极化库仑场散射对GaN基电子器件栅源和栅漏寄生电阻的影响研究

发布时间：2018-05-05 14:32

本文选题：AlGaN/GaN高电子迁移率晶体管 + 极化库仑场散射　；参考：《山东大学》2017年硕士论文

【摘要】：AlGaN/GaN高电子迁移率晶体管(AlGaN/GaN HEMTs)具有很多优秀的性能特性,例如高击穿场强、高输出功率、高饱和电子漂移速度。此外,AlGaN/GaN异质结材料的自发和压电极化效应使其在不掺杂的情况下,仍可产生密度高达1013cm-2的二维电子气,因此在高频、大功率集成电路中的应用十分广泛。随着新器件结构和新器件工艺的运用,AlGaN/GaN HEMTs器件性能越来越接近氮化镓材料物理特性的极限。随着对器件内部等效电路研究逐渐深入,最近研究人员发现器件非本征参数寄生电阻严重影响器件的高频性能和可靠性。其中器件在大信号下的截止振荡频率fT和非本征跨导gm,严重受制于寄生电阻,制约着器件在噪声容限、开态电阻和传输延时时间等指标上的进一步优化。为了解寄生电阻的产生原因和作用机制,本文对沟道二维电子气电子在沟道中输运所受的主要散射作用进行讨论,其中包括极化库仑场(PCF)散射、极化光学声子散射、界面粗糙度散射和压电散射,并重点就PCF散射进行研究。PCF散射与栅源偏压、源漏偏压和栅面积均相关,导致栅源和栅漏寄生电阻RS和RD也与栅源偏压、源漏偏压和栅面积相关,从而对应电流-电压(I-V)输出特性曲线的线性区和饱和区R和RD也不同。本论文分别研究了 AlGaN/GaN HEMTs器件线性区寄生电阻RS和饱和区寄生电阻RS与RD,研究了线性区RS与栅长和正向栅源偏压的关联关系,并研究得到了饱和区确定RS和RD的方法。我们制备出不同栅面积、不同栅源间距的AlGaN/GaN HEMTs,在不同外加栅源偏压条件下测量出寄生电阻,并对器件沟道内各种散射机制展开分析。最后,经过散射理论模型计算的寄生电阻数值与实验测试值的较好拟合证实了 PCF散射是Rs的重要影响因素,AlGaN/GaN HEMTs的寄生电阻与栅源偏压、源漏偏压和栅面积密切相关。具体包括以下内容:1.极化库仑场散射对器件线性区栅源沟道寄生电阻Rs的影响器件工艺之后,器件正常欧姆接触退火工艺和栅极外加偏压会改变AlGaN/GaN异质界面处的极化电荷均匀分布状态,导致附加极化电荷的产生,引起PCF散射。经TLM法测试,我们发现相同衬底上不同测试区域的器件欧姆接触存在差异,表明同一片衬底上制作的欧姆接触并不完全一致。欧姆接触的质量差异会干扰我们对器件在外加偏压时栅下AlGaN势垒层区域处由于逆压电效应产生的附加极化电荷的研究。为了减小欧姆接触质量差异的影响,我们设计了共用源极欧姆接触的电子器件。由于同个台面上的左右两个栅极接触共用同一个源极欧姆接触,从而消除了不同欧姆接触质量差异的影响,由此可准确研究栅面积和栅源偏压对RS的影响。在欧姆接触下方区域,金属原子扩散作用减弱了AlGaN势垒层的压电极化强度,并且欧姆接触下方的附加极化电荷△σ1是一个与栅源偏压无关的负值。在VGS0的情况下,栅下区域引入的随栅源偏压变化且为正值的△σ3和欧姆区域引入的不变且为负值的△σ1共同决定PCF散射势。当VGS增大,数值为正且增大的△σ3逐渐抵消数值为负且不变的Aσ1,最终Aσ3成为PCF散射势的主导因素。对于同个样品内共用同一源极欧姆接触的两个AlGaN/GaN HEMTs器件,使用栅探针法测量RS时保持VGS在同一变化范围以保证各器件中的栅下区域的△σ3相等。栅源间距相同,对于更大栅面积的器件栅下附加极化电荷总量更大,增强了 PCF散射势的强度进而导致RS的增大。栅面积相同,器件栅下附加极化电荷总量相同,然而更大栅源间距的器件附加散射势作用区域增大,降低了散射的强度,所以RS随VGS变化幅度减小。最后,使用PCF散射理论模型,我们计算了各尺寸器件不同偏压下的寄生电阻RS,并与器件寄生电阻的测试值进行对比,较好的拟合效果证实了用PCF散射理论解释RS形成机制的合理性,也明确表明AlGaN/GaN HEMTs器件线性区RS与栅源偏压和栅面积密切相关。2.极化库仑场散射对长栅长器件饱和区寄生电阻的影响PCF散射是影响AlGaN/GaN HEMTs器件性能的重要散射机制。然而对于长栅长器件,对不同静态偏置状态下的饱和区寄生沟道电阻的研究并没有考虑PCF散射的影响。由此,考虑PCF散射,并得到AlGaN/GaN HEMTs器件饱和区寄生电阻对提升器件特性至关重要。与深亚微米栅长器件不同,长栅长器件中源漏之间的电场不能使沟道载流子达到饱和漂移速度。因此,短栅长器件栅下的线性电势分布并不适用于长栅长器件。长栅长器件的沟道电势分布情况需要进一步研究。其一,在I-V输出特性曲线中选取VGS=-3V-0V,VDS=8V的静态偏置点,并使用改进的栅探针法测得器件的RS和RD。其二,根据宽禁带半导体在制备肖特基栅极下的电荷控制模型,饱和区(VDS= 8V)时的栅下沟道电势分布被分为两个部分。缓变沟道近似沟道区域Ⅰ和夹断沟道区域Ⅱ分别对应栅下电势从VC(0)变到Vknee和从Vknee变到VC(L)的区域。VC(0)和VC(L)分别是源、漏测栅极边缘处的沟道电势,Vknee近似认为是沟道恰好夹断的沟道电势。然后,使用PCF散射理论分析和确定AlGaN/GaN HEMTs器件沟道各处的附加极化电荷△σ的分布及其决定的附加散射势。最后,综合考虑极化光学声子散射、界面粗糙度散射、压电散射和极化库仑场散射在内的各种散射机制,模拟计算出不同偏置状态下的RS和RD。理论计算结果和测试得到的RS和RD呈现较好的一致性,证明了理论计算的准确性。对于样品3中的器件,欧姆接触下方区域的附加极化电荷△σ1是一个与栅源偏压无关的负值。各偏置状态下的VGS为负值,因此栅下区域附加极化电荷△σ3为负值。取值为负值的△σ1和△σ3共同确定了 PCF附加散射势。各测试点的栅源偏压变化范围是-3V到0V,逐渐减小的△σ3和固定不变的△σ1减弱了 PCF散射势的强度,导致RS和RD的减小。另外,对于其他几种散射机制,非栅极沟道区域内电子温度Te和二维电子气密度n2D决定了它们的散射强度。由于样品3中器件的电流较小不足以导致载流子明显的热声子效应和自热效应。常温条件下,栅源和栅漏之间的沟道处的n2D在不同栅源偏压VGS下为固定值。因此,各不同静态偏置状态下RS和RD的差异只能归因于PCF散射势的差异。这些研究结果证实由于PCF散射,AlGaN/GaN HEMTs器件寄生电阻RS和RD与栅源和源漏偏压相关;研究得到的确定AlGaN/GaN HEMTs器件饱和区寄生电阻RS和RD的方法是正确可行的方法。
[Abstract]:The AlGaN/GaN high electron mobility transistor (AlGaN/GaN HEMTs) has many excellent performance characteristics, such as high breakdown field strength, high output power and high saturation electron drift speed. In addition, the spontaneous and piezoelectric polarization effect of AlGaN/GaN heterojunction materials makes it still produce a two-dimensional electron gas with a density up to 1013cm-2 in the absence of doping. This is widely used in high frequency and high-power integrated circuits. With the application of new device structure and new device technology, the performance of AlGaN/GaN HEMTs devices is getting closer to the limit of physical properties of gallium nitride materials. With the study of the internal equivalent circuit of the device, the recent researchers found that the device is not the intrinsic parameter parasitic resistance. The high frequency performance and reliability of the device are seriously affected. The cut-off oscillation frequency fT and the non eigentransconductance GM under the large signal are seriously affected by the parasitic resistance, which restricts the further optimization of the device in the noise tolerance, open state resistance and transmission delay time. In order to solve the cause and mechanism of the generation resistance, this paper is concerned. The main scattering effects of the channel two-dimensional electron gas electron transport in the channel are discussed, including polarized Coulomb field (PCF) scattering, polarization optical phonon scattering, interface roughness scattering and piezoelectric scattering, and the study of PCF scattering is focused on.PCF scattering with gate source bias, source leakage bias and gate area, leading to gate source and grid. The leakage parasitic resistance RS and RD are also related to the gate bias voltage, the source leakage bias and the gate area, thus the linear region of the current voltage (I-V) output characteristic curve and the saturated zone R and RD are different. This paper studies the parasitic resistance RS and the parasitic resistance RS and RD of the linear region of the AlGaN/GaN HEMTs device, respectively, and studies the linear region RS and the gate length and the forward direction. The relationship between the bias voltage of the gate and the method of determining the RS and RD in the saturation area is studied. We have prepared the AlGaN/GaN HEMTs with different gate area and different gate spacing, and measured the parasitic resistance under the different bias voltage of the grid source, and analyzed the scattering mechanism in the channel. Finally, the scattering theory model was used to calculate the distribution. The good fitting of the value of the raw resistance and the test test confirmed that the PCF scattering is an important factor in the Rs. The parasitic resistance of the AlGaN/GaN HEMTs is closely related to the grid source bias, the source leakage bias and the gate area. The following contents are included: 1. the influence of the polarizing Coulomb scattering on the parasitic resistance Rs of the linear gate channel of the device, after the device process, The normal ohm contact annealing process and the grid applied bias will change the uniform distribution of polarization charge at the AlGaN/GaN heterointerface and lead to the generation of the additional polarized charge and cause the PCF scattering. By the TLM method, we find that the ohm contact of the devices on the same substrate is different, indicating that the same substrate is made on the same substrate. The ohm contact is not exactly the same. The mass difference of ohm contact interferes with the study of the additional polarization charge caused by the reverse piezoelectric effect at the AlGaN barrier layer under the applied bias voltage. In order to reduce the influence of the mass difference in ohmic contact, we designed the electronic devices that share the ohmic contact with the source. The influence of different ohm contact mass differences is eliminated by sharing the same source ohm contact with the left and right two grids on the same platform, which can accurately study the effect of gate area and gate bias on RS. In the area below ohm contact, the diffusion of metal atoms weakens the piezoelectric polarization of the AlGaN barrier layer. The additional polarized charge under the contact of the ohm is a negative value independent of the grid source bias. In the case of VGS0, the PCF scattering potential is determined by the variation of the grid source bias and the positive delta sigma 3 and the ohm region introduced in the lower gate region. When VGS increases, the value is positive and increasing delta sigma 3 gradually counteracts the number. The A sigma 1 is negative and constant, and the final A sigma 3 becomes the leading factor in the PCF scattering potential. For the two AlGaN/GaN HEMTs devices that share the same source ohm contact in the same sample, the VGS in the same range is kept in the same range by the gate probe method to ensure that the delta 3 in the sub gate area of the devices is equal. The gap between the gate source is the same, and the larger grid is for the larger grid. The total amount of additional polarized charge under the area of the device is greater, which increases the intensity of the PCF scattering potential and leads to the increase of the RS. The gate area is the same, the total amount of the additional polarized charge under the gate is the same. However, the additional scattering potential area of the device with larger gate spacing increases and the intensity of the scattering is reduced, so the amplitude of RS decreases with the VGS. Finally, the amplitude of the scattering is reduced. Using the PCF scattering theory model, we calculated the parasitic resistance RS under the different bias voltage of each size device, and compared with the test values of the parasitic resistance of the device. The better fitting results confirmed the rationality of the interpretation of the RS formation mechanism by the PCF scattering theory, and clearly indicated that the RS in the linear region of the AlGaN/GaN HEMTs device is biased with the gate source and the gate area density. The influence of.2. polarizing Coulomb scattering on the parasitic resistance of the long gate long device saturation region PCF scattering is an important scattering mechanism affecting the performance of AlGaN/GaN HEMTs devices. However, for long gate long devices, the study of the parasitic channel resistance in the saturated zone of different static bias States does not take into account the effect of PCF scattering. Thus, PCF dispersion is considered. It is important to shoot and obtain the parasitic resistance of the saturation region of the AlGaN/GaN HEMTs device. Unlike the deep sub micron gate long devices, the electric field between the source and leakage of the long gate long devices can not make the channel carrier reach the saturation drift velocity. Therefore, the linear potential distribution under the short gate grid is not suitable for long gate long devices. The distribution of channel potential in the long device needs further study. First, the VGS=-3V-0V, VDS=8V static bias point is selected in the I-V output characteristic curve, and the RS and RD. of the device are measured by the improved gate probe method. The charge control model under the wide band gap semiconductor under the Schottky gate and the saturation zone (VDS= 8V) is under the grid. The distribution of the channel potential is divided into two parts. The approximate channel region I and the clip channel region II correspond to the grid potential from VC (0) to Vknee and the region.VC (0) and VC (L) from Vknee to VC (L) respectively as the source, and the channel potential at the edge of the gate is missed, and Vknee approximately considers that the channel is exactly clipped trench potential. Then, so that The PCF scattering theory is used to analyze and determine the distribution of the additional polarization charge and the additional scattering potential of the additional polarized charge in the channel of the AlGaN/GaN HEMTs device. Finally, a variety of scattering mechanisms, such as polarization optical phonon scattering, interfacial roughness scattering, piezoelectric scattering and polarization Coulomb scattering, are considered. The theoretical calculation results of RS and RD. are in good agreement with the tested RS and RD, which proves the accuracy of the theoretical calculation. For the device in the sample 3, the additional polarized charge in the area below the ohm contact delta 1 is a negative value independent of the gate bias voltage. The VGS in each bias state is negative, so the polarizing electricity in the lower grid region is attached. The negative value of delta sigma 3 is negative. The negative value delta sigma 1 and delta 3 jointly determine the PCF additional scattering potential. The variation range of the gate source bias of each test point is -3V to 0V, the decreasing delta sigma 3 and the fixed delta sigma 1 weaken the intensity of the PCF scattering potential, resulting in the decrease of RS and RD. In addition, for several other scattering mechanisms, the non grid channel region The internal electron temperature Te and the two-dimensional electron gas density n2D determine their scattering intensity. Because the small current in the sample 3 is not enough to lead to the apparent thermal phonon effect and the self heat effect of the carrier. Under the normal temperature condition, the n2D between the gate and the gate leakage channel is fixed under the bias voltage of different gate sources. Therefore, the different static biasing. The difference between RS and RD can only be attributed to the difference of PCF scattering potential. These results confirm that due to PCF scattering, the parasitic resistance RS and RD of AlGaN/GaN HEMTs devices are related to the gate source and source leakage bias, and the method to determine the parasitic resistance RS and RD is a correct and feasible method to determine the saturation zone resistance of AlGaN/GaN HEMTs devices.

【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN386

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