JPH01167623A - stress sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a stress sensor used, for example, to measure stress strain in structural members of civil engineering and construction machinery, and stress in various other equipment.

[Conventional technology]

Generally, metal gauges and semiconductor strain gauges are widely used as stress sensors used as pressure sensors, strain sensors, torque sensors, load sensors, and the like. Among these, the latter semiconductor strain gauge in particular has been widely used in recent years because it has a higher gauge factor than the former metal gauge and can generate a large change in resistance value in response to a slight mechanical strain. There is.

Among these stress sensors, a diaphragm pressure sensor according to the prior art will be described with reference to FIGS. 11 to 13.

In the figure, l is a diaphragm made of a silicon single crystal, a metal material, an insulating synthetic resin, etc. The diaphragm 1 has a thin disk-shaped strain part IA and a thick-walled cylindrical shape on the outer periphery of the strain part IA. It consists of a non-strain portion IB integrally formed with the top surface thereof, and its upper surface is a flat circuit forming surface IC.

2 is a strain detecting section provided on the circuit forming surface IC of the diaphragm l; 3A, 3B, 3C, and 3D constitute the strain detecting section 2, and are located in the strain generating section IA and arranged in a rectangular shape. done 4
Gauge resistance (hereinafter referred to as
The gauge resistor 3 is formed by forming a resistive thin film on the circuit forming surface IC by the P-CVD method (plasma-CVD method) using, for example, 5iHa and 8286, and then forming the thin film by photolithography. It is formed as a resistance.

4A, 4B, 4C, 4D, 4E, 4F are thin film conductors (hereinafter collectively referred to as conductors 4) that connect the gauge resistor 3 to form a Wheatstone bridge circuit;
A is a first i-film conductor connected to one end of the first gauge resistor 3A, and 4B is a second thin film connected to the other end of the gauge resistor 3A and one end of the second gauge resistor 3B. conductor, 4
C is a third resistor connected to the other end of the second gauge resistor 3B.
4D is a fourth IIM conductor connected to one end side of the third gauge resistor 3C, and 4E is connected to the other end side of the third gauge resistor 3C and one end side of the fourth gauge resistor 3D. The connected fifth thin film conductor, 4F, indicates the sixth thin film conductor connected to the other end side of the fourth gauge resistor 3D, and its outer end is for connecting the wiring of the power supply or measuring instrument. terminals 5A and 5B.

They are formed as 5C, 5D, 5E, and 5F.

Here, the thin film conductor 4 is formed by forming a conductive thin film made of a good conductive material such as gold, aluminum, copper, etc. on the circuit forming surface IC using a vacuum evaporation method, and then connecting the gauge resistor 3 using a photolithography method. It is patterned to form a Wheatstone bridge circuit.

Next, 6 and 7 are thin film conductors 4A formed as described above,
4F and between the thin film conductors 4C and 4D, respectively, and the balancing resistors 6 and 7 are fixed resistors such as film fixed resistors, square chip fixed resistors, etc. A resistor is used. Here, the balancing resistor 6,
As mentioned above, since the resistance values of the gauge resistors 3 formed on the diaphragm 1 are not uniform, the output of the Wheatstone bridge circuit is not zero-balanced.
This is provided for adjustment because there is a potential difference between A and 50, and the resistance value of the balancing resistor 6.7 is equal to the gauge resistor 3.
Calculated from the resistance value of Note that the balancing resistors 6 and 7 are appropriately externally attached on the diaphragm l or inside the measuring instrument case.

The pressure sensor of the prior art is constructed as described above, and a Wheatstone bridge circuit is formed using the terminals 5A, 5D and the terminals 5B (5C), 5E (5F), and the terminal 5
A measuring device such as a voltmeter or an ammeter is connected between A and 50, and a power source is connected between terminals 5B (5G) and 5E (5F) to measure the strain in the strain-generating portion IA of the diaphragm 1. If the strain generating part IA is under no load, the electrical resistance of the gauge resistor 3 will not change, so no potential difference will occur between the terminals 5A and 50, and no current will flow to the measuring instrument. When part IA is distorted, the electrical resistance of gauge resistor 3 changes, and as a result, terminal 5A
, 50 and a current flows, the strain can be measured with a measuring instrument.

[Problem that the invention seeks to solve]

By the way, according to the above-mentioned conventional technology, different types of resistors having different compositions are used for the gauge resistor 3 and the balancing resistors 6 and 7, and their resistance temperature coefficients are different.

In addition, since the balancing resistors 6 and 7 are externally attached to each gauge resistor 3, if the balancing resistors 6 and 7 and the gauge resistor 3 are installed in different locations, the environmental temperatures will also differ. It's coming. ' In this way, the gauge resistor 3 and the balancing resistor 6.7 have different temperature coefficients of resistance and different environmental temperatures, so even if the zero balance is adjusted at a certain reference temperature, the zero balance of the Wheatstone bridge circuit will collapse due to temperature changes. , terminal 5A
, 50 do not have the same potential, and the temperature characteristics of the pressure sensor are extremely poor.

The present invention was devised in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a stress sensor that has excellent temperature characteristics and can be downsized and reduce manufacturing costs.

A further object of the present invention is to provide a pressure sensor that is formed on a base by a film forming method and that allows the resistance value of a balancing resistor connected to a Wheatstone bridge circuit to be adjusted accurately and at low cost. .

[Means for solving problems]

A first aspect of the invention configured to solve the above-mentioned problems includes a base body having a strain-generating portion and a non-strain-generating portion, and at least one strain-generating portion located in the strain-generating portion of the base body. A plurality of gauge resistors provided on a base body, a balancing resistor for resistance balance adjustment located in a non-strain part of the base body, and a balancing resistor provided on the base body to connect each of the gauge resistors and the balancing resistor. and a conductor forming a Wheatstone bridge circuit, and the balancing resistor and the gauge resistor are made of the same material.

Further, the means of the second invention is provided on a base body that receives an external force, and is connected between a plurality of gauge resistors forming a Wheatstone bridge circuit and a pair of gauge resistors among the plurality of gauge resistors, and the Wheatstone bridge It consists of a balancing resistor that balances the output of the circuit, and a plurality of adjustment wires connected between the balancing resistor and the gauge resistor, and the adjustment wires are connected based on the output voltage of the Wheatstone bridge circuit. The resistance value of the balancing resistor is set by cutting any one of the adjustment wirings.

[Effect]

In the first invention, the gauge resistor constituting the Wheatstone bridge circuit and the balancing resistor for adjusting the balance of the output of the bridge circuit are made of the same material.
Since both have the same resistance temperature coefficient, the stress sensor does not lose the zero balance of the Wheatstone bridge circuit due to temperature changes, and has excellent temperature characteristics.

Further, in the second invention, since the resistance adjustment of the balancing resistor is performed without contacting the resistor, the film quality of the resistor is not impaired and the resistance value can be adjusted accurately.

〔Example〕

Embodiments of the first invention will be described in detail below with reference to FIGS. 1 to 7. Note that the same reference numerals are given to the same components as those of the prior art described above, and the explanation thereof will be omitted.

In the figure, reference numeral 11 denotes a strain detection section 12A, 12B formed on the circuit forming surface 1C of the diaphragm 1.

12c and 120 constitute the strain detecting section 11, and the strain generating section IA
A gauge resistor (hereinafter collectively referred to as gauge resistor 12) is composed of four semiconductor strain gauges arranged above, and the gauge resistor 12 has a P - It is formed by CVD method and photolithography method.

13A, 13B, 13C, 130, 13E.

13F is a thin film conductor (hereinafter referred to as thin film conductor 13) that connects the gauge resistor 12 to form a Wheatstone bridge circuit.
), and the thin film conductor 13 is formed using a good conductive material such as gold, aluminum, copper, etc., using a vacuum evaporation method and a photolithography method, as in the prior art. Note that the thin film conductors 13A, 13B, . . . are connected to the gauge resistors 12. Since the connection relationship connecting to ... is the same as that of the prior art, the details thereof will be referred to the explanation of the prior art. Further, the outer ends of each thin film conductor 13A, 13B, . . . are terminals 14A, 14B, 14C, 14D.

14E and 14F.　　.

15.16 is between the thin film conductors 13A and 13F and 13c
, a pair of balancing resistors connected between , 130, respectively,
Each of the balancing resistors 15 and 16 is located on the non-strain portion IB of the diaphragm l, and is connected to the gauge resistor 12 as will be described in detail later.
They are simultaneously formed by the same P-CVD method using the same S i Ha and B2 H6.

Thus, the strain detecting section 11 of the embodiment has a gauge resistor 12 and a balancing resistor 15, 16 formed in the strain-generating part IA and the non-strain-generating part IB of the diaphragm l, respectively, using the same material and the same forming method. In order to connect the gauge resistor 12 and the balancing resistors 15 and 16 to form a bridge circuit, a circuit forming surface IC is formed using a different forming method from that of the gauge resistor 12 and the like.
A thin film conductor 13 is formed on top of the conductor.

The pressure sensor of the embodiment is constructed as described above, and first, a method of manufacturing the same will be explained with reference to FIGS. 3 to 7.

First, for example, an insulating synthetic resin material is processed, and the strain-generating portion IA is
After forming the diaphragm 1 having the non-strain portion IB,
A gauge resistor 12 is placed on the circuit forming surface tC of the diaphragm 1.
Resistor thin IIA for forming balancing resistor 15.16
& molding (see Fig. 3). As mentioned above, this film forming method uses a known method (see Fig. 3) using SiHs, B2Hb, etc.
7) P-CVD method is used.

After forming the resistor F[A, four gauge resistors 12A, 12B, and 12C are placed on the strain-generating portion IA by photolithography using a metal mask or the like.

120 is formed, and at the same time, 2 m of balancing resistors 15 and 16 located on the non-strain portion IB are formed (see FIG. 4).

After that, the gauge resistor 12 formed simultaneously as described above,
A thin film conductor 13 for connecting the balancing resistors 15 and 16 is formed using a vacuum evaporation method in the same manner as in the prior art (see Figure 5).Next, a metal layer is formed using a photolithography method. Thin NIH for the conductor using mass, glue, etc.
A thin film conductor 13 connecting the gauge resistor 12 and the balancing resistor 15, 18 is patterned (see FIG. 6).

As described above, the four gauge resistors 12A and 12B
.

After forming the strain detecting section 11 in which two balancing resistors 15 and 16 are incorporated in the Wheatstone bridge circuit consisting of 12c and 12D, the gauge resistor 12A is formed.

12B, ... and the resistance values of the balancing resistors 15 and 16, and between the terminals 14A and 140 and between the terminals 14B (14c),
The balancing resistors 15 and 18 are trimmed to adjust the resistance so that the potential difference between 14E (14F) becomes zero balance.This trimming is performed, for example, by a laser trimming method, etc., as shown in FIG. 7 and described in detail later. Let's do it.

Finally, a SiN film, 5i0
By forming two protective passivation films, the pressure sensor of the embodiment is completed.

The pressure sensor of the embodiment is as described above, and the strain-generating portion I
The strain of A is detected by four gauge resistors 12, and the terminals 14A,
Since there is no substantial difference from the prior art in measuring the potential difference generated between 14B and 14B, a description thereof will be omitted.

According to the embodiment, the gauge resistor 12 and the balancing resistors 15 and 16 constituting the strain detecting section 11 are made of the same material and manufactured by the same manufacturing method, and the gauge resistor 12 is placed on the strain generating section IA. The resistors 15 and 16 are respectively formed on the non-strain portion IB. Therefore, although the balancing resistors 15 and 16 are made of the same resistor as the gauge resistor 12, even if the resistance value of the gauge resistor 12 changes due to pressure stress, the balancing resistor 15.
Since the resistance value of 5.16 does not change, strain measurements can be made in the same manner as in the prior art.

Moreover, the balancing resistor 15.18 is manufactured using the same material as the gauge resistor 12, and its temperature coefficient of resistance is the same as that of the gauge resistor 12. Therefore, depending on the environmental temperature, the balancing resistor 15.16 and the gauge resistor 12 It is possible to prevent the zero balance of the Wheatstone bridge circuit from being lost due to different resistance values, and it is possible to create a pressure sensor with excellent temperature characteristics.

Further, according to the embodiment, the gauge resistor 12 and the balancing resistor 1
5.16 are both provided on the circuit forming surface Ic of the diaphragm 1, and the environmental temperature is the same, so the temperature 'IIF
As a result, the zero balance fluctuation of the bridge circuit can be reduced, resulting in a pressure sensor with good temperature characteristics.

Furthermore, the balancing resistor 15.16 is 1l on the diaphragm l.
Since it is provided as an lfl resistor, the pressure sensor can be made smaller. Furthermore, a gauge resistor 12 and a balancing resistor 15.16
Since they are formed simultaneously on the diaphragm l by the same manufacturing method, the number of manufacturing steps can be reduced compared to the prior art in which different types of balancing resistors 6 and 7 are provided, and as a result, manufacturing costs can be reduced.

Next, FIGS. 8 to 10 show an embodiment according to the second invention.

The second invention was made in view of the drawbacks of the laser trimming method that has been widely used in the past for adjusting the resistance of the above-mentioned balancing resistors 15 and 16.

That is, the laser trimming method has been adopted as a trimming method superior to other trimming methods such as anodizing and ultrasonic methods, and as shown in FIG. 7, the balancing resistor 15 ( By cutting off part 15A (18A) of 1B) from the cutting point indicated by arrow C,
This method attempts to determine the resistance value of the balancing resistor 15 (18).

However, the laser trimming method described above has the following drawbacks. The first problem is that the trimming device becomes large because it uses laser light. The second problem is that the film quality near the cut end of the balancing resistor 15 (16) irradiated with the laser beam changes in quality, so the resistance value after trimming differs from the resistance value calculated in advance, resulting in complete failure. The problem is that it cannot be set to zero balance. For this reason, the laser beam must be aligned to the trimming location.

The trimming process, such as setting the movement speed, is complicated, and
There is a problem that the high precision increases the cost of trimming, and that highly reliable trimming cannot be achieved.

The present invention was made in view of the above-mentioned drawbacks, and provides a balancing resistor that does not require large equipment, is low cost, does not damage film quality, and allows resistance adjustment to a desired resistance value. The present invention provides a pressure sensor equipped with a pressure sensor.

In the embodiment of the second invention described below, the same components as those of the embodiment of the first invention described above are given the same reference numerals, and the explanation thereof will be omitted.

In the figure, 21.22 is the non-strain part I of the diaphragm l.
Similar to the balancing resistor 15°16 in the first embodiment, a p-
A pair of balancing resistors formed by the cvn method, one end of one balancing resistor 21 is connected to the first resistor through a connection wiring 23.
is connected to the fourth thin film conductor 13A, and one end side of the other balancing resistor 22 is connected to the fourth thin film conductor 1 via another connection wiring 24.
Connected to 3D. Both of the first and second connection wirings 23 and 24 are thin film conductors 13A.

Like 13D, it is molded by vacuum evaporation and photolithography.

25A, 25B, 25C, 25D, 25E.

25F and 25G are seven adjustment wirings (hereinafter collectively referred to as adjustment wirings 25) connected radially between one of the balancing resistors 21 and the sixth thin film conductor 13F; 25 is connected to the balancing resistor 21 at predetermined intervals along the longitudinal direction, and the other end is connected to the sixth thin film conductor 1.
Connections are concentrated at a connection point 13F' in the middle of 3F.

On the other hand, 26A, 26B, 26C, 260° 26E, 26
F, 26G are seven other adjustment wirings (hereinafter collectively referred to as adjustment wirings 26) connected radially between the other balancing resistor 22 and the third thin film conductor 13c; Similarly to the adjustment wiring 25, one end of each wiring is connected to the balancing resistor 22 at predetermined intervals along the longitudinal direction, and the other end is connected to the middle of the third thin film conductor 13C. The connections are concentrated at the connection point 13C'.

This embodiment is constructed as described above, and the resistance is adjusted by the trimming method described below.

First, prepare in advance four gauge resistors 12 and two balancing resistors 2.
Thin film conductors 13A, 13B, 13C are formed on the upper side of the diaphragm 1.

130.13E, 13F, connection wirings 23, 24, and adjustment wirings 25.26 are integrally formed. For this formation, a film forming method such as a vacuum evaporation method or a sputtering method, and a pattern forming method using a photolithography method are used. At the time of this molding, one of the balancing resistors 21 has seven adjustment wirings M2.
5A, 25B, . . . , the sixth Fl film conductor 13F
(see Figure 9), and similarly, the other balancing resistor 22 is also connected to the third Q film conductor 13C through seven adjustment wirings 26A, 28B, . There is. Therefore, for example, a current flowing from the terminal 14A to the connection wiring 23 side passes through a part of the balancing resistor 21, and from the adjustment wiring 25 to the sixth thin film conductor 13 via the connection point 13F'.
It will flow to F.

Next, each gauge resistance 12A, 12B was measured.

Based on the resistance value of ..., perform trimming for resistance adjustment of the balancing resistors 21 and 22 in order to maintain zero balance.
This trimming is performed by cutting one or more of the seven adjustment wirings 25 by any cutting method such as laser beam irradiation, mechanical cutting with a cutter, chemical cutting by etching, etc. In the ninth factor, a + b + C+ e + f
*Each point g indicates a cutting location in the adjustment wiring 25.

According to this trimming method, as described above, the current flowing from the terminal 14A to the connection wiring 23 side passes through the balancing resistor 21 and from the uncut adjustment wiring 25D to the connection point 13.
By flowing to the sixth thin film conductor 13F via F', the resistance value of the balancing resistor 21 is set. in this way,
The zero balance of the Wheatstone bridge circuit can be adjusted by selecting one or more adjustment wires 25 that will not be cut.

Although the above-mentioned adjustment wiring 25 may be cut by laser light irradiation, the wiring 25 is AfL.

Since it is formed into a thin film using a relatively large number of materials such as Au and Cu, it is possible to perform mechanical cutting in which a part of the wiring 25 is removed using a cutter or the like, or chemical cutting in which a part of the wiring 25 is removed by etching. This is extremely easy to do.

Note that the method for forming and cutting the adjustment wiring 26 connected between the other adjustment resistor 22 and the third thin film conductor 13C is the same as that described above, so the description thereof will be omitted.

Further, in the embodiment, seven trees of adjustment wirings 25 and 26 are formed, but by forming more adjustment wirings than in the embodiment when forming the wiring pattern by photolithography, even more adjustment wirings 25 and 26 are formed. Highly accurate trimming becomes possible.

Although it has been described that the diaphragm l in each embodiment is molded from an insulating synthetic resin material, it may also be molded from a metal material. In this case, the circuit forming surface IC is coated with an insulating film in advance. Alternatively, the diaphragm l may be molded from a ceramic material.

On the other hand, gauge resistance 12 and balancing resistance 15° 16.25
．． Although it has been described that the resistive thin film for forming 26 is formed by the P-CVD method, various thin film 11! J molding method can be used. on the other hand,
A thick film forming method using mask printing and baking using a resistive material paste may also be used.

Furthermore, although it has been described that the thin film conductor 13 and the connection wirings 23 and 24 are formed using the vacuum evaporation method and the photolithography method, similar to the gauge resistor 12, the thin film conductor 13 and the connection wires 23 and 24 may be formed using the sputtering method, laser film forming method, or ion blating method. Alternatively, a thick film forming method using mask printing may be used.

Further, in the embodiment, a pressure sensor using four semiconductor strain gauges 12 has been exemplified, but at least one strain gauge 12 may be disposed in the strain-generating portion IA of the diaphragm l. A metal gauge such as a resistance wire strain gauge may be used instead of the strain gauge.

Furthermore, although the embodiments have been exemplified by pressure sensors, the inventions can also be applied to load cells, anti-levers, differential pressure gauges, etc. as long as they are stress sensors using a Wheatstone bridge circuit.

〔Effect of the invention〕

The present invention has been described in detail above, and has the following effects.

■ The strain gauges that make up the Wheatstone bridge circuit and the balancing resistors that are externally attached to the Wheatstone bridge circuit to adjust the balance between the outputs of the Wheatstone bridge circuit are made of the same material and are installed in the non-strain part of the diaphragm. , the strain gauge and the balancing resistor can have the same temperature coefficient of resistance, and a stress sensor with excellent temperature characteristics that is unaffected by environmental temperature can be obtained.

■ Since the strain gauge and the balancing resistor can be manufactured simultaneously using the same material and the same manufacturing method, the number of parts and manufacturing steps can be reduced, and the manufacturing cost of the stress sensor can be reduced.

■ Trimming work can be performed without contacting the balancing resistor, which prevents the risk of deteriorating the film quality as with laser trimming, and provides highly reliable trimming that allows the resistance value of the balancing resistor to be set with high accuracy. can be done.

(2) The resistance of the balancing resistor can be adjusted by mechanical cutting or chemical cutting, and laser trimming, which requires large equipment, can be omitted, reducing equipment costs.

■ Trimming can be done by simply cutting the adjustment wiring at any position; the cutting area is wide, and operations such as high-precision positioning are not required, making trimming work easy.
Improves work efficiency.

(2) The number of adjustment wirings can be easily and significantly increased using various thin film and thick film forming methods, making it possible to trim with high precision.

[Brief explanation of the drawing]

1 to 7 show an embodiment according to the first invention,
Fig. 1 is a front view of the pressure sensor, Fig. 2 is a bottom view of Fig. 1, and Figs. 3 to 6 show the manufacturing process of the pressure sensor.
Fig. 3 is an explanatory diagram of a resistor thin film formed on a diaphragm, Fig. 4 is an explanatory diagram of a strain gauge and a balancing resistor manufactured from the resistor g film, and Fig. 5 is an explanatory diagram of a conductor thin film formed on a diaphragm. FIG. 6 is an explanatory diagram showing a thin film conductor constituting a Wheatstone bridge circuit manufactured from the conductor thin film, FIG. 7 is an explanatory diagram showing the adjustment resistor after laser trimming, and FIGS. 8 to 10. The figures show an embodiment according to the second invention, Fig. 8 is a front view of the pressure sensor showing the connection state before resistance adjustment, Fig. 9 is an enlarged view of the main part in Fig. 8, and Fig. 1θ is for adjustment. An explanatory diagram showing the state in which the resistance has been adjusted by cutting the resistor at the same position as in Figure 9, Figures 11 to 1
3 relates to the prior art, FIG. 11 is a front view of the pressure sensor, FIG. 12 is a sectional view in the direction of the mowing-■ arrow in FIG.
Figure 3 is a circuit diagram of a Wheatstone bridge connected to a balancing resistor. l... diaphragm, IA... strain generating part, IB...
Non-strain parts, 12A, 12B, 12G, 120...Semiconductor strain gauges, 13A, 13B, 13C, 13D. 13E, 13F...g membrane conductor, 15.16, 21゜2
2...Balancing resistor, 25A, 25B, 25C. 25D, 25E, 25F, 25G, 26A. 26B, 26C, 26D, 26E, 26F. 26 G-・Adjustment wiring, a, b, c, e, f, g・
...Cut point. Figure 1 Figure 2 Figure 1A Figure 6 Figure 7 Figure 10 Figure 11 Figure 12?

Claims (2)

[Claims] (1) A base body having a strain-generating portion and a non-strain-generating portion, a plurality of gauge resistors provided on the base body such that at least one of the gauge resistors is located in the strain-generating portion of the base body, and a non-strain-generating portion of the base body. and a conductor provided on the base body to connect each of the gauge resistors and the balancing resistor to form a Wheatstone bridge circuit. A stress sensor in which the gauge resistors are formed of the same material. (2) Provided on a base that receives external force and connected between a plurality of gauge resistors constituting a Wheatstone bridge circuit and a pair of gauge resistors among the plurality of gauge resistors to balance the output of the Wheatstone bridge circuit. It consists of a balancing resistor and a plurality of adjustment wires connected between the balancing resistor and the gauge resistor, and the output voltage of any one of the plurality of adjustment wires is determined based on the output voltage of the Wheatstone bridge circuit. A stress sensor configured to set the resistance value of the balancing resistor by cutting the adjustment wiring.