阅读说明：本技术 一种saw称重传感器 (SAW weighing sensor ) 是由 孙成亮 林炳辉 刘炎 胡博豪 于 2021-06-07 设计创作，主要内容包括：本发明涉及一种SAW称重传感器。该称重传感器包括：声表面波器件和称重机械结构；所述声表面波器件安放在所述称重机械结构上；所述声表面波器件包括：基底、沉积在基底上的压电薄膜以及沉积在压电薄膜上的叉指电极和反射栅；所述称重机械结构包括：平台、固定在所述平台上的基座、与所述基座以铰链形式连接的杠杆、与所述杠杆成滑块结构的托盘以及一端与所述杠杆的末端连接且一端与所述声表面波器件的中心位置接触的探头；所述探头与所述声表面波器件的中心位置接触的区域为接触区。本发明通过SAW的频率漂移感应压力变化,并且能够对感知压力进行放大或缩小,提高传感量程,能够准确的测量待测物的质量且实现量程可调的效果。(The invention relates to a SAW weighing sensor. This weighing sensor includes: surface acoustic wave devices and weighing mechanisms; the surface acoustic wave device is arranged on the weighing mechanical structure; the surface acoustic wave device includes: the device comprises a substrate, a piezoelectric film deposited on the substrate, and an interdigital electrode and a reflecting grid deposited on the piezoelectric film; the weighing mechanism comprises: the device comprises a platform, a base fixed on the platform, a lever connected with the base in a hinge mode, a tray forming a slider structure with the lever, and a probe, wherein one end of the probe is connected with the tail end of the lever, and the other end of the probe is contacted with the central position of the surface acoustic wave device; the contact area of the probe and the center of the surface acoustic wave device is a contact area. The invention senses the pressure change through the frequency drift of the SAW, can amplify or reduce the sensed pressure, improves the sensing range, can accurately measure the quality of the object to be measured and realizes the effect of adjustable range.)

1. A SAW load cell, comprising: surface acoustic wave devices and weighing mechanisms; the surface acoustic wave device is arranged on the weighing mechanical structure;

the surface acoustic wave device includes: the device comprises a substrate, a piezoelectric film deposited on the substrate, and an interdigital electrode and a reflecting grid deposited on the piezoelectric film;

the weighing mechanism comprises: the device comprises a platform, a base fixed on the platform, a lever connected with the base in a hinge mode, a tray forming a slider structure with the lever, and a probe, wherein one end of the probe is connected with the tail end of the lever, and the other end of the probe is contacted with the central position of the surface acoustic wave device; the contact area of the probe and the center of the surface acoustic wave device is a contact area.

2. A SAW load cell as claimed in claim 1, wherein said interdigital electrodes are spaced on either side of said contact area, and said reflective grating is located on the outer side of both of said interdigital electrodes.

3. A SAW load cell as claimed in claim 1, wherein circular, square and rectangular cavities are etched into the back cavity of the substrate.

4. A SAW load cell as claimed in claim 1, wherein the tray rests on any position of the lever.

5. A SAW load cell as claimed in claim 1, wherein the probe is of an insulating material.

6. A SAW load cell as claimed in claim 1, wherein the substrate is of high resistivity, high resistivity silicon.

7. A SAW load cell according to claim 1, wherein the interdigital electrodes are metal conductive electrodes.

8. A SAW weighing sensor according to claim 5, wherein the material of said metal conducting electrodes is Mo, Pt, Au or Al.

9. A SAW load cell according to claim 1, wherein the piezoelectric film is an AlN piezoelectric film, a Sc doped AlN piezoelectric film, a PZT piezoelectric film or a ZnO piezoelectric film.

10. A SAW load cell according to claim 1, wherein the height of the hinge and lever from the ground is adjusted in accordance with the height of the SAW device;

the length of the probe is adjusted according to the length of the surface acoustic wave device.

Technical Field

The invention relates to the field of sensors, in particular to a SAW weighing sensor.

Background

With the continuous development of the production process automation field and the increasing demand of the actual life symmetrical retransmission sensors, the technical requirements of the market symmetrical retransmission sensors are higher: the volume and the quality are reduced, the response sensitivity is improved, the measurement error is small, the variety is increased, and the digitization and the controllability are realized. The weighing sensor is a device which actually converts a mass signal into a visual electric signal to be output, the sensor is required to accurately measure the mass of a measured object in the environment, and the correct selection of the weighing sensor is crucial, so that the working principle of the sensor cannot be influenced by the environment to cause measurement deviation; another aspect is whether the sensor is matched to the working environment, concerning its safety and service life etc.

The existing weighing sensors mainly comprise a resistance strain type sensor, a capacitance type sensor and the like, wherein the resistance strain type sensor is most widely used, but the existing weighing sensors have the defects of large nonlinearity and weak output signal for large strain. Taking a product based on a capacitance principle as an example, the capacitance-type capacitance sensor converts measured change into capacitance change, but the capacitance-type capacitance-.

Although the existing product and technology can realize the weighing function of the measured object, various conversion principles have certain limitations, and technical or economic problems still occur in the product, so that a novel, simple and effective method is urgently needed, real-time monitoring can be realized, and the quality of the measured object can be conveniently and accurately obtained. The piezoelectric sensor based on the piezoelectric material has the characteristics of large dynamic range, wide frequency range, firmness, durability, small external interference, external power supply and the like, wherein the sensor based on the piezoelectric acoustic surface wave resonator (SAW) has obvious application potential in the aspects of temperature sensing, gas concentration detection, pressure sensing and the like. Therefore, the invention provides a piezoelectric weighing sensor, which can sense pressure change through frequency drift of the SAW, and can amplify or reduce sensed pressure so as to improve the sensing range.

Disclosure of Invention

The invention aims to provide an SAW weighing sensor which can accurately measure the quality of an object to be measured and realize the effect of adjustable measuring range.

In order to achieve the purpose, the invention provides the following scheme:

a SAW load cell comprising: surface acoustic wave devices and weighing mechanisms; the acoustic surface wave device is arranged on the weighing mechanical structure;

the surface acoustic wave device includes: the device comprises a substrate, a piezoelectric film deposited on the substrate, and an interdigital electrode and a reflecting grid deposited on the piezoelectric film;

the weighing mechanism comprises: the device comprises a platform, a base fixed on the platform, a lever connected with the base in a hinge mode, a tray in a sliding block structure with the lever, and a probe, wherein one end of the probe is connected with the tail end of the lever, and the other end of the probe is contacted with the central position of the surface acoustic wave device; the contact area of the probe and the central position of the surface acoustic wave device is a contact area.

Optionally, the interdigital electrodes are separated at two sides of the contact region, and the reflective grating is located at the outer sides of the two interdigital electrodes.

Optionally, a cavity with a circular shape, a square shape or a rectangular shape is etched in the back cavity of the substrate.

Optionally, the tray rests on any position of the lever.

Optionally, the probe is made of an insulating material.

Optionally, the substrate is high-resistivity high-resistance silicon.

Optionally, the interdigital electrode is a metal conductive electrode.

Optionally, the metal conductive electrode is made of Mo, Pt, Au or Al.

Optionally, the piezoelectric film is an AlN piezoelectric film, a Sc-doped AlN piezoelectric film, a PZT piezoelectric film, or a ZnO piezoelectric film.

Optionally, the height of the hinge and the lever from the ground is adjusted according to the height of the surface acoustic wave device;

the length of the probe is adjusted according to the length of the surface acoustic wave device.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

the invention provides a SAW weighing sensor, wherein the SAW device comprises: the mass of a measured object can be accurately measured by the substrate, the piezoelectric film deposited on the substrate, and the interdigital electrode and the reflecting grating deposited on the piezoelectric film; meanwhile, the tray and the lever form a sliding block structure, namely the position of the tray on the lever can be moved, so that the pressure of a measured object on the SAW resonator caused by gravity can be amplified or reduced, and the effect of adjustable measuring range is further realized.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive labor.

FIG. 1 is a schematic structural diagram of a SAW load cell provided in the present invention;

FIG. 2 is a schematic top view of a surface acoustic wave device in an embodiment of the present invention;

FIG. 3 is a schematic sectional view of the surface acoustic wave device of FIG. 2 in the A-A direction;

FIG. 4 is a schematic view of a weighing mechanism in an embodiment of the present invention;

FIG. 5 is a schematic diagram of a surface acoustic wave device having a rectangular cavity in an embodiment of the present invention;

FIG. 6 is a schematic diagram of a surface acoustic wave device having a square cavity in an embodiment of the present invention;

FIG. 7 is a schematic diagram of a surface acoustic wave device having a circular cavity in an embodiment of the present invention;

FIG. 8 is a strain diagram of the SAW device of FIG. 5 under a point load in the center;

FIG. 9 is a strain diagram of the SAW device of FIG. 6 under a point load in the center;

FIG. 10 is a strain diagram of the SAW device of FIG. 7 under a point load in the center;

FIGS. 11-23 are schematic views of a method of making a load cell of the present invention.

Description of the symbols:

the method comprises the following steps of 1-substrate, 2-piezoelectric film, 3-photoresist, 4-metal conductive electrode film, 5-interdigital electrode, 6-reflection grating, 7-busbar, 8-silicon dioxide, 9-surface acoustic wave device, 10-platform, 11-base, 12-lever, 13-tray, 14-probe, 15-weighing mechanical structure and 16-weighing sensor.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention aims to provide an SAW weighing sensor which can accurately measure the quality of an object to be measured and realize the effect of adjustable measuring range.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Fig. 1 is a schematic structural diagram of a SAW load cell 16 according to the present invention, and as shown in fig. 1, the SAW load cell 16 according to the present invention includes: a surface acoustic wave device 9 and a weighing mechanism 15; the saw device 9 is mounted on the weighing mechanism 15.

As shown in fig. 2 and 3, the surface acoustic wave device 9 includes: the device comprises a substrate 1, a piezoelectric film 2 deposited on the substrate 1, and an interdigital electrode 5 and a reflecting grid 6 deposited on the piezoelectric film 2; namely, the interdigital electrode 5, the piezoelectric film 2 and the substrate 1 are in a sandwich structure, and the substrate 1, the piezoelectric film 2 and the interdigital electrode 5 are arranged from bottom to top in sequence.

Specifically, the substrate 1 is high-resistivity high-resistance silicon. The interdigital electrode 5 is a metal conductive electrode. The metal conductive electrode is made of Mo, Pt, Au or Al. The piezoelectric film 2 is an AlN piezoelectric film, a Sc-doped AlN piezoelectric film, a PZT piezoelectric film or a ZnO piezoelectric film.

As shown in fig. 4, the weighing mechanism 15 comprises: a platform 10, a base 11 fixed on the platform 10, a lever 12 connected with the base 11 in a hinge manner, a tray 13 in a sliding block structure with the lever 12, and a probe 14 connected with the end of the lever 12 and with one end contacting with the central position of the surface acoustic wave device 9.

Specifically, the tray 13 stays at an arbitrary position of the lever 14. The probe 14 is an insulating material.

As shown in fig. 1, the area where the probe 14 contacts the center position of the saw device 9 is a contact area.

The lever 12 is connected with the base 11 in a hinge structure to form a fulcrum, the height of the fulcrum and the lever 12 from the platform 10 is adjustable, the tray 13 and the lever 12 form a slider structure, and the tray 13 can stop at any position of the lever 12.

The height of the hinge and the lever 12 from the ground is adjusted according to the height of the surface acoustic wave device 9;

the length of the probe 14 is adjusted according to the length of the surface acoustic wave device 9.

The weighing mode of the invention is as follows: the object to be measured is placed on the tray 13, and for the lever 12 with the fulcrum, the pressure of the object to be measured on the lever 12 forms power, and the surface acoustic wave device 9 forms resistance on the reaction force of the probe 14, and according to the size of the power arm and the resistance arm, the acting force of the probe 14 on the surface acoustic wave device 9 can be calculated. According to the formula defined by the SAW resonant frequency:resonant frequency f of SAW is defined by phase velocity v_phAnd the influence of the length lambda of the period section, when the probe 14 generates pressure on the surface acoustic wave device 9, the surface acoustic wave deviceThe phase velocity of the acoustic wave on the surface acoustic wave device 9 and the spacing between the fingers are changed, which causes the resonance frequency of the surface acoustic wave device 9 to shift and changeTherefore, the mass of the object to be measured corresponds to the amount of change in the resonance frequency of the surface acoustic wave device 9.

Besides, a slider mechanism is formed between the tray 13 and the lever 12, the tray 13 can stay at any position of the lever 12, the power arm is changed due to the change of the position of the tray 13 according to the definition of the lever 12 on the power arm, under the condition that the power arm and the resistance arm are not changed, the acting force of the probe 14 and the surface acoustic wave device 9 is changed, namely the corresponding relation between the mass of the object to be measured and the variation of the resonant frequency of the surface acoustic wave device 9 is changed, in other words, the tray 13 can be moved towards the direction close to the fulcrum within the pressure range which can be borne by the surface acoustic wave device 9, and the maximum measurement of the mass of the object to be measured is realized by reducing the size of the power arm. Similarly, the tray 13 can be moved away from the pivot to measure a measured object with a small mass.

In conclusion, the invention realizes the function of weighing the measured object, realizes the characteristic of adjustable measuring range by adjusting the position of the tray 13 on the lever 12, amplifies or reduces the pressure of the measured object on the SAW resonator due to gravity, can realize the measurement of the measured object with large mass and small mass, and further realizes the effect of adjustable measuring range

In order to provide a space for the probe 14 to make contact with the surface of the surface acoustic wave device 9 at a contact area and avoid a situation where the probe 14 damages the interdigital structure when applying pressure to the surface acoustic wave device 9, the interdigital electrodes 5 are separated on both sides of the contact area, and the reflective grating 6 is located on both outer sides of the interdigital electrodes 5.

Circular, square and rectangular cavities are etched in the back cavity of the substrate 1 as described in fig. 5-7. FIGS. 8-10 are strain charts of a SAW device 9 having rectangular, square, and circular shaped cavities, respectively, under point loading in the center, including perpendicular to the SAW propagation directionTransverse strain and longitudinal strain parallel to the direction of propagation of the surface acoustic wave. And the middle dashed frame area is the area where the interdigital electrode 5 is located. It will be appreciated that changes in the phase velocity of the saw device 9 directly affect the resonant frequency, and that when the probe 14 exerts a force on the saw device 9, the device is subjected to stress strain which results in a change in the modulus of elasticity of the material, thereby affecting the phase velocity. And for a specific silicon substrate 1, the formula of the change of the phase velocity with strain is as follows: v. of_ph＝v₀(1+γε)，v₀In the phase velocity in the unstrained state, ε represents a strain value, and γ represents an influence coefficient of strain on the phase velocity. The transverse strain has an opposite influence coefficient to the longitudinal strain on the phase velocity, the transverse strain decreasing the phase velocity and the longitudinal strain increasing the phase velocity. For the surface acoustic wave device 9 with the rectangular cavity, the influence of transverse strain is mainly exerted, so that the strain reduces the phase velocity on the whole, and the frequency is negatively deviated; for the surface acoustic wave device 9 with the square and circular cavities, the distribution of the transverse strain and the longitudinal strain is equal, and the absolute value of the influence coefficient of the longitudinal strain on the phase velocity is higher than that of the transverse strain on the phase velocity, so that the phase velocity is improved by the strain on the whole, and the frequency is shifted in the positive direction.

Therefore, the invention also provides a method for controlling the sensor electric signal to realize forward deviation or reverse deviation. Different shaped cavities are etched under the sensor, for example, when the cavity is rectangular, the frequency of the sensor is shifted negatively during weighing, and when the cavity is square or circular, the frequency of the sensor is shifted positively during weighing.

Fig. 11-23 show process steps for the load cell shown in fig. 1, as follows:

as shown in fig. 11-12, a piezoelectric film 2 is deposited on a substrate 1;

as shown in fig. 13, a layer of photoresist 3 is spin-coated on the piezoelectric film 2;

as shown in fig. 14, the photoresist 3 in the area where the interdigital electrode and the reflective gate are to be prepared is removed by etching;

as shown in fig. 15, a metal conductive electrode thin film 4 is deposited on the patterned photoresist 3;

as shown in fig. 16, the excessive photoresist 3 and the excessive metal conductive electrode film 4 are removed by a lift-off process, so that the interdigital electrode 5 and the reflective gate 6 are formed on the piezoelectric film 2;

as shown in fig. 17, a silicon dioxide film 8 is deposited on the back of the substrate 1;

as shown in fig. 18, a layer of photoresist 3 is coated on the back of the silicon dioxide film 8;

as shown in fig. 19, the photoresist 3 in a partial region is removed by etching;

as shown in fig. 20, the exposed silicon dioxide 8 is removed by etching;

as shown in fig. 21, the excess photoresist 3 is removed;

as shown in fig. 22, the back cavity etches the substrate 1;

as shown in fig. 23, silicon dioxide 8 is etched away;

as shown in fig. 1, the surface acoustic wave device 9 is mounted on a weighing mechanism 15 to form a weighing cell.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.