Omnidirectional color filters capitalizing on a nano-resonator of Ag-TiO2-Ag integrated with a phase compensating dielectric overlay

We present a highly efficient omnidirectional color filter that takes advantage of an Ag-TiO2-Ag nano-resonator integrated with a phase-compensating TiO2 overlay. The dielectric overlay substantially improves the angular sensitivity by appropriately compensating for the phase pertaining to the structure and suppresses unwanted optical reflection so as to elevate the transmission efficiency. The filter is thoroughly designed, and it is analyzed in terms of its reflection, optical admittance, and phase shift, thereby highlighting the origin of the omnidirectional resonance leading to angle-invariant characteristics. The polarization dependence of the filter is explored, specifically with respect to the incident angle, by performing experiments as well as by providing the relevant theoretical explanation. We could succeed in demonstrating the omnidirectional resonance for the incident angles ranging to up to 70°, over which the center wavelength is shifted by below 3.5% and the peak transmission efficiency is slightly degraded from 69%. The proposed filters incorporate a simple multi-layered structure and are expected to be utilized as tri-color pixels for applications that include image sensors and display devices. These devices are expected to allow good scalability, not requiring complex lithographic processes.This work was supported by a National Research Foundation of Korea grant funded by the Korean government (MEST) (No. 2013-008672 and 2013-067321), and also by a research grant from Kwangwoon University in 2014. The work was partly supported by the Australian Research Council Future Fellowship (FT110100853, Dr. Duk-Yong Choi) and was performed in part at the ACT node of the Australian National Fabrication Facilit

Periodically patterned structures for nanoplasmonic and biomedical applications

Periodically patterned nanostructures have imparted profound impact on diverse scientific disciplines. In physics, chemistry, and materials science, artificially engineered photonic crystals have demonstrated an unprecedented ability to control the propagation of photons through light concentration and diffraction. The field of photonic crystals has led to many technical advances in fabricating periodically patterned nanostructures in dielectric/metallic materials and controlling the light-matter interactions at the nanoscale. In the field of biomaterials, it is of great interest to apply our knowledge base of photonic materials and explore how such periodically patterned structures control diverse biological functions by varying the available surface area, which is a key attribute for surface hydrophobicity, cell growth and drug delivery. Here we describe closely related scientific applications of large-scale periodically patterned polymers and metal nanostructures. The dissertation starts with nanoplasmonics for improving photovoltaic devices, where we design and optimize experimentally realizable light-trapping nanostructures using rigorous scattering matrix simulations for enhancing the performance of organic and perovskite solar cells. The use of periodically patterned plasmonic metal cathode in conjunction with polymer microlens array significantly improves the absorption in solar cells, providing new opportunities for photovoltaic device design. We further show the unprecedented ability of nanoplasmonics to concentrate light at the nanoscale by designing a large-area plasmonic nanocup array with frequency-selective optical transmission. The fabrication of nanostructure is achieved by coating non-uniform gold layer over a submicron periodic nanocup array imprinted on polystyrene using soft lithography. The gold nanocup array shows extraordinary optical transmission at a wavelength close to the structure period. The resonance wavelength for transmission can be tuned by changing the period of the gold nanocup array, which opens up new avenues in subwavelength optics for designing optoelectronic devices and biological sensors. We then demonstrate strong exciton-plasmon coupling between non-toxic CuInS2/ZnS quantum dots in solution and plasmonic gold nanocup array. The photoluminescence decay rate of quantum dots can be enhanced by more than an order of magnitude due to the high electric field intensity enhancement inside the plasmonic nanocup cavity. This solution based metal-nanocrystal coupled system has great promise for biological applications such as biosensing and biolabeling. Moving to the area of biomedical applications, we fabricate nanopatterned biopolymers as templates for controlling the release of therapeutic drugs coated on the polymer surface. From careful drug release experiments performed over extended time periods (e.g. eight days), we find that nanopatterned polymers release the drug slower as compared to the flat polymer surfaces. The slow-down in the drug release from nanopatterned surfaces is attributed to increase in the surface hydrophobicity confirmed by the contact angle measurements and microfluidic simulations. This nanoscale drug release control scheme has great promise for improving the performance of drug-eluting stents in cardiac therapies

고해상도 CMOS 이미지 센서를 위한 나노광학소자

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2021.8. 이병호.Image sensor is a device that converts electromagnetic waves scattered by the objects or environment into electric signals. Recently, in the mobile device and autonomous vehicle industries, multiple image sensors having different purposes are required for a single device. In particular, image sensors with more than 100 million pixels are being developed in response to the development of a display to a high resolution of 8K or more. However, due to the limited space of the mobile device, the size of pixels constituting the sensor must be reduced for a high-resolution image sensor, which causes factors that reduce image quality, such as a decrease in light efficiency, a decrease in quantum efficiency, and color interference. Metasurface is a device that modulates electromagnetic waves through an array of antennas smaller than wavelength. It has been proposed as a device that replaces the color filter, lens, and photodiode constituting the optical system of the image sensor. However, the performance of the metasurface corresponding to the miniaturized pixel size was limited by the operating principle that requires several array of nano-antennas. In this dissertation, I present a metasurface optical device that can improve the image quality of an existing image sensor composed of micropixels. First, an absorption type color filter that suppresses reflection is discussed. The reflection that inevitably occurs in the conventional metasurface color filter elements causes a flare phenomenon in the captured image. In this dissertation, I design a color filter that transmits only a specific band and absorbs the rest of the absorption resonant band of a hyperbolic metamaterial antenna using a particle swarm optimization method. In particular, I present a Bayer pattern color filter with a pixel size of 255 nm. Second, I introduce a color distribution meta-surface to increase the light efficiency of the image sensor. Since the photodiode converts light having energy above the band gap into an electric signal, an absorption type color filter is used for color classification in image sensor. This means that the total light efficiency of the image sensor is limited to 33% by the blue, green, and red filters constituting one pixel. Accordingly, a freeform metasurface device is designed that exceeds the conventional optical efficiency limit by distributing light incident on the sub-pixel in different directions according to color. Finally, an optical confinement device capable of increasing signal-to-noise ratio (SNR) in low-illuminance at near-infrared is presented. Through the funnel-shaped plasmonic aperture, the light is focused on a volume much smaller than the wavelength. The focused electric and magnetic fields interact with the spatially distributed semiconductors, which achieve a Purcell effect enhanced by the presence of the metasurface. This dissertation is expected to overcome the conventional nanophotonic devices for image sensors and become a cornerstone of the development of micropixel or nanopixel image sensors. Furthermore, it is expected to contribute to building a new image sensor platform that will replace the optical system constituting the image sensor with metasurface.이미지 센서는 환경에 의해 산란되는 전자기파를 전기신호로 바꾸는 소자로, 최근 모바일 기기와 자율 주행 자동차 산업에서 단일 디바이스에 다른 목적을 가진 이미지 센서들이 요구되고 있다. 특히, 디스플레이가 8K 이상의 고해상도로 발전함에 대응하여 1억화소 이상의 이미지 센서가 개발되고 있다. 그러나, 모바일 기기의 제한된 공간에 의해 고해상도 이미지 센서를 위해서는 센서를 구성하는 픽셀의 크기를 줄여야 하며, 이는 광 효율 감소, 양자 효율 감소, 색 간섭 등의 화질을 감소시키는 요소들을 야기한다. 메타표면은 파장보다 작은 안테나들의 배열을 통해 전자기파를 변조해주는 소자로, 이미지 센서의 광학 시스템을 구성하는 색 필터, 렌즈, 포토 다이오드를 대체하는 소자로 제안되었다. 하지만, 소형화 된 픽셀 크기에 대응하는 메타표면은 나노 안테나의 동작원리와 배열의 한계에 의해 성능이 제한되었다. 본 논문에서는 초소형 픽셀로 구성된 기존 이미지 센서에 대한 화질을 높일 수 있는 메타표면 광학소자를 제시한다. 첫째로, 반사를 억제하는 흡수형 색 필터에 대해서 논의한다. 기존 메타표면 색 필터 소자에서 필연적으로 발생하는 내부 반사는 찍은 이미지에서 플레어 현상을 유발한다. 본 논문에서는 쌍곡 메타물질 안테나의 흡수 공진 대역을 입자 무리 최적화 방식을 이용해 특정 대역 만을 투과하고 나머지는 흡수하는 색 필터를 설계한다. 특히, 255 nm 크기 픽셀의 베이어 패턴 색 필터를 제시한다. 둘째로, 이미지 센서의 광 효율을 높이기 위한 색 분배 메타표면을 제시한다. 이미지 센서의 포토 다이오드는 밴드 갭 이상의 에너지를 가지는 빛에 대해 전기신호로 변환하므로, 색 구분을 위해 흡수형 색 필터를 사용한다. 이는 하나의 픽셀을 구성하는 청, 녹, 적색 필터에 의해 이미지 센서의 전체 광 효율이 33 %로 제한되는 것을 의미한다. 따라서, 서브 픽셀에 입사하는 빛을 색에 따라 다른 방향으로 빛을 분배하여 기존의 광 효율 한계를 넘어서는 자유형 메타표면 소자를 설계한다. 마지막으로, 저조도의 근적외선에서 신호 대 잡음비를 높일 수 있는 광 집속 소자를 제시한다. 깔대기 모양의 플라즈모닉 개구를 통해 빛을 파장보다 매우 작은 크기의 영역에 집중시킨다. 집속된 전기장과 자기장은 공간적으로 분포된 반도체와 상호작용함으로써, 메타표면의 존재에 따라 강화된 Purcell 효과를 얻는다. 본 박사학위 논문은 이미지 센서를 위한 기존의 제한된 메타표면 소자를 극복하고, 초소형 픽셀의 이미지 센서 개발의 초석이 될 것으로 기대된다. 나아가, 이미지 센서를 구성하는 광학 시스템을 메타표면으로 대체할 새로운 플랫폼을 구축하는 것에 기여할 것으로 기대된다.Chapter 1 Introduction 1 1.1 Overview of CMOS image sensors 1 1.2 Toward high-resolution miniaturized pixel 2 1.3 Nanophotonic elements for high-resolution camera 3 1.4 Dissertation overview 5 Chapter 2 Light interaction with subwavelength antennas 7 2.1 Overview of plasmonic antenna 7 2.2 Overview of dielectric metasurface 9 2.3 Overview of hyperbolic metamaterials 11 Chapter 3. Absorptive metasurface color filter based on hyperbolic metamaterial for noise reduction 14 3.1 Introduction 14 3.2 Principle of hyperbolic metamaterial absorbers 17 3.3 Absorptive color filter design based on particle swarm optimization method 19 3.4 Numerical analysis on optimized metasurface color filters 23 3.4.1 Single color filter optimization 23 3.4.2 Angle tolerance for optimized metasurface color filters 26 3.5 Sub-micron metasurface color filter array 29 3.6 Conclusion 35 Chapter 4 High-efficient full-color pixel array based on freeform nanostructures for high-resolution image sensor 37 4.1 Introduction 37 4.2 Optimization of metasurface full-color splitter 40 4.3 Implementation of color splitters 46 4.4 Image quality evaluation 52 4.5 Discussion about off-axis color splitters 55 4.6 Conclusion 59 Chapter 5 Plasmonic metasurface cavity for simultaneous enhancement of optical electric and magnetic fields 60 5.1 Introduction 60 5.2 Working principle and numerical results 63 5.2.1 Principle of funnel-shaped metasurface cavity 63 5.2.2 Discussion 67 5.3 Experimental results 69 5.4 Purcell effect 72 5.5 Conclusion 74 Chapter 6 Conclusion 75 Appendix 78 A.1 Colorimetry 78 A.2 Color difference CIEDE2000 79 B. Related work 80 Bibliography 81박

Organic Molecular Crystal Engineering via Organic Vapor-Liquid-Solid Deposition

Control over the size, shape, topology, orientation, and crystallographic phase of organic molecular materials is critical for a wide array of applications ranging from optoelectronics to pharmaceutical development. Herein, we demonstrate a relatively low-cost approach for fabricating single crystals with controlled sizes, shapes, microscale periodic features, preferred orientations and specific molecular packing modes. These features allow for the fabrication of intricate arrangements of single crystals for incorporation into complex device architectures, and potentially the endowment of tailored optical, electronic, thermal, and mechanical properties onto these materials. Patterning is achieved by utilizing an organic-vapor-liquid-solid (OVLS) deposition scheme paired with traditional photolithography methods. The OVLS approach involves spin coating a layer of a low vapor pressure solvent onto a substrate in order to drive up the critical nucleus size required for crystal nucleation, resulting in large grain sizes. This substrate is placed above a hot plate with the organic material to be sublimed. Our results show that millimeter-scale, ultrathin, planar organic molecular crystals can be grown on patterned substrates with rudimentary equipment (hot plate, spin coater, photoresist, photomask, UV source). We show that this technique is not only compatible with organic semiconductors, but also other organic molecular crystals such as pharmaceuticals

Plasmonic nano apertures for molecular sensing and colour displays

The discovery of extraordinary optical transmissions through metallic periodical subwavelength apertures has seen promising applications in filtering and sensing. Such a unique optical property is due to the excitation of surface plasmon resonance. Through accurate control of the aperture’s geometrical shape and dimension, the optical resonance of such nanostructure can be tuned in a wide range from the visible to near infrared. In addition, the highly confined resonant electromagnetic field supported by such a nanostructure can be utilised in surface enhanced Raman spectroscopy. This thesis studied metallic nano aperture arrays for the application of molecular sensing and colour displays. The development of nanofabrication processes for making complex metallic nano apertures was the foundation of this research. Gold was chosen as the appropriate material for sensing mainly due to its stable chemical and physical properties. Aluminium was selected for making colour pixels because its optical resonant frequency can be tuned over the whole visible range. One aspect of this research relating to surface enhanced Raman spectroscopy considered symmetrical gold nano apertures: annular aperture arrays and circular aperture arrays. Comparisons between two annular aperture arrays and between one annular aperture array and one circular aperture array were carried out. The asymmetrical gold nanostructures studied were split-ring shaped aperture arrays. One structure can be used to generate two polarisation dependent resonances in which one of them was able to match the laser in the Raman spectrometer for molecular interrogation and the other was not. The other aspect related to dual-colour pixels. Aluminium cross-shaped aperture arrays were fabricated. By varying the structural dimensions and incident polarisation, colours could be tuned over the whole visible range. Polarisation controlled chromatic displays were demonstrated by employing these pixels

Filtrage spectral plasmonique à base de nanostructures métalliques adaptées aux capteurs d'image CMOS

Image sensors have experienced a renewed interest with the prominent market growth of wireless communication, together with a diversification of functionalities. In particular, a recent application known as Ambient Light Sensing (ALS) has emerged for a smarter screen backlight management of display-based handheld devices. Technological progress has led to the fabrication of thinner handsets, which imposes a severe constraint on light sensors' heights. This thickness reduction can be achieved with the use of an innovative, thinnest and entirely on-chip spectral filter. In this work, we present the investigation and the demonstration of plasmonic filters aimed for commercial ALS products. The most-efficient filtering structures are identified with strong emphasis on the stability with respect to the light angle of incidence and polarization state. Integration schemes are proposed according to CMOS compatibility and wafer-scale fabrication concerns. Plasmon resonances are studied to reach optimal optical properties and a dedicated methodology was used to propose optimized ALS performance based on actual customers' specifications. The robustness of plasmonic filters to process dispersions is addressed through the identification and the simulation of typical 300 mm fabrication inaccuracies and defects. In the light of these studies, an experimental demonstration of ALS plasmonic filters is performed with the development of a wafer-level integration and with the characterization and performance evaluation of the fabricated structures to validate the plasmonic solution.Les capteurs d'image connaissent un regain d'intérêt grâce à la croissance remarquable du secteur de la communication sans fil, et leurs fonctionnalités tendent à se diversifier. Plus particulièrement, une application récente connue sous le nom de capteur de luminosité ambiante (ALS de l'acronyme anglais) est apparue dans le but de proposer un ajustement intelligent du rétro-éclairage dans les appareils mobiles pourvus d'écrans. Les avancées technologiques ont permis la fabrication de smartphones toujours plus fins, ce qui impose une contrainte importante sur la hauteur des capteurs de lumière. Cette réduction d'épaisseur peut être réalisée grâce à l'utilisation de filtres spectraux innovants, plus fins et entièrement sur puce. Dans cette thèse, nous présentons l'étude et la démonstration de filtres plasmoniques adaptés à une intégration dans des produits ALS commerciaux. Les structures de filtrage les plus performantes sont identifiées avec une importance particulière accordée à la stabilité des filtres par rapport à l'angle d'incidence de la lumière et à son état de polarisation. Des schémas d'intégration compatibles CMOS et respectant les contraintes d'une fabrication à l'échelle du wafer sont proposés. Les résonances de plasmon sont étudiées afin d'atteindre des propriétés optiques optimales et une méthodologie spécifique à partir d'un véritable cahier des charges client a été utilisée pour obtenir des performances ALS optimisées. La robustesse des filtres plasmoniques aux dispersions de procédé est analysée à travers l'identification et la modélisation des imprécisions et des défauts typiques d'une fabrication sur wafer 300 mm. A la lumière de ces travaux, une démonstration expérimentale de filtres ALS plasmoniques est réalisée avec le développement d'une intégration à l'échelle du wafer et avec la caractérisation et l'évaluation des performances des structures fabriquées afin de valider la solution plasmonique

Hybrid Materials for Integrated Photonics

In this review materials and technologies of the hybrid approach to integrated photonics (IP) are addressed. IP is nowadays a mature technology and is the most promising candidate to overcome the main limitations that electronics is facing due to the extreme level of integration it has achieved. IP will be based on silicon photonics in order to exploit the CMOS compatibility and the large infrastructures already available for the fabrication of devices. But silicon has severe limits especially concerning the development of active photonics: its low efficiency in photons emission and the limited capability to be used as modulator require finding suitable materials able to fulfill these fundamental tasks. Furthermore there is the need to define standardized processes to render these materials compatible with the CMOS process and to fully exploit their capabilities. This review describes the most promising materials and technological approaches that are either currently implemented or may be used in the coming future to develop next generations of hybrid IP devices

hybrid materials for integrated photonics

In this review materials and technologies of the hybrid approach to integrated photonics (IP) are addressed. IP is nowadays a mature technology and is the most promising candidate to overcome the main limitations that electronics is facing due to the extreme level of integration it has achieved. IP will be based on silicon photonics in order to exploit the CMOS compatibility and the large infrastructures already available for the fabrication of devices. But silicon has severe limits especially concerning the development of active photonics: its low efficiency in photons emission and the limited capability to be used as modulator require finding suitable materials able to fulfill these fundamental tasks. Furthermore there is the need to define standardized processes to render these materials compatible with the CMOS process and to fully exploit their capabilities. This review describes the most promising materials and technological approaches that are either currently implemented or may be used in the coming future to develop next generations of hybrid IP devices