High Mobility Flexible Amorphous IGZO Thin-Film Transistors with a Low Thermal Budget Ultra-Violet Pulsed Light Process.

Transcription

1 High Mobility Flexible Amorphous IGZO Thin-Film Transistors with a Low Thermal Budget Ultra-Violet Pulsed Light Process. M. Benwadih 1*, R. Coppard 1, K. Bonrad 2, A. Klyszcz 2, D. Vuillaume 3 1 : Univ. Grenoble Alpes, CEA, F Grenoble, France 2: Merck TU-Darmstadt Laboratories, Darmstadt, Germany 3 : Institute for Electronics Microelectronics and Nanotechnology, CNRS, University of Lille, 59652, Villeneuve d'ascq, France * corresponding author: mohammed.benwadih@cea.fr SUPPORTING INFORMATION 1. Spectral emission of the UV. We used the pulsed UV light equipment Sinteron 2000 (Xenon company) with the lamp B, which has the spectral emission shown in Fig. S1 and a spectral cut-off at 240 nm. Figure S1. Spectral cut-off wavelengths

2 2. UV-vis absorption of IGZO film The absorption spectrum of the IGZO thin film was measured with an ultraviolet visible (UV-Vis) spectrophotometer Perkin Elmer LAMBDA 950. Quartz substrates were used to minimize interferences during transmittance measurements. Figure S2 shows UV absorption spectra of the precursor solutions used for IGZO film preparation, and of IGZO films on glass substrates. Figure S2. Absorption spectra of IGZO solution and film. The IGZO solution (in 2 methoxyethanol) and the IGZO film exhibit a strong light absorption below 350 nm. Irradiation at these wavelengths facilitates the metal-oxygen-metal (M-O-M) condensation of the photochemical activated precursor molecules. [1] 3. Thermal stability of Kapton.

3 The analysis was carried out up to 400 C under air flow. Figure S3 shows the mass loss (in black) and differential thermal analysis (blue). From the evolution of the mass loss of Kapton, only degassing steps at 30 C and 176 C are detected resulting in a slight loss of mass given rise to a decrease of about 1% of the TGA signal and a peak on the DSC signal. We conclude that Kapton can therefore withstand temperatures of about 350 C for 1h. Figure S3. TGA and DSC analysis of Kapton Inset : zoom of the TGA curve.

4 4. Surface morphology of Kapton and smoothing. The roughness of the Kapton was measured by interferometric profilometry (see Experimental Section). The surface is indeed very rough, and has many defaults with very large peak heights (typically 2 µm height) and large areas (diameters larger than 5 µm) (Figure S4). The roughness of the interface between the semiconductor and the substrate can disrupt the charge carrier mobility in the channel of the TFT. In the case of a top gate architecture, if the thickness of the semiconductor layer is insufficient, excessive roughness of the surface of Kapton may cause areas without IGZO film. A method to reduce the surface roughness is to deposit an insulating organic smoothing layer between the substrate and the semiconductor. In our case, the deposition of a smoothing polyimide layer PI2611 from HD MicroSystems greatly reduces the roughness and covers the major defects of Kapton (Figure S4). This smoothing layer has two advantages: first, it has the same chemical nature as the substrate and, it is resistant to high temperatures (up to 350 C). [2] After smoothing, a low roughness value is finally measured, in the range of 11 nm. This allows to process IGZObased transistors with a top gate architecture.

5 Kapton a) Kapton+PI2610 (3µm) b) Figure S4. Interferometric profilometry images of the surface of : a) Kapton and b) coated Kapton with smoothing polyimide layers. 5. Histograms of electron mobilities. Figure S5 compares the electron mobilities for the IGZO TFTs with the photonic annealing fabricated on Si/SiO 2 and Kapton substrates. 16 devices were measured for 300 C/1 min 50 flashes and 350 /1min 50 flashes. Fig. S5-b clearly shows that the mobility data are more dispersed for TFTs on Kapton than on Si/SiO 2 substrate.

6 a) b) Figure S5. Electron mobilities histogram for IGZO on (a) Si/SiO 2 and (b) Kapton.

7 6. Electrical characteristics of Ti-Au/polymer/Au capacitors. Figure S6 shows the typical current density as a function of voltage for capacitors fabricated on Kapton substrates. Figure S6. Electrical characteristics of Ti-Au/polymer/Au capacitors. All polymers have a thickness of 400 nm (50 nm/350 nm for PS/PVP bilayer). 7. SEM of IGZO thin films. The IGZO TFTs measured in this work have 4 layers with a total thickness of the IGZO film around 20 nm. 4 layers 20 nm

8 Figure S7. Cross-section observations of IGZO thin films (4 layers). REFERENCES (1) Kim, Y. H.; Heo, J. S.; Kim, T. H.; Park, S.; Yoon, M. H.; Kim, J.; Oh, M. S.; Yi, G. R.; Noh, Y. Y.; Park, S. K. Photo-Activation of Solution-Processed Metal-Oxide Semiconductors by DUV. Nature. 2012, 489, (2) Jang, J.; Choi, M. H.; Kim, B. S.; Lee, W. G.; Seok, M. J.; Ryu, D. S. Robust TFT Backplane for Flexible AMOLED. SID Symposium Digest of Technical Papers, 2012, Volume 43, Issue 1, pages