JP4111288B2 - Wavelength selective photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a wavelength selecting detector which is small-sized, increases integration, and is superior in a wavelength distribution power to enhance characteristics of an optical system by providing drive means for variable-controlling a distance apart from first and second distributing Bragg reflectors. SOLUTION: First, a photodiode 5 is formed on a silicon substrate 1, and a lower DBR (lower distributing Bragg reflector) 11 and an upper DBR (upper distributing Bragg reflector) 12 are sequentially integrated thereunder to constitute a Fabry-Perot interferometer 10. Here, the upper DBR 12 has a membrane structure supported by a flexible arm 15 expanding from four anchors 14 formed on the substrate 1, and a movable side driving electrode 16 is formed on an upper face of the upper DBR 12. Furthermore, a fixing side driving electrode 17 is provided in opposition to the movable side driving electrode 16 on a lower side of the lower DBR 11. A center part on an upper face of the upper distributing Bragg reflector is a transmitting light window 18 for transmitting vertical incident lights on the interferometer 10.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength selective photodetector having a wavelength filter used for image recognition, an optical spectrum analyzer, and the like, and in particular, a wavelength selective light integrated with a highly sensitive wavelength filter that can be manufactured by silicon micromachining. It relates to a detector.
[0002]
[Prior art]
In recent years, with the sophistication and high functionality of many systems for optical applications, higher sensitivity and higher integration have been required for the photodetectors which are the main components.
[0003]
A photodiode is well known as a typical light receiving element used in an optical information system. Examples of the photodiode include a photodiode having a simple PN junction, a PIN photodiode, and an avalanche photodiode. In either case, photocurrent is extracted from electrons and holes generated by light absorption, but the response speeds are different. Silicon (Si) is used in the visible light region. By combining this with a wavelength filter, it is expected that a wavelength-sensitive photodetector will be obtained.
[0004]
Wavelength filters are attracting a great deal of attention with the recent progress of wavelength multiplexing communication technology. For example, US Pat. No. 5,629,951 (hereinafter, Prior Art 1) discloses a wavelength filter using an electrostatically driven cantilever for continuously tuning the detection wavelength. Here, the upper side of the two distributed Bragg reflectors constituting the Fabry-Perot interferometer is a cantilever, and the detection wavelength is changed by controlling the distance between the distributed Bragg reflectors by electrostatic drive.
[0005]
U.S. Pat. No. 5,291,502 (hereinafter referred to as Prior Art 2) discloses a similar Fabry-Perot interferometer constituted by a membrane rather than a cantilever.
[0006]
In addition, “A FABRY-PEROT MICROINTERFEROMETER FOR VISIBLE WAVELENGTH”, IEEE, MEMS '92, 1992, PP170-173 (hereinafter referred to as prior art 3) has Fabry-Perot interference produced by micromachining for light in the visible region. The total is shown. Here, the Fabry-Perot interferometer consists of two mirrors supported by a silicon nitride (SiN) membrane, each of these mirrors having a refractive index of 1.44.₂HfO with film and refractive index 1.80₂It consists of a multilayer film.
[0007]
Many modulators using a Fabry-Perot interferometer have been studied. For example,
In “PROCESS AND DESIGN CONSIDERATIONS FOR SURFACE MICROMACHININED BEAMS FOR A TUNABLE INTERFEROMATER ARRAY IN SILICON”, IEEE, MEMS '93, 1993, PP230-235 (hereinafter referred to as Conventional Technology 4), a Fabry-Perot interferometer is integrated on a photodiode. A high speed optical modulator is shown. Here, the Fabry-Perot interferometer is a silicon oxide (SiO2) on the substrate.₂) / Polysilicon (poly-Si), a poly-Si / SiN / poly-Si membrane, and an intermediate air gap.
[0008]
“MHz OPTO-MECAHNICAL MODULATOR”, TRANSDUCERS '95. A modulator is also shown in EUROSENSORS IX, 1995, PP289-292 (hereinafter referred to as Prior Art 5). Here, 2.8 Mbit / sec. The modulation speed is obtained. The Fabry-Perot interferometer consists of two parallel layers of poly-Si.
[0009]
By the way, systems that require a light detection function include, for example, an optical spectrum analyzer and a solid-state imaging device. As an optical spectrum analyzer, a combination of a photodiode array and a diffraction grating is generally used.
[0010]
In addition, the solid-state imaging device has several hundred thousand to over one million pixels arranged, and a photodiode is provided for each pixel. The color screen is separated into three primary colors of red, green, and blue, and is captured as a signal of each brightness.
[0011]
[Problems to be solved by the invention]
By the way, photodiodes are often used as light receiving elements, and many wavelength filters have been studied. However, photodiodes and wavelength filters are integrated, wavelength resolution is good, and a wide wavelength region is used. An optical detector that covers the above has not been realized. For example, the above-described prior arts 1 and 2 only disclose the configuration of a wavelength filter with a variable detection wavelength.
[0012]
Wavelength filters being studied for wavelength division multiplexing communication are Al integrated on a GaAs substrate._0.09Ga_0.91As and Al_0.09Ga_0.91Since an As multilayer film is used as a distributed Bragg reflector, wavelength resolution is good, but light in the visible region cannot be selectively transmitted.
[0013]
SiO as in the prior art 3 described above₂And HfO₂Fabry-Perot interferometers composed of multiple layers are not integrated with photodiodes, and since the difference in refractive index is small, it is necessary to increase the number of layers to increase wavelength resolution. is there.
[0014]
In addition, the optical modulators as described in the prior arts 4 and 5 modulate light of that wavelength with respect to monochromatic light, and do not realize bandpass filtering of wavelength with respect to white light. Absent.
[0015]
By the way, in the conventional form of the optical spectrum analyzer that requires a light detection function, it is necessary to increase the entire system because it is necessary to increase the optical path length in order to improve the wavelength resolution. Further, since the solid-state imaging device recognizes light by separating it into three primary colors of red, green, and blue, it does not necessarily represent all colors, that is, absolute wavelengths.
[0016]
In view of the above points, the present invention has a structure in which a photodiode and a Fabry-Perot interferometer composed of a distributed Bragg reflector are integrated as a wavelength filter, and is small, highly integrated, and has excellent wavelength resolution. An object of the present invention is to provide an optical detector, and to improve the characteristics of an optical system by using the photodetector.
[0017]
Other objects and novel features of the present invention will be clarified in embodiments described later.
[0018]
[Means for Solving the Problems]
  In order to achieve the above object, a wavelength selective photodetector according to claim 1 of the present invention includes a photodiode formed on a silicon substrate, and first and second distributed type Braggs integrated on the photodiode. A Fabry-Perot interferometer composed of reflectors, and driving means for variably controlling the distance separating the first and second distributed Bragg reflectorse,
  The driving means includes a piezoelectric film whose thickness is changed by applying a voltage with a material that transmits light, and the piezoelectric film is provided as an intermediate layer between the first and second distributed Bragg reflectors. It is characterized by that.
[0021]
  Claims of the invention2The wavelength selective photodetector isIn the configuration of claim 1, theA photodiode;SaidA plurality of Fabry-Perot interferometers are arranged on the silicon substrate.
[0022]
  Claims of the invention3The wavelength selective photodetector of claim 12In the configuration, one Fabry-Perot interferometer is formed corresponding to one photodiode, and one set of the photodiode and one Fabry-Perot interferometer corresponding to the photodiode is respectively provided. The detection wavelength is selected independently.
[0023]
  Claims of the invention4The wavelength selective photodetector of claim 12 or 3In the configuration, the first and second distributed Bragg reflectors constituting each Fabry-Perot interferometer are:SaidFor each Fabry-Perot interferometer, the intermediate layer has a different layer thickness corresponding to the selected wavelength.
[0024]
  Claims of the invention5The wavelength selective photodetector isIn the configuration of claim 1, theA photodiode;SaidA pair with a Fabry-Perot interferometer separates the first and second distributed Bragg reflectors.SaidA plurality of cells are arranged on the silicon substrate by changing the thickness of the intermediate layer to detect a plurality of wavelengths, and a plurality of cells are arranged on the silicon substrate.
[0025]
  Claims of the invention6The wavelength selective photodetector of claim 1, 2, 3, 4Or 5In the configuration, the first and second distributed Bragg reflectors are each composed of a multilayer film in which at least four pairs of two kinds of films having different refractive indexes are stacked.
[0026]
  Claims of the invention7The wavelength selective photodetector of claim 1, 2, 3, 4, 5Or 6In the configuration, the first and second distributed Bragg reflectors are materials that transmit light in the visible region, and the wavelength-selected light in the visible region is received by the photodiode.
[0027]
  Claims of the invention8The wavelength selective photodetector of claim 16 or 7The thickness of each film constituting the first and second distributed Bragg reflectors is λ (1 + 2m) / 4n (with respect to the refractive index n of each film and the wavelength λ of the selected light. Where m is 0 or a natural number), and the distance separating the first and second distributed Bragg reflectors is λ / 2n.₀(However, n₀: Refractive index of the medium separating the first and second distributed Bragg reflectors).
[0028]
  Claims of the invention9The wavelength selective photodetector of claim 16, 7 or 8In the structure, the first and second distributed Bragg reflectors are composed of a high refractive index silicon nitride film and a low refractive index silicon oxide or silicon oxynitride film.
[0029]
  Claims of the invention10The wavelength selective photodetector of claim 11-9In any of the above structures, the photodiode is obtained by forming a PN junction or a PIN junction on the silicon substrate.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a wavelength selective photodetector according to the present invention will be described with reference to the drawings.
[0031]
FIG. 1 is a schematic perspective view of a wavelength selective photodetector according to a first embodiment of the present invention, and FIG. 2 (E) is a sectional view thereof. First, a photodiode 5 is formed on a silicon (Si) substrate 1, and a lower distributed Bragg reflector (lower DBR) 11 and an upper distributed Bragg reflector (upper DBR) 12 through an air gap 13 thereon. A Fabry-Perot interferometer 10 is constructed by being sequentially accumulated. Here, the upper distributed Bragg reflector 12 has a membrane structure supported by flexible arms 15 extending from four anchors 14 formed on the substrate 1, and the upper distributed Bragg reflector 12. A movable drive electrode 16 is formed on the upper surface. A fixed driving electrode 17 is provided below the lower distributed Bragg reflector 11 so as to face the movable driving electrode 16. The central portion of the upper surface of the upper distributed Bragg reflector 12 serves as a transmitted light window 18 in which the movable drive electrode 16 is not formed in order to transmit incident light perpendicular to the Fabry-Perot interferometer 10 (fixed). Similarly, a transmission light window is formed on the side drive electrode 17).
[0032]
An extended portion of the movable drive electrode 16 is drawn out to the upper surface of one anchor 14. The photodiode 5 is formed, for example, by forming a PN junction on the Si substrate 1, and a photocurrent detection electrode 19 connected to the photodiode 5 is drawn to the upper surface of the substrate.
[0033]
The movable side driving electrode 16 provided on the upper distributed Bragg reflector 12 and the fixed side driving electrode 17 provided on the lower distributed Bragg reflector 11 are the lower distributed Bragg reflector 11 and the upper distribution. An electrostatic actuator as a driving means for variably controlling the distance separating the type Bragg reflector 12 is configured, and the upper distributed Bragg reflector 12 is applied by applying a voltage between the movable side and fixed side driving electrodes 16 and 17. The air gap 13 can be adjusted by pulling toward the substrate side with an electrostatic force. Here, the wavelength λ of the transmitted light and the air gap interval t indicate the refractive index of the medium (in this case, air) between the gaps.₀As t = λ / 2n₀Thus, the wavelength of transmitted light can be selected by adjusting the gap.
[0034]
Next, a manufacturing method of the wavelength selective photodetector according to the first embodiment will be described with reference to FIG.
[0035]
First, as shown in FIG. 2A, the n-type Si (100) substrate 1 is thermally oxidized to form 100 nm silicon oxide (SiO 2).₂) Layer 21 is formed on the surface as a thermal oxide film. This SiO₂The layer becomes a pattern that allows alignment in a later process. Subsequently, as shown in FIG. 5B, a photoresist 22 is applied, and then exposed and developed to form a pattern for a subsequent ion implantation process. Then, boron (B) is implanted using the photoresist 22 of a predetermined pattern as a mask, and a PN junction 23 to be a photodiode is formed. Injection conditions are BF²⁺Ion is 55 keV and dose is 5 × 10¹⁵cm^-2It was. Thereafter, a heat treatment is usually performed for ion diffusion. However, in this embodiment, the heat treatment step can be omitted because there is a long time film formation at a high temperature. In addition, as the fixed-side driving electrode 17, a portion having an excessive ion dose and having conductivity is formed on the upper surface of a portion to be a photodiode.
[0036]
In this embodiment, since the characteristics of the photodiode itself are not particularly taken into consideration, a simple PN junction photodiode is used as described above. Of course, in order to improve the response speed of the photodiode itself, a PIN photodiode is formed. It can also be used.
[0037]
Subsequently, as shown in FIG. 2C, after removing the photoresist of the mask, the lower distributed Bragg reflector 11 and the upper distributed Bragg reflector 12 are sequentially formed by LPCVD (Low Pressure Chemical Vapor Deposition). And accumulate. These distributed Bragg reflectors 11 and 12 include a silicon nitride (SiN) film 24 having a refractive index of 2.0 and a silicon oxide night having a refractive index of 1.5 as shown in the enlarged cross-sectional view of FIG. It consists of a multilayer film in which a plurality of pairs of ride (SiON) films 25 are formed. In the figure, there are 6 pairs. A buffer layer 28 having a low refractive index is formed of a SiON film between the lower distributed Bragg reflector 11 and the substrate 1. The thickness of each film constituting these distributed Bragg reflectors 11 and 12 is derived from λ (1 + 2m) / 4n with respect to the center wavelength λ of light to be transmitted (where n is the thickness of each film). Refractive index, m: 0 or natural number). Here, since 638 nm is the wavelength center when no voltage is applied, the SiN film 24 and the SiON film 25 are formed to have a thickness of 79.8 nm and 106.3 nm from λ / 4n, respectively. The LPCVD deposition conditions are 850 ° C. and 0.5 Torr, and the SiN film is SiH._Four, NH_ThreeSiON film is SiH_Four, NH_Three, N₂Each film is formed using O as a source gas. In order to form an air gap (reference numeral 13 in FIG. 1) in the intermediate layer 26 later, λ / 2n₀(N to make an air gap₀= 1) A poly-Si film having a thickness calculated from 1) is formed as a sacrificial layer. The film formation is also performed by LPCVD. The film forming conditions are 600 ° C. and 1.0 Torr, and SiH._FourIs formed as a source gas. This poly-Si film is later patterned with an upper distributed Bragg reflector 12 on the membrane as shown in FIG. To do. The upper distributed Bragg reflector 12 can be etched with BHF (buffered hydrofluoric acid), but since the etching rate of the SiN film is slow, RIE (Reactive ion etching) can be combined with the SiN film. is there.
[0038]
Then, through holes 27 for light detection electrodes are formed by RIE as shown in FIG. 2E using a photoresist as a mask. Further, Au is deposited as the photocurrent detection electrode 19 and the movable drive electrode 16 by sputtering. Here, the Au of the upper distributed Bragg reflector 12 is patterned and etched so as to be removed from the light transmitting portion (window 18). Similarly, the fixed-side driving electrode 17 on the surface of the photodiode is not formed in the light transmitting portion.
[0039]
Next, the wavelength characteristics of the Fabry-Perot interferometer 10 integrated and integrated on the photodiode 5 in the first embodiment will be described.
[0040]
FIG. 3 shows the dependence of the transmitted light spectrum on the number of pairs. A film (SiN) of the mirror (the lower distributed Bragg reflector 11 and the upper distributed Bragg reflector 12) of the Fabry-Perot interferometer 10 has a high refractive index. The effect of stacking pairs of film 24) and low film (SiON film 25) is shown. That is, it is confirmed that the wavelength resolution is improved as the number of multilayer films is increased.
[0041]
FIG. 4 shows the relationship between the transmitted light intensity and the wavelength when the air gap 13 is adjusted, and shows the movement of the spectrum when the air gap is changed in the visible light region. Here, each distributed Bragg reflector is formed of 10 pairs of multilayer films. Eight points between wavelengths 614 nm and 637 nm are adjusted by changing the gap from 283.5 nm to 327.6 nm. First, it is confirmed from FIG. 4 that the wavelength filter is excellent in wavelength resolution with a half width of 1 nm. By detecting the transmitted light with a photodiode, the wavelength can be selected and an optical signal can be detected as an electrical signal.
[0042]
According to the first embodiment, the following effects can be obtained.
[0043]
(1) A Fabry-Perot interferometer 10 including a photodiode 5 formed on a Si substrate 1, and lower and upper distributed Bragg reflectors 11 and 12 integrated on the photodiode, and a distributed Bragg Drive means (movable side drive electrode 16 and fixed side drive electrode 17) for variably controlling the distance separating the reflectors 11 and 12, and between the movable side drive electrode 16 and the fixed side drive electrode 17; By applying a voltage to generate an electrostatic force and controlling the distance separating the lower and upper distributed Bragg reflectors 11 and 12, the wavelength of light to be detected can be selected.
[0044]
(2) The lower and upper distributed Bragg reflectors 11 and 12 include two types of films having different refractive indexes, that is, a silicon nitride (SiN) film 24 having a refractive index of 2.0 and a refractive index of 1.5. Each of the silicon oxide nitride (SiON) films 25 is formed of a multi-layered film, and the wavelength resolution can be changed by changing the number of film forming pairs. Further, as can be seen from FIG. 3, it is possible to obtain an appropriate wavelength resolution by constituting each of the multilayer films in which at least four pairs are stacked.
[0045]
(3) The distributed Bragg reflectors 11 and 12 have a laminated structure of the SiN film 24 and the SiON film 25 and are made of a material that transmits light in the visible region. The wavelength-selected visible region light is received by the photodiode 5. can do.
[0046]
(4) The film thicknesses of the films 24 and 25 constituting the distributed Bragg reflectors 11 and 12 are such that the refractive index n of each film and the wavelength λ of the light to be selected are λ (1 + 2m) / 4n (where m: 0 or a natural number) and the distance separating the distributed Bragg reflectors 11 and 12 = λ / 2n₀(However, n₀: Select a wavelength to be a refractive index of a medium separating the first and second distributed Bragg reflectors, and receive the light by the photodiode 5. Therefore, the air gap 13 between the distributed Bragg reflectors 11 and 12 can be arbitrarily controlled by applying a voltage between the driving means by electrostatic force, that is, the movable side driving electrode 16 and the fixed side driving electrode 17, The selected distributed Bragg reflector 12 can be pulled toward the substrate side to continuously change the selected wavelength.
[0047]
In the first embodiment, a voltage is applied between the driving electrodes 16 and 17 to adjust the air gap 13 and the wavelength to be transmitted is selected. However, light in the visible region is transmitted through the air gap 13. Replacing with a transparent piezoelectric film, the piezoelectric film is provided as an intermediate layer between the lower distributed Bragg reflector 11 and the upper distributed Bragg reflector 12, and a voltage is applied to the piezoelectric film to adjust the film thickness or refractive index. It is good also as a structure which selects the wavelength to permeate | transmit.
[0048]
FIG. 5 shows a second embodiment of the present invention, in which a Fabry-Perot interferometer 40 including lower and upper distributed Bragg reflectors 41 and 42 is formed on a plurality of photodiodes 35 formed on an Si substrate 31. Fig. 2 shows an outline of a compact optical spectrum analyzer that is integrated in each.
[0049]
Here, one Fabry-Perot interferometer 40 including a pair of a lower distributed Bragg reflector 41 and an upper distributed Bragg reflector 42 is formed corresponding to one photodiode 35, and the Fabry-Perot interferometer is formed. 40 into eight arrays, each with a Fabry-Perot interferometer, with different wavelengths λ through each transmitted light window 48₁~ Λ₈Are individually selected and detected by the corresponding photodiode 35. The space between the lower distributed Bragg reflector 41 and the upper distributed Bragg reflector 42 is not an air gap but an intermediate layer 43 having a fixed layer thickness, and the transmitted light wavelength is changed by changing the intermediate layer thickness for each Fabry-Perot interferometer. It is adjusted. This functions as an optical spectrum analyzer. Of course, the larger the number of arrays, the better the resolution.
[0050]
The configurations of the lower distributed Bragg reflector 41 and the upper distributed Bragg reflector 42 are the same as those in the first embodiment described above, and a plurality of SiN films having a large refractive index and SiON films having a small refractive index are provided. It is composed of a multilayer film formed in pairs.
[0051]
FIG. 6 shows the relationship between the intermediate layer thickness and the transmitted light wavelength when white light is incident on the optical spectrum analyzer (center wavelength 630 nm) of FIG. Here, the intermediate layer is a SiON layer (refractive index n: 1.50) as a low refractive index layer, and the layer thickness is changed from 189.0 nm to 218.4 nm to cover the wavelength from 610 nm to 640 nm. Yes. It is a wavelength filter excellent in wavelength resolution with a half-value width of 1 nm. However, since the wavelength range that can be covered is narrow in the eight arrays of the present embodiment, it is desirable to increase the number of arrays and design the film configuration so as to cover a wider range of wavelengths.
[0052]
Next, a method of changing the intermediate layer of the optical spectrum analyzer of the second embodiment for each Fabry-Perot interferometer will be described with reference to FIG. First, as shown in FIG. 7A, a lower distributed Bragg reflector 41 is formed on a Si substrate 31 on which a photodiode 35 is formed, and a SiON intermediate layer 43 is detected on the lower distributed Bragg reflector 41. The film is formed with a thickness corresponding to the longest wavelength. This is etched stepwise as shown in FIGS. Etching was performed with BHF diluted to 1/20, and the etching mask 45 was a resist. When each region of a certain film thickness is divided into two, the number of etching times N is 2^NSteps are formed. Here, eight steps are produced as shown by three etchings to form an array of Fabry-Perot interferometers with eight different intermediate layer thicknesses.
[0053]
According to the second embodiment, one set of distributed Bragg reflectors 41 and 42 is formed corresponding to one photodiode 35, and these are configured as an array. A detection wavelength can be selected, and a plurality of wavelengths can be detected simultaneously.
[0054]
FIG. 8 shows a Fabry-Perot interference comprising a photodiode formed on a silicon substrate 51 and lower and upper distributed Bragg reflectors integrated on the photodiode as a third embodiment of the present invention. A cell (pixel) 53 for detecting a plurality of wavelengths by arranging a plurality of light detection units 52 formed of a meter with a silicon substrate 51 by changing a thickness of an intermediate layer separating the lower and upper distributed Bragg reflectors. An outline of an absolute wavelength detection type CCD image pickup device in which a large number of cells 53 are arranged on a silicon substrate 51 in a plane is shown. Here, in the distributed Bragg reflector constituting each Fabry-Perot interferometer, a plurality of pairs of SiN films having a large refractive index and SiON films having a small refractive index are formed as shown in the first embodiment. It is composed of a multilayer film, and a SiON intermediate layer having a fixed layer thickness is formed between the lower and upper distributed Bragg reflectors as in the second embodiment. Here, sixteen photodetecting parts 52 formed by integrating Fabry-Perot interferometers having different intermediate layer thicknesses are arranged to form one cell 53, and a large number of them are arranged to form a planar array. Accordingly, while a normal solid-state imaging device captures light by separating it into three primary colors of red, green, and blue, in the present embodiment, lower and upper distributed Bragg reflectors are provided in one cell 53. A color screen can be captured by decomposing into 16 wavelengths corresponding to the intermediate layer thickness to be separated. This improves the accuracy of the color screen to be recognized. Of course, by increasing the number of light detection units 52 having different intermediate layer thicknesses in one cell, it is possible to resolve the light into more wavelengths.
[0055]
The intermediate layer thickness is such that the wavelength region from 400 nm to 700 nm is divided into 20 nm intervals so as to cover the light in the visible region, and a total of 16 wavelengths can be detected within one pixel. However, even if only the intermediate layer thickness is changed with a Fabry-Perot interferometer using a pair of distributed Bragg reflectors with the same film thickness configuration, the entire wavelength region cannot be covered. There are four reflector film configurations (four types of film thickness), and each film configuration has four types of intermediate layer thicknesses to detect light of a total of 16 wavelengths.
[0056]
FIG. 8 also shows a peripheral circuit 54 for CCD addressing and a peripheral circuit 55 for reading data such as an amplifier, an A / D converter, and a multiplexer. The charges generated by the light detected in each cell 53 flow in the direction shown in the figure as data as in a normal CCD, and are processed in the peripheral circuit.
[0057]
FIG. 9 shows the spectrum when the detection wavelength is 16 channels. Here, in order to give sensitivity to visible light of all wavelengths, the resolution is deliberately lowered, and the number of pairs in the distributed Bragg reflector is four.
[0058]
According to the third embodiment, each cell 53 captures a color screen by decomposing into a wavelength corresponding to the intermediate layer thickness separating the lower and upper distributed Bragg reflectors of the plurality of photodetectors 52 provided. It is possible to improve the accuracy of the color screen to be recognized, and by increasing the number of the photodetecting parts 52 having different intermediate layer thicknesses in one cell, it is possible to decompose into more wavelengths. Is possible.
[0059]
FIG. 10 shows an outline of an absolute wavelength detection type CCD image pickup device in which the fixed intermediate layer of the CCD image pickup device of the third embodiment is replaced with an air gap as a fourth embodiment of the present invention. In this case, a wavelength-selective photodetection unit composed of one Fabry-Perot interferometer and a photodiode serving as a variable air gap corresponds to one cell (pixel) 63, and the cell 63 is placed on the Si substrate 61. Many are arranged in a plane. Each cell 63 may have the same configuration as that of the first embodiment. As a peripheral circuit, a peripheral circuit 64 for CCD addressing and a peripheral circuit 65 for reading data such as an amplifier, an A / D converter, and a multiplexer are provided as in the third embodiment of FIG. ing. However, in order to detect light by applying an alternating voltage for changing the air gap to each cell 63 and oscillating between the lower and upper distributed Bragg reflectors at a frequency of about 1 kHz, a peripheral for CCD addressing It is necessary to add a circuit for generating an air gap adjustment drive voltage to the circuit 64.
[0060]
In this case, by applying an alternating voltage to each cell 63 from the peripheral circuit 64, the lower and upper distributed Bragg reflectors are vibrated at a frequency of about 1 kHz to detect light. That is, each moment corresponds to a wavelength, and by monitoring the time, the detected light can correspond to the wavelength of the light itself. This improves the accuracy of the color screen to be recognized.
[0061]
The charges generated by the light detected in each cell 63 flow in the direction shown in the figure as data in the same way as in a normal CCD, and are processed by peripheral circuits.
[0062]
In the distributed Bragg reflector of each of the embodiments described above, the SiN film is exemplified as the high refractive index film, and the SiON film is exemplified as the low refractive index film.₂A film may be used, and other film configurations are possible.
[0063]
Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.
[0064]
【The invention's effect】
As described above, according to the present invention, the wavelength resolution can be obtained by integrating the Fabry-Perot interferometer, which is fabricated on a Si substrate by micromachining and using two distributed Bragg reflectors as a mirror, with a photodiode. It is possible to realize a wavelength-selective photodetector having a small wavelength filter that is excellent in size.
Further, by integrating the Fabry-Perot interferometer array and the photodiode array, it is possible to realize a small spectrum analyzer with excellent wavelength resolution or a CCD imaging device capable of detecting an absolute wavelength.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing a first embodiment of a wavelength selective photodetector according to the present invention.
FIG. 2 is an explanatory diagram showing a method of manufacturing the wavelength selective photodetector according to the first embodiment.
FIG. 3 is a graph showing the relationship between the wavelength resolution and the number of stacked layers of the wavelength selective photodetector according to the first embodiment.
FIG. 4 is a graph showing the relationship between the wavelength and the transmitted light intensity when the air gap of the wavelength selective photodetector according to the first embodiment is changed.
FIG. 5 is a schematic perspective view showing a small optical spectrum analyzer according to a second embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the intermediate layer thickness and the transmitted light intensity of the compact optical spectrum analyzer shown in the second embodiment.
FIG. 7 is an explanatory diagram showing a method for stepping an intermediate layer of the compact optical spectrum analyzer shown in the second embodiment.
FIG. 8 is a schematic perspective view showing an absolute wavelength detection type CCD image pickup device according to a third embodiment of the present invention, in which an intermediate layer fixed Fabry-Perot interferometer is arrayed.
FIG. 9 is a graph showing a spectrum of an absolute wavelength detection type CCD image pickup device according to a third embodiment;
FIG. 10 is a schematic perspective view showing an absolute wavelength detection type CCD image pickup device according to a fourth embodiment of the present invention, in which an Fabry-Perot interferometer whose air gap is an air gap is an array.
[Explanation of symbols]
1, 31, 51, 61 Silicon substrate
5,35 photodiode
10, 40 Fabry-Perot interferometer
11, 41 Lower distributed Bragg reflector
12,42 Upper distributed Bragg reflector
13 Air gap
14 Anchor
15 Flexible arm
16 Movable drive electrode
17 Fixed drive electrode
18 Transmitted light window
19 Electrode for photocurrent detection
21 Silicon oxide layer
22 photoresist
23 PN junction
24 Silicon nitride film
25 Silicon oxide nitride film
26,43 Middle layer
27 Through hole for electrode
28 Buffer layer
45 Etching mask
52 Photodetector
53,63 cells
54, 55, 64, 65 Peripheral circuits

Claims (10)

A Fabry-Perot interferometer comprising a photodiode formed on a silicon substrate, first and second distributed Bragg reflectors integrated on the photodiode, and the first and second distributed Bragg the distance separating the reflectors example Bei and drive means for variably controlling,
The driving means has a piezoelectric film whose thickness is changed by applying a voltage with a material that transmits light, and the piezoelectric film is provided as an intermediate layer between the first and second distributed Bragg reflectors. A wavelength selective photodetector. 2. The wavelength selective photodetector according to claim 1 , wherein a plurality of said photodiodes and said Fabry-Perot interferometers are arranged on said silicon substrate. One Fabry-Perot interferometer is formed corresponding to one photodiode, and one set of the photodiode and one corresponding Fabry-Perot interferometer is detected independently. 3. The wavelength selective photodetector according to claim 2 , wherein the wavelength selective photodetector is configured to select a wavelength. Each of the Fabry - the constituting Perot interferometer first and second distributed Bragg reflectors, are separated via the intermediate layer, each of the Fabry - the intermediate layer for each Perot interferometer selected wavelengths The wavelength-selective photodetector according to claim 2 or 3 , having different layer thicknesses corresponding to. And the photodiode, the Fabry - a set of the Perot interferometer, wherein the plurality of wavelengths and arrayed on the silicon substrate by changing the thickness of the intermediate layer separating the first and second distributed Bragg reflector build a cell for detecting the wavelength selective optical detector according to claim 1, wherein a plurality arranged the cell in the silicon substrate. Said first and second distributed Bragg reflector, the claims are configured each pair of two kinds of films having different refractive index multilayer film stacked least four pairs or more 1, 2, 3 4 or 5 The described wavelength-selective photodetector. The first and second distributed Bragg reflectors are made of a material that transmits light in a visible region, and receive light in the visible region that is wavelength-selected by the photodiode. 5. The wavelength selective photodetector according to 5 or 6 . The thickness of each film constituting the first and second distributed Bragg reflectors is λ (1 + 2m) / 4n (where m: 0 or a natural number, and the distance separating the first and second distributed Bragg reflectors is λ / 2n ₀ (where n _{0 is} the refraction of the medium separating the first and second distributed Bragg reflectors) The wavelength selective photodetector according to claim 6 or 7 , wherein 9. The wavelength selective light according to claim 6, 7 or 8, wherein the first and second distributed Bragg reflectors are composed of a high refractive index silicon nitride film and a low refractive index silicon oxide or silicon oxynitride film. Detector. The wavelength selective photodetector according to any one of claims 1 to 9 , wherein the photodiode has a PN junction or a PIN junction formed on the silicon substrate.

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