The scanning laser display technology is one of the most promising technologies for highly integrated projection display
applications (e. g. in PDAs, mobile phones or head mounted displays) due to its advantages regarding image quality,
miniaturization level and low cost potential. As a couple of research teams found during their investigations on laser
scanning projections systems, the image quality of such systems is - beside from laser source and video signal
processing - crucially determined by the scan engine, including MEMS scanner, driving electronics, scanning regime
and synchronization. Even though a number of technical parameters can be measured with high accuracy, the test
procedure is challenging because the influence of these parameters on image quality is often insufficiently understood.
Thus, in many cases it is not clear how to define limiting values for characteristic parameters.
In this paper the relationship between parameters characterizing the scan engine and their influence on image quality will
be discussed. Those include scanner topography, geometry of the path of light as well as trajectory parameters.
Understanding this enables a new methodology for testing and characterization of the scan engine, based on evaluation
of one or a series of projected test images. Due to the fact that the evaluation process can be easily automated by digital
image processing this methodology has the potential to become integrated into the production process of laser displays.
This paper describes the application of a micromachined resonator to verify the vacuum pressure and sealing of cavities in micromechanical components. We use an electrostatic driven and capacitively sensed bulk silicon resonator fabricated by Bonding and Deep Reactive Ion Etching (BDRIE) technology. The resonator operates at the first fundamental frequency. The damping is used as a degree of the pressure. Transversal comb structures act as squeeze film damping sources. Post-processing gap reduction substructures are used to increase the damping in the vacuum pressure range. This method makes it possible to observe the pressure over the time of smallest gas volumes by monitoring the damping of integrated micro mechanical resonant structures. Therewith it is possible to estimate the hermetic sealing quality of the closed sensor package. A transfer curve with a logarithmic characteristic is measured.
In this paper we present the very promising results for two methods of the so-called Bonding and Deep RIE (BDRIE) technology, characterised by bonding of two wafers with pre-patterned vertical gaps and subsequent RIE trench etching of the active layer. In case of the anodically bonded silicon-glass compound detection electrodes for vertical movement are integrated. The silicon layer contains the movable structure as well as drive and detection electrodes for lateral movement. It is advantageous that finally the mechanical active elements consist of single crystalline silicon without any additional layers. The BDRIE approach allows a great variation of parameters. The active layer thickness can be defined due to application issues. Our examples show active layers thickness ranging from 30 up to 200 μm, patterned by dry etching steps with maximum aspect ratio between 20:1 and 30:1. Structures with trench width variations of more than 50 (widest/smallest trench) have been fabricated successfully. Methods and results of preventing notching and backside etching of the active layer are presented as well. The size of the vertical gap can be as small as 1.5 μm for a very sensitive detection or several tens or hundreds of microns in order to reduce damping and parasitic capacitance. Holes for release in the movable structure are not necessary and will therefore not restrict the design. However, restrictions are given by the minimum size of bond area and the relation between layer thickness, free standing area above the groove and bond pressure, which are discussed within the paper. Applications of BDRIE are inertial sensors like gyroscopes, step-by-step switchgears as well as micro mirrors.
The paper presents a novel kind of Hadamard transform optic. First investigations are made with a micro mirror array in a Hadamard transform spectrometer (HTS) whereby the usually used detector array is replaced by the micro mirror array. All the mirrors are imaged onto a single detector. The measurement is performed using a Hadamard matrix, i.e. while each detector reading a certain combination of mirrors given by the matrix is reflecting the light towards the detector. All the rest of them are reflecting the light beside it. The consequence is an improvement of the signal to noise ratio (SNR). The novelty of the realized spectrometer is that in contrast to other applications the mirrors are not statically switched but they are forced to oscillate at their resonant frequency. By this way a special Hadamard matrix can be used that improves the SNR best.
Recently scanning actuator arrays have developed using metal, e.g. aluminium, or polysilicon as mirror material. Design and technology of micro mirror arrays mad of monocrystalline silicon are discussed in this paper as well as experimental results characterizing 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 and metallization. A novel modified BESOI technology with CMP, wafer bonding with buried refractory metal electrodes and sacrificial layer etching has ben developed and will be discussed. The design process is based on simple analytical calculations of the mechanical behavior, 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 characterize the electro-mechanical behavior of micro mirror arrays are discussed. In order to evaluate theoretical models describing the behavior, 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 behavior.