RU2463687C1 - Bounded semiconductor strain gauge - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: bounded semiconductor strain gauge contains a polymer substrate 1 (made, for example, of lacquer VL-931 with a thickness of 20÷30 mcm), a carrier 2 made of thin (3÷10 mcm) metal (for example, constantan) foil, a dielectric separating film 3 (for example, of silicon monoxide SiO) with a thickness of (1÷3 mcm) 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, after a lithographic operation, represents two pads connected to with a string with a width of 50÷200 mcm (dumb-bell shape). The dielectric film 3 and the strain-sensitive films 4 sedimented on the carrier 2 also repeat the carrier shape while the metal contacts 7 are made, for example, of nickel with a thickness of 1÷2 mcm and are located at the ends of the strain-sensitive film 4 strings on its wide pads. The polymer substrate 1 is formed on the reverse side of the carrier 2.

EFFECT: enhancement of axial sensitivity to deformation and transversal sensitivity reduction.

3 cl, 6 dwg

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, 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.

Also known are strain gauges having a substrate, a strain-sensitive strip of samarium monosulfide, contact pads and a separating dielectric film (patents: WO 99/24804, G01L 1/22, 25/00, 27/00, publ. 15.12.1994 and RU 2367062, H01L 29/84, published on 09/10/2009). In these technical solutions, the substrate is made of metal or organic material, such as glass, and serves as an elastic element. The disadvantage of these strain gauges is the limited scope. they can only be used in integrated circuits on the elastic elements of sensors of mechanical quantities and cannot be used in strength tests to measure strain, although they have a greater strain sensitivity due to the use of a strain gauge element made of samarium monosulfide.

These solutions are considered as analogues only because in them, as a sensitive element, a polycrystalline film of samarium monosulfide is used. In fact, this film is made integrally with an elastic element (in the description of analogues it is incorrectly called a substrate), that is, it is a single whole with it and cannot be used independently as a glued strain gauge. The specified film does not have a substrate in accordance with GOST 20420-75 "TENSOR RESISTORS. Terms and definitions ”, and can condense on a separating dielectric film if the elastic element is metallic, or directly on the elastic element if it is a dielectric.

There are known semiconductor strain gauges that can be used in strength tests to measure strain, 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 by 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.

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 at the ends of a strain-sensitive film (DT Ankudinov, KN Mamaev, “Low-base resistance strain gauges”, “Mechanical Engineering”, 1968 pg. 47-50). In the solution taken as a prototype, the strain-sensitive film is made of bismuth and has a low strain-sensitivity.

The disadvantage of the prototype is its low strain sensitivity and the presence of lateral sensitivity.

The invention is aimed at achieving a technical result, which consists in increasing the axial sensitivity to deformation and reducing the transverse sensitivity.

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

To achieve the specified technical result, the proposed glued semiconductor strain gauge, in contrast to the closest known to it, is equipped with a metal foil carrier made in the form of a thread with wide areas at its ends (in the form of a dumbbell), and a release dielectric film formed on the carrier and repeating its shape, while the strain-sensitive film is a polycrystalline samarium monosulfide, formed on a dielectric film and also repeats the shape of the nose Itel. Metal contacts are formed on wide areas of the strain-sensitive film and are connected to the ends of its filament, and a polymer substrate is formed on the back of the carrier. The width of the thread is in the range of 50 ÷ 200 μm, the polymer material of the substrate is, for example, varnish VL-931 with a thickness of 20 ÷ 30 μm, and the carrier can be made of constantan foil with a thickness of 3 ÷ 10 μm. A dielectric separation film made, for example, of silicon monoxide SiO with a thickness of 1 ÷ 3 μm, separates from the conductive material (carrier) a part of the measuring circuit — a strain-sensitive film with contact pads.

All specified size intervals are determined empirically. Going beyond their boundaries or worsens the metrological characteristics, or complicates the process.

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 the deposited dielectric and strain-sensitive films of samarium monosulfide in the form of a dumbbell, i.e. in the form of two sites connected by a thread with a width in the range of 50–200 μm, it is possible to obtain a strain gauge with virtually 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 a thin thread (the narrow part of the dumbbell), which, depending on size, undergoes minimal or no transverse deformation.

The invention is illustrated by drawings, on which:

- figure 1 is a General view of the strain gauge;

- figure 2 is a longitudinal section aa;

- figure 3 is a longitudinal section bB;

- figure 4 is a transverse section bb;

- figure 5 - glued to the part of the strain gauge in the undeformed state;

- figure 6 - glued to the part of the strain gauge in a deformed state.

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 a 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 a dielectric film 3. The carrier 2 after lithographic operations is two sites connected by a thread with a width of 50 ÷ 200 μm (dumbbell shape). The sequentially dielectric 3 and strain-sensitive 4 films deposited on the carrier 2 in vacuum also repeat its shape. The metal contacts 5 are made, for example, of nickel 1-2 microns thick and are located at the ends of the thread of the strain-sensitive film 4, on its wide areas. The polymer substrate 1 is formed on the back of the carrier 2.

The use of thin foil as a carrier is explained by the fact that evaporation and condensation of the samarium monosulfide film occurs at high temperatures. So, the temperature of the evaporator is 2600 ° ÷ 3000 ° С. The deposition of dielectric 3, strain-sensitive 4 and metal (contacts 5) films on the carrier 2 is carried out at a temperature (350 ÷ 400 ° C), which no polymer binder can withstand, 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 the condensation of the films 3, 4, 5.

Another advantage of thin metal foil as a carrier 2 is the possibility, as mentioned above, of using lithographic processes to obtain the desired topology and, in particular, the possibility of forming thin filaments, which, depending on their size, undergo minimal or no transverse deformation, which allows to obtain strain gauges without lateral sensitivity for strength tests.

The strain gauge works as follows. According to appropriate technology, it is glued to the surface of the investigated part 6 (figure 5). Under mechanical forces, the part is deformed (stretched or compressed), and the strain gauge (Fig. 6) is stretched or compressed by the ΔL strain gauge (Fig. 6), obtaining a relative deformation ΔL / L, which, in turn, leads to a relative change in resistance (ΔR / R) strain gage. Values ΔL / L and ΔR / R are interconnected through the coefficient of strain sensitivity:

ΔR / R = KΔL / L,

where K is the coefficient of strain sensitivity;

ΔL / L is the relative deformation;

ΔR / R is the relative change in resistance.

The measurement of the relative change in resistance is carried out using strain gauges (not shown).

Thus, the design of the proposed strain gauge made it possible to combine the advantages of strain gauges indicated as analogues and prototype by combining the polymer substrate with a strain-sensitive film of samarium monosulfide, using a thin metal foil as a heat-resistant carrier, which also made it possible to obtain the above topology, reducing the transverse sensitivity, practically to zero at high strain sensitivity of samarium monosulfide. This strain gauge 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.).

Claims (3)

1. Adhesive semiconductor strain gauge containing a polymer substrate, a strain-sensitive film and metal contacts at the ends of the strain-sensitive film, characterized in that it is equipped with a carrier of metal foil, made in the form of a thread, a width of 50 ÷ 200 microns with pads at its ends, and a dielectric separation a film formed on a carrier and repeating its shape, while the strain-sensitive film is a polycrystalline samarium monosulfide formed on a dielectric film and also follows the shape of the carrier and the metallic contacts are formed at the sites gage film and connected to the ends of its filaments, in addition, the polymer substrate is on the back side of the medium. 2. The semiconductor strain gauge according to claim 1, characterized in that the polymer substrate material is VL-931 varnish with a thickness of 20 ÷ 30 μm. 3. The semiconductor strain gauge according to claim 1, characterized in that the carrier is made of constantan foil with a thickness of 3 ÷ 10 μm.

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