Study On Positive And Negative Square Wave Amplitude Modulation Power Supply And Electrostatic Probe Data Acquisition And Analysis System

Plasma is a basic form of material existence in addition to the fourth kind of material form outside the solid,liquid and gas,it widely exists in the universe and human life,widely used in areas such as physics,chemistry,material science,microelectronics,lamps.As an experimental method of plasma performance,electrostatic probe diagnostic technology has become an important analytical technique.Experimental diagnosis of plasma materials processing,can obtain correlation between macroscopic parameters and plasma correlation variables,understand the association between plasma occurs in the physical and chemical processes,as well as the interaction of plasma and material so as to establish the material structure,properties,obtain microscopic mechanism of material properties change,to achieve control of the process of plasma process-cycle.As one of the essential tools for low pressure plasma parameter diagnosis,although probe measurement theory in 100 years ago has been mature,but the actual measurement error has been relatively rough,only has the magnitude of reference in probe measurement data.We analyze the source of error,in which the saturation flow of electrons is large,so that the errors caused by the self heating of the probe become larger.In actual use,the probe voltage is driven by an external power source and the current forms a measuring loop through the measured plasma and probe.The resistance of the plasma load across 5 orders of magnitude,current of the electron is greater than that of the hydronium,resulting in the current measuring range acquisition also needs to cross 5 orders of magnitude,which is a difficult problem,and currently on the market a probr measurement system can not eliminating the probe error resistance effect is of the price of 50 thousand yuan the above.(an imported equipment is of the price of about 200 thousand yuan).Aiming at the shortcomings of existing diagnostic instruments,this paper introduces the design of a USB bus based on the high performance and high precision with plasma voltage and current in one of the positive and negative square wave amplitude modulation power supply and electrostatic probe data acquisition and analysis system adopting variable-difference 16 bit high precision analog signal for acquisition(maximum sampling rate of 500KSPS)and achieve the internal clock synchronization of DA and AD,what achieve the synchronization DA output on the rising or falling edge of clock collection,And useing the LabVIEW software to realize the precise synchronization control and measurement of the whole process on the host computer.