A method for preparing a full-silk-screen-printed flexible ZnO ultraviolet photodetector

Abstract

This invention belongs to the field of semiconductor device technology, specifically relating to a method for fabricating a flexible ZnO ultraviolet photodetector using full screen printing. Through a full screen printing process, the integrated fabrication of the flexible ZnO ultraviolet detector is achieved. The process is simple, low-cost, and suitable for large-area manufacturing. This invention sequentially fabricates a ZnO photosensitive layer and silver interdigitated electrodes via screen printing, followed by optimized heat treatment and low-temperature curing to form a metal-semiconductor-metal structure device. Through synergistic optimization of ink formulation, printing process, and electrode structure, the photoresponse current is effectively improved while maintaining a high light-to-dark current ratio and responsivity.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, specifically relating to a method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector. Background Technology

[0002] Ultraviolet (UV) photodetectors have wide applications in UV imaging, space communication, and flame detection. Currently, most UV detectors are based on silicon, but due to silicon's narrow bandgap (approximately 1.1 eV), it also absorbs non-UV light, leading to detection bias. Furthermore, silicon-based devices are complex to fabricate, costly, and difficult to integrate with flexible substrates.

[0003] Zinc oxide (ZnO), as a third-generation wide-bandgap semiconductor material (Eg≈3.37eV), possesses excellent ultraviolet absorption characteristics, biocompatibility, and suitability for solution processing, making it an ideal material for fabricating flexible ultraviolet detectors. Existing ZnO detectors are mostly fabricated using vacuum processes such as magnetron sputtering and atomic layer deposition, which suffer from problems such as complex processes, high costs, and difficulty in achieving large-area flexible manufacturing.

[0004] Screen printing technology has advantages such as low cost, simple operation, and applicability to large-area and patterned fabrication. However, there is currently little research on the fabrication of flexible ZnO ultraviolet photodetectors by full screen printing, especially in terms of achieving high responsivity, high light-dark-current ratio, and imaging arrays. Summary of the Invention

[0005] To address the problems raised in the background art, this invention provides a method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector.

[0006] The technical solution of the present invention is as follows: This invention provides a method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector, comprising the following steps: (1) ZnO nanoparticles are mixed with organic solvents to form ZnO ink; (2) Screen printing ZnO thin film on a flexible substrate; (3) The ZnO film is annealed at 150-300℃; (4) After screen printing silver interdigitated electrodes on the annealed ZnO film, it is cured at low temperature.

[0007] Based on the above-described method for preparing a flexible ZnO ultraviolet photodetector by full screen printing, the ZnO ink in step (1) is a mixture of ZnO nanoparticles and the organic solvent terpineol.

[0008] Furthermore, the organic solvent is α-terpineol.

[0009] Based on the above-described method for preparing a flexible ZnO ultraviolet photodetector by full screen printing, in step (4), the particle size or pore size of the ZnO nanoparticles in the annealed ZnO film is 20-90 nm.

[0010] Based on the above-described method for preparing a flexible ZnO ultraviolet photodetector by full screen printing, in step (3), the ZnO thin film is annealed at 150-300℃ for 60-120 min.

[0011] Based on the above-described method for fabricating a flexible ZnO ultraviolet photodetector using full screen printing, the parameters of the silver forked electrode in step (4) are as follows: The number of interdigital pairs is 2-20, the finger width is 5-500μm, the finger spacing is 5-500μm, and the finger length is 100-2000μm.

[0012] Furthermore, the number of interdigital pairs is 4-8, the finger width is 100-300μm, the finger spacing is 100-300μm, and the finger length is 500-1000μm.

[0013] Based on the above-described method for preparing a flexible ZnO ultraviolet photodetector by full screen printing, the low-temperature curing step (4) is a treatment at 70-90℃ for 10-25 minutes.

[0014] The flexible ZnO ultraviolet photodetector prepared by the above-described method of fabricating a fully screen-printed flexible ZnO ultraviolet photodetector has a metal-semiconductor-metal structure.

[0015] The fabrication method of the flexible ZnO ultraviolet photodetector based on the above-described method further includes an imaging array fabrication step: constructing a row-column addressing imaging matrix by sequentially printing ZnO dot matrix, silver wire, insulating layer, and top electrode through multi-layer overprinting.

[0016] Beneficial effects This invention achieves integrated fabrication of flexible ZnO ultraviolet detectors through a full screen printing process. The process is simple, low-cost, and suitable for large-area manufacturing.

[0017] This invention fabricates a ZnO photosensitive layer and silver interdigitated electrodes sequentially via screen printing, followed by optimized heat treatment and low-temperature curing to form a metal-semiconductor-metal structure device. Through synergistic optimization of ink formulation, printing process, and electrode structure, the photoresponse current is effectively improved while maintaining a high photocurrent-to-dark-current ratio and responsivity. Multiple experiments revealed that a detector fabricated from a ZnO thin film annealed at 200-300℃ for 90-120 min exhibits a responsivity of 12.8 A / W and a photocurrent-to-dark-current ratio as high as 3.83 × 10⁻⁶ under 365 nm ultraviolet light irradiation. 6The external quantum efficiency exceeds 3900%, and the detectivity reaches 9.96 × 10⁻⁶. 14 Jones. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the fabrication process and structure of the fully screen-printed flexible ZnO ultraviolet photodetector of this invention.

[0019] Figure 2 The following are the characterization results of the ZnO thin film in Example 1, where a is the SEM image, b is the XRD pattern, c is the UV-Vis transmission spectrum, and d is the bandgap fitting diagram.

[0020] Figure 3 This is a schematic diagram of the working principle of the ZnO ultraviolet detector in Example 1, where a represents the state without light and b represents the state under ultraviolet light.

[0021] Figure 4 The photoelectric performance analysis of the ZnO ultraviolet detector in Example 1 is shown in the figure. In the figure, a is the photoresponse current curve at λ=254nm, b is the photoresponse current curve at λ=365nm, c is the photoresponse as a function of voltage, and d is the current as a function of light intensity.

[0022] Figure 5 This is a comparison of the interdigitated electrode structure and single-electrode performance of the ZnO ultraviolet detector in Example 2. In the figure, a is a schematic diagram of the interdigitated electrode size, b is the photocurrent under 5V bias, c is the photocurrent-to-dark-current ratio under 5V bias, d is the responsivity, e is the detectivity, and f is the external quantum efficiency.

[0023] Figure 6 The figures show the cyclic stability and bending test curves of the ZnO ultraviolet detector in Example 2, where a represents the cyclic stability test of the ZnO ultraviolet photodetector under different voltages; b represents the cyclic stability test of the response current of the ZnO ultraviolet photodetector changing with time under changes in voltage and ultraviolet light intensity; and c represents the logarithmic volt-ampere characteristic curve of the photocurrent before and after bending.

[0024] Figure 7 The diagram shows the ZnO ultraviolet imaging array structure and imaging effect of Example 3. In the diagram, a is a schematic diagram of the planar structure of the ZnO ultraviolet photodetector matrix, b is a schematic diagram of the planar structure of the ZnO ultraviolet photodetector matrix during testing, and c is an ultraviolet imaging image of the ZnO ultraviolet photodetector matrix on the "mountain" pattern. Detailed Implementation

[0025] The following examples are intended to illustrate the present invention, and not to further limit the invention.

[0026] This invention provides a method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector, such as... Figure 1As shown, it includes the following steps: (1) ZnO nanoparticles are mixed with organic solvents to form ZnO ink.

[0027] In this ink, the surface of ZnO nanoparticles is pre-dispersed, which can be done by ultrasonic dispersion, and the particle size is controlled at the tens of nanometer level to improve the printing uniformity and film quality of the ink.

[0028] This ink formulation has the following unique characteristics.

[0029] Compared to traditional thin film morphologies, ZnO nanoparticles have a larger specific surface area, which is beneficial for enhancing ultraviolet light absorption and oxygen adsorption / desorption effects, thereby improving photoresponse performance. In existing technologies, adhesives (such as ethyl cellulose) and solvents are selected to formulate ZnO inks to meet film-forming requirements; otherwise, the ink viscosity is uncontrollable, making printing difficult. However, the ink of this invention does not contain binders; it forms a porous structure solely through the self-assembly of nanoparticles. This loose and porous ZnO film can further increase the photosensitive area and improve photoelectric conversion efficiency.

[0030] Furthermore, in the ZnO ink, the ratio of ZnO nanoparticles to the organic solvent terpineol is 2:1.

[0031] To further ensure the uniformity of ZnO nanoparticle dispersion, the organic solvent is α-terpineol.

[0032] The ink formula has been determined through multiple experiments to simultaneously meet the requirements of screen printing suitability, film uniformity, and photoelectric transmission without the need for binders.

[0033] (2) Screen printing ZnO thin film on a flexible substrate.

[0034] The flexible substrate is selected from polyethylene terephthalate, polyimide, or polyethylene naphthalate.

[0035] (3) The ZnO film is annealed at 150-300℃ for 60-120 min.

[0036] Preferably, annealing at 200-300℃ for 90-120 minutes can yield a ZnO film with good crystallinity and uniform porous structure, while avoiding thermal deformation of the flexible substrate.

[0037] Most preferably, annealing is performed at 200°C for 90 minutes.

[0038] Among them, the particle size and pore size of ZnO nanoparticles in the annealed ZnO film are 20-90 nm.

[0039] Compared to ZnO inks formulated using binders, the present invention exhibits higher carrier mobility and, by utilizing the large specific surface area of ​​its porous structure, achieves a photocurrent-to-dark current ratio as high as 3.83 × 10⁻⁶. 6 .

[0040] (4) After screen printing silver interdigitated electrodes on the annealed ZnO film, it is cured at low temperature.

[0041] This invention enhances the electric field distribution and photogenerated carrier collection efficiency by optimizing the interdigitated structure. The parameters of the silver interdigitated electrodes are as follows: The number of interdigital pairs is 2-20, the finger width is 5-500μm, the finger spacing is 5-500μm, and the finger length is 100-2000μm.

[0042] Preferably, the number of interdigital pairs is 4-8, the finger width is 100-300μm, the finger spacing is 100-300μm, and the finger length is 500-1000μm.

[0043] Most preferably, the number of interdigital pairs is 6, the finger width is 200μm, the finger spacing is 200μm, and the finger length is 1000μm.

[0044] To improve the photoelectric response and stability of the device, the low-temperature curing is performed at 70-90℃ for 10-25 minutes.

[0045] In addition, the fabrication of the fully screen-printed flexible ZnO ultraviolet photodetector also includes the imaging array fabrication step: ZnO dot matrix, silver wire, insulating layer and top electrode are printed sequentially through multi-layer overprinting to construct a row-column addressing imaging matrix.

[0046] This invention achieves integrated fabrication of flexible ZnO ultraviolet detectors through a full screen printing process. The process is simple, low-cost, and suitable for large-area manufacturing.

[0047] This invention fabricates a ZnO photosensitive layer and silver interdigitated electrodes sequentially via screen printing, followed by optimized heat treatment and low-temperature curing to form a metal-semiconductor-metal structure device. Through synergistic optimization of ink formulation, printing process, and electrode structure, the photoresponse current is effectively improved while maintaining a high light-to-dark current ratio and responsivity.

[0048] The ZnO detector prepared in this invention exhibits a responsivity of 12.8 A / W and a photocurrent-to-dark-current ratio as high as 3.83 × 10⁻⁶ under 365 nm ultraviolet light irradiation. 6 The external quantum efficiency exceeds 3900%, and the detectivity reaches 9.96 × 10⁻⁶. 14 Jones boasts excellent overall performance.

[0049] The ZnO detector prepared by this invention operates stably in a wide voltage range of 1-100V and exhibits good mechanical reliability in bending tests, with performance degradation of less than 7% after 100 bends.

[0050] Example 1 This embodiment provides a method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector, including the following steps: (1) Disperse ZnO nanoparticles in the organic solvent α-terpineol (ZnO: α-terpineol = 2:1 (mass ratio)) to make ZnO ink.

[0051] (2) A 1.2 mm × 2.4 mm ZnO film was screen printed on a polyimide (PI) substrate.

[0052] (3) The ZnO film was annealed at 200℃ for 90 min.

[0053] (4) After screen printing silver electrodes on the annealed ZnO film, cure at 90°C for 10 min.

[0054] The photoelectric performance of the obtained metal-semiconductor-metal structure ZnO ultraviolet detector was tested. Under a 5V bias voltage and 365nm ultraviolet light illumination, the device exhibited a photocurrent-to-dark-current ratio of 3.1 × 10⁻⁶. 6 The response time is 12.8 A / W.

[0055] Example 2 This embodiment provides a method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector, including the following steps: (1) Disperse ZnO nanoparticles in the organic solvent α-terpineol (ZnO: α-terpineol = 2:1 (mass ratio)) to use as ZnO printing ink.

[0056] (2) A 1.2 mm × 2.4 mm ZnO film was screen printed on a polyimide (PI) substrate.

[0057] (3) The ZnO film was annealed at 200℃ for 90 min.

[0058] (4) Screen print 6 pairs of silver forked electrodes on the annealed ZnO film, with a finger width of 200 μm, a finger spacing of 200 μm, and a finger length of 1000 μm.

[0059] The photoelectric performance of the obtained ZnO ultraviolet detector was tested. The device was tested at a bias voltage of 5V and a strength of 3150μW / cm². 2 Under ultraviolet light intensity, the photocurrent reaches 237 μA, and the photocurrent-to-dark-current ratio is 3.83 × 10⁻⁶. 6 The response time is 11.5 A / W.

[0060] Example 3 In this embodiment, a 10×10 ZnO ultraviolet imaging array is constructed by preparing a ZnO matrix, silver wires and an insulating layer through a multi-layer overprinting process.

[0061] High-contrast ultraviolet imaging of a "mountain"-shaped mask was achieved under a 5V bias voltage, verifying the imaging capability of the array.

[0062] The main performance parameters of the ZnO ultraviolet detector (Example 3) under 5V bias and 365nm ultraviolet light are shown in Table 1.

[0063] Table 1 Main performance parameters of ZnO ultraviolet detector The experimental tests are as follows.

[0064] 1. Characterization of ZnO thin films like Figure 2 As shown. Figure 2 As can be seen from Figure a, the ZnO thin film is composed of many nanoscale crystal particles, and the film surface forms a uniform porous morphology. The pore size and particle size range are generally 20-90 nm, which is beneficial to improving the photoelectric response and stability of the device.

[0065] Figure 2 As can be seen from Figure b, the screen-printed ZnO films all exhibited a hexagonal wurtzite crystal structure at different annealing temperatures. Among them, the ZnO film annealed at 200°C for 90 min showed the optimal hexagonal wurtzite crystal structure.

[0066] Figure 2 As can be seen from c, the transmittance in the visible light region (400-800nm) is less than 80%; Figure 2 As can be seen from d, the optical band gap is approximately 3.27 eV.

[0067] 2. Working principle of ZnO ultraviolet detector like Figure 3 As shown. In the absence of light ( Figure 3 In (a), oxygen in the air attaches to the surface of ZnO in the form of oxygen molecules, which reduces the number of freely flowing electrons, thus forming a depletion semiconductor with low conductivity.

[0068] However, when ultraviolet light irradiates the ZnO surface ( Figure 3 (b) Photons excite electron-hole pairs within the semiconductor. Simultaneously, some oxygen molecules desorb from the semiconductor surface after ultraviolet light irradiation, releasing more electrons and forming a region with high conductivity. Finally, electrons and holes generate a photocurrent under the influence of an applied electric field.

[0069] 3. Photoelectric performance analysis like Figure 4 As shown, the ZnO detector maintains stable operation under long-term switching tests, with a linear relationship between responsivity and voltage. At a wavelength of 365nm, the photocurrent and responsivity are increased by more than 8 times.

[0070] 4. Comparison of performance between interdigitated electrode structure and single electrode group like Figure 5 As shown, after optimizing the ZnO detector electrodes to a 6-group interdigitated structure, the responsivity, detectivity, and external quantum efficiency did not change significantly. However, the photoresponse current reached 237 μA at a 5V bias, which is more than 10 times higher than that of the single-group electrode structure (compared to Example 2, only the number of groups changed). At the same time, the photocurrent-to-dark-current ratio remained at 3.83 × 10⁻⁶. 6 High level.

[0071] 5. Stability and bending test like Figure 6 As shown, the photocurrent of the ZnO ultraviolet detector remains stable over time, with the highest current change being less than 5%; after 100 bends, the photocurrent attenuation of the ZnO ultraviolet detector is less than 7%.

[0072] 6. ZnO Ultraviolet Imaging Array Analysis like Figure 7 As shown, the yield rate of the screen-printed 10×10 ZnO detector matrix is ​​100%, enabling high-contrast ultraviolet pattern imaging.

[0073] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector, characterized in that, Includes the following steps: (1) ZnO nanoparticles are mixed with organic solvents to form ZnO ink; (2) Screen printing ZnO thin film on a flexible substrate; (3) The ZnO film is annealed at 150-300℃; (4) After screen printing silver interdigitated electrodes on the annealed ZnO film, it is cured at low temperature.

2. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, The ZnO ink mentioned in step (1) is a mixture of ZnO nanoparticles and the organic solvent terpineol.

3. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 2, characterized in that, The organic solvent is α-terpineol.

4. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, In step (4), the particle size or pore size of the ZnO nanoparticles in the annealed ZnO film is 20-90 nm.

5. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, In step (3), the ZnO film is annealed at 150-300℃ for 60-120 min.

6. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, The parameters of the silver fork electrode mentioned in step (4) are as follows: The number of interdigital pairs is 2-20, the finger width is 5-500μm, the finger spacing is 5-500μm, and the finger length is 100-2000μm.

7. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 6, characterized in that, The number of interdigital pairs is 4-8, the finger width is 100-300μm, the finger spacing is 100-300μm, and the finger length is 500-1000μm.

8. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, The low-temperature curing in step (4) is to treat at 70-90℃ for 10-25 minutes.

9. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, The prepared flexible ZnO ultraviolet photodetector has a metal-semiconductor-metal structure.

10. The method for fabricating a fully screen-printed flexible ZnO ultraviolet photodetector according to claim 1, characterized in that, It also includes the imaging array fabrication step: ZnO dot matrix, silver wires, insulating layer and top electrode are printed sequentially through multi-layer overprinting to construct a row-column addressed imaging matrix.

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