JP2000323925A - Temperature compensation type crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a phase noise characteristic from being deteriorated even if an oscillator is installed on a semiconductor integrated circuit. SOLUTION: A first conductivity type diffused region 35 of high concentration is installed in a second conductivity type diffused region 15 of low concentration in a first electrode. Thus, the fluctuation of the potential of the first electrode is synchronized with the fluctuation of a power, the fluctuation of the capacitance of a frequency component different from a crystal oscillation frequency is removed and the deterioration of the phase noise characteristic is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a temperature-compensated crystal oscillator mounted on a communication device such as a portable telephone.

[0002]

2. Description of the Related Art A temperature-compensated crystal oscillator to be mounted on a communication device is constituted by using a 10 MHz band AT-cut crystal oscillator as a vibration source and using a frequency adjusting circuit to form a temperature-compensation circuit. The oscillation frequency is stabilized by canceling out the temperature characteristic of the cubic curve of the crystal resonator.

Conventional temperature-compensated crystal oscillators have been mainly analog-compensated crystal temperature-compensated crystal oscillators of the direct compensation system composed of many discrete components. However, since it is not possible to meet the demands for miniaturization, weight reduction, and expansion of the temperature compensation range, recently, a temperature compensation type crystal of an indirect compensation type in which circuit components other than the crystal oscillator are mounted on a one-chip semiconductor integrated circuit. Oscillators are becoming mainstream.

A temperature-compensated crystal oscillator of the indirect compensation type is:
It comprises a crystal oscillation circuit, a temperature compensation signal generation circuit, and a variable capacitance circuit under control of the temperature compensation signal generation circuit and connected to the crystal oscillation circuit.

[0005] The variable capacitance circuit is configured using at least one variable capacitance element, and one example of a conventional configuration is shown in FIG.

As shown in the circuit diagram of FIG. 4, a fixed capacitor 7 for blocking a DC signal and a variable capacitor 9 are connected in series, and the other terminal of the variable capacitor 9 is connected to an arbitrary potential such as a power supply.

Then, an input resistor 11 is connected to a connection point between the fixed capacitance 7 and the variable capacitance 9. The control signal for the variable capacitor 9 is applied via the input resistor 11.

The input resistor 11 serves to cut off an AC signal. If the output impedance of a circuit for generating a control signal is sufficiently high, the input resistor 11 may be omitted.

The connection destination of the variable capacitor 9 may be the other terminal of the fixed capacitor having one terminal connected to a power supply.

When a variable capacitance circuit as shown in FIG. 4 is mounted on a semiconductor integrated circuit, the variable capacitance 9 is composed of a variable capacitance diode or a MOS type capacitor, and the fixed capacitance 7 is a two-layer polycrystalline silicon film. In general, it is composed of

Among these, the variable capacitance diode must not bias the pn junction in the forward direction, so that the potential relationship between the two electrodes can be restricted, which is disadvantageous in terms of the capacitance change rate as compared with the MOS type capacitor. Therefore, it is advantageous to mount a MOS capacitor having a wide frequency variable width and capable of expanding the temperature compensation range.

FIG. 5 shows an example of the temperature-compensated crystal oscillator constructed as described above.

FIG. 5 is a block diagram showing the configuration of a temperature-compensated crystal oscillator. Of the variable capacitance circuits, a sectional view of a semiconductor integrated circuit is shown. However, in this cross-sectional view, a metal wiring film, a protective film, and the like are not shown to avoid complication.

As shown in FIG. 5, a variable capacitance circuit 5 under the control of a temperature compensation signal generation circuit 3 is connected to the crystal oscillation circuit 1.

The variable capacitance circuit 5 is composed of three elements.

First, a low-concentration diffusion region 15 of the second conductivity type of the first electrode is formed on the surface of the semiconductor substrate 13 of the first conductivity type.
And a high concentration diffusion region 17 of the second conductivity type of the first electrode
Consisting of a gate insulating film 19 and a second electrode 21
The OS type capacitor is configured as the variable capacitor 9 shown in FIG.

Further, a capacitor including the fourth electrode 25, the interlayer insulating film 27, and the third electrode 29 is formed on the field oxide film 23 as the fixed capacitor 7 shown in FIG.

Further, on the field oxide film 23, an input resistor 11 made of a polycrystalline silicon film containing an appropriate concentration of impurities is formed.

The second electrode 21, the fourth electrode 25, and the input resistor 11 are connected by a metal wiring film or the like, but are shown in FIG. 5 as an electric circuit connection.

The second electrode 21, the fourth electrode 25, and the input resistor 11 can be formed by using the same polycrystalline silicon film as a starting material and changing the type and concentration of impurities. is there. Alternatively, the third electrode 29 and the input resistor 11 may be formed from the same polycrystalline silicon film.

Alternatively, the second electrode 21 and the fourth electrode 25 may be formed of a refractory metal polycide film or the like.

In any case, it is not difficult to form a temperature-compensated crystal oscillator by mounting the variable capacitance circuit shown in FIG. 4 together with an oscillation circuit on a one-chip semiconductor integrated circuit.

[0023]

However, in a temperature-compensated crystal oscillator mounted on a one-chip semiconductor integrated circuit, the phase noise characteristic is deteriorated as compared with a temperature-compensated crystal oscillator composed of discrete components. There is.

It is an object of the present invention to provide a temperature-compensated crystal oscillator that does not degrade phase noise characteristics even when mounted on a semiconductor integrated circuit.

[0025]

In order to achieve the above object, the structure of a temperature compensated crystal oscillator according to the present invention is as follows.

That is, the structure of the temperature compensated crystal oscillator according to the present invention comprises a crystal oscillation circuit, a temperature compensation signal generation circuit, and a variable capacitance circuit connected to the crystal oscillation circuit and under the control of the temperature compensation signal generation circuit. The variable capacitance circuit comprises a low-concentration diffusion region of a second conductivity type on a surface of a semiconductor substrate of a first conductivity type, and a high-concentration diffusion region of a second conductivity type in the diffusion region. A first electrode consisting of: and a low-concentration portion of the first electrode with an insulating film interposed therebetween;
A MOS capacitor including a metal film or a second electrode made of a semiconductor film containing a high concentration of impurities is a variable capacitance element, and a first conductivity type is formed in a low concentration diffusion region of the second conductivity type of the first electrode. Characterized by having a high concentration diffusion region.

In this temperature-compensated crystal oscillator, the high-concentration diffusion region of the first conductivity type in the low-concentration diffusion region of the second conductivity type is separated from the high-concentration diffusion region of the second conductivity type. It is characterized by being.

Further, in this temperature-compensated crystal oscillator, the high-concentration diffusion region of the first conductivity type in the low-concentration diffusion region of the second conductivity type is formed on the surface of the low-concentration diffusion region of the second conductivity type. It is characterized by being near the center.

[Operation] In order for the capacitance of the MOS capacitor to be variable, the width of the depletion layer on the surface of the first electrode on the semiconductor substrate side must be changed by the electric field from the second electrode. In addition, the impurity concentration other than the connection portion with the metal wiring must be low. Therefore, most of the first electrodes have a high resistance.

Since an arbitrary signal such as an external frequency control signal may be applied to the first electrode, it is necessary to electrically separate the first electrode from a surrounding semiconductor substrate which is a power supply potential. Is employed.
Therefore, a junction capacitance exists between the first electrode and the surrounding semiconductor substrate.

Considering such junction capacitance and electrode resistance, the actual circuit diagram of the conventional variable capacitance circuit shown in FIG. 5 is as shown in FIG.

As shown in FIG. 6, an electrode resistor 33 is connected between the variable capacitor 9 and an arbitrary potential, and a junction capacitor 31 is connected between the variable capacitor 9 and a power supply.

The power supply to which the junction capacitor 31 is connected is pulsating under the influence of the crystal oscillation circuit, and fluctuations in its potential are transmitted to the first electrode of the variable capacitor 9 through the junction capacitor 31. Because of the electrode resistance 33, this fluctuation of the potential cannot be suppressed, and the potential of the first electrode also pulsates.

If the pulsation of the potential of the first electrode is synchronized with the pulsation of the power supply, there is no frequency component other than the crystal oscillation frequency, so that no modulation is applied to the crystal oscillation frequency.

However, in the conventional variable capacitor 9, since the pulsation of the potential of the first electrode cannot follow the crystal oscillation frequency, the fluctuation of the frequency component different from the crystal oscillation frequency is superimposed on the first electrode. I will.

Since the capacitance value of the MOS type capacitor is determined by the potential difference between the first electrode and the second electrode, the fluctuation of this potential causes fluctuation of the capacitance value of a frequency component different from the crystal oscillation frequency. Modulates the crystal oscillation frequency. This modulation is observed as deterioration of the phase noise characteristic.

Therefore, in order to prevent the phase noise characteristic from deteriorating, a configuration in which the junction capacitance 31 and the electrode resistance 33 do not exist, or a configuration in which the junction capacitance 31 and the electrode resistance
3 is to provide an ingenuity so that there is no effect even if 3 exists. Since the former method is physically difficult, the present invention employs the latter method.

The most important feature of the present invention is that the second electrode of the first electrode
A high-concentration diffusion region of the first conductivity type is provided in a low-concentration diffusion region of the conductivity type.

From another viewpoint, the fluctuation of the potential of the first electrode is an operation of alternately promoting the generation of majority carriers and the generation of minority carriers.

Since the majority carrier is literally present in a large number, the response to the disturbance is fast. For this reason, it is possible to respond instantaneously to a disturbance that encourages the generation of majority carriers.

On the other hand, the generation speed of minority carriers depends on the crystal defect density and the like, but is much slower than that of majority carriers, and usually cannot respond to signals of 1 kHz or more. For this reason, it is impossible to follow the disturbance of the crystal oscillation frequency in the 10 MHz band, and a slow frequency component is superimposed on the fluctuation of the potential of the first electrode.

Therefore, a storage for minority carriers is provided in advance, and when a disturbance occurs, minority carriers are injected from this storage.

With such a mechanism, the generation of minority carriers can be substantially increased at a high speed, and it is possible to follow the disturbance. What corresponds to this storage is a high-concentration diffusion region of the first conductivity type.

In the high-concentration diffusion region of the first conductivity type,
There are a large number of conductivity type majority carriers,
Are injected as minority carriers into the low-concentration diffusion region of the second conductivity type of the first electrode.

This injection mechanism is exactly the same as the operation of the MOS transistor, and is much faster than the disturbance in the 10 MHz band. Therefore, the fluctuation frequency of the potential of the first electrode matches the crystal oscillation frequency. For this reason, other frequency components do not exist, and deterioration of phase noise can be prevented.

The semiconductor substrate, the low concentration diffusion region of the first electrode, and the high concentration diffusion region of the opposite conductivity type are structurally the same as a junction type bipolar transistor. Therefore, in order to prevent the operation as a variable capacitor from being hindered, they must be prevented from operating as a bipolar transistor.

There are various methods for preventing the device from operating as a bipolar transistor. The simplest method is to float a high-concentration diffusion region of the opposite conductivity type serving as an emitter, or to use a high-concentration diffusion region of the opposite conductivity type. A thick diffusion region is provided near the center of the low-concentration diffusion region of the first electrode to increase the base thickness, or a combination of both.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a temperature compensated crystal oscillator according to the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described.

FIG. 1 is a block diagram showing a configuration of a temperature-compensated crystal oscillator according to a first embodiment of the present invention. Among them, a variable capacitance circuit is a sectional view of a semiconductor integrated circuit. However, in this sectional view,
In order to avoid complication, illustration of a metal wiring film, a protective film, and the like is omitted.

[Description of First Embodiment: FIG. 1] As shown in the block diagram of FIG. 1, a variable capacitance circuit 5 under the control of a temperature compensation signal generating circuit 3 is connected to a crystal oscillation circuit 1. .

The variable capacitance circuit 5 is composed of three elements.

First, a low concentration diffusion region 15 of the second conductivity type of the first electrode is formed on the surface of the semiconductor substrate 13 of the first conductivity type.
And a high concentration diffusion region 17 of the second conductivity type of the first electrode
, A first conductive type high-concentration diffusion region 35, a gate insulating film 19, and a second electrode 21 to form a MOS capacitor. This MOS capacitor is the variable capacitor 9 shown in FIG.

On the field oxide film 23, a fourth
, An interlayer insulating film 27 and a third electrode 29 constitute a capacitor. This capacitor is shown in FIG.
The fixed capacity 7 shown in FIG.

Further, on the field oxide film 23, an input resistor 1 made of a polycrystalline silicon film containing appropriate impurities is formed.
1.

The second electrode 21, the fourth electrode 25, and the input resistor 11 are connected by a metal wiring film or the like, but are shown in FIG. 1 as connections in an electric circuit. Also, descriptions of a protective film and the like are omitted.

As shown in FIG. 1, since the first electrode is of the second conductivity type, a junction capacitance exists between the first electrode and the semiconductor substrate 13 of the first conductivity type.

The semiconductor substrate 13 of the first conductivity type is connected to a power supply and is originally kept at a constant potential.

However, the crystal oscillation circuit in the 10 MHz band has a large pulsation of current, and the metal wiring of the semiconductor integrated circuit does not have enough power to suppress the fluctuation of the potential due to the pulsation. I will.

Therefore, the potential of the semiconductor substrate 13 of the first conductivity type is constantly pulsating during the operation of the crystal oscillation circuit.

The pulsation of the potential of the semiconductor substrate 13 of the first conductivity type is transmitted to the first electrode via the junction capacitance.

Most of the first electrode is a low-concentration diffusion region 15 of the second conductivity type, so that it has a high resistance and has no force to suppress transmitted pulsation. Therefore, the potential of the low concentration diffusion region 15 of the second conductivity type of the first electrode also pulsates.

Looking at this potential pulsation from another viewpoint, it is an operation of alternately promoting the generation and recombination of majority carriers and minority carriers.

Since there are literally many majority carriers, the majority carrier responds instantaneously to a disturbance that prompts generation.

On the other hand, if the crystal defect density is at a level at which the semiconductor integrated circuit operates normally, the generation of minority carriers in the low-concentration diffusion region 15 of the second conductivity type is slow, and is usually higher than 1 kHz. It cannot follow speed disturbances.

Therefore, if this state is left as it is, a delay occurs in the fluctuation of the potential of the first electrode, and fluctuation of a frequency component different from the crystal oscillation frequency is superimposed. The deterioration of the phase noise in the prior art is due to this.

Therefore, in the present invention, as shown in FIG. 1, a high-concentration diffusion region 35 of the first conductivity type is provided in a low-concentration diffusion region 15 of the second conductivity type.

In the high-concentration diffusion region 35 of the first conductivity type, there are many majority carriers of the first conductivity type, and a disturbance which promotes the generation of minority carriers in the low-concentration diffusion region 15 of the second conductivity type. Comes, the majority carriers of the first conductivity type are injected as minority carriers from the high concentration diffusion region 35 of the first conductivity type into the low concentration diffusion region 15 of the second conductivity type.

This injection mechanism is the same as the operation for forming the channel of the MOS transistor, and is very fast. Therefore, it easily follows disturbances in the 10MHz band.
There is no delay in fluctuation of the potential of the first electrode.

For this reason, since the fluctuation of the potential of the first electrode is synchronized with the fluctuation of the power supply, there is no frequency component different from the crystal oscillation frequency.

Therefore, by providing the high-concentration diffusion region 35 of the first conductivity type in the low-concentration diffusion region 15 of the second conductivity type as in the present invention, deterioration of phase noise can be prevented. .

The high-concentration diffusion region 35 of the first conductivity type is in contact with the low-concentration diffusion region 15 of the second conductivity type, and the low-concentration diffusion region 15 of the second conductivity type is in contact with the first conductivity type. Since they are in contact with the semiconductor substrate 13, they have a junction type bipolar transistor structure.

If this structure electrically operates as a bipolar transistor, it cannot operate as a variable capacitor. Therefore, it is necessary to prevent operation as a bipolar transistor.

The first measure is to prevent the first
This is a method of floating the high-concentration diffusion region 35 of the conductivity type.

In order to operate the bipolar transistor, it is necessary to bias the emitter and the base so that they are in the forward direction. However, if the emitter is floating, it becomes impossible to bias in the forward direction. It cannot operate as a transistor.

Then, the high concentration diffusion region 3 of the first conductivity type
In the case of No. 5, since it is sufficient to store the majority carriers corresponding to the fluctuation of the potential of the first electrode, floating is sufficient if there is a certain volume. Therefore, the operation as a bipolar transistor can be prevented without impairing the original function of the high-concentration diffusion region 35 of the first conductivity type.

By the way, the high-concentration diffusion region 35 of the first conductivity type corresponds to the high-concentration diffusion region 1 of the second conductivity type of the first electrode.
7 makes a pn junction between high concentrations,
The reverse breakdown voltage becomes low.

In this case, the high-concentration diffusion region 35 of the first conductivity type and the high-concentration diffusion region 1 of the second conductivity type of the first electrode are used.
7 is almost in a short-circuit state, so that the high-concentration diffusion region 35 of the first conductivity type is not in a floating state.

Therefore, the first conductive type high concentration diffusion region 3
5 is a high concentration diffusion region 17 of the second conductivity type of the first electrode.
It must be formed separately from. This is the second aspect of the present invention.
It is a feature of.

The second measure for preventing the operation of the bipolar transistor is to make the base thickness as large as possible.

The base thickness is a distance between the high-concentration diffusion region 35 of the first conductivity type and the semiconductor substrate 13 of the first conductivity type.

For this purpose, the high-concentration diffusion region 35 of the first conductivity type is arranged near the center of the surface of the low-concentration diffusion region 15 of the second conductivity type. This is the third feature of the present invention.

Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing a configuration of a temperature-compensated crystal oscillator according to a second embodiment of the present invention. Among them, a variable capacitance circuit is a cross-sectional view of a semiconductor integrated circuit. However, in this cross-sectional view, a metal wiring film, a protective film, and the like are not shown to avoid complication.

[Description of Second Embodiment: FIG. 2] As shown in the block diagram of FIG. 2, a variable capacitance circuit 5 under the control of a temperature compensation signal generation circuit 3 is connected to a crystal oscillation circuit 1. .

The variable capacitance circuit 5 is composed of three elements.

First, a low-concentration diffusion region 15 of the second conductivity type of the first electrode is formed on the surface of the semiconductor substrate 13 of the first conductivity type.
And a high concentration diffusion region 17 of the second conductivity type of the first electrode
, A first conductive type high-concentration diffusion region 35, a gate insulating film 19, and a second electrode 21 to form a MOS capacitor. This MOS capacitor is the variable capacitor 9 shown in FIG.

On the field oxide film 23, the fourth
, An interlayer insulating film 27 and a third electrode 29 constitute a capacitor. This capacitor is shown in FIG.
The fixed capacity 7 shown in FIG.

Further, on the field oxide film 23, an input resistor 1 made of a polycrystalline silicon film containing appropriate impurities is formed.
1.

The second electrode 21, the fourth electrode 25, and the input resistor 11 are connected by a metal wiring film or the like, but are shown in FIG. 2 as connections in an electric circuit. Also, descriptions of a protective film and the like are omitted.

The difference between the second embodiment shown in FIG. 2 and the first embodiment shown in FIG. 1 is that the second electrode 21 is provided above the high-concentration diffusion region 35 of the first conductivity type. Is present or not.

Although both the electric operation and the effect are the same, both have different manufacturing methods.

In the method of manufacturing a semiconductor integrated circuit, the high-concentration diffusion region such as the second-conductivity-type high-concentration diffusion region 17 of the first electrode is formed simultaneously with the formation of the source / drain of the MOS transistor. Generally, after the second electrode 21 is formed, the second electrode 21 is formed by ion implantation and heat treatment.

Therefore, as shown in FIG.
If the vicinity of the center of 1 is removed, the high-concentration diffusion region 35 of the first conductivity type can also be formed after the formation of the second electrode 21.

That is, in the second embodiment shown in FIG. 2, the high-concentration diffusion region 35 of the first conductivity type can be formed without changing the usual method of manufacturing a semiconductor integrated circuit. An increase in manufacturing cost can be prevented.

In the second embodiment shown in FIG.
A high-concentration diffusion region 35 of the first conductivity type is disposed near the center of the surface of the low-concentration diffusion region 15 of the second conductivity type, and
Separation from the conductive type high concentration diffusion region 17 is necessary to prevent operation as a bipolar transistor.

Next, a third embodiment of the present invention will be described. FIG. 3 is a block diagram showing a configuration of a variable capacitance circuit according to the third embodiment of the present invention. Among the variable capacitance circuits, a sectional view of a semiconductor integrated circuit is shown. However, in this cross-sectional view, a metal wiring film, a protective film, and the like are not shown to avoid complication.

[Description of Third Embodiment: FIG. 3] As shown in the block diagram of FIG. 3, a variable capacitance circuit 5 under the control of the temperature compensation signal generation circuit 3 is connected to the crystal oscillation circuit 1. .

The variable capacitance circuit 5 is composed of three elements.

First, a low concentration diffusion region 15 of the second conductivity type of the first electrode is formed on the surface of the semiconductor substrate 13 of the first conductivity type.
And a high concentration diffusion region 17 of the second conductivity type of the first electrode
, A first conductive type high-concentration diffusion region 35, a gate insulating film 19, and a second electrode 21 to form a MOS capacitor. This MOS capacitor is the variable capacitor 9 shown in FIG.

Further, a capacitor comprising the interlayer insulating film 27 and the third electrode 29 is formed on the second electrode 21. This capacitor is the fixed capacitance 7 shown in FIG.

Further, on the field oxide film 23, an input resistor 1 made of a polycrystalline silicon film containing appropriate impurities is formed.
1.

Although the second electrode 21 and the input resistor 11 are connected by a metal wiring film or the like, FIG. 3 shows the connection as an electric circuit. Also, descriptions of a protective film and the like are omitted.

In the third embodiment shown in FIG. 3, when the fixed capacitor 1 is formed on the field oxide film 23 as shown in FIG. 1 or FIG. The fixed capacitance 1 is formed on the second electrode 21 so as to avoid a decrease in the capacitance change rate due to the parasitic capacitance between the fixed electrodes 1.

Even in the case of such a stack structure, the first
There is no change in the effect of tuning the fluctuation of the potential of the first electrode to the fluctuation of the power supply by minority carrier injection from the high-concentration diffusion region 35 of the conductivity type to the low-concentration diffusion region 15 of the second conductivity type.

As described above, the present invention has been specifically described based on the embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the present invention. It is.

For example, in the third embodiment shown in FIG. 3, the second electrode 21 and the third electrode 29 are present above the high-concentration diffusion region 35 of the first conductivity type. 2
These electrodes may be removed from the upper part of the high-concentration diffusion region 35 of the first conductivity type as in the second embodiment shown in FIG.

[0106]

As described above, the pulsation of the potential of this electrode is synchronized with the pulsation of the power supply by providing the diffusion region of the opposite conductivity type serving as a storage for minority carriers in the electrode on the semiconductor substrate side of the variable capacitance. As a result, it is possible to eliminate frequency components other than the crystal oscillation frequency, thereby preventing the phase noise characteristic from deteriorating.

Therefore, the size of the temperature compensated crystal oscillator can be reduced by the semiconductor integrated circuit without deteriorating the characteristics, and the effect is very large.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a temperature compensated crystal oscillator according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a temperature-compensated crystal oscillator according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a temperature compensated crystal oscillator according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a variable capacitance circuit according to the related art.

FIG. 5 is a block diagram illustrating a configuration of a temperature-compensated crystal oscillator according to the related art.

FIG. 6 is a practical circuit diagram of a variable capacitance circuit according to the related art.

[Explanation of symbols]

1: crystal oscillation circuit 3: temperature compensation signal generation circuit 5: variable capacitance circuit 13: semiconductor substrate of the first conductivity type 15: low-concentration diffusion region of the second conductivity type of the first electrode 17: of the first electrode High-concentration diffusion region of second conductivity type 19: Gate insulating film 21: Second electrode 25: Interlayer insulation film 29: Third electrode 35: High-concentration diffusion region of first conductivity type

Claims (3)

[Claims] 1. A temperature-compensated crystal oscillator comprising a crystal oscillation circuit, a temperature compensation signal generation circuit, and a variable capacitance circuit connected to the crystal oscillation circuit and under the control of the temperature compensation signal generation circuit. A first electrode formed of a low-concentration diffusion region of the second conductivity type on the surface of the semiconductor substrate of the first conductivity type; and a high-concentration diffusion region of the second conductivity type in the diffusion region; A MOS capacitor including a second electrode made of a metal film or a semiconductor film containing a high concentration of impurities is opposed to a low-concentration portion of the first electrode with an insulating film interposed therebetween. In the low concentration diffusion region of the second conductivity type,
A temperature-compensated crystal oscillator having a high-concentration diffusion region of a conductivity type. 2. A temperature compensated crystal oscillator comprising a crystal oscillation circuit, a temperature compensation signal generation circuit, and a variable capacitance circuit connected to the crystal oscillation circuit and under the control of the temperature compensation signal generation circuit. A first electrode formed of a low-concentration diffusion region of the second conductivity type on the surface of the semiconductor substrate of the first conductivity type; and a high-concentration diffusion region of the second conductivity type in the diffusion region; A MOS capacitor including a second electrode made of a metal film or a semiconductor film containing a high concentration of impurities is opposed to a low-concentration portion of the first electrode with an insulating film interposed therebetween. In the low concentration diffusion region of the second conductivity type,
A high-concentration diffusion region of the first conductivity type in the low-concentration diffusion region of the second conductivity type, wherein the high-concentration diffusion region of the second conductivity type is separated from the high-concentration diffusion region of the second conductivity type; A temperature-compensated crystal oscillator characterized in that: 3. The temperature compensated crystal oscillator according to claim 1, wherein the high-concentration diffusion region of the first conductivity type in the low-concentration diffusion region of the second conductivity type has a low-concentration diffusion region of the second conductivity type. A temperature-compensated crystal oscillator located near the center of the surface of the diffusion region.