| Due to the short wavelength and wide bandwidth,millimeter wave has the advantages of high resolution,large Doppler frequency shift,and small system size,and has important application prospects in high-speed and large-capacity communication,millimeter-wave radar and other systems.Due to the inherent characteristics of wide bandgap,high two-dimensional electron gas concentration,high electron mobility and high breakdown electric field,GaN（Gallium Nitride）devices have excellent performance such as high power density,radiation resistance,high temperature resistance and ultra-high frequency,which can meet the requirements of weapon equipment for amplifiers with higher output power,higher operating frequency,smaller system size and more severe conditions（higher temperature）.However,due to the backward level of semiconductor technology and circuit design,our country is far behind foreign countries in the research and development of millimeter-wave power amplifiers,which limits the demand for millimeter-wave amplifiers for national weapon equipment and intelligent manufacturing,so it is urgent to carry out the design,development and engineering application of millimeter-wave amplifiers.In view of the current backward status quo in the research and development of millimeter-wave amplifiers in our country,our work focuses on the performance improvement of millimeter-wave amplifiers such as power,efficiency and bandwidth,and studies the process improvement methods,testing and modeling technologies of GaN HEMT（High Electron Mobility Transistor）devices in millimeter-wave frequency bands,as well as the design technology of high-power amplifiers in millimeter-wave frequency bands,and wideband amplifiers.The specific research contents are as follows:（1）Research on high-performance millimeter-wave GaN HEMT devices.In order to solve the problems of power drop and frequency characteristic deterioration of GaN HEMT devices in the millimeter wave frequency band,the transient characteristics of the devices were simulated,and the relationship between the large signal operating characteristics of GaN HEMT devices with the working frequency and drain voltage of the devices was studied and analyzed.The physical phenomenon is revealed that the PAE decreases with the increase of frequency and drain voltage during RF operation,and the short gate length device obtains a high cut-off frequency but does not output high power.In order to improve the frequency characteristics of millimeter-wave GaN HEMT devices,a strongly polarized Al N/GaN heterojunction structure was proposed to replace the traditional Al GaN/GaN heterojunction structure,which effectively suppressed the short-channel effect of the device,a double-layer adhesive one-time exposure floating T-gate fabrication process was developed,and a high aspect ratio nano-T-gate was successfully fabricated to improve the power density and gain of the device,and a"two-step"annealing process was developed to reduce the parasitic resistance and improve the frequency characteristics of the device.Finally,100 nm and 50 nm GaN HEMT devices with excellent performance were successfully fabricated,among which the f T/f MAX of 100nm GaN HEMT devices reached 95/230 GHz,and the power density was increased from3 W/mm to 3.5 W/mm,and the f T/f MAX of 50 nm GaN HEMT devices reached 182/402GHz and the power density reached 0.6 W/mm,which met the design requirements of millimeter wave power amplifiers.（2）Research on high-accuracy millimeter-wave GaN HEMT device testing and modeling.In the millimeter wave frequency band,the parasitic effects of pads and transmission lines and other interconnection elements between the probe and the die,and even the effects of probe mutual coupling and transmission line distribution that are ignored at low frequencies also begin to affect the measurement accuracy.In order to solve this problem,the differences of different calibration algorithms and de-embedding methods in the millimeter wave frequency band were compared and analyzed,and the calibration and de-embedding methods suitable for the millimeter wave frequency band were found.In order to solve the problem that the traditional calibration structure does not converge in the millimeter wave frequency band,a new calibration structure surrounded by dense through holes is designed to improve the transmission characteristics and accuracy in the millimeter wave frequency band.In order to accurately characterize the parasitic effects of the device in the millimeter-wave frequency band,the traditional15-element equivalent model topology was replaced by a 21-element equivalent model topology,which improved the fitting accuracy of small signals and reduced the average fitting error to less than 4%in the frequency band within 110 GHz.The EEHEMT1nonlinear current equation is improved,and the piecewise function is used to describe the die current characteristics.The Angelov GaN capacitance equation used to describe the intrinsic gate drain capacitance Cgd and gate source capacitance Cgs is improved,and the parameters are added to describe the interaction between Vds and Vgs,which improves the accuracy of the large signal model.（3）Research on the design of high-power millimeter-wave GaN amplifier MMIC（Monolithic Microwave Integrated Circuit）.In order to solve the problems of small output power and low efficiency in the design of high-power millimeter-wave amplifiers,the design methods of high-power millimeter-wave amplifiers were studied in typical millimeter-wave frequency bands.Firstly,the different frequency characteristics of passive circuit elements in the low-frequency and millimeter-wave frequency bands are compared.Then,a narrowband power amplifier was implemented in the V-band,with an output power of more than 4 W and an additional efficiency of more than 24%in the 57-61 GHz band,which has the highest additional efficiency among the reported V-band amplifiers greater than 1 W.The influencing factors of the synthesis efficiency of the millimeter-wave band distributed transmission line synthesis network are studied,and then a W-band narrowband power amplifier is designed based on the distributed transmission line synthesis network to achieve an output power greater than 2 W in the92-96 GHz frequency band,and on this basis,the power synthesis is carried out by Wilkinson power divider and Langer bridge to realize the W-band power MMIC with an output power greater than 6 W,which is the W-band power monolithic with the highest output power that has been reported.The W-band 2 W power amplifier was used to develop a W-band solid-state power amplifier with 100-watt output power.In addition,an efficient design method for the integration of W-band power amplifier,switch and low-noise amplifier on the chip is proposed,and a multi-functional chip for W-band transceiver is realized.Finally,a G-band amplifier with an output power greater than18d Bm was designed.The amplifier was used for power synthesis,and the output power of greater than 1 W was achieved at the highest point,which was the first time in the world that the output power of solid-state power amplifier greater than 1 W was reported in the G-band.（4）Research on the design of broadband millimeter-wave GaN amplifier chips.In order to solve the problems of narrow bandwidth and large impedance conversion ratio in the design of broadband millimeter wave amplifiers,the design methods of broadband millimeter wave amplifiers were studied in typical millimeter wave frequency bands.Based on the reactance/resistance matching method combined with the balanced topology,a wideband amplifier covering 40-75 GHz with an output power greater than 2 W is designed,which increases the output power by more than 4 d B compared with the similar frequency band amplifier reported in the literature,and the bandwidth is broadened by 23GHz compared with the similar power amplifier reported in the literature.A chain synthesis method based on Langer bridge was proposed for the design of E-band broadband power amplifier,which solved the problem of high impedance conversion ratio when multiple transistors were combined in the millimeter wave frequency band while realizing broadband matching,and designed an E-band broadband amplifier covering 60-90 GHz with an output power greater than 1.7 W,which increased the output power by more than 4 d B and broadened the bandwidth by 11 GHz compared with similar frequency band amplifiers reported in the literature.Finally,a millimeter-wave high-band broadband amplifier covering 180-280 GHz with a gain of more than 20 d B was designed by using the coplanar waveguide circuit design technology. |
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