A series of high-entropy ceramics with the nominal composition(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)(0≤x≤0.4)has been successfully synthesized using the conventional solid-phase method.T...A series of high-entropy ceramics with the nominal composition(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)(0≤x≤0.4)has been successfully synthesized using the conventional solid-phase method.The(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics are confirmed to be composed of the main phase(Zn,Mg,Li)TiO_(3)and the secondary phase Ca_(0.5)Sr_(0.5)TiO_(3)by X-ray diffractometer,Rietveld refinement,and X-ray spectroscopy analysis.The quality factor(Q×f)of the samples is inversely proportional to the content of the Ca_(0.5)Sr_(0.5)TiO_(3)phase,and it is influenced by the density.The secondary phase and molecular polarizability(α_(T))have a significant impact on the dielectric constant(ε_(r))of the samples.Moreover,the temperature coefficient of resonant frequency(τ_(f))of the samples is determined by the distortion of[TiO_(6)]octahedra and the secondary phase.The results indicate tha(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics achieve ideal microwave dielectric properties(ε_(r)=17.6,Q×f=40900 GHz,τ_(f)=-8.6 ppm/℃)when x=0.35.(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics possess the potential for application in wireless communication,and a new approach has been provided to enhance the perform-ance of microwave dielectric ceramics.展开更多
This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical syst...This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical systems(MEMS)disk resonators through analysis and simulation.These parameters include the crystallographic orientation,dopant,substrate thickness,and temperature.The resonators operate in the elliptical,higher order,and flexural modes.The simulation results show that i)the turnover points of the resonators exist at 55°C,-50°C,40°C,and-10°C for n-doped silicon with the doping concentration of 2×1019 cm-3 and the Si thickness of 3.5μm,and these points are shifted with the substrate thickness and mode variations;ii)compared with pure Si,the modal-frequency splitting for n-doped Si is higher and increases from 5%to 10%for all studied modes;iii)Q of the resonators depends on the temperature and dopant.Therefore,the turnover,modal-frequency splitting,and Q of the resonators depend on the thickness and material of the substrate and the temperature.This work offers an analysis and design platform for high-performance MEMS gyroscopes as well as oscillators in terms of the temperature compensation by n-doped Si.展开更多
Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated fo...Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.展开更多
Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants...Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants of NdCOB crystal were investigated over the temperature range of-80-200℃,and their temperature coefficients were evaluated.It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities(<3%).The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07×10^(-4)/℃.The temperature coefficients of the elastic compliances are obtained to be in the range of-33.0×10^(-4)/℃-32.2×10^(-4)/℃.Particularly,the sand swere found to show low temperature coefficients of the elastic compliances,i.e.1.0×10^(-4)/℃and-0.4×10^(-4)/℃,respectively,indicating the existence of zero temperature coefficient of frequency crystal cut.Furthermore,the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied.The electromechanical coupling factor kand piezoelectric coefficient dare determined to be~30.8%and~15.2 pC/N at room temperature,respectively.The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.展开更多
In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal struc...In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal structure,microstructure,and microwave dielectric properties were carried out.Rietveld refinements show that the SrEr_(2)O_(4)ceramics crystallize in the orthorhombic with the space group Pnam.The SrEr_(2)O_(4)ceramic sintered at 1575℃ exhibits the good performance of permittivity(ε_(r))=14.44,quality factor(Q × f)=23271 GHz,and resonant temperature frequency coefficient(τ_(f))=-21.5 ppm/℃,which is attributed to its high lattice energy,packing fraction,and relative density.In addition,to satisfy the requirement of temperature stability for communication devices,near-zero τ_(f) value is obtained by adding CaTiO_(3) at the cost of a small quality factor loss.The SrEr_(2)O_(4)+1.25 wt% CaTiO_(3) composite exhibits decent properties with ε_(r)=18.57,Q×f=19940 GHz,and T_(f)=+3.99 ppm/℃,making it an ideal candidate for microwave band applications.展开更多
This study investigates the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) series ceramics synthesised by solid-state reaction.According to the X-ray diffraction and micros...This study investigates the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) series ceramics synthesised by solid-state reaction.According to the X-ray diffraction and microstructural analyses,the as-prepared MgO-2B_(2)O_(3) ceramics possess a single-phase structure with a rod-like morphology.The effects of different quantities of H_(3)BO_(3) and BaCu(B_(2)O5)(BCB)on the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) ceramics were investigated.Accordingly,the optimal sintering temperature was obtained by adding 30 wt%H_(3)BO_(3) and 8 wt%BCB.We also reduced the sintering temperature to 825°C.Furthermore,the addition of 40 wt%H_(3)BO_(3) and 4 wt%BCB increased the quality factor,permittivity,and temperature coefficient of resonance frequency of MgO-2B_(2)O_(3) to 44,306 GHz(at 15 GHz),5.1,and-32 ppm/℃,respectively.These properties make MgO-2B_(2)O_(3) a viable low-temperature co-fired ceramic with broad applications in microwave dielectrics.展开更多
基金supported by the Sichuan Science and Technology Program,China(No.2023YFQ0082)the Guangdong Provincial Key Laboratory of Electronic Functional Materials and Device,China(No.EFMD2022005Z)the State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals,China(No.SKL-SPM-202021).
文摘A series of high-entropy ceramics with the nominal composition(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)(0≤x≤0.4)has been successfully synthesized using the conventional solid-phase method.The(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics are confirmed to be composed of the main phase(Zn,Mg,Li)TiO_(3)and the secondary phase Ca_(0.5)Sr_(0.5)TiO_(3)by X-ray diffractometer,Rietveld refinement,and X-ray spectroscopy analysis.The quality factor(Q×f)of the samples is inversely proportional to the content of the Ca_(0.5)Sr_(0.5)TiO_(3)phase,and it is influenced by the density.The secondary phase and molecular polarizability(α_(T))have a significant impact on the dielectric constant(ε_(r))of the samples.Moreover,the temperature coefficient of resonant frequency(τ_(f))of the samples is determined by the distortion of[TiO_(6)]octahedra and the secondary phase.The results indicate tha(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics achieve ideal microwave dielectric properties(ε_(r)=17.6,Q×f=40900 GHz,τ_(f)=-8.6 ppm/℃)when x=0.35.(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics possess the potential for application in wireless communication,and a new approach has been provided to enhance the perform-ance of microwave dielectric ceramics.
文摘This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical systems(MEMS)disk resonators through analysis and simulation.These parameters include the crystallographic orientation,dopant,substrate thickness,and temperature.The resonators operate in the elliptical,higher order,and flexural modes.The simulation results show that i)the turnover points of the resonators exist at 55°C,-50°C,40°C,and-10°C for n-doped silicon with the doping concentration of 2×1019 cm-3 and the Si thickness of 3.5μm,and these points are shifted with the substrate thickness and mode variations;ii)compared with pure Si,the modal-frequency splitting for n-doped Si is higher and increases from 5%to 10%for all studied modes;iii)Q of the resonators depends on the temperature and dopant.Therefore,the turnover,modal-frequency splitting,and Q of the resonators depend on the thickness and material of the substrate and the temperature.This work offers an analysis and design platform for high-performance MEMS gyroscopes as well as oscillators in terms of the temperature compensation by n-doped Si.
基金financially supported by the National Nature Science Foundation of China (No. 61223002)Sichuan Youth Science and Technology Innovation Research Team Funding (No. 2011JTD0006)
文摘Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.
基金Project supported by the National Natural Science Foundation of China(51872165)the Primary Research&Development Plan of Shandong Province(2019JZZY010313)+1 种基金Shandong Provincial Natural Science Foundation(ZR2020KA003)the Shandong Province Innovative Talents Support Program(62350070311104)。
文摘Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants of NdCOB crystal were investigated over the temperature range of-80-200℃,and their temperature coefficients were evaluated.It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities(<3%).The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07×10^(-4)/℃.The temperature coefficients of the elastic compliances are obtained to be in the range of-33.0×10^(-4)/℃-32.2×10^(-4)/℃.Particularly,the sand swere found to show low temperature coefficients of the elastic compliances,i.e.1.0×10^(-4)/℃and-0.4×10^(-4)/℃,respectively,indicating the existence of zero temperature coefficient of frequency crystal cut.Furthermore,the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied.The electromechanical coupling factor kand piezoelectric coefficient dare determined to be~30.8%and~15.2 pC/N at room temperature,respectively.The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.
基金Porject supported by National Natural Science Foundation of China (61761015, 11664008)Guangxi Natural Science Foundation(2018GXNSFFA050001, 2024GXNSFDA010060)High-Level Innovation Team and Outstanding Scholar Program of Guangxi Institutes。
文摘In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal structure,microstructure,and microwave dielectric properties were carried out.Rietveld refinements show that the SrEr_(2)O_(4)ceramics crystallize in the orthorhombic with the space group Pnam.The SrEr_(2)O_(4)ceramic sintered at 1575℃ exhibits the good performance of permittivity(ε_(r))=14.44,quality factor(Q × f)=23271 GHz,and resonant temperature frequency coefficient(τ_(f))=-21.5 ppm/℃,which is attributed to its high lattice energy,packing fraction,and relative density.In addition,to satisfy the requirement of temperature stability for communication devices,near-zero τ_(f) value is obtained by adding CaTiO_(3) at the cost of a small quality factor loss.The SrEr_(2)O_(4)+1.25 wt% CaTiO_(3) composite exhibits decent properties with ε_(r)=18.57,Q×f=19940 GHz,and T_(f)=+3.99 ppm/℃,making it an ideal candidate for microwave band applications.
基金supported by the National Natural Science Foundation of China(Nos.61761015 and 12064007)the Natural Science Foundation of Guangxi(Nos.2018GXNSFFA050001,2017GXNSFDA198027,and 2017GXNSFFA198011)High Level Innovation Team and Outstanding Scholar Program of Guangxi Institutes.
文摘This study investigates the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) series ceramics synthesised by solid-state reaction.According to the X-ray diffraction and microstructural analyses,the as-prepared MgO-2B_(2)O_(3) ceramics possess a single-phase structure with a rod-like morphology.The effects of different quantities of H_(3)BO_(3) and BaCu(B_(2)O5)(BCB)on the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) ceramics were investigated.Accordingly,the optimal sintering temperature was obtained by adding 30 wt%H_(3)BO_(3) and 8 wt%BCB.We also reduced the sintering temperature to 825°C.Furthermore,the addition of 40 wt%H_(3)BO_(3) and 4 wt%BCB increased the quality factor,permittivity,and temperature coefficient of resonance frequency of MgO-2B_(2)O_(3) to 44,306 GHz(at 15 GHz),5.1,and-32 ppm/℃,respectively.These properties make MgO-2B_(2)O_(3) a viable low-temperature co-fired ceramic with broad applications in microwave dielectrics.
