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• 1. [Article] Evaluation of amorphous oxide semiconductors for thin film transistors (TFTs) and resistive random access memory (RRAM) applications

  Thin-film transistors (TFTs) are primarily used as a switching element in liquid crystal displays. Currently, amorphous silicon is the dominant TFT technology for displays, but higher performance TFTs ...

  Citation × Citation Citation Abstract Copy Title: Evaluation of amorphous oxide semiconductors for thin film transistors (TFTs) and resistive random access memory (RRAM) applications Author: Rajachidambaram, Jaana Saranya Thin-film transistors (TFTs) are primarily used as a switching element in liquid crystal displays. Currently, amorphous silicon is the dominant TFT technology for displays, but higher performance TFTs will become necessary to enable ultra-definition resolution high-frequency large-area displays. Amorphous zinc tin oxide (ZTO) TFTs were fabricated by RF magnetron sputter deposition. In this study, the effect of both deposition and post annealing conditions have been evaluated in regards to film structure, composition, surface contamination, and device performance. Both the variation of oxygen partial pressure during deposition and the temperature of the post-deposition annealing were found to have a significant impact on TFT properties. X-ray diffraction data indicated that the ZTO films remain amorphous even after annealing to 600° C. Rutherford backscattering spectrometry indicated that the Zn:Sn ratio of the films was ~1.7:1 which is slightly tin rich compared to the sputter target composition. X-ray photoelectron spectroscopy data indicated that the films had significant surface contamination and that the Zn:Sn ratios changed depending on sample annealing conditions. Electrical characterization of ZTO films using TFT test structures indicated that mobilities as high as 17 cm² V⁻¹ s⁻¹ could be obtained for depletion mode devices. It was determined that the electrical properties of ZTO films can be precisely controlled by varying the deposition conditions and annealing temperature. It was found that the ZTO electrical properties could be controlled where insulating, semiconducting and conducting films could be prepared. This precise control of electrical properties allowed us to incorporate sputter deposited ZTO films into resistive random access memory (RRAM) devices. RRAM are two terminal nonvolatile data memory devices that are very promising for the replacement of silicon-based Flash. These devices exhibited resistive switching between high-resistance states to low-resistance states and low-resistance states to high-resistance states depending on polarity of applied voltages and current compliance settings. The device switching was fundamentally related to the defect states and material properties of metal and insulator layers, and their interfaces in the metalinsulator-metal (MIM) structure. Title: Evaluation of amorphous oxide semiconductors for thin film transistors (TFTs) and resistive random access memory (RRAM) applications Author: Rajachidambaram, Jaana Saranya Thin-film transistors (TFTs) are primarily used as a switching element in liquid crystal displays. Currently, amorphous silicon is the dominant TFT technology for displays, but higher performance TFTs will become necessary to enable ultra-definition resolution high-frequency large-area displays. Amorphous zinc tin oxide (ZTO) TFTs were fabricated by RF magnetron sputter deposition. In this study, the effect of both deposition and post annealing conditions have been evaluated in regards to film structure, composition, surface contamination, and device performance. Both the variation of oxygen partial pressure during deposition and the temperature of the post-deposition annealing were found to have a significant impact on TFT properties. X-ray diffraction data indicated that the ZTO films remain amorphous even after annealing to 600° C. Rutherford backscattering spectrometry indicated that the Zn:Sn ratio of the films was ~1.7:1 which is slightly tin rich compared to the sputter target composition. X-ray photoelectron spectroscopy data indicated that the films had significant surface contamination and that the Zn:Sn ratios changed depending on sample annealing conditions. Electrical characterization of ZTO films using TFT test structures indicated that mobilities as high as 17 cm² V⁻¹ s⁻¹ could be obtained for depletion mode devices. It was determined that the electrical properties of ZTO films can be precisely controlled by varying the deposition conditions and annealing temperature. It was found that the ZTO electrical properties could be controlled where insulating, semiconducting and conducting films could be prepared. This precise control of electrical properties allowed us to incorporate sputter deposited ZTO films into resistive random access memory (RRAM) devices. RRAM are two terminal nonvolatile data memory devices that are very promising for the replacement of silicon-based Flash. These devices exhibited resistive switching between high-resistance states to low-resistance states and low-resistance states to high-resistance states depending on polarity of applied voltages and current compliance settings. The device switching was fundamentally related to the defect states and material properties of metal and insulator layers, and their interfaces in the metalinsulator-metal (MIM) structure. Close

• 2. [Article] Fabrication process assessment and negative bias illumination stress study of IGZO and ZTO TFTs

  Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. ...

  Citation × Citation Citation Abstract Copy Title: Fabrication process assessment and negative bias illumination stress study of IGZO and ZTO TFTs Author: Hoshino, Ken Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. Unpassivated IGZO and ZTO TFTs suffer from severe NBIS instabilities. Zinc-tin-silicon oxide is found to be an effective passivation layer for IGZO and ZTO TFTs, significantly improving the NBIS stability. NBIS instabilities in unpassivated TFTs are attributed to an NBIS-induced desorption of chemisorbed oxygen from the channel layer top surface, exposing surface oxygen vacancies. A ZTSO layer protects the channel layer top surface from adsorbed gas interactions and also appears to reduce the density of oxygen vacancies. The best device architectures investigated with respect to TFT electrical performance are found to be staggered with aluminum electrodes for unpassivated TFTs and coplanar with ITO electrodes for ZTSO-passivated TFTs. Annealing in wet-O₂ is not found to be effective for improving the performance of IGZO or ZTO TFTs or for reducing the post-deposition annealing temperature. Title: Fabrication process assessment and negative bias illumination stress study of IGZO and ZTO TFTs Author: Hoshino, Ken Indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) are investigated for thin-film transistor (TFT) applications. Negative bias illumination stress (NBIS) is employed for electrical stability assessment. Unpassivated IGZO and ZTO TFTs suffer from severe NBIS instabilities. Zinc-tin-silicon oxide is found to be an effective passivation layer for IGZO and ZTO TFTs, significantly improving the NBIS stability. NBIS instabilities in unpassivated TFTs are attributed to an NBIS-induced desorption of chemisorbed oxygen from the channel layer top surface, exposing surface oxygen vacancies. A ZTSO layer protects the channel layer top surface from adsorbed gas interactions and also appears to reduce the density of oxygen vacancies. The best device architectures investigated with respect to TFT electrical performance are found to be staggered with aluminum electrodes for unpassivated TFTs and coplanar with ITO electrodes for ZTSO-passivated TFTs. Annealing in wet-O₂ is not found to be effective for improving the performance of IGZO or ZTO TFTs or for reducing the post-deposition annealing temperature. Close