Centimeter-scale subwavelength photolithography using metal-coated elastomeric photomasks with modulated light intensity at the oblique sidewalls

Skin effect photon-trapping enhancement in infrared photodiodes

With the development of infrared optoelectronic technology, high responsivity, ultra-low dark current, and high response speed have become important factors of the next generation of infrared photodiodes. However, the minimum thickness of the absorber layer is limited to approximately one or several wavelength lengths to acquire high quantum efficiency, which results in a long transit time of photogenerated carriers. In this work, we propose a photon-trapping structure that uses the skin effect of metals to generate horizontal local modes to enhance the absorption of infrared photodiodes. The photon-trapping structure consists of an artificial grating structure covered by a metallic film. Importantly, we develop a simplified theoretical model to describe the local mode, which is then being used to design the realistic photon-trapping structure presented in this work. This design method is universal and we discuss the optical properties of the photon-trapping structure in InAs, InSb, InAs/GaSb type-II superlattices, InAs/InAsSb type-II superlattices, and HgCdTe infrared photodiodes. Both absorption of optical properties and responsivity of optoelectrical properties are numerically investigated in a systematic way. The optical simulations indicate that the absorption of the HgCdTe infrared photodiodes exceeds 80% at 8.5 ∼ 11 µm with a maximum value of 95% at 9.73 µm. The optoelectrical simulations show that the responsivity at 7 ∼ 10 µm is significantly enhanced compared to that of the plain HgCdTe infrared photodiodes without the photon-trapping structure. We further investigate the optical crosstalk in the HgCdTe pixel array employing the photon-trapping structure. The optical crosstalk significantly reduces as the pixel spacing increases. Our work provides a design method for developing small pixel, large scale, and low dark current focal plane array infrared photodiodes.

Recent Progress in Simple and Cost-Effective Top-Down Lithography for ≈10 nm Scale Nanopatterns: From Edge Lithography to Secondary Sputtering Lithography

The development of a simple and cost-effective method for fabricating ≈10 nm scale nanopatterns over large areas is an important issue, owing to the performance enhancement such patterning brings to various applications including sensors, semiconductors, and flexible transparent electrodes. Although nanoimprinting, extreme ultraviolet, electron beams, and scanning probe litho-graphy are candidates for developing such nanopatterns, they are limited to complicated procedures with low throughput and high startup cost, which are difficult to use in various academic and industry fields. Recently, several easy and cost-effective lithographic approaches have been reported to produce ≈10 nm scale patterns without defects over large areas. This includes a method of reducing the size using the narrow edge of a pattern, which has been attracting attention for the past several decades. More recently, secondary sputtering lithography using an ion-bombardment technique was reported as a new method to create high-resolution and high-aspect-ratio structures. Recent progress in simple and cost-effective top-down lithography for ≈10 nm scale nanopatterns via edge and secondary sputtering techniques is reviewed. The principles, technical advances, and applications are demonstrated. Finally, the future direction of edge and secondary sputtering lithography research toward issues to be resolved to broaden applications is discussed.

Tip-Based Nanofabrication for Scalable Manufacturing

Tip-based nanofabrication (TBN) is a family of emerging nanofabrication techniques that use a nanometer scale tip to fabricate nanostructures. In this review, we first introduce the history of the TBN and the technology development. We then briefly review various TBN techniques that use different physical or chemical mechanisms to fabricate features and discuss some of the state-of-the-art techniques. Subsequently, we focus on those TBN methods that have demonstrated potential to scale up the manufacturing throughput. Finally, we discuss several research directions that are essential for making TBN a scalable nano-manufacturing technology.

Large-Area Sub-Wavelength Optical Patterning via Long-Range Ordered Polymer Lens Array

Fabrication of large-area, highly orderly, and high-resolution nanostructures in a cost-effective fashion prompts advances in nanotechnology. Herein, for the first time, we demonstrate a unique strategy to prepare a long-range highly regular polymer lens from photoresist nanotrenches based templates, which are obtained from underexposure. The relationship between exposure dose and the cross-sectional morphology of produced photoresist nanostructures is revealed for the first time. The polymer lens arrays are repeatedly used for rapid generation of sub-100 nm nanopatterns across centimeter-scale areas. The light focusing properties of the nanoscale polymer lens are investigated by both simulation and experiment. It is found that the geometry, size of the lens, and the exposure dose can be deployed to adjust the produced feature size, spacing, and shapes. Because the polymer lenses are derived from top-down photolithography, the nearly perfect long-range periodicity of produced nanopatterns is ensured, and the feature shapes can be flexibly designed. Because this nanolithographic strategy enables subwavelength periodical nanopatterns with controllable feature size, geometry, and composition in a cost-effective manner, it can be optimized as a viable and potent nanofabrication tool for various technological applications.