RU2379638C1 - Resonant sensor of pressure, force or motion and method of its manufacturing - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention is related to the field of measurement equipment, namely to metering converters of pressure, force, accelerations and other mechanical parametres on the basis of resonators arranged from crystalline material, in particular crystalline quartz. Resonant sensor of pressure, force or motion comprises flat membrane and resonators of elastic oscillations arranged from crystalline material and rigidly joined to each other. On surface of membrane there is cantilever formed as a whole with it, having shape of plate, in body of which there are resonators arranged. Cantilever is combined with membrane by one of side faces or areas of one of side faces or areas of one of large faces. Cantilever may have shape of plates, and side faces of resonators may be arranged by means of through holes in plate. Orientation of cantilever faces relative to crystallographic axes of sensor material is selected with account of anisotropy of chemical or plasma-chemical milling speed in sensor material. Some areas of membrane surface inverted to cantilever and at least part of cantilever faces are formed by means of slits in section. Some faces of cantilever plate and some areas of membrane surface - large-size ones - are formed with slits, and other ones - creating thinner and more delicate details of sensor - by chemical or plasma-chemical or ultrasound milling.

EFFECT: improved accuracy of resonant crystalline sensor of low and medium pressures.

8 cl, 17 dwg

Description

The invention relates to the field of measuring equipment, namely, pressure transducers (sensors) of pressure, force, acceleration and other mechanical parameters based on resonators made of crystalline material, in particular crystalline quartz.

Known quartz measuring transducers of pressure, force or displacement, having as a sensitive element a resonator of elastic vibrations of the plate or rod. Elastic vibrations of the resonator can be excited, for example, optically or using the Lorentz force in a magnetic field, or using the piezoelectric effect. An example of the transducers under consideration are piezoresonance sensors containing a housing, a working chamber with a resonant sensing element - a sensor, an electronic circuit that excites oscillations through the piezoelectric effect / Malov V.V., Energoatomizdat, Moscow, 1989 /. As a rule, for high-precision transducers, the sensor is entirely made of crystalline material and is a sealed manometric block with an elastic membrane element, to which a strain-sensitive resonator of thickness-shear or bending vibrations is rigidly attached. Under the influence of the measured parameter on the sensor, the deformation of the elastic element occurs, which entails the deformation of the resonator. The resonant frequency of the resonator changes, respectively, the frequency of the periodic pulses of the output signal of the oscillator changes.

An example of such a device is a pressure transducer, the sensor of which is cylindrical and made entirely of crystalline quartz / Benjaminson A., Hammond D.L., Piezoelectric transducer and method for mounting same. Pat USA 3617780, 1971 /. The strain-sensitive resonator of this sensor is a lenticular plate in the form of a partition in the cylinder of the sensor. Thickness-shear oscillations are excited in the plate at a frequency of 5 MHz at the third harmonic. The role of the elastic element is performed by the cylindrical membrane of the sensor. The manufacturing technology of such a sensor includes operations of cutting the crystal into blanks, orienting the blank relative to the crystallographic axes of quartz, grinding, mechanically milling the volume of the blank, giving it a cylindrical shape, drilling cylindrical holes to form a cylindrical membrane, polishing the surfaces of the plate and membrane. This design and technology allows the sensor to be made entirely of crystalline quartz and to obtain unique metrological characteristics. However, the described sensor has a significant drawback. The working range of the sensor is hundreds of atmospheres, and the sensors for small and medium pressure ranges made using this technology have insufficient sensitivity. To increase the sensitivity of the sensor, it is necessary to use a more sensitive - thin flat membrane.

Known crystalline sensor with a flat membrane, which is the prototype of the proposed / Malov VV, Moscow, Energoatomizdat, 1989, pp. 162, 163). In the prototype, the membrane and the resonator plate are made separately, while they are rigidly connected to each other so that the plate is rigidly attached to one of the membrane surfaces by its faces or separate areas of faces. The deformation of the membrane is transmitted to the resonator plate, which leads to a change in the frequency of the resonator. In the embodiments, several resonator plates are used, included in a differential circuit, which reduces the errors of the converter.

The manufacture of the membrane and the piezoelectric element includes operations of cutting the crystal into blanks, orienting the blank relative to the crystallographic axes of quartz, grinding, mechanical or chemical, or other milling, polishing the surfaces of the plate, applying film electrodes to it to excite vibrations. In addition to the above operations, operations are also used to attach the resonator plate to the membrane using various materials such as glue, low-melting metals and glass, etc. However, the connecting material degrades the accuracy of the sensor due to the fact that the yield strength of the connecting material is many times lower than the yield strength of the crystalline material from which the resonator and membrane are made. Due to the occurrence of a yield process in the connecting material, the performance of the sensor becomes irreproducible, with hysteresis, and the sensor has insufficient accuracy. This is a serious disadvantage of the prototype.

To solve the problem in cases where the sensor material allows, etching or epitaxial growth technology is used to fabricate the entire sensor (both the membrane and the resonator) from a single crystal (Yuji, et al., Silicon resonant type pressure sensor. Pat USA 7013733, 2006 ) However, this is possible only for those materials that have approximately the same etching rate in all three directions or allow the use of epitaxial growth technology, for example, silicon. In the case of crystalline quartz and a number of other piezoelectrics, it is impossible to obtain a three-dimensional part using such technologies. For example, the rate of chemical etching along the Z axis of crystalline quartz is two orders of magnitude higher than in other directions. This leads to a large parasitic undercut in the transverse direction and the inability to obtain a resonator of the necessary geometric shape. The growth of three-dimensional resonant volumes from crystalline quartz is impossible due to the occurrence of a large number of defects in the crystal structure.

The objective of the invention is to improve the accuracy of the resonant crystalline sensor of small and medium pressures.

The problem is solved as follows.

In a pressure, force, or displacement sensor containing a flat membrane made of crystalline material and rigidly connected to each other and elastic resonators, on the surface of the membrane in areas with non-zero mechanical stresses caused by the measured parameter, one or more consoles are formed at the same time having a plate shape, in the body of which resonators are made. Moreover, the console is combined with the membrane of one of the side faces or areas of one of the side faces, or areas of one of the larger faces.

The consoles can be in the form of plates, and the side faces of the resonators can be made through holes in the plate.

In an embodiment, the orientation of the cantilever faces with respect to the crystallographic axes of the sensor material is selected taking into account the anisotropy of the rate of chemical or plasma chemical milling in the sensor material. For example, large edges of the console are perpendicular to directions in which the milling speed is close to maximum. In the case when the sensor is made of crystalline quartz, these directions lie in the solid angle, which constitutes 70-90 ° with the optical axis of quartz (Z axis).

In another embodiment, the cantilevers are formed by a single plate connected to the surface of the membrane in the central region.

According to the definition given in the Great Soviet Encyclopedia (http://infotrash.ru/index.php), a console is “a structure (eg, a beam or a truss) rigidly fixed at one end with a free other, or a part of the structure that protrudes beyond the support ". In this case, this design is a plate rigidly fixed at one end or edge to the surface of the membrane.

The proposed technical solution allows the formation of a membrane and a plate with a resonator in a single workpiece by means of cuts with the tool entering from the free edge of the console, i.e. the proposed and described below manufacturing method.

The plate-like shape of the cantilever makes it possible to perform traditional flat-shaped resonators in the cantilever with the formation of oscillating parts of the resonator by means of through slots in the plate, as in the case of a double microamerton strain-sensitive resonator.

The orientation of the cantilever faces relative to the crystallographic axes of the sensor material, taking into account the anisotropy of the chemical or plasma chemical milling speeds in the sensor material, simplifies the solution of the problem of forming three-dimensional resonator structures in a material with high milling speed anisotropy - large faces can be formed using mechanical sawing operations, and small faces of the console plate can be using the milling operation.

The execution of several consoles by means of one plate connected to the surface of the membrane in the Central region, allows to obtain a higher identity of the characteristics of the resonators implemented in different consoles of the same plate, which allows to increase the accuracy of the sensor with differential inclusion of the resonators. Additional resonators in the console plate can also be used as an additional information channel for increasing the accuracy of measurements by statistical processing methods.

In a method for manufacturing a resonant pressure, force, or displacement sensor, the structure of which includes a flat membrane made of a single crystal and a console on its surface, comprising the operations of forming crystalline parts in the form of sawing a crystal blank and milling, for example, mechanical and / or chemical, and / or plasmochemical and / or ultrasonic, at least some regions of the membrane surface facing the consoles and at least a part of the console faces are formed by means of pairs llelnyh and / or converging angle cuts in the workpiece, such as wire or band saws, and propylene was carried out with the setting tool from the free end of the console and to produce the junction of the membrane with the console.

Modern crystal sawing technologies, especially using multi-blade band and wire saws with a free abrasive, make it possible to obtain thin plane-parallel crystal faces of large transverse dimensions with a high surface finish. It is these properties of the membrane faces and the console plate with resonators that are necessary for high-precision sensors. In this case, the spatial positioning of the console plate and the membrane selected in the proposed technical solution, namely the cantilever connection of the plate to the membrane, allows them to be made from one crystal by means of converging cuts. Saws forming the sides of the cantilever and the membrane surface facing the cantilever are performed with the tool approaching from the free end of the cantilever and converge at the junction of the cantilever and the membrane.

In an embodiment of the sensor manufacturing method, some faces of the cantilever plate and some areas of the membrane surface — large-sized — are formed by cuts, and others — forming more delicate and delicate parts of the sensor — by milling, for example, by chemical or plasma-chemical. In this case, the direction of the cuts is chosen taking into account the milling speed in one direction or another in the workpiece, for example, by guiding the cuts along the direction with the minimum milling speed. This solves the problem of the low speed of certain types of milling (in particular, chemical and plasmochemical) along certain directions in the crystals by cutting along the direction with a minimum milling speed. In this embodiment, the combination of cuts with milling allows you to get a sensor with a complex configuration of the side faces of the resonator, such as, for example, a double tuning fork, when the use of cuts is impossible due to the small size and complexity of the shape of the workpiece.

The simultaneous execution of cuts forming large edges of the console plate using multi-blade cutting allows to obtain high parallelism of the plate, which is a prerequisite for the manufacture of the sensor. Moreover, in order to obtain the required plate thickness, it is necessary that the step (or distance) between the cuts is equal to the sum of the thickness of the console plate and the thickness of the cut.

The invention is illustrated in FIGS. 1, 2, 3, 4. FIG. 1 schematically shows: a route process for manufacturing a pressure gauge sensor (FIG. 1, a - FIG. 1, g) and the design of such a sensor (FIG. 1, g) with the plane of the plate perpendicular to the plane of the membrane. Figure 2 schematically shows: route manufacturing process (Figure 2, a - Figure 2, e) and the design of the sensor of the dynamometer (or displacement meter) with the plane of the plate parallel to the plane of the membrane (Figure 2, e). Figure 3 shows a fragment of the route manufacturing process (Figure 3, a - Figure 3, c) of the dynamometer sensor design (Figure 2, e) with the formation of the sensor by combining cuts and chemical milling of crystalline quartz. Figure 4 shows a fragment of a pressure sensor with a membrane and two resonators made in the console. Due to the symmetry of the structure in the drawings, as a rule, two projections of the image of the sensor blank are used. In the absence of symmetry with respect to one of the axes, three projections are used (Figure 2, d, e, e and Figure 3, c).

The following notation is used in the drawings: 1 - a blank of crystalline material, 2 - a recess in the blank, 3 - a membrane, 4 - a console in the form of a plate, 5 - a resonator, 6 - film electrodes, 7 - a cover, 8 - a hole in the cover for feeding on the membrane of the measured parameter P, for example pressure, or force, or displacement, 9-17 - cuts in the workpiece, 18 - through holes, 19 - connection for measuring the measured force, 20 - protrusions on the membrane surface, 21 - workpiece surface parallel to the membrane plane , 22 - the plane of the membrane facing the cons oli, 23 — additional resonator, 24 — central region of the cantilever plate 4, 25 and 26 — free edges of the cantilever, X, Y, Z — directions of crystallographic axes of crystalline quartz, X — axis of symmetry of the second order, Z — axis of symmetry 3 th order is the optical axis.

In the sensor depicted in FIG. 1, g, in the console 4, the resonator 5 of shear thickness oscillations is formed by film electrodes 6, and in the sensors depicted in FIG. 2, e, FIG. 3, c, FIG. 4, bending vibration resonators (dual micro tuning forks) 5 and 23 are formed through holes 18 (electrodes on micro tuning forks are not shown due to the complexity of their configuration). The console 4 and the membrane 3 are made of a single preform 1, made, in turn, of crystalline (piezocrystalline) quartz. The cover 7 in the design of the pressure gauge sensor (Figure 1, g) is necessary for the formation of a chamber into which the measured parameter P - pressure enters through the hole 8. The fitting 19 in FIG. 2, e serves to receive the measured force and transfer it to the membrane 3, which in this case serves to center the force or move P and seal the internal volume of the sensor.

The console 4 in the sensor shown in FIG. 4 is formed by a plate fixed on the membrane 3 in the central region 24. In the region of the free edges 25 and 26, resonators 5 and 23 are made.

The proposed sensor and method of its manufacture in one embodiment are as follows (Figure 1).

Figure 1, a - the formation of the workpiece using traditional technological operations of cutting, orientation, grinding. Figure 1, b - the formation in the workpiece 1 using the recess 2, made by, for example, ultrasonic milling, the surface of the membrane 3 in contact with the measured parameter R.

Figure 1, in - the formation of large faces of the console 4 by means of parallel cuts 9.

Figure 1, g - the formation of part facing the console surface of the membrane 3 by means of cuts 10, converging at right angles with cuts 9.

Figure 1, e - the formation of the side faces of the console 4 with parallel cuts 11 and the formation of the remaining parts of the membrane surface 3 facing the console by means of parallel cuts 12, converging at right angles to the cuts 11.

Figure 1, e - the formation of the protrusions 20 in the console 4 and the application on the console 4 of the electrodes 6.

Figure 1, g - attachment of the plate 7 with the hole 8 to the membrane 3.

Another version of the sensor and the method of its manufacture are as follows (Figure 2).

Figure 2, a - technological operations of manufacturing the workpiece and the formation of the outer surface of the membrane similarly to Figure 1, a and Figure 1, b.

Figure 2, b - the formation of one of the side faces of the console and part of the protrusion 20 with a cut or pickle 13.

Figure 2, in - the formation of the part facing the console surface of the membrane facing the membrane of the large faces of the console and the other part of the protrusion 20 cuts 14 and 15.

Figure 2, g - the formation of two side faces of the console by cutting or etching 16.

Figure 2, d - the formation of the rest of the membrane surface facing the console.

Figure 2, e - the formation of the resonator (double micrometer) by etching in the plate of the console 4 through rectangular holes 18.

Another embodiment of the sensor and its manufacturing method — by combining the operations of cutting and chemical etching — is illustrated in FIG. 3 and consists in the following.

Figure 3, a - operations are similar to Figure 1, a, b and Figure 2, a.

Figure 3, b - the formation of the part facing the console surface of the membrane facing the membrane of the large faces of the console and part of the protrusion 20 with a cut 15.

Figure 3, c - the formation of the rest of the membrane surface facing the console, the side faces of the console and the resonator, part of the protrusion 20 by chemical etching of the workpiece plane 21 to the surface 22 of the membrane 3 (including through holes 18).

The sensor works as follows. The measured parameter P acts on the membrane 3 and causes mechanical stresses in it. These voltages are transmitted through the junction of the membrane with the console plate to the console 4 (since the consoles are located in areas with non-zero mechanical stresses) and to the resonator 5 (resonators 5 and 23). The resonant frequency of the resonator changes. This change is recorded by an electronic circuit (not shown) connected to the resonator by means of electrodes 6. The console 4 of the resonator 5 is made integral with the membrane 3, therefore, the deformation of the membrane is transmitted to the resonator without loss of accuracy.

The proposed technical solution makes it possible to implement a sensor of small mechanical parameters (pressures, forces, accelerations, etc.) with a hysteresis-free operating characteristic, because it does not contain non-crystalline materials in its design that experience mechanical stresses outside the elastic range. This design and manufacturing method gives the sensor higher accuracy parameters.

Claims (8)

1. A resonant pressure, force, or displacement sensor containing a membrane made of crystalline material and resonators of elastic vibrations, characterized in that on the surface of the membrane in areas with non-zero mechanical stresses caused by the measured parameter, a cantilever is formed integrally with the membrane in the body which perform resonators, and the console is in the form of a plate and combined with the membrane of one of the side faces, or areas of one of the side faces, or areas of one of the larger faces. 2. The device according to claim 1, characterized in that the side faces of the resonators are made through through holes in the plate. 3. The device according to claim 1, characterized in that the orientation of the console faces relative to the crystallographic axes of the sensor material is selected taking into account the anisotropy of the chemical or plasma chemical milling speeds in the sensor material, for example, large faces of the sensor console made of crystalline quartz make up with the optical axis of quartz angle from 70 to 90 °. 4. The device according to claim 1, characterized in that the cantilever is formed by a plate connected to the surface of the membrane in the central region. 5. A method of manufacturing a resonant pressure, force, or displacement sensor, the structure of which includes a membrane made of a single crystal and a cantilever on its surface, in the body of which there are resonators containing the operations of shaping crystalline parts in the form of sawing a crystal billet and milling, for example, diamond, and / or ultrasound, and / or chemical, and / or plasmachemical, characterized in that at least some areas of the membrane surface facing the console and at least an hour s consoles edges formed by cuts in the workpiece, such as wire or band saws, wherein the saw cuts produce calling instrument from the free end of the console to the place of the membrane with a console connection. 6. The method according to claim 5, characterized in that some faces of the consoles and one area of the membrane surface are formed by cuts, and others by milling, for example, chemical or ultrasonic. 7. The method according to claim 5, characterized in that the orientation and direction of the cuts are selected taking into account the milling speed in one direction or another in the workpiece, for example, by guiding the cuts along the direction with a minimum milling speed. 8. The method according to claim 5, characterized in that the large edges of the console are formed using multi-blade cutting by simultaneously performing at least two cuts with a step equal to the sum of the thickness of the console and the thickness of the cut.

Images