SU1196705A1 - Integral pressure transducer - Google Patents

Description

The invention relates to instrument making and can be used to increase the sensitivity of integrated strain gauge transducers, designed to measure small pressures of liquid and gaseous media.

“The purpose of the invention is to increase the sensitivity. by reducing the stiffness of the membrane. ’

Figure 1 shows the integrated pressure transducer; figure 2 - node 1 in figure 1.

The integrated pressure transducer contains a single crystal 1 η-type silicon wafer, conductivity with a plane of crystallographic orientation (100).

In the silicon plate 1 with a thickness of H and a size of 2 anisotropic etching-2, a recess 2 is made, which forms a thin membrane 3, which is integral with the supporting pinning 4.

Membrane 3 is a 2.

thinned silicon wafer 5 of size a, on both surfaces of which there is a thermally grown silicon dioxide film of the same thickness b ,. Tensionally sensitive 7, heating 8 and 9, and thermosensitive 10 elements are P-type conductivity resistors obtained by diffusing boron into a single-crystal silicon wafer 1.

The strain gauges 7 are located on the membrane 3 at the embedment, are made with a length not exceeding 0.05 <ί, are oriented in the plane of the membrane in the direction of maximum strain sensitivity <. 110> and connected in. pavement measuring circuit, the output diagonal of which is supplied

supply voltage, and a signal proportional to the measured pressure R is taken from the output diagonal.

Heating resistors 8 are located. in the central part of the membrane 3 on an area whose center coincides with the center of the membrane, and the distance from the center of the membrane to the contour line b of the area b is determined by the ratio b / a = 0.2 and within the specified area the resistors are oriented in the direction of the minimum tensile sensitivity <100> eliminating the effect of deformation of the membrane on them m are interconnected in parallel .. The heating resistors 9 are located on the undeformable support base 4 along the line. Finishing 11 of the membrane 3 and are at a distance from the center of the membrane ,, determined by the C / o ratio | = 0.55 "and the total resistance value of the heating resistors 9 is equal to the total resistance value of the heating resistors 8. Thermistor 10 is placed on the membrane 3. between the embedment and the area contour of the heating resistors 8, with the center of the thermistor located on the line 12, separated from the center of the membrane ¹ standing SZ, determined by the ratio <5 (0.5ts + b) = 0.5 (taking into account, γτο b / a - '0.2, the indicated ratio can be represented as (ί / a =. ·

0.35) ^ and the thermistor itself is oriented in the plane of the membrane in the direction of the minimum tensile sensitivity <100> in order to eliminate the effect of deformation of the elastic element on it. Thermistor 10 is the active shoulder of the heat-sensitive bridge 13, the output of which! connected to the input of the amplifier 14 ^ a

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the output of the latter is with the input of the regulating element 15. To the output of the regulator, the molding element 15 is connected nag * cutting resistors 8 and 9, which are interconnected with each other in parallel. five

Increasing the sensitivity of the integral strain gauge by reducing the rigidity of the membrane by longitudinal compressive forces is achieved by choosing the thickness of the silicon dioxide film 6 based on the ratios

0.8 ~ Ü, / * * ⁰ , ⁹ ' _ж A n / M ^{2 L} p 1-9' E, n-ΙαΗο ^ Λ, μτ ^ γ '15 where Ε ^, οί, - - film thickness

Poiss Ratio. son, modulus of elasticity and temperature • coefficient of expansion of silicon dioxide;

"thickness of silicon membrane, Poisson's ratio, MO-25 of elasticity and temperature coefficient of expansion of silicon;

B, b ₂ - critical thicknesses - 30

silicon dioxide ** and silicon membranes, respectively, in which the membrane loses 35 stability;

" ⁼ ^ 1kr ⁴ * ¹ 2 | ₍ р'2Ь, + Ь ₂ - membrane thickness;

And - the thickness of the reference

grounds;

o - side of the square - ₄ θ Noah or the diameter of a circular membrane;

K is the membrane shape factor (K = 2.0597 for a square membrane 45; K = 2.2516 for a round membrane);

T _{0 (} : - thermal oxidation temperature silicon ad;

T _about ^- ambient temperature equal to 20 ° C + 1 ° C.

The device works as follows.

Under pressure, the membrane bends and a signal proportional to pressure is taken from the strain gauges. .

Ensuring that the sensitivity of the strain gauge is unambiguous under conditions of varying ambient temperature is achieved by the use of an arrangement of heating resistors 8 and 9 and a thermistor 10. The heat generated by the heating resistors 8 and 9 forms two opposing heat flux-heat flux from the heating resistors 8 directed from the center of the membrane 3 to its sealing and the heat flux from the heating resistors 9 is directed from the seal to the center of the membrane. · Heat fluxes, overlapping one another, create an area membrane temperature distribution close to uniform. This temperature IU, mbrana fixes the thermistor 10. The temperature control system, which includes heating resistors 8 and 9, thermistor 10, thermosensitive bridge 13, amplifier 14 and regulating. element 15, maintains such a state of an integrated strain gauge, in which the temperature of the membrane 3 always remains equal to the set, including when the ambient temperature changes. In this case, the adjustment of the temperature control system is carried out in such a way that the set temperature of the membrane is at least 10 ° C higher than the temperature of the upper point of the temperature range of operation of the integral strain gauge. Improving the accuracy of maintaining the set temperature of the membrane 3 contributes to the orientation of the heating resistors' 8 and the thermistor 10 in the direction of the minimum strain sensitivity <§10 in the plane of the membrane.

1196705

Claims (1)

INTEGRAL PRESSURE TRANSFORMER, containing silicon membrane, made in one piece with the supporting base, stress-sensitive and temperature-sensitive elements, as well as heating elements located in the central part of the membrane in the square, center which coincides with the center of the membrane, and the distance from the center of the membrane to the contour line of the plateau and the contour line of the membrane is determined respectively by the ratio - = 0.2, characterized in that, in order to increase sensitivity by reducing the stiffness of the membrane, it is equipped with additional heating elements located on the support base along the contour of the membrane at a distance from the center of the membrane equal to = 0.55, while the temperature-sensitive element is located from the center of the membrane at a distance determined by the ratio - ~ —— = 0.5, and at every 0.5 h ♦ b This membrane surface is a film of silicon dioxide of the same thickness, determined from the ratios 1m. = .Л _. / Ц ² · х n _2kr 1-9 'E, n'CHA) (“H -“,) (T ₀ , -T ₀ )' where a is the square side or diameter of the circular membrane; B is the distance from the center of the membrane to the contour line of the area of heating elements located in the central part of the membrane; C is the distance from the center of the membrane to the contour line located on the supporting base of the heating elements; <ί - distance from the center of the membrane to the line on which the center of the temperature-sensitive element is located; film thickness, Poisson's ratio, mo-. hollow elasticity and temperature expansion coefficient of silicon dioxide; L ₂ 3 ₂ Е ₂ о: _{g the} thickness of the silicon membrane, the Poisson coefficient, the modulus of elasticity ^ and the temperature coefficient of expansion of silicon ₄ n _2k p are the critical thicknesses of two silicon oxide and silicon 1196705 > 1196705 membranes, respectively, in which the membrane loses stability; H is the thickness of the base; K - membrane shape factor; N'2b Τ „ _χ is the temperature of thermal oxidation of silicon; - ambient temperature, T _about = 20 ° С ±; ° С р ⁺ ^ гкр ' ^: ^^ 1 ⁺ ^ g “membrane thickness.