高纯度石英玻璃40-110 GHz频段电参数的表征.pdf

第 42 卷第 4 期2023 年 8 月红 外 与 毫 米 波 学 报J.Infrared Millim.WavesVol.42，No.4August，2023文章编号：1001-9014（2023）04-0490-07DOI：10.11972/j.issn.1001-9014.2023.04.010Characterization of electrical parameters of high-purity quartz glass in the 40-110 GHz frequency bandZHU Xiang-Bao1，SUN Xu1*，YUE Hai-Kun2，QIAN Ling-Xuan1，NI Lei3（1.University of Electronic Science and Technology of China，Chengdu 611731，China；2.Microsystem&Terahertz Research Center，China Academy of Engineering Physics，Chengdu 610200，China；3.Key Laboratory of Testing Technology for Manufacturing Process，Southwest University of Science and Technology，Mianyang 621010，China）Abstract：The transmission line structures such as coplanar waveguide（CPW）and microstrip ring resonator（MRR）were designed on a high-purity quartz substrate（99.9997%）with a thickness of 127 m.The average insertion loss for the CPW line varied from 0.096 to 0.176 dB/mm in the frequency range of 40-110 GHz.Furthermore，the relative permittivity and loss tangent of the quartz were extracted by the MRR method.The relative permittivity of the quartz substrate in the V-band and W-band ranged with 3.7-3.85 and 3.85-4，respectively.The loss tangent value was approximately 0.004 in the V-band and 0.004-0.006 in the W-band.The performance comparison with other substrates shows that this high-purity quartz has excellent and stable electrical properties and its potential for designing high-performance passive and packaging structures.Key words：quartz glass，coplanar waveguide，microstrip ring resonator，V-band，W-band高纯度石英玻璃40110 GHz频段电参数的表征朱香宝1，孙旭1*，岳海昆2，钱凌轩1，倪磊3（1.电子科技大学，四川 成都 611731；2.中国工程物理研究院 微系统与太赫兹研究中心，四川 成都 610200；3.西南科技大学 制造过程测试技术教育部重点实验室，四川 绵阳 621010）摘要：基于127 m的高纯度石英（99.999 7%）基底设计了共面波导（CPW）、微带环形谐振器（MRR）结构，通过测试得到在40110 GHz的频率范围内，CPW线的平均插入损耗在0.0960.176 dB/mm之间。此外，采用MRR方法提取了石英的相对介电常数和损耗角正切值，该石英基底在V波段和W波段的相对介电常数分别介于3.73.85和3.854之间，损耗角正切值在V波段约为0.004，在W波段介于0.0040.006之间。通过与其他基底性能对比表明，该高纯度石英具有良好稳定的电性能，其在设计高性能无源和封装结构方面具有一定的潜力。关键词：石英玻璃；共面波导；微带环形谐振器；V波段；W波段中图分类号：TN817；TN815 文献标识码：AIntroductionThe development of modern wireless communication technology requires a lot of bandwidth，so the fifth-generation（5G）mobile network has been widely used in everyday life1.The performance of 5G networks will be further enhanced by using carrier frequencies in the millimeter wave region，which will achieve higher data rates2.However，as more and more high-frequency bands are utilized，numerous new issues arise due to the rapid increase in dielectric substrate loss.For instance，transmission line loss rises as frequency rises；in a similar vein，the dielectric constant of the substrate fluctuates with increasing frequency，causing a significant departure from the design in terms of circuit performance.SigReceived date：2022 09 28，revised date：2023 04 17 收稿日期：2022 09 28，修回日期：2023 04 17Biography：ZHU Xiang-bao（1997-），male，Wuhu，China，master.Research area involves Microwave theory and simulation.E-mail：*Corresponding author：E-mail：4 期 ZHU Xiang-Bao et al：Characterization of electrical parameters of high-purity quartz glass in the 40-110 GHz frequency bandnificant improvements in equipment，packaging techniques，and other areas of the millimeter wave frequency spectrum are necessary to meet these demands3-5.The majority of modern millimeter wave packages are comprised of ceramic，fan-out，etc6-7.Ceramics are chosen for 5G applications due to their low loss and consistent performance in the millimeter wave spectrum；nevertheless，their expense and integration constraints impede their growth8.Fan-out wafer level packaging（FOWLP），which allows for nearly monolithic integration，is becoming more popular.However，it uses compression molding to form rewiring，which can result in significant die shifts.Furthermore，antennas and other high-performance RF structures must be integrated at the top of the module to dissipate heat from the bottom of the chip through silicon pass holes，resulting in a mismatch in the coefficient of thermal expansion（CTE）between the silicon module and the PCB，which can cause reliability issues.Because of their superior dimensional stability，quartz-based packages are becoming ideal candidates for millimeter wave technology implementation.The CTE of the quartz is customizable，which makes it more compatible with the device structure9.For this reason，the basic electrical properties of high-purity quartz（99.9997%）are studied in this paper.The result shows that the quartz has a lower loss tangent and better performance in the high-frequency band，demonstrating the advantages of high-purity quartz packaging in the 5G frequency band.1 Design of test structures Coplanar waveguides are frequently used for planar transmission lines，and their insertion loss provides a good indication of a materials aptitude for high-frequency applications.Additionally，a microstrip ring resonator is used to extract the electrical characteristics（dielectric constant and loss tangent）of the quartz substrate in the broadband V-band and W-band.The bottom of the quartz is covered with a 1 m thick gold layer as a metal ground in all structural designs，and a 4 m thick gold layer is subsequently employed to finish the construction of the quartz front，as illustrated in Fig.1（a）.1.1Coplanar waveguide(CPW)linesThe design of CPW is predicated on the quasi-static model of an elliptic integral function subject to conformal transformation10.The relationship between the characteristic impedance of CPW，the effective dielectric constant of the substrate and the substrate thickness h，the signal line width W，and the slot spacing g is given by equations（1-4）.Z0=60eff1K(k)K(k)+K(kt)K(kt),（1）k=W2g+W,k=1-k2,（2）kt=1-kt2,kt=tanh(W4h)tanh(W+2g)4h),（3）eff=1+rK(k)K(k)K(kt)K(kt)1+K(k)K(k)K(kt)K(kt).（4）In this model，with the increase of h/W，the effective dielectric constant eff decreases with the change of g/W.In this paper，we need to extract the effective permittivity and relative permittivity values of the high-purity quartz substrate，so we need eff to be as stable as possible when designing the CPW，which is the main direction of concern in our optimization.Furthermore，design optimization should consider the processing processs accuracy，the probes specification used in the W-band of 100 m，and the practical requirements for testing the characteristic impedance design of 50.Based on the above design specifications，the parameters W and g are optimized and simulated，with the simulation results shown in Fig.2.As can be seen from the figure，the combination of g=25 m and W=140 m does not produce resonance and has a lower S21.The dimensions of the designed CPW are provided in Table 1.Two different lengths of CPW were modeled and designed to characterize the insertion loss per unit length.The structure schematic is shown in Fig.1（b）.1.2Microstrip ring resonator(MRR)The MRR method is a reliable method for high-frequency dielectric material characterization.The inserFig.1Test structures,(a)material stack up,(b)CPW line,(c)microstrip ring resonator图1测试结构，(a)材料堆叠，(b)共面波导线，(c)微带环形谐振器491红 外 与 毫 米 波 学 报42 卷tion loss of the MRR has a resonant period peak.The dielectric constant is calculated using the location of the resonant period peak in the insertion loss of the MRR.And the loss tangent of the material is determined using the resonant peaks no-load quality factor.The desired resonant frequency and the corresponding ring radius are derived from equation（5）.f0=nc2rmeff,（5）where f0 is the nth resonant frequency of a ring of average radius rm，the effective permittivity is eff，and c is the speed of light in a vacuum11-12.Two MRRs with 10 GHz and 15 GHz fundamental frequencies and Thru-Reflect-Line（TRL）structures were designed to measure multiple resonances in the V and W bands13.TRL structures can eliminate the impact of CPW to microstrip transition on the feeder，as well as the impact of the slight impedance mismatch.The response of MRR can be accurately extracted by shifting the measurement reference plane through the TRL structures.Figure 1（c）depicts a schematic diagram of the MRRs structure.2 Fabrication A summary of the fabrication method is provided below.The processing is based on a 127 m thick quartz substrate.For the top and bottom metalized layers，the epitaxial growth of the metal layer is first guided by the formation of a seed layer on the quartz surface，followed by the drawing of the photoresist using a designed mask and the formation of the desired metal pattern using lithography techniques.Eventually，the photoresist is removed and the seed layer is etched to obtain the desired structure.The manufactured test structure is depicted in Fig.3，both CPW lines and MRR structures are processed on the quartz front with a metal thickness of 4 m，and the quartz back is entirely covered with a metal thickness of 1 m.3 Measurement and analysis The measurement setup shown in Fig.4 employs a probe stage to test the generated and processed samples.For accurate calibration，the frequency step change is 0.1 GHz across the whole frequency range of the test.3.1Coplanar waveguide(CPW)linesMultiple identical structures processed in the same batch were tested to ensure the accuracy of the test data.Figure 5 shows the results of fabricating and measuring two different lengths of CPW（3 mm and 5 mm）.The reflection coefficients in Fig.5 are generally less than-10 dB，which indicates good impedance matching.Because the sample structure tested was a thin-film circuit processed on a 2-inch quartz wafer，there would be some processing deviation of the graphic structure at different positions on the wafer.This also resulted in a slight difference in the test results，with the S21s difference within the acceptable range of 0.2 dB.The S21 per unit length（dB/mm）is shown in Fig.6.The insertion loss for CPW lines varies from 0.096 to Table 1Parameters of the CPW and MRR(m)表1CPW和MRR参数尺寸(m)StructureCPW 3 mmCPW 5 mmMRR 10 GHzMRR 15 GHzParametergWL（3 mm）L（5 mm）rm（10 GHz）rm（15 GHz）gapnumerical value（m）251403 0005 0002 7001 80040Fig.23 mm CPW line optimization simulation results图23 mm CPW线优化仿真结果Fig.3 Fabricated test structure,(a)partial samples,(b)CPW line,(c)microstrip ring resonator图3制备的测试结构，(a)部分样片，(b)共面波导线，(c)微带环形谐振器4924 期 ZHU Xiang-Bao et al：Characterization of electrical parameters of high-purity quartz glass in the 40-110 GHz frequency band0.176 dB/mm in the frequency range of 40-110 GHz.According to the data in Fig.6，the insertion loss of the CPW line on the quartz substrate at 40 GHz，77 GHz，and 110 GHz is 0.096 dB/mm，0.125 dB/mm，and 0.176 dB/mm，respectively.At the same time，the average insertion loss of the high-purity quartz-based transmission line has been compared with the performance of other high-frequency material transmission lines，such as ABF/glass/ABF14，Rogers RT Duriod 600215，and LCP materials16 in the frequency region from 40 to 110 GHz.As can be seen from Table 2，the test results are slightly better than some high-frequency materials，which indicates the good transmission performance of the high-purity quartz.In addition，quartz material can support high wiring density，excellent assembly spacing，and other advantages，and the quartz thermal expansion coefficient is customizable，which makes it more compatible with device structures.3.2Microstrip ring resonator(MRR)MRRs with two resonant frequencies（10 GHz and 15 GHz）were designed to avoid characterization errors caused by manufacturing and measurement errors.The measured results for multiple samples are shown in Fig.7.Sharp resonances have been captured across the frequency region.Since the dispersion of the microstrip line is prominent at high frequency，the dispersion model is adopted to extract the effective permittivity value from the resonant frequency of S21 of the MRR，and then calculate the relative permittivity according to the extracted effective permittivity value17.For the MRR，the effective permittivity can be obtained from Equation（6）.eff=(nc2rmf0)2,（6）Fig.4The schematic diagram of the test device,(a)measurement setup,(b)sample ready to be probed,(c)measurements underway图4测试装置示意图，(a)测试设置，(b)样品准备测试，(c)进行测试Fig.5 Measured S-parameter of CPW lines,(a)S11 measured value of 3 mm CPW line,(b)S21 measured value of 3 mm CPW line,(c)S11 measured value of 5 mm CPW line,(d)S21 measured value of 5 mm CPW line图5共面波导线S参数测量值，(a)3 mm CPW线的 S11 测量值，(b)3 mm CPW线的 S21 测量值,(c)5 mm CPW线的 S11 测量值，(d)5 mm CPW线的 S21 测量值493红 外 与 毫 米 波 学 报42 卷where f0 is the nth resonant frequency of a ring of average radius rm，eff is the effective permittivity，and c is the speed of light in a vacuum.As shown in Equation（7），the relative permittivity of quartz can be calculated using the effective permittivity and the size of the microstrip line.r=2eff+M-1M+1,（7）where M=（1+12h/Weff）-1/2，Weff is the effective strip width accounting for the nonzero strip thickness，Weff=W+（t/h）ln（2h/t）+1，h is the thickness of the quartz substrate，t and W are the physical thickness and width of the gold conductor.Figure 8 displays the relative permittivity that is obtained from the extraction.The vertical bars represent a confidence interval of 95%.It can be seen that the quartz substrates dielectric constant is stable in the V-band between 3.7 and 3.85 and in the W-band between 3.85 and 4，indicating that the quartz substrates dielectric constant is relatively stable in both bands.The dielectric loss18 is calculated using the ring resonator method by subtracting the theoretical conductor loss value from the total loss at each resonant peaks frequency location.d=total-c,（8）where total is the total loss，c is the conductor loss，and d is the dielectric loss.Then the loss tangent tan is obtained by substituting d into the following equation（9）.tan=d0eff(r-1)r(eff-1),（9）where 0 is the free-space wavelength，eff is the effective Fig.6S21（dB/mm）per unit length图6单位长度的 S21（dB/mm）值Table 2Comparison of the performance of quartz-based transmission lines with other high-frequency materials(dB/mm)表2石英基传输线与其他高频材料性能比较(dB/mm)LCPABF/glass/ABFRogersQuartz（this work）40 GHzNA0.0950.0750.09660 GHz0.150.120.100.11177 GHz0.1750.170.130.125110 GHz0.2250.25NA0.176Fig.7Measured S21 response of microstrip ring resonator,(a)r=1.8 mm(15 GHz),(b)r=2.7 mm(10 GHz)图7微带环形谐振器 S21 测量值，(a)r=1.8 mm(15 GHz)，(b)r=2.7 mm(10 GHz)Fig.8Dielectric constant of extracted quartz substrate,(a)V-band,(b)W-band图8提取的石英基板介电常数，(a)V波段，(b)W波段4944 期 ZHU Xiang-Bao et al：Characterization of electrical parameters of high-purity quartz glass in the 40-110 GHz frequency banddielectric constant，and r is the relative dielectric constant.According to Fig.9，which depicts the extracted loss tangent，the loss tangent is around 0.004 in the V-band and increases slightly between 0.004 and 0.006 in the W-band.The vertical bars represent a confidence interval of 95%.Table 3 is the comparison between the extracted loss tangent and other high-frequency stacking materials，such as ABF/glass/ABF13 and ZIF/glass/ZIF8.It can be seen from the table that the loss tangent of the high-purity quartz substrate is lower and m