In this work, the electrostatic and radio frequency performances of 22 nm FDSOI nMOSFETs with p-type or n-type doped backplane (BP, highly doped layer of silicon below thin buried oxide) at cryogenic temperatures have been investigated. Greater enhancement of drain current I d , maximum transconductance g m,max and threshold voltage V TH values have been demonstrated at liquid nitrogen temperatures. Furthermore, FDSOI nMOSFETs with n-type BP achieve the maximum transconductance at lower bias voltage and smaller V ZTC , which is mainly due to its small threshold voltage. The variation of threshold voltage of BP-p devices is greater with the decrease of temperature. About 40% improvement of f T and 30% improvement of f max depended on the W f of devices have been shown. Relevant small-signal parameters (e.g., transconductance g m , gate capacitance C gg , gate resistance R g and output conductance g ds ) are also extracted for comparison and analysis. This study presents both 22 nm FDSOI nMOSFETs with p-type or n-type backplane as good candidates for cryogenic applications down to 77 K, and especially, BP-n FDSOI are more suitable for low power operation applications because of their lower threshold voltage. Similar g m.max and the peak values of RF FOMs can be obtained at lower bias voltage compared with BP-p devices.INDEX TERMS Backplane (BP) doping, cryogenic, fully-depleted silicon-on-insulator (FDSOI), RF

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