In today’s information-network based society, electronic displays that provide high-quality image information can be regarded as hardware platform technology. Flexible displays, which dramatically expand freedom in designing, carrying, installing, are seen as fundamental, next-generation media technologies for creating a range of viewing styles and human interfaces. Award-winning Dr. Fujikake started flexible display research around 1997 (he first presented his work at an academic conference in 1998), at a time when there was active research into liquid crystal (LC) monitors for medium-sized personal computers. It was also a time when there was no concept of bendable, high-quality video image displays. He advanced the concept of flexible displays and their applications and described the impact they would have in realizing ultra-large screen, super high-definition television (Fig. 1) that evoke a real sense of presence, and large-screen mobile information terminals with excellent portability to facilitate a moving image delivery service. He first established the basic device technology that is vital to its realization. By demonstrating that a moving image display using bendable soft materials was feasible, he pioneered the research and development on flexible high image-quality displays.

In a series of studies aimed at realizing large-screen flexible LC displays (Fig. 2), he was involved in developing many advanced technologies. These included flexible plastic substrate technology with high-precision processing (Fig. 3), a spacer formation method able to hold two substrates, printing/coating formation methods for the component materials used in displays, flexible backlights, and low temperature fabrication of thin film transistors (TFTs) for matrix voltage driving. As a particularly unique innovation, by replacing the hard glass substrate with a soft plastic film substrate, and by suppressing display property distortion due to fluctuations of the substrate gap filled with liquid LC materials, he created a new structure where the entire surfaces of two counter substrates were bonded and fixed with an LC/polymer composite film (1,2). Furthermore, the self-organizing phase separation phenomenon of LC and polymer was investigated in detail, and a method (3-5) was devised that allowed molecularly-oriented polymer wall spacers capable of displaying high contrast to be formed without distorting the LC orientation. With these technologies, he was able to develop LC devices that were flexible enough to be rolled up. Later, he demonstrated that the LC device could be rolled up to have a diameter of just a few mm by combining the LC/polymer composite structure and ultra-thin plastic film substrates fabricated by a coating-debonding forming process (6).

In addition, he introduced a relief (flexographic) printing method, which allows the screen size to be increased in the manufacture LC/polymer composite film, leading to the development of a large A4-sized flexible color display panel. He has also developed optical phase compensation technology (7) for LC using plastic substrates, to achieve a wide viewing angle and high contrast ratio in flexible LC displays, and has shown that it is possible to obtain high image quality equal to that of glass-based LC displays. Recently, as a next-generation flexible display production technology, he has created and fabricated a stretchable LC device using LC gel (8), so that it can be freely attached to curved surfaces of many three-dimensional structures including the human body. He pointed out the usefulness and importance of the self-recovering properties of gel materials in deformable display devices.

As TFT technology for driving flexible displays, he created a TFT fabrication technology using flexible high-mobility organic semiconductors (9), and polycrystalline silicon that can be formed at low temperatures. He has also developed two types of flexible backlights (light guide plate and direct-lighting methods) using small light-emitting diode (LED) chips with a wide color gamut. By making full use of these elemental technologies, he developed a TFT-driven 5-inch full-color display, and demonstrated that a moving image display can be achieved through flexible TFT technology.

A flexible LC display has the advantages of easy fabrication of large screen and high definition display panels, and lifetime free, while an organic light-emitting diode (OLED) has a high contrast ratio and facilitates thinning and softening. The features of the two display methods are complementary in each other. Therefore, to increase the screen size of a flexible OLED, he promoted research and development into such areas as high brightness and high efficiency in OLED materials, the coating process (10) of organic TFTs, and low temperature formation of metal oxide TFTs. Using these technologies, his research group was able to develop and demonstrate flexible full-color OLED displays.

His cross-disciplinary research work in image electronics and organic electronics have received widespread acclaim, and both in Japan and overseas he has delivered numerous invited lectures and written many articles, as well as presenting and publishing many original academic papers. For these endeavors he has received the title of Fellow from the Institute of Electronics, Information and Communication Engineers, the Institute of Image Information and Television Engineers, and the Japan Society of Applied Physics. Accordingly, given his remarkable achievements, the awardee is eminently of receiving the Achievement Award.

References

1. H. Fujikake, T. Aida, J. Yonai, H. Kikuchi, M. Kawakita and K. Takizawa, “Rigid Formation of Aligned Polymer Fiber Network in Ferroelectric Liquid Crystal,” Jpn. J. Appl. Phys., vol.38, no.9A, pp.5212-5213 (1999).
2. H. Fujikake, T. Murashige, H. Sato, Y. Iino, M. Kawakita and H. Kikuchi, “Flexible Ferroelectric Liquid- Crystal Devices Containing Fine Polymer Fibers,” J. SID, vol.10, no.1, pp.95-99 (2002.3).
3. H. Sato, H. Fujikake, Y. Iino, M. Kawakita and H. Kikuchi, “Flexible Grayscale Ferroelectric Liquid Crystal Devices Containing Polymer Walls and Ntworks,” Jpn. J. Appl. Phys., vol.41, no.8, pp.5302-5306 (2002).
4. H. Fujikake, H. Sato and T. Murashige, “Polymer-Stabilized Ferroelectric Liquid Crystal for Flexible Displays,” Displays, vol.25, pp.3-8 (2004).
5. H. Fujikake and H. Sato, “Flexible Display Technologies Using Ferroelectric Liquid Crystal: Low Driving-Voltage Panel Fabrication,” Ferroelectrics, vol.364, pp.86-94 (2008).
6. Y. Obonai, Y. Shibata, T. Ishinabe, H. Fujikake, “Foldable Liquid Crystal Devices Using Ultra-Thin Polyimide Substrates and Bonding Polymer Spacers,” IEICE Trans. Electronics, vol.E100-C, no.11, pp.1039-1042 (2017).
7. T. Ishinabe, A. Sato and H. Fujikake, “Wide-Viewing-angle Flexible Liquid Crystal Displays with Optical Compensation of Polycarbonate Substrates,” Appl. Phys. Exp., vol.7, no.11, pp.111701-1 - 111701-4 (2014).
8. Y. Shibata, R. Saito, T. Ishinabe, H. Fujikake, “Mechanical Stability and Self-Recovery Property of Liquid Crystal Gel Films with Hydrogen-Bonding Interaction,” IEICE Trans. Electronics, vol. E102-C, no.11, pp.813-817 (2019).
9. Y. Fujisaki, H. Sato, H. Fujikake, Y. Inoue, S. Tokito, and T. Kurita, “Liquid Crystal Display Cells Fabricated on Plastic Substrate Driven by Low-Voltage Organic Thin-Film Transistor with Improved Gate Insulator and Passivation Layer,” Jpn. J. Appl. Phys, vol.44, no.6A, pp.3728-3732 (2005).
10. Y. Nakajima, Y. Fujisaki, T. Takei, H. Sato, M. Nakata, M. Suzuki, H. Fukagawa, G. Motomura, T. Shimizu, K. Sugitani, Y. Isogai, T. Katoh, S. Tokito, T. Yamamoto, and H. Fujikake, “Low-Temperature Fabrication of 5-in. QVGA Flexible AMOLED Display Driven by OTFTs Using Olefin Polymer as the Gate Insulator,” J. SID, vol.19, no.12, pp.861-866 (2011).