Electrostatically driven film light modulators for display applications

Abstract

Electrostatic film based light modulators are discussed. Electrostatically driven microstructures can close or open parts of a transparent substrate modulating the incident light. The surface of the microstructures can be used as shutter or as mirror or simultaneously in both functions. Photolithography and thin film technologies have been used to build microshutter-micromirror arrays. Refractive, diffractive and micro-optical systems based on glasses or polymers can be combined with the presented arrays in integrated solutions. Finally a display integrated in an automotive instrument cluster is discussed. IntroductionThe present instrument cluster is an agglomerate of different components, developed by different technologies usually located in different plants. The instrument panel has an on board electronics, bulky mechanical parts (stepper motors), independent lamps and/or complex wave guides that transmit light to the visible surface, small liquid crystal displays. Many cables link the instruments to the external world: speedometer, thermocouples, etc. The Fig. 1 is an exploded view of an instrument cluster.The evolution of the automotive instrument cluster is driven by two main needs: improved functionality for a user friendly presentation of the information and manufacturing process simplification. The enabling technology consists in a new approach on microsystems fabrication.On Fig. 2 we show a sketch of the proposed instrument cluster designed as a flat structure integrating flat panel displays, advanced pointer movements and electronic components. The connections from the external world flow on a bus to a microprocessor which drives the flat electrostatic pointer movers, the displays and the light sources. Compatible technologies are under study at CRF to develop the display (made by electrostatic microshutters) pointer movers (made by flat electrostatic films) and the light wave guides and sources. The following figure shows a possible integration of the technologies mentioned above in a compact instrument cluster design.The electrostatic pointer actuators have been presented in a previous work [1]. In the present paper we will focus on the microshutter-based displays. Automotive displaysThe most widely used technology in automotive display is liquid crystal display technology (LCD). A coarse classification can be done dividing LCD displays in two main categories: passive matrix (PMLCD) and active matrix (AMLCD). The first class find application in small size displays mounted in the instrument cluster. The main problem with enlarging PMLCD is the degraded contrast and viewing angle as more and more lines are multiplexed. AMLCD are often used for large area screens as for instance for navigational displays but a wider application is limited by cost.Other technologies are under study for automotive flat panel displays: of particular interest is the light emitting polymer (LEP or OLED) technology but at the moment because of cost, lifetime, temperature range the materials are not suitable for an automotive...

MOEMS micromirror arrays in smart windows for daylight steering

“…Likewise, metal-based but in the relaxed state nonplanar (i.e., curled/rolled), in contrast, are optical MEMS that are usually called shutter arrays [12][13][14][15][16][17] or microblinds. 18 Shutter-array-based MOEMS have been reported for transmission modulated smart glass, 12,18 space instrumentation, 13 camera shutters, 15 and displays.…”

“…18 Shutter-array-based MOEMS have been reported for transmission modulated smart glass, 12,18 space instrumentation, 13 camera shutters, 15 and displays. 16,19 These MOEMS shutter arrays are curled in the open state and unrolled by electrostatic actuation to obtain the flat closed condition. One type of these MOEMS is shutter systems defined as rolled elements found in many different application fields.…”

“…One type of these MOEMS is shutter systems defined as rolled elements found in many different application fields. Pizzi et al 16 developed curled microshutter arrays aiming at low-cost applications and a replacement of infrared (IR) photodetector arrays. A similar system designed by Mori et al 20 is electrostatically reconfigurable microshutter arrays implemented between window planes for modulating incoming sunlight.…”

Review of microshutters for switchable glass

“…5(a)]. 33,34 They did not reveal much about the fabrication; nevertheless, their microshutters are relatively big (0.5 to 2 mm) and required around 80 V actuation voltage. Modeling results were obtained in collaboration with the Université de Bordeaux.…”

“…Microblinds were also compared with other switchable glass technologies in review papers 14,15 and market reports. [19][20][21] Several groups have worked on various versions of microshutters, namely NRC, 17 New Visual Media Group (NVMG), 22,23 University of Kassel, 24,25 Institut National d'Optique (INO), 26 University of Tokyo, 27 Samsung, 28 U.S. Air Force (USAF), 29 Korea Advanced Institute of Science and Technology (KAIST), 30,31 Microelectronic Center of North Carolina (MCNC), 32 Fiat, 33,34 and University of Stuttgart. 35 These groups used various versions of curling electrodes actuated by electrostatic forces for switchable glass applications (window, display, imaging, eyewear, etc.).…”