Technological approaches for fabrication of elastomer-based spatial light modulators

Abstract

We present novel approaches to the fabrication of spatial light modulators based on thin viscoelastic layers. These layers are formed against two chips: the bottom one carries an interdigitated electrode structure and the top one is a sacrificial chip coated with a metal layer or a stack of materials. By etching away the top chip with bulk silicon techniques, a directly coated and planarized elastic layer results with very high optical quality. The surface is deformed in a sinusoidal shape under electrostatic load when alternating potentials are applied on the underlying electrodes. With this effect, solid-state alternatives for Eidophor projectors can be fabricated. The top chip can contain either a 125nm gold layer or a 50nm nitride and 80nm aluminum layer. After curing, the chip is encapsulated in a flexible elastomer based etch holder and placed in a 33wt% KOH solution at 85°C. This etches away the silicon of the top chip and stops on either the nitride or gold. The surface has a 100% optical fill factor over the active region and can scale easily to various resolutions and spectral ranges. Measurements of the surface has shown local initial deformations below 0.10 λ. Experiments done with devices with 50-100μm electrode size and 5μm spacer distance have shown significant far-field scattering under application of 300V potential difference between the electrodes. Further development will include optimizations of the modulation efficiency. Applications can be found in high performance projection displays, optical lithography and optical communication networks.