A monolithic resonant micro actuator was developed, fabricated by CMOS-compatible micro machining technology, tested and evaluated. The component is able to measure acceleration in at least two directions. The device made of single-crystal silicon oscillates perpendicularly to the surface plane at a constant frequency in the 8 kHz range. A square-pulse shaped voltage of double the oscillation frequency drives it. It comprises an oscillating plate with a capacitance formed by interdigitating comb fingers. The acceleration in the direction orthogonal to the surface plane is detected by comparing the position of the plate to a reference plane. Without acceleration applied the position is centred in average. Upon acceleration the crossover point of the oscillation is shifted and the magnitude of acceleration can be related to the difference. The acceleration in a second direction can be measured by the common way of comparing e.g. the change of capacitance of two electrodes to each other. The component’s stability in frequency and amplitude during testing is shown. Simulation and measurement data is presented and compared.
This paper presents a demonstrator of a low cost image projection device that has been developed at the Fraunhofer Institute of Photonic Microsystems. The image projection is not based on the common line by line raster scanning of the image. Instead, a resonant 2-dimensional micro scanning mirror is used for the deflection of a modulated laser beam. The mirror is operated at a low ratio of horizontal and vertical oscillation frequency. In particular, a ratio with a small shift from an integer value is used to enable a scan of the whole projection screen with a Lissajous pattern. The control circuit performs an excitation of both mirror axes by driving them with fixed frequency according to the response curves of the actuator. Programmable counters are used to generate the driving frequencies and to determine the actual beam position during the scanning process. That enables a very simple and low cost control circuit. A micro scanning mirror, fabricated at Fraunhofer IPMS, was used in the demonstrator set up. It is operated at oscillation frequencies of 1.4 kHz (slow axis) and 9.4 kHz (fast axis). The control circuit was realized and successfully tested with a FPGA implementation. The image resolution provided by the control circuit is 256 x 256 pixels.
We present an ASIC for synchronized excitation of electrostatically driven resonant micro scanning mirrors which have been developed and fabricated at the Fraunhofer IMS for several years. The mirror oscillation is excited with a rectangular driving signal and operated close to the characteristic frequency or higher. Deflection amplitude is maximum if the driving voltage is switched off precisely at the cross-over of the oscillation. We have developed and fabricated a mixed signal ASIC that starts the oscillation and runs the mirror with high efficiency by detecting the oscillation cross-over. For that, the ASIC senses the varying capacitance of the actuator’s comb-drive electrodes and converts it with a clocked charge amplifier into a voltage. The amplified capacitance signal is processed by a synchronization module which detects the minimum of the capacitance signal corresponding to the cross-over of the oscillation. An integrated charge pump provides the driving voltage. The ASIC has been fabricated at the facilities of the IMS with a 1.2 μm CMOS process. Tests with a demonstrator PCB have shown that the synchronization works highly efficient with a value of appr. 96 %. A mechanical deflection angle of ± 13° was achieved for a micro-mirror with a characteristic frequency of 250 Hz at a driving voltage of 13.5 V, only.