Studies of the Stability of Amorphous Silicon Thin Film Transistors

1992 ◽  
Vol 258 ◽  
Author(s):  
T. Globus ◽  
M. Shur ◽  
M. Hack
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Leakage Current ◽  
Thin Film Transistors ◽  
Experimental Studies ◽  
Gate Insulator ◽  
Localized States ◽  
Silicon Thin Film ◽  
Insulator Layer ◽  
Voltage Stress

ABSTRACTOur experimental studies confirm that changes in a-Si Thin Film Transistors (TFTs) under voltage stress occur in the device channel and not in the contacts. We demonstrate that stressing an a-Si TFT not only shifts the device threshold voltage but can also changes the slope of the semilog subthreshold current dependence on the gate voltage. In addition, stressing can decrease the minimum leakage current. The creation of new localized states in the amorphous silicon under voltage stress qualitatively explains all these effects, while carrier tunneling and trapping in the gate insulator layer cannot by itself explain our data. At large negative gate voltages, the leakage current increases due to the holes injected into the channel. This hole current is also affected by voltage stress as can be predicted by the state creation mechanism.

Temperature and Frequency Dependent Characteristics of Amorphous Silicon thin film Transistors

1995 ◽  
Vol 377 ◽  
Author(s):  
H. C. Slade ◽  
M. S. Shur ◽  
M. Hack
Keyword(s):  
Thin Film ◽  
Temperature Dependence ◽  
Amorphous Silicon ◽  
Thin Film Transistors ◽  
Field Effect ◽  
Experimental Studies ◽  
Localized States ◽  
Field Effect Mobility ◽  
Silicon Thin Film ◽  
Capacitance Voltage

ABSTRACTOn the basis of our experimental studies of the temperature dependence of amorphous silicon thin film transistor current-voltage and capacitance-voltage characteristics, we have developed an analytical device model suitable for implementation in circuit simulators. This model describes the above-threshold (on) current and the subthreshold (off) current [1]. In addition, the model is able to incorporate changes in the distribution of localized states which arise from thermal and/or bias stress. In this paper, we identify the temperature-dependent parameters, which describe the temperature dependence of both the on and off currents, and we model the leakage current at large negative gate biases. The modeling results are in good agreement with our experimental data. We also discuss capacitance-voltage characteristics of amorphous silicon thin film transistors for varying gate lengths, temperatures, and frequencies. The measured capacitance-voltage characteristics show strong frequency dispersion, which is related to the trap-limited transport of carriers in the channel. The characteristic time constant, which determines when the channel capacitance becomes dependent on frequency, is on the order of the transit time calculated with the field-effect mobility and the electric field. The field-effect mobility takes into account carrier trapping by the localized states and is a function of gate voltage and temperature.

Investigation of the off-current in amorphous silicon thin film transistors for SiO2 and SiNx. gate insulators

1996 ◽  
Vol 424 ◽  
Author(s):  
Jeong Hyun Kim ◽  
Woong Sik Choi ◽  
Chan Hee Hong ◽  
Hoe Sup Soh
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Thin Film Transistors ◽  
Chemical Vapor ◽  
Interface State ◽  
State Density ◽  
Gate Insulator ◽  
Defect States ◽  
Silicon Thin Film ◽  
Pressure Chemical

AbstractThe off current behavior of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) with an atmospheric pressure chemical vapor deposition (APCVD) silicon dioxide (SiO2) gate insulator were investigated at negative gate voltages. The a-Si:H TFT with SiO2 gate insulator has small off currents and large activation energy (Ea) of the off current compared to the a-Si:H TFT with SiNx gate insulator. The holes induced in the channel by negative gate voltage seem to be trapped in the defect states near the a-Si:H/SiO2 interface. The interface state density in the lower half of the band gap of a-Si:H/SiO2 appears to be much higher than that for a-Si:H/SiNx.

Effects of Mechanical Strain on Amorphous Silicon Thin-Film Transistors

2002 ◽  
Vol 715 ◽  
Author(s):  
H. Gleskova ◽  
S. Wagner ◽  
W. Soboyejo ◽  
Z. Suo
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Leakage Current ◽  
Thin Film Transistors ◽  
Tensile Strain ◽  
Mechanical Strain ◽  
Positive Sign ◽  
Silicon Thin Film ◽  
Polyimide Foil

AbstractWe evaluated a-Si:H TFTs fabricated on polyimide foil under uniaxial compressive or tensile strain. The strain was induced by bending or stretching. All experiments confirmed that the on-current and hence the electron linear mobility depend on strain å as μ = μ0 (1 + 26·ε), where tensile strain has a positive sign. Upon the application of stress the mobility changes instantly and then remains unchanged in measurements up to 40 hours. In the majority of the TFTs the off-current and leakage current do not change. In tension, the TFTs fail mechanically at a strain of ∼ 3x10-2 but recover if the strain is released ‘immediately’.

Characterization of Photo Leakage Current of Amorphous Silicon Thin-Film Transistors

1999 ◽  
Vol 38 (Part 1, No. 11) ◽  
pp. 6202-6206 ◽  
Author(s):  
Yoshimi Yamaji ◽  
Mitsushi Ikeda ◽  
Masahiko Akiyama ◽  
Takahiko Endo
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Leakage Current ◽  
Thin Film Transistors ◽  
Silicon Thin Film

Material Properties Controlling the Performance of Amorphous Silicon Thin Film Transistors

1984 ◽  
Vol 33 ◽  
Author(s):  
M. J. Powell
Keyword(s):  
Thin Film ◽  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Density Of States ◽  
Threshold Voltage ◽  
Material Properties ◽  
Thin Film Transistors ◽  
Gate Insulator ◽  
Dangling Bond ◽  
Silicon Thin Film

ABSTRACTAmorphous silicon thin film transistors have been fabricated with a number of different structures and materials. To date, the best performance is obtained with amorphous silicon - silicon nitride thin film transistors in the inverted staggered electrode structure, where the gate insulator and semiconductor are deposited sequentially by plasma enhanced chemical vapour deposition in the same growth apparatus.Localised electron states in the amorphous silicon are crucial in determining transistor performance. Conduction band states (Si-Si antibonding σ*) are broadened and localised in the amorphous network, and their energy distribution determines the field effect mobility. The silicon dangling bond defect is the most important deep localised state and their density determines the prethreshold current and hence the threshold voltage. The density of states is influenced by the gate insulator interface and there is probably a decreasing density of states away from this interface. The silicon dangling bond defect in the bulk amorphous silicon nitride also leads to a localised gap state, which is responsible for the observed threshold voltage instability.Other key material properties include the fixed charge densities associated with primary passivating layers placed on top of the amorphous silicon. The low value of the bulk density of states in the amorphous silicon layer increases the sensitivity of device characteristics to charge at the top interface.

Improvement of Gate-Insulator/Silicon Interface Characteristics in Amorphous Silicon Thin Film Transistors

1994 ◽  
Vol 33 (Part 2, No. 6B) ◽  
pp. L834-L836 ◽  
Author(s):  
Toshiyuki Sameshima ◽  
Atsusi Kohno ◽  
Mitsunobu Sekiya ◽  
Masaki Hara ◽  
Naoki Sano
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Thin Film Transistors ◽  
Gate Insulator ◽  
Silicon Thin Film ◽  
Interface Characteristics ◽  
Silicon Interface
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