Category Archives: LED Manufacturing

Oxygen is indispensable to animal and plant life, but its presence in the wrong places can feed a fire and cause iron to rust.

In the fabrication of solid state lighting devices, scientists are learning, oxygen also plays a two-edged role. While oxygen can impede the effectiveness of gallium nitride (GaN), an enabling material for LEDs, small amounts of oxygen in some cases are needed to enhance the devices’ optical properties. GaN doped with europium (Eu), which could provide the red color in LEDs and other displays, is one such case.

Last week, an international group of researchers shed light on this seeming contradiction and reported that the quantity and location of oxygen in GaN can be fine-tuned to improve the optical performance of Eu-doped GaN devices. The group includes researchers from Lehigh, Osaka University in Japan, the Instituto Superior Técnico in Portugal, the University of Mount Union in Ohio, and Oak Ridge National Laboratory in Tennessee.

Writing in Scientific Reports, a Nature publication, the group said that small quantities of oxygen promote the uniform incorporation of Eu into the crystal lattices of GaN. The group also demonstrated a method of incorporating Eu uniformly that utilizes only the oxygen levels that are inevitably present in the GaN anyway. Eu, a rare earth (RE) element, is added to GaN as a “dopant” to provide highly efficient red color emission, which is still a challenge for GaN-based optoelectronic devices.

The devices’ ability to emit light is dependent on the relative homogeneity of Eu incorporation, said Volkmar Dierolf, professor and chair of Lehigh’s physics department.

“Some details, such as why the oxygen is needed for Eu incorporation, are still unclear,” said Dierolf, “but we have determined that the amount required is roughly 2 percent of the amount of Eu ions. For every 100 Eu ions, you need two oxygen atoms to facilitate the incorporation of Eu to GaN.

“If the oxygen is not there, the Eu clusters up and does not incorporate. When the oxygen is present at about 2 percent, oxygen passivation takes place, allowing the Eu to incorporate into the GaN without clustering.”

The article is titled “Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications.” The lead author, Brandon Mitchell, received his Ph.D. from Lehigh in 2014 and is now an assistant professor of physics and astronomy at the University of Mount Union and a visiting professor at Osaka University.

 

A comprehensive study

Gallium nitride, a hard and durable semiconductor, is valued in solid state lighting because it emits light in the visible spectrum and because its wide band gap makes GaN electronic devices more powerful and energy-efficient than devices made of silicon and other semiconductors.

The adverse effect of oxygen on GaN’s properties has been much discussed in the scientific literature, the researchers wrote in Scientific Reports, but oxygen’s influence on, and interaction with, RE dopants in GaN is less well understood.

“The presence of oxygen in GaN,” the group wrote in their article, which was published online Jan. 4, “…is normally discussed with a purely negative connotation, where possible positive aspects of its influence are not considered.

“For the continued optimization of this material, the positive and negative roles of critical defects, such as oxygen, need to be explored.”

The group used several imaging techniques, including Rutherford Backscattering, Atomic Probe Tomography and Combined Excitation Emission Spectroscopy, to obtain an atomic-level view of the diffusion and local concentrations of oxygen and Eu in the GaN crystal lattice.

Its investigation, the group wrote, represented the “first comprehensive study of the critical role that oxygen has on Eu in GaN.” The group chose to experiment with Eu-doped GaN (GaN:Eu), said Dierolf, because europium emits bright light in the red portion of the electromagnetic spectrum, a promising quality given the difficulty scientists have encountered in realizing red LED light.

The group said its results “strongly indicate that for single layers of GaN:Eu, significant concentrations of oxygen are required to ensure uniform Eu incorporation and favorable optical properties.

“However, for the high performance and reliability of GaN-based devices, the minimization of oxygen is essential. It is clear that these two requirements are not mutually compatible.”

Preliminary LED devices containing a single 300-nanometer active GaN:Eu layer have been demonstrated in recent years, the group reported, but have not yet achieved commercial viability, in part because of the incompatibility of oxygen with GaN.

To overcome that hurdle, said Dierolf, the researchers decided that instead of growing one thick, homogeneous layer of GaN:Eu they would grow several thinner layers of alternating doped and undoped regions. This approach, they found, utilizes the relatively small amount of oxygen that is naturally present in GaN grown with organo-metallic vapor phase epitaxy (OMVPE), the common method of preparing GaN.

“Instead of growing a thick layer of Eu-doped GaN,” said Dierolf, “we grew a layer that alternated doped and undoped regions. Through the diffusion of the europium ion, oxygen from the undoped regions was utilized to incorporate the Eu into the GaN. The europium then diffused into the undoped regions.”

To determine the optimal amount of oxygen needed to circumvent the oxygen-GaN incompatibility, the researchers also conducted experiments on GaN grown with an Eu “precursor” containing oxygen and on GaN intentionally doped with argon-diluted oxygen.

They found that the OMVPE- grown GaN contained significantly less oxygen than the other samples.

“The concentration of this oxygen [in the OMVPE- grown GaN] is over two orders of magnitude lower than those [concentrations] found in the samples grown with the oxygen-containing Eu…precursor,” the group wrote, “rendering the material compatible with current GaN-based devices.

“We have demonstrated that the oxygen concentration in GaN:Eu materials can be reduced to a device-compatible level. Periodic optimization of the concentration ratio between the normally occurring oxygen found in GaN and the Eu ions resulted in uniform Eu incorporation, without sacrificing emission intensity.

“These results appear to coincide with observations in other RE-doped GaN materials. Adoption of the methods discussed in this article could have a profound influence on the future optimization of these systems as well as GaN:Eu.”

The group plans next to grow GaN quantum well structures and determine if they enable Eu to incorporate even more favorably and effectively into GaN. Toward that end, Dierolf and Nelson Tansu, professor of electrical and computer engineering and director of Lehigh’s Center for Photonics and Nanoelectronics, have been awarded a Collaborative Research Opportunity (CORE) grant from Lehigh.

Light and electricity dance a complicated tango in devices like LEDs, solar cells and sensors. A new anti-reflection coating developed by engineers at the University of Illinois at Urbana Champaign, in collaboration with researchers at the University of Massachusetts at Lowell, lets light through without hampering the flow of electricity, a step that could increase efficiency in such devices.

An array of nanopillars etched by thin layer of grate-patterned metal creates a nonreflective surface that could improve electronic device performance. Credit: Image courtesy of Daniel Wasserman

The coating is a specially engraved, nanostructured thin film that allows more light through than a flat surface, yet also provides electrical access to the underlying material – a crucial combination for optoelectronics, devices that convert electricity to light or vice versa. The researchers, led by U. of I. electrical and computer engineering professor Daniel Wasserman, published their findings in the journal Advanced Materials.

“The ability to improve both electrical and optical access to a material is an important step towards higher-efficiency optoelectronic devices,” said Wasserman, a member of the Micro and Nano Technology Laboratory at Illinois.

At the interface between two materials, such as a semiconductor and air, some light is always reflected, Wasserman said. This limits the efficiency of optoelectronic devices. If light is emitted in a semiconductor, some fraction of this light will never escape the semiconductor material. Alternatively, for a sensor or solar cell, some fraction of light will never make it to the detector to be collected and turned into an electrical signal. Researchers use a model called Fresnel’s equations to describe the reflection and transmission at the interface between two materials.

“It has been long known that structuring the surface of a material can increase light transmission,” said study co-author Viktor Podolskiy, a professor at the University of Massachusetts at Lowell. “Among such structures, one of the more interesting is similar to structures found in nature, and is referred to as a ‘moth-eye’ pattern: tiny nanopillars which can ‘beat’ the Fresnel equations at certain wavelengths and angles.”

Although such patterned surfaces aid in light transmission, they hinder electrical transmission, creating a barrier to the underlying electrical material.

“In most cases, the addition of a conducting material to the surface results in absorption and reflection, both of which will degrade device performance,” Wasserman said.

The Illinois and Massachusetts team used a patented method of metal-assisted chemical etching, MacEtch, developed at Illinois by Xiuling Li, U. of I. professor of electrical and computer engineering and co-author of the new paper. The researchers used MacEtch to engrave a patterned metal film into a semiconductor to create an array of tiny nanopillars rising above the metal film. The combination of these “moth-eye” nanopillars and the metal film created a partially coated material that outperformed the untreated semiconductor.

“The nanopillars enhance the optical transmission while the metal film offers electrical contact. Remarkably, we can improve our optical transmission and electrical access simultaneously,” said Runyu Liu, a graduate researcher at Illinois and a co-lead author of the work along with Illinois graduate researcher Xiang Zhao and Massachusetts graduate researcher Christopher Roberts.

The researchers demonstrated that their technique, which results in metal covering roughly half of the surface, can transmit about 90 percent of light to or from the surface. For comparison, the bare, unpatterned surface with no metal can only transmit 70 percent of the light and has no electrical contact.

The researchers also demonstrated their ability to tune the material’s optical properties by adjusting the metal film’s dimensions and how deeply it etches into the semiconductor.

“We are looking to integrate these nanostructured films with optoelectronic devices to demonstrate that we can simultaneously improve both the optical and electronic properties of devices operating at wavelengths from the visible all the way to the far infrared,” Wasserman said.

Hybrid optoelectronic devices based on blends of hard and soft semiconductors can combine the properties of the two material types, opening the possibility for devices with novel functionality and properties, such as cheap and scalable solution-based processing methods. However, the efficiency of such devices is limited by the relatively slow electronic communication between the material components that relies on charge transfer, which is susceptible to losses occurring at the hybrid interface.

A phenomenon called Förster resonant energy transfer (FRET) was recently theoretically predicted and experimentally observed in hybrid structures combining an inorganic quantum well with a soft semiconductor film. Förster resonant energy transfer is a radiationless transmission of energy that occurs on the nanometer scale from a donor molecule to an acceptor molecule. The process promotes energy rather than charge transfer, providing an alternative contactless pathway that avoids some of the losses caused by charge recombination at the interface.

Now researchers from the University of Cyprus and Cyprus University of Technology, along with colleagues from the University of Crete, Greece have conducted a comprehensive investigation on how various structural and electronic parameters affect FRET in structures of nitride quantum wells with light-emitting polymers. Based on their studies, the researchers discuss the process to optimize the energy transfer process and identify the limitations and implications of the Förster mechanism in practical devices. The work demonstrates the importance of understanding FRET in hybrid structures that could pave the way for developing novel devices such as high-efficiency LEDs and solar cells. The researchers present their work in a paper published this week in the Journal of Chemical Physics, from AIP Publishing.

In the top left is a schematic of Förster Resonant Energy Transfer from a near-surface nitride quantum well to a polymer overlayer. In the top right is fluorescence from solutions containing light emitting polymer materials. In the bottom left high resolution transmission electron microscope image from an InGaN/GaN quantum well. In the bottom right absorption and fluorescence spectra from various polymers used in our study. Credit: Grigorios Itskos/University of Cyprus, Cyprus

In the top left is a schematic of Förster Resonant Energy Transfer from a near-surface nitride quantum well to a polymer overlayer. In the top right is fluorescence from solutions containing light emitting polymer materials. In the bottom left high resolution transmission electron microscope image from an InGaN/GaN quantum well. In the bottom right absorption and fluorescence spectra from various polymers used in our study. Credit: Grigorios Itskos/University of Cyprus, Cyprus

“Pioneering theoretical and experimental work has demonstrated that energy can be efficiently transferred across hybrid semiconductors via the Förster mechanism. However, our understanding is not complete and many material and structural parameters affecting FRET in such hybrids remain unexplored. Our work employs for a first time a comprehensive approach that combines fabrication, theoretical modeling and optical spectroscopy to fully understand FRET in a nitride quantum well-polymer hybrid structure,” said Grigorios Itskos, the primary researcher and an assistant professor from the Department of Physics at the University of Cyprus.

“We used a systematic approach to optimize the FRET efficiency by tuning various parameters of the nitride quantum well component. The process allowed us to study unexplored aspects of the mechanism and identify competing mechanisms that limit the energy transfer efficiency in hybrid planar structures. The outcome of our investigation can guide future efforts towards a rational design of hybrid geometries that can optimize FRET and limit competing losses to render FRET-based devices feasible,” he said.

Itskos noted that the researchers chose to study structures based on nitrides because the material is well-researched and is used in niche applications such as blue light emitting LEDs. “However, the functionality [of nitride structures] can be further increased by combining them with other soft semiconductors such as light-emitting polymers. The spectral tunability and high light-absorption and emitting efficiency of the polymers can be exploited to demonstrate efficient down-conversion of the blue nitride emission, providing a scheme for efficient hybrid LEDs,” Itskos said.

In the study, the researchers initially sought to produce and study near-surface nitride quantum wells to allow a close proximity with the light-emitting polymer deposited on their top surface.

“The nanoscale proximity promotes efficient interactions between the excitations of the two materials, leading to fast Förster transfer that can compete with the intrinsic recombination of the excitations,” Itskos explained. Förster resonant energy transfer is a strongly distance-dependent process which occurs over a scale of typically 1 to 10 nanometers. The contactless pathway of energy transmission could avoid energy losses associated with charge recombination and transport in hybrid structures.

Using a sequence of growth runs, theoretical modeling and luminescence spectroscopy (a spectrally-resolved technique measuring the light emission of an object), the researchers identified the way to optimize the surface quantum well emission.

“We studied the influence of parameters such as growth temperature, material composition, and thickness of the quantum well and barrier on the optoelectronic properties of the nitride structures. Increase of the quantum confinement by reducing the width or increasing the barrier of the quantum well increases the well emission. However, for high quantum well confinement, excitations leak to the structure surface, quenching the luminescence. So there is an optimum set of quantum well parameters that produce emissive structures,” Itskos said. He also pointed out that the studies indicate a strong link between the luminescence efficiency of the nitride quantum well with the FRET efficiency of the hybrid structure, as predicted by the basic theory of Förster. The correlation could potentially provide an initial and simple FRET optimization method by optimizing the luminescent efficiency of the energy donor in the absence of the energy acceptor material.

“Our studies also indicated that electronic doping of the interlayer between the nitride quantum well and the polymer film reduces the efficiency of FRET. This constitutes a potential limitation for the implementation of such hybrid structures in real-world electronic devices, as electronic doping is required to produce efficient practical devices. Further studies are needed to establish the exact influence of doping on FRET,” Itskos noted.

He said the team’s next step is to perform a systematic study of hybrid structures based on doped nitride quantum wells to investigate the mechanisms via which electronic doping affects the characteristics of the Förster resonant energy transfer.

Cambridge Nanotherm, a producer of thermal management technology, has won the “LED Lighting Product of the Year” award at the 2015 Elektra Awards for its “Nanotherm DM” product. The industry’s largest technology and business awards, the Elektras is in its 13th year of celebrating the best the electronics industry has achieved.

Cambridge Nanotherm beat stiff competition from NASDAQ listed ON Semiconductor, Khatod Optoelectronics and Zeta Specialist Lighting to win the LED Lighting Product of the Year category. Commenting on the award the judges noted that Nanotherm DM is uniquely compatible with standard manufacturing processes and picked up on the fact that the company manufactures Nanotherm DM at its facility near Cambridge and exports to customers in the US and Asia.

Nanotherm DM is a robust and cost effective alternative to aluminium nitride, an electronics grade ceramic that is used in thermally challenging electronics. The production of Nanotherm DM involves a patented ‘ECO’ process (Electro Chemical Oxidation) that converts the surface of aluminium into a nanoceramic dielectric layer. The nanoceramic aluminium is completed with a copper circuit sputtered onto the nanoceramic to customer specifications. This results in a material with thermal properties that rival aluminium nitride but with the mechanical properties of aluminium that offers the best thermal performance to price ratio available.

Initially targeted at Chip-on-Board modules and LED packaging markets, Nanotherm DM enables LED manufacturers to make significant cost savings without impacting the performance of their products.

Collecting the award on Tuesday night Mike Edwards, Sales Director, said: “Winning an Elektra award is testament to the hard work and dedication our team has put into the development and commercialisation of Nanotherm DM. It cements Nanotherm’s place at the vanguard of UK high-technology manufacturing and I’m delighted to be taking the award back to our manufacturing facility in Haverhill. 2016 is shaping up to be a very exciting year for Nanotherm as we continue to ramp up our production capabilities to meet unprecedented demand for our thermal management solutions.”

The win follows on from Nanotherm being shortlisted for the R&D 100 awards and winning the 2015 Insider Media Made in the East technology award.

The winners of the 2015 were announced on the Tuesday 24th November at the awards ceremony taking place at The Lancaster, London.

Trillium US Inc, headquartered in Clackamas, OR, has announced the acquisition of the Oxford Instruments – Austin division, formerly known as Austin Scientific, effective November 23rd, 2015.  Focused on the helium compression based vacuum and temperature management and control sector, Oxford Instruments-Austin provides cryo pump, cold head and compressor service, a range of new cryogenic pumps, cold heads and helium compressors, as well as a full line of related spare parts and accessories.

“The Oxford Instruments-Austin acquisition serves a number of purposes for Trillium,” announced Graham Stone, President and CEO of Trillium. “We acquire a significant range of complementary products while strengthening our existing service capabilities, allowing us to further leverage our customer relationships, while also taking us into new markets,” he added.

Trillium currently operates a 12,000 SF facility in North Austin servicing primarily rough vacuum pumps and blowers, while the existing 23,000 SF Oxford Instruments-Austin facility is located in South Austin. “We have been very encouraged with the depth of engineering and the high quality level at Oxford Instruments-Austin . Bringing them into the Trillium family will allow us to achieve significant synergies and a larger critical mass by consolidating our TX operations to a single South Austin location,” said Glen Murray, Trillium’s General Manager and VP-Operations.

Trillium has significantly grown its offerings over the past five years from providing repair service and refurbished equipment to also include new products and spare parts. This transition began as part of the merger with Hamburg, NJ’s United Vacuum in 2011, and continues now with this most recent acquisition. “Adding Oxford Instruments-Austin’s portfolio to our existing product line further enhances Trillium’s value to the customer,” added Rob Breisch, Trillium’s VP-Sales and Marketing. “Our new cryogenic customers can now rely on us to provide a broader range of vacuum products and services, and our existing customer base can take advantage of Oxford Instruments-Austin’s world class support for cryo pumps and helium compressors,” he explained.

The business integration is already underway and Trillium plans to transact from South Austin starting November 23rd.  “Our immediate focus and number one priority is to ensure this transition is implemented quickly and seamlessly for our customers,” stated Graham Stone. He added, “Later phases in the process will include business system migration and consolidation of the facilities.”

Trillium expects to complete the full transition by June 2016.

The use of sapphire in the manufacturing of Light Emitting Diodes (LEDs) is covered in the second part of a two part series.

BY WINTHROP A. BAYLIES and CHRISTOPHER JL MOORE, BayTech-Resor LLC, Maynard, MA

In Part 1 of this article, we discussed the optical and mechanical properties of sapphire and its use in the mobile device industry. In part 2, we will discuss the use of sapphire in the LED process including some of the newer technologies that produce these devices.

Solid state lighting (or “LED bulbs” as they are commonly known) have become a mainstream product in our culture. Their longer life time and lower power usage (along with the banning of incandescent bulbs) have ensured that more and more consumers are moving to this type of lighting. Like a fluorescent light (where the white light is produced by a phosphor coating excited by the excited gas molecules) solid state lights use a phosphor excited by the short wavelength light emitted by an LED. What you may not know is that about 8 out of every 10 LED bulbs sold uses sapphire as the starting material for their manufacturing process.

As we summarized in part 1, sapphire has some good points: hard, strong, optically transparent and chemically inert (there is a reason high end watches use sapphire crystals) and some bad points: hard, strong, and chemically inert (which is why sapphire crystals are more expensive than glass). What we did not discuss is that single crystal sapphire has turned out to be an ideal material on which to grow the layers of material needed to make an LED.

As FIGURE 1 shows an LED is made by growing epitaxial layers of Gallium Nitride (GaN), AlGan or InGaN on a substrate. Ideally one would use GaN as the substrate material (similar to growing epitaxial Si on Si for integrated circuits) as this would result in the highest quality material and thus the most efficient LED’s. Unfortunately GaN substrates are very difficult to make in any reasonable size and the costs have ruled out using this approach except in certain niche markets. The three main substrate alternatives have been silicon (Si), silicon carbide (SiC) and sapphire.

Sapphire 1

As a substrate material Si would be expected to be the best choice due to its high quality, low cost and ready availability. To date, the quality of GaN type layers grown on Si has not been sufficient for large scale manufacturing processes. Work continues on improving this process and although it may one day dominate the process it currently remains a small part of the business.

SiC substrates are higher cost than Si but have been successfully used for LED manufacturing processes. Much of the LEDs produced by Cree (who also manufacture SiC substrates) use this type of substrate. However, the higher cost and limited availability of 6 inch SiC material means that the majority of LED producers use sapphire.

Thus sapphire substrates account for the majority of LED devices produced [1]. Although not as cheap as Si they are cheaper than SiC, available from a number of manufacturers and are able to survive the high temperature processes needed to produce a short wavelength LED. FIGURE 2 schematically shows the production process for a typical non-patterned sapphire wafer.

Sapphire 2

The sapphire production process starts when a seed crystal and a mixture of aluminum oxide and crackle (un-crystallized sapphire material) is heated in a crucible. Included in this mix is a cookie-sized seed crystal which forms the pattern to be replicated as the crystal grows. Each furnace manufacturer has its own special recipe which heats the material using a specific temperature/ time profile based on the size of melt and the type of crystal to be grown. Once the correct growth temperature is reached the melt is cooled (this process can take two weeks depending on the amount of sapphire being produced) using another set of carefully controlled time/temperature profiles. When done correctly, the cookie-sized seed grows and produces a single-crystal sapphire boule. (FIGURE 3). In reality, two weeks is a long time and any number of can go arise during this process including gas bubbles, mechanical faults such as cracks and contamination. Each of these problems affects the sapphire and its crystal properties. Each crystal fault can become a nucleation site for defects in the epitaxy grown on wafers produced from the boule. There is a clear correlation between the time taken to grow a boule and the potential quality of the boule produced. Many of the problems encountered in the upscaling of the sapphire production process have come from trying to grow large boules at high speeds.

Sapphire 3

At this point in the process you have a boule which in fact has the wrong crystal orientation for growing GaN epitaxy. Unlike the Si crystal growth process where the cylindrical boules can be ground to size and then cut into wafers, sapphire boules are often cored at right angles to the boule axis. Some companies produce sapphire using a silicon like process [2] but the majority of sapphire produced has to be cored. Thus the next step in the process is to “core-drill” a boule to produce one or more smaller round cylinders (ingots) depending on the original boule size and the size of wafers to be produced.

The ability to grow large sized boules on a regular basis is not in question; most important is how much of that boule is bubble-, crack- and impurity-free. In some cases the boules are inspected with various metrology techniques to determine which sections of the boule can be used and which cannot. The section of the boules not used is recycled into the original growth process (unless contaminated). Obviously if one is producing 6 inch wafers larger volumes of the boule need to be defect free than if one is producing 2 inch or 4 inch. Currently most of the LEDs produced are produced on 4 inch wafers with a few newer 6 inch lines and a number of older 2 inch lines. 8 inch sapphire wafers do exists but are not in mass production at this time.

The process after this is very similar to that used in the silicon industry to produce the wafers which will be used as substrates. A diamond saw (remember, Sapphire is a very hard material) is used to cur the ingot into a number of thin disc shapes by cutting perpendicular to the ingot’s long sides. Each of these discs is then ground to its final size, surface-ground and mechanically and chemically polished to produce sapphire substrates. These substrates, after cleaning, can be used as starting material for the epitaxial process used to produce the LED structure. FIGURE 4 shows some pictures of typical 2, 4 and 5 inch sapphire substrates. As discussed earlier the more defect free the surface is the better the quality of epitaxial film that can be grown. The video listed in reference [3] produced by GTAT shows many of the steps discussed above.

Sapphire 4

Recently one further step has been taken to produce what are called patterned sapphire substrates (PSS). The multiple quantum well layer shown in Fig. 1 is the layer that generates light in an LED. As you can imagine this light is emitted in all directions. However, once packaged most LED’s emit light from only one surface of the device. In the case of Fig. 1, a typical package collects the light emitted from the top of the device. This of course means that all of the light emitted in any other direction is wasted. In particular, since sapphire is transparent, little of the light emitted toward the substrate can be used.

One obvious solution to this would be to coat the substrate with something that reflects the light (i.e. metal). Unfortunately this interferes with the epitaxial layer growth process, producing poor devices. One partial solution to the reflection problem is to pattern the sapphire surface such that it reflects light. This pattern can be a series of microscopic pyramidal structures or more rounded bump like structures on the surface. FIGURE 5 shows top and side view SEM pictures of some of the patterns produced by manufacturers. These patterns scatter the light and reflect some of it back towards the surface of the device increasing the light output from the LED. In addition to increasing the apparent light output a number of manufacturers have claimed that epitaxial layers grown on patterned substrates is of better quality than that grown on bare sapphire substrates.

Sapphire 5

Patterned substrates can be produced by the manufacturer of the sapphire substrates. However, factories now exist which begin with a non-patterned substrate and produce specific patterns (normally via chemical etch) for specific LED manufacturers.

Once valued only as a gemstone, sapphire is now an engineered material with a wide variety of industrial uses. These two article have concentrated on its use in mobile devices for everything from camera lens covers to touch sensors and touch screens to the starting material on which most of the solid state lights produced are made. Cost of the material continues to be a limiting factor in its widespread adoption for certain industries. However, as the technology for producing sapphire matures material costs are decreasing and in some ways sapphire substrates have become a commodity rather than a rarity.

Additional reading and viewing material

1. http://rubicontechnology.com/sites/default/files/Opportu- nities%20for%20Sapphire%20White%20Paper-Rubicon%20 Technology.pdf
2. http://www.arc-energy.com/products-services/CHES/Foundations/1
3. https://www.youtube.com/embed/mHrDXyQGSK0

Due to the growth of the semiconductor business, the wider adoption of Cu pillar solutions and the introduction of Flip Chip technology for LED and CMOS Image Sensors (CIS) applications, the Flip Chip market is expending. Under this context, more and more industrial companies including OSATs, IDMs IC foundries and bumping house undertake in this market.

The “More than Moore” market research and strategy consulting company Yole Développement (Yole) explored this industry and proposes today a detailed technology and market report, entitled “Flip Chip: Technologies & Market Trends”. Yole’s team is daily discussing with the leaders of the Advanced Packaging industry. Based on these interactions, the consulting company highlights the evolution of the technical needs and market trends. These major results make Yole’s analysts to think that full capacity should be reached in 2017.

What are the required investments to support this growth? Are there competitive technologies such as TSMC’s new solution, high-performance integrated fan-out wafer level packaging (InFO-WLP), that could answer the market needs and compete Flip Chip technology?

Under “Flip Chip: Technologies & Market Trends” report, Yole’s advanced packaging team provides an overview of Flip Chip technology and market trends. The company reviews the competitive landscape including player dynamics and key market trends; they also detail the Flip Chip market capacity and wafer forecast. Yole’s report also includes a detailed technology roadmap.

“Based on the discussions we had with the major advanced packaging companies, at Yole, we think that demand for Flip Chip is expected to reach the current maximum capacity in 2017,” said Santosh Kumar, Senior, Technology & Market Analyst, Advanced Packaging & Semiconductor Manufacturing at Yole. And he adds: “Therefore, new investment will be needed starting in 2018.”

Since Cu pillar processing can be performed by standard foundries and IDMs, the supply chain may see some slight modification. Yole’s analysts expect higher investment in Cu pillar 12” line wafer bumping lines from wafer foundries such as TSMC and SMIC. This change will affect OSATs’ wafer bumping revenue since foundries will gain market share.

OSATs will maintain their strong position in wafer bumping and assembly thanks to of their huge experience and low cost solutions. Their business model enables them to better control the supply chain, as they provide for the complete set of flip-chip services: package design and qualification, wafer bumping, substrate in-sourcing, assembly and final test.

However, big IDM companies like Intel and Samsung maintain their dominance in terms of wafer bumping capacity.

flip chip bump

“At Yole, we expect that even in 2020 Intel will remain the highest-capacity player in Cu pillar wafer bumping,” commented Thibault Buisson, Technology & Analyst, Advanced Packaging at Yole. Foundries and OSATs are also establishing joint ventures for wafer bumping to provide turnkey solutions to customers from chip fabrication to assembly at competitive cost.

And what about the Chinese companies? Do they have a role to play in the Flip Chip market? Chinese players are significantly increasing their presence in wafer bumping and Flip Chip assembly by mergers and acquisitions. JCET acquired STATS ChipPAC and FCI was acquired by Tianshui Huatian Technology Company.

In that context, Yole’s report, Flip Chip: Technologies & Market Trends report gives insights on the future strategies that players may adopt. A detailed description of this report is available on www.i-micronews.com, advanced packaging reports section.

Systematic – and predictive – cost reduction in semiconductor equipment manufacturing

BY TOM MARIANO, Foliage, Burlington, MA

After a period of double-digit growth, the semiconductor equipment industry has now stabilized to the point where recent market forecasts are predicting anemic single-digit growth rates. This is driven by total market demand from chipmakers. For example, despite strong growth of 12.9 percent in 2014, Gartner, Inc. projects worldwide semiconductor capital spending to only grow 0.8 percent in 2015, to $65.7 billion. [1] Additionally, this industry has always been subject to volatile demand cycles that are notoriously difficult to predict.

Translation: It’s extremely challenging for today’s semiconductor equipment manufacturers to improve their financial performance. There are fewer and fewer opportunities to grow topline revenue through innovation and new product development. And, after several years of cutting costs on existing products and not realizing enough cost reduction to improve margins, it’s difficult to know how to do it differently.

Yet a viable alternative to improve financial performance does exist: A disciplined, rigorous, and systematic approach to reducing costs that delivers more predictive results.

A systematic approach to cost reduction

Where cutting costs was once perceived as the end result of “desperate times, desperate measures,” many innovators are now using this approach much more proactively. By
meeting the idea of cost reduction head on – as an opportunity, not a last resort – many semiconductor equipment makers are uncovering wasteful, inefficient, and costly processes, often in areas they once overlooked. At this point, you may be thinking, “All of this sounds great, but what is a systematic approach to cost reduction, and how is it different from what I’m doing?”

Remember that many manufacturers (in all industries) tend to have a hard time driving costs down. They may set cost reduction goals and then attempt to achieve them using various ad hoc approaches. But they really need to understand exactly what their true costs are, where they exist, and which areas will improve their margins.

A systematic approach to cost reduction gives them this insight. With improved visibility into the entire organization, various processes, and how they execute, semiconductor equipment manufacturers can’t identify the right places to cut costs and hit their cost savings goals. This is a very detailed and planned approach in which organizations closely examine areas such as cost of goods sold, R&D, and service to make more informed decisions that will position their business for long-term success. This is the value of a systematic approach to cost reduction.

This approach also introduces the element of speed, helping equipment makers realize cost savings much faster than ad hoc cost-cutting initiatives and puts them on a path to achieve more predictive results. Beyond the positive (and more obvious) impact successful cost reduction has on a semiconductor equipment manufacturer’s bottom line, it also provides a number of significant benefits such as improving productivity, freeing up key personnel, and providing needed capital to fuel new growth.

The path to predictive results

Even if the concept of a more strategic approach to cutting costs sounds reasonable, many semiconductor equipment manufacturers struggle with how to begin and where to focus. All to often they resort to making reactive decisions regarding existing products without the necessary data, leading them to ask questions such as, “Should we have an obsolescence plan for this product?” “How much could we save?” and “Will this lead to bigger problems down the road?”

Without understanding where your best opportunities for cost cutting are, it’s a lot larder to predict when, and if, cost reduction goals will be met. A systematic approach to cost reduction includes establishing clear cost targets, communicating them to leadership, and measuring and reporting results along the way.

The first step is to engage with an outside firm that has a singular focus on cost reduction, and one that is clearly separated from day-to-day operations and current organizational dynamics. Such an engagement will yield an actionable list of improvements with specific cost targets, realistic timelines for achieving these goals, and future plans for reinvesting the cost savings.

More specifically, a systematic cost reduction approach will focus on three key areas: material costs, R&D costs, and service costs:

1. Material costs: The bill of materials is one of the most common ways to see all the components needed to produce the end product. But this goes well beyond the pure cost of materials. Research has shown that improving the way these components are managed can affect 80-90% of the product’s total costs.[2]

For semiconductor equipment manufacturers, the cost reduction process should start with the selection of the products or sub-assemblies that have the highest potential for savings. Focus on those products that are still generating significant revenue, but may not be receiving much attention in terms or engineering upgrades and enhancements. Thoroughly examine the bill of materials for these products by addressing materials, design, complexity reduction, the potential to create common assemblies, and more.

Value engineering efforts can simultaneously improve product functionality and performance while reducing bill of material costs. This effort should factor in ways to meet RoHS requirements and when to make end-of-life decisions for various electrical components to improve design efficiency and the effectiveness of the product.

A realistic cost reduction goal can then be created and a resulting value-engineering project can commence, often using low-cost offshore resources to best achieve those savings.

2. R&D costs: Making better decisions related to R&D processes and product development can shave considerable costs. Some areas to focus on include:

• When to officially end of life non-performing products
• When to consolidate products, or possibly even entire R&D departments
• When and how to move sustaining engineering efforts offshore, or to other lower-cost alternatives

The critical next step is to look at all products and all product variations to determine if an official end-of-life program should be employed. These decisions are notoriously hard to make and often require difficult conversations with key customers, but they are necessary nonetheless.

Many semiconductor equipment manufacturers have grown through acquisitions, creating redundant engineering groups that can be eliminated or downsized. Performing an organizational analysis of all R&D activities may uncover opportunities to consolidate and combine functions or create centers of excellence that focus on specific technical areas eliminating redundancies of technical specialty.

3. Service costs: Examine engineering and design processes to find ways to improve performance, reliability, and costs. For example, adding data collection technology or product diagnostics to enhance remote support efforts and predictive maintenance.

Improvement of product reliability is usually a large multiplier when it comes to service and spare parts costs. Collect and analyze field data to find the most significant issues driving service costs and then look to cut where possible.

For example, equipment in the field often does not have the capability to report enough information to effectively identify a problem. Adding increased data logging and communication can be used to clarify machine status and point services in the right direction. Connectivity can also help with remote diagnostics, all of which helps reduce costs, uptime, and customer satisfaction.

Cost Reduction as a Competitive Advantage

Short-term market forecasts will continue to make it challenging for semiconductor equipment manufacturers to deliver improved financial results. Yet the concept of a systematic approach to cost reduction is a proven way for them to proactively cut costs – in the right places – and also make better decisions related to existing products and other business systems and processes.

By taking a disciplined, rigorous, and objective look at any and all parts of their organization, semiconductor equipment makers can capitalize on new opportunities to free valuable resources, improve processes and future technology, and reinvest savings for future growth. For many equipment manufacturers the greatest obstacle to successfully exploiting these opportunities is insufficient experience and expertise with a disciplined and unconventional way of approaching cost reduction projects. A systematic approach to cost reduction will be the key to success for companies looking to improve their competitive advantage.

References

1. Gartner, Inc., “Gartner Says Worldwide Semiconductor Capital Spending to Increase 0.8 Percent in 2015: Conser- vative Investment Strategies Paving the Way to Slower Growth in 2015,” January 13, 2015. http://www.gartner. com/newsroom/id/2961017.

2. Forbes, “Product Lifecycle Management: A New Path to Shareholder Value?” August 5, 2011, http://www. forbes.com/sites/ciocentral/2011/08/05/product-lifecycle- management-a-new-path-to-shareholder-value/.

Sapphire is hard, strong, optically transparent and chemically inert.

BY WINTHROP E. BAYLIES and CHRISTOPHER JL MOORE, BayTech-Resor LLC, Maynard, MA

Have you ever wondered what blue gemstone earrings, an LED lightbulb and an Apple Watch have in common? The answer (at least for this article) is that all depend on sapphire as part of their manufacturing process. In part 1 of the following two part article, we will discuss how sapphire is becoming an important part of the mobile device food chain. Part 2 will concentrate on how sapphire is used in LED production.

Sapphire (chemical composition Al2O3) has a high melting point of 2040°C (3704°F) and is chemically resistant even at high temperatures. It is an anisotropic material meaning that its mechanical/thermal properties depend on the direction of the crystal plane that is cut and polished. An insulator with a 9.2 eV energy gap it is optically transparent. With a hardness of 9 on the Mhos scale, it is almost as hard and strong as diamond (10 Mhos).

To summarize, sapphire has some good points: hard, strong, optically transparent and chemically inert (there is a reason high end watches use sapphire crystals) and some bad points: hard, strong, and chemically inert (which is why sapphire crystals are more expensive than glass). That is, the very properties that make it ideal for applications needing mechanical strength and hardness mean that it is a difficult material to grow, machine and polish.

There are several places where sapphire can be (or is now) used in the manufacture of mobile devices. The most publicity in this area was generated in 2014 with significant speculation in both the trade magazines and newspapers (such as the Wall Street Journal) that the iPhone 6 would be released with a sapphire touch screen or at the very least a sapphire cover glass over the existing touchscreen. Part of this speculation was fueled by the large number (1700 to 2500 depending on source) of sapphire producing furnaces being installed at an Apple facility in Mesa Arizona. However, the sapphire iPhone 6 was not released due in part to the difficulties in growing and processing enough sapphire screens at a reasonable cost to supply the significant number of phones produced. There are now sapphire touch screen phones available from other suppliers and recently, the Apple Watch was released with a sapphire screen. In addition, many fingerprint sensors and camera cover glasses are now produced using sapphire as the cover material.

Requirements for sapphire material is clear (forgive the pun). For screens and cameras, it must be of good optical quality i.e. transmit light well and have low surface roughness. For fingerprint sensors, it needs consistent surface quality and electrical properties.

Production process

FIGURE 1 shows a schematic of the production process for sapphire used in a mobile device screen. The following paragraphs provide more detail on this process [1] as well as a few of problems encountered along the way.

Sapphire Fig 1

The sapphire production process starts when a seed crystal and a mixture of aluminum oxide and crackle (un-crystallized sapphire material) is heated using a specific temperature/time profile, then cooled (this process can take two weeks depending on the amount of sapphire being produced) using a carefully controlled set of time/temperature profiles. When done correctly, the cookie sized seed grows and produces a single-crystal sapphire boule. That at least is the theory. In reality, two weeks is a long time and any number of problems can go wrong during this process including gas bubbles, mechanical faults such as cracks and contamination. Each of these problems can affect the sapphire and its optical/electrical properties. There is a clear correlation between the time taken to grow a boule and the potential quality of the boule produced. Many of the problems encountered in the upscaling of the sapphire production process sprang from trying to grow large boules at high speeds.

It is at the next step in the process where boule size does matter. Typically, the boule will be drilled or cut to produce material near the size needed for the particular application. It makes a significant difference if the material is for a watch crystal (say 1.5 inch diameter ~ 1.7 square inches). Here you can “core-drill” a boule to produce a number of smaller cylinders. For a phone screen/cover plate (at 4 by 6 inch i.e. 24 square inches) a larger portion of the boule is needed for a box shape. The ability to grow large sized boules on a regular basis is not in question; most important is how much of that boule is bubble-, crack- and impurity-free. In some cases the boules are inspected with various metrology techniques to determine which sections of the boule can be used and which cannot. The section of the boules not used is recycled into the original growth process (unless contaminated).

Given the hardness of the sapphire, diamond wire saws or diamond core drills are used for cutting or coring the boules. The yield from any boule is a function of the original boule size, the size of the cores or slabs being produced and the volume of the boule free from imperfections. As was discussed earlier, and is typical of many processes, the larger the size of the piece the lower the yield.

The next step is to take the cylindrical cores (or rectangular slabs) and cut them into appropriate sized pieces. The thickness of the desired part and the amount the producer is willing to invest in high technology solutions determines what is done next. On one end of the technology scale, the parts are cut using a wire saw or an abrasive cutoff saw. On the other end of the scale, you can ion implant the surface to produce a damaged layer at a depth below the surface determined by the original ion energy. If the slab is heated after sufficient implantation is done, a thin sheet will separate from the surface. Both processes result in parts of the approximate size needed for the application; a discussion of the pros and cons of each approach is beyond the scope of this article.

The process after this point depends on the parts’ final application and their manufacturer. Given the difficulty of polishing a material this hard many of the bigger companies have developed proprietary process for grinding or mechanically polishing the sapphire parts to the desired shape and surface roughness/finish. From a mechanical strength standpoint, it is important that there be no significant scratching of the surface or chipping of the edges which could severely limit the mechanical strength of the final piece. From an optical standpoint, it is important to produce a uniform finish so as not to effect the overall appearance of the part. At this stage, the parts are then ground to their final size and any additional shaping of the part including holes/ profiles is done. FIGURE 2 shows a variety of sapphire parts at this stage of the process.

Sapphire Fig 2

In most sapphire part production these parts are next coated with a variety of optical and/or electrical and/ or chemical films again depending on their application. Because of its high index of refraction (1.76) a sapphire screen or watch crystal is highly reflective. For this application, the parts are typically coated with a series of films to produce an anti-reflection coating enhancing final screen readability. For parts that will be touched on a regular basis such as touchscreens or fingerprint sensors coatings, it is important that they be “self-cleaning.” In these cases, hydrophobic and oleophobic coatings are used to make sure your fingerprints are less likely to stay behind after the material has been touched. FIGURE 3 shows a series of parts after the coating and silk screening process. They are now ready for assembly into the mobile device.

Sapphire Fig 3

The use of sapphire in mobile devices is driven by two main concerns. One is that the final screen/sensor be mechanically stronger and harder than most glasses. There are a number of videos [2] available showing cement blocks being dragged over cell phones to show the sapphire screens’ scratchproof capabilities. The second (and not as well known) factor is the significant data showing that touch sensors made using sapphire have better performance characteristics due to its superior electrical properties and electrical uniformity. This allows the development of sensors which have improved performance in the field.

The downside of using sapphire remains its cost. Estimates [3] have reported sapphire costs 2 to 10 times the price of an equivalent glass part. Although these costs are coming down, in price sensitive applications glass continues to dominate at this time and it is expected that only higher end phones will use sapphire screens.

In the second part of this article, we will discuss the importance of sapphire in the LED industry and the difference in process needed for this material.

Additional reading/viewing material

1. http://www.businessinsider.com/how-sapphire- glass-screens-are-made-2014-9
2. Video Aero Gear’s Flight Glass SX Sapphire Crystal vs a Concrete
3. http://seekingalpha.com/article/2230553-ignore- the-sapphire-threat-corning-is-on-a-roll

Baltimore, MD — November 11, 2015 — Pixelligent, a leader in high-index advanced materials, today launched a new family of PixClear® materials for display and optical components and films. The PixClear product line is now available in a new solvent system — a low boiling ethyl acetate (ETA) — that delivers the same high performance while easing integration with customer manufacturing processes. Now leading manufacturing companies will have the choice of a standard, high boiling propylene glycol methyl ether acetate (PGMEA) or the low boiling ETA for their testing. These materials are available in both 20 percent and 50 percent loadings for PixClear PG and PixClear PB.

“The launch of our new PixClear ETA materials is a response to customer demand. These low boiling ETA dispersions will result in brighter, clearer devices produced at a lower cost, which directly supports reducing time to innovation for our customers in the display and adhesives space,” said Craig Bandes, President and CEO of Pixelligent. “At Pixelligent, we continue to expand our matrix of high quality, high-index nanomaterials in order to support the growth of our customers.” Matt Healy, Vice President of Product Management adds, “In August, we launched a full OLED materials family, which includes four products for testing internal light extraction structures for OLED lighting. All totaled, we have introduced 12 new products for customer testing in the past three months.”

PixClear zirconia dispersions are now available for order in two solvents, and at two different loadings, to complement the processes used for the production of displays and optical components.