RU2558675C1 - Sensor of absolute pressure of increased sensitivity based on semiconductor sensitive element - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: absolute pressure sensor comprises a body with a nozzle, a metal membrane, transmitting pressure action via non-compressible liquid to a semiconductor sensitive element, made in the form of a profiled single crystal of silicon of plane (100) with a square membrane, connected by electrostatic method in vacuum with a glass base, on the flat surface of the profiled single crystal there are strain gauges combined into a bridge measurement circuit. Centres of strain gauges are arranged at the distance l from mutually perpendicular axes Ox and Oy, pulled via the centre of the membrane, lying in the plane and parallel to borders of the thin part of the membrane with the base of the semiconductor sensitive element, which is determined on the basis of the following ratio: $$l=\frac{a_m}{2}\cdot \frac{\mathrm{0,99}}{1-\mathrm{0,948}\cdot e^{-\mathrm{0,359}\cdot \frac{a_m}{h_m}}}\left(1\right),$$

where a_m - size of membrane of semiconductor crystal; hm - thickness of membrane of semiconductor crystal.

EFFECT: increased sensitivity of a device.

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Description

The present invention relates to measuring technique and can be used to measure pressure in measurement systems, control and management.

Semiconductor pressure sensors with strain gauges formed in a semiconductor sensor are known. Strain gages are combined in a bridge measuring circuit [1, 2].

A known design of the sensor element of the membrane type pressure sensor [3], which is a n-type single crystal silicon crystal, the planar side of which is oriented along the crystallographic plane (100) with a recess on the back of the crystal, forming a square membrane in plan. Four p-type conductivity strain gauges are formed on the planar side of the membrane so that their longitudinal axes are parallel to one of the main axes of the membrane, which coincides with the crystallographic direction [110].

The closest in technical essence to the proposed solution is the design of a semiconductor absolute pressure sensor selected as a prototype [4]. Such a sensor comprises a housing with a fitting, a metal membrane transmitting the effect of pressure through an incompressible liquid to a semiconductor sensitive element. The semiconductor sensitive element is made in the form of a profiled silicon single crystal of the (100) plane with a square membrane connected electrostatically in a vacuum to a glass base. Strain gages are formed on the flat surface of the shaped crystal, combined into a bridge measuring circuit. Inside the sensing element, between the crystal and the glass base, there is a vacuum cavity, which provides absolute pressure measurements.

от центра мембраны, и это расстояние зависит от отношения размера стороны мембраны к ее толщине a_м/h_м.A common drawback of the designs of the sensitive elements of the pressure sensors described in [1-4] is the insufficiently high sensitivity due to the fact that the strain gauges located at the membrane boundary experience strains that are not the maximum possible for shaped crystals with a square membrane. It was found that the maximum relative deformations are at a relative distance $$r_{{\max }_m}$$

from the center of the membrane, and this distance depends on the ratio of the size of the side of the membrane to its thickness a _m / h _m .

The task of the invention is to increase sensitivity due to the optimal location of the strain gauges in the zones of maximum relative deformations. In addition, the objective of the invention is to increase accuracy by increasing sensitivity.

The technical result of the invention is to increase the sensitivity due to the location of the strain gauges in the zones of maximum relative deformations. At the same time, with increasing sensitivity, accuracy also increases. In addition, the technical result is to increase the manufacturability of the sensor, since it seems possible to determine in advance the optimal location of the strain gauges, providing the maximum sensitivity of the designed sensors, with different ratios of the membrane size to its thickness a _m / h _m .

This is achieved by the fact that in the absolute pressure sensor of increased sensitivity containing a housing with a fitting, a metal membrane that transmits the pressure through an incompressible liquid to a semiconductor sensitive element made in the form of a profiled silicon single crystal of the (100) plane with a square membrane connected electrostatically in a vacuum with with a glass base, strain gauges are formed on a flat surface of a profiled single crystal, combined into a bridge Yelnia circuit in accordance with the decision centers of strain gauges arranged at a distance l from perpendicular axes Ox and Oy, effected through membrane center lying in its plane and parallel borders thin membrane portion to the base of the semiconductor sensor element, which is defined by the relation:

$$l=\frac{a_m}{2}\cdot \frac{0.99}{\mathrm{one}-0.948\cdot e^{-0.359\cdot \frac{a_m}{h_m}}},\left(\mathrm{one}\right)$$

where a _m is the size of the semiconductor crystal membrane; h _m - the thickness of the membrane of a semiconductor crystal.

In FIG. 1 shows the design of the proposed absolute pressure sensor of increased sensitivity based on a semiconductor sensing element. The sensor comprises a housing 1 with a fitting 2, a sealing contact block 3, a metal membrane 4, an incompressible liquid 5, a semiconductor sensing element 6. An incompressible liquid is poured through a tube 7 located in the contact block 3.

In FIG. 2, a semiconductor sensor element of the sensor is shown separately. It consists of a profiled silicon single crystal of plane 8 (100) with a thickness of N _cr with a square membrane of size a _m and thickness h _m , connected electrostatically in a vacuum to a glass base 9 (Fig. 2, b). On the flat surface of the profiled crystal 8, strain gauges R10-R13 are formed, combined into a bridge measuring circuit. The strain gages normal to the Ox axis occupy the same area as the strain gages normal to the Oy axis, and the length of the strain gages normal to the Oy axis is equal to the width of the strain gages normal to the Ox axis.

The centers of the R10-R13 strain gages are located at a distance l from the center of the membrane, determined from relation (1). This ratio was obtained on the basis of the condition:

$$l=\frac{{\mathrm{but}}_m}{2}\cdot r_{{\max }_m}\left(a_m,h_m\right),\left(2\right)$$

- расстояние от центра мембраны до ее края); h_м - толщина мембраны полупроводникового кристалла; $$r_{{\max }_{м}}\left({а}_{м},h_{м}\right)$$

- относительное расстояние, соответствующее местоположению максимальных относительных деформаций.where a _m is the size of the semiconductor crystal membrane ( $$\frac{{\mathrm{but}}_m}{2}$$

- distance from the center of the membrane to its edge); h _m is the thickness of the semiconductor crystal membrane; $$r_{{\max }_m}\left({\mathrm{but}}_m,h_m\right)$$

- the relative distance corresponding to the location of the maximum relative deformations.

, входящего в выражение (2), было получено в результате моделирования деформаций методом конечных элементов, который описан в [5, 6]. Вначале было определено, что основным геометрическим параметром формы, влияющим на местоположение максимальных относительных деформаций, является отношение размера стороны мембраны к ее толщине a_м/h_м. На практике это отношение обычно лежит в пределах:Ratio for relative distance $$r_{{\max }_m}\left({\mathrm{but}}_m,h_m\right)$$

included in expression (2) was obtained as a result of modeling deformations by the finite element method, which is described in [5, 6]. At first it was determined that the main geometric shape parameter affecting the location of the maximum relative deformations is the ratio of the size of the side of the membrane to its thickness a _m / h _m . In practice, this ratio usually lies within:

$$5\le \frac{{\mathrm{but}}_m}{h_m}\le 120.\left(3\right)$$

For example, for a _m = 2.4 mm, the thickness of the membrane usually lies in the range of h _m = 20 ... 480 microns.

For fixed values of the membrane side size a _m, the membrane thickness h _m changed taking into account (3). So, in the case a _m = 2.4 mm, the membrane thickness varied in the range of 20 ... 480 μm (commonly used in practice).

.During the simulation, the values of the distance corresponding to the location of the maximum relative deformations were determined. The data obtained were approximated in the range of values satisfying condition (3) by a polynomial. As a result, the dependence was determined $$r_{{\max }_m}\left({\mathrm{but}}_m,h_m\right)$$

.

от отношения размера стороны мембраны к ее толщине a_м/h_м, имеет вид:The established dependence of the relative distance corresponding to the location of the maximum relative deformations, $$r_{{\max }_m}\left({\mathrm{but}}_m,h_m\right)$$

from the ratio of the size of the side of the membrane to its thickness a _m / h _m , has the form:

$$r_{{\max }_m}\left(a_m,h_m\right)=\frac{0.99}{\mathrm{one}-0.948\cdot e^{-0.359\cdot \frac{a_m}{h_m}}}.\left(\mathrm{four}\right)$$

, соответствующего местоположению максимальных относительных деформаций, от отношения размера стороны мембраны к ее толщине a_м/h_м (точки - расчет, кривая - аппроксимация).In FIG. 3 shows the dependence of the relative distance $$r_{{\max }_m}$$

corresponding to the location of the maximum relative deformations, from the ratio of the size of the side of the membrane to its thickness a _m / h _m (points — calculation, curve — approximation).

Consider an example.

Take the size of the semiconductor crystal membrane a _m = 3 mm, the thickness of the semiconductor crystal membrane h _m = 40 microns.

In accordance with expression (1), we determine the distance l corresponding to the location of the centers of the strain gauges in the areas of maximum relative strain:

$$l=\frac{a_m}{2}\cdot r_{{\max }_m}\left({\mathrm{but}}_m,h_m\right)=\frac{{\mathrm{but}}_m}{2}\cdot \frac{0.99}{\mathrm{one}-0.948\cdot e^{-0.359\cdot \frac{{\mathrm{but}}_m}{h_m}}}=\frac{3mm}{2}\cdot \frac{0.99}{\mathrm{one}-0.948\cdot e^{-0.359\cdot \frac{3mm}{0.04mm}}}=\mathrm{1,485}mm.$$

In this case, the relative distance $$r_{{\max }_m}=\frac{2l}{{\mathrm{but}}_m}=\mathrm{0.99.}$$

When the membrane size a _m = 3 mm and the membrane thickness h _m = 300 μm, the distance l corresponding to the location of the centers of the strain gauges in the areas of maximum relative deformation:

$$l=\frac{a_m}{2}\cdot r_{{\max }_m}\left({\mathrm{but}}_m,h_m\right)=\frac{{\mathrm{but}}_m}{2}\cdot \frac{0.99}{\mathrm{one}-0.948\cdot e^{-0.359\cdot \frac{{\mathrm{but}}_m}{h_m}}}=\frac{3mm}{2}\cdot \frac{0.99}{\mathrm{one}-0.948\cdot e^{-0.359\cdot \frac{3mm}{0.3mm}}}=\mathrm{1,525}mm.$$

In this case, the relative distance $$r_{{\max }_m}=\frac{2l}{{\mathrm{but}}_m}=\mathrm{1.02.}$$

An absolute pressure sensor of increased sensitivity based on a semiconductor sensitive element operates as follows. The measured pressure acts on the metal membrane 4, which transmits the pressure through the incompressible liquid 5 to the semiconductor sensitive element 6 (Fig. 1), consisting of a profiled semiconductor crystal 8, which is connected electrostatically to the glass base 9 in vacuum (Fig. 2a, b). As a result of the pressure on the flat surface of the semiconductor crystal 8, deformations arise, which are perceived by the strain gauges 10-13 included in the bridge measuring circuit. The change in the resistance of the strain gages is converted by a bridge measuring circuit into the output voltage. In connection with the location of the centers of the strain gages 10-13 at a distance l from the center of the crystal, determined from relation (1), they turn out to be located in the zone of maximum relative deformations. Due to this arrangement of strain gages, the sensitivity of the sensor is increased, due to this, the accuracy of the sensor is also increased compared to the prototype.

The proposed absolute pressure sensor of increased sensitivity on the basis of a semiconductor sensitive element has a high adaptability, since it seems possible to pre-determine the optimal location of the strain gauges for various ratios of the size of the side of the membrane to its thickness a _m / h _m .

Thus, due to the distinguishing features of the invention, the sensitivity of the sensor is increased due to the location of the strain gauges in the zones of maximum relative deformations. In addition, manufacturability is improved due to the possibility of placing strain gauges in an optimal way for various membrane thicknesses (in the range from 20 to 480 microns).

Sources of information taken into account during the examination

1. Vaganov V.I. Integrated strain gauges. - M .: Energoatomizdat, 1983. - 136 p.

2. Raspopov V.Ya. Micromechanical devices / Tula State University - Tula, 2002. - 392 p.

3. Belikov L.V., Razumikhin V.M. The sensitive element of the membrane type // Pat. 93027803 Russian Federation, IPC G01L 9/04. Application 93027803/10 of 05/18/1993; publ. 12/27/1995.

4. Barinov I.N. Semiconductor strain gauge pressure sensors based on KND structure. Components and technologies №5. 2009 .-- S. 12-15.

5. Alyamovsky A.A. COSMOSWorks. Fundamentals of structural strength analysis in SolidWorks / A.A. Alamovsky. - M.: DMK Press, 2011 .-- 784 p.

6. Alyamovsky A.A. Engineering calculations in SolidWorks Simulation / A.A. Alamovsky. - M .: DMK Press, 2011 .-- 464 p.

Claims (1)

An absolute pressure sensor of increased sensitivity, comprising a housing with a fitting, a metal membrane that transmits pressure through an incompressible liquid to a semiconductor sensitive element made in the form of a profiled silicon single crystal of a plane (100) with a square membrane, electrostatically connected in vacuum with a glass base, on a flat surface profiled single crystal formed strain gauges, combined in a bridge measuring circuit, characterized it that the centers of strain gauges arranged at a distance l from perpendicular axes Ox and Oy, effected through membrane center lying in its plane and parallel borders thin membrane portion to the base of the semiconductor sensor element, which is defined by the relation:

where a _m is the size of the semiconductor crystal membrane; h _m - the thickness of the membrane of a semiconductor crystal.

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