Research On The Local Piezoelectricity And Ferroelectricity Of The Thin Film HfLaO_x Of The Stress Luminescent Material CaTiO₃:Pr³⁺

Since piezoelectricity was reported in 1880,people have made deep research on the development of piezoelectric materials and the force-electricity coupling effect.Piezoelectric property refers to the phenomenon that some crystals are polarized under the action of external stress,and equal charge is generated on both surfaces in the vertical direction of force.Ferroelectric property refers to the phenomenon that spontaneous polarization also exists in crystals without external stress.Piezoelectric materials are widely used in drivers,sensors and so on,and piezoelectricity is also considered to play an important role in mechanoluminescence(ML).Ferroelectric is a special kind of piezoelectric material,which has broad application prospects in memory and large-scale integrated circuit components.However,the research on piezoelectricity/ferroelectricity on micro scale and the research on regularity are limited.The microscopic origin and mechanism of piezoelectricity and ferroelectricity of new materials are unclear.Piezoresponse force microscopy(PFM)is an effective means to characterize piezoelectricity at micro scale based on inverse piezoelectric effect.In this paper,p PFM is used to study the piezoelectricity of ML materials and the ferroelectricity of ferroelectric ultrathin films on micro scale,and the role of piezoelectricity in ML mechanism is explored,and the ferroelectricity of thin films is characterized by nonlinear resonance response test method.The research content of this paper includes the following two aspects:(1)Investigation of local piezoelectricity induced ML mechanism in CaTiO₃:Pr³⁺materials.Recoverable mechanoluminescence(RML)has shown attractive potential in diverse fields of stress sensors,lighting,displays,and bio-excitation.However,efficient RML materials are universally constructed with non-centrosymmetric lattice as the matrix,encountering limitation in obtaining centrosymmetric-lattice availability.In this work,we report a RML in the well-known persistent phosphor CaTiO₃:Pr³⁺with a centrosymmetric structure,which exhibits intense,reproducible and quantitative emission under the stimulation of mechanical compression and friction.The systematic investigations of thermoluminescence and PFM indicate that local piezoelectricity caused by structural defects plays a key role in de-trapping the electrons captured by traps,thereby generating recoverable piezoluminescence in CaTiO₃:Pr³⁺.Our results reveal the availability of centrosymmetric lattice as the material matrix to achieve high-efficiency RML,which is expected to broaden the horizons of designing novel RML materials.(2)Investigation on ferroelectric properties of La-doped Hf O₂ ferroelectric thin films on Ga As compound semiconductors.The ultra-thin hafnium-based oxide gate dielectric film will show ferroelectric properties under strain control,and then showing negative capacitance effect in the device to reducing the standard switching power loss of FET devices.Ga As-based compound semiconductors have been widely used in microelectronic devices as substrates of high mobility devices,but the ferroelectric properties of thin films based on Hf O₂ on Ga As compound semiconductors have not been well characterized.In this paper,La-doped Hf O₂ultrathin films with a thickness of 5 nm were prepared on Ga As semiconductor by atomic layer deposition(ALD).The ferroelectric properties of Hf La Ox ultrathin films on Ga As substrates were characterized by using the new technology of PFM.The results show that strain is introduced into 5 nm Hf La Ox thin films by annealing,which leads to the intrinsic ferroelectricity of Hf La Ox thin films.These research results provide experimental basis for the fabrication of ferroelectric negative capacitance transistors,and are expected to support the development of low-power devices and promote the development of portable devices and Internet of Things.