Study On Ion-implantation And Exfoliation Mathods For The Fabrication Of Single Crystallline Lithium Niobate Thin Film

Lithium niobate?LiNbO₃,LN?,as a kind of synthetic crystal,has excellent piezoelectric,photoelectric and ferroelectric properties.As the development of devices towarding high-density integration and miniaturization,there is an urgent demand on the fabrication of high quality LN thin films on Si substrate.However,deposition of LN thin films remains a difficult task due to the lattice mistach and the volatility of Lithium,thus the crystallization quality and physical properties of LN films deposited using traditional thin film techniques are much worse than those of LN single crystals.In this thesis,the fabrication of submicrometer thick single crystalline LN thin films based on wafer bonding and ion slicing processes is studied,in order to provide high quality LN thin film material for related devices.The main contents of this thesis include following aspects:Firstly,the heterogeneous wafer bonding of LN on Si with BCB is investigated.The influences of spinning-coating rotate speed,pre-baking temperature and pre-baking time on the pre-bonding quality were studied;the effects of bonding pressure,curing temperature,curing time and temperature curve on the bonding quality were studied.The results showed that setting the spinning speed 3000 r/min,pre-baking temperature at 90? and pre-baking time 80 s results in the best pre-bonding quality.It lead to failure of pre-bonding when the pre-baking temperature was too high or pre-baking time was too long,and it lead to spilling of BCB if the pre-baking temperature was too low or pre-baking time was too short.During the bonding process,a bonding pressure higher than 1 MPa causes the crash of LN substrate,and a bonding pressure lower than 0.4 MPa causes the inperfection of bonding layer.The curing time and curing temperature is inversely proportional.When the curing temperature was higher than 300? or the heating rate is faster than 2.5?/min,the LN substrate crashes.Finally,the optimal bonding conditions of LN on Si with BCB are: bonding pressure of 0.8 MPa,curing temperature of 250?,and heating rate of 2?/min.Secondly,submicrometer thick LN thin films were successfully transferred onto Si substrate by ion slicing.The effect of annealing temperature on the exfoliation of He+ ion-implanted LN was studied.The effects of bonding pressure,annealing temperature,annealing time and annealing temperature curve on the quality of LN films were studied.The results showed that when the He+ dose was 2×1016 ions/cm2,the surface blistering occurs when the annealing temperature was 225?.The implantation dose and annealing temperature were inversely proportional.When the LN film was transferred,under the conditions that the bonding pressure was between 0.7 MPa to 0.9 MPa,the annealing temperature was between 250? and 275?,and the annealing time was above 200 min,and the temperature curve was lower than 2oC/min,LN film could be obtained.Finally,the optimal conditions for the fabrication of LN films are: bonding pressure of 0.7 MPa,annealing temperature of 250?,annealing time of 250 min,and ramping and cooling rate of about 1?/min.The structural analysis of LN thin films by X-ray diffraction showed that the transferred LN films were single crystalline,and the piezoelectric coefficient of LN films was measured to be 52.6 pm/V.