JPH08136598A - Capacitance detection circuit - Google Patents

Abstract

PURPOSE: To obtain a capacitance detection circuit by which an influence on a circuit operation due to a leakage current is eliminated and by which a capacitance can be detected precisely even when an ambient temperature is high by a method wherein the circumference of a p-n junction region forming every diode is enclosed by a box-shaped insulating film. CONSTITUTION: The circumference of a p-n junction region forming every diode is enclosed by a box-shaped insulating film which is formed of an electric insulator such as a silicon oxide, polysilicon or the like and which comprises sidewalls 11 and a bottom wall 12. Then, a CMOS circuit 10 is formed, by an ordinary CMOS process, on an n-type silicon substrate 9 at the outside of the p-n junction region 8 for the diode. Then, a metal interconnection 14 is formed on the surface side of the n-type silicon substrate 9, and a p-type semiconductor p<+> and an n-type semiconductor n<+> which form the p-n junction region 8 are connected respectively to the CMOS circuit 10. A leakage current is not thereby generated. Even when an ambient temperature is high, the capacitance of a capacitor can be detected precisely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance detection circuit used in a capacitance type sensor or the like for detecting detection information of an object to be detected such as pressure, displacement, flow rate, humidity and acceleration based on a change in capacitance. It is about.

[0002]

2. Description of the Related Art FIG. 2 shows a capacitance detection circuit of a diode capacitor bridge type known as a circuit of various capacitance type sensors such as an acceleration sensor. This circuit has a diode D corresponding to each bridge side of the four sides.
_{1 to} D ₄ are arranged to form a diode bridge 6,
A capacitance detection unit 1 is provided between a pair of detection ends A ₁ and A ₂ facing each other of the bridge circuit.

In the capacitance detecting section 1, for example, as shown in FIG. 4, a movable electrode 4 is arranged at an intermediate position (center position) between a pair of opposed fixed electrodes 2 and 3, and the fixed electrode 2 and the movable electrode 4 are arranged. To form a capacitor C ₁ , and the movable electrode 4 and the fixed electrode 3 form a capacitor C _1.
2 is formed, as shown in the circuit of FIG. 2, is obtained by connecting a capacitor C ₁ and C ₂ in series, each capacitor C _1,
C ₂ functions as a variable capacitor whose electrostatic capacitance changes according to the displacement of the movable electrode 4. The connection between the capacitors C ₁ and C ₂ is grounded to the ground whose reference voltage is zero voltage, and the resistors R ₁ and R ₂ are respectively connected.
Is connected to the non-inverting input terminals of the operational amplifiers A ₁ and A ₂ .

In this circuit, operational amplifiers A ₁ , A
_An amplifier circuit is formed by including ₂ and the operational amplifier A ₃ , the output terminal side of the operational amplifier A ₁ is connected to the inverting input terminal of the operational amplifier A ₃ , and the output terminal side of the operational amplifier A ₂ is the non-inverting terminal of the operational amplifier A ₃ . It is connected to the input terminal.

The output end G ₁ of the circuit of the diode bridge 6
Is connected to the AC electromotive oscillator 5 functioning as an oscillation circuit via the coupling capacitor C _c1 and the output end G ₂ via the coupling capacitor C _C2 having the same capacity. The electromotive oscillator 5 oscillates and outputs an AC voltage.

In this capacitance type detection circuit, for example, when acceleration is applied to the capacitance detection section 1 and the movable electrode 4 is displaced by this acceleration, a difference occurs between the capacitances of the capacitors C ₁ and C ₂ . Then, the voltage corresponding to this capacitance difference is amplified by the amplifier circuit and detected as a voltage output.

By the way, conventionally, the electrostatic capacitance detection circuit as described above is composed of individual parts such as a diode, a capacitor, a resistor, and an operational amplifier. If the circuit is composed of such individual parts, the circuit is There are problems that the scale becomes large and that the capacitance detection sensitivity and the resolution decrease due to the parasitic capacitance in the circuit and the stray capacitance determined by the arrangement of the above components.

Therefore, in order to solve these problems,
It is being considered to integrate the capacitance detection circuit into an IC,
Each diode D _{1 to} D _{4 of the} diode bridge 6
Is being studied for a structure as shown in FIG.
As shown in the figure, in each diode, for example, a pn junction region 8 in which a p-type semiconductor p ⁺ and an n-type semiconductor n ⁺ are joined is formed in a semiconductor substrate such as an n-type silicon substrate 9, and p
A p-type semiconductor p ⁻ is interposed between the n-junction region 8 and the n-type silicon substrate 9. A reverse bias is normally applied to the n-type silicon substrate 9 of this transistor for use, and a parasitic bipolar transistor operation is not performed between the pn junction region 8 and the n-type silicon substrate 9.

[0009]

By the way, in the diode shown in FIG. 3, a pn junction is formed between the n-type silicon substrate 9 and the p-type semiconductor p ⁻ region.
Since the junction is in the reverse bias state, a leak current is generated from the n-type silicon substrate 9 side to the pn junction region 8 side. This leak current is almost negligible at room temperature, but the leak current increases as the temperature rises. Therefore, if the ambient temperature of the circuit rises above 50 ° C, it will be affected by this leak current. However, there is a problem that the detection sensitivity of the capacitance detection circuit becomes low and the detection operation is stopped at a temperature exceeding 100 ° C.

The present invention has been made to solve the above problems, and an object thereof is to be able to accurately detect electrostatic capacitance even when the ambient temperature is a high temperature of, for example, 50 ° C. or higher. Another object is to provide a capacitance detection circuit having good temperature characteristics.

[0011]

In order to achieve the above object, the present invention is constructed as follows. That is, the present invention includes an oscillation circuit, a diode bridge formed by providing a plurality of diodes, and two variable capacitors whose capacitances change, and outputs the difference between the capacitances of the two variable capacitors as a voltage output. In the capacitance detection circuit, the diodes are formed by forming pn junction regions in the semiconductor substrate, and side walls and a bottom formed by an electrical insulator around the pn junction regions forming the diodes. It is characterized by being surrounded by a box-shaped insulating film having a wall.

It is also a characteristic feature of the present invention that a CMOS circuit having an oscillation circuit formed by a CMOS process is provided in the semiconductor substrate region outside the pn junction region of the diode surrounded by the insulating film. There is.

[0013]

In the present invention having the above-described structure, the pn junction region forming each diode is surrounded by a box-shaped insulating film having a side wall and a bottom wall formed of an electric insulator, so that the pn junction is formed. The region and the semiconductor substrate are electrically insulated from each other, and the generation of leak current from the semiconductor substrate to the pn junction region is prevented. Therefore, the circuit operation is not affected by the leak current, and the capacitance detection operation is accurately performed even when the ambient temperature is high.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals will be given to the same names as those in the above-described examples, and the duplicated description will be omitted. The electrostatic capacitance detection circuit of the present embodiment is configured by a circuit similar to the circuit diagram shown in FIG. 2. In FIG. 1, the diode structure in the electrostatic capacitance detection circuit of the present embodiment shows an electromotive oscillator. It is shown with a CMOS circuit 10 with 5, etc. The electrostatic capacitance detection circuit of this embodiment has four diodes D ₁ to D ₁ having the same structure as the diode structure shown in FIG.
D ₄ is provided to form the diode bridge 6 of the circuit of FIG. 2. The most characteristic feature of this embodiment is that the silicon is formed around the pn junction region 8 forming each of the diodes D _{1 to} D _4. That is, it is surrounded by a box-shaped insulating film having a side wall 11 and a bottom wall 12 formed of an electric insulator such as oxide or polysilicon.

A CMOS (Complementary Metal Oxide Semicond) is formed in the n-type silicon substrate 9 (semiconductor substrate) region outside the pn junction region 8 surrounded by the insulating film.
The CMOS circuit 10 formed by the uctor) process is provided, and the circuit configuration except the capacitance detection unit 1 and the diode bridge in the circuit diagram shown in FIG.
It is composed of 10. In this embodiment, the capacitance detection unit 1 is provided outside the n-type silicon substrate 9.

The present embodiment is configured as described above,
When forming the diode structure shown in FIG. 1, first,
A semiconductor substrate having a structure in which an insulating layer 13 such as silicon oxide is sandwiched between n-type silicon substrates 9 is formed. Insulation layer 13
Ion implantation, silicon on insulator technology,
It is formed by a CVD (Chemical Vapor Deposition) method or the like. Next, a groove reaching from the surface of the semiconductor substrate to the insulating layer 13 is formed, and a side wall 11 is formed of polysilicon in the groove. The side wall 11 is formed by the CVD method or the like. As a result, the side wall 11 and the bottom wall 12 of the insulating layer 13 form a box-shaped insulating film surrounding the pn junction region 8.

Then, the n-type silicon substrate 9 outside the pn junction region 8 of the diode surrounded by the side wall 11 and the bottom wall 12 is formed.
Then, the CMOS circuit 10 is provided by forming the circuit configuration except the diodes D _{1 to} D ₄ and the capacitance detecting section 1 of the circuit of FIG. 2 by a normal CMOS process. Next, a metal wiring 14 formed of a film of aluminum, gold, copper or the like is provided on the surface side of the n-type silicon 9 to form a p-type semiconductor p ⁺ and an n-type semiconductor n ⁺ which form a pn junction region 8. CMOS circuit
Connect with 10.

The electrostatic capacitance detection circuit of this embodiment also operates similarly to the conventional electrostatic capacitance detection circuit, and the electrostatic capacitance difference between the capacitors C ₁ and C ₂ of the capacitance detection unit 1 is detected as a voltage output. In the present embodiment, the sidewalls formed by an electrical insulator are formed around the pn junction region 8 forming each of the diodes D _{1 to} D _4.
Because it is surrounded by an insulating film having 11 and a bottom wall 12,
The leak current, which has been a problem in the capacitance detection circuit having the diode structure shown in FIG. 3, does not occur. Therefore, unlike the electrostatic capacitance detection circuit having the diode structure shown in FIG. 3, when the ambient temperature rises, the detection sensitivity is not lowered and the detection operation is not stopped due to the influence of the leak current. Even if the ambient temperature is high, the capacitance difference between the capacitors C ₁ and C ₂ can be accurately detected.

Further, according to this embodiment, the electromotive oscillator 5
Are used as the CMOS circuit 10 formed by the CMOS process. By forming the circuit by applying the semiconductor manufacturing technique in this way, the capacitance detection circuit can be easily manufactured, and the CMOS circuit is Since the power consumption is low, the operation speed is high, and the integration is high, the circuit can be downsized and the detection accuracy of the circuit can be improved.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, in the above embodiment, the insulating film on the side wall 11 is formed of polysilicon, but the insulating film may be formed of an electric insulator other than polysilicon, such as silicon oxide or an organic insulator.

The method of forming the diode structure shown in FIG. 1 is not particularly limited and may be set appropriately. For example, when forming a semiconductor substrate, n
The type silicon substrate 9 and the insulating layer 13 may be bonded together.

Further, in the above embodiment, the semiconductor substrate is n
Although the semiconductor substrate has a structure including the type silicon substrate 9 and the insulating layer 13, the semiconductor substrate has a structure other than the n type silicon substrate 9, such as a p type silicon substrate, and the insulating layer 13,
The structure may be such that the insulating layer 13 is embedded in a substrate such as a die-type silicon substrate.

Further, in the above embodiment, the circuit configuration except the capacitance detecting section 1 and the diode bridge is formed by the CMOS circuit 10. However, these circuit configurations are not necessarily CMOS.
It is not always formed by the circuit 10. For example, only the electromotive force oscillator 5 and the amplifier circuit may be formed by a CMOS circuit, or all the circuit configurations may be formed by a circuit other than the CMOS circuit. However, if the above circuit is CMO
If the S circuit 10 is used and a circuit is formed by applying semiconductor manufacturing technology, the manufacturing of the capacitance detection circuit becomes easy, and moreover,
A CMOS circuit is preferable because the circuit can be downsized and the detection accuracy of the circuit can be improved.

Further, in the above embodiment, the connection portion of the capacitors C ₁ and C ₂ of the capacitance detection unit 1 is connected to the ground to give the zero voltage as the reference voltage. However, a voltage other than the zero voltage is used as the reference voltage. May be given.

Further, in the above embodiment, the neutral position of the movable electrode 4 of the capacitance detecting section 1 is set to the intermediate position (center position) between the fixed electrodes 2 and 3, but the neutral position of the movable electrode 4 is not necessarily the fixed electrode. It does not have to be an intermediate position between the two and three, and may be a position closer to the fixed electrode on one side.

Furthermore, in the above embodiment, for example, the amplifier circuit has a configuration having operational amplifiers A ₁ , A ₂ , and A ₃ , but the configuration of the amplifier circuit and the like is not particularly limited.
The circuit configuration of the capacitance detection circuit of the present invention includes an oscillation circuit,
A diode bridge formed by providing a plurality of diodes and two variable capacitors whose electrostatic capacities change are provided, and variously configured to detect a difference in electrostatic capacities of these two variable capacitors as a voltage output. It is a thing.

Further, although the above description has been made by taking the electrostatic capacitance detection circuit provided in the acceleration sensor as an example, the electrostatic capacitance detection circuit of the present invention is not limited to the acceleration sensor, and may be, for example, a pressure sensor. , A displacement sensor, a flow sensor, a humidity sensor, and the like, which are used in various capacitive sensors that detect detection information of a detection target.

[0028]

According to the present invention, a sidewall and a bottom wall formed of an electrical insulator are formed around a pn junction region forming each diode formed by forming a pn junction region in a semiconductor substrate. Since it is surrounded by the box-shaped insulating film having the above, it becomes possible to prevent the generation of a leak current from the semiconductor substrate. As a result, it is possible to prevent the sensitivity detection circuit from lowering its sensitivity at high temperatures (for example, 50 ° C or higher), which has been conventionally caused by the generation of leak current. It can be a circuit.

Further, according to the present invention, a CMOS circuit having an oscillation circuit formed by a CMOS process is provided in a semiconductor substrate region outside a pn junction region of a diode surrounded by an insulating film. By forming the circuit, it is possible to easily manufacture the capacitance detection circuit, and it is possible to reduce the size of the circuit and improve the detection accuracy of the circuit.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a diode structure in an embodiment of a capacitance detection circuit according to the present invention.

FIG. 2 is a circuit diagram showing an example of a capacitance detection circuit.

FIG. 3 is an explanatory view showing a diode structure in a conventional IC-based capacitance detection circuit.

FIG. 4 is an explanatory diagram showing an example of a capacitance detection element of a capacitance detection circuit.

[Explanation of symbols]

5 electromotive oscillator 6 diode bridge 8 pn junction regions 10 CMOS circuit 11 side wall 12 bottom wall D ₁ to D ₄ diodes C _1, C ₂ capacitors

Claims (2)

[Claims] 1. An oscillating circuit, a diode bridge formed by providing a plurality of diodes, and two variable capacitors whose electrostatic capacities change, the difference between the electrostatic capacities of the two variable capacitors being used as a voltage output. In the capacitance detecting circuit for detecting, each diode is pn in a semiconductor substrate.
An electrostatic capacitor characterized in that it is constituted by forming a junction region, and a pn junction region forming each of these diodes is surrounded by a box-shaped insulating film having a side wall and a bottom wall formed of an electric insulator. Capacitance detection circuit. 2. A diode pn surrounded by an insulating film.
The electrostatic capacitance detection circuit according to claim 1, wherein a CMOS circuit having an oscillation circuit formed by a CMOS process is provided in the semiconductor substrate region outside the junction region.