Characterization Of AiGaN/GaN HEMT And The Study Of Microwave Power Amplifers

The rapid development of radio frequency communication technology requireshigh demand for microwave transistors. Nowadays, in a lower microwave frequcncy,the microwave transistor is Si-based LDMOS. But it is only for the frequency below3GHz. In a higher microwave frequency, the GaAs transistors which have high electronmobility are the first choice. But the power desity of GaAs is low because of its materialperformance. So new materials which satisfy the demand for high frequency and powerdesity are crucial. The microwave transitors based on wide band-gap materials becomethe research focus. GaN-based heterostructures, which have wide band-gap, high twodimensional eletronn gas density and high saturated electon velocity are studied widely.And the AlGaN/GaN HEMTs are proved the ideal transistors for power amplifierdesign.In the dissertation, the DC-IV, small signal performance and large signalperoformance are measured. Based on this, a small signal model and an EEHEMT largesignal model are represented by equivalent circuit and mathematical relations. Thepower amplifiers were designed by using the laod-pull data. The application based onGaN is studied. The major results are represented as follow:1. The set-up of laodpull measurement system for die and power measurement systemfor discrete device are developed. The power afforded and frequecny range must beconsidered because GaN HEMTs are a new generation transistor with high voltage andlarge power. Finally, the loadpull system can support20W of average power and1.8GHz¹8GHz of frequency range. The pakaged transistor can be measured forfrequency rangeing from0.8GHz to12GHz and50W of power.2. The characterization and research on GaN HEMTs. Based on the IV measurementdata, the self-heating effect and RF dispersion are researched. The relation beteweensmall signal performance of device with gate width of100um and DC bias and the smallsignal performance of different structurral devices are measured and studied. The largesignal measurements including the load-pull measurements and power sweepmeasurements were carried on. The Source–pull map and laod-pull map were obtained.Under V_ds=30V，V_gs=-3.6V, CW operating condition at5.5GHz, the amplifier moduleexhibits line gain of20dB with power added efficiency of52.8%, and power density of8.57W. The relations between ouptut power, gain and frequency were studied. The source pull and load pull characterizations were performed. The effect of self-heating onmaximum saturated current, peak transconductance, current cut-off frequency, outputpower and scalling rule were analyzed3. The small signal model and EEHEMT model were developed. The19-parametersmall-signal equivalent circuit mdoel is proposed. Based on the S parameter results, theparasitic and intrinsic elements were extracted and the results simulated by small signalmodel and results measured were compared. The dependences of intrinsic parameter onthe drain voltage and gate voltage were illuminated. And based on the small signalmodel, a large-signal model was built up. The measured S parameter results andsimualted results, the measured power sweep results and simulated power sweep resultswere compared and explored. The comparison shows that model can predict devicebehavior. And the effect that causes model error is discussed.4. GaN-based one-stage power amplifier and two-stage power amplfier module werefabricated. Based on S parameter results and load-pull measurements, one-stage andtwo-stage GaN solid-state power amplifier module were designed. The devices withgate width of100um and1.5mm were characterized. The extrinsic cutoff gain frequencyft, maximum frequency of oscillation fmaxand stable factor were analyzed. Thetwo-stage1/4wavelength matching and multi-stage shunt admittance matching aredesigned. Microstrip stubs and1/4wavelength can become the RF chock cicuit. R-Cnetworks are used for cancellation of self-oscillation of low frequency and radiofrequency. The module is fabracated after calculating the oscillation frequency. UnderV_ds=27V，V_gs=-4.0CW operating condition at8GHz, the one-stage amplifier moduleexhibits maximum line gain of5.6dB with output power of40.25dBm andpower-added efficiency of30.5%, and the maximum line gain of8.6dB with outputpower of38.9dBm and power-added efficiency of30.5%were achieved.5. The X-band two-way and four-way combined GaN solid-state power amplifiermodules are fabricated. The branches of length3/4λ for Wilkinson power couplers areused to substitute the traditional1/4λ transformer. The3-dB Wilkinson hybrid couplerand6-dB Wilkinson hybrid coupler are designed and measured. At8GHz, the insertionloss is less than0.5dB and the measured return loss in the input port and output port aremore than10dB and15dB. The isolation is more than15dB. At8GHz, under V_ds=27V，V_gs=-4.0, the two-way combined amplifier module exhibits maximum line gain of5.6dB with output power of41.46dBm and power-added efficiency of23.4%, and forfour-way combined power amplifier, the maximum gain of5dB, power addedeffieciency of17.9%and the maximum output power of42.93dBm are achieved. At last, the reason that causes the reduction of combining results are analyzed and discussed.Above all, in the dissertation, the DC-IV measurement, small signal measurementand large signal measurement for small gate width and large gate width are performed.The results are analyzed and explored. Based on this, the small signal equivalent cicuitmodel and large signal model are built up. Accoding to the load-pull data, the poweramplifiers are designed. The two-way and four-way combined GaN power amplifiermodules are designed and fabricated by using power combining technology. Themeasurement results demonstrated that GaN-based amplifiers are promising in thefuture. Hopfully, the results in the dissertation are valuable for GaN-basedherterostructure in the various applications.