A perovskite photodetector array integrated based on lithium niobate waveguide and a preparation method thereof

Abstract

This invention discloses a method for fabricating a perovskite photodetector array based on a thin-film lithium niobate waveguide. Its key feature is the use of lithium niobate on insulator as the integration platform, utilizing its low-loss optical waveguide as the light transmission carrier, and combining the high light absorption characteristics and low dark current advantages of perovskite materials to achieve high-performance on-chip photodetector functionality. The detector unit consists of a lithium niobate ridge waveguide, symmetrical electrodes, a perovskite light-absorbing layer, and a PMMA hydrophobic protective layer, and is arrayed and integrated using micro-nano processes. Compared with existing technologies, this invention exhibits high responsivity and good performance consistency under weak light conditions, and boasts advantages such as simple process, low cost, and ease of large-scale fabrication. It provides an effective technical path for high-performance, large-scale on-chip photodetector arrays, with broad application prospects in optical communication, sensing, and integrated optoelectronic chips.

Description

A lithium niobate waveguide-based integrated perovskite photodetector array and its fabrication method Technical Field

[0001] This invention relates to the field of photodetectors and integrated photonic devices, and in particular to a method for fabricating an integrated perovskite photodetector array based on a lithium niobate waveguide. Background Technology

[0002] Photonic integrated circuits play a crucial role in future ultra-high-speed optical communication, sensing, and computing. Lithium niobate (LNO) is renowned for its excellent electro-optic coefficient, nonlinear optical properties, relatively high refractive index, low loss, and wide transmission window, making it a highly regarded photonic integration platform. LNO possesses good physical and chemical stability, a wide low-loss optical window (0.35-5 μm), excellent nonlinear effects, and a high electro-optic coefficient, making it an ideal photonic platform for fabricating high-speed programmable photonic integrated chips. In particular, the mass production of LNOI wafers has spurred the rapid development of LNO-based photonics in the last fifteen years. In recent years, numerous high-performance photonic devices with on-chip functions have been realized on the LNO platform, including on-chip laser sources, integrated waveguide amplifiers, optical delay lines, electro-optic modulators, and optical frequency combs. However, photonic signal processing requires detection after optical signal generation and processing; therefore, on-chip photodetectors capable of converting optical signals into electrical signals are essential. Due to the inherent limitations of lithium niobate crystals, it is necessary to integrate photosensitive materials with lithium niobate photonic platforms.

[0003] In summary, existing photodetector structures and fabrication methods cannot meet the requirements of high responsivity and low dark current. However, perovskites exhibit significant advantages in heterogeneous integration with lithium niobate photonic platforms. Perovskite fabrication is relatively simple and easier for large-scale production. Low-temperature solution-based perovskite fabrication has been shown to reduce stress and enhance compatibility with lithium niobate platforms. Perovskites, due to their low cost and abundant material availability, possess significant advantages, making them highly suitable for large-scale applications. Therefore, exploring and developing heterogeneous integration technologies for perovskite materials and lithium niobate optical waveguides has significant scientific and social value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fabricating a lithium niobate waveguide-integrated perovskite photodetector array to address the shortcomings of existing technologies. Employing micro-nano processes and using lithium niobate on an insulator as the integration platform, this method achieves array integration. It utilizes the low-loss optical waveguide as the light transmission carrier, combining the high light absorption characteristics and low dark current advantages of perovskite materials to achieve high-performance on-chip photodetector functionality. The detector unit consists of a lithium niobate ridge waveguide, symmetrical electrodes, a perovskite light absorption layer, and a polymethyl methacrylate (PMMA) hydrophobic protective layer. This photodetector array exhibits high responsivity and good performance consistency under weak light conditions, and boasts advantages such as simple fabrication, low cost, and ease of large-scale fabrication. It provides a heterogeneous integration technology of perovskite and lithium niobate optical waveguides for high-performance, low-cost, large-scale on-chip photodetector arrays. This device uses lithium niobate on an insulator as the integration platform, utilizing its low-loss optical waveguide as the light transmission carrier, and combining the high light absorption characteristics and low dark current advantages of perovskite materials to achieve excellent performance with high responsivity and low dark current. It has broad application prospects in optical communication, sensing, and integrated optoelectronic chips.

[0005] The specific technical solution to achieve the purpose of this invention is: a method for fabricating a lithium niobate waveguide-integrated perovskite photodetector array. The photodetector unit is characterized by being composed of a lithium niobate ridge waveguide, symmetrical electrodes, a perovskite light-absorbing layer, and a polymethyl methacrylate hydrophobic protective layer, and is integrated into an array using micro / nano technology to detect weak light on-chip. The specific fabrication includes: Step 1: Structural design of the lithium niobate waveguide-integrated perovskite photodetector array. The lithium niobate waveguide-integrated perovskite photodetector array is designed to consist of four straight waveguides, four sets of symmetrical electrodes, a perovskite thin film as the light transmission layer, and a PMMA thin film as the hydrophobic layer. Based on the design, a layout of the lithium niobate photonic chip can be obtained, with the layout consisting of four straight waveguides.

[0006] Step 2: Fabrication of Lithium Niobate Waveguide Array and Electrodes Step 2-1: Take a lithium niobate substrate on an insulator, mainly composed of three layers. The bottom layer is a silicon substrate about 100 micrometers thick, with a silicon dioxide layer of several micrometers on its upper surface, and a thin film of lithium niobate on the upper surface of the silicon dioxide layer. Deposit a chromium film on the lithium niobate film, and use femtosecond laser direct writing technology to prepare a mask pattern with a specific structure to obtain a mask containing the waveguide array. Use chemical mechanical polishing to polish and etch the substrate with the mask to transfer the mask pattern onto the thin film of lithium niobate. Then use a chromium etching solution to etch away the chromium mask on the surface of the substrate to obtain the optical waveguide array structure.

[0007] Step 2-2: Metal coating is performed on the integrated chip waveguide using magnetron sputtering, and then femtosecond laser is used to write on the titanium mask of the substrate to obtain the symmetrical electrode mask of the waveguide array.

[0008] Steps 2-3: Use an etching solution to etch away the unprotected metal on the substrate surface, and then use an acid or alkali solution to clean the substrate to obtain the electrode structure of the photodetector array.

[0009] Step 3: Fabrication of the Lithium Niobate Waveguide Integrated Perovskite Photodetector Array. To ensure that the electrodes required for subsequent testing are not covered by the material, one end of the electrodes is covered using a PDMS thin film. The lithium niobate waveguide array substrate with existing electrodes undergoes a hydrophilic treatment, which is performed in two steps. The first step involved cleaning the substrate in an oxygen plasma cleaner at 100 W for 5 minutes. The second step involved ozone treatment for 20 minutes to add hydrophilic groups and improve solution adhesion. The substrate was then placed in a glove box to ensure an inert gas environment throughout the synthesis process. Next, the substrate was placed on a spin coater, and 10 μL of precursor solution was applied and spin-coated at 500 rpm for 10 seconds, followed by a high-speed spin coat at 3000 rpm for 60 seconds. During spin-coating, 20 μL of chlorobenzene (CB) solution was added to the film 12 seconds before the end of the spin-coating process. The film was then annealed at 50 °C for 3 minutes and then at 150 °C for 3 minutes to obtain a perovskite film. Finally, PMMA solution was spin-coated onto the perovskite film surface at 3000 rpm for 60 seconds and immediately annealed at 80 °C for 10 minutes to obtain a hydrophobic protective layer. Thus, a lithium niobate waveguide integrated perovskite photodetector array was successfully fabricated.

[0010] The precursor solution is an inorganic perovskite precursor solution prepared by mixing 0.184 g lead iodide, 0.095 g cesium bromide, and 1 mL dimethyl sulfoxide solvent.

[0011] The silicon dioxide has a thickness of 2.5–6.75 micrometers; the lithium niobate film has a thickness of 450–550 nanometers; and the chromium film has a thickness of 30 nanometers.

[0012] The lithium niobate waveguide integrated perovskite photodetector array has a maximum responsivity of 55 mA / W; the device materials include lithium niobate, silicon dioxide, silicon, gold, chromium, and perovskite; the photodetector array can realize the conversion process of optical signals to electrical signals on the chip.

[0013] Compared with existing technologies, this invention has the following beneficial technical effects and significant technological advancements: 1) It is the first time that a perovskite photodetector array has been integrated on a lithium niobate photonic platform; 2) It achieves low-cost, large-scale fabrication of a high-performance on-chip photodetector array. Compared with the high-temperature and complex epitaxial growth process required for III-V semiconductor fabrication and the two-dimensional materials obtained through mechanical exfoliation, the lithium niobate waveguide integrated perovskite photodetector fabrication method is simple, low-cost, and has excellent performance, making it more suitable for large-scale fabrication; 3) This on-chip integrated photodetector has an ultra-low dark current of 43 pA at a 1 V bias voltage and a light-to-dark-current ratio as high as 104. The ultra-low dark current highlights the device's performance in detecting weak light signals; 4) This photodetector exhibits a high responsivity of 55 mA / W at a coupled light intensity of 4.1 μW, confirming its ability to respond to ultra-low input light power. Attached Figure Description

[0014] Figure 1 is a schematic diagram of the lithium niobate waveguide integrated perovskite photodetector array structure of Example 1; Figure 2 is a schematic diagram of the process of Example 1; Figure 3 is a graph of the photocurrent and dark current of the on-chip perovskite photodetector of Example 1; Figure 4 is a graph of the responsivity of the on-chip perovskite photodetector of Example 1; Figure 5 is a graph of the stability of the packaged and unpackaged lithium niobate waveguide integrated perovskite photodetector of Example 1 in air. Detailed Implementation

[0015] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0016] Example 1 The fabrication of this example includes the following steps: Step 1: The structural design of the lithium niobate waveguide integrated perovskite photodetector array is shown in Figure 1. The lithium niobate waveguide integrated perovskite photodetector array is designed to consist of four straight waveguides spaced 250 μm apart, four sets of symmetrical electrodes spaced 10 μm apart, a CsPbI2Br thin film, and a PMMA thin film as a hydrophobic layer. According to the design, a design layout of the lithium niobate photonic chip can be obtained. The design layout includes four parallel straight waveguides.

[0017] Step 2: Fabrication of Lithium Niobate Waveguide Array and Electrodes 1) Take a lithium niobate substrate on an insulator, which mainly consists of three layers: the bottom layer is a 525 μm thick silicon substrate, with a 4.7 μm silicon dioxide layer on its upper surface, and a 500 nm thick thin film of lithium niobate on the upper surface of the silicon dioxide layer; deposit a chromium film on the lithium niobate film, and use photolithography to prepare a mask pattern with a specific structure.

[0018] 2) The design layout of the lithium niobate waveguide amplifier is converted into a photolithographic layout, and a femtosecond laser is used to etch it on a chromium mask on the substrate to obtain a mask containing the waveguide array.

[0019] 3) The substrate with the mask is polished and etched using chemical mechanical polishing to transfer the mask pattern onto the thin film lithium niobate. Then, the chromium mask on the surface of the substrate is etched away using a chromium etching solution to obtain the optical waveguide array structure.

[0020] 4) Metal coating is performed on the integrated chip waveguide using magnetron sputtering, and then femtosecond laser is used to write on the metal mask of the substrate to obtain a symmetrical electrode mask.

[0021] 5) Use an etching solution to sequentially etch away the gold, titanium, and chromium on the substrate surface, and then use an acid or alkaline solution to clean the substrate to obtain the electrode structure of the photodetector array.

[0022] Step 3: Fabrication of the lithium niobate waveguide integrated perovskite photodetector array (refer to Figure 2). To ensure that the electrodes required for subsequent testing are not covered by the material, one end of the electrode is covered with a PDMS film. The lithium niobate waveguide array substrate with existing electrodes undergoes a hydrophilic treatment in two steps. First, the substrate is cleaned in an oxygen plasma cleaner at 100 W for 5 minutes. Second, the substrate is subjected to ozone treatment for 20 minutes to add hydrophilic groups to the surface and increase solution adhesion. The substrate is then placed in a glove box to ensure it remains in an inert gas environment throughout the fabrication process.

[0023] Next, the substrate was placed on a spin coater, and 10 μL of CsPbI₂Br precursor solution was placed on the substrate and spin-coated at 500 rpm for 10 s and then at 3000 rpm for 60 s. During the spin-coating process, 20 μL of chlorobenzene solution was added to the film 12 s before the end of the step. Subsequently, the film was annealed at 50 °C for 3 min and then at 150 °C for 3 min to obtain the CsPbI₂Br film. Finally, PMMA solution was spin-coated onto the surface of the CsPbI₂Br film, and the film was spin-coated at 3000 rpm for 60 s and immediately annealed at 80 °C for 10 min to obtain a hydrophobic protective layer.

[0024] The precursor solution is an inorganic perovskite precursor solution prepared by mixing 0.184 g lead iodide, 0.095 g cesium bromide, and 1 mL dimethyl sulfoxide solvent.

[0025] Step 4: Photoelectric Performance Testing of the Lithium Niobate Waveguide Integrated Perovskite Photodetector Array. Photoelectric performance testing included photocurrent, dark current, and impulse response. To perform static photoresponse testing on the on-chip photodetector, a laser generated by a 638 nm light source was coupled into the waveguide through a tapered fiber lens, and the on-chip photodetector converted the input optical signal into an electrical signal. A bias voltage was applied to the electrodes of the photodetector using a Keithley 2400 source meter, and the photocurrent was measured to obtain the static photocurrent curve. Simultaneously, the dark current was measured under different DC bias voltages. For impulse response analysis, a modulated optical signal was input to the photodetector, and the resulting electrical signal was collected using an oscilloscope. The stability of the device in an air environment was also tested. By testing the responsivity change over different time periods, it was found that the PMMA layer effectively protects the device and improves its stability in air.

[0026] Referring to Figure 3, the photodetector achieves a low dark current of 43 pA under a 1 V bias. With a coupled light intensity of 4.1 μW, the device exhibits an ultra-high on / off ratio exceeding 10⁴, which is beneficial for improving the signal-to-noise ratio of photodetector. Referring to Figure 4, the photocurrent and responsivity of the detector change with light intensity when the applied bias is 1 V, showing that the responsivity exceeds 55 mA / W at its highest.

[0027] Referring to Figure 5, the photodetector packaged in PMMA exhibits a responsivity 200 times higher than that of the unpackaged device after 50 hours of aging.

[0028] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. 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 method for fabricating an integrated perovskite photodetector array based on a lithium niobate waveguide, characterized in that, This photodetector unit employs a lithium niobate ridge waveguide, symmetrical electrodes, a perovskite light-absorbing layer, and a polymethyl methacrylate (PMMA) hydrophobic protective layer. It is integrated into an array using micro / nano technology to detect weak on-chip light. The specific fabrication includes: Step 1: Structural design of the lithium niobate waveguide integrated perovskite photodetector array. The lithium niobate waveguide integrated perovskite photodetector array is designed to consist of four straight waveguides, four sets of symmetrical electrodes, a perovskite thin film with a light transmission layer, and a PMMA thin film with a hydrophobic layer, resulting in the design layout of the lithium niobate photonic chip; Step 2: Fabrication of the lithium niobate waveguide array and electrodes. Step 2-1: Using a silicon substrate with a silicon dioxide layer and a lithium niobate thin film sequentially arranged as the substrate, a chromium thin film is deposited on the lithium niobate thin film. Using femtosecond laser direct writing technology, the mask pattern designed in Step 1 is fabricated to obtain a mask containing the waveguide array. The thickness of the silicon dioxide is 2.5–6.75 micrometers; the thickness of the lithium niobate thin film is 450–550 micrometers. Nanometers; the thickness of the chromium thin film is 30 nanometers; Step 2-2: Polish and etch the substrate with the mask using chemical mechanical polishing to transfer the pattern of the mask onto the lithium niobate thin film, and then use a chromium etching solution to etch away the chromium mask on the substrate surface to obtain a substrate with an optical waveguide array structure; Step 2-3: Perform metal deposition on the optical waveguide array of the substrate using magnetron sputtering, and then use a femtosecond laser to write on the metal mask of the substrate to obtain a substrate with a symmetrical electrode mask; Step 2-4: Use an etching solution to sequentially etch the unprotected metal on the substrate surface, and then use an acid and alkali solution to clean the substrate to obtain a substrate with an electrode structure; Step 3: Fabrication of lithium niobate waveguide integrated perovskite photodetector array After the substrate with the electrode structure is cleaned by oxygen plasma and treated with ozone, a perovskite thin film is prepared on the substrate, and then encapsulated with polymethyl methacrylate to obtain a lithium niobate on-chip waveguide integrated perovskite photodetector array.

2. The method for fabricating a lithium niobate waveguide-based integrated perovskite photodetector array according to claim 1, characterized in that, Step 3 specifically includes: Step 3-1: Cleaning the substrate in an oxygen plasma cleaner with a power of 100 W for 5 minutes; Step 3-2: Ozone treatment of the substrate for 20 minutes to add hydrophilic groups to the surface and increase solution adhesion, while maintaining an inert gas environment throughout the treatment; Step 3-3: Spinning 10 μL of precursor solution onto the substrate at 500 rpm for 10 seconds, followed by 3000 rpm for 60 seconds, and adding 20 μL of chlorobenzene solution 12 seconds before the spin-coating is finished, then annealing at 50°C for 3 minutes and then at 150°C for 3 minutes to obtain a perovskite film; Step 3-4: Spin-coating PMMA solution onto the surface of the perovskite film, rotating at 3000 rpm for 60 seconds, and then annealing at 80°C for 10 minutes. A hydrophobic protective layer was obtained, and a lithium niobate on-chip waveguide integrated perovskite photodetector array was fabricated; the precursor solution was an inorganic perovskite precursor solution prepared by 0.184 g lead iodide, 0.095 g cesium bromide and 1 mL dimethyl sulfoxide solvent.

3. The method for fabricating a lithium niobate waveguide-based integrated perovskite photodetector array according to claim 1, characterized in that, The lithium niobate film has a thickness of 450–550 nanometers; the silicon dioxide layer has a thickness of 2.5–6.75 micrometers; the electrode is made of gold-chromium, with a gold layer thickness of 200 nanometers and a chromium layer thickness of 30 nanometers; and the perovskite film has a thickness of 100–200 nanometers.

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