Gate-structure optimization for high frequency power AlGaN/GaN HEMTs

The influence of gate-head and gate-source-spacing on the performance of AlGaN/GaN HEMTs was studied.Suggestions are then made to improve the performance of high frequency power AlGaN/GaN HEMTs by optimizing the gate-structure.Reducing the field-plate length can effectively enhance gain,current gain cutoff frequency and maximum frequency of oscillation.By reducing the field-plate length,devices with 0.35 μm gate length have exhibited a current gain cutoff frequency of 30 GHz and a maximum frequency of oscillation of 80 GHz.The maximum frequency of oscillation can be further optimized either by increasing the gate-metal thickness,or by using a t-shape gate (the gate where the gate-head tends to the source side).Reducing the gate-source spacing can enhance the maximum drain-current and breakdown voltage,which is beneficial in enhancing the maximum output power of AlGaN/GaN HEMTs.     

高频功率AlGaN/GaN HEMT 的栅结构优化

本文研究了栅帽、栅源间距对AlGaN/GaN HEMT性能的影响。基于研究结果得出了优化高频功率AlGaN/GaN HEMT栅结构的方法。缩小栅场板可以有效提高器件的增益、截止频率（ft）、最大震荡频率（fmax）。通过减小栅场板长度,栅长0.35 器件的ft达到了30GHz、fmax达到了80GHz。采用tao型栅（栅帽偏向源侧）或者增加栅金属厚度还可以进一步优化 。缩小栅源的距离可以提高饱和漏电流和击穿电压,从而提高器件的输出功率。     

A semi empirical approach for submicron GaN MESFET using an accurate velocity field relationship for high power applications

A semi empirical model has been proposed for sub-micron GaN MESFET's to calculate the I-V characteristics using an accurate velocity-field relationship obtained by fitting it with the Monte Carlo (MC) simulation. The results so obtained are compared with the experimental results to validate our model and are also compared with the results obtained from the simple saturation model to present the influence of electron drift velocity modeling on the device parameters. The model has been extended to predict the microwave parameters such as transconductance and output conductance of the device.     

Unpassivated GaN/AlGaN/GaN power high electron mobility transistors with dispersion controlled by epitaxial layer design

In this paper, a novel GaN/AlGaN/GaN high electron mobility transistor (HEMT) is discussed. The device uses a thick GaN-cap layer (∼250 nm) to reduce the effect of surface potential fluctuations on device performance. Devices without Si₃N₄ passivation showed no dispersion with 200-ns-pulse-width gate-lag measurements. Saturated output-power density of 3.4 W/mm and peak power-added efficiency (PAE) of 32% at 10 GHz (V_DS=+15 V) were achieved from unpassivated devices on sapphire substrates. Large gate-leakage current and low breakdown voltage prevented higher drain-bias operation and are currently under investigation.     

An 8 GHz high power AlGaN/GaN HEMT VCO

A high power X-band hybrid microwave integrated voltage controlled oscillator(VCO) based on Al-GaN /GaN HEMT is presented.The oscillator design utilizes a common-gate negative resistance structure with open and short-circuit stub microstrip lines as the main resonator for a high Q factor.The VCO operating at 20 V drain bias and-1.9 V gate bias exhibits an output power of 28 dBm at the center frequency of 8.15 GHz with an efficiency of 21%.Phase noise is estimated to be -85 dBc/Hz at 100 kHz offset and -1...     

一个8GHz高功率AlGaN/GaN HEMT VCO

基于中科院微电子所的AlGaN/GaN HEMT工艺研制了一个X波段高功率混合集成压控振荡器（VCO）。电路采用源端调谐的负阻型结构,主谐振腔由开路微带和短路微带并联构成,实现高Q值设计。在偏置条件为VD=20V, VG=-1.9V, ID=150mA时,VCO在中心频率8.15 GHz处输出功率达到28 dBm,效率21%,相位噪声-85 dBc/Hz@100 KHz,-128 dBc/Hz@1 MHz。调谐电压0~5V时,调谐范围50 MHz。分析了器件闪烁噪声对GaN HEMT基振荡器相位噪声性能的主导作用。测试结果显示了AlGaN/GaN HEMT工艺在高功率低噪声微波频率源中的应用前景。     

The effect of built-in electric field in GaN/AlGaN quantum wells with high AIN mole fraction

Spontaneous and piezoelectric polarization in hexagonal GaN/AlGaN heterostructures give rise to large built-in electric fields. The effect of the builtin electric field in GaN/Al_xGa_1−xN quantum wells was investigated for x=0.2 to 0.8 by photoluminescence studies. The quantum well structures were grown by molecular beam epitaxy on (0001) sapphire substrates. Cross-sectional transmission electron microscopy performed on the samples revealed abrupt interfaces and uniform layer thicknesses. The low temperature (4 K) photoluminescence peaks were progressively red-shifted due to the quantum confined Stark effect depending on the AlN mole fraction in the barriers and the thickness of the GaN quantum well. Our results verify the existence of very large built-in electric fields of up to 5 MV/cm in GaN/Al_0.8Ga_0.2N quantum wells.     

一个Ku波段高功率密度AlGaN/GaN HEMTs单片集成功率放大器

本文报道了一款工作于Ku波段的高功率密度单片集成功率放大器。该放大器采用金属有机化学气相淀积技术在2英寸半绝缘 4H-SiC衬底上生长0.2um AlGaN/GaN HEMTs工艺制作而成。在10%占空比的脉冲偏置Vds=25V,Vgs=-4V条件下,该单片放大器在12-14GHz频率范围内得到最大输出功率38dBm(6.3W),最高PAE 24.2%和线性增益6.4到7.5dB。以这种功率水平而论,该放大器的功率密度超过5W/mm。     

A Ku-band high power density AlGaN/GaN HEMT monolithic power amplifier

A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3μm AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating（SI） 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range,the single chip amplifier demonstrates a maximum power of 38 dBm（6.3 W）, a peak power added efficiency（PAE） of 24.2%and linear gain of 6.4 to 7.5 dB under a 10%duty pulse condition when operated at V_ds = 25 V and V_gs = -4 V.At these power levels,the amplifier exhibits a power density in excess of 5 W/mm.     

X波段AlGaN/GaN HEMTs厂栅场板结构研究

基于SiC衬底成功研制X波段0.25um栅长带有г栅场板结构的AlGaN/GaN HEMT,对比T型栅结构器件,研究了г栅场板引入对器件直流、小信号及微波功率特性的影响.结果表明,г栅场板结构减小器件截止频率及振荡频率,但明显改善器件膝点电压和输出功率密度.针对场板长度分别为0.4、0.7、0.9、1.1 um,得出一定范围内增加场板长度,器件输出功率大幅度提高,并结合器件小信号模型提参结果分析原因.在频率8 GHz下,总栅宽1 mm,场板长度0.9um的器件,连续波输出功率密度7.11 W/mm,功率附加效率(PAE)35.31%,相应线性增益10.25 dB.     

8W AlGaN/GaN HEMT功率器件的研制

报道了基于国产衬底以及国产外延的AlGaN/GaN HEMT X波段功率器件的研究进展.利用国产衬底以及外延材料,优化了器件栅场板的结构,研制成功栅长0.35μm,栅宽为lmm的微波功率器件.该器件输出电流密度达到0.83A/mm,击穿电压大于100V,跨导为236mS/mm,截止频率(fT)达到30GHz,最大振荡频率(fmax)为32GHz,8GHz下在片进行连续波测试,漏端电压为40V时测试得到功率增益4.9dB,输出功率达8W,功率附加效率(PAE)为45%.     

8W AlGaN/GaN HEMT功率器件的研制

报道了基于国产衬底以及国产外延的AlGaN/GaN HEMT X波段功率器件的研究进展.利用国产衬底以及外延材料,优化了器件栅场板的结构,研制成功栅长0.35μm,栅宽为lmm的微波功率器件.该器件输出电流密度达到0.83A/mm,击穿电压大于100V,跨导为236mS/mm,截止频率(fT)达到30GHz,最大振荡频率(fmax)为32GHz,8GHz下在片进行连续波测试,漏端电压为40V时测试得到功率增益4.9dB,输出功率达8W,功率附加效率(PAE)为45%.     

11.2 W/mm power density AlGaN/GaN high electron-mobility transistors on a GaN substrate

In this letter, high power density AlGaN/GaN high electron-mobility transistors (HEMTs) on a freestanding GaN substrate are reported. An asymmetric Γ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance. The breakdown voltage (BV) is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92 μm. A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V. The maximum oscillation frequency (f_max) and unity current gain cut-off frequency (f_t) of the AlGaN/GaN HEMTs exceed 30 and 20 GHz, respectively. The results demonstrate the potential of AlGaN/GaN HEMTs on free-standing GaN substrates for microwave power applications.     

Optimized power simulation of AlGaN/GaN HEMT for continuous wave and pulse applications

An optimized modeling method of 8 × 100 μm AlGaN/GaN-based high electron mobility transistor (HEMT) for accurate continuous wave (CW) and pulsed power simulations is proposed. Since the self-heating effect can occur during the continuous operation, the power gain from the continuous operation significantly decreases when compared to a pulsed power operation. This paper extracts power performances of different device models from different quiescent biases of pulsed current-voltage (I-V) measurements and compared them in order to determine the most suitable device model for CW and pulse RF microwave power amplifier design. The simulated output power and gain results of the models at V_gs = -3.5 V, V_ds = 30 V with a frequency of 9.6 GHz are presented.     

Simulation and fabrication of high voltage AlGaN/GaN based Schottky diodes with field plate edge termination

In this paper, we report the breakdown voltage (BV) of AlGaN/GaN based Schottky diodes with field plate edge termination. Simulation and fabrication of AlGaN/GaN Schottky diodes were carried out. The simulations were performed using the commercial 2-D device simulator DESSIS. From the simulations, it is found that for a given gate-Ohmic distance (L_gd) of 10 μm, 2DEG of 1 × 10¹³ cm⁻² and field plate length (L_FP) of 2.5 μm, highest BV can be obtained for a silicon nitride thickness of 8000 Å and this BV value is more than 5 times that for a Schottky diode without field plate. The breakdown voltages were also simulated for different field plate lengths. The BV values obtained on the fabricated Schottky diodes are compared with the simulation data and the experimental results follow the trend obtained from the simulation. Simulations were also carried out on a Schottky diode with field plate placed over a stepped insulator with L_gd = 10 μm, L_FP = 5 μm and 2DEG = 1 × 10¹³ cm⁻² and the obtained BV values are about 7 times that without field plate.     

应用于大功率MMIC开关的AlGaN背势垒GaN HEMT

报道了应用于大功率开关的AlGaN背势垒0.25μm GaN HEMT。通过引入AlGaN背势垒,MOCVD淀积在3英寸SiC衬底上的AlGaN/GaN异质结材料缓冲层的击穿电压获得了大幅度的提升,相比于普通GaN缓冲层和掺Fe GaN缓冲层击穿电压提升幅度分别为4倍和2倍。采用具有AlGaN背势垒AlGaN/GaN 外延材料研制的GaN HEMT开关管在源漏间距为2μm、2.5μm、3μm、3.5μm和4μm时,估算得到的关态功率承受能力分别为25.0W、46.2W、64.0W、79.2W和88.4W。基于源漏间距为2.5μm的GaN HEMT开关管设计了DC-12GHz的单刀双掷MMIC开关。该开关采用了反射式串-并-并结构,整个带内插入损耗最大1.0dB、隔离度最小30dB,10GHz下连续波测试得到其功率承受能力达44.1dBm。     

14.2 W/mm internally-matched AlGaN/GaN HEMT for X-band applications

High-performance X-band AlGaN/GaN high electron mobility transistor (HEMT) has been achieved by Γ-gate process in combination with source-connected field plate. Both its Schottky breakdown voltage and pinch-off breakdown voltage are higher than 100 V. Beside, excellent superimposition of direct current (DC) I-V characteristics in different V_ds sweep range indicates that our GaN HEMT device is almost current collapse free. As a result, both outstanding breakdown characteristics and reduction of current collapse effect guarantee high microwave power performances. Based upon it, we have developed an internally-matched GaN HEMT amplifier with single chip of 2.5 mm gate periphery, which exhibits power density of 14.2 W/mm with 45.5 dBm (35.5 W) output power and a power added efficiency (PAE) of 48% under V_ds = 48 V pulse operating condition at 8 GHz. To the best of our knowledge, it is the highest power density at this power level.     

Fabrication and characterization of AlGaN/GaN HEMTs with high power gain and efficiency at 8 GHz

State-of-the-art AlGaN/GaN high electron mobility structures were grown on semi-insulating 4H-SiC substrates by MOCVD and X-band microwave power high electron mobility transistors were fabricated and characterized.Hall mobility of 2291.1 cm2/(V·s) and two-dimensional electron gas density of 9.954 × 1012 cm-2 were achieved at 300 K.The HEMT devices with a 0.45-μm gate length exhibited maximum drain current density as high as 1039.6 mA/mm and peak extrinsic transconduct-ance of 229.7 mS/mm.The fT of 30.89 GHz and fmax of 38.71 GHz were measured on the device.Load-pull measurements were performed and analyzed under (-3.5,28) V,(-3.5,34) V and (-3.5,40) V gate/drain direct current bias in class-AB,respectively.The uncooled device showed high linear power gain of 17.04 dB and high power-added efficiency of 50.56％ at 8 GHz when drain biased at (-3.5,28) V.In addition,when drain biased at (-3.5,40) V,the device exhibited a saturation output power dens-ity up to 6.21 W/mm at 8 GHz,with a power gain of 11.94 dB and a power-added efficiency of 39.56％.Furthermore,the low fmax/fT ratio and the variation of the power sweep of the device at 8 GHz with drain bias voltage were analyzed.     

蓝宝石衬底AlGaNöGaN 功率HEM Ts 研制

基于蓝宝石衬底的高微波特性 Al Ga N/Ga N HEMTs功率器件 ,器件采用了新的欧姆接触和新型空气桥方案。测试表明 ,器件电流密度 0 .784A/mm,跨导 1 97m S/mm,关态击穿电压 >80 V,截止态漏电很小 ,栅宽 1 mm的器件的单位截止频率 ( f T)达到 2 0 GHz,最大振荡频率 ( fmax) 2 8GHz,2 GHz脉冲测试下 ,栅宽 0 .75 mm器件 ,功率增益1 1 .8d B,输出功率 3 1 .2 d Bm,功率密度 1 .75 W/mm。     

Implications of gate-edge electric field in AlGaN/GaN high electron mobility transistors during OFF-state degradation

Gate degradation in high electron mobility transistors (HEMTs) under OFF-state stress results from the high electric field near the gate edge. We investigate the evolution of this field over time in AlGaN/GaN HEMTs upon OFF-state stress using a combination of electroluminescence (EL) microscopy and spectroscopy. EL analysis suggests that the electric field at the sites of generated surface defects is lowered after the stress, with greater lowering at higher stress temperature. The ON-state EL spectrum remains unchanged after the stress, suggesting that the regions without generated defects are not affected during the degradation. A finite element model is employed to further demonstrate the effect of surface defects on the local electric field. A correlation is observed for the spatial distribution of the EL intensity before and after the generation of leakage sites, which provides a prescreening method to predict possible early failures on a device.