Germanium has been attracting a lot of interest due to its much higher electron and hole mobility than those in Si,and thus been considered as the most promising channel material for future MOSFET devices.In order to realize high performance Ge MOSFETs,it is mandatory to obtain superior Ge gate stacks with ultrathin thickness and low interface trap density simultaneously,which is extremely difficult because typically the interface trap density increases significantly with reducing the gate stack thickness.Recently,two approaches have been developed to scaled down the thickness of Ge gate stacks with maintaining a superior electrical properties.The first one is to use the oxygen plasma to oxidize the interface of thin ALD deposited high-k/Ge interfaces(Figs.(a)).The high-k film serves as the protecting layer to the ultrathin GeOx/Ge interface formed by plasma oxidation,as well as the oxygen barrier to prevent the growth of unneeessarily thick GeOx layer.The other method is to use rate earth doped GeO2 film as the gate insulator where the rare earth atom can sufficiently increase the stability of GeO2 while decrease tzhe interface state density(Figs.(b)).High performance Ge MOSFETs have been revealed with those gate stack structures,with both higher mobility than Si MOSFETs and ultrathin equivalent oxide thickness smaller than 1 nm.These results indicate the feasibility of the Ge MOSFETs in future CMOS technology.