Two-dimensional rectification type gas sensor based on asymmetric electrode structure

Abstract

The invention discloses a two-dimensional rectification type gas sensor based on an asymmetric electrode structure, and relates to the technical field of sensors. The lower metal electrode is positioned on the surface of the substrate; the two-dimensional material layer covers a partial region of the lower metal electrode; the upper metal electrode is located on the upper surface of the two-dimensional material layer, and the vertical projection of the upper metal electrode and the vertical projection of the lower metal electrode are not overlapped; the work function difference of the lower metal electrode, the upper metal electrode and the two-dimensional material layer is larger than or equal to 0.5 eV, asymmetric Schottky contact is formed, and local work function offset is triggered through asymmetric Schottky contact design and a vertical projection non-overlapping structure and gas adsorption, so that carriers are forced to longitudinally penetrate through the two-dimensional material layer. According to the mechanism, the barrier change is directly converted into the exponential amplification effect of the rectification ratio, the rectification ratio change rate of 1ppb NH3 is larger than or equal to 2000%, the detection limit is as low as 0.2 ppb, and the sensitivity is improved by more than three times.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and more specifically, to a two-dimensional rectified gas sensor based on an asymmetric electrode structure. Background Technology

[0002] Traditional horizontal electrode structures (typically represented by interdigitated electrodes) generate an electric field through an alternating arrangement of anodes and cathodes in a plane. Their performance is limited by the following issues:

[0003] Insufficient interfacial contact area and controllability: The active interface of interdigitated electrodes is limited to a finite area within a plane. The gap between the electrode fingers (interdigital spacing) determines the effective reaction area, but due to limitations in microfabrication precision, the gap is difficult to further reduce (typically >10 μm). This results in a limited contact area between the electrode and the sensitive material, low interfacial charge transport efficiency, and difficulty in actively controlling the interfacial electric field distribution, thus restricting the improvement of gas adsorption and electrochemical reaction kinetics.

[0004] The gas diffusion path is complex and slow to respond: the target gas must penetrate vertically through the sensitive layer to the electrode plane, and then diffuse horizontally to the interdigital space. This multi-stage diffusion path significantly prolongs the time it takes for the gas to reach the electrochemically active sites, resulting in response times generally exceeding 10 seconds. Especially in the detection of low-concentration gases, the low diffusion efficiency further reduces the signal-to-noise ratio.

[0005] The existing patent (CN113990666A) uses a horizontal dual-electrode structure to detect NH3. Although the detection limit has been reduced to 10 ppb by optimizing the sensitive material, it still requires external heating to 80°C to accelerate gas diffusion and surface reaction. This design not only increases energy consumption but also accelerates the aging of the sensitive material due to the high-temperature environment, affecting long-term stability.

[0006] Based on this, the present invention provides a two-dimensional rectified gas sensor based on an asymmetric electrode structure. Summary of the Invention

[0007] To address the problems mentioned in the background art, the present invention provides a two-dimensional rectified gas sensor based on an asymmetric electrode structure.

[0008] The two-dimensional rectifier gas sensor based on an asymmetric electrode structure provided by this invention adopts the following technical solution:

[0009] A two-dimensional rectifier gas sensor based on an asymmetric electrode structure, including a substrate;

[0010] The lower metal electrode is located on the surface of the substrate;

[0011] A two-dimensional material layer covers a portion of the lower metal electrode;

[0012] The upper metal electrode is located on the upper surface of the two-dimensional material layer and does not overlap with the vertical projection of the lower metal electrode;

[0013] The work function difference between the lower metal electrode, the upper metal electrode, and the two-dimensional material layer is ≥0.5eV, forming an asymmetric Schottky contact.

[0014] Preferably, the area of ​​the two-dimensional material layer covering the lower metal electrode is 10%-50% of the surface area of ​​the two-dimensional material layer.

[0015] Preferably, the contact area between the upper metal electrode and the two-dimensional material layer is ≤100μm. 2 .

[0016] Preferably, the two-dimensional material layer is a P-type semiconductor or an N-type semiconductor.

[0017] Preferably, when the two-dimensional material layer is a P-type semiconductor, the lower metal electrode and the upper metal electrode are selected from metals with low work function, that is, ≤4.5eV.

[0018] Preferably, the low work function metal includes Ti, Al, or Cr.

[0019] Preferably, when the two-dimensional material layer is an N-type semiconductor, the lower metal electrode and the upper metal electrode are selected from metals with high work function, and their work function is ≥5.0eV.

[0020] Preferably, the high work function metal includes Au, Pt, or Pd.

[0021] A method for manufacturing a two-dimensional rectifier gas sensor based on an asymmetric electrode structure includes the following steps:

[0022] S1. The metal electrode is fabricated on the substrate by photolithography and sputtering processes;

[0023] S2. Transfer the two-dimensional material layer to the surface of the lower metal electrode;

[0024] S3. Metal electrodes are fabricated on the surface of a two-dimensional material layer using photolithography and sputtering processes.

[0025] In summary, the present invention has the following beneficial technical effects:

[0026] 1. Through an asymmetric Schottky contact design and a non-overlapping structure with vertical projection, gas adsorption induces a local work function shift, forcing charge carriers to longitudinally traverse the two-dimensional material layer. This mechanism directly converts the barrier change into an exponential amplification effect of the rectification ratio, achieving a rectification ratio change rate of ≥2000% for 1ppb NH3, with a detection limit as low as 0.2ppb and a sensitivity improvement of more than 3 times;

[0027] 2. The vertical electrode configuration eliminates the complex gas diffusion path of traditional horizontal structures, allowing the target gas to directly penetrate to the active interface. The response time is shortened to within 3 seconds, meeting the real-time requirements of explosive detection, medical monitoring, and other scenarios; the back-to-back Schottky junction suppresses leakage current to <10pA, requiring no external heating and achieving stable zero-power operation at room temperature, while improving the signal-to-noise ratio by two orders of magnitude.

[0028] 3. The lower metal electrode can be pre-integrated into the CMOS wafer, ensuring compatibility with semiconductor production lines. Combined with standardized photolithography / lifting processes, it supports mass production of 8-inch wafers, providing an industrialization path for chip-level integration of gas sensors.

[0029] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a two-dimensional rectifier gas sensor based on an asymmetric electrode structure in an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the side structure of the two-dimensional rectifier gas sensor based on an asymmetric electrode structure in an embodiment of the present invention;

[0032] Figure 3 This is a manufacturing process diagram of a two-dimensional rectifier gas sensor based on an asymmetric electrode structure in an embodiment of the present invention;

[0033] Figure 4 This is the energy band diagram of the device before gas adsorption in an embodiment of the present invention;

[0034] Figure 5 This is the energy band diagram of the device after gas adsorption in an embodiment of the present invention.

[0035] Explanation of reference numerals in the attached figures: 1. Substrate; 2. Lower metal electrode; 3. Two-dimensional material layer; 4. Upper metal electrode. Detailed Implementation

[0036] The following is in conjunction with the appendix Figures 1 to 5 The present invention will be described in further detail below.

[0037] It should be noted that the accompanying drawings are schematic and not to scale. For clarity and convenience, the relative dimensions and proportions of the parts shown are exaggerated or reduced in size; all dimensions are merely illustrative and not limiting. Furthermore, the same reference numerals are used for the same structures, elements, or fittings appearing in more than two drawings to indicate similar features.

[0038] This invention discloses a two-dimensional rectified gas sensor based on an asymmetric electrode structure. (Refer to...) Figures 1 to 3 A two-dimensional rectifier gas sensor based on an asymmetric electrode structure includes a substrate 1, a lower metal electrode 2, a two-dimensional material layer 3, and an upper metal electrode 4. The lower metal electrode 2 is located on the surface of the substrate 1. The two-dimensional material layer 3 covers a portion of the lower metal electrode 2. The upper metal electrode 4 is located on the upper surface of the two-dimensional material layer 3 and does not overlap with the vertical projection of the lower metal electrode 2. The work function difference between the lower metal electrode 2, the upper metal electrode 4, and the two-dimensional material layer 3 is ≥0.5eV, forming an asymmetric Schottky contact.

[0039] Specifically, by using a vertically stacked configuration to overcome the limitations of traditional planar electrodes, the work function difference between the lower metal electrode 2 and the upper metal electrode 4, which act as a carrier blocking layer, and the two-dimensional material layer 3 is ≥0.5eV, forming a back-to-back Schottky junction. This structure suppresses leakage current to <10pA (1 / 100 of the traditional structure).

[0040] like Figure 2 As shown, the projections of the lower metal electrode 2 and the upper metal electrode 4 do not overlap, which increases the effective gas contact area of ​​the two-dimensional material layer 3 by more than 3 times (compared to the interdigitated electrode). At the same time, the electric field concentration effect at the edge of the lower metal electrode 2 actively regulates the height of the Schottky barrier, and the rectification ratio is increased to 3.5 times that of the traditional structure.

[0041] Specifically, the area of ​​the metal electrode 2 covered by the two-dimensional material layer 3 is 10%-50% of the surface area of ​​the two-dimensional material layer 3.

[0042] Specifically, the contact area between the upper metal electrode 4 and the two-dimensional material layer 3 is ≤100μm. 2 .

[0043] Specifically, the lower metal electrode 2 can be pre-integrated onto the CMOS wafer.

[0044] Specifically, the two-dimensional material layer 3 is a P-type semiconductor or an N-type semiconductor.

[0045] Specifically, when the two-dimensional material layer 3 is a P-type semiconductor, the lower metal electrode 2 and the upper metal electrode 4 are selected from metals with low work function, with a work function ≤ 4.5 eV.

[0046] Specifically, low work function metals include Ti, Al, or Cr.

[0047] Specifically, when the two-dimensional material layer 3 is an N-type semiconductor, the lower metal electrode 2 and the upper metal electrode 4 are selected from metals with high work function, with a work function ≥ 5.0 eV.

[0048] Specifically, high work function metals include Au, Pt, or Pd.

[0049] Specifically, such as Figure 4 and Figure 5 As shown, a strong asymmetric Schottky contact is constructed between a metal electrode with a specific work function (such as Ti / Al / Cr for P-type materials and Au / Pt / Pd for N-type materials) and a two-dimensional material layer 3. Gas adsorption can induce a local work function shift, resulting in a highly nonlinear change in the Schottky barrier, enabling the rectification ratio to exceed 2000% in response to trace amounts of gas.

[0050] A method for manufacturing a two-dimensional rectifier gas sensor based on an asymmetric electrode structure includes the following steps:

[0051] S1. The lower metal electrode 2 is fabricated on the substrate 1 by photolithography and sputtering processes;

[0052] S2. Transfer the two-dimensional material layer 3 to the surface of the lower metal electrode 2;

[0053] S3. A metal electrode 4 is fabricated on the surface of the two-dimensional material layer 3 using photolithography and sputtering processes.

[0054] Example

[0055] Substrate selection:

[0056] A 4-inch p-type silicon substrate (resistivity 1-10 Ω·cm, thickness 500±5 μm) was cleaned to remove surface contaminants using RCA standard cleaning.

[0057] Machining of lower metal electrode 2:

[0058] Photolithography defines the electrode pattern: AZ5214 photoresist was used, with an exposure dose of 120 mJ / cm². 2 Magnetron sputtering deposition;

[0059] P-type two-dimensional material: sputtered Ti electrode (40 nm thick, work function 4.33 eV), sputtering power 200 W, Ar gas flow rate 20 sccm;

[0060] N-type two-dimensional material: sputtered Au electrode (40nm thick, work function 5.1eV), sputtering power 150W;

[0061] After peeling, the electrode is annealed in nitrogen at 300°C for 30 minutes to enhance electrode-substrate adhesion.

[0062] Two-dimensional materials (CVD-grown monolayer WSe2 (P-type) or MoS2 (N-type), thickness 0.7 nm, carrier mobility ≥100 cm⁻¹) 2 / V·s) transfer:

[0063] Polymethyl methacrylate (PMMA) was spin-coated onto the growth substrate (3000 rpm, 300 nm thickness);

[0064] A Cu foil substrate was etched with a 1 mol / L KOH solution to release a PMMA / two-dimensional material film.

[0065] After cleaning with deionized water, it is attached to the lower metal electrode 2, heated to 60°C for curing, and PMMA is dissolved in acetone.

[0066] Preparation of upper metal electrode 4:

[0067] A contact lithography machine is used, with an overlay accuracy of ±0.5μm. The distance between the upper electrode pattern (5μm×5μm) and the edge of the Ti lower electrode is ≥3μm (strictly non-overlapping in vertical projection).

[0068] Metal deposition:

[0069] P-type device: sputtered Ti (50nm thick, work function 4.33eV);

[0070] N-type device: sputtered Au (50nm thick, work function 5.1eV);

[0071] Ultrasonic ablation (acetone, 100W power) removes redundant metal, forming a top electrode with steep edges.

[0072] Performance testing:

[0073] Test conditions parameter gas concentration <![CDATA[1 ppb NH3 (N2 balance gas)]]> bias -1V → +1V scan (step size 0.1V) Initial rectification ratio 150 (Gas-free environment) Rectification ratio after adsorption 3200 (Δ rate of change 2033%) <![CDATA[Response time (T 90 )]]> 2.8 seconds (traditional structure > 10 seconds) Background current <8pA (back-to-back Schottky junction suppression)

[0074] As shown above, through asymmetric Schottky contact design (work function difference ≥ 0.5 eV) and non-overlapping vertical projection structure, gas adsorption induces a local work function shift (≥ 0.2 eV), forcing charge carriers to longitudinally traverse the two-dimensional material layer. This mechanism directly converts the barrier change into an exponential amplification effect of the rectification ratio, achieving a rectification ratio change rate of ≥ 2000% for 1 ppb NH3 (compared to ≤ 800% for traditional techniques), a detection limit as low as 0.2 ppb, and a sensitivity improvement of more than 3 times.

[0075] The vertical electrode configuration eliminates the complex gas diffusion path of traditional horizontal structures, allowing the target gas to directly penetrate to the active interface. The response time is shortened to within 3 seconds, meeting the real-time requirements of explosive detection, medical monitoring, and other scenarios. The back-to-back Schottky junction suppresses leakage current to <10pA, requiring no external heating (compared to 80℃ for existing technologies), achieving stable zero-power operation at room temperature, and improving the signal-to-noise ratio by two orders of magnitude.

[0076] The lower metal electrode 2 can be pre-integrated into the CMOS wafer. Combined with standardized photolithography / stripping processes, it supports mass production of 8-inch wafers, providing an industrialization path for chip-level integration of gas sensors.

[0077] The accompanying drawings of the embodiments disclosed in this invention only involve structures relevant to the embodiments disclosed in this invention. Other structures can be referred to with common designs. Unless otherwise specified, the same embodiment and different embodiments of this invention can be combined with each other.

[0078] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-dimensional rectifier gas sensor based on an asymmetric electrode structure, characterized in that, include: Substrate (1); The lower metal electrode (2) is located on the surface of the substrate (1); A two-dimensional material layer (3) covers a portion of the lower metal electrode (2); The upper metal electrode (4) is located on the upper surface of the two-dimensional material layer (3) and does not overlap with the vertical projection of the lower metal electrode (2); The work function difference between the lower metal electrode (2), the upper metal electrode (4), and the two-dimensional material layer (3) is ≥0.5eV, forming an asymmetric Schottky contact.

2. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 1, characterized in that: The area of ​​the two-dimensional material layer (3) covering the lower metal electrode (2) is 10%-50% of the surface area of ​​the two-dimensional material layer (3).

3. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 1, characterized in that: The contact area between the upper metal electrode (4) and the two-dimensional material layer (3) is ≤100μm. 2 .

4. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 1, characterized in that: The two-dimensional material layer (3) is a P-type semiconductor or an N-type semiconductor.

5. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 4, characterized in that: When the two-dimensional material layer (3) is a P-type semiconductor, the lower metal electrode (2) and the upper metal electrode (4) are selected from metals with low work function, and their work function is ≤4.5eV.

6. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 5, characterized in that: The low work function metals include Ti, Al, or Cr.

7. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 4, characterized in that: When the two-dimensional material layer (3) is an N-type semiconductor, the lower metal electrode (2) and the upper metal electrode (4) are selected from metals with high work function, and their work function is ≥5.0eV.

8. The two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to claim 7, characterized in that: The high work function metals include Au, Pt, or Pd.

9. A method for manufacturing a two-dimensional rectifier gas sensor based on an asymmetric electrode structure according to any one of claims 1-8, characterized in that, Includes the following steps: S1. The lower metal electrode (2) is prepared on the substrate (1) by photolithography and sputtering process; S2, Transfer the two-dimensional material layer (3) to the surface of the lower metal electrode (2); S3. A metal electrode (4) is prepared on the surface of the two-dimensional material layer (3) using photolithography and sputtering processes.

Images