Research On Preparation Of Er Doped Aluminum Nitride Thin Films On Sapphire Substrate

Recently,many MEMS devices such as resonators,filters,switches,energy harvesters,ultrasonic transducers,microphones,strain sensors,chemical sensors,and accelerometers were widely used in industry and daily life of people.With the rapid development of communications industry,communications system and devices gradually tend to possess many characteristics including high properties,high frequency,intergration,high stability,miniaturization and so on.Consequently,how to change and improve the properties of piezoelectric films has become research goals of relavant scientists.This paper deposited Er-doped AlN films on sapphire substrates using RF reactive sputtering.Combined with many test results including XRD,SEM,AFM,PFM,ferroelectric test system,automatic scratch tester and so on,we systematically studied the influence of sputtering parameters on crystal structure,surface morphology,electrical and mechanical property of ErAlN films.The main research results are as follow:1.Reaserch about influence of different sputtering parameters on crystal strcture and surface morphology of films:With the increasing of sputtering power,crystal orientation firstly becomes better,reaching the best state at 250W,then the intensity of（002）starts decreasing as well as crystal quality.Besides,with increasing power from 140W to 250W,the uniformity and density of films improves while the surface roughness decreases.Then some grains start growing unuaually and some clusters and cavity come out,increasing the roughness.When N₂ concentration increases from 20%to 25%,the intensity of（002）peak enhances apparently.The intensity of（002）peak does not keep improving and the crystal quality decreases with further increasing N₂ concentration.On the other hand,the grains become uniform and dense gradually with increasing N₂ concentration while they grow unusually and some clusters come out with further increasing N₂concentration.Correspondingly,the surface roughness firstly decreases and then improves.The（002）orientation becomes better when sputtering pressure increases from 0.6Pa to 0.8 Pa.However,it starts decreasing and weak（100）peak comes out,causing crystal quality worsing when continuously increasing pressure.In the meantime,the grains become denser and the roughness becomes higher as the pressure improves.With further increasing pressure,some grains becomes bigger and some clusters appear,which improves the roughness.At the range of 100-500℃,with increasing temperature,the intensity of（002）peak firstly improves and then decreases,achieving the highest value and orientation at200℃.Besides,with increasing temperature,the grains firstly become denser and the surface roughness becomes higher.Then some grains become bigger unusually and some defects like cavity,texture and threading dislocation appear,resulting in high roughness.2.Reaserch about electrical property of films:The change of insulating property of films on sputtering parameters is simarly with the change of crystal quality on sputtering parameters.Usually,more excellent crystal quality results in higher resistivity,lower leakage current and better insulating property.And the dielectic constant and piezoelectric constant decreases with increasing the FWHM of rocking curves.The smaller FWHM leads to better crystal orientation and more excellent dielectric and piezoelectric property.In our paper,the biggest d₃₃ of ErAlN films is 9.41pm/V,which is almost twice larger than that of AlN.3.Research about element component and adhesion between film and substrateWe tested the element component of ErAlN films by EDS,and the results indicate the existence of Er element,which is close with the theory value.In addition,we studied the adhension between film and substrate by automatic scratch tester,and it shows that critical load between ErAlN film and sapphire substrate is 22.6N,which completely meets the needs of devices.