Roel Beernaert

Design and Wrinkling Behavior of a Contact Lens With an Integrated Liquid Crystal Light Modulator

A new design of a spherically molded liquid crystal cell intended for embedding in a contact lens is proposed. Wrinkle formation in these cells was investigated and a correlation was found between the total thickness of the cell and its smoothness. Smooth cells with minimal thickness were obtained by using an asymmetric configuration with a thin layer at the convex side and a thicker but threshold dependent layer at the concave side. Active liquid crystal cells filled with a guest-host liquid crystal mixture exhibited uniform light modulation along their surface, paving the way towards a modulation-based contact lens display.

SiGe MEMS technology: a platform technology enabling different demonstrators

In imecs 200mm fab a dedicated poly-SiGe above-IC MEMS (Micro Electro-Mechanical Systems) platform has been set up to integrate MEMS and its readout and driving electronics on one chip. In the Flemish project Gemini the possibilities of this platform have been further explored together with the project partners. Three different demonstrators were realized: mirrors for display applications, grating light valves (GLV) and accelerometers. Whereas the mirrors and GLVs are made with a similar to 300 nm thick SiGe structural layer plus optical coating, the SiGe structural layer thickness for the accelerometers is 4 mu m in order to improve the capacitive readout of in-plane devices. The processing and measurement results of these functional demonstrators are shown in this paper. These new demonstrators reconfirm the generic nature of the SiGe MEMS platform.

Efficient disparity vector prediction schemes with modified P frame for 2D camera arrays

An efficient disparity estimation algorithm for multi-view video sequences, recorded by a two-dimensional camera array in which the cameras are spaced equidistantly, is presented. Because of the strong geometrical relationship among views, the disparity vectors of a certain view can for most blocks be derived from the disparity vectors of other views. A frame constructed using that idea is called a D frame in this work. Three new prediction schemes which contain D frames are proposed for encoding 5x3 multi-view video sequences. The schemes are applied to several multi-view image sequences taken from a camera-array and they are compared in terms of quality, bit-rate and complexity. The experimental results show that the proposed prediction schemes significantly decrease the complexity of the encoder at a very low cost of quality and/or bit-rate.

Efficient disparity vector coding for multi-view 3-D displays

Disparity estimation can be used for eliminating redundancies between different views of an object or a scene recorded by an array of cameras which are arranged both horizontally and vertically. However, estimation of the disparity vectors is a highly time consuming process which takes most of the operation time of the multi-view video coding. Therefore, either the amount of data that is to be processed or the complexity of the coding method needs to be decreased in order to encode the multi-view video in a reasonable time. It is proven that the disparities of a point in the scene photographed by cameras which are spaced equidistantly are equal. Since there is a strong geometrical correlation of the disparity vectors, the disparity vector of a view can for most blocks be derived from the disparity vector of another view or views. A new algorithm is presented that reduces the amount of processing time needed for calculating the disparity vectors of each neighboring view except the principal ones. Different schemes are proposed for 3x3 views and they are applied to several image sequences taken from a camera-array. The experimental results show that the proposed schemes yield better results than the reference scheme while preserving the image quality and the amount of encoded data.

An investigation of stiction in poly-SiGe micromirror

Permanent or temporary stiction remains one of the most critical reliability concerns for micro-electro-mechanical systems (MEMS). In this paper, we present an investigation of stiction of standard poly-SiGe MEMS. This is done by analyzing the hysteresis in the displacement-versus-voltage characteristics of electrostatically actuated micromirrors. The width of the “pull-in window” is used as an indication of the amount of mirror-to-surface stiction. Differences in the pull-out voltage of micromirrors within an array indicate varying levels of stiction from mirror to mirror. A FDTS self-assembled monolayer (SAM) is applied to reduce this in-use stiction. Analytical and finite element methods are used to quantify the magnitude of stiction.

Novel analog pulse‐width‐modulated 15‐μm SiGe micromirrors

A novel six-electrode SiGe micromirror pixel enabling analog pulse-width modulation (PWM) in display applications is presented. Instead of utilizing bitplanes, arbitrary duty cycles can be realized, resulting in an analog gray-level distribution. This eliminates the posterization (contouring) effect that is typical for digital micromirrors. Moreover, the pixel design does not require the incorporation of electronic comparators and the gamma compensation can be processed externally. Two out of the six electrodes are used as landing electrodes. The other four attracting electrodes are driven by two anti-phase saw-tooth signals and two fixed analog voltage signals. By applying this signal scheme, the duty cycle of the mirror is modulated in an analog manner. Test vehicles were manufactured where SiGe is the microelectromechanical systems (MEMS) material. The use of SiGe as a structural layer is advantageous to build MEMS since the CMOS and MEMS layers can be deposited in a monolithic manner. Measurements using a Laser Doppler Vibrometer (LDV) have confirmed the feasibility of analog PWM for 15-μm SiGe micromirrors.

SiGe micromirrors for optical applications

Micromirrors are a typical example of Micro-Electromechanical Systems (MEMS) with many applications including optical scanners, optical switching, projection displays, etc. We have succeeded in producing MEMS micromirrors in a SiGe structural layer, which can be used to realize CMOS-integrated MEMS structures. Several pixel designs were simulated using COMSOL multiphysics and subsequently verified in hardware. They differ in mirror size, hinge length and number of attracting electrodes (two or four). One particular mirror design enables variable Pulse Width Modulation (PWM) addressing. In this design, the mirror switches between two extreme states with a variable duty cycle determined by two generic high voltage signals and two CMOS-compatible pixel-specific DC voltages applied to the four attracting electrodes. The processed arrays were subjected to Laser Doppler Vibrometer (LDV) measurements in order to verify the simulation results. The simulated and measured pull-in voltages are compared for 8, 10 and 15μm mirrors. The agreement between simulation and measurement lies within the expectations, which is an encouraging result for future designs.