Physical degradation of GaN HEMT devices under high drain bias reliability testing

The AlGaN/GaN heterostructure HEMTs were epitaxially grown using MOCVD on semi-insulating SiC substrates. Standard III-V commercial production processing technology was used to fabricate the devices, which were then subjected to stress under accelerated DC life-tests with base-plate temperatures of 82, 112, and 142 °C. Drain bias of 40 V and time-zero drain current of 250 mA/mm were applied. TEM samples were prepared via the lift-out technique using a focused ion beam (FIB). TEM analysis revealed that electrically degraded devices always contain a pit-like defect next to the drain in the top AlGaN layer. It has been found that the degree of the defect formation strongly correlates to drain current (I_Dmax) degradation.     

Determination of GaN HEMT reliability by monitoring IDSS

In this paper, we investigate the importance and necessity to determine the reliability of GaN HEMT devices by monitoring I_DSS during accelerated DC life-test measurements at elevated ambient temperatures. The influence of interrupting this test and cooling the device to measure I_DSS at room temperature is investigated. But also methods are investigated to replace this measurement to speed up the reliability measurements and reduce the thermo-mechanical stress induced due to periodically cooling and heating of the devices. One method parameter to monitor is the so called intrinsic I_DSS, which is the parameter measured at the ambient temperature of the life-test. The investigation shows that monitoring the intrinsic I_DSS is a solid tool to determine the life-time, but too often measurement of this parameter could add additional stress to the device.In addition we saw that intermediate measurements of the output and transfer characteristics did not introduce measureable addition stress as suspected. We also observed that for stress tests at constant P_Diss the drift of the gate voltage can be used as failure criterion, although it has no linear relationship to I_DSS and therefore the gate voltage drifts more than I_DSS and leads to more conservative life-time.     

AlGaN/GaN double-channel HEMT

The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied.     

Nonlinear characterization of GaN HEMT

DC I-V output, small signal and an extensive large signal characterization (load-pull measurements) of a GaN HEMT on a SiC substrate with different gate widths of 100μm and 1 mm have been carried out. From the small signal data, it has been found that the cutoff frequencies increase with gate width varying from 100μm to 1 mm, owing to the reduced contribution of the parasitic effect. The devices investigated with different gate widths are enough to work in the C band and X band. The large signal measurements include the load-pull measurements and power sweep measurements at the C band (5.5 GHz) and X band (8 GHz). When biasing the gate voltage in class AB and selecting the source impedance, the optimum load impedances seen from the device for output power and PAE were localized in the load-pull map. The results of a power sweep at an 8 GHz biased various drain voltage demonstrate that a GaN HEMT on a SiC substrate has good thermal conductivity and a high breakdown voltage, and the CW power density of 10.16 W/mm was obtained. From the results of the power sweep measurement at 5.5 GHz with different gate widths, the actual scaling rules and heat effect on the large periphery device were analyzed, although the effects are not serious.The measurement results and analyses prove that a GaN HEMT on a SiC substrate is an ideal candidate for high-power amplifier design.     

AlGaN/GaN double-channel HEMT

正The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported.Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure.The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region.The buffer trap is suggested to be related to the wide region of high transconductance.The RF characteristics are also studied.     

X波段GaN HEMT的研制

采用双台面隔离工艺,实现了器件有源区隔离,隔离电压大于250 V/10μA.通过对金属化前和介质膜淀积前的预处理过程的改进,实现了较理想的肖特基势垒特性,电压也得到了大幅度提高,理想因子n值小于1.7,源漏击穿电压大于50 V/1 mA,栅源击穿电压大于40 V/1 mA,最终实现器件X波段连续波输出功率20 W,功率增益7 dB,功率密度8 W/mm.     

氮化镓器件非线性特性表征

对100um和1mm碳化硅衬底的氮化镓器件进行直流特性,小信号特性和大信号特性的表征。100um和1mm器件小信号特性测试结果发现,随栅长增大,由于电容寄生效应的减小,电流截止频率fT增大。从数据看出,器件可用在C波段和X波段。大信号测试包括C波段和X波段负载牵引测试和功率扫描测试。器件偏置在AB类工作点,并且选定源端阻抗,做负载牵引测试。在负载牵引园图上,最大功率阻抗点和最佳效率阻抗点可以确定。根据5.5GHz的不同栅长的器件的功率扫描结果分析器件尺寸变换效应与和大尺寸器件的自热效应密切相关。8GHz 不同漏极偏置的器件的功率扫描结果说明碳化硅衬底的氮化镓器件有好的热导率,高击穿电压和10.16W/mm 功率密度。从分析可证明碳化硅衬底的氮化镓器件是放大器设计的理想材料。     

AlGaN/GaN HEMT device reliability and degradation evolution: Importance of diffusion processes

A methodology based on combined electrical trapping analysis with UV-assisted preparation of trap states and electroluminescence analysis was developed to gain detailed understanding of trap generation in AlGaN/GaN HEMTs during off and on-state stress. This is used to identify electronic trap location laterally and vertically in a device structure and the nature of the degradation mechanism. We identify the generation of traps with activation energies in the range from 0.45 to 0.65 eV near the gate edge on its drain side in AlGaN/GaN HEMTs as electronic traps in the AlGaN device layer, as a result of on- and off-state stress. Degradation studied on devices subjected to stress under different backplate temperatures, points to diffusion processes playing an important role for early device degradation. Diffusion constants showed thermal activation energies of ∼0.26 eV consistent with diffusion processes along dislocations, with possible additional contributions from bulk diffusion accelerated by converse/inverse piezo-electric strain and leakage currents.     

C波段高效率GaN HEMT功率放大器

通过负载牵引测试验证了源端二次谐波对器件效率的影响,同时又进一步验证了输出谐波匹配对放大器的作用。基于此结果,研制了两款采用0.25μm工艺的GaN功率MMIC 4.0~5.6GHz高效率放大器芯片,芯片采用二级放大的结构。第一款输出级只考虑基波的匹配;第二款输出级匹配电路兼顾二次和三次谐波进行匹配。两款的末前级均考虑二次谐波的匹配,同时级间优化推动比,进一步提高效率。输入级和级间匹配电路采用有耗匹配,提高稳定性。芯片在4.0~5.6 GHz范围内漏压28 V,脉宽100μs,占空比10%条件下输出功率41dBm,功率增益20~21dB,功率附加效率分别在48%和45%以上。芯片面积3.9mm×3.3mm。     

AlGaN/GaN HEMT器件的研制

介绍了AlGaN/GaN HEMT器件的研制及室温下器件特性的测试.漏源欧姆接触采用Ti/Al/Pt/Au,肖特基结金属为Pt/Au.器件栅长为1μm,获得的最大跨导为120mS/mm,最大的漏源饱和电流密度为0.95A/mm.     

一种新型的常通型GaN HEMT器件

对新型常通型GaN HEMT器件的特性和参数进行了研究。阐述了其静态特性、动态特性及电流崩塌问题。针对其动态特性,与相近规格的Si MOSFET器件（TK2Q60D）在开通、关断时间与栅源电压的关系方面进行了对比,探讨了常通型GaN HEMT器件在不同输入电压和不同开关频率下的电流崩塌现象,并采用Boost电路,对常通型GaN HEMT器件和Si MOSFET器件的最高工作频率能力进行了对比。实验结果表明,常通型GaN HEMT器件具有更高的工作频率,且工作频率的升高不影响电流崩塌现象。     

C波段GaN HEMT内匹配功率放大器

基于通信对功率放大器的宽带和高效率的需求,给出了一款C波段GaN HEMT内匹配功率放大器的设计过程。该器件由2个3 mm栅宽的GaN功率管芯和制作在Al_2O_3陶瓷基片上的输入输出匹配电路组成。通过调节键合丝和电容,实现了功率放大器在4.4~5.0 GHz,5.2~5.9 GHz和6.0~6.6 GHz三个典型工程应用频段的设计,功放在这3个典型工程应用频段内输出功率均大于43 d Bm(20 W),附加效率大于60%,功率增益大于10 d B,充分显示了GaN功率器件宽带、高效率的工作性能。     

Ka波段GaN HEMT功率器件

设计了Ka波段GaN功率高电子迁移率晶体管(HEMT)外延材料及器件结构,采用AlN插入层提高了二维电子气(2DEG)浓度.采用场板结构提高了器件击穿电压.采用T型栅工艺实现了细栅制作,提高了器件高频输出功率增益.采用钝化工艺抑制了电流崩塌,提高了输出功率.采用通孔工艺减小源极寄生电阻,通过优化钝化层厚度减小了寄生电容,提高了器件增益.基于国产SiC外延材料及0.15 μm GaN HEMT工艺进行了器件流片,最终研制成功Ka波段GaN HEMT功率器件.对栅宽300 μm器件在29 GHz下进行了微波测试,工作栅源电压为-2.2V,源漏电压为20 V,输入功率为21 dBm时,器件输出功率为30 dBm,功率增益为9 dB,功率附加效率约为43％,功率密度达到3.3 W/mm.     

AlGaN/GaN HEMT器件的研制

介绍了AlGaN/GaNHEMT器件的研制及室温下器件特性的测试.漏源欧姆接触采用Ti/Al/Pt/Au ,肖特基结金属为Pt/Au .器件栅长为1μm ,获得的最大跨导为12 0mS/mm ,最大的漏源饱和电流密度为0 95A/mm .     

Poly-Si gate electrodes for AlGaN/GaN HEMT with high reliability and low gate leakage current

AlGaN/GaN HEMT with a BF₂-implanted polycrystalline Si gate has been characterized through comparison to TiN gate electrodes. Positive threshold voltage (V_th) shift was observed with the addition of F ions, which in turn degraded the effective electron mobility (μ_eff) by diffusion into the AlGaN/GaN interface and GaN layer. A large reduction in gate leakage current (J_g) was achieved and the property was maintained even after strong reverse-bias stressing. No additional degradation in μ_eff was observed, suggesting the formation of a stable poly-Si/AlGaN interface. Therefore, poly-Si gate electrodes have advantages in reducing the J_g and robustness against reverse-bias stressing.     

X-波段AlGaN/GaN HEMT 功率MMIC

AlGaN/GaN高电子迁移率晶体管(HEMT)以其高输出功率密度、高电压工作和易于宽带匹配优势将成为下一代高频固态微波功率器件.     

High-power monolithic AlGaN/GaN HEMT oscillator

A monolithic X-band oscillator based on an AlGaN/GaN high electron mobility transistor (HEMT) has been designed, fabricated, and characterized. A common-gate HEMT with 1.5 mm of gate width in conjunction with inductive feedback is used to generate negative resistance. A high Q resonator is implemented with a short-circuit low-loss coplanar waveguide transmission line. The oscillator delivers 1.7 W at 9.556 GHz into 50-/spl Omega/ load when biased at V/sub ds/=30 V and V/sub gs/=-5 V, with dc-to-RF efficiency of 16%. Phase noise was estimated to be -87 dBc/Hz at 100-kHz offset. Low-frequency noise, pushing and pulling figures, and time-domain characterization have been performed. Experimental results show great promise for AlGaN/GaN HEMT MMIC technology to be used in future high-power microwave source applications.