RU2753475C1 - Micromechanical accelerometer - Google Patents

Abstract

FIELD: professional equipment.

SUBSTANCE: invention relates to the field of instrument engineering. The micromechanical accelerometer contains a base, a sensing element consisting of upper and lower caps, an inertial mass, and a separation layer. The separation layer additionally contains a decoupling plane, a glass substrate. In the decoupling plane, elastic-deformable beams are formed with mounting pads located on them to the lower cover of the sensor element and the glass substrate, and to the glass substrate from the lower side, and to the lower cover of the sensor element from the upper side of the decoupling plane. Elastic-deformable beams in the areas between the mounting pads, as well as in the areas between the mounting pads and the decoupling plane are made in the form of a meander with “x” number of bends.

EFFECT: increased accuracy of the micromechanical accelerometer.

1 cl, 2 dwg

Description

The invention relates to the field of instrumentation and can be used in the manufacture of micromechanical accelerometers, microgyroscopes, integral pressure sensors.

A device is known where the sensitive element (SE) of the sensor is made of monocrystalline silicon and a glass substrate made of borosilicate glass. Moreover, the inertial mass - a pendulum, a frame, elastic torsion bars, areas of attachment to the glass substrate are formed, at the same time by the method of liquid etching and connected through the attachment areas by the method of anodic fit to a substrate made of borosilicate glass. In the body of the sensor, the SE is fixed to the base with glue - sealant. In this case, the glue - sealant is applied arbitrarily to the entire area of the glued surfaces or some parts of it [1]. The disadvantage of this device is that mechanical stress occurs in the SE. These stresses lead to significant errors in the micromechanical accelerometer. In the production of sensors, the sensitive element is mounted in the housing by simply gluing the SE surface to the base. Borosilicate glass, used for anodic welding, in the manufacture of CE has a low thermal conductivity in comparison with silicon. So, when exposed to positive and negative temperatures, a large voltage arises in the glass substrate, which occurs during a transient thermal regime. Such a relatively high mechanical stress leads to errors in the accelerometer that cannot be compensated algorithmically due to the time dependence of the transient. Another disadvantage is the presence of an adhesive sealant on a glass substrate.

Glue - a sealant applied to the base of the micromechanical accelerometer and, accordingly, to one of the sides of the glass substrate is also a source of stress. These voltages are temperature dependent and affect sensor sensitivity and zero offset. To ensure the strength of the bond against vibration, the impact area must be large enough, and the increase in the area of the adhesive bond increases the stress on the sensor element of the sensor. Thus, the stresses caused by the difference between the coefficients of thermal expansion of monocrystalline silicon, borosilicate glass from which the sensitive element of the micromechanical accelerometer is made, the base of the accelerometer and the adhesive-sealant increase the displacement of the zero signal of the accelerometer, and this reduces the accuracy of the micromechanical accelerometer.

A sensitive element of a micromechanical accelerometer is known, containing a double-arm pendulum made of monocrystalline silicon, a glass plate and an outer frame with attachment points to the glass plate, X-shaped torsion bars connected to the pendulum and an outer frame, the axis of symmetry of the inertial mass is aligned with the axis passing through the cruciform torsion bars. The attachment pads are located in the immediate vicinity of the X-shaped torsion bars. The outer frame simultaneously serves as a rigid frame of the sensitive element, while the connection of the sensitive element with the fixed base of the accelerometer is carried out through the back side of the glass plate [2].

The anodic connection of the glass substrate to the monocrystalline silicon sensitive element is carried out at an elevated temperature. After cooling of the "glass substrate-monocrystalline silicon sensitive element" structure, partial deformation of the outer frame of the sensitive element occurs. This deformation is transmitted to the elastic torsion bars. This significantly affects the stability of the elastic properties of the latter.

Since the sensitive element is fixed on the base of the accelerometer, the effect of positive or negative temperatures is transmitted from the base through the glass cover to the outer frame and, accordingly, to the X-shaped torsion bars. As a result, the X-shaped torsion bars are deformed, and as a result, the pendulum is displaced in the absence of acceleration. Thus, a temperature shift of the zero signal occurs, and this reduces the accuracy of the accelerometer. The stiffness of the torsion bars will also change and, as a consequence, the steepness of the displacement transducer will change. This is also a significant way. Another disadvantage of this device is the instability of the offset of the zero signal due to the high level of contact stresses arising in the locations of the attachment pads and transmitted to the X-shaped torsion bar.

Also known are devices with a symmetrical design so that the deformations caused by the stresses compensate each other. However, this seriously limits the design.

The closest in technical essence is an accelerometer, the SE of which is connected to the base through additional separating layers and a layer of glue. Additional separating layers are placed between the SE and the base of the micromechanical accelerometer, aligned strictly symmetrically with the SE. The adhesive layer is formed in the center of symmetry of the additional separating layer and the base of the micromechanical accelerometer. Moreover, the adhesive layer is limited in the area of its application. [3].

In the known device, the fastening element of the SE located in the center of symmetry is mounted directly on the surface of the base through a layer of glue or solder. As a consequence, it is also directly exposed to the loads transmitted by the base. As a result, temperature-dependent stresses are created between the SE of the micromechanical accelerometer, the fastening material, and the base material of the sensor.

In addition, the fastener material (glue or solder material) is unstable over time and prone to plastic deformation, which can cause the sensor output to drift with aging. In addition, a high positioning accuracy of such a SE design is required on the base - strictly in the center of symmetry. And this, in turn, greatly affects how much mechanical stress is successfully "filtered out", leading to a deterioration in the accuracy of the sensor.

Thus, this design does not completely eliminate the plastic deformations transmitted from the base to the SE of the sensor. And this causes a shift in the output signal in the absence of a measurable parameter and, therefore, reduces the accuracy of the micromechanical accelerometer.

Thus, the additional separating layer should have sufficient elasticity and sufficient rigidity, it should not be absolutely rigid. The additional separating layer should be elastic enough to damp, to minimize the deformation created by mechanical stresses arising under the influence of harmful factors on the micromechanical accelerometer and then on the base and then on the SE of the micromechanical accelerometer. The problem to be solved by the invention is to improve the accuracy of the micromechanical accelerometer.

1. To achieve this, in a micromechanical accelerometer containing a base, a sensing element consisting of upper and lower covers, an inertial mass, and a separating layer facing the base and one of the sides of the sensing element and an adhesive sealant according to the invention, a separating layer additionally contains a decoupling plane and a glass substrate, elastically deformable beams are formed in the decoupling plane, with the pads for attachment to the lower cover of the sensitive element and the glass substrate located on them, and to the glass substrate from the lower side of the decoupling plane, and to the lower cover of the sensitive element from the upper the sides of the decoupling plane, the attachment pads are formed for attachment to the bottom cover of the sensing element and are located on opposite to each other formed resiliently deformable beams, the attachment sites are formed for attachment to the glass substrate and are located on the other opposite formed elastically deformable beams located on the decoupling plane, the elastically deformable beams in the sections between the attachment sites, as well as in the sections between the attachment sites and the decoupling plane, are made in the form of a meander with n number of bends. 2. Distinctive features of the claimed device is that the separating layer additionally contains a decoupling plane and a glass substrate, elastically deformable beams are formed in the decoupling plane, with areas for attachment to the bottom cover of the sensing element and a glass substrate located on them, and to the glass substrate from the lower side of the decoupling plane, and to the lower cover of the sensitive element from the upper side of the decoupling plane, the attachment areas are formed for attachment to the lower cover of the sensitive element and are located on oppositely formed elastically deformable beams, the attachment sites are formed for attachment to the glass substrate and are located on other opposite from each other formed elastically deformable beams located on the decoupling plane, elastically deformable beams in the areas between the attachment sites, as well as in the areas between the attachment sites and the decoupling with a connecting plane are made in the form of a meander with n number of bends. In a micromechanical accelerometer, the sensing element is mounted on the base of the housing through a separating layer, namely, through a decoupling plane, which in turn is fixed on a glass substrate (pedestal) made of borosilicate glass. Elastically deformable beams are formed in the decoupling plane along the perimeter, separately from each other, and are located on them with attachment areas to the SE and to the glass substrate. The elastically deformable beams themselves are made in the form of a meander with the same number of bends and are strictly symmetric with respect to the longitudinal and transverse axes of symmetry of the sensitive element. In this case, the areas of attachment to the SE and the glass substrate are formed along the periphery of the decoupling plane. To the underside of the glass substrate. To the bottom cover of the sensing element from the upper side of the decoupling plane. The pads for attachment to the SE and the glass pedestal are formed separately from each other on mutually opposite sides of the decoupling plane, and are also connected to elastically deformable beams. Such formation of attachment sites with elastically deformable beams in the decoupling plane and attachment to a glass substrate allows minimizing deformation from external factors acting through the base. Thus, the glass substrate (pedestal) is fixed to the substrate with a soft or elastomeric adhesive, which provides partial stress relief, but has certain disadvantages such as time-dependent curing processes. On the other side of the glass substrate, a decoupling plane is attached by anodic welding through the attachment pads.

The glass substrate (pedestal) is made of borosilicate glass whose CTE is almost equal to silicon. Thereby, further reducing thermomechanical stresses.

The other side of the decoupling plane is fixed to the SE of the accelerometer. Fastening can be done by direct splicing of silicon parts. Thus, the decoupling plane due to the elastically deformable beams and the attachment pads formed at the same time with them additionally relieve the stresses transmitted from the base. Thus, in the aggregate, soft or elastomeric glue - a thickened glass pedestal (8 times thicker than SE) - a decoupling plane with elastically deformable beams and attachment sites allows minimizing deformation from external factors, while deformation in the area of attachment of elastic suspensions is practically reduced to zero , and a symmetrical arrangement - to compensate to a minimum of harmful effects, thereby increasing the accuracy of the micromechanical accelerometer.

The invention is illustrated by the drawings: FIG. 1, fig. 2a and FIG. 2b.

FIG. 1 shows a micromechanical accelerometer assembly, in section.

FIG. 2a and FIG. 2b shows the decoupling plane, where:

1 - inertial mass;

2 - top cover;

3 - bottom cover;

4 - elastic suspension;

5 - outer frame of the SE;

6 - decoupling plane;

7 - pads for attachment to the bottom cover of the SE;

8 - platforms for attaching to a glass substrate;

9 - elastically deformable beams;

10 - glass substrate;

11 - base.

The micromechanical accelerometer contains a sensitive element consisting of an inertial mass 1 enclosed between the upper 2 and the lower covers 3, connected, for example, by anodic fit or direct splicing or any other other method. A separating layer is located between the sensitive element, its lower cover 3 and the base 11. This layer consists of a glass substrate 10 and a decoupling plane 6. Decoupling plane 6 is fixed to the bottom cover 3 of the SE, for example, by direct splicing through the attachment pads to the bottom cover 7, but it can also be glued. The SE assembly - the decoupling plane is fixed on the glass substrate 10 through the pads of attachment to the glass substrate 8. Elastically deformable beams 9 are formed along the periphery of the decoupling plane 6. The glass substrate 10 is glued to the base 11 with an elastic adhesive sealant (not shown).

When the micromechanical accelerometer is exposed to harmful external factors, stresses arise in the base 11. Thermomechanical stresses are transmitted to the glass substrate 10. In this case, the stresses are partially reduced in the elastic adhesive - sealant. Owing to the glass substrate 10, which is thick compared to the silicon SE, the voltages also decrease, but still remain. Stresses from the glass substrate 10 transforming into plastic deformation are transferred to the decoupling plane 6. This deformation through the attachment sites to the glass substrate 8 bends the elastically deformable beams 9. Further, the residual deformation is transmitted through the same elastically deformable beams 9 and already through the attachment sites to bottom cover SE 7. Already minimized deformation from the bottom cover 3 through the outer frame of SE 5 to elastic suspension 4. The influence of mechanical stresses on elastic suspensions 4 is practically reduced to zero.

The noted properties confirm the advantages of the claimed invention over the known solutions.

The operation of the device is based on the well-known principle of moving the inertial mass 1 under the influence of linear acceleration and measuring this movement, for example, in a capacitive way.

The sensitive element of a micromechanical accelerometer can be made of monocrystalline silicon with a wafer orientation <100> ÷ <110> by anisotropic etching or plasma etching.

The prototype tests carried out showed a positive effect of both this micromechanical sensor and its assembly method both in manufacturability and in accuracy, that is, in reducing the offset of the zero signal.

Sources of information:

1. Parshin V.A., Kharitonov V.I. Features of the technology of multisensor sensors with undoped elastic suspensions // Sensors and Systems. 2002. No. 2. S. 22-24.

2. RF patent 2251702.

3. Application US 20170107098-prototype.

Claims (1)

A micromechanical accelerometer containing a base, a sensing element consisting of upper and lower covers, an inertial mass, and a separating layer facing the base and one of the sides of the sensing element and sealant glue, characterized in that the separating layer additionally contains a decoupling plane and a glass a substrate, elastically deformable beams are formed in the decoupling plane with attachment points located on them to the lower cover of the sensitive element and the glass substrate, and to the glass substrate from the bottom side, and to the lower cover of the sensitive element - from the upper side of the decoupling plane, the attachment areas are formed for attachment to the bottom cover of the sensing element and are located on opposite from each other formed elastically deformable beams, the attachment areas are formed for attachment to the glass substrate and are located on other formed elastically deformable beams opposite to each other elastically deformable beams located on the decoupling plane, elastically deformable beams in the sections between the attachment sites, as well as in the sections between the attachment sites and the decoupling plane, are made in the form of a meander with n number of bends.

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