Patent Application
20230245809
The present invention relates to a nanogranular magnetic film and an electronic component.
Recent mobile devices, such as smartphones and smartwatches, have been required to have a larger display, a larger battery capacity, a smaller size, and less weight at the same time. The requirements of having a larger display and a larger battery capacity are inconsistent with the requirements of having a smaller size and less weight. To achieve these inconsistent requirements, circuit boards have been required to have a smaller size. In particular, power supply circuits, which occupy large areas in the circuit boards, have been required to have a smaller size. More in particular, reducing the size of inductors, which occupy large areas in the power supply circuits, enables the power supply circuits to be smaller.
One way to reduce the size of the inductors is to enable the power supply circuits to be used at higher frequencies. To enable the power supply circuits to be used at higher frequencies, switching elements included in the power supply circuits are required to be operable at high frequencies.
In recent years, semiconductors such as GaN and SiC described in Patent Document 1 have been practically used as semiconductors included in the switching elements. For example, as described in Patent Document 2, semiconductors other than silicon have been included in the switching elements.
Including the semiconductors (e.g., GaN) having excellent high-frequency properties in the switching elements enables the switching elements to operate at high frequencies. As the switching elements have become operable at high frequencies, it has become possible to increase the operating frequency of the power supply circuits, meaning that the power supply circuits have become usable at higher frequencies.
As the power supply circuits have become usable at higher frequencies, small inductors that can operate at high frequencies and reduce the size of the power supply circuits have been in demand.
To achieve such a small inductor operable at high frequencies, use of a thin film inductor is effective. The thin film inductor is manufactured by laminating a coil, a terminal, a magnetic film, and an insulating layer or the like on a substrate through semiconductor manufacturing processes. In the thin film inductor, the magnetic film is the magnetic core of the thin film inductor. Thus, it is essential that the magnetic film of the thin film inductor have the requisite properties to enable the thin film inductor to have these properties.
Patent Document 3 discloses a nanogranular magnetic film having a structure including nano-sized crystals dispersed in an insulating matrix. The nano-sized crystals include mainly a metal simple substance, an alloy, or a compound. Examples of the metal simple substance include a simple substance of Fe, a simple substance of Co, and a simple substance of Ni. Examples of the alloy include an alloy containing at least one selected from the group consisting of Fe, Co, and Ni. Examples of the compound include a compound containing at least one selected from the group consisting of Fe, Co, and Ni.
Nanogranular magnetic films have a higher saturation magnetic flux density (Bs) than ferrite materials. The nanogranular magnetic films further have a higher specific resistance (p) than normal metal materials. For having a high saturation magnetic flux density (Bs) and a high specific resistance (p), the nanogranular magnetic films have a high permeability even at high frequencies. Because the nanogranular magnetic films have a high permeability, application of the nanogranular magnetic films to high-frequency thin film components (e.g., thin film inductors) has been under consideration.
Unfortunately, although the saturation magnetic flux density (Bs) of the nanogranular magnetic films is typically higher than that of magnetic films including typical ferrite materials, the saturation magnetic flux density (Bs) is lower than that of other typical magnetic films (e.g., CZT) for thin film inductors. The saturation magnetic flux density (Bs) of a magnetic film is in proportion to the volume of a magnetic core including the magnetic film and is roughly in proportion to the area of an inductor including the magnetic film. Consequently, the nanogranular magnetic films are required to have an increased saturation magnetic flux density (Bs).
It is an object of the present invention to provide a nanogranular magnetic film having a high saturation magnetic flux density (Bs).
To achieve the above object, a nanogranular magnetic film according to the present invention comprises a structure including first phases comprised of nano-domains dispersed in a second phase, wherein
the first phases include at least one selected from the group consisting of Fe, Co, and Ni,
the second phase includes at least one selected from the group consisting of O, N, and F,
a ratio of a volume of the first phases to a total volume of the first phases and the second phase is 65% or less, and
a noble gas element is included at 0.20 at % or more and 0.80 at % or less.
In the nanogranular magnetic film according to the present invention, the first phases comprised of the nano-domains may have an average size of 30 nm or less.
In the nanogranular magnetic film according to the present invention, a total of Fe, Co, and Ni may occupy 75 at % or more in the first phases.
An electronic component according to the present invention includes the above-mentioned nanogranular magnetic film.
Hereinafter, an embodiment of the present invention will be explained with reference to the drawings.
As shown in
The first phases 11 (nano-domains) have a nanoscale average size, namely an average size of 50 nm or less. The average size of the first phases 11 (nano-domains) may be 30 nm or less. The size of the respective first phases 11 (nano-domains) may be measured by any method. For example, the equivalent circular diameter of each first phase 11 (nano-domain) in a cross section of the nanogranular magnetic film 1 may be regarded as the size of the first phase 11 (nano-domain).
Note that the equivalent circular diameter of the first phase 11 (nano-domain) in the cross section of the nanogranular magnetic film 1 means the diameter of a circle having the same area as the area of the first phase 11 (nano-domain) in the cross section of the nanogranular magnetic film 1.
The first phases 11 may be composed of a pure substance or may be composed of a mixture.
The first phases 11 are phases including a metal element. Specifically, the first phases 11 include at least one selected from the group consisting of Fe, Co, and Ni. The at least one element selected from the group consisting of Fe, Co, and Ni may be included in the first phases 11 in any way. For example, the at least one element selected from the group consisting of Fe, Co, and Ni may be included in the first phases 11 as a simple substance, as an alloy of the at least one element and another metal element, or as a compound of the at least one element and another element. The compound in the first phases 11 may be an oxide magnetic material, such as a ferrite.
The total amount of Fe, Co, and/or Ni in the first phases 11 is not limited to particular values. The ratio of the total amount of Fe, Co, and Ni in the first phases 11 to the total amount of Fe, Co, Ni, X1, and X2 in the first phases 11 may be 75 at % or more and may be 80 at % or more.
X1 is a metalloid element. For example, X1 may be at least one metalloid element selected from the group consisting of B, Si, P, C, and Ge.
X2 is a metal element other than Fe, Co, and Ni. For example, X2 may be at least one metal element selected from the group consisting of Cr, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Cu, Ag, Zn, Al, Sn, Bi, Y, La, and Mg, or at least one metal element selected from the group consisting of Cr, V, Mo, Zr, Nb, Ti, Mn, Zn, Al, Cu, and Y.
The first phases 11 may include elements other than Fe, Co, Ni, X1, and X2. The ratio of the total amount of the elements other than Fe, Co, Ni, X1, and X2 in the first phases 11 to the total amount of Fe, Co, Ni, X1, and X2 in the first phases 11 may be 5 at % or less.
The second phase 12 may be composed of a pure substance or may be composed of a mixture.
The second phase 12 is a phase including a non-metal element. Specifically, the second phase 12 includes at least one selected from the group consisting of O, N, and F. The at least one element selected from the group consisting of O, N, and F may be included in the second phase 12 in any way. For example, the at least one element selected from the group consisting of O, N, and F may be included in the second phase 12 as a compound of the at least one element and another element.
The compound in the second phase 12 may be any compound. For example, the compound may be SiO2, Al2O3, AlN, ZnO, MgF2, SnO2, GaO2, GeO2, Si3N4·Al2O3, and BN. The compound may be at least one selected from SiO2, Al2O3, AlN, ZnO, MgF2, SnO2, GaO2, GeO2, and Si3N4·Al2O3.
The ratio of the volume of the first phases 11 to the total volume of the first phases 11 and the second phase 12 is 65% or less. In other words, provided that V1 denotes the proportion of the volume of the first phases 11 and V2 denotes the proportion of the volume of the second phase 12, V1/(V1+V2) has a value of 0.65 or less. The value of V1/(V1+V2) may be 0.60 or less. An excessively large ratio of the volume of the first phases 11 to the total volume of the first phases 11 and the second phase 12 makes it difficult for a noble gas element (described later) to occupy a large proportion of the nanogranular magnetic film 1.
There is no lower limit of the ratio of the volume of the first phases 11 to the total volume of the first phases 11 and the second phase 12. The lower limit may be 30% or more. In other words, the value of V1/(V1+V2) may be 0.30 or more. The value of V1/(V1+V2) may be 0.40 or more. The smaller the ratio of the volume of the first phases 11 to the total volume of the first phases 11 and the second phase 12, the higher the specific resistance, and unfortunately the lower the saturation magnetic flux density.
The ratio of the volume of the first phases 11 to the total volume of the first phases 11 and the second phase 12 may be measured by any method. For example, the ratio can be calculated from the results of measurement of the nanogranular magnetic film 1 using XRF. The ratio may also be calculated from the ratio of the area of the first phases 11 to the total area of the first phases 11 and the second phase 12 through observation of a cross section of the nanogranular magnetic film 1 using a TEM. In this case, the ratio in terms of area is converted to the ratio in terms of volume.
The nanogranular magnetic film 1 may include only the first phases 11 and the second phase 12. The nanogranular magnetic film 1 may further include different phases other than the first phases 11 and the second phase 12. The different phases may occupy any proportion. The different phases may occupy 10% or less of the area of a cross section of the nanogranular magnetic film 1 observed with a TEM. The different phases may partly or entirely be a void.
The nanogranular magnetic film 1 according to the present embodiment includes the noble gas element at 0.20 at % or more and 0.80 at % or less. Including the noble gas element within this range, especially at 0.20 at % or more, enables the saturation magnetic flux density (Bs) of the nanogranular magnetic film 1 to be particularly increased without its composition being substantially changed.
The noble gas element is not limited to particular elements. For example, the noble gas element may be at least one selected from the group consisting of Ar, Kr, and Xe, or may be Ar.
The nanogranular magnetic film 1 may have any thickness. For example, the thickness may be 0.05 m or more and 200 m or less. A suitable thickness may be appropriately determined based on usage. The actual thickness of the nanogranular magnetic film 1 may be measured by any method. For example, the thickness can be measured with a TEM, a SEM, or a surface profiler. Also, the reliability of measurement results may be checked by correlating multiple measurement apparatuses with each other in advance.
Hereinafter, a method of manufacturing the nanogranular magnetic film 1 (soft magnetic thin film) according to the present embodiment will be explained.
The soft magnetic thin film according to the present embodiment may be manufactured by any method, such as sputtering.
First, a substrate on which to form the nanogranular magnetic film is prepared. The substrate may be any substrate. For example, the substrate may be a silicon substrate, a silicon substrate having a thermal oxide film, a ferrite substrate, a non-magnetic ferrite substrate, a sapphire substrate, a glass substrate, a glass epoxy substrate, or the like. However, the substrate is not limited to these substrates. Any of various ceramic substrates or semiconductor substrates can be used. When it is difficult to check various properties using only the thin film to be formed on the substrate (sample substrate), a dummy substrate may also be used as necessary. The thin film may be formed on the sample substrate and the dummy substrate simultaneously, and the properties of the thin film on the dummy substrate may be regarded as the properties of the thin film on the sample substrate.
Next, a sputtering apparatus is prepared. The sputtering apparatus is capable of multi-target simultaneous sputtering. The sputtering apparatus is further capable of changing the distance between sputtering targets and the substrate per sputtering target.
Next, a metal sputtering target and a ceramic sputtering target are prepared as the sputtering targets. The metal sputtering target is a sputtering target mainly including Fe, Co, and/or Ni. The ceramic sputtering target is a sputtering target mainly including the compound in the second phase 12. The composition of the metal sputtering target and the composition of the ceramic sputtering target are appropriately adjusted so that the nanogranular magnetic film has a desired compositional ratio.
Next, the metal sputtering target and the ceramic sputtering target are attached to a sputter gun for metal and a sputter gun for ceramics of the sputtering apparatus respectively. Then, the nanogranular magnetic film is formed on the substrate by multi-target simultaneous sputtering.
Controlling the voltage applied to each sputtering target can control the film deposition speed and the ratio of the volume of the first phases to the total volume of the first phases and the second phase. The film deposition speed can be, for example, 1 Å/s or more and 100 Å/s or less.
Controlling the film deposition speed and the film deposition time can control the thickness of the nanogranular magnetic film.
The present inventors have found that controlling the gas pressure of the noble gas during sputtering and/or the distance between the sputtering targets and the sample substrate can control the amount of the noble gas element in the nanogranular magnetic film.
Specifically, lowering the gas pressure of the noble gas during sputtering can increase the amount of the noble gas element in the nanogranular magnetic film. Also, reducing the distance between the sputtering targets and the sample substrate can increase the amount of the noble gas element in the nanogranular magnetic film.
Now, a mechanism by which the noble gas element is introduced in the nanogranular magnetic film will be explained.
In sputtering, the sputtering targets have negative charge. The noble gas atoms between the sputtering targets and the substrate are ionized to produce noble gas positive ions and electrons. The noble gas positive ions undergo elastic collision with the sputtering targets having negative charge. At this time, the noble gas positive ions receive electrons from the sputtering targets to become noble gas atoms. In response to the kinetic energy of the noble gas positive ions, sputtering particles are sputtered out of the sputtering targets. These sputtering particles are deposited on the substrate to form a sputtering film.
At the same time as the sputtering particles are sputtered out of the sputtering targets, the noble gas atoms, which are produced when the noble gas positive ions undergo elastic collision with the sputtering targets and receive the electrons, recoil from the sputtering targets. The recoiled noble gas atoms are introduced in the deposited sputtering film.
The shorter the distance between the sputtering targets and the substrate, the less likely it is for the noble gas atoms to undergo elastic collision with the each other before reaching the substrate. Consequently, the shorter the distance between the sputtering targets and the substrate, the larger the amount of the noble gas element in the nanogranular magnetic film.
Also, especially when the distance between the ceramic sputtering target and the substrate is long, the amount of the noble gas element in the nanogranular magnetic film is likely to be small. In contrast, changing the distance between the metal sputtering target and the substrate is not likely to change the amount of the noble gas element. Consequently, bringing only the ceramic sputtering target closer to the substrate can increase the amount of the noble gas element. Preferably, the amount of the noble gas element in the nanogranular magnetic film is increased so that the amount is controlled within 0.20 at % or more and 0.80 at % or less. When the physical distance between the metal sputtering target and the ceramic sputtering target is too close, plasmas produced on each sputtering target at the time of film formation may interfere with each other and cause unstable discharge.
The distance between the ceramic sputtering target and the substrate may be changed by any method. The distance is changed by a method appropriate for the sputtering apparatus. Typically, the sputter gun for ceramics is moved to change the distance between the ceramic sputtering target and the substrate.
When only moving the sputter gun for ceramics cannot reduce the distance between the ceramic sputtering target and the substrate to an intended distance, for example, the substrate holder where the substrate is attached may be moved closer to the sputter gun for ceramics than a specified value. Also, a jig or a shutter around the substrate may be detached. Further, a spacer may be attached between a transport tray and the substrate, or an aluminum plate may be attached between the substrate and the substrate holder. In this case, the sputter gun for metal is moved as necessary to change the distance between the sputter gun for metal and the substrate as well.
Conversely, when only moving the sputter gun for ceramics cannot increase the distance between the ceramic sputtering target and the substrate to an intended distance, for example, the loading position of the substrate may be moved farther from the sputter gun for ceramics than a specified value. In this case, the sputter gun for metal is moved as necessary to change the distance between the sputter gun for metal and the substrate as well.
The magnetic properties of the nanogranular magnetic film may be measured by any method. For example, a vibrating sample magnetometer (VSM) can be used for measurement.
Hereinabove, one embodiment of the present invention has been explained, but the present invention is not to be limited to the embodiment.
The nanogranular magnetic film according to the present embodiment may be used for any purpose. A magnetic material including the nanogranular magnetic film is suitable for electronic components that are particularly used at a high frequency and are required to have a high saturation magnetic flux density (Bs). Examples of the electronic components include a perpendicular recording medium, a TMR head for a magnetoresistive random access memory (MRAM), a magneto-optical element, a thin film inductor, a noise filter, and a high-frequency capacitor.
The magnetic material including the nanogranular magnetic film in the above-mentioned electronic components may have a single-layer structure including only the nanogranular magnetic film, or may have a multilayer structure including the nanogranular magnetic film and other films (e.g., SiO2 films) containing other materials. The number of layers is not limited to particular numbers.
Hereinafter, the present invention will be specifically explained with examples.
Two silicon substrates (6×6×0.6 mmt) each having a thermal oxide film were prepared as sample substrates for measurement with a VSM. One silicon substrate (6×6×0.6 mmt) having a thermal oxide film with a resist (length: 6 mm, width: 0.5 to 1 mm) thereon was prepared as a dummy substrate for film thickness measurement. One sapphire substrate (p 2 inches, 0.4 mmt) was prepared as a dummy substrate for composition check. On each of these substrates, a nanogranular magnetic film was formed simultaneously. A multi-target simultaneous sputtering apparatus (ES340 manufactured by EIKO Corporation) was used for film formation. Further details will be explained below.
In Experiment 1, a metal sputtering target made of an alloy having an atomic ratio of Fe60Co40 and a ceramic sputtering target made of SiO2 were prepared as sputtering targets. Next, the sputtering targets were attached to different sputter guns.
In Experiment 1, the gas pressure of Ar during sputtering was fixed to 0.4 Pa. The distance (TS distance) between the ceramic sputtering target and the sample substrates was set to a value shown in Table 1 to control the amount of Ar in the nanogranular magnetic film.
When multi-target simultaneous sputtering was performed with the above-mentioned apparatus, simultaneously reducing the TS distance and the distance between the metal sputtering target and the sample substrates was not preferable. It was because plasmas produced on each sputtering target would interfere with each other and cause unstable discharge. Thus, the distance between the metal sputtering target and the sample substrates was fixed to 90 mm, at which the above-mentioned phenomenon was not caused.
Sputtering was performed with controlled power input to each sputtering target so that the ratio of the volume of first phases to the total volume of the first phases and a second phase was about 55% and the film deposition speed was 1.0 Å/s, to form the nanogranular magnetic film. The nanogranular magnetic film had a thickness of 300 nm. The thickness of the nanogranular magnetic film was measured with a surface profiler (KLA-Tencor P-16+), which had been correlated with a TEM in advance. Specifically, the actual thickness of the thin film formed on the dummy substrate for film thickness measurement was measured with the surface profiler. The measured film thickness was regarded as the actual film thickness of each sample.
The nanogranular magnetic film formed on the sapphire substrate was measured with an XRF spectrometer (Primus IV manufactured by Rigaku Corporation) to calculate the ratio of the volume of the first phases to the total volume of the first phases and the second phase. Table 1 shows the results.
Using a TEM (JEM-2100F manufactured by JEOL Ltd.), it was confirmed that the nanogranular magnetic film formed on one silicon substrate having the thermal oxide film of each sample had a structure including the first phases 11 (nano-domains) dispersed in the second phase 12. Using the TEM, it was further confirmed that the first phases (nano-domains) had an average size of 30 nm or less. Using TEM-EDS, it was also confirmed that the ratio of the total amount of Fe, Co, and Ni in the first phases to the total amount of Fe, Co, Ni, X1, and X2 in the first phases was 75 at % or more.
The amount of Ar in the nanogranular magnetic film formed on the sapphire substrate of each sample was measured with the XRF spectrometer (Primus IV manufactured by Rigaku Corporation). The amount of Ar measured using the nanogranular magnetic film formed on the sapphire substrate of each sample was regarded as the amount of Ar in the nanogranular magnetic film of each sample. A thin film FP method was used with a measurement diameter of p 30 mm. Table 1 shows the results.
The Bs value of the nanogranular magnetic film formed on the other silicon substrate having the thermal oxide film of each sample was measured with a VSM. The magnetic properties were measured with the VSM (TM-VSM331483-HGC) manufactured by TAMAKAWA CO., LTD. at a magnetic field of −10,000 Oe to +10,000 Oe. Table 1 shows the results.
The high saturation magnetic flux density (Bs) was regarded as good when the ratio (may be referred to as “Bs ratio”) of a Bs value to the Bs value of a sample having a TS distance (distance between the ceramic sputtering target and the sample substrates) of 90 mm was 1.10 or more. Table 1 shows the results.
According to Table 1, it was confirmed that, the shorter the TS distance, namely the shorter the distance between the ceramic sputtering target and the sample substrates, the larger the amount of Ar. It was also confirmed that Examples 1 to 3 having an Ar amount of 0.20 at % or more had higher Bs values than the Comparative Examples under substantially the same conditions except for the amount of Ar.
Experiment 2 was carried out as in Experiment 1, except that the ratio of the volume of the first phases to the total volume of the first phases and the second phase was about 47%. Table 2 shows the results. For Examples and Comparative Examples having a TS distance of 25 mm or less, a p 1.5-inch aluminum plate having a thickness of 30 mm was attached to a y 2-inch substrate holder, and the sample substrates were attached to the aluminum plate. The distance between the metal sputtering target and the substrates was adjusted to 90 mm.
According to Table 2, it was confirmed that, the shorter the TS distance, namely the shorter the distance between the ceramic sputtering target and the sample substrates, the larger the amount of Ar. It was also confirmed that Examples 4 to 9 having an Ar amount of 0.20 at % or more and 0.80 at % or less had higher Bs values than the Comparative Examples under substantially the same conditions except for the amount of Ar.
Experiment 3 was carried out as in Experiment 1, except that the composition of the metal sputtering target was changed to change the composition of the first phases as shown in Tables 3A and 3B. Tables 3A and 3B show the results. Note that, when Si was intentionally not included in the metal sputtering target, it may be that the first phases included a small amount of Si attributable to the ceramic sputtering target. However, such a small amount of Si was not taken into account in Tables 3A and 3B.
According to Tables 3A and 3B, it was confirmed that, even when the composition of the first phases was changed, the shorter the TS distance, namely the shorter the distance between the ceramic sputtering target and the sample substrates, the larger the amount of Ar. It was also confirmed that Examples 2 and 10 to 30 having an Ar amount of 0.20 at % or more and 0.80 at % or less had higher Bs values than the Comparative Examples under substantially the same conditions except for the amount of Ar.
When the amount of Fe in the metal sputtering target was small, the ratio of the total amount of Fe, Co, and Ni in the first phases did not reach 75 at % or more even at a TS distance of 55 mm. Thus, the amount of Ar did not reach 0.20 at % or more. Consequently, the Bs value was not higher than that of the Comparative Examples under substantially the same conditions except for the amount of Ar.
Experiment 4 was carried out as in Example 2 and Comparative Example 3 of Experiment 1, except that the noble gas was changed from Ar. Table 4 shows the results.
According to Table 4, it was confirmed that, even when the noble gas was changed, provided that the amount of the noble gas was 0.20 at % or more and 0.80 at % or less, the Bs value was higher than that of the Comparative Examples under substantially the same conditions except for the amount of the noble gas.
Experiment 5 was carried out as in Example 2 and Comparative Example 3 of Experiment 1, except that the ratio of the volume of the first phases to the total volume of the first phases and the second phase was changed. Table 5 shows the results.
According to Table 5, when the ratio of the volume of the first phases to the total volume of the first phases and the second phase was 65% or less, a TS distance of 55 mm enabled the amount of Ar to be 0.20 at % or more. Consequently, the Bs value was higher than that of the Comparative Examples under substantially the same conditions except for the amount of Ar.
When the ratio of the volume of the first phases to the total volume of the first phases and the second phase was 75%, the amount of Ar was not 0.20 at % or more even at a TS distance of 55 mm. Consequently, the Bs value was not higher than that of the Comparative Example under substantially the same conditions except for the amount of Ar.
Experiment 6 was carried out as in Example 2 and Comparative Example 3 of Experiment 1, except that the compound included in the second phase was changed. To change the compound included in the second phase, the ceramic sputtering target was changed. Table 6 shows the results.
According to Table 6, it was confirmed that, even when the compound included in the second phase was changed, provided that the amount of the noble gas was 0.20 at % or more and 0.80 at % or less, the Bs value was higher than that of the Comparative Examples under substantially the same conditions except for the amount of the noble gas.
Experiment 7 was carried out as in Comparative Example 3 of Experiment 1, except that the distance (“TS2 distance”) between the metal sputtering target and the sample substrates was changed. Table 7 shows the results.
According to Table 7, when the TS2 distance was 65 mm, plasmas produced on each sputtering target interfered with each other and caused unstable discharge. Thus, discharge stopped, which resulted in failure to form the nanogranular magnetic film.
The substrate temperature during sputtering was increased to change the average particle size of the first phases 11 of the nanogranular magnetic film, namely the average size of the first phases (nano-domains). Samples were manufactured as in Example 2 except that the substrate temperature was different, and were compared. Table 8 shows the results.
According to Table 8, as the average particle size of the first phases 11 increased, namely as the average size of the first phases (nano-domains) increased, the amount of Ar gradually decreased. In accordance with the reduction of the amount of Ar, the Bs value decreased, and the He value increased. When the average particle size, namely the average size of the first phases (nano-domains), exceeded 30 nm, the amount of Ar reduced to 0.20 at %, Bs reduced to a value lower than that of other Examples, and He increased to a value rather higher than that of other Examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-011792 | Jan 2022 | JP | national |
