DE102019213367A1 - Ferroelectrics, as well as suitable processes and uses therefor - Google Patents

Abstract

Describes a ferroelectrics which has a piezoelectric material with a hafnium content of 2% or less, the use of such a ferroelectrics in energy generation and for implementation in memory, processor and sensor technologies, the use of a ferroelectrics in which the energy requirement is reduced Superconductivity is lowered, as well as a method for producing a ferroelectrics in which a sintering method is used.

Description

The present invention relates to a ferroelectrics and suitable methods and uses therefor.

Conventional ferroelectrics, particularly piezoelectric materials with perovskite structure containing zirconium and titanium inside the molecular structure (B-side) such as PZT and BZT based materials, are the most common piezoelectric materials on the market.

Zirconium oxide is used in the production of e.g. PZT (lead zirconate titanate). When it is mined in a mine, zirconium oxide has primarily a hafnium content of 2-3% due to its natural occurrence, although up to 5% is also possible. Thus, PZT materials are usually made with a zirconium oxide that contains 2 - 2.5% hafnium.

Furthermore, from the U.S. 7,059,709 It is already known that the reduction of hafnium compared to the natural occurrence has a positive effect on certain piezoelectric properties, in particular when using thin layers, such as for example in inkjet printers. A disadvantage of the prior art, however, is that the results have so far only been able to be achieved in special applications, such as, for example, in the case of inkjet printers.

The objects of the present invention are to overcome the disadvantages of the prior art. Furthermore, the aim is to improve the piezoelectric properties of ferroelectrics not only for thin-film technologies. In addition, the proportion of the rhombohedral structure of the ferroelectrics is to be increased.

These objects are achieved with the subjects of claims 1, 9, 10, 11 and 12.

According to the invention it has been shown that ferroelectrics z. B. PZT, and materials that are made with a zirconium oxide that contains less than 2% hafnium, have significantly better piezoelectric properties. The zirconium oxide used should preferably be as pure as possible, i.e. it should contain almost no hafnium at all. If a zirconium oxide with a relevant hafnium content of z. B. is used over 2%, then the hafnium has the property of supporting the tetragonal phase and at the same time suppressing the rhombohedral phase. In contrast, if a relevant proportion of hafnium of z. B. is used below 2%, preferably below 1%, then the hafnium has the property of suppressing the rhombohedral phase less.

Due to the reduction in the proportion of hafnium by less than 2%, which does not occur naturally, the ferroelectrics according to the application can be used on the one hand for energy generation and on the other hand for implementation in memory, processor and sensor technology. It has also been shown that the energy requirement is reduced when and by the superconductivity.

Further developments of the features according to the invention are the subject of the subclaims.

According to the application, a dielectric loss factor of 0.2% or less is advantageously achieved with a hafnium proportion that is reduced compared to the natural occurrence. This is achieved in particular with a constant dielectric constant and / or piezoelectric effect d33. Thus, the ferroelectrics according to the application can lead to considerable energy savings when using electrical components or circuits.

Advantageously, a two-phase or multiphase material is also used as ferroelectrics, so that the rhombohedral phase is increased or less suppressed with a reduced hafnium content. By increasing the rhombohedral phase, the piezoelectric properties are increased.

A further advantage has been shown to be that with a reduced hafnium content of equal to or less than 2% with constant electrical loss, ie between comparable ferroelectrics with and without a reduced hafnium content, an increase in the relative dielectric constant and / or the piezoelectric effect d33 of at least 50% or more is achieved. Furthermore, if the relative dielectric constant remains almost the same, a Reduction in electrical loss of at least 50% achieved. Furthermore, it has advantageously been shown that, with the piezoelectric effect d33 remaining the same, a reduction in the electrical loss of at least 50% is achieved. These effects also contribute to an improved energy balance when they are used. Due to the improved energy balance, the packing density of the components can be increased, whereby higher clocks or clock frequencies can also be achieved compared to conventional components.

Based on the knowledge according to the invention of increasing the rhombohedral phase by reducing the hafnium content, it is advantageously possible for materials, in particular not only to be produced using thin-film technology, but in material thicknesses of between 5 nanometers up to approximately 4 cm.

As special materials, piezoelectric materials based on: PZT (lead zirconate titanate), PLZT (lead lanthanum zirconate titanate), PSZT (lead strontium zirconate titanate), PLSZT (lead lanthanum strontium zirconate titanate), BZT (barium zirconate titanate), and / or BSZT (barium strontium zirconate titanate) can be used, in which the rhombohedral structure can be increased by reducing the proportion of hafnium, whereby the piezoelectric properties are improved. So if a PZT material is produced that is set in the direction of a rhombohedral phase, i.e. contains a zirconium / titanium ratio of Zr52% / Ti48% or more zirconium, then the effect becomes more and more noticeable.

For example, with PZT with a quasi-hafnium-free zirconium oxide (highly pure zirconium oxide, reactor grade), which contains a Zr / Ti ratio of approx. Zr53% / Ti47%, or more zirconium, a phase-critical area can be reached in which the rhombohedral phase and the tetragonal phase are present at the same time. Such a material has excellent properties in almost every respect (dielectric constant, piezoelectric deformation and loss factor), which can be significantly better than comparable PZT materials.

Further advantageous developments are the subject of the further subclaims.

In summary, it should be stated that an improvement in the piezoelectric properties of the above-mentioned piezoelectric materials of 100% or more is achieved in those materials that are produced with a zirconium oxide that contains less than 2 or 1.5% hafnium, compared to identical materials, made with a zirconia containing 2% or more hafnium. Highly pure zirconium oxide is preferably used, and as little hafnium as possible. In general, it has been shown that hafnium-reduced or hafnium-free piezoelectric material, which is based on z. B. PZT or BZT based, the best properties of hard PZT's combined with the good properties of soft PZT's and can therefore be used excellently in applications for energy conversion.

The following examples show the respective piezoelectric properties between commercially available piezoelectric materials as ferroelectrics with a naturally contained hafnium proportion compared with a reduced hafnium proportion.

Basically, the lower the dielectric losses, the lower the other values of the piezoelectric properties, such as the relative dielectric constant and the piezoelectric effect.

According to Example 1, it can be seen that the material according to the application with a reduced hafnium content, here less than 0.01%, compared to the best comparable conventional material with a natural hafnium content, here 0.6%, from industry has significantly higher values for the relative dielectric constant and has the piezoelectric effect. Example 1: Improvement of the dielectric constant and the piezoelectric effect material Del-Piezo DL-40 with Hafnium 0.6% QPM PZT # 1 Hafnium content <0.01% relative dielectric constant ε 350 1574 dielectric losses tan δ 0.3% 0.2% piezoelectric effect d33 145 361 Example 2: Improvement of the dielectric losses material Del-Piezo DL-45HD with Hafnium 0.6% QPM PZT # 1 Hafnium content <0.01% relative dielectric constant ε 1550 1574 dielectric losses tan δ 0.5% 0.2% piezoelectric effect d33 360 361 Example 3: Improvement of the dielectric losses material Standard APC material 841 with hafnium 0.6% QPM PZT # 1 Hafnium content <0.01% relative dielectric constant ε 1375 1374 dielectric losses tan δ 0.4% 0.2% piezoelectric effect d33 300 315

According to example 2 and 3 it is shown that the material according to the application with a reduced hafnium content, here less than 0.01%, with comparable values of the piezoelectric properties such as relative dielectric constant and the piezoelectric effect d33, result in significantly less dielectric loss. Here, the dielectric loss is reduced by, for example, at least 50% or more. Example 4: further improved dielectric losses material QPM PZT # 2 Hafnium content <0.01% relative dielectric constant ε 1347 dielectric losses tan δ 0.1% piezoelectric effect d33 300

According to example 4 it is made clear that a dielectric loss of 0.1% can also be achieved, depending on the material composition, with almost constant piezoelectric properties such as the relative dielectric constant and the piezoelectric effect, and shows a further halving of the losses with only slightly smaller values in the case of the relative Dielectric constant and the piezoelectric effect.

In addition to reducing the dissipation factor, the ferroelectrics can still be converted to the state of superconductivity by reducing or even removing hafnium in order to significantly reduce the energy losses in corresponding applications, such as in electrical components or circuits. It is well known that the superconductivity of a material is related to the formation or the presence of a rhombohedral phase. This relationship was recognized when researching the interface between lanthanum aluminate and strontium titanate. According to this, this material, consisting of lanthanum aluminate and strontium titanate, changes to a rhombohedral phase below 30 Kelvin, whereby its electrical resistance steadily decreases with falling temperature. Superconductivity occurs below 200 millikelvin.

According to the application, the reduction or removal of hafnium thus favors the formation of a rhombohedral phase at room temperature, which enables high-temperature superconductivity.

For example, a compound QPM PZT with the elements lead Pb, strontium Sr, zirconium Zr, titanium Ti, iron Fe, lanthanum La, aluminum AL and nickel Ni with a hafnium content below 0.01% has a corresponding superconductivity .

According to the 1 it can be seen to what extent the rhombohedral structure or phase was significantly increased by reducing the hafnium content. The measurement was carried out using common diffractometer measuring methods, as described for example in the book "Rietveld Refinement, Practical Diffraction Pattern Analysis using TOPAS" by Dinnebier, Leineweber, Evans, 2018, in the Debye-Scherrer Geometry, where the intensity is determined in relation to the diffraction angle theta. The respective phases are determined from the measured total intensity signal convoluted.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 7059709 [0004]

Claims (13)

Ferroelectrics, which have a piezoelectric material with a hafnium content of 2%, preferably 1%, or less. Ferroelectrics after Claim 1 , the dielectric loss factor being 0.2% or less, in particular with a dielectric constant ε of more than 1000, preferably of 1574, and a piezoelectric effect d33 of more than 300, preferably of 315 or 361. Ferroelectrics according to one of the Claims 1 or 2 , which consists of a two- or multi-phase material, the rhombohedral phase is preferably increased. Ferroelectrics according to one of the Claims 1 to 3rd which achieves an increase in the relative dielectric constant and / or the piezoelectric effect d33 of at least 50% with constant electrical loss. Ferroelectrics according to one of the Claims 1 to 3rd which achieves a reduction in electrical loss of at least 50% with the same relative dielectric constant. Ferroelectrics according to one of the Claims 1 to 3rd which, with the piezoelectric effect d33 remaining the same, achieves a reduction in electrical loss of at least 50%. Ferroelectrics according to one of the Claims 1 to 6th which has a thickness of at least 5 nanometers up to 4 cm. Ferroelectrics according to one of the Claims 1 to 5 , wherein the piezoelectric material is a PZT, BZT or the like. Use of a ferroelectrics, in particular according to one of the Claims 1 to 7th , in energy generation. Use of a ferroelectrics, in particular according to one of the Claims 1 to 7th , for implementation in memory, processor and sensor technologies. Use of a ferroelectrics, in particular according to one of the Claims 1 to 7th , whereby the energy requirement is reduced by superconductivity, in particular high-temperature superconductivity. Method for producing a ferroelectrics according to one of the Claims 1 to 7th , using a sintering process. Procedure according to Claim 12 , whereby a ZrO2 powder is used for production.

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