Experimental Study On Field Effect Of Amorphous HfO₂/Crystal STO Interface

In recent years,various experiments have shown that Quasi two-dimensional electron gas(Q2DEG)occurs when SrTiO₃ is bombarded by Ar⁺,which makes it possible for SrTiO₃ to change from an insulating state to a semiconductor.Traditional gate oxides cannot meet development needs during the development process,and high-K(dielectric constant)gate oxides have attracted attention.HfO₂ has the characteristics of high dielectric constant and good contact with the substrate.It is considered as a substitute for the next generation of gate oxide.This paper studies the TDDB characteristics of the amorphous HfO₂ gate dielectric layer,and evaluates the quality of the amorphous HfO₂gate dielectric.The focus is on the characteristics of amorphous HfO₂/crystalline STO field effect transistors.The channel is the surface conductive layer produced by Ar⁺bombarding the SrTiO₃ crystal.The insulating layer of the gate dielectric layer is the amorphous HfO₂ film prepared by RF magnetron sputtering.The metal electrode is DC magnetron sputtering.Ti/Pt electrode prepared by DC magnetron sputtering.The research content of this article mainly includes the following three aspects:1.Evaluate the quality of the gate oxide amorphous HfO₂ film.First,study the leakage mechanism of Pt/HfO₂/Pt samples.At room temperature,the gate voltage of the sample of the Pt/HfO₂/Pt structure between 0 V and 1 V conforms to the space charge limited current(SCLC)mechanism,and the voltage between 1 V and 2 V conforms to the Schottky emission effect.Then the TDDB characteristics of the amorphous HfO₂ gate dielectric layer are studied.The test samples were studied at a temperature of 300 K and voltage stresses of 3 V,4 V,and 5 V.Through calculation,it is found that under 3 V,4 V,and 5 V stress,the characteristic life(?)is 15 s,40 s,265 s,and the shape parameter(?)value is 1.21,1.28,1.31,respectively.When the electric field strength is 0.05 MV/cm and the failure rate is 50%,the expected working life is 6901 h.Finally,the dielectric constant of the MOS structure capacitor is corrected and calculated.The experimentally prepared MOS capacitor has contact resistance.In order to deduct the influence of the contact resistance,the corrected dielectric constant is calculated by impedance spectroscopy and Debye relaxation.At high frequencies,the dielectric constant values of 100 K,200 K,and300 K before fitting are larger than those after fitting,and the maximum difference is about 0.2 F/m,0.23 F/m,0.1 F/m.2.Study the performance of amorphous HfO₂/crystalline STO field effect transistors.Firstly,the transport properties of SrTiO₃ conductive layer bombarded by Ar⁺at different temperatures are studied.Ar⁺bombarded the surface of SrTiO₃ crystals to introduce oxygen vacancies.Since most carriers are electrons,the sample is n-type conductivity.The test temperature is 4 K to 300 K.As the temperature increase,the carrier concentration data increases between 10¹⁴ cm^-3?10¹⁵ cm^-3;the mobility of the sample carrier also decreases,which leads to the increase of the conductivity of the sample.The mobility decreased from 1005 cm²V^-1s^-1 at 4 K to 2.5 cm²V^-1s^-1 at 300 K.Then the field effect characteristic curve of the sample is analyzed,and the test temperature is 100 K,200 K and 300 K.Observing the I_DS-V_DS curve of the sample shows that the gold-half contact of the sample is an ohmic contact.The analysis of the transfer characteristic curve and the output characteristic curve of the sample found that as the temperature decreases,the switching ratio of the device decreases from 10⁵ at 300 K to 10³ at 100 K,and the threshold voltage drift distance is less than 2 V,which is a common characteristic of oxides.As the temperature decreases,the field-effect mobility is also decreasing,and the sub-threshold swing is also decreasing at the same time,indicating that the gate voltage can enhance the control of the channel.Finally,the stability of the sample was tested at100 K,200 K and 300 K,and it was stable after 10 tests.The threshold drift before and after the test was less than 1 V.It can be seen that the experimentally prepared amorphous HfO₂/crystalline STO field effect transistor is relatively stable at the same temperature.3.Study the C-V characteristics of field effect transistors.Prepare MOS capacitors with the same process as amorphous HfO₂/crystalline STO field effect transistors.When the temperature is 100 K,200 K and 300 K,the oxygen vacancy equivalent doping concentration is 2.99×10¹⁹ cm^-3,5.50×10¹⁸ cm^-3,7.94×10¹⁷ cm^-3,respectively.The C-V curve of the LCR test is a typical MOSFET capacitor C-V curve.At different temperatures and at the same frequency,the absolute value of the gate bias voltage keeps increasing,and the capacitance value keeps decreasing,and the hysteresis window of the CV curve also shows an increasing trend.As the V_GS increases,the applied bias will expand the depletion zone and cause Ar⁺bombardment.The conductive region formed by SrTiO₃com becomes narrower,and the doping concentration gradually decreases.