Humidity sensor and method of manufacturing the same

Abstract

The application discloses a humidity sensor and a preparation method thereof. The humidity sensor comprises an insulating substrate, an electrode layer arranged on the insulating substrate, a two-dimensional transition metal sulfide layer and a two-dimensional transition metal oxide layer. The two-dimensional transition metal oxide layer is combined on the two-dimensional transition metal sulfide layer, and the two form a composite structure. The two-dimensional transition metal oxide layer and the two-dimensional transition metal sulfide layer have a Fermi energy level difference capable of causing charge transfer, thereby forming a space charge region and a potential barrier at the interface of the composite structure. The humidity sensor has high sensitivity, stability and corrosion resistance, and the working temperature and humidity range are also improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a humidity sensor and a preparation method thereof. BACKGROUND

[0002] A humidity sensor is a device or instrument that can sense water molecules and their concentration in the environment, and it can convert information related to the content of water molecules in the gas into electrical, optical, acoustic, etc. signals that can be directly read, quantified by equipment, and thus detected, monitored, analyzed, and alarmed. Mature humidity sensors represented by transition metal oxide semiconductors such as MoO3 and WO3 have developed rapidly due to their high sensitivity, fast response speed, economy and reliability, small size, easy portability, and compatibility with current electronic devices. At present, it has become one of the sensors with the largest output and the widest application in the world.

[0003] Two-dimensional transition metal sulfides have high carrier mobility, high mechanical strength, good chemical stability and thermal stability. At the same time, due to its molecular level thickness and large specific surface area, its electrical properties are easily affected by the surrounding environment and surface adsorbed water molecules. When TMDCs are directly applied to humidity sensing, the two-dimensional TMDCs material film is both a humidity sensitive layer and a conductive channel. At this time, as the thickness of the two-dimensional material decreases, the carrier will be more and more affected by surface scattering. The charge transfer between the two-dimensional material and the adsorbed molecules not only changes the carrier concentration in the material, but also significantly reduces the mobility of the carrier as a scattering center, so the change in resistance is difficult to truly reflect the change in humidity.

[0004] Therefore, it is necessary to improve the humidity sensor to solve the above problems. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a humidity sensor based on a two-dimensional transition metal sulfide and an oxide composite structure, and a preparation method thereof, which improves sensitivity and stability.

[0006] The technical scheme adopted by the present application to solve the technical problem is to provide a humidity sensor, comprising an insulating substrate, an electrode layer arranged on the insulating substrate, a two-dimensional transition metal sulfide layer, and a two-dimensional transition metal oxide layer.

[0007] The two-dimensional transition metal oxide layer is compounded on the two-dimensional transition metal sulfide layer, and the two form a composite structure. And the two-dimensional transition metal oxide layer and the two-dimensional transition metal sulfide layer have a Fermi level difference that can cause charge transfer, thereby forming a space charge region and a potential barrier at the interface of the composite structure.

[0008] Preferably, the two-dimensional transition metal oxide layer is MoO3, and the two-dimensional transition metal sulfide layer is MoS2.

[0009] Preferably, the two-dimensional transition metal oxide layer is WO3, and the two-dimensional transition metal sulfide layer is WS2.

[0010] Preferably, the two-dimensional transition metal oxide layer is WO3, and the two-dimensional transition metal sulfide layer is WSe2.

[0011] Preferably, the material of the insulating substrate comprises at least one of glass, quartz, ceramic and sapphire.

[0012] Preferably, the insulating substrate is a semiconductor substrate with an insulating layer; the thickness of the insulating layer is 20-2000 nm.

[0013] Preferably, the semiconductor substrate is a semiconductor wafer; the semiconductor wafer is made of one or more of elemental semiconductors Si and Ge, and compound semiconductors GaAs and InP.

[0014] Preferably, the material of the insulating layer comprises at least one of SiO2, Al2O3, HfO2 and AlN.

[0015] Preferably, the material of the electrode layer comprises at least one of Au, Pt, Ni, Ti, Cr and alloys thereof.

[0016] Preferably, the material of the electrode layer comprises at least one of conductive silicides, nitrides and carbides.

[0017] Preferably, the thickness of the electrode layer is 20-1000 nm.

[0018] Preferably, the electrode layer is an interdigital electrode layer, the width of the interdigital segments is 20 um, and the spacing between adjacent interdigital segments is 10 um.

[0019] Preferably, the working temperature of the humidity sensor is 0-100℃, and the humidity range is 11-95%.

[0020] The application also provides a preparation method of the humidity sensor, comprising the following steps:

[0021] S1, providing an insulating substrate, the surface of which is provided with a two-dimensional transition metal sulfide layer;

[0022] S2, patterning the two-dimensional transition metal sulfide layer, and removing the part of the two-dimensional transition metal sulfide layer other than the target conductive channel;

[0023] S3, providing a two-dimensional transition metal oxide layer on the two-dimensional transition metal sulfide layer, to form a composite structure.

[0024] S4. An electrode layer is disposed on the surface of the insulating substrate, and the electrode layer also covers the composite structure.

[0025] The beneficial effects of this invention are as follows: The humidity sensor of this invention is based on a two-dimensional transition metal sulfide and its oxide composite structure. It utilizes the space charge region and potential barrier generated by the two-dimensional composite structure and its interface. When water molecules are adsorbed on the surface of the two-dimensional transition metal oxide layer, charge transfer occurs, causing a change in the carrier concentration within the two-dimensional transition metal oxide layer. This, in turn, leads to a change in the space charge region and potential barrier of the composite structure, ultimately altering the sensor resistance under forward bias, thereby achieving the sensing of ambient humidity. This humidity sensor combines the mature humidity-sensitive characteristics of two-dimensional transition metal oxide layers with the advantages of two-dimensional transition metal sulfide layers, such as large specific surface area, high sensitivity, and stable performance. The resulting humidity sensor exhibits high sensitivity, stability, and corrosion resistance, while also improving the operating temperature and humidity range.

[0026] The humidity sensor of this invention is easy to integrate onto a semiconductor base chip, which is in line with the development trend of miniaturization, portability and intelligence of humidity sensors. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0028] Figure 1 This is a longitudinal cross-sectional structural diagram of a humidity sensor according to an embodiment of the present invention;

[0029] Figure 2 This is a top view of a humidity sensor according to an embodiment of the present invention. Detailed Implementation

[0030] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0031] like Figure 1 , 2 As shown, a humidity sensor according to an embodiment of the present invention includes an insulating substrate 100, an electrode layer 200 disposed on the insulating substrate 100, a two-dimensional transition metal sulfide layer 300, and a two-dimensional transition metal oxide layer 400.

[0032] A two-dimensional transition metal oxide layer (two-dimensional TMOs) 400 is composited on a two-dimensional transition metal sulfide layer (two-dimensional TMDCs) 300, forming a composite structure (TMOs-TMDCs). Furthermore, there is a Fermi level difference between the two-dimensional transition metal oxide layer 400 and the two-dimensional transition metal sulfide layer 300, which can induce charge transfer, thereby forming a space charge region and a potential barrier at the interface of the composite structure.

[0033] Specifically, the insulating substrate 100 has a first surface and a second surface opposite to each other, and the electrode layer 200, the two-dimensional transition metal sulfide layer 300 and the two-dimensional transition metal oxide layer 400 are all disposed on the first surface of the insulating substrate 100.

[0034] Alternatively, the insulating substrate 100 may be made of at least one of the following materials: glass, quartz, ceramic, and sapphire. Since all of the aforementioned materials are insulating, a substrate made from one or more of these materials in combination possesses insulating properties. The insulating substrate 100 may also be a multilayer structure, with each layer made of the same or different materials.

[0035] Alternatively, the insulating substrate 100 may be a semiconductor substrate with an insulating layer. The thickness of the insulating layer is 20 nm to 2000 nm. The material of the insulating layer includes at least one of SiO2, Al2O3, HfO2, and AlN, that is, the insulating layer can be made of any one or more of the above, or it can be a stacked structure, with each layer being the same or different materials. The semiconductor substrate is preferably a semiconductor wafer; the semiconductor wafer is made of one or more of the elemental semiconductors Si and Ge, and the compound semiconductors GaAs and InP.

[0036] On the insulating substrate 100, a two-dimensional transition metal sulfide layer 300 is patterned, having a corresponding shape or orientation according to the required conductive channel, serving as the conductive channel. A two-dimensional transition metal oxide layer 400 is composited on the two-dimensional transition metal sulfide layer 300, serving as a humidity-sensitive layer for contact with water molecules. It protects the two-dimensional transition metal sulfide layer 300, preventing direct interaction between the two-dimensional transition metal sulfide layer 300 and water molecules, thereby improving the stability of the humidity sensor. When water molecules adsorb onto the surface of the two-dimensional transition metal oxide layer 400 and cause charge transfer, the carrier concentration within the two-dimensional transition metal oxide layer 400 changes. Simultaneously, the width of the space charge region and the barrier height at the composite structure (TMOs-TMDCs) interface also change, leading to a change in the resistance of the conductive channel, thus sensing the humidity to be measured.

[0037] Two-dimensional transition metal oxide layer 400, i.e., two-dimensional TMOs, with the molecular formula MO3, where M is the transition metal element Mo or W. Two-dimensional transition metal sulfide layer 300, i.e., two-dimensional TMDCs, with the molecular formula MX2, where M is the transition metal element Mo or W, and X is the chalcogen group element S or Se.

[0038] The two-dimensional transition metal sulfide layer 300 is at least one of MoS2, MoSe2, WS2, and WSe2; the two-dimensional transition metal oxide layer 400 is at least one of MoO3 and WO3.

[0039] Alternatively, the two-dimensional transition metal oxide layer 400 is MoO3, and the two-dimensional transition metal sulfide layer 300 is MoS2. Or, the two-dimensional transition metal oxide layer 400 is WO3, and the two-dimensional transition metal sulfide layer 300 is WS2. Or, the two-dimensional transition metal oxide layer 400 is WO3, and the two-dimensional transition metal sulfide layer 300 is WSe2.

[0040] The thickness of the two-dimensional transition metal sulfide layer 300 can be 0.6nm-100nm, and the thickness of the two-dimensional transition metal oxide layer 400 is 1nm-2nm.

[0041] Furthermore, the two-dimensional transition metal sulfide layer 300 can be a single-layer or multi-layer structure; the two-dimensional transition metal oxide layer 400 can be a single-layer or multi-layer structure.

[0042] On the insulating substrate 100, the electrode layer 200 partially covers the two-dimensional transition metal oxide layer 400, forming a conductive connection with the two-dimensional transition metal oxide layer 400. The electrode layer 200 can be made of at least one of Au, Pt, Ni, Ti, and Cr elemental metals, or an alloy of at least one of the above elemental metals, or a mixture of the above elemental metals and metal alloys. Alternatively, the material of the electrode layer 200 includes at least one of conductive silicides, nitrides, and carbides, i.e., it is made of at least one of the aforementioned compounds.

[0043] On the insulating substrate 100, the electrode layer 200 has a thickness of 20 nm to 1000 nm. In this embodiment, as... Figure 2 As shown, the electrode layer 200 is an interdigitated electrode layer 200, the width of its interdigitated segments is 20um, and the spacing between adjacent interdigitated segments is 10um.

[0044] Specifically, in Figure 2 In the illustrated embodiment, the electrode layer 200 includes two sets of interdigitated electrodes, which are disposed opposite to each other on the insulating substrate 100. The main body portions of the two sets of interdigitated electrodes are located on the first surface of the insulating substrate 100 and are respectively located on opposite sides of the composite structure. The interdigitated segments of each interdigitated electrode extend toward the composite structure, and the interdigitated segments of the two sets of interdigitated electrodes are respectively arranged crosswise on the composite structure.

[0045] The humidity sensor of this invention operates at a temperature of 0°C to 100°C and has a humidity range of 11% to 95%.

[0046] refer toFigure 1 , 2 The method for preparing the humidity sensor of the present invention may include the following steps:

[0047] S1. An insulating substrate 100 is provided, and a two-dimensional transition metal sulfide layer 300 is provided on the surface of the insulating substrate 100.

[0048] The insulating substrate 100 is made of at least one of the following materials: glass, quartz, ceramic, and sapphire. Alternatively, the insulating substrate 100 is a semiconductor substrate with an insulating layer.

[0049] The two-dimensional transition metal sulfide layer 300 is grown directly on the insulating substrate 100, or transferred to the insulating substrate 100 by micromechanical lift-off. Direct growth includes chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods. The two-dimensional transition metal sulfide layer 300 is preferably grown directly on the surface of the insulating substrate 100 by CVD.

[0050] The thickness of the two-dimensional transition metal sulfide layer 300 is 0.6 nm to 100 nm. The two-dimensional transition metal sulfide layer 300 is at least one of MoS2, MoSe2, WS2, and WSe2.

[0051] S2. Pattern the two-dimensional transition metal sulfide layer 300 and remove the portion of the two-dimensional transition metal sulfide layer 300 outside the target conductive channel.

[0052] After the patterning is completed, the two-dimensional transition metal sulfide layer 300 has the shape or orientation corresponding to the target conductive channel to form the conductive channel of the humidity sensor.

[0053] S3. A two-dimensional transition metal oxide layer 400 is disposed on the two-dimensional transition metal sulfide layer 300, and the two form a composite structure.

[0054] In this step, an oxygen plasma treatment or ozone oxidation method can be used to oxidize the surface of the two-dimensional transition metal sulfide layer 300 to form a two-dimensional transition metal oxide layer 400. Specifically, the two-dimensional transition metal oxide layer 400 is at least one of MoO3 and WO3. The thickness of the formed two-dimensional transition metal oxide layer 400 is 1 nm-2 nm.

[0055] The two-dimensional transition metal oxide layer 400 is positioned above the two-dimensional transition metal sulfide layer 300, serving as a humidity-sensitive layer that contacts water molecules, while the two-dimensional transition metal sulfide layer 300 does not contact water molecules, thus improving the stability of the humidity sensor.

[0056] S4. An electrode layer 200 is disposed on the surface of the insulating substrate 100, and the electrode layer 200 also covers the composite structure.

[0057] Specifically, the electrode layer 200 partially covers the two-dimensional transition metal oxide layer 400 on the insulating substrate 100, and forms a conductive connection with the two-dimensional transition metal oxide layer 400.

[0058] On the insulating substrate 100, the electrode layer 200 has a thickness of 20nm-1000nm.

[0059] exist Figure 2 In the illustrated embodiment, the electrode layer 200 includes two sets of interdigitated electrode layers 200, which are disposed opposite to each other on the insulating substrate 100. The main body portions of the two sets of interdigitated electrodes are located on the first surface of the insulating substrate 100 and are respectively located on opposite sides of the composite structure. The interdigitated segments of each interdigitated electrode extend toward the composite structure, and the interdigitated segments of the two sets of interdigitated electrodes are respectively arranged crosswise on the composite structure.

[0060] The width of the interdigitated segments of the electrode layer 200 is 20 μm, and the spacing between adjacent interdigitated segments is 10 μm.

[0061] In one practical embodiment, the method for fabricating the humidity sensor of the present invention can be operated as follows: The insulating substrate 100 is selected from p-type resistive silicon with a resistivity of 0.001 Ωcm as the semiconductor wafer substrate and also as the back gate electrode layer. 300 nm thermally oxidized SiO2 is used as the insulating layer and can serve as the back gate dielectric. A single layer or a few layers (1-10 layers) of MoS2 thin film are prepared on the insulating substrate 100 using a mechanical lift-off method, serving as the two-dimensional transition metal sulfide layer 300. The two-dimensional transition metal oxide layer 400 is directly grown or oxidized using oxygen plasma to form a layer covering the conductive channels of the two-dimensional transition metal sulfide layer 300, serving as the humidity-sensitive layer. The specific method is as follows:

[0062] On the one hand, a two-dimensional transition metal oxide film (i.e., two-dimensional transition metal oxide layer 400) can be directly formed on the surface of the conductive channel of the two-dimensional transition metal sulfide layer 300 using methods such as chemical vapor deposition and atomic layer deposition; on the other hand, the two-dimensional transition metal sulfide layer 300 can be oxidized using an oxygen plasma cleaner to form a two-dimensional transition metal oxide film (i.e., two-dimensional transition metal oxide layer 400) on the surface of the conductive channel of the two-dimensional transition metal sulfide layer 300.

[0063] Among them, a MoO3 thin film with a thickness of 1-2 nm is selected as the humidity-sensitive layer (i.e., the two-dimensional transition metal oxide layer 400) because the MoO3 thin film is a naturally n-type medium-doped material, so that it can form a composite structure with MoS2 with different doping degrees, thereby forming a significant space charge region in the two-dimensional transition metal sulfide layer 300. At the same time, the two-dimensional transition metal sulfide layer 300 is used as the conductive channel and the two-dimensional transition metal oxide layer 400 is used as the humidity-sensitive layer. The thin (1-2 nm) MoO3 thin film helps to prevent the humidity-sensitive layer from participating in the conduction, avoiding the adverse effects in the transport process.

[0064] When using a Cr / Au metal stack as electrode layer 200, the following settings are made:

[0065] S1805 photoresist was spin-coated on the surface of the insulating substrate 100 and the composite structure. First, the photoresist was uniformly coated at 500 rpm for 5 seconds, and then spin-coated at 4000 rpm for 60 seconds to form a photoresist film layer with a thickness of about 500 nm. After that, it was dried at 110°C for 3 minutes.

[0066] Photolithography involves exposing photoresist to a pre-designed photomask at an exposure dose of 40 mJ / cm². 2 After development for 20 seconds, the image is immediately fixed in a large amount of deionized water, thereby forming an interdigitated pattern structure on the photoresist.

[0067] The film is placed in a thermal evaporation coating machine and vacuumed, and then a 10nm Cr and 60nm Au stack is deposited.

[0068] The adhesive is removed in acetone to form an electrode layer 200.

[0069] An ohmic contact is formed between the insulating substrate 100 and the surface of the composite structure and the electrode layer 200 by annealing at 500°C for 45 minutes in a high-purity N2 atmosphere using a rapid thermal annealing furnace (RTP).

[0070] The working principle of the humidity sensor of the present invention lies in the charge transfer caused by the Fermi level difference between the two-dimensional transition metal sulfide layer 300 and the two-dimensional transition metal oxide layer 400, thereby generating a space charge region and forming a potential barrier at the interface of the composite structure. When water molecules are adsorbed on the surface of the two-dimensional transition metal oxide layer 400, charge transfer occurs, causing a change in the carrier concentration within the two-dimensional transition metal oxide layer 400, which in turn leads to changes in the space charge region and potential barrier of the composite structure. Ultimately, this changes the resistance of the conductive channel under forward bias, thereby achieving the sensing of ambient humidity.

[0071] Under low humidity conditions, water molecules are affected by surface defects in the composite material and decompose into H+. + and OH - And H +Electrons are harvested from the material surface, reducing the hole barrier, flattening the depletion layer, and lowering the impedance; under high humidity, water molecules adsorb onto the surface of the composite structure, generating a large amount of H3O. + It combines with conductive ions to participate in transport during the conduction process, resulting in a decrease in impedance and an increase in conductivity; by changing the resistance, it obtains the change in ambient humidity, thereby realizing the function of humidity sensing.

[0072] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A humidity sensor, characterized in that, The humidity sensor includes an insulating substrate, an electrode layer disposed on the insulating substrate, a two-dimensional transition metal sulfide layer, and a two-dimensional transition metal oxide layer; The two-dimensional transition metal oxide layer is composited on the two-dimensional transition metal sulfide layer, and the two form a composite structure; and there is a Fermi level difference between the two-dimensional transition metal oxide layer and the two-dimensional transition metal sulfide layer that can cause charge transfer, thereby forming a space charge region and a potential barrier at the interface of the composite structure. The two-dimensional transition metal sulfide layer is at least one of MoS2, WS2, and WSe2; the two-dimensional transition metal oxide layer is at least one of MoO3 and WO3.

2. The humidity sensor according to claim 1, characterized in that, The two-dimensional transition metal oxide layer is MoO3, and the two-dimensional transition metal sulfide layer is MoS2; or... The two-dimensional transition metal oxide layer is WO3, and the two-dimensional transition metal sulfide layer is WS2; or... The two-dimensional transition metal oxide layer is WO3, and the two-dimensional transition metal sulfide layer is WSe2.

3. The humidity sensor according to claim 1, characterized in that, The insulating substrate is made of at least one of glass, quartz, ceramic, and sapphire.

4. The humidity sensor according to claim 1, characterized in that, The insulating substrate is a semiconductor substrate with an insulating layer; the thickness of the insulating layer is 20 nm - 2000 nm.

5. The humidity sensor according to claim 4, characterized in that, The semiconductor substrate is a semiconductor wafer; the semiconductor wafer is made of one or more of the elemental semiconductors Si and Ge, and the compound semiconductors GaAs and InP.

6. The humidity sensor according to claim 4, characterized in that, The insulating layer is made of at least one of SiO2, Al2O3, HfO2, and AlN.

7. The humidity sensor according to claim 1, characterized in that, The electrode layer is made of at least one of the following: elemental metals: Au, Pt, Ni, Ti, Cr, and alloys of the above elemental metals; or... The electrode layer is made of at least one of conductive silicides, nitrides, and carbides.

8. The humidity sensor according to claim 1, characterized in that, The thickness of the electrode layer is 20nm-1000nm; The electrode layer is an interdigitated electrode layer, with the width of the interdigitated segments being 20 μm and the spacing between adjacent interdigitated segments being 10 μm.

9. The humidity sensor according to any one of claims 1-8, characterized in that, The humidity sensor operates at a temperature of 0℃ to 100℃ and has a humidity range of 11% to 95%.

10. A method for preparing a humidity sensor according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Provide an insulating substrate, wherein a two-dimensional transition metal sulfide layer is provided on the surface of the insulating substrate; S2. Pattern the two-dimensional transition metal sulfide layer and remove the portion of the two-dimensional transition metal sulfide layer outside the target conductive channel. S3. A two-dimensional transition metal oxide layer is formed on the two-dimensional transition metal sulfide layer, and the two form a composite structure. S4. An electrode layer is disposed on the surface of the insulating substrate, and the electrode layer also covers the composite structure.

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