基于有限元法对发射极指分段结构的多指SiGe HBT的研究

针对传统多指SiGe HBT发射极指中心区域和器件中心区域温度较高导致热不稳定问题,提出了新型发射极指分段结构来抑制功率SiGe HBT中心区域的自热效应,提高器件温度分布均匀性.利用有限元软件ANSYS对器件进行建模和三维热模拟,研究器件温度分布的改善情况.结果表明,与传统不分段结构的器件相比,新型分段结构的多指SiGe HBT的指上的温度分布更加均匀、不同指上的温差和集电结结温明显降低,自热效应得到有效抑制,器件的热稳定性得到增强.     

改善不同环境温度下SiGe HBT热稳定性的技术

提出了发射极非均匀指间距技术以增强多发射极指SiGe HBT在不同环境温度下的热稳定性。通过建立热电反馈模型对采用发射极非均匀指间距技术的SiGe HBT进行热稳定性分析,得到多发射极指上的温度分布。结果表明,与传统的均匀发射极指间距SiGe HBT相比,在相同的环境温度及耗散功率下,采用发射极非均匀指间距技术的SiGe HBT,其最高结温明显降低,热阻显著减小,温度分布更加均匀,有效地提高了多发射极指功率SiGe HBT在不同环境温度下的热稳定性。     

非均匀条间距结构功率SiGe HBT

成功研制出非均匀发射极条间距功率SiGe异质结双极晶体管(HBT)用以改善功率器件热稳定性.实验结果表明,在相同的工作条件下,与传统的均匀发射极条间距HBT相比,非均匀结构HBT的峰值结温降低了22K.在不同偏置条件下,非均匀结构SiGe HBT均能显著改善芯片表面温度分布的非均匀性.由于峰值结温的降低以及芯片表面温度分布非均匀性的改善,采用非均匀发射极条间距结构的功率SiGe HBT可以工作在更高的偏置条件下,具有更高的功率处理能力.     

非均匀条间距结构功率SiGe HBT

成功研制出非均匀发射极条间距功率SiGe异质结双极晶体管(HBT)用以改善功率器件热稳定性.实验结果表明,在相同的工作条件下,与传统的均匀发射极条间距HBT相比,非均匀结构HBT的峰值结温降低了22K.在不同偏置条件下,非均匀结构SiGe HBT均能显著改善芯片表面温度分布的非均匀性.由于峰值结温的降低以及芯片表面温度分布非均匀性的改善,采用非均匀发射极条间距结构的功率SiGe HBT可以工作在更高的偏置条件下,具有更高的功率处理能力.     

改善多指HBT热稳定性的非均匀指间距技术

建立了多发射极指功率SiGe HBT的热电反馈模型,研究了发射极指间距的变化对多指功率SiGe HBT表面温度分布的影响.在此基础上,提出了发射极指间距的非均匀化优化技术.在不同偏置下,对具有均匀间距和非均匀间距的多指HBT各指之间的温度分布进行模拟.结果表明,具有非均匀指间距结构的SiGe HBT峰值温度明显下降,各指之间的温度分布均匀性得到加强,这是传统均匀指间距技术无法比拟的,显示了非均匀指间距优化技术的优越性.     

多发射极指分段结构功率SiGe HBT的热分析

提出了一种有效的方法—采用多发射极指分段结构来增强功率SiGe HBT的热稳定性。为了对分段结构进行精确的热分析,针对器件多层结构的特点,建立起适当的热模型,模型中充分考虑了各个部分的热阻。根据此热模型,使用有限元方法,对一个十指的分段结构功率SiGe HBT进行了热模拟。考虑到模拟的精确性及软件的功能限制,采用两步模拟法:衬底模拟和有源区模拟。通过模拟,得到了发射极指的三维温度分布。结果表明,分段结构功率HBT的最高结温和热阻都明显低于完整发射极指结构,新结构有效地提高了器件的热稳定性。     

基区不同Ge组分分布的多指SiGe HBT热学特性

基于半导体器件仿真工具SILVACO TCAD,研究了三种常见的基区Ge组分分布(矩形、梯形和三角形)对多指功率SiGe异质结双极型晶体管(HBT)的热学特性的影响。结果表明,基区Ge组分为梯形分布和三角形分布的多指SiGe HBT的增益随温度变化比较平缓,各发射极指的峰值温度明显小于矩形分布的各指峰值温度,器件纵向和表面温度分布也更加均匀,因此,与矩形分布相比,梯形分布和三角形分布的多指SiGe HBT在热学特性上有了很大的改善,电学特性也相对热稳定。在这三种结构中,梯形分布可以更好地兼顾增益特性和热学特性。     

基于热电模型的多发射极功率HBTs非均匀镇流电阻设计

在考虑发射结电压随温度的变化和发射极加入镇流电阻的情况下,给出简化的三维热电模型,用以计算功率HBT芯片表面温度分布.分析表明,对于采用均匀发射极镇流电阻设计的功率HBT,芯片中心发射极条温度最高,严重限制了器件的功率处理能力.因此提出非均匀发射极镇流电阻设计方案,并以12指Si0.8Ge0.2HBT为例,详细地给出非均匀发射极镇流电阻设计流程.结果表明,在总发射极镇流电阻阻值(各指发射极镇流电阻并联值)不变的情况下,非均匀发射极镇流电阻设计与传统的均匀设计相比,芯片中心结温显著降低,芯片表面温度趋于一致.还发现当各指发射极镇流电阻阻值从芯片边缘到中心按指数形式分布时,功率HBT的芯片表面温度更容易趋于均匀,大大提高了HBT的功率处理能力,为功率HBT的设计提供了指导.     

基于热电模型的多发射极功率HBTs非均匀镇流电阻设计

在考虑发射结电压随温度的变化和发射极加入镇流电阻的情况下,给出简化的三维热电模型,用以计算功率HBT芯片表面温度分布.分析表明,对于采用均匀发射极镇流电阻设计的功率HBT,芯片中心发射极条温度最高,严重限制了器件的功率处理能力.因此提出非均匀发射极镇流电阻设计方案,并以12指Si0.8Ge0.2HBT为例,详细地给出非均匀发射极镇流电阻设计流程.结果表明,在总发射极镇流电阻阻值(各指发射极镇流电阻并联值)不变的情况下,非均匀发射极镇流电阻设计与传统的均匀设计相比,芯片中心结温显著降低,芯片表面温度趋于一致.还发现当各指发射极镇流电阻阻值从芯片边缘到中心按指数形式分布时,功率HBT的芯片表面温度更容易趋于均匀,大大提高了HBT的功率处理能力,为功率HBT的设计提供了指导.     

一种新型双多晶自对准结构的高压功率SiGe HBT

为了改善高压功率SiGe HBT的综合性能,应用图形外延SiGe工艺,研制出了一种新型的双多晶自对准SiGe HBT器件.相对于双台面结构的SiGe HBT而言,该结构的SiGe HBT在发射极总周长不变的情况下,其发射结面积减少超过50%,集电结面积减少近70%,BVCBO也提高了近28%.经测试,器件的结漏电和直流增益等参数均符合设计要求.     

发射极空气桥InGaP/GaAs HBT的DC和RF特性分析

为抑制电流增益崩塌,提高HBT的热稳定性,研制了发射极空气桥互连结构的HBT晶体管,应用ICCAP提取参数建立VBIC模型,结合模型参数对三种不同结构HBT的DC和RF特性进行比较分析.与引线爬坡互连结构相比,发射极空气桥互连结构HBT的热阻得到改善,热稳定性提高;与发射极电阻镇流方式相比,发射极空气桥HBT的截止频率(fT)相同,最大振荡频率(fmax)提高,最大稳定功率增益(MSG)高出约5dB.     

基区重掺杂对SiGe HBT热学性能的影响

相对于同质结晶体管,异质结双极晶体管(HBT)由于异质结的存在,电流增益不再主要由发射区和基区掺杂浓度比来决定,因此可以通过增加基区掺杂浓度来降低基区电阻,提高频率响应,降低噪声系数,但基区掺杂浓度对器件热特性影响的研究却很少。以多指SiGeHBT的热电反馈模型为基础,利用自洽迭代法分析了基区重掺杂对器件集电极电流密度和发射极指温度的影响。通过研究发现,随着基区浓度的增加,SiGe HBT将发生禁带宽度变窄,基区反向注入发射区的空穴电流增大;同时,基区少子俄歇复合增强,这些都将减小集电极电流密度,降低发射极指温度,从而抑制发射极指热电正反馈,提高器件的热稳定性。     

Thermal performance of collector-up HBTs for small high-power amplifiers with a novel thermal via structure underneath the HBT fingers

We will describe the thermal performance of a special heterojunction bipolar transistor (HBT) structure for mobile communication systems, called a collector-up HBT. We calculated the thermal resistance between the HBT fingers and the bottom surface of a GaAs substrate using a finite element method (FEM). The results suggest that the thermal resistance of collector-up HBTs with thermal via structures can be reduced by 64% compared to the thermal resistance of ordinary emitter-up HBTs. They also show that the thickness of the InGaP emitter layer effects the thermal resistance of, and the temperature distribution in, the collector fingers of collector-up HBTs. Even though the thermal resistance of collector-up HBTs can be much smaller than that of emitter-up HBTs, a thermal interaction between the collector fingers still exists in multi-finger structures. We analyzed the temperature distribution in the collector fingers of a four-finger HBT structure and found that the thickness of the plated heat sink (PHS) was not sufficient to reduce the thermal interaction between the HBT fingers, and that optimization of the HBT location was needed to minimize the thermal interaction. We also found that the thickness of the InGaP emitter layer was the most important parameter for reducing thermal resistance, even in four-finger HBT structures. These calculation results can be used to reduce the temperature of collector-up HBTs and the temperature differences between the HBT fingers in the development of power amplifiers with collector-up HBTs.     

基区设计对InGaP/GaAs HBT热稳定性的影响

研究了不同基区设计对多发射极指结构功率InGaP/GaAs异质结双极型晶体管热稳定性的影响。以发生电流增益崩塌的临界功率密度为热稳定性判定标准,推导了热电反馈系数Φ、集电极电流理想因子η和热阻Rth与基区掺杂浓度NB、基区厚度dB的理论公式。基于TCAD虚拟实验,观测了不同基区掺杂浓度和不同基区厚度分别对InGaP/GaAs HBT热稳定性的影响。结合理论公式,对仿真实验曲线进行了分析。结果表明,基区设计参数对热稳定性有明显的影响,其影响规律不是单调变化的。通过基区外延层参数的优化设计,可以改进多指HBT器件的热稳定性,从而为多指InGaP/GaAs HBT热稳定性设计提供了一个新的途径。     

1 W Ku-band AlGaAs/GaAs power HBT's with 72% peak power-addedefficiency

High power and high-efficiency multi-finger heterojunction bipolar transistors (HBT's) have been successfully realized at Ku-band by using an optimum emitter ballasting resistor and a plated heat sink (PHS) structure. Output power of 1 W with power-added efficiency (PAE) of 72% at 12 GHz has been achieved from a 10-finger HBT with the total emitter size of 300 μm². 72% PAE with the output power density of 5.0 W/mm is the best performance ever reported for solid-state power devices with output powers more than 1 W at Ku-band     

Design of multi-finger HBTs with a thermal–electrical model

Multi-finger heterojunction bipolar transistors (HBTs) with uniform spacing exhibit a higher temperature at the center of devices. The temperature distribution on the emitter fingers of the HBT is studied with a three-dimensional thermal–electrical model. Using this model, multi-finger HBTs are designed with non-uniform spacing to improve temperature distribution. Depending on the number of emitter fingers, different design approaches are demonstrated. For a six-finger or 12-finger HBT, the design is more straightforward. For a complex structure such as a 26-finger HBT, an efficient design procedure is necessary. In all of these cases, the calculated results show significant temperature reduction on non-uniform spacing devices.     

Structure optimization of multi-finger power SiGe HBTs for thermal stability improvement

The two-dimensional temperature profile of a power SiGe HBT with traditional uniform emitter finger spacing is calculated, which shows that there is a higher temperature in the central region of the device. With the aid of the theoretical analysis, an optimized structure of the HBT with non-uniform emitter finger spacing is presented. The peak temperature is lowered by 23.82 K, and the thermal resistance is also improved by 15.09% compared with that of the uniform one. The improvements above are ascribed to the increasing the spacing between fingers, and hence suppressing the heat flow from adjacent fingers to the center finger. Based on the analytical results, two types of HBTs with uniform emitter finger spacing and non-uniform emitter finger spacing are fabricated and their temperature profiles and thermal resistance are measured. The measured results agree well with the calculated results, verifying the accuracy of the calculations. For the HBT with non-uniform emitter finger spacing, the peak temperature and the thermal resistance are improved markedly over a wide biasing range compared with that of the uniform one. Therefore, both the calculated results and the experimental results verify that the optimized structure of power HBT with non-uniform emitter finger spacing is superior to the uniform emitter spacing structure for enhancing the thermal stability of power devices over a wide biasing range.