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

Abstract

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.

Keywords

• Backplane (BP) doping
• cryogenic
• fully- depleted silicon-on-insulator (FDSOI)
• RF Figures of merit (FOMs)