Evaluation of grain boundary trap states in polycrystalline–silicon thin-film transistors by mobility and capacitance measurements

Abstract

A method for evaluating localized grain boundary (GB) trap states in polycrystalline–silicon thin-film transistors (poly-Si TFTs) is proposed. Field effects in poly-Si TFTs are analyzed by decomposition of the two-dimensional Poisson’s equation. This analysis gives the theoretical basis for evaluating the localized GB trap state density. The trap states are evaluated with the GB barrier potential given by the activation energy of the effective mobility and with the surface potential calculated from the capacitance–voltage characteristics in poly-Si TFTs. This evaluating method was applied to several different types of poly-Si TFTs fabricated with excimer laser annealing crystallization processes. This method has succeeded experimentally in eliminating the error effects related to oxide–semiconductor interface trap states and in clarifying that the GB barrier potential has a peak in its gate bias dependence. This method has also elucidated that the GB trap state density has almost the same value independent of the grain size when the hydrogenation efficiency in poly-Si is in the same level between TFTs. The good agreement of the simulated and the measured drain currents confirm the validity of this method.

Simulation Study of the Dependence of Submicron Polysilicon Thin-Film Transistor Output Characteristics on Grain Boundary Position

“…[20][21][22] or as Gaussian terms used in refs. [26][27][28]. We chose to use Gaussian terms because the studies dealing with SPC films suggest a peak in trap states near the mid gap and we are considering SPC films in this work.…”

“…These have consisted of single energy level models, 17,18) models with single 19) or double [20][21][22] exponential tail states, Gaussian shaped distributions 1,23,24) or both. 25,26) It has been suggested that while tail states dominate the above-threshold behavior, mid-gap states primarily effect the subthreshold behaviour. 19,20) Although in this study we are only concerned with the above-threshold region, to ensure a realistic model we choose to include both mid-gap and tail states.…”

A Physics-Based Effective Mobility Model for Polycrystalline Silicon Thin Film Transistor Considering Discontinuous Energy Band at Grain Boundaries

“…Unlike Ikeda's results, [11][12][13] which consider the tunneling effect of the additional potential barrier as a fixed coefficient, the relation between M and D varies with v d .…”

Threshold Voltage Variations Due to Oblique Single Grain Boundary in Sub-50-nm Polysilicon Channel

“…2. The energy profile of N it in the poly-Si GB can be affected by various post-treatment methods, such as oxygen plasma, H 2 O vapor annealing, and hydrogen annealing [21], [22]. We use a similar peak value and distribution shape of the N it as in the previous studies without any treatments [23].…”