Threshold Voltage Variations By Oxide Fixed Charges On Silicon-On-Insulator MOSFETs

This study evaluates the fixed charge effects provided by oxides on silicon-on-insulator (SOI) metal-oxidesemiconductor field-effect-transistors (MOSFETs) by the numerical simulations. Fixed charge signs are unique to the oxide materials, and the gate oxide and the buried oxide (BOX) materials of SiO2 (the positive sign) and Al2O3 (the negative sign) are considered. It is found that the certain choice of the gate oxide and the BOX materials provide the good leak current suppression however the suitable oxide choices are different between n-MOSFET and p-MOSFET due to the opposite majority charge polarization. Also, the fixed charge effect is dominant on fullydepleted SOI (FD-SOI) process, and the partially-depleted SOI (PD-SOI) is less sensitive to the fixed charge effect. Then, p-MOSFET on FD-SOI process is extremely sensitive, and using SiO2 BOX provides the strongly inhibited leak current however this SiO2 BOX is harmful on n-MOSFET. It is suggested that the suitable SOI process selection is required depending on the ratio of the amount of n-MOSFETs and p-MOSFETs on the entire chip.