Scaling Down Effect on Low Frequency Noise in Polycrystalline Silicon Thin-Film Transistors

Abstract

Scaling down effects on conduction and low frequency noise characteristics are investigated in a set of p-type polycrystalline silicon thin-film transistors (poly-Si TFTs) with fixed channel width (W=8 μm) and different channel lengths (L=2, 4, 8, 12, and 20 μm). First, short channel effects on threshold voltage, field effect mobility, and sub-threshold swing are examined, while the presence of contact may induce to the degradation of field effect mobility in the short channel devices. Subsequently, the drain current noise power spectral densities are measured at varied effective gate voltages and drain currents. The slopes of normalized noise against effective gate voltage are varied from −1.1 to −2 with decreasing channel length, which indicates that poly-Si TFTs varied from bulk dominated devices to interface dominated devices. Based on N-μ model, the flat-band voltage noise spectral density and coulomb scattering coefficient are extracted. Therefore, measured normalized noises are simulated by considering of contact resistance. Finally, short channel effects on some noise parameters (such as Hooge's parameter, etc.) are studied and discussed.

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

“…3(a). Based on transmission line method [12], [23], the calculated total resistance is close to the value of contact resistance when the channel length approximated to 0. Therefore, the value of contact resistance can be extracted by use of linear extrapolation.…”

“…The degradation of field effect mobility in short channel devices may dominate by the contact resistance [12], [17]. Unlike conventional MOSFETs, ITO-stabilized ZnO TFTs do not have a stable doped source/drain regions.…”

“…A weak ohmic contact may exist caused by the mismatch between the work functions of the active region and the electrode. Thus, the contacts may play a dominant role in short devices, which caused mobility decreases with the decrement of channel lengths [12], [17].…”

“…Low frequency noise (LFN) is a key parameter for analog and RF applications [8]- [10], and it sets the lower limit of the signal that can be processed and detected in the subsequent circuits and modules [11]. Moreover, LFN may up-convert to high frequencies and then become to a source of phase noise, which may adversely affect the application of devices in RF fields [8], [12]. The source and dominant mechanism of LFNs in metal oxide TFTs have been examined by many groups [9], [13]- [15].…”

“…To integrate more functions on the same substrate, the channel length of devices should be reduced from typical values of L=10 μm to L=1-2 μm, or less [12], [16]. Thence, contact resistance and short channel effects may affect device performance and there should be controlled for proper operation of these devices [17]- [20].…”