JP5019040B2 - Piezoelectric vibrator and oscillator - Google Patents

Description

  The present invention relates to a piezoelectric vibrator and a manufacturing method thereof, an oscillator, a real time clock, and a radio clock receiver module.

  In information devices such as clocks and microcomputers, a tuning fork type 32 kHz crystal resonator is used in the oscillator portion of the clock module in order to make use of conventional design assets and power saving. However, in the case of a tuning fork type 32 kHz crystal resonator, the arm length of the tuning fork is several mm, and the total length including the package may be close to 10 mm.

In recent years, a piezoelectric vibrator has been developed in which a driving unit in which a piezoelectric thin film is sandwiched between upper and lower electrodes is provided on a silicon substrate instead of quartz. As such a piezoelectric vibrator, those having a beam-like structure (see FIG. 1 of Patent Document 1) and tuning-fork types having two beams (see FIG. 1 of Patent Document 2) are known. Even in such a piezoelectric vibrator, since the thickness of the silicon substrate can only be about 100 μm at most, when obtaining a resonance frequency in the tens of kHz band, the arm length of the beam becomes several mm or more, and the clock module It may be difficult to reduce the size.
JP 2005-291858 A JP 2005-249395 A

  An object of the present invention is to provide a piezoelectric vibrator that is extremely small and capable of obtaining a resonant frequency of, for example, several tens of kHz, and a method for manufacturing the same. Another object of the present invention is to provide an oscillator, a real-time clock, and a radio clock receiver module having the piezoelectric vibrator.

The piezoelectric vibrator according to the present invention is
A base having a substrate, an insulating layer formed above the substrate, and a semiconductor layer formed above the insulating layer;
A support formed using a portion of the semiconductor layer;
One vibration part formed using a part of the semiconductor layer, one end fixed to the support part and the other end free,
A drive unit that is formed above the vibrating unit and generates bending vibration of the vibrating unit,
The drive unit is
A first electrode;
A piezoelectric layer formed above the first electrode;
A second electrode formed above the piezoelectric layer,
One end of the piezoelectric layer is aligned with the fixed end of the vibration part in plan view,
The length ratio of the piezoelectric layer to the vibrating portion is 0.3 or more and 0.7 or less.
The piezoelectric vibrator according to the present invention is
A base having a substrate, an insulating layer formed above the substrate, and a semiconductor layer formed above the insulating layer;
A support portion comprising a part of the semiconductor layer;
One vibration part comprising a part of the semiconductor layer, one end fixed to the support part and the other end free;
A drive unit that is formed above the vibrating unit and generates bending vibration of the vibrating unit,
The drive unit is
A first electrode;
A piezoelectric layer formed above the first electrode;
A second electrode formed above the piezoelectric layer.

  In the piezoelectric vibrator according to the present invention, since the vibration part is constituted by the semiconductor layer of the base, the thickness of the vibration part can be extremely reduced. Accordingly, in the piezoelectric vibrator that generates the resonance frequency of the oscillator used in the clock module, the length of the vibrating portion (beam) can be shortened. That is, for example, the piezoelectric vibrator can be reduced in size as compared with a piezoelectric vibrator using quartz.

  In the description according to the present invention, the word “upward” refers to, for example, “another specific thing (hereinafter referred to as“ B ”) formed“ above ”a specific thing (hereinafter referred to as“ A ”)”. Etc. In the description of the present invention, in the case of this example, there are a case where B is directly formed on A and a case where B is formed on A via another. The word “above” is used as included.

In the piezoelectric vibrator according to the present invention,
The substrate may be an SOI (Silicon On Insulator) substrate.

In the piezoelectric vibrator according to the present invention,
One end of the piezoelectric layer is aligned with the fixed end of the vibration part in plan view,
A length ratio of the piezoelectric layer to the vibrating portion may be 0.3 or more and 0.7 or less.

  In the present invention, the length of the vibration part means a distance from the fixed end to the free end of the vibration part in plan view. Further, the distance between both ends of the vibration part in the direction orthogonal to the length direction of the vibration part is referred to as the width of the vibration part. Further, for example, the length of the piezoelectric layer refers to the length of the piezoelectric layer in the length direction of the vibrating portion, and the width of the piezoelectric layer refers to the piezoelectric body in the width direction of the vibrating portion. The width of the layer.

In the piezoelectric vibrator according to the present invention,
When the boundary between the vibration part and the support part is an origin, and the direction from the boundary toward the free end of the vibration part is a positive direction,
The ratio of the length from the position of the starting end of the piezoelectric layer to the origin with respect to the length of the vibrating portion is −0.1 or more and 0.05 or less,
The ratio of the length from the end position of the piezoelectric layer to the origin to the length of the vibrating portion may be 0.4 or more and 0.7 or less.

In the piezoelectric vibrator according to the present invention,
The ratio of the length from the position of the starting end of the piezoelectric layer to the origin with respect to the length of the vibrating part is −0.05 or more and 0.01 or less,
The ratio of the length from the end position of the piezoelectric layer to the origin to the length of the vibrating portion may be 0.45 or more and 0.65 or less.

In the piezoelectric vibrator according to the present invention,
A ratio of the thickness of the piezoelectric layer to the thickness of the vibrating portion may be ¼ or more and 1 or less.

In the piezoelectric vibrator according to the present invention,
The ratio of the length from the starting end position of the piezoelectric layer to the origin to the length of the vibrating portion, and the ratio of the length from the end position of the piezoelectric layer to the origin to the length of the vibrating portion are: The piezoelectric vibrator may be set so that the electromechanical coupling coefficient is maximized.

  In the present invention, the maximum case includes the case where the maximum is achieved and the case where the maximum is achieved.

In the piezoelectric vibrator according to the present invention,
The vibrating part may have a thickness of 20 μm or less.

In the piezoelectric vibrator according to the present invention,
The vibration part may have a length of 2 mm or less.

In the piezoelectric vibrator according to the present invention,
The resonance frequency can be not less than 2 14 Hz (16.384 kHz) and not more than 2 16 Hz (65.536 kHz).

In the piezoelectric vibrator according to the present invention,
The driving unit may include a base layer formed between the vibrating unit and the first electrode.

  An oscillator according to the present invention has the above-described piezoelectric vibrator.

  A real-time clock according to the present invention includes the above-described piezoelectric vibrator.

  A radio clock receiver module according to the present invention includes the above-described piezoelectric vibrator.

A method for manufacturing a piezoelectric vibrator according to the present invention includes:
Providing a substrate, a base having an insulating layer formed above the substrate, and a semiconductor layer formed above the insulating layer;
Forming a drive unit that generates bending vibration of the vibration unit above the base;
The semiconductor layer is patterned to form a support portion, one vibration portion provided so that the support portion is a base end and the other end is not in contact with the support portion, and an opening for exposing the insulating layer. Process,
Removing a part of the insulating layer from a portion exposed by the opening, and forming a gap at least below the vibrating portion,
The step of forming the driving unit includes:
Forming a first electrode;
Forming a piezoelectric layer above the first electrode;
Forming a second electrode above the piezoelectric layer.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  1. First, the piezoelectric vibrator 100 according to this embodiment will be described. FIG. 1 is a plan view schematically showing a piezoelectric vibrator 100 according to the present embodiment, and FIG. 2 is a cross-sectional view schematically showing the piezoelectric vibrator 100. 2 is a cross-sectional view taken along the line II-II in FIG.

  As shown in FIGS. 1 and 2, the piezoelectric vibrator 100 includes a base 1, a support part 40, a vibration part 10, and a drive part 20.

For example, as shown in FIG. 2, the base 1 includes a substrate 2, an insulating layer 3 formed on the substrate 2, and a semiconductor layer 4 formed on the insulating layer 3. As the substrate 1, for example, an SOI substrate can be used. Examples of the SOI substrate include a SIMOX (silicon implanted oxide) substrate and a bonded SOI substrate. For example, a silicon substrate can be used as the substrate 2, a silicon oxide layer can be used as the insulating layer 3, and a silicon layer can be used as the semiconductor layer 4. Various semiconductor circuits can be formed in the semiconductor layer 4. The use of a silicon layer as the semiconductor layer 4 is advantageous in that a general semiconductor manufacturing technique can be used. The thickness of the insulating layer 3 is, for example, 0.1 μm to 4 μm, and the thickness of the semiconductor layer 4 is, for example, 1 μm to 20 μm. The thickness of the semiconductor layer 4 is desirably 20 μm or less in order to reduce the size of the piezoelectric vibrator 100. Note that an oxide layer 7 made of, for example, silicon oxide (SiO ₂ ) may be formed under the substrate 2. The thickness of the oxide layer 7 is 1 μm, for example.

  The support part 40 is made of a part of the semiconductor layer 4. The support part 40 can support the vibration part 10. The support portion 40 is formed in a rectangular frame shape as shown in the figure, for example.

  The vibration unit 10 is formed of a part of the semiconductor layer 4. One end of the vibration part 10 is fixed inside the support part 40, and the other end is free. The vibration unit 10 is composed of one beam, and the piezoelectric vibrator 100 is a unimorph type. The planar shape of the vibration unit 10 is, for example, a rectangle (rectangle and square), and is a rectangle in the illustrated example. As shown in FIG. 2, the vibration part 10 is formed on a gap 80 formed by removing a part of the insulating layer 3. The void 80 is formed on an opening (second opening) 82 of the substrate 2 and the oxide layer 7 formed by removing a part of the substrate 2 and a part of the oxide layer 7. The planar shape of the gap 80 and the opening 82 is, for example, a rectangle, which is a rectangle in the illustrated example, and the longitudinal direction thereof is the same direction (X direction) as the length direction of the vibration unit 10.

  Around the vibration part 10, an opening (first opening) 42 of the semiconductor layer 4 that allows vibration of the vibration part 10 is formed. The first opening 42 and the vibration part 10 coincide with, for example, the gap 80 and the second opening 82 when viewed integrally in a plan view (FIG. 1).

  The drive unit 20 is formed on the vibration unit 10. The drive unit 20 generates bending vibration of the vibration unit 10. As shown in FIG. 1, one drive unit 20 is provided for one beam. The planar shape of the drive unit 20 is, for example, a rectangle, and is a rectangle in the illustrated example, and its longitudinal direction is the same direction (X direction) as the length direction of the vibration unit 10. As shown in FIG. 2, the drive unit 20 includes a first electrode 22 formed above the base 1 (more specifically, the semiconductor layer 4), a piezoelectric layer 24 formed on the first electrode 22, and And a second electrode 26 formed on the piezoelectric layer 24. The driving unit 20 can further include a base layer 5 formed between the semiconductor layer 4 and the first electrode 22. The main part of the drive unit 20 is formed on the fixed end side of the vibration unit 10 as shown in FIGS. 1 and 2, for example, and a part of the drive unit 20 (more specifically, the underlayer 5 and The first electrode 22) is also formed on the support 40, for example. Although not shown, for example, the outer edges of the underlayer 5, the first electrode 22, the piezoelectric layer 24, and the second electrode 26 can be matched in a plan view.

  The piezoelectric layer 24 can be formed vertically above a part of the vibration unit 10. One end in the length direction (X direction) of the piezoelectric layer 24 can overlap, for example, the fixed end 10b of the vibration unit 10 in a plan view. The piezoelectric layer 24 is provided so that one end in the length direction of the piezoelectric layer 24 is aligned with the position of the fixed end 10 b of the vibration unit 10 in plan view. In this case, the length ratio of the piezoelectric layer 24 to the vibrating portion 10 (the length of the piezoelectric layer 24 / the length of the vibrating portion 10) is preferably 0.3 or more and 0.7 or less. By setting the length ratio within this range, the electromechanical coupling coefficient of the piezoelectric vibrator 100 can be increased as shown in FIG. As a result, the piezoelectric vibrator 100 can be reduced in size and efficiency. FIG. 3 is a graph showing the result of obtaining the electromechanical coupling coefficient of the piezoelectric vibrator 100 by simulation while changing the length ratio.

The underlayer 5 is an insulating layer such as a silicon oxide (SiO ₂ ) layer or a silicon nitride (Si ₃ N ₄ ) layer. The underlayer 5 may be composed of two or more composite layers, for example. The thickness of the foundation layer 5 is 1 μm, for example.

  As the 1st electrode 22, what laminated | stacked the platinum (Pt) layer on the titanium (Ti) layer, for example can be used. The thickness of the 1st electrode 22 should just be the thickness from which a sufficiently low electrical resistance value is acquired, for example, can be 10 nm or more and 5 micrometers or less.

The piezoelectric layer 24 may be made of, for example, a piezoelectric material such as lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT), lead zirconate titanate solid solution, aluminum nitride (AlN), or aluminum nitride solid solution. it can. Examples of the lead zirconate titanate solid solution include lead zirconate titanate niobate (Pb (Zr, Ti, Nb) O ₃ : PZTN). The thickness of the piezoelectric layer 24 is preferably about 1/10 times or more and equal to or less than the thickness of the semiconductor layer 4. When the thickness is within this range, a driving force that sufficiently vibrates the beam can be ensured. For example, when the thickness of the semiconductor layer 4 is 1 μm to 20 μm, the thickness of the piezoelectric layer 24 can be 0.1 μm to 20 μm.

  As the second electrode 26, for example, a platinum (Pt) layer laminated on a titanium (Ti) layer can be used. The thickness of the second electrode 26 may be any thickness that provides a sufficiently low electrical resistance value, and may be, for example, 10 nm or more and 5 μm or less.

  In the illustrated example, in the drive unit 20, only the piezoelectric layer 24 exists between the first electrode 22 and the second electrode 26, but a layer other than the piezoelectric layer 24 is provided between the electrodes 22 and 26. You may have. The film thickness of the piezoelectric layer 24 can be appropriately changed according to the resonance condition.

  In the piezoelectric vibrator 100 according to the present embodiment, the vibration unit 10 can be flexibly vibrated in the vertical direction (Z direction) by alternately applying a reverse electric field to the drive unit 20.

The resonance frequency of the piezoelectric vibrator 100 according to the present embodiment can be not less than 2 14 Hz (16.384 kHz) and not more than 2 16 Hz (65.536 kHz). For example, a resonance frequency of 2 15 Hz (32.768 kHz) (also simply referred to as “32 kHz”) is suitable for a clock module. By setting the resonance frequency to 2 ¹⁵ = 32.768 kHz, it is possible to generate a signal of 1 Hz by dividing by a 15-stage flip-flop circuit. Further, from the viewpoint of power consumption, the flip-flop circuit can be 14 stages or 16 stages. Therefore, the resonance frequency of the piezoelectric vibrator 100 according to the present embodiment can be in a range from 2 ¹⁴ = 16.384 kHz to 2 ¹⁶ = 65.536 kHz.

  2. Next, a numerical calculation example will be described.

In this numerical calculation example, mode analysis is performed using the finite element method for the piezoelectric vibrator 100 according to the present embodiment, the resonance frequency and the antiresonance frequency in the first-order bending vibration mode are calculated, and the difference between them is calculated. The electromechanical coupling coefficient k was calculated. The conditions used for the numerical calculation are as follows.
-Constituent material of the vibration part 10: Silicon-Density of the vibration part 10: 2.33 g / cm ³
-Elastic constants of the vibration part 10: Y ₁₁ = 167 GPa, Y ₄₄ = 80 GPa
-Constituent material of the piezoelectric layer 24: lead zirconate titanate (Pb (Zr, Ti) O ₃ )
Density of the piezoelectric layer 24: 7.50 g / cm ³
The dielectric constant of the piezoelectric layer 24: ε ₁₁ = 804.6, ε ₃₃ = 659.7
Piezoelectric e constant of the piezoelectric layer 24: e ₃₁ = −4.1 C / m ² , e ₃₃ = 14.1 C / m ² , e ₁₅ = 10.5 C / m ²
Elastic constants of the piezoelectric layer 24: Y ₁₁ = 132 GPa, Y ₃₃ = 115 GPa, Y ₄₄ = 30 GPa
-Length L of vibration part 10: 400 μm
-Width of vibration part 10: 50 μm
-Thickness T ₀ of vibration part 10: 4 μm, 1 μm
-Thickness T ₁ of the piezoelectric layer 24: 1 μm

Next, the result of numerical calculation will be described. 4 and 5 show the distribution of the square k ² [%] of the electromechanical coupling coefficient when the starting position X ₀ and the terminal position X ₁ (see FIG. 2) of the piezoelectric layer 24 are changed, respectively. FIG. As shown in FIG. 2, one point of the boundary 10b between the vibration part 10 and the support part 40 (fixed end of the vibration part 10) is the origin, and the length direction (X direction) of the vibration part 10 is the same. Thus, the direction from the boundary 10b toward the free end 10a of the vibration unit 10 is a positive direction. Further, FIG. 6 shows that the ratio (X ₀ / L) of the length X ₀ from the position of the starting end of the piezoelectric layer 24 to the origin to the length L of the vibrating portion 10 is fixed to 0, and only X ₁ is changed. It is a figure which shows the square k < ² > [%] of the electromechanical coupling coefficient in the case of. In FIG. 7, the ratio (X ₁ / L) of the length X ₁ from the end position of the piezoelectric layer 24 to the origin to the length L of the vibrating portion 10 is fixed to 0.5, and only X ₀ is set. It is a figure which shows the square k < ² > [%] of the electromechanical coupling coefficient at the time of changing. 4, 6, and 7, when the thickness T ₀ of the vibrating portion 10 is 4 μm, that is, the ratio of the thickness T ₁ of the piezoelectric layer 24 to the thickness T ₀ of the vibrating portion 10 (T ₁ / T ₀ ) is 1/4, and FIG. 5 shows the result when T ₀ is 1 μm, that is, when T ₁ / T ₀ is 1/1 = 1. .

As shown in FIG. 4, when T ₁ / T ₀ is 1/4, the square k ² of the electromechanical coupling coefficient is X ₀ /L=−0.025, X ₁ /L=0.55. It can be seen that the vicinity of the position is distributed as a maximum. Further, as shown in FIG. 5, when T ₁ / T ₀ is 1, k ² is distributed with the maximum near the position of X ₀ /L=−0.025 and X ₁ /L=0.65. You can see that A practically preferable range of T ₁ / T ₀ as the piezoelectric vibrator is about ¼ or more and about 1 or less, but as shown in FIGS. 4 and 5, in this range, the electromechanical coupling coefficient k is It can be seen that the distribution trends are almost the same.

As shown in FIGS. 4 to 7, when X ₀ / L is −0.1 or more and 0.05 or less and X ₁ / L is 0.4 or more and 0.7 or less, about 3% It can be seen that such a large k ² can be secured. Furthermore, when X ₀ / L is −0.05 or more and 0.01 or less and X ₁ / L is 0.45 or more and 0.65 or less, a region where k ² is maximized (in the drawing, most color white area) and can be secured k ² in the vicinity of the. Further, X ₀ / L and X ₁ / L are preferably set so that k ² is maximized, that is, the electromechanical coupling coefficient k of the piezoelectric vibrator 100 is maximized. Note that, as the parallel capacitance of the piezoelectric vibrator 100 becomes smaller, the power consumption of an oscillation circuit (described later) becomes smaller. Therefore, it is preferable that X ₀ / L is larger and X ₁ / L is smaller. Further, the numerical ranges of X ₀ / L and X ₁ / L described above are also suitable for the similar shape of the structure of the piezoelectric vibrator 100 in the present numerical calculation example, for example.

  3. Next, an example of a method for manufacturing the piezoelectric vibrator 100 according to the present embodiment will be described with reference to the drawings. 8 to 11 are cross-sectional views schematically showing one manufacturing process of the piezoelectric vibrator 100 of the present embodiment, and each correspond to the cross-sectional view shown in FIG.

  (1) First, as shown in FIG. 8, a base 1 in which an insulating layer 3 and a semiconductor layer 4 are arranged in this order on a substrate 2 is prepared.

  (2) Next, as shown in FIG. 8, the drive unit 20 is formed on the base 1. Specifically, for example, the base layer 5, the first electrode 22, the piezoelectric layer 24, and the second electrode 26 constituting the driving unit 20 are formed on the base 1.

  First, the underlayer 5, the first electrode 22, the piezoelectric layer 24, and the second electrode 26 are formed in this order on the entire surface of the substrate 1. In addition, when the base layer 5 is formed, the oxide layer 7 can also be formed on the back side of the substrate 2 at the same time. The underlayer 5 and the oxide layer 7 are formed by a thermal oxidation method, a CVD (Chemical Vapor Deposition) method, a sputtering method, or the like. The first electrode 22 is formed by vapor deposition, sputtering, or the like. The piezoelectric layer 24 is formed by a solution method (sol-gel method), laser ablation method, vapor deposition method, sputtering method, CVD method, or the like. The second electrode 26 is formed by vapor deposition, sputtering, CVD, or the like.

  Next, for example, the second electrode 26 and the piezoelectric layer 24 can be patterned into a desired shape. For the patterning, for example, a photolithography technique and an etching technique can be used.

  Next, for example, the first electrode 22 and the base layer 5 can be patterned into a desired shape. For the patterning, for example, a photolithography technique and an etching technique can be used.

  (3) Next, the semiconductor layer 4 of the substrate 1 is patterned into a desired shape to form the support portion 40, the single vibrating portion 10, and the first opening 42. The support part 40 and the vibration part 10 are obtained by forming a first opening 42 that penetrates the semiconductor layer 4 and exposes the insulating layer 3. The vibration part 10 is provided so that the other end of the vibration part 10 does not contact the support part 40 with the inner side of the support part 40 as a base end.

  First, after applying a resist on the entire surface of the substrate 1, the resist is patterned by a photolithography method, thereby forming a resist layer 90 covering a region other than the first opening 42 as shown in FIG. A resist opening 92 opened in the resist is formed on the first opening 42. Next, a part of the semiconductor layer 4 is removed by a dry etching method, a wet etching method, or the like using the resist layer 90 as a mask. In this etching step, the insulating layer 3 can be used as an etching stopper layer. That is, when the semiconductor layer 4 is etched, the etching rate of the insulating layer 3 is slower than the etching rate of the semiconductor layer 4.

  (4) Next, the substrate 2 and the oxide layer 7 of the base 1 are patterned into a desired shape to form a second opening 82. The second opening 82 is formed through the substrate 2 and the oxide layer 7 so as to expose the insulating layer 3.

  First, after applying a resist over the entire surface of the substrate 1 and under the oxide layer 7, by patterning the resist applied under the oxide layer 7 by photolithography, as shown in FIG. A resist layer 94 is formed to cover a region other than the second opening 82. A resist opening 96 opened in the resist is formed under the second opening 82. The resist layer 94 can embed the first opening 42, for example. Next, using the resist layer 94 as a mask, a part of the substrate 2 and a part of the oxide layer 7 are removed by a dry etching method or the like. In the etching process of the substrate 2, the insulating layer 3 can be used as an etching stopper layer. That is, when the substrate 2 is etched, the etching rate of the insulating layer 3 is slower than the etching rate of the substrate 2.

  (5) Next, a part of the insulating layer 3 of the base 1 is removed from the portion exposed by the second opening 82 to form a gap 80 at least under the vibrating portion 10 as shown in FIG. . The gap 80 is formed so that the vibrating portion 10 can bend and vibrate in a state where the mechanical restraint force on the free end 10a of the vibrating portion 10 is lost (described later). For example, the gap 80 is formed under the vibrating portion 10 and the first opening 42. When the insulating layer 3 is made of silicon oxide, the insulating layer 3 can be removed by, for example, a wet etching method using hydrofluoric acid. In this etching step, the semiconductor layer 4 can be used as an etching stopper layer using the substrate 2 as a mask. That is, when the insulating layer 3 is etched, the etching rate of the substrate 2 and the semiconductor layer 4 is slower than the etching rate of the insulating layer 3.

  Next, the first resist layer 90 and the second resist layer 94 are removed by ashing. By removing the resist layers 90 and 94, the mechanical restraining force with respect to the free end 10a of the vibration part 10 is eliminated, and the vibration part 10 can sufficiently vibrate.

  (6) Through the above steps, the piezoelectric vibrator 100 of the present embodiment is formed as shown in FIGS.

  4). In the piezoelectric vibrator 100 of the present embodiment, since the vibration unit 10 is configured by the semiconductor layer 4 of the base 1 (for example, an SOI substrate), the thickness of the vibration unit 10 can be extremely reduced (for example, 20 μm or less). ). Thereby, in the piezoelectric vibrator 100 that generates the resonance frequency of the oscillator used in the clock module, the length of the vibrating portion (beam) 10 can be shortened. That is, for example, the piezoelectric vibrator 100 according to the present embodiment can be reduced in size as compared with a piezoelectric vibrator using quartz. For example, when a resonance frequency of 32 kHz is used, the thickness of the vibration part 10 can be 20 μm or less, the length of the vibration part 10 can be 2 mm or less, and the package length of the piezoelectric vibrator 100 can be 3 mm or less.

  Specific examples of the piezoelectric vibrator 100 according to this embodiment are as follows.

  As a first example, the thickness of the first electrode 22 is 0.1 μm, the thickness of the piezoelectric layer 24 is 2 μm, the thickness of the second electrode 26 is 0.1 μm, the thickness of the semiconductor layer 4 is 20 μm, The vibration unit 10 has a beam length of 1280 μm and a beam width of 40 μm. Moreover, the long side of the space | gap part 80 is 2 mm, and a short side is 100 micrometers. When the piezoelectric vibrator 100 having this configuration was simulated by solving the equation of motion by the finite element method, the resonance frequency of the bending vibration was 32 kHz.

As a second example, the thickness of the first electrode 22 is 0.1 μm, the thickness of the piezoelectric layer 24 is 1 μm, the thickness of the second electrode 26 is 0.1 μm, the thickness of the semiconductor layer 4 is 4 μm, The vibration unit 10 has a beam length of 410 μm and a beam width of 40 μm. Further, the ratio (X ₀ / L) of the length X ₀ from the position of the starting end of the piezoelectric layer 24 to the origin to the length L of the vibrating portion 10 is −0.025, and the position of the end of the piezoelectric layer 24 is The ratio (X ₁ / L) of the length X ₁ from the origin to the length L of the vibrating portion 10 is 0.55. Moreover, the long side of the space | gap part 80 is 1 mm, and a short side is 100 micrometers. When the piezoelectric vibrator 100 having this configuration was simulated by solving the equation of motion by the finite element method, the resonance frequency of the bending vibration was 32 kHz.

  Further, in the unimorph type piezoelectric vibrator 100 of the present embodiment, the resonance frequency is proportional to the thickness of the vibration part 10. Therefore, according to the piezoelectric vibrator 100, the resonance frequency can be adjusted by the thickness of the vibration part 10. For example, when the vibration part has a tuning fork shape, the resonance frequency is proportional to the width of the vibration part. Therefore, in the tuning fork type piezoelectric vibrator, in order to lower the resonance frequency, it is possible to reduce the width of the vibration part, but there are cases where there is a limit of processing technology. On the other hand, in the unimorph type piezoelectric vibrator 100 of the present embodiment, in order to lower the resonance frequency, it is possible to reduce the thickness of the vibrating portion 10 (semiconductor layer 4). Therefore, a desired resonance frequency can be obtained regardless of the limit of the processing technique of the semiconductor layer 4.

  Further, in the unimorph type piezoelectric vibrator 100 of the present embodiment, one drive unit 20 is provided for one beam (vibration unit) 10. For this reason, the piezoelectric vibrator 100 of the present embodiment is structurally advantageous for downsizing.

Further, according to the piezoelectric vibrator 100 of the present embodiment, the ratio (X ₀ / L) of the length X ₀ from the position of the starting end of the piezoelectric layer 24 to the origin to the length L of the vibrating portion 10 and the piezoelectric layer By setting the ratio (X ₁ / L) of the length X ₁ from the position of the terminal 24 to the origin to the length L of the vibrating part 10 within the above-mentioned numerical range, the electromechanical coupling coefficient k is extremely increased. be able to. For this reason, vibration energy becomes difficult to leak to the support part 40 side. Therefore, even if the piezoelectric vibrator is downsized, it is possible to suppress an increase in crystal impedance (CI) value.

  Note that the piezoelectric vibrator 100 according to the present embodiment can be used as a trigger generator even in a circuit that originally does not require a timing device such as an asynchronous circuit.

  In the piezoelectric vibrator 100 of the present embodiment, a piezoelectric vibrator module can be formed by using the SOI substrate as the base 1 and mounting the semiconductor integrated circuit and the piezoelectric vibrator 100 on the insulating layer 3. Thereby, a module package can be reduced in size.

  Further, in the piezoelectric vibrator 100 according to the present embodiment, the oscillation circuit and the piezoelectric vibrator 100 can be mixedly mounted on the insulating layer 3 by using an SOI substrate as the base 1. In the device using the SOI substrate, the operating voltage can be lowered. Therefore, according to the piezoelectric vibrator 100 of this embodiment, a one-chip clock module with low power consumption can be provided.

  5). Next, a modification of the piezoelectric vibrator and the manufacturing method thereof according to the present embodiment will be described with reference to the drawings. Differences from the above-described piezoelectric vibrator 100 and its manufacturing method (hereinafter referred to as “example of the piezoelectric vibrator 100”) will be described, and description of similar points will be omitted. FIG. 12 is a cross-sectional view schematically showing a piezoelectric vibrator 300 of this modification.

  In the example of the piezoelectric vibrator 100, the case where the second opening 82 is provided below the gap 80 has been described. However, in the present modification, the second opening 82 can be omitted. In the piezoelectric vibrator 300 of this modification, as shown in FIG. 12, the substrate 2 is not provided with an opening. In the example shown in FIG. 12, the oxide layer 7 (see FIG. 2) is not provided.

  In order to obtain the piezoelectric vibrator 300 of the present modification, for example, first, similarly to the example of the piezoelectric vibrator 100, the step of forming the support portion 40, the vibration portion 10, and the first opening portion 42 (see FIG. 9). Do up to. Next, a part of the insulating layer 3 of the base 1 is removed from the portion exposed by the first opening 42 by a wet etching method or the like, so that a gap 80 is formed at least under the vibrating portion 10. In this etching step, the insulating layer 3 can be selectively removed. That is, when etching the insulating layer 3, the etching rate of the semiconductor layer 4 and the substrate 2 is slower than the etching rate of the insulating layer 3. Since the semiconductor layer 4 is difficult to be etched, the etching solution can reach under the vibrating portion 10 and the insulating layer 3 under the vibrating portion 10 can be removed. Thereafter, the first resist layer 90 is removed by ashing.

  Through the steps as described above, the piezoelectric vibrator 300 of this modification can be formed.

  In addition, the modification mentioned above is an example, Comprising: It is not necessarily limited to this.

  6). Next, an oscillator having the above-described piezoelectric vibrator will be described.

  FIG. 13 is a circuit diagram showing a basic configuration of an oscillator 500 having the piezoelectric vibrator 100 described above. This circuit (oscillation circuit) includes, for example, an amplifier 401 composed of a CMOS inverter and a feedback circuit connected between the input and output of the amplifier 401. The feedback circuit includes the piezoelectric vibrator 100, a resistor 403, and two capacitors 404 and 405. A voltage E is applied to the amplifier 401 from a DC power supply. When the power supply voltage E is increased and the oscillation start voltage is reached, the current I increases rapidly and oscillation starts. When the power supply voltage E is further increased, the current I increases almost proportionally while maintaining the oscillation state.

  FIG. 14 is a plan view schematically showing the oscillator 500 according to the present embodiment, and FIG. 15 is a cross-sectional view schematically showing the oscillator 500. 15 is a cross-sectional view taken along line XV-XV in FIG. 14 and 15 show the piezoelectric vibrator 100 in a simplified manner for convenience.

  The oscillator 500 is sealed with a sealing material 502. The IC (integrated circuit) 503 is connected to the external terminal 570 by a bonding wire 504 such as a gold wire. The external terminal 570 is electrically connected to the mounting terminal 541 via the lead frame 505 and the bonding material 506. The mounting terminal 541 is electrically connected to each electrode of the piezoelectric vibrator 100 by wiring (not shown). The piezoelectric vibrator 100 is sealed with a lid member 539, a seal member 540, and the like.

  FIG. 16 is a diagram schematically showing a manufacturing process example of the oscillator 500 according to the present embodiment.

  First, tape attachment and dicing are performed on the IC wafer. Next, the chip of the IC 503 is mounted on the lead frame 505. Next, wire bonding is performed on the IC 503 using the bonding wires 504.

  Next, the mounting terminal 541 of the piezoelectric vibrator 100 is joined to the lead frame 505 using a joining material 506 such as solder, and the piezoelectric vibrator 100 is mounted. Next, the piezoelectric vibrator 100, the IC 503, and the like are resin-sealed using a sealing material (mold material) 502. After that, characteristic inspection and marking are performed, taping, packing, and shipment.

  Although not shown, an IC that is planarly adjacent to the piezoelectric vibrator 100 is formed on the base body 1 (see FIG. 2) on which the piezoelectric vibrator 100 is formed by using a semiconductor process, and according to the present embodiment. An oscillator can also be formed. Thereby, the package can be omitted, and a one-chip type oscillator can be formed.

  7). Next, a real-time clock having the above-described piezoelectric vibrator will be described.

  FIG. 17 is a circuit block diagram schematically showing a real-time clock 600 having the oscillator (OSC) 500 described above. The integrated circuit portion of the real-time clock 600 is integrated on a single substrate 601 and connected to a microprocessor (not shown).

  A clock pulse of high frequency (for example, 32 kHz) is output from the oscillator 500 connected to the timing connection terminals 602 and 603. The clock pulse is frequency-divided by the frequency dividing circuit 605, and a time measuring pulse of 1 Hz is input to the time counting counter 606. The clock counter 606 includes, for example, a second clock bit s, a minute clock bit m, a clock clock bit h, a day clock bit d, a daily clock bit D, a monthly clock bit M, and an annual clock bit Y. Has been. When a predetermined number of timing pulses are input to the timing counter 606, each timing bit can be incremented.

  When rewriting the clock bit of the clock counter 606, first, a select signal is supplied from the microprocessor to the select input terminal 607. Next, external information composed of a data bit representing information to be rewritten, an address bit representing the address of the timekeeping bit, and an operation bit representing a write operation to the timekeeping counter 606 is input from the microprocessor to the data input terminal 608. Supply. As a result, the external information is stored in the shift registers 609 and 610 connected in series. Then, the command decoder 612 sends a write enable signal to the time counter 606 based on the operation bit and address bit stored in the shift register 610 and outputs an address signal designating the time bit. As a result, the data bits stored in the shift register 609 are written into the timekeeping bits of the timekeeping counter 606, and real-time data is rewritten.

  When real-time data is read from the time counter 606, external information having an operation bit indicating a read operation is transmitted from the microprocessor. Then, the command decoder 612 sets the write enable signal to the time counter 606 to an inactive state. As a result, the inverter 613 supplies the write enable signal in the active state to the shift register 609, the shift register 609 becomes ready for reading, and the contents of the time counter 606 are read to the shift register 609. The real-time data read to the shift register 609 is transferred to the data output terminal 615 in synchronization with the clock signal applied to the clock input terminal 614, and is sent to, for example, a microprocessor register.

  For example, data such as calculation results can be stored in a random access memory (RAM) 616.

  18 is a top perspective view schematically showing the real-time clock 600 according to the present embodiment, and FIG. 19 is a side perspective view schematically showing the real-time clock 600. FIG. 19 is a view seen in the direction of arrow XIX in FIG.

  An IC chip 651 having an oscillation circuit or the like is bonded and fixed to the island portion 653 of the lead frame 652 with a conductive adhesive or the like. Each electrode pad 654 provided on the upper surface of the IC chip 651 is electrically connected to an input / output lead terminal 656 disposed on the outer periphery of the package by a bonding wire 655. In plan view, a vibrator housing 657 that houses the piezoelectric vibrator 100 is disposed next to the IC chip 651. In the vibrator housing 657, for example, the piezoelectric vibrator 100 shown in FIGS. 1 and 2 is sealed in an airtight state. Leads 658 that are electrically connected to the respective electrodes of the piezoelectric vibrator 100 protrude from the vibrator housing 657 to the outside. The lead 658 is bonded and fixed to the connection pad 659 of the lead frame 652 with a conductive adhesive or the like. The IC chip 651, the lead frame 652, and the vibrator housing 657 are integrally molded with a resin 660 and packaged.

  Although not shown, an IC that is planarly adjacent to the piezoelectric vibrator 100 is formed on the base body 1 (see FIG. 2) on which the piezoelectric vibrator 100 is formed by using a semiconductor process, and according to the present embodiment. A real time clock can also be formed. As a result, the package can be omitted, and a one-chip real-time clock can be formed.

  8). Next, a radio clock receiver module having the above-described piezoelectric vibrator will be described.

  FIG. 20 is a circuit block diagram schematically showing the radio clock receiver module according to the present embodiment.

  The frequency filter 805 of the radio clock receiver module includes the piezoelectric vibrator 100 (100A, 100B) described above.

  The radio timepiece is a timepiece having a function of receiving a standard radio wave including time information and automatically correcting and displaying the correct time. In Japan, there are transmitting stations that transmit standard radio waves to Fukushima Prefecture (40 kHz) and Saga Prefecture (60 kHz).

  The antenna 801 receives a long standard wave of 40 kHz or 60 kHz. The standard radio wave is obtained by applying time modulation (AM) to a carrier wave of 40 kHz or 60 kHz and carrying time information (time code).

  The received standard radio wave is amplified by the amplifier 802 and filtered and tuned by the frequency filter 805 having the piezoelectric vibrators 100A and 100B having the same resonance frequency as the carrier frequency. The filtered signal having a predetermined frequency is detected and demodulated by a detection / rectification circuit 806. Then, the time code is taken out via the waveform shaping circuit 807 and counted by the central processing unit (CPU) 808. The CPU 808 reads information such as the current year, accumulated date, day of the week, and time, for example. The read information is reflected in a real time clock (RTC) 809, and accurate time information is displayed.

  Since the carrier wave is 40 kHz or 60 kHz, the piezoelectric vibrator according to the present invention is suitable for the piezoelectric vibrators 100A and 100B of the frequency filter 805.

  Although not shown, an IC that is planarly adjacent to the piezoelectric vibrator 100 is formed on the base body 1 (see FIG. 2) on which the piezoelectric vibrator 100 is formed by using a semiconductor process, and according to the present embodiment. A radio clock receiver module can also be formed. As a result, the package can be omitted, and a one-chip radio timepiece receiving module can be formed.

  9. Although the embodiments of the present invention have been described in detail as described above, those skilled in the art will readily understand that many modifications are possible without substantially departing from the novel matters and effects of the present invention. Accordingly, all such modifications are intended to be included in the scope of the present invention.

FIG. 3 is a plan view schematically showing the piezoelectric vibrator according to the embodiment. FIG. 3 is a cross-sectional view schematically showing the piezoelectric vibrator according to the embodiment. The graph which shows the relationship between the length ratio with respect to the vibration part of a piezoelectric material layer, and an electromechanical coupling coefficient. It shows the distribution of k ² in the case of changing the start position and end position of the piezoelectric layer. It shows the distribution of k ² in the case of changing the start position and end position of the piezoelectric layer. The figure which shows the change of the square of the electromechanical coupling coefficient k with respect to the terminal position of a piezoelectric material layer. The figure which shows the change of the square of the electromechanical coupling coefficient k with respect to the starting end position of a piezoelectric material layer. Sectional drawing which shows roughly one manufacturing process of the piezoelectric vibrator of this embodiment. Sectional drawing which shows roughly one manufacturing process of the piezoelectric vibrator of this embodiment. Sectional drawing which shows roughly one manufacturing process of the piezoelectric vibrator of this embodiment. Sectional drawing which shows roughly one manufacturing process of the piezoelectric vibrator of this embodiment. Sectional drawing which shows schematically the modification of the piezoelectric vibrator of this embodiment. 1 is a circuit diagram showing a basic configuration of an oscillator according to an embodiment. FIG. 2 is a plan view schematically showing the oscillator according to the embodiment. 1 is a cross-sectional view schematically showing an oscillator according to an embodiment. The figure which shows schematically the example of a manufacturing process of the oscillator of this embodiment. FIG. 2 is a circuit block diagram schematically showing a real-time clock according to the present embodiment. FIG. 2 is a top perspective view schematically showing a real-time clock according to the present embodiment. FIG. 3 is a side perspective view schematically showing a real-time clock according to the present embodiment. 1 is a circuit block diagram schematically showing a radio clock receiver module of the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base | substrate, 2 Substrate, 3 Insulating layer, 4 Semiconductor layer, 5 Underlayer, 7 Oxide layer, 10 Oscillating part, 20 Drive part, 22 1st electrode, 24 Piezoelectric layer, 26 2nd electrode, 40 Support part, 42 First opening portion, 80 gap portion, 82 second opening portion, 90 first resist layer, 92 resist opening portion, 94 second resist layer, 96 resist opening portion, 100, 300 piezoelectric vibrator, 401 amplifier, 403 resistance 404,405 capacitor, 500 oscillator, 502 sealing material, 503 integrated circuit, 504 bonding wire, 505 lead frame, 506 bonding material, 539 lid member, 540 sealing member, 541 mounting terminal, 570 external terminal, 600 real-time clock, 601 circuit board, 602, 603 timing connection terminal, 605 frequency dividing circuit, 606 timing counter, 607 Select input terminal, 608 Data input terminal, 609, 610 Shift register, 612 Command decoder, 613 Inverter, 614 Clock input terminal, 615 Data output terminal, 616 Random access memory, 651 Integrated circuit chip, 652 Lead frame, 653 Island part , 654 Electrode pad, 655 Bonding wire, 656 Input / output lead terminal, 657 Vibrator housing, 658 Lead, 659 Connection pad, 660 Resin, 801 Antenna, 802 Amplifier, 805 Frequency filter, 806 Detector / rectifier circuit, 807 Waveform shaping circuit, 808 Central processing unit

Claims (2)

A base having a substrate, an insulating layer formed above the substrate, and a semiconductor layer formed above the insulating layer;
A support formed using a portion of the semiconductor layer;
One vibration part formed using a part of the semiconductor layer, one end fixed to the support part and the other end free,
A drive unit that is formed above the vibrating unit and generates bending vibration of the vibrating unit,
The drive unit is
A first electrode;
A piezoelectric layer formed above the first electrode;
A second electrode formed above the piezoelectric layer,
One end of the piezoelectric layer is aligned with the fixed end of the vibration part in plan view,
A piezoelectric vibrator in which a length ratio of the piezoelectric layer to the vibrating portion is 0.3 or more and 0.7 or less. An oscillator comprising the piezoelectric vibrator according to claim 1 .