Advanced MEMS-based technologies and displays

MEMS (microelectromechanical systems) are used in many fields including display applications, which are extensively studied both in academia and industry. For practical devices, numbers of advanced technologies have been developed based on MEMS concept. For display technologies, projection displays, reflective displays, transmissive displays and other display modes have been achieved by different MEMS modes. In this review, the current MEMS-based display technologies are introduced and discussed including digital micromirror device (DMD), laser scanning display (LSD), interferometric modulator display (IMOD), digital micro-shutter (DMS), time multiplexed optical shutter (TMOS), grating light valve (GLV) and others. The typical structure and fundamental of each display mode are interpreted.     

A silicon‐chip‐based light valve with reflective twisted‐nematic mode for high‐definition projectors

Crystalline‐silicon‐chip‐based reflective light valves are suitable for realizing high definition and bright liquid‐crystal projectors. We have developed an XGA (1025 × 769 pixels) silicon‐chip‐based light valve with a diagonal display area of 2.54 cm (1 in.). The reflective twisted‐nematic mode was examined by using the Jones matrix method as a display mode, and the normally white reflective twisted‐nematic mode was selected. This mode is suitable for a narrow cell gap, and a fast response time can be expected. In addition, the driving voltage of this mode is low and has good chromaticity with small retardation. The cell gap of the light valve is 2 μm. The cell gap support is made using spacer posts formed on the silicon chip with a photodefinable resin. The response time is 12 msec, including both rise and fall times. The contrast ratio is more than 1000 at 5 Vrms.     

Transmissive electrowetting‐based displays for portable multimedia devices

Abstract— Electrowetting‐based displays have been successfully demonstrated in reflective mode, showing video capability and high optical performance. However, because this technology is based on a high‐efficiency optical switch operating between a light‐absorbing state and a light‐transmitting state, the technology lends itself naturally to a transmissive mode enabling a complete range of applications. This paper describes the first active‐matrix full‐color transmissive electrowetting displays including its main technical and system aspects. Two architectures have been demonstrated: one uses color filters, the other field‐sequential‐color illumination. The paper also introduces alternative concepts for more efficient color transmissive electrowetting displays with multiple absorbing layers.     

Effects of ambient illuminance on users' visual performance using various electronic displays

Abstract— This study investigated the effect of ambient illuminance (50, 500, 1500, 3000, 6000, and 9000 lx) on participants' visual performance using four electronic displays (conventional LCD under transmissive mode, conventional LCD under reflective mode, Ch‐LC display, and E‐ink display). Analysis results indicate that participants' visual performance shows significant difference under various ambient illuminance and electronic displays. The interaction between ambient illuminance and electronic display also has significant effect on participants' visual performance. When participants use the conventional LCD under transmissive mode, ambient luminance has no significant effect on participants' visual performance. However, participants' visual performance is significantly different under various ambient illuminances using the conventional LCD under reflective mode, Ch‐LC display, and E‐ink display. The conventional LCD under transmissive mode is the only choice at a lower illuminance of 50 lx. Higher illuminance (500 lx) for E‐ink displays may result in as good a performance as the conventional LCD under transmissive mode; nevertheless, much higher illuminance (1500 lx) for the conventional LCD under reflectance mode and Ch‐LC display may achieve better performance.     

Laser display with single‐mirror MEMS scanner

Abstract— While arrayed DMD and LCD microdisplays are well‐established approaches for visualization tasks, image‐forming laser scanners are an emerging technology used to build miniaturized projection displays. A directly modulated RGB‐laser module consisting of diode lasers for red and blue and a frequency‐doubled semiconductor laser for green with color combining optics form the light source for the laser scanner have been developed. Subsequent beam‐shaping optics suppresses unwanted stray light and enables optimum illumination of the scanning mirror. The MEMS device features a single scanning mirror oscillating in two directions in resonant mode. This requires appropriate data delivery realized by a custom‐made driving logic, which converts the pixel stream originally arranged in rows and columns to the Lissajous‐like spot trajectory on the screen. Additionally, the increased image brightness at the vertical and horizontal borders of the field of view (FOV) is also compensated by the modulation of laser power. Theoretical investigations of the resulting maximum achievable system transmission are presented. Different systems, such as an extremely miniaturized monochrome projection head with an integrated diode laser and a full‐color projector have been realized. Important problems to be tackled are fast analog modulation of the laser power with high resolution and improved suppression of stray light and speckle.     

Generalized mixed-mode reflective LCDs with large cell gaps and high contrast ratios

Abstract— A generalized mixed twisted-nematic/birefringent-effect mode reflective LCD is presented. This new mode encompasses all previously published reflective nematic LCD modes and is clearly shown on the parameter space diagrams. We also discuss how to obtain operating conditions of this generalized mixed-mode display with large cell gaps, low color dispersion, and high contrast at low voltages. This operating mode is particularly suitable for reflective crystalline-silicon-backplane active-matrix LCDs.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

Measurement of light incident on mobile displays in various environments

Abstract— By using a single‐lens digital camera with an attached 180° fisheye lens, the incident light at the surface of a mobile display in 112 different environments, including outdoor and indoor environments and inside an automobile, were measured. The data were analyzed for some typical environments in which mobile displays are used. The results of this research can be used in the design of reflective and transflective LCDs, making maximum use of ambient light.     

Comparison of reflective PNLCDs and reflective single‐polarizer Heilmeier guest‐host displays

In this paper, the applicability of a zero‐polarizer reflective display (PNLC) and a single‐polarizer reflective display (Heilmeier guest host) for direct‐view applications is analyzed. A measurement set‐up is designed to analyze the applicability of all types of reflective displays. Simulation of the different types of illumination caused by the environmental light is essential for this set‐up. The measurements indicate that the contrast ratio and reflectance greatly depend on the type of illumination. It is demonstrated that the worst‐case illumination for one display technology may be the best‐case illumination for another one and vice versa.     

Effects of electronic‐book display and inclination on users' comprehension under various ambient illuminance conditions

Abstract— This study used several electronic‐book (e‐book) displays (a conventional LCD under transmissive mode, a conventional LCD under reflective mode, a Ch‐LC display, and an e‐ink display) to investigate the effect of e‐book inclination (105° and 135°) and ambient illuminance (200, 800, 1500, and 2200 lux) on the comprehension of subjects. Results indicate that the ambient illuminance does not significantly affect the comprehension of subjects. However, their comprehension differed significantly when using different e‐book displays. In addition, the interaction between illuminance and e‐book display had a significant effect on their comprehension. When the ambient illuminance was set at 800, 1500, and 2200 lux, the subjects' comprehension for reading different e‐book displays did not show a significant difference. When the ambient illuminance was set at 200 lux, however, their comprehension for reading a Ch‐LC display, an e‐ink display, and a conventional LCD under transmissive mode were better than their comprehension of reading a conventional LCD under reflective mode. Regarding the inclination for using e‐books, the subjects' comprehension was better under 105° than that under 135°.     

A dual‐cell‐gap transflective liquid‐crystal display with identical response time in transmissive and reflective regions

Abstract— A dual‐cell‐gap transflective liquid‐crystal display (TR‐LCD) with identical response time in both the transmissive and reflective regions is demonstrated. In the transmissive region, strong anchoring energy is used to decrease the response time, while in the reflective region, weak anchoring energy is used to increase the response time. And overdrive voltage technology is adopted to make the response time identical in both the transmissive and reflective regions. The device structure and operating principle of the TR‐LCD was analyzed, the anchoring energy in the transmissive and reflective regions was designed, and the response time and electro‐optic characteristics of the TR‐LCD was calculated. The simulated dual‐cell‐gap TR‐LCD demonstrated good performances.     

Portable multi‐gray scale video playing scheme for high‐performance electrowetting displays

Electrowetting display technology is realized by tuning the surface energy of a hydrophobic surface by applying a voltage based on electrowetting mechanism. Electrowetting displays have favorable optical properties combined with reflective paper‐like performance. It has been successfully demonstrated in reflective mode with high switching speed. In this paper, we propose a portable driving scheme that can display 4‐bit gray scale dynamic video using an active matrix electrowetting display. The proposed driving scheme includes an electronic system and a dynamic driving waveform design. High‐performance multi‐gray video playing and quick response were obtained for a Quarter Video Graphics Array electrowetting display cell fabricated by our team.     

用三维MEMS力学量传感器对涌浪微观形态测量的研究

涌浪的形态对舰船驾驶航行、渔业生产、海洋作业和堤坝设施等具有很大的影响.对海浪的形态研究在军事、水上交通、海洋工业、渔业和民生方面都具有特殊的意义.MEMS力学量传感器是一种环境适应能力极强的微机电器件,用三维MEMS力学量传感器可以测量动态质点的速度、加速度、摆角和倾角等参数.通过三维MEMS力学量传感器的三维参数测量和分解可以得到涌浪质点的实时运动速度和运动轨迹数据,从而为涌浪的微观形态研究提供了依据.MEMS力学量传感器具有体积小、重量轻和输出灵敏度高等特点,特别适合于对海浪实时形态的研究.     

A video‐speed reflective display based on electrowetting: principle and properties

Abstract— Electrowetting is presented as a novel principle for a reflective display. By contracting a colored oil film electrically, an optical switch is obtained with many attractive properties that make it very suitable for use as a reflective display, for instance, as electronic paper. Firstly, it has the high reflectivity (>40%) and contrast ratio (15) required for a paper‐like optical appearance. In addition, the principle shows a video‐rate response time (<10 msec) and has a clear route toward a high‐brightness color display. Finally, the electro‐optical response is independent of cell‐gap thickness, which will be very beneficial when moving toward a flexible display.     

Super multi-view and holographic displays using MEMS devices

Holographic displays and super multi-view (SMV) displays have been developed to solve the accommodation–vergence conflict that is responsible for visual fatigue caused by the 3D images that are generated by conventional three-dimensional (3D) displays upon which the eye cannot focus. However, holographic and SMV displays provide 3D images upon which the eye can readily focus so that the accommodation–vergence conflict does not occur. Because these two display techniques require the generation of a very large amount of image data, the high data bandwidth of microelectromechanical (MEMS) devices is effectively utilized. The present article describes the holographic display system that employs a MEMS spatial light modulator (SLM), which increases the screen size and viewing zone angle. Two SMV displays are also described, where one employs MEMS SLMs and the other an array of MEMS projectors. The resolution and the number of viewpoints of the SMV displays have increased. Moreover, the technique using a MEMS SLM to eliminate speckles from holographic reconstructed images is also described.     

Thin‐film micromirror array (TMA) for large information‐display systems

Abstract— The thin‐film micromirror array (TMA) is a new reflective‐type spatial light modulator fabricated with microelectromechanical systems (MEMS) technology. Micromachined thin‐film piezoelectric actuators are used to control the tilt angle of each micromirror, which defines the gray scale of the matching screen pixel. A working projector prototype of 5400 true ANSI lumens was presented at Asian Display '98 with three VGA‐format TMAchips and a 1‐kW xenon lamp. The prototype showed a light‐transmitting efficiency of 22%. An XGA‐format TMA was developed for commercial purposes. The size of each micromirror of the XGA‐format TMA is reduced to half the size of the micromirror of a VGA‐format TMA. Efforts have been made to maintain the light‐transmitting efficiency of the XGA TMA projector over 21%, as well as to improve the uniformity.     

Flexible and bistable FLC and cholesteric displays on plastic substrates for mobile applications and smart cards

Abstract— New smart-card applications like purse cards, etc. require an integrated display which allows the card-holder to read information which is stored on the IC of the card. On the other hand, the integration of a display into a plastic card requires some very specific features like flexibility and pressure stability, low-voltage CMOS-addressing, memory capability, and, of course, a reflective mode since no backlight is available. In this paper, two bistable reflective LCD solutions using ferroelectric and cholesteric LCs are discussed and very promising prototype results are presented. Pressure and bending tests as well as contrast measurements are compared in order to show the potential of meeting the requirements for use in smart cards.     

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

Abstract— A single‐cel l‐gap transflective liquid‐crystal display with two types of liquid‐crystal alignment based on an in‐plane‐switching structure is proposed. The transmissive region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the reflective region has a homeotropic liquid‐crystal alignment. For every driving voltage for a positive‐dielectric‐anisotropy nematic liquid crystal, the effective cell‐retardation value in the transmissive region becomes larger than that in the reflective region because of optical compensation film which is generated by low‐pretilt‐angle liquid crystal in the transmissive region. Under the optimization of the liquid‐crystal cell and alignment used in the transmissive and reflective areas, the transmissive and reflective parts have similar gamma curves. An identical response time in both the transmissive and reflective regions and a desirable viewing angle for personal portable displays can also be obtained.     

Optimization of polymer-stabilized bistable black-white cholesteric reflective display

Abstract— Cholesteric liquid crystals at zero field exhibit two optically contrasting stable states: planar texture and focal-conic texture. When a cholesteric liquid crystal is in the planar texture, the helical axis is perpendicular to the cell surface; the material Bragg-reflects colored light. When the liquid crystal is in the focal-conic texture, the helical axis is more or less parallel to the cell surface; the material is forward-scattering and has a black appearance if the back plate of the cell is painted black. We develop a cholesteric liquid-crystal/polymer composite in which a small amount of polymer is dispersed in the liquid crystal. The dispersed polymer changes the planar texture to a poly-domain structure, which has a white appearance but has little effect on the optical properties of the focal-conic texture. The result is a bistable black-white reflective display which is a good candidate for electronic-paper applications.     

Full-color reflective display device using holographically fabricated polymer-dispersed liquid crystal (HPDLC)

Abstract— A method of controlling the color of a holographic polymer-dispersed liquid-crystal (HPDLC) reflective display device has been achieved. By merely controlling the optical setup during fabrication, without changing the materials or laser light source, three primary-color devices were fabricated. Since the color of the device can be controlled continuously, a large color-reproducible area on the chromaticity diagram can be obtained. The resulting device was adequately transparent at other wavelengths to enable multiple devices to be stacked to obtain a mixture of colors. There was no significant change in color when applying an electric field. The three devices had similar reflectances and electro-optical characteristics. Therefore, this device has good potential for full-color display applications.