针对缓冲层改进的4H-SiC MESFETs新结构设计与仿真

发布时间：2018-02-28 11:30

本文关键词： 4H-SiC MESFET 缓冲层改进双凹栅双凹陷缓冲层 Γ栅凹陷缓冲层　出处：《西安电子科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：碳化硅作为第三代宽带隙半导体材料,表现出优异的材料特性,且金属半导体场效应管器件频率高、不易发生二次击穿。4H-SiC MESFETs器件凭借输出功率密度大、良好的热传导性和高可靠性等特性,在微波频段的通信、雷达等设备中拥有广泛的应用。然而,陷阱效应、表面态过高、电场轰击效应等因素会导致器件的输出功率和频率的下降,因此有必要改进器件结构、提高器件性能。提高沟道厚度会导致相互制约、相互矛盾的结果:漏端输出电流增加但击穿电压减少,栅源电容减少但跨导也减少。因此,需要针对性地对缓冲层进行局部改进,还应结合顶部改进才能解决上述制约关系。本文首次提出了具有双凹陷缓冲层和多凹陷沟道的4H-SiC MESFET结构(DRB-MESFET)。仿真结果表明,凹陷源/漏漂移区能够削弱栅极拐角处的电场集边效应,继而提高器件的击穿电压。同时,凹陷的区域抑制栅耗尽层向源/漏两侧延伸,降低栅源和栅漏寄生电容,从而改善器件的频率特性、提高小信号增益性能。另外,通过引入双凹陷缓冲层,有效沟道厚度变宽,电流得到提高,而栅极相对于沟道距离没变,导致栅极对电流的控制作用变强,改善跨导特性。与仅含有凹陷源/漏漂移区的结构相比较,栅源电容基本保持不变,而漏端输出电流和跨导显著提高,使得器件的直流特性和频率特性有显著的提升。与传统的双凹栅结构(DR-MESFET)相比较,DRB-MESFET结构比漏端饱和电流提高38%,击穿电压提高27%,最大功率密度提高74%,栅源电容减少32%,并且截止频率和最大振荡频率分别从16.7、57.2GHz提高到24.7、63.9GHz。本文首次提出一种新的具有Γ栅凹陷缓冲层的4H-SiC MESFET结构(ΓRB-MESFET)。通过改变高栅、低栅相对沟道表面的位置,使得栅下的沟道厚度变大,得到更大的漏端输出电流。低栅源侧不再向下凹陷,减少该处的电场集边效应,提高器件的击穿电压。同时缓冲层向沟道凹陷,使得低栅与沟道底部的相对距离保持不变,确保沟道电流能够有效地被栅压控制,从而提高器件频率特性。仿真结果表明,ΓRB-MESFET结构的最大功率密度比DR-MESFET结构增加42%,截止频率增加19%。若增加高栅相对沟道表面的高度,使得高栅下的耗尽层区域在沟道层的面积减少,不仅增大漏端饱和电流,同时进一步阻碍栅耗尽层向源/漏两侧扩展,降低栅源电容和漏栅电容。更为明显的是,随着高栅相对沟道表面的距离增加,高栅边缘源侧将出现新的电场密度峰值,这将有效缓解电场集边效应,提高器件的击穿电压。
[Abstract]:As the third generation wide band gap semiconductor material, silicon carbide has excellent material properties, and the metal semiconductor FET device has high frequency and is not easy to occur secondary breakdown. 4H-SiC MESFETs device has high output power density. Good thermal conductivity and high reliability have been widely used in microwave communication, radar and other equipment. However, the trap effect, the surface state is too high, The electric field bombardment effect and other factors will lead to the decrease of the output power and frequency of the device, so it is necessary to improve the device structure and improve the device performance. Contradictory results: the leakage output current increases but the breakdown voltage decreases, the gate source capacitance decreases but the transconductance decreases. In this paper, the 4H-SiC MESFET structure with double indentation buffer layer and multi-depression channel is proposed for the first time. The simulation results show that, The drift region of the source / drain can weaken the electric field side effect at the corner of the grid and increase the breakdown voltage of the device. At the same time, the region of the depression can restrain the grid depletion layer from extending to the source / drain, and reduce the parasitic capacitance of the gate source and drain. In addition, the effective channel thickness is widened, the current is increased, and the gate is not changed relative to the channel distance by introducing a double sag buffer layer to improve the frequency characteristics of the device and the small signal gain. As a result, the grid control effect on the current becomes stronger, and the transconductance is improved. Compared with the structure containing only the recessed source / drain drift region, the gate source capacitance remains basically unchanged, while the drain end output current and transconductance are significantly increased. Compared with the traditional double-concave gate structure DR-MESFET, the DRB-MESFET structure increases the saturation current at the leakage end by 38, the breakdown voltage increases by 27, the maximum power density increases by 74, and the gate source capacitance decreases by 32. The cutoff frequency and the maximum oscillation frequency are increased from 16.7g ~ 57.2GHz to 24.7 ~ 63.9GHz respectively. In this paper, a new 4H-SiC MESFET structure (螕 RB-MESFETT) with 螕 -gate sag buffer layer is proposed for the first time. The location of the low gate relative to the channel surface increases the thickness of the channel under the gate, resulting in a larger leakage output current. Increase the breakdown voltage of the device. At the same time, the buffer layer sags to the channel, so that the relative distance between the low gate and the bottom of the channel remains unchanged, ensuring that the channel current can be effectively controlled by the gate voltage. The simulation results show that the maximum power density and cutoff frequency of 螕 RB-MESFET structure are 42 more than those of DR-MESFET structure. If the height of high gate relative to channel surface is increased, the area of depletion layer under high gate will decrease. It not only increases the saturation current at the drain end, but also further hinders the expansion of the drain layer to both sides of the source / drain, reducing the gate source capacitance and the leakage gate capacitance. More obviously, with the increase of the distance between the high gate and the channel surface, There will be a new peak electric field density at the edge of the high gate, which can effectively alleviate the electric field side effect and increase the breakdown voltage of the device.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN386

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