JP2574565B2 - Microwave integrated circuit and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a microwave integrated circuit in which a GaAs active device and a quartz electroacoustic device are integrated.
In particular, the present invention relates to reduction in size, weight, performance, and cost of a voltage controlled oscillator.

[0002]

2. Description of the Related Art Conventionally, a voltage-controlled oscillator using an electroacoustic element, for example, a crystal oscillator, has a transistor as an active element for causing oscillation, and a crystal oscillator for oscillating at a desired frequency and a capacitor by a voltage. Of variable capacitance diodes and some electrical components such as capacitors and resistors. The crystal unit used here has a predetermined value as a vibration frequency, and is sealed in a container such as a metal tube so that its performance is stable for a sufficiently long period. However, the size of the crystal unit is several times larger than the size of the crystal itself, and in devices such as car phones and mobile phones where miniaturization is extremely important, miniaturization is an extremely important issue. Has become.

In order to increase the frequency, the thickness of the quartz oscillator is reduced by polishing or etching. However, when the thickness of the quartz oscillator is reduced to 10 μm or less, the mechanical strength is reduced. Was extremely weak, so handling was difficult, mass productivity was extremely poor, the price was expensive, and it was not practical.

[0004]

As described above, a voltage controlled oscillator constructed by a method of individually connecting a crystal oscillator, a transistor, and related components housed in a container to a substrate becomes large and heavy, so that a cellular phone becomes large and heavy. For devices where small size and light weight are the most important factors, such as mobile phones,
There was a problem that it was not favorable. Further, it is extremely difficult to reduce the thickness of the crystal unit in terms of mass productivity, and it has been substantially difficult to obtain a high-frequency voltage-controlled oscillator exceeding 500 MHz using the crystal unit.

[0005]

Means for Solving the Problems In order to solve the above problems, an electroacoustic element using quartz is directly bonded and integrated on a GaAs substrate having a transistor and the like, and these are housed in a container. It is.

[0006]

With the above configuration, a small, lightweight, high-performance, low-cost microwave integrated circuit, particularly a voltage-controlled oscillator, can be obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a microwave integrated circuit according to an embodiment of the present invention,
In particular, a configuration when applied to a voltage controlled oscillator and a manufacturing method thereof will be described with reference to the drawings.

(Embodiment 1) FIG. 1 shows a first example of the structure of the voltage controlled oscillator of this embodiment. In the figure, 1 is GaAs
An s substrate, 2 is a crystal unit bonded on a GaAs substrate 1, 3 is a field effect transistor (FET) formed on a GaAs substrate, 4 is a variable capacitance diode chip whose capacitance changes with voltage, and 5 is Passive chip components such as capacitors, inductors and resistors, 6 is the upper electrode of the crystal oscillator, 7 is the lower electrode of the crystal oscillator, and the lower electrode and GaAs
The wiring on the board is connected to via holes (through holes provided in the board, the inside of which is covered with a conductor, and the upper and lower sides of the board are electrically connected) and the like. Although not shown in the figure, the upper and lower electrodes of the crystal unit are connected by wiring so as to be a voltage controlled oscillator. Numeral 8 is a silicon oxide film or a silicon film formed on the GaAs substrate, whereby the GaAs substrate and the quartz plate are directly bonded. Further, the voltage-controlled oscillator integrated as above is housed in a sealed container. An oscillator is composed of a field-effect transistor, various electric components, and a quartz oscillator. By changing the voltage applied to the variable capacitance diode, the capacitance can be changed and the oscillation frequency can be changed. With such a structure, the oscillation circuit unit and the crystal unit are integrated into a single body, so that the size can be significantly reduced as compared with the related art. With such a configuration, the volume is reduced to about 1/10 and the weight is reduced to about 1/5 as compared with a conventional case where a quartz resonator is individually sealed in a container.

If bonding is performed using an adhesive such as a general resin, there is a problem that the semiconductor process cannot be performed thereafter from the viewpoint of heat resistance and chemical resistance, but the method of this embodiment is used. For example, GaAs substrate and crystal (single crystal of silicon oxide)
Is formed by reacting and joining silicon oxide on the surface of the quartz crystal itself and silicon oxide or silicon formed on the GaAs substrate. Therefore, the bonding is made of an inorganic substance, and such a problem is greatly improved. . In addition, when a resin adhesive is used, there are problems such as weakness against heat and long-term reliability due to mechanical strain due to a large difference in thermal expansion coefficient between an organic resin and an inorganic GaAs substrate or quartz. But,
Such a problem can be solved by bonding with an inorganic material as in this embodiment.

Embodiment 2 FIG. 2 shows a second example of the structure of the voltage controlled oscillator of this embodiment. In the figure, 1 is GaAs
An s substrate 2 is a quartz crystal resonator bonded on a GaAs substrate 1, 3 is a field effect transistor (FET) formed on a GaAs substrate, 4 ′ is a variable capacitance diode chip whose capacitance changes according to a voltage, 5. 'Is a passive chip component such as a capacitor, an inductor, a resistor, etc., 6 is an upper electrode of the crystal oscillator, 7 is a lower electrode of the crystal oscillator, and the lower electrode is GaAs.
The wiring on the s substrate is connected to via holes (through holes provided in the substrate, the inside of which is covered with a conductor, and the upper and lower sides of the substrate are electrically connected) and the like. Although not shown in the figure, the components and the upper and lower electrodes of the crystal unit are hard-wired so as to be a voltage controlled oscillator. Numeral 8 is a silicon oxide film or a silicon film formed on the GaAs substrate, whereby the GaAs substrate and the quartz plate are directly bonded. An oscillator is composed of a field-effect transistor, various electric components, and a quartz oscillator.
By changing the voltage applied to the variable capacitance diode,
By changing the capacitance, the oscillation frequency can be changed. Further, the voltage-controlled oscillator integrated as above is housed in a sealed container. What is different from Example 1 is 4 ′,
5 'is integrally formed on a GaAs substrate.
If a GaAs substrate is used, the variable capacitance diode can be easily integrated. The resistance is a thin film resistance such as GaAs resistance or tantalum nitride formed by diffusion processing, the capacitor is a silicon oxide thin film, etc., and the inductor is
It can be easily obtained by forming the wiring pattern in a spiral shape or the like. With such a configuration, the size can be further reduced more easily than in the case of the first embodiment, and the trouble of mounting the chip components is not required, so that the mass production is also facilitated.

(Embodiment 3) An example of a method of manufacturing the voltage controlled oscillator of this embodiment will be described.

First, a concave portion is formed in a predetermined portion of a GaAs substrate by etching or the like, and a series of semiconductor processing processes including a process performed at 870 ° C. or higher, for example, a diffusion process, are performed inside the concave portion to obtain an FET and a variable capacitor. A diode or the like is formed. The diffusion process is typically 10
It is performed at a high temperature of 00 degrees C or more. Next, after forming a protective film on the GaAs portion where the various elements are formed, other GaAs is formed.
Part s and the surface of the quartz plate are extremely cleaned. In particular,
The GaAs surface layer is removed by etching with a mixed solution of hydrogen peroxide and ammonia. The quartz surface is cleaned with buffered hydrofluoric acid. On the GaAs substrate, a silicon oxide film is further formed thereon by a chemical vapor deposition method or the like. The thickness of the silicon oxide film is about 0.5-3 microns. Further, the silicon oxide surface is cleaned with buffered hydrofluoric acid. After that, the surfaces of both the silicon oxide film and the quartz formed on the GaAs substrate are sufficiently washed with pure water and immediately superimposed uniformly, and the hydroxyl groups adsorbed on the silicon oxide surface and the quartz (single-crystal silicon oxide) surface are obtained. Thus, direct bonding can be easily obtained. Even in this state, a sufficiently strong joint can be obtained. However, if the heat treatment is further performed at a temperature of 100 ° C. to 860 ° C. in this state, the bonding between the quartz plate and the GaAs substrate is further strengthened. When the heat treatment temperature is high, there is a difference in the coefficient of thermal expansion between the GaAs substrate and the quartz plate, so that some restrictions are imposed on the shape, dimensions, and the like. If the thickness is reduced and the area is reduced, the bonding strength can be improved without peeling or breakage. Next, after covering other portions with a resist or the like so that only the portion directly below the quartz plate other than the holding portion of the quartz plate can be etched, etching is performed, and only the portion directly below the quartz plate other than the holding portion of the quartz plate is etched. Remove. Next, various processes for processing at a temperature equal to or lower than the heat treatment temperature for bonding and at a temperature equal to or lower than 860 ° C., for example, electrode formation are performed. Further, a wiring pattern is formed by ordinary photolithography. Aluminum or gold is used for the electrodes. The heat treatment effect of bonding reinforcement is, for example, 200 ° C.
Thus, the bonding strength is increased several times even if it is maintained for about one hour, and a strength of several tens of kg / square cm can be obtained. If the temperature is raised to 860 ° C. or higher, the crystal form of the crystal changes and the predetermined performance as a crystal oscillator cannot be obtained. Therefore, the bonding temperature needs to be 860 ° C. or lower.

(Embodiment 4) Another example of the method of manufacturing the voltage controlled oscillator of this embodiment will be described.

In the same manner as in the third embodiment, after at least active elements are formed in predetermined concave portions of the GaAs substrate, a bonding process with a quartz plate is performed. Next, the quartz plate is thinned by polishing or etching. As a result, initially 200μ
Even a quartz substrate having a length of about m can be easily processed to 5 μm or less. If a more precise etching is used, the thickness can be further reduced, and a thickness of 1 μm can be realized. When a crystal AT cut is used, a fundamental wave oscillation at about 1 GHz is possible if the thickness is 1 μm. Thereafter, by performing the same process as in the third embodiment, it becomes possible to manufacture a voltage-controlled oscillator in which a GaAs substrate and a quartz oscillator are integrated integrally. The voltage controlled oscillator configured as described above can oscillate at a high frequency of 1 GHz, which cannot be obtained conventionally. In particular, when a GaAs substrate is used, a transistor which can operate at a frequency several times higher than that in a case where silicon is used can be formed.
This is extremely advantageous in a high frequency region of z or more. If the frequency exceeds 1 GHz, wiring routing causes deterioration of high-frequency characteristics. Therefore, if integrated as in this embodiment, performance can be further improved.

(Embodiment 5) Another example of the method of manufacturing the voltage controlled oscillator of this embodiment will be described.

In the same manner as in the third embodiment, at least an active element is formed in a predetermined recess of a GaAs substrate, and then an amorphous silicon film is formed on at least a GaAs substrate to be a bonding surface by plasma CVD or the like. The thickness of the amorphous silicon film to be formed is about 0.5 to 3 μm, almost the same as in the third embodiment. Then, as in the third embodiment, the surfaces of the amorphous silicon and the quartz plate are extremely cleaned. The specific method is
This is almost the same as 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 superposed one upon the other, so that bonding can be easily obtained. Next, as in the third embodiment, the quartz plate is thinned by polishing or etching as necessary. Thereafter, by performing the same process as in the third embodiment, it becomes possible to manufacture a voltage-controlled oscillator in which a GaAs substrate and a quartz oscillator are integrated integrally.
The same effect as that of No. 4 can be obtained. In this case, the value of the bonding strength was 2 to 5 times that of the case where 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.

(Embodiment 6) Another example of the method of manufacturing the voltage controlled oscillator of this embodiment will be described.

After forming at least an active element in a predetermined concave portion of the GaAs substrate in the same manner as in the third embodiment, a single-crystal silicon film is formed on at least a GaAs substrate serving as a junction surface by a molecular beam epitaxy (MBE). Form.
The single crystal silicon film can be grown at a relatively low temperature of 300 to 400 ° C., after forming an amorphous silicon buffer film, and then at a higher temperature. The thickness of the single-crystal silicon to be formed is about 0.5 to 3 μm, almost as in the case of the third embodiment. Thereafter, as in the third embodiment, the surfaces of the single crystal silicon and the quartz substrate 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 superposed one upon the other, so that bonding can be easily obtained. Next, as in the case of the third embodiment, the quartz crystal is thinned by polishing or etching as necessary. Thereafter, by performing the same process as in the third embodiment, it becomes possible to manufacture a voltage controlled oscillator in which the GaAs substrate and the crystal unit are integrated integrally, and the same effects as those of the third and fourth embodiments can be obtained. The bonding strength in this case was even stronger than when using an amorphous silicon film, and a value 5 to 10 times higher than when using a silicon oxide film was obtained. Since this bonding can be performed at room temperature, it can be performed after the entire process is performed.

[0019]

Since the present invention has the above-described structure and manufacturing method, it exhibits the following effects.

In any of the embodiments, first,
Electro-acoustic elements such as transistors and crystal oscillators, which are the basic components that cause oscillation, are integrated into one,
It is possible to greatly reduce the size and weight of the voltage controlled oscillator, and it is possible to reduce the volume by about 1/10 and the weight by about 1/5 compared to the case of using a crystal oscillator housed in a conventional container. Easy.

Further, when the polishing and etching treatment of the quartz crystal shown in Example 4 and the like is performed, the thickness can be easily reduced to 5 μm or less. 2), a voltage-controlled oscillator based on the fundamental wave oscillation can be easily formed. This enables high performance and low cost.

Further, since the transistor is integrated on a GaAs substrate, the high-frequency characteristics as a transistor are several times better than when integrated with a silicon transistor, and the performance as a voltage-controlled oscillator can be several times higher. .

In the bonding method of the present embodiment, since the GaAs substrate and the quartz are directly bonded with a silicon-based inorganic material on the order of microns, the design and setting of the vibration frequency are easy, and the reliability against heat, vibration, and the like is high. Is also greatly improved. .

In the method of this embodiment, since bonding at room temperature is basically possible, the degree of freedom of the manufacturing process is very large, which is preferable in manufacturing.

In this embodiment, an example of the configuration of the voltage controlled oscillator has been shown. However, basically, an electroacoustic element and an active element such as a transistor can be integrated integrally. It can be widely applied to microwave integrated circuits in general such as integration of amplifiers and amplifiers.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view showing the configuration of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 Quartz crystal resonator 3 Field effect transistor (FET) 4 Variable capacitance diode 5 Passive component 6 Quartz crystal upper electrode 7 Quartz crystal lower electrode 8 Silicon oxide or silicon film

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shodai Venus 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 (6)

(57) [Claims] 1. A GaAs substrate having at least an active element
Surface of a quartz plate having an electroacoustic element and an electroacoustic element
Of the above, at least the surface of the GaAs substrate has an acid
A silicon oxide film or a silicon film, wherein the GaAs substrate and the quartz plate adhere to each bonding surface;
A microwave integrated circuit characterized by being directly bonded by a hydroxyl group . 2. A GaAs substrate having at least an active element
Surface of a quartz plate having an electroacoustic element and an electroacoustic element
Of the above, at least the surface of the GaAs substrate has an acid
A silicon oxide film or a silicon film, wherein the GaAs substrate and the quartz plate
And heat treatment for superposition and direct contact
Features and to luma microwave integrated circuits that have been engaged. 3. A quartz plate having electrodes disposed on upper and lower surfaces thereof,
A quartz oscillator having a lead-out conduction path onto an As substrate
3. The microwave according to claim 1, wherein
Integrated circuit. Providing an active element on a GaAs substrate;
The surface of the bonding side of the GaAs substrate and the quartz plate
That is, at least the silicon oxide is provided on the surface of the GaAs substrate.
Providing a silicon film or silicon film, and adding a hydroxyl group
And direct joining by overlapping
When manufacturing method of <br/> features and to luma microwave integrated circuits that consist of a step of providing a electro-acoustic element to the quartz plate. Providing an active element on a GaAs substrate;
The surface of the bonding side of the GaAs substrate and the quartz plate
That is, at least the silicon oxide is provided on the surface of the GaAs substrate.
Providing a silicon film or silicon film, and adding a hydroxyl group
And direct joining by overlapping
And a portion directly below the quartz plate of the GaAs substrate is etched.
Method of manufacturing features and to luma microwave integrated circuit <br/> that and a step of forming a crystal oscillator is removed by grayed. 6. After the step of direct bonding, the temperature ranges from 100 ° C. to 860 ° C.
Characterized by adding a step of heat treatment in the temperature range of
A method of manufacturing the microwave integrated circuit according to claim 4.
Law.