Browsing by Author "Fu, Sze Ming"

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A fully functionalized metamaterial perfect absorber with simple design and implementation
(2016-10-26)
Fu, Sze Ming
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Zhong, Yan Kai
;
Tu, Ming Hsiang
;
Chen, Bo Ruei
;
Lin, Albert
Broadband perfect metamaterial absorbers have been drawing significant attention in recent years. A close-to-unity absorption over a broad spectral range is established and this facilitates many photonic applications. A more challenging goal is to construct a broadband absorber with a tailored spectral absorption. The spectral absorption control and spectral shaping are very critical in many applications, such as thermal-photovoltaic, thermal emitters, spectrum imaging system, biomedical and extraterrestrial sensing, and refractive index sensor. In this work, one-dimensional (1D) planar stacking structure is designed to achieve the ultimate goal of a functionalized absorber with a fully tailorable spectral absorption. The lithography and etching process are totally eliminated in this proposed structure, and the fabrication is fully compatible with the regular silicon IC processing. By using similar to 2 nm ultra-thin metallic layers with a 10-pair (10X) SiO2/Si3N4 integrated dielectric filter, we can achieve decent spectral response shaping. The planar configuration of the ultra-thin-metal metamaterial perfect absorber (MPA) is the key to the easy design/integration of the dielectric filters on top of the MPA. Specifically, band-rejected, high-pass, low-pass and band-pass structure are constructed successfully. Finally, experimental evidence to support our simulation result is also provided, which proves the feasibility of our proposal.
A Multimetal Broadband Metamaterial Perfect Absorber With Compact Dimension
(2016-04-01)
Zhong, Yan Kai
;
Fu, Sze Ming
;
Tu, Ming-Hsiang
;
Chen, Bo-Ruei
;
Lin, Albert
We propose an extremely simple multiple-metal metamaterial perfect absorber (MPA). The dimension of our proposed design is only 221 nm for the visible wavelength range from 400 to 700 nm. This is comparable with past efforts on MPAs using plasmonics at the same wavelength range, whereas the plasmonic excitation is absent in our proposal. A unity broadband absorption can be achieved with ultrathin metallic films. In addition, the wavelength scalability is possible using our design, and the fully planar simple configuration facilitates large-area photonic design without the need for lithography and etching. The physics is the field penetration and the field absorption for the photons at different wavelength ranges using different metallic layers. We also show that the adjustment of the individual layer thickness is critical to attaining a perfect wave impedance matching to vacuum. The titanium (Ti), nickel (Ni), and aluminum (Al) triple-metal configuration is used to demonstrate the concept experimentally, and a close match to the theoretical result is observed. The absorption band can be further widened with more stacking layers with various metals. We believe that the proposed design is very promising in the aspects of simple processing and scalable for large-area broadband unity absorption. It thus improves the future implementation of MPAs and facilitates a wide range of relevant applications.
A Planarized Thermophotovoltaic Emitter With Idealized Selective Emission
(2016-08-01)
Fu, Sze Ming
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Zhong, Yan Kai
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Tu, Ming Hsiang
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Chen, Bo Ruei
;
Lin, Albert
Compared with conventional solar cells, thermophotovoltaics (TPV) can be more efficient and, thus, exceeds the detailed balance efficiency limit. In particular, the emitter of TPV is a critical design since it determines whether the thermalization loss can be reduced and whether the sub-band-gap radiation can be suppressed, as far as the photovoltaic (PV) process is concerned. In this paper, we propose a selective planar emitter composed of alternating ultrathin metal and dielectric layers. An aperiodic dielectric stacking is designed to tailor the emission spectrum by shaping the emission peak and by adjusting the emission wavelength. We show that the peak emission wavelength (lambda(emission)) is adjustable from lambda = 1500 nm to lambda = 2500 nm. Furthermore, the long-wavelength cutoff is very sharp for our proposed emitter structure, and the absorption is suppressed to 0.1 beyond the cutoff. The preliminary experiment is also conducted to fulfill the concept of a fully planar ultrathin refractory metal emitter design, and the result is similar to the calculated ones. We believe that the planar thermal emitter based on ultrathin metals and aperiodic dielectric stacking is very promising for future thermal emission applications since it requires no lithography and etching, provides strong peak emission power, and possesses wide wavelength scalability.
An ultra-compact blackbody using electrophoretic deposited carbon nanotube films
(2018-01-01)
Lin, Albert
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Yang, Chien-Chih
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Parashar, Parag
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Lin, Chien-Yung
;
Jian, Ding Rung
Carbon nanotubes (CNTs) possesses decent optical properties and thus can be considered as a candidate for perfect absorbers due to their close-to-air refractive index and minimal extinction. However, weak absorption in porous materials, due to the low extinction coefficients, requires an inevitably thick absorption layer (similar to 100 mu m) for the perfect opaque absorbers. Thus, the requirement of large thicknesses of CNTs prohibits them from being used as miniaturized integrated photonic devices. Here, we propose an electrophoretic deposited (EPD) CNT resonant cavity structure on tantalum (Ta) to enhance optical absorption. Efficient random light scattering along with the resonant cavity structure using Ti/SiO2 stacking enhances the absorption in our proposed EPD-CNT film while maintaining the total device thickness to <1 mu m. The experiment results reveal that the absorption band covers the entire UV-VIS-NIR spectrum (lambda = 0.3-2.6 mu m), using resonant-cavity EPD-CNT design. The EPD deposition process is done at relatively low temperature < 120 degrees C. We believe that this proposal is very promising for sensing, antenna, and thermophotovoltaics (TPV), in terms of bandwidth, compactness and cost.
Analytics-statistics mixed training and its fitness to semisupervised manufacturing
(2019-08-13)
Parashar, Parag
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Chen, Chun Han
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Akbar, Chandni
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Fu, Sze Ming
;
Rawat, Tejender S.
While there have been many studies using machine learning (ML) algorithms to predict process outcomes and device performance in semiconductor manufacturing, the extensively developed technology computer-aided design (TCAD) physical models should play a more significant role in conjunction with ML. While TCAD models have been effective in predicting the trends of experiments, a machine learning statistical model is more capable of predicting the anomalous effects that can be dependent on the chambers, machines, fabrication environment, and specific layouts. In this paper, we use an analytics-statistics mixed training (ASMT) approach using TCAD. Under this method, the TCAD models are incorporated into the machine learning training procedure. The mixed dataset with the experimental and TCAD results improved the prediction in terms of accuracy. With the application of ASMT to the BOSCH process, we show that the mean square error (MSE) can be effectively decreased when the analytics-statistics mixed training (ASMT) scheme is used instead of the classic neural network (NN) used in the baseline study. In this method, statistical induction and analytical deduction can be combined to increase the prediction accuracy of future intelligent semiconductor manufacturing.
Approaching conversion limit with all-dielectric solar cell reflectors
(2015-02-09)
Fu, Sze Ming
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Lai, Yi-Chun
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Tseng, Chi Wei
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Yan, Sheng Lun
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Zhong, Yan Kai
Metallic back reflectors has been used for thin-film and wafer-based solar cells for very long time. Nonetheless, the metallic mirrors might not be the best choices for photovoltaics. In this work, we show that solar cells with all-dielectric reflectors can surpass the best-configured metal-backed devices. Theoretical and experimental results all show that superior large-angle light scattering capability can be achieved by the diffuse medium reflectors, and the solar cell J-V enhancement is higher for solar cells using all-dielectric reflectors. Specifically, the measured diffused scattering efficiency (D.S.E.) of a diffuse medium reflector is >0.8 for the light trapping spectral range (600nm-1000nm), and the measured reflectance of a diffuse medium can be as high as silver if the geometry of embedded titanium oxide(TiO2) nanoparticles is optimized. Moreover, the diffuse medium reflectors have the additional advantage of room-temperature processing, low cost, and very high throughput. We believe that using all-dielectric solar cell reflectors is a way to approach the thermodynamic conversion limit by completely excluding metallic dissipation. (C) 2015 Optical Society of America
Arbitrarily-Wide-Band Dielectric Mirrors and Their Applications to SiGe Solar Cells
(2015-08-01)
Zhong, Yan Kai
;
Fu, Sze Ming
;
Yan, Sheng Lun
;
Chen, Po Yu
;
Lin, Albert
The dielectric mirror is an important optical component for optoelectronic devices, passive photonic devices, and solar cells. Unfortunately, the reflection bandwidth of distributed Bragg reflectors (DBRs) and high-index contrast mirrors (HCGs) are limited by the index contrast of the material system used. Here, an aperiodic design for dielectric mirrors is proposed, and it is shown that for a fixed index contrast, the bandwidth of the reflection band can be arbitrarily widened by simply incorporating more dielectric layers. This is pronouncedly different from the fixed bandwidth of HCGs and DBRs. The physics behind the broadband reflection for the aperiodic stacking is identified as the photonic bandgap widening due to the annihilation of the quasi-guided modes in nonperiodic structures. This observation applies very well to aperiodic auto-cloned 3-D photonic crystal reflectors, to aperiodic DBRs, and even to diffuse dielectric mirrors that have recently emerged to be very promising for solar cells due to their zero plasmonic absorption nature. Experimentally, the white paint diffuse medium reflectors are applied to SiGe solar cells to confirm their high reflectance and the feasibility of enhancing solar cell efficiency.
Broadband Polarization-Insensitive Metamaterial Perfect Absorbers Using Topology Optimization
(2016-10-01)
Fu, Sze Ming
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Zhong, Yan Kai
;
Ju, Nyan Ping
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Tu, Ming-Hsiang
;
Chen, Bo-Ruei
A novel scheme for a perfect hyperbolic metamaterial (HMM) absorber is proposed, and experimental verification is provided. It has been shown previously that tapered HMM stacks can provide adiabatic waveguiding over a wide spectral range and thus are an ideal opaque absorber. Here, nontapered shape-optimized HMM absorbers are proposed, which facilitates the fabrication and promotes the large-area applications such as thermophotovoltaics (TPV). In the synthesis of the optimal patterns, we use 5-harmonic rigorously coupled wave analysis (RCWA) and experimental trials to shorten the trial-and-error time. The best pattern provides an averaged broadband experimental absorption of 88.38% over lambda = 1 mu m to lambda = 2 mu m, which is comparable to the state-of-the-art experimental effort using tapered HMM. The nontapered nature can be easier to fabricate from the semiconductor processing viewpoint. The physics behind the pattern-optimized HMM cavity is the broadband light coupling by the air-cavity and the unbounded photonic density of the states (PDOS) associated with the HMM. The topology optimized air cavity effectively couples the incident photons into the metal-dielectric stacking, eliminating the need of sidewall tapers. We believe the proposed topology-optimization methodology benefits the future design of compact metamaterial perfect absorbers (MPA), sensors, antenna, and thermophotovoltaic emitters, and absorbers.
Experimentally-implemented genetic algorithm (Exp-GA): toward fully optimal photovoltaics
(2015-09-21)
Zhong, Yan Kai
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Fu, Sze Ming
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Ju, Nyan Ping
;
Chen, Po Yu
;
Lin, Albert
The geometry and dimension design is the most critical part for the success in nano-photonic devices. The choices of the geometrical parameters dramatically affect the device performance. Most of the time, simulation is conducted to locate the suitable geometry, but in many cases simulation can be ineffective. The most pronounced examples are large-area randomized patterns for solar cells, light emitting diode (LED), and thermophtovoltaics (TPV). The large random pattern is nearly impossible to calculate and optimize due to the extended CPU runtime and the memory limitation. Other scenarios that numerical simulations become ineffective include three-dimensional complex structures with anisotropic dielectric response. This leads to extended simulation time especially for the repeated runs during its geometry optimization. In this paper, we show that by incorporating genetic algorithm (GA) into real-world experiments, shortened trial-and-error time can be achieved. More importantly, this scheme can be used for many photonic design problems that are unsuitable for simulation-based optimizations. Moreover, the experimentally implemented genetic algorithm (Exp-GA) has the additional advantage that the resultant objective value is a real one rather than a theoretical one. This prevents the gaps between the modeling and the fabrication due to the process variation or inaccurate numerical models. Using TPV emitters as an example, 22% enhancement in the mean objective value is achieved. (C) 2015 Optical Society of America
Fully Planarized Perfect Metamaterial Absorbers With No Photonic Nanostructures
(2016-02-01)
Zhong, Yan Kai
;
Fu, Sze Ming
;
Ju, Nyan Ping
;
Tu, Ming-Hsiang
;
Chen, Bo-Ruei
In the past, perfect metamaterial absorbers (PMAs) have required nanolitho-graphy patterning to boost broadband absoprtion. Tapered structures, in particular, are shown to achieve close-to-unity absorption over broadband using adiabatic light coupling. A nontapered PMA is desirable due to the fact that it is easier to fabricate using regular lithography techniques. This facilitates the scalability to large-area photonic applications such as thermophotovoltaics. In this work, we propose a fully planarized design with ultrathin metallic films for broadband PMAs. The design provides close-to-unity absorbance over a wide spectral range and is wavelength scalable from middle ultraviolet to long wavelength infrared. The planarized design is extremely easy to fabricate, and it requires no lithography nor etching. The design can be used with different moderate-extinction metals such as tungsten, titanium, tantalum, and nickel. The physics is that the thin layer of the moderate-extinction metal allows photons to penetrate through itself. The insertion of the dielectric between thin metal layers is necessary to spatially separate the ultrathin metallic thin film to boost the effect of thin-film absorption. As far as the bandwidth normalized to center wavelength is concerned, we believe that the experimental result demonstrated here shows the broadest bandwidth to date.
Low Cost All-Dielectric Thin-Film Solar Cell Using Diffuse Medium Reflectors
(2014)
Tseng, Chi Wei
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Fu, Sze Ming
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Lai, Shih-Yun
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Lai, Wei-Ming
;
Yan, Sheng Lun
Diffuse reflectors can be beneficial for solar cells, due to no plasmonic loss, higher reflectance, decent light scattering, and low cost. Experimental and theoretical works are presented here to demonstrate its feasibility for photovoltaics.
Non-reciprocal meta-surfaces for nanophtonic light trapping: optical isolators versus solar cells
(2015)
Fu, Sze Ming
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Zhong, Yan Kai
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Yan, Sheng Lun
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Ju, Nyan Ping
;
Chen, Po Yu
Nano-photonic concept has been shown to be very effective for boosting solar cell conversion efficiency. In this work, the novel concepts of non-reciprocality and chiral meta-surface are demonstrated to be very useful for photovoltaics. The asymmetric chiral patterns are designed and optimized using genetic algorithm. The enhanced optical absorption is observed and it is attributed to the non-reciprocal nature of the solar cell front meta-surface. The asymmetric solar cell front surface enhances the anti-reflection and, at the same time, forbids the photon escape once it enters the devices. This concept is very similar to optical isolators where one-way transmission is intentionally designed for enhanced optical diode effect. Preliminary experimental results are supplied to confirm the superiority of asymmetric chiral design. The ongoing experimental effort is adjusting the PECVD deposition conditions to boost the efficiency on patterned substrates.
Omnidirectional, polarization-independent, ultra-broadband metamaterial perfect absorber using field-penetration and reflected-wave-cancellation
(2016-05-16)
Zhong, Yan Kai
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Lai, Yi-Chun
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Tu, Ming-Hsiang
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Chen, Bo-Ruei
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Fu, Sze Ming
In this work, we present the result of nickel (Ni)-based metamaterial perfect absorbers (MPA) with ultra-broadband close-to-one absorbance. The experimental broadband characteristic is significantly improved over the past effort on metamaterial perfect absorbers. An indepth physical picture and quantitative analysis is presented to reveal the physical origin of its ultrabroadband nature. The key constituent is the cancellation of the reflected wave using ultra-thin, moderate-extinction metallic films. The ultra-thin metal thickness can reduce the reflection as the optical field penetrates through the metallic films. This leads to minimal reflection at each ultra-thin metal layer, and light is penetrating into the Ni/SiO2 stacking. More intuitively, when the layer thickness is much smaller than the photon wavelength, the layer is essentially invisible to the photons. This results in absorption in the metal thin-film through penetration while there is minimal reflection by the metal film. More importantly, the experimental evidence for omni-directionality and polarization-insensitivity are established for the proposed design. Detailed measurement is conducted. Due to the ultrathin metal layers and the satisfactory tolerance in dielectric thickness, the broadband absorption has minimal degradation at oblique incidence. Such a wide angle, polarization-insensitive, ultra-broadband MPA can be very promising in the future, and the optical physics using sub-skin-depth metal film can also facilitate miniaturized high-performance nano-photonic devices. (C) 2016 Optical Society of America.
Photonic Density of State (PDOS) Enhancement by Brillouin Zone Engineering
(2015)
Fu, Sze Ming
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Zhong, Yan Kai
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Yan, Sheng Lun
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Ju, Nyan Ping
;
Chen, Po Yu
The material absorption can be enhanced by increased photonic density of state(PDOS). Here we demonstrate that through the design in the Brillouin zone of nanophotonic light trapping structures, the PDOS can be effectively increased. The theoretical work using rigorously coupled wave calculation shows the increased spectral absorption and the optimal quasi-guided mode excitations in terms of their quality factors and the number of excited modes. The experimental work is currently ongoing and the preliminary result confirms enhanced short circuit current if the PDOS is properly adjusted. Unlike random structures, the proposed Brillouin zone engineered structures are more feasible from modeling and device process viewpoints.
Physics-Prior Bayesian Neural Networks in Semiconductor Processing
(2019-01-01)
Chen, Chun Han
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Parashar, Parag
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Akbar, Chandni
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Fu, Sze Ming
;
Syu, Ming-Ying
With the fast scaling-down and evolution of integrated circuit (IC) manufacturing technology, the fabrication process becomes highly complex, and the experimental cost of the processes is significantly elevated. Therefore, in many cases, it is very costly to obtain a sufficient amount of experimental data. To develop an efficient method to predict the results of semiconductor experiments with a small amount of known data, we use a novel method based on Bayesian framework with the prior distribution constructed by technology computer-aided-design (TCAD) physical models. This method combines the advantages of statistical models and physical models in the aspect that TCAD can provide visionary guidance on an experiment when a limited amount of experimental data is available, and a machine learning model can account for subtle anomalous effects. Specifically, we use aspect ratio dependent etching (ARDE) phenomenon as an example and use variational inference with Kullback-Leibler divergence minimization to achieve the approximation to the posterior distribution. The relation between etching process input parameters and etching depth is learned using the Bayesian neural network with TCAD priors. Using this method with 35 neurons per hidden layer, mean square error (MSE) in the test set is reduced from 0.2896 to 0.0175, 0.058 to 0.0183, 0.0563 to 0.0188, 0.058 to 0.019 for partition =10, 20, 30, 40, respectively, reference to the baseline BNN where a regular normal distribution prior with zero mean and unity standard deviation N(0,1) is used.
Polarization- selective ultra-broadband super absorber
(2017-02-20)
Zhong, Yan Kai
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Fu, Sze Ming
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Huang, Weiming
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Rung, Ding
;
Huang, Jian Yi-Wen
While a broadband metamaterial perfect absorber (MPA) has been implemented and proposed intensively in recent years, an ultra-broadband perfect absorber with polarization selectivity has not been realized in literature. In this work, we propose a configuration of polarization-selective (PS) MPA with ultra-wide absorption bandwidth. The aluminum wire grid is integrated on top of the ultrathin-metal-dielectric stacking. The transverse electric (TE) wave is blocked due to the requirement of zero tangential electric field at the metal surface. The transverse magnetic field can pass the aluminum wire-grids because the normal electric field can be supported by the surface charge density at the metal surface, and full absorption of the TM wave is accomplished by the metal-dielectric stacking beneath. Theoretical calculation using rigorously coupled wave analysis demonstrates the wavelength selectivity from lambda = 1.98 mu m to lambda = 11.74 mu m where the TE absorption is <0.04 while TM absorption is >0.95, using 300 nm thick aluminum (Al) wire grid with 16-pair SiO2/Ti stacking. Additionally, the design is wavelength scalable by adjusting the dielectric thickness (t(sio2)) and the wire grid period (P) and height (t). The experimental result is demonstrated using Al grids and Ti/SiO2, and the measured result fully supports the calculated prediction. (C) 2017 Optical Society of America
The Coupled Electrical-Optical Simulation of Solar Cell J-V Degradation with Grating Heights
(2014)
Lin, Yu Chiun
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Zhong, Yan-Kai
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Fu, Sze Ming
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Tseng, Chi Wei
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Lai, Shih-Yun
Solar cell with grating structure is used frequently for increased optical absorption, but it can lead to electrical degradation. Here coupled simulation is conducted to clarify the physical reason causing this J-V degradation.
The External Light Trapping for Perovskite Solar Cells Using Nanoimprinted Polymer Metamaterial Patterns
(2016-01-01)
Lin, Albert
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Fu, Sze Ming
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Chen, Bo-Ruei
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Yan, Sheng-Lun
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Zhong, Yan Kai
In this work, we develop the process flow for nano-imprinted metamaterial patterns for perovskite solar cell light trapping. Nanoimprint can be scaled for large-area photovoltaics at low cost, compared to conventional lithography techniques. While conventional grating is normally underneath the solar cell active layers, the degraded electrical characteristic can be a problem. On the other hand, the external light trapping separates the electrical and optical designs and, therefore, it is more promising for complex photonic management without sacrificing the diode characteristics. We demonstrate the concept by perovskite solar cells with metamaterial patterns. Imprinting a deeper metamaterial pattern is suggested to enhance the far field effect for further efficiency improvement.
The External Light Trapping Using Down-Conversion Polymer and Diffuse Trench Reflectors
(2016-01-01)
Lin, Albert
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Han, Hau-Vei
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Huang, Chien-Yao
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Chen, Bo-Ruei
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Fu, Sze Ming
External light trapping has been proposed as an alternative to internal light trapping. The advantage is that the electrical and optical characteristics can be designed separately. This enhances the degree of improvement that nano-photonics can contribute to the solar cell efficiency and J(SC). In this work, we use diffuse trench reflectors with down-conversion polymer to demonstrate the concepts of a low-cost, widely applicable scheme for the external light trap. A >50% enhancement of the J(SC) can be observed with proper designs and configurations. The proposed external light trap can be applied to nearly all thin-film solar cell technologies since the external optical components do not affect the electrical diode characteristic of the solar cells. The efficient external light trap is attributed to the high reflectance of the disuse mirror and its wide-angle diffractions, optical confinement due to the trench reflector, and the additional short-wavelength spectral enhancement by the down-conversion mechanism.
The rigorous wave optics design of diffuse medium reflectors for photovoltaics
(2014-04-21)
Lin, Albert
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Fu, Sze Ming
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Zhong, Yan Kai
;
Tseng, Chi Wei
;
Chen, Po Yu
Recently, diffuse reflectors are being incorporated into solar cells, due to the advantage of no metallic absorption loss, higher reflectance, decent light scattering property by embedded TiO2 scatterers, and the ease of fabrication. Different methods have been employed to analyze diffuse reflectors, including Monte Carlo method, N-flux method, and a one-dimensional approximation based on semi-coherent optics, and the calculated reflectance is around 80% by these methods. In this work, rigorous wave optics solution is used, and it is shown that the reflectance for diffuse medium mirrors can actually be as high as >99% over a broad spectral range, provided the TiO2 scatterer geometry is properly optimized. The bandwidth of diffuse reflectors is un-achievable by other dielectric mirrors such as distributed Bragg reflectors or high index contrast grating mirror, using the same index contrast. Finally, it is promisingly found that even if the distribution of TiO2 is random, the wide-band reflection can still be achieved for the optimized TiO2 geometry. Initial experimental result is included in the supplementary material which shows the high feasibility of diffuse medium mirrors for solar cells. (C) 2014 AIP Publishing LLC.