Silicon mirror arrays fabricated by using bulk- and surface-micromachining

Recently scanning actuator arrays have been developed using metal, e.g. aluminium, or polysilicon as mirror material. Design and technology of micro mirror arrays made of monocrystalline silicon an discussed in this paper as well as experimental results characterising the arrays. Micro mirror arrays with up to 1000 simultaneously movable electrostatically operated cells convenient for continuous scanning with frequencies of several hundred Hz up to some kHz will be presented. The technological approaches consist of the use of silicon wet- and dry-etching, wafer bonding (silicon fusion and anodic bonding) and metallization. A novel modified BESOI technology with CMP, wafer bonding with buried refractory metal electrodes and sacrificial layer etching has been developed and will be discussed. The design process is based on simple analytical calculations of the mechanical behaviour, the fluid flow surrounding the movable mirror and the electrostatic field as well as numerical simulations by means of the finite element method and network analysis. Furthermore, some experimental methods to characterise the electro-mechanical behaviour of micro mirror arrays are discussed. In order to evaluate theoretic models describing the behaviour, the natural frequencies, the damping coefficients and the frequency transfer function are measured. The adaptation of the model parameters leads to more accurate values simulating the behaviour.