JPH11136082A - Piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element which has its reduced insertion loss compared with another piezoelectric element that is made of a single material by using a material of a large electromechanical coupling coefficient at an exciting/receiving part of elastic waves and also using a material of a small electromechanical coupling coefficient and a small propagation damping factor at a propagating part of elastic waves. SOLUTION: A piezoelectric ceramic having an electromechanical coupling coefficient larger than that of LiTaO3 is formed on a piezoelectric ceramic including an LiTaO3 crystal, and further elastic wave transmitting and receiving electrodes are formed thereon. That is, an LiNbO3 thin film 2 of 1 μm is stacked on an LiTaO3 single crystal substrate 1 and then an elastic wave transmitting comb-like electrode 3 and an elastic wave receiving comb-like electrode 4 are formed of aluminum on the film 2. Thus, an SAW device is produced. Then the electromechanical coupling coefficient is increased twice or more at the working center frequency of 300 MHz by stacking the film 2 on the substrate 1. As a result, the conversion efficiency of a piezoelectric element can be well satisfied and the advantages of piezoelectric ceramics can be sufficiently utilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a manufacturing method of a piezoelectric element widely used in mobile communication and the like.

[0002]

BACKGROUND OF THE INVENTION beginning with PHS (P ersonal H andy Phone S ystem), in a mobile communication system, a number of ceramic electronic components, semiconductors, and the like are used. Among them, piezoelectric ceramics are mainly used for filters.

[0003]

The above-mentioned piezoelectric materials have their own characteristics. Electromechanical coupling coefficient k ² representing the conversion efficiency from electrical energy to the piezoelectric energy, LiN
bO ₃ is as large as 5 to 20%, and LiTaO ₃ is 0.5 to 8%. In general, as k ² is larger, an elastic wave due to an electric signal is more likely to be induced. On the other hand, the propagation attenuation rate of the elastic wave is LiTaO
₃ is almost zero, whereas 0.04 dB / λ for LiNbO ₃
And it is about 100 times larger than crystal. The propagation attenuation rate directly affects the insertion loss of the piezoelectric element, and it goes without saying that the smaller the propagation attenuation rate, the more advantageous. Therefore, LiNb
O _3, LiTaO ₃ of ceramics, LiNb _1-x Ta x O
_{The three-} phase ceramics cannot satisfy a sufficient conversion efficiency of the piezoelectric element, and an element structure utilizing the advantages of the piezoelectric ceramic has not yet been provided.

[0004]

According to the present invention, there is provided a piezoelectric element comprising:
A piezoelectric ceramic B having a larger electromechanical coupling coefficient than LiTaO ₃ is formed on a piezoelectric ceramic A containing at least a LiTaO ₃ crystal, and an electrode for transmitting and receiving an elastic wave is further formed thereon.

In the above structure, the piezoelectric ceramic B is made of at least LiNbO ₃ , Li ₂ B ₄ O ₇ , Zn
_{O, AlN, Ta 2 O5,} Pb-Nd-Ti-Mn-In-O, Pb-
Zn-Ti-O, it is desirable that one material selected from the KNbO _3.

In the above structure, the piezoelectric ceramic B is preferably a thin film.

In the above structure, it is desirable that the thickness of the piezoelectric ceramic B is smaller than 1λ (where λ indicates the wavelength of the elastic wave).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in a piezoelectric material, the electromechanical coupling coefficient k ² and the propagation attenuation rate of an elastic wave are:
There are conflicting relationships. The present inventors, using a material having a large electromechanical coupling coefficient k ² is the excitation and reception portion of the elastic wave, the propagation part of the acoustic wave, the electromechanical coupling coefficient k ²
Therefore, it was considered that the insertion loss was small when a material having a small propagation loss, that is, a material having a small propagation attenuation rate was used as compared with a piezoelectric element made of a single material.

Therefore, a LiNbO ₃ thin film 2 is deposited to a thickness of 1 μm on a LiTaO ₃ single crystal substrate 1 as shown in FIG. The SAW element was manufactured by forming the elastic wave transmitting comb electrode 3 and the elastic wave receiving comb electrode 4 from aluminum, and the insertion loss was measured and compared with the case without the thin film 2. Table 1 shows the comparison results. The operating center frequency is 30
0 MHz.

[0010]

[Table 1]

As a result, the insertion loss hardly changes while the LiTaO ₃ substrate 1 remains low, and the electromechanical coupling coefficient k
² is to deposit a LiNbO ₃ film 2 on the substrate 1,
It was found to increase more than twice.

[0012]

As described above, according to the present invention, LiNb
O _3, LiTaO ₃ of ceramics, LiNb _1-x Ta x O
_{Even with} the mixed-phase ceramics of ₃ , the sufficient conversion efficiency of the piezoelectric element can be satisfied, and an element structure fully utilizing the advantages of the piezoelectric ceramic can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a SAW element.

[Explanation of symbols]

Reference Signs List 1 LiTaO ₃ substrate 2 LiNbO ₃ film 3 Comb electrode for transmission 4 Comb electrode for reception

Claims (4)

[Claims] 1. A piezoelectric ceramic B having a larger electromechanical coupling coefficient than LiTaO ₃ is formed on a piezoelectric ceramic A containing at least a LiTaO ₃ crystal, and an electrode for transmitting or receiving an elastic wave is formed thereon. Piezoelectric element. 2. The piezoelectric ceramic B has at least L
_{iNbO 3, Li 2 B 4 O} 7, ZnO, AlN, Ta 2 O5, Pb-
Nd-Ti-Mn-In- O, Pb-Zn-Ti-O, the piezoelectric element according to claim 1, characterized in that they are composed of one or more selected from the KNbO _3. 3. The piezoelectric element according to claim 1, wherein the piezoelectric ceramic B is a thin film. 4. The piezoelectric ceramic B has a thickness of 1λ.
(1) where λ represents the wavelength of an elastic wave.
3. The piezoelectric element according to item 1.