WO2021114493A1

WO2021114493A1 - Thin film bulk acoustic wave sensor for liquid testing

Info

Publication number: WO2021114493A1
Application number: PCT/CN2020/077378
Authority: WO
Inventors: 陈达; 彭杰; 王鹏; 张小军; 邵林; 孟令龙; 李忠丽
Original assignee: 山东科技大学
Priority date: 2019-12-09
Filing date: 2020-03-02
Publication date: 2021-06-17
Also published as: CN110967380B; CN110967380A

Abstract

A thin film bulk acoustic wave sensor for liquid testing, comprising a substrate (101), an acoustic reflection layer (102), a piezoelectric thin film (103), a metal electrode pair (105), and a microfluidic channel (104). The metal electrode pair (105) consists of two metal excitation electrodes (105a, 105b). One of the metal excitation electrodes is located at one side of the piezoelectric thin film (103), and the other is located at the other side of the piezoelectric thin film (103). The microfluidic channel (104) is provided between the piezoelectric thin film (103) and one of the metal excitation electrodes. High frequency electric fields generated by the metal electrode pair (105) can pass through the liquid in the microfluidic channel (104), so that the sensor has strong sensitivity characteristics on electrical properties of the tested liquid such as the conductivity and the dielectric property. Bulk acoustic waves generated by exciting the piezoelectric thin film (103) by the electric fields propagate in the liquid to form resonance in the liquid and directly contact with the tested substance, which facilitates improving the sensitivity of the sensor.

Description

A thin film bulk acoustic wave sensor for liquid detection

Technical field

The invention belongs to the field of piezoelectric resonators and acoustic wave sensing, and relates to a thin-film bulk acoustic wave sensor for liquid detection.

Background technique

In recent years, thin-film bulk acoustic wave sensors have received extensive attention in the fields of radio frequency communication and biochemical sensing. Thin-film bulk acoustic wave sensors can be applied to chemical substance analysis, biological gene detection, protein analysis, and so on.

The thin film bulk acoustic wave sensor is generally composed of a layer of piezoelectric film and upper and lower metal excitation electrodes. The upper and lower metal excitation electrodes are respectively located on the upper and lower surfaces of the piezoelectric film to form a "sandwich" sandwich structure.

The film bulk acoustic wave sensor is based on the principle of high-frequency electroacoustic resonance generated by piezoelectric film. The sensor's resonant frequency, phase or amplitude changes with the detected substance as the sensor's response. The sensitivity of the mass change of the surface adsorption layer can reach the single molecular weight level. Therefore, it has a very broad application prospect. At present, in order to achieve high-throughput online real-time detection of biological substances, it is necessary to set up micro-channels in the thin-film bulk acoustic wave sensor to transport the analysis samples. E.g:

Patent Document 1 discloses a microfluidic channel acoustic wave sensor for liquid detection. By setting the microfluidic channel as a Bragg reflective layer, longitudinal waves are used instead of shear waves to propagate in the liquid to improve the quality factor of the sensor.

Patent Document 2 discloses a piezoelectric thin-film resonant sensor with semi-elliptical micro-channels. By setting the micro-fluidic channel into a semi-elliptical shape, the loss of sound wave energy is reduced to a certain extent, so as to improve the resonance and transmission of the sensor.感性。 Performance.

Non-Patent Document 1 discloses a solution of a thin film bulk acoustic wave sensor in which a micro flow channel is constructed in a silicon substrate under a piezoelectric thin film electrode, in which the micro flow channel is located under the bottom electrode.

Non-Patent Document 2 discloses a scheme in which AlN is used as a microfluidic framework above the piezoelectric film electrode.

Prior art literature

Patent literature

Patent Document 1 Publication Number: CN109870504A, Publication Date: June 11, 2019.

Patent document 2 publication number: CN103234562A, publication date: August 7, 2013.

Non-patent literature

Non-Patent Document 1 The article “AlN-based sputter-deposited shear mode thin film bulk acoustic receiver (FBAR) for Surface&Coatings Technology (surface and coating technology) 2010 Vol. biosensor applications-A review".

Non-Patent Document 2 The article “On-chip nanofluidic integration of acoustic sensors towards high” by Ji Liang et al., State Key Laboratory of Precision Measurement Technology and Instruments, Tianjin University, in Applied Physics Letters, Vol. 111, Issue 20, 2017 Q in liquid".

Summary of the invention

technical problem

By reading the prior art documents, the inventor found that the microfluidic channels for transporting the test liquid in the above device structures are all located outside the resonant structure composed of the piezoelectric film and the upper and lower metal excitation electrodes.

The thin film bulk acoustic wave sensor with this structure has the following two problems when detecting liquids:

1. The excitation electric field generated by the upper and lower metal excitation electrodes only exists in the piezoelectric film. Because the excitation electric field cannot enter the microfluidic channel, the resonance characteristics of the thin film bulk acoustic wave sensor cannot be sensitive to the electrical properties of the test liquid;

2. The bulk acoustic wave generated by the piezoelectric film needs to pass through the metal excitation electrode before entering the test liquid. Because the two sides of the metal excitation electrode through which the bulk acoustic wave passes are solid and liquid interfaces, when the bulk acoustic wave passes through the metal excitation The large reflection and loss of the electrode are not conducive to the improvement of the sensing sensitivity and the improvement of the quality factor of the sensor.

The solution to the problem

Technical solutions

One of the objectives of the present invention is to provide a thin film bulk acoustic wave sensor for liquid detection, so that the sensor has a strong sensitivity to the electrical properties of the liquid being measured, and at the same time, it is beneficial to improve the sensitivity of the sensor to the liquid being measured.

In order to achieve the above objective, the present invention adopts the following technical solutions:

A thin film bulk acoustic wave sensor for liquid detection, including:

Substrate, acoustic reflection layer, metal electrode pair, piezoelectric film and microfluidic channel;

The metal electrode pair is composed of two metal excitation electrodes, namely the first metal excitation electrode and the second metal excitation electrode;

The acoustic reflection layer is arranged on one side surface of the substrate;

The No. 1 metal excitation electrode is arranged on the surface of the acoustic reflection layer away from the substrate;

The piezoelectric film is arranged on the surface of the No. 1 metal excitation electrode away from the substrate;

The No. 2 metal excitation electrode is located on the side of the piezoelectric film away from the substrate;

The microfluidic channel is located between the piezoelectric film and the second metal excitation electrode, and the surface of the microfluid channel close to the substrate is in contact with the piezoelectric film, and the surface away from the substrate is in contact with the second metal excitation electrode.

Preferably, there is at least one metal excitation electrode in the metal electrode pair, the width of the metal excitation electrode is less than or equal to the width of the microfluidic channel, and the length of the metal excitation electrode is less than or equal to the length of the microfluidic channel.

Preferably, the length of the microfluidic channel is 1/2 to 1 times the length of the piezoelectric film, the width of the microfluidic channel is 2/3 to 1 times the width of the piezoelectric film, and the thickness of the microfluidic channel is the thickness of the piezoelectric film 1 to 2 times as much.

Preferably, the substrate is made of monocrystalline silicon, quartz, gallium arsenide or sapphire; the acoustic reflection layer adopts a diaphragm structure, an air gap structure, or a Bragg structure composed of alternate layers with different periodic acoustic impedances. ；

The piezoelectric film is doped by any one of aluminum nitride, zinc oxide and lead zirconate titanate film, or at least two of aluminum nitride, zinc oxide and lead zirconate titanate film as a matrix. Made of composite piezoelectric film material.

Preferably, the microfluidic channel is made of polydimethylsiloxane and manufactured by nanoimprinting or soft photolithography.

The second objective of the present invention is to provide a thin film bulk acoustic wave sensor with a different structure from the above-mentioned structure, which can also have strong sensitivity to the electrical properties of the liquid being measured, and at the same time improve the sensitivity of the sensor to the liquid being measured.

A thin film bulk acoustic wave sensor for liquid detection, including:

The acoustic reflection layer is arranged on one side surface of the substrate;

The piezoelectric film is located on the side of the No. 1 metal excitation electrode away from the substrate;

The microfluidic channel is located between the first metal excitation electrode and the piezoelectric film, and the surface of the microfluid channel close to the substrate is in contact with the first metal excitation electrode, and the surface away from the substrate is in contact with the piezoelectric film;

The No. 2 metal excitation electrode is arranged on the side surface of the piezoelectric film away from the substrate.

The beneficial effects of the invention

Beneficial effect

As described above, the present invention proposes a thin film bulk acoustic wave sensor for liquid detection. The sensor includes a substrate, an acoustic reflection layer, a piezoelectric film, a metal electrode pair, and a microfluidic channel. The metal electrode pair is composed of two metal excitation electrodes. Composition, one of the metal excitation electrodes is located on one side of the piezoelectric film, the other metal excitation electrode is located on the other side of the piezoelectric film, and the microfluidic channel is set between the piezoelectric film and one of the metal excitation electrodes (ie, the piezoelectric film It is separated from the metal excitation electrode by the liquid), the high-frequency electric field generated by the metal electrode pair can pass through the liquid in the microfluidic channel, so that the sensor has a strong sensitivity to the electrical properties of the tested liquid, such as electrical conductivity and dielectric properties. . In addition, the bulk acoustic wave generated by the piezoelectric film can propagate in the liquid to form a resonance, and directly contact the liquid to be tested, which is beneficial to improve the sensitivity of the sensor.

Brief description of the drawings

Description of the drawings

Figure 1 is a front view of a thin film bulk acoustic wave sensor for liquid detection in Embodiment 1 of the present invention;

2 is a top view of the thin film bulk acoustic wave sensor used for liquid detection in Embodiment 1 of the present invention;

3 is a simulation diagram of admittance characteristics when a 30% glycerin solution is passed through in Example 1 of the present invention;

4 is a front view of a thin film bulk acoustic wave sensor for liquid detection in Embodiment 2 of the present invention;

5 is a top view of a thin film bulk acoustic wave sensor for liquid detection in Embodiment 2 of the present invention;

Fig. 6 is a simulation diagram of admittance characteristics when a 30% concentration glycerin solution is passed through in Example 2 of the present invention.

FIG. 7 is an equivalent circuit diagram of a thin film bulk acoustic wave sensor for liquid detection in Embodiment 1 of the present invention.

Among them, 101-substrate, 102-acoustic reflection layer, 103-piezoelectric film, 104-microfluidic channel, 105-metal electrode pair, 105a-number one metal excitation electrode, 105b-number two metal excitation electrode.

Invention embodiment

Embodiments of the present invention

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

Example 1

As shown in Figures 1 and 2, this embodiment 1 describes a thin film bulk acoustic wave sensor for liquid detection, which includes a substrate 101, an acoustic reflection layer 102, a piezoelectric film 103, a microfluidic channel 104, and a metal electrode. That's 105.

The metal electrode pair 105 is composed of two metal excitation electrodes, namely the first metal excitation electrode 105a and the second metal excitation electrode 105b. The two metal excitation electrodes preferably both use aluminum (Al) electrodes, gold (Au) electrodes, or the like.

The connection relationship between the components of the film bulk acoustic wave sensor is as follows:

The acoustic reflection layer 102 is disposed on one side surface of the substrate 101, such as the upper surface of the substrate 101 shown in FIG. 1.

The first metal excitation electrode 105a is disposed on the surface of the acoustic reflection layer 102 away from the substrate 101, and the side surface is, for example, the upper surface of the acoustic reflection layer 102 shown in FIG. 1.

The piezoelectric film 103 is disposed on the surface of the first metal excitation electrode 105a away from the substrate 101, and the side surface is, for example, the upper surface of the first metal excitation electrode 105a shown in FIG. 1.

The second metal excitation electrode 105b is located on the side of the piezoelectric film 103 away from the substrate 101, and this side is, for example, the upper side of the piezoelectric film 103 shown in FIG. 1. The microfluidic channel 104 is located between the piezoelectric film 103 and the second metal excitation electrode 105b.

The surface of the microfluidic channel 104 close to the substrate (that is, the lower surface of the microfluidic channel 104) is in contact with the piezoelectric film, and the surface of the microfluidic channel 104 away from the substrate (that is, the upper surface of the microfluidic channel 104) is in contact with the No. 2 metal excitation electrode 105b contact.

The principle that the thin film bulk acoustic wave sensor in the first embodiment is highly sensitive to the electrical conductivity and dielectric properties of the liquid being tested is as follows:

In the conventional thin film bulk acoustic wave sensor with microfluidic channels, the microfluidic channel is arranged outside the resonant structure composed of a metal electrode pair and a piezoelectric film. The electric field cannot enter the liquid of the microfluidic channel, which results in the resonance characteristics of the thin film bulk acoustic wave sensor It is not sensitive to the electrical properties of the test liquid.

The difference between this embodiment 1 and the conventional structure is that the microfluidic channel is arranged inside the resonant structure composed of a pair of metal electrodes and a piezoelectric film, specifically between the piezoelectric film 103 and the second metal excitation electrode 105b, the piezoelectric film 103 and the second metal excitation electrode 105b are separated by the liquid in the microfluidic channel 104. The high-frequency electric field generated by the metal electrode pair 105 can pass through the liquid in the microfluidic channel. So there is a strong sensitivity.

The process of using the above-mentioned thin film bulk acoustic wave sensor to solve the electrical conductivity of the tested liquid will be described as an example.

A piezoelectric resonator is an electromechanical transducer, which can be expressed as a coupling between the mechanical end and the electrical end under no load. When the electrode passes through the liquid, it will be subjected to the synergistic effect of the mechanical acoustic load of the liquid and the dielectric loss.

Under no-load conditions, the density and viscosity of the liquid affect the mechanical end of the piezoelectric resonator. When the electrode passes through the liquid, it is related to the conductivity and permittivity of the liquid and reacts to the electrical end of the piezoelectric resonator. .

The equivalent circuit diagram in this embodiment 1 is shown in Figure 7. The high-frequency electric field generated by the metal electrode pair 105 is _{applied to the piezoelectric film 103 through the series solution R s} and C _s , so the equivalent circuit parameters of the piezoelectric film 103 and the solution are The nature is closely related.

To measure the electrical properties of the liquid, first connect the thin film bulk acoustic wave sensor with an impedance analyzer with a high-frequency test frame, and scan the admittance within the resonance range to obtain the admittance B _m and the series resonance corresponding to the admittance B _m Frequency f _s .

_{The relationship between the resonance frequency f s} and the property parameters of the solution is calculated according to the following formula.

Among them, the resonance frequency shift Δf caused by the conductivity κ of the solution is:

Among them, f ₀ is the resonant frequency of the sensor when there is no load, and the expression of _{f 0 is:}

In the formula, G = 1/R _s =kκ, k is the conductivity cell constant, L _q , C _q , R _q , and C ₀ are the dynamic capacitance, inductance, resistance and static capacitance of the piezoelectric film 103 respectively, R _s , C _s is the resistance and capacitance of the solution respectively.

According to the above formula, the conductivity of the liquid in the microfluidic channel 104 is obtained.

The principle of improving the sensitivity of the thin-film bulk acoustic wave sensor to the tested liquid in the first embodiment is as follows:

In a conventional thin film bulk acoustic wave sensor with microfluidic channels, the microfluidic channel is arranged outside a resonant structure composed of a metal electrode pair and a piezoelectric film, and the bulk acoustic wave generated by the piezoelectric film needs to pass through the metal excitation electrode before entering the test liquid. The two sides of the metal excitation electrode through which the bulk acoustic wave passes are respectively solid and liquid interfaces. Therefore, when the bulk acoustic wave passes through the metal excitation electrode, there is greater reflection and loss, which is not conducive to the improvement of the sensing sensitivity.

The difference between this embodiment 1 and the conventional structure is that the microfluidic channel is arranged inside the resonant structure composed of a pair of metal electrodes and a piezoelectric film, specifically between the piezoelectric film 103 and the second metal excitation electrode 105b, the pair of metal electrodes The high-frequency electric field generated by 105 excites the piezoelectric film 103 to generate a bulk acoustic wave. The bulk acoustic wave does not need to pass through the metal excitation electrode to enter the test liquid, but can directly contact the test liquid, thus effectively avoiding the generation of bulk acoustic waves when passing through the metal excitation electrode. Larger reflection and loss will help improve the sensitivity of the sensor to the liquid being tested.

In a preferred manner, the substrate 101 is made of single crystal silicon (Si), quartz, gallium arsenide or sapphire.

In a preferred manner, the acoustic reflection layer 102 adopts a diaphragm structure, an air gap structure, or a Bragg structure composed of alternately formed film layers with different periodic acoustic impedances.

In a preferred manner, the piezoelectric film 103 is made of any one of aluminum nitride (AlN), zinc oxide (ZNO) and lead zirconate titanate (PZT) films, or aluminum nitride (AlN), zinc oxide ( At least two of the ZNO) and lead zirconate titanate (PZT) films are made of composite piezoelectric film materials made by doping the matrix.

In a preferred manner, the microfluidic channel 104 is made of a thermoplastic polymer material such as polydimethylsiloxane (PDMS), and is manufactured by a nanoimprinting process or a soft lithography process.

In addition, in order to ensure that all the electric fields excited by the metal electrode pair 105 can pass through the liquid in the microfluidic channel 104, a metal excitation electrode far from the substrate 101, that is, the width of the second metal excitation electrode 105b is less than or equal to that of the microfluidic channel 104 The width of the metal excitation electrode is less than or equal to the length of the microfluidic channel 104, as shown in FIG. 2.

At this time, all the electric fields excited by the metal electrode pair 105 can pass through the liquid in the microfluidic channel 104.

Of course, it is also possible to design the width of the first metal excitation electrode 105a to be less than or equal to the width of the microfluidic channel 104, and the length of the first metal excitation electrode 105a to be less than or equal to the length of the microfluidic channel 104.

At this time, all the electric fields excited by the metal electrode pair 105 can also pass through the liquid in the microfluidic channel 104.

Of course, the width and length of the first metal excitation electrode 105a and the second metal excitation electrode 105b can also be designed to satisfy the above relationship, so as to ensure that all the electric fields excited by the metal electrode pair 105 can pass through the liquid in the microfluidic channel 104.

In addition, in order to ensure that the thin-film bulk acoustic wave sensor in the first embodiment has a higher resonant frequency, the first embodiment also has a reasonable design for the structural size of the microfluidic channel 104, namely:

The length of the microfluidic channel 104 is 1/2 to 1 times the length of the piezoelectric film 103, and more preferably, the length of the microfluidic channel 104 is 2/3 times the length of the piezoelectric film 103.

The width of the microfluidic channel 104 is 2/3 to 1 times the width of the piezoelectric film 103, and more preferably, the width of the microfluidic channel 104 is 3/4 times the width of the piezoelectric film 103.

The thickness of the microfluidic channel 104 is 1 to 2 times the thickness of the piezoelectric film 103, and more preferably, the width of the microfluidic channel 104 is 3/2 times the width of the piezoelectric film 103.

Wherein, the length direction of the microfluidic channel 104 is, for example, the left and right direction shown in FIG. 1, the width direction is, for example, the front and back direction shown in FIG. 1 (that is, the direction perpendicular to the paper), and the thickness direction is shown in FIG. Up and down direction shown.

The purpose of setting the length and width ratio of the microfluidic channel 104 to the piezoelectric film 103 is to ensure that the area of the microfluidic channel 104 is smaller than the area of the piezoelectric film 103 (that is, length×width), so that the entire liquid area is covered on the piezoelectric film On 103, if the area of the microfluidic channel 104 is larger than that of the piezoelectric film 103, the liquid to be detected will be wasted.

The thickness ratio between the microfluidic channel 104 and the piezoelectric film 103 is an optimized parameter obtained through simulation. If the microfluidic channel 104 is too thick (for example, the thickness of the microfluidic channel 104 exceeds twice the thickness of the piezoelectric film 103), it will cause the electric field to reduce the degree of excitation of the piezoelectric film 103. If the thickness of the microfluidic channel 104 is too thin (for example, The thickness of the microfluidic channel 104 is less than 1 times the thickness of the piezoelectric film 103), it is difficult to realize in the manufacturing process.

In summary, when the thickness of the microfluidic channel 104 is designed to be 1 to 2 times the thickness of the piezoelectric film 103, it is ensured that the electric field has a good excitation effect on the piezoelectric film 103 and that the microfluidic channel 104 is easier to realize in the manufacturing process.

The thin film bulk acoustic wave sensor in the first embodiment can be used to detect liquid characteristics, such as viscosity and electrical characteristics including conductivity and permittivity. At this time, the surface of the metal excitation electrode remains empty.

Of course, the thin film bulk acoustic wave sensor in this embodiment 1 can also be used to detect trace substances in liquid. At this time, when a metal excitation electrode far away from the substrate 101 (ie, the second metal excitation electrode 105b) is in contact with the microfluidic channel 104 The side surface assembly can absorb sensitive substances of the detection substance, such as corresponding antibodies/antigens, DNA, aptamers, etc.

When in use, the metal electrode pair 105 is connected to an oscillating circuit or an impedance analyzer, and the quality sensitivity of the adsorbent is measured by measuring the resonance frequency, phase or amplitude of the thin-film bulk acoustic wave sensor.

This embodiment 1 also provides a specific example to illustrate that the above-mentioned thin film bulk acoustic wave sensor has high sensitivity.

Among them, the parameters of each constituent structure in this specific example are selected as follows:

The substrate 101 is a silicon (100) wafer.

The acoustic reflection layer 102 is _{a diaphragm structure with Si 3} N ₄ as a support layer, and the part below the resonance region is etched to form a solid-gas interface to reflect sound waves. _{The thickness of the Si 3} N ₄ layer is 800 nanometers.

The piezoelectric film 103 is an aluminum nitride (AlN) film with a thickness of 1 micrometer, a length of 100 micrometers, and a width of 60 micrometers.

The metal electrode pair 105 is an aluminum (Al) electrode.

The material of the microfluidic channel 104 is polydimethylsiloxane (PDMS).

The microfluidic channel 104 is arranged on the side of the piezoelectric film 103 away from the substrate 101, that is, between the piezoelectric film 103 and the second metal excitation electrode 105b. The piezoelectric film 103 and the second metal excitation electrode 105 are in the microfluidic channel 104 The liquid is separated by the second metal excitation electrode 105 and the piezoelectric film 103 at the same time.

A metal electrode pair 105 consisting of the first metal excitation electrode 105a on one side of the piezoelectric film 103 (for example, the lower side of the piezoelectric film 103 in FIG. 1) and the second metal excitation electrode 105b on the other side of the piezoelectric film 103 An electric field passing through the liquid in the microfluidic channel 104 is generated. A bulk acoustic wave propagating in the thickness direction is excited in the piezoelectric film 103, and the bulk acoustic wave propagates in the range including the piezoelectric film 103 and the liquid in the microfluidic channel 104 and forms a standing wave resonance.

When in use, a liquid sample to be measured is passed into the microfluidic channel 104. Fig. 3 is a simulation diagram of admittance characteristics when a glycerin solution with a concentration of 30% is passed through in Example 1. It can be seen from FIG. 3 that the thin film bulk acoustic wave sensor in this embodiment 1 has obvious resonance near 3.32 GHz. The simulated admittance characteristics of the conventional thin-film bulk acoustic wave sensor with the same structural parameters are also shown in this figure, and its resonance frequency is only 2.81 GHz, which is significantly lower than the resonance frequency in the first embodiment.

Since the quality sensitivity of the sensor in this embodiment 1 increases as its resonance frequency increases, the higher resonance frequency obtained in this embodiment 1 has higher quality sensitivity performance. At the same time, compared with the existing conventional thin-film bulk acoustic wave sensor, the admittance peak obtained in Example 1 is significantly wider, indicating that this structure can better reflect the electrical characteristics of the tested liquid.

Example 2

The second embodiment also describes a thin-film bulk acoustic wave sensor for liquid detection. The sensor is different from the above-mentioned embodiment 1 except for the following technical features, and the rest of the technical features can be referred to the above-mentioned embodiment 1.

As shown in Figures 4 and 5, this embodiment 2 provides a thin film bulk acoustic wave sensor with a structure different from that in the above embodiment 1, which includes a substrate 101, an acoustic reflection layer 102, a piezoelectric film 103, and a microfluidic channel 104 And a pair of metal electrodes 105.

The metal electrode pair 105 includes a first metal excitation electrode 105a and a second metal excitation electrode 105b.

The acoustic reflection layer 102 is disposed on one side surface of the substrate 101, such as the upper surface of the substrate 101 shown in FIG. 4.

The No. 1 metal excitation electrode 105a is disposed on a side surface of the acoustic reflection layer 102 away from the substrate 101, and the side surface is, for example, the upper surface of the acoustic reflection layer 102 shown in FIG. 1.

The piezoelectric film 103 is located on the side of the first metal excitation electrode 105a away from the substrate 101, such as the upper side of the first metal excitation electrode 105a in FIG. 1, and the microfluidic channel 104 is located between the first metal excitation electrode 105a and the piezoelectric film 103 .

The surface of the microfluidic channel 104 close to the substrate (that is, the lower surface of the microfluidic channel 104) is in contact with the No. 1 metal excitation electrode 105a, and the surface of the microfluidic channel 104 away from the substrate (that is, the upper surface of the microfluidic channel 104) is in contact with the piezoelectric The film 103 is in contact.

The second metal excitation electrode 105b is disposed on the surface of the piezoelectric film 103 away from the substrate 101, for example, on the upper surface of the piezoelectric film 103 shown in FIG. 4.

The principle that the thin-film bulk acoustic wave sensor in the second embodiment is highly sensitive to the electrical conductivity and dielectric properties of the liquid being tested is as follows:

The difference between this embodiment 2 and the conventional structure is that the microfluidic channel is arranged inside the resonant structure composed of a pair of metal electrodes and a piezoelectric film, specifically between the first metal excitation electrode 105a and the piezoelectric film 103, and the first metal The excitation electrode 105a and the piezoelectric film 103 are separated by the liquid in the microfluidic channel 104. The high-frequency electric field generated by the metal electrode pair 105 can pass through the liquid in the microfluidic channel. Strong sensitivity.

The principle of improving the sensitivity of the thin film bulk acoustic wave sensor to the liquid under test in the second embodiment is as follows:

A conventional thin film bulk acoustic wave sensor with a microfluidic channel, the microfluidic channel is arranged on the outside of a resonant structure composed of a metal electrode pair and a piezoelectric film. The bulk acoustic wave generated by the piezoelectric film needs to pass through the metal excitation electrode before entering the test liquid. Since the two sides of the metal excitation electrode through which the bulk acoustic wave passes are solid and liquid interfaces, there are large reflections and losses when the bulk acoustic wave passes through the metal excitation electrode, which is not conducive to the improvement of the sensing sensitivity.

This embodiment 2 differs from the conventional structure in that the microfluidic channel is arranged inside the resonant structure composed of a pair of metal electrodes and a piezoelectric film, specifically between the No. 1 metal excitation electrode 105a and the piezoelectric film 103, the pair of metal electrodes The high-frequency electric field generated by 105 excites the piezoelectric film 103 to generate a bulk acoustic wave. The bulk acoustic wave does not need to pass through the metal excitation electrode to enter the test liquid, but can directly contact the test liquid, thus effectively avoiding the generation of bulk acoustic waves when passing through the metal excitation electrode. Larger reflection and loss, which helps to improve the sensor's sensitivity to the liquid being tested.

The thin-film bulk acoustic wave sensor in the second embodiment can be used to detect liquid characteristics, such as viscosity and electrical characteristics including conductivity and permittivity. At this time, the surface of the metal excitation electrode remains empty.

Of course, the thin-film bulk acoustic wave sensor in this embodiment 2 can also be used to detect trace substances in liquid. At this time, a metal excitation electrode near the substrate 101 (ie, the first metal excitation electrode 105a) is in contact with the microfluidic channel 104. The side surface assembly can absorb sensitive substances of the detection substance, such as corresponding antibodies/antigens, DNA, aptamers, etc.

The second embodiment also provides a specific example to illustrate that the above-mentioned thin film bulk acoustic wave sensor has high sensitivity.

Among them, the parameters of each composition structure in this specific example are selected as follows: the substrate 101 is a silicon (100) wafer.

The acoustic reflection layer 102 is composed of a film layer of silicon dioxide (SiO ₂ ) and tungsten (W) alternating for 3 periods, wherein the _{thickness of silicon dioxide (SiO 2} ) is 0.8 μm, and the thickness of tungsten (W) is 0.9 μm.

The piezoelectric film 103 is a zinc oxide (ZnO) film with a thickness of 2 micrometers, a length of 100 micrometers, and a width of 60 micrometers.

The metal electrode pair 105 is provided as a gold (Au) electrode.

The material of the microfluidic channel 104 is polydimethylsiloxane (PDMS).

The microfluidic channel 104 is arranged on the side of the piezoelectric film 103 close to the substrate 101, that is, between the first metal excitation electrode 105a and the piezoelectric film 103, the piezoelectric film 103 and the first metal excitation electrode 105a are in the microfluidic channel 104 Spaced by the liquid, the liquid is in contact with the No. 1 metal excitation electrode 105a and the piezoelectric film 103 at the same time.

A metal electrode pair 105 consisting of the first metal excitation electrode 105a on one side of the piezoelectric film 103 (for example, the lower side of the piezoelectric film 103 in FIG. 4) and the second metal excitation electrode 105b on the other side of the piezoelectric film 103 An electric field passing through the liquid in the microfluidic channel 104 is generated, and the bulk acoustic wave propagating in the thickness direction is excited in the piezoelectric film 103. The bulk acoustic wave propagates in the range including the piezoelectric film 103 and the liquid in the microfluidic channel 104 and A standing wave resonance is formed.

When in use, a liquid sample to be measured is passed into the microfluidic channel. FIG. 6 is a simulation diagram of admittance characteristics when a glycerin solution with a concentration of 30% is passed through in Example 2. FIG. It can be seen from FIG. 6 that the thin-film bulk acoustic wave sensor in the second embodiment has obvious resonance near 1.78 GHz. The simulated admittance characteristics of a conventional thin-film bulk acoustic wave sensor with the same structural parameters are also shown in this figure, and its resonance frequency is only 1.61 GHz, which is significantly lower than the resonance frequency in the second embodiment.

Since the quality sensitivity of the sensor in the second embodiment increases as its resonance frequency increases, the higher resonance frequency obtained in the second embodiment has a higher quality sensitivity performance. At the same time, compared with the existing conventional thin-film bulk acoustic wave sensor, the admittance peak obtained in Example 2 is significantly wider, indicating that this structure can better reflect the electrical characteristics of the tested liquid.

Of course, the above description is only the preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments. It should be noted that any person skilled in the art can make all equivalent substitutions under the teaching of this specification. The obvious deformation forms fall within the essential scope of this specification and should be protected by the present invention.

Claims

A thin film bulk acoustic wave sensor for liquid detection, which is characterized in that:

Including substrate, acoustic reflection layer, metal electrode pair, piezoelectric film and microfluidic channel;

The metal electrode pair is composed of two metal excitation electrodes, namely, the first metal excitation electrode and the second metal excitation electrode;

The acoustic reflection layer is arranged on one side surface of the substrate;

The No. 1 metal excitation electrode is arranged on the surface of the acoustic reflection layer away from the substrate;

The piezoelectric film is arranged on the surface of the first metal excitation electrode away from the substrate;

The No. 2 metal excitation electrode is located on the side of the piezoelectric film away from the substrate;

The microfluidic channel is located between the piezoelectric film and the second metal excitation electrode, and the surface of the microfluid channel close to the substrate is in contact with the piezoelectric film, and the surface away from the substrate is in contact with the second metal excitation electrode contact.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 1, wherein:

There is at least one metal excitation electrode in the metal electrode pair, the width of the metal excitation electrode is less than or equal to the width of the microfluidic channel, and the length of the metal excitation electrode is less than or equal to the length of the microfluidic channel.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 1, wherein:

The length of the microfluidic channel is 1/2 to 1 times the length of the piezoelectric film, the width of the microfluidic channel is 2/3 to 1 times the width of the piezoelectric film, and the thickness of the microfluidic channel is the piezoelectric film 1 to 2 times the thickness.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 1, wherein:

The substrate is made of monocrystalline silicon, quartz, gallium arsenide, or sapphire; the acoustic reflection layer adopts a Bragg structure composed of a diaphragm structure, an air gap structure, or alternately composed film layers with different periodic acoustic impedances. structure;

The piezoelectric film is doped by any one of aluminum nitride, zinc oxide, and lead zirconate titanate films, or at least two of aluminum nitride, zinc oxide, and lead zirconate titanate films as a matrix. It is made of composite piezoelectric film material.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 1, wherein:

The microfluidic channel is made of polydimethylsiloxane by a nanoimprint process or a soft photolithography process.
A thin film bulk acoustic wave sensor for liquid detection, which is characterized in that:

Including substrate, acoustic reflection layer, metal electrode pair, piezoelectric film and microfluidic channel;

The metal electrode pair is composed of two metal excitation electrodes, namely, the first metal excitation electrode and the second metal excitation electrode;

The acoustic reflection layer is arranged on one side surface of the substrate;

The No. 1 metal excitation electrode is arranged on the surface of the acoustic reflection layer away from the substrate;

The piezoelectric film is located on the side of the No. 1 metal excitation electrode away from the substrate;

The microfluidic channel is located between the first metal excitation electrode and the piezoelectric film, and the surface of the microfluid channel close to the substrate is in contact with the first metal excitation electrode, and the surface away from the substrate is in contact with the piezoelectric film contact;

The No. 2 metal excitation electrode is arranged on the side surface of the piezoelectric film away from the substrate.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 6, wherein:

There is at least one metal excitation electrode in the metal electrode pair, the width of the metal excitation electrode is less than or equal to the width of the microfluidic channel, and the length of the metal excitation electrode is less than or equal to the length of the microfluidic channel.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 6, wherein:

The length of the microfluidic channel is 1/2 to 1 times the length of the piezoelectric film, the width of the microfluidic channel is 2/3 to 1 times the width of the piezoelectric film, and the thickness of the microfluidic channel is the piezoelectric film 1 to 2 times the thickness.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 6, wherein:

The substrate is made of monocrystalline silicon, quartz, gallium arsenide, or sapphire; the acoustic reflection layer adopts a diaphragm structure, an air gap structure, or a Bragg structure composed of alternate film layers with different periodic acoustic impedances ；

The piezoelectric film is doped by any one of aluminum nitride, zinc oxide, and lead zirconate titanate films, or at least two of aluminum nitride, zinc oxide, and lead zirconate titanate films as a matrix. It is made of composite piezoelectric film material.
The thin-film bulk acoustic wave sensor for liquid detection according to claim 6, wherein:

The microfluidic channel is made of polydimethylsiloxane by a nanoimprint process or a soft photolithography process.