An alternative approach to flat nanoimprint lithography ͑NIL͒-roller nanoimprint lithography ͑RNIL͒ is demonstrated. Compared with flat NIL, RNIL has the advantage of better uniformity, less force, and the ability to repeat a mask continuously on a large substrate. Two methods for RNIL are developed: ͑a͒ rolling a cylinder mold on a flat, solid substrate; ͑b͒ putting a flat mold directly on a substrate and rolling a smooth roller on top of the mold. Using our current roller nanoimprint system, sub-100 nm resolution pattern transfer has been achieved.

Imprint pressure uniformity is crucial to the pattern uniformity and yield of nanoimprint lithography (NIL) and, hence, its applications. We studied a novel imprint method, air cushion press (ACP), in which the mold and substrate are pressed against each other by gas pressure rather than solid plates, and compared it with a common method, solid parallel-plate press (SPP). We found that (a) under normal imprinting conditions the measured pressure distribution across a 100-mm-diameter single imprint field in ACP is nearly an order of magnitude more uniform; (b) ACP is immune to any dust and topology variations on the backside of the mold or substrate; (c) when a dust particle is between the mold and substrate, ACP reduces the damage area by orders of magnitude; (d) ACP causes much less mold damage because of significantly less lateral shift between the mold and substrate; and (e) ACP has much smaller thermal mass and therefore significantly faster speed for thermal imprinting.

We report an experimental and theoretical study of two most critical yet still to-be-answered issues in dispensing-based nanoimprint lithography (D-NIL): air bubble formation and absorption, and discuss their impact on NIL yield and throughput. Using real-time observation via video, we found two different mechanisms for air bubble formation (feature pinning and multi-droplet encircling), and studied the dynamic behaviour of the air absorption and air bubble shrinking under different conditions. Furthermore, we developed theoretical models and simulation programs of the air absorption and bubble shrinking based on molecular diffusion theory and hydrodynamics. We compared these models with experiments, and found excellent agreement. Our study shows that the key factors that affect the air dissolution time (and hence the air bubble shrinking time) are air bubble initial size, imprinting pressure, air solubility, and resist residue layer thickness. One of our key conclusions from the study, which has significant practical importance, is that although the air in a bubble can be completely dissolved in a resist liquid as long as the bubble is smaller than a certain size, the air absorption time might be too long for the dispensing-NIL operating in atmosphere or poor vacuum to have a necessary throughput in mass manufacturing.

We demonstrated an economical way of fabricating gel-film-based devices by combining nanoimprint lithography ͑NIL͒ and a sol-gel technique. A novel imprinting procedure, new mold surface passivation, and an effective surfactant added to sol were developed. Gratings with 300 nm pitch and 80 nm linewidth and waveguide gratings with varying periods were imprinted in a single step and with excellent uniformity into the gel films coated on a quarter of 4 in. wafers, respectively. Surface roughness measurements of waveguide gratings by atomic force microscope showed smooth profiles with root mean square roughness less than 6 nm. NIL is an excellent patterning technology for gel-film-based optical devices.

We demonstrate a tunable filter consisting of a subwavelength resonant grating filter cladded by a liquid crystal cell. The resonant wavelength of the grating filter is tuned by electrically varying the refractive index of the liquid crystal. A tuning range of around 20 nm has been achieved.

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Abstract. We propose a distributed and adaptive topology management algorithm, called PATM (Priority-based Adaptive Topology Management), that constructs and maintains a connected backbone topology based on a minimal dominating set of the network. PATM provides a succinct presentation of the network topology to routing protocols, and therefore reduces the control overhead in routing updates. Two optimizations are proposed to further reduce the topological information exchanges among the nodes by piggybacking topology updates in packets transmitted by each node, and adaptively adjusting the topology update intervals. The efficiency of the algorithm is validated by simulations based on DSR (Dynamic Source Routing) protocol. The simulation results demonstrate that PATM not only significantly reduces the routing control overhead, but also substantially improves the network data forwarding performance.