Interferometric modulator display

Interferometric modulator display (IMOD, trademarked mirasol) is a technology used in electronic visual displays that can create various colors via interference of reflected light. The color is selected with an electrically switched light modulator comprising a microscopic cavity that is switched on and off using driver integrated circuits similar to those used to address liquid crystal displays (LCD). An IMOD-based reflective flat panel display includes hundreds of thousands of individual IMOD elements each a microelectromechanical systems (MEMS)-based device. In one state, an IMOD subpixel absorbs incident light and appears black to the viewer. In a second state, it reflects light at a specific wavelength, using a diffraction grating effect. When not being addressed, an IMOD display consumes very little power. Unlike conventional back-lit liquid crystal displays, it is clearly visible in bright ambient light such as sunlight. IMOD prototypes as of mid-2010 could emi

Low voltage electrostatic 90° turning flap for reflective MEMS display

Nico de Rooij, François Gueissaz, Fabio Jutzi, Wilfried Noell

A low voltage electrostatically actuated 90° turning flap is modeled and fabricated. The application is a new kind reflective, low-power, MEMS-based display with high contrast and reflectance. The system consists of a poly-silicon flap fabricated onto a silicon substrate with a transparent counter electrode on glass and a device layer of a silicon-on-insulator (SOI) wafer as spacer in between them. Actuation voltages down to 20V are achieved.

IEEE2010

Optical Modulators Based on Microfabricated Tilting Flaps Operating at low Actuation Voltages

Fabio Jutzi

In this thesis the concept, modelling, design, fabrication process and characterization of novel optical modulators are presented. The devices consist of flaps exhibiting a large tilt with electrostatic actuation at low voltages. The applications comprise, but are not limited to, a monochromatic reflective display, a transmissive shutter array and switchable diffraction-gratings. Nowadays the LCD-technology for reflective displays which is the most widely used technology exhibits a low contrast and reflectivity. Different technologies have been developed or commercialised, but still do not reach the quality of printed paper. It is demonstrated that the technology developed in this thesis is very competitive. If it is applied as reflective display it could reach an overall reflectivity of 45% in the white state, a contrast ratio of 50, a 100 dpi resolution, a fast switching time of 0.5ms and an actuation voltage below 40V; leading to low power consumption. When the device is employed as a transmissive shutter array a 40% fill-factor of the modulated area is obtained. The modulators consist of flaps with 250 µm width and 50 µm height. They are in vertical position at rest and in particular after fabrication. The flaps in array-configuration are suspended by a torsion beam and are electrostatically tilted to almost horizontal position. For applications as a reflective display, light gets absorbed on an underlying black-layer as the flaps are in vertical rest state, giving a black pixel. At tilted position incoming irradiation is reflected and the pixel is perceived as white. In the application as transmissive shutter array light passes through as the flaps are in rest-state and light is blocked in the actuated-state. A model of the device is presented which permits us to properly design the dimensions, knowing the scaling laws. A novel bulk microfabrication process was developed that employs micro-moulding for obtaining flaps and torsion beams made out of poly-silicon. Thin high aspect-ratio trenches are refilled by poly-silicon followed by dry etching of the surrounding material. With this process a large variety of flap shapes are fabricated, such as a wave-, lens- , comb- and grid-form. For electromechanical and optical characterization special setups and methodologies were conceived. Typically 60° tilt angles for 60V actuation voltages were measured. Depending on the geometry there was a hysteresis in the actuation trajectory and some flaps exhibited tilt angles close to 90°. The actuation voltage ranged from 35 to 85V. The resonance frequency was at 700 Hz in the rest state and at 2.3kHz in the actuated state. The poly-silicon flap surface had a reflectivity of 37% and an absorbance of 85 to 96%, depending on the wavelength. When the configuration was used as a reflective display a maximal contras ratio of 145, with typical values between 30 and 40, was measured on the active modulation area. The use of a blazed-grating shaped flap as switchable diffraction-grating was also demonstrated. Besides the concept of vertical flaps, a study is presented for the design of surface micromachined horizontal flaps actuated electrostatically to vertical position towards a transparent electrode.

EPFL2012

Electrostatic torsional vertical flaps for reflective MEMS display

Nico de Rooij, Fabio Jutzi, Wilfried Noell

A new kind of high contrast, MEMS-based reflective display system is being developed. The system consists of light reflective flaps on an optically absorptive surface. The novelty is that the flaps are in vertical position at their rest state. They can be electrostatically turned to horizontal state. A trench refilling technique on a silicon-on-insulator (SOI) wafer is used to fabricate the torsional polysilicon flaps. Low voltage and low power is required for actuation. With the same process also novel shutter and flap structures can be fabricated.

IEEE2011

Optical Modulators Based on Microfabricated Tilting Flaps Operating at low Actuation Voltages

Fabio Jutzi

EPFL2012