JP2001124645A - Semiconductor pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor pressure sensor having the combined structure of a piezoresistance with a diaphragm, which can measure pulsation pressure in addition to differential pressure and static pressure with one chip. SOLUTION: An inlet port having a throttle mechanism is formed on the lower surface intermediate layer of a diaphragm, so that the smoothed pressure of the diaphragm upper surface is applied through the inlet port. According to this structure, a pressure difference by the portion of pulsation pressure is generated between the upper surface and lower surface of the diaphragm. In addition to this pulsation pressure measuring diaphragm, differential pressure measuring and static pressure measuring diaphragms are formed, whereby various pressure measurements can be performed with one chip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor used for measuring pressure, flow rate and the like in various plants.

[0002]

2. Description of the Related Art It is well known that a piezoresistor is disposed as a strain-sensitive gauge on a silicon diaphragm which is displaced by receiving a pressure of an object to be measured to constitute a pressure sensor. Usually, the pressure sensor is a differential pressure sensor for measuring the pressure difference between the upper surface and the lower surface of the diaphragm as disclosed in Japanese Patent Application Laid-Open No. 5-157648, and a static pressure sensor for measuring the pressure change on the upper surface by sealing the lower surface of the diaphragm to a constant pressure. In general, various types of pressure sensors are integrated. However, in some cases, the differential pressure is superimposed on the actual pressure, and the pulsating pressure is superimposed on the static pressure. In the structure as disclosed in Japanese Patent Application Laid-Open No. 5-157648, the pressure can be detected only in a form in which the pulsating pressure is superimposed on both the differential pressure sensor and the static pressure sensor.

On the other hand, Japanese Patent Application Laid-Open No. Hei 5-40069 provides a pressure sensor structure capable of detecting a pulsating pressure by adding an integrating throttle and an integrating tank outside the pressure sensor chip.

[0004]

However, in the above-mentioned known example, since the integrating throttle and the integrating tank are provided separately from the pressure sensor chip, the whole sensor is complicated and the volume becomes large. Further, due to the structure, it is impossible to simultaneously detect the differential pressure and the static pressure.

It is an object of the present invention to form a pressure inlet having a throttle mechanism in an intermediate layer on the lower surface of the diaphragm, and to form the inlet toward the side of the sensor so that the pressure on the upper surface of the diaphragm is applied to the pulsation pressure. Is to provide a structure capable of measuring the

[0006]

As a means for solving the above problems, a displacement region of a diaphragm and a pressure inlet are formed by a concave portion of an intermediate layer formed between a single crystal silicon substrate and a single crystal silicon film. Structure. By reducing the conductance of the pressure inlet, a pulsating pressure can be measured by using a throttle mechanism.

When this structure is used, the differential pressure sensor and the static pressure sensor can be easily integrated on the same sensor chip, and various pressure measurements can be performed with a single chip sensor.

[0008]

FIG. 1 is a top view showing a schematic structure of an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AOB of FIG. Single crystal silicon substrate 51 and n-type (10
The single-crystal silicon film 52 of the 0) plane is provided, and the single-crystal silicon is disposed, for example, with a Pyrex glass layer 53 interposed therebetween. A part of the single-crystal silicon substrate 51 is formed with a through hole by etching removal processing, and a lower surface side of the post is made of, for example, a Te-Ni post having a differential pressure detection inlet 35 through a low melting point glass layer 54, for example. 55. The Pyrex glass layer 53 has a dynamic pressure detecting inlet 34 connected to the side of the sensor chip by etching and a dynamic pressure detecting hollow portion 36 to which the dynamic pressure detecting inlet 34 is connected. Inlet 34
The portion where the Pyrex glass layer 53 is etched off in the region where the through-hole is formed in the single crystal silicon substrate 51 where the hollow portion 37 for static pressure detection which is not connected to is formed becomes the hollow portion 38 for differential pressure detection. .

It is necessary to reduce the conductance of the dynamic pressure detecting inlet 34 to such an extent that it cannot follow the change of the pulsating pressure, and it may have a self-folding structure as shown in FIG.
The groove may be shallow or narrow.

The differential pressure detecting diaphragm 31 on the differential pressure detecting hollow portion 38 has a differential pressure detecting piezoresistor 21a-2 for detecting stress when the diaphragm is deformed by receiving a differential pressure.
1d is a dynamic pressure detecting piezoresistor 22a to 22d which receives a dynamic pressure and detects a stress when the diaphragm is deformed by the dynamic pressure detecting diaphragm 32 on the dynamic pressure detecting hollow portion 36.
However, the static pressure detecting diaphragm 33 on the static pressure detecting hollow portion 37 is provided with static pressure detecting piezoresistors 23a to 23d for detecting stress when the diaphragm is deformed by receiving a static pressure.

On the single-crystal silicon film 52, a piezoresistor 24 for temperature detection is formed in a place that is not a diaphragm region. 25 is a wiring of a p-type high concentration impurity layer, 26 is an aluminum wiring, and 1 to 16 are aluminum contact pads.

The p-type piezoresistors formed near the respective surfaces of the differential pressure detecting diaphragm 31 and the four dynamic pressure detecting diaphragms 32 and the four static pressure detecting diaphragms 33 diffuse boron to diffuse. It is formed in the <110> direction that is most sensitive to stress. The piezo resistance increases when a tensile stress acts in the longitudinal direction. Gauges arranged in this direction are called L gauges. Further, when a tensile stress acts in the lateral direction, the resistance value decreases. Gauges arranged in this direction are called T gauges. In the example of FIG. 1, all four piezoresistors on the differential pressure detecting diaphragm 31 are arranged near the diaphragm support, and two L gauges 21a, 2b whose longitudinal direction is parallel to the radial direction of the diaphragm.
1c, two T gauges 21b and 21d whose longitudinal direction is parallel to the tangential direction of the diaphragm are arranged. L gauges 22a and 22c are provided on the diaphragm 32 for detecting dynamic pressure.
T gauges 22b and 22d are arranged. The L gauges 23a and 23c and the T gauges 23b and 23d are arranged on the static pressure detection diaphragm 33. The method of arranging the piezoresistors is, in addition to the example shown in FIG. 1, a method of arranging all two L gauges and two T gauges near the rigid part, two L gauges near the diaphragm support part and two L gauges near the rigid part. How to place,
There is a method of arranging two T gauges near the diaphragm support portion and two T gauges near the rigid body portion.

21a to 21d, 22a to 22d, 23a
The piezoresistors of .about.23d constitute three sets of Wheatstone bridges as shown in FIG. Here, a portion composed of the bridge of the differential pressure detecting diaphragms 31 and 21a to 21d is referred to as a differential pressure sensor, and the dynamic pressure detecting diaphragms 32 and 22 are connected.
a part composed of the bridges a to 22d is a dynamic pressure sensor,
The portion composed of the static pressure detecting diaphragm 33 and the bridge of 23a to 23d is called a static pressure sensor. When pressure is applied to the diaphragms, each of the diaphragms bends, and each bridge composed of piezoresistors formed on the diaphragm produces sensor outputs V ₁ , V ₂ , V _{3 which} are almost proportional to the pressure difference between the upper surface and the lower surface. Occurs. Here, the differential pressure sensor measures the pressure difference (differential pressure) between the upper surface and the lower surface of the diaphragm, while the dynamic pressure sensor measures the pressure on the upper surface of the diaphragm on which the pulsating pressure is superimposed and the diaphragm smoothed through the throttle mechanism. The difference between the upper surface pressure (dynamic pressure) and the static pressure sensor is the pressure difference (static pressure) between the upper surface of the diaphragm and the sealed constant pressure part
Will be measured.

On the other hand, the piezoresistor 24 for temperature detection, which is integrated on the same substrate as the diaphragm, is also formed by diffusing boron, but shows almost no change in resistance to stress change. By arranging in the direction,
Make it sensitive only to temperature. A portion composed of the piezoresistor 24 is called a temperature sensor, and is connected to a piezoresistive bridge of a differential pressure sensor and a static pressure sensor as shown in FIG.

For the wiring between the piezoresistors and to the aluminum contact pads 1 to 16, a p-type impurity diffusion layer 25 in which boron is diffused at a higher concentration and an aluminum wiring 26 are used in combination. In the present embodiment, aluminum wiring having a small resistance value is used in places where the influence of temperature hysteresis is relatively small, such as outside the diaphragm or in a place apart from the piezoresistor. A wiring method in which the wiring is a high-concentration impurity layer is also possible.

Next, the operation of the sensor when pressure is applied to the diaphragm will be described with reference to FIG. When a pressure difference occurs between the upper surface and the lower surface of the diaphragm, if the upper surface side has a higher pressure, the diaphragm is deformed as shown in FIG. When the diaphragm is deformed, the stress generated near the surface of the diaphragm where the piezoresistor is formed becomes as shown in FIG. On the diaphragm, a maximum tensile stress σ ₁ is generated in the vicinity of the diaphragm support. Assuming that the outer diameter of the diaphragm is X and the thickness is h, σ ₁ when the differential pressure ΔP is applied is expressed by the following equation.

[0017]

Σ ₁ = 3X ² ΔP / (16h ² ) As shown in FIG. 1, when ^two L gauges and two T gauges are respectively arranged near the support of the diaphragm, the output V of the differential pressure sensor ₁ is represented by the following equation.

[0018]

V ₁ = (１ ／) · π ₄₄ (1-ν) σ ₁ · V where ν is Poisson's ratio, π ₄₄ is the shear piezoresistance coefficient, and V is the excitation voltage.

Next, the sensed pressure of each sensor when the pressure on which the pulsating pressure is superimposed is applied will be described. Usually, in a plant, an orifice or the like is placed in a pipeline, and a pressure difference before and after the orifice is measured. Therefore, the pressure on the upper surface and the pressure on the lower surface of the differential pressure detecting diaphragm 31 have a substantially synchronized pressure distribution. At this time, since the pressure in the dynamic pressure detecting hollow portion 36 cannot follow the change in the pulsating pressure due to the presence of the throttle mechanism, the pressure change becomes smooth as shown by the dashed line in FIG. Therefore, each sensor detects a differential pressure, a dynamic pressure, and a static pressure indicated by arrows in FIG.

FIGS. 6A to 6D are cross-sectional views showing the steps of manufacturing the pressure sensor shown in the above embodiment. Hereinafter, the manufacturing process will be described.

(A) First, a through hole serving as a differential pressure detecting hollow portion is formed in single crystal silicon 52 by thermal oxidation, photolithography, and KOH etching. Thereafter, the entire surface of the oxide film is etched, and the Pyrex glass 53 is anodically bonded.

(B) Pyrex glass is etched with HF to form regions to be a differential pressure detecting hollow portion, a dynamic pressure detecting hollow portion 36, a static pressure detecting hollow portion 37, and a dynamic pressure detecting inlet 34. . Thereafter, an n-type (100) plane single crystal silicon substrate is anodically bonded and polished to form a single crystal silicon film 52.

(C) Boron is diffused on the single crystal silicon film 52 to form a piezoresistor, a p-type high-concentration impurity layer wiring, an aluminum wiring, and a contact pad.

(D) Finally, the post 55 is bonded via the low melting point glass 54.

The pressure sensor is then welded or bonded to an output take-out fitting (seal fitting) 56 as shown in FIG. 7, and the pads 1 to 16 of the sensor and the output take-out terminal 57 are connected by a seed wire 58. . This metal fitting has an airtight structure by a hermetic seal, and is finally incorporated into a differential pressure transmitter.

[0026]

According to the present invention, three types of pressure measurement can be performed by adding a pulsating pressure in addition to a differential pressure and a static pressure, and various pressure measurements can be performed with a one-chip sensor.

[Brief description of the drawings]

FIG. 1 is a schematic top view of a pressure sensor showing one embodiment of the present invention.

FIG. 2 is a schematic sectional view taken along the line AOB of FIG. 1;

FIG. 3 is a connection diagram of a piezo resistor.

FIG. 4 is a diagram showing a distribution of stress generated when pressure is applied.

FIG. 5 is a diagram illustrating a pressure detected by each sensor when pressure is applied.

FIG. 6 is a manufacturing process diagram of the pressure sensor.

FIG. 7 is a view of assembling a pressure sensor into a seal fitting.

[Explanation of symbols]

1 to 16: aluminum contact pads for extracting pressure sensor output, 21a to 21d: piezoresistors for detecting differential pressure, 22
a to 22d: piezoresistors for detecting dynamic pressure, 23a to 23d:
Piezo resistor for detecting static pressure, 24 ... Piezo resistor for detecting temperature,
25 ... p-type high concentration impurity layer wiring, 26 ... aluminum wiring, 31 ... diaphragm for detecting differential pressure, 32 ... diaphragm for detecting dynamic pressure, 33 ... diaphragm for detecting static pressure, 34 ...
Inlet for detecting dynamic pressure, 35: Inlet for detecting differential pressure, 36: Hollow for detecting dynamic pressure, 37: Hollow for detecting static pressure, 38: Hollow for detecting differential pressure, 51: Single crystal silicon substrate, 52: single crystal silicon film, 53: Pyrex glass layer, 54: low melting point glass layer, 55: post, 56: hermetic seal, 57: output terminal, 58: lead wire.

Claims (5)

[Claims] An intermediate layer having a concave portion on one surface of a single crystal silicon substrate, and an intermediate layer disposed on one surface side of the single crystal silicon substrate so as to cover the concave portion, wherein at least one piezoresistor is provided. Having a single-crystal silicon film formed,
In a semiconductor pressure sensor having a diaphragm that displaces the single-crystal silicon film in accordance with pressure, a pressure inlet formed by a recess in the intermediate layer is provided in a space formed by the diaphragm and the recess in the intermediate layer. Characteristic semiconductor pressure sensor. 2. The semiconductor pressure sensor according to claim 1, wherein said pressure inlet has a zigzag structure. 3. A semiconductor pressure sensor according to claim 1, wherein a space portion comprising a diaphragm having no pressure inlet and a concave portion of the intermediate layer is formed separately from the diaphragm, and a static pressure is formed on the diaphragm. A semiconductor pressure sensor, wherein a piezoresistor is formed as a detection element. 4. The semiconductor pressure sensor according to claim 1, wherein at least one of the spaces formed by the diaphragm and the recess of the intermediate layer is formed on a single-crystal silicon substrate on the side of the intermediate layer having the recess. A semiconductor pressure sensor having a pressure introduction port penetrating to an opposite surface, and having a piezoresistor formed as a differential pressure detecting element on the diaphragm. 5. The semiconductor pressure sensor according to claim 1, wherein the piezoresistor is formed on the same silicon film.
A semiconductor pressure sensor, wherein a piezoresistor is formed as a temperature detecting element.