Momentum for Materials
by Ion Bita
It is my pleasure to welcome you to a new issue of Information Display magazine and to wish you a wholehearted “Happy New Year” as we begin 2014.
One of the topics we are highlighting in this issue is materials and their role in advancing information displays. Reflecting back on the evolution of the technology and on the new product landscapes of the past year, two trends stand out relative to this topic: advancing display image quality and enhancing the capabilities for user interactivity. While it is outside the practical scope of this note to survey in detail the many relevant developments in each of these areas, let me pick just a few that will help provide context for the Frontline Technology articles on materials in this issue.
Among other drivers, the pursuit of TV displays with increased resolution (to 8K ultra-HD) and refresh rates (to 240 Hz for OLED TV) has been fueling intense work on amorphous metal-oxide-based TFTs. The display community is already looking beyond the recently established InGaZnO (i.e., IGZO) family of materials in order to develop alternatives with higher electron mobilities (e.g., InSnZnO and ZnON) and to maintain manufacturing scalability to Gen 8 (2.2 × 2.5 m) glass substrates.1 In the area of image quality, a material that received renewed accolades last year is semi-conductor quantum dots as used in backlights to enable LCDs with color performance rivaling that of OLEDs.2 Among early stage developments, we should also note the introduction of a new class of “hyperfluorescent” organic molecules that allows light emission from initially triplet excited states and thus achieves high light-emission efficiencies comparable to those of organometallic phosphorescent complexes, the backbone of most of the current OLED display products.3
Given the current importance and increasing impact of OLED displays, we are fortunate to include in this issue an article that addresses the present and future of OLED materials. With the perspective of an established materials provider to this industry, authors Kai Gilge, Ansgar Werner, and Sven Murano from Novaled AG (Germany)
examine the properties of the organic chemical compounds required for compatibility within the current OLED-display manufacturing infrastructure and highlight material requirements expected to be critical in next-generation platforms.
As mentioned in the introduction, another important trend that is shaping the evolution of information-display products is enhancing capabilities for user interactivity. Touch screens are now the main input interface for smartphones and tablets and are on a path for widespread adoption in most portable computing devices. With projected-capacitive touch sensing as the dominant technology, transparent conductor materials have become a subject of renewed interest. As reviewed in an earlier issue of Information Display by Paul Semenza,4 indium tin oxide (ITO) is a standard choice due to the extensive experience that manufacturers have accumulated over decades in the use of display panels. New requirements for improved electrical, mechanical, and optical properties, adding to the drive for reducing the cost of touch sensors, have led to the development of ITO alternatives based on conductive nano- and micro-structured materials (metal meshes, silver nanowires, metal nanoparticles, carbon nanotubes) as well as conductive films (polymers, graphene sheets). Furthermore, the need for an efficient fabrication of sensing electrode structures in the display stack has led to additional material and processing innovations that are now enabling a transition from discrete touch panels to thinner, more integrated configurations, including sensors patterned directly on chemically strengthened protective glass covers and display panel integrated touch sensors (such as on-/in-cells for LCDs).
With so much activity directed at improving touch-input interfaces, we are delighted to include an article that focuses on developing complementary materials and devices enabling touch-output interfaces. Also known as haptics, tactile feedback in mobile devices is an evolving field currently dominated by zero-dimensional architectures (whole-body device motions induced by electromagnetic motors). The authors, Christophe Ramstein and Ausra Liaukeviciute of Novasentis, Inc. (U.S.), a company known until recently as SPS, Inc., describe the use of electroactive mechanical actuator films for the next generation of haptics with spatially localized feedback. In particular, the properties and benefits of electromechanical polymers are examined, with a focus on ferroelectric fluorocarbon polymers capable of piezoelectric or electro-strictive responses to applied electric fields. These relatively thin film actuators were shown at Display Week 2013’s Innovation Zone (I-Zone) and have recently garnered the Novasentis team the 2014 CES Innovations Design and Engineering Award in Embedded Technologies.
We hope you will enjoy reading these articles along with the rest of this issue.
1For example, see the March/April 2013 issue of Information Display magazine and the 2013 SID Symposium Digest of Technical Papers.
2See Nanosys/3M’s QDEF and QDVision’s ColorIQ quantum-dot technologies, both recipients of the SID’s Gold Display Component of the Year Award (in 2012 and 2013, respectively) and both shipping in volume (e.g., QDEF in the new Kindle Fire HDX 7-in. tablet and ColorIQ in the new Sony Bravia line of LCD TVs).
3H. Uoyama, K. Goushi, K. Shizu, H. Nomura, and C. Adachi, “Highly efficient organic light-emitting diodes from delayed fluorescence,” Nature 492 (7428), 234–238 (Dec. 2012).
4For example, see the July/August 2013 issue of the Information Display magazine and references therein. •