RU2244970C1 - Method for manufacturing temperature-compensated resistive-strain sensor - Google Patents

Abstract

FIELD: electronic engineering including thin-film microelectronics.

SUBSTANCE: proposed method includes evaporation of resistive layers on flexible insulating substrate and formation of strain-sensing elements of resistive-strain sensor using photolithography method, their resistance being measured in the course of adjusting temperature-compensated resistance of resistive-strain sensor by means of ohmmeter connected to respective contact pads. Resistive-strain sensor is manufactured from two resistive materials differing in value and sign of temperature-compensated resistance; two series-connected strain-sensing elements are formed on substrate, their integrated leads are connected to contact pad disposed on one end of substrate, and two remaining leads are connected to contact pads disposed in immediate proximity on other end of substrate; temperature compensation is effected by laser adjustment of resistance ratios of sensing elements having previously determined method for electrical connection of different strain-sensing elements. After that contact pads disposed in immediate proximity are connected by resistance welding or soldering for their parallel connection and use is made of two leads connected to contact pads disposed close to substrate on one end as resistive-strain sensor leads for their series connection.

EFFECT: enhanced precision of temperature compensation; facilitated manufacture Of temperature-compensated resistive-strain sensor.

1 cl, 1 dwg

Description

The technical field to which the invention relates.

The present invention relates to electronic equipment, in particular, to thin-film microelectronics.

The level of technology.

The work of strain gages is based on the phenomenon of the strain effect, which consists in changing the resistance of conductors and semiconductors during their mechanical deformation [1-4]. The quality of strain gauges depends on sensitivity to mechanical stresses, linearity of the relative change in resistance over a wide range of stresses (mechanical loads) and ambient temperature, reliability and dimensions of the structure, as well as other factors.

Known microsensor semiconductor strain gauge MS 115-350 [3, p.122], which is manufactured in the following way. A flexible rectangular filament of p-type silicon single crystal is cut in the [111] direction with a resistivity of ρ = 0.017 Ohm · cm, with dimensions of 0.0177 mm (thickness), 0.5 mm (width) and 19 mm (length). The disadvantage of this sensor is its low linearity in the operating temperature range, as well as the impossibility of fitting (adjusting) its parameters to the specific conditions of the measurement experiment.

A known method of adjusting the characteristics of electronic components using a laser (see French application No. 2616263, H 01 C 17/24, IMS No. 7, 1989), which consists in the fact that in order to adjust the resistance of the thin-film resistor to the nominal value, the laser beam is cut on the semi-profile, the radius of which is determined by the calculation method.

The disadvantage of this method is its limited capabilities associated with the inability to adjust the linearity of the conversion characteristics of the strain gauge in the operating temperature range.

A known method of manufacturing a film strain gauge [1, p.130], which consists in the fact that the strain gauge itself is made by one of the known methods [1-4], and to eliminate or reduce the influence of temperature on its conversion characteristic compensate for its temperature coefficient of resistance (TCR) by the fitting method, which consists in annealing at a certain temperature, a certain time, which depends on the material of the film.

The main disadvantage of this method is that annealing fails in a wide temperature range to achieve thermal compensation. In addition, the annealing process is long; it does not fit well with the simultaneous measurement control of the TCS value.

SUMMARY OF THE INVENTION

The aim of the present invention is to improve the accuracy of thermal compensation while reducing the complexity of manufacturing a thermally compensated film strain gauge.

The technical result achieved is ensured by the fact that the manufacturing technology of a thin-film thermocompensated strain gage includes spraying resistive layers on a flexible dielectric substrate, forming contact pads, forming sensitive elements of the strain gage by photolithography, the measurement of the resistances of which in the process of fitting the TKS strain gage is carried out with an ohmmeter connected to the corresponding contact areas moreover, the strain gauge is made of two materials different values and signs of the TCS, form on the substrate two connected in series sensitive elements, the combined leads, which are connected to a contact pad located on one side of the substrate, and the two remaining leads are connected to contact pads located in the immediate vicinity on the other side of the substrate, provide thermal compensation adjustment of the ratio of the resistances of the sensitive elements by the beam of a laser fitting tool.

Information confirming the possibility of implementation.

According to [1, p. 129] for a film strain gauge mounted on a freely expandable sample with a given coefficient of linear expansion, the temperature characteristic for a small temperature range is described by the equation:

where α is the temperature coefficient of resistance of the film element;

β _m - temperature coefficient of linear expansion of the material of the sample (part) on which the strain gauge is installed;

β _h - temperature coefficient of linear expansion of the sensitive element of the strain gauge;

t ₀ , t is the initial and final temperature of the temperature range;

To _pr - the conversion coefficient of deformation by the sensitive element:

K _ave = δR / δl

δR and δl are relative increments of resistance and strain gauge length.

The temperature increment of the resistance of the strain gage can be equal to zero if the right-hand side of equation (1) is equal to zero, i.e. on condition:

According to [1], equation (2) is used as a fitting criterion, which is performed by annealing the strain gauge at a certain temperature.

Such a fitting method consists in changing (densifying) the structure of the material of the film sensitive element. The annealing process lasts for hours in a heat chamber, and the adjustment range of the TCS is of little importance. Monitoring and measuring this parameter during annealing is also quite difficult due to limited access to the heat chamber.

According to the patent of the Russian Federation No. 2133514, H 01 C 17/22, 17/24 and a positive decision to grant a patent dated January 24, 2003 according to application No.2000109988 / 09 (0/0280), the ratios between the resistances and the TCS of thin-film resistors connected in parallel are of the form :

where R ₁ , R ₂ - the resistance of the first and second element of the thin-film resistive structure; α ₁ , α ₂ - TCS of the first and second resistive element; α ₀ - TCS of an integrated thin-film resistor with resistance R ₀ obtained by parallel connection of the resistances R ₁ and R ₂ with TCS - α ₁ and α ₂ .

For the integrated resistor obtained by the series connection of the resistances R ₁ and R ₂ , the ratio is true:

Choosing the resistance value R _{0 of the} strain gage, the ratio R1 / R2, the type of resistive materials with certain values of TCS - α ₁ , α ₂ and the method of joining the sensitive strain gauges obtained by photolithography on the substrate, it is possible to select TCS - α ₀ integral using ratios (3-4) a strain gauge in a wide range of values for various materials of the sample with specific values of β _m (2).

The exact value of α ₀ can be obtained by laser fitting of the resistances R ₁ , R _{2 of the} strain-sensing elements using an ohmmeter connected directly to the terminals R ₁ and then to R ₂ in the fitting mode.

The drawing shows a design variant of a thin-film strain gauge manufactured by the proposed method.

The sensitive element of such a strain gauge is made of two thin-film elements 1 and 2. Element 1 has a resistance of R ₁ and is made of nichrome alloy (constantan, aluminum alloys, titanium alloys, etc. are possible). Element 2 has a resistance of R ₂ and is made of cermet alloy (K-20C, K-30C, etc.).

Sensitive elements 1 and 2 of the strain gauge are located on a flexible dielectric substrate 3, on the opposite sides of which there are contact pads 4. The design of such a strain gauge has adjustable jumpers 5 for adjusting (fitting) the resistive element 1. The possibility of adjusting (fitting) the resistance of element 2 is shown by a laser cutter of the type 6. The contact pads located in the immediate vicinity determined by the insulation resistance make it possible to create a single contact by soldering without significant rat, with the parallel connection of elements 1 and 2.

The sensitivity to change the resistances of elements 1 and 2, connected in series, is defined as

and with their parallel connection:

it will be less for the case of parallel connection, however, in a design with parallel connection of elements 1 and 2, the overall sensitivity to mechanical stresses can be increased by increasing the number of sections of element 1. In addition, it is much easier to achieve the fitting of a specific TCS in a certain range in a design with parallel connection of sensitive strain elements from dissimilar materials.

The laser method of adjustment in comparison with thermal (annealing) allows to reduce the time of fitting of the TCS due to the speed of the laser tool of adjustment, to increase the accuracy of fitting (in particular, through the use of fitting sections and special forms of laser cut, type 6, see drawing), expand the range TKS fitting by combining the ratios of resistances of the strain-sensitive elements, types of their electrical connections (parallel, serial), as well as the use of special adjustable sections (adjustable jumpers 5, Fig. 1).

LITERATURE

1. Klokova N.P. Strain gages: Theory, methods of calculation, development. - M.: Mechanical Engineering, 1990. - 224 p.

2. Levshina E.S., Novitsky P.V. Electrical measurements of physical quantities: (measuring transducers). Textbook manual for universities. - L .: Energoatomizdat. Lehning. Ot.-tion, 1983 .-- 320 s.

3. Semiconductor strain gauges (translation from English). Edited by M. Dean. - M.L .: Energy, 1965 .-- 216 p.

4. Meizda F. Electronic measuring instruments and measurement methods: Per. from English - M.: Mir, 1990 .-- 535 p.

Claims (1)

A method of manufacturing a thermally compensated strain gauge, including spraying resistive layers on a flexible dielectric substrate, forming contact pads, forming the sensitive elements of the strain gauge by photolithography, the measurement of the resistances of which in the process of fitting the TCS strain gauge is carried out with an ohmmeter connected to the corresponding contact pads, characterized in that the strain gauge is made of two resistors resistive materials with various sizes and signs of TCS, form on vile If two strain-sensitive elements connected in series, the combined terminals of which are connected to a contact pad located on one side of the substrate, and the two remaining leads are connected to contact pads located in close proximity to the other side of the substrate, perform laser compensation by adjusting the ratio of the resistance of the sensitive elements, having previously determined Method for electrical connection of strain-sensitive heterogeneous elements, then for parallel method and their connections located in the immediate vicinity of the contact pads are connected by contact welding or soldering and used to connect to a common terminal, and in the case of a series connection, the terminals of the strain gauge are connected to the contact pads located on one side.