7-1223-SiGe (Silicon Germanium) HBT technology

7-1223-SiGe (Silicon Germanium) HBT technology - SiGe...

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Unformatted text preview: SiGe Technology SiGe ECE 3080 ECE Eung Jung, Kim Eung 901683362 Contents Contents SiGe SiGe HBT (Heterojunction Bipolar Transistor) History, Advantage, Application Strain, Dislocations and Critical thickness Three main designs of Ge base profile The band structure for each base design Enhancement of SiGe HBTs Current Market Trend SiGe (Silicon Germanium) SiGe History First Demonstrated in 1987 and has been manufactured since 1998 SiGe HBT is the most mature type of device which may integrated with SiGe CMOS technology Many companies are now producing either Bipolar or BiCMOS products Maximum advantage from Si and Ge aximum and Advantages from Si Silicon insulators (SiO2, Si3N4 ) allow deposition and selective etching process to be developed with exceptionally high uniformity and yields. Advantages from Ge Overcome the drawbacks of Si such as low mobility, low Overcome velocity saturation, and indirect bandgap velocity SiGe (Silicon Germanium) SiGe Application Analogue electronics where low noise and high linearity should be Analogue should combined with high speed High speed digital applications (Bipolar devices are typically operated with higher power dissipation (Bipolar than MOSFETs but can be operated at higher frequencies and with lower noise) lower SiGe (Silicon Germanium) SiGe Strain, Dislocations and Critical thickness Germanium has a 4.2% larger lattice constant than silicon Germanium Compressive strain and tensile strain method The band alignments and discontinuities for (a) a compressive strained SiGe Heterolayer grown on relaxed silicon (b) a tensile strained Si layer grown on relaxed SiGe SiGe (Silicon Germanium) SiGe Critical thickness : Maximum thickness above which it cost too much energy to strain additional layers into coherence with the substrate Above critical thickness: Defects appear (dislocations) Degrading the performance of devices by changing electronic, optical, and thermal properties of the material) SiGe (Silicon Germanium) SiGe The band alignments and discontinuities for (a) compressively strained SiGe Grown on relaxed Si and (b) a tensile strained Si layer grown on relaxed SiGe Quantum wells: Manipulating band discontinuity, a quantum well can be produced (a a quantum well for holes ( (b a quantum well for electrons ( SiGe HBT (Heterojunction Bipolar Transistor) SiGe The three main designs of Ge base profile for SiGe HBT. (a) A rectangular or box SiGe base (b) A linearly graded SiGe base and (c) A trapezoidal base HBT. (Combination of (a) and (b)) Why is SiGe base superior to Si base? *SiGe base can be doped to much higher density Less resistivity at base Less Reduced RC time constant Faster switching *Hetero junction discontinuity between base and emitter Reduce the hole injection into Reduce the emitter the *Reduced bandgap and built-in electric filed Higher gain of the transistor (a) The band structure for a rectangular base profile SiGe HBT. (b) The band structure for a linearly graded SiGe HBT. Enhancement of SiGe HBTs SiGe Box Profile Carrier density Collector current density Gain Gain-early voltage product Emitter transit time Enhanced Early voltage Base transit time Not improved Linear Profile Base transit time is reduced e enhanced gain and llector current can be traded for higher doping in the base Table 1. Changes to the main bipolar parameters for a box profile SiGe HBT and also a linearly graded base HBT. ich allows thinner base widths d reduced base resistance, thereby shorter base transit time increasing fmax Current Market Trend Current Many researchers have claimed that new technologies will supersede silicon as the dominant mainstream microelectronic technology Not happened due to the amount of capital and knowledge presently tied up in both Si production and research Research engineers predicts that CMOS should go to at least 50nm before short channel effects become overwhelming. Major limiting factor in performance of CMOS is p-channel MOSFET (2.5 times lower mobility and higher effective masses ) Transistors in CMOS have to be scaled to balance the circuits Need ability to match the size and performance of the p-channel device to that of the n-MOS By having a pseudomorphic SiGe channel grown below the oxide with a large mobility comparable to the electron mobility will be ideal SiGe HBTs are already in the GaAs RF market and its low cost with high frequency operating point will increase the market for SiGe HBTs in the future. High possibility that all silicon transistors, electronic and optoelectronic devices may have at least some SiGe material in them. Any Questions? Any ...
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This note was uploaded on 08/23/2011 for the course ECE 3080 taught by Professor Staff during the Spring '08 term at Georgia Tech.

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