Microwave atomic force microscope probe based on coplanar waveguide structure and preparation method thereof
By integrating microwave transmission lines into a coplanar waveguide structure within a microwave atomic force microscope probe, the problems of limited design flexibility and high-frequency loss were solved, achieving low-loss microwave transmission and efficient fabrication.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2026-04-08
- Publication Date
- 2026-07-21
AI Technical Summary
In existing microwave atomic force microscope probes, the design flexibility of parallel plate waveguide structures is limited, high-frequency microwave transmission loss is high, and the fabrication process is complex and has a low success rate.
A coplanar waveguide structure is used to integrate microwave transmission lines. By setting a coplanar waveguide on a cantilever beam and converting it into a coaxial transmission line at the tip, the microwave transmission and probe structure are integrated into one, taking advantage of the low loss and flexible design of the coplanar waveguide.
It reduces high-frequency microwave transmission loss, improves design flexibility and fabrication feasibility, simplifies processing technology, and enhances probe design efficiency and manufacturing precision.
Smart Images
Figure CN121995084B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of micro-nano measurement and atomic force microscopy, and proposes a microwave atomic force microscope probe based on a coplanar waveguide structure and its preparation method. Background Technology
[0002] Atomic force microscopy (AFM) is a high-resolution microscopy technique that utilizes the interaction forces between a nanoscale tipped microcantilever probe and the atoms on the sample surface to characterize the surface morphology and physicochemical properties of materials. Depending on the interaction mode between the probe and the sample, its operating modes are mainly divided into contact, tapping, and non-contact modes. To achieve the characterization of sample micro-waveform morphology and the measurement of local electrical properties, microwave atomic force microscopy (M-AFM) was developed. It combines microwave detection with atomic force microscopy, utilizing the interaction between near-field microwaves and the sample to simultaneously acquire sample morphology and local electrical properties at the nanoscale.
[0003] Most existing microwave atomic force microscope probes employ parallel plate waveguide structures to transmit microwaves. However, the characteristic impedance of this transmission method can only be designed by adjusting the probe substrate thickness, limiting design flexibility. Furthermore, parallel plate waveguides suffer from high losses during high-frequency microwave transmission, affecting the probe's measurement accuracy and signal transmission efficiency.
[0004] Furthermore, in terms of manufacturing processes, microwave atomic force microscope probes are typically fabricated using a self-wafer processing method, including etching, photolithography, coating, and release processes. Although this method enables mass production, it suffers from problems such as long fabrication cycles, complex processes, and low success rates. Summary of the Invention
[0005] This invention addresses the shortcomings of existing technologies by providing a method for fabricating microwave atomic force microscope (AFM) probes based on a coplanar waveguide structure, thus overcoming the low success rate of probe fabrication. Specifically, this invention proposes a probe fabrication method based on a microwave transmission channel. The core of this method lies in integrating a coplanar waveguide (CPW) transmission line into the probe structure and extending this structure along a cantilever beam to the probe tip region, thereby converting it into a coaxial transmission line structure. This fully utilizes the advantages of coplanar waveguides, such as low loss and flexible design under high-frequency conditions, achieving integrated microwave transmission and probe structure, thus providing a novel probe design solution.
[0006] To achieve the above objectives, the first aspect of the present invention discloses a microwave atomic force microscope probe based on a coplanar waveguide structure, including a clamping part and a cantilever beam;
[0007] The clamping part has a flat rectangular structure, including a substrate and a coplanar waveguide structure disposed on the upper surface of the substrate;
[0008] The cantilever beam is a slender rectangular shape, and a coplanar waveguide structure is provided on the upper surface of the cantilever beam. One end of the cantilever beam is fixed to the front end of the clamping part and is flush with the front upper surface of the clamping part, while the other end is a free end. The axis of the cantilever beam is collinear with the axis of the clamping part.
[0009] A central conductor is laid on the upper surface axis of both the clamping part and the cantilever beam. A metal grounding layer is symmetrically arranged on both sides of the central conductor, and there is a gap between the metal grounding layer and the two sides of the central conductor. The central conductor and the metal grounding layer are strip-shaped conductive strips made of gold film. The central conductor, the metal grounding layer and the gap between them constitute a coplanar waveguide structure of the upper surface of the clamping part substrate and the upper surface of the cantilever beam. The central conductor of the clamping part is connected to the central conductor of the cantilever beam, and the metal grounding layer of the clamping part is connected to the metal grounding layer of the cantilever beam, together forming a microwave transmission circuit.
[0010] The free end of the cantilever beam is provided with a protruding needle tip. The microwave transmission circuit is converted into a coaxial transmission line structure on the surface of the needle tip at the needle tip. The coaxial transmission line structure is provided with an inner conductor, an intermediate layer and an outer conductor in sequence from the inside to the outside. The inner conductor is connected to the center conductor on the cantilever beam and the outer conductor is connected to the metal grounding layer on the cantilever beam.
[0011] Preferably, in order to achieve impedance matching for 75-110GHz microwave transmission, the width of the center conductor at the rear end of the clamping part is 320-440µm, the width of the metal grounding layer at the rear end of the clamping part is 440-480µm, and the gap width between the center conductor at the rear end of the clamping part and the metal grounding layer is 50-150µm.
[0012] Preferably, in order to achieve impedance matching for 75-110GHz microwave transmission, the width of the center conductor of the cantilever beam is 5-15µm, the width of the metal grounding layer of the cantilever beam is 8-12µm, the gap width between the center conductor of the cantilever beam and the metal grounding layer is 3-8µm, and the dimensions of the coplanar waveguide structure at the front end of the clamping part are consistent with those at the cantilever beam.
[0013] Preferably, an impedance matching line is provided near the front end of the clamping part at the rear end of the clamping part. The impedance matching line gradually shrinks from back to front to form an impedance transition section, and the coplanar waveguide structure at the rear end of the clamping part gradually shrinks along the impedance transition section.
[0014] A second aspect of this invention discloses a method for fabricating a microwave atomic force microscope probe based on a coplanar waveguide structure, used to fabricate the aforementioned microwave atomic force microscope probe based on a coplanar waveguide structure, comprising:
[0015] Step S1: Establish an electromagnetic simulation model of the microwave atomic force microscope probe based on the coplanar waveguide structure and perform simulation analysis. Export the characteristic impedance and scattering matrix data of the microwave transmission circuit on the upper surface of the probe. Then, based on the microwave target operating frequency band, obtain the dimensional parameters of the coplanar waveguide structure that meet the characteristic impedance requirements.
[0016] Step S2: After cleaning the probe substrate, perform surface modification, then perform HMDS surface pretreatment and keep it for 30-50 minutes.
[0017] Step S3: Coat the probe surface with photoresist. After dispensing the photoresist, wait 10-14 seconds and then remove the excess photoresist from the probe surface. After spin coating, dry the probe for 220-260 seconds to allow the photoresist to set.
[0018] Step S4: The probe is exposed and developed for the first time to create a central conductor pattern and an inner conductor structure at the tip. A gold film is formed on the central conductor by electron beam evaporation. The excess gold film is then peeled off to form the central conductor.
[0019] Step S5: Wrap the tip of the needle with tin foil and leave space for the outer conductor structure of the needle tip. Grow a silicon dioxide isolation layer on the probe surface by plasma chemical vapor deposition.
[0020] Step S6: Repeat step S3 and perform a second exposure and development on the probe to create a metal grounding layer pattern and an outer conductor structure of the probe tip. Then, form a gold film of the metal grounding layer by electron beam evaporation. After peeling off the excess gold film, the metal grounding layer is formed, and the preparation is completed.
[0021] Preferably, the dimensional parameters of the coplanar waveguide structure in step S1 include the width of the center conductor and the metal grounding layer, the gap width between the center conductor and the metal grounding layer, and the thickness of the center conductor, the metal grounding layer, and the impedance matching line.
[0022] Compared with the prior art, the beneficial technical effects of the present invention are reflected in the following aspects:
[0023] (1) In view of the complexity of the design of high-frequency microwave atomic force microscope probes and the problem of signal loss in 75-110GHz, this invention proposes a microwave atomic force microscope probe based on coplanar waveguide integration and its preparation method.
[0024] In existing technologies, most probes use parallel-plate waveguide structures for microwave transmission, confining the electromagnetic field primarily within the dielectric substrate. This results in significant transmission loss at high frequencies. Furthermore, the characteristic impedance can only be adjusted by changing the probe size, limiting design flexibility. In contrast, this invention employs a coplanar waveguide structure for microwave transmission, distributing the electromagnetic field mainly within the dielectric and air between the central conductor and the metal grounding layer. This effectively reduces microwave transmission loss within the dielectric and minimizes dispersion effects at high frequencies. Moreover, the characteristic impedance of the coplanar waveguide can be flexibly adjusted by modifying the width of the central conductor and the gap between the central conductor and the metal grounding layer. The coplanar integration of the central conductor and the metal grounding layer simplifies the fabrication process and enhances design flexibility and fabrication feasibility.
[0025] (2) This invention provides an efficient and flexible method for constructing microwave transmission circuits. Through this invention, key parameters can be directly adjusted and optimized during the modeling stage, improving the adaptability and versatility of probe design. Compared with methods that rely on repeated experimental trials to determine the optimal parameters, this invention determines the key dimensions required for manufacturing processes through model prediction, significantly reducing trial-and-error costs. This enables different types of microwave atomic force microscope probes to be conveniently and quickly designed and optimized for microwave transmission structures, improving design efficiency and manufacturing accuracy. Attached Figure Description
[0026] Figure 1 This represents the original overall structural features of a standard commercial atomic force microscope probe.
[0027] Figure 2 This is a schematic diagram of the microwave atomic force microscope probe structure based on the coplanar waveguide structure described in this invention;
[0028] Figure 3 This is a schematic diagram of the rear end structure of the microwave atomic force microscope probe clamping part based on the coplanar waveguide structure.
[0029] Figure 4 This is a schematic diagram of the coplanar waveguide structure at the front end of the microwave atomic force microscope probe clamping part based on the coplanar waveguide structure;
[0030] Figure 5 This is a schematic diagram of the structure at the cantilever beam of the microwave atomic force microscope probe based on the coplanar waveguide structure.
[0031] Figure 6 This is a schematic diagram of the coaxial transmission line structure at the tip of the microwave atomic force microscope probe based on the coplanar waveguide structure.
[0032] Figure 7 This is a schematic diagram of the simulation results of the S-parameters and characteristic impedance of the microwave atomic force microscope probe based on the coplanar waveguide structure.
[0033] Figure 8 This describes the method for preparing the microwave atomic force microscope probe based on the coplanar waveguide structure.
[0034] In the figure, 1-rear end of clamping part, 2-front end of clamping part, 3-etching mark at the front end of clamping part, 4-cantilever beam, 5-base, 6-rear center conductor, 7-rear first metal grounding layer, 8-rear second metal grounding layer, 9-impedance matching line, 10-rear first gap, 11-rear second gap, 12-front center conductor, 13-front first metal grounding layer, 14-front second metal grounding layer, 15-front first gap, 16-front second gap, 17-cantilever beam center conductor, 18-cantilever beam first metal grounding layer, 19-cantilever beam second metal grounding layer, 20-cantilever beam free end metal grounding layer, 21-cantilever beam first gap, 22-cantilever beam second gap, 23-needle tip, 24-needle tip structure, 25-inner conductor, 26-intermediate layer, 27-outer conductor. Detailed Implementation
[0035] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structural features and technical advantages of the present invention is provided in conjunction with the accompanying drawings and specific implementation examples.
[0036] It should be noted that exemplary examples will be described in detail herein, and when the following description refers to the accompanying drawings, the same numbers in different drawings represent the same elements unless otherwise indicated.
[0037] This invention provides a microwave atomic force microscope probe based on a coplanar waveguide structure and its fabrication method for high-frequency microwave signals in the 75-110 GHz range. The probe is fabricated by placing a coplanar waveguide structure on the surface of the atomic force microscope probe and converting it into a coaxial transmission line structure at the tip 23 at the free end of the cantilever beam.
[0038] Figure 1 The image shows the original morphology of the atomic force microscope probe, including the clamping part and the cantilever beam 4; the clamping part has a flat rectangular structure; the successfully fabricated microwave atomic force microscope probe clamping part includes a substrate 5 and a coplanar waveguide structure on the upper surface of the substrate 5. The substrate is made of silicon-based material, or a commercially available probe can be directly selected as the substrate.
[0039] In this embodiment, the substrate 5 uses RTESA-525 manufactured by Bruker Corporation, which is made of antimony-doped silicon with a resistivity of 0.01-0.025 Ω·cm.
[0040] The cantilever beam 4 is in the shape of a slender rectangle and is made of antimony-doped silicon. One end of the cantilever beam 4 is fixed to the front end face of the clamping part and is flush with the upper surface of the clamping part, while the other end is a free end. The axis of the cantilever beam 4 is collinear with the axis of the clamping part.
[0041] The clamping part consists of the rear end 1 and the front end 2 of the clamping part. During the manufacturing process of the probe, a raised etching mark 3 will be left on the center of the upper surface of the front end 2 of the clamping part. The etching mark 3 extends from the connection between the cantilever beam 4 and the clamping part to the step at the junction of the front end 2 and the rear end 1 of the clamping part.
[0042] In this embodiment, the length of the etching mark 3 at the front end of the clamping part is 1.46 mm and the width is 40 µm; the thickness of the rear end 1 of the clamping part is 300 µm, the length is 2 mm and the width is 1.5 mm; the thickness of the front end 2 of the clamping part is 270 µm, the length is 1.5 mm and the width is 1.5 mm; and the thickness of the cantilever beam 4 is 6.5 µm, the length is 128 µm and the width is 40 µm.
[0043] The present invention provides coplanar waveguide structures on the surfaces of the rear end 1, the front end 2, and the cantilever beam 4 of the clamping part of the microwave atomic force microscope probe. The overall structure of the probe is as follows: Figure 2 The coplanar waveguide structure consists of a central conductor and two symmetrically arranged grounded metal layers spaced a certain distance apart on either side of the central conductor. The central conductor and the grounded metal layers are strip-shaped conductive strips covered with a gold film. The key parameters of the coplanar waveguide structure are calculated and determined based on the probe's geometry, material properties, and the microwave target's operating frequency band. The coplanar waveguide structure of each part will be described below.
[0044] Figure 3 The structure of the rear end 1 of the clamping part is shown, including the coplanar waveguide structure and the impedance matching line 9.
[0045] The coplanar waveguide structure includes a rear center conductor 6, a rear first metal ground layer 7, and a rear second metal ground layer 8. The rear center conductor 6 is laid from the rear end of the clamping part 1 to the front end, tapering towards the front end. This design aims to avoid tip effects caused by drastic size changes, thereby reducing losses in high-frequency microwave transmission. The axis of the rear center conductor 6 coincides with the axis of the clamping part 1, and its width ranges from 320 to 440 µm. The rear first metal ground layer 7 and the rear second metal ground layer 8 are symmetrically laid at a certain distance on both sides of the rear center conductor 6, parallel to and of equal length. Their widths range from 440 to 480 µm. A rear first gap 10 is formed between the rear first metal ground layer 7 and the rear center conductor 6, and a rear second gap 11 is formed between the rear second metal ground layer 8 and the rear center conductor 6. The widths of the rear first gap 10 and the rear second gap 11 range from 50 to 150 µm.
[0046] An impedance matching line 9 is also provided near the front end of the clamping part at the rear end 1 of the clamping part. The impedance matching line gradually shrinks from back to front to form an impedance transition section. The coplanar waveguide structure of the rear end 1 of the clamping part gradually shrinks along the impedance transition section. The key parameters of the impedance matching line 9 are obtained according to the impedance matching calculation formula.
[0047] In this embodiment, the width of the rear center conductor 6 is 320µm, the gold film thickness of the rear center conductor 6, the rear first metal ground layer 7, the rear second metal ground layer 8 and the impedance matching line 9 is 50nm, and the width of the rear first gap 10 and the rear second gap 11 is 125µm.
[0048] Figure 4The diagram shows the coplanar waveguide structure of the front end 2 of the clamping part. This coplanar waveguide structure is disposed on the etching mark 3 at the front end of the clamping part and includes a front end center conductor 12, a front end first metal ground layer 13, and a front end second metal ground layer 14. The front end center conductor 12 is connected to the impedance matching line 9 on the surface of the rear end 1 of the clamping part. The axis of the front end center conductor 12 coincides with the axis of the front end 2 of the clamping part, and the width of the front end center conductor 12 ranges from 5 to 15 µm. The front end first metal ground layer 13 and the front end second metal ground layer 14 are symmetrically laid on both sides of the front end center conductor 12 at a certain distance, both parallel to the front end center conductor 12 and of equal length. The front end first metal ground layer 13 is connected to the rear end first metal ground layer 7, and the front end second metal ground layer 14 is connected to the rear end second metal ground layer 8. The width of the front end first metal ground layer 13 and the front end second metal ground layer 14 ranges from 8 to 12 µm. A first gap 15 is formed between the first metal grounding layer 13 and the center conductor 12, and a second gap 16 is formed between the second metal grounding layer 14 and the center conductor 12. The widths of the first gap 15 and the second gap 16 are in the range of 3-8µm.
[0049] In this embodiment, the width of the front-end center conductor 12 is 10µm, the gold film thickness of the clamping part of the front-end center conductor 12, the front-end first metal ground layer 13 and the front-end second metal ground layer 14 is 50nm, and the width of the front-end first gap 15 and the front-end second gap 16 is 5µm.
[0050] Figure 5The structure on the cantilever beam 4 is shown, including a coplanar waveguide structure, a metal grounding layer 20 at the free end of the cantilever beam, and a needle tip 23. The coplanar waveguide structure includes a cantilever beam center conductor 17, a first metal grounding layer 18, and a second metal grounding layer 19. The cantilever beam center conductor 17 is connected to the front center conductor 12, and the axis of the cantilever beam center conductor 17 coincides with the axis of the cantilever beam 4. The first metal grounding layer 18 and the second metal grounding layer 19 are symmetrically laid on both sides of the cantilever beam center conductor 17 at a certain distance, both parallel to the cantilever beam center conductor 17 and of equal length. The first metal grounding layer 18 is connected to the front first metal grounding layer 13, and the second metal grounding layer 19 is connected to the front second metal grounding layer 14. The width of the first metal grounding layer 18 and the second metal grounding layer 19 ranges from 8 to 12 µm. A first gap 21 is formed between the first metal grounding layer 18 and the center conductor 17 of the cantilever beam, and a second gap 22 is formed between the second metal grounding layer 19 and the center conductor 17 of the cantilever beam. The free end of the cantilever beam 4 has a triangular structure, and the metal grounding layer 20 at the free end of the cantilever beam covers the triangular structure and is connected to the first metal grounding layer 18 and the second metal grounding layer 19 of the cantilever beam to form a circuit. The free end of the cantilever beam is provided with a pin tip 23, which is pyramid-shaped.
[0051] In this embodiment, the width of the cantilever beam center conductor 17 is 10µm, the gold film thickness of the cantilever beam center conductor 17, the cantilever beam first metal grounding layer 18 and the cantilever beam second metal grounding layer 19 is 50nm, and the width of the cantilever beam first gap 21 and the cantilever beam second gap 22 is 5µm.
[0052] Thus, the rear end 1 and front end 2 of the clamping part are connected to the coplanar waveguide structure on the upper surface of the cantilever beam 4 to form a microwave transmission circuit. This microwave transmission circuit transforms into a coaxial transmission line structure on the surface of the needle tip 23 at the needle tip 23, such as... Figure 6 As shown.
[0053] The innermost layer of the coaxial transmission line structure is a needle tip structure 24. A metal layer is placed outside the needle tip structure 24 as the inner conductor 25 of the coaxial transmission line structure. The inner conductor 25 is connected to the center conductor 17 of the cantilever beam. A silicon dioxide layer is placed outside the inner conductor 25 as an intermediate layer 26, which is used to isolate the inner and outer conductors to prevent short circuits and to act as a medium for microwave propagation. A metal layer is placed outside the intermediate layer 26 as the outer conductor 27 of the coaxial transmission line structure. The outer conductor 27 is connected to the first metal grounding layer 18 of the cantilever beam, the second metal grounding layer 19 of the cantilever beam, and the grounding metal layer 20 of the free end of the cantilever beam.
[0054] In this embodiment, the height of the needle tip 23 is 9.6µm, the gold film thickness of the inner conductor 25 is 50nm, the gold film thickness of the outer conductor 27 is 50nm, and the thickness of the intermediate layer 26 is 60nm.
[0055] The microwave atomic force microscope probe based on a coplanar waveguide structure provided by this invention transmits microwaves through the coplanar waveguide structure of the rear end 1, front end 2, and cantilever beam 4 to the coaxial transmission line structure of the tip 23. The near field is confined by the tip 23, allowing the microwave signal to converge at the tip 23 and be emitted onto the sample surface, thereby acquiring the sample's morphological and electrical information. When probing the sample, a microwave signal of a predetermined frequency propagates on the central conductor of the coplanar waveguide structure and is transmitted to the inner conductor 25 of the coaxial transmission line structure of the tip 23. The microwave frequency is 75-110 GHz. Under the influence of the microwave near field, the reflected microwave signal is received, thereby determining the sample's electrical properties.
[0056] This invention also provides a method for fabricating a microwave atomic force microscope probe based on a coplanar waveguide structure, applicable to the fabrication of the aforementioned microwave atomic force microscope probe based on a coplanar waveguide structure. The fabrication process is as follows: Figure 8 As shown, it includes the following steps:
[0057] Step S1: Select a commercially available probe as the substrate. In this embodiment, the Bruker RTESPA-525 probe is used as substrate 5. Establish a probe model. Based on the target structure, geometric dimensions and material properties of the probe of this invention, establish an electromagnetic simulation model and perform simulation analysis to derive the characteristic impedance and scattering matrix data of the microwave transmission circuit. Then, based on the target microwave operating frequency band (75 GHz to 110 GHz), calculate the width of the center conductor and the metal grounding layer of each coplanar waveguide structure and the gap width between the center conductor and the metal grounding layer when the characteristic impedance requirement (50Ω in this embodiment) is met under the thickness of substrate 5, so as to achieve good impedance matching and low-loss microwave transmission.
[0058] In this embodiment, the center operating frequency of the probe is set to 94GHz when transmitting microwave signals. To make the calculation more accurate, the mesh division points of the probe model are set to 401.
[0059] Step S2: After standard cleaning, the Bruker RTESPA-525 probe is placed in a plasma cleaner for surface modification to enhance its hydrophilicity and remove surface residues; then it is placed in an HMDS oven for liquid filling and kept for 30-50 minutes to improve the wettability of photoresist on the probe surface and improve the uniformity and adhesion of the photolithography process.
[0060] Step S3: Place the probe processed in step S2 on a hot plate and coat it with photoresist. After dispensing the photoresist, wait 10-14 seconds and place the probe off-center on the spin stage. Spin the excess photoresist off by spin-coating off-center. After spin-coating is completed, move the probe to the drying stage and dry for 220-260 seconds to set the photoresist.
[0061] Step S4: Move the probe obtained in step S3 to the photolithography machine and perform the first exposure and development through the mask. Create the central conductor pattern and the inner conductor 25 structure of the tip 23 on the probe clamping part and the cantilever beam 4. Then, form a gold film on the central conductor through electron beam evaporation process. Finally, use ultrasonic cleaning to peel off the excess gold film and form the first layer of central conductor on the probe surface.
[0062] Step S5: A silicon dioxide isolation layer is grown on the probe surface obtained in step S4 by plasma vapor phase chemical deposition. During the growth, tin foil is used to wrap the probe tip and leave space for the outer conductor 27 structure of the tip 23.
[0063] Step S6: Repeat step S3 and move the probe to the photolithography machine for a second exposure and development using a mask. A metal ground layer pattern and the outer conductor 27 structure of the tip 23 are fabricated on the probe clamping part and the cantilever beam 4. A gold film is formed on the metal ground layer by electron beam evaporation coating process. Then, the excess gold film is peeled off by ultrasonic cleaning to ensure that the metal ground layer is complete and uniform. Thus, a microwave atomic force microscope probe based on a coplanar waveguide structure is obtained.
[0064] The scattering parameters (S-parameters) and characteristic impedance simulation results of the microwave atomic force microscope probe based on a coplanar waveguide structure provided by this invention are as follows: Figure 7 As shown in (a) and (b) in the figure, the S-parameters are used to represent the energy transmission and reflection at each port of the microwave transmission circuit. 11 and S 21 This indicates that the probe has good signal transmission capability under 94GHz high-frequency microwave, and the characteristic impedance of the transmission circuit at this frequency is close to 50Ω.
[0065] The microwave atomic force microscope probe based on a coplanar waveguide structure provided by this invention uses transverse electromagnetic waves as its propagation mode, exhibiting advantages such as low loss and low dispersion at high frequencies. This probe allows for flexible adjustment of its characteristic impedance during the modeling stage by directly changing the gap size between the central conductor and the metal ground layer. Furthermore, since the central conductor and the metal ground layer are located in the same plane, the structural design is flexible, facilitating miniaturization and integration with other devices. This enables the convenient and rapid design and optimization of microwave transmission structures for different types of microwave atomic force microscope probes, improving the adaptability and versatility of probe design.
[0066] The above embodiments are only used to illustrate the design concept and features of the present invention and are not intended to limit the present invention. All equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.
Claims
1. A microwave atomic force microscope probe based on a coplanar waveguide structure, characterized in that, Includes the clamping part and the cantilever beam; The clamping part has a flat rectangular structure, including a substrate and a coplanar waveguide structure disposed on the upper surface of the substrate; The cantilever beam is a slender rectangular shape, and a coplanar waveguide structure is provided on the upper surface of the cantilever beam. One end of the cantilever beam is fixed to the front end of the clamping part and is flush with the front upper surface of the clamping part, while the other end is a free end. The axis of the cantilever beam is collinear with the axis of the clamping part. A central conductor is laid on the upper surface axis of both the clamping part and the cantilever beam. Symmetrical metal grounding layers are arranged on both sides of the central conductor, with gaps between the metal grounding layers and the sides of the central conductor. The central conductor and the metal grounding layers are strip-shaped conductive strips made of gold film. The central conductor, the metal grounding layers, and the gaps between them constitute a coplanar waveguide structure on the upper surface of the clamping part substrate and the upper surface of the cantilever beam. The central conductor of the clamping part is connected to the central conductor of the cantilever beam, and the metal grounding layer of the clamping part is connected to the metal grounding layer of the cantilever beam, together forming a microwave transmission circuit. An impedance matching line is also provided at the rear end of the clamping part. The impedance matching line gradually tapers from back to front to form an impedance transition section, and the coplanar waveguide structure at the rear end of the clamping part tapers along the impedance transition section. The free end of the cantilever beam has a triangular structure and a protruding needle tip, which is pyramid-shaped. The microwave transmission circuit is converted into a coaxial transmission line structure on the surface of the needle tip at the needle tip. The coaxial transmission line structure has an inner conductor, an intermediate layer and an outer conductor arranged sequentially from the inside to the outside. The inner conductor is connected to the center conductor on the cantilever beam and the outer conductor is connected to the metal grounding layer on the cantilever beam. To achieve impedance matching for 75-110GHz microwave transmission, the width of the center conductor at the rear end of the clamping part ranges from 320-440µm, the width of the metal grounding layer at the rear end of the clamping part ranges from 440-480µm, and the gap width between the center conductor and the metal grounding layer at the rear end of the clamping part ranges from 50-150µm; the width of the center conductor of the cantilever beam ranges from 5-15µm, the width of the metal grounding layer of the cantilever beam ranges from 8-12µm, and the gap width between the center conductor and the metal grounding layer of the cantilever beam ranges from 3-8µm; the dimensions of the coplanar waveguide structure at the front end of the clamping part are consistent with those at the cantilever beam.
2. The probe according to claim 1, characterized in that, The coplanar waveguide structure at the rear end of the clamping part includes a rear center conductor and two rear metal grounding layers. The rear center conductor is laid along the axis of the rear end of the clamping part, and the two rear metal grounding layers are symmetrically laid on both sides of the rear center conductor. Both rear metal grounding layers are parallel to the rear center conductor and of equal length, and there is a gap between the two rear metal grounding layers and the rear center conductor.
3. The probe according to claim 1, characterized in that, The coplanar waveguide structure on the cantilever beam includes a central conductor of the cantilever beam and two cantilever beam metal grounding layers. The axis of the central conductor of the cantilever beam coincides with the axis of the cantilever beam. The two cantilever beam metal grounding layers are symmetrically laid on both sides of the central conductor of the cantilever beam. Both cantilever beam metal grounding layers are parallel to the central conductor of the cantilever beam and of equal length. There is a gap between the two cantilever beam metal grounding layers and the central conductor of the cantilever beam.
4. The probe according to claim 1, characterized in that, The coplanar waveguide structure at the front end of the clamping part includes a front-end center conductor and two front-end metal grounding layers. The axis of the front-end center conductor coincides with the axis of the front end of the clamping part. The two front-end metal grounding layers are symmetrically laid on both sides of the front-end center conductor. Both front-end metal grounding layers are parallel to the front-end center conductor and of equal length, and there is a gap between the two front-end metal grounding layers and the front-end center conductor.
5. A method for fabricating a microwave atomic force microscope probe based on a coplanar waveguide structure, used to fabricate the microwave atomic force microscope probe based on a coplanar waveguide structure as described in claim 1, characterized in that, include: Step S1: Establish an electromagnetic simulation model of the microwave atomic force microscope probe based on the coplanar waveguide structure and perform simulation analysis. Export the characteristic impedance and scattering matrix data of the microwave transmission circuit on the upper surface of the probe. Then, based on the microwave target operating frequency band, obtain the dimensional parameters of the coplanar waveguide structure that meet the characteristic impedance requirements. Step S2: After cleaning the probe substrate, perform surface modification, then perform HMDS surface pretreatment and keep it for 30-50 minutes. Step S3: Coat the probe surface with photoresist. After dispensing the photoresist, wait 10-14 seconds and then remove the excess photoresist from the probe surface. After spin coating, dry the probe for 220-260 seconds to allow the photoresist to set. Step S4: The probe is exposed and developed for the first time to create a central conductor pattern and an inner conductor structure at the tip. A gold film is formed on the central conductor by electron beam evaporation. The excess gold film is then peeled off to form the central conductor. Step S5: Wrap the tip of the needle with tin foil and leave space for the outer conductor structure of the needle tip. Grow a silicon dioxide isolation layer on the probe surface by plasma chemical vapor deposition. Step S6: Repeat step S3 and perform a second exposure and development on the probe to create a metal grounding layer pattern and an outer conductor structure of the probe tip. Then, form a gold film of the metal grounding layer by electron beam evaporation. After peeling off the excess gold film, the metal grounding layer is formed, and the preparation is completed.
6. The preparation method according to claim 5, characterized in that, The dimensional parameters of the coplanar waveguide structure in step S1 include the width of the center conductor and the metal grounding layer, the gap width between the center conductor and the metal grounding layer, and the thickness of the center conductor, the metal grounding layer, and the impedance matching line.