Research On Micro Sensor Based On Planar Coil And Its Manufacturing Technologies

With the development of microelectronic and micromachining techniques, more and more micro sensors and actuators have been reported for using in various application. According to the different sensing-actuation mechanisms, micro devices can be classified into serval categories: electrostatic, piezoelectric, thermal, and magnetic. The properties of various types MEMS devices diverse greatly, which has been a hotspot in engineering application.Larger displacement and force could be achieved through magnetical micro devices than others. A key issue of this type device is the fabrication of micro coil and magnetic component. Some key technologies such as the fabrication, assemble and test of micro magnetic sensor and actuator using planar coil were studied in the paper, with the micro magnetic relay and micro eddy current sensor as targets. A prototype eddy current sensor with 2.4 mm diameter and 1.6 mm thickness was fabricated and studied. The whole work play an important role in the application of magnetic MEMS devices based on the planar coil. Several aspect of works, as follows, were carried out in this paper.Firstly, the electromagnetic field distribution and inductance attribute of micro planar coil were investigated based on the fundmental theory. Combined with Finite element method (FEM), an analytical model of an eddy current sensor for noncontact distance measurement was presented, which laid the foundations for future experiment.With SU-8 photoresist, the large area micro pattern on the metal substrate fabricated by using photolithographic technology was studied in this paper. In order to obtain the suitable parameters of the various thickness photoresist, an artificial neural network (ANN) with 5 layers was built in research. The ANN was trained based on orthogoality experiment using back propagation algorithm. Compared to the experiment results, the prediction error was less than 2.0%, which proved that the ANN was effective. Definitions of image feature were put forward. Based on these concepts, develop process was analysised in detail, the optimal process of SU-8 based on the stainless substrate was given.The characteristics of the microelectroforming process was analysed systematically through Finite element analysis (FEA) of electric field and flow field of the micro deposit area. The effects of the main parameters, current density and stiring style, on the deposit quality (uneven thickness distribution, etc.) were discussed in detail. The mechanism and influencing on ultrasonic stiring in the microelectroforming was explained, based on the studies, the optimal ultrasonic power and current density was introduced. The results showed that the mass transfer was the control factors of deposit quality. A planar coil with 70μm line width,30μm line distance was fabricated according to the above research.This paper was focused on the composition controlling, coating microstructure and electromagnetic character of Ni-Fe deposit for MEMS device. The relation between the deposit composition and the main parameters, such as current density, temperature, electrolyte concentration, were investigated in deep. The results indicated that the Ni-Fe deposit was bright and compact. The resistivity of deposit was about 30μ?·cm, when the Fe(wt.%) ranged from 10% to 50% in the deposit. Electrodeposited Ni-Fe has a strong paramagnetism effect and the coercivity showed a monotonic decrease with increasing Fe content in deposit, the saturation magnetization was only 10% of that of the IJ85 permalloy, which proven that the electroformed Ni-Fe alloy had good electromagnetic property and could be used in MEMS actuator fabrication.Finally, a prototype of eddy current sensor was fabricated with UV-LIGA technology and the electroforming magnetic core process. The device consists of two planar coil (driver coil and pickup coil) stacked on the magnetic core. The character of the device was tested with micro motion platform and data acquisition system developed independently. The optimal sensitivity was 0.55 mv/μm and resolute was 20μm. The whoil work was a beneficial trial to the practice of magnetic MEMS devices based on the planar coil.