Study Of Ohmic Contact Of GeTe Thin Films And Preparation Of Phase Change Switch

Phase change switches can be used for signal transfer,signal relaying,and other network reconfiguration activities,etc.It has a wide range of applications in satellite systems,military fields,etc.This work studies from the perspective of GeTe film preparation and ohmic contact between GeTe and metal,a direct heating phase change switch structure is designed,the GeTe phase change switch has been developed and its performance has been tested.The optimum sputtering conditions for the GeTe films were obtained by optimising the sputtering parameters to 160 W,1.6 Pa,80 sccm.Amorphous to crystalline resistance ratios over 10^-5?are achieved.GeTe films annealed at temperatures above 220°C can undergo phase transformation,preferentially growing along the(202)and(220)crystal planes.The annealed surface shows the formation of the oxides Te O₂ and GeO₂.The crystalline GeTe films have two vibrational modes,Ge-Te and Te-Te,and the amorphous state is obtained by split-peak fitting as a possible combination of five structures.The specific contact resistivity of the GeTe film in contact with the NiCr film was quantified by TLM and CTLM at first time,which were 3.66×10^-7?·cm~2 and 7.45×10^-7?·cm~2,respectively.The specific contact resistivity of the GeTe/Ni Cr structure decreased after annealing.EDS results showed that there was interdiffusion at the interface after annealing,which was the main reason for the decreased specific contact resistivity.We found that the pretreatment of aqueous ammonia solution could enrich Ge²⁺on the GeTe surface and promote the decrease of the specific contact resistivity of GeTe/Ni Cr contact.The HCl solution enriches the surface of the GeTe film with Te,which increases the specific contact resistivity.A new two-port direct heating type phase change switch was designed with using Ni Cr as a heating electrode,and the device was prepared and tested.The minimum turn-on pulse voltage is 8 V,and the turn-off pulse is as fast as 20 ns.From 0-25 GHz,the isolation is greater than 30 d B and the insertion loss is less than 1.7 d B.On this basis,a four-port directly heated GeTe phase change switch has been designed with an off pulse of 14 V-30 ns and an on pulse of 10 V-7?s,both of which meet the requirements of an RF switch for RF front-end applications.