A solid-state assembled micro-mass sensor with all-metal structure and a preparation method thereof

Abstract

The application discloses a full-metal structure solid-state assembled micro-mass sensor and a preparation method thereof. The sensor comprises a substrate, a Bragg reflection layer, a lower electrode layer, a piezoelectric layer, an insulating layer and an upper electrode layer. The full-metal solid-state assembled micro-mass sensor is constructed by adopting six or eight Bragg reflection layers. The micro-mass sensor can work in the frequency domain and the change of the frequency domain is between 2.28GHz and 2.25GHz by changing the thickness of the upper electrode to simulate the change of the mass load. Meanwhile, the structure design of the application has simple overall process. The ingenious cooperation of the insulating layer, the piezoelectric layer and the upper electrode layer can prevent the faults caused by the slope difference during the deposition, increase the voltage standing wave ratio caused by the change of the thickness and affect the characteristic impedance value, prevent the short circuit of the upper and lower electrodes and affect the measurement, reduce the mass defects, avoid the parasitic effect caused by the excessively large piezoelectric layer and improve the precision and sensitivity of the sensor in the field of the micro-mass sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of full metal structure solid-state assembly type micro mass sensor and its preparation method, belong to micro mass sensor technical field. BACKGROUND

[0002] Traditional mass sensor is roughly divided into two kinds, one sensor is based on quartz crystal thickness shear wave mode work, limited to the process level of quartz crystal, cannot be made very thin wafer, leading to its sensor sensitivity is not high.Another sensor is based on surface acoustic wave work, using voltage base on interdigital transducer to receive the signal to be measured and convert it into the change of device resonant frequency, mass sensitivity mainly depends on the width of interdigital electrode, although high precision, but complex process let people step back, and the sensing area of this sensor is large, not suitable for the mass change of small area.

[0003] Limited by other process technology and preparation difficulty, how to prepare the mass sensor with high precision, high sensitivity, suitable for a variety of environment becomes the problem that needs to be solved urgently at present. SUMMARY

[0004] The present application provides a kind of full metal structure solid-state assembly type micro mass sensor and its preparation method, to be used for by reasonable composition and connection build full metal structure solid-state assembly type micro mass sensor, and for realizing the preparation of full metal structure solid-state assembly type micro mass sensor.

[0005] The technical scheme of the present application is: a kind of full metal structure solid-state assembly type micro mass sensor, including substrate 1, Bragg reflection layer 2, lower electrode layer 3, piezoelectric layer 4, insulating layer 5, upper electrode layer 6;Wherein, Bragg reflection layer 2 is arranged on substrate 1, Bragg reflection layer 2 is provided with lower electrode layer 3, piezoelectric layer 4, insulating layer 5, and lower electrode layer 3 is located between Bragg reflection layer 2 and piezoelectric layer 4, insulating layer 5 is close to piezoelectric layer 4 side away from lower electrode layer 3 and is same height with piezoelectric layer 4, upper electrode layer 6 is set on piezoelectric layer 4 and insulating layer 5, and upper electrode layer 6 is not in the same layer with lower electrode layer 3.

[0006] The Bragg reflection layer 2 is a full metal Bragg reflection layer, which is composed of 3-4 reflection groups, each reflection group is composed of two impedance layers, one high acoustic impedance layer and one low acoustic impedance layer.

[0007] The lower electrode layer 3 and the upper electrode layer 6 have basically the same structure, and are each composed of an effective piezoelectric region, a lead region and a pad region of irregular pentagons connected in sequence.

[0008] The piezoelectric layer 4 is deposited on the lower electrode layer 3, and the effective piezoelectric region and a part of the lead region of the lower electrode layer 3 are covered by the piezoelectric layer 4.

[0009] The material of the substrate 1 is Si, the surface roughness of the Bragg reflection layer 2 for deposition is less than 10 nm; the material of the high acoustic impedance layer in the Bragg reflection layer 2 is W, the thickness of each high acoustic impedance layer is 530 nm, the material of the low acoustic impedance layer is Al, the thickness of each low acoustic impedance layer is 628 nm; the material of the lower electrode layer 3 and the upper electrode layer 6 is Al, the effective piezoelectric area of the irregular pentagon of the two is 20150 nm, the thickness of the lower electrode layer 3 is 150 nm, the thickness of the upper electrode layer 6 is 150-200 nm; the material of the piezoelectric layer 4 is AlN; the thickness is in the range of 1000 nm; the material of the insulating layer 5 is insulating material, and the thickness is the same as that of the piezoelectric layer 4.

[0010] According to another aspect of the embodiment of the present application, a preparation method of a full-metal solid-state assembled micro-mass sensor is provided, comprising:

[0011] depositing a full-metal Bragg reflection layer 2 on the substrate 1;

[0012] depositing a lower electrode layer 3 on the Bragg reflection layer 2;

[0013] depositing a piezoelectric layer 4 on the lower electrode layer 3 and the Bragg reflection layer 2;

[0014] depositing an insulating layer 5 close to the piezoelectric layer 4 away from the lower electrode layer 3;

[0015] depositing an upper electrode layer 6 on the piezoelectric layer 4 and the insulating layer 5.

[0016] The substrate 1 is a single crystal silicon with one polished surface, the resistivity is 1-10 Ω·cm, and the surface roughness of the polished surface is less than 10 nm; the single crystal silicon is cleaned using standard RCA; after the single crystal silicon surface is dried by blowing nitrogen, the single crystal silicon is baked from room temperature to 100℃ in an oven; wherein the baking is divided into two stages: the heating stage and the constant temperature stage; the time ratio of the heating stage to the constant temperature stage is 5:1, the heating stage refers to the stage of rising from room temperature to 100℃, and the constant temperature stage refers to the stage of keeping 100℃; the total baking time is 20-30 min.

[0017] The deposition of the full-metal Bragg reflection layer 2 on the substrate 1 comprises: using a physical magnetron sputtering system to first deposit a layer of thickness 530 A high acoustic impedance thin film W, a pure W target material with a purity of 99.95% is selected, a radio frequency power of 60 W is set, a sputtering pressure of 1.2 Pa is set, a substrate temperature of room temperature water cooling is set, and an argon gas flow of 20 Sccm is set after the deposition is completed, and then a low acoustic impedance thin film Al with a thickness of 628 A low acoustic impedance thin film Al, a pure Al target material with a purity of 99.99% is selected, a radio frequency power of 300 W is set, a sputtering pressure of 0.5 Pa is set, a substrate temperature of room temperature water cooling is set, and an argon gas flow of 20 Sccm is set; the above steps are repeated to prepare a Bragg reflection layer with 3-4 groups of reflection groups;

[0018] The deposition of the lower electrode layer 3 on the Bragg reflection layer 2 includes: first, the prepared Bragg reflection layer 2 is subjected to adhesion treatment using an HDMS liquid, and a layer of photoresist with a thickness of 1 um is uniformly spin-coated on the surface of the entire Bragg reflection layer 2; after the spin-coating is completed, a pre-baking treatment is performed; exposure is performed under the pattern of the corresponding lower electrode mask; the required lower electrode pattern is developed using a developing solution; before the magnetron sputtering, whether the developed pattern has defects is observed: if there are defects, the photoresist on the sample is cleaned, and the above steps are repeated until it is qualified; after the development is qualified, a hardening process is performed, the sample is cleaned using deionized water, and then the cleaned sample is placed in an oven for baking; after the baking is completed, the lower electrode thin film is deposited, the radio frequency power of the magnetron sputtering system is set to 300 W, the sputtering pressure is set to 0.5 Pa, the purity of the target material is set to 99.99% pure Al, the argon gas flow is set to 20 Sccm, and the substrate temperature is set to room temperature water cooling; after the sputtering is completed, the photoresist is stripped to form a patterned lower electrode layer 3;

[0019] The deposition of the piezoelectric layer 4 on the lower electrode layer 3 and the Bragg reflection layer 2 includes: the patterning process is basically the same as the preparation process of the lower electrode layer 3, except that the radio frequency power of the magnetron sputtering system is set to 400 W, the flow ratio of argon and nitrogen is 3:1, the sputtering pressure is 0.23 Pa, the substrate temperature is 100 DEG C, and a pure Al target material with a purity of 99.99% is used; the piezoelectric layer is subjected to photoetching alignment before exposure; the thickness of the required photoresist is greater than 2.2 um;

[0020] The deposition of the insulating layer 5 on the side of the piezoelectric layer 4 far away from the lower electrode layer 3 includes: the patterning process is basically the same as the preparation process of the piezoelectric layer 4, except that the radio frequency power of the magnetron sputtering system is set to 100 W, the sputtering pressure is 1.2 Pa, the flow ratio of argon and oxygen is 5:3, the substrate temperature is set to room temperature water cooling, and a pure Si target material with a purity of 99.9% is used;

[0021] The deposition of the upper electrode layer 6 on the piezoelectric layer 4 and the insulating layer 5 comprises a patterning process which is basically the same as the preparation process of the lower electrode layer 3, except that the radio frequency power of the magnetron sputtering system is set to 300 W, the sputtering pressure is 0.5 Pa, the argon flow is 20 Sccm, the substrate temperature is set to room temperature water cooling, and the purity of the target material is 99.99% Al; and the upper electrode layer is subjected to photoetching alignment before exposure.

[0022] In the preparation process of the piezoelectric layer 4, the specific operation of the photoresist spin coating is as follows: first drop a drop of photoresist, set the spin coating speed to 3000 rpm, and set the time to 40 s, the photoresist thickness is 1.3 um, after the first spin coating is completed, do not perform baking operation, then drop a drop of photoresist on it, still set the spin coating speed to 3000 rpm, and set the time to 40 s, the thickness of the photoresist layer is greater than 2.2 um.

[0023] In the preparation process of the piezoelectric layer, the electrode pattern needs to be observed through a microscope before exposure, and the position of the piezoelectric layer mask is adjusted so that the piezoelectric layer photoetching alignment mark 9 on the piezoelectric layer mask is aligned with the lower electrode layer alignment mark 8, and then magnetron sputtering is performed; the lower electrode + piezoelectric layer alignment mark 10 is formed on the Bragg reflection layer;

[0024] In the preparation process of the insulating layer, the electrode pattern needs to be observed through a microscope before exposure, and the position of the insulating layer mask is adjusted so that the insulating layer photoetching alignment mark 11 on the insulating layer mask is aligned with the lower electrode + piezoelectric layer alignment mark 10, and then magnetron sputtering is performed; the lower electrode + piezoelectric layer + insulating layer alignment mark 12 is formed on the Bragg reflection layer;

[0025] In the preparation process of the upper electrode layer, the electrode pattern needs to be observed through a microscope before exposure, and the position of the upper electrode layer mask is adjusted so that the upper electrode layer photoetching alignment mark 13 is aligned with the lower electrode + piezoelectric layer + insulating layer alignment mark 12, and then magnetron sputtering is performed; the lower electrode + piezoelectric layer + insulating layer + upper electrode layer alignment mark 14 is formed on the Bragg reflection layer.

[0026] The beneficial effects of the present application are: the present application adopts six or eight layers of Bragg reflection layer to construct a full-metal solid-state assembled micro mass sensor, and by changing the thickness of the upper electrode to simulate the change of the mass load, it is found that the sensor can work in the frequency domain change between 2.28 GHz~2.25 GHz micro mass detection; at the same time, the structure design of the present application has simple overall process, the ingenious cooperation of the insulating layer and the piezoelectric layer, the upper electrode layer not only can prevent the occurrence of fault due to slope difference during deposition, or the increase of voltage standing wave ratio due to the change of thickness, and prevent the short circuit of the upper and lower electrodes from affecting the measurement, but also can reduce the quality defects, and can avoid the parasitic effect caused by the too large piezoelectric layer (the parasitic effect will cause the performance of the sensor to decrease, and in serious cases, the sensor cannot work), which is crucial for improving the precision and sensitivity of the sensor in the field of micro mass sensor. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the present application;

[0028] Figure 2 is a structural perspective schematic diagram of the present application;

[0029] Figure 3 is a top view of the present application;

[0030] Figure 4 is a schematic diagram showing effective resonance region;

[0031] Figure 5 is a sectional view of the present application;

[0032] Figure 6 is an energy leakage spectrum diagram of 4 layers of Bragg reflection layer;

[0033] Figure 7 is an energy leakage spectrum diagram of 6 layers of Bragg reflection layer;

[0034] Figure 8 is an energy leakage spectrum diagram of 8 layers of Bragg reflection layer;

[0035] Figure 9 is an energy leakage spectrum diagram of 10 layers of Bragg reflection layer;

[0036] Figure 10 is a mask plate design schematic diagram of the upper electrode layer;

[0037] Figure 11 is a mask plate design schematic diagram of the insulating layer;

[0038] Figure 12 is a mask plate design schematic diagram of the piezoelectric layer;

[0039] Figure 13 is a mask plate design schematic diagram of the lower electrode layer;

[0040] Figure 14 is a lithography alignment mark distribution and alignment schematic diagram;

[0041] Figure 15 is a preparation flow chart of the present application;

[0042] Figure 16 is an impedance frequency response curve diagram calculated by finite element simulation;

[0043] Figure 17 is a resonance frequency curve diagram changing with mass (upper electrode thickness);

[0044] The labels in the figure are as follows: 1-substrate, 2-Bragg reflector layer, 3-lower electrode layer, 4-piezoelectric layer, 5-insulating layer, 6-upper electrode layer, 7-3-inch photomask, 8-lower electrode layer alignment mark, 9-piezoelectric layer photolithography alignment mark, 10-lower electrode + piezoelectric layer alignment mark, 11-insulating layer photolithography alignment mark, 12-lower electrode + piezoelectric layer + insulating layer alignment mark, 13-upper electrode layer photolithography alignment mark, 14-lower electrode + piezoelectric layer + insulating layer + upper electrode layer alignment mark. Detailed Implementation

[0045] The invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of the invention is not limited to the description.

[0046] Example 1: As Figures 1-17 As shown, a solid-state assembled micro-mass sensor with an all-metal structure includes a substrate 1, a Bragg reflector layer 2, a lower electrode layer 3, a piezoelectric layer 4, an insulating layer 5, and an upper electrode layer 6. The Bragg reflector layer 2 is disposed on the substrate 1, and the lower electrode layer 3, the piezoelectric layer 4, and the insulating layer 5 are disposed on the Bragg reflector layer 2. The lower electrode layer 3 is located between the Bragg reflector layer 2 and the piezoelectric layer 4. The insulating layer 5 is close to the piezoelectric layer 4 on the side away from the lower electrode layer 3 and is at the same height as the piezoelectric layer 4. The upper electrode layer 6 is disposed on the piezoelectric layer 4 and the insulating layer 5. The upper electrode layer 6 and the lower electrode layer 3 are not on the same layer.

[0047] Optionally, the Bragg reflector 2 is an all-metal Bragg reflector, which consists of 3-4 reflector groups, each of which consists of two impedance layers, a high acoustic impedance layer and a low acoustic impedance layer.

[0048] Optionally, the lower electrode layer 3 is composed of three sequentially connected irregular pentagonal effective piezoelectric regions, lead regions, and pad regions; wherein the lead regions and pad regions are T-shaped; the effective piezoelectric regions of the lower electrode layer are the same size and shape as the upper electrode and are corresponding vertically (the centers of the upper and lower electrodes are on a vertical line). Figure 3 The size and shape of the pad region of the lower electrode layer are the same as those of the upper electrode layer. The width of the lead region of the lower electrode layer is the same as that of the lead region of the upper electrode layer, and the length of the lead region of the upper electrode layer is greater than that of the lead region of the lower electrode layer.

[0049] Optionally, the piezoelectric layer 4 is deposited on the lower electrode layer 3, and the effective piezoelectric region of the lower electrode layer 3 and a portion of the lead region are covered by the piezoelectric layer 4.

[0050] Optionally, the substrate 1 is made of Si, and the surface roughness of the Bragg reflector layer 2 is less than 10 nm; the high acoustic impedance layer in the Bragg reflector layer 2 is made of W, and the thickness of each high acoustic impedance layer is 530 nm. , the material of the low acoustic impedance layer is Al, the thickness of each low acoustic impedance layer is 628 ; the material of the lower electrode layer 3 and the upper electrode layer 6 is Al, the effective piezoelectric area of the irregular pentagon is 20150 , the thickness of the lower electrode layer 3 is 150 , the thickness of the upper electrode layer 6 is 150-200nm; the material of the piezoelectric layer 4 is AlN; the thickness is in the range of ; the material of the insulating layer 5 is insulating material, and the thickness is the same as that of the piezoelectric layer 4. Optionally, the piezoelectric layer 4 is a rectangle with a length of 300 , a width of 200 , and a thickness in the range of , which is the core layer of the micro mass sensor; the insulating layer 5 is a rectangle with a length of 300 , a width of 150 .

[0051] Specifically, the piezoelectric layer 4 is deposited on the lower electrode layer 3, the effective piezoelectric area of the lower electrode layer and a part of the lead are covered by the piezoelectric layer 4, the insulating layer 5 is designed to be close to the side of the piezoelectric layer 4 away from the lower electrode layer 3, and the upper electrode layer 6 is arranged on the insulating layer 5 and the piezoelectric layer 4. The overlapping area of the upper and lower electrode layers and the piezoelectric layer 4 cooperates to form a resonance area (i.e. the working area of the sensor). The structure adopts a graphical design, which can effectively reduce the parasitic effect, improve the measurement accuracy and sensitivity, and to some extent, also reduce the complexity of the process. It can prevent faults caused by slope difference during deposition, prevent the increase of voltage standing wave ratio (VSWR) caused by changes in characteristic impedance, prevent short circuit of the upper and lower electrodes from affecting measurement, and reduce quality defects (such as avoiding structural defects caused by direct disconnection of the upper electrode layer on the piezoelectric layer). It can also avoid the increase of the probability of transverse wave excitation caused by the piezoelectric layer being too large (i.e. it can reduce the probability of transverse wave excitation, thereby reducing the parasitic effect and improving the performance of the sensor). The solid assembled micro mass sensor of the present application can use a 1mm wide GS type double-ended radio frequency probe to measure the change of the micro electric signal caused by the change of mass. The large wide measurement can avoid affecting the normal work of the effective resonance area during measurement.

[0052] According to another aspect of the embodiment of the present application, a preparation method of a solid assembled micro mass sensor with a full metal structure is also provided, which comprises: depositing a full metal Bragg reflection layer 2 on a substrate 1; depositing a lower electrode layer 3 on the Bragg reflection layer 2; depositing a piezoelectric layer 4 on the lower electrode layer 3 and the Bragg reflection layer 2; depositing an insulating layer 5 close to the side of the piezoelectric layer 4 away from the lower electrode layer 3; and depositing an upper electrode layer 6 on the piezoelectric layer 4 and the insulating layer 5.

[0053] Optionally, the substrate 1 is prepared as follows: the substrate 1 is selected from single-sided polished N-type (100) monocrystalline silicon (or single-sided polished P-type (110)), with a resistivity of 1~10Ω·cm, and the surface roughness of the polished surface of the N-type monocrystalline silicon is less than 10nm (preferably, the value is 6≤roughness<10, to avoid material defects affecting sensor performance during later processing); the N-type monocrystalline silicon is cleaned with standard RCA to remove impurities from the silicon wafer surface and avoid impurities affecting sensor performance; after the surface moisture of the cleaned N-type monocrystalline silicon is dried with nitrogen, it is baked in a baking chamber from room temperature to 100℃ to completely dry the N-type monocrystalline silicon; the baking is divided into two stages: a heating stage and a constant temperature stage; the time ratio of the heating stage to the constant temperature stage is 5:1, the heating stage refers to the stage of raising from room temperature to 100℃, and the constant temperature stage refers to the stage of maintaining 100℃; the total baking time is 20min-30min. (For example, if the baking time is 30 minutes, the heating stage is controlled at 25 minutes, that is, it takes 25 minutes to go from room temperature to 100℃, and the remaining 5 minutes are spent drying at 100℃; the baking time can also be 20 minutes, 25 minutes, etc.) By gradually increasing the temperature and then keeping it constant, it is possible to avoid the increase in material stress caused by the temperature rising too quickly, resulting in structural damage that is not visible to the naked eye.

[0054] Optionally, the all-metal Bragg reflector layer 2 is fabricated using a physical magnetron sputtering system (the chamber vacuum background of the magnetron sputtering system is...). Pa, target-substrate distance is 6cm (all basic magnetron sputtering parameters in this invention are set to these parameters). A layer with a thickness of 530 Pa is first deposited on the dried, polished single-crystal silicon surface. The high acoustic impedance thin film W was deposited using a pure W target with a purity of 99.95%. The RF power was set to 60W, the sputtering pressure to 1.2Pa, the substrate temperature to room temperature with water cooling, and the argon gas flow rate to 20 Sccm. After deposition, a 628mm thick film was then deposited on the surface of the high acoustic impedance thin film W. A low acoustic impedance thin film Al was prepared using a pure Al target with a purity of 99.99%. The RF power was set to 300W, the sputtering pressure to 0.5Pa, the substrate temperature to room temperature with water cooling, and the argon flow rate to 20 Sccm. The above steps were repeated to prepare a Bragg reflector layer with three reflector groups (the Bragg reflector layer obtained in this way ensures good reflectivity while reducing process complexity). Optionally, the reflector groups are 3-4. Specifically, the Bragg reflector layer is an all-metal structure composed of Al (low acoustic impedance) and W (high acoustic impedance), with 3-4 reflector groups. In this solid-state assembled mass sensor, the Bragg reflector layer 2, located near the lower electrode layer, is a low-impedance layer with a thickness of 628 μm per layer. The layer closest to the substrate is a high acoustic impedance layer, with a thickness of 530 μm per layer. . i.e. Figure 1 , 5 The structure from top to bottom is low-high-low-high-low-high as shown in the three groups in FIG. 2.

[0055] The selection process of the number of Bragg reflection layers is given as follows:

[0056] The more the number of Bragg reflection layers, the better the energy confinement. However, the increase in the number of layers increases the complexity of the process and the cost of the device. Selecting an appropriate number of Bragg reflection layers can not only reduce energy leakage, but also facilitate the processing and manufacturing of the device. The following will simulate and analyze the number of Bragg reflection layers as 4, 6, 8, and 10, and obtain the energy leakage spectrum of different numbers of Bragg reflection layers as shown in FIG. 3. The peak-to-peak ratio of energy at resonance is used as the energy efficiency Figures 6-9 , , The smaller the energy efficiency, the better the energy confinement. The maximum peak and the minimum peak in the leakage spectrum are taken to calculate the energy efficiency as shown in Table 1.

[0057] It is found by comparison that the energy efficiency difference between 4 layers and 6 layers is , the energy efficiency difference between 6 layers and 8 layers is , and the energy efficiency difference between 8 layers and 10 layers is . Since the number of Bragg reflection layers of the device is different, the wavelength at resonance is different, so it is meaningless to compare the absolute value of the energy in Si. The absolute value of the peak energy in the film should be compared with the absolute value of the peak energy in Si to truly reflect the energy efficiency. The smaller the energy efficiency, the better the energy confinement. As can be seen from the table, when the number of layers is 6, the energy efficiency has reached 3.78%, which is less than 5%. The benefits brought by the continuous increase in the number of Bragg reflection layers show a cliff-like drop. From the process cost and complexity, 6 layers can still ensure that the energy leakage is as small as possible while reducing the difficulty of the process, so the present application selects 6 layers as the best device in terms of comprehensive performance, that is, the number of reflection groups is 3.

[0058] Table 1 Calculation of energy efficiency

[0059]

[0060] Optionally, the lower electrode layer 3 is prepared as follows: first, the upper surface of the prepared Bragg reflection layer 2 is treated with HMDS liquid for adhesion promotion, and a layer of photoresist AZ600 with a thickness of 1 um is uniformly spin-coated on the entire upper surface of the Bragg reflection layer, and the spin coater speed is set to 4000 rpm and the spin coating time is 40 s; after the spin coating is completed, pre-baking treatment is performed, the hot plate temperature is set to 100°C, the photoresist is baked for 60 s, the photoresist is evaporated to lose flow, the residual solvent in the photoresist film is removed, the mechanical stress of the photoresist film is eliminated, the adhesion of the photoresist film is enhanced, and the photosensitivity of the photoresist film is improved and stabilized, so as to facilitate subsequent exposure treatment; the corresponding lower electrode mask plate (attachedFigure 13

[0061] The effective piezoelectric area of the irregular pentagon is 20150 The effective piezoelectric area of the irregular pentagon is 20150 Figure 4 The effective piezoelectric area of the irregular pentagon is 20150 The effective piezoelectric area of the irregular pentagon is 20150

[0062] Optionally, the piezoelectric layer 4 is prepared as follows: the patterning process is basically the same as the preparation process of the lower electrode layer 3, except that the radio frequency power of the magnetron sputtering system is set to 400 W, the flow ratio of argon and nitrogen is 3:1 (specifically, the argon flow is 48 Sccm, and the nitrogen flow is set to 16 Sccm), the sputtering pressure is 0.23 Pa, the substrate is 100°C, and a piezoelectric layer thin film with a thickness of 2.18 um is prepared by using a pure Al target with a purity of 99.99% and nitrogen at a high temperature of 100°C, and is patterned (see the piezoelectric layer mask diagram in the attached Figure 12 ​​, the thickness of the required photoresist is above 2.2um, one spin coating cannot reach the required thickness, and two spin coatings are required, and no pre-baking operation is performed in the second spin coating; the piezoelectric layer is subjected to photoetching alignment before exposure. The specific operation of photoresist spin coating is as follows: first drop a drop of photoresist, set the spin coating speed to 3000 rpm, and set the time to 40 s, the gel thickness is 1.3um, and no drying operation is performed after the first spin coating, then drop another drop of photoresist on it, still set the spin coating speed to 3000 rpm, and set the time to 40 s, so that the thickness of the gel layer is greater than 2.2um (the thickness of the photoresist is directly related to the speed, and the time is set to obtain uniform photoresist, and the default time is generally set to 40s), two drops of glue are continuously dropped, although the thickness is less than the sum of the thickness of two single drops of glue, but the thickness is still greater than 2.2um without affecting the properties of the photoresist.

[0063] Optionally, the insulating layer 5 is prepared as follows: the patterning process is basically the same as the preparation process of the piezoelectric layer 4, except that the radio frequency power of the magnetron sputtering system is set to 100W, the sputtering pressure is 1.2Pa, the flow ratio of argon and oxygen is 5:3 (specifically, the argon flow is 50 Sccm, and the oxygen flow is 30 Sccm), the substrate temperature is set to room temperature water cooling, and the pure Si target material with a purity of 99.9% is used to prepare and pattern the silicon oxide film in an argon and oxygen mixed gas environment to form the insulating layer 5 (see the attached Figure 11 ).

[0064] Optionally, the upper electrode layer 6 is prepared as follows: the preparation process of the upper electrode is the last stage of the preparation of the solid-state assembled micro-mass sensor, and at the same time, considering that the mass sensitivity of the micro-mass sensor is extremely high, the thickness of the upper electrode is changed to simulate the change of the load mass, and Al with smaller density is selected as the upper electrode material. Since the preparation of the upper electrode is performed after the preparation of the electrode patterning, the piezoelectric layer, and the insulating layer, the patterning process is basically the same as the preparation process of the lower electrode layer 3, except that the radio frequency power of the magnetron sputtering system is set to 300W, the sputtering pressure is 0.5Pa, the argon flow is 20Sccm, the substrate temperature is set to room temperature water cooling, and the target material has a purity of 99.99% and a deposition thickness of 150-200nm. The upper electrode is patterned. (See the attached Figure 10 ) The upper electrode layer needs to be subjected to photoetching alignment before exposure, and the alignment method described below can effectively ensure that the centers of the upper and lower electrodes are in the same position.

[0065] The lower and upper electrode layers are made of Al target material. This application simulates several electrode materials including Mo, Al, W, Au, and Pt. Finite element simulations revealed that, for the same thickness, the resonant frequencies of different materials, from lowest to highest, are Pt, Au, Mo, and Al. Table 2 shows that Al, selected in this invention, possesses excellent characteristics such as high quality factor and high impedance, and also has the advantage of low density. For the same volume, Al exhibits the smallest mass change, allowing for the simulation of mass load variations by changing its thickness.

[0066] Table 2 Resonance Points and Quality Factors

[0067]

[0068] Furthermore, the alignment process of the piezoelectric layer, insulating layer, and upper electrode layer is as follows: Figure 14 As shown:

[0069] During the fabrication of the piezoelectric layer, the electrode pattern needs to be observed under a microscope before exposure. The position of the piezoelectric layer mask is adjusted so that the piezoelectric layer photolithography alignment mark 9 on the piezoelectric layer mask is aligned with the lower electrode layer alignment mark 8 before magnetron sputtering is performed. The lower electrode + piezoelectric layer alignment mark 10 is formed on the Bragg reflector layer.

[0070] During the preparation of the insulating layer, before exposure, the electrode pattern needs to be observed with a microscope. The position of the insulating layer mask is adjusted so that the insulating layer photolithography alignment mark 11 on the insulating layer mask is aligned with the lower electrode + piezoelectric layer alignment mark 10 before magnetron sputtering is performed. The lower electrode + piezoelectric layer + insulating layer alignment mark 12 is formed on the Bragg reflector layer.

[0071] During the fabrication of the upper electrode layer, the electrode pattern needs to be observed under a microscope before exposure. The position of the upper electrode layer mask is adjusted so that the upper electrode layer photolithography alignment mark 13 is aligned with the lower electrode + piezoelectric layer + insulating layer alignment mark 12 before magnetron sputtering is performed. The lower electrode + piezoelectric layer + insulating layer + upper electrode layer alignment mark 14 is formed on the Bragg reflector layer.

[0072] The piezoelectric layer photolithographic alignment mark 9, the insulating layer photolithographic alignment mark 11, and the upper electrode layer photolithographic alignment mark 13 adopt a hollow structure (such as a hollow cross structure); the hollow shape and size of the piezoelectric layer photolithographic alignment mark 9 are the same as the shape and size of the lower electrode layer alignment mark 8, and the two are compatible; the hollow shape and size of the insulating layer photolithographic alignment mark 11 are the same as the shape and size of the piezoelectric layer photolithographic alignment mark 9, and the two are compatible; the hollow shape and size of the upper electrode layer photolithographic alignment mark 13 are the same as the shape and size of the insulating layer photolithographic alignment mark 11, and the two are compatible. Specifically, the lower electrode layer 3, piezoelectric layer 4, insulating layer 5, and upper electrode layer 6 masks are all equipped with "+" alignment marks for easy overlay alignment. As shown in the three-inch mask 7, 16 photolithographic alignment marks are attached to the center line of the four regions of the mask. Each mask is also designed with an "L"-shaped direction alignment mark 15, located directly above the mask, to avoid the inability to identify the direction. The lower electrode layer alignment mark 8, piezoelectric layer photolithographic alignment mark 9, insulating layer photolithographic alignment mark 11, and upper electrode layer photolithographic alignment mark 13 have the same shape and can all adopt a cross structure. The piezoelectric layer photolithographic alignment mark 9, insulating layer photolithographic alignment mark 11, and upper electrode layer photolithographic alignment mark 13 adopt a hollow cross structure. The hollow shape and size of the piezoelectric layer photolithographic alignment mark 9 are the same as the shape and size of the lower electrode layer alignment mark 8. The two are compatible, forming the shape of lower electrode + piezoelectric layer alignment mark 10. The others are similar.

[0073] Using the above alignment method in the fabrication process of the piezoelectric layer, insulating layer, and upper electrode layer can effectively ensure that the error between layers is within the allowable range, and reduce the reduction of sensor performance due to process errors and other factors.

[0074] To verify the feasibility of the micro-mass sensor proposed in this application, the resonance characteristic curves of the example were calculated using finite element simulation analysis software. The series resonant frequency was 2.28 GHz, and the parallel resonant frequency was 2.33 GHz. Figure 16 By changing the thickness of the upper electrode, it was found that the sensor can operate in the micro-mass detection range of 2.28 GHz to 2.25 GHz in the frequency domain (referring to the frequency variation range of the series resonant point; the thickness variation range of the upper electrode is 150 nm to 200 nm, and the larger the thickness, the more the resonant frequency shifts to the left (becomes smaller), as shown in Table 3). Simulation results show that the Al thickness has a linear relationship with the frequency variation, which also indicates that the mass load has a linear relationship with the frequency variation. The sensor of this invention is feasible and effective. The simulation experiment of this invention is based on three-dimensional multiphysics simulation, which is more in line with reality; from Figure 17 It can be seen that for every 10nm increase in the thickness of the upper electrode, the mass load of the upper electrode changes by 0.544ng, and the resonant frequency shifts to the left by 7MHz. Figure 17In the middle, the horizontal coordinate value 0 represents the initial upper electrode layer thickness, i.e. 150 nm, which is increased by a step of 10; according to the Sauerbrey equation, the mass sensitivity of the micro-mass sensor is calculated to be i.e. a mass change of 1 ng, a unit area (cm 2 ) of 2.5926 x 10 3 HZ.

[0075] Table 3 Resonance frequency corresponding to the upper electrode thickness

[0076]

[0077] The specific embodiments of the present application are described above in detail with reference to the accompanying drawings, but the present application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A solid state assembled micro-mass sensor of all-metallic construction, characterized by: The application relates to a full-metal structure solid-state assembled micro-mass sensor, which comprises a substrate (1), a Bragg reflection layer (2), a lower electrode layer (3), a piezoelectric layer (4), an insulating layer (5) and an upper electrode layer (6); the Bragg reflection layer (2) is arranged on the substrate (1), the lower electrode layer (3), the piezoelectric layer (4) and the insulating layer (5) are arranged on the Bragg reflection layer (2), the lower electrode layer (3) is located between the Bragg reflection layer (2) and the piezoelectric layer (4), the insulating layer (5) is tightly arranged on a side of the piezoelectric layer (4) far from the lower electrode layer (3) and has the same height as the piezoelectric layer (4), the upper electrode layer (6) is arranged on the piezoelectric layer (4) and the insulating layer (5), and the upper electrode layer (6) and the lower electrode layer (3) are not in the same layer. The lower electrode layer (3) and the upper electrode layer (6) have basically the same structure and are composed of effective piezoelectric regions, lead regions and pad regions in irregular pentagons which are sequentially connected. The piezoelectric layer (4) is deposited on the lower electrode layer (3), the effective piezoelectric regions and a part of the lead regions of the lower electrode layer (3) are covered by the piezoelectric layer (4), and the remaining regions are not covered by the piezoelectric layer (4). The Bragg reflection layer (2) is a full-metal Bragg reflection layer and is composed of 3-4 reflection groups, each reflection group is composed of two impedance layers, namely a high acoustic impedance layer and a low acoustic impedance layer. The material of the high acoustic impedance layer in the Bragg reflection layer (2) is W, the thickness of each high acoustic impedance layer is , the material of the low acoustic impedance layer is Al, and the thickness of each low acoustic impedance layer is ; The deposition of an all-metal Bragg reflector layer (2) on the substrate (1) includes: first depositing a layer with a thickness of [missing information] on the dried single-crystal silicon using a physical magnetron sputtering system. For the high acoustic impedance thin film W, a pure W target with a purity of 99.95% was selected. The RF power was set to 60W, the sputtering pressure to 1.2Pa, the substrate temperature to room temperature, and water cooling. The argon flow rate was 20 sccm. After deposition, a thickness of [missing information] was deposited on the W film surface. For the low acoustic impedance thin film Al, a pure Al target with a purity of 99.99% was selected, the radio frequency power was set to 300W, the sputtering pressure to 0.5Pa, the substrate temperature to room temperature with water cooling, and the argon flow rate to 20Sccm; the above steps were repeated to prepare a Bragg reflector layer with 3-4 reflector groups. The sensor works in the frequency domain and changes to 2.25GHz-2.28GHz by changing the upper electrode thickness in the range of 150nm-200nm.

2. The all-metal solid-state assembled micro-mass sensor of claim 1, wherein: The material of the substrate (1) is Si, the surface roughness for depositing the Bragg reflection layer (2) is less than 10 nm; the material of the lower electrode layer (3) and the upper electrode layer (6) is Al, the effective piezoelectric area of the irregular pentagon is 20150 , the thickness of the lower electrode layer (3) is , the thickness of the upper electrode layer (6) is 150-200 nm; the material of the piezoelectric layer (4) is AlN; thickness in ; the material of the insulation layer (5) is insulation material, and the thickness is same as that of the piezoelectric layer (4).

3. A method of fabricating a solid-state assembled micro-mass sensor of an all-metallic structure as claimed in claim 1, characterized by: The application comprises the following steps: depositing a full-metal Bragg reflection layer (2) on a substrate (1); depositing a lower electrode layer (3) on the Bragg reflection layer (2); depositing a piezoelectric layer (4) on the lower electrode layer (3) and the Bragg reflection layer (2); depositing an insulating layer (5) on a side of the piezoelectric layer (4) far from the lower electrode layer (3); depositing an upper electrode layer (6) on the piezoelectric layer (4) and the insulating layer (5).

4. The method of claim 3, wherein: The substrate (1) is single-crystal silicon with one polished surface, the resistivity is 1-10 ohm*cm, the surface roughness of the polished surface is less than 10nm, the single-crystal silicon is cleaned by using standard RCA, the surface moisture of the cleaned single-crystal silicon is blown dry by using nitrogen, and the single-crystal silicon is baked from room temperature to 100 DEG C in an oven; the baking is divided into two stages, namely a temperature rising stage and a constant temperature stage; the time ratio of the temperature rising stage to the constant temperature stage is 5:1, the temperature rising stage refers to the stage of rising from room temperature to 100 DEG C, and the constant temperature stage refers to the stage of keeping 100 DEG C; the total baking time is 20min-30min.

5. The preparation method of the full-metal structure solid-state assembled micro-mass sensor according to claim 4. The deposition of the lower electrode layer (3) on the Bragg reflection layer (2) comprises the following steps: firstly, the prepared Bragg reflection layer (2) is subjected to adhesion treatment by using HDMS liquid, and a layer of photoresist with a thickness of 1 um is uniformly spin-coated on the surface of the Bragg reflection layer (2); after the spin-coating, pre-baking treatment is performed; exposure is performed under the pattern of the corresponding lower electrode mask; the required lower electrode pattern is obtained by using a developing solution; before magnetron sputtering, whether the developed pattern has defects is observed; if there are defects, the photoresist on the sample is cleaned, and the above steps are repeated until the sample is qualified; after the development is qualified, the photoresist is baked, the cleaned sample is placed in an oven for baking; after the baking is completed, the lower electrode film is deposited, the radio frequency power of the magnetron sputtering system is set to 300 W, the sputtering pressure is 0.5 Pa, the purity of the target material is 99.99% pure Al, the argon flow rate is 20 Sccm, and the substrate temperature is set to room temperature water cooling; after the sputtering is completed, the photoresist is stripped to form a patterned lower electrode layer (3); The deposition of the piezoelectric layer (4) on the lower electrode layer (3) and the Bragg reflection layer (2) comprises the following steps: the patterning process is basically the same as the preparation process of the lower electrode layer (3), except that the radio frequency power of the magnetron sputtering system is set to 400 W, the flow rate ratio of argon and nitrogen is 3:1, the sputtering pressure is 0.23 Pa, the substrate temperature is 100 DEG C, and the purity of the target material is 99.99% pure Al; the piezoelectric layer is subjected to photoetching alignment before exposure; the thickness of the required photoresist is greater than 2.2 um; The deposition of the insulating layer (5) on the side of the piezoelectric layer (4) far from the lower electrode layer (3) comprises the following steps: the patterning process is basically the same as the preparation process of the piezoelectric layer (4), except that the radio frequency power of the magnetron sputtering system is set to 100 W, the sputtering pressure is 1.2 Pa, the flow rate ratio of argon and oxygen is 5:3, the substrate temperature is set to room temperature water cooling, and the purity of the target material is 99.9% pure Si; The deposition of the upper electrode layer (6) on the piezoelectric layer (4) and the insulating layer (5) comprises the following steps: the patterning process is basically the same as the preparation process of the lower electrode layer (3), except that the radio frequency power of the magnetron sputtering system is set to 300 W, the sputtering pressure is 0.5 Pa, the argon flow rate is 20 Sccm, the substrate temperature is set to room temperature water cooling, and the purity of the target material is 99.99% Al; the upper electrode layer is subjected to photoetching alignment before exposure.

6. The method of claim 4, wherein: In the preparation process of the piezoelectric layer (4), the specific operation of the photoresist spin coating is as follows: a drop of photoresist is first dripped, the spin coating speed is set to 3000 rpm, the time is set to 40 s, the photoresist thickness is 1.3 um, and no drying operation is performed after the spin coating is completed; then a drop of photoresist is dripped again, the spin coating speed is still set to 3000 rpm, and the time is set to 40 s, so that a photoresist layer with a thickness greater than 2.2 um is obtained.

7. The method of claim 4, wherein the full metal structure is a solid-state assembled micro-mass sensor. In the process of preparing the piezoelectric layer, the electrode pattern needs to be observed by microscope before exposure, the position of the piezoelectric layer mask is adjusted so that the piezoelectric layer lithography alignment mark (9) on the piezoelectric layer mask is aligned with the lower electrode layer alignment mark (8), and then magnetron sputtering is performed; the lower electrode + piezoelectric layer alignment mark (10) is formed on the Bragg reflection layer; In the process of preparing the insulating layer, the electrode pattern needs to be observed by microscope before exposure, the position of the insulating layer mask is adjusted so that the insulating layer lithography alignment mark (11) on the insulating layer mask is aligned with the lower electrode + piezoelectric layer alignment mark (10), and then magnetron sputtering is performed; the lower electrode + piezoelectric layer + insulating layer alignment mark (12) is formed on the Bragg reflection layer; In the process of preparing the upper electrode layer, the electrode pattern needs to be observed by microscope before exposure, the position of the upper electrode layer mask is adjusted so that the upper electrode layer lithography alignment mark (13) is aligned with the lower electrode + piezoelectric layer + insulating layer alignment mark (12), and then magnetron sputtering is performed; the lower electrode + piezoelectric layer + insulating layer + upper electrode layer alignment mark (14) is formed on the Bragg reflection layer.

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