RU2362132C1 - Integrated pressure transducer - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used for measurement of mechanical effect. Integrated pressure transducer is made in the form of monocrystal silicone slab oriented in plane (100) with n-type conductivity; on the first side diffusion strain gages with p-type conductivity are formed, they are prolonged in [011] direction and are united into Wheatstone bridge. On the second side of monocrystal silicone slab there is pocket not exceeding edge of slab; pocket consists of parallel grooves and cavities interconnecting their ends and common flat bottom. Together with the first side of slab this bottom forms thin part of membrane surrounding rigid centers. Each arm of Wheatstone bridge consists of one or several strain gages and located at separate straight thin part of membrane over one respective groove, which longitudinal axis is parallel to longitudinal axis of respective strain gage. Straight thin section on the second side of membrane has certain width and length. Longitudinal boundaries of membrane thin section are parallel to strain gage and there are three rigid centres in gaps between membrane sections.

EFFECT: enhancement of efficiency and extension of functionality.

2 cl, 4 dwg

Description

The invention relates to measuring technique and can be used to measure mechanical stress (pressure, force, etc.).

Preferably, the invention is aimed at providing high-precision measurements in the low-pressure range from 0.1 kPa to 100 kPa in a wide temperature range with an upper limit of + 125 ° C.

The closest in its technical essence is US patent No. 4065970, IPC G01L 9/00, publ. May 14, 1976, author WILNER LESLIE V. titled "Diffused semiconductor pressure gauge". The author proposes an integrated pressure transducer with a round membrane with side sections located in the (100) plane, on which two wide solid regions of different widths (hard centers) elongated in the [011] direction are formed by anisotropic etching. In this case, membrane sections with a small thickness are formed between the edges of the membrane and the edges of the rigid centers. The distance between the edges of the rigid centers in the plane of the bottom of the membrane is two times greater than the distance between the edge of the membrane and the edge of the first hard center and several times less than the distance between the edge of the membrane and the edge of the second hard center. Four diffusion resistors are arranged in pairs in the middle of the first two sections of the membrane with a small thickness in the direction [011], in which, according to the author of the patent, the same mechanical stresses are created under pressure. In this case, under the influence of pressure, the resistance of the first two resistors increases, and the two second resistors decrease. Resistors are combined into a Wheatstone bridge. To reduce mechanical hysteresis and reduce the resistance of the lead-in conductors, the connection of the strain gauges with the external metal wiring on the thin part of the membrane is made by wide p-type regions with the same concentration as the strain gauges and aluminum conductors on solid centers.

The proposed design made it possible to realize a low pressure transducer with high sensitivity and good linearity. A significant disadvantage of the invention is the uneven size of the hard centers and the unevenness of their location. It seems unobvious that the stresses in the area of the strain gauge are equal. In this case, due to the asymmetry of the arrangement of the hard centers, there is an uneven heat removal from the strain gauges and, as a consequence, temperature hysteresis. In this design, the temperature hysteresis of the output signal should be significant due to the close location of aluminum conductors to sections of the membrane with a small thickness. The uneven shape of the ends of the strain gages leads to increased initial imbalance of the bridge.

Known works [1, 2], which give the characteristics of integrated pressure transducers (IPD) with a flat membrane and with a membrane on which one or more rigid centers are formed. The use of pressure transmitters with a flat membrane below the boundary of 100 kPa is possible, but with lower metrological characteristics. The lower the measured pressure, the thinner the membrane should be. With thinning of the membrane, the linear portion of the conversion characteristic is reduced and all errors increase.

In [1], for an integrated pressure transducer with one rigid center, all strain gages are identical in geometry and parallel to each other. Two of them are located at the edge of the rigid center in the compression zone (when loading the membrane from above), two at the edge of the membrane in the tension zone. The identity of all strain gages provides a minimum initial imbalance of the bridge, and their tangential arrangement minimizes the nonlinearity of the conversion characteristic. This is explained by the fact that in the case of tangential strain gages they are in the zone of equal mechanical stresses, and in the case of radial strain gages, they are in the zone with their variable value. In the case of a flat membrane or a membrane with one rigid center, the very design of the radial strain gauge makes it virtually impossible to ensure conditions for a uniform distribution of mechanical stresses along the strain gauge in comparison with the design of tangential resistors.

In [2], the authors indicate that the nonlinearity of the conversion characteristic for an integral converter with three rigid centers decreases with respect to the nonlinearity for an integral converter with one rigid center for the same geometric parameters of the membrane: area and thickness, which makes it possible to increase the output signal level and reduce the measurement range in region of lower pressures, but data on the design parameters of integral pressure transducers with several rigid centers does not lead Xia.

Known patent of the Russian Federation 2271523 C2, IPC G01L 9/04 publ. March 10, 2006, authors Barinov Ilya Nikolaevich, Kozin Sergey Alekseevich under the name "Semiconductor pressure transducer". The authors propose a design containing a profiled membrane with two rigid centers. The center of each of the four strain gauges coincides with the edge of the membrane or rigid center, and the authors do not determine the distance between the rigid centers. If the concentrators are far apart, then the gain due to an increase in the number of concentrators will be insignificant. In addition, in the manufacture of the transducer, a small misregistration of the patterns for forming a strain diagram on the front side of the plate and the pattern for forming the membrane on the reverse side leads to pairwise displacement of the resistors in the region with different values of mechanical tension, which leads to an increase in the nonlinearity of the conversion characteristic. The patent proposes a technical solution according to which a membrane thickness of 2-3 μm can be realized, and the measured pressure is less than 10 Pa. The proposed technical solution cannot be used to create strain gauges with a membrane thickness from the range from 15 to 30 microns, necessary for pressures from 0.1 to 100 kPa.

The aim of the invention is to increase the efficiency of converting pressure into an electrical signal and expanding the functionality of an integrated pressure transducer.

The goal is achieved by the fact that the integral pressure transducer is made in the form of a single-crystal silicon wafer oriented in the (100) plane, n-type conductivity, on the first side of which diffusion p-type strain gages are formed, stretched in the [011] direction and united by electrical bonds in Wheatstone Bridge. On the second side of the indicated single-crystal silicon wafer, a recess is made that does not extend to the edge of the wafer, consisting of parallel grooves and cavities connecting their ends with each other having a common flat bottom, which together with the first side of the wafer forms a thin part of the membrane surrounding the rigid centers. Each arm of the Wheatstone bridge, consisting of one or more strain gauges, is placed on a separate rectilinear thin section of the membrane above one corresponding groove, the longitudinal axis of which is parallel to the longitudinal axis of the corresponding strain gauge. A rectilinear thin section on the second side of the membrane has a width of 5 to 100 μm and a length of at least 0.7 the length of the strain gauge. The longitudinal boundaries of the specified thin section of the membrane are parallel to the strain gauge, and in the spaces between these thin sections of the membrane are three rigid centers.

The technical result of the totality of the features of the invention is the provision of high-precision measurements in the low-pressure range from 0.1 to 100 kPa in a wide temperature range with an upper limit of + 125 ° C. The integrated pressure transmitter of the proposed design gives an electric signal at the output of the Wheatstone bridge twice as large as the IPD of known structures at the same pressure and all other conditions being equal (size and thickness of the membrane, voltage at the entrance of the Wheatstone bridge). The general symmetry of the structure with increased sensitivity provides a reduction in temperature errors, which ensures increased accuracy in a wider temperature range, thereby expanding the functionality of the integrated pressure transducer.

The integral pressure transducer has the interface of the surfaces of thin sections of the membrane with the lateral faces of the membrane and rigid centers, which is made by a curved surface with a radius of fillet from 3 to 10 microns.

This is done in order to increase the resistance and strength of the membrane to pressure overload.

Figure 1 presents a view of the plate of the integrated pressure transducer from the side of the electrical connection diagram.

Figure 2 presents a view of the plate integrated pressure transducer from the side of the recess.

Figure 3 is a fragment of the view of Fig 2.

Figure 4 presents a cross section of a plate of an integrated pressure transducer.

Figure 1 presents a view of the plate 1 of the integrated pressure transducer from the side of the electrical connection diagram. On plate 1, oriented in the (100) plane, there are four p-type diffusion resistors 2, 3, 4, 5, elongated in the [011] direction and integrated into the Wheatstone bridge, and the temperature compensation circuit 17. Electrical connections are made by wide areas 15 p + -type of conductivity connected to the metal wiring 16 outside the recess formed on the other side of the plate (see Figure 2), which reduces the temperature hysteresis of the initial output signal (or zero), feel the temperature hysteresis nosti and maintains the accuracy characteristics over a wide temperature range.

Figure 2 presents a view of the plate 1 of the integrated pressure transducer from the side of the recess. Figure 3 is a fragment of it on an enlarged scale. The recess consists of parallel grooves 6 and cavities 7 connecting their ends. The grooves 6 and cavities 7 have a common bottom 18 (Figure 4) and together with the first side of the plate 1 form a thin part of the membrane surrounding the rigid centers 12 and form thin rectilinear sections 8, 9, 10, 11 (Figure 4) on the second side membranes with a width of 5 to 100 microns and a length of at least 0.7 the length of the strain gauge. The longitudinal axis 19 of each thin section, the boundaries of the membrane 14 and the rigid center 13 within the rectilinear thin section are located in the [011] direction and are parallel to the axis 20 of the corresponding strain gauge.

Figure 4 presents a cross section of a plate 1 of an integrated pressure transducer. Diffusion strain gages 2, 3, 4, 5 formed on the first side of the plate 1, with each strain gauge placed on a separate thin section of the membrane 8, 9, 10, 11 parallel to the direction [011]. With this arrangement, the strain gauges are in the zone of maximum mechanical stress and maximum sensitivity. The width of the rectilinear thin portion of the membrane provides almost a doubling of the mechanical stresses on the membrane in the region between the faces due to the addition of stresses arising at the edge of a separate rigid center. A further increase in width leads to a decrease in sensitivity. When the width is below 5 μm, the sensitivity also decreases, since the strain gauge is on the thick part of the membrane. The length of a rectilinear thin section of the membrane provides the same mechanical stress along the strain gauge, which is necessary for the linearity of the conversion characteristics.

With such an arrangement of strain gages, the value of the non-linearity of the conversion characteristic is almost the same both under pressure on the first side of the plate where the tensor circuit is located (work "on the clamp"), and on the reverse side - when working "on separation". The equality of non-linearity values in these two cases expands the possibilities of using strain gauges in sensors for various purposes, for example, in pressure-rarefaction sensors. In addition, this arrangement of strain gages is resistant to some technological misregistration and disorientation of the patterns to form the first and second sides of the strain gauge, that is, for example, when there is no parallelism to the axis 19 of the thin section 11 of the axis of the strain gauge 20.

At the junction of the side faces of the membrane 21 of the faces of the rigid center 22 with the plane (100), curved mating surfaces with a radius of 3 to 10 μm are made, which provides a multiple increase in the strength to overload pressures.

Information sources

1. V.N. Zimin, N.L. Danilova, V.V. Pankov, D.V. Shabratov. Basic constructions of integrated strain gauges for a number of pressures from 0.01 to 40 MPa // Sensors and systems. 1999, No. 2.

2. N.A. Shelepin, V.V. Amelichev, N.L. Danilova, A.Yu. Pavlov, V.V. Pankov. Development of a series of integrated pressure transducers // Defense complex - to the scientific and technological progress of Russia. 2007, No. 1.

3. US Pat. No. 4,065,970 Diffused semiconductor pressure gauge. 1978-01-03, authors Wilner Leslie B, Becton Dickinson CO, IPC G01L 9/00, G01L 9/06.

4. Patent RU 2271523 C2, IPC G01L 9/00, publ. 2006.01, authors: Ilya Nikolaevich Barinov, Sergey Alekseevich Kozin, “Semiconductor pressure transducer”.

Claims (2)

1. An integral pressure transducer made in the form of a single-crystal silicon wafer oriented in the (100) plane, n-type conductivity, on the first side of which are formed p-type conductivity diffusivity resistors elongated in the [011] direction and joined by electrical connections to the Wheatstone bridge and, on the second side of the single-crystal silicon wafer, a recess is made that does not extend to the edge of the wafer, consisting of parallel grooves and cavities connecting their ends to each other, having a common flat but, which together with the first side of the plate forms a thin part of the membrane surrounding the rigid centers, characterized in that each arm of the Wheatstone bridge, consisting of one or more diffusion strain gages, is placed on a separate rectilinear thin section of the membrane above one corresponding groove, the longitudinal axis of which is parallel the longitudinal axis of the corresponding diffusion strain gage, and the rectilinear thin section on the second side of the membrane has a width of 5 to 100 μm and a length of at least 0.7 of the length of the diffuser Zeon strain gauge, the longitudinal boundaries of the thin portion of the membrane parallel to the diffusion strain gages, and in the intervals between the thin portions of the membrane are three rigid center. 2. The integral pressure transducer according to claim 1, characterized in that the surface of the thin sections of the membrane is mated to the lateral faces of the membrane and the rigid centers by a curved surface with a radius of fillet of 3 to 10 μm.

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