Design And Research Of Probe Based On Near-field Microwave Scanning

In the design and manufacture of integrated circuits and semiconductor chips,the electromagnetic parameters of microwave materials have a very significant effect on structure and size.Complex dielectric constant,as a representative of electromagnetic parameters,is an important physical quantity that characterizes the electromagnetic performance of a device,and its accurate measurement is worth further study.The conventional measurement method of complex permittivity is to measure the average parameter value of a sample as a whole,and it is impossible to measure the local parameters of the material.Microwave near-field microscopy is used to solve the problem of the limitation of far-field imaging resolution.Combine the microwave near-field microscopy system with the dielectric constant measurement system to achieve high-resolution measurement of the dielectric constant to meet the testing needs of composite materials in the microwave frequency band.The topic of this article comes from the National Natural Science Foundation of China’s special scientific instrument project-microwave high-power semiconductor chip thermal parameter comprehensive analyzer.In the whole system,the probe transmits energy to the sample and forms a near-field action area at the tip of the needle.It is the core component of the whole system and the object of this article.Based on the near-field microscopy theory and combining the wideband test requirements from 10 MHz to 110 GHz,this study proposes two design schemes that meet the requirements and verify them.The main work can be summarized into the following three points:(1)The role of the probe in the microwave near-field is analyzed,and the mechanism of the near-field evanescent wave are introduced.In the sub-wavelength region near the tip,the electromagnetic field exhibits static characteristics and stores electromagnetic field energy that is reactive and affected by the nature of the sample.Then the application of the nearfield probe in measuring the dielectric constant is introduced.Finally,the design requirements of the near-field probe are proposed and a probe test platform is set up.(2)Since the interaction between microwave and material is a function of frequency,the microwave frequency band is first considered to be grouped and the properties of microwave are analyzed in the corresponding frequency band group.A specific design scheme is proposed based on the design requirements of the probe.At the same time,two typical probe types,coaxial and rectangular waveguides,are specifically designed.Starting from the distribution of the electromagnetic fields of the two structures,through analysis of factors such as loss and power during transmission,specific size requirements are proposed.According to the corresponding dimensional design requirements and material requirements,the two probes were verified by simulation and experiment respectively.Experiments show that the use of coaxial and rectangular waveguides can achieve microwave near-field testing under certain frequency limits.(3)A scheme for designing probes using a coplanar waveguide structure that does not have a cutoff frequency is proposed to meet the test requirements.Coplanar GSG(Ground-SignalGround)probe is a planar near-field probe consisting of three metal conductors.Firstly,the characteristics of the coplanar probe are introduced.The electromagnetic field distribution,characteristic impedance and loss of the coplanar waveguide structure are analyzed theoretically.The size selection method in the design of the coplanar waveguide is proposed.The coplanar waveguide structure is verified by simulation Distribution of electromagnetic fields when transmitting microwave energy and measuring standard samples.The electromagnetic field energy is basically bounded between the gaps of the coplanar waveguide and interacts with the sample at the end.Finally,the actual coplanar waveguide was fabricated using printed circuit board technology and the actual return loss was measured.Experiments show that it is necessary to accurately obtain the reflection coefficient of the coplanar waveguide structure probe in the near field through dimensional design and calibration for subsequent analysis.According to the requirements of wide-band near-field microwave testing,based on the nearfield microwave microscopy theory,the near-field probes in the measurement of complex permittivity are analyzed,and the corresponding design requirements are proposed.Secondly,two types of probes are proposed.The specific probe design scheme was verified through a combination of theoretical analysis,simulation verification and experimental testing.