摘要:
基区Ge组分的加入可以改善SiGe HBT的直流特性、频率特性和噪声特性,但Ge组分及其分布对HBT热学特性的影响报道还很少.本文利用SILVACO半导体器件仿真工具,建立了多指SiGe HBT模型,对基区具有不同Ge组分梯度结构的SiGe HBTs的热学特性和电学特性的热稳定性进行了研究.研究发现,在Ge组分总量一定的条件下,随着Ge组分梯度的增大,器件的特征频率明显提高,增益β和特征频率fΤ随温度变化变弱,器件温度分布的均匀性变好,但增益变小;而基区均匀Ge组分（Ge组分梯度为零）的HBT的增益较大,但随温度的变化较大,器件温度分布的均匀性也较差.在此基础上,将基区Ge组分均匀分布和Ge组分缓变分布相结合,提出了兼顾器件热学特性、增益特性和频率特性的新型基区Ge组分分布-分段分布结构.结果表明,相比于基区Ge组分均匀分布的器件,新器件温度明显降低;β和fΤ保持了较高的值,且随温度的变化也较小,显示了新结构器件的优越性.这些结果对HBT的热学设计具有重要的参考意义,是对SiGe HBT性能研究的一个补充.
Abstract:
As is well known, the base Ge composition can improve the DC characteristics, frequency characteristics and noise characteristics of SiGe HBTs. However, the reports about the effects of Ge profile on HBTs thermal characteristics are rare. In this paper, by use of SILVACO simulator, the effects of different Ge gradients on thermal and electrical characteristics of SiGe HBT are investigated. It is found that under the same total Ge amount condition, as Ge gradient increases, the fT of device increases significantly, the uniformity of temperature distribution becomes better, the influences of temperature on the β and fT are weakened, but the gain β becomes smaller. For the device with uniform Ge composition, the β is high, but the influence of temperature on the β is enormous, the uniformity of temperature distribution is poor. Based on these results, in order to make a tradeoff among thermal, gain and frequency characteristics, a novel Ge composition structure with the combination of the uniform and graded Ge composition is proposed. The results show that the novel Ge composition structure SiGe HBT has good performances lower peak temperature, better uniform temperature profile, smaller variabilities of β and fT with temperature, sufficient high β and fT compared with the uniform Ge composition device. These new results provide valuable reference for the device thermal design, and are supplemental to the research and application of SiGe HBTs.
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