At SID's Display Week 2015 event in San Jose, CA, USA (31 May-5 June), Grenoble-based micro/nanotechnology R&D center CEA-Leti of France announced that it has demonstrated a path to fabricating high-density micro-LED arrays for the next generation of wearable and nomadic systems in a process that is scalable to the IC manufacturing process.
High-brightness, enhanced-vision systems such as head-up and head-mounted displays can improve safety and performance in fields such as aeronautics and automotive, where the displays allow pilots and drivers to receive key navigation data and information in their line of sight. For consumers, smart glasses or nomadic projection devices with augmented reality provide directions, safety updates, advertisements and other information across the viewing field. LED microdisplays are suited to such wearable systems because of their low footprint, low power consumption, high contrast ratio and ultra-high brightness, says Leti.
Leti researchers have developed gallium nitride (GaN) and indium gallium nitride (InGaN) LED technology for producing high-brightness, emissive microdisplays for these applications, which are expected to grow dramatically in the next 3-5 years. For example, the firm MarketsandMarkets forecasts that the market for head-up displays alone will grow from $1.37bn in 2012 to $8.36bn in 2020.
"Currently available microdisplays for both head-mounted and compact head-up applications suffer from fundamental technology limitations that prevent the design of very low-weight, compact and low-energy-use products," notes Ludovic Poupinet, head of Leti's Optics and Photonics Department. "Leti's technology breakthrough is the first demonstration of a high-brightness, high-density micro-LED array that overcomes these limitations and is scalable to a standard microelectronic large-scale process," he adds. "This technology provides a low-cost, leading-edge solution to companies that want to target the fast-growth markets for wearable vision systems."
Leti says that its technology innovation is based on micro-LED arrays that are hybridized on a silicon backplane. Key developments include epitaxial growth of LED layers on sapphire or other substrates, micro-structuring of LED arrays (10μm pitch or smaller), and 3D heterogeneous integration of such LED arrays on CMOS active matrices.
These innovations make it possible to produce a brightness of 1 million cd/m2 for monochrome devices and 100kcd/m2 for full-color devices with a device size below 1-inch and 2.5 million pixels. This is a 100- to 1000-times improvement compared with existing self-emissive microdisplays, with very good power efficiency, it is reckoned. The technology should also allow the fabrication of very compact products that significantly reduce system integration constraints.
The high-density micro-LED array process was developed in collaboration with III-V Lab (a joint venture between Paris-based Alcatel-Lucent Bell Labs France, Thales Research and Technology, and CEA-Leti).
