A piezoelectric MEMS sensor

Abstract

The application discloses a piezoelectric MEMS sensor, comprising: a substrate having a cavity; a vibration support layer formed above the substrate and covering the cavity; a lower electrode layer formed above the vibration support layer; a piezoelectric layer formed above the lower electrode layer; and an upper electrode layer having a groove and the groove divides the upper electrode layer into a center electrode layer and an outer ring electrode layer; wherein, in a first case, a first pad of the center electrode layer is used to output a first electric signal, and a second pad of the outer ring electrode layer is grounded to compensate for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor; or in a second case, the first pad of the center electrode layer is used to output a second electric signal, the second pad of the outer ring electrode layer is used to output a third electric signal, and the lower electrode layer is grounded. The piezoelectric MEMS sensor effectively eliminates the voltage generated by the pyroelectric effect and improves the output voltage generated by the pressure difference.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a piezoelectric MEMS (Micro-Electro-Mechanical System) sensor. BACKGROUND

[0002] An electronic cigarette is an electronic product that simulates a cigarette, and the principle is to heat liquid tobacco to produce a misty aerosol and inhale it into the mouth to simulate the effect of smoking real cigarettes. Since the electronic cigarette does not have carbon monoxide and tar and other major harmful substances, it is much less harmful than real cigarettes, so it is loved by more and more smokers and young people. When a smoker uses an electronic cigarette, a certain degree of negative pressure will be generated in the smoke channel, causing the pressure sensor diaphragm to deform to output an electrical signal, causing the electronic cigarette to start working, and when there is no smoking action, the electronic cigarette is turned off. The pressure sensor in the current electronic cigarette basically adopts a capacitive type, but the pressure difference applied to it and the capacitance change are nonlinear. And because the gap between the diaphragm and the back plate is very small, a lot of damping will be generated, causing the response time to slow down. Relatively speaking, the piezoelectric pressure sensor has the advantages of fast response time and high linearity. However, piezoelectric materials have pyroelectric effect under non-isothermal conditions, so they are limited to working in environments with a small temperature change rate. When the electronic cigarette is in working condition, the electronic components in it will heat up, causing the sensor to change in temperature in a short period of time, thereby causing pyroelectric effect. The output signal of the pyroelectric effect will interfere with the output signal generated by the pressure difference, causing false triggering and affecting the use experience of the electronic cigarette. SUMMARY

[0003] To solve the problems in the related art, the present application provides a piezoelectric MEMS sensor that can effectively compensate for the voltage generated by pyroelectric effect.

[0004] The technical solution of the present application is as follows:

[0005] According to one aspect of the present application, a piezoelectric MEMS sensor is provided, comprising:

[0006] a substrate having a cavity;

[0007] a vibration support layer formed above the substrate and covering the cavity;

[0008] a lower electrode layer formed above the vibration support layer;

[0009] a piezoelectric layer formed above the lower electrode layer;

[0010] an upper electrode layer having a trench and the trench divides the upper electrode layer into a center electrode layer and an outer ring electrode layer, wherein the lower electrode layer, the piezoelectric layer and the upper electrode layer constitute a piezoelectric functional layer;

[0011] wherein, in the first case, the first pad of the center electrode layer is used to output a first electric signal, and the second pad of the outer ring electrode layer is grounded to compensate for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor;

[0012] or, in the second case, the first pad of the center electrode layer is used to output a second electric signal, the second pad of the outer ring electrode layer is used to output a third electric signal, and the lower electrode layer is grounded to compensate for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor in the form of a differential output voltage.

[0013] wherein the voltage generated by the pyroelectric effect includes:

[0014] the voltage of the first-order pyroelectric effect, i.e. the potential difference caused by the change in polarization intensity directly caused by temperature change:

[0015] the voltage of the second-order pyroelectric effect, i.e. the potential difference generated by the pyroelectric effect through material deformation caused by temperature change:

[0016] the total voltage generated by the pyroelectric effect is equal to the algebraic sum of the voltage of the first-order pyroelectric effect and the voltage of the second-order pyroelectric effect;

[0017] wherein P, d 31 , ε are the pyroelectric coefficient, piezoelectric coefficient and dielectric constant of the piezoelectric layer, A, t are the area and thickness of the piezoelectric functional layer, ΔT, σ are the temperature change and the in-plane thermal stress caused by temperature change.

[0018] wherein the diameter of the piezoelectric functional layer is less than 10 mm, the thickness is 0.1 to 10 μm, the thermal conductivity of the piezoelectric functional layer is greater than 0.1 W / (m·K), and the temperature difference from the center to the edge of the piezoelectric functional layer is less than 10℃.

[0019] wherein preferably, the diameter of the piezoelectric functional layer is less than 2 mm, the thermal conductivity of the piezoelectric functional layer is greater than 1 W / (m·K), and the temperature difference from the center to the edge of the piezoelectric functional layer is less than 1℃.

[0020] wherein the distance r of the trench to the center of the piezoelectric functional layer, wherein R is the distance from the center to the edge of the piezoelectric functional layer.

[0021] The neutral surface of the vibration support layer and the piezoelectric functional layer is disposed at the interface between the piezoelectric layer and the vibration support layer, so that the in-plane stress in the thickness direction of the piezoelectric layer has the same sign. The relationship between the thickness of the piezoelectric layer and the thickness of the vibration support layer is as follows: Where E p h p E s h s These represent the Young's modulus and thickness of the piezoelectric layer and the vibration support layer, respectively.

[0022] The piezoelectric MEMS sensor is used as a switch in an electronic cigarette. The maximum operating temperature range of the piezoelectric MEMS sensor is -40℃ to 125℃, and the maximum temperature rise rate is 20℃ / s.

[0023] The piezoelectric MEMS sensor operates in a temperature range of 0 to 90°C, with a maximum temperature rise rate of 5°C / s.

[0024] In the first scenario, the first external circuit module receives the first electrical signal, amplifies the voltage or charge after impedance matching, and then outputs the amplified signal to the first signal processing unit. The first signal processing unit analyzes the amplified signal and controls the heating wire to turn on or off.

[0025] In the second scenario, the second external circuit module receives the second electrical signal and the third electrical signal, amplifies the voltage or charge after impedance matching, and then outputs the amplified signal to the second signal processing unit. The second signal processing unit analyzes the amplified signal and controls the heating wire to turn on or off.

[0026] In the first scenario, the outer ring electrode layer extends to the edge to form the second pad, the outer ring electrode layer has a radial opening, and the central electrode layer extends to the edge through the radial opening to form the first pad. Both the first pad and the second pad are located above the piezoelectric layer.

[0027] In the second scenario, the outer ring electrode layer extends to the edge to form the second pad, the outer ring electrode layer has a radial opening, the central electrode layer extends to the edge to form the first pad through the radial opening, the first pad and the second pad are both located above the piezoelectric layer, the lower electrode layer extends to the edge to form the third pad, the third pad is grounded, and the third pad is located above the exposed vibration support layer.

[0028] The piezoelectric MEMS sensors described above effectively eliminate the voltage generated by the pyroelectric effect and increase the output voltage generated by the pressure difference. Attached Figure Description

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed in the embodiments will be briefly introduced as follows. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and for those of ordinary skill in the art, other drawings can be obtained based on these accompanying drawings without any creative effort.

[0030] Figure 1 A perspective view of a piezoelectric MEMS sensor is shown according to some embodiments;

[0031] Figure 2 A top view of a piezoelectric MEMS sensor is shown according to some embodiments;

[0032] Figure 3 A cross-sectional view of a piezoelectric MEMS sensor is shown according to some embodiments;

[0033] Figure 4 A series voltage equivalent circuit diagram is shown according to some embodiments;

[0034] Figure 5 A perspective view of a piezoelectric MEMS sensor is shown according to some embodiments;

[0035] Figure 6 A differential voltage equivalent circuit diagram is shown according to some embodiments;

[0036] Figure 7 A normalized distribution diagram of the sum of radial and tangential stresses on the middle surface of a piezoelectric layer is shown according to some embodiments. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0038] Referring to Figure 1 , Figure 2 and Figure 3According to an embodiment of this application, a piezoelectric MEMS sensor is provided, which has the function of compensating for the voltage generated by the pyroelectric effect. The piezoelectric MEMS sensor includes a substrate 10, a vibration support layer 20a, a lower electrode layer 20b, a piezoelectric layer 20c, and an upper electrode layer. This piezoelectric MEMS sensor is applied in the switch of an electronic cigarette. The maximum operating temperature range of the piezoelectric MEMS sensor is -40°C to 125°C, and the maximum temperature rise rate is 20°C / s. Preferably, the operating temperature range of the piezoelectric MEMS sensor is 0 to 90°C, and the maximum temperature rise rate is 5°C / s. Therefore, the piezoelectric MEMS sensor applied in electronic cigarettes needs to consider both the piezoelectric effect and the pyroelectric effect. The following will describe this piezoelectric MEMS sensor in detail.

[0039] The substrate 10 has a cavity 11. A vibration support layer 20a is formed above the substrate 10 and covers the cavity 11. A lower electrode layer 20b is formed above the vibration support layer 20a. A piezoelectric layer 20c is formed above the lower electrode layer 20b. The upper electrode layer has a trench 21, and the trench 21 divides the upper electrode layer into a central electrode layer 20e and an outer ring electrode layer 20d. The lower electrode layer 20b, the piezoelectric layer 20c, and the upper electrode layer constitute a piezoelectric functional layer.

[0040] like Figure 2 As shown, in the first scenario, the first pad 22 of the central electrode layer 20e is used to output a first electrical signal, and the second pad 23 of the outer ring electrode layer 20d is grounded to compensate for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor. In the first scenario, the outer ring electrode layer 20d extends the second pad 23 towards the edge and has a radial opening. The central electrode layer 20e extends the first pad 22 towards the edge through the radial opening. Both the first pad 22 and the second pad 23 are located above the piezoelectric layer 20c.

[0041] Or, such as Figure 5 As shown, in the second scenario, the first pad 22 of the central electrode layer 20e is used to output the second electrical signal, the second pad 23 of the outer ring electrode layer 20d is used to output the third electrical signal, and the lower electrode layer 20b is grounded, so as to achieve differential output voltage compensation for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor. In the second scenario, the lower electrode layer 20b extends to the edge with a third pad 24, which is grounded.

[0042] The following will explain in detail the principle of compensating for the voltage generated by the pyroelectric effect of this piezoelectric MEMS sensor.

[0043] The total voltage generated by the pyroelectric effect is equal to the algebraic sum of the voltage generated by the first-order pyroelectric effect and the voltage generated by the second-order pyroelectric effect.

[0044] The voltage of the first order pyroelectric effect, i.e. the potential difference generated by the change in the polarization intensity directly caused by the temperature change:

[0045] The voltage of the second order pyroelectric effect, i.e. the potential difference generated by the material deformation caused by the temperature change, and then by the piezoelectric effect:

[0046] Wherein, P, d 31 , ε are the pyroelectric coefficient, piezoelectric coefficient, and dielectric constant of the piezoelectric layer 20c, A, t are the area and thickness of the piezoelectric functional layer, ΔT, σ are the temperature change and the in-plane thermal stress caused by the temperature change.

[0047] Wherein, the diameter of the piezoelectric functional layer is less than 10 mm, the thickness is 0.1 to 10 μm, the thermal conductivity of the piezoelectric functional layer is greater than 0.1 W / (m·K), and the temperature difference from the center to the edge of the piezoelectric functional layer is less than 10℃. Preferably, the diameter of the piezoelectric functional layer is less than 2 mm, the thermal conductivity of the piezoelectric functional layer is greater than 1 W / (m·K), and the temperature difference from the center to the edge of the piezoelectric functional layer is less than 1℃. At this time, the temperature change of the piezoelectric functional layer of the piezoelectric MEMS sensor is always approximately uniform. In some embodiments, the thermal conductivity of PVDF (polyvinylidene fluoride) is 0.17-0.2 W / (m·K), the thermal conductivity of PZT (lead zirconate titanate) is 1.3 W / (m·K), the thermal conductivity of zinc oxide is 30 W / (m·K), and the thermal conductivity of aluminum nitride is 170-230 W / (m·K).

[0048] As can be seen from the expression, the voltage of the first order pyroelectric effect is independent of the area of the piezoelectric functional layer, and when the heating is uniform, the thermal stress in the piezoelectric functional layer is also uniformly distributed. The voltage of the second order pyroelectric effect is also independent of the area. Based on the above theory, the present application proposes a piezoelectric MEMS sensor which can effectively compensate for the output voltage error caused by the pyroelectric effect.

[0049] Figure 4The voltage equivalent circuit diagram of the piezoelectric MEMS sensor in the first case is shown. The upper electrode layer is divided into the center electrode layer 20e and the outer ring electrode layer 20d by the groove 21. The outer ring electrode layer 20d is grounded, and the center electrode layer 20e is used to output the first electric signal, and the lower electrode layer 20b is in series. Wherein C1, C2, R1, R2 are the capacitance and leakage resistance of each part, V1, V2, V3 are the voltage generated by the first pyroelectric effect, the voltage generated by the second pyroelectric effect and the voltage generated by the piezoelectric effect of the pressure difference respectively. Because the whole piezoelectric functional layer is uniformly heated, the voltage of the first pyroelectric effect of the center electrode layer 20e and the outer ring electrode layer 20d is equal in size and the same in direction. Because the stiffness of the whole piezoelectric functional layer is continuous and equal along the radial direction, the thermal stress generated by thermal expansion in the piezoelectric layer 20c is also uniform. Therefore, the voltage of the second pyroelectric effect of the center electrode layer 20e and the outer ring electrode layer 20d is also equal in size and the same in direction. From the equivalent circuit diagram, it can be seen that after the lower electrode layer 20b is connected in series, the voltage V1(II) of the first pyroelectric effect of the center electrode layer 20e in the whole circuit loop is equal in size and opposite in direction to the voltage V1(I) of the first pyroelectric effect of the outer ring electrode layer 20d, and the voltage V2(II) of the second pyroelectric effect of the center electrode layer 20e is equal in size and opposite in direction to the voltage V2(I) of the second pyroelectric effect of the outer ring electrode layer 20d. And the output voltage V3(II) of the center electrode layer 20e caused by the pressure difference is the same in direction as the output voltage V3(I) of the outer ring electrode layer 20d. At this time, the size of the output voltage of the whole piezoelectric MEMS sensor is the sum of the absolute values of the output voltage V3(II) of the center electrode layer 20e and the output voltage V3(I) of the outer ring electrode layer 20d caused by the pressure difference. In this way, not only the influence of the pyroelectric effect is completely eliminated, but also the output voltage signal caused by the pressure difference is improved. Figure 4

[0050] Figure 6 ​The voltage equivalent circuit of the piezoelectric MEMS sensor in the second case is shown. The lower electrode layer 20b is connected to ground, and the outer ring electrode layer 20d and the center electrode layer 20e are respectively used as output terminals. It can be seen that the voltage V1(II) of the first pyroelectric effect of the center electrode layer 20e in the entire circuit loop is equal in size and direction to the voltage V1(I) of the first pyroelectric effect of the outer ring electrode layer 20d, and the voltage V2(II) of the second pyroelectric effect of the center electrode layer 20e is equal in size and direction to the voltage V2(I) of the second pyroelectric effect of the outer ring electrode layer 20d. However, the output voltage V3(II) of the center electrode layer 20e caused by the pressure difference is opposite in direction to the output voltage V3(I) of the outer ring electrode layer 20d. When the output terminals of the outer ring electrode layer 20d and the center electrode layer 20e are connected through a voltage difference, the voltage caused by the pyroelectric effect can also be eliminated, and the output voltage caused by the pressure difference can be improved. At this time, the output voltage of the entire piezoelectric MEMS sensor is the sum of the absolute values of the output voltage V3(II) of the center electrode layer 20e and the output voltage V3(I) of the outer ring electrode layer 20d caused by the pressure difference. Compared with the piezoelectric MEMS sensor in the first case, the piezoelectric MEMS sensor in the second case can effectively suppress the common-mode noise in the circuit. Figure 4 The equivalent circuit shown in the second case, Figure 6 The equivalent circuit shown in the second case can effectively suppress the common-mode noise in the circuit.

[0051] Figure 7 The normalized distribution of the sum of the radial and tangential stresses on the middle surface of the piezoelectric layer 20c caused by the pressure difference is shown. R represents the distance from the center to the edge of the piezoelectric functional layer. It can be seen that the stress is distributed in a parabolic form along the radius, and the signs of the stresses at the center and the edge are opposite. Therefore, the center electrode layer 20e and the outer ring electrode layer 20d should be respectively arranged on the two sides of the stress sign change position, i.e. the position of the groove 21, to avoid charge neutralization. At this time, the output voltages of the center electrode layer 20e and the outer ring electrode layer 20d caused by the pressure difference are opposite in direction.

[0052] In some embodiments, the distance r from the groove 21 to the center of the piezoelectric functional layer, wherein R is the distance from the center to the edge of the piezoelectric functional layer.

[0053] The neutral surface of the entire piezoelectric functional layer is arranged at the interface between the piezoelectric layer 20c and the vibration support layer 20a, so that the in-plane stresses in the thickness direction of the piezoelectric layer 20c are of the same sign, and the thickness of the piezoelectric layer 20c and the thickness of the vibration support layer 20a satisfy the following relationship: wherein E p , h p , E s , h s respectively represent the Young's modulus and the thickness of the piezoelectric layer 20c and the vibration support layer 20a.

[0054] In addition, since the piezoelectric MEMS sensor is applied in the electronic cigarette, in the first case, the first external circuit module receives the first electric signal, amplifies the voltage or charge after impedance matching, and then outputs the amplified signal to the first signal processing unit. The first signal processing unit analyzes the amplified signal and controls the opening or closing of the heating wire in the electronic cigarette.

[0055] In the second case, the second external circuit module receives the second electric signal and the third electric signal, amplifies the voltage or charge after impedance matching, and then outputs the amplified signal to the second signal processing unit. The second signal processing unit analyzes the amplified signal and controls the opening or closing of the heating wire in the electronic cigarette.

[0056] In summary, by means of the above technical solutions of the present application, the piezoelectric MEMS sensor provided by the present application has the function of compensating the voltage generated by the pyroelectric effect. The piezoelectric MEMS sensor divides the upper electrode layer into the outer ring electrode layer 20d grounded and the center electrode layer 20e outputting the first electric signal by the groove 21. Or the lower electrode layer 20b is grounded, and the outer ring electrode layer 20d and the center electrode layer 20e are respectively connected in differential mode as output terminals. The piezoelectric MEMS sensor effectively eliminates the voltage generated by the pyroelectric effect and improves the output voltage generated by the pressure difference.

[0057] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A piezoelectric MEMS sensor, characterized in that, include: Substrate with a cavity; A vibration support layer is formed above the substrate and covers the cavity; A lower electrode layer is formed above the vibration support layer; A piezoelectric layer is formed above the lower electrode layer; The upper electrode layer has a trench that divides the upper electrode layer into a central electrode layer and an outer ring electrode layer, wherein the lower electrode layer, the piezoelectric layer and the upper electrode layer constitute a piezoelectric functional layer; In the first scenario, the first pad of the central electrode layer is used to output a first electrical signal, and the second pad of the outer ring electrode layer is grounded to compensate for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor. Alternatively, in the second scenario, the first pad of the central electrode layer is used to output a second electrical signal, the second pad of the outer ring electrode layer is used to output a third electrical signal, and the lower electrode layer is grounded, so as to compensate for the voltage generated by the pyroelectric effect of the piezoelectric MEMS sensor in a differential output voltage manner.

2. The piezoelectric MEMS sensor according to claim 1, characterized in that, The voltage generated by the pyroelectric effect includes: The voltage of the first-order pyroelectric effect, that is, the potential difference generated by the change in polarization intensity directly caused by the temperature change: ; The voltage of the second-order pyroelectric effect is generated by the deformation of the material due to temperature changes, which then produces a potential difference through the piezoelectric effect. ; The total voltage generated by the pyroelectric effect is equal to the algebraic sum of the voltage of the first-order pyroelectric effect and the voltage of the second-order pyroelectric effect; Among them, P and d 31 ε represents the pyroelectric coefficient, piezoelectric coefficient, and dielectric constant of the piezoelectric layer, A and t represent the area and thickness of the piezoelectric functional layer, and ΔT and σ represent the temperature change and the in-plane thermal stress caused by the temperature change.

3. The piezoelectric MEMS sensor according to claim 2, characterized in that, The diameter of the piezoelectric functional layer is less than 10 mm, the thickness is 0.1 to 10 μm, the thermal conductivity of the piezoelectric functional layer is greater than 0.1 W / (m·K), and the temperature difference from the center to the edge of the piezoelectric functional layer is less than 10 °C.

4. The piezoelectric MEMS sensor according to claim 3, characterized in that, The diameter of the piezoelectric functional layer is less than 2 mm, the thermal conductivity of the piezoelectric functional layer is greater than 1 W / (m·K), and the temperature difference from the center to the edge of the piezoelectric functional layer is less than 1℃.

5. The piezoelectric MEMS sensor according to claim 1, characterized in that, The distance r from the trench to the center of the piezoelectric functional layer , where R is the distance from the center to the edge of the piezoelectric functional layer.

6. The piezoelectric MEMS sensor according to claim 1, characterized in that, The neutral plane of the vibration support layer and the piezoelectric functional layer is disposed at the interface between the piezoelectric layer and the vibration support layer, so that the in-plane stress in the thickness direction of the piezoelectric layer has the same sign. The relationship between the thickness of the piezoelectric layer and the thickness of the vibration support layer is as follows: E p h p E s h s These represent the Young's modulus and thickness of the piezoelectric layer and the vibration support layer, respectively.

7. The piezoelectric MEMS sensor according to claim 1, characterized in that, The piezoelectric MEMS sensor is used in the switch of an electronic cigarette. The maximum operating temperature range of the piezoelectric MEMS sensor is -40℃ to 125℃, and the maximum temperature rise rate is 20℃ / s.

8. The piezoelectric MEMS sensor according to claim 7, characterized in that, The piezoelectric MEMS sensor operates in a temperature range of 0 to 90°C, with a maximum temperature rise rate of 5°C / s.

9. The piezoelectric MEMS sensor according to claim 1, characterized in that, In the first scenario, the first external circuit module receives the first electrical signal, amplifies the voltage or charge after impedance matching, and then outputs the amplified signal to the first signal processing unit. The first signal processing unit analyzes the amplified signal and controls the heating wire to turn on or off.

10. The piezoelectric MEMS sensor according to claim 1, characterized in that, In the second scenario, the second external circuit module receives the second electrical signal and the third electrical signal, amplifies the voltage or charge after impedance matching, and then outputs the amplified signal to the second signal processing unit. The second signal processing unit analyzes the amplified signal and controls the heating wire to turn on or off.

11. The piezoelectric MEMS sensor according to claim 1, characterized in that, In the first scenario, the outer ring electrode layer extends to the edge to form the second pad, the outer ring electrode layer has a radial opening, and the central electrode layer extends to the edge through the radial opening to form the first pad, with both the first pad and the second pad located above the piezoelectric layer.

12. The piezoelectric MEMS sensor according to claim 1, characterized in that, In the second scenario, the outer ring electrode layer extends to the edge to form the second pad, the outer ring electrode layer has a radial opening, the center electrode layer extends to the edge to form the first pad through the radial opening, the first pad and the second pad are both located above the piezoelectric layer, the lower electrode layer extends to the edge to form the third pad, the third pad is grounded, and the third pad is located above the exposed vibration support layer.

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