Research On Electrical Discharged Machining Of Semiconductor Crystal Materials

Because of its special characteristics of light, heat, electricity and magnetism, semiconductor become one of the most active advanced materials in the cutting-edge science and technology, and played an important role in the field of industrial manufacturing, defense industry, aviation, aerospace, and so on. However, its poor machinability, high brittleness, low fracture toughness, being prone to the overall fracture in processing, being difficult to process parts with complex curves and face, being hard to guarantee precision, low efficiency, all these factors severely restrict its application. Electrical discharge machining uses electrical energy to remove material, and materials in any hardness, strength, toughness, brittle can be processed with EDM. The resistivity of the common semiconductor materials is 3~4 orders of magnitude higher than that of metals, and the common semiconductor has very special electrical characteristics. The mechanism and law of conventional electrical discharge machining which is established based on the conductive material can not be applied to semiconductor. Therefore, a bran-new system of electrical discharge machining system must be established to process semiconductor. In this paper, based on the specific conductivity of semiconductor materials, the relevant discharge model is created and the key issues about the characteristics of the electrical inlet, body resistance, erosion mechanism and of semiconductor crystal in the process of electrical discharge machining are researched. Some aspects of work are completed as follows:(1) The electrical discharge machining system of semiconductor crystal is established. The dedicated pulse power, special conduction system and three-dimensional discharge experimental platform is designed for researching and analyzing the discharge machining mechanism of semiconductor. Besides, in order to achieve the discharge machining of silicon, germanium and other semiconductors, the WEDM machine tool, circulating system of working fluid are reformed.(2) The basic characteristics of the intrinsic semiconductors, doped semiconductors, and Schottky junction were summarized. The volt-ampere characteristic curve of resistance and diode in series and parallel were researched. It was found that there was Schottky barrier in the contact position in the process of the discharge machining of semiconductor and at the same time, the equivalent circuit model of semiconductor was set. Through investigation, it was known that the basic circuit of discharge machining was composed of resistance and reverse diode in series and its basic characteristics of voltage-ampere curve included on-resistance, breakdown voltage and breakdown resistance.(3) The equivalent circuit model of semiconductor of P-type and N-type semiconductor in the condition of positive polarity and negative polarity, which can be represented by resistors and diodes were set. It is cleared that there were two clients in the electrical discharge machining of semiconductor, clamping-side and discharge-side. At first, the contact area and contact pressure on the characteristics of fixed electrical inlet through the feed model at both ends of the inlet metal clamping were studied. On the other hand, the characteristics of the discharge end was researched with the combination of electrical discharge machining theory, and the single perforating guide principle of the electrical discharge machining of semiconductor was obtained.(4) The calculation formulas of body resistance was researched in different contact forms and different discharge conditions. It was known that the body resistance of semiconductor in the process of EDM was determined by the equivalent contact radius. Above all, it is found that, because of the heat of the discharge end, body resistance decreases when equivalent contact radius increases in the process of discharge machining, which conduces significant climbing characteristics of discharge current.(5) A simplified calculation model of energy distribution between electrodes based on the optical transmitter theory was brought forward, and the polarity effect in EDM was reinterpreted. Then the thermal field, stress field of electrodes and workpiece were simulated through ANSYS software, and the erosion mechanism of brittle semiconductor materials was brought forward.(6) A light-reflecting transmission model was established to analyze the pile of anti-reflection. The anti-reflectivity of the structure of various trap morphologies in optical was calculated and optical trap structural optimization theory was proposed to improve the texture of the anti-reflective effect and increase the absorption of solar light.(7) The discharge machining of the commonly used semiconductor crystal was completed. The coating isolation method and servo conduction mode were brought forward to eliminate passivating materials generated by electrochemical action and to machine large profiled germanium windows. With the use of electrochemical reaction in the discharge side, electrolytic micro-pits was formed on the workpiece, resulting in subsidence light the role of solar-grade silicon to achieve the discharge cutting and texturing technology. In the semiconductor silicon crystal, the deep hole whose machining diameter ratio was 30 was realized .