The 1/f1.7 noise in submicron SOI MOSFETs with 2.5 nm nitrided gate oxide

The low-frequency noise of partially depleted silicon-on-insulator (SOI) MOSFETs is studied in the ohmic regime. In the frequency range 0.7 Hz ≤ f ≤ 50 Hz, a power spectral density is observed which follows a 1/fⁿ law, with n ∼ 1.7 for a broad range of operation conditions. This noise is to be distinguished from the usual 1/f-like noise, occurring at higher frequency for devices with a length smaller than 1 μm. From the dependence on the gate voltage and device length, it is concluded that the 1/f^1.7 noise is of the McWhorter type and, therefore, is generated by carrier exchange between the front channel and traps in the 2.5 nm NO gate oxide. This type of noise is absent in the back-channel or in the gate current. A model will be presented, from which it is derived that the responsible traps are most likely associated with the polysilicon gate/oxide interface and, furthermore, show a steep concentration profile over a small depth range. A similar noise behavior is observed in bulk devices with thin gate dielectrics.