Characterization of traps in the gate dielectric of amorphous and nanocrystalline silicon thin-film transistors by 1/f noise

Abstract

The low frequency noise technique is used to obtain the volume profile of traps in the SiNx gate dielectric of hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) thin film transistors (TFTs). In both a-Si:H and nc-Si:H TFTs, within the range of probing depth in the gate dielectric, the traps have a uniform spatial distribution which is consistent with the observed pure 1/f noise. The experimental results show that the gate dielectric trap properties near the interface are dependent on the channel material with the trap density in nc-Si:H TFTs being much smaller in comparison with the a-Si:H TFTs.

Origin of Low-Frequency Noise in the Low Drain Current Range of Bottom-Gate Amorphous IGZO Thin-Film Transistors

“…However, the same trend is found for the quantities S I /I 2 d and (g m /I d ) 2 , which indicates that the 1/f noise originates from carrier number fluctuations due to electron exchange between channel and traps located in the gate insulator close to the a-IGZO/SiO 2 interface as in crystalline Si MOSFETs [10]. Similar origin for the 1/f noise was found also in polycrystalline, nanocrystalline, and amorphous silicon TFTs [12], [13]. It has been recognized that the interface of these TFTs is distinguished from that of the crystalline Si/SiO 2 by comprising the bulk traps, in addition to the gate oxide traps, i.e., channel material of higher disorder has a more profound effect on the gate dielectric trap properties.…”

“…where S V fb is the flatband voltage spectral density, q is the electron charge, kT is the thermal energy, C ox is the gate capacitance per unit area, N t is the density of the gate insulator traps, and α t is the tunneling attenuation coefficient of the electron wave function taken to be 10 8 cm −1 in the SiO 2 [13]. From the obtained value of S V fb = 8 × 10 −8 V 2 /Hz in Fig.…”

“…The obtained value is N ss = 3 × 10 12 cm −2 eV −1 , which is close to the N st value determined from the 1/f analysis, implying that the same trap states are likely involved. The generation of pure 1/f noise indicates uniform spatial distribution of the traps in the gate oxide [13]. The spatial trap distribution can be determined by converting the frequency to tunneling depth through the relation 1/2πf = τ o exp(α t x), where τ o is the time constant at the interface and x is the distance into the gate oxide from the interface.…”

Analysis of low frequency noise characteristics inp-type polycrystalline silicon thin film transistors

“…3(b). Following the conventional tunneling theory, the relationship between S ID /I 2 ds and the flat-band voltage noise power spectral density (S V f b ) is given by 18 :…”

“…In order to have a qualitative spatial distribution of traps in the gate oxide, the frequency is converted to the tunneling depth as follows 18,19 :…”