than a threshold value is applied, the ferroelectric liquid crystal changes from a planer state due to a low electric field to a homeotropic state in which a helical structure disappears, going into a transparent state, wherein, in the homeotropic state, a cyclic change of refractive index disappears and liquid crystal molecules are arranged in the direction of the electric field. The change in this case is performed fast because the ferroelectric liquid crystal has spontaneous polarization. The ferroelectric liquid crystal may be filled between a pair of transparent substrates each having a transparent electrode formed thereon to apply electric fields in a direction parallel to or almost parallel to the helical axes.

The invention provides a rapid multifunctional electronic component temperature characteristic measuring device and instrument, and a testing cavity. Temperature characteristic curves of parameters such as capacitance, inductance, resistance, dielectric coefficients, dielectric loss, voltage-current curves and spontaneous polarization of a plurality of electronic components and material samples can be measured. The rapid multifunctional electronic component temperature characteristic measuring device and instrument and the testing cavity is small in size, light in weight, high in speed, high in automatic degree, multi-functional, high in precision and low in cost. The device, instrument and the testing cavity can be applied by an enterprise to rapidly detect temperature characteristics of electronic components, can also be used by scientific research laboratories to research temperature characteristics of specific parameters of the devices and the material samples, and can further be used in the aspect such as experiment demonstration and class teaching.

Periodic electrodes in a pattern of many lines are formed on a first surface of a nonlinear single crystal substrate. The nonlinear single crystal substrate is put in a vacuum chamber, and heated with a heater. Then, high voltage is applied to the nonlinear single crystal substrate. Thus, the direction of spontaneous polarization of the nonlinear single crystal substrate is reversed in portions facing to the periodic electrodes, which are referred to as reversed portions. After the nonlinear single crystal substrate is bonded to a support substrate, only non-reversed portions of the nonlinear single crystal substrate are removed by wet etching, and grooves with a high aspect ratio are left between the remaining reversed portions. The grooves are filled with an X-ray absorbing material such as gold. The grooves filled with the gold compose X-ray absorbing portions of a grid, while the reversed portions compose X-ray transparent portions.

A tunneling transistor is provided as an effective means for miniaturization of a semiconductor integrated circuit having nonvolatile memory. An insulating layer is disposed on a silicon substrate. A source and a drain are disposed on the insulating layer, with an insulator of a few nanometers in thickness that provides a tunnel barrier being interposed between the source and the drain. A ferroelectric layer that exhibits spontaneous polarization is disposed directly above a region of the source that is adjacent to the insulator. With this construction, when the ferroelectric layer is polarized in a predetermined direction, at least a portion of the region of the source adjacent to the insulator forms a depletion region, with it being possible to vary the amount of current tunneling through the insulator depending on whether the ferroelectric layer is polarized or not.

The present invention provide a high-luminosity stress-stimulated luminescent material which emits visible light even in daylight, a manufacturing method thereof, and a typical example of the use thereof. The stress-stimulated luminescent material of the present invention satisfies conditions for light emission by at least one of: a luminescence mechanism using static electricity caused by friction; a luminescence mechanism using micro plasma caused by friction; a luminescence mechanism using a piezoelectric effect caused by strain; a luminescence mechanism using lattice defect; and a luminescence mechanism using thermal generation. For example, in case where a base material made of at least one type of aluminate is includes as the stress-stimulated luminescent material, the base material includes a crystal structure with spontaneous polarization, e.g. α-SrAl₂O₄, in order to realize the luminescence mechanism using the piezoelectric effect caused by strain.

A GaN-based semiconductor light-emitting element capable of suppressing the occurrence of piezoelectric spontaneous polarization in the thickness direction of an active layer and reducing the driving voltage of a light-emitting diode is provided. The GaN-based semiconductor light-emitting element has a structure with a first GaN-based compound semiconductor layer 21 having the top face parallel to the a-plane and having a first conductivity type, an active layer 22 having the top face parallel to the a-plane, a second GaN-based compound semiconductor layer 23 having the top face parallel to the a-plane and having a second conductivity type, and a contact layer 24 composed of a GaN-based compound semiconductor and having the top face parallel to the a-plane, stacked in that order. The GaN-based semiconductor light-emitting element further includes a first electrode 25 disposed on the first GaN-based compound semiconductor layer 21 and a second electrode 26 disposed on the contact layer 24.

The invention discloses a ferroelectric film grid reinforced GaN heterojunction field effect transistor and belongs to the technical field of microelectronics. The ferroelectric film grid reinforced GaN heterojunction field effect transistor comprises a GaN heterojunction formed by a (0001) crystal orientation GaN film and an AlxGal-xN (x is more than 0 but less than and equal to 1.) film, wherein a grid electrode, a source electrode and a drain electrode are formed on the AlxGal-xN film; a grid medium film is arranged between the grid electrode and the AlxGal-xN film; and the grid medium film may be a LiNbO3(LNO) ferroelectric film, a LiTaO3(LTO) ferroelectric film, or an M element-doped LNO or LTO ferroelectric film. Due to the ferroelectric spontaneous polarization in the LNO or LTO ferroelectric film in the C+ direction, 2DEG in an AlGaN/GaN heterojunction is completely exhausted, so that the ferroelectric film grid reinforced GaN heterojunction field effect transistor has a characteristic of normal close, namely a reinforced apparatus is formed; and the ferroelectric film grid reinforced GaN heterojunction field effect transistor has the characteristics of simple structure, simple implementing process, high repeatability and high stability and reliability.