| Due to compatibility with Si standard process and tailored base energy band,SiGe base heterojunction bipolar transistors?HBTs?have high performance/price ratio,and have made remarkable achievements in the frequency characteristics,power characteristics.However,due to the small energy gap of SiGe compared with Si,SiGe base HBT has low breakdown voltage?BV?compared with Si BJT.In order to improve BV,the simple decease of doping density of collector will cause degradation of cutoff frequency?fT?significantly,therefore,the FOM?Figure Of Merit?of f T×BV is improved little or not improved.On the other hand,the performance parameters such as currenr gain?,fT,and the FOM of?and Early voltage VA in SiGe HBT on bulk Si drift or degrade as the temperature changes.The manner by simply adjusting Ge fraction or Ge distribution in the base often only improve one parameter such as?or f T and its temperature sensitivity.Thirdly,as for SOI SiGe HBT,the introduction of insulator substrate in SOI structure results in the decrease of electron density in part collector,the increase of collector resistance and the large decrease of f T,eventually the degradation of fT×BVCEO FOM although BVCEO may increase to some extent.The increase of SOI insulation layer thickness can improve fT,and the FOM of fT×BVCEO,but can lead to self-heating effect seriously.By increasing the doping concentration of N epitaxial layer above N+buried layer in the collector,fT can be improved,but BVCEO is degraded and the FOM of fT×BVCEO can not be improved.How to further boost the performance in SiGe HBT has attracted a great attention from USA and European researchers.In this paper,research on techniques are performed to improve FOM of fT×BV,?,fT,and?×VA in SiGe HBT on bulk Si as well as their temperature sensitivity,to simultaneously enhance FOM of fT×BVCEO and thermal characteristics in SOI SiGe HBT in term of collector doping engineering and multiple combination Ge distribution in the base.The main works are as follows:First,the technology for improving the FOM of f T×BV by introducing a novel composite of P+and N-doping layers?N-P+CDL?inside the collector-base?CB?space charge region?SCR?is investigated.A novel composite P+and N-doping layers deep in the CB space-charge region?SCR?reduces the electric field near the CB junction,and consequently suppress impact ionization,which improves BVCEO and BVCES with little degradation in fT.The reason is that?cb,SiGeis affected slightly,therefore FOM of f T×BVCEO and f T×BVCES are improved greatly,the classical“Johnson”limitation is broken.The results show that,compared with traditional(NC=1×1016cm-3)SiGe HBT on bulk Si,the FOM of fT×BVCEO in SiGe HBT on bulk Si with novel doping technology in CB SCR is improved from 309.51GHz×V to 326.35GHz×V,increased by 5.5%.The FOM of fT×BVCES in SiGe HBT on bulk Si with novel doping technology in CB SCR is improved from 537.57GHz×V to 556.4GHz×V,increased by 3.5%.All are better than the FOM of fT×BV of SiGe HBT on traditional bulk Si.Secondly,the technology of band-gap engineering in the base for improving the temperature sensitivity of?,fT and FOM of?×VA in SiGe HBT on bulk Si is investigated.The introduce of a novel multiple combination Ge distribution in the base named as Multiple Segmented Step Box?MSSB?,can not only make the device own high?,fT and FOM of?×VA,but also make the device own weaker temperature sensitivity of?,fT and FOM of?×VA.The results show as follows that,in the temperature range from 300K to 350K:?1?the temperature sensitivity of?in MSSB SiGe HBT is weaker than Box SiGe HBT,and the former?decreases by only 31.5%,while the latter?decreases as high as 49.2%.Meanwhile,?in MSSB SiGe HBT is higher than Triangular SiGe HBT.At T=300K,compared with the latter??106?,the former??130?is increased by 24;?2?The temperature sensitivity of fT in MSSB SiGe HBT is weaker than Trianglar SiGe HBT,and the former fT decreases by only 7.9%,while the latter fT decreases as high as 15.1%.Meanwhile,fT in MSSB SiGe HBT is higher than Box SiGe HBT.At T=300K,compared with the latter fT?53GHz?,the former fT?57GHz?is increased by 4GHz;?3?The temperature sensitivity of the FOM of?×VA in MSSB SiGe HBT is weaker than Trianglar SiGe HBT.Meanwhile,FOM of?×VA in MSSB SiGe HBT is higher than Box SiGe HBT.At T=300K,compared with the latter FOM of?×VA?3688V?,the former f T?5200V?is increased by 1512V.Thirdly,the technology of N+buried layers into N collector region for simultaneously improving the FOM of f T×BVCEO and thermal characteristics in SOI SiGe HBT is investigated.The results indicate that the N+buried layer not only obviously increases f T with slight decrease in BVCEO,which significantly improves the FOM of fT×BVCEO of SOI SiGe HBT,but also decreases the device temperature,hence weakens the self-heating effect of the device,improving the thermal stability of the device.The results show that compared with traditional SOI SiGe HBT,the FOM of fT×BVCEO in SOI SiGe HBT with N+buried layer is improved by 363.3GHz×V,the maximum increase amplitude of 195%,and the peak temperature TPEAK drops down to310.4K,and the maximum decrease of peak temperature(TPEAK)is 6.6K.Furthermore,the self-heating effect of the device is weakened.Therefore,the technique of a thin N+buried layer in N collector region can successfully alleviate negative impacts such as the decrease of electron concentration in collector region and the degradation of self-heating effect caused by the simple increase of TBOX,and improve overall performance of SOI SiGe HBT.Fourthly,Box and MSSB SiGe HBTs on bulk Si are fabricated and tested.The experimental results show that,compared with Box SiGe HBT,MSSB SiGe HBT owns higher VA,weaker temperature sensitivity of?,higher FOM of?×VA,also weaker temperature sensitivity of?×VA FOM. |
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