Conventional lithographic techniques, though highly developed, cannot produce three-dimensional structures in a single step. However, such structures are needed to implement the photonic crystal devices which are envisioned to produce the first truly dense integrated photonic circuits and systems. Multiple Beam Interference Lithography (MBIL) offers a promising technique for the fabrication of photonic crystal devices. However, MBIL, in its present form, is not compatible with 1) microelectronics manufacturing or with 2) integration of multiple circuit elements. The objective of the present research is to overcome these shortcomings by developing a new photo-mask concept that allows the fabrication and integration of a multiplicity of optimized photonic crystal devices, in parallel, across an entire wafer.
Intellectual Merit However, the path to achieving such a fabrication breakthrough is impeded by the limited design space for interference patterns that is currently available. The intellectual merit of the present research lies in the dramatic definition and application of an exhaustive set of conditions for primitive-lattice-vector direction equal contrasts, which, for the first time, show the full richness of interference patterns usable with both positive and negative photoresists. These results will affect all applications of interference lithography including the photo-mask implementation of this proposal.
Broader Impact The use of MBIL to produce dense integrated photonic circuits and systems will, in turn, enable developments in security (through sensing, uninterruptible communications, control, etc.) and in economic growth (through systems that provide efficient interactive access to a broad range of business, medical, financial, research, and data base information.).
Though highly developed, conventional lithographic techniques cannot produce integrated three-dimensional periodic structures in a single step. The outcome of this research project was the analysis, design, construction, and testing of the first such system to able to fabricate these structures directly without using the traditional multiple processing steps that have been required in the past . This newly developed technology, called Pattern-Integrated Interference Lithography (PIIL), is poised to have an impact on a wide range of fields including nano- and micro-electronics, photonic crystal devices, metamaterials, subwavelength structures, optical trapping, and biomedical structures. In nano- and micro-electronics, spatially regular designs have been introduced to improve manufacturability. However, regular designed layouts typically require an interference step followed by a trim step. These multiple steps increase cost and reduce yield. PIIL has now been introduced to overcome this problem. PIIL represents the integration of interference lithography and superposed pattern mask imaging, combining the interference and the trim into a single-exposure step. Thus significant cost savings can be achieved. Photonic crystal devices have the potential to produce the first truly dense integrated photonic circuits and systems (DIPCS). Individual components that are being developed include resonators, antennas, sensors, multiplexers, filters, couplers, and switches. The integration of these components would produce DIPCS to perform functions such as image acquisition, target recognition, image processing, optical interconnections, analog to digital conversion, and sensing. Further, the resulting DIPCS would be very compact in size and highly field portable. Metamaterials technology offers the control of light propagation at a size scale much smaller than the wavelength of light. Accordingly, metamaterial-based devices have many important possible commercial applications including ultra-compact objective lenses, frequency-doubling devices, parametric amplifiers, electromagnetic cloaking, and parametric oscillators. Subwavelength structures have a wide range of applications including synthesized-index elements, form-birefringent polarization elements, guided-mode resonant elements [226], field-emission devices, plasmonic structures, surface texturing, magnetic nanostructures, and numerous other nanotechnology efforts. Optical trapping relies on the increased electrical field associated with the localized optical intensity of a focused beam. A dielectric particle is, in turn, guided by the increased electric field force to the point of the highest light intensity. By this mechanism, optical traps have been used to manipulate a range of particles including polymer spheres, metallic particles, and biological specimens. Recently, techniques to manipulate suspended micro- and nano-scale particles have been realized through the use of holographic optical tweezers, trapping multiple objects simultaneously. In this application, the focused beams are replaced by computer-defined beam arrays generated by a spatial light modulator. Using this method, sophisticated algorithms have been developed to provide updates to the computer generated hologram to control dynamically the orientation of the multiple trapped particles. Recently, this techniques was used to control and study rod-shaped bacteria and zeolite L crystals. Biomedical structures that are periodic or quasi-periodic in three-dimensions are critically important in a wide variety of areas. Some representative example applications are described here to enable gauging the impact that they have in biomedicine. In regenerating nerves, arrays of microchannels are needed to guide nerve growth. In facilitating bone regrowth, periodic meshes are needed to retain and sequester bone morphogenetic protein. This process reduces protein dose by localizing the morphogenetic stimulus. In the forming, maintaining, and repairing of tissue, engineered surfaces are needed that present controlled densities of peptides to direct the assembly of extracellular matrices. In measuring the strength of cell adhesion to the extracellular matrix, meshes are needed to control the size and position of cells to be able to determine the individual contributions of the various structures present. In identifying genetic biomarkers for human disease, high density microarrays are needed for the detection of dozens of polymorphisms in a single analysis. For example, 11 micron square positions are used so that highly redundant oligonucleotide probes can ensure robustness. In studying the functions of a cell (gene expression, adhesion, migration, proliferation, and differentiation), micropatterning of the cells is needed since the cell functions are affected by the microscale and nanoscale environment. In enhancing bone formation in vivo, it is necessary to microstructure the titanium implant surfaces. For example, 100 μm cavities are found to produce osteoblast attachment and growth. In the controlled delivery of insulin, a permeable membrane mesh is needed that allows insulin and nutrients to pass through while blocking larger immune cells, T-cells, and antigen-presenting cells.
