A technique for simultaneously improving the product of cutoff frequency-breakdown voltage and thermal stability of SOI SiGe HBT

• Published in: Chinese physics B Vol. 25; no. 12; pp. 308 - 313
• Main Author: 付强 张万荣 金冬月 赵彦晓 王肖
• Format: Journal Article
• Language: English
• Published: 01.12.2016
• Subjects: HBT; SiGe; SOI衬底; 击穿电压; 异质结双极晶体管; 截止频率; 热稳定性; 绝缘层厚度
• ISSN: 1674-1056; 2058-3834
• DOI: 10.1088/1674-1056/25/12/124401

The product of the cutoff frequency and breakdown voltage （fT x BVCEo） is an important figure of merit （FOM） to characterize overall performance of heterojunction bipolar transistor （HBT）. In this paper, an approach to introducing a thin N＋-buried layer into N collector region in silicon-on-insulator （SOI） SiGe HBT to simultaneously improve the FOM of fT×BVCEO and thermal stability is presented by using two-dimensional （2D） numerical simulation through SILVACO device simulator. Firstly, in order to show some disadvantages of the introduction of SOl structure, the effects of SOI insulation layer thickness （TBox） on fT, BVCEO, and the FOM of fT×BVCEO are presented. The introduction of SOI structure remarkably reduces the electron concentration in collector region near SOI substrate insulation layer, obviously reduces fw, slightly increases BVcEO to some extent, but ultimately degrades the FOM of fTXBVcEo. Although the fT, BVcEo, and the FOM of fTXBVCEO can be improved by increasing SOI insulator SiO2 layer thickness TBOX in SOI structure, the device temperature and collector current are increased due to lower thermal conductivity of SiOa layer, as a result, the self-heating effect of the device is enhanced, and the thermal stability of the device is degraded. Secondly, in order to alleviate the foregoing problem of low electron concentration in collector region near SOI insulation layer and the thermal stability resulting from thick TBOX, a thin N＋-buried layer is introduced into collector region to not only improve the FOM of fT ×BVCEO, but also weaken the self-heating effect of the device, thus improving the thermal stability of the device. Furthermore, the effect of the location of the thin N＋-buried layer in collector region is investigated in detail. The result show that the FOM of fT xBVcEo is improved and the device temperature decreases as the N＋-buried layer shifts toward SOI substrate insulation layer. The approach to introducing a thin N＋-buried layer into collector region provides an effective method to improve SOI SiGe HBT overall performance.