CN113188655A - Optical sensor based on bulk acoustic wave and preparation method thereof - Google Patents
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
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Abstract
The invention relates to the technical field of optical sensors, in particular to an optical sensor based on bulk acoustic waves and a preparation method thereof. The optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. The photosensitive piezoelectric oscillation layer is prepared by combining a photosensitive film and a piezoelectric film to form a piezoelectric oscillation stack with photosensitive characteristics, the frequency characteristics of the piezoelectric layer are influenced by the piezoelectric effect and the photoelectric effect together, and the detected optical signal is represented by the change of the resonant frequency. The method has the advantages of high sensitivity and low signal noise.
Description
Technical Field
The invention relates to the technical field of optical sensors, in particular to an optical sensor based on bulk acoustic waves and a preparation method thereof.
Background
Along with modern science and technology entering the intelligent era, sensors play more and more important roles in the fields of industrial robots and the like. How to convert various signals in the environment into more intuitive and observable signal modes by using the sensor is a key topic in the field of sensor research. The optical sensor is a device for converting an optical signal into an electrical signal to perform optical detection, and has been widely used in various industries. The photosensitive device in the optical sensor generally depends on photo-generated carriers to influence the photosensitive characteristic, and the detection efficiency of the photosensitive device is generally related to the light absorption efficiency of the material, the mobility of the material and the collection efficiency of the electrode on the carriers, so that the detection efficiency of the optical sensor is mainly adjusted and improved in the three aspects. Such as increasing the light absorption efficiency of the material by reducing the thickness of the material, increasing the mobility by changing the nanostructure of the material, and increasing the collection of carriers by reducing the interface contact resistance by providing an electrode buffer layer. However, the above three improvements have problems such as complicated operation and limited sensitivity improvement.
Therefore, it is necessary to provide an optical sensor having high sensitivity and low signal noise.
Disclosure of Invention
In view of the above, it is desirable to provide a bulk acoustic wave based optical sensor. The photosensitive film and the piezoelectric film are combined to form a piezoelectric oscillation stack with photosensitive characteristics, a photosensitive piezoelectric oscillation layer is prepared, the piezoelectric effect and the photoelectric effect are utilized to jointly influence the frequency characteristics of the piezoelectric layer, and the detected optical signal is represented through the change of the resonant frequency.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a bulk acoustic wave-based optical sensor, including a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top.
Further, in the bulk acoustic wave-based optical sensor described above, the substrate is one of Si, GaN, and sapphire.
Further, in the above bulk acoustic wave-based photosensor, the thickness of the photosensitive film is 200nm to 2 μm; the photosensitive film includes but is not limited to one or a combination of ZnO and InGaN. When the thickness of the photosensitive film is larger than 2 μm, the film is easily damaged when the thickness of the film is larger than 2 μm because the photosensitive film generates a stress accumulation phenomenon in the growth process. When the thickness of the photosensitive film is less than 200nm, the photosensitive film is too fragile, and the mechanical stability in the vibration process is poor, so that the photosensitive film cannot be used for preparing the sensor.
Preferably, in the bulk acoustic wave-based photosensor described above, the photosensitive thin film component is doped with Al.
Further, in the bulk acoustic wave based photosensor described above, the piezoelectric film includes, but is not limited to, one of AlN, PZT; the thickness of the piezoelectric film is 100 nm-2 mu m.
Further, in the bulk acoustic wave based optical sensor, the upper electrode and the lower electrode include, but are not limited to, one or more of gold, silver, molybdenum, titanium, and tungsten; the thickness of the upper electrode or the lower electrode is 0.1-1 μm.
Further, in the above bulk acoustic wave-based optical sensor, a buffer layer is provided between the upper electrode and the piezoelectric film.
Preferably, in the bulk acoustic wave-based photosensor described above, the buffer layer is one of AlN, AlGaN, and GaN; the thickness of the buffer layer is 10nm-200 nm.
In a second aspect, the present invention provides a method for manufacturing a bulk acoustic wave-based optical sensor, including the following steps:
step S1: patterning the substrate by adopting a photoetching technology, then etching an air cavity by a dry method, and filling a PSG material into the air cavity to form a PSG filling layer;
step S2: growing a lower electrode over the substrate filled with the PSG material;
step S3: depositing a piezoelectric film above the lower electrode;
step S4: sputtering or evaporating an upper electrode above the piezoelectric film;
step S5: growing a photosensitive film above the upper electrode;
step S6: and preparing a through hole by adopting an ICP (inductively coupled plasma) dry etching technology, removing the PSG (patterned sapphire glass) filling layer by acid corrosion, and leading the lower electrode to the photosensitive film.
Further, in the method for manufacturing the bulk acoustic wave-based photosensor, a buffer layer is further grown between the upper electrode and the photosensitive film in step S4.
Further, in the above method for manufacturing a bulk acoustic wave-based photosensor, it is characterized in that component doping is performed when the photosensitive film is manufactured.
The invention has the beneficial effects that:
the light sensor based on the bulk acoustic wave combines the photosensitive film and the piezoelectric film to form the piezoelectric oscillation stack with photosensitive characteristics, the photosensitive piezoelectric oscillation layer is prepared, the piezoelectric effect and the photoelectric effect are utilized to jointly influence the frequency characteristics of the piezoelectric layer, and the detected optical signal is represented by the change of the resonant frequency. The method has the advantages of high sensitivity and low signal noise.
Drawings
Fig. 1 is a structural diagram of a bulk acoustic wave-based optical sensor according to embodiment 2 of the present invention;
FIG. 2 is a cross-sectional view of a substrate after etching an air cavity in a manufacturing method according to example 2 of the present invention;
FIG. 3 is a sectional view of an air cavity filled with a PSG material according to the method of example 2;
FIG. 4 is a sectional view showing the lower electrode, the piezoelectric film and the upper electrode which are prepared in this order in the preparation method of example 2 of the present invention;
FIG. 5 is a sectional view showing a buffer layer and a photosensitive film which are sequentially formed in the manufacturing method of example 2 of the present invention;
FIG. 6 is a graph showing the frequency change of the photo-sensors prepared in examples 4 and 5 of the present invention;
FIG. 7 is a graph comparing the frequency change of the optical sensor prepared in example 4 of the present invention with the optical sensors of comparative examples 1 and 2;
in the figure: 101-substrate, 102-PSG filling layer, 103-lower electrode, 104-piezoelectric film, 105-upper electrode, 106-buffer layer, 107-photosensitive film, 108-through hole, 109-air cavity.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further clearly and completely described below with reference to the embodiments of the present invention. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A bulk acoustic wave-based optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is AlN with the thickness of 1.5 mu m; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 383nm, and the thickness of the lower electrode is 336 nm; the photosensitive film is ZnO, and the thickness of the photosensitive film is 350 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg.
The preparation method comprises the following steps:
step S1: carrying out acid washing and organic cleaning on the high-resistance single-side polished Si substrate, and carrying out graphical treatment on the substrate by adopting a photoetching technology, wherein the photoresist is positive photoresist; carrying out dry etching on the Si substrate by using RIE (reactive ion etching) combined with ICP (inductively coupled plasma) technology to obtain an air cavity; filling a PSG material into the air cavity to form a PSG filling layer, then carrying out photoetching exposure patterning treatment, and removing redundant PSG by adopting acid corrosion;
step S2: processing the substrate obtained in the step S1 by adopting a CMP chemical mechanical polishing mode to ensure that the step between the PSG filling layer and the Si substrate is less than 5 nm; growing a lower electrode above the substrate filled with the PSG material by adopting a PVD magnetron sputtering technology, and carrying out patterning treatment on the lower electrode by adopting a photoetching technology;
step S3: depositing a piezoelectric film above the lower electrode by adopting a PVD magnetron sputtering technology; carrying out graphical processing on the piezoelectric film by adopting a photoetching technology;
step S4: sputtering an upper electrode above the piezoelectric film by adopting a PVD magnetron sputtering technology; patterning the upper electrode by adopting a photoetching technology;
step S5: growing a photosensitive film above the upper electrode;
step S6: preparing a through hole by adopting an ICP (inductively coupled plasma) dry etching technology, and removing the PSG filling layer by HF (hydrogen fluoride) acid corrosion to obtain an air cavity; and the lower electrode is brought up to the photosensitive film.
Example 2
As shown in fig. 1, a bulk acoustic wave based optical sensor includes a substrate and a photosensitive piezoelectric oscillation layer thereon; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. A buffer layer is arranged between the photosensitive film and the upper electrode. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is AlN with the thickness of 1.5 mu m; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 383nm, and the thickness of the lower electrode is 336 nm; the photosensitive film is ZnO, and the thickness of the photosensitive film is 350 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg. The buffer layer is AlN and has the thickness of 50 nm.
The preparation method comprises the following steps:
step S1: carrying out acid washing and organic cleaning on the high-resistance single-side polished Si substrate, and carrying out graphical treatment on the substrate by adopting a photoetching technology, wherein the photoresist is positive photoresist; carrying out dry etching on the Si substrate by using RIE (reactive ion etching) combined with ICP (inductively coupled plasma) technology to obtain an air cavity; filling a PSG material into the air cavity to form a PSG filling layer, then carrying out photoetching exposure patterning treatment, and removing redundant PSG by adopting acid corrosion;
step S2: processing the substrate obtained in the step S1 by adopting a CMP chemical mechanical polishing mode to ensure that the step between the PSG filling layer and the Si substrate is less than 5 nm; growing a lower electrode above the substrate filled with the PSG material by adopting a PVD magnetron sputtering technology, and carrying out patterning treatment on the lower electrode by adopting a photoetching technology;
step S3: depositing a piezoelectric film above the lower electrode by adopting a PVD magnetron sputtering technology; carrying out graphical processing on the piezoelectric film by adopting a photoetching technology;
step S4: sputtering an upper electrode above the piezoelectric film by adopting a PVD magnetron sputtering technology; patterning the upper electrode by adopting a photoetching technology;
step S5: growing a buffer layer above the upper electrode by adopting an MOCVD (metal organic chemical vapor deposition) technology, and then growing a photosensitive film above the buffer layer;
step S6: preparing a through hole by adopting an ICP (inductively coupled plasma) dry etching technology, and removing the PSG filling layer by HF (hydrogen fluoride) acid corrosion to obtain an air cavity; and the lower electrode is brought up to the photosensitive film.
Example 3
A bulk acoustic wave-based optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. A buffer layer is arranged between the photosensitive film and the upper electrode. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is AlN with the thickness of 2 mu m; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 1000nm, and the thickness of the lower electrode is 1000 nm; the photosensitive film is ZnO, and the thickness of the photosensitive film is 1000 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg. The buffer layer is AlN and has a thickness of 200 nm. The preparation method is the same as example 2.
Example 4
A bulk acoustic wave-based optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. A buffer layer is arranged between the photosensitive film and the upper electrode. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is 100nm thick AlN; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 100nm, and the thickness of the lower electrode is 100 nm; the photosensitive film is ZnO, and the thickness of the photosensitive film is 200 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg. The buffer layer is AlN and has a thickness of 10 nm. The preparation method is the same as example 2.
Example 5
A bulk acoustic wave-based optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. A buffer layer is arranged between the photosensitive film and the upper electrode. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is AlN with the thickness of 1.5 mu m; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 383nm, and the thickness of the lower electrode is 336 nm; the photosensitive film is ZnO doped Al, the doping concentration of the Al is 1.5 at%, and the thickness of the photosensitive film is 350 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg. The buffer layer is AlN and has the thickness of 50 nm. In the example, the Al-doped ZnO photosensitive film can influence the acoustic impedance characteristic of the piezoelectric film below the Al-doped ZnO photosensitive film through the photoelectric effect, so that the frequency of the sensor is changed back and forth.
Comparative example 1
A bulk acoustic wave-based optical sensor is different from that of embodiment 5 in that a photosensitive film is ZnO doped with Ag, and the rest of the structure is the same. In the comparative example, the square resistance of the ZnO/Ag/ZnO composite transparent conductive film gradually decreases with the increase of the number of layers of the Ag film, and when the Ag film is repeatedly prepared for more than 3 times, the resistance decreases to less than 50% of that before being inserted into the Ag film. Therefore, the Ag doped film is easily interfered by external environmental factors, so that the frequency movement of the sensor is deviated, and the sensor is further failed. Therefore, the Ag-doped ZnO film cannot be used for preparing bulk acoustic wave optical sensors.
Comparative example 2
A bulk acoustic wave-based optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. A buffer layer is arranged between the photosensitive film and the upper electrode. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is AlN with the thickness of 50 nm; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 100nm, and the thickness of the lower electrode is 100 nm; the photosensitive film is ZnO, and the thickness of the photosensitive film is 200 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg. The buffer layer is AlN and has a thickness of 10 nm. The preparation method is the same as example 4.
Comparative example 3
A bulk acoustic wave-based optical sensor comprises a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top. A buffer layer is arranged between the photosensitive film and the upper electrode. The substrate is a high-resistance single-side polished Si substrate; the piezoelectric film is AlN with the thickness of 80 nm; the lower electrode and the upper electrode are molybdenum (Mo) metal electrode layers, the thickness of the upper electrode is 75nm, and the thickness of the lower electrode is 75 nm; the photosensitive film is ZnO, and the thickness of the photosensitive film is 100 nm; the depth of the air cavity is 2 μm, and the included angle between the two side walls of the air cavity and the substrate is 95 deg. The buffer layer is AlN and has a thickness of 10 nm. The preparation method is the same as example 4.
Test data
The optical sensors prepared in examples 4 and 5 were tested by obtaining frequency characteristics using a probe station in combination with a vector network analyzer, and the frequency variation of the sensor is shown in fig. 6. In fig. 6, the solid line shows the frequency variation of the optical sensor of example 5, and the broken line shows the frequency variation of the optical sensor of example 4. As can be seen from fig. 6, the sensor resonant frequency decreases after sensing the external light signal. In comparison with example 4, example 5 provides a photosensor doped photosensitive film having a higher quality factor at the resonance frequency and more excellent sensor power consumption characteristics.
The photosensors prepared in example 4, comparative example 2, and comparative example 3 were tested in the same manner as above, and the test results are shown in fig. 7. In fig. 7, a is a frequency change curve of the photo-sensor of comparative example 2, b is a frequency change curve of the photo-sensor of comparative example 3, and c is a frequency change curve of the photo-sensor of example 4. As can be seen from fig. 7, when the piezoelectric thin film is only 50nm (comparative example 2), resonance cannot be excited effectively; the thickness of the piezoelectric film and the thickness of the electrodes defined in this application can be operated at the optimum operating frequency and a good quality factor can be obtained, compared to comparative example 3.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A bulk acoustic wave-based optical sensor is characterized by comprising a substrate and a photosensitive piezoelectric oscillation layer above the substrate; the substrate is provided with an air cavity; the photosensitive piezoelectric oscillation layer generates frequency change according to optical signal change and comprises a lower electrode, a piezoelectric film, an upper electrode and a photosensitive film which are sequentially arranged from bottom to top.
2. The bulk acoustic wave based photosensor according to claim 1 wherein the substrate is one of Si, GaN, sapphire.
3. The bulk acoustic wave-based photosensor according to claim 1, wherein the thickness of the photosensitive thin film is 200nm-2 μ ι η; the photosensitive film is one or a combination of ZnO and InGaN.
4. The bulk acoustic wave-based photosensor according to claim 1 wherein the piezoelectric film is one of AlN, PZT; the thickness of the piezoelectric film is 100 nm-2 mu m.
5. The bulk acoustic wave-based photosensor according to claim 1, wherein the top electrode and the bottom electrode are one or more combinations of gold, silver, molybdenum, titanium, tungsten; the thickness of the upper electrode or the lower electrode is 0.1-1 μm.
6. The bulk acoustic wave-based optical sensor according to any one of claims 1 to 5, wherein a buffer layer is provided between the upper electrode and the piezoelectric film.
7. The bulk acoustic wave-based photosensor according to claim 6, wherein the buffer layer is one of AlN, AlGaN, GaN; the thickness of the buffer layer is 10nm-200 nm.
8. The method for manufacturing a bulk acoustic wave-based optical sensor according to any one of claims 1 to 5, comprising the steps of:
step S1: patterning the substrate by adopting a photoetching technology, then etching an air cavity by a dry method, and filling a PSG material into the air cavity to form a PSG filling layer;
step S2: growing a lower electrode over the substrate filled with the PSG material;
step S3: depositing a piezoelectric film above the lower electrode;
step S4: sputtering or evaporating an upper electrode above the piezoelectric film;
step S5: growing a photosensitive film above the upper electrode;
step S6: and preparing a through hole by adopting an ICP (inductively coupled plasma) dry etching technology, removing the PSG (patterned sapphire glass) filling layer by acid corrosion, and introducing the lower electrode to the photosensitive film.
9. The method for manufacturing a bulk acoustic wave-based photosensor according to claim 8, wherein a buffer layer is further grown between the upper electrode and the photosensitive film in step S5.
10. The method of claim 8, wherein the photosensitive film is doped with a component.
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