Patent Application
20080080056
a is a graph of depth vs. indices of refraction at the air-microlens interface of a conventional microlens of prior art;
b is a desirable graph of depth vs. indices of refraction at the air-microlens interface of a microlens;
a is a cross-section of the microlens of
b is a cross-section of a pixel array employing a plurality of microlenses in accordance with an embodiment of the invention;
In the following detailed description, reference is made to the accompanying drawings which form a part hereof and illustrate a specific embodiment by which the invention may be practiced. It should be understood that like reference-numerals represent like-elements throughout the drawings. This embodiment is described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and that structural, logical and electrical changes may be made.
The term “substrate” is to be understood as including silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when reference is made to a “substrate” in the following description, previous process steps may have been utilized to form regions or junctions in the base semiconductor structure or foundation. In addition, the semiconductor need not be silicon-based, but could be based on silicon-germanium, germanium, or gallium arsenide, for example.
Referring now to the drawings, where like elements are designated by like reference numerals,
Fibers 40 are then propelled in an air stream 50 toward the adhesive layer 30 on the microlens 20, as shown in
Moreover, because the transparent fibers 40 on the surface of the microlens 20 themselves bring the refractive index at the surface of the microlens closer to that of air, the index of refraction of the fiber material is not of great importance. So long as the fibers have the dimensions and coverage as described above, they perform that function.
The fibers 40 are then placed in an aligned arrangement such that they stand generally at a 90 degree angle to the surface of the layer 10, as shown in
Once placed in the field, all of fibers 40 become charged positively (or negatively, depending upon the direction of the field) at one end and begin to repel one another. In order to maximize the distance away from each other, the fibers 40 stand up vertically. The adhesive layer 30 is then subjected to UV radiation or heat radiation to cure the adhesive layer 30, thereby affixing the fibers 40 to the adhesive layer 30 in the aligned orientation.
The formation of vertical fibers on the surface of a microlens creates a microlens outer surface with an index of refraction closer to the index of air to reduce reflection caused by the sharp reflective index change from air to the microlens 20. A gradual index change is obtained at the surface by providing a microlens 20 having a rough lens-air surface. Therefore, reflection from the interface between the two media can be reduced by a better matching of their indices of refraction. By providing an outer layer on a lens having an index of refraction closer to that of the surrounding medium, such as that of air, reflection is reduced and the efficiency and accuracy of the lens is improved.
b is a cross-section of a pixel array 301 having an array of pixels 100 and a microlens 20 having an adhesive layer 30 and fibers 40 over each pixel 100.
The CMOS imager 300 is operated by a timing and control circuit 306, which controls decoders 303, 305 for selecting the appropriate row and column lines for pixel readout, and row and column driver circuitry 302, 304, which apply driving voltages to the drive transistors of the selected row and column lines. The pixel signals, which typically include a pixel reset signal Vrst and a pixel image signal Vsig for each pixel are sampled by sample and hold circuitry 307 associated with the column driver 304. A differential signal Vrst−Vsig is produced for each pixel, which is amplified by an amplifier 308 and digitized by analog-to-digital converter 309. The analog to digital converter 309 converts the analog pixel signals to digital signals, which are fed to an image processor 310 form a digital image in accordance with the present invention.
The processor system 400, for example a digital still or video camera system, generally comprises a lens for focusing an image on pixel array 301, central processing unit (CPU) 495, such as a microprocessor which controls camera and one or more image flow functions, which communicates with one or more input/output (I/O) devices 491 over a bus 493. Imaging device 300 also communicates with the CPU 495 over bus 493. The system 400 also includes random access memory (RAM) 492 and can include removable memory 494, such as flash memory, which also communicates with CPU 495 over the bus 493. Imaging device 300 may be combined with the CPU, with or without memory storage on a single integrated circuit or on a different chip. Although bus 493 is illustrated as a single bus, it may be one or more busses or bridges or other communication paths used to interconnect the system components.
While an embodiment has been described and illustrated above, it should be understood that it has been presented by way of example, and not limitation. For example, although the invention has been described and illustrated in conjunction with pixel structures and a pixel array readout circuit associated with CMOS imagers, it is not so limited and may be employed with any solid state imager pixel structure and associated array readout circuit. It will be apparent to that various changes in form and detail can be made to the described embodiment.
