Light sources with digitally addressable elements have many potential uses in the lighting and display space. At the lighting end of the application range, recent developments have resulted in phosphor-converted segmented LEDs and mini-LEDs with single element dimensions of the order of 100 µm. When combined with suitable directional optics and controls this device architecture can generate dynamic light distributions for a wide variety of scenarios. Initially developed for Adaptive Driving Beam (ADB) technology for vehicle headlights, the basic concepts translate to many general lighting applications where they provide a completely new approach to reduced power consumption, improved illuminance uniformity and digitized design and commissioning. At the display end of the range, micro-LED technology with typical pixel sizes of the order of 1 µm to 10 µm promises to reduce power consumption of both direct-view and projection displays, enabling practical wearable AR/VR devices. In this paper, we will present our integral approach to micro- and mini-LED device technology and backplane integration across this application range and describe a prototype light engine designed to evaluate the benefits of this technology in lighting applications.
This paper focuses on micro LED R, G, B emitter technologies for low power wearable displays. Selection of materials, novel micro LED architectures, LED driving schemes, backplanes and their impact on LED performance trade-off will be presented to meet long battery life wearable display requirements. An objective comparison will be presented based on strengths and weaknesses of micro LED technologies for their fit and wide adoption in displays vs. status quo. Micro LED technologies are expected to gain significant adoption in a wide range of wearable display products in near future.
KEYWORDS: Light emitting diodes, Solid state lighting, LED lighting, Systems engineering, Manufacturing, Light sources and illumination, Reliability, System integration, Lamps
As solid-state lighting adoption moves from bulb socket replacement to lighting system engineering, luminaire manufacturers are beginning to actualize far greater cost savings through luminaire optimization rather than the simplistic process of component cost pareto management. Indeed, there are an increasing number of applications in which we see major shifts in the value chain in terms of increasing the L1 (LED) and L2 (LED array on PCB) value. The L1 value increase stems from a number of factors ranging from simply higher performing LEDs reducing the LED count, to L1 innovation such as high voltage LEDs, optimizing driver efficiency or to the use of high luminance LEDs enabling compact optics, allowing not only more design freedom but also cost reduction through space and weight savings. The L2 value increase is realized predominantly through increasing L2 performance with the use of algorithms that optimize L1 selection and placement and/or through L2 integration of drivers, control electronics, sensors, secondary lens and/or environmental protection, which is also initiating level collapse in the value chain. In this paper we will present the L1 and L2 innovations that are enabling this disruption as well as provide examples of fixture/luminaire level benefits.
We have investigated the use of atomic-hydrogen-based cleaning to remove Sn contamination from extreme ultraviolet (EUV) multilayer mirrors. Mo and Si surfaces were cleaned at a relatively slow rate due to catalyzed dissociation of tin hydride on these surfaces. Mo/Si mirrors with B4C and Si3N4 cap layers and DLC-terminated DLC/Si mirrors showed complete removal of 10 nm Sn in 20 sec with full restoration of EUV reflectance. In addition, a prolonged cleaning treatment of 300 sec of a DLC/Si mirror resulted in only a minor EUV peak reflection loss of 1.2% absolute and no significant changes in infrared reflectance.
In this paper, a new type of spectral filter mirrors for extreme ultraviolet radiation based on DLC/Si multilayer coatings
is presented (DLC - diamond-like carbon). The coating is nearly transparent for infrared radiation (IR) of λ = 10.6 nm
but highly reflective at λ = 13.5 nm (EUV). We deposited DLC/Si multilayers by ion beam sputter deposition with 40
and 60 periods exhibiting maximum EUV reflectances of about Rmax = 43 % and Rmax = 50 %, respectively. Combining
IR antireflective and EUV reflective coatings, first prototype mirrors have been fabricated with an EUV reflectance of
about 42.5 % and an IR reflectance of about 4.4 % at the same time.
Investigations on the thermal behavior of the multilayer stack and the cleaning properties for tin contaminated mirror
surfaces have been carried out. Excellent stabilities of EUV peak position and reflectance values have been found using
annealing temperatures of up to 700 °C. Furthermore, several cycles of Sn etching under H2 reactive conditions have
been applied to the mirrors without significant changes of the filter performance.
We have developed a grid-type spectral purity filter (SPF) for suppression of infrared radiation in laser-produced plasma (LPP) EUV sources for high-volume EUV lithography. The SPF is a silicon grid with sub-wavelength periodicity that is metalized to make it reflective for infrared radiation. EUV radiation is transmitted geometrically through the open area of the grid. The first prototype samples show an in-band EUV transmittance of 74% at normal incidence. Infrared spectrometry exhibits a clear cut-off behavior as expected, with a transmittance of <0.1% at a wavelength of 10.6 µm. In a first power-load test, a grid was exposed to a CO2 laser at 100 W/cm2 in vacuum for 8 hours. Another grid was kept at 800 °C in a vacuum oven for 24 hours. Both grids remained structurally intact and maintained an infrared transmittance of <0.1%.
Practical EUV sources not only generate the desired EUV radiation at a wavelength of 13.5 nm but also produce debris that severely limits the lifetime of the collecting optics in the lithographic system. In this paper, we address the possibility of reducing the exposure of the collecting optics to debris by using directional gas flows, focusing particularly on mitigation of ballistic microparticles. The purpose of the gas flow is to change the direction of the particles such that they can subsequently be captured by a foil trap.
Two types of gas flows are considered: (i) longitudinal gas flows, i.e. with a flow direction essentially parallel to the velocity of the microparticles, and (ii) transversal gas flows, having a flow direction essentially perpendicular to that of the microparticles. We have conducted contamination experiments using both types of flows in Xe- and Sn-based experimental EUV sources with Ar gas.
The experiments show that directional gas flows suppress microparticles in the same way a buffer gas does unless the flow velocity becomes of the same order as the thermal velocity of the gas (~ 102 m/s). A high-speed longitudinal gas flow is expected to be more efficient in thermalizing the microparticles than a stationary buffer gas; this could however not be confirmed due to experimental constraints. Our experiments with a high-speed transversal gas flow show that submicron debris particles can successfully be suppressed by one order of magnitude. A transversal gas flow combined with a suitable foil trap structure may thus present an effective method for mitigation of microparticles.
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