JPH0750788B2 - Pressure sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure sensor, and more particularly to a pressure sensor having no sensitivity variation.

(Prior Art and its Problems) In the field of pressure sensors, it has been a major problem to reduce the variation in pressure sensitivity among products. The causes of the pressure sensitivity variation are (1) the difference in the film thickness of the diaphragm, (2) the difference in the sensitivity of each pressure sensitive element due to the variation in the impurity concentration, etc., (3) the displacement of the pressure sensitive element on the diaphragm, etc. The factors are: In recent years, it has become possible to control the thickness of the diaphragm by electrochemical etching, etc.
It is used to reduce pressure sensitivity variation due to factor (1). Further, the progress of the semiconductor manufacturing apparatus has made it possible to reduce the variation in the impurity concentration in the above (2).

On the other hand, normally, the positioning of the pressure sensitive element is performed by using a microscope.
A technician makes an alignment according to a pre-marked mark. Therefore, some displacement is unavoidable. Hereinafter, a conventional example will be described with reference to the drawings, and at the same time, its drawbacks will be described.

FIG. 9 is a structural example of a conventional pressure transducer, and FIG. 10 is a view of a conventional diaphragm as viewed from above. In FIG. 9, the diaphragm type pressure sensor 3 composed of the diaphragm 13 and the pedestal 14 on which the diffusion type strain gauge resistor 1 is placed has a linear expansion coefficient very close to the linear expansion coefficient of the pressure sensor 3. It is adhered to glass 4 (for example, Corning 7740 Pyrex glass) by electrostatic bonding.

Furthermore, the glass 4 is packaged in gold, tin or gold,
Bonded by tin eutectic alloy 5. The package 6 is sealed by a cap 9. The operating principle of the pressure converter will be described below. A gas 10 whose pressure is to be measured is supplied through a conduit 8 while a reference gas 11 is supplied through a conduit 12 attached to a cap 9. 12 may be released to the atmosphere. Distortion occurs in the diaphragm 13 of the pressure sensor 3 due to the difference in gas pressure between the upper surface and the lower surface, and in the Wheatstone bridge circuit that is formed on the diaphragm 13 and is composed of a gauge resistance, the output voltage change of the bridge circuit is detected. To be done. The excitation voltage and the output voltage of the bridge circuit are input and output from the lead 7 via the thin metal wire 2.

The diaphragm 13 in FIG. 10 normally uses the (100) plane of silicon and is oriented in the peripheral <110> direction of the diaphragm. In such a case, the gauge resistor 1 is positioned near the periphery of the diaphragm 13 for the purpose of increasing the sensitivity. FIG. 11 shows a distribution of uniaxial stress in the same direction generated on the diaphragm center line (A-A 'in FIG. 10) when pressure is applied. In the figure, 30 is a gauge resistance 1
Shows the position where the is placed. As is clear from the figure,
Conventionally, the position where the gauge resistor 1 is placed has also been a place where the stress changes abruptly. Therefore, in the pressure sensor with the conventional structure, as described above, even if a slight deviation inevitably occurs during the positioning of the gauge resistance, a large change in sensitivity occurs, and eventually the pressure There is a drawback in that it is impossible to avoid variations in the sensitivity of the sensor.

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a pressure sensor with no sensitivity variation.

(Structure of the Invention) In order to achieve the above object, the present invention provides a pressure-sensitive element responsive to an applied pressure and a pressure-sensitive element (100).
A square diaphragm with a main surface facing the direction,
In a silicon pressure sensor composed of a pedestal that fixes the periphery of the diaphragm, the peripheral portion of the diaphragm is made thicker than the central portion, and the pressure sensitive element is arranged at a position where the amount of stress variation in the peripheral portion is small. It is a thing.

(Principle of Operation of the Invention) In the pressure sensor of the present invention, the diaphragm on which the pressure sensitive element is placed does not have a uniform thickness as in the prior art, but the peripheral portion is thicker than the central portion. When the stress generated on the center line of the diaphragm is shown for the uniaxial stress in the same direction, the relationship of FIG. 3 is obtained, and it has been clarified that the change in stress at the position where the pressure sensitive element is placed is extremely small. Therefore, in the present invention, the diaphragm on which the pressure-sensitive element is placed is thicker in the peripheral portion than in the central portion, and the pressure-sensitive element is installed at a position where stress change is small. Could be significantly reduced.

(Example) Hereinafter, the Example of this invention is described with reference to drawings.

1 and 2 are views showing an embodiment of the present invention.
FIG. 1 is a sectional view, and FIG. 2 is a view of the diaphragm of FIG. 1 seen from above. In the figure, the ninth example shown as a conventional example
The same reference numerals as those in FIG. 10 and FIG. 10 indicate the same components. FIG. 1 and FIG. 9 of the conventional example have the same structure except for the difference in the structure of the diaphragm. The diaphragm will be described below, and the other elements will be omitted.

In the diaphragm 40a, the peripheral portion 41 is thicker than the central portion 42, and the gauge resistance 1 is placed in the peripheral portion 41. To manufacture the diaphragm 40a, for example, a first-stage mask is used for the lower surface of the pedestal 14 to protect it, and then the peripheral portion 41 is formed by etching, and then the second-stage mask is used for the pedestal 14 and the peripheral portion. It is preferable to use a method of forming the central portion 42 using the lower surface of 41. When performing the etching, the upper surface of the diaphragm 40a must be protected at all times to prevent the etching. Further, as the etching technique, chemical etching, electric discharge machining, or the like can be used.

FIG. 3 shows the stress generated on the center line of the diaphragm 40a (B-B 'in FIG. 2) when the pressure is applied, for the uniaxial stress in the same direction. In the figure, 60 indicates the position where the pressure sensitive element, for example, the gauge resistor 1 is placed. Unlike the conventional example shown in FIG. 11, the change in stress is remarkably small at the position where the pressure sensitive element is placed. Therefore, in the pressure sensor having the structure of this embodiment, it is possible to reduce the sensitivity variation caused by the displacement of the pressure sensitive element.

4 to 7 show another embodiment of the present invention. In the figure, the same numbers as in FIG. 1 indicate the same components.
In these embodiments, the peripheral portion 41 of the diaphragm has a shape in which the diaphragm 40b has a thicker taper toward the periphery in FIG. 4 and the diaphragm 40c has a thicker taper shape toward the inside in FIG. Also, in FIG. 6, the diaphragm 40d
The peripheral portion 41 is formed by two steps. In FIG. 7, the diaphragm 40e is formed by a taper gradually thicker around the central portion 42. In addition to the above-described embodiment, the peripheral portion 41 may have a configuration of two or more steps or taper. Further, the present invention also includes a configuration in which the above steps, the taper, and FIG. 7 are arbitrarily combined.

FIG. 8 is a diagram showing another embodiment of the present invention. In the figure, the same numbers as in FIG. 1 indicate the same components. This embodiment has a constriction 80 in the peripheral portion 41 of the embodiment shown in FIG.
Although it has a structure different from that of the above-mentioned embodiment in that the above-mentioned structure is formed, the same effect as that of the embodiment shown in FIGS.

The present invention has been described in detail above with reference to examples.
The configuration of the present invention is not limited to the other constituent elements except the diaphragm 40a (including the peripheral portion 41 and the central portion 42) of the first embodiment shown in FIG. included.

In addition, the pressure applied to the diaphragm is made by forming the diaphragm with a metal and attaching a strain gauge to one or both surfaces of the metal, or depositing a strain gauge made of a metal or a semiconductor. The present invention also includes a configuration for detecting, a configuration in which the surface of the diaphragm made of a semiconductor such as silicon is protected by an oxide film such as silicon, a nitride film or the like, and a peripheral circuit formed on the surface.

It should be noted that in the above-described embodiment, the larger the peripheral area and thickness, the more gradual the distribution of stress acting on the gauge resistance, and accordingly the variation in sensitivity decreases. However, in this case, since the absolute value of stress decreases at the same time,
The sensitivity is reduced. Therefore, when designing the pressure sensor, the dimensions of the peripheral portion of the diaphragm must be determined so as to optimize the sensitivity and the sensitivity variation in consideration of the above effects.

(Effects of the Invention) As described above, according to the present invention, it is possible to supply a pressure sensor without variations in sensitivity, and as a result, it is possible to improve the quality of the pressure sensor and reduce the manufacturing cost. It is a thing.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a view of the diaphragm of FIG. 1 as seen from above, and FIG. 3 is B- of FIG.
FIG. 4 to FIG. 8 are sectional views of the diaphragm of another embodiment of the present invention, FIG. 9 is a sectional view of a conventional pressure sensor, and FIG. FIG. 9 is a view of the diaphragm seen from above, and FIG. 11 is AA ′ of FIG.
It is a distribution diagram of the stress generated along. 1 ... Gauge resistance, 2 ... Metal wire, 3 ... Pressure sensor, 4 ... Glass, 5 ... Eutectic alloy such as gold, tin, 6 ...
... Package, 7 ... Lead, 8,12 ... Continuing tube, 9 ...
Cap, 10, 11 ... Gas, 13 ... Diaphragm, 14 ...
… Pedestals, 30,60 …… Gauge resistance positions, 40,40a,
40b, 40c, 40d, 40e, 40f …… diaphragm, 41 …… peripheral part, 42 …… central part, 80 …… constriction.

Claims (1)

[Claims] 1. A pressure-sensitive element responsive to an applied pressure, a square diaphragm having a main surface in a direction facing the (100) direction in which the pressure-sensitive element is placed, and a pedestal for fixing the periphery of the diaphragm. In the silicon pressure sensor described above, the peripheral portion of the diaphragm is made thicker than the central portion, and the pressure sensitive element is arranged at a position where the amount of stress variation in the peripheral portion is small.