Research On GaN Internally-matched Power Devices In Base Transceiver Station

Due to the superior capabilities of high breakdown voltage,high power density,high electron mobility and wide band-gap,AlGaN/GaN High Electron Mobility Transistor?HEMT?is the most promising candidate for high power,high frequency and high reliability application.Under this research background,thorough research on the AlGaN/GaN HEMT is presented in this dissertation,including the improvement of the key processes of device,the electrical characterization of the device,establishment of the small signal models of the device.S-band internally matched high-efficiency power amplify is designed.The main achievements of this work are summarized as follows:1.The key fabrication technologies of AlGaN/GaN HEMT are studied.The effects of different surface treatments on the specific contact resistivity and the Schottky reverse leakage current are compared.We found that the sample treated by HCl have a higher specific contact resistivity than the sample treated with NH₄OH.The sample treated by BOE have a smaller interface state density than the sample treated with NH₄OH or HCl,so the Schottky reverse leakage current of the gate is the lowest.At the same time,the viahole etching and drilling technologies have been developed,which can solve the problem of heat dissipation of large gate width to a certain extent and improve the reliability of the device.2.Device characterization and analysis of AlGaN/GaN HEMT are carried out.Thorough characterization and analysis of AlGaN/GaN HEMT with 0.6mm gate-width are performed,including the output characteristic,transfer characteristic,Schottky characteristic,small signal S-parameters and power characteristics are all measured.A comprehensive evaluation of the capability of a device in high frequency and high power applications are proposed.3.An improved small signal model for AlGaN/GaN HEMT are established.A new 23elements small signal equivalent circuit model is set up.In order to characterize the changes of depletion region under various drain voltages,the drain delay factor is involved in the output conductance of the device.For high voltage microwave transistors,the introduction of?_ds has a great significance,which makes the equivalent circuit model more accurately to characterize the physical characteristics of the actual device.In order to evaluate the accuracy of the model,the amplitude relative errors and the absolute phase errors of the S-parameter are introduced.In the frequency range from 0.1GHz to 20GHz,the amplitude relative error is less than 6%and the absolute phase error is less than 9°,so the improved model has higher accuracy.4.A research on S-band internally-matched high efficiency high power amplifier is carried on.A class-AB power amplifier operating from 1.8GHz².2GHz is designed by using the small signal S-parameters and the Loadpull results on the self-developed AlGaN/GaN HEMT with 6mm gate width.To realize wide-band design of the amplifier,a method of three LCL impedance transform network is used and an ideal band-width is obtained.To obtain high output power,the PA contains four parallel 6mm GaN HEMTs working as its active components.A Wilkinson power divider and a combiner are introduced to the circuits to separate the signals transformed into four ways.Through this way,the phase imbalance caused by the large gate width reduced.The simulation results show that the reflection coefficients S₁₁ and S₂₂ are less than-10dB,the power gain S₂₁ is greater than 15dB,and the stability factor k is greater than 1 in the whole frequency band.