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1. INTRODUCTION SNO film was used to manufacture a MOSFET transistor. The film deposited by RF magetron sputtering was not phase pure, as apart from the main phase contained Sm2O3, NiO, Sm2Si2O7, Sm2SiO5 (56). It had a MI transition at 130 ◦C and a surface roughness of Ra = 1.32 nm and RMS = 1.88 nm which is acceptable for film gate insulators. Figure 1.12: Application of the SNO film as a transistor and capacitor - Prototypes of a MOS capacitor (a) and MOSFET transistors (b) based on thin film of SNO as a gate material (56) The measured structural parameters and capacitance allowed estimation of dielectric constant as 26 and equivalent oxide thickness tSNO x (kSiO2/kSNO) as 100 nm. Capacitance vs. gate voltage curves were found to be asymmetric and hysteretic and temperature dependent as well. The asymmetry was seen as a shift of curve towards lower gate voltages, with a peak capacitance at -1.9 V at all temperatures (RT up to 415 K). It was explained to be a result of nonuniform work function of electrodes and internal electric field. The hysteresis occurred with the direction of sampling of the gate voltage. By analogy to SrTiO3 the authors ascribed the hysteresis to excess space charge (SC) caused by oxygen vacancies. The oxygen vacancies would occur due to instability of Ni3+ ions. Application of external electric field would de-trap electron and make the otherwise neutral vacancies - positively charged. Thus variation of internal electric field by the vacancies would influence polarization and reduce the dielectric permittivity of the crystal. Both in MOS and MOSFET with SmNiO3 the gate capacitance is hysteretic and frequency dependent. However in MOSFET device the hysteresis is coun- terclockwise, which is opposite to MOS. This was written to be consistent with polarization switching, alike in C-V characteristics of a transistor. It was said to be a gate-field effect as there was a treshold voltage shift with absence of channel current. It occurs also at room temperature. All this was explained as effect of space charge polarization in SNO film. Also the state retention was seen to decay 32PDF Image | Investigation of metal-insulator transition in magnetron sputtered samarium nickelate thin films
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