JP2607199B2 - Hybrid integrated circuit and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hybrid integrated circuit in which a Si active element and a surface acoustic wave resonator, which is an electroacoustic element, are integrated, and more particularly to a compact, lightweight and high performance voltage-controlled oscillator.

[0002]

2. Description of the Related Art Conventionally, a voltage controlled oscillator using an electroacoustic element, for example, a lithium niobate or lithium tantalate surface acoustic wave resonator, has a transistor as an active element for causing oscillation and oscillates at a desired frequency. And a variable capacitance diode whose capacity varies depending on the voltage, and some electrical components such as capacitors and resistors.

The surface acoustic wave resonator used here has a predetermined value as a vibration frequency, and is sealed in a container such as a metal tube so that the performance is stable for a long period of time. For this reason, the shape and dimensions of the surface acoustic wave resonator are several times larger than the size of the resonator itself, and miniaturization is extremely important for devices such as car phones and mobile phones where miniaturization is extremely important. Is an important issue.

[0004]

As described above, a voltage controlled oscillator constructed by a method of individually connecting a surface acoustic wave resonator, a transistor, and related components housed in a container to a substrate becomes large and heavy. In a device such as a mobile phone or a mobile phone in which small and light weight is the most important factor, there is a problem that it is not preferable.

[0005] In view of the above problems, an object of the present invention is to reduce the size and weight of a voltage controlled oscillator and improve its performance.

[0006]

According to the present invention, a surface acoustic wave resonator which is an electroacoustic element using lithium niobate or lithium tantalate is directly bonded and integrated on a Si substrate having a transistor and the like. Is stored in a container.

[0007]

According to the present invention, a small-sized, light-weight, high-performance hybrid integrated circuit, particularly a voltage-controlled oscillator, can be obtained by adopting the above configuration.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a hybrid integrated circuit according to an embodiment of the present invention, particularly a voltage controlled oscillator, and a method of manufacturing the same.

FIG. 1 shows a sectional structure of a voltage controlled oscillator according to a first embodiment. In the figure, 1 is Si
Substrate 2, 2 is a lithium niobate or lithium tantalate surface acoustic wave resonator bonded on Si substrate 1, 3 is S
i Field effect transistor (FET) formed on the substrate,
Reference numeral 4 denotes a variable capacitance diode whose capacitance changes according to voltage, 5 denotes a passive component such as a capacitor, an inductor, or a resistor, 6 denotes an electrode of the surface acoustic wave resonator 2, and 7 denotes an electrode of the surface acoustic wave resonator 2 and Si. Although not shown in the drawing, each of the components on the Si substrate 1 and the electrodes 6 of the surface acoustic wave resonator are wired and connected to form a voltage controlled oscillator. ing. Reference numeral 8 denotes a silicon oxide film or a silicon film formed and bonded on the Si substrate 1 and the lithium niobate plate or the lithium tantalate plate.
Thereby, the Si substrate and the lithium niobate plate or the lithium tantalate plate are directly joined.

Further, the voltage-controlled oscillator integrated as above is housed in a sealed container. An oscillator is constituted by the field effect transistor 3, various voltage components, and the surface acoustic wave resonator 2. By changing the voltage applied to the variable capacitance diode 4, the capacitance can be changed and the oscillation frequency can be changed.

With such a structure, the oscillation circuit section and the surface acoustic wave resonator 2 are integrated into a single body, so that the size can be significantly reduced as compared with the related art. Also,
As compared with the conventional case where the surface acoustic wave resonator 2 is individually provided with the container sealed, the volume is about 1/10 and the weight is about 1/5.

If the bonding is performed using an adhesive such as a general resin as in the prior art, there is a problem that the semiconductor process cannot be performed thereafter from the viewpoint of heat resistance and chemical resistance. According to the method described above, the Si substrate and the lithium niobate or lithium tantalate are directly bonded by the silicon oxide film or the silicon film formed on the respective substrate surfaces, and thus are bonded by inorganic substances. Is greatly improved.

[0013] Further, when bonding is performed using an adhesive such as a resin, the parallelism between the Si substrate and the lithium niobate plate or lithium tantalate plate attached thereon becomes poor, and thereafter, the lithium niobate plate or lithium tantalate plate is deteriorated. The dimensional accuracy of a comb-shaped electrode formed on a plate by photolithography is deteriorated. For example, when the resonance frequency is about 1 GHz, the electrode size becomes about 1 micron in width. Therefore, if the parallelism is poor, a quasi-microwave band surface acoustic wave resonator cannot be formed. However, in this embodiment, the adhesion is formed by a silicon oxide film or a silicon film, and the formation of these films can be generally controlled in the order of nm, so that the above-mentioned problems are solved. This effect is particularly large at high frequencies.

Further, when a resin adhesive is used, there is a problem of mechanical weakness due to a problem of being weak to heat or a thermal expansion coefficient that is greatly different between an organic resin and an inorganic Si substrate or lithium niobate or lithium tantalate. Although there was a problem of long-term reliability, such a problem can be solved by bonding with an inorganic material as in this embodiment.

(Embodiment 2) FIG. 2 shows a sectional structure of a voltage controlled oscillator according to a second embodiment. In the figure, reference numeral 4 'denotes a variable capacitance diode whose capacitance changes according to voltage, 5'
Are passive components such as capacitors, inductors, resistors, and the like.
This means that the passive components 5 'are integrally formed on the Si substrate 1. The variable capacitance diode 4 'can easily be integrally formed by using the Si substrate 1. The resistor is formed by a thin film resistor such as Si resistor or tantalum nitride formed by diffusion processing, the capacitor is formed by a silicon oxide thin film, etc., and the inductor is formed by spirally forming a wiring pattern.
Can be easily obtained. With such a configuration, it is easier to reduce the size than in the case of the first embodiment, and it is not necessary to mount the chip components, which facilitates mass production.

(Embodiment 3) A first embodiment of a method of manufacturing a voltage controlled oscillator will be described with reference to FIG.

First, a concave portion is formed in a predetermined portion of the Si substrate 1 by etching or the like, and a series of semiconductor process processes including a process performed at a temperature higher than a heat treatment temperature for direct bonding, for example, a diffusion process, etc. And F
The ET 3 and the variable capacitance diode 4 are formed. The diffusion process is usually performed at a high temperature of 1000 ° C. or more.

Next, after forming a protective film on the Si portion where the various elements are formed, the surfaces of the other Si portions are extremely cleaned. Specifically, the Si surface layer is removed by etching with a hydrofluoric acid-based etchant. Similarly, after cleaning the surface of a lithium niobate plate or a lithium tantalate plate with a hydrofluoric acid-based etchant, a silicon oxide film is formed on each plate by a chemical vapor deposition method or the like. The thickness is about 0.1 to 3 microns, and the thickness and uniformity can be easily controlled.

Further, the surface of the silicon oxide film 8 is cleaned with buffered hydrofluoric acid. Thereafter, the surfaces of the silicon oxide films formed on the respective plates are sufficiently washed with pure water and immediately superimposed uniformly, so that direct bonding can be easily obtained by the hydroxyl groups adsorbed on the surfaces of the silicon oxide films. Even in this state, a sufficiently strong joint can be obtained. However, in this state,
When the heat treatment is performed at a temperature of 100 ° C. to 800 ° C., the bonding is further strengthened. When the heat treatment temperature is high, there is a difference in the coefficient of thermal expansion between the Si substrate and the lithium niobium oxide plate or lithium tantalate plate, so that some restrictions are imposed on the shape, dimensions and the like. If the thickness of the lithium niobate plate or lithium tantalate plate is thinner and the area is reduced, the bonding strength can be improved without peeling or breakage.

Next, various processes for performing treatment at a temperature lower than the heat treatment temperature for bonding, such as electrode formation, are performed. At that time or thereafter, electrodes are formed on the surface of lithium niobate or lithium tantalate by vacuum deposition or the like. A wiring pattern is formed by ordinary photolithography. For this wiring pattern, electrodes such as aluminum and gold are used. The heat treatment effect of bonding strengthening is, for example, 20
Even if it is held at 0 ° C. for about one hour, the bonding strength increases several times, and a strength of several tens kg / cm ² can be obtained. If the temperature is raised to 800 ° C or higher, lithium will escape from the surface of the lithium niobate electrode or lithium tantalum oxide plate, and the surface properties will be greatly degraded, and the desired performance as a surface acoustic wave resonator will not be obtained. The heat treatment temperature needs to be 800 ° C. or less.

(Embodiment 4) A second embodiment of a method of manufacturing a voltage controlled oscillator will be described.

After forming at least an active element in a predetermined recess of the Si substrate in the same manner as in the third embodiment, an amorphous silicon film is formed on a lithium niobate plate or a lithium tantalate plate serving as a bonding surface. , By plasma CVD or the like. The film thickness of the amorphous silicon to be formed is about 0.1 to 3 μm, almost the same as in the third embodiment. Thereafter, as in the third embodiment, the surfaces of the amorphous silicon and the lithium niobate plate or the lithium tantalate plate are extremely cleaned. The specific method is almost the same as that of the third embodiment. The silicon surface is cleaned with a buffered hydrofluoric acid-based etchant. Thereafter, both surfaces are sufficiently washed with pure water and immediately superimposed uniformly, thereby easily joining.

Next, by performing the same process as in the third embodiment as required, it becomes possible to manufacture a voltage controlled oscillator in which the Si substrate 1 and the surface acoustic wave resonator 2 which is an electroacoustic element are integrally integrated. Thus, the same effect as in the third embodiment can be obtained. In this case, the value of the bonding strength was 2 to 5 times that obtained when the silicon oxide film was used. Since this bonding can be performed at room temperature, it can be performed after the entire process is performed.

In the above-described embodiments (1) and (2), the example of the configuration of the voltage controlled oscillator is shown. However, basically, an electroacoustic element and an active element such as a transistor can be integrated integrally. The present invention is not limited to the voltage controlled oscillator, but can be widely applied to hybrid integrated circuits in general such as integration of a filter and an amplifier.

[0025]

As described above, the hybrid integrated circuit and the method of manufacturing the same according to the present invention have the following effects.

Since the transistor and the electroacoustic element such as a surface acoustic wave resonator, which are the basic components that cause oscillation, are integrated, the voltage controlled oscillator can be significantly reduced in size and weight. It is easier to reduce the volume to about 1/10 and the weight to about 1/5 as compared with the case where a surface acoustic wave resonator housed in a conventional container is used.

In the bonding method, since the Si substrate and the lithium niobate plate or lithium tantalate plate are directly bonded with a silicon-based inorganic material having a controlled film thickness, the flatness is extremely good, and it is necessary to set the vibration frequency. In addition, submicron photolithography can be performed, and reliability against heat, vibration, and the like is greatly improved.

In addition, since the bonding method can basically be performed at room temperature, the degree of freedom of the manufacturing process is very large, which is preferable in manufacturing.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention applied to a voltage controlled oscillator.
FIG. 3 is a sectional structural view of the embodiment of FIG.

FIG. 2 shows a second embodiment in which the present invention is applied to a voltage controlled oscillator.
FIG. 3 is a sectional structural view of the embodiment of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Si board | substrate, 2 ... Surface acoustic wave resonator, 3 ... Field effect transistor (FET), 4, 4 '... Variable capacitance diode, 5, 5' ... Passive components, 6 ... Electrode, 7 ... Wiring wire, 8 ... Silicon oxide film or silicon film.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuyoshi Kotara 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-56-79487 (JP, A) JP-A-2 JP-A-137218 (JP, A) JP-A-62-122148 (JP, A) JP-A-2-183510 (JP, A) JP-A-3-91227 (JP, A) JP-A-63-14449 (JP, A) )

Claims (4)

(57) [Claims] An Si substrate having at least an active element and
Lithium or tantalum having electroacoustic element
Lithium luate single-crystal piezoelectric substrate bonding surface
That is, a silicon oxide film or silicon
A silicon film and the single crystal piezoelectric substrate is attached to each bonding surface.
A hybrid integrated circuit characterized by being directly joined by the attached hydroxyl group . 2. An Si substrate having at least an active element,
Lithium or tantalum having electroacoustic element
Lithium luate single-crystal piezoelectric substrate bonding surface
That is, a silicon oxide film or silicon
A silicon film, and the Si substrate and the single-crystal piezoelectric substrate
A treatment to attach acid groups and a superposition heat treatment
And characterized in that it is contact bonded to Ruha hybrid integrated circuits. Providing an active element on a Si substrate;
Si substrate and lithium niobate or lithium tantalate
Of the bonding surface of the single crystal piezoelectric substrate
A silicon oxide film or a silicon film is provided on at least one of the surfaces.
And attaching a hydroxyl group to each joint surface,
Superimposing and directly joining, and the single crystal piezoelectric substrate
Providing an electroacoustic element in the hybrid integrated circuit. After 4. A direct bonding to step, from 100 ° C. 8
4. The method for manufacturing a hybrid integrated circuit according to claim 3, further comprising a step of performing a heat treatment in a temperature range of 00 ° C.