A picometer-scale micro-displacement sensor based on surface plasmon polariton self-imaging

Abstract

This invention belongs to the technical field of microelectromechanical systems (MEMS) and micro-displacement devices, specifically relating to a picometer-level micro-displacement sensor based on surface plasmon resonance (SPP) self-imaging. The sensor includes a laser, a reflecting prism, a microscope objective, a sample stage, a sample, and a probe. The reflecting prism is positioned along the optical path of the laser, the microscope objective is positioned along the reflected optical path of the prism, the sample stage is positioned along the optical path of the microscope objective, the sample is placed on the sample stage, and the probe is positioned directly above the sample. This invention utilizes a one-dimensional circular aperture microstructure to excite the in-plane SPP self-imaging effect through optical excitation, observing a spatial near-field light intensity distribution consistent with the parameters of the one-dimensional circular aperture structure within the surface of the metal thin film. The displacement can be calculated by detecting the magnitude of the light intensity. Combined with a high-magnification subdivision circuit, picometer-level resolution displacement measurement is achieved.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems and micro-displacement devices, specifically relating to a picometer-level micro-displacement sensor based on surface plasmon self-imaging. Background Technology

[0002] Micro-displacement sensors, as an important branch of sensors, are typically used to convert physical quantities such as displacement, position, deformation, vibration, and size into electrical quantities that are easy to quantitatively detect and convenient for information transmission and processing. They have wide applications in precision measurement, microfabrication, and microelectronics manufacturing. With the development of semiconductor devices, MEMS processing, and integrated systems, higher demands are being placed on the miniaturization and integration of high-precision displacement sensors. Currently, most miniaturized and integrated micro-displacement sensors are based on electrical structures, with sensing principles primarily based on potentiometric and capacitive principles, converting mechanical displacement into resistance, capacitance, or voltage signals with a fixed functional relationship. These sensors have resolutions only on the order of millimeters / nanometers and are susceptible to electromagnetic interference, exhibiting poor resistance to environmental interference. Currently, optical micro-displacement sensors based on grating diffraction interference have received widespread attention in recent years due to their immunity to electromagnetic interference. However, limited by the diffraction limit of laser wavelength, the optical period of these sensors is on the order of 100 nm, and the overall resolution is on the order of 0.1 nm. In summary, although traditional grating-based micro-displacement sensors are immune to electromagnetic interference, their resolution is difficult to break through the 0.1 nm level. The aforementioned devices are insufficient to meet the requirements of ultra-precision machining and measurement applications such as dual-stage positioning in high-performance lithography machines (7nm and below nodes) and tool head positioning in ultra-precision machine tools for ultra-high resolution (picometer-level) micro-displacement sensors. Summary of the Invention

[0003] To address the technical challenge of traditional grating-type micro-displacement sensors failing to achieve resolutions on the order of 0.1 nm, this invention provides a picometer-level micro-displacement sensor based on surface plasmon resonance (SPP) self-imaging. This overcomes the optical diffraction limit; traditional grating-type micro-displacement sensors have optical periods on the order of 100 nm, while this method utilizes a one-dimensional circular aperture microstructure (with a period on the order of 10 nm) to excite an in-plane SPP self-imaging effect through optical excitation. Displacement is calculated by detecting periodic light intensity changes through the movement of a near-field probe, and combined with a high-magnification subdivision circuit, the resolution is improved to the order of 1-10 pm. This represents a resolution improvement of 1-2 orders of magnitude compared to traditional grating-type displacement sensors.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A picometer-scale micro-displacement sensor based on surface plasmon polariton self-imaging includes a laser, a reflecting prism, a microscope objective, a sample stage, a sample, and a probe. The reflecting prism is arranged in the optical path of the laser, and the microscope objective is arranged in the reflected optical path of the reflecting prism. The light reflected by the reflecting prism is incident on the sample stage through the microscope objective. The sample is placed on the sample stage, and the probe is arranged directly above the sample.

[0006] It also includes a piezoelectric ceramic tube, a photomultiplier tube, a Z-axis actuator, an XY-axis actuator, and a computer control and image processing system. The probe is fixedly connected to the piezoelectric ceramic tube, and the piezoelectric ceramic tube is electrically connected to the Z-axis actuator and the XY-axis actuator, respectively.

[0007] The piezoelectric ceramic tube is electrically connected to a photomultiplier tube, which is electrically connected to a Z-direction actuator.

[0008] Both the Z-axis driver and the XY-axis driver are electrically connected to the computer control and image processing system.

[0009] The laser is a HeNe laser or an Ar laser. + The laser, wherein the HeNe laser has a wavelength of 632.8 nm, and the Ar... + The laser has a wavelength of 514 nm; the sample is a gold or silver film with a thickness of 50 ± 10 nm, and the sample is evaporated onto a thin coverslip; the probe is an aluminum-coated glass fiber tip with a radius of 50-100 nm.

[0010] The piezoelectric ceramic tube has a diameter of 6.35 mm, a length of 25 mm, and a wall thickness of 0.5 mm; its maximum scanning range is 10 μm × 10 μm; and the photomultiplier tube has a parameter conversion sensitivity of 2 × 10⁻⁶. 5 V / W, the resolution of the photomultiplier tube is 20nW.

[0011] A measurement method for a picometer-scale micro-displacement sensor based on surface plasmon polariton self-imaging includes the following steps:

[0012] S1. The light with wavelength λ0 emitted by the laser beam is refracted by the reflecting prism and enters the microscope objective. After collimation, the beam is incident from the back of the metal thin film sample onto the lower surface of the metal thin film sample. The incident direction is along the z-axis.

[0013] S2. On the metal thin film sample, there is a row of circular holes distributed along the x direction with a spacing of a and a diameter of 0.5a. When incident light shines on the circular hole array structure, each nanopore is equivalent to a secondary wave source and excites the SPP oscillation in the metal thin film sample under the action of the momentum matching principle.

[0014] S3. Plasma waves on the surface of the metal thin film sample move at a wavelength λ. sp SPP waves generated by different secondary wave sources propagate along the y-direction and coherently superimpose on the thin film surface, thus exciting a self-imaging effect on the thin film surface.

[0015] S4. At this time, a pattern with a period equal to the period a of the circular aperture array will be observed at a certain distance from the small hole. The repetition period of the self-image is defined as the self-image distance τ in the y direction.

[0016] S5. The SPP wave on the surface of the metal thin film sample will excite the near-field light intensity distribution in space. This light intensity distribution is the same as the spatial distribution of the SPP wave. Using a scanning probe, the near-field light component is scattered to the far field and collected.

[0017] S6. The piezoelectric ceramic tube located at the tip of the probe is controlled by the Z-direction driver and the XY-direction driver so that the probe is always located at a fixed height h above the metal thin film sample. When h is less than the evanescent field range of SPP, the far-field detector will detect the light signal scattered to the far field.

[0018] S7. The optical signal is further received and amplified into an electrical signal by a photomultiplier tube. When the probe is displaced relative to the metal thin film sample, the intensity of the near-field light component at the probe's location changes, which in turn causes the intensity of the scattered light detected in the far field to change.

[0019] In S2, the light beam is incident as a plane wave and irradiates the back of the metal film perpendicularly; the electromagnetic field emitted from the small hole in the metal film is approximated as the electromagnetic field radiated by a dipole, and the oscillation frequency of the dipole is the same as the frequency of the incident light.

[0020]

[0021] λ0 is the wavelength of the incident light, and c is the speed of light in a vacuum.

[0022] In S4, plasmons propagate along the y-direction to the far-field plasma, until precise self-imaging is achieved at the paraxial Tb distance τ, where τ is expressed as:

[0023]

[0024] 'a' represents the spatial period of the aperture array, and 'λ' represents the spatial period of the aperture array. sp The wavelength of the plasmon is λ0. To ensure a good SPP periodic self-image, the spatial period of the aperture array is less than or equal to the wavelength of the plasmon, i.e., a ≤ λ0.

[0025] The wavelength of the plasmon polariton satisfies the following relationship with the wavelength of the incident light:

[0026]

[0027] ε is the dielectric function of the metal at the SPP oscillation frequency.

[0028] Compared with the prior art, the beneficial effects of this invention are:

[0029] This invention utilizes a one-dimensional circular aperture microstructure to excite the in-plane SPP self-imaging effect via optical excitation, observing a spatial near-field light intensity distribution consistent with the parameters of the one-dimensional circular aperture structure within the surface of the metal thin film. Furthermore, this invention uses a near-field probe to extract this periodic near-field light component. When the near-field probe is displaced relative to the one-dimensional circular aperture metal micro / nanostructure, the intensity of the extracted light component changes periodically accordingly. Therefore, the displacement can be calculated by detecting the light intensity. Combined with a high-magnification subdivision circuit, picometer-level resolution displacement measurement is achieved. Attached Figure Description

[0030] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0031] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0032] Figure 1 This is a schematic diagram of the structure of the present invention;

[0033] Figure 2 This is a diagram of the Taber effect of the present invention;

[0034] Figure 3 This is an enlarged view of the detection area of ​​the present invention;

[0035] Figure 4 This is a diagram showing the arrangement of the nanopores in this invention;

[0036] Figure 5 This is a graph showing the function of the probe moving distance Δx along the x-axis as a function of the scattered light intensity I.

[0037] Figure 6 This is a graph showing the relationship between the circular aperture period and the optical period in this invention.

[0038] Figure 7 This is a graph showing the functional relationship between the period of the circular hole and the resolution after combining a 5000x potential subdivision plate according to the present invention.

[0039] Wherein: 1 is the laser, 2 is the reflecting prism, 3 is the microscope objective, 4 is the sample stage, 5 is the sample, 6 is the probe, 7 is the piezoelectric ceramic tube, 8 is the photomultiplier tube, 9 is the Z-axis actuator, 10 is the XY-axis actuator, and 11 is the computer control and image processing system. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. These descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the claims of the present invention. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0042] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0043] In this embodiment, as Figure 1 As shown, it consists of a laser 1, a reflecting prism 2, a microscope objective 3, a sample stage 4, a sample 5, a probe 6, a piezoelectric ceramic tube 7, a photomultiplier tube 8, a Z-axis actuator 9, an XY-axis actuator 10, and a computer control and image processing system 11. A schematic diagram of the detection area is shown below. Figure 2As shown, light with wavelength λ0 emitted from laser beam 1 is refracted by reflecting prism 2 and enters the microscope objective 3. After collimation, the beam is incident on the lower surface of the metal thin film sample 5 from the back (incident direction along the z-axis). A row of circular holes is distributed along the x-axis on the metal thin film sample 5, spaced at intervals of a, with a hole diameter of 0.5a. When incident light irradiates the array of circular holes, each nanopore acts as a secondary wave source, and under the principle of momentum matching, excites SPP oscillations in the metal thin film sample 5. Surface plasmon waves travel at wavelength λ0 on the surface of the metal thin film sample 5. sp The SPP waves generated by different secondary sources coherently superimpose on the surface of metal thin film sample 5, exciting a self-imaging effect on the surface of metal thin film sample 5. At this time, a pattern with a period in the x-direction equivalent to the period 'a' of the circular aperture array can be observed at a certain distance from the aperture, such as... Figure 2 As shown. The repetition period of self-imaging is defined in the y-direction as the self-imaging distance τ.

[0044] The SPP wave on the surface of metal thin film sample 5 will excite a near-field light intensity distribution in space, which is the same as the spatial distribution of the SPP wave. Using scanning probe 6, the near-field light component can be scattered to the far field and collected, such as... Figure 3 As shown, the piezoelectric ceramic tube 7 located at the top of the probe 6 is controlled by the Z-direction driver 9 and the XY-direction driver 10, ensuring that the probe 6 is always positioned at a fixed height h above the metal thin film sample 5. When h is less than the evanescent field range of the SPP, the far-field detector detects the light signal scattered to the far field. This signal is further received and amplified into an electrical signal by the photomultiplier tube 8. When the probe is displaced relative to the metal thin film sample 5, the intensity of the near-field light component at the probe's location changes, causing a corresponding change in the intensity of the scattered light detected in the far field.

[0045] The specific analysis is as follows:

[0046] In this case, the light beam is incident in the form of a plane wave and is perpendicularly irradiated on the back side of the metal thin film sample 5.

[0047] The electromagnetic field emitted from the small hole on the metal thin film sample 5 can be approximated as the electromagnetic field radiated by a dipole, and the oscillation frequency of the dipole is the same as the frequency of the incident light.

[0048]

[0049] Where λ0 is the wavelength of the incident light, and c is the speed of light in a vacuum.

[0050] In this process, plasmons propagate along the y-axis to the far-field plasma, precisely achieving self-imaging at the paraxial Tb distance τ. The expression for τ is:

[0051]

[0052] In the formula, a is the spatial period of the aperture array, and λ is... sp The wavelength of the plasma exciton.

[0053] In order to obtain a better SPP periodic self-image, the structural period should be less than or equal to the wavelength of the plasma, i.e., a≤λ0.

[0054] The wavelength of the plasma and the wavelength of the incident light satisfy the following relationship:

[0055]

[0056] In this process, light propagates in the SP mode after being converted to its normal frequency (SP) on a flat metal surface, but gradually weakens due to losses caused by metal absorption. This attenuation depends on the dielectric function ε of the metal at the SP oscillation frequency. In practical applications, silver has the lowest light loss in the visible spectrum, exhibiting minimal light attenuation.

[0057] The probe used is an aluminum-coated glass fiber tip with a radius of 50-100nm.

[0058] The probe moves parallel to the surface of the metal film at the same distance. Since the metal coating on the probe affects the propagation of SP, the maximum signal is measured at a distance of about 30 nm from the contact point.

[0059] The specific implementation parameters are as follows:

[0060] Laser 1 source parameters: The source is HeNe or Ar + Laser, i.e., 632.8nm or 514nm;

[0061] The magnification of the oil immersion microscope objective 3 is 40×, and the NA is 1.3.

[0062] Sample 5 is a gold / silver film with a thickness of 50±10 nm, which is evaporated onto a thin coverslip;

[0063] The duty cycle d / a is approximately 0.5;

[0064] The dielectric constant of silver is ε = -130.83 + i3.32, |ε| >> 1, so λsp ≈ λ0;

[0065] The probe 6 used has an aluminum-coated glass fiber tip with a radius of 50-100nm, which has low loss and high sensitivity;

[0066] The piezoelectric ceramic tube 7 has a diameter of 6.35 mm, a length of 25 mm, and a wall thickness of 0.5 mm. The maximum scanning range is 10 μm × 10 μm.

[0067] Photomultiplier tube 8-parameter conversion sensitivity 2×105 V / W, resolution 20nW.

[0068] Laser 1 emits a laser beam with a wavelength of 632.8 nm. After passing through a reflecting prism, the beam is refracted by the microscope objective 3 and collimated to obtain a plane wave, which is then incident perpendicularly from the back of the metal thin film sample 5. Figure 4 As shown, the number of nanopores is 10, the spatial period is a = 50 nm, the diameter is d = 25 nm, and the calculated Talber distance τ = 7.90 nm.

[0069] After the plane light passes through the sample, it forms a self-image at a distance of one Talbot distance (7.90 nm). After being scanned parallel to the probe, as shown... Figure 5 , Figure 6 As shown, the photomultiplier tube 8 receives scattered light intensity, and the intensity of the scattered light changes with displacement in a periodic sinusoidal pattern. The optical period is consistent with the period of the circular aperture, as shown... Figure 7 As shown, combined with a 5000x subdivision circuit, the resolution is increased to the 1-10pm level.

[0070] In summary, the picometer-level micro-displacement sensor based on surface plasmon polariton self-imaging (SPP) overcomes the optical diffraction limit by leveraging the strong localization characteristics of SPP. Traditional grating-type micro-displacement sensors have an optical period on the order of 100 nm, while this method utilizes a one-dimensional circular aperture microstructure (with a period on the order of 10 nm) to excite the in-plane SPP self-imaging effect through optical excitation. Displacement is calculated by detecting periodic light intensity changes through the movement of a near-field probe, and combined with a 5000-fold subdivision circuit, the resolution is improved to the order of 1-10 pm. This represents a resolution improvement of 1-2 orders of magnitude compared to traditional grating-type displacement sensors.

[0071] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A measurement method for a picometer-scale micro-displacement sensor based on surface plasmon self-imaging, characterized in that: Includes the following steps: S1. The laser beam with a wavelength of λ0 is refracted by the reflecting prism and enters the microscope objective. After collimation, the beam is incident from the back of the metal thin film sample onto the lower surface of the metal thin film sample, with the incident direction along the z-axis. S2. On the metal thin film sample, there is a row of circular holes distributed along the x direction with a spacing of a and a diameter of 0.5a. When incident light shines on the circular hole array structure, each nanopore is equivalent to a secondary wave source and excites the SPP oscillation in the metal thin film sample under the action of the momentum matching principle. S3, the surface plasmon wave of the metal film sample is on the surface of the metal film with wavelength λ sp The SPP waves generated by different wave sources are coherent superimposed on the surface of the film, and the self-imaging effect is excited on the surface of the film. S4. At this point, a pattern with a period equal to the period 'a' of the circular aperture array will be observed at a certain distance from the pinhole. The repetition period of the self-image is defined as the paraxial Talbot distance in the y-direction. ; S5. The SPP wave on the surface of the metal thin film sample will excite the near-field light intensity distribution in space. This light intensity distribution is the same as the spatial distribution of the SPP wave. Using a scanning probe, the near-field light component is scattered to the far field and collected. S6. The piezoelectric ceramic tube located at the tip of the probe is controlled by the Z-direction driver and the XY-direction driver so that the probe is always located at a fixed height h above the metal thin film sample. When h is less than the evanescent field range of SPP, the far-field detector will detect the light signal scattered to the far field. S7. The optical signal is further received and amplified into an electrical signal by a photomultiplier tube. When the probe is displaced relative to the metal thin film sample, the intensity of the near-field light component at the probe location changes, which in turn causes the intensity of the scattered light detected in the far field to change. The displacement is calculated by detecting the periodic light intensity change through the movement of the near-field probe, and combined with a 5000x subdivision circuit, the resolution is improved to the order of 1-10 pm.

2. The measurement method of a picometer-scale micro-displacement sensor based on surface plasmon self-imaging as described in claim 1, characterized in that: In S2, the light beam is incident as a plane wave and irradiates the back of the metal film perpendicularly; the electromagnetic field emitted from the small hole in the metal film is approximated as the electromagnetic field radiated by a dipole, and the oscillation frequency of the dipole is the same as the frequency of the incident light. λ0 is the wavelength of the incident light, and c is the speed of light in a vacuum.

3. The measurement method of a picometer-scale micro-displacement sensor based on surface plasmon self-imaging as described in claim 1, characterized in that: In S4, plasma polarons are transported along the y-direction to the far-field plasma, up to the paraxial Tuber distance. The expression for τ is: [The text abruptly ends here, so the translation stops as well.] 'a' represents the spatial period of the aperture array, and 'λ' represents the spatial period of the aperture array. sp The wavelength of the plasmon is λ0. To ensure a good SPP periodic self-image, the spatial period of the aperture array is less than or equal to the wavelength of the plasmon, i.e., a ≤ λ0.

4. The measurement method of a picometer-level micro-displacement sensor based on surface plasmon self-imaging as described in claim 1, characterized in that: The wavelength of the plasmon polariton satisfies the following relationship with the wavelength of the incident light: ε is the dielectric function of the metal at the SPP oscillation frequency.

5. A picometer-scale micro-displacement sensor based on surface plasmon resonance self-imaging according to any one of claims 1-4, characterized in that: The device includes a laser (1), a reflecting prism (2), a microscope objective (3), a sample stage (4), a sample (5), and a probe (6). The laser (1) has a reflecting prism (2) in the direction of its optical path. The microscope objective (3) is arranged in the reflected optical path of the reflecting prism (2). The light reflected by the reflecting prism (2) is incident on the sample stage (4) through the microscope objective (3). The sample (5) is placed on the sample stage (4). The probe (6) is arranged directly above the sample (5).

6. A picometer-scale micro-displacement sensor based on surface plasmon resonance self-imaging according to claim 5, characterized in that: It also includes a piezoelectric ceramic tube (7), a photomultiplier tube (8), a Z-direction actuator (9), an XY-direction actuator (10), and a computer control and image processing system (11). The probe (6) is fixedly connected to the piezoelectric ceramic tube (7), and the piezoelectric ceramic tube (7) is electrically connected to the Z-direction actuator (9) and the XY-direction actuator (10) respectively.

7. A picometer-scale micro-displacement sensor based on surface plasmon resonance self-imaging according to claim 6, characterized in that: The piezoelectric ceramic tube (7) is electrically connected to a photomultiplier tube (8), and the photomultiplier tube (8) is electrically connected to a Z-direction driver (9).

8. A picometer-scale micro-displacement sensor based on surface plasmon resonance self-imaging according to claim 6, characterized in that: The Z-direction driver (9) and XY-direction driver (10) are both electrically connected to the computer control and image processing system (11).

9. A picometer-scale micro-displacement sensor based on surface plasmon resonance self-imaging according to claim 5, characterized in that: The laser (1) is a HeNe laser or an Ar laser. + The laser, wherein the HeNe laser has a wavelength of 632.8 nm, and the Ar... + The wavelength of the laser is 514 nm; the sample (5) is a gold or silver film with a thickness of 50±10 nm, and the sample (5) is evaporated onto a thin cover glass; the probe (6) is an aluminum-coated glass fiber tip with a radius of 50-100 nm.

10. A picometer-scale micro-displacement sensor based on surface plasmon resonance self-imaging according to claim 6, characterized in that: The piezoelectric ceramic tube (7) has a diameter of 6.35 mm, a length of 25 mm, and a wall thickness of 0.5 mm; the maximum scanning range of the piezoelectric ceramic tube (7) is 10 μm × 10 μm; the parameter conversion sensitivity of the photomultiplier tube (8) is 2 × 10⁻⁶. 5 V / W, the resolution of the photomultiplier tube (8) is 20nW.

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