Diffusion-activated high performance ZnSnO/Yb2O3 thin film transistors and application in low-voltage-operated logic circuits

doi:10.1016/j.jmst.2020.08.042

Abstract

Abstract:

The flourishing metal-oxide high-k dielectric materials have been regarded as the vital components of low voltage operated flexible transparent electronic devices. We herein report that ytterbium oxide (Yb₂O₃) and ZnSnO (ZTO) thin films were firstly integrated into ZTO-based thin film transistors (TFTs) with superior performance. Results have indicated that the 500 ℃-annealed ZTO/Yb₂O₃ TFTs possess the large saturation mobility of 9.1 cm ² V ^-1 S ^-1 and the high on/off current ratio of 2.15 × 10 ⁷, which even surpass those of reported In-based TFTs. The deteriorative electrical properties in the aging process can be attributed to the carrier capture mechanism. However, the 460 ℃-processed TFTs demonstrate a tenfold increase in saturated mobility and an increase in on/off current ratio after 10 days aging. The inspiring electrical properties are attributed to the diffusion-activated carrier enhancement mechanism and electrons donor role of water molecular, which introduces a facile method to boost the device performance at lower processing temperatures. The neglected threshold voltage variations of 0.06 V and -0.2 V have been detected after bias stability experiments. The superior bias stability can be attributed to the charge delay effect induced by the continuous electric field. Meanwhile, the ultrahigh on/off current ratio of 1.1 × 10 ⁷ and the recoverable transferring performance have verified the aging-activated mechanism. To confirm its potential application in digital circuits, a resistor-loaded inverter with gain of 5.6 has been constructed and good dynamic response behavior have been detected at a low voltage of 2 V. As a result, it can be concluded that the high temperature annealing TFTs need immediate encapsulation, while the performance of the lower temperature processing samples can be optimized after aging treatment, indicating the potential prospect in low power consumption large-scale flexible transparent devices.

Key words: Ytterbium oxide (Yb₂O₃), Thin-film transistors (TFTs), Diffusion-activated, Bias stability, Inverter

Bing Yang, Gang He, Wenhao Wang, Yongchun Zhang, Chong Zhang, Yufeng Xia, Xiaofen Xu. Diffusion-activated high performance ZnSnO/Yb₂O₃ thin film transistors and application in low-voltage-operated logic circuits[J]. J. Mater. Sci. Technol., 2021, 70: 49-58.

Figures/Tables 12

Fig. 1. (a) Optical transmission spectra of Yb2O3 thin films annealed at different temperatures. The inset shows the Tauc plots of the corresponding Yb2O3 thin films. (b) TG result of Yb2O3 xerogel with a heating rate of 5 ℃ min-1. (c) XRD pattern of Yb2O3thin films as a function of annealing temperature.

Fig. 2. (a) O 1s XPS spectra for Yb2O3 thin films as a function of annealing temperature. (b) Semiquantitative analyses of the oxygen component for the corresponding Yb2O3 thin films. (c) Yb 4d XPS spectra for Yb2O3 thin films as a function of annealing temperature.

Fig. 3. AFM images of Yb2O3 thin films annealed at different temperatures of 310 ℃ (a), 410℃ (b), and 510 ℃ (c).

Fig. 4. (a) Frequency dependent areal capacitance of Yb2O3thin films annealed at different temperatures. The inset shows frequency dependent dielectric constant of Yb2O3 thin films annealed at different temperatures. (b) Leakage current density of Yb2O3 thin films annealed at various temperatures.

Table 1 Electrical parameters of ZTO TFTs at various annealing processing and aging conditions.

Sample	μ_sat (cm² V^-1 S^-1)	I_on/I_off	V_TH(V)	SS (V dec^-1)
420 °C-ZTO/Yb₂O₃ without aging	0.018	5.8 × 10⁴	0.9	0.21
460 °C -ZTO/Yb₂O₃ without aging	0.556	1.4 × 10⁵	1.25	0.11
500 °C -ZTO /Yb₂O₃ without aging	9.1	2.15 × 10⁷	1.7	0.12
420°C-ZTO/Yb₂O₃ aging for 10 days	0.77	5.3 × 10⁶	1.27	0.07
460°C-ZTO/Yb₂O₃ aging for 10 days	5.9	8.7 × 10⁶	1.0	0.064
500°C-ZTO/Yb₂O₃ aging for 10 days	6.5	1.8 × 10⁵	0.7	0.098
420°C-ZTO/Yb₂O₃ aging for 20 days	0.68	8.17 × 10	-0.25	0.91
460°C-ZTO/Yb₂O₃ aging for 20 days	3.6	1.0 × 10⁵	0.05	0.12
500°C-ZTO/Yb₂O₃ aging for 20 days	3.97	6.8 × 10⁴	0.08	0.12
500°C-ZTO/Yb₂O₃ aging for 30 days	3.37	2.13 × 10⁴	0.16	0.21
500°C-ZTO/Yb₂O₃ aging for 40 days	1.17	5.7 × 10³	0.41	0.27
500°C-ZTO/ZrO₂¹⁵	2.5	10⁶	1.0	0.23
500°C-ZTO/DyO_X¹⁶	2.5	2.4 × 10⁶	0.5	0.08
500°C-ZTO /Gd₂O₃¹⁷	1.9	6 × 10³	0.82	0.76
600°C-In₂O₃ /SrO_X¹⁹	5.61	10⁷	1.23	0.11
510°C-ZTO/ZrGdOx²⁰	3.1	3.3 × 10⁵	0.5	0.091
500°C-In₂O₃ /Yb₂O₃²¹	4.98	10⁶	0.38	0.07

Fig. 5. (a) Transfer characteristics of the ZTO/Yb2O3 TFTs as a function of annealing temperature of ZTO layer without aging treatment. (b) Transfer characteristics of the ZTO/Yb2O3 TFTs as a function of annealing temperature of ZTO layer aged for 10 days. The inset is the transfer characteristics of 10 days aged ZTO/Yb2O3 TFTs at the low operating voltage of 2 V. (c) Transfer characteristics of the ZTO/Yb2O3 TFTs as a function of annealing temperature of ZTO layer aged for 20 days. The inset is the output characteristics of the ZTO/Yb2O3 TFTs as a function of annealing temperature of ZTO layer. (d) Transfer characteristics of the 500 °C ZTO/510 ℃ Yb2O3 TFTs aged for various days.

Fig. 6. (a) The schematic diagram of diffusing H2O from the air ambient to the TFT. (b) The energy band comparison of H2O diffused film.

Fig. 7. (a) Two channel surface conduction modes of ZTO/Yb2O3 TFTs as well as the leakage current path resulting from grain boundary and interface defect. (b) The model of electron transmission in aging diffusion. (c) Model of biased interface change under PBS and NBS experiments.

Fig. 8. (a) Transfer curves of ZTO/Yb2O3 TFTs under PBS tests. (b) The VTH shift as a function of stress time. The inset shows the time dependence of ΔVTH in the ZnSnO/Yb2O3 TFTs under the bias stress of 1.5 V.

Fig. 9. (a) The immediate second PBS result of 460 ℃C-ZTO/510 ℃-Yb2O3 TFTs and recovery under the 1.5 V bias voltage. (b) NBS result and recovery under the -1.5 V bias voltage.

Fig. 10. (a) Transfer curves of aged 40 days ZTO/Yb2O3 TFTs under PBS tests. (b) The VTH shift as a function of stress time. The inset shows the time dependence of ΔVTH in the ZnSnO TFT with the Yb2O3 gate dielectric under the bias stress of 1.5 V.

Fig. 11. (a) The resistor-loaded inverter structure with 460 ℃-ZTO/510 ℃-Yb2O3 TFTs. (b) The voltage transfer characteristic (VTC) curves Voltage at various VDD values. (c) The gains of the inverter at various VDD values. (d) Dynamic switching behavior of the inverter under AC square waves at 1 Hz.

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Diffusion-activated high performance ZnSnO/Yb₂O₃ thin film transistors and application in low-voltage-operated logic circuits

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