阅读说明：本技术 一种基于表面等离激元的开环式面外加速度传感器及方法 (Open-loop type out-of-plane acceleration sensor and method based on surface plasmons ) 是由 卢乾波 王逸男 王筱轲 王小旭 姚远 白剑 王学文 黄维 于 2019-11-19 设计创作，主要内容包括：本发明一种基于表面等离激元的开环式面外加速度传感器,属于加速度计领域；包括加速度敏感结构、近场光学谐振腔和压电薄膜；加速度敏感结构由质量块、蛇形悬臂梁和硅外框构成；近场光学谐振腔由亚波长硅光栅、空气间隙、硅基底和覆盖在亚波长硅光栅及硅基底上的上下银膜构成。通过耦合波分析法和遗传算法优化得到的近场光学谐振腔,其出射光强对腔长变化异常敏感；加速度敏感结构提供了合适的机械性能；压电薄膜可以调控光腔腔长,使得加速度传感器工作在灵敏度最大处。本发明利用了表面等离激元的耦合谐振,拥有超越已报道加速度传感器的超高灵敏度,并且压电薄膜提供了零位调整和调制的途径,可以实现具有更高可行性的超灵敏加速度测量。(The invention relates to an open-loop type out-of-plane acceleration sensor based on surface plasmons, belonging to the field of accelerometers; the device comprises an acceleration sensitive structure, a near-field optical resonant cavity and a piezoelectric film; the acceleration sensitive structure consists of a mass block, a snake-shaped cantilever beam and a silicon outer frame; the near-field optical resonant cavity consists of a sub-wavelength silicon grating, an air gap, a silicon substrate and upper and lower silver films covering the sub-wavelength silicon grating and the silicon substrate. The emergent light intensity of the near-field optical resonant cavity obtained by optimization of a coupled wave analysis method and a genetic algorithm is sensitive to the abnormal change of the cavity length; the acceleration sensitive structure provides suitable mechanical properties; the piezoelectric film can regulate and control the cavity length of the optical cavity, so that the acceleration sensor works at the position with the maximum sensitivity. The invention utilizes the coupling resonance of surface plasmon, has ultrahigh sensitivity exceeding the reported acceleration sensor, and the piezoelectric film provides a way for zero adjustment and modulation, thereby realizing the ultrasensitive acceleration measurement with higher feasibility.)

1. An open-loop type out-of-plane acceleration sensor based on surface plasmons comprises a fixed outer frame, a first photoelectric detector and a second photoelectric detector; the first photoelectric detector is arranged on the inner side wall of the fixed outer frame and is opposite to the direction of reflected laser, and the second photoelectric detector is arranged above the first photoelectric detector; the method is characterized in that: an acceleration sensitive structure and an out-of-plane displacement sensing unit are arranged in the fixed outer frame;

the acceleration sensitive structure comprises a mass block, a snake-shaped cantilever beam and a silicon outer frame; the mass block is of a cuboid structure with the same length and width, and is fixed in the silicon outer frame through four snake-shaped cantilever beams uniformly distributed along the circumferential direction; the snake-shaped cantilever beam is etched between the mass block and the silicon outer frame and comprises a plurality of shin beams and a plurality of thigh beams, the length of the shin beams is greater than that of the thigh beams, the shin beams are vertically arranged, the shin beams are connected end to end through the thigh beams to form a snake-shaped structure, and the shin beams are parallel to the side edges of the mass block; the center of the mass block is provided with a sub-wavelength silicon grating, the period of the sub-wavelength silicon grating is 531 +/-10 nm, the duty ratio is 32%, the thickness of the sub-wavelength silicon grating is the same as that of the mass block and is 1142 +/-10 nm;

the out-of-plane displacement sensing unit comprises a laser, an optical isolator, a beam splitter prism, a sub-wavelength silicon grating on the mass block, an air gap, a piezoelectric film, a silicon dioxide layer, a silicon substrate, a silver film covering the sub-wavelength silicon grating and a silver film covering the silicon substrate; the silicon substrate is arranged on the inner bottom surface of the fixed outer frame; the laser is arranged at the top in the fixed outer frame, an optical isolator is arranged below the laser, and a beam splitter prism is arranged right below the optical isolator; the silicon outer frame is arranged above the silicon substrate through a silicon dioxide layer and a piezoelectric film, the piezoelectric film is composed of a titanium/platinum bottom electrode, a lead zirconate titanate film and a titanium/platinum top electrode from bottom to top in sequence, and the silicon dioxide layer is arranged between the titanium/platinum bottom electrode and the silicon substrate; the mass block is suspended above the silicon substrate through a snake-shaped cantilever beam, and an air gap is formed between the sub-wavelength silicon grating and the silicon substrate; ensuring that the sub-wavelength silicon grating is positioned right below the light splitting prism, and simultaneously ensuring that the sub-wavelength silicon grating and the silicon substrate are parallel to each other; a near-field optical resonant cavity is formed by the sub-wavelength silicon grating covered with the silver film, the silicon substrate covered with the silver film and the air gap;

the position of the silver film covered on the silicon substrate is that the orthographic projection of the sub-wavelength silicon grating grid line on the silicon substrate translates by 69 +/-100 nm along the direction vertical to the sub-wavelength silicon grating grid line; the silver film covering the sub-wavelength silicon grating has a period of 531 +/-10 nm, a duty ratio of 32% and a thickness of 196 +/-20 nm; the silver film covered on the silicon substrate has a period of 531 +/-10 nm, a duty ratio of 68% and a thickness of 196 +/-20 nm; the height of the air gap is 2280 +/-10 nm.

2. The surface plasmon-based open-loop out-of-plane acceleration sensor of claim 1, wherein: the thickness of the mass block is 1142 +/-10 nm and is consistent with that of the snake-shaped cantilever beam.

3. The surface plasmon-based open-loop out-of-plane acceleration sensor of claim 1, wherein: the thickness of the titanium/platinum bottom electrode and the thickness of the titanium/platinum top electrode are both 120nm, wherein the thickness of titanium is 20nm, and the thickness of platinum is 100 nm; the thickness of the lead zirconate titanate film is 1000 +/-100 nm.

4. The surface plasmon-based open-loop out-of-plane acceleration sensor of claim 1, wherein: and the four snake-shaped cantilever beams are respectively fixed at four corners of the cuboid mass block.

5. The surface plasmon-based open-loop out-of-plane acceleration sensor of claim 1, wherein: the laser wavelength output by the laser is 1550nm, and the mode is a TE mode.

6. A method of fabricating an acceleration sensitive structure and a near field optical resonator according to claim 1, characterized by the following steps:

the method comprises the following steps: manufacturing and patterning a metal silver film on the polished surface of the single polished monocrystalline silicon wafer by using an electron beam exposure process, a stripping process and an electron beam evaporation process to form a lower silver film covering the silicon substrate;

step two: carrying out thermal oxidation treatment on the metallized monocrystalline silicon wafer, and carrying out chemical mechanical polishing to form a silicon dioxide layer with the thickness of 1080 +/-40 nm;

step three: manufacturing a piezoelectric film: firstly, growing a layer of titanium/platinum film on the silicon dioxide layer through magnetron sputtering to form a titanium/platinum bottom electrode; then, growing a layer of lead zirconate titanate film with the thickness of 1000 +/-100 nm and the piezoelectric constant of more than 100pC/N on the titanium/platinum bottom electrode through magnetron sputtering; finally, growing a layer of titanium/platinum film on the lead zirconate titanate film through magnetron sputtering to form a titanium/platinum top electrode;

step four: patterning the piezoelectric film, and etching the piezoelectric film in the area right below the mass block and the snake-shaped cantilever beam to a silicon dioxide layer by a reactive ion beam etching process to form an annular piezoelectric film;

step five: growing a silicon dioxide layer on the silicon dioxide layer thermally oxidized in the second step by utilizing chemical vapor deposition in the ring of the annular piezoelectric film, and thinning the silicon dioxide layer by utilizing chemical mechanical polishing until the silicon dioxide layer is flush with the upper surface of the titanium/platinum top electrode;

step six: growing a polysilicon layer on the whole wafer obtained in the fifth step by using chemical vapor deposition;

step seven: manufacturing and patterning a metal silver film on the polycrystalline silicon layer in the sixth step through an electron beam exposure process, a stripping process and an electron beam evaporation process to form an upper silver film covering the sub-wavelength silicon grating;

step eight: utilizing electron beam exposure to complete the graphic manufacture of the sub-wavelength silicon grating and the snake-shaped cantilever beam on the polycrystalline silicon layer, and adopting reactive ion beam etching to manufacture the sub-wavelength silicon grating and the snake-shaped cantilever beam;

step nine: and removing the silicon dioxide layer in the air gap by wet etching to finish the release of the acceleration sensitive structure.

7. The method of claim 6, wherein the acceleration sensitive structure and the near field optical resonator are formed by: the thickness of the monocrystalline silicon wafer is 300-500 mu m, the thickness of a thermal oxidation silicon dioxide layer positioned between the silicon substrate and the piezoelectric film is 1080 +/-40 nm, and the thickness of a polycrystalline silicon layer deposited by chemical vapor deposition is 1142 +/-10 nm.

Technical Field

The invention belongs to the field of accelerometers, and particularly relates to an open-loop type out-of-plane acceleration sensor and method based on surface plasmons.

Background

The measurement principle of the existing optical accelerometer is that acceleration is generally converted into displacement through an acceleration sensitive structure, and then displacement measurement is performed by using the interference, diffraction and other effects of light. Such measurements are typically based on a light scalar diffraction theory approximation which has high accuracy at structure dimensions and ranges greater than the wavelength of light, but the sensitivity and accuracy of optical displacement and acceleration measurements are limited by the wavelength of light at the diffraction limit of light in these scenarios.

Scalar diffraction theory is not suitable for the field of near field and structure size smaller than light wavelength, Woods discovered that the phenomenon of abnormal absorption/reflection occurs when light passes through a micro-nano periodic structure as early as 100 years ago, and later discovered that the phenomenon is the result of coupling resonance of surface plasmon generated by the incident light to a sub-wavelength structure [ BARNES W L, DEREUX A, EBBESEN T W.S. surface plasmon resonance [ J. ] Nature,2003,424(6950):824-30 ]. By utilizing the surface plasmon resonance enhancing means, the sensitivity of optical displacement measurement can be improved to the magnitude of picometers and sub-picometers [ DWC, JP S, TA F. However, in the existing scheme based on the surface plasmon, the structure of the near-field optical resonance is complex, the processing difficulty is very high, or the design of the acceleration sensitive structure is unreasonable, so that the sensitivity and the reliability are not high; in addition, the relative position of the acceleration sensitive structure cannot be regulated and controlled by the existing scheme, so that the acceleration sensor is difficult to work at the position with the maximum sensitivity.

For example, the nanooptoelectromechanical systems acceleration sensors proposed by Dustin et al of Sandia laboratories, USA [ KEELERB E N, BOGART G R, CARR D W.Laternally deformed optical NEMS gradings for initial sensing applications; technologies, Devices, and Applications, F,2005[ C ], the near-field optical interference cavity of which is composed of two movable sub-wavelength gratings, an air gap and a medium absorption layer, wherein the movable sub-wavelength grating is made of amorphous diamond, the medium absorption layer is made of silicon dioxide and silicon nitride, the structure is complex, and the light intensity displacement sensitivity is less than 2%/nm; a hybrid surface plasmon accelerometer designed by Ztong et al, university of southeast (patent with Chinese patent number CN201811464465, "a low temperature drift hybrid surface plasmon accelerometer"), which is not high in acceleration displacement sensitivity and unknown in reliability due to the use of a flexible sensitive structure; an opto-mechanical accelerometer [ KRAUSE A G, WINGER M, BLASTIUS T D, et al.A. high-resolution microchip optical accelerometer [ J ]. Nature electrophonics, 2012,6(11):768-72 ] based on a photonic crystal optical cavity is designed by Painter et al of California university, the optical displacement measurement sensitivity of the scheme is very high, but a proper acceleration sensitive structure is not designed, so the acceleration measurement sensitivity is not high; a sub-wavelength grating-array accelerometer designed by the university of Beijing aerospace [ Yao B Y; feng L S; wang X; although the structure is simple, the two groups of sub-wavelength gratings of the scheme are equivalent to one diffraction grating only and do not utilize the nonlinear effect brought by the surface plasmon, so that the sensitivity is lower than 0.5%/mg.

Generally, the existing scheme or structure based on the surface plasmon is complex, or the design of the acceleration sensitive structure is unreasonable, so that the acceleration measurement sensitivity is lower than 3%/mg, and a means for regulating and controlling the relative position of the acceleration sensitive structure is lacked.

Disclosure of Invention

The technical problem to be solved is as follows:

in order to avoid the defects of the prior art, the invention provides the open-loop type out-of-plane acceleration sensor and the method based on the surface plasmon, the near-field optical resonant cavity can greatly improve the displacement measurement sensitivity while reducing the structural complexity, the piezoelectric film provides a way for regulating and controlling the acceleration sensitive structure, and the acceleration sensitive structure in the form of the snake-shaped beam cantilever beam are matched to realize the ultra-high-sensitivity out-of-plane acceleration measurement.

The technical scheme of the invention is as follows: an open-loop type out-of-plane acceleration sensor based on surface plasmons comprises a fixed outer frame, a first photoelectric detector and a second photoelectric detector; the first photoelectric detector is arranged on the inner side wall of the fixed outer frame and is opposite to the direction of reflected laser, and the second photoelectric detector is arranged above the first photoelectric detector; the method is characterized in that: an acceleration sensitive structure and an out-of-plane displacement sensing unit are arranged in the fixed outer frame;

the acceleration sensitive structure comprises a mass block, a snake-shaped cantilever beam and a silicon outer frame; the mass block is of a cuboid structure with the same length and width, and is fixed in the silicon outer frame through four snake-shaped cantilever beams uniformly distributed along the circumferential direction; the snake-shaped cantilever beam is etched between the mass block and the silicon outer frame and comprises a plurality of shin beams and a plurality of thigh beams, the length of the shin beams is greater than that of the thigh beams, the shin beams are vertically arranged, the shin beams are connected end to end through the thigh beams to form a snake-shaped structure, and the shin beams are parallel to the side edges of the mass block; the center of the mass block is provided with a sub-wavelength silicon grating, the period of the sub-wavelength silicon grating is 531 +/-10 nm, the duty ratio is 32%, the thickness of the sub-wavelength silicon grating is the same as that of the mass block and is 1142 +/-10 nm;

the out-of-plane displacement sensing unit comprises a laser, an optical isolator, a beam splitter prism, a sub-wavelength silicon grating on the mass block, an air gap, a piezoelectric film, a silicon dioxide layer, a silicon substrate, a silver film covering the sub-wavelength silicon grating and a silver film covering the silicon substrate; the silicon substrate is arranged on the inner bottom surface of the fixed outer frame; the laser is arranged at the top in the fixed outer frame, an optical isolator is arranged below the laser, and a beam splitter prism is arranged right below the optical isolator; the silicon outer frame is arranged above the silicon substrate through a silicon dioxide layer and a piezoelectric film, the piezoelectric film is composed of a titanium/platinum bottom electrode, a lead zirconate titanate film and a titanium/platinum top electrode from bottom to top in sequence, and the silicon dioxide layer is arranged between the titanium/platinum bottom electrode and the silicon substrate; the mass block is suspended above the silicon substrate through a snake-shaped cantilever beam, and an air gap is formed between the sub-wavelength silicon grating and the silicon substrate; ensuring that the sub-wavelength silicon grating is positioned right below the light splitting prism, and simultaneously ensuring that the sub-wavelength silicon grating and the silicon substrate are parallel to each other; a near-field optical resonant cavity is formed by the sub-wavelength silicon grating covered with the silver film, the silicon substrate covered with the silver film and the air gap;

the position of the silver film covered on the silicon substrate is that the orthographic projection of the sub-wavelength silicon grating grid line on the silicon substrate translates by 69 +/-100 nm along the direction vertical to the sub-wavelength silicon grating grid line; the silver film covering the sub-wavelength silicon grating has a period of 531 +/-10 nm, a duty ratio of 32% and a thickness of 196 +/-20 nm; the silver film covered on the silicon substrate has a period of 531 +/-10 nm, a duty ratio of 68% and a thickness of 196 +/-20 nm; the height of the air gap is 2280 +/-10 nm.

The further technical scheme of the invention is as follows: the thickness of the mass block is 1142 +/-10 nm and is consistent with that of the snake-shaped cantilever beam.

The further technical scheme of the invention is as follows: the thickness of the titanium/platinum bottom electrode and the thickness of the titanium/platinum top electrode are both 120nm, wherein the thickness of titanium is 20nm, and the thickness of platinum is 100 nm; the thickness of the lead zirconate titanate film is 1000 +/-100 nm.

The further technical scheme of the invention is as follows: and the four snake-shaped cantilever beams are respectively fixed at four corners of the cuboid mass block.

The further technical scheme of the invention is as follows: the laser wavelength output by the laser is 1550nm, and the mode is a TE mode.

A method for manufacturing an acceleration sensitive structure and a near-field optical resonant cavity is characterized by comprising the following specific steps:

the method comprises the following steps: manufacturing and patterning a metal silver film on the polished surface of the single polished monocrystalline silicon wafer by using an electron beam exposure process, a stripping process and an electron beam evaporation process to form a lower silver film covering the silicon substrate;

step two: carrying out thermal oxidation treatment on the metallized monocrystalline silicon wafer, and carrying out chemical mechanical polishing to form a silicon dioxide layer with the thickness of 1080 +/-40 nm;

step three: manufacturing a piezoelectric film: firstly, growing a layer of titanium/platinum film on the silicon dioxide layer through magnetron sputtering to form a titanium/platinum bottom electrode; then, growing a layer of lead zirconate titanate film with the thickness of 1000 +/-100 nm and the piezoelectric constant of more than 100pC/N on the titanium/platinum bottom electrode through magnetron sputtering; finally, growing a layer of titanium/platinum film on the lead zirconate titanate film through magnetron sputtering to form a titanium/platinum top electrode;

step four: patterning the piezoelectric film, and etching the piezoelectric film in the area right below the mass block and the snake-shaped cantilever beam to a silicon dioxide layer by a reactive ion beam etching process to form an annular piezoelectric film;

step five: growing a silicon dioxide layer on the silicon dioxide layer thermally oxidized in the second step by utilizing chemical vapor deposition in the ring of the annular piezoelectric film, and thinning the silicon dioxide layer by utilizing chemical mechanical polishing until the silicon dioxide layer is flush with the upper surface of the titanium/platinum top electrode;

step six: growing a polysilicon layer on the whole wafer obtained in the fifth step by using chemical vapor deposition;

step seven: manufacturing and patterning a metal silver film on the polycrystalline silicon layer in the sixth step through an electron beam exposure process, a stripping process and an electron beam evaporation process to form an upper silver film covering the sub-wavelength silicon grating;

step eight: utilizing electron beam exposure to complete the graphic manufacture of the sub-wavelength silicon grating and the snake-shaped cantilever beam on the polycrystalline silicon layer, and adopting reactive ion beam etching to manufacture the sub-wavelength silicon grating and the snake-shaped cantilever beam;

step nine: and removing the silicon dioxide layer in the air gap by wet etching to finish the release of the acceleration sensitive structure.

The further technical scheme of the invention is as follows: the thickness of the monocrystalline silicon wafer is 300-500 mu m, the thickness of a thermal oxidation silicon dioxide layer positioned between the silicon substrate and the piezoelectric film is 1080 +/-40 nm, and the thickness of a polycrystalline silicon layer deposited by chemical vapor deposition is 1142 +/-10 nm.

Advantageous effects

The invention has the beneficial effects that: the acceleration measuring sensitivity of the out-of-plane acceleration sensor is far higher than that of the traditional optical measuring scheme by combining a strict coupled wave analysis method and a genetic algorithm and through the global optimization of all parameters of the near-field optical resonant cavity, the maximum acceleration measuring sensitivity of the out-of-plane acceleration sensor can reach 30%/mg (the acceleration displacement sensitivity of the acceleration sensitive structure is assumed to be 1nm/mg), namely when 1mg of out-of-plane acceleration is input, the light intensity variation of a reflected light beam is 30% of the light intensity of incident laser.

The integrated piezoelectric film designed by the invention can drive the acceleration sensitive structure to realize out-of-plane displacement with nanometer precision through the inverse piezoelectric effect, not only can ensure that the acceleration sensor works at the position with the maximum sensitivity, but also provides a way for further improving the signal-to-noise ratio by adding modulation and demodulation.

The staggered design of the two silver films is designed through the global optimization mentioned above, and the staggered design and the staggered parameter setting are only sensitive to outside-face displacement and not sensitive to inside-face displacement.

The invention adopts the snake-shaped cantilever beam design, when the out-plane acceleration is input, the acceleration sensitive structure is subjected to the action of inertia force to generate elastic deformation, the mass block generates out-plane displacement opposite to the acceleration direction, and the displacement and the input acceleration are in a linear relation within the elastic range of the material. Because the snake-shaped cantilever beam has elastic coefficients far smaller than the elastic coefficients in two directions in the plane in the out-of-plane direction, the acceleration sensitive structure has high acceleration-displacement sensitivity in the out-of-plane direction (sensitive axial direction) and lower off-axis crosstalk. Meanwhile, the sub-wavelength silicon grating is positioned in the center of the mass block and is used as a part of the mass block, so that the near-field optical resonant cavity can be perfectly integrated with the acceleration sensitive structure.

In the design process of the invention, the machining precision which can be realized by the existing micro-machining process is considered, and the parameter tolerance design of the acceleration sensitive structure and the near-field optical resonant cavity is completed based on the machining precision, so that the process feasibility of the whole scheme is ensured.

Drawings

FIG. 1 is a schematic view of an open-loop out-of-plane acceleration sensor of the present invention;

FIG. 2 is a schematic diagram of an acceleration sensitive structure based on a serpentine cantilever beam;

FIG. 3 is a schematic process flow diagram of a near-field optical microresonator;

FIG. 4 is a schematic process flow diagram of an acceleration sensitive structure;

FIG. 5 is a graph of reflected beam light intensity as a function of acceleration for an out-of-plane acceleration input;

FIG. 6 is an electromagnetic field distribution of the near-field optical resonant cavity in the reflection mode (a) and the transmission mode (b).

Description of reference numerals: 1. the laser comprises a laser, 2, an optical isolator, 3, a beam splitter prism, 4, a near-field optical resonant cavity, 5, an acceleration sensitive structure, 6, a first photoelectric detector, 7, a second photoelectric detector, 8, a fixed outer frame, 9, a packaging tube shell, 10, an upper silver film, 11, a sub-wavelength silicon grating, 12, a lower silver film, 13, a silicon substrate, 14, an air gap, 15, a silicon dioxide layer, 16, a titanium/platinum bottom electrode, 17, a lead zirconate titanate film, 18, a titanium/platinum top electrode, 19, incident laser, 20, reflected light beams, 21, snake-shaped cantilever beams, 22, a mass block, 23, a silicon outer frame, 24, a bend, 25, a shin beam, 26, a strand beam, 27, a single crystal silicon wafer, 28, a silicon dioxide layer grown by thermal oxidation, 29, a silicon dioxide layer deposited by chemical vapor deposition, and a polysilicon layer.

Detailed Description

The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention.

The drawings provided in the present embodiment are only for illustrating the basic idea of the present invention in a schematic view, and related components in the schematic view are not necessarily drawn according to the number, shape and size of components in actual implementation.

The embodiment of the invention and the implementation process thereof are as follows:

as shown in fig. 1, the invention provides an open-loop type out-of-plane acceleration sensor based on surface plasmons, which comprises a laser 1, an optical isolator 2, a beam splitter prism 3, a near-field optical resonant cavity 4, an acceleration sensitive structure 5, a first photoelectric detector 6, a second photoelectric detector 7, a fixed outer frame 8, a packaging tube shell 9 and a piezoelectric film composed of a titanium/platinum bottom electrode 16, a lead zirconate titanate film 17 and a titanium/platinum top electrode 18; the near-field optical resonant cavity 4 is composed of an upper silver film 10, a sub-wavelength silicon grating 11, a lower silver film 12, a silicon substrate 13 and an air gap 14;

the acceleration sensitive structure 5 comprises four snake-shaped cantilever beams 21, a mass block 22 and a silicon outer frame 23; as shown in fig. 2, the mass block 22 is a rectangular parallelepiped structure with the same length and width, and is fixed in the silicon outer frame by four serpentine cantilevers evenly distributed along the circumferential direction; the serpentine cantilever beam is etched between the mass block and the silicon outer frame, the serpentine cantilever beam 21 comprises a plurality of bends 24, one bend 24 comprises a shin beam 25 and a thigh beam 26, the length of the shin beam 25 is greater than that of the thigh beam 26, the shin beam 25 is connected end to end through the thigh beam 26 to form a serpentine structure, the shin beam 25 is perpendicular to the thigh beam 26, and the shin beam 25 is parallel to the side edge of the mass block 22; the number of bends 24 can be adjusted depending on the design criteria. The center of the mass block 22 is provided with a sub-wavelength silicon grating 11, the period of the sub-wavelength silicon grating 11 is 531 +/-10 nm, the duty ratio is 32%, and the thickness is the same as that of the mass block and is 1142 +/-10 nm;

the out-of-plane displacement sensing unit consists of a laser 1, an optical isolator 2, a beam splitter prism 3, a sub-wavelength silicon grating on the mass block 22, an air gap 14, a piezoelectric film, a silicon dioxide layer 15, a silicon substrate 13, a silver film 10 covering the sub-wavelength silicon grating and a silver film 12 covering the silicon substrate; the position of the silver film 12 covering the silicon substrate is that the orthographic projection of the grating line of the sub-wavelength silicon grating 11 on the silicon substrate 13 translates by 69 +/-100 nm along the direction vertical to the grating line of the sub-wavelength silicon grating 11 (the direction vertical to the grating line is set as an x axis); the silicon substrate 13 is arranged on the inner bottom surface of the fixed outer frame 8; the laser 1 is arranged at the top in the fixed outer frame 8, the optical isolator 2 is arranged below the laser 1, and the beam splitter prism 3 is arranged right below the optical isolator 2; the silicon outer frame 23 is arranged on the upper surface of the silicon substrate 13 through a silicon dioxide layer 15 and a piezoelectric film, the piezoelectric film is composed of a titanium/platinum bottom electrode 16, a lead zirconate titanate film 17 and a titanium/platinum top electrode 18 from bottom to top in sequence, and the silicon dioxide layer 15 is arranged between the titanium/platinum bottom electrode 16 and the silicon substrate 13; the mass block 22 is suspended above the silicon substrate 13 through a serpentine cantilever beam 21, and an air gap 14 is formed between the sub-wavelength silicon grating 11 and the silicon substrate 13; ensuring that the sub-wavelength silicon grating 11 is positioned right below the beam splitter prism 3, and simultaneously ensuring that the sub-wavelength silicon grating 11 and the silicon substrate 13 are parallel to each other; a near-field optical resonant cavity 4 is formed by a sub-wavelength silicon grating 11 covered by an upper silver film 10, a silicon substrate 13 covered by a lower silver film 12 and the air gap 14;

the upper silver film 10 covering the sub-wavelength silicon grating 11 has a period of 531 +/-10 nm, a duty ratio of 32% and a thickness of 196 +/-20 nm; the period of the lower silver film 12 covered on the silicon substrate 13 is 531 +/-10 nm, the duty ratio is 68%, and the thickness is 196 +/-20 nm; the height of the air gap 14 is 2280 ± 10 nm.

The specific measurement principle of the present invention is described as follows:

when out-of-plane acceleration is input, the mass block 22 in the acceleration sensitive structure 5 is subjected to the action of inertia force to generate out-of-plane displacement, and because the sub-wavelength silicon grating 11 is positioned in the center of the mass block 22, the sub-wavelength silicon grating 11 also generates out-of-plane displacement relative to the silicon substrate 13, and at the moment, the coupling condition of the surface plasmon in the near-field optical resonant cavity 4 is changed; the laser 1 emits TE mode laser with the wavelength of 1550nm, and the incident laser 19 passes through the optical isolator 2 and the beam splitter prism 3 and then vertically enters the near-field optical resonant cavity 4; since the line width characteristics of the sub-wavelength silicon grating 11, the upper silver film 10 and the lower silver film 12 and the air gap 14 are smaller than the wavelength of the incident laser 19, the incident laser 19 is converted into a surface plasmon after passing through the upper silver film 10; the surface plasmon propagates in the near-field optical resonant cavity 4 and is coupled to the sub-wavelength silicon grating 11 and the lower silver film 12; when the sub-wavelength silicon grating 11 is displaced out of the plane, the boundary condition of the near-field optical resonant cavity 4 is changed, the coupling condition of the surface plasmon is also changed, and the light intensity of the reflected light beam 20 is changed dramatically. When the air gap 14 is 2.27 μm, the near-field optical resonant cavity 4 is in the reflection mode, as shown in fig. 6(a), and the intensity of the reflected light beam 20 is strongest; when the air gap 14 is 2.28 μm, the near-field optical resonator 4 is in the transmission mode, as shown in FIG. 6(b), where the intensity of the reflected light beam 20 is the weakest; the acceleration measurement interval of the acceleration sensor is defined between the two, and acceleration measurement with high sensitivity and high linearity can be realized in the interval.

The graph of the intensity of the reflected light beam 20 as a function of the acceleration out of the input plane is shown in fig. 5, which corresponds to an acceleration displacement sensitivity of 1nm/mg for the acceleration sensitive structure 5. It can be found that the light intensity acceleration sensitivity in the linear interval exceeds 30%/mg, i.e. the out-of-plane acceleration changes by 1mg, and the variation of the light intensity of the reflected beam 20 is 30% of the light intensity of the incident laser light 19. Even if various tolerances are considered, the light intensity acceleration sensitivity can exceed 20%/mg, and surpass the existing near-field optical resonant cavity scheme.

The parameters of the near-field optical resonator 4 include: the wavelength of the incident laser light 19 is 1550 nm; the period of the sub-wavelength silicon grating 11 is 531 +/-10 nm, the duty ratio is 32%, and the thickness is 1142 +/-10 nm; the period and the thickness of the upper silver film 10 and the lower silver film 12 are the same, the period is 531 +/-10 nm, the thickness is 196 +/-20 nm, the duty ratio of the upper silver film 10 is 32 percent, the duty ratio of the lower silver film 12 is 68 percent, and the upper silver film 10 and the lower silver film 12 are staggered in the x direction with the distance of 69 +/-100 nm; the air gap 13 is 2280 + -10 nm.

The parameters of the acceleration sensitive structure 5 include: the mass blocks 22 have the same length and width, and the thickness is 1142 +/-10 nm; the thickness of the silicon outer frame 23 is 1142 +/-10 nm; the width and thickness of the tibial beam 25 and the femoral beam 26 are the same, the thickness is 1142 +/-10 nm, and the width and length of the beams and the length and width of the mass block 22 can be adjusted according to different design indexes.

The thickness of the titanium/gold bottom electrode 16 and the thickness of the titanium/gold top electrode 18 in the piezoelectric film are both 120nm, wherein the thickness of titanium is 20nm, and the thickness of platinum is 100 nm; (ii) a The thickness of the lead zirconate titanate film 17 is 1000 +/-100 nm;

referring to FIGS. 3 and 4, the present invention also provides a method for fabricating the near-field optical resonator 4 and the acceleration sensitive structure 5, wherein the substrate is a single-polished single-crystal silicon wafer 27 as shown in FIG. 3(a) and has a thickness of 300-500 μm. The manufacturing method comprises the following steps:

the method comprises the following steps: manufacturing and patterning a metal silver film on the polished surface of the single polished monocrystalline silicon wafer 27 by using an electron beam exposure, stripping process and electron beam evaporation process to form a lower silver film 12 covering the silicon substrate 13;

step two: carrying out thermal oxidation treatment on the metallized monocrystalline silicon wafer 27, and carrying out chemical mechanical polishing to form a silicon dioxide layer 28 with the thickness of 1080 +/-40 nm;

step three: manufacturing a piezoelectric film: firstly, growing a titanium/platinum film on the silicon dioxide layer 28 by magnetron sputtering to form a titanium/platinum bottom electrode 16; then, growing a layer of lead zirconate titanate film 17 with the thickness of 1000 +/-100 nm and the piezoelectric constant of more than 100pC/N on the titanium/platinum bottom electrode 16 through magnetron sputtering; finally, growing a titanium/platinum film on the lead zirconate titanate film 17 through magnetron sputtering to form a titanium/platinum top electrode 18;

step four: patterning the piezoelectric film, and etching the piezoelectric film in the area right below the mass block 22 and the snake-shaped cantilever beam 21 to a silicon dioxide layer by a reactive ion beam etching process to form an annular piezoelectric film;

step five: growing a silicon dioxide layer 29 on the silicon dioxide layer 28 thermally oxidized in the second step by using chemical vapor deposition in the ring of the annular piezoelectric film, and thinning the silicon dioxide layer by using chemical mechanical polishing until the silicon dioxide layer is flush with the upper surface of the titanium/platinum top electrode 18;

step six: growing a polysilicon layer 30 on the whole wafer obtained in the fifth step by chemical vapor deposition;

step seven: manufacturing and patterning a metal silver film on the polycrystalline silicon layer 30 in the sixth step through an electron beam exposure process, a stripping process and an electron beam evaporation process to form an upper silver film 10 covering the sub-wavelength silicon grating 11;

step eight: completing the graphic manufacture of the sub-wavelength silicon grating 11 and the snake-shaped cantilever beam 21 on the polycrystalline silicon layer 30 by using electron beam exposure, and manufacturing the sub-wavelength silicon grating 11 and the snake-shaped cantilever beam 21 by adopting reactive ion beam etching;

step nine: and removing the silicon dioxide layer in the air gap by wet etching to finish the release of the acceleration sensitive structure 5.

Therefore, the optical displacement measurement with ultrahigh sensitivity is realized by using the optimally designed near-field optical resonant cavity, the optimized near-field optical resonant cavity has larger parameter tolerance, can be realized by adopting the conventional micromachining process, can be well integrated with the acceleration sensitive structure, and improves the reliability of the device while improving the integration level. The piezoelectric film designed by the invention provides a zero adjustment and modulation way, and the feasibility of a scheme is ensured.

The present invention has been described in terms of embodiments, and those skilled in the art can modify or change the embodiments described above without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made in the above embodiments by those of ordinary skill in the art without departing from the principle and spirit of the present invention.