Mobility Investigation by Geometrical Magnetoresistance in Fully Depleted MOSFETs and FinFETs

The operation of advanced planar MOSFET and FinFET transistors on SOI is investigated under high magnetic field. The geometrical magnetoresistance is observed when the Hall field is suppressed thanks to the device geometry. This method is free from any assumptions (oxide and body thickness, effective channel length, etc.) and delivers the most accurate and indisputable value of carrier mobility. Our measurements show, for the first time, the mobility behavior in FinFETs with double- and triple-gate and in ultrathin SOI MOSFETs. The magnetoresistance reveals the electron mobility in front or back channels as well as the impact of their interaction. A marked difference in mobility value and variation with gate voltage between the front and back channels is highlighted. A mobility discrepancy also appears between planar and FinFET transistors. Nonuniversal mobility curves with multibranch aspect result from the coexistence of several channels. This nonconventional behavior is explained by the variations in effective field and inversion charge centroid. The geometric magnetoresistance effect arises even in the lateral channels of FinFETs, an intriguing aspect that results from the device configuration.