Room-temperature high-sensitivity resonance type micro-electro-mechanical infrared thermal detector

Abstract

The invention discloses a room-temperature high-sensitivity resonance type micro-electro-mechanical infrared thermal detector, which comprises a first cantilever resonator, a coupling structure and a second cantilever resonator which are sequentially connected with a fixed structure to realize weak coupling, the number of the metasurface infrared absorber structures is two, the first metasurface infrared absorber is arranged at the top end of the first cantilever resonator, and the second metasurface infrared absorber is arranged at the bottom of the second cantilever resonator; the metasurface infrared absorber structure comprises a cross-shaped patterned array micro-nano structure, a dielectric layer and a metal layer, the dielectric layer is connected with the cross-shaped patterned array micro-nano structure and the metal layer to form a metal-dielectric-metal metasurface infrared absorber, the cross-shaped patterned array micro-nano structure is arranged on the uppermost layer of the metasurface infrared absorber structure, and the metal-dielectric-metal metasurface infrared absorber structure is arranged on the middle layer of the metasurface infrared absorber structure. The dielectric layer is located on the middle layer of the metasurface infrared absorber structure, the metal layer is located on the lowermost layer of the metasurface infrared absorber structure, and the metal layer is arranged at the tail end of the end, not connected with the fixed structure, of the cantilever resonator.

Description

Technical Field

[0001] The invention relates to the technical field of micro-electromechanical infrared thermal detection, and in particular to a room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector. Background Art

[0002] Microelectromechanical (MEMS) infrared thermal detectors have become one of the main methods of infrared detection due to their outstanding advantages such as small size, low power consumption, no wavelength response restrictions, and the ability to work at room temperature without ultra-low temperature refrigeration. Traditional MEMS infrared thermal detection methods are generally integrated with filters and Fresnel lenses to achieve spectral band identification and light energy focusing detection, which can provide better infrared detection solutions for application scenarios with low portability, low cost and low sensitivity requirements. As society continues to develop in the direction of intelligence, functionality and miniaturization, civilian consumer-grade room temperature high-precision miniature infrared detectors have received more and more attention and will appear in electronic devices such as smart phones, smart bracelets, and smart glasses, and will be used in human health monitoring, environmental toxic and harmful gas detection and other fields. However, at present, the detection rate of MEMS infrared thermal detectors under room temperature conditions can only reach 10 10 cm√HzW -1 (Jones) order of magnitude, and the noise equivalent temperature difference is greater than 30mK. For the above application scenarios, the detection rate of conventional infrared thermal detectors is low and the noise level is relatively high, which cannot meet the needs of high-sensitivity detection. Summary of the invention

[0003] In view of the above problems, the present invention provides a room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector method, wherein the detector comprises: a fixed structure, a first cantilever resonator, a second cantilever resonator, a coupling structure and a metasurface infrared absorber structure;

[0004] The first cantilever resonator, the coupling structure and the second cantilever resonator are connected to the fixed structure in sequence to achieve weak coupling; there are two metasurface infrared absorber structures, the first metasurface infrared absorber structure is arranged on the upper surface of the free end of the first cantilever resonator, and the second metasurface infrared absorber structure is arranged on the lower surface of the free end of the second cantilever resonator; the metasurface infrared absorber structure includes a cross-shaped patterned array micro-nano structure, a dielectric layer, and a metal layer, the dielectric layer is respectively connected to the cross-shaped patterned array micro-nano structure and the metal layer to form a metal-dielectric-metal metasurface infrared absorber, the cross-shaped patterned array micro-nano structure is arranged on the uppermost layer of the metasurface infrared absorber structure, the dielectric layer is located in the middle layer of the metasurface infrared absorber structure, the metal layer is located in the lowermost layer of the metasurface infrared absorber structure, and the metal layer is arranged at the free end of the cantilever resonator that is not connected to the fixed structure end.

[0005] Optionally, the first cantilever resonator and the second cantilever resonator have the same size, and a weak coupling effect is achieved through a coupling structure.

[0006] Optionally, the metal-dielectric-metal metasurface infrared absorber is used to achieve coupled enhanced absorption of specific electromagnetic waves through a surface plasmon resonance effect, and convert light energy into thermal energy through a photothermal effect to form thermal stress.

[0007] Optionally, the thermal stress causes the resonant mode amplitude of the resonator to change, and through the weak coupling effect, local energy output and modal amplitude amplification are achieved.

[0008] Optionally, the modal amplitude change is converted into a spectral energy change through a quantity transfer relationship, thereby achieving high-sensitivity detection of the infrared spectrum.

[0009] Optionally, the cross-shaped patterned array micro-nano structure of the metasurface infrared absorber structure includes a number of periodic units, and one periodic unit contains two cross structures, including two first cross-shaped structures and two second cross-shaped structures. The first cross-shaped structure is composed of two rectangles with a length of a1 and a width of b1, and the two rectangles are vertically distributed; the second cross-shaped structure is composed of two rectangles with a length of a2 and a width of b2, and the two rectangles are vertically distributed.

[0010] Optionally, the cross-shaped patterned array micro-nanostructure is formed by the cross-distribution of two cross-shaped structures to form a periodic unit, and a metasurface infrared absorber is formed based on the unit periodic arrangement.

[0011] Optionally, the thickness of the cross-shaped structure is 100 nm, and the structural material is titanium.

[0012] Optionally, the dielectric layer material is amorphous silicon and has a thickness of 400 nm.

[0013] Optionally, the metal layer is made of titanium and has a thickness of 100 nm.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention provides a room-temperature highly sensitive resonant micro-electromechanical infrared thermal detector, which is designed and uses a metasurface infrared absorber structure to achieve high-absorption rate absorption of 5μm-16μm broadband infrared electromagnetic waves, with a peak absorption rate greater than 90%. The absorption wavelength and absorption bandwidth can be regulated by changing the unit structure size, period and material properties, while maintaining polarization insensitivity and incident angle insensitivity.

[0016] Secondly, the infrared light energy absorbed by the infrared absorber is converted into thermal energy inside the resonator through the photothermal effect, and the resonant mode of the resonator is changed by applying disturbance on the cantilever beam resonator through thermal stress. Furthermore, the energy of the disturbance point is localized and amplified through the designed mutually weakly coupled double cantilever resonator system. The principle is that in a multi-degree-of-freedom weakly coupled mechanical resonance system, when the resonator is not disturbed, the modal amplitudes of each resonator are the same. When one of the resonators is disturbed by external physical effects, the energy of the mutually weakly coupled multi-degree-of-freedom resonators will be localized to a specific resonator, causing its modal amplitude to change dramatically, thereby achieving a highly sensitive response to external disturbances (i.e., infrared spectrum). The sensitivity is improved by nearly three orders of magnitude compared to traditional frequency shift detection methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 This is a schematic diagram of the structural design of a room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector provided by the present invention;

[0019] Figure 2 This is an experimental diagram of the absorption effect of the super-surface infrared absorber provided by the present invention on infrared electromagnetic waves;

[0020] Figure 3 This is a diagram of the "mass-stiffness-damping" equivalent mechanical model of a dual-degree-of-freedom weakly coupled resonance system according to an embodiment of the present invention;

[0021] Figure 4 Schematic diagram of the first-order vibration mode (in phase) and the second-order vibration mode (anti-phase) of the resonator according to an embodiment of the present invention;

[0022] Figure 5 Graphs of amplitude-frequency curves of first and second order vibration modes of the first cantilever resonator and the second cantilever resonator under different light and heat disturbances in an embodiment of the present invention;

[0023] Figure 6 is a curve showing the relationship between the amplitude ratio of the first cantilever resonator and the second cantilever resonator and the illumination power under the photothermal disturbance of an embodiment of the present invention;

[0024] Figure 7 is a curve showing the relationship between the amplitude ratio of the first cantilever resonator and the light power in the first-order resonance mode and the second-order resonance mode of the embodiment of the present invention;

[0025] Figure numerals: 1 is the infrared spectrum to be measured, 2 is the first cantilever resonator, 3 is the fixed structure, 4 is the coupling structure, 5 is the second cantilever resonator, 6 is the metasurface infrared absorber structure I, 7 is the metasurface infrared absorber structure II, 8 is the cross-shaped patterned array micro-nano structure, 9 is the dielectric layer, 10 is the metal layer, and 11 is a periodic unit of the metasurface infrared absorber structure. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Example

[0028] The present invention provides a room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector, such as Figure 1 As shown, the detector comprises:

[0029] A fixed structure 3, a first cantilever resonator 2, a second cantilever resonator 5, a coupling structure 4, and a metasurface infrared absorber structure I 6 and a metasurface infrared absorber structure II 7;

[0030] The first cantilever resonator 2, the coupling structure 4 and the second cantilever resonator 5 are connected to the fixed structure 3 in sequence to achieve weak coupling; the metasurface infrared absorber I6 structure and the metasurface infrared absorber II7 are arranged on the first cantilever resonator 2 and the second cantilever resonator 5 respectively; the metasurface infrared absorber structures are arranged at the free end of the end not connected to the fixed structure, the metasurface infrared absorber structure I is arranged on the upper surface of the first cantilever resonator, and the metasurface infrared absorber structure II is arranged on the lower surface of the second cantilever resonator. The cross-shaped patterned array micro-nano structure of the metasurface infrared absorber structure includes a number of periodic units, such as Figure 1 As shown in (c), a periodic unit includes two cross structures, including two first cross structures and two second cross structures. The first cross structure is composed of two rectangles with a length of a1 and a width of b1, and the two rectangles are vertically distributed; the second cross structure is composed of two rectangles with a length of a2 and a width of b2, and the two rectangles are vertically distributed. The metasurface infrared absorber structure includes a cross-shaped patterned array micro-nano structure 8, a dielectric layer 9, and a metal layer 10. The dielectric layer 9 is respectively connected to the cross-shaped patterned array micro-nano structure 8 and the metal layer 10 to form a "metal-dielectric-metal" metasurface infrared absorber, as shown in FIG. Figure 1As shown in (b), the cross-shaped patterned array micro-nano structure 8 is located at the uppermost layer of the super-surface infrared absorber structure, the dielectric layer 9 is located at the middle layer of the super-surface infrared absorber structure, and the metal layer 10 is located at the lowermost layer of the super-surface infrared absorber structure, and the metal layer 10 is arranged at the end of the cantilever resonator that is not connected to the fixed structure 3. The first cantilever resonator 2 and the second cantilever resonator 5 have exactly the same size, structure and material properties. In this weakly coupled double cantilever resonant system, a periodic driving force is applied to it so that both cantilever resonators work in a resonant state, at which time they have the same resonant frequency and resonant amplitude. At this time, the disturbance effect of the measured value is introduced into any cantilever resonator. The disturbance force induces a modal localization effect through the weak coupling effect of the double cantilever, so that the energy of the resonant system is localized in a certain resonator, causing its amplitude to change dramatically, thereby realizing a highly sensitive detection of the measured disturbance through the modal amplitude offset.

[0031] In order to effectively introduce the measured disturbance into the cantilever resonator, one end of the dual cantilever resonator system is fixed by a fixed structure 3, and the other end is suspended to form a cantilever beam structure. At the free end of the cantilever beam, a metasurface infrared absorber is prepared by micro-nano processing technology, which converts the absorbed light energy into a disturbance and feeds it into the resonant system. Taking the light-irradiated metasurface infrared absorber I6 as an example, the metasurface infrared absorber 6 realizes enhanced absorption and electromagnetic regulation of infrared electromagnetic waves in different bands through the surface plasmon resonance effect of the cross-shaped patterned array micro-nanostructure 8. In order to enhance the electric coupling and magnetic coupling of the absorber structure, a dielectric layer 9 and a metal layer 10 are designed under the cross-shaped patterned array micro-nanostructure 8 to form a "metal-dielectric-metal" absorber structure. The metasurface infrared absorber is used to realize coupling-enhanced absorption of specific (5μm~16μm) electromagnetic waves through the surface plasmon resonance effect, and convert light energy into thermal energy through the photothermal effect to form thermal stress. Theory and experiments show that this structure can achieve perfect absorption of electromagnetic waves in the strongest absorption band with an absorption rate close to 100%. Note that the metasurface infrared absorber I6 and the metasurface infrared absorber II7 are arranged on different surfaces at the free ends of the first cantilever resonator 2 and the second cantilever resonator 5, respectively. As Figure 1 (a), which ensures that only one cantilever resonator receives the light perturbation at the same time.

[0032] Take the light irradiation metasurface infrared absorber I6 as an example. Figure 1 The infrared absorber I6 at the free end of the metasurface receives infrared spectrum radiation and absorbs strongly. Figure 2Figure (a) shows the absorption effect of infrared electromagnetic wave TE wave at different incident angles, and Figure (b) shows the absorption effect of infrared electromagnetic wave TM wave at different incident angles. Through the design of metasurface cross-patterned array micro-nanostructure, the metasurface infrared absorber I6 is insensitive to the polarization and angle of the incident light. The absorption effect is not much different under different TE and TM polarization modes and different incident angles, and it has perfect absorption with an absorption rate close to 100% at wavelengths of 6.0μm, 9.3μm and 11.7μm.

[0033] After the metasurface infrared absorber I6 absorbs the energy of infrared electromagnetic waves, it converts light energy into heat energy under the action of photothermal energy and forms thermal stress. The thermal stress exerts disturbance on the cantilever resonator, inducing the modal localization effect and realizing the local amplification output of the modal amplitude. Its working mechanical model is as follows: Figure 3-Figure 4 As shown, m1, k1, c1, m2, k2 and c2 are the mass, bending stiffness and damping coefficient of the first cantilever resonator 2 and the second cantilever resonator 5 respectively; f1 and f2 are the driving forces applied to the two cantilever resonators; x1 and x2 are the displacements of the free ends of the two cantilever resonators; and kc is the stiffness of the coupling beam. According to the design of the invention example, the relationship m1=m2=m, k1=k2=k, c1=c2=c is satisfied, and the metasurface infrared absorber I6 at the free end of the first cantilever resonator 2 irradiates the infrared light to be measured, that is, only an external optomechanical disturbance is introduced to a single resonator. The dynamic equation of the model can be expressed as shown in formula (1):

[0034]

[0035] In formula (1): f2 = 0, ω0 = (k / m) 1 / 2 is the first-order natural frequency of the resonator, Q is the quality factor of the system, κ is the coupling coefficient, and κ=kc / k, κ>0, δ represents the stiffness disturbance of the resonator caused by external photothermal stress, that is, δ=Δk / k.

[0036] Further analysis of the modal amplitude response of the photothermal perturbation micromechanical resonator is carried out, and the vibration dynamics equation of each resonator is modeled as f = Fe iωt Simple harmonic oscillation, where F is the excitation force amplitude, then the displacement x = Xe iωt , X is the displacement amplitude, ω is the frequency of the driving force. Substituting f1=f into formula (1), the displacement of the two resonators can be expressed as shown in formula (2):

[0037]

[0038] In formula (2), Λ is the transfer factor of the displacement function, which can be expressed as:

[0039]

[0040] The amplitude-frequency calculation curves of the first cantilever resonator 2 and the second cantilever resonator 5 under different external photothermal disturbances δ are shown in Figure 5 As shown. The negative value of δ means that when the external photothermal stress disturbance increases, the stiffness of the resonator decreases. It can be seen that when the photothermal disturbance is zero, the amplitudes of the first cantilever resonator 2 and the second cantilever resonator 5 in the first-order vibration mode or the second-order vibration mode are the same. When the photothermal disturbance increases, the modal amplitude begins to change, the first-order modal amplitude of the first cantilever resonator 2 decreases, while the second-order modal amplitude increases, indicating that the vibration energy gradually transfers from the first-order mode to the second-order mode, that is, the modal localization phenomenon occurs. For the second cantilever resonator 5, the modal amplitudes between the two modes basically remain the same in size, and tend to decrease with the increase of external disturbances. The total energy of the second resonator gradually weakens, and the energy migrates to the second-order vibration mode of the first cantilever resonator, that is, the vibration energy is confined to a specific mode of a specific resonator. This vibration modal distribution is the essential attribute of modal localization.

[0041] Since the external disturbance δ of the weakly coupled micromechanical resonant system analyzed above is caused by the temperature change of the photothermal effect, the relationship between the disturbance and the temperature change in the resonator is further studied. This temperature change causes the Young's modulus of the resonator material to change, and their mutual relationship can be expressed as shown in formula (4):

[0042]

[0043] In formula (4), TCE is the thermal conductivity, E is the Young's modulus, ΔE is the change in Young's modulus, and ΔT is the temperature change. According to Hooke's law, the relationship between the stiffness of the micromechanical resonant system and the Young's modulus is Δk / k = ΔE / E. Therefore, the stiffness perturbation in the resonator is expressed as:

[0044]

[0045] When the resonator is heated by infrared light, the heat energy Q absorbed by the resonator A Relative to the temperature rise ΔT, it can be expressed as

[0046] ΔT=Q A / c s m (6)

[0047] Where c s is the specific heat capacity of the resonator. The heat energy absorbed by the resonator can be expressed as Q A =α A *P0t, P0 is the power of infrared illumination. Therefore, we get the relationship between external disturbance and infrared illumination power, which can be expressed as follows:

[0048] δ=ΓP0 (7)

[0049] Figure 6 The relationship curve between the amplitude ratio and the illumination power of two resonators with weak coupling to each other in the first-order resonance mode and the second-order resonance mode is shown. The results show that the amplitude ratio is not linear with the illumination power. The linear detection range of the first cantilever resonator 2 in the first-order resonance mode is narrow and the detection sensitivity is poor. Therefore, the detection is selected in the second-order resonance mode. Its linear detection range is 0.5mW-2.5mW, and the linear sensing sensitivity is -4.4736 / mW. Figure 7 In contrast, based on the traditional frequency shift sensing method, its detection sensitivity S f =(Δω / ω) / P0=[(1+δ) 1 / 2 -1] / P0≈(δ / 2) / P0=Γ / 2=-0.0073 / mW, and the detection sensitivity is improved by about 613 times. This new infrared thermal detection method based on the modal localized weak coupling sensitive mechanism provides a new method for further improving the sensitivity of room temperature infrared detection.

[0050] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector, characterized in that: The detector comprises: a fixed structure, a first cantilever resonator, a second cantilever resonator, a coupling structure and a metasurface infrared absorber structure; The first cantilever resonator, the coupling structure and the second cantilever resonator are connected to the fixed structure in sequence to achieve weak coupling; there are two metasurface infrared absorber structures, the first metasurface infrared absorber structure is arranged on the upper surface of the free end of the first cantilever resonator, and the second metasurface infrared absorber structure is arranged on the lower surface of the free end of the second cantilever resonator; the metasurface infrared absorber structure includes a cross-shaped patterned array micro-nano structure, a dielectric layer, and a metal layer, the dielectric layer is respectively connected to the cross-shaped patterned array micro-nano structure and the metal layer to form a metal-dielectric-metal metasurface infrared absorber, the cross-shaped patterned array micro-nano structure is arranged on the uppermost layer of the metasurface infrared absorber structure, the dielectric layer is located in the middle layer of the metasurface infrared absorber structure, the metal layer is located in the lowermost layer of the metasurface infrared absorber structure, and the metal layer is arranged at the free end of the cantilever resonator that is not connected to the fixed structure end.

2. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 1, characterized in that: The first cantilever resonator and the second cantilever resonator have the same size, and a weak coupling effect is achieved through a coupling structure.

3. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 1, characterized in that: The metal-medium-metal supersurface infrared absorber is used to achieve coupled enhanced absorption of specific electromagnetic waves through the surface plasmon resonance effect, and convert light energy into thermal energy through the photothermal effect to form thermal stress.

4. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 3, characterized in that: The thermal stress causes the resonant mode amplitude of the resonator to change, and through the weak coupling effect, the local energy output and the amplification of the mode amplitude are achieved.

5. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 4, characterized in that: The modal amplitude change is converted into spectral energy change through a quantity transfer relationship, thereby achieving high-sensitivity detection of the infrared spectrum.

6. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 5, characterized in that: The cross-shaped patterned array micro-nano structure of the metasurface infrared absorber structure includes a number of periodic units, and one periodic unit contains two cross structures, including two first cross-shaped structures and two second cross-shaped structures. The first cross-shaped structure is composed of two rectangles with a length of a1 and a width of b1, and the two rectangles are vertically distributed; the second cross-shaped structure is composed of two rectangles with a length of a2 and a width of b2, and the two rectangles are vertically distributed.

7. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 6, characterized in that: The cross-shaped patterned array micro-nanostructure is composed of two cross-shaped structures that are cross-distributed to form a periodic unit, and a metasurface infrared absorber is formed based on the periodic arrangement of the units.

8. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 7, characterized in that: The thickness of the cross-shaped structure is 100 nm, and the structural material is titanium.

9. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 1, characterized in that: The dielectric layer is made of amorphous silicon and has a thickness of 400 nm.

10. The room temperature high-sensitivity resonant micro-electromechanical infrared thermal detector according to claim 1, characterized in that: The metal layer is made of titanium and has a thickness of 100 nm.

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