CN115000107A - Multispectral imaging chip, multispectral imaging component, preparation method and mobile terminal - Google Patents
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Abstract
The invention discloses a multispectral imaging chip, a multispectral imaging component, a manufacturing method and a mobile terminal. The chip includes: a microlens structure layer; a super-surface filter structure layer; an image detector layer; the super-surface filter structure layer comprises a protective layer, a metal grating layer, a waveguide layer and a substrate layer which are sequentially stacked from top to bottom. The invention solves the problems of large frequency spectrum offset and low light energy utilization rate in large-field-angle optical imaging, and improves the light energy utilization rate in large-field-angle scenes.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a multispectral imaging chip, a multispectral imaging component, a manufacturing method and a mobile terminal.
Background
The conventional three primary color (Red, Green, Blue, abbreviated as RGB) image sensor is mainly used for acquiring a geometric color image, but cannot acquire multispectral information due to too large spectral bandwidth and too few channels.
The spectrum imaging chip technology in the related art can simultaneously acquire a two-dimensional space image and a reflection spectrum of a detection target by arranging integration of a plurality of filter channel arrays and an image sensor.
The application of mobile terminals such as a smart phone camera is the most potential application direction of a spectral imaging chip, and can be used for developing leading-edge technology applications such as true color recovery, material identification or face recognition.
The smart phone camera head exhibition trend has two directions: the first direction is large field angle, wide field of view imaging. A large Chief Ray Angle (CRA) imaging optical path is a mainstream design in the related art, and the CRA assembled with a Micro Lens Array (MLA) can reach 30 degrees. The second direction is to capture a clear image under low illumination, and requires a high light energy utilization rate of the optical system.
In the related art, there are two common technologies for realizing paths of a spectral imaging chip: one is a Fabry-Perot (F-P) resonant interference filtering technique. The resonance transmission peak is a single peak, the transmission wavelength is adjusted by changing the thickness of the resonance cavity, for example, an F-P interference narrow-band multispectral imaging chip is directly integrated on a CMOS image sensor by Belgian microelectronic research center (IMEC); the other is a spectral calculation technology, which modulates and demodulates an incident spectrum by means of a micro-nano structure, the modulated incident spectrum is an incoherent and irregular spectrum, and the spectral reconstruction is completed by algorithms such as compressed sensing and the like, for example, the computational spectrum reconstruction is completed by adopting pore structure modulation in the case of the catalytic exercise of the Qinghua university.
In summary, the multispectral imaging chip has large spectrum deviation and low light energy utilization rate when in large-field-angle optical imaging.
Disclosure of Invention
The invention provides a multispectral imaging chip, a multispectral imaging component, a preparation method and a mobile terminal, which are used for solving the problems that in the related technology, the multispectral imaging chip has large frequency spectrum deviation and low light energy utilization rate during large-field-angle optical imaging.
According to an aspect of the present invention, there is provided a multispectral imaging chip, including: a microlens structure layer; a super-surface filter structure layer; an image detector layer; the super-surface filter structure layer comprises a protective layer, a metal grating layer, a waveguide layer and a substrate layer which are sequentially stacked from top to bottom.
Preferably, the metal grating layer comprises a two-dimensional metal grating layer; the two-dimensional metal grating layer comprises a plurality of unit structures which are formed by dividing a planar metal film into grooves.
Preferably, the transmission wavelength λ of the multispectral imaging chip is determined by the following formula:
wherein n is the refractive index of the metal grating layer, n2 is the refractive index of the waveguide layer, P is the period of the unit structure of the metal grating layer, and h is the thickness of the waveguide layer.
Preferably, a buffer layer is further included between the metal grating layer and the waveguide layer, wherein a refractive index of the buffer layer is smaller than a refractive index of the waveguide layer.
Preferably, the transmission wavelength λ of the multispectral imaging chip is determined by the following formula:
wherein n1 is the refractive index of the buffer layer, n2 is the refractive index of the waveguide layer, P is the period of the unit structure of the metal grating layer, and h is the thickness of the waveguide layer.
Preferably, the thickness of the metal grating layer ranges from 10 to 200 nm; the thickness range of the buffer layer is 0 to 500 nanometers; the waveguide layer has a thickness in the range of 10 to 500 nanometers.
According to another aspect of the invention, a multispectral imaging assembly is provided, comprising a front-end optical imaging lens and a multispectral imaging chip according to the above.
Preferably, the front end optical imaging lens includes: lenses, aperture stops, or filters.
Preferably, the reconstructed incident spectrum P of said multi-spectral imaging assembly is determined by the following formula reconstruction ：
P reconstruction ＝[(M T M+am T Q T QM) -1 M T S]T*V
Wherein the measurement matrix M is the pixel transmittance T of the nano-structure filter layer and the quantum efficiency eta of the image detector QE Product of (i.e. M ═ T ═ η - QE The Laplace matrix Q is a first-order or second-order Laplace matrix, the ideal Gaussian transformation matrix S is a constructed ideal Gaussian distribution curve, the half-peak width and the central wavelength interval of the Gaussian curve can be adjusted according to the characteristics of a spectrum channel, a smoothing factor alpha is a denoising smoothing factor item, alpha is zero when denoising is not needed, and a DN value V is a difference value between a gray value of an incident spectrum after passing through a filtering unit of the image detector and a dark noise value of the image detector under the current parameter and environment.
According to another aspect of the present invention, there is provided a method for manufacturing a multispectral imaging chip, including: depositing a layer of first medium film on the surface of a photosensitive element of an image sensor to flatten the surface of the photosensitive element to be used as a substrate layer; depositing a second medium film on the upper surface of the substrate layer to form the waveguide layer; manufacturing a groove structure of a two-dimensional transverse and/or longitudinal periodic sub-wavelength mask on the surface of the metal thin film layer to form the two-dimensional metal grating layer; depositing a third medium film on the upper surface of the metal grating layer to flatten the surface of the metal grating layer to serve as the protective layer; depositing a fourth medium film on the surface of the protective layer, and manufacturing the micro-lens structure layer by etching and other methods; the refractive index of the first dielectric film is A, the refractive index of the second dielectric film is B, the refractive index of the third dielectric film is C, and the refractive index of the fourth dielectric film is D.
Preferably, a fifth dielectric film is deposited on the upper surface of the waveguide layer to form the buffer layer, wherein the refractive index of the buffer layer is smaller than that of the waveguide layer.
Preferably, the first dielectric film, the second dielectric film, the third dielectric film and the fourth dielectric film are subjected to film deposition by one of the following methods: plasma chemical vapor deposition, magnetron sputtering, and physical vapor deposition.
Preferably, the microlens structure layer is fabricated by one of the following methods: laser direct writing, a photoresist thermal reflux etching method, a reactive ion etching method and a hot pressing film forming method.
Preferably, the multispectral imaging chip is packaged, and the packaged multispectral imaging chip is mounted on a frame to form the multispectral imaging component, wherein a front-end optical imaging lens is mounted in the frame.
According to still another aspect of the present invention, there is also provided a mobile terminal including: the multispectral chip is prepared according to the above-described preparation method, according to the above-described multispectral chip or according to the above-described multispectral imaging component.
Through the embodiment, the multispectral imaging chip comprising the micro-lens structure layer, the super-surface filtering structure layer and the image detector layer is provided, and the problems that in the related technology, the multispectral imaging chip is large in frequency spectrum deviation and low in light energy utilization rate when in large-field-angle optical imaging are solved, and the light energy utilization rate in a large-field-angle scene is improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a cross-sectional view of a multispectral imaging chip according to an embodiment of the invention;
FIG. 2 is a top view of a multispectral imaging chip according to an embodiment of the invention;
FIG. 3 is a Scanning Electron Microscope (SEM) top view of a two-dimensional metal grating of a multispectral imaging chip according to an embodiment of the invention;
FIG. 4 is a schematic diagram of the transmittance vs. wavelength for a 16-spectral multispectral imaging chip with a spectral bandwidth of 60nm according to an embodiment of the present invention;
FIG. 5 is a graph of measured transmission spectra of a set of 6 channels of a multi-spectral imaging chip at incident light angles of 0, 10, 20, and 30, respectively, according to an embodiment of the invention;
FIG. 6 is a cross-sectional view of one embodiment of a multispectral imaging chip according to an embodiment of the present invention;
FIG. 7 is a top view of a 3 × 3 mosaic filter bank according to an embodiment of the present invention;
FIG. 8 is a top view of one embodiment of filling the entire detector target surface with mosaic filter banks, according to an embodiment of the present invention;
FIG. 9 is a cross-sectional view of one embodiment of a multi-spectral imaging component according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of a spectral inversion calculation method according to an embodiment of the invention;
FIG. 11 is an input parameter S distribution diagram of an ideal Gaussian transformation matrix according to an embodiment of the spectral reconstruction algorithm according to the invention;
FIG. 12 is a set of reconstructed spectra from a spectral reconstruction algorithm applied to a 16 spectral band multi-spectral imaging component to recover 18 color patches of a color palette in accordance with an embodiment of the present invention;
FIG. 13 is a set of reconstructed spectra of a spectral reconstruction algorithm applied to a 16 spectral segment multi-spectral imaging assembly to recover narrow-band monochromatic light according to an embodiment of the present invention;
FIG. 14 is a schematic diagram of a mobile terminal according to an embodiment of the present invention;
fig. 15 is a flow chart of a method of manufacturing a multispectral imaging chip according to an embodiment of the invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
In the drawings, structurally identical elements are represented by like reference numerals, and structurally or functionally similar elements are represented by like reference numerals throughout the several views. The size and thickness of each component shown in the drawings are arbitrarily illustrated, and the present invention is not limited to the size and thickness of each component. The thickness of the components has been exaggerated in some places in the drawings where appropriate for clarity of illustration.
The present embodiment provides a multispectral imaging chip, as shown in fig. 1, including: a micro-lens structure layer 7, a super-surface filter structure layer 6 and an image detector layer 1. The super-surface filter structure layer 6 comprises a protection layer 5, a metal grating layer 4, a waveguide layer 3 and a substrate layer 2 which are stacked in sequence from top to bottom.
In the embodiment, the multispectral imaging chip comprises a microlens structure layer 7, a protective layer 5, a metal grating layer 4, a waveguide layer 3, a substrate layer 2 and an image detector layer 2 which are stacked in sequence, multispectral imaging can be achieved, the problems of the multispectral imaging chip in the related technology are solved, the multispectral imaging chip is applied in a large-field-angle scene, and the light energy utilization rate of the multispectral imaging chip in the large-field-angle scene is improved.
As a preferred embodiment, the metal grating layer may comprise a two-dimensional metal grating layer. The two-dimensional metal grating layer includes: the planar metal film is divided into a plurality of unit structures by the grooves. Preferably, the adjustment and control of the transmission wavelength can be realized by changing the period P of the unit structure of the metal grating layer.
As another preferred embodiment, the transmission wavelength λ of the multispectral imaging chip is determined by the following formula:
wherein n is the refractive index of the metal grating layer, n2 is the refractive index of the waveguide layer, P is the period of the unit structure of the metal grating layer, and h is the thickness of the waveguide layer. In the preferred embodiment, the transmission wavelength λ can be adjusted by adjusting parameters of the metal grating layer and the waveguide layer. For example, in some special scene applications, the multispectral mosaic image shot by the multispectral imaging component can be used for performing various functional applications such as material identification and face recognition by setting an infrared spectrum segment (by adjusting the transmission wavelength to the infrared spectrum segment). For example, a 940nm waveband spectrum channel is adopted for face recognition, so that disguised attack means such as a dummy and a photo can be effectively prevented. The near-infrared imaging can be used for detecting living bodies through infrared light reflectivity of different materials, and has strong defense capability against attacks of screen videos, photos, dummy molds and the like.
As another preferred embodiment, a buffer layer may be further included between the metal grating layer and the waveguide layer. By the preferred embodiment, the metal grating layer can be prevented from being oxidized by air, and the service life of the multispectral imaging chip is prolonged; the groove and gap of the metal grating layer can be filled, so that the micro-lens structure layer can be conveniently manufactured on the filter layer. Preferably, the buffer layer may have a refractive index less than that of the waveguide layer. With this preferred embodiment, a grating/waveguide coupled filter structure can be constructed. The incident light passes through the super-surface filter structure layer to generate a resonance filter effect, and a transmission peak with adjustable bandwidth is formed.
The thickness of the buffer layer has a large influence on the transmission spectrum bandwidth, the buffer layer has a thickness range of 0-500nm, and it should be noted that the thicker the buffer layer is, the narrower the bandwidth is.
Preferably, the material refractive index of the buffer layer (refractive index of the buffer layer) is lower than the material refractive index of the waveguide layer (refractive index of the waveguide layer). The material of the buffer layer may include one or a combination of SiO2, MgF2, Al2O 3.
Preferably, the adjustment and control of the transmission wavelength can be realized by changing the period P of the unit structure of the metal grating layer. As another preferred embodiment, the transmission wavelength λ of the multispectral imaging chip can be determined by the following formula:
wherein n1 is the refractive index of the buffer layer, n2 is the refractive index of the waveguide layer, P is the period of the unit structure of the metal grating layer, and h is the thickness h of the waveguide layer. In practice, the refractive index and/or P may be adjusted to select the transmission wavelength (wavelength of the incident wave) first. The bandwidth control of the transmission spectrum can be controlled by varying the thickness of the waveguide layer. A buffer layer of low refractive index medium may also be inserted between the metal grating layer and the waveguide layer to further tune the bandwidth (wavelength) of the transmitted spectrum. For example, in some special scene applications, the multispectral mosaic image shot by the multispectral imaging component can be further completed by setting infrared spectral bands (by adjusting the transmission wavelength to the infrared spectral band)And multiple functional applications such as substance identification and face recognition. For example, a 940nm waveband spectrum channel is adopted for face recognition, so that disguised attack means such as a dummy and a photo can be effectively prevented. The near-infrared imaging can be used for detecting living bodies through infrared light reflectivity of different materials, and has strong defense capability against attacks of screen videos, photos, dummy molds and the like.
As another preferred embodiment, the thickness of the metal grating layer ranges from 10 to 200 nm; the thickness range of the buffer layer is 0 to 500 nanometers; the thickness of the waveguide layer ranges from 10 to 500 nanometers.
As another preferred embodiment, the reconstructed incident spectrum P of the multispectral imaging chip can be determined by the following formula reconstruction ：
P reconstruction ＝[(M T M ten alpha M T Q T QM) -1 M T S] T V. Wherein, the measurement matrix M is the pixel transmittance T of the nano-structure filter layer and the quantum efficiency eta of the image detector QE Product of (i.e. M ═ T ═ η - QE The Laplace matrix Q is a first-order or second-order Laplace matrix, the ideal Gaussian transformation matrix S is an ideal Gaussian distribution curve which is constructed, the half-peak width and the central wavelength interval of the Gaussian curve can be adjusted according to the spectral channel characteristics, the smoothing factor alpha is a denoising smoothing factor item, alpha is zero when denoising is not needed, and the DN value V is the difference value between the gray value of an incident spectrum after passing through a filtering unit of the image detector and the dark noise value of the image detector under the current parameter and environment. The preferred embodiment enables the reconstruction of the spectrum.
The embodiment provides a multispectral imaging component, which comprises a front-end optical imaging lens and the multispectral imaging chip in the above embodiment and the preferred implementation manner thereof.
As a preferred embodiment, the front end optical imaging lens may include: lenses, aperture stops, or filters. The front-end optical imaging lens in the preferred mode can select different lenses according to different applications. It should be noted that the description in this application is only for example and should not be construed as limiting the present application.
Preferably, the reconstructed incident spectrum P of the multispectral imaging component can be determined by the following formula reconstruction ：P reconstruction ＝[(M T M ten alpha M T Q T QM) -1 M T S] T V. Wherein, the measurement matrix M is the pixel transmittance T of the nano-structure filter layer and the quantum efficiency eta of the image detector QE Product of (i.e. M ═ T ═ η - QE The Laplace matrix Q is a first-order or second-order Laplace matrix, the ideal Gaussian transformation matrix S is an ideal Gaussian distribution curve which is constructed, the half-peak width and the central wavelength interval of the Gaussian curve can be adjusted according to the spectral channel characteristics, the smoothing factor alpha is a denoising smoothing factor item, alpha is zero when denoising is not needed, and the DN value V is the difference value between the gray value of an incident spectrum after passing through a filtering unit of the image detector and the dark noise value of the image detector under the current parameter and environment.
In the related technology, both the F-P cavity interference filtering technology and the spectrum calculating technology have strong sensitivity to incident angles, transmission spectrums can drift along with incident angles, the spectrum frequency shift is larger when the incident angle is larger, the transmission spectrums at different view field positions are different, so that different view field pixel spectrum reconstruction algorithms are different, the reconstruction algorithms are difficult, the spectrum reconstruction precision is seriously influenced, and the method is not suitable for large-field-angle optical imaging. The preferred embodiment solves the technical problem, realizes the reconstruction of the spectrum, and is suitable for large-field-angle optical imaging.
The present embodiment provides a method for manufacturing a multispectral imaging chip, as shown in fig. 15, including the following steps S1502 to S1510.
Step S1502 is depositing a first dielectric film on the surface of the photo-sensor of the image sensor to planarize the surface of the photo-sensor as a base layer.
And step S1504, sequentially depositing second medium films on the upper surface of the substrate layer to form a waveguide layer.
Step S1506, a two-dimensional metal grating layer is formed by fabricating a trench structure of a two-dimensional transverse and/or longitudinal periodic sub-wavelength mask on the surface of the metal thin film layer.
Step S1508, depositing a third dielectric film on the upper surface of the metal grating layer to planarize the surface of the metal grating layer as a protection layer.
Step S1510, depositing a fourth dielectric film on the surface of the protection layer, and fabricating a microlens structure layer by an etching method.
The refractive index of the first medium film is A, the refractive index of the second medium film is B, the refractive index of the third medium film is C, and the refractive index of the fourth medium film is D.
Through the steps, the preparation of a plurality of layers of the multispectral imaging chip is realized.
As another preferred embodiment, a fifth dielectric film is deposited on the upper surface of the waveguide layer to form a buffer layer, wherein the buffer layer has a refractive index smaller than that of the waveguide layer. With the present preferred embodiment, the bandwidth control of the transmission spectrum can be controlled by changing the thickness of the waveguide layer. A buffer layer of low refractive index medium may also be inserted between the metal grating layer and the waveguide layer to further tune the bandwidth (wavelength) of the transmitted spectrum. Preferably, the transmission wavelength λ of the multispectral imaging chip can be determined by the following formula:
As a preferred embodiment, the first dielectric film, the second dielectric film, the third dielectric film and the fourth dielectric film may be deposited by one of the following methods: plasma chemical vapor deposition, magnetron sputtering, and physical vapor deposition. By the preferred embodiment, the thin film deposition can be carried out in various ways.
As another preferred embodiment, the microlens structure layer is fabricated by one of the following methods: laser direct writing, a photoresist thermal reflux etching method, a reactive ion etching method and a hot pressing film forming method. By the preferred embodiment, the microlens structure layer is fabricated by a variety of process methods.
Preferably, the multispectral imaging chip is packaged, and the packaged multispectral imaging chip is mounted on a frame to form a multispectral imaging component, wherein a front-end optical imaging lens is mounted in the frame. The preferred embodiment enables the preparation of a multispectral imaging component.
The embodiment provides a mobile terminal, including: according to the multispectral chip in the above examples and preferred embodiments thereof or according to the multispectral imaging component in the above examples and preferred embodiments thereof, the multispectral chip is prepared according to the above preparation method.
Example 1
The present embodiment provides a multispectral imaging chip, fig. 1 is a cross-sectional view of a multispectral imaging chip according to an embodiment of the present invention, and fig. 2 is a top view of a multispectral imaging chip according to an embodiment of the present invention. As shown in fig. 1 and fig. 2, the multispectral imaging chip 101 includes: the micro-lens structure layer 7, the protective layer 5, the metal grating layer 4, the waveguide layer 3, the substrate layer 2 and the image detector layer 1 are stacked in sequence from top to bottom, wherein the protective layer 5, the metal grating layer 4, the waveguide layer 3 and the substrate layer 2 can form a super-surface filter structure layer 6. A buffer layer 8 of low refractive index medium may also be interposed between the metal grating layer 4 and the waveguide layer 3.
In this embodiment, the microlens structure layers 7 may be arranged in a hexagonal or tetragonal array.
As a preferred embodiment, the multispectral imaging chip may include a protective layer. By the preferred embodiment, the metal grating layer can be prevented from being oxidized by air, and the service life of the multispectral imaging chip is prolonged; the groove and gap of the metal grating layer can be filled, so that the micro-lens structure layer can be conveniently manufactured on the filter layer.
As another preferred embodiment, in the super-surface filter structure layer, the refractive index of the material of the waveguide layer is higher than the refractive indices of the materials of the protective layer and the substrate layer. With this preferred embodiment, a grating/waveguide coupled filter structure can be constructed. The incident light passes through the super-surface filter structure layer to generate a resonance filter effect, so that a transmission peak with adjustable bandwidth is formed, and the regulation and control of the transmission wavelength can be realized by changing the period of the metal grating layer.
In this embodiment, the metal grating layer may be a two-dimensional metal grating layer (two-dimensional periodic structure). The two-dimensional periodic structure may be a rounded square or a cylinder. Fig. 3 is a top view of a Scanning Electron Microscope (SEM) of a two-dimensional metal grating of a multispectral imaging chip according to an embodiment of the present invention, and as shown in fig. 3, the side length/period duty ratio of the periodic structure in the metal grating layer can be selectively adjusted within a range from 0.5 to 0.9.
In this embodiment, the bandwidth of the transmission spectrum is in the range of 40-80 nm. The bandwidth control of the transmission spectrum can be controlled by changing the thickness of the waveguide layer. A buffer layer of low refractive index medium may also be inserted between the metal grating layer and the waveguide layer to further adjust the bandwidth.
The transmission peak wavelength of the multispectral imaging chip can form different wavelength spectrum channels by changing the period P of the unit structure of the metal grating layer. Fig. 4 is a schematic diagram of "transmittance-wavelength" of a 16-spectral-band multispectral imaging chip with a spectral bandwidth of-60 nm according to an embodiment of the present invention, as shown in fig. 4, the spectral bandwidth of the multispectral imaging chip is 16-spectral-band of-60 nm, and the 16 spectral-bands correspond to periods P of unit structures of different metal grating layers, where the transmission spectrum covers a visible light interval of 400-750 nm.
Fig. 5 is an actually measured transmission spectrum diagram of a group of 6 channels of the multispectral imaging chip according to the embodiment of the present invention under incident light angles of 0 °, 10 °, 20 °, and 30 °, as shown in fig. 5, the peak wavelength of the curve is counted through actual tests, and the average spectrum frequency shift amount of the incident light of 30 ° compared with 0 ° of the 6 channels is only 4nm, where θ is the incident light angle, and 101 is the multispectral imaging chip. Through simulation comparison, in an F-P interference filtering structure and a calculated spectrum structure in the related art, the spectral frequency shift amount is usually 25nm under 30 degrees compared with 0 degrees of incident light. As can be seen from the above, the multispectral imaging chip in this embodiment and its preferred embodiments has a low sensitivity to incident angles, and can be applied to large-field optical imaging.
Preferably, the material of the microlens structure layer may include one or more of Si3N4, TiO2, ZnS, ZnSe, Nb2O5, GaN.
Preferably, the material of the protective layer may comprise a low refractive index material, for example: SiO2, MgF2, Al2O3 and SiON.
Preferably, the material of the metal grating layer may include one or a combination of more of Au, Ag, Al, Pt, Cu, Cr, Sn; the waveguide layer material may comprise one or a combination of more of Si3N4, TiO2, ZnS, ZnSe, Nb2O5, Ta2O5, ZnO, WO3, V2O5, MoO3, GaN.
The material of the substrate layer may include SiO2 or MgF 2; or a combination of the two.
In this embodiment, the image detector may convert the optical signal into an electrical signal, and the working mechanism is that polychromatic light irradiates the microlens structure layer to be focused, the light is decomposed into light of different wavelength bands when passing through the super-surface filter structure layer, the light of different wavelength bands is converged on the photosensitive element surface of the image sensor, and then the image sensor converts the optical signal into an electrical signal DN value, and the obtained electrical signal can be restored into patterns of various colors on various electronic devices. The image sensor used in the above process may be a Charge-coupled Device (CCD) or a Complementary Metal Oxide Semiconductor (CMOS). The CCD can change light rays into electric charges, store and transfer the electric charges, and can also take out the stored electric charges to change voltage; a CMOS image sensor is a typical solid-state image sensor, and has a common historical source with a CCD. The CMOS image sensor generally comprises several parts, such as an image sensing cell array, a row driver, a column driver, a timing control logic, an AD converter, a data bus output interface, and a control interface, which can be integrated on the same silicon chip, and the working process of the CMOS image sensor can be generally divided into a plurality of parts, such as reset, photoelectric conversion, integration, and readout.
Example 2
The embodiment provides a multispectral imaging chip. Fig. 6 is a cross-sectional view of an embodiment of the multispectral imaging chip according to the embodiment of the present invention, as shown in fig. 6, based on the structure of the multispectral imaging chip of embodiment 1, in this embodiment, a filter layer design scheme of the multispectral imaging chip is inserted with a buffer layer, and a dielectric buffer layer 8 is inserted between the metal grating layer 4 and the waveguide layer 3, where the multispectral chip includes: the optical waveguide grating structure comprises an image detector layer 1, substrate layers 2 and 3, a waveguide layer, a metal grating layer 4, a protective layer 5, a super-surface filter structure layer 6, a micro-lens structure layer 7 and a buffer layer 8.
The thickness of the buffer layer has a large influence on the transmission spectrum bandwidth, the buffer layer has a thickness range of 0-500nm, and it should be noted that the thicker the buffer layer is, the narrower the bandwidth is.
Preferably, the buffer layer has a material refractive index lower than that of the waveguide layer. The material of the buffer layer may include one or a combination of SiO2, MgF2, Al2O 3.
In this embodiment, the transmission wavelength λ of the multispectral imaging chip is determined by the refractive index n1 of the buffer layer, the refractive index n2 of the waveguide layer, the period P of the unit structure of the metal grating layer, and the thickness h of the waveguide layer, and the transmission wavelength can be adjusted by changing the period of the metal grating layer, where the above parameters may satisfy the following relation:
example 3
In this embodiment, a metal grating layer in a super-surface filter structure layer is composed of two-dimensional periodic structure units, multiple mosaic filter groups are repeatedly arranged in the two-dimensional filter structure, and each mosaic filter group in the multiple mosaic filter groups may be filled with a two-dimensional periodic unit structure array with a different period. These two-dimensional periodic unit structures can be set to different periods according to the characteristics and wave bands of different multispectrals of the split light, so as to adapt to the incidence of light with different wavelengths.
Fig. 7 is a top view of a 3 × 3 mosaic filter group according to an embodiment of the present invention, the inside of the mosaic filter group is filled with a two-dimensional periodic structure array, as shown in fig. 7, the mosaic filter group is a 3 × 3 nine-grid arrangement, which is divided into C1, C2, C3, C4, C5, C6, C7, C8, and C9, and the period P of the two-dimensional periodic unit structure array may gradually increase with C1-C9. In a mosaic filter group, C1-C9 represent 9 different filter units, and correspond to 9 different peak wavelength transmission spectra, and DN values of 9 points are processed and calculated by a spectrum reconstruction algorithm to restore incident multi-spectra.
It should be noted that the mosaic filter group or the nine-grid arrangement in the preferred embodiment is only for illustration. Those skilled in the art can select other arrangement modes of multispectral imaging chip arrangement in the related art according to the actual situation of the recovered multispectral. Fig. 8 shows the repeated arrangement of the 3 × 3 mosaic filter sets shown in fig. 7 on the surface of the image detector, and the two-dimensional periodic structure array fills the entire target surface of the image detector.
Example 4
The embodiment provides a method for preparing a multispectral imaging chip, which can comprise the following steps:
s02: a medium film with lower refractive index is deposited on the surface of a photosensitive element of the image sensor to flatten the surface and serve as a substrate layer.
S04: and sequentially depositing a waveguide layer and a metal thin film layer on the upper surface of the substrate layer.
In this embodiment, preferably, the material of the substrate layer may be one or a combination of two of SiO2 and MgF 2.
In practice, the deposition method in the related art can be adopted by those skilled in the art, such as: plasma chemical vapor deposition, magnetron sputtering, or physical vapor deposition. It should be noted that the present example is only for illustration and is not intended to limit the present application.
Preferably, the metal thin film layer material can be one or more of Au, Ag, Al, Pt, Cu, Cr and Sn;
preferably, the material of the waveguide layer may include: si3N4, TiO2, ZnS, ZnSe, Nb2O5, Ta2O5, ZnO, WO3, V2O5, MoO3 and GaN.
S06: and manufacturing a two-dimensional periodic structure on the surface of the metal thin film layer by methods such as photoetching and etching to form the metal grating layer.
In this step, the method of fabricating the two-dimensional metal grating structure may include: one of electron beam exposure, ion beam exposure, X-ray exposure, deep ultraviolet exposure, or nano imprint; the etching method may include: is one of sputter etching, reactive ion etching, inductively coupled plasma etching or laser ablation.
In this embodiment, the two-dimensional periodic unit structures are periodically distributed, and the arrangement mode is hexagonal or tetragonal arrangement; the structural unit is a square block, a round corner square block or a cylinder; the duty ratio of the side length/period of the two-dimensional periodic structure is 0.5-0.9.
S08: and depositing a layer of low-refractive-index medium on the surface of the metal grating layer to serve as a protective layer and flattening the surface.
Preferably, the deposition method comprises: electron beam evaporation, thermal evaporation or magnetron sputtering.
Preferably, the thickness range of the waveguide layer includes: 10nm to 500 nm; the thickness range of the metal layer includes: 10nm to 200 nm.
S10: and depositing a medium film with a higher refractive index on the surface of the protective layer, and manufacturing the micro-lens structure layer by etching and other methods.
S12: and (4) slicing and packaging the structure to prepare the multispectral imaging chip.
In the present embodiment, the protective layer may be one of low refractive index materials such as SiO2, MgF2, Al2O3, and the like. By the scheme of the embodiment, the metal grating on the surface of the chip can be protected from being oxidized or damaged by the external environment; the groove gap of the super-surface filter structure layer can be filled, and subsequent processing of the micro-lens structure layer is facilitated.
Preferably, the dielectric thin film material with a higher refractive index adopted by the microlens structure layer can be one of Si3N4, TiO2, ZnS, ZnSe, Nb2O5 and GaN; the thickness of the micro-lens structure layer is deposited to enable the focus of incident light converged by the micro-lens array to be located on the focal plane of the image sensor.
Preferably, the thin film deposition method includes: plasma chemical vapor deposition, magnetron sputtering, or physical vapor deposition. The arrangement mode of the micro lens array is hexagonal or tetragonal arrangement.
Preferably, the method for manufacturing the microlens structure layer may be any one or a combination of two or more of laser direct writing, a photoresist thermal reflow etching method, a reactive ion etching method and a hot compression molding method.
Example 5
The present embodiment provides a multispectral imaging component, and the technical solution of the present embodiment includes the multispectral imaging chip in embodiments 1 to 4 and the preferred implementation manner thereof. Fig. 9 is a cross-sectional view of one embodiment of a multispectral imaging component 201, as shown in fig. 9, in accordance with an embodiment of the present invention, comprising: the multispectral imaging device comprises a multispectral imaging chip 101 and a front-end optical imaging lens 11, wherein a mirror bracket 12 is fixedly arranged on the upper surface of the multispectral imaging chip, and the mirror bracket 12 is assembled with the front-end optical lens 11 to form a multispectral imaging component.
In the multispectral imaging chip in the multispectral imaging component, the mosaic group filter array is tiled periodically across the entire surface of the image detector.
As a preferred embodiment, the front end optical imaging lens may include, but is not limited to, a combination of optical elements such as lenses, aperture stops, and filters. By the preferred embodiment, the incident light rays are converged, and the imaging point is positioned on the photosensitive element surface of the multispectral imaging chip. Preferably, the optical lens may adopt a wide-angle imaging lens with a large field angle.
The optical filter in the front-end optical imaging lens in this embodiment may be a bandpass filter, and functions to filter photon interference outside a target spectrum coverage range, and provide recovery accuracy of a spectrum in a current operating band range.
Example 6
The embodiment provides a spectrum reconstruction method, which can be used in a spectrum reconstruction step in a multispectral imaging component, is used as a data processing algorithm for matching, can perform spectrum reconstruction calculation on a signal DN value acquired by the multispectral imaging component, and can invert a reflection spectrum curve of a detection target with high precision.
Fig. 10 is a flowchart of a spectrum inversion calculation method according to an embodiment of the present invention, as shown in fig. 10, a power spectrum of incident light entering a multispectral imaging component is x (λ), the incident light passes through a front-end optical imaging lens and then irradiates a microlens structure layer to be focused, light is decomposed into light of different wavelength bands when passing through a super-surface filter structure layer, the light of different wavelength bands is converged on a photosensitive element surface of an image sensor, and then the image sensor converts an optical signal into an electrical signal DN value.
The incident light power spectrum and the measurement matrix have the following relational expression: m x z (λ) ═ V.
The spectral reconstruction process inverts x (λ) knowing M and V. The spectral wavelength is used as an unknown number, the number of the unknown number is far larger than the number of channels of the multispectral imaging chip, and the equations can be solved into an underdetermined equation set.
Wherein, the measurement matrix M is the pixel transmittance T of the nano-structure filter layer and the quantum efficiency eta of the image detector QE Product of (i.e. M ═ T ═ η - QE And performing spectrum calibration test on the multispectral imaging component to obtain a measurement matrix M (calibration DN-dark noise of each channel)/calibration light source power spectrum.
The spectral reconstruction algorithm is based on a Wiener-Hough (Wiener-Hopf) filtering equation, a noise smoothing factor item is added, and a linear projection algorithm is adopted to carry out regularized spectral reconstruction estimation based on the principle of least square.
The spectrum reconstruction algorithm can comprise five input parameters including a measurement matrix M, a Laplace matrix Q, an ideal Gaussian transformation matrix S, a smoothing factor alpha and a detector DN value V.
The spectral reconstruction algorithm has the calculation formula as follows:
P reconstruction ＝[(M T M+aM T Q T QM) -1 M T S] T v. Wherein, P reconstruction For reconstruction of the incident spectrum, dimension nn 1; measuring a matrix M, dimension M n; q is a laplace matrix, dimension m; alpha is flatA slip factor; s is an ideal Gaussian transformation matrix, and dimension m is nn; v is the value DN of the signal collected by the multispectral imaging component, and the dimension n is 1. Wherein M is the number of spectral wavelength points of the measurement matrix M, n is the number of filter channels of the multispectral imaging chip, and nn is the number of reconstruction wavelength points.
The laplacian matrix Q is a first or second order laplacian matrix, wherein the first order laplacian matrix is:
a second order Laplace matrix of
As shown in fig. 11, the ideal gaussian transformation matrix S is an ideal gaussian distribution curve, and the half-peak width and the center wavelength interval of the gaussian curve can be adjusted according to the calculation requirement.
The smoothing factor alpha is a denoising smoothing factor item, alpha is zero when denoising is not needed, the larger the alpha value is, the smoother the reconstructed spectrum curve is, but the fineness of the reconstructed spectrum is reduced, and the specific value of alpha needs to be assigned in combination with the environment characteristics of the reconstructed spectrum and the application needs.
And the DN value V is a gray value acquired by the detector after the incident light passes through the super-surface filter structure layer, and the current parameter and the dark noise value of the detector under the environment need to be subtracted.
Fig. 12 shows the application of the spectrum reconstruction algorithm to the 16-spectral multispectral imaging component, and the spectrum reconstruction results of 18 color patches in the color chart restored by the spectrum reconstruction algorithm are compared with the test spectrum of the standard spectrometer, and the similarity between the two is up to 93%, as shown in fig. 12, the light-color straight line-spectrometer actually measured reference spectrum curve and the black point line-spectrum reconstruction algorithm restore the spectrum curve.
Fig. 13 shows a set of reconstructed spectra of narrowband monochromatic light recovered using a spectral reconstruction algorithm applied to a 16-spectral-band multi-spectral imaging component. As shown in fig. 13, the straight line is the reference spectrum curve measured by the spectrometer, and the dotted line is the spectrum curve restored by the spectrum reconstruction algorithm. The reference narrow-band monochromatic light spectrum bandwidth actually measured by the spectrometer is 5-6 nm, and the bandwidth is far smaller than the resolution of the multispectral chip, so that the multispectral imaging component can be identified as monochromatic light. And performing Gaussian fitting on the spectral curve restored by the spectral reconstruction algorithm, wherein the full width at half maximum (FWHM) of the reconstructed spectral curve of Gaussian fitting represents the spectral resolution of the multispectral imaging component. Through experimental test statistics, the average FWHM of the reconstructed monochromatic spectrum can optimally reach 18 nm.
Although for the design of a wide-spectrum multispectral imaging chip, spectrum aliasing exists between different spectrum channels, spectrum crosstalk can be caused, and the spectrum recovery precision is influenced. However, the spectral reconstruction algorithm provided by the invention can effectively inhibit spectral crosstalk among different channels and greatly improve the resolution and precision of a recovered spectrum, and the spectral resolution reconstructed by the multispectral imaging chip is less than 20nm through actual test and is far lower than the 60nm transmission spectral bandwidth of a filtering channel of the multispectral imaging chip.
Therefore, the multispectral imaging chip in the application is combined with the spectrum reconstruction algorithm in the application, so that the multispectral imaging chip with a wide spectrum not only can exert the advantage of high light energy utilization rate, but also can realize high spectral resolution and high-precision spectrum inversion by adopting the algorithm.
Example 7
As shown in fig. 14, the mobile terminal 13 may include the multispectral imaging chip and the multispectral imaging component 201 in the foregoing embodiments and preferred embodiments thereof, and the multispectral imaging component 201 may serve as one of a plurality of camera components in the mobile terminal, and converts an external optical signal into an electronic signal that can be recognized by the mobile terminal, so as to implement functions of snapshot-type photographing, and the like. On the basis of the photographed image, the multispectral mosaic image photographed by the multispectral imaging component can be used for assisting the images, such as RGB, RYYB and the like photographed by the main camera to complete true color recovery. On the other hand, the multispectral mosaic image shot by the multispectral imaging component can more accurately find a white point and acquire the ambient color temperature through spectral imaging analysis, so that the color image shot by the main camera is assisted to complete a white balance correction function, the color cast phenomenon caused by the ambient color temperature is removed, and the original color display of the object is recovered.
As a better implementation mode, the multispectral mosaic image shot by the multispectral imaging component can be used for completing various functional applications such as material identification, face recognition and the like by setting an infrared spectrum section. For example, a 940nm waveband spectrum channel is adopted for face recognition, so that camouflage attack means such as a dummy and a photo can be effectively prevented. The near-infrared imaging can be used for detecting living bodies through infrared light reflectivity of different materials, and has strong defense capability against attacks of screen videos, photos, dummy molds and the like.
It should be noted that the mobile terminal includes, but is not limited to: cell-phone, notebook, panel computer, unmanned aerial vehicle, wearable equipment (like intelligent wrist-watch, intelligent bracelet, intelligent glasses, intelligent helmet etc.), head display equipment, virtual reality equipment, car etc.. The mobile terminal can be an intelligent mobile terminal device or a non-intelligent mobile terminal device, and the mobile terminal can have a communication function or not. The mobile terminal applies the multispectral imaging chip and the imaging component, or applies the spectrum reconstruction method in the above embodiment and the preferred embodiment thereof in the spectrum recovery step. The multispectral imaging chip and the imaging component in the embodiment and the preferred embodiment thereof can be applied to optical imaging in a large-field-angle and low-illumination environment, can be arranged in various mobile terminals for use, can further expand the application functions of the mobile terminals by applying the multispectral imaging chip and the imaging component, can greatly reduce the cost of the mobile terminals, and improve the efficiency.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
In summary, the embodiments and the preferred embodiments thereof provide a multispectral imaging chip, a multispectral imaging assembly and a manufacturing method thereof.
Compared with the prior art, the multispectral imaging chip has the following advantages:
1) the multispectral channel adopts a wide-spectrum design, the transmission spectrum bandwidth is designed to be 40-80nm, the transmittance is high, the luminous flux is large, the light energy utilization rate is high, and compared with the existing narrow-band design technology, the imaging advantage is obvious in a low-illumination environment;
2) by matching with the spectral reconstruction algorithm provided by the invention, the reconstruction spectral resolution can be greatly improved by adopting the regularization unmixing filtering reconstruction, and the average spectral resolution of the actually measured 16-channel spectral imaging chips is less than 20 nm.
3) The large-angle incident spectrum has small frequency shift and low incident angle sensitivity, and can be applied to large-field optical imaging. Actually measuring the peak spectral frequency shift quantity of 30-degree and 0-degree incident lights to be less than 5 nm. However, the existing F-P interference filtering technology and the existing spectrum calculating technology simulate the peak spectrum frequency shift quantity of 30-25 nm of incident light and 0-degree incident light. As can be seen by comparison, the multispectral imaging chip in the technical scheme of the application has extremely low incident angle sensitivity. In addition, the method can further perform targeted structure compensation design on the marginal field area with small frequency shift amount, so that the purpose of realizing no frequency shift of the full field area is achieved. Therefore, the same spectrum reconstruction algorithm can be adopted for full-field-of-view imaging, so that the spectrum reconstruction robustness is higher, the spectrum reconstruction precision is high, the method can be used for large-field-angle optical imaging, and the application range is wide.
In summary, the multispectral imaging chip in the application has low angular sensitivity, and has high light energy utilization rate and high spectral resolution, so that the problem that a conventional RGB detector cannot collect spectra is solved, the problem that the spectral resolution and the light energy utilization rate of a spectral imaging chip technology in the related technology cannot be obtained simultaneously is also solved, and the technical bottleneck that the application of a large field angle is limited due to the strong angular sensitivity of the current spectral imaging chip is particularly solved.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (16)
1. A multispectral imaging chip, comprising:
a microlens structure layer;
a super-surface filter structure layer;
an image detector layer;
the super-surface filter structure layer comprises a protective layer, a metal grating layer, a waveguide layer and a substrate layer which are sequentially stacked from top to bottom.
2. The multispectral imaging chip of claim 1,
the metal grating layer comprises a two-dimensional metal grating layer; the two-dimensional metal grating layer comprises a plurality of unit structures which are formed by dividing a planar metal film into grooves.
3. The multispectral imaging component of claim 1,
the transmission wavelength lambda of the multispectral imaging chip is determined by the following formula:
wherein n is the refractive index of the metal grating layer, n2 is the refractive index of the waveguide layer, P is the period of the unit structure of the metal grating layer, and h is the thickness of the waveguide layer.
4. The multispectral imaging chip of claim 1,
and a buffer layer is also arranged between the metal grating layer and the waveguide layer, wherein the refractive index of the buffer layer is less than that of the waveguide layer.
5. The multispectral imaging component of claim 4,
the transmission wavelength lambda of the multispectral imaging chip is determined by the following formula:
wherein n1 is the refractive index of the buffer layer, n2 is the refractive index of the waveguide layer, P is the period of the unit structure of the metal grating layer, and h is the thickness of the waveguide layer.
6. The multispectral imaging chip according to any one of claims 1 to 5,
the thickness range of the metal grating layer is 10-200 nanometers;
the thickness range of the buffer layer is 0 to 500 nanometers;
the waveguide layer has a thickness in the range of 10 to 500 nanometers.
7. The multispectral imaging chip according to any one of claims 1 to 5, wherein the reconstructed incident spectrum P of the multispectral imaging chip is determined by the following formula reconsttuction ：
P reconstruction ＝[(M T M+αM T Q T QM) -1 M T S] T *V
Wherein the measurement matrix M is the pixel transmittance T of the nano-structure filter layer and the quantum efficiency eta of the image detector QE Product of (i.e. M ═ T ═ η - QE The Laplace matrix Q is a first or second order Laplace matrix, and the ideal Gaussian transformation matrix S is a structureThe half-peak width and the central wavelength interval of the Gaussian curve can be adjusted according to the characteristics of the spectral channel, the smoothing factor alpha is a denoising smoothing factor item, alpha is zero when denoising is not needed, and the DN value V is the difference value between the gray value of the incident spectrum after passing through the filtering unit of the image detector and the dark noise value of the image detector under the current parameter and environment.
8. A multispectral imaging assembly comprising a front-end optical imaging lens and a multispectral imaging chip according to any one of claims 1 to 7.
9. The multispectral imaging component of claim 8, wherein the front-end optical imaging lens comprises: a lens, an aperture stop, or a filter.
10. The multispectral imaging component of claim 8 or 9, wherein the reconstructed incident spectrum P of the multispectral imaging component is determined by the formula reconstruction ：
P reconstruction ＝[(M T M+αM T Q T QM) -1 M T S] T *V
Wherein the measurement matrix M is the pixel transmittance T of the nano-structure filter layer and the quantum efficiency eta of the image detector QE Product of (i.e. M ═ T ═ η - QE The Laplace matrix Q is a first-order or second-order Laplace matrix, the ideal Gaussian transformation matrix S is a constructed ideal Gaussian distribution curve, the half-peak width and the central wavelength interval of the Gaussian curve can be adjusted according to the characteristics of a spectrum channel, a smoothing factor alpha is a denoising smoothing factor item, alpha is zero when denoising is not needed, and a DN value V is a difference value between a gray value of an incident spectrum after passing through a filtering unit of the image detector and a dark noise value of the image detector under the current parameter and environment.
11. A method for preparing a multispectral imaging chip is characterized by comprising the following steps:
depositing a layer of first medium film on the surface of a photosensitive element of an image sensor to flatten the surface of the photosensitive element to serve as a substrate layer;
depositing a second medium film on the upper surface of the substrate layer to form the waveguide layer;
manufacturing a groove structure of a two-dimensional transverse and/or longitudinal periodic sub-wavelength mask on the surface of the metal thin film layer to form a two-dimensional metal grating layer;
depositing a third medium film on the upper surface of the metal grating layer to flatten the surface of the metal grating layer as a protective layer;
depositing a fourth medium film on the surface of the protective layer, and manufacturing the micro-lens structure layer by etching and other methods;
the refractive index of the first dielectric film is A, the refractive index of the second dielectric film is B, the refractive index of the third dielectric film is C, and the refractive index of the fourth dielectric film is D.
12. The production method according to claim 11,
and depositing a fifth medium film on the upper surface of the waveguide layer to form the buffer layer, wherein the refractive index of the buffer layer is less than that of the waveguide layer.
13. The production method according to claim 11 or 12,
the first dielectric film, the second dielectric film, the third dielectric film and the fourth dielectric film are subjected to film deposition in one of the following modes:
plasma chemical vapor deposition, magnetron sputtering, and physical vapor deposition.
14. The production method according to claim 11 or 12,
the micro-lens structure layer is manufactured in one of the following modes:
laser direct writing, a photoresist thermal reflux etching method, a reactive ion etching method and a hot pressing film forming method.
15. The production method according to claim 1 or 12,
and packaging the multispectral imaging chip, and mounting the packaged multispectral imaging chip on a mirror bracket to manufacture the multispectral imaging component, wherein the mirror bracket is internally provided with a front-end optical imaging lens.
16. A mobile terminal, comprising: the multispectral chip according to any one of claims 1-7 or the multispectral imaging component according to any one of claims 8-10, the multispectral chip being prepared according to the method of preparation of claims 11-15.
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