Wafer level vacuum packaging of micro-mirrors with buried signal lines

Abstract

This paper presents the vacuum wafer level packaging of in-house manufactured two-dimensional micro- mirrors based on the electrostatic driving principle, fabricated using a bulk technology on bonded-silicon-on-insulator wafers. The so called buried signal line concept is used in order to obtain a wafer bond friendly bonding frame. Two versions of the buried signal line concept are described in the paper: crystalline Si and poly-Si based. Anodic and glass frit bonding methods were used to bond a stack of four wafers, resulting in a vacuum-sealed package. The fabrication technology, alignment, bonding, dicing and electrical characterization are discussed. A vacuum level of 120 Pa with no getter materials was reached in the package. Due to vacuum packaging the driving voltage of the micro-mirrors after dicing could be significantly decreased from approximately 170 V to less than 35 V.