Patent Publication Number: US-2021183929-A1

Title: Image sensing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent document claims the priority and benefits of Korean patent application No. 10-2019-0168712, filed on Dec. 17, 2019, which is incorporated by reference in its entirety as part of the disclosure of this patent document. 
     TECHNICAL FIELD 
     The technology and implementations disclosed in this patent document generally relate to an image sensing device. BACKGROUND 
     An image sensor is a device for converting an optical image into electrical signals. With the recent development of automotive, medical, computer and communication industries, the demand for high-performance image sensors is increasing in various devices such as digital cameras, camcorders, personal communication systems (PCSs), game consoles, surveillance cameras, medical micro-cameras, robots, etc. 
     SUMMARY 
     Various embodiments of the disclosed technology relate to an image sensing device for increasing light efficiency by minimizing crosstalk between contiguous pixels. 
     In an embodiment of the disclosed technology, an image sensing device may include a pixel array that includes a plurality of unit pixels, each unit pixel structured to convert incident light into an electrical signal in response to the incident light and electrical signals from the pixel array represent an image captured by the pixel array. The pixel array may include a plurality of color filters placed relative to the plurality of unit pixels and configured to filter the incident light to transmit light at predetermined wavelengths to be received by the plurality of unit pixels, a plurality of grid structures disposed between the plurality of color filters, and configured to prevent optical crosstalk from occurring between adjacent color filters, and a lens layer disposed over the color filters and the grid structure, and configured to direct the incident light to converge upon the plurality of color filters. The lens layer may include a plurality of main microlenses located to spatially correspond to the plurality of unit pixels, respectively, so that each main microlens directs incident light to a corresponding unit pixel and at least one edge microlens disposed offset from the main microlenses to commonly overlap at least partially with adjacent main microlenses, and configured to refract light rays incident upon the main microlenses to corresponding unit pixels to improve image sensing. 
     In another embodiment of the disclosed technology, an image sensing device may include a plurality of color filters formed to filter incident light to transmit light at predetermined wavelengths, a plurality of main microlenses respectively disposed over the plurality of color filters in a manner that the main microlenses are disposed to correspond to the color filters on a one to one basis, and at least one edge microlens disposed to be between and to overlap with adjacent main microlenses in a manner that the at least one edge microlens commonly overlaps at least partially with the plurality of main microlenses. 
     In another embodiment of the disclosed technology, an embodiment of the disclosed technology, an image sensing device may include a pixel array in which a plurality of unit pixels formed to convert incident light into an electrical signal corresponding to the incident light is arranged. The pixel array may include a plurality of color filters configured to filter out visible light from the incident light, a plurality of grid structures disposed between the plurality of color filters, and configured to prevent optical crosstalk from occurring between color filters contiguous to each other, and a lens layer disposed over the color filters and the grid structure, and configured to enable the incident light to converge upon the plurality of color filters. The lens layer may include a plurality of main microlenses, each of which is formed per unit pixel, and at least one edge microlens disposed between the main microlenses and the color filters to commonly overlap with the main microlenses contiguous to each other, and configured to refract light incident upon the main microlenses. 
     In another embodiment of the disclosed technology, an image sensing device may include a plurality of color filters formed to filter out visible light from incident light, a plurality of main microlenses respectively disposed over the plurality of color filters in a manner that the main microlenses are disposed to correspond to the color filters on a one to one basis, and at least one edge microlens disposed between the color filters and the main microlenses in a manner that the at least one edge microlens commonly overlaps with the plurality of main microlenses 
     It is to be understood that both the foregoing general description and the following detailed description of the disclosed technology are illustrative and explanatory and are intended to provide further explanation of the disclosure as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of an image sensing device based on some implementations of the disclosed technology. 
         FIG. 2  is a plan view illustrating an example of lens layers of unit pixels formed in a pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
         FIG. 3  is a cross-sectional view illustrating an example of the unit pixels taken along the line A-A′ shown in  FIG. 2  based on some implementations of the disclosed technology. 
         FIG. 4A  is a conceptual diagram illustrating an example of a propagation direction of light incident upon an edge region of a main microlens arranged without an edge microlens based on some implementations of the disclosed technology. 
         FIG. 4B  is a conceptual diagram illustrating an example of the propagation direction of light incident upon the edge region of the main microlens arranged with the edge microlens based on some implementations of the disclosed technology. 
         FIGS. 5A to 5C  are cross-sectional views illustrating examples of a method for forming a lens layer shown in  FIG. 3  based on some implementations of the disclosed technology. 
         FIGS. 6A to 6F  are cross-sectional views illustrating other examples of a method for forming the lens layer shown in  FIG. 3  based on some implementations of the disclosed technology. 
         FIG. 7  is a plan view illustrating an example of the lens layers of the unit pixels formed in the pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
         FIG. 8  is a plan view illustrating another example of the lens layers of the unit pixels formed in the pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
         FIG. 9  is a plan view illustrating still another example of the lens layers of the unit pixels formed in the pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
     
    
    
     DETAILED DESCRIPTION 
     This patent document provides implementations and examples of an image sensing device that can increase the light collection efficiency of microlenses disposed over the imaging pixel array by inserting additional microlenses at the edge regions of the main microlenses such that the additional microlenses overlap with edge regions or dead zones of the main microlenses. The disclosed technology can be used in some embodiments to implement an image sensing device which can increase light efficiency by minimizing crosstalk between contiguous pixels. 
     Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts. In the following description, a detailed description of related known configurations or functions incorporated herein will be omitted to avoid obscuring the subject matter. 
       FIG. 1  is an example of a block diagram illustrating an image sensing device based on some implementations of the disclosed technology. 
     In some implementations, the image sensing device may include a pixel array  100 , a correlated double sampler (CDS)  200 , an analog-to-digital converter (ADC)  300 , a buffer  400 , a row driver  500 , a timing generator  600 , a control register  700 , and a ramp signal generator  800 . 
     The pixel array  100  may include unit pixels (PXs) consecutively arranged in rows and columns in a two-dimensional (2D) array. Each of the unit pixels (PXs) may convert incident light into an electrical signal to generate a pixel signal, which is sent to the correlated double sampler (CDS)  200  through column lines. Each unit pixel (PX) may include a photoelectric conversion element formed in a substrate. In some implementations, the unit pixels (PXs) are formed in a substrate that includes a first surface upon which light is incident and a second surface facing away from the first surface. A lens layer is arranged above a photoelectric conversion element to cause light rays to converge upon the photoelectric conversion element. The lens layer may include a specific structure which enables light incident upon the edge region of the unit pixel (PX) to converge upon the photoelectric conversion element. 
     The correlated double sampler (CDS)  200  may be used to remove an undesired offset value of pixels by sampling a pixel signal twice to remove the difference between these two samples. In some implementations, the correlated double sampler (CDS)  200  may hold and sample electrical image signals received from the pixels (PXs) of the pixel array  100 . For example, the correlated double sampler (CDS)  200  may perform sampling of a reference voltage level and a voltage level of the received electrical image signal in response to a clock signal received from the timing generator  600 , and may generate an analog signal corresponding to a difference between the reference voltage level and the voltage level of the received electrical image signal. The analog signal is sent to the analog-to-digital converter (ADC)  300  for digitalization. 
     The analog-to-digital converter (ADC)  300  is used to convert analog signals to digital signals. Examples of the analog-to-digital converter (ADC)  300  may include a ramp-compare type analog-to-digital converter that compares the analog pixel signal with a reference signal such as a ramp signal that ramps up or down, and a timer counts until a voltage of the ramp signal matches the analog signal. In some implementations, the analog-to-digital converter (ADC)  300  may compare a ramp signal received from the ramp signal generator  800  with a sampling signal received from the correlated double sampler (CDS)  200  to determine whether the voltage level of the ramp signal matches the voltage level of the sampling signal. The analog-to-digital converter (ADC)  300  may receive clock signals from the timing generator  600  to count the clock signals until the voltage level of the ramp signal matches the voltage level of the sampling signal, and may output a count value as a converted digital signal to the buffer  400 . 
     The buffer  400  may temporarily store each of the digital signals received from the analog-to-digital converter (ADC)  300 , and may sense and amplify each of the digital signals to output each of the amplified digital signals. Therefore, the buffer  400  may include a memory (not shown) and a sense amplifier (not shown). The memory may store the count value, which is a digital signal converted from the output signals of the plurality of unit pixels (PXs). The sense amplifier may sense and amplify each count value received from the memory. 
     The row driver  500  may selectively activate the pixel array  100  on a row line basis in response to an output signal of the timing generator  600 . For example, the row driver  500  may generate a selection signal to select any one of the plurality of row lines. 
     The timing generator  600  may generate a timing signal to control the operations of the row driver  500 , the correlated double sampler (CDS)  200 , the analog-to-digital converter (ADC)  300 , and the ramp signal generator  800 . 
     The control register  700  may generate control signals to control the operations of the ramp signal generator  800 , the timing generator  600 , and the buffer  400 . 
     The ramp signal generator  800  may generate a ramp signal to convert an image signal received from the buffer  400  to digital signals in response to a control signal received from the control register  700  and a timing signal received from the timing generator  600 . 
       FIG. 2  is a plan view illustrating an example of lens layers of unit pixels formed in the pixel array  100  shown in  FIG. 1  based on some implementations of the disclosed technology.  FIG. 3  is a cross-sectional view illustrating an example of the unit pixels taken along the line A-A′ shown in  FIG. 2  based on some implementations of the disclosed technology. 
     Referring to  FIGS. 2 and 3 , the pixel array  100  of the image sensing device may include a substrate  110 , a buffer layer  120 , a color filter layer  130 , grid structures  140 , and a lens layer  150 . 
     The substrate  110  may include a semiconductor substrate having a first surface and a second surface facing away from each other. 
     The semiconductor substrate  110  may include a material in a monocrystalline state. In one example, the semiconductor substrate  110  may include a silicon-containing material. That is, the semiconductor substrate  110  may include a monocrystalline silicon-containing material. The semiconductor substrate  110  may include P-type impurities diffused or implanted therein. The semiconductor substrate layer  110  may include photoelectric conversion elements  112  such that each unit pixel (PX) includes one of the photoelectric conversion elements  112  isolated from adjacent photoelectric conversion elements by a device isolation film  114 . 
     Each of the photoelectric conversion elements  112  may include an organic or inorganic photodiode. The photoelectric conversion element  112  may include impurity regions vertically stacked in the substrate  110 . For example, each of the photoelectric conversion elements  112  may include a photodiode in which an N-type impurity region and a P-type impurity region are vertically stacked on top of one another. The N-type impurity region and the P-type impurity region may be formed by ion implantation. The device isolation film  114  may include a deep trench isolation (DTI) structure. 
     The buffer layer  120  may operate as a planarization layer for planarization of the layers formed over the first surface of the substrate  110 . In addition, the buffer layer  120  may operate as an anti-reflection film that allows incident light received through the lens layer  150  and the color filter layers  130  to transmit to the photoelectric conversion elements  112 . The buffer layer  120  may include a multilayer structure formed by stacking different materials having different refractive indices. For example, the buffer layer  120  may include a multilayer structure formed by stacking a nitride film  122  and an oxide film  124  on top of one another. The nitride film  122  may include a silicon nitride film (Si x N y , where each of ‘x’ and ‘y’ is a natural number) or a silicon oxide nitride film (Si x O y N z , where each of ‘x’, ‘y’, and ‘z’ is a natural number). The oxide film  124  may include a monolayer structure or a multilayer structure formed by stacking oxide films. The oxide film  124  may include at least one of an undoped silicate glass (USG) film and an ultra low temperature oxide (ULTO) film. The oxide film  124  may be formed simultaneously with the capping film  146  of the grid structure  140 . For example, the oxide film  124  may be formed of the same material as the capping film  146  of the grid structure  140 , and the oxide film  124  and the capping film  146  may be simultaneously formed through the same deposition process. 
     The color filter layer  130  may include optical filters located above the photoelectric conversion elements  112  to filter the light to be detected by the photoelectric conversion elements  112 . In some implementations, the color filter layer  130  may transmit visible light at a certain wavelength while blocking light at other wavelengths. The color filter layer  130  may include a plurality of color filters. Each unit pixel (PX) includes at least one color filter structured to fill the lower parts of the gaps between the grid structures  140 . The color filter layer  130  may include a plurality of red color filters (Rs), a plurality of green color filters (Gs), and a plurality of blue color filters (Bs). Each red color filter (R) may transmit only red light from among RGB lights of visible light. Each green color filter (G) may transmit only green light from among RGB lights of visible light. Each blue color filter (B) may transmit only blue light from among RGB lights of visible light. In an implementation, the red color filters (Rs), the green color filters (Gs), and the blue color filters (Bs) may be arranged in a Bayer pattern. In another implementation, the color filter layer  130  may include a plurality of cyan color filters, a plurality of yellow color filters, and a plurality of magenta color filters. 
     The grid structures  140  may be arranged at intervals between adjacent color filters to prevent optical crosstalk from occurring between the color filters. In an example implementation, the grid structure  140  may be formed in a hybrid structure that includes a metal layer  142 , a low refractive index material layer such as an air layer  144  disposed over the metal layer  142 , and a capping film  146 . The capping film  146  may be an outermost layer of the grid structure  140  structured to cover the metal layer  142  and the air layer  144 . The capping film  146  may be formed to extend to a lower portion of the color filter layers  130 . In this case, the capping film  146  formed below the color filter layers  130  may be used as a portion  124  of the buffer layer  120 . In another example implementation, the grid structures  140  can also be formed without including the air layer. 
     The lens layer  150  may be formed over the color filter layers  130  and the grid structures  140  to enable incident light to converge upon color filters of the color filter layers  130 . The lens layer  150  may include an over-coating layer  152 , an edge microlens  154 , and a main microlens  156 . 
     The over-coating layer  152  may operate as a planarization layer for planarization of the layers formed by the grid structure  140  and the color filter layer  130 . It is difficult to control a thickness (height) of the color filter layer  130  and a thickness of the grid structure  140 , rendering the surface of the resultant structure uneven. The over-coating layer  152  may be formed over the color filter layer  130  and the grid structure  140  to provide an even surface for the subsequently formed microlens layers. 
     In some implementations, the over-coating layer  152  may be formed of the same materials as those of the main microlens  156 . 
     For example, the over-coating layer  152  may include a photoresist material or an oxide film. 
     The disclosed technology may be implemented in some embodiments to provide an image sensing device that can increase the light collection efficiency of microlenses disposed over the imaging pixel array by inserting additional microlenses (e.g., edge microlens  154 ) at the edge regions of the main microlenses (e.g., main microlens  156 ). 
     The edge microlens  154  may refract light rays incident upon the edge region of the main microlens  156  to direct the refracted lights toward the photoelectric conversion element  112  of the corresponding unit pixel. 
     When viewed in a vertical plane, the edge microlens  154  may be formed between the main microlens  156  and the over-coating layer  152 . For example, the edge microlens  154  may be formed between the main microlens  156  and the over-coating layer  152  such that the edge microlens  154  can vertically overlap with the edge region of the main microlens  156 . Each of the edge microlenses  154  may be formed in a dome shape that has a flat bottom surface and a convex top surface having a curved profile. 
     When viewed in a horizontal plane, the edge microlenses  154  may be formed in a circular shape, and the center portion of the edge microlens  154  may be located at a boundary region between adjacent main microlenses  156  in a manner that one edge microlens  154  can overlap the edge regions of adjacent main microlenses  156 . 
     In an implementation, an edge microlens  154  can be arranged at a boundary region between two adjacent main microlenses  156 . For example, the edge microlenses  154  may be spaced apart from each other by a predetermined distance in a first direction (e.g., X-axis direction) and a second direction (e.g., Y-axis direction) perpendicular to the first direction in a manner that the grid structure  140  disposed between neighboring color filters can vertically overlap with the center portion of the edge microlens  154 . That is, one edge microlens  154  may overlap with the edge regions of two adjacent main microlenses  156 . In another implementation, an edge microlens  154  can be arranged at a boundary region between four adjacent main microlenses  156  as will be discussed with reference to  FIG. 7 . 
     In some embodiments of the disclosed technology, the edge microlens  154  may be formed of a material having a higher refractive index than the main microlens  156 . 
     Each unit pixel includes one main microlens  156  to direct light rays to the color filter layer  130  of the corresponding unit pixel. For example, the main microlenses  156  may respectively correspond to the unit pixels on a one to one basis, and may be formed over the over-coating layer  152  and the edge microlens  154  in the corresponding pixel region. 
     The main microlens  156  may be divided into a center region and edge regions surrounding the center region. An edge region of the main microlens  156  may be formed to partially overlap with the edge microlens  154 . For example, edge regions formed to meet X-axis and Y-axis that pass through the center region of the main microlens  156  may be formed to overlap with the corresponding edge microlens  154 . The center portion of the main microlens  156  may be formed to overlap with the center portion of the photoelectric conversion element  112 . 
     Light rays incident upon the edge region of the main microlens  156  formed to overlap with the edge microlens  154  may be refracted toward the color filter layer  130 . 
     The main microlens  156  may include light transmission material having a lower refractive index than the edge microlens  154 . For example, the main microlens  156  may include a photoresist material or an oxide film. 
       FIG. 4A  is a conceptual diagram illustrating an example of the propagation direction of light incident upon the edge region of the main microlens arranged without the edge microlens based on some implementations of the disclosed technology.  FIG. 4B  is a conceptual diagram illustrating an example of the propagation direction of light incident upon the edge region of the main microlens arranged with the edge microlens based on some implementations of the disclosed technology. 
     Functions and operations of the edge microlens based on some implementations of the disclosed technology will hereinafter be described with reference to  FIGS. 4A and 4B . 
     Referring to  FIG. 4A , if the edge microlens  154  does not exist, light incident upon the edge region of the main microlens  156  may be refracted from the surface of the main microlens  156 , and the refracted light may pass through the main microlens  156  and the over-coating layer  152 . 
     In contrast, as shown in  FIG. 4B , if the edge microlens  154  is disposed below the main microlens  156 , light incident upon the edge region of the main microlens  156  may be primarily refracted by the main microlens  156  and may then be secondarily refracted by the edge microlens  156 . 
     Since the edge microlens  154  is higher in refractive index than the main microlens  156  and has a curvature, light rays refracted by the edge microlens  154  may have a smaller refraction angle than the other light rays passing through only the main microlens  156 . The refraction angle of the light rays refracted by the edge microlens  154  can be adjusted depending on a refractive index of the edge microlens  154 , a radius of curvature (RoC) of the edge microlens  154 , and other characteristics of the edge microlens  154 . 
     If light rays having penetrated the lens layer  150  has a small refraction angle, the degree of light scattering in the buffer layer  120  can become relatively smaller as compared to light rays having a large refraction angle. Therefore, the optical crosstalk caused by light scattering in the buffer layer  120  can be reduced, while increasing the amount of light rays converging upon the photoelectric conversion element  112 . 
     In addition, even if the over-coating layer  152  is formed of the same materials as those of the main microlens  156 , light scattering may still occur at a boundary region between the over-coating layer  152  and the main microlens  156 . However, if the angle of incidence of light rays incident upon the over-coating layer  152  is reduced by the edge microlens  154 , less light scattering may occur. Therefore, since the edge microlens  154  is used, the optical crosstalk caused by the over-coating layer  152  can be effectively reduced. 
       FIGS. 5A to 5C  are cross-sectional views illustrating examples of a method for forming the lens layer shown in  FIG. 3  based on some implementations of the disclosed technology. 
     Referring to  FIG. 5A , the over-coating layer  152  may be formed over a lower structure including the color filter layers  130  and the grid structures  140 . 
     The color filter layers  130  and the grid structures  140  can be formed as discussed above. 
     The over-coating layer  152  may be used as a planarization layer for planarization of the layers including the color filter layer  130  and the grid structure  140 , and may include a photoresist material. 
     Subsequently, high-refractive-index material patterns  154 ′ may be formed in regions where the edge microlenses are to be formed, over the over-coating layer  152 . The high-refractive-index material pattern  154 ′ may include a material having a higher refractive index than the main microlens to be formed in a subsequent process. For example, each of the high-refractive-index material patterns  154 ′ may include a polyimide-based resin in which microparticles (e.g., nanoparticles) having high-refractive-index materials are evenly dispersed in the form of granules within a polymer layer. In this case, the high-refractive-index material may include at least one of high-refractive-index oxide materials, for example, titanium oxide (TiO 2 ), tantalum oxide (TaO 2 , Ta 2 O 5 ), zirconium oxide (ZrO 2 ), zinc oxide (ZnO), tin oxide (SnO), aluminum oxide (Al 2 O 3 ), lanthanum oxide (La 2 O 3 ), cesium oxide (CeO 2 ), yttrium oxide (Y 2 O 3 ), silicon oxide nitride (SiON), etc. 
     Referring to  FIG. 5B , through a thermal reflow process on the high-refractive-index material pattern  154 ′, dome-shaped edge microlenses  154  may be formed over the over-coating layer  152 . 
     Subsequently, an organic material pattern  156 ′ for forming the main microlens may be formed between the edge microlenses  154 . For example, the organic material pattern  156 ′ may include a photoresist pattern. 
     Referring to  FIG. 5C , a thermal reflow process is performed on the organic material pattern  156 ′, such that the dome-shaped main microlenses  156  may be formed over the over-coating layer  152  and the edge microlenses  154 . In this way, the edge regions of the main microlenses  156  may be formed to overlap with the edge microlenses  154 . 
       FIGS. 6A to 6F  are cross-sectional views illustrating other examples of a method for forming the lens layer shown in  FIG. 3  based on some implementations of the disclosed technology. 
     Referring to  FIG. 6A , the over-coating layer  152  may be formed over a lower structure including the color filter layers  130  and the grid structures  140 . 
     Subsequently, a high-refractive-index material layer  157  may be formed over the over-coating layer  152 . The high-refractive-index material layer  157  may include at least one of high-refractive-index oxide materials, for example, titanium oxide (TiO 2 ), tantalum oxide (TaO 2 , Ta 2 O 5 ), zirconium oxide (ZrO 2 ), zinc oxide (ZnO), tin oxide (SnO), aluminum oxide (Al 2 O 3 ), lanthanum oxide (La 2 O 3 ), cesium oxide (CeO 2 ), yttrium oxide (Y 2 O 3 ), silicon oxide nitride (SiON), etc. 
     Subsequently, organic material patterns  158  may be formed in regions where the edge microlenses are to be formed, over the high-refractive-index material layer  157 . For example, each of the organic material patterns  158  may include a photoresist pattern. 
     Referring to  FIG. 6B , a thermal reflow process is performed on the organic material pattern  158 , such that a dome-shaped edge-lens mask pattern  158 ′ may be formed over the high-refractive-index material layer  157 . 
     Referring to  FIG. 6C , a lower high-refractive-index material layer  157  may be etched using the edge-lens mask patterns  158 ′ as an etch mask, thereby forming dome-shaped edge microlenses  154  over the over-coating layer  152 . 
     Subsequently, an insulation layer  159  may be formed over the over-coating layer  152  and the edge microlenses  154 . In this case, the insulation layer  159  may include an oxide film that has a lower refractive index than each of the edge microlenses  154 . 
     Referring to  FIG. 6D , the organic patterns  156 ′ may be formed in regions where the main microlenses are to be formed, over the insulation layer  159 . For example, each of the organic patterns  156 ′ may include a photoresist pattern. 
     Referring to  FIG. 6E , a thermal reflow process is performed on the organic patterns  156 ′, thereby forming dome-shaped main-lens mask patterns  156 ″ over the insulation layer  159 . 
     Referring to  FIG. 6F , a lower insulation layer  159  disposed below the main-lens mask pattern  156 ″ may be etched using the main-lens mask patterns  156 ″ as an etch mask, such that dome-shaped main microlenses  156  are formed over the over-coating layer  152  and the edge microlenses  154 . In this case, the edge regions of the main microlenses  156  may be formed to overlap with the edge microlenses  154 . 
       FIG. 7  is a plan view illustrating an example of the lens layers of the unit pixels formed in the pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
     In some implementations, the center portion of each edge microlens  154  may be located at a boundary region between the corresponding main microlenses  156  in a manner that the edge microlenses  154  can be located to span the edge regions of four contiguous main microlenses  156 . 
     For example, each of the edge microlenses  154  may be formed in a circular dome shape in a manner that the center portion of the edge microlenses  154  can be located at a boundary region (i.e., a dead zone) between four adjacent main microlenses  156  and can partially overlap with the edge regions of the four main microlenses  156 . 
     In this case, the center portion of the edge microlenses  154  may be formed to overlap with a specific region in which one grid structure  140  extending in the X-axis direction and another grid structure  140  extending in the Y-axis direction are arranged to cross each other. 
     The remaining structures other than structures of the edge microlenses shown in  FIG. 7  are similar or identical to those of 
       FIG. 3 , and as such a detailed description thereof will herein be omitted for convenience of description. 
       FIG. 8  is a plan view illustrating another example of the lens layers of the unit pixels formed in the pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
     In some implementations, each of the edge microlenses  154  may be formed to overlap the edge regions of the contiguous main microlenses  156  adjacent to each other, and may be formed in a grid shape that overlap with the main microlenses  156  except the center region of the main microlenses  156 . For example, the edge microlenses  154  are formed to overlap with the dead zones in a situation in which only the center region of each of the main microlenses  156  is formed in a circular shape, such that the edge microlenses  154  can be formed in a single integrated lens shape overlapping with the edge regions (e.g., entire edge regions). 
     The remaining structures other than structures of the edge microlenses shown in  FIG. 8  are similar or identical to those of  FIG. 3  and, as such, a detailed description thereof will herein be omitted for convenience of description. 
       FIG. 9  is a plan view illustrating still another example of the lens layers of the unit pixels formed in the pixel array shown in  FIG. 1  based on some implementations of the disclosed technology. 
     In some implementations, while each of the edge microlenses  154  may be formed in the same grid shape as that of the grid structure  140 , each of the edge microlenses  154  may have a larger width than each of the grid structures  140 . For example, the edge microlenses  154  are formed to overlap with the dead zones in a situation in which only the center region of each of the main microlenses  156  is formed in a rectangular shape, such that the edge microlenses  154  can be formed in a single integrated lens shape overlapping with the edge regions. 
     The remaining structures other than structures of the edge microlenses shown in  FIG. 9  are similar or identical to those of  FIG. 3  and, as such, a detailed description thereof will herein be omitted for convenience of description. 
     As is apparent from the above description, the image sensing device based on some implementations of the disclosed technology can increase the light collection efficiency by minimizing the optical crosstalk between contiguous pixels. 
     Those skilled in the art will appreciate that the embodiments may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the disclosure. 
     Although a number of illustrative embodiments have been described, it should be understood that numerous other modifications and embodiments can be devised based on what is disclosed and/or illustrated.