Energy Storage And Pyroelectric Properties Of Silicon-doped Hafnium Oxide Antiferroelectric Thin Films

Recently,many portable,wearable,and implantable electronic devices are incorporated with our daily lives,which have several key components,such as energy harvesters,energy storage elements,sensors,data storage elements,and cooling elements.With the advancement of semiconductor technology,the sizes of these components are shrinking with time.In the past,several materials(such as polymers-based,ceramics-,single crystal-,and glass-based)have been studied for energy-related applications.However,due to a large deposition thickness,complicated composition,and poor compatibility with existing Si-based complementary metal-oxide-semiconductor(CMOS)technology,these materials cannot be appropriate for future devices.In 2011,Boscke et al.first reported the ferroelectric(FE)and antiferroelectric(AFE)properties in HfO2-based thin films.HfO2-based materials manifest numerous properties as compared to the conventional materials,such as a low deposition thickness(in nm scale),simple composition,compatibility with CMOS technology,mature atomic layer deposition process,and suitability for the integration within 3-dimensional(3-D)nanostructures.HfO2-based FE materials are appropriate for memory applications,such as ferroelectric random-access memory(FeRAM)and ferroelectric field-effect transistor(FeFET).On the other hand,HfO2-based AFE materials can be used for energy-related applications,such as energy harvesting,energy storage,inferred detection,and solid-state cooling.Si-doped HfO2(Si:HfO2)AFE materials can exhibit excellent energy storage properties.However,the existing research has a lack of study on electrical characterization of Si:HfO2 AFE thin films,especially the lack of in-depth exploration of temperature stability,frequency dependency,and endurance properties.Si:HfO2 AFE thin films also exhibit excellent electrocaloric and pyroelectric properties.However,a detailed investigation is needed to evaluate the feasibility of using this AFE material in future cooling devices.The aim of this research is a detailed experimental investigation of electric field amplitude(from 0.25 up to 4.5 MV/cm),temperature(210-400 K),and frequency(50 Hz-45 kHz)dependent polarization reversal behaviour as well as energy storage properties of 10 nm thick Si:HfO2 AFE films.In addition,endurance characteristics are studied under bipolar pulsed-field operation.The pyroelectric and electrocaloric properties,and their relationship with the electric field-induced phase transition of Si:HfO2 AFE thin films are also investigated.The material aspects of Si:HfO2 thin films are studied at first in order to gain a better insight into the occurrence of the FE and AFE properties in this system and to acquire guidelines for the fabrication of the energy-related devices.The film's composition is shown to have a strong impact on the electrical properties of Si:HfO2 thin films.By varying the Si concentration,FE or AFE behaviour is induced.The 5.0 mol%Si:HfO2 thin films exhibit a single hysteresis loop,which is a property of FE materials.This property is suggested to be generated from the non-centrosymmetric Pca2i orthorhombic phase.Similarly,the 6.0 mol%Si:HfO2 thin films exhibit a double hysteresis loop,which is a property of AFE materials.This behaviour in HfO2 results from the electric field-induced phase transition between the nonpolar tetragonal and polar orthorhombic phase.Due to double hysteresis loops,the 6.0 mol%Si:HfO2 AFE thin films can be appropriate for energy storage capacitors.The experimental results show that owing to high field-induced polarization and a slim double hysteresis,an enormous energy storage density(ESD)value of 61.2 J/cm3 is achieved at the electric field of 4.5 MV/cm with high efficiency of?65%.Both ESD and efficiency are increased with increasing temperature,which is due to the increasing the stability or fraction of the tetragonal phase at high temperatures.However,ESD and efficiency are decreased when the frequency is increased from 50 Hz to 45 kHz.In endurance measurements,AFE Si:HfO2 thin films exhibit better fatigue and breakdown resistance under the bipolar field cycling.The AFE Si:HfO2 thin films can endure 4 MV/cm cycle field up to 109 cycles without breakdown.Moreover,the ESD of Si:HfO2 AFE film is kept at 43 J/cm3 after field cycling up to 109 cycles,which is reduced by 18%compared with the initial value.The field cycling leads to a progressive phase transition from the AFE to FE phase in the film.The maximum value of the pyroelectric coefficient(-0.09224 ?C/(cm2·K))of Si:HfO2 AFE thin films is attained at zero electric field.For the electrocaloric properties of Si:HfO2 AFE thin films,the isothermal entropy change(?S)and adiabatic temperature change(?T)are evaluated by the indirect method.With the increase of temperature,the values of AS and AT have been increased,followed by subsequent reduction.The maximum ?S and AT are 11.13 J/(K·kg)and 13.42 K,respectively,at 340 K.Moreover,Si:HfO2 AFE thin films are exhibited good figures of merit(FOMs)for solid-state cooling,pyroelectric energy harvesters,and infrared sensors as compared to those of other HfO2-based materials.The detailed insights into switching characteristics of Si:HfO2 AFE thin films are also investigated,which can be gained from the measurement of first-order reversal curves(FORCs).This method describes the distribution of coercive field(Ec)and electric bias field(Ebias)of single-domain grains in polycrystalline Si:HfO2 AFE thin films.Furthermore,the Ec is decreased and Ebias is increased with increasing temperature.The collected results of this research are of immense technical importance in evaluating the feasibility of using AFE materials in ultracompact energy storage capacitors,pyroelectric devices,and solid-state cooling devices.The results from the current study have also suggested a multifunctional monolithic system can be achieved by the energy-related properties as mentioned above of Si:HfO2 AFE material.