半绝缘GaAs衬底中位错对MESFETs旁栅效应的影响

在位错密度不同的LEC半绝缘（SI）GaAs衬底上离子注入制做MESFETs，观察衬底位错对MESFETs旁栅效应的影响．结果表明，衬底中高位错密度可以抑制旁栅效应．

(NH_4)_2S_x溶液改善GaAs MESFETs击穿特性的机理研究

使用 (NH4) 2 Sx 溶液对GaAsMESFETs进行处理。处理后 ,器件各栅偏压下的源漏饱和电流降低了 ,栅漏击穿电压有了显著提高。我们认为负电荷表面态影响着栅边缘的电场 ,负电荷表面态密度的增大会提高器件的击穿电压 ,这就是 (NH4) 2 Sx

Fabrication of SiC MESFETs for Microwave Power Applications

4H-SiC MESFETs are fabricated on semi-insulating SiC substrates. Key processes are optimized to obtain better device performance. A microwave power amplifier is demonstrated from a 1mm SiC MESFET for S band operation. When operated at a drain voltage of 64V, the amplifier shows an output power of 4.09W, a gain of 9.3dB,and a power added efficiency of 31.3%.

Theoretical Investigation of Pinch off Voltage of Box-Like Ion-Implanted 4H-SiC MESFETs

A precise theoretical calculation off the pinch of voltage of the box-like ion implantation 4H-SiC MESFETs is investigated with the consideration of the effects of the ion-implanted channel and the depth of MESFETs channel.The implant depth profile is simulated using the Monte Carlo simulator TRIM.The effects of parameters such as temperature,acceptor density,and activation rate on channel depth a,pinch off voltage are studied.

改善GaAs MESFETs硫钝化稳定性研究的新探索

硫钝化可以明显改善GaAs金属半导体场效应晶体管(MESFETs)的击穿特性,但钝化效果不稳定。我们利用硫钝化和PECVD SiNx 钝化相结合的方法,使钝化的稳定性得到了提高,但同时击穿电压会出现下降。击穿电压下降的主要原因是:As S键很不稳定,在较高温度下分解,使GaAs表面负电荷密度减小,击穿电压下降。

Experimental and numerical analysis of the multi-recessed gate structure for microwave silicon carbide power MESFETs

This paper reports that multi-recessed gate 4H-SiC MESFETs （metal semiconductor filed effect transistors） with a gate periphery of 5-mm are fabricated and characterized.The multi-recessed region under the gate terminal is applied to improve the gate-drain breakdown voltage and to alleviate the trapping induced instabilities by moving the current path away from the surface of the device.The experimental results demonstrate that microwave output power density,power gain and power-added efficiency for multi-finger 5-mm gate periphery SiC MESFETs with multi-recessed gate structure are about 29%, 1.1dB and 7% higher than those of conventional devices fabricated in this work using the same process.

GaAs MESFETs欧姆接触的快速评估和改进

提出了金属-半导体欧姆接触退化的快速评估方法-温度斜坡快速评价法，并建立了自动评估系统，用该方法和系统测得的欧姆接触退化激活能，和传统方法相比，耗时少，所需样品少，所得结果和传统方法一致．同时，针对传统AuGeNi／Au欧姆接触系统的缺点，提出了加TiN扩散阻挡层的新型欧姆接触系统．实验表明，新型欧姆接触系统的可靠性远远优于传统AuGeNi／Au欧姆接触系统．

Numerical Analysis of Gate-to-Source Distance Effects in SiC MESFETs

Two-dimensional DC and small-signal analysis of gate-to-source scaling effects in SiC-based high-power field-effect transistors have been performed in this paper. The simulation results show that a downscaling of gate-to-source distance can improve device performance, i.e. enhancing drain current, transconductance, and maximum oscillation frequency. This is associated with the peculiar dynamic of electrons in SiC MESFETs, which lead to a linear velocity regime in the source access region. The variations of gate-to-source capacitance, gate-to-drain capacitance, and cut-off frequency with respect to the change in gate-to-source length have also been studied in detail.

A New Empirical Large Signal Model of 4H-SiC MESFETs for the Nonlinear Analysis

A new comprehensive empirical large signal model for 4H-SiC MESFETs is proposed. An enhanced drain current model,along with an improved charge conservation capacitance model,is presented by the improvement of the channel length modulation and the hyperbolic tangent function coefficient based on the Materka model. The Levenberg-Marquardt method is used to optimize the parameter extraction. A comparison of simulation resuits with experimental data is made,and good agreements of I-V curves, Pout （output power）, PAE （power added efficiency） ,and gain at the bias of Vos = 20V, Ips = 80mA as well as the operational frequency of 1.8GHz are obtained.

半绝缘非掺GaAs材料制备的MESFETs背栅效应

设计了一套适用于二种工艺（离子注入隔离工艺和半绝缘衬底自隔离工艺）的背栅效应测试版图，用选择离子注入形成有源层和欧姆接触区，在非掺杂的半绝缘ＧａＡｓ 衬底上制备ＧａＡｓ ＭＥＳＦＥＴｓ 器件．研究了这二种不同工艺制备的ＭＥＳＦＥＴｓ 器件的背栅效应以及不同距离背栅电极的背栅效应大小．结果表明，采用离子注入隔离工艺制备的ＭＥＳＦＥＴｓ 器件的背栅效应要比采用半绝缘衬底自隔离工艺制备ＭＥＳＦＥＴｓ器件的背栅效应小，背栅效应的大小与距离近似成反比，采用隔离注入的背栅阈值电压随距离变化的趋势比采用衬底自隔离的更大．

A CAD oriented quasi-analytical large-signal drain current model for 4H-SiC MESFETs

This paper reports that a 4H-SiC MESFET （Metal Semiconductor Field Effect Transistor） large signal drain current model based on physical expressions has been developed to be used in CAD tools. The form of drain current model is based on semi-empirical MESFET model, and all parameters in this model are determined by physical parameters of 4H-SiC MESFET. The verification of the present model embedded in CAD tools is made, which shows a good agreement with measured data of large signal DC I-V characteristics, PAE （power added efficiency）, output power and gain.

Advanced SPICE-Modeling of 4H-SiC MESFETs

A modified drain source current suitable for simulation program with integrated circuit emphasis （SPICE） simulations of SiC MESFETS is presented in this paper. Accurate modeling of SiC MESFET is achieved by introducing three parameters in Triquint＇s own model （TOM）. The model, which is single piece and continuously differentiable, is verified by measured direct current （DC） I-V curves and scattering parameters （up to 20 GHz）.

Physical simulations and experimental results of 4H-SiC MESFETs on high purity semi-insulating substrates

In this paper we report on DC and RF simulations and experimental results of 4H-SiC metal semiconductor field effect transistors （MESFETs） on high purity semi-insulating substrates. DC and small-signal measurements are compared with simulations. We design our device process to fabricate n-channel 4H-SiC MESFETs with 100 #m gate periphery. At 30 V drain voltage, the maximum current density is 440 mA/mm and the maximum transconductance is 33 mS/mm. For the continuous wave （CW） at a frequency of 2 GHz, the maximum output power density is measured to be 6.6 W/mm, with a gain of 12 dB and power-added efficiency of 33.7%. The cut-off frequency （fT） and the maximum frequency （fmax） are 9 GHz and 24.9 GHz respectively. The simulation results of fT and fmax are 11.4 GHz and 38.6 GHz respectively.

Electrothermal simulation of the self-heating effects in 4H-SiC MESFETs

A thermal model of 4H-SiC MESFET is developed based on the temperature dependences of material parameters and three-region I - V model. The static current characteristics of 4H-SiC MESFET have been obtained with the consideration of the self-heating effect on related parameters including electron mobility, saturation velocity and thermal conductivity. High voltage performances are analysed using equivalent thermal conductivity model. Using the physicalbased simulations, we studied the dependence of self-heating temperature on the thickness and doping of substrate. The obtained results can be used for optimization of the thermal design of the SiC-based high-power field effect transistors.

Improved dual-channel 4H-SiC MESFETs with high doped n-type surface layers and step-gate structure

An improved dual-channel 4H-SiC MESFET with high doped n-type surface layer and step-gate structure is proposed, and the static and dynamic electrical performances are analyzed.A high doped n-type surface layer is applied to obtain a low source parasitic series resistance, while the step-gate structure is utilized to reduce the gate capacitance by the elimination of the depletion layer extension near the gate edge, thereby improving the RF characteristics and still maintaining a high breakdown voltage and a large drain current in comparison with the published SiC MESFETs with a dual-channel layer.Detailed numerical simulations demonstrate that the gate-to-drain capacitance, the gate-to-source capacitance, and the source parasitic series resistance of the proposed structure are about 4%, 7%, and 18% smaller than those of the dual-channel structure, which is responsible for 1.4 and 6 GHz improvements in the cut-off frequency and the maximum oscillation frequency.

Improved empirical DC I-V model for 4H-SiC MESFETs

A novel empirical large signal direct current （DC）Ⅰ-Ⅴ model is presented considering the high saturation voltage, high pinch-off voltage, and wide operational range of drain voltage for 4H-SiC MESFETs. A comparison of the presented model with Statz, Materka, Curtice-Cubic, and recently reported 4H-SiC MESFET large signal Ⅰ-Ⅴ models is made through the Levenberg-Marquardt method for fitting in nonlinear regression. The results show that the new model has the advantages of high accuracy, easily making initial value and robustness over other models. The more accurate results are obtained by the improved channel modulation and saturation voltage coefficient when the device is operated in the sub-threshold and near pinch-off region. In addition the new model can be implemented to CAD tools directly, using for design of 4H-SiC MESFET based RF＆MW circuit, particularly MMIC （microwave monolithic integrate circuit）.

Effects of channel-substrate interface on hysteresis of sidegating effect in GaAs MESFETs

With sidegating bias,hysteresis of sidegating effect is usually observed in drain current.The experimental results presented in this letter demonstrate that the hysteresis with time-based characteristics is closely related to EL2 traps and channel-substrate(C-S)junction peculiarities.The response of depletion region of C-S junction to the electron capture and emission by trap-EL2 plays an important role in the hysteresis.Furthermore,a new mechanism is proposed to explain the time-based characteristics of hysteresis,i.e.,there is a "steady-state" in which the hysteresis disappears.

Frequency dispersion investigation of output reactance and capacitance in GaAs MESFETs by means of dielectric loss tangent consideration

The aim of this article is to investigate the effect of dielectric loss tangent on frequency dispersion of output reactance and capacitance in GaAs MESFETs.For this purpose,measurements of output impedance modulus and phase have been carried out within a frequency range of 10 Hz to 10 kHz,and various voltage values of gatesource（Vgs= 0,-0.2,-0.3,-0.35,-0.4,-0.45,-0.5 and-0.6 V） and drain-source（Vds= 0.7,0.9,1,1.5and 2 V） Based on the concept of complex permittivity of semiconductor material,complex capacitance is used to analyze and simulate frequency dispersion of output reactance and capacitance of GaAs MESFETs.The results show that conductor losses which dominate the dielectric loss tangent are attributed to trapping mechanisms at the interface of devices;so they influence the frequency dispersion of output reactance and capacitance in particular at low frequencies.This reveals that frequency dispersion of these parameters is also related to dielectric loss tangent of semiconductor materials which affects the response of electronic devices according to frequency variation.

基于各向异性导电膜的射频SP8T开关无损测试

为了解决射频器件无损测试的难点,基于各向异性导电膜Z轴(ACF-Z)连接结构,设计并实现了射频器件无损测试技术。针对表面贴装式GaAs金属半导体场效应晶体管(MESFET)单刀八掷(SP8T)开关,该测试技术使用ACF-Z轴连接结构实现器件与测试板的无损连接,通过矢量网络分析仪对GaAs MESFET SP8T开关性能进行测试,最多可同时测试SP8T开关的8个通道。测试结果显示,1~8 GHz内,器件的插入损耗为-15~-35 dB,回波损耗为-15~-35 dB,测试过程中未对器件造成损伤。

双沟4H-SiC MESFET优化结构的解析模型及性能

优化双沟4H-SiC MESFET结构,通过求解一维和二维泊松方程,建立优化结构的解析模型,分析这种结构的直流和交流特性.结果表明,饱和电流密度的计算结果与实验一致,结构优化后4H-SiC MESFET的饱和电流密度和击穿电压分别为420μA·μm-1和155 V,明显高于优化前的275μA·μm-1和141 V;最高输出功率密度为7.4 W·mm-1,比优化前提高约64%;截止频率和最高振荡频率比优化前略微提高.双沟结构经优化后其交流小信号特性未退化而功率特性获得明显改善.