Interface trap density estimation in FinFETs from the subthreshold current

Abstract

In this work we present a measurement approach to determine the interface trap density in FinFETs as a function of their energy. It is hased on the precise determination of the gate voltage dependent ideality factor of the suhthreshold current in this device. The required measurement accuracy for temperature, drain current and transconductance is derived, and we propose an implementation for wafer-level device measurement on contemporary test set-ups. Exemplary interface trap distributions are shown as obtained from two FinFET device technologies, featuring the commonly observed bathtub shape.

Interface States Characterization of UTB SOI MOSFETs From the Subthreshold Current

“…The general limit of detection for trap densities is 10 10 cm −2 eV −1 determined by fitting FEM simulations without traps. This corresponds well to the lower limit reported in [22]. An input delta-peak trap density could not be translated back to the correct energy level due to the thermal noise, as was previously reported [7].…”

“…The drain current I D was measured as a function of V FG and the coupled V BG = k • V FG with V DS = 25 mV. We used 0 ≤ V FG ≤ 0.3 V with a small voltage step size of V FG = 0.2 mV (see [22]).…”

“…The drain current slope in subthreshold can be rather noisy when obtained using direct differentiation. Therefore, we use regression analysis on the drain current data within a regression window range of V FG ± u T /2, imposing I D,reg ∝ exp (V FG /u T ) to acquire the slope around V FG [22].…”

Subthreshold Conduction of Disordered ZnO-Based Thin-Film Transistors

“…The subthreshold swing is defined as the required gate voltage for changing the drain current by one order of magnitude [ 14 ]. In the case of metal-oxide-semiconductor field-effect transistors (MOSFETs), the subthreshold swing exhibits a relatively constant value and is thereby utilized for determining the sharpness of the on-to-off transition [ 27 , 28 ]. However, in the case of the ZnO TFTs, due to the detrimental increment, the minimally deduced value cannot be used for evaluating the sharpness.…”

“…However, the subthreshold swing seems to be seriously degraded: as the gate bias increases, the subthreshold swing increases as extracted to 1.8 V/dec at V gs = 9 V but to 8.1 V/dec at V gs = 15 V. We posit that the disorderedness of the ZnO films would result in the degradation; hence, we derived the subthreshold current–voltage relationship by considering that the disorderedness factors, which are the interface trap capacitance and the diffusion coefficient of electrons, can be modeled with gate-dependent power laws [ 24 , 25 , 26 ]. Following the relationships, the gate-voltage-independent disorderedness factors were successfully extracted and consistent with those obtained by the g m / I ds method [ 27 ]. In addition, we can identify that the interface traps hinder the subthreshold charge transport of the ZnO films by comparing the interface trap density with the density of states of ZnO TFTs.…”