Study Of Measuring Methods Of Phase-change Film For The Application In The Electrical Memory

As a new nonvolatile memory,phase-change random access memory（PCRAM）utilize the difference in resistivity between the crystalline and amorphous phases of chalcogenide compounds.It has the advantages of high density,high reliability,low power consumption,low cost,fast speed,good compatibility with CMOS technology.PCRAM is expected to replace Flash as the next generation of mainstream memory,and has a bright future.The core part of the PCRAM is phase change material,which is a significant matter to the device capability.According to the different target,such as data retention,speed,switching ratio,operating current,improving the capability of phase change materials has become the focus of academia and industry,the test work has already penetrated into all aspects of the development process.In this paper,the method of phase change film testing is studied,and the main contents are as follows:Firstly,a high temperature photoelectric test system is established based on LabVIEW,a data acquisition card,photoelectric detector,Keithley-2400 constant current source and Keithley-2182A nanovoltmeter included in the equipment.The system capability is evaluated by sample test and error analysis,the results show that the system has high stability and precision,the systematic error is only 0.2%⁰.6%in the sheet resistance range of 10^-24×10⁶ ohm per square.At the same time,the temperature change photoelectric characteristics of GST thin films were tested by using this system.It was found that the sheet resistance of the film decreased by 2orders of magnitude when heated to 150℃²00℃,while the reflected intensity of the film surface increased by 50%.Secondly,a semiconductor test system is constructed by using Keithley-4200and probe station system.And the DC and pulsed electrical characteristics of GST thin film are tested and analyzed by this system.The results show that both the threshold voltage and threshold current of the GST film increase with the film thickness,but the threshold value of the pulse scan test is larger than that of the DC scan test.Variable temperature test show that the threshold voltage decrease with the increase of temperature.In variable pulse width measurement,the threshold voltage decreases with the increase of pulse width.The switching ratio of GST films with different thicknesses obtained by set pulse crystallization test is more than 5,which can meet the needs of practical engineering applications.In the Reset pulse amorphization test,we found that the range of amorphization increases with the increase of thickness when the film thickness is lower,however,when the film exceeds a certain thickness,it can remain stable at high resistance state after amorphization.