PIEZOELECTRIC BODY AND MEMS DEVICE USING SAME

Abstract

There are provided a piezoelectric body of ytterbium-doped aluminum nitride, having a greater piezoelectric coefficient d.sub.33 or g.sub.33 than those not doped with ytterbium, and a MEMS device using the piezoelectric body. The piezoelectric body is represented by a chemical formula Al.sub.1-xYb.sub.xN where a value of x is more than 0 and less than 0.37 and having a lattice constant ratio c/a in a range of 1.53 or more and less than 1.6. The piezoelectric body with such a configuration has a greater piezoelectric coefficient d.sub.33 or g.sub.33 than those not doped with ytterbium.

Claims

1. A nitride material represented by a chemical formula Al.sub.1-xYb.sub.xN where a value of x is more than 0 and less than 0.37 and having a lattice constant ratio c/a in a range of 1.53 or more and less than 1.6.

2. The nitride material according to claim 1, wherein the value of x is within a range of more than 0.27 and less than 0.37.

3. The nitride material according to claim 2, wherein the lattice constant ratio c/a is within a range of 1.53 or more and 1.555 or less.

4. The nitride material according to claim 1, wherein the value of x is within a range of more than 0 and less than 0.1.

5. The nitride material according to claim 4, wherein the lattice constant ratio c/a is within a range of 1.57 or more and less than 1.6.

6. A piezoelectric body wherein the piezoelectric body according to claim 10 is disposed on a substrate, and at least an intermediate layer is disposed between the piezoelectric body and the substrate.

7. The piezoelectric body according to claim 6, wherein the intermediate layer includes at least one of aluminum nitride, gallium nitride, indium nitride, titanium nitride, scandium nitride, ytterbium nitride, molybdenum, tungsten, hafnium, titanium, ruthenium, ruthenium oxide, chromium, chromium nitride, platinum, gold, silver, copper, aluminum, tantalum, iridium, palladium, and nickel.

8. The piezoelectric body according to claim 6, wherein a diffusion layer is further disposed between the intermediate layer and the piezoelectric body, the diffusion layer including a substance constituting the intermediate layer and a substance constituting the piezoelectric body.

9. A MEMS devise using the piezoelectric body according to claim 10.

10. The piezoelectric body comprising the nitride material according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] FIG. 1 is a schematic side view of a piezoelectric thin film according to a first embodiment.

[0042] FIG. 2 is a table showing a concentration of Yb, a lattice constant ratio c/a, and a piezoelectric coefficient d.sub.33 of each thin film.

[0043] FIG. 3 is a graph showing the relation between the concentration of ytterbium and the piezoelectric coefficient d.sub.33 in Examples of the first embodiment and Comparative examples.

[0044] FIG. 4 is a graph showing the relation between the lattice constant ratio c/a and the piezoelectric coefficient d.sub.33 in Examples of the first embodiment and Comparative examples.

[0045] FIG. 5 is a schematic side view of a piezoelectric thin film according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

[0046] Hereinafter, embodiments relating to thin films of piezoelectric bodies according to the present invention will be described with reference to the accompanying drawings. Note that, needless to say, the present invention is not limited to the following embodiments and the piezoelectric body may not be formed in a thin film shape.

First Embodiment

[0047] FIG. 1 is a schematic side view of a piezoelectric thin film according to the present embodiment. As illustrated in this drawing, a piezoelectric thin film 1 is formed on a substrate 10. The thickness of the piezoelectric thin film is not particularly limited. However, it is preferably within a range of 0.1 to 30 μm, and particularly preferably within a range of 0.1 to 2 μm for exhibiting excellent adhesion.

[0048] Note that the thickness, material, etc. of the substrate 10 are not particularly limited as long as the piezoelectric thin film 1 can be formed on the surface of the substrate 10. Examples of the substrate 10 may include a silicon substrate, a heat resistant alloy substrate such as Inconel, and a resin film such as a polyimide.

[0049] The piezoelectric thin film 1 is constituted by ytterbium (Yb)-doped aluminum nitride, which is represented by a chemical formula Al.sub.1-xYb.sub.xN where a value of x is more than 0 and less than 0.37, and has a lattice constant ratio c/a within a range of 1.53 or more and less than 1.6. The piezoelectric thin film with such a configuration has a greater piezoelectric coefficient d.sub.33 or g.sub.33 than piezoelectric thin films of aluminum nitride not doped with ytterbium.

[0050] Further, in the aforementioned chemical formula, the value of x is preferably within a range of more than 0.27 and less than 0.37. The piezoelectric thin film 1 with such a configuration has the greater piezoelectric coefficient d.sub.33 or g.sub.33.

[0051] Further, it is particularly preferable that, in the aforementioned chemical formula, the value of x is within a range of more than 0.27 and less than 0.37 and the lattice constant ratio c/a is within a range of 1.53 or more and 1.555 or less. The piezoelectric thin film 1 with such a configuration has the particularly high piezoelectric coefficient d.sub.33 or g.sub.33.

[0052] On the other hand, in the aforementioned chemical formula, the value of x is preferably within a range of more than 0 and less than 0.1. The piezoelectric thin film 1 with such a configuration has the greater piezoelectric coefficient d.sub.33 or g.sub.33 than aluminum nitride not doped with ytterbium, despite having been doped with less ytterbium.

[0053] Further, it is particularly preferable that, in the aforementioned chemical formula, the value of x is within a range of more than 0 and less than 0.1 and the lattice constant ratio c/a is within a range of 1.57 or more and less than 1.6. The piezoelectric thin film 1 with such a configuration has the sufficiently high piezoelectric coefficient d.sub.33 or g.sub.33 despite having been doped with less ytterbium.

[0054] Furthermore, sensors using these piezoelectric thin films 1 exhibit a low loss and can be operated in a wide band. As a result, portable devices that use the piezoelectric thin films can operate at high frequencies and are more compact and power efficient. Note that the configuration of the sensor is not particularly limited, and any known configuration of sensor is compatible for manufacturing.

[0055] Next, a method for producing the piezoelectric thin film according to the present embodiment will be described. The piezoelectric thin film 1 can be produced using methods such as a sputtering method and a deposition method in the same manner as for a general piezoelectric thin film. Specifically, for example, it can be produced by a sputtering treatment in which an ytterbium target and an aluminum target are simultaneously sputtered on the substrate 10 (e.g., a silicon (Si) substrate) under a nitrogen gas (N.sub.2) atmosphere or a mixed atmosphere of nitrogen gas (N.sub.2) and argon gas (Ar) (with a gas pressure of 1 Pa or less). Note that an alloy containing ytterbium and aluminum in a specific ratio may be used as a target.

EXAMPLES AND COMPARATIVE EXAMPLES

[0056] The apparatus, sputtering targets, etc. described below were used to produce a plurality of piezoelectric thin films of ytterbium-doped aluminum nitride. Each piezoelectric thin film formed on an n-type silicon substrate with a specific resistance of 0.02 Ωcm had a thickness of 0.4 to 1.5 μm.

[0057] Sputtering apparatus: BC3263 (manufactured by ULVAC)

[0058] Ytterbium sputtering target material (concentration: 99.999%)

[0059] Aluminum sputtering target material (concentration: 99.999%)

[0060] Gas: mixed gas of nitrogen (purity: 99.99995% or higher) and argon gas (purity: 99.9999% or higher) (mixing ratio 40:60)

[0061] Substrate heating temperature: 300 to 600° C.

[0062] Film forming experiments were performed after the air pressure inside a sputtering chamber was reduced to a high vacuum state of 10.sup.−6 or lower using a vacuum pump. Further, the target surface was subjected to a cleaning treatment immediately after the installation of the targets and immediately before each film forming experiment in order to prevent contamination by impurities such as oxygen.

[0063] FIG. 2 shows the concentration of ytterbium (Yb), the lattice constant ratio (c/a), d.sub.33, the specific dielectric constant ε.sub.r, and g.sub.33 of each piezoelectric thin film obtained. In this figure, the lattice constant ratio c/a was calculated using an X-ray diffractometer (SmartLab manufactured by Rigaku Corp.), and the piezoelectric coefficient d.sub.33 and capacitance were measured using a piezometer (PM300 manufactured by Piezotest Pte Ltd.). These values were used to calculate the specific dielectric constant ε.sub.r and g.sub.33. Note that the Yb concentration (x) was obtained by taking the average of measurements at 5 or more points in each sample using an EDX device (an energy dispersive X-ray spectrometer EX-420, manufactured by Horiba, Ltd.) inside a scanning electron microscope (S-4300 manufactured by Hitachi High-Tech Corp.). An error of x in the measurement was about ±0.003.

[0064] Further, a graph showing the relation between the concentration x of ytterbium and the piezoelectric coefficient d.sub.33 is shown in FIG. 3 and a graph showing the relation between the lattice constant ratio (c/a) and the piezoelectric coefficient d.sub.33 is shown in FIG. 4.

[0065] In the graphs, square plotted points indicate results of aluminum nitride not doped with ytterbium, circle plotted points indicate results of Examples, and triangle plotted points indicate results of Comparative examples.

[0066] As evident from these graphs, it was found that the piezoelectric coefficient d.sub.33 of the piezoelectric thin film in which the value of x in the aforementioned chemical formula was more than 0 and less than 0.37 and the lattice constant ratio c/a was in a range of 1.53 or more and less than 1.6 was greater than that of the piezoelectric thin film of aluminum nitride not doped with ytterbium.

[0067] Further, the graph shows that the piezoelectric thin film in which the value of x in the aforementioned chemical formula was in a range of more than 0.27 and less than 0.37 and the lattice constant ratio c/a was in a range of 1.53 or more and 1.555 or less had the particularly high piezoelectric coefficient d.sub.33.

[0068] Further, the graph shows that the piezoelectric thin film in which the value of x was in a range of more than 0 and less than 0.1 and the lattice constant ratio c/a was in a range of 1.57 or more and less than 1.6 had the sufficiently high piezoelectric coefficient d.sub.33 despite having been doped with less ytterbium.

Second Embodiment

[0069] In the aforementioned first embodiment, the piezoelectric thin film was produced directly on the substrate. However, the present invention is not limited thereto. For example, as shown in FIG. 5, an intermediate layer 20 may be disposed between the substrate 10 and a piezoelectric thin film 1A.

[0070] In this configuration, the material, the thickness, etc. of the intermediate layer 20 are not particularly limited as long as the piezoelectric thin film 1A can be formed on the intermediate layer 20. Examples of the intermediate layer may include layers having a thickness of 50 to 200 nm constituted by aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), titanium nitride (TiN), scandium nitride (ScN), ytterbium nitride (YbN), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), ruthenium (Ru), ruthenium oxide (RuO.sub.2), chromium (Cr), chromium nitride, platinum (Pt), gold (Au), silver (Ag), copper (Cu), aluminum (Al), tantalum (Ta), iridium (Ir), palladium (Pd), and nickel (Ni).

[0071] Disposing a layer like the intermediate layer 20 on the substrate 10 improves the crystallinity (degree of crystallization) of the piezoelectric thin film. Thus, the piezoelectric thin film of ytterbium-doped aluminum nitride can have the further greater piezoelectric coefficients d.sub.33 or g.sub.33 than those not doped with ytterbium.

Third Embodiment

[0072] In the aforementioned second embodiment, the piezoelectric thin film was formed directly on the intermediate layer. However, the present invention is not limited thereto. For example, a diffusion layer may be further disposed between the intermediate layer and the piezoelectric thin film. The diffusion layer includes a substance a substance constituting the intermediate layer and a substance constituting the piezoelectric thin film. Note that the diffusion layer can be formed by, for example, forming the piezoelectric thin film on the intermediate layer and then heating the resulting product. The same effects as that in the second embodiment can be obtained when the diffusion layer is disposed in this manner.

REFERENCE SIGNS LIST

[0073] 1, 1A piezoelectric thin film [0074] 10 substrate [0075] 20 diffusion layer