Patent Number: 062815083
Section: description

DETAILED DESCRIPTION FIGS. 3a-3b show a microlens component 51 according to the present invention. Microlens component 51 is, for example, a 500 .mu.m thick, 7 mm.times.7 mm silicon chip. At the center of microlens component 51 is a 1 to 1.5 .mu.m thick, 1 mm.times.1 mm membrane window 53, at the center of which is a 2.5 .mu.m diameter aperture 55. (These dimensions are merely illustrative.) FIG. 3b is a side view of the FIG. 3a structure. Aperture 55 must be precisely aligned with the apertures of the other microlens components (not shown) when the microlens is assembled. Rather than utilizing the painstaking prior art process of manually aligning the apertures using a microscope to observe the alignment, the present process utilizes a structure such as a standard optical fiber 59 to align the multiple layers. First, alignment openings 57a-57b are formed in the microlens component 51. Because microlens component 51 is of silicon, conventional silicon processing techniques may be utilized to form the openings 57a-57b through the microlens component 51. Such techniques are well known in the art and enable the etching of holes in silicon to very precise tolerances. Optical lithography can be used to first pattern the holes in the silicon, followed by a silicon etching process to etch the holes through the microlens component 51. Techniques such as electron-cyclotron-resonance (ECR) etching, active silicon ion etching, reactive ion etching (RIE), inductively-coupled-plasma (ICP) etching, or any of the known methods for etching silicon may be used to quickly, reproducibly, and precisely form alignment openings 57a-57b. These techniques can be used to etch silicon with tolerances in the nanometer range, thereby allowing the apertures 55 to be positioned accurately with respect to the alignment openings 57a-57b. For improved efficiency, this etching step may be carried out in conjunction with and using the same processes as the etching steps required for forming window 53 and aperture 55. After the alignment openings 57a-57b are formed, aligners 59a-59b are inserted through the openings 57a-57b. In one embodiment, aligners 59a-59b are short lengths of standard optical fiber, which are circular dielectric waveguides typically used to transport optical energy and information. These commercially available fibers are made of doped silica, possibly coated with several layers of cushioning material, such as acrylate. One suitable fiber material is commonly known as Pyrex. Pyrex optical fibers are commercially available from the Newport Corporation. This is just one example of the materials that may be used as the aligner. It is only necessary that the aligners be sufficiently strong and stiff to prevent shearing or bending of the assembled microlens, as described below. In addition, if the aligners are not removed from the microlens after assembly, typically they must be electrically nonconductive as well. The optical characteristics of the fibers are of no importance; optical fibers are utilized in this embodiment because they are relatively inexpensive, readily available, nonconductive, and are formed with very tight dimensional tolerances. Also, over the short lengths needed, they are sufficiently rigid. FIGS. 4a-4d illustrate in side views the assembly of a microlens according to one embodiment of the present invention using the FIG. 3a, 3b structures. FIG. 4a shows a side view of microlens component 51 after formation of window 53, aperture 55a, and alignment openings 57a-57b. Aligners 59a-59b are inserted into alignment openings 57a-57b, respectively, of microlens component 51, as shown in FIG. 4b. Next, an insulating spacer 61 is attached to the assembly by threading aligners 59a-59b through alignment openings 57c-57d in the spacer 61, and positioning spacer 61 atop microlens component 51. Spacer 61 is provided with large aperture 63, which must be aligned so as not to block aperture 55 in microlens component 51. Because the purpose of spacer 61 is to provide separation and insulation between the electrode layers of the microlens, aperture 63 can be made quite large and is not particularly difficult to properly align. As can be seen in FIG. 4d, successive microlens components 65 and 69 each define small apertures 55b-55c which are to be precisely aligned with aperture 55a of the base microlens component 51. Microlens components 65 and 69 include alignment openings 57e-57f through which aligners 59a-59b are threaded. Because aligners 59a-59b are sufficiently rigid, when the elements of the microlens are assembled as shown in FIG. 4d, the layers are securely held relative to each other so that the alignment openings 57a-57f of each layer are precisely aligned. By accurately etching the alignment openings 57a-57f in relation to the apertures 55a-55c in each layer, the apertures 55a-55c will all also align correctly. In the embodiments shown in FIGS. 3a-3b and 4, two aligners 59a-59b are used in the assembly of the microlens. The invention is not limited to only two aligners; it is also possible to assemble a microlens using a greater number of aligners or just one. When using only one aligner fiber, another structure may be used to better stabilize the microlens and prevent rotation of the microlenses relative to each other. For example, one edge of each microlens component may be aligned with another structure to prevent misalignment of the apertures caused by relative rotation of the layers. FIG. 5 shows a side view of a completed microcolumn according to the present invention. The microcolumn is formed of layers of microlens elements and other components 51a-51i alternating with layers of insulating spacers 61a-61h, with aligners 59a-59b serving to keep the components properly aligned. At the top is conventional tip assembly 77, which may include, for example, a scanning tunneling microscope mounted in microlens 51i. Beneath the tip assembly 77 is the source lens 79 of the microcolumn, followed by the dual silicon deflector 81 and the Einzel lens 83. After the microcolumn structure is complete, the layers may be bonded together to provide increased strength and stability. This is accomplished anodically as described above, e.g., by connecting the assembled structure to a voltage source and applying a potential across the layers of the microcolumn under elevated temperatures. By applying both a positive followed by a negative potential across the alternating glass-silicon layers, the individual layers of the microcolumn are anodically bonded. This may also result in the bonding of the optical fiber aligners 59 to the microlenses 51. Alternatively, the layers are laser bonded. Aligners 59 are used to maintain the precise alignment of the assembly while the laser spot welding is carried out, and may be removed, if desired, after the layers are bonded together. However, because the aligners 59 are sufficiently small relative to the overall surface area of the microlens components 51 and usually are not located too close to the aperture 55 of the microlens components 51, they should not interfere with the operation of the microcolumn and do not have to be removed after assembly. Excess length of aligner 59 is clipped off the microcolumn, or left in place to allow for additional structures to be added later. The accuracy of the alignment of the microlens components is dependent on the accuracy of the aligners 59 and the precision of the alignment openings 57. Because the aligners 59 are used to precisely align the apertures 55 of the microlenses, it is advantageous that the aligners 59 be precisely fitted into the alignment openings 57. This is balanced with the desire to increase the efficiency of the assembly process, however. Micromachining the alignment openings 57 to exactly the diameter of the fiber aligner 59 may provide accurate alignment of the apertures 55, but the threading of the aligner 59 through the equally-sized alignment opening 57 may be problematic. The alignment openings 57 are larger than the diameter of the aligners 59 to ease threading. Two methods of addressing this problem are illustrated in FIGS. 6a-6b and 7. FIGS. 6a-6b each illustrate in perspective and plan views an embodiment in which the alignment opening 100 of microlens component 104 includes two eccentrically formed holes, threading portion 101 and locking portion 103. Threading portion 101 has a diameter slightly larger than the diameter of optical fiber aligner 102. Locking portion 103 has a diameter closely approximating that of aligner 102. In one embodiment, aligner 102 has a cross-sectional diameter of 250 .mu.m, threading portion 101 has a diameter of 300-350 .mu.m, and locking portion 103 has a diameter of 250-260 .mu.m, depending on the tolerance requirements for the apertures 55 of the microlenses. FIG. 6a shows the first step in which aligner 102 is threaded through the threading portion 101 of the alignment opening 100. Because of the increased diameter of threading portion 101, threading the aligner 102 through the alignment opening 100 is easily accomplished. After the aligner 102 is inserted, it is then moved into the locking portion 103 of the alignment opening 100 in the direction of arrow 105. FIG. 6b shows aligner 102 fixed in locking portion 103. Precise etching of the location of locking portion 103 with reference to the location of aperture 55 (not shown in FIGS. 6a-6b) in each microlens component ensures that all layers will align properly. FIG. 7 shows in a plan view a different method of providing for accurate alignment of the components. Here, alignment openings 107a-107b are formed in the shape of a square, each side of the square being slightly longer than the diameter of the associated aligner 111a-111b. After aligners 111a-111b are threaded through the alignment openings 107a-107b, they are pushed towards each other in the direction of arrows 105a-105b. A manipulator located beneath the bottom layer of the microlens is used to force the protruding ends of the aligners 111a-111b together. When the aligner 111a is pushed towards an edge of the alignment opening 107a, the aligner 111a contacts the alignment opening at two contact points 109a-109b, which are located along two adjacent sides of the square alignment opening 107a. These two contact points 109a-109b provide the reference location for properly aligning the apertures 55 of the microlenses (not shown in FIG. 7). Because the optical fiber aligners 111a-111b are relatively short, they are sufficiently stiff to provide proper alignment throughout the length of the microcolumn. Because the aligner 111a is pressed against the two contact points 109a-109b, the size of the alignment opening 107a does not affect the precision of the alignment, provided that the two contact points 109a-109b are properly placed. In this case, the aligners 111a-111b are locked against the two edges of the square alignment openings 107a-107b and the alignment accuracy is defined by the variation in the diameters of the fiber aligners 111a-111b, the reproducibility and positioning of the square alignment openings 107a-107b, and the perpendicularity of the two edges which define the placement accuracy. It is not necessary that the alignment openings 107a-107b have perfectly square shapes, or that they be located at opposite corners of the microlens component 108. It is additionally not required that the aligners 111a-111b be forced inwards toward the center of the microlens 108. It is only necessary that the aligners 111a-111b be able to precisely align the multiple components by contacting an edge of the alignment openings 107a-107b to provide an identifiable reference location. For example, the two alignment openings 107a-107b can both be formed in the upper half of the microlens component 108 shown in FIG. 7, and can be formed as rectangles, triangles, or any other size polygon, so long as the contact points 109 can be accurately identified and positioned. Furthermore, the aligners 111a-111b may, for example, be arranged so that they are forced in a direction away from each other, so long as the forces they apply against the microlens component 108 complement each other in such as way as to maintain a stable alignment. Although the invention has been described with reference to particular embodiments, the description is only an example of the invention's application and should not be taken as a limitation. Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention as defined by the following claims.