The Study On Temperature Stable Microwave Dielectric Materials

In the 5G era,base stations are widely deployed around the world,coupled with the introduction of Massive MIMO technology,putting forward higher requirements for the stability of the communication system.Taking communication base stations as an example,the number of microwave passive components in the RF front-end has increased significantly compared with 4G.With the increase in system energy consumption,it is easy to make the devices generate heat during operation and affect their reliability.At the same time,the deployment scenarios of communication equipment are complex,and the global temperature is complex and changeable.The devices need to work in various extreme environments.Reducing the power consumption of microwave passive devices and improving their stability in a wide temperature range（-40°C～105°C）are the keys to ensure the reliability of the communication system.As the cornerstone of microwave passive devices,the quality factor（Q）and the temperature coefficient of resonant frequency（τ_f）of microwave dielectric ceramics directly determine the energy consumption and temperature stability of the devices.Therefore,the study of high Q microwave dielectric ceramics with near zeroτ_f value in a wide temperature range has important application value for the development of high-performance communication systems.At present,the research on temperature stability of microwave dielectric ceramics is mostly limited to 25°C～85°C,and the exploration of temperature stability in wide temperature range（-40°C～105°C）needs to be further improved.Aiming at the application requirements of microwave passive components for low power consumption,high performance and high reliability,this paper selects Mg Ti O₃ system with high quality factor as the research object,and two-phase composite method is used to tune the temperature coefficient of resonant frequency.Furthermore,the research scope of temperature stability is extended to a wide temperature range,and the result shows that the resonant frequency changes nonlinearly,leading to a large difference between theτ_f values in the positive and negative temperature range,and it is difficult to achieve the temperature stability in the wide temperature range.On this basis,this paper systematically studies the influence mechanism of nonlinear variation of resonant frequency,optimizes the linearity through system formulation design,and tunes theτ_fvalue near to zero in a wide temperature range.Then the X-ray diffraction analysis,Raman spectroscopy and other testing methods are used to explore the influence mechanism of microwave dielectric properties.Finally,with the help of multilayer architecture and electromagnetic field simulation analysis,the dielectric properties are optimized.And high-performance Mg Ti O₃-based microwave dielectric ceramics with near zeroτ_fvalue in a wide temperature range is prepared.The main contents of this paper are as follows:（1）Research on the comprehensive influence mechanism of low loss and temperature stability in the positive temperature range:The single-phase solid solution(Ca_0.8Na_0.1Ce_0.1)Ti O₃ with a positiveτ_f value is selected to combined with Mg Ti O₃,achieving a near zeroτ_f value in the positive temperature range（25°C～85°C）.On this basis,the correlation mechanism between the phase composition of the composite ceramics and the microwave dielectric properties is established by the theoretical model calculations.With the help of the crystal structure and micro-morphology characterization,the influence mechanism of the dielectric properties is further explored.Finally,the 0.91Mg Ti O₃-0.09(Ca_0.8Na_0.1Ce_0.1)Ti O₃ ceramic sintered at 1175°C has the following microwave dielectric properties:ε_r=20.4,Q×f=66,000 GHz（@8.2 GHz）andτ_f=0.2 ppm/°C.（2）Research on the influence mechanism of nonlinear resonant frequency in a wide temperature range:Based on the above system,the research range of temperature stability is widened from 25°C～85°C to-40°C～105°C.The resonant frequency of the system shows a nonlinear variation in a wide temperature range.When theτ_f value in the positive temperature range（25°C～105°C）is near zero,the temperature stability in the negative temperature region（-40°C～25°C）is poor（τ_f=15ppm/°C）,which is difficult to meet the requirements of temperature stability in the wide temperature range.On this basis,the influence mechanism of the linearity of resonant frequency is studied based on the dielectric mixing theory.Then,Li₂Ti O₃ with similar dielectric constant and positive resonant frequency temperature coefficient are selected to composite with Mg Ti O₃.The microwave dielectric properties are as follow:ε_r=19.7,Q×f=50,000 GHz（@8.0 GHz）,τ_f+=-3.5 ppm/°C（25°C～105°C）,τ_f-=3.3 ppm/°C（-40°C～25°C）.（3）Research on the optimization mechanism of the microwave dielectric properties of multilayer architecture:Based on the Mg Ti O₃-Li₂Ti O₃ system with aτ_fvalue near zero in a wide temperature range,the introduction of the multilayer architecture further optimizes its comprehensive dielectric properties.With the help of HFSS electromagnetic field simulation,the influence mechanism of different multilayer architecture and phase composition on the microwave dielectric properties of the sample was systematically studied.Finally,the Mg Ti O₃/Li₂Ti O₃/Mg Ti O₃ceramic exhibts the best microwave dielectric properties:ε_r=21.2,Q×f=80,000 GHz,τ_f+=-3.0 ppm/°C（25°C～105°C）,τ_f-=2.7 ppm/°C（-40°C～25°C）.Compared with the random distribution method,the Q×f value is improved by about 60%.It can meet the application requirements of 5G high-performance microwave passive devices and provide strong support for the development of new generation communication devices.