Study On GaN-based FP-HEMT With High Performance

Due to its superior properties,GaN-based high-electron mobility transistor(HEMT)is of great interest for high-power,high-temperature,and high-frequency applications since their first demonstration in 1993.The high operation voltage based on the high breakdown voltage,has been one of the most important and efficient catalysts for improving the microwave power performance of GaN-based HEMT.In order to further explore the intrinsic physical mechanisms of the high breakdown voltage,the main studies of the field-plate(FP)HEMT(FP-HEMT)with high breakdown voltage and high reliability have been carried out in this dissertation.The major research work and results are as follows:1.The current collapse phenomena of the devices with a gate FP or a gate-source FP are investigated.And the intrinsic physical mechanisms on the suppression of the current collapse with the FP in GaN HEMT are revealed by means of experiments and numerical device simulations.2.A two-dimensional analytical model,with the polarization effect and the lateral spread of the depletion region,for the gate FP-HEMT is proposed on the basis of two-dimensional Poisson’s solution for the first time.The influence of the device structure parameters on the channel potential and electric field distributions is analyzed in terms of this model in detail.The studies show a good agreement between the proposed model and the numerical simulation results obtained by Silvaco-atlas.3.The FP-HEMT with an HfO2 passivation layer(HfO2-FP-HEMT)is developed successfully.With the HfO2 high k material,the FP modulation of the channel electric field is enhanced,which improves the device breakdown performance significantly.The breakdown voltage of as high as 181 V and a record FP efficiency of 276 V/μm are achieved in the device with only a 0.3 μm FP.These experimental results are explained.Meanwhile,based on the theoretical and experimental researches,an approach for the FP structure,named the proportional design is proposed,with which the optimal dielectric thickness beneath the FP can be predicted effectively.4.A novel and more effective FP-HEMT,named as floating field-plate(FFP)device is proposed.And the device samples with high performance are developed successfully.These devices,with a gate length of 0.6μm,show afT of 13.8GHz,afmax of 34GHz and a breakdown voltage of as high as 313V,respectively,which indicates significant improvements compared with the conventional FP with the same FP size.5.The high performance AlInN/AlN/GaN MOS-HEMT with a 3 nm ultra-thin atomic layer deposited(ALD)Al2O3 gate dielectric layer and a 0.3μm FP is developed successfully.This device,with a gate length of 0.6μm,exhibits a breakdown voltage of 133V,a FP efficiency of 170 V/μm,a good suppression of the current collapse and a maximum output current of 1141 mA/mm at VGS=3V.With the adoption of the 3 nm ultra-thin Al2O3 gate dielectric layer,the peak transconductance(325 mS/mm)of this device is not decreased but rather is increased a little than that of the HEMT.And the fT and fmax for this device are 14.5 GHz and 43.3GHz,respectively,which is approximately equal to those of the HEMT.6.The AlInN/AlN/GaN field-plate MIS-HEMT with a 7nm PECVD SiN gate dielectric layer is developed successfully.This device,with a gate length of 0.6μm,exhibits a breakdown voltage of 120V,as well as good suppressions of the current collapse and the gate leakage current.The output current at VGS=5V could reach 121 1mA/mm,which is 375 mA/mm greater than the peak current of the HEMT.And the fT and fmax are 10.3GHz and 25GHz,respectively.