JPH0738333A - Crystal oscillator - Google Patents

Abstract

PURPOSE:To provide a crystal oscillator facilitating miniaturization of the crystal oscillator, and highly stable in temperature change. CONSTITUTION:This crystal oscillator is constituted so that a vibration crystal plate 1 having at least a pair of excitation electrodes 2 on both faces are joined by direct joining on a semiconductor substrate 3 on which an oscillation circuit 4 and a thermosensible element 5 are formed integrally, and the oscillation circuit 4 and the vibration crystal plate 1 are joined by direct joining, and moreover, the thermosensible element 5 is formed integrally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small and highly stable crystal oscillator.

[0002]

A crystal oscillator is used as a reference signal oscillator in information communication due to its high frequency stability. With the recent development of satellite communication and mobile phones, miniaturization and high performance of each device have been set as one of the major goals, and the crystal oscillator is no exception. In order to obtain a particularly stable reference signal, a temperature compensating circuit including a crystal oscillator and a temperature sensitive element is used by compensating the temperature change of the output signal of the crystal oscillator as much as possible.

As a conventional crystal oscillator, there is one in which a crystal oscillator, an oscillation circuit, and a temperature sensitive element are formed on a resin substrate and covered with a metal case to be integrated. FIG. 7 shows an example of these crystal oscillators. In FIG. 7, 8 is a sealed crystal unit, 9 is a thermistor, and 10 is a component.
Is a transistor, 11 is a capacitor, and 12
Is a resistor, 13 is a resin substrate, and 14 is a crystal oscillator housing.

The crystal unit 8, the thermistor 9, the transistor 10, the capacitor 11 and the resistor 12 are made of a resin substrate 13.
The oscillator is configured by being electrically connected to the above. The oscillation frequency of the thermistor 9 is temperature-compensated so that it has a constant frequency by utilizing the fact that the resistance value of the thermistor 9 changes depending on the ambient temperature.

In such a crystal oscillator, the size of the crystal oscillator is increased in order to hold and hermetically seal the crystal, and each element constituting the crystal oscillator is composed of chip parts, which limits the miniaturization. The size of the crystal oscillator itself is 1 due to the large size and the large thermistor.
A size of not less than a centimeter square and a thickness of not less than 5 mm was required. Further, in order to satisfy the demand for miniaturization, very detailed work has been required for its manufacture. Also, the crystal unit 8, the thermistor 9, the transistor 10, the capacitor 1
1. Since the resistors 12, etc. are fixed to the resin substrate 13 by using solder, low temperature solder must be used when soldering the crystal oscillator to the resin substrate inside the device such as the mobile communication terminal. There was a problem. Further, since the temperature sensitive element and the crystal unit are separated, the respective temperatures are different, so that strict temperature compensation cannot be performed. Further, since the adhesive is used to fix the crystal plate inside the crystal oscillator 8, the deterioration of the adhesive causes the generation of gas and stress, and the heat resistance and adhesive strength of the adhesive itself. There was a problem that the stability of the crystal unit deteriorated and the characteristics of the crystal oscillator deteriorated.

In order to further reduce the size of such a crystal oscillator, for example, Japanese Patent Laid-Open Publication No. 62-12665.
6) describes a structure in which an oscillation circuit is composed of an IC. The structure of this crystal oscillator is shown in FIG. In the figure, 4 is an oscillating circuit, 8 is a crystal oscillator, 15 is a metal lead terminal for connecting a crystal oscillator, and 1
6 is a metal lead terminal for fixing a crystal oscillator, and 17 is a mold resin.

In a crystal oscillator having such components, capacitors, resistors, transistors, etc. are integrated into an IC on an oscillating circuit. Therefore, the size of the oscillating portion of the crystal oscillator is significantly larger than that of the conventional example. Has been miniaturized.

[0008]

However, since the crystal unit itself is large and is not integrated with the oscillator,
The size of the entire crystal oscillator depends on the size of the crystal unit. Further, even with such a configuration, there is a problem that low temperature solder must be used when soldering the crystal oscillator to the resin substrate inside the device such as the mobile-to-communication terminal. There is a problem that strict temperature compensation cannot be performed due to the temperature difference of the child, and furthermore, since the adhesive is used to fix the crystal plate inside the crystal resonator 8, the generation of gas due to the deterioration of the adhesive, The problem that the stability of the crystal unit deteriorates due to the generation of stress, the heat temperature of the adhesive itself, the adhesive strength, and the like, and the characteristics of the crystal oscillator deteriorate, cannot be solved.

As described above, in the conventional crystal oscillator,
The size of the crystal oscillator is so large that it is difficult to downsize the entire crystal oscillator. Further, strict temperature compensation could not be performed due to the temperature difference between the temperature sensitive element and the crystal unit. This is because the stability of the crystal oscillator is one of the factors that determine the stability of the crystal oscillator, and it is necessary to incorporate a crystal oscillator having good vibration characteristics into the oscillator. This highly stable crystal oscillator is difficult to handle, and it is a major cause that it has a relatively large vibrating part and holding part, and that it is necessary to seal the crystal plate in an airtight package. There is.

The present invention is intended to overcome the above-mentioned drawbacks of a crystal oscillator, and an object thereof is to provide a small-sized and highly stable crystal oscillator.

[0011]

In order to achieve the above object, the present invention provides at least a semiconductor substrate, a vibrating crystal plate, an oscillation circuit formed on the semiconductor substrate, and at least one element integrally formed on the semiconductor substrate. The crystal oscillator for vibration is composed of one temperature sensitive element, the crystal plate for vibration and the semiconductor substrate are directly bonded and fixed, and the temperature sensitive element is configured as a crystal oscillator for compensating a temperature change of the oscillation frequency of the oscillation circuit.

[0012]

With the above structure, the vibrating crystal plate, the semiconductor substrate and the temperature sensitive element can be integrated without using a resin substrate, metal terminals, an adhesive or the like. Further, the adhesive strength of the direct joint is strong, the stability against vibration and the like is improved, it is stable and does not deteriorate with respect to heat due to soldering, and the vibration characteristic does not deteriorate due to generation of gas. Moreover, since the vibrating crystal plate and the semiconductor circuit can be integrally sealed, it is easy to reduce the size of the entire crystal oscillator, and it is possible to perform strict temperature compensation by integrating with the temperature sensitive element.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) In FIGS. 1 to 3, as components of a crystal oscillator, 1 is a vibrating crystal plate, 2 is an excitation electrode, 3 is a semiconductor substrate, 4 is an oscillation circuit, 5 is a temperature sensitive element, 6 is an electrode, Reference numeral 7 is a wire bonding for connection.

In the present embodiment, at least a part of the peripheral portion of the vibrating crystal plate 1 is fixed to the semiconductor substrate 3 by direct bonding, and the oscillator circuit 4 is provided on the semiconductor substrate 3.
And the temperature sensitive element 5 is integrally formed. Also, FIG.
As shown in the circuit diagram of FIG. 3, the crystal oscillator including the vibrating crystal plate 1 is electrically connected to the oscillation circuit 4 by the connection wire bonding 7, and the temperature sensitive element 5 is electrically connected to the oscillation circuit 4. The power supply, ground, and output terminals of the oscillator circuit 4 can be taken out of the crystal oscillator as the electrodes 6.

In the crystal oscillator shown in this embodiment,
The oscillation frequency is determined by the oscillation circuit 4 and the vibrating crystal plate 1 formed on the semiconductor substrate 3. However,
Generally, the resonance frequency of a crystal unit depends on its temperature.
In the case of a T-cut crystal resonator, it varies by several tens of ppm within the range of -30 ° C to 80 ° C. In order to correct this frequency change, the oscillation circuit 4 is responsive to the input from the temperature sensitive element 5.
The oscillation frequency is kept constant by changing the circuit constant on the side.

By using a diode as the temperature sensitive element 5 integrally formed on the semiconductor substrate 3,
The existing semiconductor manufacturing process can be used, and it can be manufactured simultaneously with the oscillation circuit 4. At this time, the Zener voltage of the diode formed on the semiconductor substrate 3 usually has a temperature characteristic of ± several millimeters to several tens of millimeters V / ° C. Therefore, it is possible to measure the ambient temperature by measuring this voltage. The oscillation frequency f of the crystal oscillator is usually given by the following equation. f = fr (1 + C1 / (C0 +
CL)). fr is the resonance frequency of the crystal unit, C1, C0
Is the series equivalent capacitance and parallel equivalent capacitance of the crystal unit, and CL is the load capacitance on the oscillator side. In the case of an AT-cut crystal unit, the resonance frequency fr changes according to a cubic function according to the temperature of the crystal unit. Therefore, the oscillation frequency f of the crystal oscillator can be kept constant by changing the value of CL so as to cancel this change.

At this time, if there is a temperature difference among the temperature sensitive element 5, the oscillation circuit 4, and the vibrating crystal plate 1, strict temperature compensation cannot be performed. Since they are integrated in a small area, and since they are present on the same semiconductor substrate 3,
These temperature differences are so small that they can be ignored.

Here, the direct joining will be described. Direct bonding refers to the covalent bond between the crystal surface constituent atoms on the non-fixed surface of the semiconductor substrate and the crystal surface constituent atoms of the other substrate without interposing an adhesive between the semiconductor substrate and the crystal substrate. With the technique of directly fixing using, polishing,
In this method, a semiconductor substrate or a crystal plate that has undergone cleaning or the like is brought into contact with it in a clean atmosphere, and heat treatment is performed to obtain a firm bond. This fixing strength shows a value of about several tens of kgw / cm2 even in the initial stage of contact after the surface treatment, but the value increases to several hundreds kgw / cm2 or more by applying the heat treatment. In the fixing using the direct bonding, the fixing strength is high, and since no adhesive is used, it is resistant to heat treatment, vibration, etc., and unnecessary gas is not released.

After forming the crystal oscillator, it is necessary to perform reflow at 200 ° C. or more for soldering on the substrate.
However, when a conductive adhesive is used for fixing the vibrating crystal plate 1, the reliability against solder reflow is poor, and the resonance frequency of the vibrating crystal plate 1 is generally 2 to before and after the solder reflow. It varies by 3 ppm. In contrast,
Since the crystal oscillator having the structure of this embodiment does not use a conductive adhesive, the characteristics of the vibrating crystal plate 1 are greatly improved.

Further, in the crystal oscillator shown in this embodiment, the oscillation frequency is determined by the oscillation circuit 4 formed on the semiconductor substrate 3 and the vibrating crystal plate 1. However, generally, the resonance frequency of the crystal unit depends on its temperature, and in the case of the AT-cut crystal unit, it varies by several tens of ppm within the range of -30 ° C to 80 ° C. In order to correct this frequency change, the oscillation frequency is kept constant by changing the circuit constant on the oscillation circuit 4 side in accordance with the input from the temperature sensitive element 5. In this embodiment, since the excitation crystal plate 1, the oscillation circuit 4 and the temperature sensitive element 5 are very close to each other, a temperature difference is unlikely to occur among them. Therefore, it is possible to strictly temperature-compensate the change in the oscillation frequency due to the temperature change by using the temperature sensitive element 5.

For example, as a concrete example, 12.8 [M
[Hz] crystal oscillator with the structure of a conventional crystal oscillator, an AT-cut crystal plate of 1 mm x 3 mm as a vibration crystal plate, two chip type transistors, two thermistors,
When several resistors and capacitors were used, the size of the resin substrate was 15 mm × 12 mm, and the height of the component on the resin substrate was 5 mm. However,
When the structure of the present embodiment is used, the size of the crystal oscillator is 2 mm × by using the AT-cut crystal plate of 0.5 mm × 1 mm as the vibrating crystal plate 1 and the semiconductor substrate of 2 mm × 3 mm as the semiconductor substrate. 3 mm, height 2 mm
The following crystal oscillator was created. Also, after encapsulating each in a metallic casing, solder reflow was used to solder to a resin substrate. As a result, the oscillation frequency is 0.5p
In the crystal resonator of the present embodiment, the number of changes of pm or more was less than half of that of the conventional crystal oscillator. The frequency temperature change at this time was within ± 1 ppm in the range of -30 ° C to 80 ° C.

Further, in this embodiment, the change in ambient temperature was measured by using the change in the Zener voltage of the diode, but it is clear from the structure of the diode and the transistor that the same effect can be obtained. .
Similarly, the resistance value of a resistor formed on a semiconductor substrate changes with temperature. It is also clear that temperature compensation can be performed by measuring the amount of change in this resistance. Furthermore, the capacitance value of a capacitor formed on a semiconductor substrate also changes with temperature. The same thing is clear for the capacitance between the electrodes of the transistor, and it is clear that this change can be used to measure the temperature and temperature compensate the oscillation frequency of the oscillator.

Furthermore, although a silicon substrate is used as the semiconductor substrate in this embodiment, GaAs is used as the material.
Similarly, it is possible to bond directly using a substrate,
It is clear that the same effect can be obtained. (Embodiment 2) FIGS. 4 to 6 show another embodiment of the present invention.
In these figures, 1 is a plurality of vibrating crystal plates, 2 is an excitation electrode, 3 is a semiconductor substrate, 4 is an oscillation circuit, 6 is an electrode, and 7 is wire bonding for connection.

In this embodiment, at least a part of the peripheral portion of each of the two vibrating crystal plates 1 is fixed to the semiconductor substrate 3 by direct bonding, and the oscillation circuit 4 is formed on the semiconductor substrate 3. ing. Further, in the circuit diagram of FIG. 7, the vibrating crystal plate 1 is electrically connected to the oscillating circuit 4 through the connecting wire bonding 7, and the power supply, ground, and output terminals of the oscillating circuit 4 are the electrodes 6. It can be taken out as a crystal oscillator.

Also, in the crystal oscillator shown in this embodiment, the oscillation frequency is determined by the oscillation circuit 4 and the vibrating crystal plate 1 formed on the semiconductor substrate 3. However, generally, the resonance frequency of the crystal unit depends on its temperature, and in the case of the AT-cut crystal unit, it varies by several tens of ppm within the range of -30 ° C to 80 ° C. In this embodiment, there are two vibrating crystal plates 1, each having a resonance frequency of f1,
f2. Assuming that the temperature changes of these two resonance frequencies are the same, the difference between the two resonance frequencies is calculated and f = f1−
By setting f2 as the oscillation frequency, the oscillation frequency can be kept constant. If the temperature change has the opposite sign,
By setting f = f1 + f2 as the oscillation frequency, the oscillation frequency can be kept constant. Further, since the two vibrating crystal plates 1 and the oscillating circuit 4 are very close to each other and are on the same semiconductor substrate 3, the temperature difference between them is so small as to be negligible, which is strict. Temperature compensation becomes possible.

Furthermore, since direct bonding is used to connect the vibrating crystal plate 1 and the semiconductor substrate 3, the fixing strength is high, and no adhesive is used, so it is strong against heat treatment, vibration, etc. and unnecessary. No gas is released.

Further, after the crystal oscillator is formed, it is necessary to perform reflow at 200 ° C. or more for soldering on the substrate. However, when a conductive adhesive is used to fix the vibrating crystal plate, the reliability of the solder reflow is poor, and the resonance frequency of the vibrating crystal plate generally varies by 2 to 3 ppm before and after the solder reflow. On the other hand, in the crystal oscillator having the structure of this embodiment, since the conductive adhesive is not used, the characteristics of the vibrating crystal plate are greatly improved.

For example, as a concrete example, 12.8 [M
[Hz] crystal oscillator with the structure of a conventional crystal oscillator, two 1 mm × 3 mm AT-cut crystal plates, two chip-type transistors, and thermistors 2 are used as vibration crystal plates.
When several pieces, resistors and capacitors were used, the size of the resin substrate was 15 mm × 18 mm, and the height of the component on the resin substrate was 5 mm. However, when the structure of the present embodiment is used, the size of the crystal oscillator can be reduced by using two 0.5 mm × 1 mm AT-cut crystal plates as the vibration crystal plate and a 2 mm × 3 mm semiconductor substrate as the semiconductor substrate. 2.5mm × 3mm, height 2
A crystal oscillator of mm or less could be created. Also, after encapsulating each in a metallic casing, solder reflow was used to solder to a resin substrate. As a result, the oscillation frequency is 0.
The amount of change of 5 ppm or more was one-third or less in the crystal oscillator of the present example compared to that of the conventional crystal oscillator. The frequency temperature change at this time is from -30 ° C to 8
It was within ± 1 ppm in the range of 0 ° C.

Further, in this embodiment, two vibrating crystal plates having substantially the same temperature characteristics are used, but the temperature characteristics are opposite.
Alternatively, it is clear that the oscillation frequency can be kept constant by applying the two resonance frequencies to an appropriate function and obtaining the oscillation frequency even if a vibrating crystal plate having completely different temperature characteristics is used. It is obvious that the oscillation frequency can be kept constant by applying the respective resonance frequencies to an appropriate function and obtaining the oscillation frequency even if the above vibrating crystal plate is used. Further, although two crystal plates for vibration are used in this embodiment, one crystal plate may be used to generate two or more vibrations. Even in this case, it is clear from the principle that the oscillation frequency can be kept constant by applying the resonance frequency of each vibration to an appropriate function and obtaining the oscillation frequency.

Further, it is possible to obtain the resonance frequency by using a piezoelectric thin film element such as zinc oxide deposited on the semiconductor substrate 3 on at least one of the plurality of vibrating crystal plates 1. At this time, it is apparent that the oscillation frequency of the vibrating crystal plate 1 can be held by the oscillation frequency of the piezoelectric thin film element to perform temperature compensation.

[0031]

As is apparent from the above description of the embodiments, the present invention allows the vibrating crystal plate, the semiconductor substrate and the temperature sensitive element to be integrated without using a resin substrate, a metal terminal, an adhesive, or the like. Solder due to the problem that the stress due to the expansion and contraction of the adhesive at the time of adhesion is applied to the vibration crystal plate, the sufficient adhesive strength is not enough and a large adhesive area is required, and the heat resistance of the conductive adhesive is a problem. Can only be processed at low temperature during attachment, release of gas due to hardening of conductive adhesive, not sufficiently stable against mechanical vibration, and further deterioration of adhesive, temperature and mechanical vibration There are no problems such as unstable characteristics. Moreover,
Since the vibrating crystal plate and the semiconductor circuit can be integrated, it is easy to reduce the size of the crystal oscillator as a whole, and by integrating the temperature sensitive element, it is possible to obtain a crystal oscillator that is more compact and highly stable against temperature changes.

[Brief description of drawings]

FIG. 1 is a perspective view of a crystal oscillator according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the crystal oscillator.

FIG. 3 is a circuit diagram of the crystal oscillator.

FIG. 4 is a perspective view of a crystal oscillator according to a second embodiment of the present invention.

FIG. 5 is a sectional view of the crystal oscillator.

FIG. 6 is a circuit diagram of the crystal oscillator.

FIG. 7 is a perspective view of a conventional crystal unit.

FIG. 8 is a block diagram of a conventional crystal unit.

[Explanation of symbols]

 1 Vibration Crystal Plate 2 Excitation Electrode 3 Semiconductor Substrate 4 Oscillation Circuit 5 Temperature Sensing Element 6 Electrode 7 Wire Bonding for Connection

Claims (4)

[Claims] 1. A vibrating crystal plate, comprising: a semiconductor substrate, a vibrating crystal plate, an oscillation circuit formed on the semiconductor substrate, and at least one temperature sensitive element integrally formed on the semiconductor substrate. A crystal oscillator, wherein the semiconductor substrate is fixed by direct bonding, and the temperature sensing element is used for compensating a temperature change of an oscillation frequency of an oscillation circuit. 2. The crystal oscillator according to claim 1, wherein at least one of a diode, a transistor, a resistor and a capacitor is used as the temperature sensitive element. 3. The crystal oscillator according to claim 1, wherein a piezoelectric element is used as the temperature sensitive element. 4. The crystal oscillator according to claim 1, wherein a silicon substrate or a GaAs substrate is used as the semiconductor substrate.