| As a kind of functional thin films,ferroelectric thin films have been widely used in the field of MEMS.For example,PZT thin films have been used in the fabrication of MEMS devices such as micro energy collector,micro accelerometer,micro force sensor and SAW devices due to its excellent piezoelectric,ferroelectric,dielectric and electro-optic effects.For MEMS devices,the quality of the functional thin films often determines the performance of these devices,so it is significant to measure the characteristic parameters of the films.Hysteresis loop is an important characteristic of ferroelectric thin films,which can reflect the ferroelectric properties of the material.On the other hand,some relevant parameters can also be obtained.For example,the remanent polarization is obtained,which can be used to estimate the piezoelectric coefficient of the material.In foreign countries,the measurement of the characteristic parameters of ferroelectrics has been studied for a long time and many advanced measuring instruments have been designed,but these instruments are expensive.Many domestic universities developed instruments for measuring hysteresis loops.However,compared with foreign similar instruments,these instruments have the defects including poor measurement accuracy,large volume and narrow application range.At present,the measurement method of hysteresis loops includes ballistic galvanometer method and Sawyer-Tower circuit method.The latter has become the main method of hysteresis loop measurement because of its advantage of simplicity and low cost.In this paper,According to the demand of ferroelectric hysteresis loop measurement in scientific research,the hysteresis loop measurement of ferroelectric thin films is studied.The hysteresis loop measurement system is designed and manufactured,which can be applied to the majority of ferroelectric thin films.The amplitude and frequency of the excitation voltage can reach 40 V and 1 KHz respectively.The system can also obtain the parameters such as linear capacitance,leakage resistance,saturation polarization,remanent polarization and coercive electric field and has the function of data storage.With the PZT thin film as the test material,the hysteresis loop test is performed on the built system and the experimental results show that the results of the measured hysteresis loops are reliable.The main work of this paper is as follows:(1)The hardware circuit of the system is designed based on Sawyer-Tower circuit method.The circuit can complete the measurement of the hysteresis loop,the generation of sine signal,the collection of data and the power supply of the system.According to the needs of system,the FPGA core board is selected.(2)Based on the platform of Quartus Ⅱ software,the temporal logic of FPGA is designed.The whole timing logic includes A/D driver module,FIFO module,DDS module,serial communication module and so on.Through the simulation function of the software,the functional simulation of each module is carried out.According to the functional modules,the top-level schematic is built.(3)Based on LabVIEW software,front panel and block flow diagram of system is designed.The front panel completes the control of the measurement process,the input and output of the parameters,the display of the waveform and the display of the hysteresis loop.The program can realize the functions of data communication,data processing,data storage and compensation of hysteresis loop.The block flow diagram can realize the functions of data communication,data processing,data storage and compensation of hysteresis loop.(4)According to the design of hardware and software,combined with test materials and probe platform,the hysteresis loop measurement system is built.In this paper,PZT thin film is used as the test material and the hysteresis loop measurement experiment was done in the ultra clean environment. |
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