Research On Phase Change Material Of Germanium Telluride Film For Microwave Switch

The function of microwave switch is to control the switching of microwave signal channel,which is widely used in radar,communications,electronic warfare and other fields.The microwave switch based on phase change material has the advantages of high R_off/R_on,high speed,small size,low parasitic capacitance and low power consumption.Especially,the crystallization temperature of GeTe thin film is higher,and the resistance ratio of the switch is greater than before and after phase transition.Firstly,we analyzed the microstructure and surface morphology of GeTe thin films before and after phase transition,and then we used the voltage pulse to realized the “ON” and “OFF” state of GeTe thin film.Finally,we designed and manufactured the switch device based on GeTe films.The main conclusions are as follows:1.Prepared GeTe thin films and analyzed the microstructure.The GeTe film prepared by the optimized RF magnetron sputtering process have Roff /Ron up to 5 orders of magnitude and Ron is about 20?.The result of XRD indicated that the structure of GeTe changed from amorphous to crystalline through annealing and form a diamond structure after annealing in 200?.The surface morphology of the film was observed by AFM,obtained the surface roughness increased after annealing.Through tested UV-VIS absorption,figured out the band gap of amorphous and crystalline 0.81 e V and 0.64 eV,respectively.By the Hall test,we found the carrier concentration in the crystallization process is increased which leads to the increase of the conductivity.From the impedance spectroscopy we obtained high capacitance in amorphous GeTe films,blocking the transfer of carrier,resulting in high resistivity,after crystallization capacitance is very small,even negligible,so carrier mobility increases and resistivity decreases.2.Analyzed the influence of DC voltage pulse on phase transition of GeTe thin films.It is found that when the pulse amplitude is 5V,the width is 980 ns,GeTe thin films from the amorphous state to the crystalline state,when amplitude is 10 V and the width is 20 ns,GeTe thin films turned into crystalline from amorphous state.It takes about 1?s to implement a switch.3.Designed and simulated the low loss microwave switches based on GeTe thin films.The simulation results indicated that insertion loss can be decreased to 1dB and isolation increased to 20 dB though changed the geometric.But it is difficult to significantly improve both aspects at the same time.4.Fabricated the microwave switches and tested insertion loss and isolation.The switching were fabricated by photolithography process.In the frequency range of 0-20 GHz,the insertion loss was about 10 dB and the isolation was about 20 dB.