RU2463686C1 - Bounded semiconductor strain gauge - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: semiconductor strain gauge contains a polymer substrate 1, a carrier 2 made of thin (3÷10 mcm) metal (constantan) foil, a dielectric separating film 3 (SiO) formed on the carrier 2 and a strain-sensitive film 4 (on the film 3) of samarium monosulphide (SmS) with a thickness of 0.5÷1 mcm. The carrier 2 represents two pads 5 connected with strings 6 the width whereof is equal to 50÷200 mcm (lattice shape). The dielectric film 3 and the strain-sensitive film 4 sedimented on the carrier 2 also repeat the carrier shape. The contacts 7 are made of nickel with a thickness of 1÷2 mcm and are partly formed on the pads 5 and partly - on the strings 7 of the strain-sensitive film 4 shunting the latter. The unshunted parts of the strain-sensitive film 4 strings 6, properly representing the resistors, are electrically-connected parallel to each other. The polymer substrate 1 (lacquer VL-931 with a thickness of 20÷30 mcm) is formed on the reverse side of the carrier 2. The length of sections 8 of the metal contacts 7 located on the strings 6 is identical or varied from one string to another according to a nonlinear or nonlinear law.

EFFECT: enhancement of axial sensitivity to deformation, reduction of transversal sensitivity and ensuring the possibility of the strain gauge electric resistance reduction and modification after bonding by way of strings breakage.

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Description

The invention relates to measuring technique and can be used both in strength tests to determine the stress state of structures, and as a sensitive element in sensors of mechanical quantities (force, pressure, weight, displacement, etc.).

Known strain gauge (SU 1717946 G01B 7/16, 7/18, publ. 07.03.1992) containing a strain-sensitive strip of samarium monosulfide, contact pads and a dielectric substrate of silicate glass.

The disadvantage of this solution is the limited scope: determination of the stress state inside the mass of concrete or other hardening materials.

Known semiconductor strain gauges that can be used in strength tests to measure deformation, in particular a glued semiconductor strain gauge, the sensitive element of which is a silicon wafer mounted on a polymer substrate, and the ends of which are connected to the contact pads with jumpers made of gold wire (I. German. " The practical use of strain gages. "Energy", 1970, p. 9).

The non-linearity of the characteristics, a large dependence on external influences (temperature, light) does not allow to realize the benefits arising from the high strain sensitivity, and the very high complexity, and therefore the price, make them inaccessible for widespread use. A silicon strain gauge plate is cut from a single crystal along the (111) crystallographic axis for the p type, and for the n type, along the (100) crystallographic axis. The strain sensitivity coefficient of such a plate is more than one hundred, while the polycrystalline silicon film has a strain sensitivity coefficient of about twenty. In addition, the disadvantage of this design is the impossibility of fitting (adjusting) its parameters to the specific conditions of the measurement experiment.

The closest technical solution is a glued semiconductor strain gauge, taken as a prototype, containing a polymer substrate, a strain-sensitive film and metal contacts located at opposite ends of the strain-sensitive film (D.T. Ankudinov, K. N. Mamaev. “Low-base resistance strain gauges”, “Engineering ", 1968, pp. 47-50). In the solution taken as a prototype, the strain-sensitive film in the form of two strips is made of bismuth and has a low sensitivity, and the strips of the strain-sensitive film are connected in series, which makes it impossible to change the resistance and obtain the desired resistance.

The disadvantage of the prototype is its low strain sensitivity, the presence of lateral sensitivity and the inability to change the resistance to obtain the desired parameters.

The invention is aimed at achieving a technical result, which consists in increasing the axial sensitivity to deformation, reducing the lateral sensitivity and making it possible to reduce the electrical resistance of the strain gage due to the parallel connection of the strain gages located on the threads, that is, the total resistance will be n times less and change it after the sticker by breakage of threads.

Below, when disclosing the invention and considering its specific implementation, other types of achieved technical result will be named.

This technical result is achieved in that a strain gauge containing a polymer substrate, a strain-sensitive film and metal contacts located at opposite ends of the strain-sensitive film is equipped with a metal foil carrier made in the form of two pads connected by threads with a width of 50 ÷ 200 μm each. In addition, the strain gauge is equipped with a separation dielectric film formed on the carrier and repeating its shape, while the strain-sensitive film is polycrystalline samarium monosulfide, formed on a dielectric film and also repeats the shape of the carrier. Metal contacts are formed on sites and partially on the threads of the strain-sensitive film, shunting it, while the unshunted parts of the threads of the strain-sensitive film are electrically connected to each other in parallel. The polymer substrate is mounted on the back of the carrier. In addition, the length of the strips of metal contacts located on the threads of samarium monosulfide can be the same or different and varies from one to another according to a nonlinear law. It is also possible to perform when the length of the strips of metal contacts located on the threads of samarium monosulfide is different and varies from one to another according to a linear law.

Thus, in the proposed strain gauge due to the use of a carrier made of heat-resistant material in the form of a thin metal foil (constantan) it became possible to use samarium monosulfide on the polymer substrate as a strain-sensitive film and, accordingly, increase the strain gauge sensitivity to deformations.

The implementation of the carrier with a dielectric and strain-sensitive film of samarium monosulfide deposited on it in the form of a lattice formed by two sites connected by threads, each of which is 50 ÷ 200 μm wide, allows one to obtain a strain gauge with practically no transverse sensitivity for strength tests. This result is also achieved through the use of a carrier made of thin metal foil, which makes it possible to use lithographic processes to obtain the desired topology: the formation of thin filaments that undergo minimal or no transverse deformation. The execution of the working part of the strain gage (polycrystalline films) in the form of thin filaments makes it possible to reduce the transverse strain sensitivity, which depends on the thickness, which is within 3 ÷ 10 μm and the width of the filaments (50 ÷ 200 μm), as well as on the thickness and stiffness of the polymer substrate.

The specific resistance of samarium monosulfide is high, and in order to reduce the resulting resistance of the strain gauge, the threads of samarium monosulfide, being actually resistors, are connected in parallel, which reduces the current load on a separate resistor, while reducing the power dissipation and, therefore, the temperature of self-heating. In addition, breaking the threads of a glued strain gauge that has already been glued, you can change its resistance.

The invention is illustrated by drawings, on which:

- figure 1 is a General view of a strain gauge with six working threads;

- figure 2 is a longitudinal section aa; passing along a thread

- figure 3 is a longitudinal section bB passing between the threads,

- figure 4 is a transverse section bb;

- figure 5 is a carrier with a separation and strain-sensitive films in plan without contact;

- figure 6 is a General view of the strain gauge, in which the length of the threads of the metal contacts varies linearly;

- Fig.7 is a General view of the strain gauge, in which the length of the threads of the metal contacts varies according to a nonlinear law;

- Fig. 8 is an equivalent circuit diagram of a six-strand strain gauge.

The proposed strain gauge contains a polymer substrate 1 made, for example, of VL-931 varnish with a thickness of 20 ÷ 30 μm, a carrier 2 made of thin (3 ÷ 10 μm) metal (for example, constantan) foil formed on a carrier 2, a dielectric separation film 3 (for example, silicon monoxide SiO) with a thickness of (1 ÷ 3 μm) and a strain-sensitive film 4 made of samarium monosulfide (SmS) with a thickness of 0.5 ÷ 1 μm made on the film 3. The carrier 2 after lithographic operations is two sites 5 connected by threads 6 of a width of 50 ÷ 200 μm each (lattice shape) (figure 5). The sequentially dielectric 3 and strain-sensitive 4 films deposited on the carrier 2 in vacuum also repeat its shape (pads 5 connected by threads 6) (Fig. 5). The metal contacts 7 are made, for example, of nickel 1-2 microns thick and are partially formed on the sites 5, performing, in fact, the role of electrical contacts, and partially on the threads 6 of the strain-sensitive film 4, acting as shunts, i.e. shunting it, while the unshunted parts of the threads 6 of the strain-sensitive film 4, being, in fact, resistors, are electrically connected to each other in parallel. Thus, the magnitude of the unshunted part of the strain-sensitive film 4 (black) on the yarns 6 is either the same (Fig. 1) or different (Figs. 6 and 7), and therefore the resistance is different. Russian GOST defines the following series of resistors: 100, 200, 400 and 800 Ohms; Western standard 120 and 350 ohms. It is understood that using a six-strand strain gauge, all standards can be covered. The polymer substrate 1 is formed on the back of the carrier 2.

All indicated dimensions are determined empirically. Going beyond them either worsens the metrological characteristics or complicates the process.

The use of thin foil as a carrier 2 is explained by the fact that the evaporation and condensation of the film 4 of samarium monosulfide occurs at high temperatures. So, the temperature of the evaporator is 2600 ÷ 3000 ° C. The deposition of dielectric 3, strain-sensitive 4 films and metal contacts 7 on the carrier 2 is carried out at a temperature of the latter of 350 ÷ 400 ° C, i.e. no polymer binder can withstand it, and evaporation from the polymer when heated does not allow to achieve high vacuum, therefore, the polymer substrate 1 is formed on the other side of the carrier 2 after condensation of the films 3, 4 and the metal of the contacts 7.

Another advantage of a thin metal foil as a carrier 2 is the possibility of using lithographic processes to obtain the desired topology and, in particular, the possibility of forming thin filaments 6, which, depending on their size, undergo minimal or no transverse deformation, which allows to obtain strain gauges without lateral sensitivity for strength tests. The shape of the carrier 2 and the films 3 and 4 before applying the contacts 7 and forming the substrate 1 on it is shown in FIG. 5, while the films 3 and 4 have, respectively, the same shape and dimensions.

Depending on the modes of evaporation and deposition, films of samarium monosulfide with various metrological characteristics are obtained. The values of resistance (r), strain sensitivity (K) and temperature coefficient of resistance (α) are correlated with each other, and an increase in one value leads to an increase in the other two. From this it follows that when obtaining strain gages with high sensitivity (80 ÷ 100), they also have a large resistance (r) (100 ÷ 200 kOhm). Using strain gauges with N number of threads, it is possible, all other things being equal, to reduce the resistance N times: R = r / N.

In addition, breaking the threads of a glued strain gauge that has already been glued, you can change its resistance.

Figure 6 shows a semiconductor strain gauge in which sections of the contacts 7 on the threads 6 of the polycrystalline film 4 have a different length, which varies linearly from thread to thread, and therefore have different lengths and unshunted sections of the polycrystalline film 4 (black color) , which also varies linearly from thread to thread.

Then the breakage of any of the threads 6 will lead to an abrupt change in the resistance of the already glued strain gauge. The described feature is very convenient for balancing the strain gages in the sensors of mechanical quantities, since when glued, the strain gages always change the resistance. The magnitude of the jump also depends on the number of threads.

The non-linear law, according to which the lengths of the sections 8 of the contacts 7 and, respectively, the unshunted sections of the threads 6 of the film 4 (resistors) are changed, is implemented in the strain gauge shown in Fig.7. For this case, of greatest practical interest is the option when, with a sequential break of the strands 6 (r), the resistance jump has the same magnitude.

The total resistance (R) for the case when the resistances on the threads 6 are equal and the number of threads 6 is six (Fig. 1) is determined by the formula: R = r / 6, and in the case of different resistance of the threads 6 (Fig. 6 and 7) the total resistance is determined by the formulas of parallel connection of resistors.

Thus, the proposed technical solution allows to obtain a technical result, which consists in increasing the axial sensitivity to deformation, reducing the transverse sensitivity and providing the ability to reduce the electrical resistance of the strain gauge and change it after the sticker.

Claims (3)

1. A glued semiconductor strain gauge containing a polymer substrate, a strain-sensitive film and metal contacts located at the ends of the strain-sensitive film, characterized in that it is provided with a carrier of metal foil made in the form of two connected by threads, pads, and a separation dielectric film formed on carrier and repeating its shape, while the strain-sensitive film is a polycrystalline samarium monosulfide, formed on a dielectric film and so e repeats the shape of the carrier, while the width of the threads is in the range of 5 ÷ 200 μm, and metal contacts are formed on the sites and partially on the threads of the strain-sensitive film, shunting it, while the unshunted parts of the threads of the strain-sensitive film are electrically connected to each other in parallel, in addition, the polymer a substrate is formed on the back of the carrier. 2. The semiconductor strain gauge according to claim 1, characterized in that the length of the sections of metal contacts located on the threads of samarium monosulfide is different and varies from one to another according to a non-linear law. 3. The semiconductor strain gauge according to claim 1, characterized in that the length of the sections of metal contacts located on the threads of samarium monosulfide is different and varies from one to another according to a linear law.

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