Laser for gas or smoke detection and preparation method and application thereof

Abstract

The invention relates to the technical field of semiconductor photoelectronics and micro electro mechanical systems, in particular to a laser for gas or smoke detection and a preparation method and application thereof. The laser includes: a light source portion; the hollow sacrificial layer, the upper-layer DBR and the control electrode are sequentially formed on the light source part, the hollow sacrificial layer and the upper-layer DBR define a gas microcavity used for collecting gas or smoke to be detected, the thickness of a central area of the gas microcavity changes based on voltage applied by the control electrode, and the thickness of the central area of the gas microcavity changes based on the voltage applied by the control electrode. And the laser outputs a wavelength corresponding to the concentration of the to-be-measured gas or smoke in response to the change of the average refractive index of the gas microcavity caused by the to-be-measured gas or smoke collected by the gas microcavity. The laser for gas or smoke detection provided by the invention at least has the advantages of high sensitivity, long service life, quick response, miniaturization, high universality and the like.

Description

Technical Field

[0001] The present invention relates to the fields of semiconductor optoelectronic technology and micro-electromechanical system technology, and in particular to a laser for gas or smoke detection and a preparation method and application thereof. Background Art

[0002] In industrial production and daily life, the detection and early warning of certain gases and smoke, especially toxic, flammable and explosive gases and smoke, are particularly important. Early and accurate early warning can minimize the occurrence of accidents and protect the safety of people's lives and property in production and life. At present, the smoke and gas detectors on the market mainly include infrared absorption type, semiconductor adsorption type, catalytic combustion type and radioactive ion type detectors. These detectors mainly use gas-sensitive materials to absorb specific gases, chemical reactions and shield radioactive particles. Some of them have poor stability and are greatly affected by the environment; or low accuracy, it is difficult to detect low concentrations of gas and smoke; or they can only detect specific gases and their applications are limited; or they are radioactive and generally safe.

[0003] Therefore, the detection of small concentrations of gas or smoke with large range, strong versatility and high sensitivity has become the focus of attention. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a laser for gas or smoke detection, and a preparation method and application thereof. Through the technical solution of the present invention, large-scale non-selective gas or smoke concentration detection can be achieved, effectively solving the problem of high-sensitivity and wide-range integrated chip detection, and solving the problems of existing gas or smoke detectors such as poor stability, low accuracy, only being able to detect specific gases, and radioactivity. Compared with traditional types of optical gas detectors such as fiber optic gas detectors, it does not require external light source input and can generate lasers whose wavelength changes with gas concentration, which is conducive to the simplification and miniaturization of the overall structure.

[0005] Specifically, according to a first aspect of the present invention, there is provided a laser for gas or smoke detection, comprising: a light source portion; and a hollow sacrificial layer, an upper DBR and a control electrode sequentially formed on the light source portion, wherein the hollow sacrificial layer and the upper DBR define a gas microcavity for collecting the gas or smoke to be detected, the thickness of the central region of the gas microcavity changes based on the voltage applied by the control electrode, and wherein the laser outputs a wavelength corresponding to the concentration of the gas or smoke to be detected in response to a change in the average refractive index of the gas microcavity caused by the gas or smoke to be detected collected by the gas microcavity.

[0006] In an embodiment of the present invention, the optical cavity length of the laser changes based on the change of the average refractive index of the gas microcavity to output a wavelength corresponding to the concentration of the gas or smoke to be measured; the thickness of the central area of ​​the gas microcavity is inversely proportional to the detected concentration of the gas or smoke to be measured.

[0007] In an embodiment of the present invention, the hollow sacrificial layer is formed by spin-coating a photoresist on the light source portion and partially etching it; the initial thickness of the gas microcavity depends on the thickness of the photoresist, and the thickness of the photoresist changes based on the dilution ratio of the photoresist.

[0008] In an embodiment of the present invention, the light source part includes a lower DBR, an active area, an oxidation restriction layer, an intermediate DBR, and a passivation layer grown in sequence on a GaAs substrate; a first electrode sputtered on the back side of the GaAs substrate and a second electrode sputtered on the passivation layer, the photoresist is spin-coated on the second electrode, and the second electrode is used to inject current into the laser.

[0009] In an embodiment of the present invention, the passivation layer, the second electrode and the control electrode each include a light exit hole, wherein the diameter of the light exit hole of the passivation layer is smaller than the diameter of the table of the light source part, and the diameter of the light exit hole of the second electrode is smaller than the diameter of the light exit hole of the passivation layer.

[0010] In an embodiment of the present invention, the first electrode and the second electrode each include a Ti / Au material system, and the second electrode includes a metal with a relatively hard texture and relatively stable chemical properties; the upper DBR is used as a cantilever beam of the gas microcavity and includes a multilayer dielectric material, and the multilayer dielectric material includes a low stress, high refractive index contrast material system; the passivation layer includes SiO 2 Passivation layer.

[0011] In an embodiment of the present invention, the photoresist comprises polyimide, and the dilution ratio of the photoresist is adjusted by a photoresist diluent, and the photoresist diluent comprises an organic solvent.

[0012] According to a second aspect of the present invention, a method for preparing a laser for gas or smoke detection is provided, which comprises the following steps: step S1: epitaxially growing a lower DBR, an active region, an oxidized limiting layer and an intermediate DBR on a GaAs substrate in sequence by metal organic chemical vapor deposition or molecular beam epitaxy to obtain an epitaxial wafer; step S2: photolithography and etching a table top, and performing lateral wet nitrogen oxidation on all sides to form an oxidized limiting hole for limiting the light field and current; step S3: growing a passivation layer and photolithography and etching a light exit hole of the passivation layer, and then sputtering a second electrode and photolithography and etching a light exit hole of the second electrode, and making the light exit hole of the passivation layer smaller than the diameter of the table top, and the light exit hole of the second electrode smaller than the light exit hole of the passivation layer, so as to form a nested structure, and complete the process. The light source part is made, and finally the first electrode is sputtered on the back of the GaAs substrate; step S4: use a coating machine to spin-coat photoresist on the second electrode and solidify it as a sacrificial layer; step S5: grow a plurality of pairs of upper DBRs on the sacrificial layer, and the upper DBRs also serve as cantilever beams of the gas microcavity; step S6: photolithography and sputtering Ni on the upper DBR to form a control electrode, peeling off the microcavity shape of the gas microcavity, and then using it as an etching mask to perform RIE patterning etching on the upper DBR to form the gas microcavity; step S7: photolithography and etching the light exit hole of the control electrode; step S8: using oxygen plasma etching to remove the photoresist of the gas microcavity, and completing the production of the laser for gas or smoke detection.

[0013] In an embodiment of the present invention, in step S1, the epitaxial wafer etching solution is CH 3 OH:H 3 PO 4 :H 2 O 2 :H 2 O=1.5~3:0.5~1.5: 0.5~1.5:4.5~5.5; in step S3, the passivation layer etching solution is HF:NH 4 F:H 2 O = 2 ~ 4ml: 5 ~ 7mg: 9 ~ 11ml; in step S6, the etching gas of the upper DBR is CHF 3 :Ar=80~120sccm:8~12sccm, Ni etching solution is HNO 3 :H 2 O=0.5~1.5: 0.5~1.5.

[0014] According to a third aspect of the present invention, there is provided an application of a laser for gas or smoke detection in the field of gas or smoke detection, comprising: Obtaining a first wavelength change for a plurality of known concentrations of the gas or smoke to be detected by the laser for gas or smoke detection; Obtaining a linear relationship between the wavelength change and the concentration of the gas or smoke to be detected based on the first wavelength change and the known concentration; and A second wavelength change for the unknown concentration of the gas or smoke to be detected is obtained by the laser for gas or smoke detection, and the concentration of the unknown concentration of the gas or smoke to be detected is determined based on the second wavelength change and the linear relationship.

[0015] The present invention proposes a laser for gas or smoke detection, a preparation method and an application thereof, wherein the laser for gas or smoke detection utilizes the cavity length and refractive index sensitivity of the FP cavity to achieve high sensitivity, long life, fast response, miniaturized non-selective gas and smoke detection, and has at least the following advantages: 1. Non-selective gas and smoke concentration detection, high sensitivity, long life, fast response and small size; 2. No external light source input is required, and the laser with wavelength changing with the gas concentration can be generated by itself, which is conducive to the simplification and miniaturization of the overall structure; 3. Using a polyimide sacrificial layer, the initial thickness of the gas microcavity can be adjusted by different dilution ratios. In addition, the thickness of the central area of ​​the gas microcavity can be controlled by controlling the electrode, thereby dynamically adjusting the responsiveness and detection range of the laser; 4. The upper DBR not only serves as a reflector but also as a cantilever beam, which avoids the cumbersome process of making a cantilever beam separately in the traditional structure and simplifies the preparation process; 5. The laser is prepared by a single-wafer deposition-etching process. Compared with double-wafer bonding and traditional single-wafer epitaxial structure and process, it has the advantages of simple preparation process and flexible customization of parameters of each part. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A three-dimensional schematic diagram of a laser for gas or smoke detection provided by one embodiment of the present invention; Figure 2 for Figure 1 An exploded schematic diagram of a laser for gas or smoke detection is shown; Figure 3-Figure 8 For preparation Figure 1-Figure 2A schematic cross-sectional view of the various stages of a laser for gas or smoke detection is shown, wherein: Figure 3 The cross-sectional schematic diagram of the light source part is shown, in which the etching of the mesa, oxidation, growth of the passivation layer and etching of the light hole, sputtering of the Ti / Au second electrode and stripping of the light hole, and then sputtering of the back first electrode have been completed; Figure 4 The light source portion and the sacrificial layer are shown; Figure 5 The light source part, sacrificial layer and upper DBR are shown; Figure 6 The light source part, sacrificial layer, upper DBR and control electrode are shown; Figure 7 The light source part, the sacrificial layer, the upper DBR, the control electrode and the light exit hole formed on the control electrode are shown; Figure 8 The laser for gas or smoke detection is shown as prepared; Fig. 9 A flow chart of a method for preparing a laser for gas or smoke detection provided by an embodiment of the present invention; Fig.10 The response of the laser for gas or smoke detection provided in the embodiment of the present invention to test the water mist particles; Fig.11 The response of the laser for gas or smoke detection provided by the embodiment of the present invention to test ethanol gas is almost linearly related to the gas concentration; Fig.12 The response of the laser for gas or smoke detection provided by the embodiment of the present invention to test carbon tetrachloride gas is almost linearly related to the gas concentration; Fig.13 The response of the laser for gas or smoke detection provided by the embodiment of the present invention to test acetone gas is almost linearly related to the gas concentration; Fig.14 A graph showing the relationship between different microcavity thicknesses and responsivity when testing ethanol gas for a laser used for gas or smoke detection. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0019] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.

[0020] As mentioned above, for gas or smoke detection, existing detectors have problems such as poor versatility and poor stability. Based on this, the present invention provides a laser for gas or smoke detection, and its preparation method and application. The laser includes a laser light source, a gas microcavity, an upper DBR and a control electrode from bottom to top. The gas microcavity is used to collect gas or smoke, change the resonance phase of the gas microcavity, and then adjust the output wavelength of the laser. Compared with traditional gas or smoke detectors, the laser of the present invention is characterized by high sensitivity, high response speed, high linearity, non-selective detection of gas or smoke, and the responsiveness and detection range can be changed by applying an external control voltage. The preparation method of the laser is made by a single-chip deposition-etching method, which is compatible with semiconductor processes, has high integration and small size.

[0021] Specifically, according to a first aspect of the present invention, a laser 100 for gas or smoke detection is provided. Figure 1 , Figure 2 and Figure 8 As shown, a laser 100 for gas or smoke detection includes: a light source portion 120; and a hollow sacrificial layer 130, an upper DBR 11 and a control electrode 12 sequentially formed on the light source portion 120, wherein the hollow sacrificial layer 130 and the upper DBR 11 define a gas microcavity 8 for collecting the gas or smoke to be detected, the thickness of the central region of the gas microcavity 8 changes based on the voltage applied by the control electrode 12, and wherein the laser 100 outputs a wavelength corresponding to the concentration of the gas or smoke to be detected in response to a change in the average refractive index of the gas microcavity 8 caused by the gas or smoke to be detected collected by the gas microcavity 8.

[0022] In an embodiment of the present invention, the laser 100 may be a VCSEL, whose optical cavity length is changed based on the change of the average refractive index of the gas microcavity 8 to output a wavelength corresponding to the concentration of the gas or smoke to be measured. In addition, the thickness of the central region of the gas microcavity 8 is inversely proportional to the detected concentration of the gas or smoke to be measured.

[0023] Specifically, the laser 100 proposed in the present invention has a gas microcavity 8 for collecting environmental gas or smoke. The difference in refractive index of different gases or smoke causes the average refractive index of the gas microcavity 8 to change, thereby changing the equivalent optical cavity length of the FP cavity of the laser 100, realizing the change of wavelength, and having no gas selectivity, it can detect a variety of gases or smoke. The minimum and maximum concentrations detected can also be dynamically adjusted by designing the thickness of the gas microcavity 8, solving the shortcoming that the detection range of traditional gas or smoke detectors is relatively fixed. Since it does not involve chemical reactions and physical adsorption, it has a fast response time, a long life, a small size, and low power consumption and heat generation, with an overall power consumption of about 50mW.

[0024] Since the FP cavity's lasing wavelength is extremely sensitive to the cavity length and the average refractive index in the cavity, a change in the cavity length of tens of nanometers can often cause a change in the wavelength of the nanometer level. The laser 100 for gas or smoke detection proposed in the present invention can achieve extremely high sensitivity in application. Since the two-dimensional area of ​​the gas microcavity 8 is very small, at the level of hundreds of micrometers, it not only improves the response speed of the laser 100 but also realizes the miniaturization of the device. Therefore, the laser 100 proposed in the present invention can achieve a faster gas or smoke concentration response, avoiding the low response speed caused by the large gas microcavity and slow gas diffusion speed. At the same time, by controlling the voltage applied by the electrode 12 to adjust the thickness of the gas microcavity 8, the sensitivity and detection range of the laser 100 can be flexibly adjusted to make it more widely applicable. For example, adjusting to a thicker gas microcavity 8 to accumulate a larger phase difference can achieve the detection of a smaller concentration of gas or smoke; while adjusting to a thinner gas microcavity 8 can achieve a larger range of concentration detection.

[0025] The hollow sacrificial layer 130 is formed by partially etching the sacrificial layer 9 after the photoresist is spin-coated on the light source part 120 to form the sacrificial layer 9, and the initial thickness of the gas microcavity 8 depends on the thickness of the photoresist, and the thickness of the photoresist changes based on the dilution ratio of the photoresist. In one embodiment, the photoresist may include but is not limited to a 5214 model photoresist. In another embodiment, the photoresist may include but is not limited to polyimide, such as but not limited to a JSR-5100 model polyimide. The initial thickness of the gas microcavity 8 can be changed by adding different proportions of diluents and adjusting the concentration of the photoresist, thereby changing the free spectral range (FSR) of the gas microcavity 8. Based on this, lasers for different gases or smoke can be prepared to improve versatility. The photoresist can adjust the dilution ratio of the photoresist through a photoresist diluent. The photoresist diluent includes an organic solvent. In one embodiment, the photoresist diluent includes but is not limited to at least one of chlorobenzene, toluene, and carbon tetrachloride. In addition, the two-dimensional size of the gas microcavity 8 is at the level of hundreds of microns, which greatly reduces the volume of the laser 100.

[0026] In general, during the preparation stage of the laser 100, the gas microcavity 8 of a predetermined initial thickness can be manufactured by adjusting the dilution ratio of the photoresist, thereby obtaining a predetermined free spectrum range of the gas microcavity 8. After the laser 100 is prepared, the thickness of the central region of the gas microcavity 8 can be adjusted by applying an external voltage through the control electrode 12. For example, the upper DBR 11 acting as a cantilever beam can be deformed under an external voltage (for example, a depression is generated in the center of the cantilever beam), so that the thickness of the central region of the gas microcavity 8 changes when the thickness of the photoresist is constant, thereby adjusting the minimum concentration and maximum concentration of the detection.

[0027] Further references Figure 8 The light source part 120 may include a lower DBR 2, an active region 3, an oxidation restriction layer 6, an intermediate DBR 7, and a passivation layer 4 sequentially grown on a GaAs substrate; a first electrode 1 sputtered on the back of the GaAs substrate and a second electrode 5 sputtered on the passivation layer 4, a photoresist is spin-coated on the second electrode 5, and the second electrode 5 is used to inject current into the laser 100. The passivation layer 4, the second electrode 5, and the control electrode 12 each include a light exit hole, wherein the diameter of the light exit hole 4a of the passivation layer 4 is smaller than the table F of the light source part 120 (at Figure 3 ), and the diameter of the light exit hole 5a of the second electrode 5 is smaller than the diameter of the light exit hole 4a of the passivation layer 4, thereby forming a nested structure. Through such a structure, the passivation layer 4 can form a side insulation effect, and the metal can realize current injection on the top of the table F. In addition, in the present invention, the gas microcavity 8 generally surrounds the area where the table F is located, that is, surrounds the light exit hole 4a and the light exit hole 5a.

[0028] The laser 100 can use a laser light source for a GaAs material system, and its wavelength includes but is not limited to 1060nm. The first electrode 1 and the second electrode 5 can each include a Ti / Au material system. The second electrode 5 can also be used as a mask in the manufacturing process, so the second electrode 5 can use a metal with a harder texture and more stable chemical properties, including but not limited to nickel (Ni), chromium (Cr), etc. The control electrode 12 can also be called a third electrode, which is used to apply a voltage to control the thickness of the microcavity, determine its static operating point, and dynamically change the detector's responsiveness and detection range. The upper DBR 11 serves as the upper DBR of the laser 100 to form optical feedback. It not only serves as a reflector but also as a cantilever beam, constituting a structural unit of the gas microcavity 8. The upper DBR 11 includes a multilayer dielectric material, which includes a low stress, high refractive index contrast material system, such as SiO 2 / TiO 2 、SiO 2 / Ta 2 O 5 In one embodiment, TiO2 and SiO 2 Alternating distribution of reflection (i.e. distributed Bragg reflector), and generally TiO 2 As the first and last layer, the passivation layer 4 comprises SiO 2 Passivation layer.

[0029] In summary, the laser 100 described in the present invention can be simply divided into two parts: a light source part 120 and a gas microcavity 8. A sacrificial layer 9, an upper DBR 11 and a control electrode 12 are sequentially deposited on the light source part 120, and then the sacrificial layer 9 is sequentially patterned and etched to form a hollow sacrificial layer 130 to complete the preparation of the laser 100.

[0030] According to a second aspect of the present invention, there is provided a method for preparing a laser for gas or smoke detection. Figure 3-Figure 9 The following specifically describes a method 300 for manufacturing a laser 100 for gas or smoke detection according to the present invention. The laser 100 is manufactured as a whole by a single-chip deposition-etching process.

[0031] like Fig. 9 The method 300 comprises the following steps: Step S1: using metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) to sequentially epitaxially grow the lower DBR 2, the active region 3, the oxidation restriction layer 6 and the middle DBR 7 on the GaAs substrate to obtain an epitaxial wafer, such as Figure 3 As shown; Step S2: Photolithography and etching to form a table surface F (on Figure 3 As shown in the figure), lateral wet nitrogen oxidation is performed around the periphery to form an oxide limiting hole to limit the light field and current; Step S3: growing a passivation layer 4 and performing photolithography and etching on the light exit hole 4a of the passivation layer 4, then sputtering a second electrode 5 and performing photolithography and etching on the light exit hole 5a of the second electrode 5, and making the light exit hole 4a of the passivation layer 4 smaller than the diameter of the table F' and the light exit hole 5a of the second electrode 5 smaller than the light exit hole 4a of the passivation layer 4, forming a nested structure, completing the manufacture of the light source part 120, and finally sputtering a first electrode 1 on the back side of the GaAs substrate; Step S4: Spin-coat the photoresist on the second electrode 5 using a coating machine and solidify it to form a sacrificial layer 9, such as Figure 4 As shown; Step S5: growing a plurality of pairs (e.g., about 10 pairs) of upper DBRs 11 on the sacrificial layer 9, such as Figure 5 As shown. The upper DBR 11 also serves as a gas microcavity 8 (in Figure 8 A cantilever beam (shown in FIG. 1 ); Step S6: Photolithography and sputtering of Ni on the upper DBR 11 to form a control electrode 12, such as Figure 6 As shown. The microcavity shape of the gas microcavity 8 is formed by peeling, and then the upper DBR 11 is patterned by RIE etching using the control electrode 12 as an etching mask to form the gas microcavity 8; Step S7: Photolithography and etching of the light exit hole 12a of the control electrode 12, such as Figure 7 As shown; Step S8: Use oxygen plasma etching to remove the photoresist of the gas microcavity 8, and complete the production of the laser to obtain Figure 8 A laser 100 for gas or smoke detection is shown.

[0032] In step S1, the epitaxial wafer etching solution is CH 3 OH:H 3 PO 4 :H 2 O 2 :H 2 O=1.5~3:0.5~1.5: 0.5~1.5:4.5~5.5; In one embodiment, the epitaxial wafer etching solution is CH 3 OH:H 3 PO 4 :H 2 O 2 :H 2 O=2:1:1:5.

[0033] In step S3, the passivation layer etching solution is HF:NH 4 F:H 2 O=2~4ml:5~7mg:9~11ml. In one embodiment, SiO 2 The etching solution is HF:NH4F:H2O=3ml:6mg:10ml.

[0034] In step S6, the etching gas for the upper DBR is CHF 3 :Ar=80~120sccm:8~12sccm, Ni etching solution is HNO 3 :H 2 O=0.5~1.5: 0.5~1.5. In one embodiment, the etching gas for the upper DBR is CHF 3 :Ar=100sccm:10sccm, Ni etching solution is HNO 3 :H 2 O=1:1.

[0035] The preparation method 300 of the laser for gas or smoke detection proposed in the present invention can realize the preparation of the laser for non-selective gas or smoke concentration detection over a wide range. The sacrificial layer of polyimide, the upper DBR and the control electrode are sequentially deposited on the light source part of the laser, and then the sacrificial layer is sequentially patterned and etched. The whole is prepared by a single-chip deposition-etching process. At the same time, the upper DBR is used not only as a reflector but also as a cantilever beam, avoiding the cumbersome process of making a cantilever beam separately in the traditional structure. Compared with double-chip bonding and traditional single-chip epitaxial structure and process, it has the advantages of simple preparation process and flexible customization of parameters of each part.

[0036] According to a third aspect of the present invention, an application of a laser for gas or smoke detection in the field of gas or smoke detection is provided. The laser 100 mentioned in the embodiment of the present invention can be applied to the field of gas or smoke detection to solve the problems existing in the prior art.

[0037] When the laser for gas or smoke detection of the present invention is used, after the gas or smoke enters the gas microcavity, the optical cavity length (i.e., physical thickness multiplied by refractive index) of the laser will change, and then the output wavelength will change. Since one output wavelength change corresponds to one gas or smoke concentration, the output wavelength can be used to detect the concentration of gas or smoke.

[0038] In an embodiment of the present invention, the application includes: Obtaining a first wavelength change for a plurality of known concentrations of the gas or smoke to be detected by a laser for gas or smoke detection; Obtaining a linear relationship between the wavelength change and the concentration of the gas or smoke to be detected based on the first wavelength change and the known concentration; and The second wavelength variation of the unknown concentration of the gas or smoke to be detected is obtained by a laser for gas or smoke detection, and the concentration of the unknown concentration of the gas or smoke to be detected is determined based on the second wavelength variation and a linear relationship.

[0039] The application will be described below by way of an example: When the gas microcavity of the laser for gas or smoke detection of the present invention collects smoke or water mist, the smoke or water mist will change the average refractive index of the gas microcavity, and the laser will output different wavelengths. In this way, the presence and concentration of smoke or water mist can be detected. Fig.10For a laser (for example, the laser 100 of the present invention) for gas or smoke detection with a central wavelength of 1060 nm, deionized water mist is used instead of smoke particles, and the wavelength variation under different test environments is 2 nm. It can be seen that the laser of the present invention can be used to detect water mist or smoke, and realize the detection of water mist or smoke, etc. The application of the laser of the present invention in gas detection is further explained below.

[0040] Figure 11-13 This is an example of a specific application of the gas or smoke detection laser of the present invention in gas detection.

[0041] Taking ethanol as an example, when the gas microcavity collects ethanol gas, the average refractive index in the gas microcavity will change (wherein, the higher the concentration of ethanol, the greater the refractive index), thereby increasing the optical cavity length (physical thickness multiplied by the refractive index) and causing the wavelength to redshift. Based on this, the gas microcavity of the laser for gas or smoke detection described in the present invention can be used to collect multiple ethanol gases of known concentrations, and for each known concentration, a spectrometer is used to measure the wavelength to obtain a first wavelength change for the ethanol gas of known concentration. Thereafter, a linear relationship between the wavelength change and the concentration of the ethanol gas is obtained based on the first wavelength change and the known concentration, for example, based on four wavelength change vs. concentration value outputs. Fig.11 The curve graph shown. Fig.11 In the above equation, the responsivity is the slope of the output curve, which is the change in wavelength divided by the change in concentration. Fig.11 The curve can be used to obtain the gas concentration corresponding to any wavelength, thus realizing the concentration detection of ethanol gas of unknown concentration. That is to say, in practical applications, ethanol gas of unknown concentration can be collected by a laser used for gas or smoke detection, and the wavelength can be measured by a spectrometer to obtain the wavelength change, and then Fig.11 Find out the relationship with the ethanol gas concentration, and thus obtain the ethanol gas concentration at this time.

[0042] In a similar way, the concentrations of carbon tetrachloride and acetone gases can be obtained, such as Figure 12-13 shown.

[0043] Taking ethanol, carbon tetrachloride and acetone as examples, the wavelength variation of the laser of the present invention is proportional to the gas concentration, has good linearity and no gas selectivity. The responsivity for ethanol, carbon tetrachloride and acetone is 0.044nm / unit percentage, 0.0085nm / unit percentage and 0.056nm / unit percentage respectively, and has different microcavity thicknesses under different control voltages, that is, it has different responsivities for the same gas.

[0044] like Fig.14As shown, different gas microcavity thicknesses result in different slopes, i.e., detection responsivity, i.e., different changes in gas concentration corresponding to unit wavelength changes. As described above, by applying a voltage to the control electrode, the thickness of the gas microcavity can be changed (due to electrostatic attraction), thereby adjusting the responsivity and detection range to adapt to different environments. The detection range and responsivity of the laser described in the present invention are mutually constrained, i.e., a large range corresponds to a weak responsivity, and a strong responsivity corresponds to a small range. The thicker the gas microcavity, the smaller the detection range, but the higher the responsivity.

[0045] In summary, the present invention provides a laser for gas or smoke detection, a preparation method and an application thereof. The laser of the present invention utilizes the cavity length and refractive index sensitivity of the FP cavity to achieve high sensitivity, long life, fast response, miniaturized non-selective gas and smoke detection.

[0046] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A laser for gas or smoke detection, characterized in that: include: Light source part; as well as A hollow sacrificial layer, an upper DBR and a control electrode are sequentially formed on the light source part, wherein the hollow sacrificial layer and the upper DBR define a gas microcavity for collecting the gas or smoke to be measured, the thickness of the central region of the gas microcavity changes based on the voltage applied by the control electrode, and The laser outputs a wavelength corresponding to the concentration of the gas or smoke to be measured in response to the change of the average refractive index of the gas microcavity caused by the gas or smoke to be measured collected by the gas microcavity.

2. The laser according to claim 1, characterized in that The optical cavity length of the laser changes based on the change of the average refractive index of the gas microcavity to output a wavelength corresponding to the concentration of the gas or smoke to be measured; the thickness of the central area of ​​the gas microcavity is inversely proportional to the detected concentration of the gas or smoke to be measured.

3. The laser according to claim 1, characterized in that The hollow sacrificial layer is formed by spin coating a photoresist on the light source portion and then partially etching it; the initial thickness of the gas microcavity depends on the thickness of the photoresist, and the thickness of the photoresist changes based on the dilution ratio of the photoresist.

4. The laser according to claim 3, characterized in that The light source part includes a lower DBR, an active area, an oxidation restriction layer, an intermediate DBR, and a passivation layer grown in sequence on a GaAs substrate; a first electrode sputtered on the back of the GaAs substrate and a second electrode sputtered on the passivation layer, the photoresist is spin-coated on the second electrode, and the second electrode is used to inject current into the laser.

5. The laser according to claim 4, characterized in that The passivation layer, the second electrode and the control electrode each include a light exit hole, wherein the diameter of the light exit hole of the passivation layer is smaller than the diameter of the table of the light source part, and the diameter of the light exit hole of the second electrode is smaller than the diameter of the light exit hole of the passivation layer.

6. The laser according to claim 4, characterized in that The first electrode and the second electrode each include a Ti / Au material system, and the second electrode includes a metal with a relatively hard texture and relatively stable chemical properties; the upper DBR serves as a cantilever beam of the gas microcavity and includes a multilayer dielectric material, and the multilayer dielectric material includes a low stress, high refractive index contrast material system; the passivation layer includes a SiO2 passivation layer.

7. The laser according to claim 3, characterized in that The photoresist includes polyimide, and the dilution ratio of the photoresist is adjusted by a photoresist diluent, and the photoresist diluent includes an organic solvent.

8. A method for preparing a laser for gas or smoke detection according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step S1: epitaxially growing a lower DBR, an active region, an oxidized limiting layer and an intermediate DBR in sequence on a GaAs substrate by metal organic chemical vapor deposition or molecular beam epitaxy to obtain an epitaxial wafer; Step S2: photolithography and etching to form a platform, and lateral wet nitrogen oxidation is performed around it to form an oxidation limiting hole to limit the light field and current; Step S3: growing a passivation layer, photolithography and etching the light exit hole of the passivation layer, then sputtering a second electrode, photolithography and etching the light exit hole of the second electrode, and making the light exit hole of the passivation layer smaller than the diameter of the table, and the light exit hole of the second electrode smaller than the light exit hole of the passivation layer, forming a nested structure, completing the manufacture of the light source part, and finally sputtering a first electrode on the back side of the GaAs substrate; Step S4: using a coating machine to spin-coat a photoresist on the second electrode and solidify the photoresist to form a sacrificial layer; Step S5: growing a plurality of pairs of upper DBRs on the sacrificial layer, wherein the upper DBRs also serve as cantilever beams of the gas microcavity; Step S6: photolithography and sputtering Ni on the upper DBR to form a control electrode, peeling off to form the microcavity shape of the gas microcavity, and then using it as an etching mask to perform RIE patterning etching on the upper DBR to form the gas microcavity; Step S7: photolithography and etching of the light exit hole of the control electrode; Step S8: using oxygen plasma etching to remove the photoresist of the gas microcavity, thereby completing the manufacture of the laser for gas or smoke detection.

9. The preparation method according to claim 8, characterized in that In step S1, the epitaxial wafer etching solution is CH3OH:H3PO4:H2O2:H2O=1.5~3:0.5~1.5: 0.5~1.5:4.5~5.5; in step S3, the passivation layer etching solution is HF:NH4F:H2O=2~4ml:5~7mg:9~11ml; in step S6, the etching gas of the upper DBR is CHF3:Ar=80~120sccm:8~12sccm, and the Ni etching solution is HNO3:H2O=0.5~1.5: 0.5~1.

5.

10. An application of a laser for gas or smoke detection according to any one of claims 1 to 7 in the field of gas or smoke detection, characterized in that: include: Obtaining a first wavelength change for a plurality of known concentrations of the gas or smoke to be detected by the laser for gas or smoke detection; Obtaining a linear relationship between the wavelength change and the concentration of the gas or smoke to be detected based on the first wavelength change and the known concentration; as well as A second wavelength change for the unknown concentration of the gas or smoke to be detected is obtained by the laser for gas or smoke detection, and the concentration of the unknown concentration of the gas or smoke to be detected is determined based on the second wavelength change and the linear relationship.

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