Dimension Scaling Effects on Conduction and Low Frequency Noise Characteristics of ITO-Stabilized ZnO Thin Film Transistors

Conduction characteristics and low frequency noises in ITO-stabilized ZnO thin film transistors (TFTs) with constant channel width (
$\text{W}= 50\,\,\mu \text{m}$
) and different channel lengths (L=5, 10, 25, 50 and
$100~\mu \text{m}$
) are measured and analysis. Firstly, dependences of threshold voltage and field effect mobility on channel length are examined. With decreasing channel length, the threshold voltage shifts to the negative direction which may attribute to carrier diffusion from source/drain to the intrinsic device channel. In addition, significant degradation of field effect mobility is observed in short channel device which are induced by the presence of series contact resistance. The value of contact resistance has also been extracted. Secondly, the drain current noise power spectral densities (
$S_{ID}$
) are measured at varied effective gate voltages. The measured noises follow a
$1/f^{\gamma }$
and
$\gamma $
is about −1.1. Moreover, the normalized noises (
$S_{ID}/I_{ds}$
) are dependent linearly on the inverse of channel length and the slope is about −0.75. Finally, the dominant mechanism of low frequency noise in ITO-stabilized ZnO thin film transistor are examined. The slope of normalized noise against effective gate voltage are extracted, which are varied from −1.03 to −1.84 with decreasing channel length and thus it indicates that ITO-stabilized ZnO TFTs varied from bulk dominated devices to interface dominated devices. By using of
$\Delta N$
-
$\Delta \mu $
model, the normalized noises are simulated by considering of contact resistance. Several noise parameters (flat-band voltage noise spectral density, etc) are extracted and analysis.