Abstract:
A low-cost resin lens is disclosed for use in miniature cameras. The resin lens features a low profile that is particularly well-suited to consumer products such as smart phones. The resin lens is mounted to an integrated circuit die that is attached to a standard four-layer substrate. The integrated circuit die includes electronic and/or optoelectronic circuits to support digital image capture, transfer, and processing. Image correction software adjusts the image to correct for distortion introduced by the resin lens.

Description:
BACKGROUND 
     Technical Field 
     The present disclosure generally relates to the design and fabrication of low profile cameras for use in consumer electronic devices, and methods of correcting images using a built-in hardware filter. 
     Description of the Related Art 
     Mobile electronic devices such as laptop computers, tablet computers, smartphones, and the like typically come equipped with miniature digital cameras that are recessed below an outside surface of the device. Because the electronic devices are thin, there is not much room for a camera lens incorporated into the case to extend in a direction transverse to the screen surface. Thus, low-profile lenses are useful in such applications. 
     In some electronic device applications, the camera lens is used primarily as a motion detector, for example, which generally does not require high quality image capture. If the camera is targeted for such applications, it is not necessary to form the camera lens out of glass and to grind the lens with precision to achieve superior optical quality and performance. However, existing cameras are often made to the same high standard, regardless of their application. 
     BRIEF SUMMARY 
     A low-profile camera module, for use in applications in which approximate image capture is sufficient, is equipped with an inexpensive resin lens, and an image compensation system. The image compensation system can be calibrated using a known test image so that an offset can be applied to images captured by the resin lens to compensate for poor lens quality. Such a low-profile camera module can be used effectively as, for example, a motion detector, a face recognition device in a security system, a device for monitoring hand movements at close range, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar elements. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. 
         FIG. 1A  is a cross-sectional view taken along lines A-A′ of  FIG. 1B  of a low profile camera module, according to one embodiment disclosed herein. 
         FIG. 1B  is a cross-sectional view of the low profile camera module shown in  FIG. 1A , taken along cut lines B-B′. 
         FIG. 2A  is a high-level process flow diagram showing an overview of a method of making the low profile camera module, according to a first embodiment. 
         FIG. 2B  is a series of illustrations showing the low profile camera after completion of the corresponding process step shown in  FIG. 2A . 
         FIG. 3A  is a high-level process flow diagram showing an overview of a method of making the low profile camera module, according to a second embodiment. 
         FIG. 3B  is a series of illustrations showing the low profile camera after completion of the corresponding process step shown in  FIG. 3A . 
         FIG. 4  is a block diagram of a microelectronic image compensation system to support the low profile camera module, as described herein. 
         FIGS. 5A and 5B  are schematic diagrams illustrating operation of the microelectronic image compensation system shown in  FIG. 4 . 
         FIG. 6  is a flow diagram showing a sequence of steps used to calibrate and operate the microelectronic image compensation system. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of semiconductor processing comprising embodiments of the subject matter disclosed herein have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
     Fabrication of microcircuits generally entails performing a series of deposition and patterning operations to build integrated structures on a semiconductor substrate, one layer at a time. Each layer is formed by growing or depositing a film on the substrate, patterning a photo-sensitive mask using lithography, and transferring the mask pattern to the film by etching. Often, structures already formed on the substrate are protected by hard masks while new structures are created. Such use of hard masks adds masking layers to the fabrication process. Overall fabrication costs scale with the number of layers used and the number of mask patterning cycles needed. Lithography masks are expensive to design and to integrate into an existing fabrication process. For these reasons, it is generally advantageous to reduce the number of mask patterning cycles if alternative processing schemes can be substituted. 
     Reference throughout the specification to integrated circuits is generally intended to include integrated circuit components built on semiconducting substrates, whether or not the components are coupled together into a circuit or able to be interconnected. Throughout the specification, the term “layer” is used in its broadest sense to include a thin film, a cap, or the like. 
     Reference in the specification to conventional thin film deposition techniques for depositing silicon nitride, silicon dioxide, metals, or similar materials include such processes as chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), metal organic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), plasma vapor deposition (PVD), atomic layer deposition (ALD), molecular beam epitaxy (MBE), electroplating, electro-less plating, and the like. Specific embodiments are described herein with reference to examples of such processes. However, the present disclosure and the reference to certain deposition techniques should not be limited to those described. For example, in some circumstances, a description that references CVD may alternatively be done using PVD, or a description that specifies electroplating may alternatively be accomplished using electro-less plating. Furthermore, reference to conventional techniques of thin film formation may include growing a film in-situ. For example, in some embodiments, controlled growth of an oxide to a desired thickness can be achieved by exposing a silicon surface to oxygen gas or to moisture in a heated chamber. 
     Reference in the specification to conventional photolithography techniques, known in the art of semiconductor fabrication for patterning various thin films, includes a spin-expose-develop process sequence typically followed by an etch process. Alternatively or additionally, photoresist can also be used to pattern a hard mask such, as a silicon nitride hard mask, which, in turn, can be used to pattern an underlying film. 
     Reference in the specification to conventional etching techniques known in the art of semiconductor fabrication for selective removal of polysilicon, silicon nitride, silicon dioxide, metals, photoresist, polyimide, or similar materials includes such processes as wet chemical etching, reactive ion etching (RIE), washing, wet cleaning, pre-cleaning, spray cleaning, chemical-mechanical planarization (CMP) and the like. Specific embodiments are described herein with reference to examples of such processes. However, the present disclosure and the reference to certain deposition techniques should not be limited to those described. In some instances, two such techniques may be interchangeable. For example, stripping photoresist may entail immersing a sample in a wet chemical bath or, alternatively, spraying wet chemicals directly onto the sample. 
     Specific embodiments are described herein with reference to a low profile camera module and associated components that have been produced; however, the present disclosure and the reference to certain materials, dimensions, and the details and ordering of processing steps are exemplary and should not be limited to those shown. The term “photonic” is used as a counterpart to the term “electronic” to describe miniaturized light circuits. The term “opto-electronic” refers to combinations of electronic and photonic circuits and/or circuit elements. 
     In the figures, identical reference numbers identify similar features or elements. The sizes and relative positions of the features in the figures are not necessarily drawn to scale. 
       FIGS. 1A and 1B  illustrate cross-sectional views of a low profile camera module  100 , according to one embodiment. The footprint area of the low profile camera module  100  is in the range of approximately 3-5 mm 2 . The low profile camera module  100  includes a microlens in the form of a resin lens  102 , a housing  104  surrounding the microlens, a multi-layer substrate  106 , and an integrated circuit die  108 . The die  108  is attached to the multi-layer substrate  106  by a die attach film  110 . In one embodiment, the low profile camera module  100  can further include an optional adjustable or removable cover—with the housing  104 . 
     The resin lens  102  of the low profile camera module  100  has a substantially hemispherical shape, having a diameter that depends at least in part on the size of an image sensor array described below in further detail. To maintain the low profile, the height of the resin lens  102  should not extend beyond the top of the housing  104 . 
     The housing  104  can be made of, for example, a reflowable or non-reflowable thermoplastic material such as a liquid crystal polymer (LCP), FAG, LA  121 , or the like. In one embodiment, the housing  104  is in the form of a one-piece arched surround structure having a center opening. The housing  104  has a circular annular inner foot  114  and a square annular outer foot  116 , so that there is open space  118  between the housing  104  and the multi-layer substrate  106 . The square annular outer foot  116  follows approximately the perimeter of the low profile camera module  100  on the multi-layer substrate  106 . The circular annular inner foot  114  follows approximately the circumference of the resin lens  102 . The open space  118  accommodates circuit components  120  mounted on the integrated circuit die  108 , while providing protection for such components. In one embodiment, the optional cover can be formed as part of the one-piece molded structure. 
     The resin lens  102  can be a microlens that is made of glass and then coated with a resin material, or the resin lens  102  can be made partially or wholly from the resin material itself. In most instances, glass provides a higher quality microlens, but the cost is significantly higher, whereas a lens can be made substantially of a thermoplastic resin at a much lower cost. When the lower-cost resin lens is used, the image produced by the sensor can be electronically improved, as explained later herein. 
     A resin lens  102  can be made from a pre-molded assembly. In one embodiment, such an assembly includes a microlens having a pre-molded resin covering and an extended resin flange  122  on which to seat the annular inner foot  114  of the housing  104 . The housing  104  then rests on the extended resin flange  122  thereby securing the resin lens  102  on top of the integrated circuit die  108 . The housing  104  thus serves as a mount for the resin lens  102 . 
     The integrated circuit die  108  can be, for example, a standard packaged optical integrated circuit die operable to capture, transmit, and process images. Such an integrated circuit die  108  can include for example, the electronic image sensor array  123 , located at a focal plane behind the resin lens  102 . Elements of the image sensor array  123  may be, for example, charge-coupled devices (CODs). The integrated circuit die  108  can further include an electronic memory for storing image data, a processor such as an image processor, and the like, as discussed with respect to  FIG. 4 . 
     The integrated circuit die is fabricated according to standard semiconductor processing techniques known in the art, and generally described above. Such processing entails deposition and patterning of a series of thin films, wherein the patterning includes application of a photosensitive mask, optical exposure of the mask according to a circuit design pattern, and etching the pattern into the underlying film. Exposed surfaces of the integrated circuit die  108  are covered with a passivation layer  124 . 
     The circuits in the integrated circuit die  108  are electrically coupled to the multi-layer substrate  106  by wire bonds  126  from contact pads  128   a  on the die to contact pads  128   b  that provide electrical signal paths to interconnects within the multi-layer substrate  106 . Various circuit components  120 , such as capacitors and resistors, are also mounted to the multi-layer substrate  106  via contacts  128   b . The contact pads  128   a  and  128   b , being exposed to the open space  118 , desirably have an upper layer made of gold or a similar non-reactive metal to avoid corrosion. The die attach film  110  is an adhesive film that attaches the integrated circuit die  108  to the multi-layer substrate  106 . Additionally or alternatively, the underside of the integrated circuit die  108  can be patterned with a ball grid array (BPA) or a land grid array (LGA) of contact pads to facilitate electrical connections to the image sensor array  123 , memory, and processor therein, via the multi-layer substrate  106 . 
     The multi-layer substrate  106  can be, for example, a standard four-layer customizable printed circuit board (PCB). The PCB can include, for example, two metal interconnect layers separated by composite material layers made of glass fiber and epoxy resin, on a semiconductor substrate. The metal interconnects can be made of copper, nickel, aluminum, gold, or combinations thereof. Exposed upper and lower surfaces of the multi-layer substrate  106  are covered with solder masks  130 . The upper solder mask  130  includes openings  132  to allow solder attachment of the circuit components  120  to the top metal layer of the multi-layer substrate  106 . 
     With reference to  FIGS. 1A, 1B, 2A, and 2B , generalized steps in a first fabrication method  140  for producing the low profile camera module  100  are described and shown, according to one embodiment. 
     At  141 , pre-molded resin micro-lenses  102  are fabricated or obtained from a supplier such as a commercial vendor, and singulated into individual units. 
     At  142 , an adhesive such as an epoxy is dispensed outside the circumference of the micro-lens  102 , on the extended resin flange  122 . 
     At  143 , the housing  104  is mounted to the extended resin flange  122  to form a mounted lens assembly  144 . After mounting the housing  104 , the housing  104  may be cured, for example, by heating to an elevated temperature, or by exposure to UV light. 
     At  145 , multi-layer substrates  106  are fabricated or obtained from a supplier such as a commercial vendor, and singulated into individual units. 
     At  146 , the integrated circuit die  108  is attached to the multi-layer substrate  106  using the die attach film  110 , to form a substrate assembly. The integrated circuit die  108  may be a commercially available chip for use in electronic cameras, or a custom chip that includes the electronic image sensors  162 , a microprocessor  164  that can be a general purpose processor or an image processor, and the memory  166 . 
     At  147 , the wire bonds  126  are added to provide electrical access to the components within the integrated circuit die  108  via the contact pads  128   a.    
     At  148 , an adhesive, for example an epoxy, is dispensed in two locations—around the perimeter of the integrated circuit die  108 , and also around the perimeter of the multi-layer substrate  106 . 
     At  149 , the mounted lens assembly  144  is attached by the adhesive to the completed substrate assembly. 
     With reference to  FIGS. 1A, 1B, 3A and 3B , generalized steps in a second, alternative fabrication method  150  for producing the low profile camera module  100  are described and shown. 
     At  152 , the integrated circuit die  108  is either custom fabricated or obtained as a commercially available unit for use in electronic cameras. The integrated circuit die  108  may be a custom chip that includes the image sensor array  123  and other electronic circuits explained elsewhere herein. 
     At  153 , the resin lens  102  is secured to the integrated circuit die  108  prior to singulation of the wafer that includes integrated circuit die  108  and prior to wire-bonding to minimize disruption to the bond wires. The microlens can be a small liquid drop of resin that is cured, or a pre-molded resin lens. At  154 , the integrated circuit die  108  is attached to a singulated multi-layer substrate  106  using the die attach film  110 , which is an adhesive. Wire bonds  126  are added to provide electrical access to the components within the integrated circuit die  108  via the contact pads  128   a.    
     At  156 , an adhesive is dispensed outside the circumference of the micro-lens  102 , on the extended resin flange  122 . The housing  104  is then attached to the extended resin flange  122 . 
     At  158 , the resin lens  102  is optionally covered with a removable or adjustable liner to prevent particles from landing on the resin lens  102  or from becoming trapped around the resin lens  102  prior to mounting in a consumer product, or when the camera module  100  is not in use. 
       FIG. 4  illustrates a schematic block diagram of a microelectronic image compensation system  160 , according to one exemplary embodiment. The microelectronic image compensation system  160  includes the resin lens  102 , an image sensor array  123 , a microprocessor  164 , a memory  166 , and code within the memory  166  containing instructions  168  for image compensation. Reference data  174  is also stored in the memory, as explained elsewhere herein. The image sensor array  123 , the microprocessor  164 , and the memory  166  can all be implemented as circuitry within the integrated circuit die  108 . 
       FIGS. 5A and 5B  illustrate an exemplary calibration procedure  180  carried out by the image compensation system  160 , according to one embodiment. Operation of the image compensation system  160  entails use of a test pattern  172  and associated reference data  174 , the low profile camera module  100 , and generation of test pattern image data  176  to produce corrected image data  178 . 
     With reference to  FIGS. 4, 5A-5B, and 6 , the calibration procedure  180  for image compensation of the low profile camera module  100  is described. Such a method can be coded as instructions  168 , stored in the memory  166 . 
     At  182 , reference data  174  that corresponds to the test pattern  172  is stored in the memory  166 . 
     At  184 , the microprocessor  164  triggers the low profile camera module  100  to acquire an image of the test pattern  172  via the image sensor array  132 . Such a trigger may occur, for example, in response to a calibration request. The image sensor array  132  produces image data  176 , which is stored in the memory  166 . Because the resin lens  102  is an inexpensive optical element of less than optimal quality, image data  176  is generally expected to be distorted as shown in  FIG. 5 . 
     At  186 , the distorted image data  176  is compared with the reference data  174 , which accurately depicts the test pattern  172 . Such a comparison is carried out in the microprocessor  164 , according to the instructions  168 . 
     At  188 , the microprocessor  164  computes an offset in the electronic data from test image  172  that represents the difference between the actual test pattern  172  and the distorted image data  176 . 
     At  190 , a correction based on the offset is applied to the distorted image data  176  to produce the corrected image data  178 . The corrected image data  178  should substantially match the actual test pattern  172 . 
     It is expected that in most embodiments there will be a plurality of test patterns  172  and corresponding reference data  174 . Each of the test patterns will be designed to mimic an expected image that the camera will take during operation. For example, a first test pattern may mimic fine line resolution and close-up images. A second test pattern may mimic human faces, including a distinction between different expressions on a face, or genders. Another test pattern may mimic landscape images, such as trees, lakes, and the like. Another test pattern may mimic close-up nature photographs such as flowers or insects, while yet another test pattern  172  may mimic long-range photographs such as mountains in the distance. Other test patterns may mimic a combination of such types of images, such as people standing with a background close behind them and also people with a distant background such as a mountain behind them. In some embodiments, only one test pattern  172  will need to be used in order to properly compute the offset amount and store the offset electronic data in the memory  166 . In other embodiments, the offset is computed after performing a number of comparisons between various different types of test patterns  172  to be matched with the corresponding reference data  174 . In one embodiment, the results of all of the comparisons between the various different types of test patterns and the reference data  174  are combined to compute an overall offset for all images to be taken with the camera. In an alternative embodiment, or in addition to the combined offset calculation, an individual offset calculation can be performed for each type of image. For example, an offset can be computed for a test pattern that includes human faces and stored as an offset to be used with respect to photographs that contain human faces. Another test pattern can be stored for distant image acquisition, such as mountains in the distance, and this offset stored as an individual, separate offset to be used only on images that are particular to that particular offset, namely long distance, landscape pictures. 
     Since general image recognition software exists today that can detect whether an image includes such features as human faces, distant mountains, and the like, the details of such software are not described herein. Similarly, the specific software code and mathematical algorithms to create the offset between the actual test pattern  172  and reference data  174  are not described herein in detail, since the use of digital offsets to modify an image in a program such as Photoshop are well known. The goal of the offset, as described and explained herein, is to compensate for the poor image quality produced by the resin lens  102 . In particular, the sensor array  132  will create an image pattern after having taken an image of the test pattern  172 . This image pattern is compared to the reference data  174  to determine by electronic comparison where the image pattern differs from the reference data  174 . The image pattern is modified electronically as appropriate in order to match the reference data  174 . The changes which need to be made from the actual image obtained of test pattern  172  to obtain the reference data  174  will be the offset amount, which is stored as an electronic file in the memory  166 . This offset can then be applied to later images that are taken in order to transform that obtained image into a form that corresponds to the actual image prior to having passed the resin lens  102 . Based on the description as provided herein, together with available publications in the art, a person of skill would be able to write the code to compute the offset to be used between an actual test pattern  172  and the reference data  174 , and therefore the specific details of this code need not be described herein. The description as provided herein of the image compensation method and its operation are sufficient for one of skill in the art to create and store such a program  168  in the memory  166 . 
     There is currently image recognition software that is well known in the art and widely available today, that can distinguish whether or not an image contains a close-up picture of a human face, a distant landscape, or other particular features. In the event that the camera takes a photograph that includes such particular and easily recognizable subjects, the offset to be used for image correction can be selected automatically or manually from various offset choices stored in memory. For example, a particular offset that has been computed for use in portrait photography can be selected if the photograph is recognized as being a portrait or primarily composed of human faces, instead of using generic offset values for a standard test pattern  172 , or instead of using a composite offset that has been computed by combining the results of multiple test patterns  172  from multiple reference data  174 . 
     Following the calibration method for image compensation  180 , an image of a scene that is acquired by the low profile camera module  100  can be automatically corrected to compensate for the resin lens  102 . Applying such a correction to the image data, after it is acquired by the resin lens  102 , can be thought of as a type of software filter, i.e., a filter for altering the image data obtained to more closely correspond to the actual image itself. Use of the software filter is much less expensive than providing a high quality lens. Furthermore, the resin lens  102  is more durable, and therefore, is better suited for use in a consumer product like a smart phone, which is likely to be heavily used, with risk of damage. 
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     It will be appreciated that, although specific embodiments of the present disclosure are described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure is not limited except as by the appended claims. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.