Cavityless chip-level image sensor package

Abstract

A cavity-free chip-level image sensor package includes a substrate, a microlens array, and a low-index layer. The substrate includes a plurality of pixels forming a pixel array. The microlens array includes a plurality of microlenses each (i) having a lens index of refraction, (ii) aligned with a respective one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the respective one of the plurality of pixels. The low-index layer has a first index of refraction less than the lens index of refraction. The low-index layer also includes a lower surface at least a portion of which is conformal with each non-planar microlens surface. The microlens array is between the pixel array and the low-index layer.

Description

Technical Field

[0001] This invention relates to image sensors, and more particularly to the packaging of pixel arrays of image sensors. Background Technology

[0002] Camera modules in products such as standalone digital cameras, mobile devices, automotive components, and medical devices typically include complementary metal-oxide-semiconductor (CMOS) image sensors. A CMOS image sensor converts light from a scene imaged by a camera lens into a digital signal, which is then converted into a displayed image and / or a file containing image data. A CMOS image sensor includes a pixel array and a corresponding microlens array, where each microlens focuses light onto a corresponding pixel. In many camera modules, the CMOS image sensor is part of a chip-scale package, which includes a protective layer over the photosensitive area of ​​the CMOS image sensor. Common problems with existing image sensors include delamination and image artifacts caused by light reflected from the protective layer. Summary of the Invention

[0003] In a first aspect, a cavity-free chip-level image sensor package includes a substrate, a microlens array, and a low-refractive-index layer. The substrate includes a plurality of pixels forming a pixel array. The microlens array includes a plurality of microlenses, each of the microlenses (i) having a lens reflectivity, (ii) being aligned with a corresponding one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the corresponding one of the plurality of pixels. The low-refractive-index layer has a first refractive index less than the lens refractive index. The low-refractive-index layer also includes a lower surface, at least a portion of which is conformal to each non-planar microlens surface. The microlens array is located between the pixel array and the low-refractive-index layer.

[0004] In a second aspect, the method for encapsulating an image sensor includes covering a pixel array of the image sensor with a low-refractive-index layer having a first refractive index. The image sensor includes a microlens array comprising a plurality of microlenses, each of the plurality of microlenses being (i) aligned with a corresponding one of the plurality of pixels, and (ii) having a non-planar microlens surface facing away from the corresponding one of the plurality of pixels. Covering the pixel array results in the lower surface of the low-refractive-index layer conforming to each non-planar microlens surface. Attached Figure Description

[0005] Figure 1 A camera including a chip-scale image sensor package is shown.

[0006] Figure 2 and Figure 3 These are a cross-sectional view and a plan view of a chip-level image sensor package, respectively.

[0007] Figure 4This is a cross-sectional schematic diagram of the first cavity-free chip-level image sensor package in the embodiment.

[0008] Figure 5 This is a cross-sectional schematic diagram of the second cavity-free chip-level image sensor package in the embodiment.

[0009] Figure 6 The image is a scanning electron microscope image of the third cavity-free chip-level image sensor package in the embodiment.

[0010] Figure 7 This is a cross-sectional schematic diagram of the fourth cavity-free chip-level image sensor package in the embodiment.

[0011] Figure 8 This is a cross-sectional schematic diagram of the fifth cavity-free chip-level image sensor package in the embodiment.

[0012] Figure 9 This is a scanning electron microscope image of the sixth cavity-free chip-level image sensor package in the embodiment.

[0013] Figure 10 This is a graph illustrating the visible light transmittance of a low-refractive-index layer in an embodiment of the cavity-free chip-scale image sensor package disclosed herein.

[0014] Figure 11 This is a graph showing the visible light transmittance of the low refractive index layer on the first side of the protective glass in an embodiment.

[0015] Figure 12 This is a flowchart illustrating a method for encapsulating an image sensor in an embodiment. Detailed Implementation

[0016] Figure 1 A camera 190 for imaging a scene is shown. The camera 190 includes a chip-level image sensor package 100, which includes a pixel array 114. Hereinafter, "CSP" stands for "chip-level image sensor package". Figure 2 This is a cross-sectional schematic diagram of CSP 200, which is an example of CSP 100. Figure 2 The cross-sectional schematic diagram is parallel to the plane formed by the orthogonal directions 298X and 298Z (298X and 298Z are orthogonal to direction 298Y respectively). Figure 3 This is a floor plan diagram of CSP 200. It's best to view it along with the description below. Figure 2 and Figure 3 .

[0017] CSP 200 includes a device substrate 210, a spacer 230, and a protective glass 250. For clarity, Figure 3Protective glass 250 is not shown. Device substrate 210 includes pixel array 214 configured to detect light transmitted through protective glass 250. Pixel array 214 includes a plurality of pixels and is an example of pixel array 114. CSP 200 may also include microlens array 220. Microlens array 220 includes a plurality of microlenses, each of which is aligned with a corresponding one of the plurality of pixels in pixel array 214. Device substrate 210 may be a semiconductor die and may be formed of or may include semiconductors (e.g., silicon, germanium, or combinations thereof). Device substrate 210 has an upper surface 219 perpendicular to direction 298Z.

[0018] Spacer 230 is on the upper surface 219 of device substrate 210 and at least partially surrounds pixel array 214. Spacer 230 has an inner surface 231, an upper surface 232, and a lower surface 233. Protective glass 250 is attached to the upper surface 232 and covers pixel array 214. CSP 100 may include (a) upper surface 232 and lower surface 250B, and (b) an adhesive between at least one of lower surface 233 and upper surface 219.

[0019] CSP 200 may also include one or more adhesive pads 205, a redistribution layer 206, and a dielectric layer 204. The redistribution layer 206 electrically connects the pixel array 214 to the conductor 204. Each adhesive pad 205 has dimensions 205X ​​and 205Y, each of which is, for example, 100±20μm. Figure 2 A bare image sensor 229 is specified, which includes a device substrate 210, a pixel array 214, and a microlens array 220. The bare image sensor 229 may also include one or more of a redistribution layer 206, a dielectric layer 208, a conductor 204, and / or an adhesive pad 205. The dielectric layer 208 may be formed of a solder mask material, such as a polymer.

[0020] The protective glass 250 can be formed from aluminosilicate glass, alkali-free glass, borosilicate glass, quartz glass, or a combination thereof. The protective glass 250 has a thickness of 259 mm, for example, between 0.20 mm and 0.50 mm.

[0021] A disadvantage of CSP 200 is that light transmitted through the protective glass 250 can be reflected from the inner surface 231 toward the microlens array 220, resulting in artifacts in the image captured by the camera 190. A second disadvantage of CSP 200 is that the spacer 230 is prone to being delaminated with the device substrate 210 and / or the protective glass 250.

[0022] Figure 4 This is a cross-sectional schematic diagram of the cavityless CSP 400. The CSP 400 is... Figure 1An example of a CSP 100 for a camera 190. A cavity-less CSP 400 includes a device substrate 410 and a low-refractive-index layer 430. The device substrate 410 includes a pixel array 214, on which a microlens array 220 is disposed. The microlens array 220 may be located between the device substrate 210 and the low-refractive-index layer 430. The device substrate 410 is an example of the device substrate 210.

[0023] The low-refractive-index layer 430 can serve the same protective function as the protective glass 250, which is supported by the spacer 230 in the CSP 200. Since the low-refractive-index layer 430 does not require the spacer 230, it provides the same benefits as the protective glass 250 without the aforementioned image artifacts and delamination issues.

[0024] The low-refractive-index layer 430 has a refractive index n3 smaller than the refractive index n2 of each microlens in the microlens array 220. The microlens array 220 has a plurality of non-planar microlens surfaces 222, each corresponding (e.g., aligned) to a corresponding one of the plurality of microlenses. The microlens surfaces 222 can form a single, continuous non-planar upper surface of the microlens array 220. The microlens array 220 has a maximum height 225 above the upper surface 219. The maximum height 225 can correspond to one or more vertices or local maximum heights of the non-planar microlens surfaces 222. Each microlens in the microlens array 220 has a width (or diameter) between 0.8 micrometers and 10 micrometers in at least one of the directions 298X or 298Y.

[0025] The low-refractive-index layer 430 has a lower surface 431 and an upper surface 439. The lower surface 431 includes a surface region 432 that conforms to the microlens surface 222. Figure 4 As shown, a low-refractive-index layer 430 covers the microlens array 220. A surface region 432 covers the microlens array 220 and conforms to the microlens surfaces 222. The low-refractive-index layer 430 and / or surface region 432 may completely cover the microlens array 220. For example, the low-refractive-index layer 430 and / or surface region 432 covers the region between each microlens surface 222 and adjacent microlens surfaces 222. A portion of the lower surface 432 may conform to and may abut the upper surface 210 of the device substrate 410. Without departing from its boundaries, the surface region 432 may correspond to the entirety of the lower surface 431. The upper surface 439 may be planar and may be parallel to the upper surface 219 of the device substrate 210 within manufacturing tolerances. The low-refractive-index layer 430 may cover one or more adhesive pads 205 of the device substrate 410.

[0026] At visible electromagnetic wavelengths, the refractive index n2 of the microlens array can exceed the refractive index n3 of the low-refractive-index layer 430 by at least Δn = 0.2. The lens refractive index n2 can be in the range of 1.50 ± 0.04 at visible electromagnetic wavelengths. The refractive index n3 can be between 1.20 and 1.25 at visible electromagnetic wavelengths. The low-refractive-index layer 430 has a minimum thickness 437 between the surface region 432 and the upper surface 439. The minimum thickness 437 can be in the range of 100 to 110 nm. The product of the minimum thickness 437 and the refractive index n3 of the low-refractive-index layer 439 can correspond to a quarter-wavelength light thickness at visible electromagnetic wavelengths. For example, the visible electromagnetic wavelength can be between 480 nm and 515 nm, or between 525 nm and 575 nm. The aforementioned refractive index and thickness ranges are advantageous for optimizing the amount of light incident on the microlens array 220 reaching the pixel array 214.

[0027] The low-refractive-index layer 430 can be a nanoporous membrane or nanoporous layer, for example, formed of silica or aluminum hydroxide (ALO(OH)). When the low-refractive-index layer 430 is a nanoporous layer, such as an aerogel, the layer may include pores with a maximum width (“pore size”) of less than one hundred nanometers so that the pores do not scatter visible light. The average pore size (e.g., root mean square) can be between 7 nanometers and 15 nanometers, for example, 10 nanometers. The low-refractive-index layer 430 can be formed via bevel deposition (a vapor deposition process).

[0028] Figure 5 This is a cross-sectional schematic diagram of the cavityless CSP 500. The CSP 500 is... Figure 1 An example of a CSP 100 for a camera 190. A cavity-less CSP 500 includes a low-refractive-index layer 530, an adhesive layer 540, and a protective glass 250 on a bare image sensor 229. The low-refractive-index layer 530 is an example of a low-refractive-index layer 430 and covers an adhesive pad 205 over the bare image sensor 229. In the cavity-less CSP 500, the adhesive pad 205 is beneath at least one of the low-refractive-index layer 530, the adhesive layer 540, and the protective glass 250. The low-refractive-index layer 530 may be in direct contact with the adhesive pad 205. A deliberate choice of the material of the low-refractive-index layer 530 (e.g., its refractive index) can also result in increased light transmission to the pixel array 214 compared to a CSP 200.

[0029] The low-refractive-index layer 530 can completely cover the microlens array 220. In an embodiment, the low-refractive-index layer 530 covers the area between each microlens surface 222 and adjacent microlens surfaces 222. Figure 5This refers to the surface region 254 and side surface 252 of the lower surface 250B of the protective glass 250. Surface region 254 is above surface region 224 of the microlens array 220. Surface region 224 may include: portions of one or more microlens surfaces 222, surfaces between adjacent microlens surfaces 222, surfaces adjacent to microlens surfaces 222, or combinations thereof. The low refractive index layer 530 may completely cover the microlens array 220 such that the volumetric elements 534 of the low refractive index layer 530 are located directly between surface region 254 and surface region 224.

[0030] The adhesive layer 540 and the protective glass 250 have corresponding refractive indices n4 and n5, each of which can exceed the refractive index n3 of the low refractive index layer 530. The refractive indices n4 and n5 can be approximately equal, for example, |n4-n5|<0.08, which has the benefit of minimizing reflections from the lower surface 250B. At visible electromagnetic wavelengths, the refractive index n4 of the adhesive layer and the refractive index n5 of the protective glass can each be in the range of 1.50 ± 0.04.

[0031] The adhesive layer 540 may be an epoxy resin, such as a two-component epoxy resin, and may be room-temperature curable. The adhesive layer 540 may have physical properties that conform to the minimum pressure applied to the protective glass 250 and the low-refractive-index layer 530. For example, the temperature range ΔT of the glass transition temperature of the multiple microlenses in the microlens array 220. L In this process, the adhesive layer 540 can have a coefficient of thermal expansion of less than 200 ppm / K. Temperature range ΔT L It can have a lower boundary greater than or equal to -15°C, and can have an upper boundary less than the glass transition temperature. For example, the glass transition temperature is between 65°C and 70°C. In an embodiment, within the temperature range ΔT... L Within the adhesive layer 540, the coefficient of thermal expansion is between 130 ppm / K and 150 ppm / K, and the elastic modulus is less than 350 mPa. In an embodiment, within the temperature range ΔT... L The thermal expansion coefficient of the adhesive layer 540 is between 65 ppm / K and 75 ppm / K, and in the temperature range above the glass transition temperature, the thermal expansion coefficient of the adhesive layer 540 is between 200 ppm / K and 220 ppm / K.

[0032] The adhesive layer 540 has a thickness 549 and a side surface 542. Reducing the thickness 549 results in improved optical performance, such as by minimizing flare and absorption losses from reflections from the side surface 542. Furthermore, reducing the thickness 549 also reduces process yield. The applicant has determined that a thickness 549 between 5 micrometers and 10 micrometers represents a satisfactory trade-off between performance and manufacturability.

[0033] The low-refractive-index layer 530 has a side surface 532. In an embodiment, the dielectric layer 208 extends upward (along a direction opposite to direction 298Z) to cover at least one of the side surfaces 532, 542, and 252 of the low-refractive-index layer 530, the adhesive layer 540, and the protective glass 250, respectively.

[0034] Figure 6 This is a scanning electron microscope image 600 of a low-refractive-index layer 630 between microlens array 620 and adhesive layer 640. Low-refractive-index layer 630 is an example of low-refractive-index layers 430 and 530. Adhesive layer 640 is an example of adhesive layer 540. Microlens array 620 is an example of microlens array 220.

[0035] The microlens array 620 includes a plurality of microlenses, each having a corresponding microlens center at a maximum height above the device substrate 210. For example, a plane 621 intersects at least one microlens center of the microlens array 620. The following description of the microlens array 620 and the low-refractive-index layer 630 considers a scanning electron microscope image 600 as a cross-section of the microlens array 620 passing through the centers of the microlenses, such that distance 624 is the microlens diameter. The microlens array has a peak-valley height 622. The low-refractive-index layer 630 has a thickness 632 above one or more microlens centers. The thickness 632 may be less than the peak-valley height 622.

[0036] Figure 7 This is a cross-sectional view of the cavityless CSP 700. The CSP 700 is... Figure 1 An example of a CSP 100 for a camera 190. A cavity-less CSP 700 includes a device substrate 410 and a low-refractive-index layer 730. A microlens array 220 may be located between the device substrate 210 and the low-refractive-index layer 730.

[0037] The low-refractive-index layer 730 has a refractive index of n3, as mentioned above. Figure 4The low-refractive-index layer 430 is described. The low-refractive-index layer 730 includes a lower surface 731 and an upper surface 739. The lower surface 731 includes a surface region 732 above the microlens surface 222, which is conformal to the microlens surface 222. The upper surface 739 includes a surface region 738 above both the microlens surface 222 and the surface region 732, conformal to the surface region 732 below it, and therefore also conformal to the microlens surface 222. Surface regions 732 and 738 may each be directly above a plurality of microlens surfaces 222. The peaks and valleys of surface region 738 may be aligned with the corresponding peaks and valleys of surface region 732, which in turn are aligned with the corresponding peaks and valleys of microlens surfaces 222. Surface region 738 may have peak-valley heights smaller than those of surface region 732. Compared to the low refractive index layer 430, the conformal relationship between surface regions 732 and 738 and the microlens surface 222 can enhance the anti-reflective properties of the low refractive index layer 730.

[0038] The low-refractive-index layer 730 may extend beyond the microlens array 220 so that the lower surface 731 abuts the upper surface 219 of the device substrate 210. In such an embodiment, the low-refractive-index layer 730 may cover one or more adhesive pads 205 of the device substrate 210. Alternatively, surface regions 732 and 738 may correspond to the entirety of the lower surface 731 and the upper surface 739, respectively.

[0039] Figure 8 This is a cross-sectional schematic diagram of the cavityless CSP 800. The CSP 800 is... Figure 1 An example of a CSP 190 for a camera 190, a cavity-less CSP 800 includes a low-refractive-index layer 830, an adhesive layer 840, and a protective glass 250 on a bare image sensor 229. The low-refractive-index layer 830 is an example of a low-refractive-index layer 730 and covers an adhesive pad 205 of the bare image sensor 229. In the cavity-less CSP 800, the adhesive pad 205 is below at least one of the low-refractive-index layer 830, the adhesive layer 840, and the protective glass 250. The low-refractive-index layer 830 may be in direct contact with the adhesive pad 205. The adhesive layer 840 may be formed of the same material as the adhesive layer 540 and therefore may have a refractive index n4. The adhesive layer 840 has a minimum thickness 849 above the microlens array 220. The minimum thickness 849 is subjected to... Figure 5 The thickness 549 of the adhesive layer 540 has similar constraints and extent. In an embodiment, the dielectric layer 208 extends upward (in a direction opposite to direction 298Z) to cover the respective side surfaces of at least one of the low refractive index layer 530, the adhesive layer 540, and the protective glass 250.

[0040] Figure 9This is a scanning electron microscope image of a low-refractive-index layer 930 between a microlens array 920 and an adhesive layer 940. The low-refractive-index layer 930 is an example of low-refractive-index layers 730 and 830. The adhesive layer 940 is an example of adhesive layer 540. The microlens array 620 is an example of microlens array 220. The low-refractive-index layer 930 includes surface regions 932 and 928, which are examples of surface regions 732 and 738, respectively. Surface region 938 has a peak-valley height 938H, which is smaller than the peak-valley height 932H of surface region 932.

[0041] The microlenses of the microlens array have a diameter 921, which can range from 1 to 12 micrometers. For example, when the raw image sensor 229 is part of a mobile device, the diameter 921 can be between 1.0 and 1.2 micrometers. When the raw image sensor 229 is part of a full-frame camera, the diameter 921 can be between 8 and 9 micrometers. The peak-to-valley height 932H is, for example, between 23% and 33% of the diameter 921. The peak-to-valley height 938H is, for example, between 13% and 23% of the diameter 921.

[0042] Figure 10 Figure 1000 shows visible light transmittances of 1010, 1020, and 1030, each representing the transmittance through a corresponding example of the protective glass and a low-refractive-index layer 530 on its first side. The protective glass is an example of protective glass 250 and has a multilayer anti-reflective coating on a second side opposite the first side. Visible light transmittance 1010 corresponds to a thickness t... 1010 =109 nm and refractive index n across the visible electromagnetic spectrum 1010 A low refractive index layer with a refractive index of 1.10. A visible light transmittance of 1020 corresponds to a layer with a thickness of t. 1020 =105 nm and refractive index n between 1.20 and 1.25 across the visible electromagnetic spectrum 1020 A low refractive index layer. A visible light transmittance of 1030 corresponds to a layer with a thickness of t. 1030 =97nm and refractive index n across the visible electromagnetic spectrum 1030 A low refractive index layer with a refractive index of 1.30. Each of the aforementioned thicknesses is... Figure 4 The minimum thickness of the low refractive index layer 430 is 437.

[0043] Transmittances of 1010, 1020, and 1030 correspond to quarter-wavelength-thickness optical coatings with a design wavelength between 480 nm and 525 nm. The low-refractive-index layer 530 may have a refractive index and thickness such that its optical thickness is equal to the visible electromagnetic wavelength, for example, between 480 nm and 525 nm.

[0044] Figure 1000 also includes a visible light transmittance of 1040, which is the transmittance of a protective glass with a multilayer coating but without a low-refractive-index layer on the first side. The multilayer antireflective coating is a six-layer coating comprising three alternating pairs of tantalum pentoxide and silicon dioxide layers. The layer thicknesses t(i) are: t(1–6) = 18.49, 28.45, 79.36, 6.75, 41.91, and 91.66 nm, wherein the odd-numbered layers (i is odd) are formed of tantalum pentoxide, and the even-numbered layers (i is even) are formed of silicon dioxide. The first layer (i = 1) is directly on the second side of the protective glass.

[0045] Figure 11 Figure 1100 shows the visible light transmittance 1120 through the protective glass and the low refractive index layer on its first side. The protective glass is an example of protective glass 250 and has a multilayer anti-reflective coating on a second side opposite to the first side. The visible light transmittance 1120 corresponds to a thickness of 105 nm and a refractive index n. 1020 The low refractive index layer.

[0046] Figure 1100 also includes a visible light transmittance of 1140, which is the transmittance of a protective glass with a multilayer coating but without a low-refractive-index layer on the first side. The multilayer anti-reflective coating is a 10-layer coating comprising 5 alternating pairs of tantalum pentoxide and silicon dioxide layers. The layer thickness t(i) is t(1–10) = 8.32, 64.64, 10.45, 230.21, 20.94, 31.17, 83.2, 11.22, 38.28, and 97.16, wherein odd-numbered layers (layer index i is an odd integer) are formed of tantalum pentoxide, and even-numbered layers (layer index i is an even integer) are formed of silicon dioxide. The first layer (i = 1) is directly on the second side of the protective glass.

[0047] Figure 12 This is a flowchart illustrating a method 1200 for packaging an image sensor. Method 1200 includes at least one of steps 1210 and 1220. Step 1210 includes covering a pixel array of the image sensor with a low-refractive-index layer having a first refractive index. The image sensor includes a microlens array comprising a plurality of microlenses, each of the plurality of microlenses being (i) aligned with a corresponding one of a plurality of pixels and (ii) having a corresponding one of a plurality of non-planar microlens surfaces facing away from the corresponding one of the plurality of pixels. Step 1210 results in the lower surface of the low-refractive-index layer conforming to each of the plurality of non-planar microlens surfaces. In step 1210, the low-refractive-index layer may be formed via an oblique deposition process, a spin coating process, a spray coating process, or a combination thereof. Step 1210 may be a wafer-level process such that each pixel array of a plurality of image sensors on a device wafer is coated with the low-refractive-index layer in the same process step.

[0048] In the first example of step 1210, the low refractive index layer 430 ( Figure 4 A low-refractive-index layer 730 is deposited on the bare image sensor 229, over the pixel array 214 to cover the microlens array 220. In the second example of step 1210, the low-refractive-index layer 730 ( Figure 7 It is deposited on the bare image sensor 229, above the pixel array 214 to cover the microlens array 220.

[0049] Step 1210 may include covering an adhesive pad located on a substrate to form an image sensor in or on the substrate. For example, step 1210 may include covering the adhesive pad 205 with a low refractive index layer 430 or a low refractive index layer 730.

[0050] Step 1220 includes bonding the protective glass to the upper surface of the low-refractive-index layer, with the upper surface opposite the lower surface. In a first example of step 1220, the protective glass 250 is bonded to the low-refractive-index layer 530 via an adhesive layer 540. Figure 5 In the example of step 1220, the protective glass 250 is bonded to the low-refractive-index layer 830 via the adhesive layer 840. Figure 8 .

[0051] Feature combination

[0052] The features described above and the features requested below can be combined in various ways without departing from their scope. The following examples illustrate some possible, non-limiting combinations:

[0053] (A1) represents a cavity-free chip-level image sensor package including a substrate, a microlens array, and a low-refractive-index layer. The substrate includes a plurality of pixels forming a pixel array. The microlens array includes a plurality of microlenses, each of the microlenses (i) having a lens refractive index, (ii) being aligned with a corresponding one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the corresponding one of the plurality of pixels. The low-refractive-index layer has a first refractive index less than the lens refractive index and a lower surface, at least a portion of the lower surface being conformal to each non-planar microlens surface, and the microlens array is located between the pixel array and the low-refractive-index layer.

[0054] (A2) In the cavityless chip-scale image sensor package represented by (A1), the first refractive index may be between 1.20 and 1.25.

[0055] (A3) In a cavity-free chip-scale image sensor package represented by one of (A1) and (A2), the thickness of the low-refractive-index layer above the vertex of one of the multiple microlens arrays can be between 95 nanometers and 115 nanometers.

[0056] (A4) In a cavity-free chip-scale image sensor package represented by one of (A1) to (A3), the low refractive index layer may have a quarter-wavelength optical thickness above the vertex of one of a plurality of microlenses at the visible electromagnetic wavelength.

[0057] (A5) In a cavityless chip-scale image sensor package represented by one of (A1) to (A4), the visible electromagnetic wavelength can be between 480 nm and 515 nm.

[0058] (A6) In a cavity-free chip-level image sensor package as shown in any of (A1) to (A5), the lens refractive index may exceed the first refractive index by at least Δn = 0.20 for the range of visible electromagnetic wavelengths.

[0059] (A7) In a cavity-free chip-scale image sensor package as shown in one of (A1) to (A6), the low refractive index layer may have a planar upper surface opposite the lower surface.

[0060] (A8) In a cavity-free chip-level image sensor package as shown in (A1) to (A6), the low refractive index layer may have a non-planar upper surface that is opposite to and conforms to the lower surface.

[0061] (A9) In a cavity-free chip-scale image sensor package as shown in one of (A1) to (A8), the lower surface of the low refractive index layer may be adjacent to multiple non-planar microlens surfaces.

[0062] (A10) In a cavityless chip-level image sensor package as shown in any of (A1) to (A9), when the pixel array is configured to detect light incident on the upper die surface of the substrate, the upper die surface may include an adhesive pad adjacent to the pixel array and below the low refractive index layer.

[0063] (A11) In a cavity-free chip-scale image sensor package represented as in (A1) to (A10), the low refractive index layer can be formed of a nanoporous material.

[0064] (A12) In a cavity-free chip-scale image sensor package represented as in (A1) to (A11), a low-refractive-index layer can completely cover the microlens array.

[0065] (A13) The cavity-free chip-scale image sensor package represented by any one of (A1) to (A12) may further include an adhesive layer and a protective glass. The adhesive layer is adjacent to the low-refractive-index layer such that the low-refractive-index layer is between the microlens array and the adhesive layer. The protective glass is disposed on the adhesive layer, opposite to the low-refractive-index layer. The adhesive layer and the protective glass have a second refractive index and a third refractive index, respectively, each exceeding the first refractive index.

[0066] (A14) In a cavityless chip-level image sensor package as shown in (A13), when the pixel array is configured to detect light incident on the upper die surface of the substrate, the upper die surface may include an adhesive pad adjacent to the pixel array and below each of the low refractive index layer, the adhesive layer, and the protective glass.

[0067] (A15) In a cavity-free chip-scale image sensor package as shown in (A13) and (A14), for the range of visible electromagnetic wavelengths, the lens refractive index, the second refractive index and the third refractive index can be approximately equal so that the difference between them is within Δn = 0.08.

[0068] (A16) In a cavityless chip-scale image sensor package represented as in (A13) to (A15), the lens refractive index, the second refractive index and the third refractive index may be in the range of 1.46 to 1.54 for the visible electromagnetic wavelength range.

[0069] (A17) In a cavity-free chip-scale image sensor package as shown in one of (A13) to (A16), the adhesive layer may have a coefficient of thermal expansion of less than 200 ppm / K for a temperature range smaller than the glass transition temperature of a plurality of microlenses.

[0070] (A18) In a cavityless chip-scale image sensor package represented as in (A13) to (A17), the adhesive layer may be between 5 micrometers and 10 micrometers thick.

[0071] (B1) represents a method for encapsulating an image sensor, including covering an image sensor pixel array with a low-refractive-index layer having a first refractive index. The image sensor includes a microlens array comprising a plurality of microlenses, each of the plurality of microlenses (i) having a lens refractive index exceeding the first refractive index, (ii) being aligned with a corresponding one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the corresponding one of the plurality of pixels.

[0072] (B2) In any of the methods represented in (B1), the low refractive index layer includes an upper surface opposite to the lower surface, and the method may further include bonding the protective glass to the upper surface.

[0073] Modifications may be made to the methods and systems described above without departing from their scope. Therefore, it should be noted that the manner in which these are included in the above description or shown in the accompanying drawings should be understood as illustrative and not limiting. Herein, unless otherwise indicated, the adjective “exemplary” means used as an example, instance, or illustration. The following claims are intended to cover all general and specific features described herein, as well as all statements regarding the scope of this method and system, and as a linguistic phenomenon, should be considered to fall within them.

Claims

1. A cavityless chip-level image sensor package, comprising: a substrate comprising a plurality of pixels forming a pixel array; a microlens array comprising a plurality of microlenses each (i) having a lens refractive index, (ii) aligned with a respective one of the plurality of pixels, and (iii) having a non-planar microlens surface facing away from the respective one of the plurality of pixels; and a low refractive index layer formed of nano-porous silica or nano-porous aluminum hydroxide having a first refractive index less than the lens refractive index and a lower surface at least a portion of which is conformal with each non-planar microlens surface, the microlens array being between the pixel array and the low refractive index layer; the low refractive index layer having a non-planar upper surface opposite the lower surface, the non-planar upper surface being conformal with the lower surface; the lower surface comprising a first surface region above the microlens surface, the upper surface comprising a second surface region above both the microlens surface and the first surface region; the second surface region having a peak-to-valley height less than a peak-to-valley height of the first surface region; a bonding layer contiguous with the low refractive index layer so that the low refractive index layer is between the microlens array and the bonding layer; and a protective glass disposed on the bonding layer opposite the bonding layer, the bonding layer and the protective glass each having a second refractive index and a third refractive index that each exceed the first refractive index. the first refractive index is between 1.20 and 1.

25. a thickness of the low refractive index layer above an apex of one of the plurality of microlenses is between 95 nanometers and 115 nanometers.

2. The cavity-free chip-level image sensor package of claim 1, wherein, at visible electromagnetic wavelengths, the low refractive index layer has a quarter- wavelength optical thickness above the apex of one of the plurality of microlenses.

3. The cavity-less chip-level image sensor package of claim 1, wherein, the visible electromagnetic wavelengths are between 480 nanometers and 515 nanometers.

4. The cavity-less chip-level image sensor package of claim 1, wherein, the lower surface of the low refractive index layer is contiguous with each non-planar microlens surface.

5. The cavity-free chip-level image sensor package of claim 4, wherein, the pixel array is configured to detect light incident to an upper die surface of the substrate, the upper die surface comprising a bond pad adjacent to the pixel array and below the low refractive index layer.

6. The cavity-free chip-level image sensor package of claim 1, wherein, For the range of visible electromagnetic wavelengths, the lens refractive index exceeds the first refractive index by at least = 0.

20.

7. The cavity-free chip-level image sensor package of claim 1, wherein, the low refractive index layer completely covers the microlens array.

8. The cavity-less chip-level image sensor package of claim 1, wherein, the pixel array is configured to detect light incident to an upper die surface of the substrate, the upper die surface comprising a bond pad adjacent to the pixel array and below each of the low refractive index layer, the bonding layer, and the protective glass.

9. The cavity-less chip-level image sensor package of claim 1, wherein, for a range of visible electromagnetic wavelengths, the lens refractive index, the second refractive index, and the third refractive index are approximately equal so that a difference between each other is no more than 0.

08.

10. The cavity-less chip-level image sensor package of claim 1, wherein, for a range of visible electromagnetic wavelengths, the lens refractive index, the second refractive index, and the third refractive index are in a range from 1.46 to 1.

54.

11. The cavity-less chip-level image sensor package of claim 1, wherein, for a temperature range less than a glass transition temperature of the plurality of microlenses, the bonding layer has a coefficient of thermal expansion less than 200 ppm / K.

12. The cavity-less chip-level image sensor package of claim 1, wherein, a thickness of the bonding layer is between 5 micrometers and 10 micrometers.

13. The cavity-less chip-level image sensor package of claim 1, wherein, 15. A method for packaging an image sensor, comprising:

14. The cavity-less chip-level image sensor package of claim 1, wherein, ​ ​ Covering a pixel array of the image sensor with a low refractive index layer formed of nano-porous silica or nano-porous aluminum hydroxide having a first refractive index, the image sensor including a microlens array including a plurality of microlenses each (i) aligned with a respective one of a plurality of pixels and (ii) having a non-planar microlens surface facing away from the respective one of the plurality of pixels, the low refractive index layer having a non-planar upper surface opposite a lower surface, the non-planar upper surface being conformal with the lower surface, the lower surface of the low refractive index layer being conformal with each non-planar microlens surface; the lower surface including a first surface region above the microlens surfaces, the upper surface including a second surface region above both the microlens surfaces and the first surface region; the second surface region having a peak-to-valley height that is less than a peak-to-valley height of the first surface region; the method further including bonding a protective glass to the upper surface by a bonding layer; wherein the bonding layer is contiguous with the low refractive index layer so that the low refractive index layer is between the microlens array and the bonding layer; and the protective glass is disposed on the bonding layer opposite the bonding layer, the bonding layer and the protective glass each having a second refractive index and a third refractive index, respectively, the second refractive index and the third refractive index each exceeding the first refractive index.

Images