Patent Application
20220262863
The present patent application claims the priority benefit of French patent application FR19/08251, which is herein incorporated by reference.
The present disclosure relates to an image sensor or electronic imager.
Image sensors are currently used in many fields, in particular in electronic devices. Image sensors are particularly present in man-machine interface applications or in image capture applications. The fields of use of such image sensors particularly are, for example, smart phones, motors vehicles, drones, robotics, and virtual or augmented reality systems.
In certain applications, a same electronic device may have a plurality of image sensors of different types. Such a device may thus comprise, for example, a first color image sensor, a second infrared image sensor, a third image sensor enabling to estimate a distance, relative to the device, of different points of a scene or of a subject, etc.
Such a multiplicity of image sensors embarked in a same device is, by nature, little compatible with current constraints of miniaturization of such devices.
There is a need to improve existing image sensors.
An embodiment overcomes all or part of the disadvantages of known image sensors.
An embodiment provides a pixel comprising:
An embodiment provides an image sensor comprising a plurality of pixels such as described.
An embodiment provides a method of manufacturing such a pixel or such an image sensor, comprising steps of:
According to an embodiment, said organic photodetectors are coplanar.
According to an embodiment, said organic photodetectors are separated from one another by a dielectric.
According to an embodiment, each organic photodetector comprises a first electrode, separate from first electrodes of the other organic photodetectors, formed at the surface of the CMOS support.
According to an embodiment, each first electrode is coupled, preferably connected, to a readout circuit, each readout circuit preferably comprising three transistors formed in the CMOS support.
According to an embodiment, said organic photodetectors are capable of estimating a distance by time of flight.
According to an embodiment, the pixel or the sensor such as described is capable of operating:
According to an embodiment, each pixel further comprises, under the lens, a color filter giving way to electromagnetic waves in a frequency range of the visible spectrum and in the infrared spectrum.
According to an embodiment, the sensor such as described is capable of capturing a color image.
According to an embodiment, each pixel exactly comprises:
According to an embodiment, for each pixel, the first organic photodetector and the second organic photodetector have a rectangular shape and are jointly inscribed within a square.
According to an embodiment, for each pixel:
An embodiment provides a sensor wherein:
The foregoing and other features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments and implementation modes in connection with the accompanying drawings, in which:
Like features have been designated by like references in the various figures. In particular, the structural and/or functional elements common to the different embodiments and implementation modes may be designated with the same reference numerals and may have identical structural, dimensional, and material properties.
For clarity, only those steps and elements which are useful to the understanding of the described embodiments and implementation modes have been shown and will be detailed. In particular, what use is made of the image sensors described hereafter has not been detailed.
Unless specified otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.
Further, a signal which alternates between a first constant state, for example, a low state, noted “0”, and a second constant state, for example, a high state, noted “1”, is called a “binary signal”. The high and low states of different binary signals of a same electronic circuit may be different. In particular, the binary signals may correspond to voltages or to currents which may not be perfectly constant in the high or low state.
In the following description, it is considered, unless specified otherwise, that the terms “insulating” and “conductive” respectively signify “electrically insulating” and “electrically conductive”.
In the following description, when reference is made to terms qualifying absolute positions, such as terms “front”, “rear”, “top”, “bottom”, “left”, “right”, etc., or relative positions, such as terms “above”, “under”, “upper”, “lower”, etc., or to terms qualifying directions, such as terms “horizontal”, “vertical”, etc., unless specified otherwise, it is referred to the orientation of the drawings or to an image sensor in a normal position of use.
Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%.
The transmittance of a layer to a radiation corresponds to the ratio of the intensity of the radiation coming out of the layer to the intensity of the radiation entering the layer, the rays of the incoming radiation being perpendicular to the layer. In the following description, a layer or a film is called opaque to a radiation when the transmittance of the radiation through the layer or the film is smaller than 10%. In the following description, a layer or a film is called transparent to a radiation when the transmittance of the radiation through the layer or the film is greater than 10%.
In the following description, “visible light” designates an electromagnetic radiation having a wavelength in the range from 400 nm to 700 nm and “infrared radiation” designates an electromagnetic radiation having a wavelength in the range from 700 nm to 1 mm. In infrared radiation, one can particularly distinguish near infrared radiation having a wavelength in the range from 700 nm to 1.7 μm.
A pixel of an image corresponds to the unit element of the image captured by an image sensor. When the optoelectronic device is a color image sensor, it generally comprises, for each pixel of the color image to be acquired, at least three components. The three components each acquire a light radiation substantially in a single color, that is, in a wavelength range below 130 nm (for example, red, green, and blue). Each component may particularly comprise at least one photodetector.
Image sensor 1 comprises an array of coplanar pixels. For simplification, only four pixels 10, 12, 14, and 16 of image sensor 1 have been shown in
According to this embodiment, pixels 10, 12, 14, and 16 are located at the surface of a CMOS support 3, for example, a piece of a silicon wafer on top and inside of which integrated circuits (not shown) have been formed in CMOS (Complementary Metal Oxide Semiconductor) technology. These integrated circuits form, in this example, an array of readout circuits associated with pixels 10, 12, 14, and 16 of image sensor 1. Readout circuit means an assembly of readout, addressing, and control transistors associated with each pixel.
In image sensor 1, each pixel comprises a first photodetector, designated with suffix “A”, and a second photodetector, designated with suffix “B”. More particularly, in the example of
Photodetectors 10A, 10B, 12A, 12B, 14A, 14B, 16A, and 16B may correspond to organic photodiodes (OPD) or to organic photoresistors. In the rest of the disclosure, it is considered that the photodetectors of the pixels of image sensor 1 correspond to organic photodiodes.
In the simplified representation of
Similarly, in image sensor 1:
In the rest of the disclosure, the first electrodes will also be designated with the expression “lower electrodes” while the second electrodes will also be designated with the expression “upper electrodes”.
According to an embodiment, the upper electrode of each organic photodetector forms an anode electrode while the lower electrode of each organic photodetector forms a cathode electrode.
The lower electrode of each photodetector of each pixel of image sensor 1 is individually coupled, preferably connected, to a readout circuit (not shown) of CMOS support 3. Each photodetector of image sensor 1 is accordingly individually addressed via its lower electrode. Thus, in image sensor 1, each photodetector has a lower electrode separate from the lower electrodes of all the other photodetectors. In other words, each photodetector of a pixel has a lower electrode separate:
Still in image sensor 1, the upper electrodes of all the first photodetectors are interconnected. Similarly, the upper electrodes of all the second photodetectors are interconnected. Thus, in the simplified representation of
In image sensor 1, each pixel comprises a lens 18, also called microlens 18 due to its dimensions. Thus, in the simplified representation of
In this top view, the first and second photodetectors have being represented by rectangles and the microlenses have been represented by circles. More particularly, in
In practice, due to the intervals between electrodes which will appear from the discussion of the following figures, it can be considered that lenses 18 totally cover the respective electrodes of the pixels with which they are associated.
In image sensor 1, in top view in
The square formed by each pixel of image sensor 1, in top view in
The first photodetector and the second photodetector belonging to a same pixel (for example, the first photodetector 10A and the second photodetector 10B of the first pixel 10) both have a rectangular shape. The photodetectors have substantially the same dimensions and are jointly inscribed within the square formed by the pixel to which they belong.
The rectangle formed by each photodetector of each pixel of image sensor 1 has a length substantially equal to the side length of the square formed by each pixel and a width substantially equal to half the side length of the square formed by each pixel. A space is however formed between the first and the second photodetector of each pixel, so that their respective lower electrodes are separate.
In image sensor 1, each microlens 18 has, in top view in
As a variation, each microlens 18 may be replaced with another type of micrometer-range optical element, particularly a micrometer-range Fresnel lens, a micrometer-range index gradient lens, or a micrometer-range diffraction grating. Microlenses 18 are converging lenses, each having a focal distance f in the range from 1 μm to 100 μm, preferably from 1 μm to 10 μm. According to an embodiment, all the microlenses 18 are substantially identical.
Microlenses 18 may be made of silica, of poly(methyl) methacrylate (PMMA), of positive resist, of polyethylene terephthalate (PET), of polyethylene naphthalate (PEN), of cyclo-olefin polymer (COP), of polydimethylsiloxane (PDMS)/silicone, or of epoxy resin. Microlenses 18 may be formed by flowing of resist blocks. Microlenses 18 may further be formed by molding on a layer of PET, PEN, COP, PDMS/silicone or epoxy resin.
For simplification, only the readout circuits associated with two pixels of image sensor 1 are considered in
The first readout circuit 20A of the first photodetector 10A of pixel 10 and the second readout circuit 20B of the second photodetector 10B of pixel 10 jointly form a readout circuit 20 of pixel 10. Similarly, the first readout circuit 22A of the first photodetector 12A of pixel 12 and the second readout circuit 22B of the second photodetector 12B of pixel 12 jointly form a readout circuit 22 of pixel 12.
According to this embodiment, each readout circuit 20A, 20B, 22A, 22B comprises three MOS transistors. Such a circuit is currently designated, with its photodetector, by expression “3T sensor”. In particular, in the example of
Each terminal 204 is coupled to a source of a high reference potential, noted Vpix, in the case where the transistors of the readout circuits are N-channel MOS transistors. Each terminal 204 is coupled to a source of a low reference potential, for example, the ground, in the case where the transistors of the readout circuits are P-channel MOS transistors.
Each terminal 206A is coupled to a first conductive track 208A. The first conductive track 208A may be coupled to all the first photodetectors of a same column. The first conductive track 208A is preferably coupled to all the first photodetectors of image sensor 1.
Similarly, each terminal 206B is coupled to a second conductive track 208B. The second conductive track 208B may be coupled to all the second photodetectors of a same column. The second conductive track 208B is preferably coupled to all the second photodetectors of image sensor 1. The second conductive track 208B is preferably separate from the first conductive track 208A.
In the example of
The gate of transistor 202 is intended to receive a signal, noted SEL_R1, of selection of pixel 10 in the case of the readout circuit 20 of pixel 10. The gate of transistor 202 is intended to receive another signal, noted SEL_R2, of selection of pixel 12 in the case of the readout circuit 22 of pixel 12.
In the example of
Each node FD_1A, FD_1B, FD_2A, FD_2B is coupled, by a reset MOS transistor 210, to a terminal of application of a reset potential Vrst, which potential may be identical to potential Vpix. The gate of transistor 210 is intended to receive a signal RST for controlling the resetting of the photodetector, particularly enabling to reset node FD_1A, FD_1B, FD_2A, or FD_2B substantially to potential Vrst.
In the example of
Still in the example of
In image sensor 1, potential Vtop_C1 is applied to the first upper electrode common to all the first photodetectors. Potential Vtop_C2 is applied to the second upper electrode common to all the second photodetectors.
In the rest of the disclosure, the following notations are arbitrarily used:
It is considered in the rest of the disclosure that the application of voltage VSEL_R1, respectively VSEL_R2, is controlled by the binary signal noted SEL_R1, respectively SEL_R2.
Other types of sensors, for example, so-called “4T” sensors, are known. The use of organic photodetectors advantageously enables to spare a transistor and to use a 3T sensor.
The timing diagram of
The timing diagram 4 illustrates an example of variation of binary signals RST and SEL_R1 as well as potentials Vtop_C1, Vtop_C2, VFD_1A, and VFD_1B of two photodetectors of a same pixel of image sensor 1, for example, the first photodetector 10A and the second photodetector 10B of pixel 10.
At a time t0, signal SEL_R1 is in the low state so that the transistors 202 of pixel 10 are off. A reset phase is then initiated. For this purpose, signal RST is maintained in the high state so that the reset transistors 210 of pixel 10 are on. The charges accumulated in photodiodes 10A and 10B are then discharged towards the source of potential Vrst.
Potential Vtop_C1 is, still at time t0, in a high level. The high level corresponds to a biasing of the first photodetector 10A under a voltage greater than a voltage resulting from the application of a potential called “built-in potential”. The built-in potential is equivalent to a difference between a work function of the anode and a work function of the cathode. When potential Vtop_C1 is in the high level, the first photodetector 10A integrates no charges.
Before a time t1 subsequent to time t0, potential Vtop_C1 is set to a low level. This low level corresponds to a biasing of the first photodetector 10A under a negative voltage, that is, smaller than 0 V. This thus enables first photodetector 10A to integrate photogenerated charges. What has been previously described in relation with the biasing of first photodetector 10A by potential Vtop_C1 transposes to the explanation of the operation of the biasing of the second photodetector 10B by potential Vtop_C2.
At time t1, a first infrared light pulse starts being emitted (IR light emitted) towards a scene comprising one or a plurality of objects, having their distance desired to be measured, which enables to acquire a depth map of the scene. The first infrared light pulse has a duration noted tON. At time t1, signal RST is set to the low state, so that the reset transistors 210 of pixel 10 are off, and potential Vtop_C2 is set to a high level.
Potential Vtop_C1 being at the low level, at time t1, a first integration phase, noted ITA, is started in the first photodetector 10A of pixel 10 of image sensor 1. The integration phase of a pixel designates the phase during which the pixel collects charges under the effect of an incident radiation.
At a time t2, subsequent to time t1 and separated from time t1 by a time period noted tD, a second infrared light pulse originating from the reflection of the first infrared light pulse by an object in the scene or by a point of an object having its distance to pixel 10 desired to be measured, starts being received (IR light received). Time period tD thus is a function of the distance of the object to sensor 1. A first charge collection phase, noted CCA is then started, in first photodetector 10A. The first charge collection phase corresponds to a period during which charges are generated proportionally to the intensity of the incident light, that is, proportionally to the light intensity of the second pulse, in photodetector 10A. The first charge collection phase causes a decrease in the level of potential VFD_1A at node FD_1A of readout circuit 20A.
At a time t3, in the present example subsequent to time t2 and separated from time t1 by time period tON, the first infrared light pulse stops being emitted. Potential Vtop_C1 is simultaneously set to the high level, thus marking the end of the first integration phase, and thus of the first charge collection phase.
At the same time, potential Vtop_C2 is set to a low level. A second integration phase, noted ITB, is then started at time t3 in the second photodetector 10B of pixel 10 of image sensor 1. Given that the second photodetector 10B receives light originating from the second light pulse, a second charge collection phase, noted CCB, is started, still at time t3. The second charge collection phase causes a decrease in the level of potential VFD_1B at node FD_1B of readout circuit 20B.
At a time t4, subsequent to time t3 and separated from time t2 by a time period substantially equal to tON, the second light pulse stops being captured by the second photodetector 10B of pixel 10. The second charge collection phase then ends at time t4.
At a time t5, subsequent to time t4, potential Vtop_C2 is set to the high level. This thus marks the end of the second integration phase.
Between time t5 and a time t6, subsequent to time t5, a readout phase, noted RT, during which the quantity of charges collected by the photodiodes of the pixels of image sensor 1 is measured, is carried out. For this purpose, the pixels rows of image sensor 1 are for example sequentially read. In the example of
From time t6 and until a time t1′, subsequent to time t6, a new reset phase (RESET) is initiated. Signal RST is set to the high state so that the reset transistors 210 of pixel 10 are turned on. The charges accumulated in photodiodes 10A and 10B are then discharged towards the source of potential Vrst.
Time period tD, which separates the beginning of the first emitted light pulse from the beginning of the second received light pulse, is calculated by means of the following formula:
In the above formula, the quantity noted ΔVFD_1A corresponds to a drop of potential VFD_1A during the integration phase of first photodetector 10A. Similarly, the quantity noted ΔVFD_1B corresponds to a drop of potential VFD_1B during the integration phase of second photodetector 10B.
At time t1′, a new distance estimation is initiated by the emission of a second light pulse. The new distance estimation comprises times t2′ and t4′ similar to times t2 and t4, respectively.
The operation of image sensor 1 has been illustrated hereabove in relation with an example of operation in time-of-flight mode, where the photodetectors of a same pixel are driven in desynchronized fashion. An advantage of image sensor 1 is that it may also operate in other modes, particularly modes where the photodetectors of a same pixel are driven in synchronized fashion. Image sensor 1 may for example be driven in global shutter mode, that is, image sensor 1 may also implement an image acquisition method where beginnings and ends of the pixel integration phases are simultaneous.
An advantage of image sensor 1 thus is to be able to operate alternately according to different modes. Image sensor 1 may for example operate alternately in time-of-flight mode and in global shutter imaging mode.
According to an implementation mode, the readout circuits of the photodetectors of image sensor 1 are alternately driven in other operating modes, for example, modes where image sensor 1 is capable of operating:
Image sensor 1 may thus be used to form different types of images with no loss of resolution, since the different imaging modes capable of being implemented by image sensor 1 use a same number of pixels. The use of image sensor 1, capable of integrating a plurality of functionalities in a same pixel array and readout circuits, particularly enables to respond to the current constraints of miniaturization of electronic devices, for example, smart phone design and manufacturing constraints.
According to this implementation mode, it is started by providing CMOS support 3, particularly comprising the readout circuits (not shown) of pixel 12. CMOS support 3 further comprises, at its upper surface 30, contacting elements 32A and 32B. Contacting elements 32A and 32B have, in cross-section view in
Contacting elements 32A and 32B are for example formed from conductive tracks formed on the upper surface 30 of CMOS support 3 (horizontal portions of contacting elements 32A and 32B) and from conductive vias (vertical portions of contacting elements 32A and 32B) contacting the conductive tracks. The conductive tracks and the conductive vias may be made of a metallic material, for example, silver (Ag), aluminum (Al), gold (Au), copper (Cu), nickel (Ni), titanium (Ti), and chromium (Cr), or of titanium nitride (TiN). The conductive tracks and the conductive vias may have a monolayer or multilayer structure. In the case where the conductive tracks have a multilayer structure, the conductive tracks may be formed by a stack of conductive layers separated by insulating layers. The vias then cross the insulating layers. The conductive layers may be made of a metallic material from the above list and the insulating layers may be made of silicon nitride (SiN) or of silicon oxide (SiO2).
During this same step, CMOS support 3 is cleaned to remove possible impurities present at its surface 30. The cleaning is for example performed by plasma. The cleaning thus provides a satisfactory cleanness of CMOS support 3 before a series of successive depositions, detailed in relation with the following drawings, is performed.
In the rest of the disclosure, the implementation mode of the method described in relation with
During this step, an electron injection material is deposited at the surface of contacting elements 32A and 32B. A material selectively bonding to the surface of contacting elements 32A and 32B is preferably deposited to form a self-assembled monolayer (SAM). This deposition thus preferably or only covers the free upper surfaces of contacting elements 32A and 32B. One thus forms, as illustrated in
As a variant, a full plate deposition of an electron injection material having a sufficiently low lateral conductivity to avoid creating conduction paths between two neighboring contacting elements is performed.
Lower electrodes 122A and 122B form electron injection layers (EIL) and photodetectors 12A and 12B, respectively. Lower electrodes 122A and 122B are also called cathodes of photodetectors 12A and 12B. Lower electrodes 122A and 122B are preferably formed by spin coating or by dip coating.
The material forming lower electrodes 122A and 122B is selected from the group comprising:
Lower electrodes 122A and 122B may have a monolayer or multilayer structure.
During this step, a non-selective deposition of a first layer 120 is performed on the upper surface side 30 of CMOS support 3. The deposition is called “full plate” deposition since it covers the entire upper surface 30 of CMOS support 3 as well as the free surfaces of contacting elements 32A, 32B and of lower electrodes 122A and 122B. The deposition of first layer 120 is preferably performed by spin coating.
According to this implementation mode, the first layer 120 is intended to form the future active layers 120A, 120B of the photodetectors 12A and 12B of pixel 12. The active layers 120A and 120B of the photodetectors 12A and 12B of pixel 12 preferably have a composition and a thickness identical to those of first layer 120.
First layer 120 may comprise small molecules, oligomers, or polymers. These may be organic or inorganic materials, particularly comprising quantum dots. First layer 120 may comprise an ambipolar semiconductor material, or a mixture of an N-type semiconductor material and of a P-type semiconductor material, for example in the form of stacked layers or of an intimate mixture at a nanometer scale to form a bulk heterojunction. The thickness of first layer 120 may be in the range from 50 nm to 2 μm, for example, in the order of 300 μm.
Examples of P-type semiconductor polymers capable of forming layer 120 are:
Examples of N-type semiconductor materials capable of forming layer 120 are fullerenes, particularly C60, [6,6]-phenyl-C61-methyl butanoate ([60]PCBM), [6,6]-phenyl-C71-methyl butanoate ([70]PCBM), perylene diimide, zinc oxide (ZnO), or nanocrystals enabling to form quantum dots.
During this step, a non-selective deposition of a second layer 124 is performed on the upper surface side of CMOS support 3. The deposition is called “full plate” deposition since it covers the entire upper surface of first layer 120. The deposition of second layer 124 is preferably performed by spin coating.
According to this implementation mode, the second layer 124 is intended to form the future upper electrodes 124A, 124B of the photodetectors 12A and 12B of pixel 12. The upper electrodes 124A and 124B of the photodetectors 12A and 12B of pixel 12 preferably have a composition and a thickness identical to those of second layer 124.
Second layer 124 is at least partially transparent to the light radiation that it receives. Second layer 124 may be made of a transparent conductive material, for example, of transparent conductive oxide (TCO), of carbon nanotubes, of graphene, of a conductive polymer, of a metal, or of a mixture or an alloy of at least two of these compounds. Second layer 124 may have a monolayer or multilayer structure.
Examples of TCOs capable of forming second layer 124 are indium tin oxide (ITO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), titanium nitride (TiN), molybdenum oxide (MoO3), and tungsten oxide (WO3). An example of a conductive polymer capable of forming second layer 124 is the polymer known as PEDOT:PSS, which is a mixture of poly(3,4)-ethylenedioxythiophene and of sodium poly(styrene sulfonate), and polyaniline, also called PAni. Examples of metals capable of forming second layer 124 are silver, aluminum, gold, copper, nickel, titanium, and chromium. An example of a multilayer structure capable of forming second layer 124 is a multilayer AZO and silver structure of AZO/Ag/AZO type.
The thickness of second layer 124 may be in the range from 10 nm to 5 μm, for example, in the order of 30 μm. In the case where second layer 124 is metallic, the thickness of second layer 124 is smaller than or equal to 20 nm, preferably smaller than or equal to 10 nm.
During this step, three vertical openings 340, 342, and 244 are formed through first layer 120 and second layer 124 down to the upper surface 30 of CMOS support 3. These openings are preferably formed by etching after masking of the areas to be protected, for example, by resist deposition, exposure through a mask, and then dry etching, for example, by reactive ion etching, or by wet etching, for example, by chemical etching. As a variant, the deposition of the etch mask is performed locally, for example, by silk-screening, by heliography, by nano imprint, or by flexography, and the etching is performed by dry etching, for example by reactive ion etching, or by wet etching, for example by chemical etching.
In the example of
Vertical openings 340, 342, and 344 aim at separating photodetectors belonging to a same row of image sensor 1. Openings 340, 342, and 344 are for example formed by photolithography. As a variant, openings 340, 342, and 344 are formed by reactive ion etching or by chemical etching by means of an adequate solvent.
One thus obtains, as illustrated in
Thus, still in the example of
Upper electrodes 124A and 124B form hole injection layers (HIL) of photodetectors 12A and 12B, respectively. Upper electrodes 124A and 124B are also called anodes of photodetectors 12A and 12B.
Upper electrodes 124A and 12B are preferably made of the same material as the layer 124 where they are formed, as discussed in relation with
During this step, openings 340, 342, and 344 are filled with a third insulating layer 35, only portions 350, 352, and 354 of which are shown in
Portions 350, 352, and 354 of third layer 35 aim at electrically insulating neighboring photodetectors belonging to a same row of image sensor 1. According to an embodiment, portions 350, 352, and 354 of third layer 35 at least partially absorb the light received by image sensor 1 to optical isolate the photodetectors of the same row. The third insulation layer may be formed from a resin having its absorption at least covering the wavelengths of the photodiodes (visible and infrared). Such a resin, having a black-colored aspect, is then called “black resin”. In the example of
The third insulating layer 35 may be made of an inorganic material, for example, of silicon oxide (SiO2) or of silicon nitride (SiN). In the case where the third insulating layer 35 is made of silicon nitride, this material is preferably obtained by physical vapor deposition (PVD) or by plasma-enhanced chemical vapor deposition (PECVD).
Third insulating layer 35 may be made of a fluorinated polymer, particularly the fluorinated polymer commercialized under trade name “Cytop” by Bellex, of polyvinylpyrrolidone (PVP), of polymethyl methacrylate (PMMA), of polystyrene (PS), of parylene, of polyimide (PI), of acrylonitrile butadiene styrene (ABS), of polydimethylsiloxane (PDMS), of a photolithography resin, of epoxy resin, of acrylate resin, or of a mixture of at least two of these compounds.
As a variant, this insulating layer 35 may be made of another inorganic dielectric, particular of aluminum oxide (Al2O3). The aluminum oxide may be deposited by atomic layer deposition (ALD). The maximum thickness of third insulating layer 35 may be in the range from 50 nm to 2 μm, for example, in the order of 100 nm.
A fourth layer 360 is then deposited over the entire structure on the side of upper surface 30 of CMOS support 3. Fourth layer 360 is preferably a so-called “planarization” layer enabling to obtain a structure having a planar upper surface before the encapsulation of the photodetectors.
Fourth planarization layer 360 may be made of a polymer-based dielectric material. Planarization layer 360 may as a variant contain a mixture of silicon nitride (SiN) and of silicon oxide (SiO2), this mixture being obtained by sputtering, by physical vapor deposition (PVD) or by plasma-enhanced chemical vapor deposition (PECVD).
Planarization layer 360 may also be made of a fluorinated polymer, particularly the fluorinated polymer commercialized under trade name “Cytop” by Bellex, of polyvinylpyrrolidone (PVP), of polymethyl methacrylate (PMMA), of polystyrene (PS), of parylene, of polyimide (PI), of acrylonitrile butadiene styrene (ABS), of polydimethylsiloxane (PDMS), of a photolithography resin, of epoxy resin, of acrylate resin, or of a mixture of at least two of these compounds.
This variant differs from the step discussed in relation with
It is assumed in the rest of the disclosure that the variant discussed in relation with
During this step, a sixth layer 370 is deposited all over the structure on the side of upper surface 30 of CMOS support 3. Sixth layer 370 aims at encapsulating the organic photodetectors of image sensor 1. Sixth layer 370 thus enables to avoid the degradation, due to an exposure to water or to the humidity contained in the ambient air, of the organic materials forming the photodetectors of image sensor 1. In the example of
Sixth layer 370 may be made of alumina (Al2O3) obtained by an atomic layer deposition method (ALD), of silicon nitride (Si3N4) or of silicon nitride (SiO2) obtained by physical vapor deposition (PVD), of silicon nitride obtained by plasma-enhanced chemical vapor deposition (PECVD). Sixth layer 370 may as a variant be made of PET, of PEN, of COP, or of CPI.
According to an implementation mode, sixth layer 370 enables to further improve the surface condition of the structure before the forming of microlenses.
During this step, microlens 18 of pixel 12 is formed vertically in line with photodetectors 12A and 12B. In the example of
According to the considered materials, the method of forming the layers of image sensor 1 may correspond to a so-called additive process, for example, by direct printing of the material forming the organic layers at the desired locations, particularly in sol-gel form, for example, by inkjet printing, photogravure, silk-screening, flexography, spray coating, or drop casting. According to the considered materials, the method of forming the layers of the image sensor may correspond to a so-called subtractive method, where the material forming the organic layer is deposited all over the structure and where the non-used portions are then removed, for example, by photolithography or laser ablation. According to the considered material, the deposition over the entire structure may be performed, for example, by liquid deposition, by cathode sputtering, or by evaporation. Methods such as spin coating, spray coating, heliography, slot-die coating, blade coating, flexography, or silk-screening, may in particular be used. When the layers are metallic, the metal is for example deposited by evaporation or by cathode sputtering over the entire support and the metal layers are delimited by etching.
Advantageously, at least some of the layers of the image sensor may be formed by printing techniques. The materials of the previously-described layers may be deposited in liquid form, for example, in the form of conductive and semiconductor inks by means of inkjet printers. “Materials in liquid form” here also designates gel materials capable of being deposited by printing techniques. Anneal steps may be provided between the depositions of the different layers, but it is possible for the anneal temperatures not to exceed 150° C., and the deposition and the possible anneals may be carried out at the atmospheric pressure.
In
In
In other words, all the first photodetectors of the pixels belonging to a same pixel column of image sensor 1 have a common active layer and a common upper electrode. The upper electrode thus enables to address all the first photodetectors of the pixels of a same column while the lower electrode enables to individually address each first photodetector.
Similarly, all the second photodetectors of the pixels belonging to a same pixel column of image sensor 1 have a common active layer and a common upper electrode of the first photodetectors of these same pixels, and another common upper electrode, separate from the common upper electrode of the first photodetectors of these same pixels. This other common upper electrode thus enables to address all the second photodetectors of the pixels of a same column while the lower electrode enables to individually address each second photodetector.
The image sensor 4 shown in
More particularly, in the example of
According to this embodiment, the color filters 41R, 41G, and 41B of image sensor 4 give way to electromagnetic waves in frequency ranges different from the visible spectrum and give way to the electromagnetic waves of the infrared spectrum. Color filters 41R, 41G, and 41B may correspond to colored resin blocks. Each color filter 41R, 41G, and 41B is capable of giving way to the infrared radiation, for example, at a wavelength between 700 nm and 1 mm and, for at least some of the color filters, of giving way to a wavelength range of visible light.
For each pixel of a color image to be acquired, image sensor 4 may comprise:
Similarly to the image sensor 1 discussed in relation with
The photodetectors of each pixel 10, 12, 14, and 16 are coplanar and each associated with a readout circuit, as discussed in relation with
Various embodiments, implementation modes, and variations have been described. Those skilled in the art will understand that certain features of these various embodiments, implementation modes, and variants may be combined, and other variants will occur to those skilled in the art.
Finally, the practical implementation of the described embodiments, implementation modes, and variations is within the abilities of those skilled in the art based on the functional indications given hereabove. In particular, the adaptation of the driving of the readout circuits of image sensors 1 to 4 to other operating modes, for example, for the forming of infrared images with or without added light, the forming of images with a background suppression, and the forming of high-dynamic range images (simultaneous HDR) is within the abilities of those skilled in the art based on the above indications.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR1908251 | Jul 2019 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/070072 | 7/16/2020 | WO |
