Ultrathin silicon-based flexible sensor and preparation method
By integrating a patterned heavily doped single-crystal silicon thin film layer and a miniature multiplexer MOS transistor on a flexible substrate, the problem that traditional sensors cannot simultaneously detect gas and mechanical signals is solved, achieving high-sensitivity and biocompatible detection in complex physiological environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-22
- Publication Date
- 2026-04-03
AI Technical Summary
Existing rigid gas sensors are difficult to attach safely and comfortably for long periods on irregular curved surfaces and in dynamic deformation environments on the human body and tissues, and cannot simultaneously detect gas and mechanical signals, thus failing to meet the needs of medical monitoring and diagnosis.
Using a patterned, heavily doped single-crystal silicon thin film as the sensing material, combined with a flexible substrate, the gas detection is achieved by inducing changes in carrier concentration through the adsorption and desorption behavior of the gas molecules on the silicon surface. Mechanical signals are detected through the stress sensing area, and time-division multiplexing is achieved using a miniature multiplexer MOSFET. The design is in the form of a star or spiral structure to adapt to complex physiological environments.
It enables the transfer of high-performance single-crystal silicon devices onto flexible substrates at room temperature, possessing intrinsic flexibility and biocompatibility, and can simultaneously achieve high-sensitivity detection of gas and mechanical signals, adapting to long-term in-situ monitoring in complex physiological environments.
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Figure CN121784099A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of bioelectronics and flexible sensing technology, and in particular to an ultrathin silicon-based flexible sensor and its fabrication method. Background Technology
[0002] In the field of medical monitoring and diagnosis, there is an increasing demand for flexible sensors that can adapt to the irregular curves and dynamic deformations of human body surfaces and tissues. Currently, most commercially available high-performance gas sensors need to operate on rigid substrates and often rely on high-temperature activation conditions. As a result, the resulting monitoring systems are usually bulky, inflexible, and difficult to attach safely and comfortably to the constantly moving human skin or tissue surfaces for extended periods.
[0003] In addition, while a single gas sensor can reflect biochemical abnormalities, it cannot simultaneously acquire physical information such as deformation, friction, or pressure in the wound area. These mechanical signals are also crucial for a comprehensive assessment of the healing process, and existing rigid sensors cannot effectively integrate gas and stress sensing functions on the same flexible platform.
[0004] Therefore, how to develop a flexible sensor that combines intrinsic flexibility, high sensing performance, and biocompatibility, and can simultaneously detect gas and mechanical signals, has become an urgent technical challenge. Summary of the Invention
[0005] The main objective of this invention is to provide an ultrathin silicon-based flexible sensor and its fabrication method, aiming to develop a flexible sensor that combines intrinsic flexibility, high sensing performance, and biocompatibility, and can simultaneously detect gas and mechanical signals.
[0006] To achieve the above objectives, the present invention proposes an ultrathin silicon-based flexible sensor, comprising: a flexible substrate; and a patterned heavily doped monocrystalline silicon thin film layer bonded to the surface of the flexible substrate; the patterned heavily doped monocrystalline silicon thin film layer is a patterned structure, which includes at least one gas sensing region; wherein the gas sensing region is configured to detect gas by means of changes in bulk carrier concentration caused by adsorption of analyte gas molecules on its surface.
[0007] Preferably, the patterned heavily doped monocrystalline silicon thin film layer further includes at least one stress sensing region electrically interconnected with the gas sensing region; the stress sensing region has a non-linear extension structure adapted to tensile deformation and is configured to detect the stress on the flexible substrate based on the piezoresistive effect of monocrystalline silicon.
[0008] Preferably, the patterned heavily doped single-crystal silicon thin film layer is constructed as a star-shaped sensing node; the gas sensing region is located at the center of the star-shaped sensing node, forming a central sensing platform; the stress sensing region consists of multiple sensing microarms extending radially outward from the central sensing platform.
[0009] Preferably, the sensing microarm has a serpentine structure, and there are eight sensing microarms distributed axially symmetrically, used to detect anisotropic strain in a two-dimensional plane.
[0010] Preferably, the surface of the sensing microarm is covered with a flexible sealing layer to isolate the influence of ambient gas on the piezoresistive signal of the sensing microarm.
[0011] Preferably, the gas sensing area is provided with a plurality of vias penetrating the patterned heavily doped single-crystal silicon thin film layer, and the vias are configured to increase the surface area to improve the gas detection sensitivity.
[0012] Preferably, the patterned heavily doped single-crystal silicon thin film layer is a highly doped P-type single-crystal silicon layer with a thickness on the nanometer scale; the sensor also includes a metal electrode fabricated on the surface of the patterned heavily doped single-crystal silicon thin film layer.
[0013] Preferably, it also includes a miniature multiplexer MOS transistor integrated on the patterned heavily doped single-crystal silicon thin film layer, the miniature multiplexer MOS transistor being configured to sequentially select the gas sensing region and the stress sensing region to achieve time-division multiplexing acquisition.
[0014] Preferably, the flexible substrate has a long strip structure, and the patterned heavily doped single-crystal silicon thin film layer constitutes multiple sensing nodes arranged in a linear spiral along the long axis of the flexible substrate for monitoring the inner wall of biological cavities.
[0015] This application also discloses a method for fabricating an ultrathin silicon-based flexible sensor as described in any of the preceding claims, characterized by comprising the following steps: providing a silicon-on-insulator (SOI) wafer, the SOI wafer comprising a bulk silicon layer, an intermediate oxide layer, and a top monocrystalline silicon layer; performing doping and annealing on the top monocrystalline silicon layer to form a top monocrystalline silicon layer with patterned heavily doped regions; performing patterned etching on the top monocrystalline silicon layer with patterned heavily doped regions to form a device structure including a gas sensing region; removing the intermediate oxide layer below the device structure by wet etching, wherein, during the wet etching process, the device structure is temporarily fixed to the bulk silicon layer using anchoring structures retained at the edges of the device structure to prevent the device structure from drifting in the etching solution; picking up the released device structure from the surface of the bulk silicon layer using a sacrificial layer material and transferring it to a flexible substrate; and removing the sacrificial layer material and forming a metal electrode on the surface of the device structure.
[0016] Preferably, the step of temporarily fixing the device structure to the bulk silicon layer using the anchoring structure retained at the edge of the device structure specifically includes: forming a photoresist layer at the edge of the pattern on the top single-crystal silicon before the wet etching, such that the photoresist layer fills the local grooves formed by etching; controlling the curing of the photoresist layer so that it is not removed during the wet etching process, thereby using the photoresist layer to connect the device structure and the bulk silicon layer.
[0017] Preferably, the step of doping the top monocrystalline silicon specifically involves spin-coating a boron-doped solvent onto the surface of the top monocrystalline silicon and performing rapid thermal annealing (RTP).
[0018] Preferably, the sacrificial layer material is polycarbonate (PPC), and the step of transferring it to the flexible substrate employs a stepped heating process.
[0019] Preferably, the method further includes the step of fabricating a MOS transistor switching circuit on the flexible substrate, the step of which includes transferring an alumina dielectric layer to a single-crystal silicon surface on the flexible substrate using a sacrificial layer transfer process.
[0020] The above technical solution has the following advantages: This invention employs patterned, heavily doped single-crystal silicon thin films as the core sensing material. Leveraging its excellent semiconductor properties and the unsaturated dangling bonds present on its surface, the direct adsorption and desorption of analyte gas molecules on the silicon surface induces a significant change in the carrier concentration within the silicon film. This achieves highly sensitive detection of volatile organic gases without the need for additional surface chemical modifications. This sensing scheme, based on the intrinsic physical mechanism of the material, not only simplifies the device structure and fabrication process, avoiding the stability issues that complex modification layers may introduce, but also combines the intrinsic flexibility of ultrathin single-crystal silicon with a flexible substrate, enabling it to conformally adhere to irregular biological tissue surfaces. This effectively solves the problem that traditional gas sensors, relying on rigid substrates and high-temperature operating conditions, cannot perform long-term, in-situ monitoring in complex physiological environments. Attached Figure Description
[0021] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a schematic diagram of the top-layer single-crystal silicon doping process provided in an embodiment of the present invention.
[0022] Figure 2 This is a schematic diagram of the top-layer monocrystalline silicon transfer process provided in an embodiment of the present invention.
[0023] Figure 3 This is a schematic diagram of the oxide transfer process provided in an embodiment of the present invention.
[0024] Figure 4 The IV characteristic curve of doped P-type top-layer single crystal silicon provided for embodiments of the present invention.
[0025] Figure 5 An optical micrograph of doped P-type top-layer single-crystal silicon provided in an embodiment of the present invention.
[0026] Figure 6 An optical micrograph of the sensor fabrication process provided in an embodiment of the present invention.
[0027] Figure 7 The diagram shows the physical MOS transistor device and its transfer characteristic curves provided in the embodiments of the present invention.
[0028] Figure 8 The graph shows the response characteristics of the gas sensor provided in this embodiment of the invention.
[0029] Figure 9 This is a schematic diagram of the structure of the sensor provided in the embodiment of the present invention, applied in a biological cavity. Detailed Implementation
[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0031] Example 1 like Figures 1 to 9 As shown, this embodiment provides an ultrathin silicon-based flexible sensor and its fabrication method. This sensor aims to solve the technical problem that traditional gas sensors rely on rigid substrates and are difficult to operate in complex deformation environments, while also providing a low-cost, high-efficiency manufacturing process.
[0032] The ultrathin silicon-based flexible sensor of this embodiment mainly includes a flexible substrate 9 and a patterned heavily doped monocrystalline silicon thin film layer 6 bonded to the surface of the flexible substrate 9. The flexible substrate 9 is made of a material with good biocompatibility and mechanical flexibility, such as Ecoflex, PDMS, or PI. In this embodiment, a silicone substrate cured with Ecoflex 00-30 is preferred. The heavily doped monocrystalline silicon thin film layer 6 is derived from the top silicon layer of a silicon-on-insulator (SOI) wafer, and its thickness is on the nanometer scale, specifically about 200 nm. This extremely thin thickness enables the originally brittle monocrystalline silicon material to bend, twist, and even stretch to a certain extent along with the flexible substrate 9, thereby achieving the intrinsic flexibility of the device.
[0033] The patterned heavily doped monocrystalline silicon thin film layer 6 has a patterned structure and includes at least one gas sensing region 16. The gas sensing region 16 utilizes its surface to directly adsorb the target gas molecules and is configured to detect gases based on changes in carrier concentration caused by surface adsorption. Specifically, when polar gas molecules such as volatile organic compounds (VOCs) are adsorbed onto the surface of the gas sensing region 16, due to the presence of unsaturated dangling bonds or modified active sites on the monocrystalline silicon surface, the gas molecules are adsorbed through van der Waals forces or hydrogen bonds, accompanied by electron exchange. This leads to a change in the carrier concentration within the patterned heavily doped monocrystalline silicon thin film layer 6, thereby causing a change in resistance. By measuring this change in resistance, the detection of a specific gas can be achieved.
[0034] This embodiment also provides a method for fabricating the aforementioned ultrathin silicon-based flexible sensor. This method enables the transfer of high-performance single-crystal silicon devices onto a high-temperature-sensitive flexible substrate 9 at room temperature. The specific steps are as follows: First, a silicon-on-insulator (SOI) wafer is provided, comprising a bottom bulk silicon layer 1, an intermediate oxide layer 2, and a top monocrystalline silicon layer 3. A p-type SOI wafer with a resistivity of 0.1 Ωcm to 1 Ωcm is selected and cleaned. After cleaning, to form a high-temperature doped hard mask, 500 nm silicon dioxide is deposited on the sample surface using plasma-enhanced chemical vapor deposition (PECVD). Channels are defined by photolithography and etched with BOE solution for 6 minutes. Finally, the photoresist is removed.
[0035] Next, the top monocrystalline silicon 3 is selectively doped and annealed to form a top monocrystalline silicon layer with patterned heavily doped regions. To avoid the high cost and lattice damage problems of traditional ion implantation processes, this embodiment uses a spin-coating method combined with a rapid thermal annealing (RTP) process. Specifically, boron-doped solvent 5 is spin-coated onto the surface of the top monocrystalline silicon 3 at a speed of 4000 r / min for 30 s. After spin-coating, it is left to stand at room temperature and then placed in a rapid thermal annealing apparatus. The RTP process uses a specific heating curve: first, the temperature is raised to 290°C and held, then rapidly raised to 1000°C and held for 1 min, and finally rapidly cooled. This rapid thermal annealing process effectively promotes the activation and diffusion of impurity ions while reducing the thermal budget. After annealing, a 2% hydrofluoric acid solution is used to remove surface oxide impurities, obtaining a P-type monocrystalline silicon layer with patterned heavily doped regions. Hall effect measurements show that its carrier concentration reaches 3.565 × 10⁻⁶. 20 / cm 3 The order of magnitude is [value missing], with a mobility of 33.37 cm² / (V·s) and a resistivity of 5.247 × 10⁻⁶. -4 Ω·cm, meeting the electrical performance requirements of the sensor.
[0036] Subsequently, the top single-crystal silicon with patterned heavily doped regions is patterned and etched to form a device structure including the gas sensing region 16. The device pattern is defined using photolithography, and excess silicon material is removed using reactive ion etching (RIE) to expose the underlying intermediate oxide layer 2.
[0037] Next, the intermediate oxide layer 2 beneath the device structure is removed by wet etching. In this step, the sample is first immersed in a 40% hydrofluoric acid solution for 5 minutes. To prevent the tiny device structure from floating and being lost in the etching solution after the intermediate oxide layer 2 is completely etched, this embodiment introduces a unique anchoring technique. After the wet etching, a photoresist layer 7 is spin-coated onto the edge of the pattern on the top monocrystalline silicon 3. Since the previous etching step created localized grooves at the lower edge of the top monocrystalline silicon 3, the photoresist layer 7 fills these grooves. The curing conditions of the photoresist layer 7 are controlled, specifically by baking at 115°C for 1 minute and 30 seconds, ensuring it is not removed during the subsequent long-duration hydrofluoric acid etching process. The sample is then immersed again in a 40% hydrofluoric acid solution for 6 hours. After the intermediate oxide layer 2 is completely etched, the device structure is temporarily fixed to the surface of the bulk silicon layer 1 only by the anchoring structure formed by the photoresist layer 7 remaining at the edge, effectively preventing device drift.
[0038] Subsequently, the released device structure is picked up from the surface of the bulk silicon layer 1 using the sacrificial layer material 8 and transferred to the flexible substrate 9. In this embodiment, the sacrificial layer material 8 is polycarbonate (PPC). The PPC film is attached to the sample surface, and a stepped heating process is used to heat it sequentially at 40°C, 60°C, and 90°C, maintaining each temperature gradient for 15 to 20 minutes to ensure tight adhesion between the PPC and the device structure. Then, PDMS is used as a carrier to peel off the PPC along with the device structure, at which point the physical connection of the photoresist layer 7 is broken. The PPC layer with the device is attached to the pre-prepared Ecoflex flexible substrate 9, and the temperature is raised again to complete the transfer. The flexible substrate 9 is prepared by mixing two-component products A and B of platinum-curing silicone Ecoflex00-30 in a 1:1 volume ratio, evacuating to remove air bubbles, and curing at room temperature for 4 hours to form a substrate approximately 3 mm thick.
[0039] Finally, the sacrificial layer material 8 is removed, and a metal electrode 13 is formed on the surface of the device structure. The transferred sample is immersed in anisole solution to dissolve and remove PPC, and then cleaned. The electrode region is defined by photolithography, and a 50 nm thick layer of platinum metal is deposited using electron beam evaporation, followed by a lift-off process to form the metal electrode 13, thus completing the fabrication of the ultrathin silicon-based flexible sensor. This method avoids damage to the flexible substrate 9 caused by high-temperature processes and achieves compatibility between high-performance silicon-based materials and flexible electronics technology.
[0040] Example 2 Based on Example 1, this embodiment further constructs a multimodal ultrathin silicon-based flexible sensor that integrates both gas and stress sensing functions.
[0041] In practical biomedical monitoring scenarios, such as wound healing, changes in biochemical substances (volatile organic compounds) are often accompanied not only by changes in these substances but also by physical deformations such as tissue swelling and contraction. Single gas detection methods are insufficient to fully reflect these complex physiological states. Therefore, in this embodiment, the patterned heavily doped monocrystalline silicon thin film layer 6 is constructed as a unique star-shaped sensing node.
[0042] The central region of this star-shaped sensing node is the gas sensing region 16, which forms the central sensing base. Multiple sensing microarms extend radially outward from this central sensing base; these microarms constitute the stress sensing regions 14. The gas sensing region 16 and the stress sensing region 14 are electrically interconnected via a miniature multiplexer MOSFET 15 integrated on the central sensing base. Specifically, the miniature multiplexer MOSFET 15 is configured to select either the gas sensing region 16 or the stress sensing region 14 according to a control signal, thereby achieving time-division multiplexing acquisition and transmission of multi-modal signals. To achieve precise capture of anisotropic strain in a two-dimensional plane, this embodiment employs eight sensing microarms arranged symmetrically. In terms of structural design, to address the inherent brittleness and poor tensile strength of monocrystalline silicon, these sensing microarms are designed with a serpentine structure. When the flexible substrate 9 is subjected to external tension or bending, the serpentine geometry effectively transforms macroscopic tensile strain into local bending deformation, thereby significantly reducing the peak stress within the monocrystalline silicon material and greatly improving the device's mechanical ductility and structural reliability.
[0043] Based on the excellent piezoresistive effect of monocrystalline silicon, its resistance changes significantly when the sensing microarm undergoes minute strain due to substrate deformation. The piezoresistive coefficient of monocrystalline silicon is much higher than that of traditional metallic materials, thus enabling highly sensitive detection of weak biomechanical signals. Furthermore, to eliminate interference from the gas environment on the piezoresistive signal and ensure measurement accuracy, this embodiment covers the surface of the sensing microarm with a flexible sealing layer. This flexible sealing layer effectively isolates the ambient gas from contact with the stress sensing area 14, allowing the sensing microarm to respond only to mechanical deformation signals, thereby achieving decoupling and synchronous monitoring of gas and stress signals at the same node.
[0044] Example 3 This embodiment optimizes the overall layout of the aforementioned ultrathin silicon-based flexible sensor to meet the monitoring needs of specific biological cavities.
[0045] For complex cavities within living organisms, such as sinuses and intestines, which have cylindrical inner walls, traditional planar sheet sensors struggle to achieve good adhesion and omnidirectional monitoring. In this embodiment, the flexible substrate 9 is designed as a long strip structure. Multiple star-shaped sensing nodes, composed of patterned heavily doped monocrystalline silicon thin film layers 6, are arranged in a linear spiral along the long axis of the flexible substrate 9.
[0046] This spiral arrangement design allows the sensing nodes to naturally conform to the inner wall of the cylindrical biological cavity when the long, flexible substrate 9 is rolled up and placed inside, forming a three-dimensional monitoring network covering the circumference and axis of the cavity. This not only solves the problem of rigid devices being unable to enter narrow and curved cavities, but also enables high spatial resolution in-situ monitoring of biochemical and physical parameters of the lesion area by adjusting the node spacing and spiral angle.
[0047] Example 4 This embodiment makes microscopic improvements to the structure of the gas sensing region 16 to further enhance the device fabrication efficiency and detection sensitivity.
[0048] In the fabrication process described in Example 1, to further shorten the time for wet etching to remove the intermediate oxide layer 2 and to prevent excessive adhesion of byproducts (such as orthosilicic acid) generated by the reaction of hydrofluoric acid and the intermediate oxide layer during long-term immersion to the device surface, thereby affecting the sensing sensitivity of the device, this embodiment has multiple through-holes penetrating the patterned heavily doped single-crystal silicon thin film layer 6 distributed in the gas sensing region 16. These through-holes have a diameter of approximately 4 μm and a spacing of approximately 44 μm.
[0049] During the preparation process, the etching solution, namely hydrofluoric acid solution, can rapidly penetrate through these pores to the underlying intermediate oxide layer 2, significantly increasing the corrosion contact area and thus greatly improving the corrosion rate. Experiments show that after introducing the porous structure, the corrosion time can be shortened to about 1.5 hours.
[0050] In terms of sensing performance, these micro-pores significantly increase the specific surface area of the gas sensing region 16, providing more adsorption sites for the gas molecules to be measured. At the same time, the abundant dangling bonds at the edges of the pores further enhance the gas adsorption capacity, making the sensor respond more rapidly and sensitively to volatile gases, with the response time reduced to less than 1 second, effectively improving the dynamic detection performance of the device.
[0051] Example 5 This embodiment provides an ultrathin silicon-based flexible sensor integrating a miniature multiplexer MOSFET 15 and its fabrication method to solve the addressing and crosstalk problems in multi-node array signal acquisition.
[0052] To enable independent control and reading of the multiple sensing nodes arranged in a spiral pattern and the different modal sensors within each node, this embodiment integrates a miniature multiplexer MOSFET 15 on a patterned heavily doped single-crystal silicon thin film layer 6. This miniature multiplexer MOSFET 15 is configured to sequentially select the gas sensing region 16 and the stress sensing region 14 to achieve time-division multiplexing acquisition.
[0053] Since the conventional gate dielectric layer, i.e. oxide layer, of a MOS transistor usually requires a high-temperature thermal oxidation process to prepare, and this temperature is far beyond the tolerance limit of the flexible substrate 9, this embodiment develops a unique oxide transfer process to prepare the gate dielectric layer of the MOS transistor.
[0054] The specific steps include: First, a gold layer 11 and an alumina dielectric layer 12 are sequentially deposited on the surface of an auxiliary silicon wafer, wherein the thickness of the gold layer 11 is 50 nm and the thickness of the alumina dielectric layer is 20 nm. The gold layer and the alumina dielectric layer 12 are then peeled off together using a sacrificial layer material 8, i.e., PPC. Subsequently, the gold layer is removed by etching with a mixed solution of potassium iodide and iodine, leaving only the alumina dielectric layer 12 on the PPC. Finally, using the same stepped temperature transfer process as in Example 1, the alumina dielectric layer 12 is precisely transferred to the pre-fabricated single-crystal silicon channel surface on the flexible substrate 9 to form the gate dielectric structure of the MOS transistor. Then, source, drain, and gate electrodes are fabricated using photolithography and metallization processes, and the alumina in the non-channel areas is etched by immersion in a 2% hydrofluoric acid solution for 1 minute.
[0055] This method successfully fabricated a high-performance single-crystal silicon MOS switching circuit on a flexible substrate that is not resistant to high temperatures, and the measured on / off ratio reached 10. 6 With a subthreshold swing of 250mV / dec, it meets the signal gating requirements of multi-channel sensor arrays, laying the hardware foundation for building a fully flexible and intelligent biological monitoring system.
[0056] Example 6 This embodiment provides process variants for different application scenarios.
[0057] Considering the different substrate modulus requirements of various biological tissues, the flexible substrate 9 can be replaced with polydimethylsiloxane (PDMS) or polyimide (PI). When using PDMS, the base adhesive and curing agent are mixed at a mass ratio of 10:1, placed in a vacuum chamber for 20 minutes under vacuum, and then heat-cured at 70°C for 1 hour. When using PI, to obtain a smooth surface, a polyimide solution can be spin-coated onto the surface of a commercial PI film. The specific spin-coating parameters are: 600 rpm for 20 seconds, followed by a 10-second pause before a second spin-coating at 1300 rpm for 50 seconds. After spin-coating, a four-stage gradient temperature curing process is performed: 80°C for 20 minutes, 120°C for 30 minutes, 150°C for 30 minutes, and 180°C for 50 minutes. The above transfer process exhibits good compatibility with these substrates.
[0058] Furthermore, to meet different detection sensitivity requirements, the doping concentration of the top-layer single-crystal silicon 3 can be adjusted by changing the number of spin-coating cycles of the boron-doped solvent 5. For example, repeating the spin-coating twice, combined with rapid thermal annealing, yields a sample with two layers of dopant on the surface, with a carrier concentration of 1.951 × 10⁻⁶. 20 / cm 3 The migration rate was 41.9 cm. 2 / (V·s), resistivity is 7.633×10 -4 Ω·cm. If spin-coating is repeated three times, a sample with three layers of dopant can be obtained, with a carrier concentration of 1.052 × 10⁻⁶. 20 / cm 3 The migration rate was 59.88 cm. 2 / (V·s), resistivity is 9.909×10 -4 Ω·cm. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. An ultrathin silicon-based flexible sensor, characterized in that, include: A flexible substrate (9); and a patterned heavily doped monocrystalline silicon thin film layer (6) bonded to the surface of the flexible substrate (9); the patterned heavily doped monocrystalline silicon thin film layer (6) is a patterned structure that includes at least one gas sensing region (16); wherein the gas sensing region (16) is configured to detect gas by changes in the bulk carrier concentration caused by the adsorption of analyte gas molecules on its surface.
2. The ultrathin silicon-based flexible sensor according to claim 1, characterized in that, The patterned heavily doped monocrystalline silicon thin film layer (6) further includes at least one stress sensing region (14) electrically interconnected with the gas sensing region (16); the stress sensing region (14) has a non-linear extension structure adapted to tensile deformation and is configured to detect the stress on the flexible substrate (9) based on the piezoresistive effect of monocrystalline silicon.
3. The ultrathin silicon-based flexible sensor according to claim 2, characterized in that, The patterned heavily doped single-crystal silicon thin film layer (6) is constructed as a star-shaped sensing node; the gas sensing region (16) is located at the center of the star-shaped sensing node, forming a central sensing platform; the stress sensing region (14) consists of multiple sensing microarms extending radially outward from the central sensing platform.
4. The ultrathin silicon-based flexible sensor according to claim 3, characterized in that, The sensing microarm has a serpentine structure, and there are eight sensing microarms distributed in an axisymmetric manner, used to detect anisotropic strain in a two-dimensional plane.
5. The ultrathin silicon-based flexible sensor according to claim 3, characterized in that, The surface of the sensing microarm is covered with a flexible sealing layer to isolate the influence of ambient gas on the piezoresistive signal of the sensing microarm.
6. The ultrathin silicon-based flexible sensor according to claim 1, characterized in that, The gas sensing area (16) is provided with a plurality of through holes that penetrate the patterned heavily doped single-crystal silicon thin film layer (6), and the through holes are configured to increase the surface area to improve the gas detection sensitivity.
7. The ultrathin silicon-based flexible sensor according to claim 1, characterized in that, The patterned heavily doped single-crystal silicon thin film layer (6) is a highly doped P-type single-crystal silicon layer with a thickness of nanometers; the sensor also includes a metal electrode (13) fabricated on the surface of the patterned heavily doped single-crystal silicon thin film layer (6).
8. The ultrathin silicon-based flexible sensor according to claim 2, characterized in that, It also includes a miniature multiplexer MOS transistor (15) integrated on the patterned heavily doped single-crystal silicon thin film layer (6), the miniature multiplexer MOS transistor (15) being configured to sequentially select the gas sensing region (16) and the stress sensing region (14) to achieve time-division multiplexing acquisition.
9. The ultrathin silicon-based flexible sensor according to claim 1, characterized in that, The flexible substrate (9) has a long strip structure, and the patterned heavily doped single-crystal silicon thin film layer (6) forms multiple sensing nodes arranged in a linear spiral along the long axis of the flexible substrate (9) for monitoring the inner wall of biological cavities.
10. A method for fabricating an ultrathin silicon-based flexible sensor as described in any one of claims 1 to 9, characterized in that, The process includes the following steps: providing a silicon-on-insulator (SOI) wafer, the SOI wafer comprising a bulk silicon layer (1), an intermediate oxide layer (2), and a top monocrystalline silicon layer (3); selectively doping and annealing the top monocrystalline silicon layer (3) to form a top monocrystalline silicon layer with patterned heavily doped regions; The top single-crystal silicon with patterned heavily doped regions is patterned and etched to form a device structure including a gas sensing region (16); the intermediate oxide layer (2) below the device structure is removed by wet etching, wherein, during the wet etching process, the device structure is temporarily fixed to the bulk silicon layer (1) by using an anchoring structure retained at the edge of the device structure to prevent the device structure from drifting in the etching solution; the released device structure is picked up from the surface of the bulk silicon layer (1) by using a sacrificial layer material (8) and transferred to a flexible substrate (9); And remove the sacrificial layer material (8) and form a metal electrode on the surface of the device structure.
11. The preparation method according to claim 10, characterized in that, The step of temporarily fixing the device structure to the bulk silicon layer (1) using the anchoring structure retained at the edge of the device structure specifically includes: forming a photoresist layer (7) at the pattern edge of the top single crystal silicon (3) before the wet etching, so that the photoresist layer (7) fills the local groove formed by etching; controlling the curing of the photoresist layer (7) so that it is not removed during the wet etching process, thereby using the photoresist layer (7) to connect the device structure and the bulk silicon layer (1).
12. The preparation method according to claim 10, characterized in that, The specific steps for doping the top single-crystal silicon (3) are as follows: spin-coating a boron-doped solvent (5) onto the surface of the top single-crystal silicon (3) and performing rapid thermal annealing (RTP).
13. The preparation method according to claim 10, characterized in that, The sacrificial layer material (8) is polycarbonate (PPC), and the step of transferring it to the flexible substrate (9) adopts a stepped heating process.
14. The preparation method according to claim 10, characterized in that, It also includes the step of fabricating a MOS transistor switching circuit on the flexible substrate (9), the step of which includes transferring an alumina dielectric layer (12) to a single-crystal silicon surface on the flexible substrate (9) by a sacrificial layer transfer process.