Light Emitting Diodes (LEDs) are the most beneficial optoelectronic devices for human lives. LEDs already dominated mainstream lightings market, not only the general lightings but also displays, medical applications, and so on, to replace conventional light sources due to their small forma factors and high efficiency. Extensive researches have been carried out ever since introduced, and reported significant enhancement in optical output for the individual LED chip, and it is also pointed out that the enhancement in optical output for the emitter and the lighting system level must be considered by improvement of packaging materials and processes. In addition, the requirement for wide color gamut as well as enhanced optical output has been more important to be applied for color displays such as liquid crystal displays (LCDs). This dissertation is focused on addressing two parts, to propose optimized packaging designs of LED emitters and displays based on the points mentioned above.

First, an optimized design of packaging materials and process of enhancement in optical output of individual LED emitters is proposed using transparent die bonding material considering optical characteristics. It is shown that the optically transparent die attach adhesive prevent light absorption from the LED chip so that a substantial amount of light output of blue and phosphor converted white LED emitters compared to the conventional LED emitters using silver (Ag) based die bonding material. This optimization includes surface mount device (SMD) and chip-on-board (COB) type LED emitters. In addition to the COB-LED emitters, a transparent substrate is also shown to enhance light output and able to form an omnidirectional LED emitter.

Second, optimized packaging designs for color conversion film are proposed for wide color gamut displays. It is shown that the converted peak wavelengths by using quantum dot (QD) materials from blue backlights are well tuned and matched with required color coordinates for LCDs with a wide color gamut. A dichroic filter applied on the color conversion film dramatically reduced the amount of QD materials required by recycling excessive blue emission. More advanced packaging design for the color conversion film as pixels is also studied to replace color filters not only for LCDs but also for OLEDs.

Most of white light emitting diode emitters (WLEDs) for lighting and backlighting application are now produced by combining a blue wavelength emitting LED chip with wavelength-conversion materials, such as phosphor and quantum dots. Those WLED emitters are fully encapsulated by optical grade silicone with an intention of photon extraction improvement, optically reflecting surfaces protection, and isolate the LED package from the attack of chemical incompatible factors, such as humidity and halide chemicals. A relentless need for opto-electronic devices with reduced manufacturing cost calls for thinner back-lighting modules and thus thinner profile LED emitters. My thesis research is directed to investigate the optimization of materials and packaging processes for phosphor or quantum dot based white LEDs. Specific projects are focusing on the investigation on the feasibility of low profile lead frame based phosphor WLED emitters free of bulk encapsulant. As well as developing a cost-effective wavelength conversion films for chip scale WLED and LCD BLU. the investigation on the role of novel nano-particles, porous and asymmetric diffusing agents in enhancing the lighting extraction efficiency and reducing the phosphor or QD amount needed as a thin wavelength conversion film.The first part of this work, The junction temperature of a phosphor based white LED (WLED) is investigated as a function of the thickness of phosphor-silicone mixture coated on the chip. It is demonstrated that, to the contrary of a common believe, for a given correlated color temperature (CCT) with a fixed amount of phosphor in the mixture, the WLED junction temperature increases with decreasing thickness of the silicone phosphor mixture coating thickness. This observation can be explained in terms of the different coating thickness dependence of thermal conductivity and the amount of backward scattering of photons into the chip respectively. Although, as expected, the thermal resistance of the coating layer will decrease as the thickness decrease which will contribute to an enhanced thermal dissipation from the chip and thus a reduced junction temperature, but a much larger decrease is expected by the amount of backward scattering of photons into the chip, which results in an overall increase in the junction temperature as the coating thickness is reduced. The second part of this work ,A packaging approach for cost effective, and ultrathin high power phosphor-based white light-emitting-diode (WLED) emitters with outstanding reliability is presented. By removing the encapsulant in the conventional method, the new approach employs a single silicone-phosphor thin layer instead of multiple phosphor layers in chip scale package (CSP) WLED for both encapsulation as well as wavelength conversion. It is demonstrated that the presented WLEDs exhibit superior optical and thermal performance, as well as life-time durability. Accordingly, the present work offers an high reliability, cost-effective alternative approach for ultrathin high power WLED emitters with significant advantages over the conventional packaging structure and chip scale packaging methods. In the third part of this work, the role of nano-sized porous TiO2 diffuser in reducing required amount of wavelength conversion agents, such as phosphor and quantum dots, in the wavelength conversion layer is reported for the first time. It is experimentally demonstrated that for a given specific correlated color temperature (CCT), the existence of nano-sized porous TiO2 diffuser can greatly reduce the required phosphor amount, compared to the non-porous nanosized TiO2. Specifically, in a wide range of CCTs, a 20% or so reduction is observed in the required phosphor amount. This great reduction is demonstrated by a significant increase in the interaction between input photon with phosphor within wavelength conversion file due to the existence of nano-pores in the nano-size porous TiO2 diffuser. In the last part of this work, we proposes a novel light-scattering film with TiO2 nanocylinder diffuser particle loaded. It is designed to improve the phosphor and quantum dot (QD) usage efficiency in cost-effective light wavelength conversion film for various optical performance in the lighting industry. The TiO2 nano cylinder diffusing agents enhances the light scattering and enables a decrease of light wavelength conversion materials necessary to obtain specific CCT. Based on the experimental result of TiO2 diffusing film diffuse properties, the phosphor usage efficiency is significantly increased, as well as the light output power enhancement. A 10% - 20% improvement was found at a driving current of 350mA in TiO2 diffusing agent loaded light wavelength conversion film. It is experimentally confirmed that the dispersion of TiO2 nanocylinder diffusing particles in light wavelength conversion film can exhibit the same level of luminous output due to the reflection reduction, scattering enhancement and Rayleigh scattering effects, even when the amount of phosphor materials used is reduced by 20%. Accordingly, with the low cost benefits, easy fabrication and superior optical characteristics, the TiO2 nano cylinder particle can be an effective performance enhancer for further phosphor and QD optical device applications.

Nowadays, the relentless need for increased functionality and speed of ubiquitous electronic and optoelectronic devices with reduced cost, size, and weight call for novel on-chip and off-chip interconnect technologies. Thus, in addition to the continuing overall push for an ever-shrinking pitch size of off-chip interconnections, there are compelling reasons to seek an alternative chip bonding approach enabling simultaneous mechanical, thermal, and electrical interconnections with a much reduced vertical dimension than what can be achieved by the current mainstream bump and bumpless methods.This dissertation explored a new die-attach method used for die-substrate electrical interconnection without requiring a prior time-consuming and expensive surface nanoscopic planarization and without requiring any intermediate conductive material. A chip bonding method with a concept of “nano-locking” (NL) is proposed: The new method takes advantage of the intrinsic nanoscopic surface roughness on the interconnecting surfaces: the two surfaces are locked together for electrical interconnection and bonding with a conventional die bonder, and the connection is stabilized by a dielectric adhesive filled into nanoscale valleys on the interconnecting surfaces. This “nano-locking” (NL) method for chip interconnection and bonding is demonstrated by its successful application for the attachment of high-power GaN based semiconductor dies to its device substrate. In Chapter3, the electrical, thermal, and optical performances of devices enabled by the present NL bonding are evaluated. The resulting bond-line thickness of devices enable by NL bonding approach achieved is shown to be as low as 30 nm, several hundred times thinner than those achieved using mainstream bonding methods, resulting in a lower overall device thermal resistance, and a reduced electrical resistance, and thus an improved overall device performance. In Chapter4, the wet high temperature operating life test and thermal cycling test are performed to evaluate the reliability of the packaged devices enabled by the NL bonding method and compared with the conventional Ag-epoxy and AuSn bonding approach. The experimental results help demonstrate the fact that the NL bonding approach helps reduce the risk of interfacial delamination during bonding operation and the chances of commonly observed failure caused by interfacial delamination and the mechanical breakdown can be significantly reduced without adding the conductive metallic fillers. Chapter5 and Chapter6 focused on the study on the influence of bond-line thickness (BLT) and surface morphology on the device performance and reliability. The performances and reliability of the devices enabled by the NL bonding method follows a power-law relationship with the different BLT and different density of surface height distribution and leads to different value of electrical and thermal resistance. The present work opens a new direction for the scalable, reliable and simple nanoscale off-chip electrical interconnection and bonding for nano- and micro-electrical devices. In addition, the present method applies to the bonding of any surfaces with intrinsic or engineered surface nanoscopic structures as well.

The packaging materials are critical for optoelectronic device packaging in terms of optical and thermal performance. Continuous innovation and improvement of packaging materials have been introduced to improve the overall efficiency of LEDs, but there are still some critical issues need to be addressed for their application in general lighting and LCD backlight displays. In this work, dual-functional silicone-filler composites are investigated and introduced to LEDs and LCD backlight units to enhance their optical and thermal management.

In the first part of this work, we optimized the reflectance of polymer-filler reflectors by controlling filler particle size, filler volume fraction and thickness of reflectors. A simple analytical model was developed to investigate the critical parameters of inorganic fillers required to obtain the highest reflectance, which is expected to accelerate the design and optimization of polymer-filler composite reflectors. Our results demonstrate for the first time that for inorganic fillers, the effect of filler size on reflectance is non-monotonic, and a critical filler size ranging from one submicron to several microns provides the maximum reflectance. The existence of a critical thickness at which the optical reflectance of a polymer-filler composite reaches its maximum value is demonstrated.

In the second part of this work, the apparent radiation cooling effect of silicone-based composite coatings was investigated for its dependence on coating thickness and filler size. It is established, contrary to prior reports, that the effective passive radiation cooling does not exhibit a significant filler size dependence. We found the apparent cooling effect is filler type dependent and the optimal thickness is around 70 µm regardless of filler type.

In the third part of this work, dual-functional polymer-filler composites with high optical diffusive reflectance and passive cooling ability is investigated for optoelectronic device applications. It was demonstrated the addition of inorganic fillers to a volume fraction higher than 0.2 can effectively improve the apparent cooling effect and light reflectance of silicone composites. The new materials we developed can be used as diffuse reflector to provide better overall optical aesthetics for displays. Meanwhile, it can be used as passive cooling coatings in advanced general LED lighting, LCD display backlighting, solar cells and other energy related applications.

Recently, there is an evident trend of ever-thinner and intricate opto-electronic package and devices, which brings about severer thermal issues as well as unprecedented challenges for the thermal design. Not only thickness of opto-electronic package itself will raise the peak temperature and pose a potential risk to electronic devices, but also the limited-space and interacted opto-electro-thermo-mechanical properties restrict the use of traditional active thermal management means and precise estimation of cooling performance. This dissertation aims to numerically and experimentally analyze thermal behaviors of various LED package configurations while thinning it as well as apply novel radiation coating and packaging materials to cooling electronic devices with limited-space. What’s more, an opto-thermal coupled numerical method in the application of LED was discussed. Last but not the least, much faster Machine Learning (ML) algorithms were adopted to predict patterns for cooling performance of our thermal radiation coating in Li-ion battery system and acceleration stage before the onset of thermal runaway, which is the key to cut-off the battery before explosion.

It’s found that: (1) LED packages have different thermal behaviors for various configurations while thinning it. There can be a 5-10 ℃ of temperature change for single-chip LED. (2) For white LEDs and light bars in direct view LED backlight units (DLED-BLUs), our thermal conductive Die Attach Adhesive (DAA) and thicker encapsulant are able to increase the power level by up to 1.5 times. (3) Our thermal radiation can effectively decrease the peak temperature by 14.5 oC for linear LED modules as well as boost the uniformity of temperature distribution. (4) The thermal performance of LED package is different with and without considering optical effect. So optical effect should not be neglected while conducting thermal simulation for opto-electronic devices. (5) Machine learning algorithms can shorten prediction time of thermal performance of passive radiation material from 1 day to less than 0.5 min, compared with finite element method. A practical system design to effectively prevent explosion of Li-ion battery system is provided, too.

Solar cells and light-emitting diodes (LEDs) are the two most beneficial optoelectronic devices to humanity with opposite functions: one converts photons into electrical power and the other one converts electrons into luminance. Remarkable advances in both applications have been made in both novel chip-level design and packaging technologies, and the continuous innovation and improvement of packaging materials and methods have played key roles in the past two decades. In this work, new packaging materials and technologies are introduced to both silicon solar cells and LEDs to enhance their performance.

The first part of this work was to develop a new silver paste with different glass frits for front-side metallization in silicon solar cells. It is shown that the replacement of micro-sized glass frits by nano-sized ones can dramatically reduce the specific contact resistivity between the resultant silver electrodes and the n-type silicon layer due to the excellent etching ability of nanopartilces on removing the anti-reflection coating (ARC). Surface modification on nano-sized glass frits by electroless plating can further improve the electrical performance by offering extra conducting channel within the insulating layers.

In the second part of this work, the influence of different die attach adhesives (DAAs) on optical and thermal performance of LED emitters was studied. The results show that with an optically clear DAA applied, the highest optical output can be achieved due to its high transparency. The optically reflective DAA also exhibit excellent optical performance, especially at low fillet coverage, which block the photons escaping from the side walls. For high power LED applications, the optically reflective DAA can achieve better thermal management than the conventional one when the bondline thickness is controlled at 7.6 micron.

The last part of this work focuses on the interaction between the LED emitters and the backside reflector, which is used to reflect the downward photons. Our results show that with both optically clear and reflective DAAs, the light output of LED emitters can be very close to that of LED emitters with backside reflectors.

Suspended sediment loads mobilized during high flow periods in rivers and streams are largely uncharacterized. In smaller and intermittent streams, a large storm may transport a majority of the annual sediment budget. Therefore monitoring techniques that can measure high suspended sediment concentrations at semi-continuous time intervals are needed. A Fiber optic In-stream Transmissometer (FIT) is presented for continuous measurement of high concentration suspended sediment in storm runoff. FIT performance and precision were demonstrated to be reasonably good for suspended sediment concentrations up to 10g/L. The FIT was compared to two commercially available turbidity devices and provided better precision and accuracy at both high and low concentrations. Both turbidity devices were unable to collect measurements at concentrations greater than 4 g/L. The FIT and turbidity measurements were sensitive to sediment particle size. Particle size dependence of transmittance and turbidity measurement poses the greatest problem for calibration to suspended sediment concentration. While the FIT was demonstrated to provide acceptable measurements of high suspended sediment concentrations, approaches to real-time suspended sediment detection need to address the particle size dependence in concentration measurements.