Effect of Insulators on the a-IGZO TFT Performance (original) (raw)
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Microelectronics Reliability, 2014
Different structures of a-IGZO (amorphous indium gallium zinc oxide) transparent thin film transistor (TTFT) were developed on glass substrate for study of gate barrier and channel buffer layer effects. The used gate barrier and the channel buffer layer are high energy band gap dielectric Al 2 O 3 and the rapid thermally annealed ZnO film, respectively. With both gate barrier and channel buffer layers, the TTFT promoted 3ordersinon/offcurrentratioandreducedleakagescurrent3 orders in on/off current ratio and reduced leakages current 3ordersinon/offcurrentratioandreducedleakagescurrent800 times. Furthermore, the average transparence was also enhanced from 84% to 86.4% in the range of 500-800 nm wavelengths. The improvement mechanisms are interpreted with comprehensive models in details.
Characterization and Modeling of a-IGZO TFTs
JOURNAL OF DISPLAY TECHNOLOGY, 2014
In this paper, we present a systematic approach to the characterization and modeling of amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs), where the key parameters are determined from the analysis of both – and – characteristics, in a step-by-step fashion, without complex interdependences that may affect the accuracy of the results. Flat band voltage and carrier concentration are extracted by a method we have previously developed, validated here by applying it to simulated data. Next, the density of deep gap states is extracted, followed by the determination, by a new method, of the shallow donor concentration. The tail states parameters are determined last, by matching the calculated to the experimental one. Simulations are then performed without any adjustable parameters. The approach is applied to the study of device to device variations, indicating that the material is strongly compensated. As for the analysis of Negative Bias under Illumination Stress (NBIS), this work confirms that the effect is due to creation of a double donor, with a shallow level close to the conduction band (positive correlation energy). Oxygen vacancies are the likely candidates. These defects are not detected in unstressed devices, where the characteristics can be accurately simulated by incorporating donors with a single shallow level.
Characterization and Modelling of a-IGZO TFTs
Journal of Display Technology, 2014
In this paper, we present a systematic approach to the characterization and modeling of amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs), where the key parameters are determined from the analysis of both -and -characteristics, in a step-by-step fashion, without complex interdependences that may affect the accuracy of the results. Flat band voltage and carrier concentration are extracted by a method we have previously developed, validated here by applying it to simulated data. Next, the density of deep gap states is extracted, followed by the determination, by a new method, of the shallow donor concentration. The tail states parameters are determined last, by matching the calculated to the experimental one. Simulations are then performed without any adjustable parameters. The approach is applied to the study of device to device variations, indicating that the material is strongly compensated. As for the analysis of Negative Bias under Illumination Stress (NBIS), this work confirms that the effect is due to creation of a double donor, with a shallow level close to the conduction band (positive correlation energy). Oxygen vacancies are the likely candidates. These defects are not detected in unstressed devices, where the characteristics can be accurately simulated by incorporating donors with a single shallow level.
Tailoring IGZO Composition for Enhanced Fully Solution-Based Thin Film Transistors
Nanomaterials
Solution-processed metal oxides have been investigated as an alternative to vacuum-based oxides to implement low-cost, high-performance electronic devices on flexible transparent substrates. However, their electrical properties need to be enhanced to apply at industrial scale. Amorphous indium-gallium-zinc oxide (a-IGZO) is the most-used transparent semiconductor metal oxide as an active channel layer in thin-film transistors (TFTs), due to its superior electrical properties. The present work evaluates the influence of composition, thickness and ageing on the electrical properties of solution a-IGZO TFTs, using solution combustion synthesis method, with urea as fuel. After optimizing the semiconductor properties, low-voltage TFTs were obtained by implementing a back-surface passivated 3-layer In:Ga:Zn 3:1:1 with a solution-processed high-к dielectric; AlOx. The devices show saturation mobility of 3.2 cm2 V−1 s−1, IOn/IOff of 106, SS of 73 mV dec−1 and VOn of 0.18 V, thus demonstrati...
Applied Physics Letters, 2010
The effects of zinc concentration on the performance of solution processed amorphous indium gallium zinc oxide ͑a-IGZO͒ thin film transistors ͑TFTs͒ have been investigated using high-k aluminum titanium oxide as gate dielectric. The x-ray diffraction results confirmed that all the IGZO channel layers are amorphous. The performance of a-IGZO TFTs were investigated in the linear regime operation. Highest linear field-effect mobility of 5.8 cm 2 / V s with an I on / I off ratio of 6 ϫ 10 7 and subthreshold swing of 0.28 V/dec were obtained for the a-IGZO ͑311͒ TFTs. The obtained performance of the a-IGZO TFTs is very promising for low-voltage display applications.
Current Applied Physics, 2013
a b s t r a c t a-IGZO films were deposited on Si substrates by d.c sputtering technique with various working power densities (p d ) in the range of 0.74e2.22 W/cm 2 . The correlation between material properties and their effects on electrical stability of a-IGZO thin-film transistor (TFTs) was studied as a function of p d . At a p d of 1.72 W/cm 2 a-IGZO film had smoothest surface roughness (0.309 nm) with In-rich and Ga-poor cation compositions as a channel. This structurally ordered TFTs exhibited a high field effect mobility of 9.14 cm 2 /Vs, a sub-threshold swing (S.S.) of 0.566 V/dec, and an oneoff ratio of 10 7 . Additionally, the V th shift in hysteresis loop is almost eliminated. It was shown that the densification of the a-IGZO film resulted in the reduction of its interface trap density (1.83 Â 10 12 cm À2 ), which contributes for the improvement in the electrical and thermal stability.
Evaluation of Y2O3 gate insulators for a-IGZO thin film transistors
Thin Solid Films, 2009
TTFT (transparent thin film transistor) Leakage current Y 2 O 3 a-IGZO In this work, Y 2 O 3 was evaluated as a gate insulator for thin film transistors fabricated using an amorphous InGaZnO 4 (a-IGZO) active layer. The properties of Y 2 O 3 were examined as a function of various processing parameters including plasma power, chamber gas conditions, and working pressure. The leakage current density for the Y 2 O 3 film prepared under the optimum conditions was observed to be~3.5 × 10 − 9 A/cm 2 at an electric field of 1 MV/cm. The RMS roughness of the Y 2 O 3 film was improved from 1.6 nm to 0.8 nm by employing an ALD (Atomic Layer Deposition) HfO 2 underlayer. Using the optimized Y 2 O 3 deposition conditions, thin film transistors (TFTs) were fabricated on a glass substrate. The important TFT device parameters of the on/off current ratio, sub-threshold swing, threshold voltage, and electric field mobility were measured to be 7.0 × 10 7 , 0.18 V/dec, 1.1 V, and 3.3 cm 2 /Vs, respectively. The stacked insulator consisting of Y 2 O 3 /HfO 2 was highly effective in enhancing the device properties.
Journal of Sensor Science and Technology, 2013
We fabricated an a-IGZO thin film transistor (TFT) with AZO/Ag/AZO transparent multilayer source/drain contacts by rf magnetron sputtering. a-IGZO TFT with AZO/Ag/AZO multilayer S/D electrodes (W/L = 400/50 µm) showed a subs-threshold swing of 3.78 V/dec, a minimum off-current of 10-12 A, a threshold voltage of 0.41 V, a field effect mobility of 10.86 cm 2 /Vs, and an on/off ratio of 9 10 9. From the ultraviolet photoemission spectroscopy, it was revealed that the enhanced electrical performance resulted from the lowering of the Schottky barrier between a-IGZO and Ag due to the insertion of an AZO layer and thus the AZO/Ag/AZO multilayer would be very appropriate for a promising S/D contact material for the fabrication of high performance TFTs.
Electronics
We have investigated the effect of electron effective mass (me*) and tail acceptor-like edge traps density (NTA) on the electrical characteristics of amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) through numerical simulation. To examine the credibility of our simulation, we found that by adjusting me* to 0.34 of the free electron mass (mo), we can preferentially derive the experimentally obtained electrical properties of conventional a-IGZO TFTs through our simulation. Our initial simulation considered the effect of me* on the electrical characteristics independent of NTA. We varied the me* value while not changing the other variables related to traps density not dependent on it. As me* was incremented to 0.44 mo, the field-effect mobility (µfe) and the on-state current (Ion) decreased due to the higher sub-gap scattering based on electron capture behavior. However, the threshold voltage (Vth) was not significantly changed due to fixed effective acceptor-like traps (NTA). ...