LED (light-emitting diode) integration-based bottom illumination type optical excitation gas sensor as well as preparation method and application thereof

Abstract

The invention relates to the technical field of gas detection, in particular to a bottom illumination type optical excitation gas sensor based on LED integration as well as a preparation method and application of the bottom illumination type optical excitation gas sensor. The invention provides a bottom illumination type optical excitation gas sensor based on LED integration. The bottom illumination type optical excitation gas sensor comprises an LED light-emitting layer, a substrate, a gas-sensitive test electrode and a gas-sensitive material layer which are sequentially stacked, the number of the gas-sensitive test electrodes is gt; the method comprises the following steps: 1, arranging the gas-sensitive test electrodes on the surface of the substrate at intervals; part of the gas-sensitive material layer is in contact with the substrate, and the rest of the gas-sensitive material layer is in contact with the gas-sensitive test electrode; and the substrate is made of a transparent insulating material. According to the bottom illumination type optical excitation gas sensor based on LED integration, integration of the optical excitation gas sensor is achieved, meanwhile, direct contact between the light-emitting layer and the gas-sensitive material layer can be avoided, and the problem that the integration technology is not easy to achieve is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to a bottom-illuminated light-excited gas sensor based on LED integration, and a preparation method and application thereof. Background Art

[0002] As people's demand for multifunctional portable devices grows, the number of sensors integrated into electronic devices is also increasing. Gas sensors are electronic devices that can quickly and accurately obtain environmental atmosphere information. If they can be integrated into portable smart devices, their application potential in environmental monitoring, food safety, medical care, and public safety can be significantly improved. Due to the dual limitations of miniaturization of electronic devices and battery life, there are currently no mature portable electronic products that integrate gas sensors. Therefore, the development of miniaturized, low-energy, and highly integrated gas sensors is an important development direction in this field.

[0003] Existing commercial gas sensor products are mainly thermally excited. This type of sensor needs to be heated to 300-500℃ to work. This not only poses high-temperature safety issues, but also increases the power consumption of the sensor, which is not conducive to its integrated application. Photoexcitation gas sensors have received widespread attention due to their room temperature working characteristics. Some researchers hope to use ambient light sources such as indoor lighting or sunlight to provide energy for the sensor, thereby reducing the overall energy consumption of the device without increasing the complexity of the device structure. However, this ambient light source is not stable. Many factors such as the distance between the sensor and the light source, the stability of the light source itself, and the interference of the surrounding light environment will affect the working stability of the sensor. In addition, in the traditional thermal excitation state, since the temperature is uniform throughout the sensitive material, the internal carrier concentration distribution is also uniform, that is, the conductivity of the material is consistent everywhere; and the light intensity in the sensitive material will gradually decay as the distance from the light source increases and is absorbed by the material, that is, the light intensity distribution inside the sensitive material is uneven, and the distribution of photogenerated carriers inside the material decreases along the direction of illumination. This uneven distribution is related to the material's absorbance and the position of the light source, which will directly affect the carrier conduction inside the sensitive material. Therefore, a stable, convenient and energy-saving light source integration method is urgently needed to provide stable light energy for light-excited gas sensors.

[0004] As a stable light source with mature technology and low cost, LED is the most common type of light source in the current research of photoexcitation gas sensors. If LED and gas sensor can be integrated on the same chip, the above-mentioned problems such as unstable light energy and separation of device structure can be directly solved. However, this integrated gas sensor is still in the theoretical research stage, and no practical device has appeared. One of the difficulties is the integration and packaging of the light source and sensor. The light energy of the photoexcitation gas sensor needs to be applied to the surface of the sensitive material. Therefore, the existing device structure is that the light source and the sensitive material are on the same side of the substrate and the light source is suspended above the sensitive material. Sufficient space must be maintained between the light source and the sensitive material so that the gas to be measured can fully flow on the surface of the sensitive material to facilitate the adsorption and desorption of the gas. However, since the light intensity will decay as the distance between the sensitive material and the light source increases, factors such as the position of the light source and the irradiation angle will directly affect the photoexcitation gas sensing performance of the sensitive material. Since light-excited gas sensors are usually top-illuminated, the light source and gas sensor are separated in structure, resulting in a large overall structural load and size of the device; since the LED preparation process is not compatible with the preparation process of other metal oxide semiconductor sensors, the deposition conditions and operating temperatures of the two different functional layers are very different, making it difficult to integrate them on the same substrate; in addition, there are significant differences in the packaging requirements of the light source and gas sensor. The LED light-emitting layer is usually completely coated with materials such as silicone or epoxy resin to prevent the external environment from interfering with the light-emitting performance; and the sensitive layer material in the gas sensor must be exposed to the environment in order to react with the gas to be measured. This special structural requirement has resulted in the absence of a mature light-excited gas sensor so far. Therefore, how to solve the above-mentioned device structural defects is a technical bottleneck that needs to be overcome urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a bottom-illuminated light-excited gas sensor based on LED integration and a preparation method and application thereof. The bottom-illuminated light-excited gas sensor based on LED integration realizes the integration of light-excited gas sensors, and can avoid direct contact between the light-emitting layer and the gas-sensitive material layer, thus avoiding the problem that the integration process is not easy to achieve.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a bottom-illuminated light-excited gas sensor based on LED integration, comprising an LED light-emitting layer, a substrate, a gas-sensitive test electrode and a gas-sensitive material layer stacked in sequence;

[0008] The number of the gas-sensitive test electrodes is greater than 1, and each gas-sensitive test electrode is arranged at intervals on the surface of the substrate;

[0009] Part of the gas-sensitive material layer is in contact with the substrate, and the remaining gas-sensitive material layer is in contact with the gas-sensitive test electrode;

[0010] The substrate is a transparent insulating material.

[0011] Preferably, the light emission wavelength of the LED light emitting layer is 200-750 nm.

[0012] Preferably, the transmittance of the substrate is >85%.

[0013] Preferably, the substrate comprises glass, sapphire, PEI or PI.

[0014] Preferably, the material of the gas-sensitive test electrode includes gold, platinum, silver or copper.

[0015] Preferably, the band gap of the gas-sensitive material layer is 1.55 to 4.0 eV.

[0016] Preferably, the material of the gas-sensitive material layer includes one or more of doped or undoped indium oxide, doped or undoped tungsten trioxide, doped or undoped tin oxide, doped or undoped titanium oxide, doped or undoped zinc oxide, doped or undoped carbon nanofibers, doped or undoped carbon nanotubes, doped or undoped graphene, doped cobalt oxide and doped cadmium oxide.

[0017] Preferably, when the material of the gas-sensitive material layer is a doped material, the doping elements include one or more of gold, silver, platinum, palladium, iron, cobalt, nickel, manganese, cerium, niobium, carbon and nitrogen.

[0018] The present invention also provides a method for preparing the bottom-illuminated light-excited gas sensor based on LED integration described in the above technical solution, comprising the following steps:

[0019] After depositing an LED light-emitting layer and a protective layer on the surface of one side of the substrate in sequence, and depositing a gas-sensitive test electrode and a gas-sensitive material layer in sequence on the other side of the substrate, the protective layer is removed to obtain the bottom-illuminated light-excited gas sensor based on LED integration.

[0020] The present invention also provides the application of the bottom-illuminated light-excited gas sensor based on LED integration described in the above technical solution or the bottom-illuminated light-excited gas sensor based on LED integration prepared by the preparation method described in the above technical solution in the field of gas detection.

[0021] The present invention provides a bottom-illuminated optically excited gas sensor based on LED integration, comprising an LED light-emitting layer, a substrate, a gas-sensitive test electrode and a gas-sensitive material layer stacked in sequence; the number of the gas-sensitive test electrodes is greater than 1, and each gas-sensitive test electrode is arranged at intervals on the surface of the substrate; part of the gas-sensitive material layer is in contact with the substrate, and the remaining gas-sensitive material layer is in contact with the gas-sensitive test electrode; the substrate is a transparent insulating material. The present invention deposits the LED light-emitting layer and the gas-sensitive material layer on both sides of the same substrate respectively, which can not only avoid the structural defects of the separation of the light source and the sensor from the structural point of view, but also use the substrate as a natural physical isolation layer, without the need to set up a corresponding structure to avoid the mutual interference between the gas-sensitive material and the LED light-emitting layer, and avoid direct contact between the LED light-emitting layer and the gas-sensitive layer; neither the light source nor the test electrode will block the contact between the test gas and the sensitive material, and there is no need to reserve a cavity between the light source and the sensitive material, which can not only shorten the optical path of the excitation light source, but also greatly simplify the device structure while reducing the device volume; the above structural design can break through the bottleneck of the incompatibility of the preparation process of the LED light-emitting layer and the gas-sensitive material layer, and promote the practical development of optically excited gas sensors.

[0022] The present invention also provides a method for preparing the bottom-illuminated optically excited gas sensor based on LED integration described in the above technical solution, comprising the following steps: depositing an LED light-emitting layer and a protective layer on the surface of one side of the substrate in sequence, depositing a gas-sensitive test electrode and a gas-sensitive material layer in sequence on the other side of the substrate, and removing the protective layer to obtain the bottom-illuminated optically excited gas sensor based on LED integration. The present invention has a breakthrough in that a protective layer is provided in the integration process to avoid mutual interference between the LED light-emitting layer and the gas-sensitive material layer in different deposition processes.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] 1) Compared with the existing thermally excited gas sensor, the device structure of the bottom-illuminated optically excited gas sensor based on LED integration of the present invention eliminates the heater part in the structure, and no heater is required to power the device, thus solving the problem that the traditional gas sensor must work at high temperature;

[0025] 2) Compared with the existing light-excited gas sensor in which the excitation light source and the sensor are separated, the device structure of the bottom-illuminated light-excited gas sensor based on LED integration of the present invention has a stable light source and a fixed position relationship between the gas-sensitive material layer, which significantly shortens the distance between the light source and the sensitive layer material, improves the utilization rate of the light energy of the light source by the sensitive layer material, and improves the problem of large device volume and low light energy utilization rate caused by the separation of the light source and the sensitive layer material of the non-integrated light-excited gas sensor;

[0026] 3) Compared with the existing light-excited gas sensor in which the excitation light source and the sensor are separated, the device structure of the bottom-illuminated light-excited gas sensor based on LED integration of the present invention avoids direct contact between the gas to be measured and the light-emitting layer material because the light source and the sensitive material layer are located on different sides of the substrate, and reduces the interference of the change of the atmosphere to be measured on the light-emitting performance of the LED light-emitting layer, thereby improving the light-emitting stability and light-emitting life of the LED light-emitting layer;

[0027] 4) Compared with the existing process, the preparation method of the bottom-illuminated light-excited gas sensor based on LED integration described in the present invention has a protective layer covering the surface of the LED light-emitting layer after the deposition of the LED light-emitting layer. This can isolate the light-emitting layer during the subsequent gas-sensitive layer deposition process, thereby avoiding interference of the gas-sensitive layer deposition environment on the light-emitting layer, thereby ensuring that the light-emitting performance of the light-emitting layer is not affected by the gas-sensitive layer deposition process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of the bottom-illuminated light-excited gas sensor based on LED integration according to the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the bottom-illuminated light-excited gas sensor based on LED integration described in Example 1;

[0030] Among them, 1 is the LED light-emitting layer, 2 is the substrate, 3 is the gas-sensitive test electrode, 4 is the gas-sensitive material layer; 5 is the sapphire substrate, 6 is the Au test electrode, 7 is the ZnO gas-sensitive material layer, 8 to 17 are the UV-LED light-emitting layers (8 is the AlN buffer layer, 9 is the n-AlGaN layer, 10 is the multiple quantum well MQWs layer, 11 is the p-AlGaN layer, 12 is the EBL layer, 13 is the p-GaN layer, 14 is the n-contact electrode, 15 is the p-contact electrode, 16 is the SiO2 passivation layer, and 17 is the reflective layer). DETAILED DESCRIPTION

[0031] The present invention provides a bottom-illuminated light-excited gas sensor based on LED integration, comprising an LED light-emitting layer, a substrate, a gas-sensitive test electrode and a gas-sensitive material layer stacked in sequence;

[0032] The number of the gas-sensitive test electrodes is greater than 1, and each gas-sensitive test electrode is arranged at intervals on the surface of the substrate;

[0033] Part of the gas-sensitive material layer is in contact with the substrate, and the remaining gas-sensitive material layer is in contact with the gas-sensitive test electrode;

[0034] The substrate is a transparent insulating material.

[0035] In the present invention, the light emission wavelength of the LED light emitting layer is preferably 200-750 nm. In the present invention, the LED light emitting layer is preferably arranged below the substrate, and the light irradiation direction of the LED light emitting layer is preferably upward.

[0036] The present invention does not have any special limitation on the structure of the LED light-emitting layer, and a structure well known to those skilled in the art may be used.

[0037] In the present invention, the LED light-emitting layer provides energy for the gas-sensitive reaction of the gas-sensitive material layer.

[0038] In the present invention, the transmittance of the substrate is preferably >85%. In the present invention, the thickness of the substrate is preferably 1 μm to 1 cm, more preferably 100 to 800 μm, and most preferably 300 to 600 μm. In the present invention, the substrate preferably includes glass, sapphire, PEI or PI. In an embodiment of the present invention, the substrate is specifically a sapphire wafer, and the sapphire wafer is a single-sided polished C-oriented sapphire (Al2O3) single crystal (0001) surface.

[0039] In the present invention, the substrate provides support for the LED light-emitting layer and the gas-sensitive material layer, and is located between the LED light-emitting layer and the sensitive film.

[0040] In the present invention, the number of the gas-sensitive test electrodes is preferably greater than 1, and more preferably 2; each gas-sensitive test electrode is preferably arranged at intervals on the surface of the substrate. In the present invention, the material of the gas-sensitive test electrodes preferably includes gold, platinum, silver or copper.

[0041] In the present invention, the thickness of the gas-sensitive test electrode is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm, and most preferably 0.5 to 5 μm.

[0042] In the present invention, the bandgap of the gas-sensitive material layer is preferably 1.55 to 4.0 eV, and more preferably 2.0 to 3.0 eV.

[0043] In the present invention, the material of the gas-sensitive material layer preferably includes one or more of doped or undoped indium oxide, doped or undoped tungsten trioxide, doped or undoped tin oxide, doped or undoped titanium oxide, doped or undoped zinc oxide, doped or undoped carbon nanofibers, doped or undoped carbon nanotubes, doped or undoped graphene, doped cobalt oxide and doped cadmium oxide; when the material of the gas-sensitive material layer is a doped material, the doping element preferably includes one or more of gold, silver, platinum, palladium, iron, cobalt, nickel, manganese, cerium, niobium, carbon and nitrogen; when the material of the gas-sensitive material layer is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

[0044] In the present invention, the thickness of the gas-sensitive material layer is preferably 200 nm to 500 μm, more preferably 1 to 100 μm, and most preferably 5 to 50 μm.

[0045] In the present invention, the gas-sensitive material layer is arranged above the substrate and covers the gas-sensitive test electrode, serving as a place for receiving excitation light and gas-sensitive reaction. After light irradiates the gas-sensitive material layer from the bottom, an upward decreasing photogenerated carrier concentration gradient will be generated in the material; the photogenerated carriers react with the ambient gas molecules and conduct within the material to form electrical signals, that is, a gas-sensitive response is generated, and gas sensing is achieved by testing the changes in the electrical properties of the gas-sensitive material layer.

[0046] The present invention also provides a method for preparing the bottom-illuminated light-excited gas sensor based on LED integration described in the above technical solution, comprising the following steps:

[0047] After depositing an LED light-emitting layer and a protective layer on the surface of one side of the substrate in sequence, and depositing a gas-sensitive test electrode and a gas-sensitive material layer in sequence on the other side of the substrate, the protective layer is removed to obtain the bottom-illuminated light-excited gas sensor based on LED integration.

[0048] In the present invention, the protective layer preferably comprises a photoresist layer, an aluminum oxide layer, a silicon nitride layer, polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE) or polyimide (PI). In the present invention, the thickness of the protective layer is preferably 0.05 to 50 μm, more preferably 0.5 to 25 μm, and most preferably 1 to 20 μm.

[0049] The present invention does not have any special limitation on the deposition process, and the deposition process may be carried out using a process well known to those skilled in the art.

[0050] In the present invention, the method for removing the protective layer is preferably immersion, plasma etching or mechanical stripping, and more preferably immersion. In the present invention, the immersion liquid used in the immersion is preferably one or more of acetone, N-methylpyrrolidone (NMP), propylene glycol methyl ether (PGME) and propylene glycol methyl ether acetate (PGMEA). When the immersion liquid is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio.

[0051] The present invention also provides the application of the bottom-illuminated optically excited gas sensor based on LED integration described in the above technical solution or the bottom-illuminated optically excited gas sensor based on LED integration prepared by the preparation method described in the above technical solution in the field of gas detection. The present invention does not have any special limitation on the method of the application, and the method well known to those skilled in the art can be used.

[0052] The bottom-illuminated light-excited gas sensor based on LED integration and its preparation method and application provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0053] Example 1

[0054] Select C-oriented sapphire single crystal (0001 surface) as the substrate;

[0055] The LED light-emitting layer is prepared on one side of the substrate: an AlGaN epitaxial layer is grown on the surface of the substrate using MOCVD technology, and the process is as follows: after growing a 2.5 μm thick AlN buffer layer on the polished surface of the substrate, a 2.5 μm thick Si-doped n-Al 0.55 Ga 0.45 N (as n-contact layer), 7 layers of Al 0.45 Ga 0.55 N(thickness 3nm) / Al 0.55 Ga 0.45 N (11nm thick) multiple quantum wells (MQWs), 25nm thick Mg-doped p-Al 0.65 Ga 0.35 N electron blocking layer (EBL), Mg-doped n-Al with a thickness of 250 nm 0.5 Ga 0.5 N layer and Mg-doped p-GaN layer (p-contact) with a thickness of 50 μm;

[0056] The AlGaN epitaxial layer is micro-machined to form an array of flip-chip structures (each unit in the array is 30 mil×30 mil in size): a mesa-shaped geometric structure with a depth of 670 nm and an exposed n-AlGaN surface are formed by etching, and an n-AlGaN / AlN deep isolation trench and sidewall with a depth of 5 μm are formed by etching; then, contact electrodes (Ti / Al / Ti / Au) of n-AlGaN and contact electrodes (Ni / Au) of the p-GaN layer are sequentially deposited; a reflective layer of SiO2 / Al is then deposited to cover the entire flip-chip structure to ensure that all photons emitted by the integrated microchip are reflected into the gas-sensitive material layer on the other side of the sapphire substrate; finally, a SiO2 passivation layer and an NP-Pad (CrPtAu) layer are sequentially deposited on the entire wafer;

[0057] A protective layer is prepared on the surface of the LED light-emitting layer: a 1 μm layer of photoresist is spin-coated by a spin coating method;

[0058] A gas-sensitive test electrode is prepared on the other side surface of the substrate: an Au test electrode (Au interdigital electrode) with a thickness of about 2 μm is deposited on the other side surface of the substrate by electron beam evaporation;

[0059] Preparation of gas-sensitive material layer: zinc oxide was deposited on the surface of the gas-sensitive test electrode and the surface exposed on the substrate by a two-step hydrothermal method; first, a ZnO seed layer with a thickness of about 40 nm was prepared on the interdigital electrode layer prepared on the non-polished surface of sapphire by radio frequency magnetron sputtering at room temperature by exciting a ZnO target; then, 0.03 M Zn(NO3)2·6H2O and 0.03 M C6H 12 N4 is used to prepare 50mL of hydrothermal reaction solution; the hydrothermal reaction solution is poured into the Teflon lining of a 60mL high-pressure reactor, and the substrate with the ZnO seed layer is inverted in the middle and placed in the high-pressure reactor for hydrothermal reaction at 80°C for 6h to grow a nanorod array; finally, the substrate on which the ZnO nanorods have been grown is rinsed with deionized water and dried at 60°C to obtain a ZnO gas-sensitive material layer (ZnO nanorod array gas-sensitive layer).

[0060] Removing the protective layer: soaking the prepared device in acetone to remove the protective layer, thereby obtaining the bottom-illuminated light-excited gas sensor based on LED integration.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A bottom-illuminated light-excited gas sensor based on LED integration, characterized in that: It includes an LED light-emitting layer, a substrate, a gas-sensitive test electrode and a gas-sensitive material layer which are stacked in sequence; The number of the gas-sensitive test electrodes is greater than 1, and each gas-sensitive test electrode is arranged at intervals on the surface of the substrate; Part of the gas-sensitive material layer is in contact with the substrate, and the remaining gas-sensitive material layer is in contact with the gas-sensitive test electrode; The substrate is a transparent insulating material.

2. The bottom-illuminated optically excited gas sensor based on LED integration as claimed in claim 1, characterized in that: The light emission wavelength of the LED light emitting layer is 200-750nm.

3. The bottom-illuminated light-excited gas sensor based on LED integration as claimed in claim 1, characterized in that: The transmittance of the substrate is >85%.

4. The bottom-illuminated optically excited gas sensor based on LED integration as claimed in claim 3, characterized in that: The substrate includes glass, sapphire, PEI or PI.

5. The bottom-illuminated light-excited gas sensor based on LED integration as claimed in claim 1, characterized in that: The material of the gas-sensitive test electrode includes gold, platinum, silver or copper.

6. The bottom-illuminated light-excited gas sensor based on LED integration as claimed in claim 1, characterized in that: The bandgap width of the gas-sensitive material layer is 1.55-4.0 eV.

7. The bottom-illuminated optically excited gas sensor based on LED integration as claimed in claim 6, characterized in that: The material of the gas-sensitive material layer includes one or more of doped or undoped indium oxide, doped or undoped tungsten trioxide, doped or undoped tin oxide, doped or undoped titanium oxide, doped or undoped zinc oxide, doped or undoped carbon nanofibers, doped or undoped carbon nanotubes, doped or undoped graphene, doped cobalt oxide and doped cadmium oxide.

8. The bottom-illuminated optically excited gas sensor based on LED integration as claimed in claim 7, characterized in that: When the material of the gas-sensitive material layer is a doped material, the doped elements include one or more of gold, silver, platinum, palladium, iron, cobalt, nickel, manganese, cerium, niobium, carbon and nitrogen.

9. The method for preparing the bottom-illuminated light-excited gas sensor based on LED integration according to any one of claims 1 to 8, characterized in that: The following steps are involved: After depositing an LED light-emitting layer and a protective layer on the surface of one side of the substrate in sequence, and depositing a gas-sensitive test electrode and a gas-sensitive material layer in sequence on the other side of the substrate, the protective layer is removed to obtain the bottom-illuminated light-excited gas sensor based on LED integration.

10. Application of the bottom-illuminated optically excited gas sensor based on LED integration according to any one of claims 1 to 8 or the bottom-illuminated optically excited gas sensor based on LED integration prepared by the preparation method according to claim 9 in the field of gas detection.

Images