Electron valence band tunnelling induced excess Lorentzian noise in fully depleted SOI transistors

The excess Lorentzian noise, associated with electron valence band (EVB) tunnelling is studied in fully depleted (FD) silicon-on-insulator (SOI) p- and n-MOSFETs, for different device lengths and with the back gate biased into accumulation. It. is shown that the characteristic time constant /spl tau/ and the plateau amplitude S/sub 10/ reduce exponentially with the front gate overdrive voltage in absolute value. It is furthermore observed that S/sub 10/ /spl sim/ /spl tau//sup n/ with n close to 1. A slightly different behaviour is found for the p- compared with the n-channel devices: while for p-MOSFETs the time constant reduces slightly for smaller L, an increase is found for the n-MOSFETs. This behaviour is also reflected in the length dependence of the amplitude. These observations are discussed in view of a recently proposed model, which considers the EVB tunnelling noise as RC filtered shot noise in the forward source-body current.