In this paper further developments [1,2] of a passive matrix projection/direct view display are presented. The device uses micromachined and electrostatic actuated Fabry-Perot filters. Applications are surface topology measurements (stereographic projection) in small cavities, laser beam writing and pattern projection e.g. in Head-Mount-displays, automotive or information panels. The display pixels with diameters in the order of 100 μm consist of a layer stack fabricated by LPCVD. The stack embeds an air gap which his created by a sacrificial etch process and a thin membrane which can be deflected electrostatically. The fabrication process has already been described elsewhere . By membrane actuation the gap thickness is lowered and the interference spectrum generated by the layer stack is varied. The careful adjustment of the
layer parameters like thickness and refractive index determines the design wavelength of the switches. They are assembled in rows and columns, resulting in an n*m-display matrix, where n*m actually is 4800. In principle the display may either be fabricated for transmission or reflection mode, depending on the substrate material (quartz or silicon). This paper focuses on transmissive displays. For pattern generation, an electric potential scan is applied on the n line contacts, and a video potential, which carries the image information, is addressed on the m column contacts. After each scan cycle, the potential polarities are reversed in order to avoid charge effects and to lower cross-talk between adjacent pixels. The response time is 100 μs, which is at least an order of magnitude faster than for common LCD technology. Further advantages are high temperature stability, low power consumption and low production costs, since only five mask layers are used in the present process. In this paper especially the electrical characteristics are evaluated and an addressing scheme for future active matrix addressing is derived.
In this paper a new approach for the realisation of a passive matrix image projection display consisting of electrostatic actuated Fabry-Perot filters for digital wavelength switching is presented. The switches either may be working by illumination with polychromatic or with monochromatic light, e.g. by a laser. In the first case the output light has to be filtered at the desired wavelength. In order to define the interferometric properties of the dielectric layers and thus the switching wavelength optical parameters like thickness and refractive index have to be adjusted carefully. The display switches can be adapted either to reflection or transmission mode, depending on whether silicon or quartz is used as substrate material. Especially hexagonal shaped pixel membranes for working either in reflection at a wavelength of 536 nm or in transmission for 500 nm are described. The assembly is arranged matrix-like in rows and columns, where at each intersection point a pixel is located. The switching of a pixel into the 'on'-state is achieved by applying a voltage on the corresponding row and column contact lines of the display. The resulting intersection potential deflects the addressed pixel membrane whereas adjacent pixels are nearly not affected. Actual measurements allow high switching frequencies of about 2 kHz at voltages in the range of 2 - 60 V, depending on the pixel design. The switching contrast maximum is aobut 80%, the contrast beteeen addressed and non-addressed adjacent pixels is 75%.