Integrated piezoelectric sensor for detecting in-plane forces such as shock, acceleration, rotational force, and the like
阅读说明:本技术 用于检测诸如冲击、加速度、旋转力等平面内的力的集成压电传感器 (Integrated piezoelectric sensor for detecting in-plane forces such as shock, acceleration, rotational force, and the like ) 是由 F·普罗科皮奥 C·瓦尔扎辛 于 2015-11-26 设计创作,主要内容包括:压电传感器(10)形成在半导体材料芯片中,该半导体材料芯片具有限定平面(XY)的表面(13A)并且集成有用于感测在平面内作用的力的感测结构(11;30;60)。芯片由限定悬臂(12;32;52;62)的衬底(13;33)形成,该悬臂(12;32;52;62)具有被约束到衬底的锚固部(15)的第一端(12A)和在外力的作用下自由弯曲的第二端(12B)。悬臂具有第一和第二纵向半部,每个纵向半部承载平行于芯片平面延伸的压电材料的相应的条状元件(16,17)。(The piezoelectric sensor (10) is formed in a chip of semiconductor material having a surface (13A) defining a plane (XY) and integrated with a sensing structure (11; 30; 60) for sensing forces acting in the plane. The chip is formed by a substrate (13; 33) defining a cantilever (12; 32; 52; 62), the cantilever (12; 32; 52; 62) having a first end (12A) constrained to an anchor (15) of the substrate and a second end (12B) free to bend under the action of an external force. The cantilever has first and second longitudinal halves, each carrying a respective strip-like element (16, 17) of piezoelectric material extending parallel to the plane of the chip.)
1. A method of manufacturing a piezoelectric sensor, comprising:
forming first and second strips along a longitudinal direction of a substrate, each of the first and second strips having a piezoelectric layer between respective first and second electrode layers;
electrically coupling the first electrode layer of the first strip to the second electrode layer of the second strip;
electrically coupling the second electrode layer of the first strip to the first electrode layer of the second strip; and
forming a cantilever extending in the longitudinal direction from the substrate by etching the substrate, the cantilever comprising the first strip and the second strip.
2. The method of claim 1, further comprising:
securing a first cover to a first surface of the substrate; and
a second cover is secured to the second surface of the substrate.
3. The method of claim 1, further comprising:
forming a passivation layer on the first and second stripes and the substrate;
exposing at least a portion of the first and second electrode layers of the first and second stripes by selectively removing a portion of the passivation layer;
forming electrical contacts by depositing metallization layers in the exposed portions of the first and second electrode layers of the first and second strips.
4. A system, comprising:
a piezoelectric sensor, the piezoelectric sensor comprising:
a semiconductor substrate;
an anchor portion;
a cantilever formed in the substrate, the cantilever having a first end and a second end, the first end being constrained to the anchor portion; and
a first strip-like element of piezoelectric material on the cantilever, the first strip-like element having a first portion and a second portion, the second portion aligned with and spaced apart from the first portion between the first end and the second end.
5. The system of claim 4, further comprising:
a measurement circuit electrically coupled to the piezoelectric sensor and configured to determine a value of an external force acting on the cantilever.
6. The system of claim 4, wherein the piezoelectric sensor comprises a second strip-like element of piezoelectric material on the cantilever, the second strip-like element being positioned laterally with respect to the first strip-like element.
Technical Field
The present invention relates to an integrated piezoelectric sensor for detecting forces in-plane, such as impacts, accelerations, uniaxial and acceleration, and rotational forces. In particular, the invention concerns sensors obtained using semiconductor technology, generally using the techniques used for the manufacture of MEMS devices, for detecting forces acting in the plane of the sensor.
Background
As is known, when piezoelectric materials are subjected to physical stress and undergo deformation, they are biased, generating a potential difference across them and an electrical charge. By connecting these materials to an external circuit, a piezoelectric current is obtained which is related to the applied force.
The above phenomena have been studied for several years and employed in order to provide sensors in which the sensing structure (typically a cantilever beam or cantilever arm having at least one piezoelectric region) undergoes deformation upon mechanical stress and generates an electrical current. By connecting the sensing circuit to measurement circuitry (such as an ammeter and processing stage), the measurement circuitry can detect the charge or potential difference and determine the force acting on the cantilever.
In this way, the piezoelectric sensor is able to measure forces such as linear and rotational forces, e.g. acceleration, shock, etc.
The geometrical dimensions, the properties of the material and generally the overall design of the sensing structure of the sensor are generally optimized according to the physical quantity to be detected.
For example, for an impact sensor, it is possible to use a
The
However, the
However, this causes a significant complication in the production of the sensing structure, since the manufacturing and assembly is complicated and requires higher costs, the overall dimensions of the sensing structure are larger, and the sensing structure has a lower accuracy than the in-plane sensing structure.
Other known solutions envisage embedding in the structure of the cantilever a layer of piezoelectric material extending according to a lying plane transverse to the plane XY (for example at 45 ° with respect to the sensor plane). However, these solutions are particularly complex from a manufacturing point of view and are therefore expensive. They are therefore not capable of being used in all low cost applications.
Disclosure of Invention
It is an object of the present invention to provide a sensor that overcomes the drawbacks of the prior art.
According to the present invention, a force sensor of the piezoelectric type is provided, as defined in
Drawings
For a better understanding of the present invention, preferred embodiments thereof will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
FIG. 1 is a perspective view of a piezoelectric force sensing structure of known type;
FIG. 2 is a perspective view of an embodiment of a force sensing structure for use in an in-plane force sensor;
FIG. 3 shows an equivalent electrical diagram of a force sensor including the sensing structure of FIG. 2;
FIG. 4 is a perspective view of a different embodiment of the sensing structure of the present force sensor;
FIG. 5 is a perspective view of a deformation of the structure of FIG. 4 in the presence of an external force;
FIG. 6 is a schematic illustration of a different embodiment of the present pressure sensor for detecting both linear and rotational forces;
FIGS. 7A and 7B are schematic illustrations of the behavior of the force sensor of FIG. 6 in the presence of an external linear force and an external rotational force, respectively; and
FIGS. 8A-8E are cross-sectional views of the sensing structure of FIGS. 2, 4 and 6 in successive fabrication steps.
Detailed Description
Fig. 2 and 3 show an embodiment of a
The
The substrate 13 monolithically forms a beam 12 of the cantilever type, the beam 12 of the cantilever type having a main extension direction (longitudinal direction) parallel to the axis Y, a first end (constrained end) 12A fixed to an anchoring region 15 of the substrate 13, and a second end (free end) 12B. The cantilever 12 may have a thickness in the direction Z smaller than the substrate 13, for example negligible with respect to the other two dimensions, however this is not mandatory, as discussed below.
A longitudinal plane parallel to the axis YZ and passing through the midline of the cantilever 12 defines two longitudinal halves of the cantilever 12.
The substrate 13 may integrate other structural and electronic components (not shown).
The two
The two
In detail, as shown in fig. 3, where each
The
In the illustrated embodiment, the free end 12b of the cantilever 12 has an extension 18, and the extension 18 achieves a reduction in the resonant frequency of the detection system by increasing the weight of the cantilever 12.
In use, in the presence of an external force acting in-plane on cantilever 12, cantilever 12 bends in the same plane XY. In the plane of the drawing of fig. 2, in practice, the free end 12b of the cantilever 12 moves to the left and right depending on the direction of the external force to cause compression on one side of the cantilever 12 and extension on the other. For example, force F directed to the left in FIG. 2 causes compression of the
The two
In particular, by connecting the two
wherein sigmaPZTIs the stress on the
It should be noted that the
Fig. 4 shows an embodiment of the
The force sensor of fig. 4 comprises a plurality of
Each
In detail, in each
In particular, the first stripes 36 (in the illustrated example, the
Thus, the arrangement of fig. 4 is equivalent to a circuit similar to fig. 3, in which eight capacitors are connected in an alternating manner.
With the arrangement of fig. 4, as shown in fig. 5, the
With the structure of fig. 4, it is possible to obtain higher sensitivity with a greater number of
Fig. 6 illustrates an embodiment that enables detection of both linear and rotational type forces.
In the sensing structure 60 of fig. 6, two pluralities of
In use, as illustrated in fig. 7A, in the presence of a linear force F1 lying in the sensor plane (plane XY), the force acts in the same manner on both of the plurality of
In contrast, as illustrated in fig. 7B, in the presence of the rotational force F2, this force acts on each of the plurality of
The measurement circuitry downstream of the sensing structure of fig. 7 is thus able to detect the type of force acting on the sensor.
The sensing structure shown in fig. 2-7 can be fabricated as described below with reference to fig. 8A-8E, which fig. 8A-8E show a cross section of a chip of semiconductor material taken in the longitudinal direction of the
Initially (fig. 8A), a bottom electrode layer 73 (e.g. formed of titanium platinum oxide), a
Next (fig. 8B), a
Then (fig. 8C), a
Next (fig. 8D), the
Finally (fig. 8E), the
The described force sensor has many advantages.
The reading based on the piezoelectric phenomenon involves low noise, and therefore the sensor has high sensitivity.
The sensor is configured according to a vertical layer structure of standard type and therefore the assembly is of standard type and does not incur additional costs like in the case of a sensor arranged rotated by 90 °.
Several manufacturing steps are required after the steps typically used to fabricate the piezoelectric structure.
The sensor has an extremely compact structure and therefore the overall size is reduced.
The sensitivity of the sensor is independent of the thickness of the cantilever, and therefore the sensor does not experience inaccuracies and process spread (process spread) due to thickness variations in the batch.
The sensors may detect different types of forces, such as shock, acceleration, linearity, and rotational forces as described above.
Finally, it is clear that modifications and variations can be made to the sensor described and illustrated herein without thereby departing from the scope of the present invention, as defined in the annexed claims. For instance, the different embodiments described may be combined to provide further solutions.
In addition, although the illustrated structure always has at least one pair of piezoelectric strips, each strip extending on a respective longitudinal half of each cantilever, it is possible to form a single strip on one longitudinal half of the respective cantilever, which is subjected to compression or tension depending on the deformation of the cantilever and whose output signal is therefore uniquely related to the magnitude and direction of the force acting on the sensing structure.
For example, the single cantilever solution of fig. 3 may also have pairs of
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