| In the past few decades,wireless communication science and technology has been developed very fast,and the solid-state electronic devices are highly required.With both of the operation frequency and the output power increased,the first and the second generation semiconductor like Si and GaAs could not meet the requirement anymore.But with a larger bandgap,the third generation semiconductor could be a strong candidate,among which GaN has been used in many applications because of its high breakdown voltage,high output power,high operation frequency,high electron saturation drift velocity,as well as splendid temperature and radiation performance.Starting from the material growth and device process,this dissertation presents the work mechanism of GaN HEMT.Since the measurements and characteristics play important roles in the semiconductor analyzing,the calculation algorithm is deeply investigated and an CPW-to-microstrip line transition structure fabricated on high Q low loss ceramic,which shows excellent performance,is designed for the microwave measurements and de-embedding.Then the SiN film material based MIM capacitors with different dimensions and dielectric thickness are processed and investigated deeply.Apart from SiN film,other materials are also used and deposited as the intermediate dielectric film to analyze the effect of different dielectric constant.At the same time,the wideband spiral inductor with air-SiN compound dielectric air-bridge is processed and the coupling effect of the air-bridge is investigated.New GaN based HEMT large signal model is established to model the kink effect and the self-heating effect in the DC curves,with which the DC model of the transistor could be established more rapidly and precisely.Thanks to the wideband power dividing and combining technique,an S band high efficiency high output power internally-matched power amplifier is designed based on the GaN HEMT.At last,a GaN HEMT based high efficiency high gain two stage power amplifier is achieved with the harmonic manipulation networks designed both in the input and the output matching networks.The main achievements in the dissertation are listed as following.1.High Q low loss AlN ceramic material substrate based broadband CPW-to-Microstrip transition structure for microwave measurements.First the traditional calibration algorithm based on the equivalent circuit is introduced,and the TRL based calibration algorithm for the asymmetrical structure is also presented which is more common compared with the symmetrical structure.Then a novel high Q low loss AlN ceramic based via-less broadband CPW-to-Microstrip line transition structure for microwave measurements application is designed.With a via-less structure,the fabrication process is more simplified and the processing precision is improved.The transition part consists of the CPW transition part and the microstrip transition part which could not only achieve the impedance matching between the CPW and the Microstrip line,but also make the field distribution much smoother.With the help of the transition part,the operation frequency band is broadened further and the performance within the band is also improved.To implement the structure in the circuit design more easily,a relevant RLC lumped model is established as well as the parameter extraction approach.Thanks to the series capacitor in the model,the broadband and bandpass behavior are well simulated.Moreover,the validation of the transition structure,as well as the model is demonstrated by the de-embedding procedure.According to the measurement,from 6.5 GHz to 46 GHz,the insertion loss of the transition structure is less than 1 dB,with a minimum value of 0.23 dB at 16 GHz.2.The SiN film dielectric material based MIM on-wafer capacitor by MMIC technology.In GaN device process technology,SiN film material is often used as the passivation layer to improve the current collapse effect.So with the relative dielectric constant of 6.7,SiN film material is also used as the dielectric of the MIM capacitor in MMIC technique.Plenty of MIM capacitors with different area range from 20?m×20?m to 200?m×200?m are fabricated and the area dependent effects are investigated deeply.According to the analysis,with the capacitor area increased,the capacitance is increased accordingly,but the self-resonant frequency will move to the low frequency end because of the more significant parasitic effect.On the contrary,when the size of the capacitor is decreased,the quality factor will increase rapidly.To investigate the phenomenon further,the capacitance and the self-resonant frequency are extracted and analyzed quantitatively.To facilitate the circuit design,the relevant RLC lumped model is established which takes the physical structure into account synthetically.With very high precision within a very broad frequency band,the scalable model could find a very used application in the IC design.In the same way,the effect of the SiN dielectric thickness on the capacitor performance is investigated.Additionally,different film materials like Polyimide?MgZnO?SrTiO3?BST and PZT are deposited and the permittivity dependent effects are also investigated in detail which lays a solid foundation for the choice of capacitors in the circuit design procedure.3.Broadband spiral inductors with SiN–air compound dielectric air-bridge in SiC-based MMIC technology.With low relative dielectric constant,4H-SiC substrate shows better parasitic effect compared to other substrate,which could improve the frequency performance of the device.We fabricated spiral inductors with the air-bridge structure on 4H-SiC substrate.Between the underpass and the air-bridge metals,there are air layer and SiN film layer which form the compound dielectric material.In a metal-insulator-metal form,a coupling capacitor is formed which is investigated deeply.The fabricated 1 nH spiral inductor on SiC substrate demonstrates a self-resonant frequency of 51.6 GHz,with a peak Q-fact of 12.14 at 22.1 GHz.From the S-parameters measurements,the exponential decay phenomenon is observed for L,Q-factor,and SRF with the air-bridge height decreased,and an analytic expression is concluded to exactly fit the measured data which can be used to predict the performance of the spiral inductor.All the coefficients in the formula have specific meaning.By means of establishing the lumped model,the parasitic coupling capacitance of the air-bridge has been extracted and presents the exponential decay with the air-bridge heights decreased as well,which indicates that this capacitor is directly related to the coupling effect of the air-bridge.The effective dielectric constant of the air-SiN compound material is considered to determine the initial value of the capacitor.Through the electromagnetic field distribution simulation,the details of the electric field around the air-bridge have been presented which demonstrate the formation and the variation principles of the coupling effect.4.A scalable active compensatory sub-circuit for accurate GaN HEMT large signal models.First based on the measurement results,the small signal model is established with 18elements in the equivalent circuit which is a tradeoff between the simulation precision and the complexity.The extrinsic parameters are extracted by cold-FET method.Afterwards,with the device biased at normal operating condition,the extrinsic parameters are de-embedded and the intrinsic parameters are calculated finally.On the basis of the small signal model,the nonlinear model could be established then.A scalable active compensatory sub-circuit that focuses on and improves the accuracy of the GaN HEMT large signal model is proposed in this dissertation.Because of the kink effect and the self-heating effect caused by the donor-state traps in the buffer layer and the high bias condition,respectively,it is hard to model the DC behavior of the transistor rapidly and precisely.With this new model,zero error between the simulated and measured DC I-V curves is obtained,and both the kink effect and the self-heating effect are taken into consideration at the same time.Combining empirical and table-based models,time-consuming procedures for parameters extraction and optimizing can be simplified.With a normalizing factor introduced,the scaling of the model is achieved.The validity of the proposed model is investigated experimentally.This model can be applied for devices with different designs and technology.5.AlGaN/GaN HEMT based high efficiency power amplifier design.First,we present an AlGaN/GaN HEMT based S-band internally matched power amplifier.The optimum source and load impedances are matched to the intermediate real impedances by the L-C-L pre-matching network.With the multi-section wideband power divider and combiner designed,the intermediate impedances are matched to the system impedance,and two transistors are combined which could increase the output power.Finally,the internally matched power amplifier is assembled and measured.In the frequency band of 1.8 GHz–2.2 GHz,the output power is larger then 100 W,with an efficiency of 60%and a power gain of 15 dB.Then a C-band high efficiency and high gain two-stage power amplifier based on AlGaN/GaN HEMT is designed and measured in this dissertation.To achieve the maximum efficiency,the input and output impedances for the optimum PAE are determined at the fundamental and 2nd harmonic frequency?f0 and 2f0?,based on which the driver stage is designed.In the input and output matching network,the harmonic manipulation circuits are designed respectively,which could help to match the 2nd harmonic to the optimum impedance.With the design of 2nd harmonic manipulation networks,the PAE is greatly improved.The validation of the harmonic manipulation network is demonstrated by the mismatching experiment.Then the 2nd stage is designed with a gate width ratio of 1:4.The optimum impedance for the two 2.5 mm devices in the final stage is scaled according to the impedance of 1.25 mm device in the driver stage.In the input and output matching networks of the final stage,the harmonic manipulation circuits are also designed to achieve the optimum PAE.Additionally,to decrease the insertion loss,the power combiner and splitter networks are carefully calculated and designed.In the operation frequency of 5.4 GHz-5.8GHz in CW mode,the amplifier delivers the maximum output power of 18.62W,with a PAE of 55.15%and an associated power gain of 28.7dB,which is an outstanding performance.In summary,thorough researches on large signal model of AlGaN/GaN HEMT,film dielectric material based passive models of relevant components,high Q low loss AlN substrate based test structure and the calibration algorithm,and the realization of the S-band internally matched power amplifier and the C-band two-stage high gain high PAE power amplifier are carried out in this dissertation.The accuracy of the active and passive models is improved further and the performance of the two stage amplifier has reached the state-of-art level which not only lays a solid foundation for the development of GaN based devices and circuits,but also puts forward new challenges. |
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