9:30 AM - 9:45 AM
▲ [20a-G203-3] Temperature Dependence of Transverse Resistance and Bipolar Switching in Ge-Sb-Te Films upon Annealing
Keywords:bipolar switching, thermal annealing, scanning probe microscopy
Applications of Ge-Sb-Te (GST) phase change materials for memory and quantum computing have relied on efficient electrical switching between different structural phases. Such phase transition involves displacement of atoms, and is sensitive to residual stress and annealing conditions.[1,2] Here, in order to elucidate electric switching behavior, temperature dependence of the surface potential and transverse resistance in GeSbTe alloy and crystalline superlattice (CSL) grains was investigated upon thermal annealing by conductive scanning probe microscopy (C-SPM).
Samples of amorphous Ge2Sb2Te5 (GST 225) alloy films and [(GeTe)2/ Sb2Te3]n SL (n=4 and 8) were prepared by the sputtering method.[3] The films were prepared on Si and sapphire substrates with pre-deposited tungsten film (50nm). GST225 alloy films were deposited at room temperature. The SL films were grown at 230oC on top of a seed Sb2Te3 layer to form crystal films confirmed by X-ray diffraction and TEM. Point I-V spectra and the surface potential maps were obtained with Ta and PtIr-coated AFM cantilevers employing a Shimadzu SPM 9700 system operating in a contact mode and a Kelvin probe mode in Ar gas. The sample temperature ramp was about 2 degree/minute in a range of 30-220oC.
The data show significant changes in I-V hysteresis at 30 and ~80oC for the crystal films. At a high resistance state (OFF-state), abrupt change in the R-T slope from positive to negative values is an indication of the transition between metallic-like and semiconducting behavior around 80oC. The M-S transition correlated with changes in (i) the switching voltage, (ii) the carrier activation energy and (iii) the surface potential, the indication of substantial changes in the electronic band structure at the M-S transition temperature. Difference in the transition temperature for annealed GST alloy and SL films suggests the stronger effect of residual stress in SL films, which has been predicted.[2]. The results emphasizes the role of thermal annealing for optimizing the device performance.
The work was supported by grant no. JPMJCR14F1 of the Japan Science and Technology Agency (JST/CREST) [1] J. Tominaga et.el. Adv. Funct. Mater. 27, 1702243 (2017); [2] ASC Appl. Mater. Interfaces 9, 23918 (2017); [3] Phys. Status Solidi B 252, 2151 (2015)
Samples of amorphous Ge2Sb2Te5 (GST 225) alloy films and [(GeTe)2/ Sb2Te3]n SL (n=4 and 8) were prepared by the sputtering method.[3] The films were prepared on Si and sapphire substrates with pre-deposited tungsten film (50nm). GST225 alloy films were deposited at room temperature. The SL films were grown at 230oC on top of a seed Sb2Te3 layer to form crystal films confirmed by X-ray diffraction and TEM. Point I-V spectra and the surface potential maps were obtained with Ta and PtIr-coated AFM cantilevers employing a Shimadzu SPM 9700 system operating in a contact mode and a Kelvin probe mode in Ar gas. The sample temperature ramp was about 2 degree/minute in a range of 30-220oC.
The data show significant changes in I-V hysteresis at 30 and ~80oC for the crystal films. At a high resistance state (OFF-state), abrupt change in the R-T slope from positive to negative values is an indication of the transition between metallic-like and semiconducting behavior around 80oC. The M-S transition correlated with changes in (i) the switching voltage, (ii) the carrier activation energy and (iii) the surface potential, the indication of substantial changes in the electronic band structure at the M-S transition temperature. Difference in the transition temperature for annealed GST alloy and SL films suggests the stronger effect of residual stress in SL films, which has been predicted.[2]. The results emphasizes the role of thermal annealing for optimizing the device performance.
The work was supported by grant no. JPMJCR14F1 of the Japan Science and Technology Agency (JST/CREST) [1] J. Tominaga et.el. Adv. Funct. Mater. 27, 1702243 (2017); [2] ASC Appl. Mater. Interfaces 9, 23918 (2017); [3] Phys. Status Solidi B 252, 2151 (2015)