Characterization of 22 nm FDSOI nMOSFETs With Different Backplane Doping at Cryogenic Temperature

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
$\text{I}_{\mathrm{ d}}$
, maximum transconductance
$\text{g}_{\mathrm{ m,max}}$
and threshold voltage
$\text{V}_{\mathrm{ TH}}$
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
$\text{V}_{\mathrm{ ZTC}}$
, 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
$\text{f}_{\mathrm{ T}}$
and 30% improvement of
$\text{f}_{\mathrm{ max}}$
depended on the
$\text{W}_{\mathrm{ f}}$
of devices have been shown. Relevant small-signal parameters (e.g., transconductance
$\text{g}_{\mathrm{ m}}$
, gate capacitance
$\text{C}_{\mathrm{ gg}}$
, gate resistance
$\text{R}_{\mathrm{ g}}$
and output conductance
$\text{g}_{\mathrm{ ds}}$
) 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
$\text{g}_{\mathrm{ m.max}}$
and the peak values of RF FOMs can be obtained at lower bias voltage compared with BP-p devices.