JPH03239939A - Capacity type pressure sensor - Google Patents

Abstract

PURPOSE:To obtain the pressure sensor which has good linearity and high accuracy by forming electrodes which have a size ratio within a specific range on a pressure sensitive diaphragm. CONSTITUTION:The pressure sensitive diaphragm 12 and a recessed part 13 are formed on a semiconductor substrate 11, an electrode 14 is formed in the center of the diaphragm 12 to a 1/5-3/5 size ratio, and the electrode 14 is connected to a circuit part 16 through a connection terminal part 17. Further, an electrode 24 is formed on the glass substrate 21 in the same shape with the electrode 14 and the substrates 11 and 21 are joined together to make the electrodes 14 and 24 face each other; and the recessed part 13 is sealed to form a reference pressure chamber 15, the electrode 24 is connected to the circuit part 16 through the terminal part 17, and the circuit 16 finds pressure from the frequency when the capacity between the electrodes 14 and 24 is charged or discharged. When the one-side size of the diaphragm 12 is denoted as (a) and the one-side size of the electrode 14 isdenoted as (b), the electrode ratio b/a is set to <=(3/5) to improve the linearity without deteriorating frequency sensitivity so much or to >=(1/5) to prevent capacity variation DELTAC from being too small and included in floating capacity, thereby improving the detection accuracy.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a capacitive pressure sensor formed by bonding substrates on which electrodes are formed.

[Prior art]

Conventionally, as a capacitive pressure sensor 30, one shown in the vertical cross-sectional view of FIG. 7 is known. In the capacitive pressure sensor 30, a pressure-sensitive diaphragm portion 32 and a recess 3 which receive a measured pressure P are placed on a semiconductor substrate 3 made of single crystal silicon.
3 is formed, and an electrode 34 is formed in the recess 33 portion. On the other hand, an electrode 44 is formed on a glass substrate 41 made of Pyrex glass. The semiconductor substrate 3/ and the glass substrate 41 are bonded using a well-known anodic bonding technique so that the electrode 34 of the semiconductor substrate 3/ and the electrode 44 of the glass substrate 41 face each other. After this bonding, the recess 33 of the semiconductor substrate 3 is sealed into the reference pressure chamber 3.
It becomes 5. Further, a circuit section 36 for determining a pressure value from the capacitance between the electrodes 34, 44 is formed and integrated on the semiconductor substrate 3/ using semiconductor manufacturing technology. Reference numeral 48 is a signal line for taking out a signal to the outside, and the signal line 48 is connected to the circuit portion 36 formed on the semiconductor substrate 3 via a conductive adhesive 49 or the like.

[Problem to be solved by the invention]

As described above, the IC-based capacitive pressure sensor directly detects the capacitance between the electrodes 34 and 44 that changes due to displacement due to the measured pressure P applied to the pressure-sensitive diaphragm section 32. The interelectrode capacitance C is calculated as follows, assuming that the displacement due to the measured pressure P applied to the pressure sensitive diaphragm section 32 is uniform, C=ε
(1) (ε: dielectric constant, A: electrode area, d: electrode spacing). Also, the electrode spacing d is given by d=do-α for the pressure to be measured P.
There is the following relationship (P-Po) (2). However, Po is the reference pressure in the reference pressure chamber 35,
In d, the external pressure is the reference pressure P. When the electrode spacing is equal to , α is a constant. Therefore, the relationship between the pressure to be measured P and the capacity C is as follows, and as shown in Fig. 3(a), the pressure to be measured P and the capacity C have a non-linearity in an inversely proportional relationship. . On the other hand, this capacitance C is determined by measuring the frequency f of the terminal voltage waveform of the capacitor C when the capacitor C is charged and discharged in the circuit section 36. The capacitance C and the frequency f are β f = -゛(41 (β: constant), and change as shown in Fig. 3 (b). From equations (3) and (4), the relationship is as follows. Therefore, the frequency r is proportional to the pressure to be measured P, and the relationship between the frequency f and the pressure to be measured P is linear.However, in reality, the pressure-sensitive diaphragm shown in FIG. As shown in the enlarged longitudinal cross-sectional view of B32, the measured pressure P
As a result, the pressure-sensitive diaphragm portion 32 is deflected, so that the electrode spacing d is not uniform over the entire surface of the pressure-sensitive diaphragm portion 32. Further, the shape of the deflection also changes depending on the pressure P to be measured. Therefore, formula (1) is more accurately expressed as the pressure sensitive diaphragm portion 32.
It must be calculated by integrating the area over the entire surface. Then, equation (6) becomes C-ε (7) using the average electrode spacing. However, the average electrode spacing d is not a linear expression of the pressure to be measured P as in equation (2), but includes higher-order components. Therefore, the relationship between the frequency f and the pressure to be measured P cannot be expressed by a linear equation as shown in equation (5) and includes higher-order components, resulting in poor linearity and reduced measurement accuracy. The present invention has been made to solve the above problems, and its purpose is to
It is an object of the present invention to improve the linearity in the characteristics between the frequency f of a directly measured value and the pressure to be measured P, and to provide a capacitive pressure sensor with higher accuracy.

[Means to solve the problem]

The structure of the invention for solving the above problem includes two substrates, at least one of which is made of a semiconductor, and which are bonded to each other, and a reference value of the measurement pressure of the micro gear knob is formed at the bonded portion of the two substrates. In a capacitive pressure sensor that has a reference pressure chamber that provides a pressure to be measured, and a pressure-sensitive diaphragm portion that is formed on one substrate and receives a pressure to be measured, a central portion of the pressure-sensitive diaphragm is applied to opposite surfaces of the reference pressure chamber. An electrode formed in a shape having a size ratio in the range of 115 to 3/5 with respect to the shape of the pressure-sensitive diaphragm portion, and a voltage formed on the semiconductor substrate to charge and discharge the capacitance between the electrodes. It is characterized by comprising a circuit section that calculates pressure from the frequency of the waveform.

[Effect]

The electrodes are placed at the central part of the pressure sensitive diaphragm part on opposite sides of the reference pressure chamber with a diameter of 11 mm, corresponding to the shape of the pressure sensitive diaphragm part.
It is formed in a shape with a dimensional ratio in the range of 5 to 3/5, and is formed in a portion of the pressure-sensitive diaphragm that receives the pressure to be measured, where the rate of change in deflection is small, so it is approximately Displaced in parallel. Since the circuit section determines the pressure from the frequency of the voltage waveform when charging and discharging the capacitance between the electrodes, the detection accuracy is improved because the linearity between the pressure to be measured and the pressure to be determined is good.

【Example】

The present invention will be described below based on specific examples. FIG. 1 is a longitudinal sectional view showing a capacitive pressure sensor according to the present invention. FIG. 2 is a plan view showing a state before the glass substrates are bonded in FIG. 1. A capacitive pressure sensor 10 of the present invention will be described with reference to FIGS. 1 and 2. Reference numeral 11 denotes a semiconductor substrate made of single crystal silicon, on which a pressure-sensitive diaphragm portion 12 and a recess 13 are formed to receive the pressure to be measured P, and an electrode 14 is formed in the recess 13 portion. The electrode 14 is located at the center of the pressure-sensitive diaphragm 12 and has a size ratio of approximately 1/5 in the range of 175 to 3/5 with respect to its shape.
It is formed into a shape having a dimension ratio of 2. Further, on the semiconductor substrate 11, a connection terminal portion 17 and a circuit portion 16 are integrally formed using the same semiconductor manufacturing technology as in the formation of the electrode 14. The electrode 14 is connected to the circuit section 16 via the connecting terminal section 17 thereof. Further, 21 is a glass substrate made of Pyrex glass on which electrodes 24 are formed. The electrode 24, like the electrode 14 described above, is formed at the center of the pressure-sensitive diaphragm B12 in a shape having a size ratio of approximately 1/2 to the shape of the pressure-sensitive diaphragm B12. Then, the electrode 14 of the semiconductor substrate 11 and the electrode 24 of the glass substrate 21 are made to face each other and are anodically bonded. After bonding, the recess 13 of the semiconductor substrate 11 is sealed with the glass substrate 21 and becomes the reference pressure chamber 15. Also, electrode 2
Similarly to the electrode 14, the electrode 4 is connected to the circuit section 16 via the connection terminal section 17. Further, 28 is a signal line for taking out the Confucian code to the outside, and the signal line 28 is connected to the circuit section 16 formed on the semiconductor substrate 11 via a conductive adhesive 29 or the like. When the measured pressure P is applied to the pressure sensitive diaphragm section 12, the deflection distribution of the pressure sensitive diaphragm section 12 is as shown in FIG. As can be seen from the characteristic diagram in FIG. 5, the rate of change in deflection is small from the center of the pressure sensitive diaphragm portion (x = 0) to about half on one side (x = 0.3). That is, the dimensions of the electrode 14.24 are adjusted to the pressure sensitive diaphragm R12.
3/5 or less compared to the dimensions of the pressure sensitive diaphragm part 1.
By arranging the electrodes 14 and 24 on opposite surfaces of the reference pressure chamber 15 at the central portion of the reference pressure chamber 15, the rate of change in deflection can be reduced. Therefore, with the above-described configuration, the displacement with respect to pressure becomes substantially uniform in the central portion of the pressure-sensitive diaphragm portion. Here, the pressure sensitive diaphragm portion 12 of the semiconductor substrate 11 is
As shown in FIG. 4, it is assumed that it is a square and the electrode 14 is located at the center 0, and the dimension of one side of the pressure-sensitive diaphragm part 120 is a, and the dimension of one side of the electrode 14 is b, and the electrode 14 is in the ratio of these dimensions. Let us express the ratio as b/a. The pressure-sensitive diaphragm part 12 has a rectangular shape with a side dimension of 1 mm, a thickness of 30 mm, an electrode interval of 1 mm, and a measured pressure P relative to the pressure of the reference pressure chamber 15 of 1 kgf/c.
Nonlinearity R (%), capacitance change ΔC (pF), frequency sensitivity K (
ppm/mm Hg> is as shown in FIG. Here, the capacitive pressure sensor shows a curve in which the larger the electrode ratio b/a, the larger the capacitance change ΔC. Further, the nonlinearity R of the pressure value to be determined with respect to the pressure to be measured becomes a downwardly convex curve with respect to the electrode ratio b/a due to the deflection of the pressure sensitive diaphragm. The frequency sensitivity representing the change in frequency when 1 kgf/cm' is applied to the pressure value of the reference pressure chamber as the measured pressure P has a curve that decreases as the electrode ratio b/a increases. Therefore, by setting the electrode dimensions to an electrode ratio b/a of 375 or less compared to the dimensions of the pressure-sensitive diaphragm portion, the nonlinearity R can be rapidly improved without significantly worsening the frequency sensitivity K. Furthermore, by setting the electrode dimensions to an electrode ratio b/a of 115 or more compared to the dimensions of the pressure-sensitive diaphragm portion, it is possible to prevent the capacitance change ΔC from becoming too small and being buried in stray capacitance. In other words, a capacitive pressure sensor having a pressure-sensitive diaphragm portion with an electrode ratio in the range of 115 to 3/5 has good linearity of output value and a large change in frequency, so it is possible to improve pressure detection accuracy. Incidentally, if the electrode ratio is approximately /2 as in this embodiment, a capacitive pressure sensor that particularly exhibits the above-mentioned effect will be obtained.

【Effect of the invention】

The present invention provides that the pressure sensitive diaphragm has a curved shape on both opposing sides of the reference pressure chamber at the central portion of the pressure sensitive diaphragm portion.
An electrode formed in a shape having a dimensional ratio in the range of 115 to 3/5, and a circuit section formed on a semiconductor substrate to calculate pressure from the frequency of a voltage waveform when charging and discharging the capacitance between the electrodes. It is equipped with 115~ of the pressure sensitive diaphragm part.
In an electrode having a size in the range of 3/5, the rate of change in deflection of the pressure sensitive diaphragm portion is small, and the electrode of the pressure sensitive diaphragm portion is displaced approximately parallel to the opposing electrode. Furthermore, a circuit section that calculates pressure from the frequency of the voltage waveform when charging and discharging the capacitance between the electrodes with respect to the measured pressure,
Since the pressure value determined for the pressure to be measured changes almost linearly, a highly accurate capacitive pressure sensor can be provided.

[Brief explanation of drawings]

FIG. v1 is a longitudinal sectional view showing a capacitive pressure sensor according to a specific embodiment of the present invention. FIG. 2 is a plan view showing the state before bonding the glass substrates in FIG. 1. Figure 3(a)
is a characteristic diagram showing the relationship between measured pressure P and capacity C; Third
Figure 3) is a characteristic diagram showing the relationship between capacitance C and frequency f. FIG. 4 is an explanatory diagram showing the dimensional relationship between the pressure sensitive diaphragm part and the electrode. Figure 5 shows the deflection of the pressure-sensitive diaphragm. IE diagram. FIG. 6 is a characteristic diagram showing nonlinearity, capacitance change, and frequency sensitivity with respect to electrode ratio. FIG. 7 is a longitudinal sectional view showing a conventional capacitive pressure sensor. FIG. 8 is an enlarged longitudinal sectional view of the pressure sensitive diaphragm shown in FIG. 7. 10 Capacitive pressure sensor 11 Semiconductor substrate 12 Pressure-sensitive diaphragm part 14.24 Electrode 15 Reference pressure chamber 1G Circuit part 21 Glass substrate P Pressure to be measured Figure 2

Claims (1)

[Scope of Claims] At least one of the substrates is made of a semiconductor, and is formed at a joint between two substrates that are bonded to each other,
In a capacitive pressure sensor that has a reference pressure chamber that provides a reference value for the measurement pressure of a minute gap, and a pressure-sensitive diaphragm portion that is formed on one substrate and receives the measured pressure, the reference pressure chamber is provided at a central portion of the pressure-sensitive diaphragm portion. 1/5 to 3/5 of the shape of the pressure sensitive diaphragm on both opposing sides of the pressure chamber.
an electrode formed in a shape having a dimensional ratio in the range of , and a circuit section formed on the semiconductor substrate to determine the pressure from the frequency of the voltage waveform when charging and discharging the capacitance between the electrodes. Characteristic capacitive pressure sensor.