JP2024156240A - Crystal Oscillator - Google Patents

Abstract

A crystal oscillator having a structure capable of suppressing frequency drift characteristics is provided.
[Solution] The crystal oscillator comprises a crystal vibration element having a rectangular shape in a plan view and excitation electrodes on the front and back, a semiconductor chip having an oscillation circuit and a temperature compensation circuit for the crystal vibration element, and a package having an oscillator chamber for the crystal vibration element and a semiconductor chamber for the semiconductor chip back to back, mounting the semiconductor chip and the crystal vibration element, and having external terminals. The crystal vibration element is mounted on the package in a cantilevered manner by a first short side and connected to a connection terminal. The excitation electrode has a long side dimension that is smaller than the long side dimension V of the crystal vibration element, which is 40 to 65% of the long side dimension V, and is provided eccentrically in the direction of a second short side opposite the first short side. The amount of eccentricity L is 16 to 18% of V.
[Selected Figure] Figure 1

Description

The present invention relates to a crystal oscillator that can reduce frequency drift characteristics.

Crystal oscillators are used as reference signal sources in various electronic devices. For example, smartphones as electronic devices can perform various functions in addition to calling and emailing. In order to realize these various functions, many electronic components are installed in the limited space inside the smartphone, and the temperature-compensated crystal oscillator is one of them. In a temperature-compensated crystal oscillator, it is desirable for the drift of the oscillation frequency to be small, but when many electronic components are installed, such as in a smartphone, each electronic component generates internal heat, and the heat (heat source) causes the oscillation frequency to drift, making it impossible to perform high-precision temperature compensation.
As one means for solving this problem, Patent Document 1 describes a structure of a container designed in consideration of heat capacity so that the temperatures of the piezoelectric vibration element and the temperature-sensing component are equal in a piezoelectric device in which a piezoelectric vibration element and a temperature-sensing component are housed in a container. Specifically, a heat conduction path between the external mounting terminal and the piezoelectric vibration element, and a heat conduction path between the external mounting terminal and the temperature-sensing component are set so that thermal equilibrium between the piezoelectric vibration element and the temperature-sensing component is quickly achieved (paragraph 56 of Patent Document 1). In addition, a crystal vibrating piece having a structure in which the planar center point of the crystal vibrating element coincides with the planar center point of the excitation electrodes provided on the front and back of the crystal vibrating piece is illustrated (Figure 1(a) of Patent Document 1).

JP 2013-102315 A

The container structure described in Patent Document 1 certainly can reduce the temperature difference between the piezoelectric vibration element and the temperature sensing component, and seems to be effective as a means of improving the frequency drift characteristics, but according to the investigations of the inventors of this application, it was found that there is still room for improvement in the frequency drift characteristics.

The present invention has been made in consideration of the above points, and the purpose of this application is to provide a crystal oscillator having a structure that can minimize frequency drift characteristics.

In order to achieve this object, the inventor of this application carried out the following simulation and prototyping of a crystal oscillator comprising a crystal resonator element having a rectangular shape in plan view and excitation electrodes on both sides, a semiconductor chip having an oscillation circuit for the crystal resonator element and a temperature compensation circuit, and a package having the crystal resonator element and the semiconductor chip mounted thereon and a plurality of connection terminals for connecting the crystal resonator to the outside, in which the crystal resonator element is mounted on the package in a cantilevered manner at a first short side. That is, a simulation model of the structure shown in Fig. 1 described later was created, and a prototype of the structure shown in Fig. 1 was also produced, and a thermal fluctuation under a predetermined condition was applied to one in which the planar center point of the crystal resonator element and the center point of the excitation electrode were aligned, and to several levels in which the excitation electrode was eccentric to the second short side side opposite to the first short side of the crystal resonator element, and the temperature change at each of the predetermined multiple locations of the semiconductor chip and the predetermined multiple locations of the crystal resonator element and the amount of deviation from the original output frequency of the output of each crystal oscillator, i.e., frequency drift, were examined by simulation and prototype. As a result, it was found that by making the excitation electrodes eccentric with respect to the quartz crystal vibrating element as described above and keeping the amount of eccentricity within a predetermined range, it is possible to reduce the frequency drift.
Therefore, according to the invention of the crystal oscillator of this application, in a crystal oscillator including a crystal vibration element that is rectangular in plan view and has excitation electrodes on both sides, a semiconductor chip that includes an oscillation circuit for the crystal vibration element and a temperature compensation circuit, and a package that mounts the crystal vibration element and the semiconductor chip and has a plurality of connection terminals that connect the crystal oscillator to the outside,
The excitation electrode is characterized in that it is provided eccentrically in the direction of a second short side opposite to the first short side.
In carrying out the present invention, it is preferable that the amount of eccentricity is an amount capable of reducing, by a predetermined amount, the thermal influence exerted on the excitation electrodes due to a predetermined thermal fluctuation condition exerted on the crystal oscillator from the outside.
In carrying out the present invention, it is preferable that the excitation electrode has a rectangular shape in a plan view, and the long side dimension of the excitation electrode is 40 to 65% of the long side dimension of the quartz crystal vibrating element. With such a dimensional range, the vibration region of the quartz crystal vibrating element can be significantly decentered toward the second side when the excitation electrode is decentered as described above.
In carrying out the present invention, the predetermined thermal change condition is preferably a predefined temperature condition in which the temperature rises by ΔT over a time t1 and returns to the original temperature over a time t2.
In carrying out this invention, it is preferable that the crystal oscillator has a long side dimension of about 1.6 mm, a short side dimension of about 1.2 mm, and a height dimension of about 0.55 mm. The effect of the present invention has been confirmed with at least this structure. Here, "about" refers to the tolerance allowed for the external dimensions of the crystal oscillator, for example, ±0.1 mm.

According to the crystal oscillator of this invention, the excitation electrodes provided on the crystal oscillator element are offset by a predetermined amount and moved away from the cantilever support, thereby reducing the effect of external heat transmitted to the crystal oscillator element via the connection terminal. As a result, even in the case of a thermal change in which the external temperature around the crystal oscillator rises to a predetermined temperature and then returns to the original temperature, the temperature change from the external heat is completed before the heat is fully transmitted to the crystal oscillator element, so the crystal oscillator element does not follow the thermal fluctuation and is considered to be less affected by thermal stress. Therefore, the frequency change caused by the temperature characteristics of the crystal oscillator element (including thermal stress) can be reduced, and the compensation value of the temperature compensation can also be reduced, so it is considered that the temperature compensation error can be reduced overall, and the frequency drift can be kept small.

1A, 1B, and 1C are diagrams for explaining an embodiment of a crystal oscillator according to the present invention. 1A and 1B are diagrams illustrating a quartz crystal vibration element according to the present invention. 13 is a graph showing frequency drift characteristics when the eccentricity is changed.

A crystal oscillator 10 of the present invention will now be described with reference to the drawings.
It should be noted that each of the drawings used in the description is merely a schematic illustration to the extent that the present invention can be understood. In addition, in each of the drawings used in the description, similar components are indicated by the same numbers, and their explanation may be omitted. Furthermore, the shapes, materials, etc. described in the following description are merely preferred examples within the scope of the present invention. Therefore, the present invention is not limited to the following embodiments.

A first embodiment of a crystal oscillator 10 of the present invention will be described with reference to FIGS.
1A is a top view of an oscillator chamber 41, FIG. 1B is a top view of a semiconductor chamber 42, and FIG. 1C is a cross-sectional view of the crystal oscillator 10 taken along the line aa' in FIG. 1A.

The crystal oscillator 10 comprises a crystal vibration element 20, a semiconductor chip 30, a package 40, and a connection terminal 50 used for connection to an external substrate.

The quartz crystal vibration element 20 is an AT-cut quartz crystal vibration element having a rectangular shape in a plan view, and includes excitation electrodes 21a and 21b on the front and back surfaces, and extraction electrodes 22a and 22b that are extracted from the excitation electrodes 21a and 21b to a first short side 23 of the quartz crystal vibration element 20. The excitation electrodes 21a and 21b are rectangular in a plan view, and are provided eccentrically in the direction of a second short side 24 that faces the first short side 23 of the quartz crystal vibration element 20.
In order to obtain the effect of the configuration of the present invention in which the excitation electrode is decentered with respect to the quartz crystal vibrating element under a predetermined condition, it is preferable that the excitation electrode is somewhat smaller than the quartz crystal vibrating element, and in particular, it is preferable that the long side dimension of the excitation electrode is somewhat shorter than the long side dimension of the quartz crystal vibrating element. On the other hand, if the long side dimension of the excitation electrode is too short, it will lead to other characteristic degradation such as a deterioration in the effective resistance of the quartz crystal vibrating element. Taking these into consideration, it is preferable that the long side dimension of the excitation electrode is selected from the range of 40 to 65% of the long side dimension of the quartz crystal vibrating element, and more preferably, it is better to select from the range of 45 to 60%.
The amount of eccentricity L will be described with reference to FIG. 2. The center point of the rectangular crystal vibrating element 20 is E, and the center point of the rectangular excitation electrode 21 is e. The distance between the center point E of the crystal vibrating element 20 and the center point e of the excitation electrode 21 is the amount of eccentricity L. Since it is better to separate the vibration region as far as possible from the first side without interfering with the characteristics of the crystal oscillator, the distance X between the edge Xa of the excitation electrode 21 on the first short side 23 side of the crystal vibrating element 20 and the first side 23 is also important. Although not limited to this, it is preferable that X is 30 to 50% of the long side dimension V of the crystal vibrating element 20. Compared to the case where the excitation electrode 21 is provided in the center of the crystal vibrating element 20, in the present invention, the excitation electrode is provided shifted toward the second short side 24 of the crystal vibrating element by the amount of eccentricity L. In the case of the present invention, for example, when the long side dimension of the crystal vibrating element 20 is V, it can be expressed as a ratio of V.
If the long side dimension V of the quartz crystal vibration element is 1.04 mm, as in the specific quartz crystal vibration element described below, and the eccentricity L is 0.104 mm, the excitation electrode is 10% eccentric with respect to the long side dimension V of the quartz crystal vibration element.

The semiconductor chip 30 is rectangular in plan view and includes an oscillation circuit and a temperature compensation circuit for the crystal vibration element 20. The temperature compensation circuit stores compensation data in a memory to make the temperature characteristics of the crystal vibration element 20 as flat as possible, for example, based on a temperature characteristic measured in advance. The crystal oscillator 10 includes a temperature sensor inside, for example, a semiconductor chip, and outputs an output that is temperature compensated for the temperature characteristics of the crystal vibration element 20 using the compensation data described above in accordance with the temperature detected by the temperature sensor. Temperature compensation is performed that is prepared in advance in the semiconductor chip 30 as a design item. The semiconductor chip 30 also includes spherical bumps 31 on the surface that is to be mounted on the package 40.
In this embodiment, the case where the bonding to the package 40 is performed by flip chip bonding has been described, but bonding by wire bonding may also be used.

The package 40 has a so-called H-shaped structure in which a concave-shaped oscillator chamber 41 in which the quartz oscillator element 20 is mounted and a concave-shaped semiconductor chamber 42 in which the semiconductor chip 30 is mounted are joined back to back. Specifically, the package 40 has a three-layer laminated structure consisting of a frame-shaped first layer 40a constituting the concave-shaped oscillator chamber 41 in which the quartz oscillator element 20 is mounted, a second layer 40b which is the common bottom surface of the oscillator chamber 41 and the semiconductor chamber 42, and a frame-shaped third layer 40c constituting the concave-shaped semiconductor chamber 42 in which the semiconductor chip 30 is mounted. This package 40 can be composed of, for example, a ceramic package.

Therefore, the vibrator chamber 41 has a wall surrounding the recess formed by the first layer 40a and a vibrator chamber bottom surface 41a formed by the second layer 40b, and is provided with connection pads 43 on the vibrator chamber bottom surface 41a for connecting the quartz vibrating element 20.
The semiconductor chamber 42 has a wall surrounding the recess formed by the third layer 40c and a bottom surface 42a formed by the second layer 40b, and is provided with mounting pads 44 on the bottom surface 42a for mounting the semiconductor chip 30. The package 40 also has a seal ring 45 on the first layer 40a. The seal ring 45 is to be bonded to a lid member (not shown).

The connection terminals 50 are provided at the four corners of the third layer 40c of the package 40. The connection terminals 50 are made of metal and are, for example, gold-plated.
Wiring 46 is provided within the three-layer stack of package 40 , and includes wiring 46 a and 46 b connecting connection terminal 50 to mounting pad 44 , and wiring 46 c connecting mounting pad 44 to connection pad 43 .

The semiconductor chip 30 is connected to the mounting pads 44 via the bumps 31 and mounted in the semiconductor chamber 42. The crystal oscillator element 20 is connected to the connection pads 43 via the conductive adhesive 25 and mounted in the oscillator chamber 41. At this time, the crystal oscillator element 20 is connected in a so-called cantilevered state, with the first short side 23 connected to the connection pad 43. After this, the inside of the oscillator chamber 41 is made into an appropriate vacuum or inert gas atmosphere, and then the seal ring 45 and the lid member (not shown) are joined by seam welding and sealed to complete the crystal oscillator 10. The lid member is rectangular in plan view and is made of, for example, metal. The completed crystal oscillator 10 is used in an external device together with other components by connecting the connection terminals 50 to an external board via solder.

Among the other components in the external device, there are some that undergo thermal fluctuations, for example, the temperature rises by 0.7 to 0.8°C over 4 to 6 seconds and returns to the original temperature over 105 to 115 seconds. At this time, the heat generated by these other components is transferred to the crystal oscillator 10 as follows.
First, heat is generated in other components, and then the heat is transferred via the wiring in the external substrate to the location where the crystal oscillator 10 is mounted. The heat is then transferred to the connection terminal 50, and the heat is transferred via the wiring 46a and 46b to the semiconductor chip 30. The heat is then transferred from the crystal terminal of the semiconductor chip 30 to the connection pad 43 via 46c, and then to the crystal vibration element 20 via the conductive adhesive 25.

The semiconductor chip 30 responds to the heat first, and then the quartz crystal vibration element 20 starts to respond. If the excitation electrode 21 is not eccentric when heat is generated, the center point E of the quartz crystal vibration element 20 and the center point e of the excitation electrode 21 are provided at the same position, so the time it takes for heat to be transmitted from the external board to the excitation electrode 21 via the connection terminal 50 is short, causing the quartz crystal vibration element 20 to react sensitively. In other words, the thermal tracking of the semiconductor chip 30 and the quartz crystal vibration element 20 starts at similar timing.
However, in the present invention, since the excitation electrode 21 is eccentric to the second short side 24 side of the quartz crystal vibrating element by the eccentricity amount L, the excitation electrode 21 can be moved away from the cantilever support portion, and the influence of external heat transmitted to the excitation electrode 21 via the connection terminal 50 can be reduced by a predetermined amount. By making the quartz crystal vibrating element structure eccentric in this way, it is considered that the temperature change of the heat source, which rises to a predetermined temperature and then slowly returns to its original temperature, is completed before the heat of the heat source is transmitted to the excitation electrode 21, and the influence of thermal stress on the vibration region can be reduced. Therefore, the frequency change caused by the temperature characteristics of the quartz crystal vibrating element can be reduced, and the compensation value of the temperature compensation can be reduced, so that the temperature compensation error can be reduced overall, and the frequency drift characteristic can be suppressed to a small value.

The results of the experiment will be described below to deepen understanding of the present invention. An experiment was conducted using a temperature-compensated crystal oscillator as the crystal oscillator 10. Specifically, three temperature-compensated crystal oscillators were created in which the eccentricity L of the excitation electrode was changed to three levels. The crystal oscillator 10 had an outer long side dimension, an outer short side dimension, and a thickness of 1.6×1.2×0.55 (unit: mm), and the crystal vibration element 20 mounted on this crystal oscillator 10 had a frequency of 32 MHz and a long side dimension×short side dimension of 1.04×0.67 (unit: mm). The excitation electrode 21 provided on this crystal vibration element had a long side dimension×short side dimension of 0.57×0.54 (unit: mm). The ratio of the long side dimension of the excitation electrode to the long side dimension of the crystal vibration element used in this experiment was 0.57/1.04=54.8%.
FIG. 3 shows a graph of the frequency drift characteristics of three types of crystal oscillators with different eccentricity L of the excitation electrode 21. The horizontal axis shows the eccentricity L, and the vertical axis shows the frequency drift. The frequency drift of each prototype was measured three times, and FIG. 3 shows nine points of data for each level. The inventor of the present invention carried out evaluations in which the eccentricity L was set to 4%, 10%, and 16% in terms of the ratio of the long side dimension V of the crystal vibrating element, aiming for a result in which the frequency drift characteristic of the crystal oscillator is less than 10 ppb/10 sec. when heat is generated outside such that the temperature rises to a certain temperature and then slowly returns to the original temperature. As a result, it was found that when the eccentricity L was 16% or more, a significant improvement was observed, and 77% of the nine measurements satisfied the frequency drift of 10 ppb/10 sec. It is expected that the frequency drift characteristics will be further improved if the eccentricity L is increased to 16% or more, for example 20%, but when checking various characteristics other than the frequency drift characteristics, such as frequency tolerance and temperature characteristics, for the evaluation product this time, it was found that a dip appears in the temperature characteristics when the eccentricity L is increased. Therefore, it is thought that the eccentricity L should be around 16% to 18%.

In the above description, the size of the crystal oscillator 10 is 1.6 x 1.2 x 0.55 (unit: mm), the size of the crystal vibration element 20 mounted on the crystal oscillator 10 is 1.04 x 0.67 (unit: mm) for 32 MHz, and the size of the excitation electrode 21 is 0.57 x 0.54 (unit: mm), but the present invention is not limited to this example and is considered to be applicable to crystal oscillators of other sizes. Furthermore, the same effect as the present invention can be obtained as long as the sizes of the crystal oscillator 10, crystal vibration element 20, and excitation electrode 21 are within a range of at least ±0.1 mm as shown above.

10: Crystal oscillator 20: Crystal vibrating element 21a, 21b: Excitation electrodes 22a, 22b: Extraction electrodes 23: First short side 24: Second short side 25: Conductive adhesive 30: Semiconductor chip 31: Bump 40: Package 40a: First layer 40b: Second layer 40c: Third layer 41: Vibrator chamber 41a: Vibrator chamber bottom surface 42: Semiconductor chamber 42a: Semiconductor chamber bottom surface 43: Connection pad 44: Mounting pad 45: Seal ring 46a, 46b, 46c: Wiring 50: Connection terminal E: Center point of crystal vibrating element e: Center point of excitation electrode L: Eccentricity Xa: Edge X on the first short side of the excitation electrode: Distance between the edge Xa on the first short side 23 side and the first side 23 V: Long side dimension of the crystal vibrating element

Claims (8)

A crystal oscillator comprising: a crystal resonator element having a rectangular shape in a plan view and excitation electrodes on both sides; a semiconductor chip having an oscillation circuit for the crystal resonator element and a temperature compensation circuit; and a package mounting the crystal resonator element and the semiconductor chip and having a plurality of connection terminals for connecting the crystal oscillator to an external device,
the crystal resonator element has a rectangular shape in a plan view, and a first side of the crystal resonator element is connected to the package in a cantilever manner;
4. A crystal oscillator comprising: a first short side and a second short side, the first short side being opposed to the first short side; The crystal oscillator according to claim 1, characterized in that the amount of eccentricity is an amount that can reduce, by a predetermined amount, the thermal effect on the excitation electrode caused by a predetermined thermal fluctuation condition acting on the crystal oscillator from the outside. The crystal oscillator according to claim 1, characterized in that the excitation electrode is rectangular in plan view, and the long side dimension of the excitation electrode is 40 to 65% of the long side dimension of the crystal vibration element. the amount of eccentricity is an amount that can reduce, by a predetermined amount, a thermal effect on the excitation electrode caused by a predetermined thermal fluctuation condition that is applied to the crystal oscillator from the outside,
2. The crystal oscillator according to claim 1, wherein the predetermined thermal change condition is a predetermined temperature condition in which the temperature rises by ΔT over a time t1 and returns to the original temperature over a time t2. The quartz crystal oscillator according to claim 1, characterized in that the amount of eccentricity is L/V, which is 16 to 18%, where L is the distance between the center point of the quartz crystal element and the center point of the excitation electrode, and V is the long side dimension of the quartz crystal element. The crystal oscillator has an outer long side dimension of 1.6 mm, an outer short side dimension of 1.2 mm, and an outer height dimension of 0.55 mm.
The quartz crystal oscillator according to claim 1, characterized in that the eccentricity is such that, when the distance between the center point of the quartz crystal vibrating element and the center point of the excitation electrode is represented as L and the long side dimension of the quartz crystal vibrating element is represented as V, L/V is 16 to 18%. The crystal oscillator has an outer long side dimension of 1.6 mm, an outer short side dimension of 1.2 mm, and an outer height dimension of 0.55 mm.
The quartz crystal vibration element has an AT cut frequency of 32 MHz, a long side dimension of 1.04 mm, and a short side dimension of 0.67 mm.
The excitation electrode is rectangular in plan view, with a long side dimension of 0.57 mm and a short side dimension of 0.54 mm,
The quartz crystal oscillator according to claim 1, characterized in that the eccentricity is such that, when the distance between the center point of the quartz crystal vibrating element and the center point of the excitation electrode is represented as L and the long side dimension of the quartz crystal vibrating element is represented as V, L/V is 16 to 18%. The crystal oscillator according to claim 1, characterized in that the package has an H-shaped structure in which an oscillator chamber in which the crystal oscillator element is mounted and a semiconductor chamber in which the semiconductor chip is mounted are joined back to back.

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