JPS58121817A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To make the resonance frequency-temperature coefficient of the resonance frequency almost zero, to make ZnO and SiO2 films thin, and to decrease the film forming time, by adopting three-layer construction for the oscillating part of a resonator comprising a thin silicon wafer, a film taking SiO2 as the major component and a piezoelectric thin film. CONSTITUTION:The oscillating part consists of the three-layer construction comprising the thin part 10d of the silicon wafer 10, the film 12 taking the SiO2 as the major component, and the ZnO film 14, and each thickness is taken as >=1/5 of the entire oscillating part. The resonance frequency versus temperature coefficient is -30ppm/ deg.C for the part 10d of the silicon wafer 10, about +100ppm/ deg.C for the film 12 taking SiO2 only as the major component, and -70ppm/ deg.C for the ZnO film 14, then the coefficient of the part 10d and the ZnO film 14 and that of the film 12 are cancelled with each other, allowing to set the resonance frequency versus temperature coefficient almost zero.

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a piezoelectric thin film is formed on a silicon substrate, and a recess is formed on the other surface of the silicon substrate facing the piezoelectric layer 4111 by anisotropic etching or the like.

Regarding piezoelectric resonators for high frequency using bulk waves & such piezoelectric resonators are "FffMDAMKNTALM"
L) DICV'kll/UHIP BtrIIK A
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Engineering UM P.

B29-855 and “Zno/810.-D M PHR
AGMGOMPO81? lii RKSONATOR
ON A B engineering LICOM #A-FMlRJ
IAL pressure CTR0N engineering Cf3 LIT'l'1)i
s 9thJu1y1981 Vol, 17 No.
, 14 F, 507-509, and has the structure shown in FIGS. 1 and 2.

In the resonator shown in Fig. 1, one side 1b of a silicon wafer 1 is doped with boron or the like to a predetermined depth from above (indicated by symbol 2), and then a recess 3 is formed on the other side 1b by anisotropic etching. A thin IQ portion 1C is formed on the silicon wafer 1, and a layer 4, etc. is deposited on one side 1a of the silicon wafer 1, including the portion 1C.
A piezoelectric thin film such as ZnO is deposited on the silicon urchin 8-1 including this electrode 4 by sputtering or the like.
form.

Further, on the piezoelectric thin M5, at least one electrode 4 is opposed to the other electrode 6 by vapor deposition, and the other electrode 6 is formed.
By applying an electrical signal between the electrodes 4 and 6 to vibrate the piezoelectric thin film 11 [5] due to the piezoelectric effect of the piezoelectric thin film 5, the composite of the shear piezoelectric thin film 5 and the portion 1C of the silicon substrate No.-1 is formed. 100 by vibrating and using the thickness vibration of the composite.
It can be advantageously operated in a high frequency region of MHII or higher. When performing the above-mentioned nine-sided etching process, it is easier to perform the etch process by providing an extremely large amount of Kll L/% BiOs on the front and back surfaces of the silicon wafer 1, which also compromises the mask function during etching. .

However, in the piezoelectric resonator described above, the resonance frequency and temperature coefficient of the piezoelectric thin SS, such as a ZnO film or a silicon wafer part 1C, which constitute the vibrating part are approximately -70p.
pm/l, about -50 PPII/l Since the LA deviation also has an eclipse value, if the resonance frequency-temperature characteristics in the fundamental mode worsens, there will be a hair edge defect.

The one in FIG. 2 has 8i on one side of the silicon wafer 7.
0. 1118 is formed on the other side, and 810. is formed on the other side. Form a recess 9 that reaches to the heel 8.
Electrode 4 similar to that shown. Piezoelectric thin 115. The electrodes 6 are formed one after another.

Such a piezoelectric resonator has a piezoelectric thin film 59 constituting the vibrating part, for example a ZnO film, whose resonance frequency and temperature coefficient are approximately -7.
0ppm/l-Jllo, which also constitutes the vibrating part,
$80 common frequency - temperature coefficient approximately +100:9 PIl
/ t, the temperature coefficients have opposite signs (“C>”)
s "O1! (!: B10m @O film thickness ratio approximately"
oIIJI: 810s III thickness': 2: I
By setting K, the resonance frequency and temperature coefficient in the fundamental mode can be made almost zero. However, 100 MI (
In the relatively low frequency region of g4 degrees, Zn0Jli, 810
．． 39, the K11l thickness is large (l), and the ZnO film is sputtered.

Created by methods such as ion brating and CyD,
810. @ is thermal oxidation treatment of silicon wafer surface, sputtering, vapor deposition, ion plating: yf, CVDf
Depending on the method used, it takes too much time to prepare, resulting in poor manufacturing efficiency. Also, 810. Since all methods except for creating @ by thermal oxidation treatment are methods of depositing films, ZnO film, 810. When the film thickness of both films increases, mechanical strain inside the film increases, resulting in a disadvantage that the IQ decreases. Sara K.

810, @If thermal oxidation treatment is used to create Cl1I, it is not possible to increase the thickness of Cl1I due to the nature of thermal oxidation treatment, and even if the film thickness can be increased, 810, 111 is formed, making it difficult to form a recess by anisotropic etching or the like. Furthermore, the resonant frequency and the temperature coefficient ζorc are z”
OIl! ``'' ``s Mll''; 2 ``'' must be 7L, so a wound crystal ZnO film in which the vibrating part is mainly a ZnO film has the disadvantage that the mechanical Q (QTB) is not good1^. be.

The present invention improves the drawbacks of the prior art described above, and
Resonant frequency - Temperature coefficient is set to almost zero, 2aoll@, 8
The purpose is to reduce the film production time by making the 10g film thinner, to reduce internal strain, and to improve Qm.

Embodiments of the present invention will now be described in detail with reference to the drawings.

In Fig. 6, 10 is a silicon wafer.

One side was doped with a predetermined amount of boron from 10 & (symbol 11
After that, a recess 100 is formed from the other surface i0b by an anisotropic etching process, and a thin portion 10 (l) is formed in the silicon quaver 10.

When performing anisotropic etching, etc., a thin 8
10j3111 is provided, the etching process becomes easier. 11 on one side of this silicon wafer 10
110. The film 12 mainly composed of is subjected to thermal oxidation treatment.

Sputtering, vapor deposition, ion blating, CVD
It is formed by the following methods. One electrode 13 is formed on this $11 by vapor-depositing 51 and the like, including a portion of the silicon wafer opposite to the thinned portion IQt1. A piezoelectric thin film is formed on the film 12 including the electrode 13 by a method such as sputtering, ion blasting, or CVD.
nO1$14 is formed and included. Furthermore, at least one part of the electrode 16 is opposed to -t"2:no11114
$12 from above ゛[Aj etc. other side゛41i15
is formed and C is present.

The thin portion 10'' of the silicon urethane 1-10, Si
The vibrating part is composed of a three-layer structure of M12 and ZnO114 whose main components are O, @, and the thickness of each layer is 175 or more than the total thickness of the vibrating part.
Part 10 of silicon sea urchin I%+10 that constitutes the vibrating part
(Resonance frequency-temperature coefficient of 1 is approximately -309%/1:',
810. For example, the temperature coefficient of 1112 whose main component is 8
10. If it is only, it is about +10 oppm/.

Note that ZnO#14cD temperature coefficient is about -7 oppm/l, silicon molecule O1l and ZnO5114
and the film 12 whose main components are 8io and 8io cancel each other out, and the resonance frequency and temperature coefficient can be set to approximately zero.

In addition, the vibrating part has a single crystal silicon part of 11
5 or more, the film thickness of ZnO114 becomes relatively thinner, and the time required for forming the II film can be shortened.
The internal strain of nO1114 can also be reduced. Moreover, since the silicon portion 101 occupies a thickness of 115 mm or more of the vibrating portion, the mechanical strength is large and the Qll is improved.

FIG. 4 shows another embodiment, and the differences from the above embodiment are as follows.
Double-sided IC of silicon sea urchin/--10 including inside of recess 100
1,101) Films 12 each containing 8101 as a main component
', 16 was formed. Each -12't16 is set so that both of them occupy a thickness of 175 or more of the entire vibrating portion. However, each of C1 1112' and 16 may have a relatively thin thickness of at least 1710 mm or more of the entire vibrating portion, which prevents internal strain from occurring, and can significantly shorten the film production time. When configuring a resonator in a low frequency range, the thickness of the vibrating portion becomes large, and internal strain, which is relatively likely to occur, can be suppressed to a small level, and this is a particularly effective structure. Since the other configurations, functions, and effects are the same as those of the above embodiment, the same reference numerals are used and the numerals "#Ii" and "#Ii" are omitted.

FIG. 5 shows still another embodiment, in which a silicon wafer 1
There is metal such as mura, mura, mura U in the recess 10C of 0 1
Eight is sio,, Muj, O,, ZnO, AjlN, Ti
According to this embodiment, after the resonator is completed, the measurement terminals (not shown) of the measuring device are connected to the electrodes 13-15 by attaching an insulator such as 0, etc. to form the frequency 11 adjustment@17. while measuring the resonance frequency.
#16 in the recess 12 located on the opposite side can be trimmed to match the resonance frequency. The other configurations and effects are the same as those of the embodiment shown in FIG. 1, so the same reference numerals are used and the explanation thereof will be omitted.

As described above, the present invention has a three-layer structure as the vibrating part of the resonator, which consists of a thin silicon wafer, a film whose main component is 810°, and a piezoelectric thin film. Increase in time, increase in internal strain 1 Mechanical strength and Qy
If the resonance frequency-temperature coefficient can be made almost zero without deterioration of m, there will be a great effect.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views showing conventional piezoelectric resonators;
3, 94, and 5 are cross-sectional views showing embodiments of piezoelectric resonators according to the present invention, respectively. 10 is a silicon wafer, 10C is a concave portion, 12°12'
*111 and 14, whose main components are 161 and 8101, are piezoelectric thin films, and tsp15 is an electrode. Patent applicant Murata Manufacturing Co., Ltd. #1 Figure 2 Figure 3 Notation 4 Figure 5 Figure 5 Procedural amendment (lj. Showa 5, May 15, 12--To the Commissioner of the Japan Patent Office) 1. Indication of the case 1988 Patent Application No. 4537 2, Name of the invention Piezoelectric gripper 3 Relationship with the case of the person making the amendment Patent applicant address 2-26-10 Tenjin, Nagaokakyo City, Kyoto Name (
623) HEEI 'Rn Co., Ltd.
Wt April 27, 1982 (shipment date) 7. Contents of amendment

Claims (1)

[Claims] On one side of the silicon substrate, a piezoelectric thin film having a resonant frequency and a temperature coefficient of opposite sign to the temperature coefficient of the silicon substrate and a piezoelectric thin film having a pair of electrodes and a silicon oxide-based material is provided. A piezoelectric resonator characterized in that a recess is provided in a portion of the other surface facing the piezoelectric thin film.