A piezoelectric bulk acoustic wave sensor capable of operating in a hybrid excitation mode

Abstract

The present invention discloses a piezoelectric bulk acoustic wave sensor that can work in a mixed excitation mode, wherein an upper electrode pair and a lower electrode are located on the upper and lower surfaces of a piezoelectric crystal sheet; the upper electrode pair uses an X-shaped electrode and two triangular electrodes one to form a transverse electric field excitation electrode pair; the X-shaped electrode and the lower electrode of the upper electrode pair form a thickness electric field excitation electrode pair; the X-shaped electrode and the lower electrode have the same shape and are directly opposite to each other; the right angle positions of the two triangular electrodes one are directly opposite to each other, and the X-shaped electrode and the two triangular electrodes two in the lower electrode are also directly opposite to each other at right angles; the two right angles of one of the triangular electrodes one are directly opposite to the two right angles of one side of the two triangular electrodes two in the X-shaped electrode, and the two right angles of the other triangular electrode one are directly opposite to the two right angles of the other side of the two triangular electrodes two in the X-shaped electrode. The present invention can be sensitive to changes in the mechanical properties of the medium to be detected, as well as changes in the conductivity and dielectric properties.

Description

Technical Field

[0001] The invention relates to the field of sensor technology, in particular to a piezoelectric bulk acoustic wave sensor which can work in a thickness field, a transverse field fast shear and a transverse field slow shear mixed excitation mode. Background Art

[0002] In recent years, transverse field excited bulk acoustic wave devices (including transverse field fast shear and transverse field slow shear modes) have received extensive attention. They have high sensitivity to changes in the electrical properties of the detected medium; while traditional thickness field bulk acoustic wave devices have high sensitivity to changes in surface mass or liquid acoustic viscosity (mechanical properties). The modern biosensing field shows a clear demand for acoustic wave sensors with high sensitivity to changes in both properties. Existing acoustic wave sensors either work in the transverse field excitation mode or in the thickness field excitation mode, and cannot provide high-sensitivity sensing of both properties. A piezoelectric bulk acoustic wave sensor that can work in a mixed excitation mode of thickness electric field and transverse electric field is urgently needed. Summary of the invention

[0003] The present invention proposes a piezoelectric bulk acoustic wave sensor that can operate in a mixed excitation mode of thickness field, transverse field fast shear and transverse field slow shear. The piezoelectric bulk acoustic wave sensor is based on a four-electrode structure (three electrodes on the upper surface of the crystal and one electrode on the lower surface) and can be used to simultaneously detect the mechanical and electrical properties of a medium.

[0004] The present invention discloses a piezoelectric bulk acoustic wave sensor that can work in a hybrid excitation mode, which is composed of a piezoelectric crystal sheet, an upper electrode pair and a lower electrode, wherein the upper electrode pair and the lower electrode are located on the upper and lower surfaces of the piezoelectric crystal sheet. The upper electrode pair uses an X-shaped electrode and two triangular electrodes one to form a transverse electric field excitation electrode pair; the X-shaped electrode and the lower electrode of the upper electrode pair form a thickness electric field excitation electrode pair. The X-shaped electrode and the lower electrode have the same shape, face each other up and down, and are both composed of two integrally formed triangular electrodes two and a connecting electrode connecting the two triangular electrodes two; the right angles of the two triangular electrodes one face each other, and the right angles of the X-shaped electrode and the two triangular electrodes two in the lower electrode also face each other; the two right angles of one triangular electrode one face each other respectively with the two right angles of one side of the two triangular electrodes two in the X-shaped electrode, and the two right angles of the other triangular electrode one face each other respectively with the two right angles of the other side of the two triangular electrodes two in the X-shaped electrode.

[0005] Preferably, the piezoelectric crystal piece is made of AT-cut quartz crystal.

[0006] Preferably, the material of the upper electrode pair and the lower electrode is gold.

[0007] Preferably, the upper electrode pair and the lower electrode are prepared on the upper and lower surfaces of the piezoelectric crystal sheet by evaporation.

[0008] Preferably, the triangular electrode 1 and the triangular electrode 2 are both isosceles right triangles, and each corner of the triangular electrode 1 and the triangular electrode 2 is cut flat.

[0009] More preferably, the hypotenuse spacing l of the two triangular electrodes is 6 The value is between 10 and 20 mm, which is the value obtained by subtracting the width of the two sharp angles of the two triangular electrodes from the distance between the hypotenuses of the two triangular electrodes. 7 =0.95l 6 , the distance between the right-angled positions of the two triangular electrodes is l 8 =0.25l 6 , the distance between the two acute angles of the triangular electrode 1 9 =0.6l 6 , the width t of the right-angled flat position of the triangular electrode 3 =0.08l 6 , the distance between the right angle side of triangular electrode 1 and the right angle side of triangular electrode 2 in the X-shaped electrode is t 4 =0.1l 6 .

[0010] More preferably, the width t of the connecting electrode 1 = 0.9t 3 , the length of the connecting electrode t 2 =t 3 , the length of the piezoelectric crystal piece l 1 =1.5~1.8l 6 , the distance between the two acute angles of the triangular electrode 2 3 =0.7~0.9l 6 , the width of the piezoelectric crystal piece l 2 =0.8l 1 , the hypotenuse distance l between the two triangular electrodes in the X-shaped electrode or the lower electrode 4 =0.8~1l 6 , the value l after deducting the width of the two sharp angles of the two triangular electrodes aligned in the X-shaped electrode or the lower electrode from the hypotenuse spacing of the two triangular electrodes 5 =0.9 l 4 .

[0011] Preferably, the thickness h of the piezoelectric crystal sheet is 2 The value is between 0.4 and 0.4 mm, and the thickness of the X-shaped electrode h 3 and the thickness of the lower electrode h 1 Both are 300 nm.

[0012] The present invention has the beneficial effects:

[0013] 1. The present invention uses a four-electrode structure to construct transverse field slow shear, transverse field fast shear and thickness field working modes, so that a piezoelectric bulk acoustic wave sensor can work in a mixed excitation mode (the working frequencies of the three excitation modes are different, so when measuring a type of analyte, the excitation mode can be switched by switching the excitation frequency), so that the device can be sensitive to changes in the mechanical properties of the medium to be detected, as well as changes in the conductivity and dielectric properties, and can obtain richer sensing information at the same time. It can be applied to fields such as biochemical reaction monitoring and medical trace testing, which significantly expands the application scope of bulk acoustic waves in the field of biochemical sensing.

[0014] 2. The present invention uses a transverse electric field excitation electrode pair composed of an X-shaped electrode and a triangular electrode to generate a transverse field excitation electric field, which can be decomposed into transverse electric fields in two directions 1 and 3, corresponding to the two working modes of transverse field fast shear and slow shear, meeting the high sensitivity requirements of the sensor for both conductivity and dielectric properties. In addition, the traditional transverse field excitation device is a straight electrode gap, while the X-shaped transverse field excitation electrode gap formed by the X-shaped electrode and the triangular electrode of the present invention is longer, which is conducive to improving the sensitivity of the sensor (usually the sensitivity near the electrode gap is the highest).

[0015] 3. The present invention increases the area of ​​the X-shaped electrode and the lower electrode (increases l within the parameter value range) 2 , l 3 and l 4 ), can improve the energy trapping effect of the device, reduce the resonant impedance, and increase the resonant quality factor, thereby improving the sensing resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a top surface diagram of the piezoelectric bulk acoustic wave sensor of the present invention.

[0017] Figure 2 It is a bottom surface diagram of the piezoelectric bulk acoustic wave sensor of the present invention.

[0018] Figure 3 It is a side view of the piezoelectric bulk acoustic wave sensor of the present invention.

[0019] Figure 4 It is a three-dimensional diagram of the piezoelectric bulk acoustic wave sensor of the present invention.

[0020] Figure 5 This is a comparison chart of the sensitivity of the piezoelectric bulk acoustic wave sensor, the lateral field sensor, and the thickness field sensor of the present invention to changes in liquid conductivity.

[0021] Figure 6 This is a comparison chart of the sensitivity of the piezoelectric bulk acoustic wave sensor, lateral field sensor, and thickness field sensor of the present invention to changes in liquid dielectricity.

[0022] Figure 7 This is a comparison chart of the sensitivity of the piezoelectric bulk acoustic wave sensor, the lateral field sensor, and the thickness field sensor of the present invention to changes in liquid acoustic viscosity. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0024] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, a piezoelectric bulk acoustic wave sensor that can work in a hybrid excitation mode is composed of a piezoelectric crystal sheet 3, an upper electrode pair and a lower electrode 4. The piezoelectric crystal sheet is made of AT-cut quartz crystal; the material of the upper electrode pair and the lower electrode is gold, which is prepared on the upper and lower surfaces of the piezoelectric crystal sheet 3 by evaporation. The upper electrode pair is composed of an X-shaped electrode 1 and two triangular electrodes 2, forming a transverse electric field excitation electrode pair; in addition, the X-shaped electrode of the upper electrode pair and the lower electrode form a thickness electric field excitation electrode pair. The X-shaped electrode and the lower electrode 4 are of the same shape, facing each other up and down, and are both composed of two integrally formed triangular electrodes 2 and a connecting electrode connecting the two triangular electrodes 2; the triangular electrode 1 2 and the triangular electrode 2 are both isosceles right triangles, and the angles of the triangular electrode 1 2 and the triangular electrode 2 are cut flat; the right angles of the two triangular electrodes 1 2 are facing each other, and the two triangular electrodes 2 in the X-shaped electrode and the lower electrode are also facing each other at right angles; the two right-angled sides of one of the triangular electrodes 1 2 are respectively facing the two right-angled sides on one side of the two triangular electrodes 2 in the X-shaped electrode, and the two right-angled sides of the other triangular electrode 1 2 are respectively facing the two right-angled sides on the other side of the two triangular electrodes 2 in the X-shaped electrode.

[0025] like Figure 1 As shown, the hypotenuse spacing between the two triangular electrodes 1 and 2 is l 6 The value is between 10 and 20 mm, which is the value obtained by subtracting the width of the two sharp angles of the two triangular electrodes 1 from the distance between the hypotenuses of the two triangular electrodes 1. 7 =0.95l 6 , the distance between the right-angled positions of the two triangular electrodes 1 and 2 is l 8 =0.25l 6 , the distance between the two sharp angles of the triangular electrode 2 is l 9 =0.6l 6 , the width t of the right-angled flat position of the triangular electrode 2 3 =0.08l 6 , the distance between the right angle side of triangular electrode 1 2 and the right angle side of triangular electrode 2 in the X-shaped electrode is t 4 =0.1l 6 .

[0026] like Figure 2 As shown, the width of the connecting electrode t 1 = 0.9t 3 , the length of the connecting electrode t 2 =t 3 , the length of the piezoelectric crystal piece l 1 =1.5~1.8l 6 , the distance between the two acute angles of the triangular electrode 2 3 =0.7~0.9l 6 , the width of the piezoelectric crystal piece l 2 =0.8l 1 , the hypotenuse distance l between the two triangular electrodes in the X-shaped electrode or the lower electrode 4 =0.8~1l 6 , the value l after deducting the width of the two sharp angles of the two triangular electrodes aligned in the X-shaped electrode or the lower electrode from the hypotenuse spacing of the two triangular electrodes 5 =0.9 l 4 .

[0027] like Figure 3 As shown, the thickness of the piezoelectric crystal is h 2 The value is between 0.4 and 0.4 mm, and the thickness of the X-shaped electrode h 3 and the thickness of the lower electrode h 1 Both are 300 nm.

[0028] The working principle of the present invention is as follows:

[0029] The X-shaped electrode is connected to the positive end of the excitation signal, and the two triangular electrodes 1 2 and the lower electrode 4 are connected to the negative end of the excitation signal.

[0030] The effective electric field directions generated by the excitation signal at the four electrode gaps (gap 1, gap 2, gap 3 and gap 4) between the X-shaped electrode and the two triangular electrodes 1 and 2 are mainly along the directions of 135°, -135°, 45° and -45°. These effective electric fields will generate components along the x-axis (direction 1) and z-axis (direction 3) of the coordinate system. For AT-cut quartz crystals, in the coupling relationship of each shear mode, the effective piezoelectric coefficient when the effective electric field is excited in the 1 direction is e 14 (The first subscript number indicates the direction of the electric field, and the second subscript number indicates the strain type), and the effective piezoelectric coefficient corresponding to the transverse field fast shear mode is e 14 , so the effective electric field in the 1 direction will excite the transverse field fast shear mode; in addition, the effective piezoelectric coefficient when the effective electric field in the 3 direction is excited is e 36 , and the effective piezoelectric coefficient corresponding to the slow shear mode in the transverse field is e 36(The effective electric field is in 3 directions), so the effective electric field in 3 directions will stimulate the transverse field slow shear mode. The transverse field can penetrate into the medium to be detected. When the electrical properties (conductance or dielectric properties) of the medium to be detected change, the resonant frequency and resonant impedance of the piezoelectric bulk acoustic wave sensor of the present invention will change, and the degree of change can reflect the magnitude of the change in the electrical properties of the medium to be detected. Among them, the transverse field slow shear mode is more sensitive to changes in conductivity characteristics, and the fast shear mode is more sensitive to changes in dielectric properties.

[0031] In addition, the X-shaped electrode of the upper electrode pair and the lower electrode form a thickness electric field excitation electrode pair, and the effective electric field direction generated by the pair is mainly along the thickness direction of the piezoelectric crystal sheet, forming a thickness field. The vibration excited by the thickness field is mainly sensitive to the mechanical properties of the medium to be detected on the surface of the piezoelectric crystal sheet, including the viscosity of the liquid, the micro-mass change on the surface of the piezoelectric crystal sheet, etc. When the mechanical properties of the medium to be detected change, the resonant frequency and resonant impedance of the piezoelectric bulk acoustic wave sensor of the present invention will change, and the degree of change can reflect the magnitude of the change in the mechanical properties of the medium to be detected.

[0032] Through specific experiments, the sensitivity of the piezoelectric bulk acoustic wave sensor of the present invention to the electrical and mechanical properties of the medium to be detected is compared with the sensitivity of the existing transverse field excited bulk acoustic wave device and thickness field bulk acoustic wave device to the electrical and mechanical properties of the medium to be detected.

[0033] The piezoelectric BAW sensor of the present invention, the existing transverse field excited BAW device and the thickness field BAW device are used to measure the conductivity of various NaCl solutions (the solvent is water), and the frequency change of the three devices is affected by the conductivity of the NaCl solution. Figure 5 As shown, it can be seen that the frequency change rates of the piezoelectric bulk acoustic wave sensor of the present invention, the existing transverse field excitation bulk acoustic wave device and the thickness field bulk acoustic wave device are affected by the conductivity of the NaCl solution and become smaller in turn, that is, the piezoelectric bulk acoustic wave sensor of the present invention has the greatest sensitivity to the change of the conductivity of the NaCl solution.

[0034] The piezoelectric BAW sensor of the present invention, the existing transverse field excited BAW device and the thickness field BAW device are used to measure the relative dielectric constants (the ratio of the dielectric constant of the isopropanol solution to the dielectric constant of the vacuum) of various isopropanol solutions (the solvent is water), and the frequency changes of the three devices are affected by the relative dielectric constant of the isopropanol solution. Figure 6 As shown, it can be seen that the frequency changes of the piezoelectric bulk acoustic wave sensor of the present invention, the existing lateral field excitation bulk acoustic wave device and the thickness field bulk acoustic wave device are affected by the relative dielectric constant of the isopropyl alcohol solution at a rate that becomes smaller in sequence, that is, the piezoelectric bulk acoustic wave sensor of the present invention has the greatest sensitivity to the change in the relative dielectric constant of the isopropyl alcohol solution.

[0035] The square roots of acoustic viscosities (acoustic viscosity, the product of viscosity and density) of various sucrose aqueous solutions were measured using the piezoelectric bulk acoustic wave sensor of the present invention, the existing transverse field excitation bulk acoustic wave device and the thickness field bulk acoustic wave device, and the frequency changes of the three devices were affected by the acoustic viscosity of the sucrose aqueous solution. Figure 7 As shown, it can be seen that the frequency changes of the piezoelectric bulk acoustic wave sensor of the present invention, the existing thickness field bulk acoustic wave device and the lateral field excitation bulk acoustic wave device are affected by the square root of the acoustic viscosity of the sucrose aqueous solution at a rate that becomes smaller in sequence, that is, the piezoelectric bulk acoustic wave sensor of the present invention has the greatest sensitivity to the square root change of the acoustic viscosity of the sucrose aqueous solution.

Claims

1. A piezoelectric bulk acoustic wave sensor capable of operating in a hybrid excitation mode, comprising a piezoelectric crystal sheet, an upper electrode pair and a lower electrode, wherein the upper electrode pair and the lower electrode are located on the upper and lower surfaces of the piezoelectric crystal sheet, and characterized in that: The upper electrode pair uses an X-shaped electrode and two triangular electrodes one to form a transverse electric field excitation electrode pair; the X-shaped electrode and the lower electrode of the upper electrode pair form a thickness electric field excitation electrode pair; the X-shaped electrode and the lower electrode have the same shape, face each other up and down, and are both composed of two integrally formed triangular electrodes two and a connecting electrode connecting the two triangular electrodes two; the two triangular electrodes one face each other at right angles, and the X-shaped electrode and the two triangular electrodes two in the lower electrode also face each other at right angles; the two right-angled sides of one triangular electrode one face each other at two right-angled sides on one side of the two triangular electrodes two in the X-shaped electrode, and the two right-angled sides of the other triangular electrode one face each other at two right-angled sides on the other side of the two triangular electrodes two in the X-shaped electrode; four electrode gaps are formed between the X-shaped electrode and the two triangular electrodes one; The piezoelectric crystal piece is made of AT-cut quartz crystal.

2. A piezoelectric bulk acoustic wave sensor capable of operating in a hybrid excitation mode according to claim 1, characterized in that: The materials of the upper electrode pair and the lower electrode are gold.

3. A piezoelectric bulk acoustic wave sensor capable of operating in a hybrid excitation mode according to claim 1, characterized in that: The upper electrode pair and the lower electrode are prepared on the upper and lower surfaces of the piezoelectric crystal sheet by evaporation.

4. A piezoelectric bulk acoustic wave sensor capable of operating in a hybrid excitation mode according to claim 1, characterized in that: The triangular electrode 1 and the triangular electrode 2 are both isosceles right triangles, and each angle of the triangular electrode 1 and the triangular electrode 2 is cut flat; The hypotenuse spacing of the two triangular electrodes is l 6 is between 10 and 20 mm, which is the value obtained by subtracting the width of the two sharp angles of the two triangular electrodes from the distance between the hypotenuses of the two triangular electrodes. l 7=0.95 l 6. The distance between the right-angled positions of the two triangular electrodes l 8=0.25 l 6. The distance between the two sharp angles of the triangular electrode l 9=0.6 l 6. The width of the right-angle cut position of the triangular electrode 1 is t3 = 0.08 l 6. The distance between the right angle side of triangular electrode 1 and the right angle side of triangular electrode 2 in the X-shaped electrode is t4=0.1 l 6; The width of the connecting electrode t 1 = 0.9 t 3. Length of connecting electrodes t 2= t 3. Length of the piezoelectric crystal l 1=1.5~1.8 l 6. The distance between the two sharp angles of triangular electrode 2 l 3 = 0.7~0.9 l 6. Width of the piezoelectric crystal l 2=0.8 l 1. The distance between the hypotenuses of the two triangular electrodes in the X-shaped electrode or the lower electrode l 4=0.8~1 l 6. The value obtained by subtracting the width of the two sharp angles of the two triangular electrodes aligned at the flat position from the hypotenuse spacing of the two triangular electrodes in the X-shaped electrode or the lower electrode. l 5=0.9 l 4; The thickness of the piezoelectric crystal sheet h 2 is between 0.4 and 0.4 mm, the thickness of the X-shaped electrode h 3 and the thickness of the lower electrode h 1 are 300 nm.

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